Micro Indentation Measurements of the Creep Properties of CABGA Doped Solder Joint

Doping SAC solder joints with some elements such as Bi (bismuth) and In (Indium) has been found to improve the thermal cycling reliability, reduce the effect of aging, and improve fatigue resistance. However, the impact of such elements on creep and mechanical properties is not well understood. In this study, the creep properties of doped solder joints and the impact on reliability are investigated. Three different lead-free solder alloy compositions are considered, including SAC305, SnAgCu-3Bi, SnAgCu-0.5Bi-6In, SnAgCu-0.5Bi-0.13In, and those were compared with Sn63Pb37 solder alloy. The test vehicle involves three 15mm Ball Grid Array (CABGA) components. Two groups of CABGA are studied. The first group is tested directly after assembly. The second group is thermally cycled between -40
^o
C to +125
^o
C. The Instron 5948 Micro Tester is used to perform the micro-indentation for individual solder joints by using a customized experimental setup with a cylindrical flat indenter. The test conditions involve applying constant load for an extended time and record the indentation depth with time. Three different loads are applied, with 3 replicates each. The test was conducted at room temperature. The results showed that the creep rate of doped alloys was notably lower than SAC305 due to the solid solution hardening of the Sn lattice structure. SAC-3Bi alloys showed improved steady-state creep rate after thermal cycling.