The μ-via in microelectronic substrate should have multiple purposes, one of them is to allow to the path of signal or current from electronic devices. The micro void can be easily formed in μ-via because μ-vias are filled with a screen printing process and the size of via is small. The residual void has been known as crack initiation of copper layer during a reliability test. The solder resist filling process and the behavior of a residual void in μ-vias were investigated. The void extraction process was very effective comparing with the conventional process to remove a residual void. As extracted with 1.5 atm for more than 30 sec, the residual void in μ-BVH was perfectly eliminated.