Drop impact reliability testing of isothermally aged doped low creep lead-free solder paste alloys

Abstract

Board level drop impact testing is one of the most important modes of evaluating the reliability of assemblies. This study examines the drop impact performance of no aged and isothermally aged flip chip packages on laminate assemblies for various doped lead-free solder paste alloys. A potential solution to replace the industrial standard solder paste Sn96.5 Ag3.0 Cu0.5 (SAC305) was carried out. The test vehicle consisted of 16 ball grid array packages (BGA) which were 15mm chip array ball grid array's (CABGA208) with perimeter solder balls on 0.8mm pitch. In this experimental study, SnAgCu solder bumps and SAC305 solder paste were selected to be the baseline, Solder pastes with 12 different dopant levels were investigated in comparison with the baseline to determine their reliability. Two sets of printed circuit boards (PCB) were manufactured, the first being no aged and the second set of boards were isothermally aged at 125C for 6 months and then tested. The boards were further categorized into 3 different reflow temperatures and 2 different stencil thicknesses, 4 mil and 6 mil respectively. JEDEC BS111 test standard was followed to conduct the drop testing where the half sine impact pulse duration of 0.5ms with peak acceleration at 1500G's was maintained. The boards were subjected to accelerated life testing where the test end state was 300 drops, and the data was collected at an interval of every 20 drops. The results of non-aged and aged samples were categorized and compared using data analytics and Weibull analysis. Failure analysis was carried out to determine best solder paste, solder ball, reflow temperature profile and stencil size for the future work.