CERAMIC SUBSTRATE FOR HYBRID MICROCIRCUITS AND METHOD OF MAKING THE SAME

摘要

An as-fired alumina substrate for a hybrid microcircuit formed of GaAs dies operating at gigahertz frequencies has a large number of about 0.013'' diameter via holes drilled on the surface thereof by use of a laser. A metal filling in each via hole is formed with about 85% sintered tungsten and 15% copper reflowed into the pores thereof to provide a composition that has a thermal coefficient of expansion that substantially matches that of the GaAs dies and the alumina substrate and also provides for hermetically sealing the via holes. The alumina substrate is further provided with a ground plane by which it is mounted on a metal block serving as a heat sink. The high frequency GaAs dies mounted on the via holes use the metal fillings therein to carry their internally generated heat to the heat sink and to provide low inductance ground paths for the microcircuit. A process for placing the metal filling in the via holes makes use of a stencil having the same large number of via holes thereon as the alumina substrate for first squeegeeing a tungsten paste with a predetermined amount of binder into the via holes of the substrate. After the tungsten is sintered, the stencil is then used to squeegee a copper paste on the top of the sintered tungsten in the via holes. The copper in the paste is then reflowed into the pores of the sintered tungsten.