Challenges and feasibility of copper wire bonding for non-hermetic packaging

In the last few years copper wire bonding has undergone a tremendous growth period. The drive behind the growth is the huge cost saving for copper wire compared with gold wire especially for those packages or applications with longer wire connection, more IOs or thicker wire. Copper wire has also other advantages like better electrical performance and mechanical performance. Thinner copper wire can have equivalent performance as the thicker gold wire. Many studies have been done on copper wire bonding for equipment capability, robust process window, and package reliability etc. most of those efforts have been put on molded BGA or leadframe packages etc. hermetic packages, where bonding wire is protected by molding compound. However, there is no much study about copper wire bonding for non-hermetic packages like MEMS microphone, camera module etc where the bonding wires are in cavities and not protected or embedded resin materials. Reliability is a great concern for such applications. The work discussed in this paper focuses on copper wire bonding for non-hermetic packaging. Due to its material properties, copper has much narrow process window for wire bonding than gold wire. It makes the copper bonding even challenging for Non-hermetic packages. With huge of work on the proper wire and capillary selection, and process window optimization, it was found that copper wire bonding is feasible for non-hermetic package, and qualified for camera module and OLGA packages. Yield and productivity are equivalent to gold wire.