Improved yield and performance of ball-grid array packages: design and processing guidelines for uniform and nonuniform arrays

Two models are presented for analyzing ball-grid array (BGA) solder interconnects: (a) a model for predicting solder joint geometries after an upright or inverted reflow process and (b) a reliability model for estimating maximum shear strain and fatigue life under a global thermal mismatch load condition. The reliability model includes a newly derived closed-form expression relating the maximum shear strain in a solder joint to the load, material, and joint shape parameters. The models are used to generate design/processing guidelines that may be used to improve the yield of a BGA soldering operation and the in-service reliability of the interconnect. Potential benefits of using a nonuniform array (i.e. one including joints of different size and shape) are explored.