Comparison with reliability of low Ag solder ball by thermal shock and cycling tests

In this paper, three different solder ball joints for board level BGA packages with Sn-1.0Ag-0.5Cu(SAC105), Sn-1.2Ag-0.5Cu(SAC1205) and Sn-3.0Ag-0.5Cu(SAC305) have been evaluated to compare with reliability of low Ag solder ball by thermal shock and cycling tests. BGA packages had 97 pads and solder ball pitch of 0.4 mm. And thermal shock tests were conducted on those packages with the temperature ranges from −40°C to 125°C (TS1) and −55°C to 125°C (TS2). Additionally, thermal cycling tests were performed with the same temperature ranges, from −40°C to 125°C (TC1) and −55°C to 125°C (TC2) with 15 minutes dwell time. Thermal cycling test follows JEDEC standard JESD22-A104D condition G and B, respectively. To verify the exact time to failure, resistances of daisy chains were monitored at every 5 minutes during both thermal shock and cycling tests. Failure sites of low Ag solder balls were identified with cross-sectional images from optical microscope and scanning electron microscope (SEM). Mechanical strengths of some low Ag solder balls were tested by using ball shear test (BST). Finally, statistical analysis was carried out on the results of all thermal shock and cycling tests.