Manufacturing sequences for high density interconnect printed circuit boards and a high density interconnect printed circuit board

A method of preparing a high density interconnect printed circuit board (HDI PCB) or integrated circuit (IC) substrates including through-holes and/or grate structures filled with copper, the method comprising the steps of:

• a) providing a substrate (10) comprising
• (i) an insulating core layer (12) having a peripheral surface, or
• (i′) a stack assembly comprising an insulating core layer (12) embedded between two electrically conductive interlayers (14) and at least one outer insulating layer (13) attached on the electrically conductive interlayer (14) and having a peripheral surface,
• (ii) an optional cover layer (16) covering the peripheral surface, and
• (iii) at least one through-hole (20) extending through all layers of the substrate (10) and/or
• a grate structure (30, 32) having multiple slots (36) extending through the optional cover layer (16) and partially extending in the insulating core layer (12) or extending through at least the optional cover layer (16) and at least one of the outer insulating layers (13);
• b) forming a non-copper conductive layer (40) or a copper layer (40) on the cover layer (16) when present, or on the insulating core layer (12) or (13) when the cover layer is not present, and on an inner surface (22) of the through-hole (20) when present, and on an inner surface of the grate structure (30, 32) when present;
• c) forming a patterned masking film (50) on the non-copper conductive layer (40) or on the copper layer (40);
• d) electrodepositing a copper inner-seal (62) inside the through-hole (20) sufficient to form two blind-microvias (64), electrodepositing a copper inlay (66) on the non-copper conductive layer (40) or on the copper layer (40) of the inner surface of the grate structure (30, 32) and a first copper layer (60) on the remaining peripheral surface of the non-copper conductive layer (40) or of the copper layer (40), in one step;
• e) removing the masking film (50);
• and
• f) electrodepositing a copper filling (70) in the blind-microvias (64), the copper inlay (66), and on the first copper layer (60) in one step.