Bondability of Second Copper Wire Bonds on Silver and Nickel-Palladium-Gold-Silver Metallization

Several types of metallization have been used in order to enhance the bondability of wire bond. The introduction of copper (Cu) wire bond further increases the requirement of finding the suitable metallization. In this paper, two types of metallization, namely silver (Ag) and nickel-palladium-gold-silver (Ni/Pd/Au/Ag), deposited on Cu substrate were used as the bond pad for the second Cu wire bond. Wire pulling test was conducted on the Cu second bond by placing the hook near the second bond in order to obtain consistence stich of Cu wire bond. The characteristic remaining area of stich was obtained using the image processing software Image J. It was observed that the pull strength of the Cu second bond was higher for Ag metallization compared with that of Ni/Pd/Au/Ag metallization. It was also shown that the Cu second bond on the Ag metallization has higher contact diameter compared with that of Ni/Pd/Au/Ag metallization. The contact diameter of the Cu second bond on Ag metallization has higher value and it can be correlated with its higher value of pull strength. The characteristic area was found to be proportionally related with the pull strength of second bond.