Chemical Removal
Chemical processing of drilled printed circuit board interconnect vias removes resin debris smeared across inner copper foil edges during mechanical drilling. The desmear operation cleans exposed copper surfaces inside drilled through-holes to enable complete electrical contact before electroless copper deposition. Resin residue blocks bond formation between internal copper land layers and electroplated copper walls if left untreated.
Permanganate chemistry strips organic films from drilled hole surfaces across multi-layer panel constructions.
Process Mechanism
Swelling and oxidation liquid chemical steps prepare target hole walls for secondary metallization. Organic solvent baths swell resin matrices, after which permanganate solutions decompose polymer fragments into water-soluble compounds. Chemical desmear creates micro-roughened surface topography along exposed resin walls, which enhances physical keying during copper plating.
Plasma etching equipment uses gas mixtures containing oxygen or tetrafluoromethane for high-frequency laminates when chemical reagents cannot etch fluoropolymer substrates efficiently. Processing temperature, immersion duration, and chemical bath activity define strict operating limits to avoid excessive resin recession or wedge voids along internal copper foils.
Hole Wall Inspection
Microsection analysis evaluates hole cleanliness by checking copper interface adhesion under cross-sectional optical microscopy. Defective cleaning appears as resin inclusions or copper separation after solder float testing under IPC-TM-650 procedures.
