Chauhan P.S, Choubey A., ZhaoWei Zh., Pecht M.G. Copper wire bonding

254 p. Springer Science+Business Media New York 2014
Wire bonds form the primary interconnections between an integrated circuit chip and the metal lead frame in semiconductor packaging. Wire bonding is considered to be a more cost-effective and flexible interconnect technology than flip–chip interconnects. As of 2013, more than 90 % of semiconductor packages were interconnected by wire bonding. Replacing Au wire with Cu wire in the wire bonding process presents many challenges. Parameter adjustments for ball bond formation, stitch bond formation, and looping profile are needed. Cu is harder than both Au and Al, and therefore bonding parameters, including bonding force, must be kept under tight control. Since Cu wire is highly prone to oxidation, inert gas such as nitrogen or forming gas must be used during the bonding process. In some cases, wire manufacturers have used palladium (Pd)-coated Cu wire, which is more resistant to oxidation than bare Cu wire. Also, since bare Al pads run the risk of being damaged by Cu wires due to the high hardness of Cu and the high bonding force required, the industry has adopted Al pads that are thicker than those used in Au wire bonding, as well as pads with nickel (Ni)-based finishes.