Solder resist layers for coreless packages and methods of fabrication
A coreless package substrate with dual side solder resist layers is disclosed. The coreless package substrate has a top side and a bottom side opposite of the top side and includes a single build-up structure formed of at least one insulating layer, at least one via, and at least one conductive layer. The coreless package substrate also includes a bottom plurality of contact pads on the bottom side, and a top plurality of contact pads on the top side. A bottom solder resist layer is on the bottom side, and a top solder resist layer is on the top side. The concept of dual side solder resist is extended to packages with interconnect bridge with C4 interconnection pitch over a wide range.
1. A method of forming a package substrate, comprising:
forming a plurality of multi-layered structures on a top surface of a temporary substrate;
forming a first solder resist layer on exposed surfaces of the temporary substrate and the plurality of multi-layered structures;
forming a build-up structure comprising least one insulating layer, a plurality of vias, and at least one conductive layer on the first solder resist layer, wherein a top conductive layer forms a second plurality of contact pads on a top surface of a topmost insulating layer, wherein the second plurality of contact pads have a first set of contact pads and a second set of contact pads, wherein the first set of contact pads have a first width different than a second width of the second set of contact pads;
forming a second layer of solder resist on a top surface of the topmost insulating layer, exposing at least a portion of the second plurality of contact pads;
removing the temporary substrate and a portion of each multi-layered structure of the plurality of multi-layered structures, a remaining portion of each multi-layered structure forming a first plurality of contact pads, wherein the first plurality of contact pads have a third set of contact pads and a fourth set of contact pads, wherein the third set of contact pads have a third width greater than a fourth width of the fourth set of contact pads; and
coupling the third set of contact pads of the first plurality of contact pads to a printed circuit board or an interposer.
2. The method of claim 1 , wherein forming the build-up structure comprises a semi-additive process.
3. The method of claim 1 , wherein forming the build-up structure further comprises placing a device within the at least one insulating layer and at least one conductive layer such that the device is embedded within the build-up structure.
4. The method of claim 1 , wherein forming the build-up structure further comprises etching through a portion of the first solder resist layer to expose the plurality of multi-layered structures, and wherein the third and fourth widths of the first plurality of contact pads is different than the first and second widths of the second plurality of contact pads.