Solder joint formation simulation and finite element analysis

The solder joint formation during renew and related subsequent solder joint reliability of surface mounted electronic devices are critical issues in the field of electronic packaging. Solder joint reflow and reliability are highly dependent on joint configuration which are governed by bond pad size, alloy material, solder paste volume, leadframe geometry, and leadframe/pad alignment, etc. The objective af this work is to develop numerical models and methods to: 1) simulate the solder joint formation during the reflow process; 2) determine the stress/strain distribution within the joint; and 3) further predict the reliability of the solder joints. The solder joint formation process during the solidification stage can be simulated using the Surface Evolver program developed by University of Minnesota. The thermomechanical force/displacement (or stress/strain) analysis can be carried out using ANSYS, a general purpose Finite Element Analysis program. The effort also include the linking of the two programs. Examples of applications of this work include study of components falling off during second (facing down) reflow, and thermal stress analysis (due to CTE mismatch) of PQFP mounted on FR4 PWB.