Optimizing the performance of the Au-Si system for high temperature die attach applications

Abstract

The operation of electronic packages under exceptionally harsh environments presents a significant challenge for the microelectronics industry, for example, in down-hole, well-logging and turbo-machinery applications. High temperature Au based solders are one potential candidate for die attachment for harsh environments and is already used in limited cases. For Au-Si die bonding, some of the Si is provided by diffusion from the Si die itself. Therefore, the interfacial reaction between the Si and Au-Si thin foil solder preform is a key factor in the control of the die bonding process. Unfortunately, during the die bonding process, defects such as voids, delaminations, and impurities are not unusual. These defects are caused by the assembly process, chemical impurities, soldering reactions, and thermal stresses. Understanding these defects is critical for the reliable performance of the devices after bonding. In this paper, optimization of the Au-Si eutectic die bonding has been performed and near 100% bonded area confirmed by scanning acoustic microscopy achieved consistently. Die attach reliability was investigated by thermal shock and thermal cycling treatments, after which the bonded area showed some signs of degradation. Shear strength testing and microstructural analysis were also carried out. Die bond optimisation gave a significant improvement in both bonded area and reliability.