Abstract: An improved detector dewar assembly in which the flange supporting the upper cap of the dewar assembly comprises a disc ceramic matrix, including buried electrical leads. This disc serves several purposes. First, it provides a vacuum tight electric feedthrough which connects a tape cable from the detector assembly to a pin assembly imbedded in the exterior portion of the disc feedthrough. Second, it includes metalizations on its top and lower surface in order to provide a surface for connecting (by brazing or soldering) the upper cap assembly and the major vessel wall. A tape cable comprising wires embedded in a flexible nonconductive matrix connects the detector element leadout wires with the electrical connectors of the feedthrough disc. The cable forms a collar which substantially surrounds the coldwell and has tabs at its basal portion which fold up to attach to pin or pad connectors on the lower surface of the disc.