Wetting in an Electronic Packaging Ceramic System: 1, Wetting of Tungsten by Glass in Controlled Oxygen Partial Pressure Atmospheres

Abstract

The wetting of tungsten by a Cr2O3‐colored, CaO‐MgO‐Al2O3‐SiO2 glass was found to be independent of temperature between 1300° and 1500°C, but strongly dependent on furnace atmosphere. Similar results using two gas buffer systems (CO/CO2 and H2/H2O) established oxygen partial pressure, p02 as the critical parameter. The contact angle decreased over a narrow p02 range as the p02 increased, with a stable contact angle existing in both lower and higher p02 ranges. The solid‐liquid interfacial energy, γSL, controlled the wetting behavior. An increase in the adsorbed oxygen layer at the solid‐liquid interface resulted in a lower γSL and a lower contact angle. The equilibrium contact angles, established after 8‐h isothermal holds, ranged from 50‐55° at a p02= 10−15.5 atm to 30° at a p02= 10−10.9 atm. Two different drop formation techniques were used to show that the temperature and atmospheric conditions at the time of solid‐liquid interface formation affect the stable contact angles. The contact angle was higher when the solid‐liquid interface was established at the test temperature (doser tube technique) than when the drop was formed in situ from a piece of glass placed on the substrate at room temperature (nondoser method). This contact angle difference was again attributed to a higher γSL from the doser method due to the presence of less adsorbed oxygen at the time of the creation of the solid‐liquid interface.