Solder joint design optimization for fine pitch component applications

Fine pitch leaded components, such as TSOP/QFP, have been widely used in portable electronics in recent years. One of the most critical issues in the electronic packaging industry is to find effective ways to reduce manufacturing related solder joint defects in these electronic components. During the fine pitch component reflow process, major failure mechanisms include solder bridging, solder opens, insufficient soldering, etc. This research aims to develop a physics-based validated modeling methodology, allowing for effective simulation of the solder joint formation process and prediction of the above solder defects. The goal of the methodology is to determine the optimal solder joint configuration (i.e. bond pad size, stencil aperture design, solder volume, etc.) in a cost-effective manner. The solder joint formation process during the solder solidification stage has been simulated using the Surface Evolver software tool. This paper consists of three integral parts: (1) simulation of the 3D solder joint formation process for the final solder joint geometry configurations; (2) determination of the optimal pad/stencil aperture; and (3) determination of the optimal solder paste volume and material. The methodology can also enable one to analyze the safety margin for a given pad/stencil aperture design. Finally, the simulation models were used to accurately pinpoint the deficiencies in certain pad/stencil aperture designs, which can cause solder bridging, opens or insufficient soldering.