Effects of Pd distribution at free air ball in Pd coated Cu wire

Bonding wire, one of the bonding materials, has been rapidly changed from Au to Cu due to an increase in gold price. Although Pd coated Cu (Au-Pd-Cu) wires, which comprise the largest market share among Cu bonding wires, show high reliability compared to bare Cu wire in high-humidity reliability, the reliability issue still appears in certain area. In the case of Pd coated Cu wire, studies have reported that the Pd distribution on the free air ball (FAB) surface is an important factor for improving the reliability. This study confirmed that the distribution of FAB could be controlled according to the wire manufacturing conditions, and that the Pd distribution further changed depending on the change of EFO conditions. The study further confirmed that the denser Pd distribution outside bonded ball induces the higher chemical resistance at the interface between bonding pad and the bonded ball, which improves the reliability at high temperature and high humidity after PKG.