Fatigue Performance of Doped SAC Solder Joints in BGA Assembly

Fatigue failure of interconnected solder joints is a critical consideration for the reliability of an electronic product. Commonly, fatigue properties of solder materials are investigated using large bulk samples. However, limited studies considered the actual solder joints that are typically found in BGA components. This study includes customized sandwich BGA test vehicles with 3 x3 solder joints connected between two substrates. Instron Micromechanical Tester is used to test the samples in both stress-controlled and strain-controlled experiments at room temperature. The testing was conducted at a constant strain rate. The tested solder materials are Sn-3Ag-0.5Cu (SAC305), Sn-3.5Ag-0.7Cu-3Bi-1.5Sb-0.125Ni (Innolot), Sn-3.41Ag-0.52Cu-3.3Bi (SAC-Q), and Sn-0.92Cu-2.46Bi (SAC-R). The displacement-load (hysteresis) loops for each sample were systematically recorded, and thus the work per cycling and plastic strain range are measured. The results showed that Innolot has better fatigue life than SAC305, SAC-Q and SAC-R in both stress-controlled test and strain-controlled test, while the fatigue performance of SAC305 in strain-controlled test is better than that in stress-controlled test.