Publications

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The assembly of ceramic components often uses soldering technologies to attach metal structures to the ceramic base material. Because many suitable solder alloys do not readily wet and spread on ceramics, a metallization layer is deposited on the latter to support wetting and spreading by the molten solder for completion of the joint The metallization layer must be sufficiently robust to retain its integrity through the soldering process as well as not negatively impact the long-term reliability of the joint A study was performed to evaluate the mechanical properties of solder joints made to a 0.200Ti/W-40Cu-2.0Pt-0.375Au (pm) thin-film metallization deposited on low-temperature co-fired ceramic (LTCC) base materials. The solder joints were made with the 63Sn-37Pb solder (wt-%, abbreviated Sn-Pb). A pin pull test was developed to measure the tensile strength of the solder joint as a function of soldering parameters. Failure mode analysis was a critical metric for assessing the roles of interfaces, bulk solder, and the ceramic on mechanical performance. The Sn-Pb solder joints experienced a nominal strength loss with increased severity of the soldering process parameters. The strength decline was attributed to changes in the solder joint microstructure, and not degradation to the thin film structures.

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Pressure losses and aerosol collection efficiencies were measured for fibrous filter materials at air-flow rates consistent with high efficiency filtration (hundreds of cubic feet per minute). Microfiber filters coated with nanofibers were purchased and fabricated into test assemblies for a 12-inch duct system designed to mimic high efficiency filtration testing of commercial and industrial processes. Standards and specifications for high efficiency filtration were studied from a variety of institutions to assess protocols for design, testing, operations and maintenance, and quality assurance (e.g., DOE, ASHRAE, ASME). Three materials with varying Minimum Efficiency Reporting Values (MERV) were challenged with sodium chloride aerosol. Substantial filter loading was observed where aerosol collection efficiencies and pressure losses increased during experiments. Filter designs will be optimized and characterized in subsequent years of this study. Additional testing will be performed with higher hazard aerosols at Oak Ridge National Laboratory.

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This study examined the cause of nonwetted regions of the gold (Au) finish on iron-nickel (Fe-Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt %, abbreviated Au-Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger electron spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au-Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. An Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au-Sn joints without risk to their mechanical strength or hermeticity.

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The run-out phenomenon was observed in Ag-Cu-Zr active braze joints made between the alumina ceramic and Kovar™ base material. Run-out introduces a significant yield loss by generating functional and/or cosmetic defects in brazements. A prior study identified a correlation between run-out and the aluminum (Al) released by the reduction/oxidation reaction with alumina and aluminum's reaction with the Kovar™ base material. A study was undertaken to understand the fundamental principles of run-out by examining the interface reaction between Ag-xAl filler metals (x = 2,5, and 10 wt-%) and Kovar™ base material. Sessile drop samples were fabricated using brazing temperatures of 965° (T769°F) or 995°C 0823°F) and times of 5 or 20 min. The correlation was made between the degree of wetting and spreading by the sessile drops and the run-out phenomenon. Wetting and spreading increased with Al content (x) of the. Ag-xAl filler metal, but was largely insensitive to the brazing process parameters. The increased Al concentration resulted in higher Al contents of the (Fe, Ni, Co)xAly reaction layer. Run-out was predicted when the filler metal has a locally elevated Al content exceeding 2-5 wt-%. Several mitigation strategies were proposed, based upon these findings.

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