PCB Technical - What is the cause of poor tin eating in PCB manufacturing

Usually in the process of PCB design and production, have you ever encountered PCB poor tin-eating problems? For engineers, once a PCB board has poor tin-eating problems, it often means that it needs to be re-soldered or even re-made., The consequences are very troublesome. So, what are the reasons for the poor tin-eating of PCB? What methods can be used to avoid this problem?

What is the cause of poor tin eating in PCB manufacturing

There are many reasons that lead to the bad situation of PCB eating tin, which can usually be summarized as the following aspects.

The main reason for the poor tin-eating phenomenon of PCB board is generally that part of the surface of the circuit is not stained with tin. This kind of PCB board that has bad tin eating,

There is also a situation that can lead to poor tin eating on PCB boards, that is, the storage time is too long or the environment is humid, and the production process is not rigorous. As a result, the tin surface of the substrate or parts is oxidized and the copper surface is dull. When this happens, switching to flux can no longer solve this problem, and the technician must re-soldering once, so as to improve the PCB's tin-eating effect.

Grease, impurities and other debris attached to the surface of the PCB board, or grinding particles left on the circuit surface during the manufacturing process of the substrate, or residual silicone oil, will cause the PCB to eat poorly. If the above situation occurs during the inspection, you can use a solvent to clean the debris. But if it is silicone oil, it needs to be washed with a special cleaning solvent, otherwise it is not easy to be cleaned.

Failure to ensure sufficient temperature or time during the PCB soldering process, or incorrect use of flux, will also lead to poor PCB tin eating. Generally, the operating temperature of soldering tin is 55～80 degree Celsius higher than its melting point temperature. Insufficient preheating time can easily lead to poor tin eating. The amount of flux distribution on the circuit surface is affected by the specific gravity. Checking the specific gravity can also eliminate the possibility of misuse of improper flux due to incorrect labeling, poor storage conditions and other reasons.

In the process of PCB soldering, the quality of the solder material and the cleanliness of the terminals are also directly related to the final result. If there are too many impurities in the solder or the terminals are dirty, it will also cause the PCB to eat badly. When soldering, you can measure the impurities in the solder on time and ensure the cleanliness of each terminal. If the quality of the solder does not meet the regulations, you need to replace the standard solder.

In addition to the above-mentioned conditions that lead to the PCB eating tin, there is another problem similar to the PCB eating tin bad situation, that is, tin stripping. PCB de-tinning mostly occurs on tin-lead-plated substrates, and its specific performance is very similar to that of poor tin-eating. However, when the surface of the tin road to be soldered is separated from the tin wave, most of the solder that has been stuck on it will be pulled back into the tin furnace. Therefore, the situation of tin stripping is more serious than poor tin eating. Resoldering the substrate may not always improve, so once this happens, the engineer must return the PCB board to the factory for repair.