Quick-Drying Photosensitive Etch-Resist Ink

What Is Photosensitive Etch-Resist Ink?

Photosensitive etch-resist ink is a light-curable coating used in chemical etching to protect the areas of a metal sheet that should remain after the etch. The metal is first cleaned, then coated with a thin film of the ink. After exposure through a phototool and development in dilute sodium carbonate, the unexposed ink washes away and the exposed ink hardens into a tough, acid-resistant mask. The sheet is then put through an etching line — ferric chloride for copper, cupric chloride for production PCB work, or a hot alkaline bath for aluminium — and only the bare metal is dissolved.

This particular ink was developed by Golden Eagle's process engineering team in 1998 and has been refined over more than 20 years of in-house production. It is widely used for watch parts, jewellery, eyeglass frames, mobile phone shells, decorative panels, industrial templates, electronic components, filter mesh and hardware keypads. It is one of the most versatile ways to put a high-resolution resist on a metal sheet when dry film or a phototool-only workflow is not the right fit.

Key Features

• Spray or screen-print application. Uniform 20–30 µm dry film with no bubbles or pinholes. Spray for full-panel coverage; 77T–100T mesh for selective print on pre-cut blanks.
• Fast pre-bake. Hot-air convection at 80–90 °C for 10–15 minutes — faster than most liquid photoresists, easier to fit into a production cycle.
• Sharp image. 6–8 grid exposure on a 21-grid exposure scale gives a clean, vertical sidewall and tight line-width control, even on fine 0.1–0.3 mm features.
• Strong adhesion and acid resistance. 100/100 adhesion on 3M medium-tack tape, hardness at least H on the Mitsubishi pencil test at 700 g load — the resist holds up through full-strength ferric chloride and nitric acid etches.
• Clean stripping. 10% NaOH at 80–90 °C removes the resist in 5–8 minutes; in an ultrasonic tank at 90 °C it lifts in 1–3 minutes.
• Compatible with most etch chemistries. Works with ferric chloride, cupric chloride, alkaline NaOH and acid etchant blends.

Process Flow

The full process from bare metal to stripped finished part is nine steps. The same sequence applies whether the ink is sprayed or screen-printed, and whether the part ends up as a thin decorative panel or a deep-etched mould.

* Post-bake at 150 °C for 30 minutes is required for deep etching only. For through-etching thin sheet, the post-bake can be skipped.

Technical Specifications

Operating Parameters — Step by Step

1. Pre-treatment. Degrease and dewax the substrate. Any oil, fingerprint or oxide layer compromises adhesion and shows up later as resist lift or ragged edges.
2. Thinning. Stir the ink thoroughly before use and let it stand 5–10 minutes. Dilute only with the ink's own thinner — typically 1 : 0.7 ink-to-thinner for spray. If another thinner has to be used, run a small compatibility test first.
3. Coating. Spray to a dry film of 20–30 µm, or screen-print through a 77T–100T mesh. Both routes give a clean, bubble-free, pinhole-free film at the recommended thickness.
4. Pre-bake. 80–90 °C in a hot-air convection oven for 10–15 minutes. The resist should be dry to the touch and tack-free before exposure.
5. Exposure. 6–8 grid on a 21-grid exposure scale. Use a fine-line test strip to confirm correct exposure for your lamp and artwork.
6. Develop. 0.8–1.2% Na₂CO₃ solution at 30 °C ± 2, spray pressure about 2 kg/cm². The unexposed resist washes away cleanly; the image should appear sharply with no scumming.
7. Post-bake (deep etch only). 150 °C for 30 minutes. Required when the etch depth is significant or the etch time is long. Skip for through-etching thin sheet.
8. Etch. Run on a metal etching machine with the chemistry matched to the substrate — ferric chloride for general use, cupric chloride for PCB, alkaline for aluminium.
9. Strip. 10% NaOH at 80–90 °C for 5–8 minutes, or 10% NaOH at 90 °C in an ultrasonic tank for 1–3 minutes. The resist lifts cleanly without attacking the underlying metal.

Typical Applications

Because the ink can be applied by spray or screen-print and tolerates a wide range of etch chemistries, it shows up across the parts of a fab that need a high-resolution resist but do not justify dry film lamination. Common uses include:

• Watch cases, dials and movement components
• Jewellery, fashion accessories, eyeglass frames
• Mobile phone shells, laptop covers and other consumer electronics enclosures
• Decorative stainless steel panels, elevator interiors, architectural trim
• Industrial templates, jigs, scales and gauges
• Precision electronic components — lead frames, shielding cans, encoder discs
• Filter mesh, sieves and micro-perforated sheets
• Hardware keypads, nameplates and signage

Storage and Safety

• Storage. Sealed, in a cool dry dark place below 25 °C. Shelf life is approximately six months in the original sealed container. Do not expose to white light or sunlight for long periods during use or storage.
• Mixing before use. Stir 3–5 minutes, then let stand about 10 minutes before use. The ink is designed to be used as supplied — only adjust viscosity with the recommended thinner.
• Surface preparation. A thoroughly clean, oxide-free substrate is essential. Skipping this step is the single most common cause of resist lift, ragged edges and pinholes.
• Skin and eye contact. In case of contact, wash immediately with soap and plenty of water, and seek medical attention if irritation persists.
• Flammability. The product is flammable. No open flames in storage or use areas.

Quality Inspection

Each batch of photosensitive etch-resist ink is tested in our own pilot line before it ships. Below: typical adhesion, exposure and development checks on production test panels.