Solder joints design attribute to no solder bridge for fine pitch device

Solder bridge is a serious defect of solder joints in ultra fine pitch devices assemblies, such as QFP256 (QFP: Quad Flat Packaging). It has been known that generation of the solder bridge is closely related to formation process of the solder joints. A three-dimensional model to simulate the formation process of the solder joints bridge of QFP256 is formed and numerically simulated to predict formation shape using Surface Evolver program in this paper. Based on these results, solder bridging mechanism and factors influencing the solder bridge are investigated, involves solder volume, wetting angle, pad size, lead position on the pad. The results show that there is a critical solder volume V/sub c/for the solder joints to avoid solder bridging, which can be used to evaluate anti-bridging ability of the solder joints.