One of the essential solder raw materials in the SMT production process is solder paste
. The solder paste is divided into lead-free environmental protection solder paste and leaded solder paste according to environmental protection standards. Among them, lead-free solder paste is divided into low-temperature solder paste according to the melting point of the solder paste. So how to choose the solder paste suitable for patch in actual production?
First of all, let's first understand the characteristics of low-temperature solder paste, medium-temperature solder paste, and high-temperature solder paste:
1. Low-temperature solder paste refers to the solder paste with a melting point of 138°C, which is called low-temperature solder paste. When the components of the chip cannot withstand the temperature of 200°C and above, low-temperature solder paste should be used for welding. Low-temperature solder paste plays a role in protecting components and PCB boards. The alloy composition of low-temperature solder paste is mainly tin-bismuth alloy, and the peak temperature of reflow soldering is 170-200°C.
2. Medium-temperature solder paste is a solder paste with a moderate melting point compared with low-temperature solder paste and high-temperature solder paste. The melting point is 172°C. The alloy composition is tin-silver-bismuth. It is mainly used for welding components that cannot withstand high temperatures. LED There are many industrial applications. The feature of medium temperature solder paste is the use of imported special rosin, which has good adhesion and can effectively prevent slumping. The amount of residue after reflow is small and transparent, which does not hinder ICT testing. Silver is added to the composition. , the firmness of welding is better.
3. High-temperature solder paste is a lead-free solder paste composed of tin, silver, copper and other alloy components with a melting point between 210-227°C. It is mainly used in the condition that the components or lamp beads can withstand high temperature during patching, the reliability is relatively high, and it is not easy to desolder and crack. High-temperature solder paste is more widely used than low-temperature and medium-temperature solder paste. For example, the soldering of some BGA, QFN, and mobile phone precision components will be better with high-temperature solder paste. It has good solder climbing effect and long service life; high activity, Low void rate, not easy to collapse; full and bright solder joints, high strength, excellent electrical conductivity; excellent printing performance and mold release performance, no pressure for fine pin pitch mounting; imported flux, can be printed for a long time without affecting Solder paste wettability and viscosity.