PCB Technical - The pcb factory takes you to understand the FPC flexible circuit board production process

The PCB factory takes you to understand the FPC flexible circuit board production process

FPC, also known as flexible circuit board, flexible circuit board, abbreviated as soft board; it is made of polyester film or polyimide as the base material and formed by etching on the copper foil to form a circuit with high reliability and insulation. Printed circuit with good flexibility.

The flexible circuit board has the characteristics of small size, light weight, and high flexibility. It can move and stretch arbitrarily in three-dimensional space to achieve the integration of component assembly and wire connection, so as to meet the high density, miniaturization and light weight of PCB circuit boards., Thinning, high reliability direction development needs.

The flexible circuit board is a special kind of board, which has certain technical threshold and difficulty in operation, and the cost is also high. How is it produced? Let's take a look at the flexible circuit board production process together:

1. Single panel production process

Blanking - Drilling - Pasting dry film - Exposure - Development - Etching - Stripping - Laminating - Laminating - Reinforcement - Curing - Surface treatment - Silk screen - Punching - Final inspection - Packaging - Shipment

2. Double-sided panel production process

Cutting - Drilling - Copper Immersion - Copper Plating - Dry Film Pasting - Exposure - Development - Etching - Stripping - Laminating - Laminating - Reinforcement - Curing - Surface Treatment - Screen Printing - Punching - Final Inspection - Packaging - Out goods

Compared with the single panel, the double panel production process has two more processes: copper sinking and copper plating.

3. Process description:

1. Cutting

FPC materials (substrate, cover film) are generally in rolls, with a width of 250mm and a length of 100 meters; the actual production board length generally does not exceed 300mm, so the material needs to be cut into small pieces manually or by machine, namely Production board, work board.

2. Drilling

Drill a certain size and number of round holes or slots on the base material, cover film or reinforcing plate as required.

Note: Square holes or other irregular holes cannot be drilled and need to be punched with a steel die or laser cut.

3. Immersion copper
It is mainly to form a thin layer of copper on the hole wall to provide a current path for subsequent electroplating of copper. During the copper sinking process, CU2+ ions get electrons and are reduced to metallic copper, which is deposited on the surface and the hole wall; the thickness of the sinking copper is about 0.5-2um.

4. Copper electroplating

Since the thickness of the previous sinking copper is only 0.5-2um, which is too thin, it needs to be thickened by copper electroplating, and the thickness can reach 12-30um.

5. Stick dry film

Paste the dry film on the substrate through a certain pressure and temperature.

6. Exposure

Using the light sensing method, the exposure light source is irradiated to the dry film (film) through the line shape of the product to make it photosensitive; the dry film hit by the light forms a protective layer, and the photosensitive film not hit by the light will not form The protective layer will be developed away during the development process, exposing the copper to be etched.

7. Development

Use developer (sodium carbonate) to wash away the dry film that has not been exposed to light to expose the copper surface to be etched or otherwise processed.

8. Etching

The copper foil that is not covered by dry film on the developed product is etched away to form the required circuit.

9. Peeling film

Peel off the remaining dry film after etching, and the directly exposed copper is the required circuit.

10. Reinforce

While the soft board is light, thin, and flexible, it also loses its rigidity. In order to increase the thickness and rigidity of the designated parts of the product for subsequent installation or assembly, a rigid board needs to be attached to these positions, Namely the reinforcement board. Reinforcing plates include stainless steel sheet, aluminum sheet, FR4, polyimide, polyester, etc.

11. Surface treatment

The role of surface treatment: to prevent oxidation of the copper surface, to provide welding or bonding layer. Commonly used surface treatment methods. Anti-oxidation (OSP), nickel-plated gold, immersed nickel-gold, tin-plated, immersed tin, immersed silver, etc.

12. Final inspection

The inspection methods are: 1. Visual inspection, 2. Microscope (minimum 10 times) inspection. Mainly check the appearance, including scratches, crushing, wrinkles, oxidation, blistering, solder mask deviation, drilling deviation, line gaps, residual copper, foreign objects, etc.

13. Packaging

The packaging includes ordinary packaging, anti-static packaging, vacuum packaging, and pallet packaging.
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