Low-Temperature Process of Fine-Pitch Au–Sn Bump Bonding in Ambient Air

Abstract

A low-temperature bonding process of 30-µm-pitch Au–Sn microbumps was developed in ambient air by the surface activated bonding (SAB) method. The surface activated process, such as Ar plasma pretreatment, is essential for Au–Sn low-temperature bonding. With a total of 4908 connections, the bond yield reaches 100% at a bonding temperature of 100–200 °C in ambient air. No electrical short circuit occurs between two adjacent bumps under the optimized bonding pressure. The bonding strength is larger than 10 MPa. Scanning electron microscope (SEM) and electron probe micro analyzer (EPMA) observations of the cross-sectional bonded interfaces were performed. Intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 appear around the bonded interfaces in the bonding at 100 and 150 °C. More one phase, a thin Au5Sn layer, was detected in the bonding at 200 °C. The bonding feasibility of Au–Sn flip-chip microbumps is confirmed at 100–200 °C in ambient air.