Underfill process and materials for singulated heat spreader stiffener for thin core panel processing

A method of making a microelectronic package, and a microelectronic package made according to the method. The method includes: bonding and thermally coupling a plurality of IC dies to an IHS panel to yield a die-carrying IHS panel, and mounting the die-carrying IHS panel onto a substrate panel including a plurality of package substrates by mounting perimeter ribs of the IHS panel to a corresponding pattern of sealant on the substrate panel and by mounting each of the plurality of dies to a corresponding one of the plurality of package substrates to yield a combination including the die-carrying IHS panel mounted to the substrate panel. Other embodiments are also disclosed and claimed.