A hermetic package for an electronic device is manufactured by providing a green glass ceramic body (10) with a green via (20)to produce a workpiece. The workpiece (24) is sintered at a temperature at or above 500 DEG C, while compressing the workpiece at a pressure at or above 100 pounds per square inch, so as to obtain a hermetic package. The green via comprises a mixture of copper and a glass ceramic material with a sufficient volume of glass to produce a hermetic package, yet with sufficient copper to have a suitable electrical conductivity. The hermetic package thus produced comprises a sintered glass ceramic body having an electrically conductive sintered via which is hermetically bonded to the glass ceramic body and which comprises a mixture of an electrically conductive material and a glass ceramic material. The electrically conductive material forms at most 50 volume percent of the via. The workpiece may be sintered in a sintering fixture having a frame (44) and a compensating insert (46). The compensating insert and frame bound a sintering chamber for accommodating the workpiece. By providing a frame having a thermal expansion coefficient greater than that of the workpiece, and by providing a compensating insert having a thermal expansion coefficient greater than that of the frame, a close fit can be assured between the workpiece and the sintering fixture over a large range of temperatures.