Interfacial reactions between Sn-Cu solder alloy and Cu/Ni coatings during reflow soldering

The interface microstructures of soldered joints under different soldering techniques were observed and analyzed. The interface reaction during soldering was studied. The growth mechanism of the IMCs was discussed and the influences of soldering temperature and dwell time on IMC evolution were investigated. The equation of the relationship between IMCs thickness and soldering conditions including soldering temperature and dwell time was developed. The results suggest that, during soldering, the joint interface between the solder and Cu/Ni coating exhibits a duplex structure of Cu₆Sn₅ and Cu₃Sn intermetallic compounds (IMCs). A parabolic relationship exists between the growth of the IMC layer and soldering time. This indicates that the mechanism of IMC growth is a diffusion-controlled process. The growth rates for the intermetallic layers increase with soldering temperature, whereas decreases with time.