CBGA SOLDER FILLET SHAPE PREDICTION AND DESIGN OPTIMIZATION

In this paper; we first present a mathematical method that can be used to predict the eutectic solder fillet shape for ceramic ball grid arr ay joints. An underlying assumption is that the solder fillets on both the module and the card sides can be represented as arcs. The fillets ' profiles are then calculated for the factors affecting the shape inc luding solder volume, pad size, solder ball size, the wetting angle be tween eutectic solder and solder ball, and the gap between solder ball and pad The second parr of the paper focuses on design for reliabilit y and investigates the effect of the interactions between the card-sid e and the module-side solder fillets on CBGA solder joint reliability. To this end, a central composite design of experiment is set up to sy stematically vary the pad size and the eutectic solder volume on both the module and the card sides. For each of the design settings, the pr oposed mathematical method is used to calculate the solder fillet shap e. Using ABAQUS and the modified Coffin-Manson relationship, the mean fatigue life is predicted. The implications of the simulations are dis cussed. In addition, a response surface model is presented to find the optimum settings for maximum reliability. Finally, a comparison is ma de for the fatigue life predictions obtained using the proposed mathem atical method and the linear solder fillet assumption.