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The cause of poor solder joint in PCB

In the process of PCB design and production, did you ever meet PCB's bad tin? For engineers, once a PCB board appears to eat bad tin problems, it often means rewelding or even remanufacturing. The consequences are very headache. So, what is the cause of PCB's bad tin? What can be used to avoid the emergence of this problem?

In general, the reason why the PCB board eats tin is the main reason is that the surface of the line is not covered with tin. This PCB board, which appears to have bad tin conditions, is usually shown in the reality, as shown in the following figure:

There are many reasons that cause PCB to eat tin, which can be summed up as the following.

The surface of the PCB board has impurities such as grease, impurities, etc., or there are polished particles in the manufacturing process, which are left on the surface of the circuit, or there are silicone oil residues, which will lead to bad PCB eating tin. In the process of inspection, if the above situation occurs, the solvent can be used to wash the impurities. But if it is silicone oil, then we need to use a special cleaning solvent for washing, otherwise it is not easy to be cleaned.

Another case may lead to bad eating of tin in PCB board, that is to say, during storage, it is too long to store or wet in environment, and the production process is not rigorous, resulting in serious oxidation of tin and oxidation of copper surface. When this happens, it is no longer possible to solve this problem by changing the flux. Technicians must re weld them once so that the tin effect of PCB can be improved.

No sufficient temperature or time in the PCB welding process, or the correct use of flux, can also cause PCB to eat tin. The general operating temperature than the melting point of the solder temperature 55 to 80 DEG C, the preheating time is not very easy to cause the bad situation of tin. The number of flux distribution on the surface of the line is influenced by the proportion of the flux. Check the proportion can be ruled out because of the wrong stickers and storage conditions and the reasons for poor misuse improper flux.

In the process of welding, the quality of the solder and the cleanliness of the terminal are also directly related to the final result. If there are too many impurities or terminals in the solder, it will also cause PCB to eat tin. In the process of welding, the impurities in the solder can be measured on time and the cleaning of each terminal is guaranteed. The standard solder should be replaced if the solder quality is not qualified.

In addition to the above mentioned conditions, there is a problem similar to PCB eating tin, which is tin. The situation of PCB tin withdrawal occurs mostly in tin plating lead substrate, which is very similar to the condition of eating tin. But in the surface to be welded with Xi Road, tin wave detachment, solder has mostly been on the stick will be pulled back to the furnace, so the tin and tin side compared to the more serious, the substrate will not necessarily improve reweld, so if this is the case, the engineer the PCB must be in depot repair.

Source: E-TECH