Palladium coated Cu wire: A robust material for die to die Cu WB interconnect

Die to die interconnection in wirebonding process these days is just common in particular to the mature packages using Gold (Au) wire as mean for interconnection. With the intense market competition to deliver a much competitive cost of the products more manufacturers, sub-contractors and even IDM (integrated device manufacturing) are now inclined with the use of Copper (Cu) wire as an alternative option. The use of Cu wire found to be even better than Au, because of its high thermal conductivity, great electrical property and importantly low cost value. However, actual application of Cu wire in wirebonding process also has its limitations such its inherent material hardness and oxidation that pose a great challenge and concern for most of the manufactures. In this paper it will tackle and discuss on how those challenges are being mitigated. Different types of wire was evaluated such the Palladium (Pd) coated Cu wire and Bare Cu wire that aims to match & satisfy the requirements of a multiple die package which has a die to die interconnection. The interconnection method is by means of the BSOB (bond-stitch-on-ball) commonly known also as reverse bonding. Ball bump formation is essential for the successful stitch bond and the type of wire to use considering that the ball bump tip surface after the bump formation will expose the inner Cu material as an effect of the shear motion of capillary during bump cutting motion thus easy to oxidize, so a different bump cutting mode or technique was studied and found can help reduced or control the oxidation with the right type of wire such as the Pd coated Cu wire.