Improved wettability of Sn-based solder over the Cu 60 Zr 30 Ti 10 bulk metallic glass surface
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H. Nishikawa Joining and Welding Research Institute (JWRI), Osaka University, Ibaraki, Osaka 0047, Japan
T. Wada, H. Kimura, and M. Fukuhara Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan
T. Takemoto Joining and Welding Research Institute (JWRI), Osaka University, Ibaraki, Osaka 0047, Japan
A. Inoue Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan
Y. Matsumotoa) Materials and Structures Laboratory (MSL), Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan (Received 25 February 2009; accepted 2 June 2009)
The wettability of Pb-free Sn-based solder over the Cu-based Cu60Zr30Ti10 bulk metallic glass surface was investigated. We observed that the as-polished surface was nonwetting for the solder, which was due to the surface oxide layer of ZrOx formed in air. After complete removal of the oxide layer, a thin layer of Ag was deposited on the clean Cu60Zr30Ti10 surface. The Ag-covered Cu60Zr30Ti10 surface showed relatively high resistivity to the reoxidation even in air, and thus the wettability of the Cu60Zr30Ti10 surface for the Sn-based solder was greatly improved. I. INTRODUCTION
Bulk metallic glass (BMG) is a class of amorphous alloys produced by rapid quenching from a molten state. However, the major difference of the BMG from the other amorphous alloys is that it has a wide supercooled region for its glassy state to be easily obtained and hence can reach a size comparable with that of bulk crystals.1,2 Recently, the BMGs have been expected to expand their application as an engineering material and for MEMS devices, owing to their important and unique chemical, physical, and mechanical properties, such as high corrosion resistivity and high tensile strength.3–7 For their practical use, new joining technologies, as mechanical and electrical joining, between different BMGs or between one BMG and other classes of materials should be developed. For a conventional joining method between different metals, the welding process is frequently used. In contrast, for the present purpose a solder joint is better than a welded joint as it is a sufficiently low temperature process to allow the BMG to retain a glassy state.
According to our empirical knowledge, however, the wettability of the BMG surface for the solder depends greatly on the composition of BMGs. For example, the solderability with a Sn-based Pb-free solder was tested for two kinds of BMGs, Pd-based Pd42.5Cu30Ni7.5P20 and Cu-based Cu60Zr30Ti10 (Cu-Zr-Ti). The former case exhibits good wetting and strong adhesion8 while the latter is completely nonwetting. One of the possible reasons for these different wetting and adhesion properties is the difference in the ability of forming a surface oxide layer, which may prevent spreading of the solder over the surface. In this study, we investigated the wetting property of the Sn-Ag-Cu solder over the Cu-Zr-Ti BMG surface as a model system to get some insight into such an effect of the oxide layer on the wetting propert
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