Relationship between Mechanical and Electrical Properties of Cu Wire and Al Pad Bonding

There are several reliability problems, while Cu wire bonding has been used instead of Au wire bonding in microelectronics packaging. A previous work indicated that after autoclave test maintaining at 394 K, 100% relative humidity and 0.2 MPa for 300 h, a shear strength of Cu wire bonding decreased to about half that of initial Cu, although a shear strength of Au wire bonding did not decreased. In this work, we investigated the relationship between mechanical and electrical properties of Au or Cu wire and Al pad bonding in more detail. For a mechanical property, the shear strength of Cu wire bonding gradually decreased to about two-fifths of that of initial Cu at 700 h. For an electrical property in a function test, 11 from 20 specimens of Cu wire bonding suddenly failed at 600 h and 3 specimens additionally failed at 650 h. From these results, the mechanical properties are different from those of electrical. Using SEM and observation, we investigated the dependence of the mechanical and electrical properties on the interface morphology between Cu wire and Al pad compared with Au wire.