Interfacial reactions of sequentially electroplated Au/Sn/Au films on Si chips

Abstract

Au−30 at-%Sn eutectic alloy was fabricated by sequentially pulse electroplating Au and Sn films on Si chips. Three kinds of Au/Sn/Au triple layer films were prepared in the present work: Au/Sn/Au (6/6/1 μm) films, Au/Sn/Au (6/6/6 μm) films and Au/Sn/Au (8/6/1 μm) films. The microstructure and phase transformation in Au/Sn/Au films during aging and reflow soldering were investigated. For Au/Sn/Au (6/6/1 μm) films during aging at 100 and 150°C, the layered AuSn/AuSn₂/AuSn₄ structure formed in the reaction region. Furthermore, the Sn film was completely consumed, and AuSn₄ finally transformed into AuSn and AuSn₂ after aging at 150°C for 15 h. For Au/Sn/Au (6/6/6 μm) films during aging at 150°C, the electroplating sequence had an important effect on the formation of Au−Sn phases. An Au₅Sn layer was present at the Au II/Sn interface but not at the Au I/Sn interface. For Au/Sn/Au (8/6/1 μm) films, the micropores that formed preferentially along the Au₅Sn/AuSn interface remarkably decreased with increasing reflow temperature from 280 to 310°C. After reflowing for 10 s, the microstructure was not an Au−Sn eutectic; however, after reflowing for 60 s, coarsened primary Au₅Sn phase and typical Au−30 at-%Sn eutectic microstructure of fine eutectic phases (AuSn+Au₅Sn) formed.

Keywords:

• LED
• Au−30 at-%Sn eutectic solder
• Aging
• Reflowing
• Alloying

The present work was supported by the programmes of the National Natural Science Foundation of China (grant no. U0734006 and no. 51171036), the programmes in Liaoning Province (grant no. 2009921058 and no. 20082163) and the Key programme in Dalian (grant no. 2006A11GX005).