Influence of mold compound type towards Palladium doped and copper doped 2N Au wire

Abstract

In automotive semiconductor industry, the behaviour of gold (Au) wire is very crucial in sustaining the reliability performance of the product. Due to the motivation to achieve lifetime of high temperature storage (HTS) of 3000hr at 175°C, gold wire with 4N purity (99.99% Au) on AlCu pad cannot be used due to kirkendall voiding after thermal aging. This kirkendall voiding could lead to 1st bond failure during product application. The kirkendall void form when the Al or Au diffuses out of one region faster than the other can diffuse in from the other side of that region [1]. Therefore, 2N wire (99% Au) is recommended to replace 4N wire where the dopants in 2N wire (Pd, Cu, Pt) can limit the intermetallic layer growth and subsequently slows down the formation of kirkendall void. During the 2N wire pre-selection study, two wire types with different dopants, Palladium (Pd) and Copper (Cu) were selected. No failure was observed after HTS for unmolded unit. However, when molded unit were subjected to HTS, lifted bond was detected during ball shear after stress for Cu doped 2N wire. Based on above finding, it is indicated that there is influence of epoxy mold compound (EMC) toward the different dopant properties of 2N wire. Study by researcher [2] also shows that conventional epoxy mold compound do have influence towards the reliability behaviour, due to the presence of halides. In this paper, Pd doped and Cu doped 2N wire will be assessed using green EMC and non-green EMC. Wire Bond (WB) process characteristic (wire pull, ball shear, stress neck, cratering, IMC coverage and IMC growth) at 0hr will be examined. For critical responses such as ball shear and IMC growth, will also be examined after HTS. Investigation on Au-Al intermetallic phase will be performed to understand the diffusion behavior of 2 different dopant wires and a model will be constructed to explain the failure mechanism. This paper will present as a fundamental guideline to select the suitable dopant base for 2N Au wire type versus epoxy mold compound without compensating the reliability performance.