Two and three-dimensional modeling of VSPA butt solder joints

The objective of this work is to develop two- and three-dimensional numerical models of VSPA, a new peripheral array package, and study its solder joint reliability. VSPA has multiple rows of butt-type leads around its periphery and is surface mounted on a standard FR-4 printed circuit board. The FR-4 and various package materials were modeled as temperature-dependent and elastic while the eutectic solder was modeled as temperature-dependent, elastic-plastic. The package and board assembly were subjected to a temperature increase (Delta T) of 85 degrees C with the assumption that the assembly is stress-free at room temperature. The results obtained from a three-dimensional 1/8th section model are compared with the results from 2-D plane-strain and plane-stress models and with 3-D ''strip'' models.