증류수 및 NaCl 용액내 SnPb 솔더 합금의 Electrochemical Migration 우세 확산원소 분석
Dominant Migration Element in Electrochemical Migration of Eutectic SnPb Solder Alloy in D. I. Water and NaCl Solutions
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인쇄회로기판이나 플라스틱 패키지 등 다양한 전자소자 부품내 배선간 간격이 갈수록 좁아짐에 따라 최근 많이 발생하고 있는 electrochemical migration(ECM) 현상은 양극에서 이온화된 금속에 의한 conductive anodic filament(CAF) 및 덴드라이트와 같은 전도성 필라멘트의 성장으로 인해 전자부품의 절연파괴를 일으키고 있다. 본 연구에서는 공정조성 Sn-37Pb 솔더 합금의 ECM 거동과 부식특성 사이의 연관성 평가를 통해 ECM 우세원소를 파악하기 위해 D.I Water 및 NaCl 용액에서 Water Drop Test(WDT)와 분극실험을 실시하여 서로 비교하였다. WDT 실시 결과 공정조성 Sn-37Pb 솔더 합금에서 Pb-rich 상이 Sn-rich 상보다 우선적으로 양극 패드에서 녹아나서 상대적으로 ECM 저항성이 낮았으며, 음극패드에서 자라난 덴드라이트에도 Pb가 훨씬 많이 존재하였다. NaCl에서의 분극실험 결과 전기화학적으로 부동태 피막을 형성하는 Sn에 비해 Pb의 부식속도가 크게 나타났으며, WDT의 결과와 같은 경향을 보였다. 따라서 공정조성 SnPb 솔더 합금의 부식저항성과 ECM 저항성 사이에는 좋은 상관관계가 존재한다.
Abstract
Higher density integration and adoption of new materials in advanced electronic package systems result in severe electrochemical reliability issues in microelectronic packaging due to higher electric field under high temperature and humidity conditions. Under these harsh conditions, metal interconnects respond to applied voltages by electrochemical ionization and conductive filament formation, which leads to short-circuit failure of the electronic package. In this work, in-situ water drop test and evaluation of corrosion characteristics for SnPb solder alloys in D.I. water and NaCl solutions were carried out to understand the fundamental electrochemical migration characteristics and to correlate each other. It was revealed that electrochemical migration behavior of SnPb solder alloys was closely related to the corrosion characteristics, and Pb was primarily ionized in both D.I. water and Cl solutions. The quality of passive film formed at film surface seems to be critical not only for corrosion resistance but also for ECM resistance of solder alloys.
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