Laser-formed vias often produce a carbon by-product that prohibits electro-less adhesion. Carbon that mixes with epoxy or polyimide resin and becomes trapped in the vias must be removed prior to metalization. Plasma cleaning removes the carbon from both conventional through-hole board vias and blind vias typically used on boards where component space is restricted.
The figures below show a via with carbon residue on the capture pad and a clean pad after plasma treatment.
