Abstract: A high density circuit package includes a pair of planar packages, the planar packages exhibiting front and back surfaces and positioned back-to-back in the high density circuit package. Each planar package includes a flexible circuit carrier having a plurality of circuit chips mounted thereon. Front and back planar metallic heat sinks sandwich the circuit carriers, at least one of the heat sinks contacting a surface of the chips mounted on the sandwiched circuit carriers. Each heat sink is provided with air flow apertures formed in its planar surface and adjacent to each circuit chip. A circuit card interconnects with the circuit carriers in an interconnection region and is pluggable into a female connector. The planar metallic heat sinks and circuit carriers are mechanically packaged so as to provide a planar arrangement which aligns the apertures in both the front and rear heat sinks.