Microstructural evolution of the Au-20 wt.% Sn solder on the Cu substrate during reflow

Reflow reactions of the Au-20wt.% Sri (Au20Sn) solder on the Cu substiateat 330 degrees C were conducted and the microstructure of as-solidified solder joint was examined. After reflow for 1 min, the as-solidified solder matrix presented a typical eutectic zeta-(Au,Cu)(5)Sn + delta-(Au,Cu)Sn lamellar microstructure and two phases, zeta-(Au,Cu)(5)Sn and AuCu. were formed at the solder/Cu interface. The zeta-(Au,Cu)(5)Sn phase grew very irregularly at the interface. Upon increasing the reflow time. par: 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 zeta-(Au,Cu)(5)Sn phase was observed and the zeta 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 zeta-(Au,Cu)(5)Sn at the interface, dendritic growth of zeta-(Au,Cu)(5)Sn in the solder matrix, and development of eutectic microstructure. was explained using related phase diagram and vertical section. (C) 2009 Elsevier B.V All rights reserved.