Sacrificial Passivation of Nanoscale Metal Powders for Transient Liquid Phase Bonding
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1079-N05-12
Sacrificial Passivation of Nanoscale Metal Powders for Transient Liquid Phase Bonding Nick S Bosco1, Beth Manhat2, and Jolanta Janczak-Rusch1 1 Laboratory for Interface and Joining Technology, Empa, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland 2 Department of Chemistry, Portland State University, Portland, OR, 97207 ABSTRACT Differential scanning calorimetry (DSC) was used to evaluate the extent of liquid phase formation in particle compacts (compressed dry powders) comprised of organically capped nanoscale Ag particles and Sn. The Ag nanoparticles employed where synthesized with various organic molecules and procedures to produce particles with a range of capping thicknesses and decomposition temperatures (Td), as measured by thermogravimetric analysis (TGA). A baseline sample containing commercially available un-capped micrometer scale Ag was also investigated for comparison. Results indicate that all of the Sn initially present formed a liquid phase when heated through its melting point when combined with Ag particles exhibiting a comparatively thick cap of low Td. Slightly smaller fractions of Sn liquid were obtained when the Ag’s cap was thin and of a high Td while particles with thin-low Td caps exhibited the highest levels of Sn consumption and similar to that observed with the un-capped micron-scale Ag particles. The reduction in the amount of Sn liquid formed is attributed to solid state reaction between the Ag and Sn particles resulting in the formation of a more refractory phase. The extent of the subsequent liquid phase reaction was also evaluated and is demonstrated to not necessarily be adversely effected by the presence of the organics. The significance of this work is the demonstration that organic molecules may be employed to prevent solid state reaction in particle compacts at elevated temperatures, yet allow the subsequent liquid phase reaction proceed uninhibited. INTRODCUTION The future commercialization of high-temperature wide band-gap semiconductors, such as SiC and GaN, for applications from laser diodes to power electronics will make current dieattach materials obsolete. Neither the solder alloys nor epoxies that are in wide use today could support the high-performance or high-reliability operational demands of these devices at temperatures beyond 250°C [1-4]. A die-attach material and process that is capable of producing microstructures tailored for their enhanced mechanical, thermal and electrical properties while obtainable through benign processing conditions is therefore required. Transient liquid phase (TLP) bonding possesses the potential to meet these needs [5]. The TLP process employs a melting point depressant (MPD), between the base metals to be joined and relies on interdiffusion for isothermal solidification at the bonding temperature. The integrity of the resulting bonds is enhanced by the presence of the liquid phase during bonding, yet the bonds are able to withstand operation at temperatures above the bonding temperature once solidification is complete.
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