Process and Consumable Development for Silver Wire Bonding

With increased demands, power modules are often required to run at higher temperatures with improved reliability. Solder joint fatigue is a major failure mode for current power modules. Silver sintering die-attach technology significantly improves power module reliability. Due to the reliability problem at the interface between aluminum (Al) wire and a silver (Ag) layer, bonding Ag wire to the Ag layer is highly desired. Ag wire is harder and stiffer than Al wire, resulting in much higher wear and significantly reduced lifetime of consumables. This paper introduced the K&S CuEx™ bond tool and studied coupling and interaction between the bond tool and Ag wire. By optimizing the bonding process, the CuEx™ bond tools achieved 400,000 touchdowns, which is 80× more than the standard bond tool lifetime of 5,000 touchdowns. The difference between the front-cut and rear-cut process is discussed. By studying and optimizing the cutting process, the standard rear-cut cutter blade lifetime is increased 4×, from 50,000 cuts to 200,000 cuts. It is observed that Ag wire did not wear a wire guide much faster than Al wire. The standard wire guide exhibited minimum wear after 200,000 bonds.