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Optimization of copper wire bonding on Al-Cu metallization

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4 Author(s)
Nguyen, L.T. ; Nat. Semicond. Corp., Santa Clara, CA, USA ; McDonald, D. ; Danker, A.R. ; Ng, P.

This paper reports the successful implementation of copper wire ball bonding for selected TO-220 devices on a high volume commercial scale. Since August 1992, copper wire bonding has been used in production at National Semiconductor Corp. The development of copper wire ball bonding involves a three-prong approach: optimum pad metal composition, modifications to the wire bonder and optimization of the assembly parameters. the critical material parameter is bond pad hardness. This needs to be above a critical threshold value to avoid silicon cratering. The metal composition best suited for the wire bonding process is sputtered Al-Cu(2%). Typical production yields of 99.8% at lead bond are obtained with 1.5 mil (37.5 μm) copper wires, with ball shear and wire pull averaging 100±20 gms and 15±2 gms, respectively. Five issues related to copper wire bonding of TO-22 power IC packages are discussed: 1) typical bonding failure modes; 2) the relation between bond pad composition and hardness; 3) the influence of the metal deposition systems; 4) the optimization of bonding conditions; 5) the reliability of the copper wire bonded devices

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Components, Packaging, and Manufacturing Technology, Part A, IEEE Transactions on  (Volume:18 ,  Issue: 2 )