Misaligned Flip-Chip Solder Joints: Prediction and Experimental Determination of Force-Displacement Curves

Abstract

The results of wetting experiments between eutectic lead-tin solder and copper pads on silicon substrates in geometries relevant to flip-chip applications are presented. Measurements of solder joint dimensions, specifically stand-off height and lateral offset (i.e., misalignment), as functions of the applied force (normal and shear), solder volume and pad diameter are presented. The experimentally-measured force-displacement relationships are compared with predictions obtained from the minimum energy model of the Surface Evolver computer code. For the case of the axisymmetric joint (zero shear) an exact solution to the capillary equations is also presented. The comparison of experimental and modeling results indicates that such models are accurate as well as extremely sensitive means for predicting the geometry of these solder joints.