1.1 The role of bypass capacitors

🍏Bypass capacitors are usually connected in parallel across the power supply of a circuit unit (such as an IC) to reduce the power supply as much as possible over the entire operating frequency band or the frequency band where the circuit may be affected. Keep the positive reactance level at a tolerable level to prevent power transmission. Harmful coupling. For the lower frequency band, the electrolytic capacitor of the regulated power supply can provide a very low impedance, but the aluminum electrolytic capacitor will start or will begin to transform into inductive when it exceeds 50kHz, and it cannot maintain the low impedance of the higher frequency band, and from the regulated power supply There is usually a long distance between the output end and each sub-circuit (such as several centimeters to more than ten centimeters is common), its parasitic inductance may reach 1uf, its inductive reactance at 50kHz is 0.314Ω, plus the impedance of the rectifier filter capacitor and The power trace resistance of the circuit board, the power output impedance seen from each sub-circuit to the power supply will be more than 1Ω, and it may reach several ohms or even 10Ω at a frequency of 500kHz. For higher frequencies would be unthinkable. Such power supply impedance is easy to produce harmful power coupling (such as parasitic oscillation or self-excitation of the amplifier circuit, false logic level of the digital circuit at high frequency, inaccurate reference power supply, etc.), and the impedance of 1UF or 0. lUF is at high The frequency is easily below 1Ω. So usually a better solution is to connect ceramic capacitors in parallel across the power supply of each sub-circuit (eg, each IC) to reduce the impedance in the high frequency band of the power supply of each sub-circuit. This is often referred to as the “rule” – large capacitors filter low frequencies, and small capacitors filter high frequencies, but a good large-capacity capacitor can filter out high-frequency ripple quite well, but it is customary to use the frequency in general applications. A misunderstanding caused by ordinary aluminum electrolytic capacitors with poor characteristics.This is the applications of ceramic capacitors.

🍎Another function of the bypass is AC bypass (short circuit), decoupling capacitor, (again short to AC) of the DC bias circuit.

🍐The bypass capacitor has no special requirements on the loss factor. In the bypass application, the bypassed circuit does not generate a high ripple current. Even if the bypass capacitor has a high loss factor, it has no effect on the bypass function of the circuit. As long as the bypass capacitor is not dissipating heat. At this time, ceramic capacitors will be the best choice, and the reason is that it has the lowest cost. If the bypassed circuit may generate a high ripple current (such as the power of the class D power amplifier and the bypass of the power supply), it is necessary to consider the heating caused by the ripple current that the bypass capacitor can withstand and select the capacitor appropriately type.

1.2. Large-capacity ceramic capacitors improve power frequency characteristics

🍊The impedance characteristics of a 100UF aluminum electrolytic capacitor in parallel with a 1UF ceramic capacitor are shown in Figure 3.75.

🍋The left picture is the characteristic curve at normal temperature, and the right picture is the characteristic curve at -25℃. The thick solid line in the figure is the impedance-frequency characteristic curve of two capacitors in parallel, the thin line on the left in the figure is the impedance-frequency characteristic curve of the ceramic capacitor, and the thin line on the stone edge is the impedance-frequency characteristic curve of the electrolytic capacitor. As can be seen from the figure, electrolytic capacitors with large capacitance have very low impedance in low frequency bands, while ceramic capacitors can have low impedance in frequency bands beyond the reach of electrolytic capacitors. The combination of the two can obtain a wide frequency range. Ideally low impedance.

🍌Bypass capacitors for high-frequency high-power circuits need to bypass large “high-frequency AC” load currents caused by the load, therefore, bypass capacitors not only need to have low ESR, but also have low dielectric frequency losses.

🍉Not only that, the volume of ceramic capacitors is very small, the leaded ceramics with 0.1~luF capacitance is only 0.2in between the pads of the container, and the 0805 package of laminated capacitors is even smaller, and the soldering size is only 2mm on the printed circuit board. Components and wiring are easy.

🍇If you choose a ceramic capacitor with a larger capacitance (such as 10uF, 22UuF or even 47uF, 100uF), it can completely replace the tantalum electrolytic capacitor.

🍓In general IC application guidelines, tantalum electrolytic capacitors are recommended for bypass capacitors where performance requirements are relatively high. Tantalum electrolytic capacitors are recommended in applications where operating temperatures are high and long lifetimes are required, such as DC/DC power modules.

🍈When applying electrolytic capacitors, it should be noted that electrolytic capacitors are polarized and cannot be used in reverse polarity.

1.3 Other bypass applications

🍒Another function of the bypass capacitor is the AC bypass (short circuit) of the DC bias circuit, and the decoupling capacitor (or short circuit to the AC). In transistor amplifiers or similar circuits, in order to reduce the AC impedance of the transistor emitter resistor, a capacitor is connected in parallel across the resistor. For low frequency circuits, aluminum electrolytic capacitors are usually used, and 0.01uF can be used for medium and high frequency circuits.

🍑The second class of low-cost ceramic dielectric capacitors, taking the intermediate frequency amplifier as an example, the capacitive reactance of the 0.01uF capacitor is 34.2Ω at 465kHz, which is 1/30 of the 1KΩ resistance. If a 0.1uF capacitor is used, the capacitive reactance is reduced to 3.42Ω , equivalent to a short circuit for a 1KΩ resistor. In the power supply decoupling circuit of some high-frequency circuits (such as the decoupling circuit of the bias power supply of the pre-stage part of the split device transistor amplifier in the past), the method of decoupling the ceramic capacitor is also used. The above circuit is shown in Figure 3.76, C2 and C4 are the bypass capacitors for the power supply of the pre-stage circuit and the bypass capacitors for the emitter resistance of the post-stage circuit respectively. Since the circuit in Figure 3.77 is a small-signal circuit, the “AC” current of the bypass is very small. Therefore, it is not necessary to consider the heating problem caused by the loss factor of the capacitor due to the dielectric loss. It is the most economical to choose a cheap ceramic capacitor. Of course, this method of decoupling the bias supply with relatively small ceramic capacitors can also be used in similar circuits.

🥭Ceramic capacitors can also be used for the input, output, and interstage coupling capacitors of AC amplifiers. The large coupling capacitors in Figure 3.77 are different from the requirements for bypass capacitors. The coupling capacitors require that the leakage current of the capacitors is as small as possible. Therefore, it is better to use ceramic capacitors with low leakage current as coupling capacitors in demanding occasions.

2 Application of large-capacity ceramic capacitors in bypassing and high-frequency rectification and filtering of switching power loads

🍍In the application of power frequency rectification and filtering, aluminum electrolytic capacitors should be irreplaceable, especially when power frequency rectification and filtering are above 100V. In this working state, a large capacitance is required to reduce the power frequency capacitive reactance as much as possible, so as to better filter the power frequency ripple and the resulting high-order harmonics. Applications of Ceramic Capacitors:Not only that, the capacitor for power frequency rectification and filtering also plays a role in energy storage, because when the capacitor is input to the filter, the rectifier is only turned on for 2~-3 ms per half power cycle, and the remaining ~8 ms is required for negative power. The electric energy of the power supply is provided by the filter capacitor. The low-voltage rectification often requires thousands or even hundreds of thousands of microfarads. The high-voltage rectification of the direct rectification of 220 V or 380 V power supply also requires hundreds or even thousands of microfarads, which is also the reason for the need for large-capacity capacitors. At this time, the role of aluminum electrolytic capacitors is irreplaceable.

🥝In applications that require large-capacity capacitors such as the bypass of switching power loads and high-frequency rectification and filtering, the usual habit is to immediately think of aluminum electrolytic capacitors. If the performance of aluminum electrolytic capacitors cannot meet the requirements, turn to tantalum electrolytic capacitors. Nowadays, there are many types of capacitors that can complete high-frequency rectification and filtering functions, and there are various options. For example, in applications with higher requirements, aluminum and tantalum polymer electrolytic capacitors with lower ESR can also be considered.

🍅It is undeniable that large-capacity ceramic capacitors should be a good choice when the price restricts the product and requires the use of higher-performance capacitors. For high-frequency rectification and filtering during switching power conversion of 100 kHz or above, the capacitive reactance of the capacitor is already very small.

🍆For example, the capacitive reactance of 100UF capacitor at 100kHz is 15.9 mΩ, while the lowest ESR of 100UF aluminum electrolytic capacitor with low ESR is about 400 mΩ, and the ESR of 1000UF low ESR aluminum electrolytic capacitor is 70m.Ω 100UF standard tantalum electrolytic capacitor The minimum ESR is about 250mΩ, even the minimum ESR of ultra-low ESR tantalum electrolytic capacitors is about 60mΩ, and the minimum ESR of aluminum polymer electrolytic capacitors is at least 20mΩ, which is higher than 15.xn--9m-fcc. At this time, electrolytic capacitors are more like resistors than capacitors at such high frequencies. The ESR of the first 10 UF ceramic capacitor is only 0.003Ω (ie 3 mΩ), which is significantly lower than the capacitive reactance of 100UF (15.9 mΩ). At this time, the role of the capacitor still plays an absolute leading role. For the 3rd, 5th, and 7th times of the square wave of 100kHz, the capacitive reactance is correspondingly reduced to 5.xn--3m-fcc, .3.xn--2m-fcc, and .2.xn--3m-fcc, which can also be capacitive characteristics. Low impedance in the frequency band above 20 kHz and below 5 MHz can be obtained if the ESR-reducing electrolytic capacitor is connected in parallel with a large-capacitance ceramic capacitor.

🥦The basis for the scientific selection of high-frequency rectifier filter capacitors is the allowable ripple current of the filter capacitor, and the allowable value of the ripple current is determined by its ESR (p=.) in most cases. For the same size package, it is allowed to When the temperature rise is the same, the smaller the ESR, the larger the allowable ripple current value. For example, the minimum ESR of standard tantalum electrolytic capacitors is 250 mΩ, while the ESR of large-capacity ceramic capacitors is generally 10~-30 mΩ. The allowable ripple current will be ~ times that of tantalum electrolytic capacitors, that is, 3.16~5.47 times. The allowable ripple current of standard tantalum electrolytic capacitors is 066 A, and the allowable ripple current of ceramic capacitors will reach their corresponding multiples of 2.08A and 3.6A.

2.1 Power supply bypass capacitors as switching power loads

🥬For the power bypass of the switching power load, the test results given by the domestic torch capacitor are as follows. Applications of Ceramic CapacitorsDC/DC converter: 5 V input, 12 V output, switching frequency 450 kHz, input current 0.34 A, output current 0.12A. The schematic diagram of the experimental circuit is shown in Figure 3.78. A 100 UF aluminum electrolytic capacitor, a 33 UF tantalum electrolytic capacitor and a 2.2 uF ceramic capacitor are connected in parallel at the power input end of the DC/DC converter. Test the ripple voltage and ripple current at the input end of the DC/DC converter as shown in the table.

🥒This test result shows that high-capacitance ceramic capacitors are effective in high-frequency rectification and filtering applications, especially at frequencies above 300kHz.

🥗Large-capacity ceramic capacitors have a good suppression effect on power supply voltage transients caused by transient loads. The test circuit is shown in Figure 3.79. The length of the wire from the power supply to the load (that is, the test point) is 40cm. This length is common between the power supply circuit and the load circuit, which is equivalent to connecting a wire of at least 100nH in series between the power supply and the load. This “in-series” inductance will have a large effect on the supply voltage on the load side. The test results are shown in Figure 3.80.

⭐️When there is no capacitor, the peak-to-peak voltage ripple of the test point reaches 2.6. This peak-to-peak voltage will cause logic errors to digital circuits, and the computer may have program errors or even crash; after the capacitor is connected, due to load transients The resulting power supply changes will be effectively suppressed. After the 47UF aluminum electrolytic capacitor is connected to the power supply end of the load, the peak value of the ripple voltage is 25m. After the 10UF tantalum electrolytic capacitor is connected, the peak-to-peak value of the ripple voltage is 25m, and the ripple voltage when the 4.7UF ceramic capacitor is connected is reduced to about 5 mV. Obviously, the ceramic capacitor is the most effective among the three capacitors, and it is also the capacitance the smallest.

🌟If the high-capacity ceramic capacitors are compared with ultra-low ESR tantalum electrolytic capacitors and polymer electrolytic capacitors (the lowest ESR can reach 5 mΩ) in high frequency rectification and filtering, if the above test results can still be obtained, it will have better performance. widely used. For higher capacitance and lower ESR, several laminated ceramic capacitors can also be combined, as shown in Figure 3.81.

✨The ESR of such a 22 UF on-chip ceramic capacitor is about 10 mΩ. For example, three parallel capacitors can obtain a capacitance of 68 UF, and the ESR can be reduced to below 3.5 mΩ, which is much lower than the 10 mΩ of a single 68 UF. Similarly, the combination of more on-chip ceramic capacitor monomers (whether it is an already combined product or a later combination of the user) can both increase the capacitance and greatly reduce the ESR, both of which are high-frequency The performance required for rectification and filtering.

2.2 Laminated ceramic capacitors are used as output filter capacitors for high frequency switching power supplies

💥The requirements for completing the high-frequency output rectification and filtering functions of the switching power supply are considered comprehensively from the aspects of capacitance, cost, high temperature resistance, low ESR, high ripple current, and good high-frequency characteristics. A laminated ceramic capacitor is probably the best choice. The fundamental reason is that chip ceramic capacitors can achieve very high capacitance, such as 1210 package can reach 100 UF, while the ESR is only 10 mΩ. It can withstand high temperatures of 125 ° C, as the price of ceramic chip capacitors is getting lower and lower. , the selection of on-chip ceramic capacitors will become more and more widespread.

🌈The most widely used laminated ceramic capacitors are DC/DC modules. DC/DC modules have much looser component price requirements than AC/DC, and high temperature requirements make it impossible to apply aluminum electrolytic capacitors, and the rest is to compete with tantalum electrolytic capacitors. Both laminated ceramic capacitors and tantalum electrolytic capacitors are capacitors with excellent performance, and the ESR of laminated ceramic capacitors is much lower than that of tantalum electrolytic capacitors. When the same volume is used, laminated ceramic capacitors will allow a higher ripple current to flow.

☀️Another advantage of laminated ceramic capacitors is that they can be stacked to form multi-chip ceramic capacitors, which not only solves the problem of capacitance retention, but also solves the problem of large-sized laminated ceramic capacitors during thermal cycling. The problem of fracture caused by the different thermal expansion coefficients of the board is greatly reduced due to the stacking method of multiple laminated ceramic capacitors, which greatly reduces the area occupied by the circuit board, and at the same time, the resulting parasitic inductance is greatly reduced.

💦It should be noted that due to the extremely low ESR of the laminated ceramic capacitor, compared with the tantalum electrolytic capacitor circuit, there may be a larger voltage overshoot when the load is abruptly changed. That is, the stability is slightly worse.

🪐For AC/DC converters with low switching frequency (such as 50~100kHz), the output filter capacitor needs a relatively large capacitance to support the “stable” of the output voltage, so aluminum electrolytic capacitors are mostly used. However, the high frequency performance of aluminum electrolytic capacitors is far inferior to that of laminated ceramic capacitors. You can make full use of the advantages of both and avoid disadvantages. Connecting laminated ceramic capacitors in parallel with the pins of the output filter capacitor or at the output end will effectively reduce the peak voltage during switching.

2.3 Prevention and control of electrolytic capacitor explosion of computer motherboard

🌺In the media, we often see recalls caused by the explosion of the electrolytic capacitors on the motherboard of a certain brand of computer. In practical applications, it is often seen that the computer fails due to the explosion of the electrolytic capacitor on the motherboard after the computer has been used for several years. It can be said that the explosion of the electrolytic capacitor of the computer motherboard or the loss of capacitance due to the drying of the electrolyte is the most common failure in the application process.

🌸So, why do computer motherboards use electrolytic capacitors? Because computer motherboards require various voltage levels, DC/DC converters are required to convert the power supply voltage into the required voltages, and the output of DCIDC converters requires filter capacitors. Since the computer is a commercial electronic product, it is necessary to pursue the price as low as possible, so the selection of electrolytic capacitors has become an inevitable choice.

🌼If three electrolytic capacitors with a capacitance of 1000UF are used, how much current can such electrolytic capacitors withstand? ESRO.xn--18-fcc.615mA rated ripple current. The electrolytic capacitors of the computer motherboard will be impacted by a much higher current than this data, here is the ripple current generated by the DC/DC converter, and a larger part is the high frequency ripple current generated by the computer motherboard circuit, these ripples If the current converges in the electrolytic capacitor, the electrolytic capacitor will inevitably heat up. If it is overheated, it will burst. If it reaches the bursting level, the electrolyte will dry up for a long time. This is the electrolysis of the computer motherboard that has been used for several years. The reason why the electrolyte does not flow out after the explosion-proof valve of the capacitor is opened.

🌻When encountering such problems, the computer can work as long as the electrolytic container is replaced. Applications of Ceramic Capacitors:However, since the replaced electrolytic capacitor may not be as good as the original electrolytic capacitor, the time required for re-exploding may be shorter. In order to solve this problem, in addition to replacing the electrolytic capacitors, two 10 UF 1206 packaged laminated ceramic capacitors can be connected in parallel on the pin pads of each electrolytic capacitor, which can be said once and for all. The reason is very simple. The ESR of a 10 UF 1206 packaged laminated ceramic capacitor is less than 10mΩ, and the ESR of two parallel capacitors is only 5 mΩ, which is much lower than the low ESR electrolytic capacitor of 1000UF. In this way, most of the high-frequency ripple current Will flow into the laminated ceramic capacitor. The burden of electrolytic capacitors will be greatly reduced.

🌝In order to prevent the electrolytic capacitor of the main board from bursting one day in the future, if you buy a newly purchased computer with an assembled machine, you can solder the purchased computer on the pin pads of the electrolytic capacitor on the main board like an audiophile “grinder”. On-chip ceramic capacitors in 10 UF 1206 package. So you can use it with confidence.

🌞The last question, how much is the 10 UF 1206 package laminated ceramic capacitor? In 2005, I bought 1000 X7R dielectric 1206 package capacitors in the Beijing electronic market for only 200 yuan, an average of 0.2 yuan per piece. If you install 6, you only spend 1.2 yuan.

The data of SYFER small high-voltage and large-capacity laminated ceramic capacitors are shown in Table 3.18 and Table 3.19.

Table 3.18 is as follows

Table 3.19 is as follows

2.4 Used for high frequency power oscillation and high frequency power bypass

🎄There is a special type of ceramic capacitors – high frequency power ceramic capacitors. It is mainly used for high-frequency power resonance (such as industrial high-frequency heating, high-frequency oscillation of high-frequency wireless transmission, etc.) high-frequency resonance tank circuit, bypass of high-frequency circuit power circuit, coupling and feeding of high-frequency circuit, etc. High-frequency power circuits are characterized by high frequency, which can range from hundreds of kilohertz to hundreds of megahertz for industrial induction heating; high power, from several kilowatts to several megawatts, semiconductor devices cannot meet the requirements and can only use vacuum tubes. Applications of Ceramic Capacitors:The high-frequency emission vacuum tube requires high voltages ranging from several thousand volts to tens of kilovolts, and high reactive power needs to be exchanged between the capacitor and the resonant inductor in the resonant tank circuit. Therefore, the biggest feature of high-frequency power ceramic capacitors is high rated voltage and rated reactive power quotient under high-frequency working conditions. This is not available in general ceramic capacitors and other dielectric capacitors.

🌲Due to the high rated voltage, sufficient insulation spacing is required between the two plates, so plate-type high-power ceramic capacitors usually need to make their insulating edges into crimping flanges. As shown on the left in Figure 3.82.

🌳If the current is large, the lead-out electrode is either connected to the external electrical connection with bolts, or is drawn from the copper plate electrode. Generally, the reactive power of high-frequency power ceramic capacitors is very large, and good cooling is required. Since high-frequency power ceramic capacitors work in a resonant tank circuit, the resonant frequency is extremely sensitive to changes in capacitance. Generally, the dielectric of this type of ceramic capacitor is the first type of ceramic dielectric, which has very good temperature stability. Applications of Ceramic Capacitors:Even as a power supply bypass for a high-frequency power circuit, it needs to flow a high-frequency alternating current generated by a high-frequency power circuit, that is to say, the high-frequency power bypass capacitor actually works in a high-frequency state, requiring A medium with low dielectric loss, so it is basically the same as that of a capacitor in a resonant tank circuit. Different from the general low-frequency circuit, the gain of the high-frequency power amplifier circuit is represented by the power gain. Therefore, the coupling capacitor will also flow a significant current, but it is smaller than the final stage current. General data for high frequency ceramic capacitors are shown in Table 3.20 and Table 3.21. See Figure 3.3 for the shape of other high frequency power ceramic capacitors.

 

The post Applications of Ceramic Capacitors appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

1 The aging problem of the second type use of ceramic dielectric capacitors

🍓X7R and Y5V media age (capacitance decay) over time. In general, the capacitance of X7R and Y5V dielectric capacitors is 99% of the initial value after passing through the Curie point (about 130°C) for 10h, and the capacitor is 99% of the initial value after 100h in the normal temperature environment, and the capacitor is the initial value after 1000h. 98% of the value: The capacitance of Y5V medium after 100h at room temperature is the initial value, after 1000h it decays to 94%, and after 10000h it decays to 88%.

🍈The method to restore the capacitance of the capacitor is relatively simple, which is to raise the temperature of the ceramic capacitor to above the Curie temperature. For example, use a soldering iron to touch and solder the pads of the multilayer ceramic capacitors for a few seconds, or place the entire circuit at 130 ℃. environment for a period of time. The former is more practical and safe, because other components are not damaged by high temperature at this time.

🍒The capacitance of X7R and Y5V dielectric ceramic capacitors decreases when a DC bias voltage is applied. In particular, the capacitance drop of Y5V dielectric ceramic capacitors is particularly obvious, and it is necessary to pay attention to the application.

2 General Precautions for Ceramic Capacitors

🍑Ceramic capacitors are fragile and abrasive substances. If handled improperly, they may cause mechanical damage to cracking or chipping. Therefore, the following aspects should be paid attention to:

2.1General handling matters needing attention

(1) Multilayer ceramic capacitors are easily broken when thrown. In addition to surface damage, capacitance changes, dissipation factor rises, insulation resistance drops, and dielectric strength drops.

(2) Rolling the bulk multilayer ceramic capacitors together will grind the metal of the terminals to the surface of the other capacitors. Metal traces left on capacitors can lead to failure hazards such as creepage.

(3)🥜Multilayer ceramic capacitors should never be handled by hand, because sweat and skin oil will make the solderability of the terminal electrodes worse, and it is difficult to clean up.

(4)🍧Multilayer ceramic capacitors are never allowed to be handled with metal tools. Metal tweezers will chip off chips or leave metal traces on the surface of the capacitor. Plastic or plastic-encapsulated metal tweezers are recommended when using tweezers. Use to keep the applied pressure to a minimum.

2.2 Matters needing attention during transportation

(1) To the extent possible, it should be shipped in its original unopened packaging. If opened, the protective material originally attached should be replaced and resealed.

(2)🍪Do not pack multilayer ceramic capacitors directly with paper or cards, because some papers contain sulfur components, which will adversely affect the solderability of the capacitors. Bulk laminated ceramic electro-pneumatics should be cushioned with foam plastic that does not contain sulfur to avoid damage caused by collision and grinding during transportation.

2.3 Storage

(1)🍦If the multilayer ceramic capacitors encounters sulfur dioxide, chlorine, other acidic gases or humid air, the electrode terminals are easily oxidized and affect the solderability.

(2)Paper and rubber contain sulfur substances and cannot be stored together with multilayer ceramic capacitors.

(3)🧁Unused multilayer ceramic capacitors should preferably be kept in their original packaging, and those that have been opened should be resealed as soon as possible. It can also be stored in an airtight container to avoid environmental impact. Therefore, some multilayer ceramic capacitors manufacturers will place multi-disc capacitors in a relatively sealed can.

(4)If it is stored for a long time, it is best to maintain it between -5 and +40 °C, and the relative humidity is between 40% and 60%.

(5)Direct sunlight will deteriorate the tape and contaminate the capacitor.

(6)🍭Stored in the above method, the original packaging can be stored for two years.

3 Mounting and Soldering

 3.1 The influence of the installation position of the components on the components

🥭Since the multilayer ceramic capacitors is easily damaged when subjected to bending force, in the PCB design, the placement position of the multilayer ceramic capacitors should pay attention to select the position where the chip is subjected to the least pressure when the PCB is bent or deflected. If the PCB is likely to be bent under force, the orientation of the components should be

🍍The direction perpendicular to the force, as shown in Figure 3.49, the placement direction of B is better than the placement direction of A. Such force will cause the least damage to the contact between the inner electrode and the outer electrode.

🥝Similarly, several or even dozens of PCBs are usually produced at the same time during PCB production. When using, each PCB needs to be separated. The separated places are usually easier to separate by perforation or gap. In this way, the different placement positions of the ceramic capacitors near the separation of the PCB, Figure 3.49 The effect of the circuit and the direction of the multilayer ceramic capacitors on the ceramic capacitor is also different when the PCB is separated.

🍅The influence of the placement position of the board on the components, as shown in Figure 3.49 below, there are four multilayer ceramic capacitors with different placement positions and orientations. The order from worst to best component placement is: A is the worst, B is slightly better, and D is the best. The reason is that when the PCB is separated, the A component is subjected to the largest force in the same direction of the component; the C component is farther away from a certain separation, so the force is smaller than that of A, but it is still subjected to the force when the PCB is separated; the position of B is in the separation. When the PCB is separated, it is a gap, so the force is better than that of C. Since the placement direction of component D is perpendicular to the force when the PCB is separated, the harmful force is the least.

3.2 Requirements for solder paste printing

🥑SMD components can be soldered to the circuit board by reflow soldering and small peak soldering, and individual components can also be manually soldered to the circuit board.

🥒The first process for reflow soldering is the printing of solder paste. Using too thick solder paste will result in too much solder. This makes the chips on the PCB more susceptible to the mechanical and thermal stress of the board, and can lead to

🌼If the chip is damaged, too little solder paste will cause insufficient bonding strength on the external electrodes, resulting in the chip falling off from the PCB. Be sure to distribute the solder paste evenly over the terminal surface with a thickness of at least 0.2mm, as shown in Figure 3.50.

3.3 Precautions when mounting SMD components

🌻When the nozzle is installed, the bottom dead center is too low, which will cause a large load on the chip, which will damage the chip, as shown in the upper picture in Figure 3.51. At this time, the bottom dead center of the nozzle can be adjusted by correcting the distortion of the PCB. Under normal circumstances , the bottom dead center of the suction nozzle must be on the upper surface of the PCB, as shown in the lower part of Figure 3.51. The nozzle pressure for chip mounting must be limited to a static load of 1 to 3N. The dust particles and dust deposited between the suction nozzle and the inner wall of the cylinder will make the suction nozzle not move smoothly, which will cause a large load on the chip during installation, resulting in damage to the chip. After the positioning claw is worn, it will exert uneven force on the chip during positioning, resulting in chip damage. The suction nozzle and positioning claw must be regularly maintained, inspected and replaced.

3.4 Reflow soldering

🌞The sudden heating of the chip will cause the chip to deform due to internal expansion and excessive internal stress, thereby damaging the chip. Therefore, during preheating, it is necessary to maintain the temperature difference ΔT within the recommended range for the components being welded. The smaller the ΔT value, the smaller the pressure on the chip. When the component is immersed in the solvent after installation, be sure to maintain the temperature difference (ΔT) between the component and the solvent within the range required by various components. The standard heating conditions and allowable time for reflow soldering are shown in Figure 3.52.

Insertion of lead components: If the PCB is bent when mounting lead components (such as transformers and ICs, etc.), the chips may be damaged and the solder joints may crack. Before mounting the pin assembly, secure the PCB with alignment pins or special clamps to avoid twisting. Note also that, in the case of repeated welding, the cumulative welding time must not exceed the welding time shown in Figure 3.52.

3.5 Wave soldering 

🍂The sudden temperature rise of the chip can cause thermal deformation, which can lead to chip breakage. If the soldering time is too long or the temperature is too high, the outer electrode will be leached by the solder, which will lead to poor bonding or reduced capacitance due to poor contact between the electrode and the terminal. During preheating, the temperature difference ΔT between the soldering temperature and the chip surface temperature should be maintained within the recommended range for the components being soldered. Of course, the smaller the ΔT value, the less stress the chip is under. The standard heating conditions and allowable time for reflow soldering are shown in Figure 3.53.

💐When components are immersed in solder after mounting, it is important to maintain the temperature difference between the components and the solder within the recommended range for the components being soldered. Do not wave solder components that are not stated to be wave solderable. However, it should also be noted that, in the case of repeated welding, the cumulative welding time shall not exceed the welding time shown in Figure 3.53.

🌷Too thick solder paste used in wave soldering will result in too much solder, which will make the chips on the PCB more susceptible to the mechanical and thermal stress of the circuit board, and may cause chip damage. Too little solder paste will cause insufficient bonding strength on the external electrodes, resulting in the chip falling off the PCB. The optimum solder volume for wave soldering is shown in Figure 3.54.

3.6 Use a soldering iron for correction or hand soldering

🌈When calibrating or hand-soldering individual components, a soldering iron is required, and the following points need to be paid attention to in this soldering environment.

🦙The sudden temperature rise of the multilayer ceramic capacitors will cause deformation due to the internal high temperature difference, which will damage the chip. Therefore, during preheating, please maintain the temperature difference ΔT within the recommended range for the components to be soldered. Of course, the smaller the ΔT value, the smaller the pressure on the chip. It should be noted that the soldering times/temperatures given in Figure 3.55 are cumulative soldering (including reflow and wave soldering) times/temperatures.

🐐Standard heating conditions and allowable times for this type of welding are within the ranges shown in Figure 3.55.

🦌Note when using a soldering iron for calibration or soldering: the optimal amount of solder paste/solder does not exceed the chip thickness, as shown in Figure 3.56. The soldering iron should be limited to 20W, the components should be preheated to 130°C, the temperature of the soldering iron tip should not exceed 300°C, the diameter of the soldering iron tip should not exceed 3mm, and the longest soldering time should be 5S. Do not let the soldering iron tip directly touch the ceramic capacitor components. itself etc. If soldering 1mm from the root of the ceramic capacitor terminal, be careful not to let the tip of the soldering iron touch the capacitor directly. But there is no need to preheat, it is best to complete the soldering with the soldering iron tip within 3S when the working temperature is lower than 270℃.

🐕Similar to wave soldering, manual soldering also requires attention to the amount of solder. The optimum soldering amount for manual soldering is shown in Figure 3.56, that is, the solder should not exceed the height of the component.

4 Effects of PCB Design on Soldered and Mounted Components

 The design of the PCB also directly affects the quality of the multilayer ceramic capacitors after installation. Therefore, the following matters should be paid attention to when designing the PCB.

4.1 Precautions for PCB layout

🐾Unlike lead components, chip components are susceptible to bending stress because they are mounted directly on the substrate. And they are more sensitive to mechanical and thermal stress than leaded components. Too much solder can increase these stresses, which can lead to chip breakage. Therefore, when designing the substrate, the pad layout and size should be considered to avoid excessive soldering. Figure 3.57 shows the PCB layout with SMD components.

🌲The common error in the layout of all the incorrect PCB components in the picture is due to the fact that there are other solder joints near the multilayer ceramic capacitors and there is no solder mask between the pads, resulting in too much solder for the multilayer ceramic capacitors and increasing the number of laminations The stress of ceramic capacitors can cause damage to multilayer ceramic capacitors. The solution is to have non-welded areas between components to avoid excess solder.

4.2 Pad size of multilayer ceramic capacitors

🦔The pad size of the multilayer ceramic capacitors also directly affects the welding quality. The pad size of different welding processes is slightly different. The specific size of the pad of the multilayer ceramic capacitors is shown in Figure 3.58.

🍀The specific dimensions of the pads of the wave-soldered multilayer ceramic capacitors are shown in Table 3.13. Pads for Reflowed multilayer ceramic capacitors

🌱The specific dimensions are shown in Table 3.14.

5 Correct application of adhesives

🌹Too thin or insufficient adhesive will cause the chip to loosen or fall off during wave soldering. The amount of adhesive should be larger than the dimension C in the dimension shown in Figure 3.59 to achieve sufficient bonding strength. The electrode thickness and pad thickness of the chip must also be taken into account. Low-viscosity adhesives will cause the chip to slip after placement, and the adhesive must have a viscosity of at least 5000Pa.s (500ps) (at 25°C). Adhesive dosage: 0603/min. 0.05mg, 0805/min. 0.1mg, 1206/min. 0.15mg.

🌺Adhesive curing: Insufficient curing of the adhesive will cause the chip to fall off during wave soldering, and the insulation resistance between the external electrodes will decrease due to moisture absorption. It is necessary to control the curing temperature and time to avoid insufficient curing.

6 Application of flux

🌸Too much flux will generate a lot of gas, resulting in reduced solderability. Therefore, a small amount of flux should be used evenly throughout the process (foaming systems are generally used for wave soldering). Too high a halide content in the flux may cause corrosion of the external electrodes unless adequate cleaning is performed. If a flux with a halide content of up to 0.2wt% is used, then a thorough cleaning is required: if not cleaned sufficiently, the water-soluble flux can cause a decrease in the insulation resistance between the external electrodes. Care must be taken not to use strongly acidic fluxes.

7 Wave Soldering

⛄️Pay attention to the temperature and time to ensure that the external electrodes are not leached by solder more than 25% of the terminal area of a single chip (that is, the full length of the ABCD surface as shown in Figure 3.60), and 25% of the AB length when mounted on the substrate , as shown in Figure 3.60.

(1)🍹Test method: Put the chip capacitor under the following conditions, then apply flux (25% rosin in ethanol solution) to the chip, and then immerse it in mixed solder at 230°C for 2s.Conditions: exposed at room temperature (6 months and 12 months respectively), placed under high temperature conditions (100h at 85°C), placed under humid conditions (90% to 95% relative humidity at 40°C) 100h).

(2)Test samples: products suitable for wave/reflow soldering.

(3)🍸Acceptance criteria: Measure the surface area of the external electrodes covering the mixed solder using a 60x optical microscope.

(4) The test results are shown in Table 3.15.

8 PCB solder volume and bending strength

(1)🪀Test method: Solder the chip capacitor on the test PCB. The amount of solder paste is subject to the thickness of the chip. Then bend the PCB as shown in Figure 3.61 and test the electrostatic capacity.

(2) Test samples: products suitable for wave/reflow soldering. Component thickness T=0.6mm (T=0.6mm is mentioned later to uniformly weld the thickness of the component). (3) Acceptance criteria: If the change in electrostatic capacity exceeds the value specified in Table 3.16, it should be regarded as a defective product. (4) Test results: The test results are shown in Figure 3.62.

🌿For glass epoxy substrates, the pass rate of the welded multilayer ceramic capacitors is 100% when the bending is within 2mm. The performance of X7R is relatively the best, X7R is relatively second, and Y5V is relatively the worst.

🌔When the soldering amount reaches the thickness of the component, the CoG dielectric capacitor can withstand about 3.3mm, the X7R can withstand about 2.7mm, and the Y5V can withstand about 2.5mm, and the components can reach 100% pass rate. When the amount of solder is too large, the bending that can pass 100% will decrease. At the same time, no matter what the conditions, excessive bending will cause the pass rate of the multilayer ceramic capacitors after welding to decrease.

9 Solder Amount and Temperature Cycling

(1) Test method: Use solder to solder the chip on various test fixtures of the substrate, and the amount of solder is subject to the required thickness of solder. The clamps were then cycled 200 times through the temperature shown in the top panel of Figure 3.63.

🐚Alumina substrates are typically used for reflow soldering, while glass epoxy or paper phenolic substrates are typically used for wave soldering, as shown in the middle panel of Figure 3.63. The material thickness is 0.64mm alumina, 1.6mm glass epoxy resin, and 1.6mm paper phenol. The above solder dosages are indicated by ①, ②, and ③ respectively in Figure 3.64. The pad dimensions are shown in the bottom image of Figure 3.63.

(2) Test sample: capacitor dielectric C0G/X7R/Y5V dielectric, thickness T=0.6mm.

(3) Acceptance criteria: If the change of electrostatic capacity exceeds the following specified value, it should be designated as a disabled product. Characteristics Capacitance change: COG within ±2.5% or ±0.25pF (whichever is greater): X7R within ±7.5%; Y5V within ±20%.

(4) The test results are shown in Figure 3.64.

🍌It can be seen from 3.64 that the substrate of any material can withstand more temperature cycles when the solder height is equal to the component height. The solder group with the same height as the component has passed the test of 200 thermal cycles. When the aluminum substrate is soldered at 1.6 times the height of the component, the defect rate begins to occur after more than 100 times. It can be seen that the height of the solder is the most important factor affecting the thermal cycling test of the multilayer ceramic capacitors.

🥧Among the three mediums, C0G has the best thermal cycle resistance, X7R is the second, and Y5V is relatively the worst. Different material substrates also have a great impact on the thermal cycle performance of the assembly, with the aluminum substrate being the largest, probably because the expansion coefficient of aluminum is the largest here. The glass epoxy substrate is better, while the paper phenol substrate, which is not very good in other properties, is relatively the best. The possible reason is that the paper phenol substrate is relatively soft.

10 Flexural strength of PCB materials

(1)💥Test method: Solder the chip on the test board, as shown in Figure 3.65. Then bend the test plate as shown in Figure 3.66, and measure the electrostatic capacity.🦋

(2)Test sample: C0G/X7R/Y5V medium, the thickness of the component is T=0.6mm.

(3)🤹Acceptance criteria: If the change of electrostatic capacitance exceeds the following specified value, it should be regarded as defective product. Characteristic Capacitance Change: C0G is within ±5% or ±0.5PF (whichever is greater); X7R is within ±12.5%; Y5V is within ±20%.

(4) The test results are shown in Figure 3.66.

🍖Among the three kinds of media, the C0G medium has the best bending resistance, and still has a 100% pass rate when the substrate is bent by 3mm, and Y5V is the worst. The glass epoxy resin substrate has a worse effect on the flexural performance of the ceramic capacitor than the paper phenol substrate, and the substrate bending is about 1.5mm worse.

11 Fracture strength use of multilayer ceramic capacitors

(1)🐻Test method: Place the chip on the steel plate shown in Figure 3.67. Increase the load near the center of the test sample.

(2) Test sample: Anti-fracture characteristics of 1206/0805 packaged G0G/X7R/Y5V dielectric capacitors.

(3)🐼Acceptance criteria: The amount of load that causes chip breakage or cracking can be defined as bending force.

(4) Explanation: The fracture strength P is proportional to the square of the thickness of the ceramic component, which can be represented by a quadratic curve:

Among them, W, T, L, y are the width (mm) of the ceramic component, the thickness of the component (mm), the distance between the fulcrums (mm) and the bending stress (N/m).

(5)🐹Test results: as shown in Figure 3.68.

12 Thermal Shaking

(1)🦄Test method: After applying flux (25% rosin in ethanol solution), immerse the chip in a solder bath (6X4 mixed solder) according to the following conditions, as shown in Figure 3.69.

(2) Test sample: C0G/X7R/Y5V dielectric multilayer ceramic capacitors in 0805 package, thickness T=0.6mm

(3)🐰Acceptance criteria: Use a 60x optical microscope to visually inspect the test samples, and chips with cracks or cracks should be rated as defective.

(4) Test results: as shown in Figure 3.70.

🍔It can be seen that all dielectric types of ceramic capacitors with a temperature difference below 275 °C have no cracks. The temperature difference is less than about 290 ℃, and the X7R has no cracking phenomenon. Even if the temperature difference reaches 320 °C, there is no cracking phenomenon in CoG. From this point of view, when manually calibrating or soldering, either preheat the device or limit the temperature of the soldering iron to at least 300°C.

13 Solder heat resistance

(1)🌝The test method is as follows.

①Reflow soldering: Apply 300um solder paste on the alumina substrate. After reflow soldering, take out the chip to check whether the external electrode has been leached by solder.

②Wave soldering: After immersing the test sample in the flux tin (mixed solder) with tweezers, check whether the external power has been leached by the solder.

(2) Test sample: multilayer ceramic capacitors in 0805 package, thickness T=0.6mm for wave/reflow soldering.

(3) Acceptance criteria: The start time of leaching should be defined as the loss of the outer electrode as shown in Figure 3.71 ABCD faces 25% of the total time length.

After immersing the test sample in static tin (mixed solder) with tweezers, check whether the external electrode has been leached by solder. The flux used was 25% rosin in ethanol.

(4) Test results: as shown in Figure 3.72

🍥It can be seen that the leaching start time of reflow soldering is the longest, about 180S. The initial leaching time of wave soldering is the shortest, about 12-13S, while dip soldering takes about 22S. In the actual welding process, corresponding to different welding methods, the welding time should be limited to the above time.

14 Thermal oscillations during calibration with a soldering iron

(1)🦟Test method: Use a soldering iron and solder wire that meet the following conditions to solder the chip welds that have been soldered on the paper phenol substrate, as shown in Figure 3.73 (Note: The soldering iron tip should not directly touch the ceramic components of the chip).

(2)Test sample: 0805 packaged multilayer ceramic capacitors COG/X7R/Y5V dielectric, thickness T=0.6mm.

(3)🦒Acceptance Criteria: Visually inspect the appearance of the test samples using a 60x optical microscope, and any samples with cracks or cracks should be rated as defective.

(4) Test results: as shown in Figure 3.74.

🍬It can be seen that cracks start to occur above 320°C. For paper phenol substrates, the soldering iron tip is generally allowed to have a higher temperature. In fact, the heat resistance of paper phenol substrates is not as good as that of glass epoxy resin substrates.

15 Problems that need to be paid attention to when cleaning

🌯Precautions for cleaning printed circuit boards：

(1) After installing all capacitors, when cleaning the printed circuit board, it should be selected according to the flux used and the purpose of cleaning (such as to remove the residual flux during soldering or other materials in the production process). Appropriate cleaning solvent.

(2) The cleaning conditions should be checked and confirmed that the cleaning process does not affect the characteristics of the capacitor.

🍫The main points of printed circuit board cleaning:

(1) If an inappropriate solvent is used, other substances such as flux residues will stick to the capacitor or damage the outer coating of the capacitor, resulting in a decrease in the electrical properties (especially insulation resistance) of the capacitor.

(2)🌺Improper cleaning conditions, insufficient cleaning, and excessive cleaning may cause damage to capacitor performance. Under the condition of ultrasonic cleaning, excessive power output may cause excessive vibration of the printed circuit board to break the capacitor body and the welded part, or reduce the strength of the terminal electrode. Therefore, please carefully consider the following conditions: the ultrasonic output is below 20W; the ultrasonic frequency is below 40kHz; the ultrasonic cleaning time is below 5min.

(3) If the ultrasonic oscillation frequency is too high during cleaning, it may cause the PCB to resonate. As a result, the chip is damaged or the solder joint is cracked. Care should be taken not to vibrate to the PCB.

The post Matters needing attention in the storage and use of multilayer ceramic capacitors appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

1.Influence of humidity on deterioration of electrical parameters

🌝When the temperature in the lost air is too high, the water film condenses on the surface of the capacitor shell, which can reduce the surface insulation resistance of the capacitor. In addition, for semi-dense structure capacitors, moisture can also penetrate into the capacitor medium, which reduces the insulation resistance and insulation ability of the capacitor medium. Therefore, the influence of high temperature and high humidity environment on the deterioration of capacitor parameters is extremely significant. The electrical properties of capacitors can be improved after drying and dehumidification, but the consequences of water molecule electrolysis cannot be eradicated. For example, under the high temperature conditions of capacitor operation, water molecules are electrolyzed into hydrogen ions (H+) and hydroxide radicals under the action of an electric field. ions (OH-), causing electrochemical corrosion of the roots. Even after drying and dehumidification, it is impossible to restore the leads.

2.Consequences of silver ion migration

🌖Most of the inorganic dielectric capacitors use silver electrodes. When the semi-sealed capacitors work under high temperature conditions, the water molecules that penetrate into the capacitors generate electrolysis. An oxidation reaction occurs at the anode, and silver ions combine with hydroxide ions to form silver hydroxide; at the cathode, a reduction reaction occurs, and silver hydroxide reacts with hydrogen ions to form silver and water. Due to the electrode reaction, the silver ions of the anode are continuously reduced to the cathode to form discontinuous metallic silver particles, which are connected by the water film and extend to the anode in a tree-like manner. The migration of silver ions not only occurs on the surface of the inorganic medium, but also diffuses into the interior of the inorganic medium, causing an increase in leakage current, and in severe cases, a complete short circuit between the two silver electrodes, resulting in capacitor breakdown.

🌗About Failure Analysis of Ceramic Capacitors.Ion migration can seriously damage the silver layer on the surface of the positive electrode. Between the lead solder joint and the silver layer on the surface of the electrode, there is silver oxide with semiconductor properties, which increases the equivalent series resistance of the inorganic dielectric capacitor, increases the loss of the metal part, and increases the loss of the capacitor. The tangent value increased significantly.

🌘As the active area of the positive electrode decreases, the capacitance of the capacitor will decrease accordingly. The surface insulation resistance is reduced due to the presence of silver oxide semiconductors on the surface of the dielectric between the two electrodes of the inorganic dielectric capacitor. When the migration of silver ions is serious, a dendritic silver bridge is erected between the two electrodes, which greatly reduces the insulation resistance of the capacitor.

✨About Failure Analysis of Ceramic Capacitors.To sum up, the migration of silver ions will not only deteriorate the electrical properties of unsealed inorganic dielectric capacitors, but may also cause the dielectric breakdown field strength to decrease, and finally lead to capacitor breakdown.

🌟It is worth mentioning that the failure of silver electrode low-frequency ceramic monolithic capacitors due to the migration of silver ions is much more serious than other types of ceramic dielectric capacitors, due to the one-time firing process and multi-layer laminate structure of this capacitor. During the first baking process of the silver electrode and the ceramic medium, silver participates in the solid-phase reaction on the surface of the ceramic medium, and penetrates into the contact point of the ceramic silver to form an interface layer. If the ceramic medium is not dense enough, the migration of silver ions can not only occur on the surface of the ceramic medium, but also penetrate the ceramic medium layer after water infiltration. When the outer electrodes are coated on both ends of the lamination layer, the silver paste penetrates into the gap, which reduces the insulation resistance of the dielectric surface and shortens the path between the electrodes, which is prone to short-circuit phenomenon when silver ions migrate.

3.Breakdown Mechanism of Ceramic Capacitors under High Humidity Conditions

☀️Breakdown failure is a common and serious problem for semi-hermetic ceramic capacitors operating in high humidity environments. The breakdown phenomenon that occurs can be roughly divided into two types: dielectric breakdown and surface-to-pole breakdown. Dielectric breakdown can be divided into early breakdown and aging breakdown according to the time of occurrence. Early breakdown exposes defects in capacitor dielectric materials and production processes. These defects lead to a significant reduction in the dielectric strength of ceramic dielectrics, so that under the action of an electric field in a high-humidity environment, capacitors may be damaged during the withstand voltage test or in the early stage of operation. Electrical breakdown occurs. Aging breakdown mostly belongs to the category of electrochemical breakdown. Electrolytic aging breakdown of ceramic capacitors has become a fairly common problem due to the migration of silver in ceramic capacitors. Yinqian

🌈The conductive dendrites formed by migration can locally increase the leakage current, which can cause thermal breakdown and cause the capacitor to break or burn. Thermal breakdown occurs mostly in tubular or disc-shaped small porcelain dielectric appliances, because local heating is severe during breakdown, and thinner tube walls or smaller porcelain bodies are easy to burn or break.

⛄️In addition, in the ceramic dielectric mainly composed of titanium dioxide, the reduction reaction of titanium dioxide may also occur under load conditions, so that the titanium ion changes from tetravalent to trivalent. The old ceramic dielectric significantly reduces the dielectric strength of the capacitor, which may cause capacitor shock. Put on. Therefore, the electrolytic breakdown of such ceramic capacitors is more serious than that of ceramic dielectric capacitors without titanium dioxide.

☃️The electric field between the electrodes of the silver ion migration capacitor is seriously distorted, and the surface of the ceramic dielectric is condensed with a water film in a high-humidity environment, which causes the corona discharge voltage on the edge surface of the capacitor to drop significantly, and the phenomenon of flying between the surface electrodes occurs under working conditions. In severe cases, it will lead to the breakdown of the flying solitary between the electrodes on the surface of the capacitor. Surface breakdown is related to factors such as capacitance structure, inter-electrode distance, load voltage, hydrophobicity and moisture permeability of the protective layer.

🥝The main reason for the breakdown of the flying solitary between the poles on the edge surface is that the amount of edge left in the dielectric is small. When working in a humid environment, the migration of silver ions and the formation of surface water film make the insulation resistance of the edge surface of the capacitor drop significantly, causing corona discharge and eventually lead to shock. Put on. Especially in high humidity environments. Since it takes a period of time for the generation and development of silver ion migration, in the initial stage of the withstand voltage test, the main failure mode is dielectric breakdown, until after 500h of the test, the main failure mode transitions to the edge-surface inter-pole flying solitary breakdown.

4.Improvements in Electrode Materials

🍭Ceramic capacitors have always used silver electrodes. The migration of silver ions and the consequent accelerated aging of titanium-containing ceramic dielectrics are the main reasons for the failure of ceramic capacitors. Some manufacturers have used nickel electrodes instead of silver electrodes in the production of ceramic capacitors, and electroless nickel plating is used on the ceramic substrate. Since nickel has better chemical stability than silver and has low electrical mobility, the performance and reliability of ceramic capacitors are improved.

🍧Another example is the monolithic low-frequency ceramic dielectric capacitor with silver as the electrode. Since the silver electrode and material are sintered at 900 ℃ for one time, the dense ceramic dielectric cannot be obtained, and there is a large porosity. The flux barium oxide will penetrate into the interior of the porcelain body, and rely on the good infiltration “mutual fusion” ability between barium oxide and silver at high temperature, so that thermal diffusion occurs inside the electrode and the medium, which is the macroscopic “porcelain absorption”. silver” phenomenon.

🍇After the silver enters the porcelain body along with the barium oxide, the effective thickness of the medium is greatly reduced, resulting in a reduction in the insulation resistance and reliability of the product. In order to improve the reliability of monolithic capacitors, silver palladium electrodes are used instead of electrodes that usually contain barium oxide, and 1% of 5# glass frit is added to the material formula. It eliminates the thermal diffusion of the metal electrode to the ceramic dielectric layer during the first sintering at high temperature, which can promote the sintering and densification of the ceramic material, so that the performance and reliability of the product are greatly improved. Compared with the original process and dielectric materials, the capacitor’s The reliability is improved by 1 to 2 orders of magnitude.

5.Fracture of laminated ceramic capacitors

🤹About Failure Analysis of Ceramic Capacitors.The most common failure of laminated ceramic capacitors is fracture, which is determined by the brittleness of the dielectric of laminated ceramic capacitors. Since the laminated ceramic capacitor is directly welded on the circuit board, it is directly subjected to various mechanical stresses from the circuit board, while the leaded ceramic capacitor can absorb the mechanical stress from the circuit board through the pins. Therefore, for laminated ceramic capacitors, the mechanical stress caused by different thermal expansion coefficients or circuit board bending will be the most important factor for the rupture of laminated ceramic capacitors.

6.Fracture Analysis of Laminated Ceramic Capacitors

🤹Figure 3.47 shows a schematic diagram of a laminated ceramic capacitor breaking after being subjected to mechanical force.

Figure 3.47

🧸After the laminated ceramic capacitor is mechanically fractured, the electrode insulation spacing at the fracture will be lower than the breakdown voltage, which will lead to the electrical discharge between two or more electrodes and completely damage the laminated ceramic capacitor. The cross-sectional microstructure of a laminated ceramic capacitor with discharge between electrodes after mechanical fracture is shown in Figure 3.48.

Figure 3.48

🎸About Failure Analysis of Ceramic Capacitors.The main methods to prevent the mechanical fracture of laminated ceramic capacitors are: reduce the bending of the circuit board as much as possible, reduce the stress of the ceramic chip capacitor on the circuit board, and reduce the difference between the thermal expansion coefficient of the laminated ceramic capacitor and the circuit board. mechanical stress.

🪕How to reduce the stress of the laminated ceramic capacitor on the circuit board will be described separately below, and will not be repeated here. Reduce the mechanical stress caused by the difference in the thermal expansion coefficient between the laminated ceramic capacitor and the circuit board, which can be alleviated by selecting a capacitor with a small package size. For example, the aluminum-based circuit board should use a package below 1810 as much as possible. It can be solved by the method of multiple parallel connection or by the method of lamination, and it can also be solved by the ceramic capacitor in the form of package with pins.

7. Electrode terminals of laminated ceramic capacitors are melted and showered

🏆When wave soldering the laminated ceramic is the container, it may occur that the electrode tip is melted off by the solder. The main reason is that the wave soldering laminated ceramic capacitors have been in contact with high-temperature solder for a long time. Now the laminated ceramics on the market are divided into containers suitable for reflow soldering process and wave soldering process.If a laminated ceramic capacitor suitable for the reflow process is used for wave soldering, it is very likely that the electrode tip of the laminated ceramic capacitor will be molten. The time characteristics of the high-temperature solder that the electrode terminals of laminated ceramic capacitors can withstand under different welding processes are described in detail in the applicable precautions for laminated ceramic capacitors, which will not be repeated here.

🍓About Failure Analysis of Ceramic Capacitors.The way to eliminate it is very simple, that is, when using the wave soldering process, use the laminated ceramic capacitors that conform to the wave soldering process as much as possible, or do not use the wave soldering process as much as possible.

The above is all about the Failure Analysis of Ceramic Capacitors .

The post Failure Analysis of Ceramic Capacitors Xuansn appeared first on Dongguan Xuanxuan Electrolytic Technology Co,.ltd.

🍒Multilayer Ceramic Capacitors

Multilayer ceramic capacitors are a landmark milestone in ceramic capacitor manufacturing technology. By using lamination technology, the capacitance of ceramic capacitors can be increased by dozens or even thousands of times under the same electrode plate area.

🍬1. Structure of multilayer ceramic capacitors

The basic method to increase the capacitance is to try to increase the plate area. It is an effective method to use multiple “capacitors” in parallel to increase the capacitance. The basic structure is shown in the figure below.

According to the formula for calculating the capacitance of the capacitor:

It can be seen that if the electrode spacing is made very thin (the d value is small, as long as the medium can meet the withstand voltage requirements), when the withstand voltage is only 6.3V or lower, the medium only needs 3um. Now the Class Ⅱ of ceramic dielectric can achieve this thickness. If the electrode can also achieve a thickness of 0.05um, a capacitor with a thickness of 1.5mm can be stacked 300 layers. Equivalent to the parallel connection of 300 capacitors, the relative permittivity of the Class Ⅱ of ceramic dielectric can reach 10,000. In this way, the capacitance of 100uF can be done.

The cross-section of a MLCC can be seen as consisting of an entire ceramic block with comb-like junction electrodes, which are electrically connected to the surface of the end of the ceramic block by sintering in the metal layer. The principle structure of a multilayer multilayer capacitor is shown in the figure below.

The packaging forms of multilayer ceramic capacitors mainly include lead type and chip type. The lead type used to be called monolithic capacitor. It is called a monolithic capacitor. Simply put, removing the leads of the monolithic capacitor is a form of SMD packaging. In fact, the development of packaging is indeed such a process. If the leadless resistors and capacitors in the past were all to obtain better high-frequency performance, and to ensure the robustness of the external electrodes, the external electrodes of passive chip devices were specially treated.

🍬2. Improvement of Frequency Characteristics of Multilayer Ceramic Capacitors.

The parasitic inductance is much reduced because the lead wire is removed from the multilayer ceramic capacitor. For the lead wire, the inductance of about 1mm length will be 1nH, so the influence of the lead wire of different length on the frequency characteristics is shown in the figure below.

It can be seen from the figure that the resonant frequency of 1nF (1000pF) with C0G dielectric ceramic capacitors without leads is about 130MHz, and when the lead length is 1.5mm, the resonant frequency drops to about 100MHz. The lead lengths are respectively 5mm and 10mm. The resonant frequency at 20mm and 20mm drops to below 70MHz, 50MHz and 33MHz respectively; the resonance frequency of 100nF X7R dielectric ceramic capacitor without lead is about 13MHz, when the lead length is 1.5mm, the resonance frequency drops to 9MHz, and the lead length is respectively When it is 5mm, 10mm, and 20mm, the resonant frequency drops below 7MHz, 5MHz, and 4MHz, respectively. It can be seen that the smaller the capacitance, the greater the influence of the lead length on the resonant frequency of the capacitor itself, that is, the worse the characteristic becomes. At 1nF, the 5mm lead wire can reduce the resonant frequency of the capacitor to half, that is, the usable frequency of the capacitor is reduced to half. At the same time, the impedance at the resonance point becomes high. This shows that in the application of high frequency, especially ultra-high frequency, the wiring length of the lead or PCB has a great influence on the circuit. When the frequency is not too high, although the influence of the lead length on the frequency characteristics of the capacitor becomes smaller, it can be seen in the table that the lead length of 5-10mm is enough to halve the resonant frequency of the capacitor, even if the capacitor is bypassed. In the application, this also shows that the narrowing of the bypassable frequency band is still detrimental to the performance of the circuit. Therefore, in applications, it is best not to use lead-type devices if chip devices can be applied, which is one of the advantages of multilayer ceramic capacitors.

🍒Low Inductance Packaged Ceramic Capacitors

🍬As can be seen from the above, the parasitic inductance of the lead wire of the ceramic capacitor can reduce the self-resonant frequency of the ceramic capacitor, and the reason is the additional parasitic inductance caused by the lead length. When the multilayer ceramic capacitor works at a very high frequency, in addition to the hope that the lead has a smaller parasitic inductance, the parasitic inductance caused by the length of the multilayer ceramic capacitor cannot be ignored. The parasitic inductance of the 1206 packaged multilayer ceramic capacitor is about 1.6nH, and the resonant frequency of the 0.1uF 1206 packaged laminated ceramic capacitor is about 12MHz. If lower parasitic inductance is required, the 1206 package will not be able to do it. Since the parasitic inductance of the multilayer capacitor is caused by its own length, if the length can be shortened, the parasitic inductance can be reduced accordingly. The most typical method is to change the ends of the multilayer ceramic capacitor from both sides of the long end to the short end. At this time, the size of the package changes from 1206 to 0612, as shown in the following figure.

Low inductance packaged laminated ceramic capacitors are available in 0508 and 0612 sizes.

🍬As the distance between the two electrodes is shortened, the parasitic inductance is reduced by about half, so that the resonant frequency of the capacitor will increase to 142% to 150% of the original 1206 package, as shown in the figure below.

🍬The relationship between the resonant frequency and capacitance of a low-inductance laminated ceramic capacitor is shown in the figure below.

Multilayer ceramic capacitors in the form of low inductance packages are mainly used in occasions where the operating frequency is very high and the peak current generated by the circuit is very high, such as the power supply bypass near the CPU chip of a computer. Possibly reduce the adverse effects of the parasitic inductance of the bypass capacitor.

From the point of view of use, unless the laminated ceramic capacitors packaged with low inductance cannot be used, the multilayer ceramic capacitors in the form of ordinary packages are generally an economical and applicable choice.

🍒Large Size Multilayer Ceramic Capacitors

The capacitance of multilayer ceramic capacitors is getting larger and larger. For example, the maximum capacitance of X7R dielectric laminated ceramic capacitors in 1206 package can only reach 10uF. As the output rectifier filter capacitor has become the best choice. At the same time, application demands require further increases in the capacitance of laminated ceramic capacitors. Generally, the small size package can no longer meet the requirements, and the large size multilayer ceramic capacitors came into being. The basic idea is to increase the package size of multilayer ceramic capacitors and stack several laminated ceramic capacitors together to greatly increase the capacitance of the capacitors.

The largest package size that can be found on the current data is 8060 (20.4mmX15.3mmX2.5mm), and the capacitance is about 100 times that of the 1206 package.

Note that manufacturers of large-capacity ceramic capacitors can use X7R dielectric to make 16V/10F in 1206 packages, while ceramic capacitor manufacturers that are conservative and pay attention to the stability and reliability of capacitors can use X7R dielectrics to make 16V in 1206 packages /2.2uF. If it is available grade Y5V, you can do 16V/47uF, or even 16V/100uF. If you choose the 1812 package, you can get the 50V/2.2uF capacitance specification of the X7R medium, while the 1206 package with the same withstand voltage can only reach 50V/0.68uF; if it is a usable Y5V, you can achieve 50V/100uF.

If it is a higher voltage, such as 500V, due to the increase of the withstand voltage, the thickness of the ceramic dielectric increases, so that the capacitance of the small-sized package laminated ceramic capacitor is very small. For example, the most common 1206 package, the X7R dielectric can generally only reach 500V /0.01uF. If a few microfarads are required, a larger package size is required. Generally, the 7XR medium in the 8060 package can only reach 500V/3.9uF, and the size is only 20.4mmX15.3mmX2.5mm, which is close to or even smaller than the aluminum electrolytic capacitor.

Since the expansion coefficient of the ceramic dielectric is different from that of the epoxy resin circuit board, large-sized laminated ceramic capacitors will generate mechanical stress on the capacitor when the temperature changes relatively large (such as the welding process). If the mechanical stress is too large, the It will tear the ceramic capacitor and cause the failure of the ceramic capacitor. If the laminated ceramic capacitor is welded on the aluminum base circuit board, the laminated ceramic capacitor will be easily torn because the expansion coefficient of the aluminum base circuit board is much larger than that of the ceramic capacitor.

Due to the coefficient of expansion, it is generally not recommended that large size (such as 1812 or larger package size) laminated ceramic capacitors be directly soldered to circuit boards, especially aluminum-based circuit boards.

To prevent ceramic chip capacitors from being torn due to welding or a relatively large operating temperature range, the following solutions can be used.

To solve the problem that large-sized laminated ceramic capacitors and circuit boards are prone to tearing due to the difference in expansion coefficient, several small-sized laminated ceramic capacitors can be stacked to achieve the original large-sized capacitance. , Due to the reduced package size, the failure of ceramic chip capacitors caused by the expansion coefficient problem can be effectively reduced.

In order to obtain a larger capacitance, when a large-sized package is used as a last resort, the pin method can be used to digest the mechanical stress on the pin.

By eliminating the mechanical stress problem caused by the expansion coefficient of ceramic capacitors by means of pins, the package size of the laminated ceramic capacitor can reach 8060, and the number of laminated layers can reach 5. In this way, for ceramic capacitors with 500V withstand voltage, the X7R dielectric can reach 12uF, and the size is 20.4mmX15.3mmX12.5mm, which is close to or even smaller than the aluminum electrolytic capacitor, while the C0G dielectric can reach 0.56uF.

🍒Flexible Terminal Ceramic Capacitors

Since multilayer ceramic capacitors cannot be bent, they may be broken when the circuit board is bent. The larger the size, the greater the possibility of being broken. This is the main reason why large-sized laminated ceramic capacitors are not recommended for general applications.

In order to reduce the possibility of the multilayer ceramic capacitor being broken as much as possible, flexible terminal multilayer ceramic capacitors are introduced, so that the multilayer ceramic capacitor will not be easily broken when the circuit board is greatly bent.

The difference between the flexible terminal multilayer ceramic capacitor and the conventional terminal multilayer ceramic capacitor is that the basic electrode terminal between the electrode and the terminal outer electrode of the flexible terminal multilayer ceramic capacitor adopts a flexible conductive material, which can greatly increase the power consumption. The tolerance of layer ceramic capacitors when the circuit board is bent, the structure of flexible terminal laminated ceramic capacitors is shown in the figure below.

 

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⭐️The capacitance of the class Ⅰ of ceramic dielectric capacitors (such as COG) is substantially invariant with frequency over the entire usable frequency range.

Q value and resonant frequency are important indicators when high-frequency/super-frequency capacitors are used in bad resonant circuits. High-frequency/ultra-high-frequency capacitors with excellent performance have good performance in this regard, such as, COG dielectric below 10pF For ultra-high frequency ceramic capacitors with capacitance, the Q value is below 400MHz and reaches more than 1000 meters. In fact, this Q value decreases with the increase of frequency, which can be explained by the increase of loss number with frequency. When the frequency is high to a certain extent, the Q value will drop sharply (the Q value starts to drop sharply after about 6.8pF to above 1.5G), as shown in Figure 3.23, which is also consistent with the increase of ESR with the increase of frequency.

Here, “ultra-high frequency” mainly means that it can work at ultra-high frequency, and of course it can also work at various frequencies below ultra-high frequency. As can be seen from the figure, the characteristic shifts to the left as the capacitance increases. In fact, the discussion of larger capacitance will be meaningless at ultra-high frequency. For example, the 1000pF capacitive reactance is only 0.318Ω at 1GHz, while the inductance of the 1cm lead is 10nH, and the resonant frequency with the 1000pF capacitor is about 50MHz, which is 1 at 1GHz. /20, that is to say, a 1000pF capacitor is used for a resonant circuit, and its resonant frequency generally does not exceed 50MHz. At a frequency of 1MHz, it can only be used for filtering or bypassing. This is the Q value. It is meaningless.

👇2. Resonant frequency, ESR and impedance frequency characteristics

⭐️Any capacitor has its own resonance frequency, that is, the frequency at which its own capacitance and parasitic inductance form series resonance. In the same package, the parasitic inductance is basically the same. Naturally, the larger the capacitance, the lower the resonant frequency, as shown in Figure 3.24, and the smaller the package size, the higher the resonant frequency.

The ESR of the classⅠ of ceramic dielectric capacitors increases with frequency, as shown in Figure 3.24, and as the frequency decreases, the ESR characteristics gradually flatten.

The ESR of the classⅠ of dielectric, such as COG dielectric capacitors, decreases with the increase of capacitance, as shown in Figure 3.25. The reason is obvious. As the capacitance increases, the area of the plate also increases. Under the same packaging conditions, only It can be obtained by increasing the number of layers of polar plates. Since the ESR of each layer of polar plates is basically the same, the number of parallel polar plates increases, and the ESR will inevitably decrease.

The relationship between ESR, capacitance and frequency of C0G dielectric ceramic capacitors is shown in Figure 3.26. The impedance frequency characteristics are shown in Figure 3.27.

⭐️Characteristics can be divided into three parts: capacitive part, resonant part, inductive part. In the capacitive part, the capacitor exhibits capacitor characteristics, which is consistent with: Xc=(πƒ·C)-1, and the impedance decreases with the increase of frequency, as shown in the left half of the curve in Figure 3.27. In the resonance part, the inductive reactance of the parasitic inductance of the capacitor increases with the frequency to the level close to the capacitive reactance. Since the inductive reactance and the capacitive reactance are opposite in sign, the actual impedance of the capacitor in this frequency band is less than the capacitive reactance of the capacitor. When the inductive reactance is equal to When the capacitive reactance is in the resonant state, the capacitive reactance is canceled by the inductive reactance, leaving only the ESR, as shown in the characteristic curve in Figure 3.27 where the impedance drops sharply. As the frequency further increases, the inductive reactance begins to be larger than the capacitive reactance, and the capacitor begins to gradually behave as an inductive characteristic, as shown in the rising part on the right side of the characteristic curve in Figure 3.27.

The impedance frequency characteristics of the Class Ⅱ of dielectric capacitors are shown in Figure 3.28. Similar to the Class Ⅰ of dielectric capacitors, the characteristics can also be divided into three parts: capacitive part, resonant part, and inductive part. The shape of the characteristic curve is also basically the same. Different from the Class Ⅰ of dielectric capacitors, generally the capacitance of the Class Ⅱ of dielectric capacitors is much larger than that of the Class Ⅰ of capacitors, and the frequency band where the characteristic curve is located is lower than that of the Class Ⅰ of dielectric capacitors. For example, the resonance frequency of a capacitor with a capacitance of 10nF is about 50MHz, the resonance frequency of a capacitor with a capacitance of 100nF is reduced to less than 20MHz, and the resonance frequency of a capacitor with a capacitance of 10UF is reduced to 2MHz.

Similar to the Class Ⅰ capacitors, as the capacitance increases, the ESR also decreases. The difference is that the frequency characteristics of ESR have changed. Taking the 50V/10UF capacitor of X5R dielectric as an example (the right side of Figure 3.28), the ESR in the low frequency band decreases with the increase of frequency, about 100kHz, in the range of 100kHz to 1MHz. The ESR of 1MHz is reduced to the lowest value, and the ESR of the frequency band above 1MHz increases with the increase of frequency.

As can be seen from the figure on the right side of Figure 3.28, the ESR of the 50V/10UF Class II ceramic capacitor is only 5mΩ, which is also an extremely low ESR value among various electrical appliances.

👇3. Frequency characteristics of loss factor

⭐️The relationship between loss factor and frequency: The loss factor of the Class Ⅰ of ceramic dielectric capacitor increases with the increase of frequency. The relationship between the loss factor of the Class Ⅰ of COG dielectric, capacitance and frequency is shown in Figure 3.29. Increasing the capacitive reactance decreases, so that the loss factor of the capacitor increases with the increase of the capacitance at the same frequency. The dissipation factor of capacitors of the same capacitance increases with frequency. In fact, the dielectric loss of COG media does not vary with frequency within the application frequency. The reason why the loss factor increases with frequency is that when the loss factor is measured under the condition that the terminal voltage of the capacitor is constant, as the frequency increases, the capacitor current increases, so the loss generated in the capacitor’s ESR also increases. When the frequency is higher than a certain value, the loss generated by the ESR becomes the main loss, and the loss factor at this time will increase linearly with the frequency.

⭐️The variation of the loss factor with frequency of the Class Ⅱ of ceramic dielectric capacitors is basically similar to that of the Class Ⅰ of dielectric.

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☀️Ageing is a unique characteristic of ceramic capacitors. As the time of delivery of ceramic capacitors increases, the capacitance of the capacitor decays. The Class Ⅰ of ceramic dielectric capacitor has no aging phenomenon; the Class Ⅱ of ceramic capacitor has an aging phenomenon.

☀️The capacitance of the Class Ⅱ of ceramic capacitor decreases with time. This process, the so-called aging, is represented by the aging constant according to the logarithmic rule. The aging constant is defined as the percentage loss of the capacitor in the process of “ten years” (approximately 100 000H). For example, in the time period, the life coordinate of the capacitor will increase by ten times (for example, from 1 to 10h).

 🌟The rule of capacitor aging is expressed by the following formula：

Among them, Ct, C1, k, t are respectively: the capacitance of t hours after the start of aging, the capacitance of 1h after the start of aging, the aging constant (the capacitance decreases every ten years), and the hours from the start of aging.

🌟Figure 1.21 shows the aging characteristics of the Class Ⅱ of ceramic capacitors:

It can be seen from the figure that the aging of the capacitance of the Class Ⅱ ceramic capacitor is not serious, and it only attenuates by about 7% in 100,000 hours (equivalent to 11 years). Less than the capacitance changes with temperature and bias voltage, generally will not affect the use.

🌟Due to aging, a constant measurement system with lifetime as a reference must be specified, and its capacitance value will be within the described tolerance.

❓How can we eliminate the aging of ceramic capacitors?

☀️The Class Ⅱ of ceramic capacitor will eliminate aging in the following process: by heating the capacitor above the Curie temperature (approximately 130~150℃), the decrease in capacitance can be terminated and the direction in which the capacitance will increase will change. After the heating process is over Another new aging begins. The surface mount device can be completely aged (deaged) through each welding process; after the welding process is over, a new aging process starts. It should be noted that the elimination of this aging can only occur when the heating temperature exceeds the Curie temperature.

🔅Through the above explanation, believe you have a certain understanding of the aging of the second type of ceramic dielectric capacitors.

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💥Silver Paste Spraying

👉Silver Paste Spraying is one of the methods for coating electrodes in ceramic, glass, mica and other inorganic dielectric capacitors. Its working principle is through spray paint, which uses 4 to 5 atmospheres of compressed air to spray silver paste on the surface of the medium covered with the template. The silver paste coated in this way is uniform and smooth.

💥Screen Printing of Silver Paste

👉Screen Printing of Silver Paste is one of the methods for coating silver electrodes such as ceramic capacitors, mica capacitors, glass and glass glaze capacitors. The pattern of the missing paste on the screen can be made by methods such as photolithography and film sticking. When printing, place the media under the screen, and then use a squeegee silver paste to print on the media. The advantages of this method are high efficiency, saving raw materials, and good consistency of electrode shape and size.

💥Silver Pastebrushing

👉Silver Pastebrushing is one of the methods of coating the silver layer. It uses a silver-coated pen or other tools to apply silver paste to the surface of the medium that needs to be coated with silver. Silver coating machines include tube type and disc type.

💥Silver Pastepring

👉Silver Pastepring is similar to stamping. The end of the “stamp” printed with silver is generally made of materials such as mud, foam, etc., which are easy to absorb silver paste and have a certain degree of flexibility.

💥Silver Electrode Firing

👉Silver Electrode Firing is the common name for burned silver electrode. The silver paste coated on the surface of ceramics, glass or mica must be fired. During this process, the silver paste reacts to form a continuous, dense and firmly bonded metal silver layer with the surface of ceramics. There are two types of silver burning equipment: tunnel furnace and box furnace. Generally, the burning temperature of silver is +500~+900℃, but the burning temperature of mica flakes must be below +600℃ (because mica will lose crystal water above +600℃, which will deteriorate the performance).

💥Silver Ink

👉Silver Ink is a paste for making silver electrodes. It is formulated with silver or its compounds, fluxes, adhesives and diluents. According to the existence form of silver, it can be divided into oxidized silver paste, carbonate silver paste, and molecular silver paste. According to the burning temperature, it can be divided into high temperature silver paste and low temperature silver paste. According to the coating method, it is divided into printing silver paste, spraying silver paste and so on.

⭐️Through the above introduction, do you have a certain understanding of the ceramic capacitor manufacturing process?

⭐️If you need to know more about ceramic capacitors, please leave a message or contact me.

coco@xuanxcapacitors.com

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The electrolytic capacitor is a metal foil with a positive electrode (aluminum or tantalum), an oxide film (aluminum oxide or tantalum pentoxide) that is in close contact with the positive electrode is a dielectric, the cathode is made of a conductive material, an electrolyte (the electrolyte can be a liquid or a solid), and the like. The materials are composed together, and since the electrolyte is the main part of the cathode, the electrolytic capacitor is named after it. At the same time, the electrolytic capacitors are not connected correctly. Aluminum electrolytic capacitors can be divided into four categories: lead-type aluminum electrolytic capacitors; horn-type aluminum electrolytic capacitors; bolt-type aluminum electrolytic capacitors; solid aluminum electrolytic capacitors.

Ceramic capacitors are also known as ceramic capacitors or monolithic capacitors. As the name suggests, is a ceramic capacitor dielectric material is a ceramic capacitor. Depending on the ceramic material, this capacitor can be divided into low-frequency ceramic capacitors with a capacity of 1 to 300 pF and high-frequency ceramic capacitors with a capacity of 300 to 22 000 pF. Classified according to the structure, it can be divided into picture capacitors, tubular capacitors, rectangular capacitors, chip capacitors, feedthrough capacitors and so on.

The differences between ceramic capacitor and electrolytic capacitor are:

• The electrolytic capacitor has large capacity, polarity, and large equivalent series inductance; the ceramic capacitor has small capacity, no polarity, and the equivalent series inductance is small.
• The low-frequency characteristics of electrolytic capacitors are good, and they are mostly used in low-frequency circuits. The high-frequency characteristics of ceramic capacitors are good, and they are mostly used in high-frequency circuits.
• Electrolytic capacitors can filter out low-frequency ripple, so they can be used as low-pass filtering. Ceramic capacitors can filter high-frequency ripple, so they can be used as high-pass filtering.
• Electrolytic capacitors cannot be used in pure AC power circuits; ceramic capacitors can be used in pure AC circuits.
• Ceramic capacitors are used as loop capacitors and pad capacitors in high-stability oscillator circuits for filtering, decoupling, and signal coupling.

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The self-inductance of the feedthrough capacitor is much smaller than the ordinary capacitor, so the self-resonant frequency is very high. At the same time, the through-the-heart design also effectively prevents high frequency signals from being directly coupled from the input to the output. This low-pass, high-impedance combination provides excellent rejection over the 1 GHz frequency range. The simplest through-heart structure is one (C type) or two capacitors (Pi type) composed of internal and external electrodes and ceramics.

Use editing
In actual engineering, the frequency of electromagnetic noise to be filtered is usually as high as several hundred MHz, or even more than 1 GHz. For such high-frequency electromagnetic noise, feedthrough capacitors must be used to effectively filter out. There are two reasons why ordinary capacitors cannot effectively filter high frequency noise.

One of the reasons is that the lead inductance of the capacitor causes resonance of the capacitor, which has a larger impedance to high-frequency signals and weakens the bypass effect of high-frequency signals.

Another reason is that the parasitic capacitance between the wires causes high-frequency signal coupling, thereby reducing the filtering effect. The reason why the feedthrough capacitor can effectively filter high frequency noise is that the feedthrough capacitor not only has no lead inductance, but also allows the resonant frequency of the capacitor to pass. The problem is low, and the core capacitor can be directly mounted on the metal plate, and the metal plate can be used for high-frequency isolation.

When using feedthrough capacitors, the problem to be noted is installation. The biggest weakness of through-core capacitors is the fear of high temperature and temperature shock, which will make it very difficult to solder through-core capacitors to metal panels. Many capacitors can be damaged during the soldering process. Especially when a large number of through-core capacitors need to be installed on the panel, as long as there is damage, it is difficult to repair, because when the damaged capacitor is removed, other capacitors will be damaged. As the complexity of electronic devices increases, hybrid circuits inside and outside the device are mixedly installed, and digital logic circuits are mixedly installed. The mutual interference between circuit modules has become a serious problem. One of the ways to solve the mutual interference of such circuit modules is to isolate circuits of different properties by using metal isolation chambers. However, all wires passing through the cofferdam will pass through the feedthrough capacitor, otherwise an isolation fault will occur.

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Here we analyze the cause of ceramic capacitor leakage current
As a result, leakage of the ceramic capacitor is reduced due to insulation. The following two reasons are summarized:

The first is the surface insulation degradation caused by surface contamination. Such leakage current is not very large. Generally, it is a micro-ampere level, and the insulation value of hot-air blowing will increase. Secondly, internal cracks, cracks caused by welding and poor capacitance of the ceramic chip produced. Leakage currents caused by such cracks will continue to rise, causing severe local fires.

To avoid leakage of ceramic capacitors, select quality-assured manufacturers with good-quality ceramic capacitors that have small leakage currents, low losses, and very consistent capacity. Reduce unnecessary risks and losses as much as possible.

Applying a rated DC operating voltage to the capacitor will observe that the change in the charging current begins to increase, and as time passes, the final value reaches a steady state at a certain final value. This final value is called a leakage current. The ceramic capacitor leakage current is very small. Micro-ampere level is generally .. to avoid the leakage of ceramic capacitors appear, select quality guaranteed manufacturers, xuansn good quality ceramic capacitors, leakage current is small; loss is small; capacity consistency is very accurate.

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