The impact of microstructure evolution, localized recrystallization and board thickness on Sn-Ag-Cu interconnect board level shock performance

The mechanical stability of solder joints with SnAgCu alloy on various board thicknesses were investigated in a high G level shock environment. A test vehicle with 31mil, 62mil and 93mil board thickness, which has three different strain and shock level condition combination per board, was used to identify the joint stability and failure modes. The results revealed that joint stability is sensitive to board thickness and that the first failure location shift from the corner location near the stand off to the center with increased board thickness. Also the impact of isothermal aging and fine grain structure transformation on mechanical shock performance of solder joints were investigated. The results revealed that joint stability during shock loading is sensitive to the level of shock that can be absorbed during each shock cycle based on the capability of single to multi grain transformation. The localized fine grain structure distributions were analyzed to identify correlations between the microstructure evolution and shock performance.