Impact of solder pad size on solder joint reliability in flip chip PBGA packages

A variety of package parameters impact package reliability. One of the parameters that does not get much attention is the variations in package design that are assembly and vendor related. It was shown in this study that the solder pad size plays a big role in solder joint reliability. The difference in solder pad size due to different vendors and processes can affect the reliability considerably. In certain cases, the pad size effect can be so significant that it will override the effect of substrate thickness. Our work indicates that in order to obtain good correlations between predictive engineering results and reliability tests data, this factor should not be ignored. In this paper, finite element analysis was used to study the impact of substrate thickness on solder reliability for flip-chip PBGA (plastic ball grid array) packages. The simulation results were experimentally validated with moire interferometry. Both numerical and experimental results indicated that better solder reliability could be achieved by using thicker substrate. However, the size of BGA solder pad was found to be crucial to BGA life. In order to achieve higher C5 (controlled collapse chip carrier connection) reliability, a larger solder pad is preferred