Failure from Malformed Via in an AC Device

Abstract The proper formation of vias is critical to device reliability. We investigate a phase-locked loop (PLL) lock failure of a returned unit. Through photoemission analysis and cross-sectional TEM imaging, the failure was traced to corrosion/oxidation at the top and bottom of a misaligned via. The misalignment caused malformation of the via which led to moisture entrapment, and promoted crevice and galvanic corrosion. During the bench testing, the impedance from the corrosion/oxidation was low and did not cause the failure initially due to the high frequency of the phase lock. It was the temperature increase of the unit that had elevated the via impedance to have eventually caused the device to fail. Mitigation strategies are proposed to enhance long-term device reliability.