Akira Ichida

CVD Tungsten and Tungsten-Rhenium Alloys for Structural Applications

Abstract The microstructures of CVD tungsten and tungsten-rhenium alloys have been investigated to evaluate their suitability as high temperature materials. We found that the partial pressure in the reaction chamber affected the microstructure and surface roughness of deposited pure tungsten and tungsten-rhenium alloys. Grain sizes smaller than 0.5 im were obtained for both deposited pure tungsten and tungsten-rhenium alloys. Fine-grained tungsten proved to have greater hardness (Hv>1000 at room temperature (R.T.)) bending strength (δ = 700-1230 MPa at R.T.-l 175 K) and thermal coefficient of linear expansion (β = 4.5-4.9 xl06K−1 at 575-1175 K) characteristics than tungsten with columnar structure.

Effect of Ni Coating Over Cu Ball on the Microstructure of Flip Chip Joints With Cu-Cored Solder Balls

Effect of Ni coating over the Cu core of Cu-cored Sn-5mass%Ag balls was investigated on the microstructures of flip chip joints with Ni/Au plated Cu pads after reflow soldering and the subsequent heat exposure at 423 K. For joints using Cu-cored Sn-5Ag balls with Ni coating over the Cu core, a Ni-Sn reaction layer forms at the Cu core/Sn-5Ag interface. A similar Ni-Sn reaction layer forms at the interface between the Sn-5Ag solder and the Ni/Au plated Cu pad. Although the Ni-Sn reaction layers grow with increasing the thermal exposure time, the growth rate is slower than that of a Cu-Sn reaction layer formed at the Cu core/Sn-5Ag interface in the joint with the Cu-cored Sn-5Ag ball without Ni coating over the Cu core.Copyright