Wetting characterization of Flip chip’s Lead-Free Solder Interconnect Using Surface Evolver.

Abstract

Smaller pitch of first interconnect has posed various challenges to the electronic packaging. The driver to smaller pitch was driven by package and die size miniaturization. In order to enable smaller pitch of first interconnection, copper pillar was introduced. In this paper, surface evolver software was used to predict the solder geometry of solder cap copper pillar onto copper pad process. The study has shown that copper pillar solder joint geometry can be successfully simulated and agreed with experiment. The relationship between various solder joint influencing factors such as die bump diameters, copper pad geometry, solder height and solder volume were established. The optimum die to copper pad width ratio can be obtained through this simulation work. The information can be used to estimate critical volume of solder needed for new, smaller pitch die bump and copper pad design which help to save money and time by avoiding a large number of experiments prior to mass production.