The dependences of T"resistivity, resistance ratio, and structure on chemical composition and sputtering conditions for Nb-Ge films have been studied. The chemical composition, impurity content, and x-ray structure were obtained using Rutherford backscattering, nuclear techniques, and x-ray diffraction. Although T, varies with composition, it is not found to be critically dependent upon exact stoichiometry; the Nb/Ge ratios vary by -13% (2.6 to 3) for films with -23-K onsets and by -40% (2.2 to 3.3) for films with -20-K onsets. For compositions similar to the bulk, the films have comparitively much higher T, 's and smaller lattice parameters. X-ray results show the films to contain predominately A-15 phase (except for Nb/Ge & 2.5) with lattice parameters varying from 5.15 A for 0 Nb-rich low-T, films to 5.12 A for Ge-rich films. Several percent of oxygen and carbon occur in low-T, amorphous films deposited at 650'C but this is considerably reduced in high-T, films made simultaneously at -750'C. No argon was found and the nitrogen content was generally less than 1%, No correlation of high T, s and impurities was found. The optimum deposition temperature and resistivity are lowest, and the resistance ratio highest for Nb/Ge ratios somewhat below 3/1. A simple correlation of T, and resistance ratio is reported which is largely independent of all sputtering conditions and composition and which suggests that slightly higher T, s may be possible. Negative bias was found to be detrimental to T, while positive bias had relatively little effect, Magnetic-field-assisted sputtering led to significant increases in the sputtering rate and the optimum deposition temperature. allow resistive heating with a temperature differ ential of 100'C across five substrates.

Defects introduced into superconducting Nb-Ge films by 2-MeV 4 He particles produce a T c -resistance-ratio correlation similar to that for as-grown films and a T c -lattice-parameter correlation resembling both film and bulk behavior. It is suggested that simple antistructure defects in a perfect lattice are not primarily responsible for lowering T c for the case of 4 He damage in the sputtered films.

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Low cycle fatigue studies of solder joints designed and fabricated to represent generic interconnection structures typical of what might be used in packaging microelectronics have been carried out to assist in the development of a better understanding of the fundamental mechanical properties that determine the reliability of such structures. These studies involve micro scale joints (micro-joints) of both eutectic and 95/5 Pb/Sn solders fabricated by several different processes. In addition to a discussion of the results of recent tests reflecting specified loss-of-strength failure criteria and extensive post-test failure mode analysis of, primarily, 95/5 Pb/Sn micro-joints, descriptions of (1) the design and fabrication of the custom shear test vehicles and (2) the high-resolution electro-mechanical loading system used to apply cyclic loadings under isothermal conditions will be presented. This computer controlled system provides for the application of fully or partially reversed shear strains (with or without dwells) to either prototypes or custom test vehicles, and can be operated to maintain either total or plastic strain control during cycling.

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