Glass on the basis of zno - b2o3 - sio2 with a thermal ausdehnungskoffizienten of 44,5 to 44,8.10 - 7 / deg.c (0 to 300 deg.c)

摘要

A glass consists essentially, in weight per cent, of ZnO 60, B2O3 23-25, SiO2 9.4-10.5, CeO2 3, Bi2O3 0-0.1, PbO 2-3, Sb2O3 0.5. This glass is used to coat an electrical device such as diode, including a silicon crystal semi-conductor element in the form of a wafer with electrical conductors connected to either side of the wafer, by applying the glass in finely divided form to the surface of a semi-conductor device comprising an N-type region and a P-type region with each region fused to an aluminium contact, each contact being bonded to a heat sink electrode member selected from (a) molybdenum; (b) tungsten; (c) an iron base alloy with 28-30% Ni, 15-18% Co and a fractional amount of Mn, to form a coating extending partially over and in sealing relation with each of the heat sink members, the surface with the coating thereon being heated to melt the glass particles together into a unitary mass sealed to the body. The coating may be applied in the form of a slurry, prepared by mixing powdered glass with a conventional organic binder, such as nitrocellulose, and a vehicle, such as deionized water, the slurry being sprayed or painted on to the substrate. The assembly is heated to drive off the binder and the vehicle, and the coating vitrified by heating at 775 DEG to 825 DEG C. for 2 to 5 minutes, vitrification taking place in an inert atmosphere, or in a vacuum, to prevent oxidation of the molybdenum parts of the diode. Prior to applying the glass coating the semi-conducting body and sealing surfaces of the heat sink members may be cleaned by etching to remove undesirable contaminants. Several layers of coating may be applied to produce the desired thickness, a thickness of at least 10,000 Angstroms being desirable. The coefficient of thermal expansion of the glass used may be controlled by heat treatment to be within the range 37.5 x 10-7/ DEG C. to 44.9 x 10-7/ DEG C., the powdered glass being heated in graphite moulds for various times and temperatures to provoke nucleation of the sintered glass. The coefficient of expansion of the coating glass can be selected to match that of the electrically conducting parts of the diode.