In this study, a detailed characterization of Au-Sn eutectic thin metal stack bonding has been performed between pyrex and silicon substrates using the Fintech Lambda flip chip bonder. Even though a thorough recipe characterization and development was performed by varying bonding temperature and pressure, this study puts special emphasis on observing the bond uniformity and metal overflow, which was possible through the transparent pyrex. Preliminary results indicate that flatness of contact is one of the most important parameters that determine the bond uniformity and thus the quality during these thin metal bonding process. In addition, we have observed the effect of sample cool down rate on microstructures within the bonded zone. For a specific case, Kirkendall voids were observed under the optical microscope at the interface between pyrex and bonded metal because of dissimilar rates of migration of Au and Sn during the eutectic reaction. Following successful characterization of metal reflow from the bond site, a simple method to control this overflow has been demonstrated by precisely controlled misalignment of the two complementary chips. This fundamental study on eutectic bonding aims to further the understanding of eutectic bonding process as well as facilitate development of novel recipes for effective low temperature, high strength bonding between chips which is immensely valuable for large scale electronic packaging industry.  


Characterization and Prevention of Metal Overflow in Au-Sn Eutectic Chip Bonding for Electronic Packaging Applications

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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