Abstract
A typical dissolution wetting system, Bi-Sn eutectic filler metal over a Bi substrate in a high-purity argon atmosphere was investigated first using real-time in situ hot stage microscopy for the extensive use of the sharp-interface model and the diffuse-interface model in the modeling of brazing/soldering related wetting systems. Subsequently, the similarities and differences between the aforementioned models in describing the issues of the wetting and spreading interfaces were discussed in terms of soldering definition and theoretical formula derivation. It is noted that (i) the mutual dissolution diffusion between the liquid Bi-Sn solder and Bi substrate were obvious. As a result, the composition and volume of the liquid solder is constantly changing during the wetting and spreading process; (ii) the sharp-interface model is a special case of the diffuse-interface model of the Cahn-Hilliard nonlinear diffuse-equation under the convective dominant condition; (iii) although there are differences between the sharp-interface model and the diffuse-interface model, both of them could be used in brazing/soldering related processes; and, (iv) the agreement between the experimental and simulation results of the sharp-interface model is not as good as that of the diffuse-interface model, which can be attributed to the effects of the elements’ diffusion and the phase transformation.
Highlights
The wetting and spreading behaviors of molten liquid on both reactive and non-reactive surfaces have been extensively studied [1,2,3]
A Linkam THMS 600 hot stage that was installed on a Carl Zeiss optical microscope system was used to record the wetting and spreading data of 57Bi43Sn filler metal over Bi substrates
The Sn elements in the BiSn solder continuously diffused into the Bi substrate; at the same time the Bi substrate continuously dissolved and diffused into the solder
Summary
The wetting and spreading behaviors of molten liquid on both reactive and non-reactive surfaces have been extensively studied [1,2,3]. The process of reactive wetting is much more complicated and is often accompanied by strong or weak chemical reactions, including fluid flow, heat transfer, diffusion-induced solute transfer, capillary phenomena, and even new phase formation. The mathematical analysis of the reactive wetting process is very complicated, and revealing its inherent mechanism has become a research focus and a more difficult topic in the field of wetting and spreading [5]. There are usually two types of reactive wetting: one is purely dissolutive wetting and the other is accompanied by the formation of intermetallic compounds (IMC).
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