This study aims to systematically investigate the failure mechanisms of plastic ball grid array (PBGA)-packaged Sn-37Pb/Cu solder joints under extreme thermal shock conditions. It specifically focuses on understanding the microstructural evolution, degradation of mechanical properties and fracture behavior induced by rapid, large temperature swings. The goal is to elucidate the synergistic effects of intermetallic compound (IMC) growth and thermomechanical stress leading to joint failure, providing insights for high-reliability electronic packaging design.
The study used extreme-temperature thermal shock cycling (−110°C to 110 °C) on Sn-37Pb/Cu solder joints within PBGA packages. Microstructural evolution was systematically analyzed using microscopy techniques. Mechanical degradation was assessed through shear strength testing at intervals up to 500 cycles. Fracture behavior and interfacial characteristics were examined. Finite element analysis (FEA) was used to model stress (von Mises), plastic strain and strain energy distribution within the solder joints, particularly focusing on the joint/pad interface corners, to identify crack initiation sites and understand the failure mechanism.
Thermal shock caused cracks initiating within the Cu6Sn5 layer at solder joint corners, propagating to the interface. The interfacial IMC layer coarsened (wavy to scalloped), forming Cu3Sn and Kirkendall voids coalescing with cycles. Shear strength decreased by 20.4% (to 44.58 MPa) after 500 cycles. Fracture mode shifted from ductile to ductile-brittle mixed. FEA confirmed significant von Mises stress, plastic strain and strain energy accumulation at corners and driving crack initiation. The characteristic life was predicted as 642.5 cycles.
This work elucidates the novel synergistic failure mechanism where extreme thermal shock simultaneously drives detrimental IMC evolution (growth, phase formation and voiding) and localized stress/strain accumulation at solder joint corners, leading to crack initiation and propagation. It provides a crucial theoretical foundation for designing reliable packaging subjected to harsh temperature environments.
