Void mechanism research and control in solder joint

Void formation mechanism was studied and so were the key factors for SMT voids. 2 kinds of solders (SAC305 & SnPb) and 2 kinds of pad finishes (ENIG and OSP) were compared. Key factors of reflow profile were also evaluated. Reflow atmosphere were evaluated to observe the effects on void. Stencil thickness on void formation was also studied. Results show that by adjusting all these factors, the maximum void size and void quantity can be controlled. It is also found that using higher melting point solder ball and lower melt point solder paste together will get void-free SMT result which also impresses the understanding of void forming mechanism: Gas of reaction and volatilization is trapped by melted solder particles in solder paste and form voids.