Heterogeneity-induced thermal mismatch in BGA interconnects: Insights from mechanical-thermal finite element modeling

Thermal expansion mismatch due to the heterogeneous materials in ball grid array (BGA) interconnects of electronic packaging structures often results in localized strain concentration, leading to creep, fatigue, or potential failure. Modeling BGA solder balls independently, without considering connected and contacting components, fails to comprehensively monitor the system's state. In this study, a mechanical-thermal finite element model (FEM) comprising solder balls, a printed circuit board (PCB), chips, and underfill is systematically developed. Time-dependent nonlinear analysis is performed on Sn-Ag-Cu (SAC) solder-bumped flip chips in PCB assemblies subjected to thermal cycling. Thermal gradient contours illustrate inhomogeneous in-plane and vertical thermal diffusion within the components. The Garofalo model is employed in the FEM to simulate visco-plastic behavior. The results reveal significant thermal gradient mismatches due to the intrinsic properties of heterogeneous components, which are often overlooked in independent material studies. Additionally, the central region of the BGA exhibits more pronounced creep strain compared to edge solder balls. These findings provide valuable insights for optimizing BGA geometric design. This work also offers a comprehensive framework to quantify thermal mismatches and simulate creep behavior under thermal cycling based on FEM.