Electroless nickel-electroless palladium-immersion gold (enepig) as a surface finish for embedded die attachments

An integrated circuit package comprising:

• an integrated circuit package substrate comprising:
• a plurality of metallization layers in dielectric buildup layers;
• an interconnect bridge circuitry die embedded in the buildup layers, the interconnect bridge circuitry die comprising a via connected between a first conductive contact on a first side of the interconnect bridge circuitry die and a second conductive contact on a second side of the interconnect bridge circuitry die opposite the first side, the second conductive contact in electrical connection with a conductive contact of a metallization layer;
• and
• conductive materials between the second conductive contact of the interconnect bridge circuitry die and the conductive contact of the metallization layer, the conductive materials comprising nickel, phosphorous, tin, and palladium;
• and
• integrated circuit dies coupled to the package substrate, at least two integrated circuit dies interconnected by the interconnect bridge circuitry die.

A method of forming an integrated circuit package substrate comprising:

• forming buildup layers on a core layer, the buildup layers comprising a plurality of metallization layers;
• forming a cavity in the buildup layers to expose a subset of conductive contacts of a metallization layer;
• forming a first surface finish layer on the subset of conductive contacts, the first surface finish layer comprising nickel and having a thickness that is greater than 5 um;
• forming a second surface finish layer on the first surface finish layer, the second surface finish layer comprising palladium;
• forming a third surface finish layer on the second surface finish layer, the second surface finish layer comprising gold;
• placing a die within the cavity such that conductive contacts of the die are in electrical connection with the subset of conductive contacts.