The Effect of Stencil Printing Optimization on Reliability of CBGA and PBGA Solder Joints

Abstract

As a follow-up and conclusion to previous work in stencil printing process modeling and optimization (Li et al., 1996), we investigate the effect of stencil printing optimization on the reliability of the ceramic and plastic ball grid arrays. For ceramic ball grid arrays, the eutectic solder fillet shape is calculated using a series of simple mathematical equations. The thermal strain distributions within the solder joints after two cycles of accelerated thermal cycling test are estimated using three-dimensional finite element models. The modified Coffin-Manson relationship is applied to calculate the mean fatigue lives of the solder joints. The results reveal that an optimized stencil printing process significantly reduces variation in the fatigue life of ceramic ball grid arrays. The results also show that the fatigue life of ceramic ball grid arrays is very sensitive to the card-side solder volume. The maximum strain region shifts from the card-side eutectic solder to the module side as the card-side eutectic solder volume increases. This shift in maximum strain suggests that there exists an optimum ratio between the card-side solder volume and the module-side solder volume for the reliability of a given ceramic ball grid array design. The implications of this for the package developers and users are discussed. The calculations indicate that the fatigue life of plastic ball grid arrays is almost insensitive to the card-side solder volume.