Discussion on the selection of tantalum capacitors by electronic manufacturers from practical cases

With the rapid development of domestic components manufacturing industry, the selection range of components, especially passive components such as resistance and capacitance, is greatly increased. However, high-end products such as small size, high precision and good stability components are still imported products, accounting for a large market share. At present, domestic manufacturers have gradually entered the field of high-end passive devices, such as MLCC and tantalum capacitors. However, how to choose the complete machine enterprises and what problems they may face in the use process have always been the topic of concern. The reader "Edison" posted a post to share his actual experience of using a famous brand tantalum capacitor of a state-owned enterprise (for details, please refer to http://forum.esm-cn.com/FORUM_ POST_ 1200409735_ HTM), and describes the actual problems encountered in the process in detail. This post replies many, and the discussion has the reference value.

"Edison" said that the performance and reliability of tantalum capacitors are good theoretically. In practical use, tantalum capacitor is a very fragile component, because some defects can not be avoided in the production process of tantalum capacitor, and these defects become the biggest hidden danger of voltage breakdown. In the process of using a famous domestic brand tantalum capacitor, the production line reflected that the defective rate (breakdown) of this brand tantalum capacitor was very high. After investigation, it is found that due to special reasons, the defective rate of some manually welded tantalum capacitors is very high, but there are also defects on the boards pasted by the mounter. Of course, tantalum capacitors are afraid of manual welding. However, due to the poor machine mounting, the preliminary positioning is the quality of the device

"The operating voltage of these tantalum capacitors has been derated by more than half, so the design problem can be ruled out (the voltage derating of tantalum capacitors is only 1 / 3, which is not reliable, it needs to be reduced by more than half to be reliable). Because tantalum capacitors are afraid of surge voltage, 100 samples were taken from the warehouse, and their surge voltage was tested according to the general industry standard (at room temperature, the condition has been relaxed). It was found that some of them had transient breakdown and self-healing phenomenon during the test process, and some of them were also punctured individually. "

After that, he sent the company's test report to the original factory, asking for replacement and providing the test report. When the next batch of products were inspected, he found that there were obvious traces on the tape, which indicated that the supplier changed the production date of the returned products. Through the test of surge voltage, it is found that the defective products have not passed the conventional withstand voltage test.

The supplier of the tantalum capacitor said that it only had the qualification certificate, but did not provide the factory test report, and said that the tantalum capacitor did not need to test the surge voltage. The poor conventional withstand voltage was due to the manual welding temperature of the soldering iron during the test. The test condition of the main building is that the temperature of soldering iron is 310 ℃, and the soldering is carried out by skilled workers in 2-3 seconds. According to the test report issued by the supplier again, the temperature of soldering iron manual welding is 220 ℃. "Can the soldering iron temperature of 220 ℃ be used to weld devices?" The landlord questioned this.

Due to no longer trust the manufacturer's technical services, the owner finally decided not to use its tantalum capacitor. He concluded that the tantalum capacitor manufacturer had three problems: "1. As the device most afraid of surge voltage, they even said that it was not necessary to measure the surge voltage. The reliability of the devices produced by such a manufacturer was not guaranteed. 2、 If there is a quality problem, they don't pay attention to it, they don't produce new batches, and they have to risk re supplying the returned capacitors, which shows that their quality awareness is very poor. 3、 Falsification in the quality report shows that they are not practical and reliable. Although this is a well-known state-owned enterprise, there are still great risks in using their devices. " After the reply of netizens also claimed that the brand of tantalum capacitor failure rate is indeed too high.

"Edison" put forward two suggestions on the use of components: first, no matter how famous they are, they should be inspected on the spot. Because some state-owned enterprises are very backward in technology, there may be other problems, which can only be found through on-the-spot investigation. 2、 Technical agreement or quality assurance agreement shall be signed, especially the test requirements for devices shall be clearly written. If necessary, the process and raw materials of some devices shall be controlled.

The reader "component expert" also analyzed the technical and operational problems in the use of tantalum capacitors. "If the tantalum capacitor is not applied well, it is easy to fail, which is mainly manifested in its inability to withstand surge voltage / surge current. It is suggested that the working voltage should be reduced to 1 / 3 rated voltage. If over-voltage or over-current, it is easy to breakdown or even burn. The reason is that TA, Ta2O5 and MnO2 in tantalum capacitor will react with each other and precipitate O2 under the condition of over current, and TA is easy to burn. At the same time, it should be explained whether there are many short circuits or bad open circuits. This problem is mainly due to the poor welding thermal performance of tantalum capacitors, because the tantalum wires connected to the positive electrode of tantalum capacitors are very fine. The temperature and welding time of the soldering iron should be paid great attention to, and the welding curve of the device should be followed

Some netizens said they didn't agree with the owner. The reader "Borton" pointed out that the building mainly specified which models had problems, otherwise people would think that all tantalum capacitors of the factory were not good. At present, the main parameter gap between domestic tantalum capacitor and imported tantalum capacitor is some limited products. Domestic tantalum capacitor can not be made or its quality is unreliable, such as 47 μ f / 6.3V for a size and 100 μ f / 6.3V for B size. From the point of view of quality, if the defect rate of their process is high, the defect rate of flow to end customers is high.

The owner also replied to clarify that "this capacitor is indeed the limit specification, and this time it is a batch problem, but the original factory's treatment method makes me feel that no matter what specification, there may be a risk of batch problems in the future."

Netizens "late start" speech represents the general voice of the industry. "The problem reflected by the owner is objective, and similar phenomena exist in domestic electronic component enterprises. I think manufacturing is one aspect, and understanding of customers' needs is another. The problem of building owners is precisely caused by the manufacturers' failure to understand the needs of customers. As for the way to deal with problems, it is a problem of ability. Without the existence of state-owned components enterprises, our complete machine manufacturers will not be able to negotiate prices with foreign component manufacturers. It is suggested that domestic enterprises should be more tolerant. "