Low-cost Palladium coating process and its effect on free-air-ball softness and second bond strength of Cu bonding wires

Palladium coated Copper (PCC) bonding wire is a popular low cost alternative for Gold wire. The quality of an innovative Pd coating technique on Cu (Direct PCC) wire is evaluated by comparing free air ball (FAB) deformability and stitch bond strength to those of Cu wire. The coating is applied to commercial Cu wire which is either thermally treated or as-delivered. FABs of 40 μm diameter are produced in two different shielding using 20 μm diameter direct PCC (DPCC) and bare Cu wires. The FABs are deformed under a force of 400 mN. The DPCC FAB made in forming gas deforms 0.60 to 1.92% more than the Cu FAB, indicating a slightly softer bonded ball. The stitch bonds are made on Ag of a QFN substrate and on Au of an BGA substrate at 200°C and 175°C, respectively. The stitch bond strength of PCC wire is 11-26 % higher than that of Cu wire.