Critical size of crack propagation from residual void in micro via in printed wiring boards

The micro-via was fabricated with diameter of 200 to 400μm, inner hole plate thickness of 18μm, hole land thickness of 18 to 20μm, and solder resist thickness of 13μm on hole land. We investigated that the size of residual void increased as that of micro-via increased; also, dominance of micro-via cracking was observed when temperature was applied at 100°C for 2 hours. When the printed circuit board containing void is heated, the micro-via cracking is accelerated in the micro-via with residual void larger than 50% of via diameter. This is significantly verified by calculation of coefficient for stress concentration in the study.