Comprehensive Comparison of the Wire Bond Reliability Performance of CU, PDCU and AG Wires

Wire bond is the most common inter-connection method used to connect microchips to the terminals of a chip package. Wire bond reliability is vital to the packaging device performance. The work here investigated and compared the wire bond reliability performances of bare copper (Cu), palladium coated copper (PdCu) and silver (Ag) wires on aluminum pad. For PdCu, different Pd distributions on bonded ball and their effects on PdCu corrosion resistance were studied in detail. Chlorine (Cl) and sulfur (S) contaminations were purposely introduced to epoxy molding compound (EMC) to accelerate the corrosion process. bHAST (biased highly accelerated stress test) was conducted to see the reliability performance of Cu, PdCu, Ag wires under Cl and S environment. The results showed that Cl played a significant role on wire bond reliability. Whilst, S did not impact much on wire bond reliability. The failure mechanisms were studied. It was found that poor Pd coverage on bonded ball led to poor reliability performance. On the other hand, excessive Pd accumulation on the bonded ball bottom will deteriorate the reliability performance.