SMT solder paste introduction, Shenzhen PCBA factory
SMT solder paste introduction

1. According to environmental protection requirements, solder paste is divided into lead solder paste and lead-free solder paste (environment-friendly solder paste):
Environmentally friendly solder paste contains only a small amount of lead. Lead is a harmful substance to people. Among the electronic products exported to Europe and the United States, the content of lead is strict. Therefore, lead-free processes are used in China. In the country's control of environmental protection, the SMT processing industry adopted a lead-free process in the passed few years.

 
In the lead-free SMT processing, it is relatively difficult to solder compared to the
Leaded process. When encountering BGA, QPN etc., normally use high-silver portion pastes containing silver. Commonly on the market the silver containing are 3 points and 0.3 points. Among the solder pastes, silver-containing solder pastes are currently more expensive.

 
2. According to the melting point, solder paste can be divided into high temperature, medium temperature and low temperature:
Commonly used high temperature paste are tin silver copper 305, 0307. There is tin, bismuth and silver in medium temperature paste, and tin and bismuth are commonly used at low temperature. In SMT processing, it is selected according to different product characteristics.

 
3. According to the fineness of the tin ball, Common used solder paste can be divided into No. 3 ball, No. 4 ball, and No. 5 ball solder paste. In the SMT processing of generally larger components (1206, 0805, LED lamps), No. 3 ball solder paste is used because its price is relatively cheap.
If there are dense-foot ICs encountered in digital products, No. 4 ball solder paste will be used in SMT processing. In the case of very precise soldered components such as BGA, QFN, and products that require high performance, such as mobile phones and tablets, In SMT processing will use No. 5 ball solder paste.