Effect of initial anodic dissolution current on the electrochemical migration phenomenon of Sn solder

As electronic packages become smaller in size, the pitch of metal line is getting shorter. Decrease of line pitch in electronic packages and substrate of electronic component causes the electrochemical migration (ECM) more frequently. If the electronic components are exposed to high temperature and high humidity environments with authorized voltage condition, the metals in packages and substrate are easily ionized and form conductive dendrites, leading to insulation failure. ECM process consists of three steps: anodic dissolution, ion migration, and dendritic growth. The first step is the most important because anodic dissolution determines strongly affect the occurrence of remaining steps. In this work, anodic dissolution of Sn solder is characterized by water-drop test (WDT) and anodic polarization teat (APT). Initial anodic dissolution current of Sn solder is measured in 0.001 wt.% NaCl, Na₂SO₄ solutions and deionized water by WDT, and the results were compared with APT results. It is found that the higher the voltage is, the shorter the time-to-failure (TTF) is. In lower-voltage condition, anodic dissolution current is limited by passivity formation. The pitting corrosion occurred in higher voltage condition with shorter TTF. The anodic dissolution current is dependent on the electrolyte: the highest value in 0.001 wt.% NaCl solution and lowest value in D.I water.