Effect of Ni or Co Addition to Sn-Ag Solder on Microstructure and Joint Strength at Interface

Among various lead-free alloys, Sn-Ag(-Cu) system solders are considered the most promising lead-free solders for both wave and reflow soldering technology. Moreover, to improve the characteristics of lead-free solders, the effect of the addition of minor elements to lead-free solders on the properties of solder and interfacial reactions have been studied. The purpose of this research was to investigate the addition of Ni or Co to the Sn-Ag solder on the microstructure and the joint strength of the interface with metallization layer of the substrate. As a metallization layer of the substrate, bare Cu and electroless Ni-P plating were used. For the reflow process, test samples were heated in a radiation furnace at 523 K for 60 s, and for the aging process, some samples were heat-treated in an oil bath at 423 K for 168 h, 504 h and 1008 h. Results show the addition of Ni or Co was effective for the IMC formation and growth at the interface with a Cu pad during reflow and aging process, and the addition of Co, except Ni, affected the pull strength of the solder joint with electroless Ni-P plating during aging process.