Microscale Self-Assembled Electrical Contacts

Report No. ARL-TR-4298
Authors: Christopher J. Morris
Date/Pages: September 2007; 38 pages
Abstract: Self-assembly, or the spontaneous organization of parts into larger structures via energy minimization, is an attractive solution to overcome packaging and integration challenges. Capillary forces from a molten alloy can be used to both bond microscale components and make electrical connections between them in a self-assembly process. This report presents a systematic study of a number of metal alloys and self-assembly media with the aim of reducing the metal contact size between microscale components. Six different alloys or pure metals with melting points below 160 ¿C and nine different fluids with boiling points over 160 ¿C are considered. Tin-based alloys were generally found to be highly susceptible to corrosion at elevated temperatures above the alloy melting point, with Sn being the primary component to corrode and react with the underlying base metal. Using a eutectic Sn-Bi alloy and glycerol at 180-200 ¿C, the self-assembly of 1500 100-µm parts and 500 40-µm parts was demonstrated, each in about 2.5 min. Thus, 40 µm square, 4 µm high contacts were shown to remain functional for self-assembly. The electrical conductance of self-assembled 20 ¿m diameter, 2.5 µm high alloy contacts based on this Sn-Bi-glycerol system was measured at 1.9 /mΩ-cm2.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2007