2. **Water cleaning:** Remove excess residual liquid from the hole and surface.
3. **PCBA black hole treatment:** Through physical adsorption, a uniform and fine conductive layer of graphite carbon black is applied to the surface of the hole wall substrate.
★ Water cleaning: Remove excess residual liquid from both the hole and the surface.
★ Drying: To eliminate moisture in the adsorption layer, employ short-term high-temperature and long-term low-temperature treatments. This improves the adhesion between graphite carbon black and the pore wall substrate surface.
★ Micro-etching treatment: First, treat with an alkali metal boron salt solution to induce micro-swelling of the graphite and carbon black layer, forming microporous channels. During PCBA black holeization, graphite carbon black adsorbs not only on the hole wall but also on the inner copper ring and the surface copper layer of the substrate. To ensure proper bonding between electroplated copper and base copper, the graphite carbon black on the copper must be removed. The treatment creates microporous channels in the graphite and carbon black layers, which can be removed by the etching solution. The etching solution then penetrates the copper layer through these microporous channels, micro-etching the copper surface by approximately 1-2μm, thus removing the graphite carbon black. The graphite and carbon black on the non-conductor substrate of the hole wall remain unchanged, providing a good conductive layer for direct electroplating.
★ Inspection: Use an inspection mirror or stereo microscope to verify that the coating on the inner surface of the hole is complete and even.
★ Electroplated copper: Introduce into the tank and use impulse current to ensure the conductive plating is fully covered.
3.6 Matters needing attention
(1) The black hole solution tank should be equipped with a circulating stirring device. For horizontal production lines, ultrasonic methods or water jet spray methods are recommended.
(2) Drying using the dipping method can be done in an oven or drying tunnel at 80–85°C for 2–3 minutes. The horizontal type should include both hot and cold air drying sections. If the processed material is not heat-resistant, dry at 60–65°C for 8–10 minutes. For FR-4, PTFE, or CEM-3 boards thicker than 1.0mm treated with black hole liquid, set the drying temperature to 95°C for 2 minutes.
(3) Regularly test the PCBA black hole liquid for solidity and pH value. Under normal usage conditions, the fixed line points should remain stable. If they decrease, use Miele’s MN-701B for adjustment. When the pH value of the black hole liquid drops below 9.5, its activity decreases, and it must be adjusted using reagent ammonia.
