Tensile strength and elastic modulus measurements of low-pressure chemical vapour deposited (LPCVD) polysilicon films were performed on freestanding microtensile specimens (fibers) fabricated from the films. Various annealing treatments were employed to alter the polysilicon grain size. Fibers were fabricated from films with grain sizes of 50, 100, and 500 nm. The fiber cross sectional area was 3.3 mu m3 and the gauge section was 30 mu m long. The fibers failed in a brittle fashion with tensile strengths between 2.7 and 3.4 GPa. Fibers fabricated from polysilicon with 500 nm grain size had uniform equiaxial grains and were stronger than fibers made from smaller grain size material. This higher strength can be attributed to the better interface between the 500 nm grains as a result of the annealing process. The average elastic modulus of the fibers was 175 GPa.
Thin film aluminum fibers with grain sizes of 35 and 100 nm were pulled in a microtensile tester. The larger grains led to greater yield and tensile strengths but smaller strains to failure. Both samples had mechanical strengths 3–6 times greater than bulk aluminum. In addition, the small grained fibers had a strain rate sensitivity exponent of 0.26 suggesting diffusion controlled plastic deformation mechanisms.
Both electrodeposited and electroless copper are widely used in the electronics industry to form signal lines and plated-through holes in printed circuit cards and boards. Because of widely differing thermal expansion coefficients of copper and of the ceramic and polymeric substrates, large mechanical stresses develop in the metallization during thermal cycles, as e.g. during solder reflow. To safeguard against premature fracture it is imperative that the metallization is sufficiently ductile. Plated thin foil copper of poor ductility is known to be susceptible to cracks in plated-through holes which, besides causing problems in the manufacture, poses a threat to device reliability in service. In this paper we show that such cracks arise as a combination of reduced ductility due to presence of initial porosity in copper and due to grain boundary sliding and diffusional cavity growth during the soldering cycle. We emphasize that there exists strong interactions between these ductility reducing effects, such that their coupled action may exceed the effect when each mechanism operates independently. We review recent research on deformation and fracture of bulk and plated copper between RT and 300°C. Finally, we briefly discuss approaches to improve mechanical properties of plated thin foil copper.
Ceramic fibers and grids of controlled geometry and composition were fabricated by electron beam evaporation of Al2O3 onto substrates patterned by optical lithography. The fibers were 4 and 5μm wide by 1μm thick. In addition, mixed metal oxide films from 0 to 10at% Ti, Zr, or Cr were produced by coevaporation with Al2O3. The compositions of the films were determined by Rutherford Backscattering Spectroscopy. TEM and electron diffraction examination showed all the films to be amorphous in structure.The Al2O3 fibers had tensile strengths between 143 and 168 ksi and the Al2O3 film had a microindentation hardness of 8.4 GPa. Films with ≈ 1at% additions of Zr, Ti, and Cr had hardnesses of 11.0, 9.7, and 8.8 GPa respectively. The hardness then decreased with higher Zr, Ti, and Cr concentrations
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