Ribbed package geometry for reducing thermal warpage and wire sweep during PBGA encapsulation

The effects of changing package shape to a ribbed geometry on thermal warpage and wire sweep of a plastic BGA (PBGA) are investigated in this paper. Three rib geometries (border, diagonal, and cross) with a variation of rib widths and thicknesses are compared with the original plane geometry. Finite element analyses of thermal warpage during the reflow process of PBGA molding with and without ribbed geometry are carried out. Numerical modeling shows that the border rib has the least thermal warpage at the reflow condition. Flow visualization was performed to study the effect of rib geometry on wire sweep, and demonstrates that the wire sweep in ribbed packages is significantly less than that in the original nonribbed package.