A high-density electrical package utilizing an array of high performance demountable electrical contacts such as UEC, T-Spring, F-Spring and their equivalent contained in a carrier in the form of an interposer between one or more components and a substrate. The carrier is made of a thermally conductive metal or contains thermally conductive metal to provide heat-spreading or dissipation functions in addition to the function of the retention and alignment of the electrical contacts. The above interposer is used for chip attach for a single chip or a stack of chips in the package. The interposer provides electrical connections through individual electrical contact to another chip or to the substrate of the package. It provides also the heat spreading or dissipation function to the chips connected thermally to a particular interposer. The interposer can further be connected thermally to an external heat spreader when necessary.