Fine pitch BGA device solder bridging mechanism investigation through solder shape modeling

In present study, an interesting phenomenon of solder bridging presents in fine pitch BGA device is reported. The failure mechanism is investigated by solder formation modeling, and examined by experimental results of multi-factors evaluation. Results show that the risk of adjacent joints bridging is highly influenced by printed circuit board design attribute. A mathematic model is applied to describe the structure attribute of solder joint based on simplifications and assumptions. Surface Evolver is applied to solder joint three-dimensional modeling and simulation. It is proved that the improper design parameters will make solder joint shift towards the adjacent joint during reflow soldering, resulting in joint bridging. This mechanism also works in BGA device, but it is often ignored due to its less effect on solder bridging failure for BGAs. However, as joint pitch continues to decrease, it increasingly becomes a problem, and will bring serious risk in solder joint bridging for fine pitch BGAs. Based on this investigation, the risk of solder-bridge during SMT assembly process can be evaluated and improved by board design optimization at development stage.