Failure analysis for via with solder bubble

A failure PCBA sample with solder bubble problem and a bare PCB sample were analyzed with the aid of stereomicroscope and SEM and cross sections, Thermal stress test and solderability test were performed on the failure PCBA sample and the bare PCB sample. The cause of vias with solder bubbles in failure PCBA sample was found after systematic analysis, the failure was caused by the residual moisture or flux permeating inside the defects in barrel plating and dielectric material surrounding the hole venting and blasting out during high-temperature soldering. The defects around the vias should be induced by the improper drilling process. To achieve good drilling quality and avoiding the solder bubbles problem, drilling materials, drill thrust, quality of surface of vias and proper drilling equipment should be well selected and controlled.