Reliability of copper wire bonding in humidity environment

Copper wire bonding is being developed rapidly in recent years to replace expensive gold wire for electronic packaging. However, one issue about reliability in humidity environment causes risk in its application. The copper wire-aluminum pad interface degradation usually leads to electrical open failure. Present paper studied all the 5 factors including pad finish of chip, molding compound, wire bonding parameters, copper wire type and protective gas type in wire bonding process that affect this issue. Through bond pull test at different stage of uHAST, the influence and significance degree of the factors were obtained. The pad finish was found has the most significant effect. No degradation occurred at copper-gold and copper-palladium interface. For aluminum finish, mold compound and wire bonding parameters have significant effect. Green EMC, high USG and low Search Force in wire bonding process is benefit to enhance reliability of copper wire bonding in humidity environment. Concerning the palladium coated copper wire and bare copper wire, forming protective gas of 5%H₂+95%N₂ and pure N₂, there was no significant effect founded. So for the safe copper wire bonding application, noble metal such as gold and palladium pad finish is the best choice. If the aluminum pad is used, green EMC and optimized wire bonding parameters are necessary to guarantee the reliability.