Numerical and experimental analysis of the Sn3.5Ag0.75Cu solder joint reliability under thermal cycling

摘要

The Sn3.5Ag0.75Cu (SAC) solder joint reliability under thermal cycling was investigated by experiment and finite element method (FEM) analysis. SAC solder balls were reflowed on three Au metallization thicknesses, which are 0.1, 0.9, and 4.0 μm, respectively, by laser soldering. Little Cu-Ni-Au-Sn intermetallic compound (IMC) was formed at the interface of solder joints with 0.1 μm Au metallization even after 1000 thermal cycles. The morphology of AuSn_4 IMC with a small amount of Ni and Cu changed gradually from needle- to chunky-type for the solder joints with 0.9 μm Au metallization during thermal cycling. For solder joints with 4 μm Au metallization, the interfacial morphology between AuSn_4 and solder bulk became smoother, and AuSn_4 grew at the expense of AuSn and AuSn_2. The cracks mainly occurred through solder near the interface of solder/IMC on the component side for solder joints with 0.1 μm Au metallization after thermal shock, and the failure was characterized by intergranular cracking. The cracks of solder joints with 0.9 μm Au metallization were also observed at the same location, but the crack was not so significant. Only micro-cracks were found on the AuSn_4 IMC surface for solder joints with 4.0 μm Au metallization. The responses of stress and strain were investigated with nonlinear FEM, and the results correlated well with the experimental results.