FEM analysis with cyclic visco-plasticity for solder bumped flip-chip packaging

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint stress-strain condition. The mechanism of substrate flexibility on improving solder joint thermal fatigue was investigated by a thermal mechanical analysis (TMA) technique. The reliability of solder joints in flip chip assemblies with both rigid and compliant substrates was studied by accelerated temperature cycling test and numerical simulation. Finite element simulations were performed to study the reliability of solder joints in flip chip on flex assembly (FCOF) and flip chip on rigid board assembly (FCOB), applying the Anand model. The results of finite element analysis showed good agreement with the experimental results. It was found that the thermal strain and stress condition in FCOF solder joints was much improved over that in FCOB solder joints. It is concluded that the thermal strain and stress in solder joints could be reduced by flex buckling or bending and flex substrates could dissipate energy that otherwise would be absorbed by solder joints. Therefore, substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during temperature cycling.