Investigation of the effect of PCB inner copper layer plastic deformation on solder joint fatigue simulations of mechanical cyclic bending tests

Microelectronic packages undergo both thermal and mechanical loading during application, which can affect solder joint lifetime. Therefore, solder joint fatigue under both cycling thermal loading and mechanical bending should be assessed. This can be done by finite element simulation method during early design stage. An accurate finite element simulation model is needed to describe the fatigue of the solder joint and derive lifetime predictions. Especially in mechanical cycle bending test simulation, the PCB mechanical properties are a key factor for accurate description of the loading on the solder joint. In this study, a multilayer FR4 PCB is used, including several copper layers, which undergo plastic deformation under bending. Copper plasticity is included in the finite element model and calibrated using force-displacement data from the bending tests. It is found that PCB inner copper plasticity should not be neglected, otherwise the loading on the solder joint would be overestimated and the lifetime prediction inaccurate.