Fatigue Analysis of a Ceramic Pin Grid Array Soldered to an Orthotropic Epoxy Substrate

Thermal stresses and strains in the solder joints and plated-through-hole (PTH) copper pads/barrels of a pin-grid array (PGA) assembly under thermal cycling conditions have been determined in the present study. There are two major systems of thermal stresses/strains acting at the solder joint and copper. One is the transverse shear and vertical normal stress/strain due to the local thermal expansion mismatch between the pin, solder, copper, and FR-4. The other is the horizontal normal stress/strain due to the global thermal expansion mismatch between the ceramic PGA and the FR-4 printed circuit board (PCB). The effects of the local thermal expansion mismatch on the reliability of solder joint and PTH copper have been determined using a 3-D orthotropic-elastoplastic finite element method. The effects of the global thermal expansion mismatch on the reliability of solder joint and PTH copper have been determined by fatigue experiments. Fatigue life of the solder joint and PTH copper was then estimated based on the calculated strains and the fatigue data on solders and coppers.