Extending the fatigue life of SGA interconnects for aerospace applications

The effect of residual stresses on the fatigue life of a solder grid array (SGA) interconnect is modeled using fracture mechanics. A fatigue crack growth model is proposed for an interconnect subject to cyclic shear loading in conjunction with either a constant crack-opening or a constant crack-closing stress. The residual stresses stem from the constant mean curvature shape of the interconnect and depend upon the volume of solder and the distance between the printed circuit board and chip carrier. Experiments are reported which support the residual force approximations. The fracture model can be used to predict how the relative fatigue life of a solder interconnect can be extended.