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Microstructure and Performance of Kovar/Alumina Joints Made with Silver-Copper Base Active Metal Braze Alloys

Description: Poor hermeticity performance was observed for Al{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramic-ceramic joints having a Kovar{trademark} alloy interlayer. The active Ag-Cu-Ti filler metal was used to braze the substrates together. The Ti active element was scavenged from the filler metal by the formation of a (Fe, Ni, Co){sub x}Ti phase (x= 2-3) that prevented development of a continuous Ti{sub x}O{sub y} layer at the filler metal/Al{sub 2}O{sub 3} interface. Altering the process parameters did not circumvent the scavenging of Ti. Molybdenum barrier layers 1000, 2500, or 5000 {angstrom} thick on the Kovar{trademark} surfaces successfully allowed Ti{sub x}O{sub y} formation at the filler metal/Al{sub 2}O{sub 3} interface and hermetic joints. The problems with the Ag-Cu-Ti filler metal for Kovar{trademark}/Al{sub 2}O{sub 3} braze joints led to the evaluation of a Ag-Cu-Zr filler metal. The Zr (active element) in Ag-Cu-Zr filler metal was not susceptible to the scavenging problem.
Date: December 15, 1999
Creator: STEPHENS, JOHN J.; VIANCO,PAUL T.; HLAVA,PAUL F. & WALKER,CHARLES A.
Partner: UNT Libraries Government Documents Department

Kovar Micro Heat Pipe Substrates for Microelectronic Cooling

Description: We describe the development of a new technology for cooling microelectronics. This report documents the design, fabrication, and prototype testing of micro scale heat pipes embedded in a flat plate substrate or heat spreader. A thermal model tuned to the test results enables us to describe heat transfer in the prototype, as well as evaluate the use of this technology in other applications. The substrate walls are Kovar alloy, which has a coefficient of thermal expansion close to that of microelectronic die. The prototype designs integrating micro heat pipes with Kovar enhance thermal conductivity by more than a factor of two over that of Kovar alone, thus improving the cooling of micro-electronic die.
Date: April 1999
Creator: Benson, David A.; Burchett, Steven N.; Kravitz, Stanley H.; Robino, Charles V.; Schmidt, Carrie & Tigges, Chris P.
Partner: UNT Libraries Government Documents Department

Recent experience in the fabrication and brazing of ceramic beam tubes for kicker magnets at FNAL

Description: Ceramic beam tubes are utilized in numerous kicker magnets in different accelerator rings at Fermi National Accelerator Laboratory. Kovar flanges are brazed onto each beam tube end, since kovar and high alumina ceramic have similar expansion curves. The tube, kovar flange, end piece, and braze foil (titanium/incusil) alloy brazing material are stacked in the furnace and then brazed in the furnace at 1000 C. The ceramic specified is 99.8% Alumina, Al{sub 2}O{sub 3}, a strong recrystallized high-alumina fabricated by slip casting. Recent experience at Fermilab with the fabrication and brazing of these tubes has brought to light numerous problems including tube breakage and cracking and also the difficulty of brazing the tube to produce a leak-tight joint. These problems may be due to the ceramic quality, voids in the ceramic, thinness of the wall, and micro-cracks in the ends which make it difficult to braze because it cannot fill tiny surface cracks which are caused by grain pullout during the cutting process. Solutions which are being investigated include lapping the ends of the tubes before brazing to eliminate the micro-cracks and also metallization of the tubes.
Date: June 1, 2008
Creator: Ader, C.R.; Jensen, C.; Reilly, R.; Snee, D.; Wilson, J.H. & /Fermilab
Partner: UNT Libraries Government Documents Department

Mechanical design of ceramic beam tube braze joints for NOvA kicker magnets

Description: The NO?A Experiment will construct a detector optimized for electron neutrino detection in the existing NuMI neutrino beam. The NuMI beam line is capable of operating at 400 kW of primary beam power and the upgrade will allow up to 700 kW. Ceramic beam tubes are utilized in numerous kicker magnets in different accelerator rings at Fermi National Accelerator Laboratory. Kovar flanges are brazed onto each beam tube end, since kovar and high alumina ceramic have similar expansion curves. The tube, kovar flange, end piece, and braze foil alloy brazing material are stacked in the furnace and then brazed. The most challenging aspect of fabricating kicker magnets in recent years have been making hermetic vacuum seals on the braze joints between the ceramic and flange. Numerous process variables can influence the robustness of conventional metal/ceramic brazing processes. The ceramic-filler metal interface is normally the weak layer when failure does not occur within the ceramic. Differences between active brazing filler metal and the moly-manganese process will be discussed along with the applicable results of these techniques used for Fermilab production kicker tubes.
Date: May 1, 2010
Creator: Ader, C.R.; Reilly, R.E.; Wilson, J.H. & /Fermilab
Partner: UNT Libraries Government Documents Department

Segregation of Si to the surface of Fe-29Ni-17Co alloy

Description: The segregation of Si impurities from the bulk to the surface of a low Cr Lot of Kovar{sup TM} (Fe-29Ni-17Co) has been investigated in order to determine the effects on the quality of the braze of Cu to these altered surfaces. It is found that oxides of Si are formed on the surface during wet hydrogen firing. Kinetics of this segregation process have been measured.
Date: September 1, 1993
Creator: Nelson, G. C. & Buttry, R. W.
Partner: UNT Libraries Government Documents Department

Tearing during pinch-off of Rolamite fill tubes

Description: A failure mechanism is proposed to explain the bubble streaming and trichloroethylene infiltration which has been observed in failed Rolamite devices. An intergranular oxide network forms in the Kovar fill tube as a result of the glass-to-metal seal processing; it is suggested that tearing occurs in this oxide network during a subsequent pinching-off operation. It is demonstratd that bending over a mandrel causes this intergranular network to widen and deepen in a tearing mode. A modified preoxidation heat treatment or partial oxidation procedure prevents this problem.
Date: November 1, 1981
Creator: Yost, F.G.
Partner: UNT Libraries Government Documents Department

[Press Release: Attention election night editors]

Description: A press release from the Gay and Lesbian Victory and Barney Frank, mentioning gay and lesbian issues during the 1992 presidency election. Barney Frank includes a letter requesting a copy of the non-discriminatory policy for gays and lesbians implemented by Vice President Dan Qualey.
Date: October 16, 1992
Partner: UNT Libraries Special Collections

High temperature grain growth and oxidation of Fe-29Ni-17Co (Kovar{trademark}) alloy leads

Description: One important application for the Fe-29Ni-17Co (Kovar{trademark}) alloy in wire form is in brazed feed through assemblies which are integral parts of vacuum electronic devices. Since Cu metal brazes are performed at process temperatures of about 1100{degrees}C, there is opportunity for significant grain growth to occur during the brazing operation. Additional high temperature exposure includes decarburization of the Fe-29Ni-17Co alloy wire in wet hydrogen for 30 min. at 1000{degrees}C prior to the Cu brazing operation. Two approaches have been used to characterize grain growth in two lots of Fe-29Ni-17Co alloy: (1) a once-through processing study to study the effect of one-time-only device thermal processing on the resulting grain size, and (2) an isothermal grain growth study involving various times at 800--1100{degrees}C. The results of the once-through processing study indicate that acceptable grain sizes are obtained from both cold worked and mill-annealed wire lots following Cu brazing. The isothermal grain growth study indicates that the linear intercept distance for Fe-29Ni-17Co can be described with a power law function of time, and that thermal exposure must be controlled at temperatures in excess of 900{degrees}C in order to avoid excessive grain growth. A second study has characterized the oxidation kinetics of Fe-29Ni-17Co alloy wire in air at temperatures ranging from 550--700{degrees}C. This study indicates the parabolic growth law applies for this material, and between 550 and 700{degrees}C, oxidation in this alloy occurs at an activation energy of 27.9 kcal/mole. Other oxidation studies at higher temperatures ({ge}750{degrees}C) indicate an activation energy of 52.2 kcal/mole for oxidation of Fe-29Ni-17Co alloy at temperatures greater than 790{degrees}C. Quantitative point analyses of the oxide scale formed at 600{degrees}C suggest that a significant fraction of the scale is close to the stoichiometry of the Fe{sub 2}O{sub 3}-type oxide.
Date: December 31, 1993
Creator: Stephens, J. J.; Greulich, F. A. & Beavis, L. C.
Partner: UNT Libraries Government Documents Department

Reducing inadvertent alloying of metal/ceramic brazes

Description: Inadvertent alloying of Cu braze metal can compromise metal/ceramic seals. Electron microprobe analyses have quantified alloying of Cu brazes in metal/ceramic feedthroughs. Pin material and processing parameters above 1084C both affect alloying levels. Using either Kovar or Ni-plated 316L stainless steel pins limits alloying compared to Palco pins. Minimizing the time during which the braze is molten also avoids excessive alloying. The original thickness of the Ni plating on the Mo-Mn metallization of the ceramic also influences the alloying content of these brazes. Metal/ceramic brazes made with long brazing cycles, Mo-Mn metallization, and Kovar components grow a layer of Mo{sub 6}(Fe{sub 3.5}CO{sub 3.5}){sub 7} on the metallization. Layer thicknesses observed do not appear to compromise joint integrity. Ni additions of approximately 10 and 20 wt.% to Cu apparently increases the stress required for stress relaxation during cooldown. to maintain creep rates required for stress relaxation during cooldown. Relative to unalloyed Cu, this strengthening effect tends to increase as temperature is decreased.
Date: December 31, 1992
Creator: Stephens, J. J. & Hlava, P. F.
Partner: UNT Libraries Government Documents Department

Failure analysis of ceramic-to-metal seals

Description: Ceramic-to-metal seal failures that occur at the next assembly level present a critical problem because of the time and expense involved in the assembly of electro-mechanical switches. A typical analysis of a failed assembly and a recommended rework process is presented. In addition, steps are proposed to minimize the occurrence of future ceramic-to-metal seal failures.
Date: March 1, 1980
Creator: Gates, W.G.
Partner: UNT Libraries Government Documents Department

Steel-SiC Metal Matrix Composite Development

Description: The goal of this project is to develop a method for fabricating SiC-reinforced high-strength steel. We are developing a metal-matrix composite (MMC) in which SiC fibers are be embedded within a metal matrix of steel, with adequate interfacial bonding to deliver the full benefit of the tensile strength of the SiC fibers in the composite.
Date: July 17, 2005
Creator: Smith, Don D.
Partner: UNT Libraries Government Documents Department

Plating on some difficult-to-plate metals and alloys

Description: Electrodeposition of coatings on metals such as beryllium, beryllium-copper, Kovar, lead, magnesium, thorium, titanium, tungsten, uranium, zirconium, and their alloys can be problematic. This is due in most cases to a natural oxide surface film that readily reforms after being removed. The procedures we recommend for plating on these metals rely on replacing the oxide film with a displacement coating, or etching to allow mechanical keying between the substrate and plated deposit. The effectiveness of the procedures is demonstrated by interface bond strengths found in ring-shear and conical-head tensile tests.
Date: February 1, 1980
Creator: Dini, J.W. & Johnson, H.R.
Partner: UNT Libraries Government Documents Department

Development of plating thickness standards. Milestone report

Description: Standards which are unavailable from the National Bureau of Standards were developed to support the nondestructive measurement of plating thickness. Their fabrication, measurement, certification, and calibration-recall schedule are discussed. Reference standards that have been put into service include aluminum/Kapton, silver/copper, tin/steel, gold/silver, cadmium/Kovar, silver/iron, rhodium/copper, and gold/ceramic. 6 figures, 3 tables.
Date: January 1, 1978
Creator: Russell, R.J.
Partner: UNT Libraries Government Documents Department

Coating of metals with titanium diboride by chemical vapor deposition

Description: This study is an experimental investigation of the chemical vapor deposition of titanium diboride on metallic substrates by the hydrogen reduction of TiCl/sub 4/ and BCl/sub 3/ at temperatures between 850/sup 0/C and 1100/sup 0/C. Kovar, tantalum, and several stainless steels were found to be suitable substrates since they could withstand the deposition temperature, had adequate resistance to HCl, a by-product of the deposition reaction, and had thermal expansion coefficients sufficiently close to that of TiB/sub 2/ (less than or equal to10 x 10/sup -6///sup 0/C). The TiB/sub 2/ coatings produced were 68.2% Ti and thus near stoichiometry and had very low impurity content. They had Knoop hardnesses averaging 3300 kg/mm/sup 2/ and exhibited extraordinary erosion resistance.
Date: January 1, 1977
Creator: Pierson, H. O. & Randich, E.
Partner: UNT Libraries Government Documents Department

Migration of iron, nickel, cobalt and chromium associated with silver brazing during ceramic-to-metal joining

Description: During the study of bond strengths of ceramic-to-metal seals under various brazing conditions, it was observed that the strength was affected by the length of time that the braze material was in the liquid state. Brazing times as short as 10 min sometimes adversely affected the strength of the seal. Photomicrographs of a typical weak bond clearly show silver braze penetration deep in the metallizing layer after 10 min at 20/sup 0/C above the melting point of the braze. A reaction layer was also observed in the photomicrographs. Considerable iron has migrated from the Kovar pin through the silver braze and formed an interface between the silver braze and the molybdenum metallizing material. Significant concentrations of cobalt and nickel were also found in the reaction zone, indicating a diffusion reaction of Kovar through the silver. Further investigations showed that while braze durations as short as 1 min at 20/sup 0/C above the liquid temperature gave much stronger bonds than 10 min did, significant migration of material was evident. In view of the significant migration of both the pin alloy and the braze material, it was concluded that brazing time and temperature should be minimized to achieve maximum bond strength.
Date: June 30, 1978
Creator: Etter, D.E.; Egleston, E.E. & Jaeger, R.R.
Partner: UNT Libraries Government Documents Department

Suitability of Tophet C-Alloy 52/Kovar components to hydrogen environments

Description: The suitability of Tophet C-Alloy 52/Kovar weldments to hydrogen embrittlement were investigated because of their potential as candidate materials in fabrication of minaturized initiators for pyrotechnics. Cathodic charged samples were statically loaded for extended periods of time resulting in no load failures and in ductile fracture surfaces indicating resistance to hydrogen embrittlement. 20 figures.
Date: June 22, 1976
Creator: Gebhart, J. M. & Kelly, M. D.
Partner: UNT Libraries Government Documents Department

An experimental/analytical comparison of strains in encapsulated assemblies

Description: A combined experimental and analytical study of strains developed in encapsulated assemblies during casting, curing and thermal excursions is described. The experimental setup, designed to measure in situ strains, consisted of thin, closed-end, Kovar tubes that were instrumented with strain gages and thermocouples before being over-cast with a polymeric encapsulant. Four bisphenol A (three diethanolamine cured and one anhydride cured) epoxy-based materials and one urethane elastomeric material were studied. After cure of the encapsulant, tube strains were measured over the temperature range of {minus}55{degrees}C to 90{degrees}C. The thermal excursion experiments were then numerically modeled using finite element analyses and the computed strains were compared to the experimental strains. The predicted strains were over estimated (conservative) when a linear, elastic, temperature-dependent material model was assumed for the encapsulant and the stress free temperature T{sub i} was assumed to correspond to the cure temperature {Tc} of the encapsulant. Very good agreement was obtained with linear elastic calculations provided that the stress free temperature corresponded to the onset of the glassy-to-rubbery transition range of the encapsulant. Finally, excellent agreement was obtained in one of the materials (828/DEA) when a viscoelastic material model was utilized and a stress free temperature corresponding to the cure temperature was assumed. 13 refs., 20 figs., 3 tabs.
Date: November 1, 1991
Creator: Guess, T.R. & Burchett, S.N.
Partner: UNT Libraries Government Documents Department

Thermodesorption of gases from various vacuum materials

Description: A number of materials are commonly used as vacuum system walls. The desorption of gases from these materials may contribute significantly to the internal pressure of an unpumped device or to the gas load which a pump must handle in a dynamic system. This report describes the thermodesorption measurements made on a number of metals (molybdenum, nickel, Kovar alloy, copper, copper-2% beryllium alloy) and two insulators (molybdenum sealing glass ceramic and high alumina ceramic). All of the materials after typical cleaning and air exposure contain considerable gas. With a long 400/sup 0/ to 500/sup 0/ vacuum bake, however, all can be cleaned sufficiently so that they will not contribute appreciable gas to their surrounding when vacuum stored at room temperature for many years. Most materials display desorption kinetics which are first order (a single bond or trap energy must be overcome for desorption). It appears that the desorption of CO from Kovar is rate limited by carbon diffusion (D/sub 0/ approx. = .4 cm/sup 2//s and E/sub d/ approx. = 27,000 cal/mol). The desorption of hydrogen from glass ceramic also appears to be diffusion rate limited (D/sub 0/ approx. = 1 x 10/sup -3/ cm/sup 2//s and E/sub d/ approx. = 11,000 cal/mol). Carbon monoxide is the major gas desorbed from metals, except copper for which hydrogen is the major desorbing species. The insulators desorb hydrogen primarily.
Date: June 1, 1979
Creator: Beavis, L.C.
Partner: UNT Libraries Government Documents Department

Fluxless laser soldering for electronic packaging

Description: Conventional soldering typically requires the use of reactive fluxes to promote wetting. The resulting flux residues are removed primarily with halogenated or chlorofluorocarbon (CFC) solvents. With the mandated phaseout of CFCs by the year 2000, there has been a concentrated effort to develop alternative, environmentally compatible manufacturing and cleaning technologies that will satisfy the restrictions placed on CFCs, but still yield high quality product. Sandia National Laboratories is currently evaluating a variety of alternative fluxless soldering technologies which can be applied to electronic packaging. Laser soldering in a controlled atmosphere has shown great potential as an environmentally compatible process. The effects of laser heating with a 100 watt CW Nd:YAG laser, joint design, and base/filler metal reactions on achieving fluxless wetting with good metallurgical bonds were examined. Satisfactory Ni-Au plated Kovar{reg sign} solder joints were made with 80In-15Pb-5Ag and 63Sn-37Pb (wt. %) solder alloys in a slightly reducing cover gas. Wetting generally increased with increasing laser power, decreasing laser beam spot size, and decreasing part travel speed. The materials and processing interaction effects are identified and discussed.
Date: January 1, 1991
Creator: Hosking, F M & Keicher, D M
Partner: UNT Libraries Government Documents Department