Solder paste is mainly a paste-like mixture composed of solder powder and flux. It is mainly used in the SMT processing industry to solder electronic components such as resistors, capacitors, and ICs on PCB boards. Solder paste is divided into lead-free solder paste and leaded solder paste. Lead-free solder paste is an important material for electronic component soldering. Lead-free solder paste refers to the requirement of lead content less than 1000ppm (<0.1%) to comply with environmental protection ROHS Standard; leaded solder paste literally means solder paste containing lead. These two solder pastes are very different. Today we will organize and analyze them as follows:

1. In terms of appearance, solder pastes are all paste-like. The difference is that the packaging of lead-free solder paste is generally green, and the lead-free solder wire is white. The paste color of lead-free solder paste is not The color of leaded solder paste is deep, and the lead-free solder paste follows the RoHS standard. The conventional way in the industry is to use green bottles to store them, so that engineers can intuitively distinguish them when they use them.

2. Lead-free solder paste is mainly composed of tin/silver/copper, or tin/bismuth/copper, tin/copper, tin-bismuth and other alloys, while the alloy composition of lead-free solder paste is mainly composed of tin and lead. The common alloy ratio is: Sn:Pb=63:37. In addition to the different components of leaded solder paste and lead-free solder paste, the activity of the two solder pastes is also different. In contrast, the activity of lead-free solder paste is stronger, while the wettability of lead-free alloy is not as good as that of lead-containing solder paste. , The most important thing in the use of lead-free solder paste is the adjustment of the temperature curve. Manufacturers of solder paste can use the data provided by the supplier for reference, plus their own experiments, and adjust the process window to achieve good results.

3. The melting point temperature of solder paste varies according to the alloy composition of the solder paste: the melting point of the solder paste of tin-copper alloy is 220-227℃; the melting point of tin-silver-copper alloy solder paste is 217-227℃; the melting point of tin-bismuth-silver alloy The melting point of solder paste is 172°C; the melting point of tin-bismuth alloy solder paste is 138°C; the melting point of tin-lead alloy (6337) leaded solder paste is 183°C. It can be concluded that there is still a big difference in the melting point of lead-free solder paste and leaded solder paste.

4. Lead-free solder paste is used in the welding process of components with environmental protection requirements. Due to the large proportion of alloy components, lead-free solder paste will have a wider range of applications. The leaded solder paste is used in the welding of products without general environmental protection requirements. The lead in the leaded solder paste is relatively harmful to the human body and nature. In the future development trend, the lead-free solder paste will definitely replace the leaded solder paste. become a necessity. The solder joints of leaded solder paste are brighter than those of lead-free solder paste, which is inseparable from the composition and operating temperature of leaded solder paste and lead-free solder paste. It does not affect the soldering performance of the solder paste. When purchasing solder paste, you must pay attention to the distinction and choose the solder paste that suits your production requirements.