Microstructure and Property of Sn–37Pb Solder Bumps in Ø0.6 mm Ball during Thermal Shock

Abstract

Sn37Pb solder bumps with Ø0.6 mm ball were used to conduct thermal shock test, microstructure and property of solder bumps were investigated. The experimental results have shown that the shear strength of solder bumps was 62.89 MPa after reflow, then dropped to between 47.31 MPa and 50.86 MPa with increasing of thermal shock cycles, but finally reached to 61.96 MPa at 2000 cycles again. Interfacial IMCs were typical scallop-type and loose in the solder bumps, but were serrated and become smoother and compact after thermal shock with 1500 cycles. The IMCs thickness of solder bumps was about 1.80∼3.05 µm, but the composition of IMCs was Cu₆Sn₅ whether thermal shock or not. 1/25 of solder bumps at 200∼1000 cycles, 2/25 of solder bumps at 1500 cycles and 3/25 of solder bumps at 2000 cycles were failure respectively. Obvious tearing crack and fiber tissue was observed in the solder bumps of as-received, and then became large after thermal shock, but dimples of solder bumps deepened after thermal shock at 2000 cycles.