Failure mechanisms of PBGA packages under coupled humidity-thermal-electrical fields: Electrochemical migration behavior and multi-physics simulation

Plastic ball grid array (PBGA) packages are widely used in modern electronic systems, yet their non-hermetic encapsulation makes them highly vulnerable to electrochemical migration (ECM) and interfacial delamination under humidity-thermal-electrical loading. In this work, the failure mechanisms of PBGA-related interconnect structures were systematically investigated through ECM experiments, hygrothermal aging tests, reflow reliability evaluation, and multi-physics finite element simulation. ECM tests revealed that bare Cu conductors exhibited rapid dendritic bridging under high humidity and electrical bias. Under a 10 V bias, dendrite initiation occurred at 29 s and electrical short-circuit bridging was achieved at 52 s. In contrast, SAC305/OSP/Cu electrodes showed more complex ECM behavior due to multi-metal dissolution and precipitation. At 10 V, dendritic growth was observed at 384 s and short-circuit failure occurred at 392 s. Hygrothermal aging results demonstrated that PBGA packages primarily failed by delamination, initiating at die corners and propagating inward. Under 60 °C/85% RH, severe delamination appeared after 192 h and expanded to nearly the entire die-molding compound interface after 1000 h. Baking treatment effectively mitigated moisture-induced damage and reduced delamination after reflowing. Multi-physics simulations indicated that Joule heating accelerated moisture diffusion by increasing package temperature. Under moisture-thermal-electrical coupling, maximum stresses reached 134.9 MPa in the interconnect region and 83.8 MPa in the die region, indicating thermal stress dominance and non-linear coupling between thermal expansion and hygroscopic swelling.