Influence of soldering conditions on void formation in large-area solder joints

Abstract

This paper aims to clarify the process factors for applying the void free soldering process to practical use. Solder cleanliness lessens the influence of the heating rate on the void formation during soldering. The lowest vacuum for the purpose of void free soldering for cleaning and Ag coating, and for soldering were 2 × 10-3 Pa and 4 × 10-1 Pa, respectively. Cooling in N2 lessens the void formation during soldering. The allowable standing time from the Ag coating to soldering is 25 h. The reliability of power modules made with this new process was satisfactory.