Characterization of Au-Sn eutectic die attach process for optoelectronics device

Eutectic Au-20wt%Sn die attach process has been widely used for laser diode and LED applications due to the superior strength and thermal property of the constructed solder joint. For eutectic die attach of AuSn pre-deposited die to substrate, temperature of substrate is heated above liquidus temperature of eutectic Au-Sn and followed by lower temperature post-bond for solidification. Depending on the setup and configuration of the eutectic bonder, the time for the die to remain on bonding stage varies before being transferred to cooler post bond zone. In this study, the interaction of Au and Sn layers at different temperature above liquidus of 280°C are analyzed. The formation of Au-Sn eutectic 80:20 and other intermetallic and phase compositions with response to different temperature and time are characterized. 20 minutes of prolonged exposure time is set as the utmost condition to characterize the property of the bonding interface and intermetallic compositions. The result from the analysis demonstrates that Au has migrated to eutectic Au-20wt%Sn to form Au rich solder interface with about Au-4.384.58wt%Sn at 300°C and Au-3.45-4.12wt%Sn at 320°C respectively after 20 minutes of exposure time. Placement accuracy of the dies is found to be unaffected after the heat exposure.