Studies of Galvanic Corrosion (Al-Ti Cell) on Microchip Al Bondpads and Elimination Solutions

Galvanic corrosion (two metal corrosion) on microchip Al bondpads may result in discolored or non-stick bondpad problem. In this paper, a galvanic corrosion case at bondpad edge will be presented. Besides galvanic corrosion (Al-Cu cell), a concept of galvanic corrosion (Al-Ti cell) is proposed, which is used to explain galvanic corrosion at bondpad edge with layers of TiN/Ti/Al metallization structure. A theoretical model of galvanic corrosion (Al-Ti cell) is proposed to explain chemically & physically failure mechanism of galvanic corrosion at bondpad edge. According to the theoretical model proposed in this paper, galvanic corrosion on microchip Al bondpads could be identified into two corrosion models: galvanic corrosion (Al-Cu cell) occurred mostly at the bondpad center and galvanic corrosion (Al-Ti cell) occurred specially at bondpad edge with TiN/Ti/Al metallization structure. In this paper, a theoretical model of galvanic corrosion (Ai-Ti cell) will be detail discussed so as to fully understand failure mechanism of galvanic corrosion the bondpad edge. Moreover possible solutions to eliminate galvanic corrosion (Al-Ti cell) are also discussed.