Ball grid array (BGA) packages with the copper core solder balls

A viscoplastic constitutive model and the strain energy density were used to analyze the thermally induced plastic and creep deformation and low cycle fatigue behavior of the solder joints in Multilayer Laminate Ball Grid Array (MLBGA) packages mounted on Printed Circuit Boards (PCB). The time-dependent and time-independent viscoplastic strain rate and plastic hardening work factors of solder material were introduced to 2-D plane strain finite element models. The viscoplastic strain rate data was fitted to the viscoplastic flow equation. The plastic hardening factors were considered in the evolution equation. Finite element models, incorporating the viscoplastic flow and evolution equations, were verified by temperature cycling tests on assembled MLBGA packages. The Ohm resistance data from the experiments was used to characterize thermal fatigue life. After satisfactory correlation between the Ohm resistance data and the strain energy density was observed, the effect of the copper core size on the response of the viscoplastic deformation was studied. Furthermore, the effects of package design variables and the temperature cyclic frequencies on the fatigue life of solder joints in MLBGA packages was investigated and the primary factors affecting solder fatigue life were subsequently presented.