The inner circuit copper foil substrate is first cut into a size suitable for processing and production. Before laminating the substrate, it is usually necessary to properly roughen the copper foil on the board surface by brushing, micro-etching, etc., and then adhere the dry film photoresist tightly to it at the appropriate temperature and pressure. The substrate with the dry film photoresist attached is sent to an ultraviolet exposure machine for exposure. The photoresist will undergo a polymerization reaction after being irradiated by ultraviolet rays in the transparent area of ??the film, and the circuit image on the film will be transferred to the dry film photoresist on the board surface. . After peeling off the protective film on the film surface, first use sodium carbonate aqueous solution to develop and remove the areas that are not exposed to light, and then use a hydrogen peroxide mixed solution to corrode and remove the exposed copper foil to form a circuit. Finally, use light sodium oxide aqueous solution to wash away the dry film photoresist.
After lamination, the inner circuit board must be bonded to the outer circuit copper foil with fiberglass resin film. Before lamination, the inner board needs to be blackened (oxidized) to passivate the copper surface to increase insulation; and the copper surface of the inner circuit is roughened to produce good adhesion to the film. When laminating, first rivet the inner circuit boards (including six layers) and above in pairs using a rivet machine. Then use a serving plate to stack them neatly between mirror steel plates, and send them to a vacuum laminating machine to harden and bond the films at the appropriate temperature and pressure. The pressed circuit board uses an X-ray automatic positioning target drilling machine to drill target holes as reference holes for alignment of inner and outer circuits. And make appropriate fine cuts on the edge of the board to facilitate subsequent processing.
Drill the circuit board using a CNC drilling machine to drill out the conductive channels for the interlayer circuit and the fixing holes for the soldered parts. When drilling, use a plug pin to fix the circuit board on the drilling machine table through the previously drilled target hole, and add a flat bottom plate (phenolic resin board or wood pulp board) and an upper cover plate (aluminum plate) To reduce the occurrence of drilling burrs
After the interlayer conduction channel is formed, a metal copper layer needs to be laid on the plated through hole to complete the conduction of the interlayer circuit. First, use heavy brushing and high-pressure flushing to clean the hair on the hole and the dust in the hole. Soak and adhere tin on the cleaned hole wall.
A copper-palladium colloid layer, and then apply It is reduced to metallic palladium. The circuit board is immersed in a chemical copper solution, and the copper ions in the solution are reduced and deposited on the hole walls through the catalytic action of palladium metal to form a through-hole circuit. Then, copper sulfate bath electroplating is used to thicken the copper layer in the via hole to a thickness sufficient to withstand subsequent processing and the impact of the use environment.
The production of secondary copper for outer layer circuits is the same as that for inner layer circuits in terms of circuit image transfer, but in terms of circuit etching, it is divided into two production methods: positive film and negative film. The production method of negative films is the same as the production of inner circuits. After development, the copper is directly etched and the film is removed, which is considered complete. The production method of positive film is to add secondary copper and tin-lead plating after development (the tin-lead in this area will be retained as an etching resist in the later copper etching step). After the film is removed, it is treated with alkaline The mixed solution of ammonia and copper chloride will corrode and remove the exposed copper foil to form a circuit. Finally, the tin-lead layer is stripped off with tin-lead stripping liquid (in the early days, the tin-lead layer was retained and used to cover the circuit as a protective layer after being re-strengthened, but it is now rarely used).
Earlier green paint for solder resist ink text printing was produced by directly heating (or ultraviolet irradiating) the paint film after screen printing to harden the paint film. However, during the printing and hardening process, the green paint often penetrates into the copper surface of the line terminal contacts, causing problems in the welding and use of parts. Nowadays, in addition to the use of circuit boards with simple and rough lines, photosensitive green paint is often used instead. for production. The text, trademark or part number required by the customer is printed on the board by screen printing, and then the text ink is hardened by heat baking (or ultraviolet irradiation).
The solder-resistant green paint for contact processing covers most of the copper surface of the circuit, leaving only the terminal contacts for component soldering, electrical testing and circuit board insertion. This endpoint needs to be added with an appropriate protective layer to avoid oxides from being produced at the endpoint connected to the anode ( ) during long-term use, which will affect circuit stability and cause safety concerns.
Forming cutting uses a CNC forming machine (or mold punch) to cut the circuit board into the dimensions required by the customer. When cutting, use a plug pin to fix the circuit board on the bed (or mold) through the previously drilled positioning hole.
After cutting, the gold finger parts are then beveled to facilitate circuit board insertion. For multi-piece circuit boards, it is often necessary to add an X-shaped break line to facilitate customer segmentation and disassembly after insertion. Finally, clean the dust on the circuit board and the ionic contaminants on the surface.
Commonly used packaging for inspection board packaging: PE film packaging, heat shrinkable film packaging, vacuum packaging, etc.