Solder joint reliability of cavity-down plastic ball grid array assemblies

A computational model was established in this study to simulate cavity-down plastic ball grid array (PBGA) assemblies. Stress analysis was performed t o investigate the solder joint reliability of a PBGA-PCB (printed circuit b oard) assembly. The packages under investigation had two different body siz es and two kinds of ball population. The diagonal cross-section of the asse mbly was modeled by plane-strain elements and was subjected to a uniform th ermal loading. The solder joints were stressed due to the mismatch of the a ssembly's coefficient of thermal expansion (CTE), The accumulated effective plastic strain was evaluated as an index for the reliability of solder joi nts. Effects on solder joint reliability such as package size and ball popu lation were identified, Furthermore, it was found that, unlike conventional PBGA assemblies, the outermost solder ball has the highest plastic strain for all cases in the present study. This peculiar phenomenon was further di scussed with the consideration of package deformation.