What Is The Processing Flow Of Circuit Board?

[Inner Circuit] the copper foil substrate is first cut into the size suitable for processing and production. Before substrate film pressing, it is usually necessary to roughen the copper foil on the plate surface by brush grinding and micro etching, and then attach the dry film photoresist to it at an appropriate temperature and pressure. The substrate pasted with dry film photoresist is sent to the ultraviolet exposure machine for exposure. The photoresist will produce polymerization reaction after being irradiated by ultraviolet in the transparent area of the negative, and the line image on the negative will be transferred to the dry film photoresist on the board surface. After tearing off the protective film on the film surface, develop and remove the non illuminated area on the film surface with sodium carbonate aqueous solution, and then corrode and remove the exposed copper foil with hydrogen peroxide mixed solution to form a circuit. Finally, the photoresist of the dry film was removed by light sodium oxide aqueous solution.


[Pressing] the inner circuit board after completion shall be bonded with the outer circuit copper foil with glass fiber resin film. Before pressing, the inner plate shall be blackened (oxygenated) to passivate the copper surface and increase the insulation; The copper surface of the inner circuit is coarsened to produce good adhesion with the film. When overlapping, the inner circuit boards with more than six layers (including) shall be riveted in pairs with a riveting machine. Then put it neatly between the mirror steel plates with a holding plate, and send it to the vacuum press to harden and bond the film with appropriate temperature and pressure. The target hole of the pressed circuit board is drilled by the X-ray automatic positioning target drilling machine as the reference hole for the alignment of the inner and outer circuits. The plate edge shall be properly finely cut to facilitate subsequent processing.


[Drilling] drill the circuit board with CNC drilling machine to drill the through hole of interlayer circuit and the fixing hole of welding parts. When drilling, use a pin to fix the circuit board on the drilling machine table through the previously drilled target hole, and add a flat lower backing plate (phenolic ester plate or wood pulp plate) and an upper cover plate (aluminum plate) to reduce the occurrence of drilling burrs.


[Plated Through Hole] after the interlayer conduction channel is formed, a metal copper layer shall be arranged on it to complete the conduction of interlayer circuit. First, clean the hair on the hole and the powder in the hole by heavy brush grinding and high-pressure washing, and soak and attach tin on the cleaned hole wall.


[Primary Copper] palladium colloidal layer, and then it is reduced to metal palladium. The circuit board is immersed in a chemical copper solution, and the copper ion in the solution is reduced and deposited on the hole wall by the catalysis of palladium metal to form a through-hole circuit. Then, the copper layer in the through hole is thickened by copper sulfate bath electroplating to a thickness sufficient to resist the impact of subsequent processing and service environment.


[Outer Line Secondary Copper] the production of line image transfer is like that of inner line, but in line etching, it is divided into positive and negative production methods. The production method of negative film is like the production of inner circuit. It is completed by directly etching copper and removing film after development. 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 removing the film, the exposed copper foil is corroded and removed with alkaline ammonia and copper chloride mixed solution to form a wire path. Finally, use the tin lead stripping solution to peel off the tin lead layer that has successfully retired (in the early days, the tin lead layer was retained and used to wrap the circuit as a protective layer after re melting, but now it is mostly not used).


[Anti Welding Ink Text Printing] the early green paint was produced by directly heating (or ultraviolet irradiation) after screen printing to harden the paint film. However, in the process of printing and hardening, it often causes the green paint to penetrate into the copper surface of the line terminal contact, resulting in the trouble of part welding and use. Now, in addition to the use of simple and rough circuit boards, they are mostly produced with photosensitive green paint.


The text, trademark or part number required by the customer shall be printed on the board by screen printing, and then the text paint ink shall be hardened by hot drying (or ultraviolet irradiation).


[Contact Processing] anti welding green paint covers most of the copper surface of the circuit, and only the terminal contacts for part welding, electrical test and circuit board insertion are exposed. Appropriate protective layer shall be added to this end point to avoid oxide generation at the end point connecting anode (+) in long-term use, affecting circuit stability and causing safety concerns.


[Molding And Cutting] cut the circuit board into the external dimensions required by customers with CNC molding machine (or die punch). When cutting, use the pin to fix the circuit board on the bed (or mold) through the previously drilled positioning hole. After cutting, the golden finger shall be grinded at an oblique angle to facilitate the insertion and use of the circuit board. For the circuit board formed by multiple chips, X-shaped break lines need to be added to facilitate customers to split and disassemble after the plug-in. Finally, clean the dust on the circuit board and the ionic pollutants on the surface.


[Inspection Board Packaging] common packaging: PE film packaging, heat shrinkable film packaging, vacuum packaging, etc.

Post time: Jul-27-2021