Accurate Prediction of Solder Stresses/Strains in Multi-Layered Electronics Packages During Temperature Cycling

Solder balls are critical for interconnecting chips and PCBs in electronics assemblies, yet they often represent the weakest link. Traditional analytical methods for assessing shear strain rely on a simplistic global coefficient of thermal expansion (CTE) mismatch between chip and PCB. However, electronic packages are multilayered structures, with each component possessing distinct material properties, primarily CTE and Young's modulus. During temperature cycling, disparities in CTE and modulus among these components affect solder's shear strain. Additionally, package warpage induces bending deformation, resulting in normal strains on solder balls. This paper introduces analytical models to evaluate both shear and normal strains on the outer-edge solder balls during temperature variations. Our analytical model significantly improves upon classical methods, exhibiting an order of magnitude higher accuracy in predicting shear strain. Furthermore, our normal strain model captures strains developed during assembly warpage, unaccounted for by classical method. Numerical simulations using finite element analysis validate our analytical models, demonstrating excellent agreement between analytical and numerical solutions. These findings underscore the superior accuracy of our developed model in predicting solder strains and life, offering significant advancements in electronic assembly reliability.