Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering.

Simge Çınar,Martin Thuo,Jiahao Chen,Ian D Tevis

doi:10.1038/srep21864

Abstract

Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

Highlights

Phase-change materials have been recognized to bear great potential
We have used the SLICE technique, which involves shearing of a liquid metal or metal melt to break it to small parts with concomitant surface oxidation and functionalization (Fig. 1)
Capillary-driven self-assembly of particles followed by removal of the outer layers by FIB, which allows the undercooled metal to flow, to form complex 3D structures that are otherwise difficult to fabricate. (ii) Mechanically stressing the droplets resulting in fracture of outer layers; leading to flow and subsequent coalescence of the undercooled liquid metal

Summary

Undercooled Metal Particles for

Heat-Free Soldering received: 29 September 2015 accepted: 02 February 2016 Published: 23 February 2016. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity. Due to the metastable nature of undercooled metal particles, their production in good yields is an experimental challenge This challenge can be overcome through; i) elimination of heterogeneous nucleating sites, or other sites with high potency for catalyzing solidification[1,7,9,10], and, ii) minimizing the container effects (nucleation) by employing the droplet dispersion or containerless techniques in synthesis of undercooled particles[3,4,11]. Main benefits of the proposed approach are; i) reduces the need for advanced instrument, ii) limited need for skilled manpower, iii) minimizes energy needs, iv) significantly improves production efficiency, v) is low-cost and uses lead-free materials, and, vi) reduces fabrication cost

Results and Discussion

Conclusions

Author Contributions

Additional Information