A MODEL TO EXPLAIN SMT OPEN-CIRCUIT JOINTS ASSOCIATED WITH ADJACENT SOLDER BRIDGES

This paper presents some preliminary results from the use of a computa tional modeling tool, The Surface Evolver, in order to understand the formation and stability of solder bridges and how these bridges may; a lso result in adjacent lean or open circuit joints. The models show th at shorts between pairs of pads are more stable than those between gro ups of three or more pads. It is also shown that, when a short become unstable, a single pad at the end of the group shorted will break away from the short and this pad will subsequently bear a much smaller vol ume of solder than will have originally been printed onto it. These mo dels therefore indicate a possible mechanism for the observed phenomen a of lean or open circuit joints occurring adjacent to shorts.