An improved high density interconnect structure may include electronic components mounted on both sides of its substrate or a substrate which is only as thick as the semiconductor chips which reduces the overall structure thickness to the thickness of the semiconductor chips plus the combined thickness of the high density interconnect structure's dielectric and conductive layers. In the two-sided structures, feedthroughs, which are preferably hermetic, provide connections between opposite sides of the substrate. Substrates of either of these types may be stacked to form a three-dimensional structure. Means for connecting between adjacent substrates are preferably incorporated within the boundaries of the stack rather than on the outside surface thereof.