Enhanced stacked microelectronic assemblies with central contacts and improved thermal characteristics

A microelectronic assembly comprising:

• first and second units, wherein the second unit overlies the first unit, each unit including:
• a dielectric element having oppositely-facing first and second surfaces and first and second apertures extending between the surfaces, the dielectric element further having conductive elements thereon;
• a first microelectronic element having a rear surface and a front surface facing the first surface of the dielectric element, the first microelectronic element having a first edge and a plurality of contacts disposed at the front surface thereof;
• a second microelectronic element having a rear surface, a front surface facing the rear surface of the first microelectronic element, a projecting portion of the front surface of the second microelectronic element extending beyond the first edge of the first microelectronic element, the projecting portion being spaced from the first surface of the dielectric element, the second microelectronic element having a plurality of contacts disposed at the projecting portion of the front surface;
• and
• first leads extending from contacts of the first microelectronic elements through the first aperture to at least some of the conductive elements and second leads extending from contacts of the second microelectronic element through the second aperture to other of the conductive elements;
• and
• a heat spreader thermally coupled to at least one of the first microelectronic element or the second microelectronic element of the first unit, wherein the heat spreader is a monolithic structure having apertures substantially aligned with the contacts of the first and second microelectronic elements of the first unit.