Comparing the copper and gold wire bonding during thermalsonic wire bonding process

Abstract

Wire bonding is one of the most important processes which connected the die and lead frame in LED packaging. Compared with other interconnect technology, wire bonding is much easier to be accomplished. Nevertheless, the gradual increased price of gold makes the cost of bonding increased. As a substitute material of gold, copper comes into sight. Its electrical conductivity is 30% higher than gold with a much lower price. However, the high Young's modulus of copper causes a series trouble, such as larger deformation in the pad and high stress transferred to chip which could result in damage of the chip below. A transient non-linear dynamic finite element model is introduced to simulate the first bond process in this paper for optimizing bonding parameters. The structure of analysis model based on the third generation LED chip. The diameter of copper and gold wire is both 25μm for comparison. Three main bonding results are discussed in this research to improve the reliability of copper wire bonding during the first bonding stage, they are bonding time, bonding force and splash on the bond pad. The stress transferred from FAB to sapphire substrate was also compared during copper wire and gold wire first bonding stage. At the end of this paper, a series of reasonable suggestions for optimizing copper wire bonding process were presented.