The manufacturing process of PCB (printed circuit board) mainly includes the following core links, which are summarized as follows in simple language:
1. Substrate preparation
Material selection: Commonly used substrates are copper clad laminates (copper foil insulating substrates, such as FR-4 epoxy resin sheets).
Panels: Cut large pieces of copper clad laminates into small panels that match the design dimensions.
2. Graphic Transfer (Line Production)
Coating photosensitive layer: Coating the surface of the copper clad laminate with photosensitive ink or dry film to form a photosensitive layer.
Exposure: Exposure through film (negative) to make the photochemical reaction of the photosensitive layer according to the circuit design (retain the line area, dissolve the non-line area).
Development: Dissolve the unphotosensitive part with a chemical solution to expose the copper foil that needs to be etched.
3. Etching
Removal of excess copper foil: Dissolve the unprotected copper foil with etching solution (e.g., ferric chloride, acid etching solution) to preserve the desired line pattern.
Stripping: Removing the photosensitive layer to reveal the complete line.
4. Drilling
Punching: Use a CNC drilling machine to drill through holes, mounting holes, etc. (for connecting multi-layer lines or mounting elements) in the circuit board.
5. Hole metallization (immersion copper)
Activation: Adsorption of catalyst on the surface of the pore wall for subsequent copper plating.
Electroless copper: A thin layer of copper is deposited on the wall and surface of the hole through a chemical reaction to make the hole conductive.
Plating thickening: The electroplating process increases the thickness of the copper layer in the hole and on the surface of the circuit to improve conductivity and reliability.
6. Lamination (multi-layer board process)
Stacking: Multiple single/double-sided sheets are stacked with prepreg sheets (PP sheets, epoxy resin binders) and copper foil as designed to form a multi-layer structure.
Hot pressing: Under high temperature and high pressure, the layers are bonded into a whole to form a multi-layer circuit board.
7. Solder mask and silk screen
Solder Mask Coating: Green (or other colored) solder mask is applied to the surface of the circuit board to preserve the pads by exposure development to prevent short circuits.
Silk screen characters: white characters such as printed component numbers and polarity identifiers are easy to assemble and maintain.
8. Surface treatment
Protect the copper layer: Treat the surface of the pad to prevent oxidation, common processes include:
Tin spraying (HASL): A layer of tin-lead alloy is plated on the surface.
ENIG: Chemically deposited nickel gold layer with high flatness and suitable for precision components.
OSP (Organic Solder Protector): A transparent protective film is applied.
9. Molding
Cut the shape: cut the circuit board into the desired shape (such as rectangle, special-shaped) according to the design, and remove edge waste.
10. Detection
Electrical test: Check the line continuity and short circuit by flying probe or bed of needle test.
Visual inspection: Manual or AOI (Automated Optical Inspection) inspection for line defects, solder mask defects, etc.
11. Packing and shipping
After the qualified products are washed and dried, they are filmed or vacuum-packed and ready for delivery.
summary
The above is the basic process of single/double-sided and multi-layer boards, and the actual process may add steps (such as back drilling, laser drilling, etc.) due to the complexity of the board (such as blind and buried vias, HDI boards) or special needs (such as high-frequency boards, thick copper plates). The core logic is "graphic transfer→ etching→ interconnection→ protection → molding".