Thermomechanical behavior of ceramic ball grid array based on experiments and FEM simulations

Abstract

In this paper, we have performed 2D finite element simulations on CBGA components assembled on FR4 card in order to evaluate the highest stressed regions of the solder joint. The maximum cumulative strain energy has been calculated as a function of the thermal cycling characteristics and of the package size to evaluate the fatigue of the solder joints. Accelerated ageing tests (0/spl deg/C to 100/spl deg/C) have been performed on CBGA samples to validate such a global approach. The analysis of the degradation have been performed using direct observation with SEM and also a specific procedure of acoustic imaging allowing the detection of defects located on the inner balls. From the previous FEM simulation results and the experimental data under thermal cycling, we propose a global interpretation, based on general mechanical laws, of the thermomechanical behavior of the CBGA solder joints under thermal cycling. Conclusions about the evolution of the CBGA assemblies criticity with both package size and ball number increase are deduced from this study.