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Knowledge For PCB PCB process description

PCB process description

June 29, 2022     Knowledge For PCB

What is the typical PCB fabrication process?

  1. Dry process: board cutting, lamination, exposure, lamination, drilling, molding
  2. Wet process: brush grinding, inner layer development, inner layer etching, inner layer de-filming, black/brown oxidation, plastic slag removal, through-hole plating, full board copper plating, outer layer development, line copper plating, tin-lead plating, outer layer de-filming, outer layer etching, tin-lead stripping, solder-proof printing, text printing, surface treatment
  3. Process Introduction.
    1. Cutting (Sheets Cutting) the substrate into working size (working panel) according to the size of the material issued on the work order. 2.
    2. Scrubbing (Scrub) Before pressing the film, the copper foil on the board surface should be properly roughened by brushing and micro-etching, and then the dry film should be adhered to it with proper temperature and pressure.
    3. Dry Film Lamination: The board is pre-treated, the surface is cleaned and micro-etched, then sent to the laminator for lamination, the surface of the board is covered with a layer of light sensitive organic film, and after exposure, the negative is transferred to the board.
    4. Exposure: The board with dry film is exposed to UV light in the transparent area of the negative, which will harden and transfer the line image from the negative to the dry film on the board surface (the dry film in this area will be retained as an etching resist in the later development and etching steps). Inner Developing dissolves the un-sensitized dry film in the developing solution. After the sensitized dry film hardens, the developing solution cannot dissolve it and it will still adhere to the board surface, forming the inner line pattern (the inner layer is the negative, and the copper surface is transparent on the negative).
    5. Inner Etching: After the un-sensitized dry film is dissolved, the copper surface underneath will be exposed, and after the board passes through the etching section, the exposed copper surface will be dissolved by the etching solution to reveal the substrate, while the copper surface with the dry film attached is preserved and forms the inner circuit. Inner Stripping removes the dry film that is hardened by photosensitivity by using a stripping solution. The purpose of Black Oxide Treatment is to generate a layer of black/brown fluff on the surface of the inner substrate through chemical agents to increase the contact bonding area and increase the bonding force between the layers after the substrate is pressed together.
    6. Pressing the inner layer of six layers (including) or more should be riveted by machine first, then stacked neatly between the steel plates in a tray, and sent to the press to make the plastic sheet harden and bond with proper temperature and pressure. The purpose of Drilling is to process the customer's required part holes, fixed holes, pilot holes, etc., and to provide positioning holes for post-processing, and also to provide slicing holes for inspection when needed for quality assurance.
    7. Desmear is caused by the softening or liquefaction of resin in the plate due to the heat when drilling, and it coats the whole hole wall with the rotation of the drill bit.
    8. Through-hole plating (PTH Plating) is also called primary copper plating, which uses chemical method to plating a thin layer of copper on the non-conductive resin and glass fiber hole wall inside the hole to make the hole wall metallized. Its purpose is to connect the inner and outer layers of the circuit, and is called a conduit hole, or as a solder parts of the pin, is called the parts of the hole. The outer layer development (Developing), line copper plating (Pattern Plating), tin-lead plating (Tin-Lead Plating) to adopt the positive process of production (positive, line or copper facial parts on the negative is black), the dry film is not sensitive to dissolve. Pattern Plating, Tin-Lead Plating is done after developing the film, followed by secondary copper and tin-lead plating (the tin-lead in this area will be retained as an etching resist in a later etching step) to increase the thickness of the outer layer. The exposed copper surface (the un-sensitized dry film area dissolved by the developer) can be coated with secondary copper and tin, and the purpose of tin plating is to protect the copper surface under the tin surface from being dissolved by the etchant in the next process.
    9. Stripping, Inner Etching, Tin-Lead Stripping, remove all the dry film from the board surface by using the stripping solution. After the outer layer of dry film is removed, the copper surface underneath will be exposed, and after etching, the exposed copper surface will be dissolved to reveal the substrate. The tin-plated copper surface will not be dissolved due to the protection of tin, and the outer layer of lines will be formed. Solder Mask is a pre-treatment process to clean the surface of the board, and then the ink is printed on the surface of the board. The pattern is formed on the surface of the solder-resistant board. The purpose of anti-solder is to leave the through holes and pads on the board to be soldered, while all other lines and copper surfaces will be covered to prevent short circuits caused by wave soldering and to save the amount of solder. The purpose of printing of Legend is to mark the location of the parts for customer's plug-in, or to facilitate customer's inspection. 18 Surface Treatment (Surface Treatment) is to prevent surface oxidation. Commonly used surface treatment are tin spraying (leaded/unleaded), OSP (Organic Solderability Preservative), gold plating (ENIG), silver plating (Immersion Silver), gold plating. NC-Routing: According to the requirements of the customer's shape drawing, the shape is processed and cut to make the size that meets the customer's needs. (The main processing methods are PUNCH, ROUTING, V-CUT, BEVEL, DRILL) Electrical Testing is to inspect the circuit of the board and to distinguish the board with short and broken circuit to be repaired or scrapped. The common testing methods are Flying Probe, Dedicated, and Universal on Grid. Final Visual Inspection is a comprehensive inspection of the product appearance to ensure the quality of shipments.


  • wdxpcb

    WDXPCB is a professional PCB manufacturer and exporter located in Shenzhen, China. providing PCB manufacturing services including HDI,FPC,Rigid-Flex PCB,High Multi-layer PCB,and MCPCB


    Tel: +86-75582944255,82945142
    Fax: +86-26648548

    Head office:Unit 502, Block B, Jinyuan Business Building, No. 300 Xixiang Avenue, Bao’An District, Shenzhen, China


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