The Process of FPC Photocoating Layer

The process of FPC photocoating layer is similar to the photoresist film used in rigid printed boards. The materials can be dry film type or liquid ink type. Solder mask dry film differs from liquid ink, but the equipment used for exposure and subsequent processes can generally be the same with some adjustments.

Application of Dry Film

• Dry film must be applied first, covering all circuit diagrams.
• A vacuum filming machine is used to prevent air bubbles between lines.

Ink Type Coating

• Circuit patterns are coated using screen printing or spraying methods.
• Screen printing is common, but a second printing may be needed for thin or uneven coatings.
• Spraying offers adjustable thickness and uniform coating, suitable for mass production.

Developing the Pattern

Pattern exposure requires precision in positioning, with an accuracy of 30-40um for a 100um disk. Developing conditions are crucial, with sodium carbonate aqueous solutions commonly used as developers. Post-curing is essential to fully cure the developed photocoating layer resin, typically done in a curing oven for 20-30 minutes.