Thermo-Elasto-Plastic Stress Analysis in Equilibrium Profile of SMT Solder Joints.

Abstract

Recently, surface mount technology (SMT) in an electronic packaging is playing a leading role compared to the plated-through-hole technology. SMT allows to place more electric components on a printed circuit board. Many investigations on mechanical and thermal properties of solder have been conducted numerically and experimentally, since the electric components are mounted by only soldering on the board. It is hard to examine the failure of electric components in experiment, since the size of solder joint is relatively small. In this case, a simulation technology is very useful for evaluating the reliability of SMT solder joint. In the present paper, before performing the stress analysis of SMT joints, the shape of solder joint was first determined numerically by solving a multiregion problem considering the surface tension of molten solder and the gravity. The joint profile changing from an initial profile to an equilibrium one was simulated by using a finite difference approximation for time and the boundary element method for domain. The scheme for remeshing technique which is combined a cubic spline and a base spline to interpolate nodes on the free surface is presented in this paper. After that, a nonlinear and thermo-elasto-plastic stress analysis using MARC was performed to study the deformation behavior of solder joints subjected to a cyclic thermal loading. Profile data of SMT solder joint employed for finite element analysis were used the equilibrium profile calculated by BEM. It was shown that a thermal stress concentration occurred in joints with a large quantity of solder and with a small gap between the chip and the base plate. Finally, it was shown that the shape of SMT solder for improving the reliability has equally a little quantity of solder at both sides, a little quantity of solder at upper fillets and a small height between the chip and the base plate.