Dynamic behavior of electronics package and impact reliability of BGA solder joints

The purposes of this study are to clarify the dynamic behavior of BGA or CSP packaging subjected to an impact loading, and to establish a simple analytical method of impact reliability assessment for solder joints. In order to take dynamic material properties into account, a high deformation speed tension test and a vibration test were carried out to obtain the strain rate dependence of yield stress and Young's modulus of solder materials and PCB. A 3-D analytical model of PCB mounted with a BGA chip was used to simulate the impact behavior of BGA packaging, and explicit-based FEM code LS-DYNA was used to carry out the dynamic analysis. It was found that the impact reliability of solder joints is greatly affected by the falling posture. However, it was found that fine meshing of solder joints causes a rapid augmentation of calculation cost. In this study, the authors proposed a new method of transient response analysis by utilizing implicit-based FEM code NASTRAN to drop the calculation cost of impact study. It was shown that the present method can accurately simulate the dynamic behavior of BGA packaging including the time histories of the deformations and stresses, and it can drop the CPU time to about one tenth of that of LS-DYNA analysis. Furthermore, based upon the analytical and experimental results, it was found that the impact reliability of solder joints is dominantly affected by the first mode vibration of PCB, and the effect of the higher modes can be neglected. Finally, a basic concept for impact reliability assessment method was proposed for CSP solder joints based on the results of the present analytical method and set of free fall drop tests of PCB mounted with a CSP chip.