Tantalum Capacitors from circuit boards

Figure. 1

Ⅰ. Circuit Design and Product Selection

Tantalummust-have product performance specifications that match the characteristics of circuit signals. However, we cannot always guarantee that the aforementioned two duties are completed in a timely manner. As a result, there will unavoidably be failures of some sort in the use process, which can be characterized as follows:

1. The use of high voltage in low-impedance circuits causes failure.

There are only two types of circuits utilized in tantalum capacitors: circuits with resistance protection and low-impedance circuits without resistance protection. Because the resistance will reduce the voltage and prevent the passage of big currents in circuits with resistance protection.  utilize it. The voltage can exceed 60 percent of the tantalum capacitor's rated voltage. Without resistance protection, there are two types of circuits:

(1) To provide a steady charging and discharging circuit, the pre-input stages have been rectified and filtered. The  acts as a discharge power supply in this type of circuit. Although a low-impedance circuit, can be used since the input parameters are stable and there is no surge. The safe operating voltage can still be up to 50% of the specified voltage, ensuring a high level of reliability.

(2) The electronic machine's power supply: in this form of circuit, capacitors are employed in parallel. In addition to filtering the incoming signal, it is frequently necessary to discharge at a specific frequency and power. Because this is a power supply circuit, the loop impedance of this sort of circuit is extremely low to ensure that the power supply's output power density is adequate. At each turn-on and turn-off instant, this form of switching power supply circuit (also known as a   circuit) will produce a duration of time. The pulse voltage value can reach at least 3 times the stable input value for high-intensity spike pulses lasting less than 1 microsecond, while the current can reach more than 10 times the steady-state value. The density of energy is really high. If the capacitor's voltage is too high, the pulse voltage actually supplied to the product will considerably exceed its rated value and cause it to fail.

As a result, the operating voltage of tantalum  utilized in these circuits must not exceed 1/3 of their rated value. The circuit is derated by 50% if the circuit's impedance type is not divided. As soon as the power is turned on, a breakdown short circuit or explosion phenomena may occur in the  DC-DC circuit with the lowest loop impedance. The level of the circuit impedance value, the size of the input and output power, and the   ripple in the circuit must all be considered when determining how much the capacitors used in this sort of circuit should be derated. The worth of the worth. The magnitude of the switch's immediate surge amplitude can be determined by the circuit impedance. The circuit with the lowest internal resistance should have a higher derated value. The magnitude of the derating range is impossible to predict. Accurate dependability estimates must be used to calculate the derating range

Figure. 2

2. The peak output current of the circuit is too large (the use voltage is suitable)

 The maximum DC current surge I that tantalum capacitors can safely withstand during operation has the following mathematical relationship with the product's own equivalent series resistance ESR and rated voltage UR:

I=UR/1+ESR

Due to current overload, a low-capacity used in a circuit with a large peak output current may burn out. This is pretty simple to comprehend.

3. Tantalum capacitors with a high equivalent series resistance (ESR) and a high AC ripple in the circuit induce failure.

Even if the operating voltage is much lower than the derating range, a sudden breakdown can occur at the moment of power-on when a tantalum capacitor with too high   is used in a filter circuit with too high AC ripple; the main reason for such problems is the serious mismatch between the  ESR of the capacitor and the size of the AC ripple in the circuit. The capacitor is a polar element that generates heat when passing through the AC ripple.  and products of various shell sizes can maintain thermal equilibrium. The calorific value that can be consumed varies. Because the ESR values of goods with different capacities are so diverse, the AC ripple values that tantalum capacitors of various specifications can safely tolerate are likewise fairly different. As a result, if the AC ripple in a circuit is greater than the AC ripple value of the capacitors utilized, the product will experience a thermal breakdown. Similarly, if the circuit's AC ripple is constant but the selected tantalum capacitor's real ESR value is too high, the result will exhibit the same behavior.

In general, tantalum capacitors with the lowest feasible ESR value should be utilized in filtering and high-power charging and discharging circuits. Many circuit designers overlook the dangers of high AC ripple in the circuit, which causes capacitor failure. Or a lack of comprehension. It's simply a problem with the capacitor's quality. There are numerous examples of this type of phenomenon.

4. The tantalum capacitor's leakage current is excessive, resulting in insufficient withstand voltage.

This problem is usually caused by the tantalum capacitor's real withstand voltage being insufficient. If the insulation resistance of the dielectric layer is low, the actual leakage current of the product will be considered when a specific field strength is applied to the capacitor for a long time. The real withstand voltage will drop for high-current items.

Another factor contributing to this issue is that the leakage current standard for tantalum capacitors is too permissive, causing certain companies who lack the capacity to manufacture tantalum electrolytic capacitors to make low-quality tantalum capacitors. At normal room temperature, the leakage current is excessively high. When a product operates at a greater temperature, its leakage current increases exponentially, reducing the actual withstand voltage at high temperatures. It is quite easy to produce a breakdown when the working temperature is high.

Because a modest change in leakage current at high temperatures is one of the most essential goals for all capacitor makers, it is self-evident that this parameter has a significant impact on reliability.

If the leakage current of the tantalum capacitor you choose is too high, it's a waste product, and issues are bound to arise.

5. When employing tantalum capacitors, failure is caused by manufacturing process variables.

Many users focus solely on the selection and design of tantalum capacitor performance, oblivious to the problems that can arise during the installation and usage of chip tantalum capacitors; examples include the following:

A. Instead of automatic mounting, use manual soldering. The product is not warmed, and a high-temperature electric soldering iron is used to heat the capacitor for an extended period of time, causing the capacitor to fail due to extreme thermal shock.

B. Manual welding does not use a preheating table to heat the product, and the soldering iron is used to heat the product repeatedly as soon as cold welding and virtual welding occur during the welding process.

C. The soldering iron tip used reaches temperatures of 500 degrees. Although this may be soldered rapidly, it is very easy to cause the chip part to fail.

It is possible to calculate the dependability of SMD tantalum capacitors in actual use. Many of our users, on the other hand, have insufficient design margins and low robustness. The small-batch tests are entirely coincidental, and batch output is consistent. At this point, the blame for the problem is frequently shifted to the capacitor manufacturer, with the search for design reliability being neglected. Many people are still unaware of the   (mean time between failures) while utilizing tantalum capacitors,  Many consumers rely on someone with only a rudimentary knowledge of reliability engineering. Experiments are overvalued at the expense of mathematical computations. As a result, the sub-circuit design's reliability is worse than that of the entire machine. As a result, issues continue to arise throughout mass production. Failure to recognize that failure is a probability issue rather than a simple individual one. In reality, there is a slew of other faults and phenomena that can occur when tantalum capacitors are utilized that aren't covered here. You will be able to contact me quickly if there are any new problems in use.

Ⅱ. Quality Problems of Tantalum Capacitors

Currently, the first-line brands AVX and   hold a substantial market share, and their quality is excellent; nevertheless, their price is also the most expensive. There are various facilities in China that produce tantalum capacitors, but the quality of AVX and KEMET is still quite diverse due to the manufacturing process and raw material quality. Domestic tantalum capacitors have a greater ESR than imported tantalum capacitors. Tantalum capacitors' reliability is not just low, but also easy to fail if their performance isn't up to par. As a result, the first criterion for ensuring reliability is to select the appropriate and appropriate items. It makes no difference if it's a little bomb. I don't recommend using tantalum capacitors if you can't assure that the product you purchase is of the highest quality. Especially in high-power charge-discharge circuits and DC-DC circuits.

Ⅲ. How to Identify Fake AVX Tantalum Capacitors?

The problem of fake AVX tantalum capacitors, as well as fraudulent   tantalum capacitors.  is causing a lot of headaches for many of my purchasing friends. Many people have problems with fake SMD tantalum capacitors, and false AVX tantalum capacitors.  and identifying fake tantalum capacitors, according to a search on Baidu. The answers are also diverse; none are perfect, and some are deceptive. Is there a simple way to tell whether a tantalum capacitor is fake? With this in mind, and based on my previous experience dealing with customer complaints, I'd like to share the following five points with you, which I believe will be beneficial to you.

Figure. 3

1. The form of tantalum electrolytic capacitors' welding feet. The original AVX tantalum capacitor welding leg has a different positive electrode than the negative electrode.

2. Disassembling the items, the transparent tape is printed with AVX at intervals of about 25CM (it is directly gravure by the machine, no color), and the false tape is generally not printed with AVX.

3. Printed text on the body of an SMD tantalum capacitor. The upper and bottom lines of printing on the tantalum capacitor body include the AVX LOGO logo, capacity value, voltage value, production batch number, and other four pieces of information. All of this information is necessary. There is no AVX LOGO logo in the upper left corner of the main body in this scenario). The tantalum capacitor container is quite large, and the printed characters are legible. Some AVX tantalum capacitors are too tiny to see properly without a magnifying glass.

4. The printing on the body of the SMD tantalum capacitor is consistent and of good quality. Many refurbished  tantalum capacitors cannot be identified as fake based on the three criteria above because they use original old or folded or low-voltage goods (a lower voltage and a lower level, such as using 10V for you as 16V) after re-grinding and printing. At this point, the quality and consistency of the printing on the body must be judged. The reconditioned goods' printing differs from the original in terms of content and layout. There will be no difference between them, but the original factory's equipment and molds aren't as good, so there will be minor variances in the details. There are two dimensions to the distinction between these details. On the one hand, there's elegance. On the one hand, the restored color is a darker red with various tones; on the other hand, it is the consistency. The original's consistency is excellent. It will seem staggered, and the contrast between the bodies will resemble that of two molds (caused by the poor accuracy of the molds). For this reason, it is difficult to make accurate and timely judgments, which is related to personal experience.

5. Check the specifications: If the parameters you're looking for aren't listed, you're probably buying a fake. Although specifications not in the specification book do not imply that the original factory does not make 100%, they do imply that the standards are not widely used, therefore the agent must have no inventory (there will be no agents who will order some partial materials for inventory). Ordinary customers find the order cycle, minimum order quantity, and prepayment ratio all undesirable when placing an order. As a result, we recommend that customers use standard products when selecting models, as non-standard products will only cause them to die in the end