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  1. Solder joints in microelectronics devices consist of low-melting solder compositions that wet and join metal contacts and are, ordinarily, used at high homologous temperatures in the as-solidified condition. Differences in solidification rate and substrate interactions have the consequence that even solder joints of similar compositions exhibit a wide range of microstructures. The variation in microstructure causes a variation in properties; in particular, the high-temperature creep properties that govern much of the mechanical behavior of the solder may differ significantly from joint to joint. The present paper reviews the varieties of microstructure that are found in common solder joints, and describesmore » some of the ways in which microstructural changes affect mechanical properties and joint reliability.« less
  2. Wettability of pretinned Cu decreases after long aging times. This work provides insight into the role Cu-Sn intermetallics play in wettability degradation. This study investigates the effects of aging in air and argon at 170{degree}C on Cu coupons which were pretinned with 75Sn-25Pb solder. Coating was applied using an electroplating technique. The coating thickness was controlled between 3 to 30 {mu}m and the specimens were aged for 0, 2, 24 h, and two weeks. Wetting balance tests were used to evaluate the wettability of the test specimens. Microstructural development was evaluated using x-ray diffraction, energy dispersive x-ray, and Auger spectroscopy,more » as well as optical and scanning electron microscopy. Results indicate that Cu-Sn intermetallics protected from oxidation do not contribute to a decrease in wettability. Oxidized intermetallics, however, significantly decrease the wettability of aged pretinned samples. The extent of degradation is determined by the type of oxide formed on the surface of the intermetallic. This study shows that a predominantly Cu oxide forms on Cu{sub 3}Sn, while a Sn oxide forms on Cu{sub 6}Sn{sub 5}. No evidence of internal oxidation was found. 20 refs., 9 figs., 1 tab.« less
  3. The addition of 3 wt.% Ag to In results in a eutectic composition with improved mechanical properties while only slightly lowering the melting temperature. Steady-state creep properties of In-Ag eutectic solder joints have been measured using constant load tests at 0, 30, 60, and 90 C. Constitutive equations are derived to describe the creep behavior. The data are well represented by an equation of the form proposed by Dorn: a power-law equation applies to each independent creep mechanism. Two parallel mechanisms were observed for the In-Ag eutectic joints. The high-stress mechanism is a bulk mechanism with a thermal dependence dominatedmore » by the thermal dependence of creep in the In-rich matrix. The low-stress mechanism is a grain boundary mechanism. Results of this work are discussed with regard to creep behavior of typical eutectic systems.« less
  4. Atmospheric CO{sub 2} and soil nutrients altered interspecific competitive performance of three grassland annuals, all exhibiting the C{sub 3} metabolic pathway. Plantago erecta, an herbaceous dicot dominant in low-fertility serpentine grassland, was the superior interspecific competitor at low soil nutrients. Bromus hordeaceus, an introduced grass dominant in higher fertility sandstone grassland, was the superior interspecific competitor at high soil nutrients. Interspecific competitive ability of Plantago was slightly enhanced under elevated CO{sub 2}, but only at high soil nutrients, whereas interspecific competitive ability of Bromus was stimulated under elevated CO{sub 2} at both low and high soil nutrients. Interspecific competitive abilitymore » of Lasthenia californica, another herbaceous dicot common in serpentine grassland, was low in all treatments, and tended to decrease with elevated CO{sub 2} at low soil nutrients. Our results suggest that elevated CO{sub 2} may shift plant species abundance of serpentine grassland in favor of Bromus hordeaceus.« less
  5. The Pluto Program is reviewed. Work directed toward the design of a reactor for sea-level flight of supersonic ramjet missiles is discussed. Choice of materials and reactor neutronics is considcred. Design problems are outlined. The reactor concepts were developed into the Tory II-A reactor and the Tory II-C reactor. These reactors are described, and test results discussed. (M.C.G.)
  6. For presentation at the meeting of the American Rocket Society to be held in Gatlinburg, Tennessee, May 1961. A review of design, operational, and engineering aspects of the Pluto program is presented. Information on the Tory reactor is included along with a description of the Nevada test site. (J.R.D.)
  7. A facility called Hot Box'' was constructed at Jackass Flats, Nevada, to be used in studies of high-temperature critical assemblies of simple geometry, in order to determine whether calculation procedures are adequate for estimating the effect of temperature changes. Uranium foils of 2-mil thickness and moderator blocks are assembled at room temperature and raised to higher temperatures by hot gas; the critical mass at one particular temperature is determined. Data are presented for graphite-moderated bare-unreflected and reflected systems at temperatures up to 12O0 deg F and should be useful for nuclear propulsion system calculations. (D.L.C.)
  8. Declassified 26 Nov 1973. A report on the irtermediate and full power tests of the Tory IIC reactor is presented. An analysis of reactor performance is included. (JWR)
  9. From time to time, in discussion of possible naval-based nuclear ramjet missile systems, a question arises concerning whether or not a particular reactor would or would fall within the `Tory II-C Technology`. Such a question is meaningless unless a definition is furnished. This report provides such a definition.

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"Reynolds, H.L."

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