With the widespread implementation of lead-free PCB soldering and the widespread application of immersion tin board in high reliability board parts, especially automotive boards, the proportion of surface treatment of immersion tin is rising, so a better understanding of the surface treatment of Imm Tin The characteristics are very important to ensure the reliability of the immersion tin PCB. This article refers to a large number of immersion tin materials, and based on actual experience, gives a more detailed introduction to Imm Tin's related quality characteristics, and also gives methods for improving Immersion tin's related quality defects, hoping to enable readers to better understand immersion tin pcb and control the quality.
Principle of Imm Tin, the imm tin reaction is the replacement reaction of tin and copper. Through the replacement reaction of tin ions and copper, tin is deposited on the copper surface to form a flat, bright metal tin layer.The reaction equation is as shown in equation (1): Cu + Sn2 + = Sn + Cu2 + (1) In theory, the potential of copper (E0Cu2 + / Cu = 0.34 V) is higher than that of tin (E0Sn2 + / Sn = -0.14V), so it is impossible for copper to replace tin If you want to replace copper with tin, you must add a copper ion complexing agent, such as thiourea, cyanide, etc., and form a stable complex with Cu2 + to negatively shift the potential of copper to achieve the purpose of immersion tin. Improper handling by PCB manufacturers may cause a lot of problems. In the process of making the double-sided solder mask opening immersion tin PCB, due to the development of the plug hole window, the ink in the hole is attacked by the potion, and there is a hole in the hole after soldering , ink spill and light transmission problems, and when sinking tin in the subsequent process, the hole in the hole is easy to leave the potion, which causes the potion to contaminate the tin surface, causing the tin surface to blacken.
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