Additive laser metal deposition onto silicon

• Published in: Additive manufacturing 2019-01, Vol.25, p.390-398
• Main Authors: Azizi, Arad, Daeumer, Matthias A., Schiffres, Scott N.
• Format: Article
• Language: English
• Subjects: Additive manufacturing of dissimilar materials; Dissimilar material bonding; Intermetallic-semiconductor interfaces; Laser bonding through the formation of intermetallics; Silicon-metal bonding
• ISSN: 2214-8604; 2214-7810
• DOI: 10.1016/j.addma.2018.09.027

[Display omitted] By employing selective laser melting (SLM), we demonstrate how Sn3Ag4Ti alloy can robustly bond to silicon via additive manufacturing. With this technology, heat removal devices (e.g., vapor chamber evaporators, heat pipes, micro-channels) can be directly printed onto the electronic package without using thermal interface materials. This has the advantage of keeping the current microprocessor about 10 °C cooler by eliminating two thermal interface materials. This reduces operating temperature, saving power and reducing electronic-waste. The bonding of common metal alloys used in additive manufacturing onto silicon is relatively weak and generally possesses high contact angles (poor wetting and interfacial strength). By using the proper interlayer material, wettability and reactivity with the silicon substrate increase drastically. Unlike conventional dissimilar material brazing that can take tens of minutes to form a strong bond, this study demonstrates how this kinetic limitation can be overcome to form a good bond in sub-milliseconds via intense laser heating. The mechanism for rapid bonding lies in using an alloy that can form a strong intermetallic bond to the substrate at a low temperature, and exposing the sample multiple times to give sufficient diffusion time for a strong bond. Bonding of Sn3Ag4Ti to silicon occurs through the formation of a thin (∼μm) titanium-silicide interfacial layer that makes the silicon wettable to the Sn3Ag4Ti. These printed parts are mechanically resistant to thermal cycling, with no mechanical failures visible after over a week of continuous thermal cycling (−40 °C and 130 °C).