Interfacial reactions of Au-20wt.%Sn solder on Cu substrate

• Main Authors: Hsiang-Mou Chung, 鍾享牟
• Other Authors: 陳志銘
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/36040278804199707816

碩士 === 國立中興大學 === 化學工程學系所 === 97 === Eutectic Au-20wt%.Sn (Au20Sn) solder alloy is commonly used in bonding applications for microelectronic and optoelectronic packages. The copper is a common substrate used in electronic equipment. The subject of this study is to investigate the microstructure evolution of the Au20Sn solder reflowed on Cu with different solder volumes of 5.4×109 and 2.84×108m3. After reflow for 1min, the as-solidified solder matrix presented a typical eutectic ζ-(Au,Cu)5Sn + δ-(Au,Cu)Sn lamellar microstructure and two phases, ζ-(Au,Cu)5Sn and AuCu, were formed at the solder/Cu interface. The ζ-(Au,Cu)5Sn phase grew very irregularly at the interface. Upon increasing the reflow time, part of the fine lamellar microstructure coarsened in the as-solidified solder matrix, and therefore the solder matrix displayed a composite microstructure of fine lamellar eutectic and coarse eutectic. In addition, dendritic growth of the ζ-(Au,Cu)5Sn phase was observed and the dendrites were found to grow at a faster rate in the solder matrix of smaller volume. The microstructural evolution at the Au20Sn/Cu solder joint during reflow, including irregular growth of ζ-(Au,Cu)5Sn at the interface, dendritic growth of ζ-(Au,Cu)5Sn in the solder matrix, and development of eutectic microstructure, was explained using related phase diagram and vertical section. After solid-state aged for 1day to 120days at 230℃, eutectic ζ-(Au,Cu)5Sn + δ-(Au,Cu)Sn lamellar microstructure coarsed. This phenomenon can be explained by Gibbs-Thomson effect . The ζ-(Au,Cu)5Sn phase grew at the interface,and it’s microstructure changed from irregular pillars to layer.