Design optimization approaches for the thermo-mechanical reliability of land grid array solder joints

This paper presents two design optimization approaches, the deterministic approach and the reliability-based approach, for the solder joint reliability of a 2^nd-level land ball array (LGA) package under temperature cycling. The printed wiring board (PWB) thickness, Young´s modulus, and coefficient of thermal expansion are considered as controllable design parameters. With the conventional deterministic design optimization, the solder joint plastic work per temperature cycle is taken as the design objective to be minimized. In the reliability-based design optimization, both the mean value of the plastic work and its variation are considered as the design objectives. Finite element simulations and response surface approximation are utilized to evaluate the thermo-mechanical performance in the design optimization procedure. A differential evolution algorithm serves as the optimum search engine. A quasi-Monte Carlo method is adopted to perform the probability analysis in the reliability-based design optimization. Finally, the optimal solutions from the two approaches are discussed and compared.