The next step in PCB fabrication is to drill holes in the board for component mounting, thru-hole vias, and the non-plated holes of mechanical features. The majority of the thru-holes used in a circuit board will be plated, and are usually drilled 0.005” larger than the specified finished hole size to allow for plating. If the design contains any blind and buried vias or laser-drilled microvias, those are fabricated before the lamination of the board. The extra process steps for these vias can add additional cost to the fabrication of the board but may be required for dense circuitry and/or electrical performance.
Once holes are drilled they get cleaned using chemical and mechanical processes to remove resin smears and debris caused by drilling. The entire exposed surface of the board, including the interior of the holes, is then chemically coated with a thin layer of copper. This creates a metallic base for electroplating additional copper into the holes and onto the surface in the next step.