Interfacial Reactions between Sn-Cu Based Multicomponent Solders and Ni Substrates during Soldering and Aging

The interfacial reactions between two Sn-Cu based multicomponent Pb-free solders, Sn-2Cu-0.5Ni and Sn-2Cu-0.5Ni-0.5Au (wt%), and Ni substrates during soldering and aging were investigated. Differential scanning calorimetry (DSC) was performed to measure the melting behaviors of the solders and determine the temperature of soldering. DSC tests show that the onset temperatures are 227.47degC and 224.78degC for Sn-2Cu-0.5Ni and Sn-2Cu-0.5Ni-0.5Au, respectively. Two intermetallic compounds (IMCs), Cu₆Sn₅ and (Cu,Ni)₆Sn₅, are formed in Sn-2Cu-0.5Ni solder. While the IMCs detected in Sn-2Cu-0.5Ni-0.5Au matrix are (Cu,Ni)₆Sn₅, (Cu,Au)₆Sn₅ and (Cu,Ni,Au)₆Sn₅. The IMC layer formed at both the solder/Ni interfaces is (Cu,Ni)₆Sn₅ with stick-lick morphology after soldering at 260degC. The interfacial IMC layers become planar when aged at 170degC for 500 h. However, cracks are found in the IMC layers at both joints when the aging time reaches 1000 h, which implies reliability problem may exist in the joints. Moreover, Au-containing IMCs are found on the top of the IMC layer in Sn-2Cu-0.5Ni-0.5Au/Ni joint after aging for 1000 h.