Investigation of Aluminum Ball Bonding Mechanism

The effects of various factors, e.g., ball hardness, amount of ball deformation, thickness, and surface cleanliness of the aluminum electrode, which can influence bonding strength were investigated. Metallurgical bonding between balls and electrodes occurs by rupturing the oxide film existing on the aluminum electrodes and proceeds from outside, inwards to the center of the bonds. The bonding strength is found to be a linear function of the true bonded area between balls and electrodes. The factors increasing the true bonded area are a high ball hardness, a large amount of deformation, a thick aluminum electrode, and a clean electrode surface. In addition, a high strength ball bonding comparable to gold can be realized by using aluminum alloy wires containing magnesium.