Predicting solder joint shape by computer modeling

Predictions of surface mount or through hole solder joint shape, based on the lead and pad geometry, solder volume, and material characteristics, can be used to improve soldering yield. This paper reports on a collaboration between Digital Equipment Corporation and Massachusetts Institute of Technology to develop a method to predict solder joint shapes. It concentrates on the application of a public domain software program called Surface Evolver to solder joint modeling. Surface Evolver uses numerical optimization techniques to compute the shape of capillary surfaces. Solder joints are one of many applications of Surface Evolver. It seems to be well suited to compute the shape of complex solder joints. Results from Surface Evolver are compared to shapes computed by other means, and to the shape of actual solder joints. Good agreement is obtained in most cases.<>