Linear finite element stress simulation of solder joints on 225 I/O plastic BGA package under thermal cycling

Linear steady state finite element models have been performed to simulate thermally induced stresses on 225 I/O plastic ball grid array (PBGA) packages under thermal cycling (TC) condition. Eutectic solder joints (63%Sn, 37%Pb) in shapes of barrel and hourglass have been studied. The effects of thermally induced stresses on the solder joints between BT (Bismaleimide Triazine) substrate of PBGA and FR-4 print circuit board (PCB) are studied as a function of four parameters: (a) coefficient of thermal expansion (CTE) of molding compound, (b) height of solder joint, (c) size of solder pad, and (d) location of silicon chip. Furthermore, the warpages of a PBGA substrate caused by transfer molding and solder reflow processes are discussed. Several PBGA designs with minimum thermal stress are proposed based on the above finite element analysis results.