Reliability Performance of Lead–Free SAC Solder Joints on Electroless Ni/Immersion Au and Electroless Ni/Electroless Pd/Immersion Au Subject to Long–Term Isothermal Aging

The thermal performance of 10 mm Pb-free, Sn–Ag–Cu (SAC) BGA packages on ENIG and ENEPIG surface finishes has been found to degrade significantly after 1 year/125 ?C aging. For SAC 105, the reliability deterioration was 40.9% on ENIG and 41.7% on ENEPIG while for SAC305, the deterioration was 32.8% on ENIG and 45.6% on ENEPIG. Sn–37Pb solder generally outperforms SAC105 and SAC305 with only one exception (SAC 305/ENIG at 125 ?C). The loss of reliability was related to microstructural and mechanical evolution due to alloy coarsening and growing interfacial intermetallic compounds. The full experimental matrix employed varying aging temperatures and solder alloys. Package sizes ranged from 19 mm, 0.8 mm pitch ball grid arrays (BGAs) to 5 mm, 0.4 mm pitch μB GAs, and 0.65 mm MLF and 2512 resistors. The isothermal aging temperatures were 55 ?C, 85 ?C, 100 ?C and 125 ?C, with aging time periods of 0, 21 days, 6 months, and 12 months. Subsequently, the specimens were thermally cycled from – 40 ?C to 125 ?C with 15 min dwell times at the high and low peak temperatures. Failure analysis showed dramatic Ni–Cu–Sn intermetallic growth at the board side interfaces. Cracks which propagate near the board side joint area were found more often in high temperature aged samples.