Photo Etching on Metal

Photo etching on metal, also known as photochemical machining (PCM), is a well‑established subtractive manufacturing technology that merges photolithography and controlled wet‑chemical corrosion to fabricate intricate thin‑metal components. Unlike stamping, laser cutting, wire‑EDM or CNC milling, photo etching removes material through chemical dissolution rather than mechanical force or thermal energy. This unique characteristic delivers burr‑free, stress‑free parts without heat‑affected zones. It excels at producing micro‑holes, narrow slots, complex outlines, half‑etched textures and large arrays of fine features that are difficult or costly to realise via conventional metalworking. Engineers across automotive, medical, new‑energy, electronics, aerospace and instrumentation industries rely on photo etching on metal for prototype sampling, pilot batches and high‑volume mass‑production.

1. Compatible Metals for Photo Etching

Photo etching on metal works for a wide spectrum of thin‑sheet metallic materials, yet each alloy requires tailored pre‑treatment, etchant formulation and process parameters to guarantee stable dimensional accuracy and surface finish.

• Stainless steel (301, 304, 316L): The most widely processed material. Special activation step is required to break the native chromium‑oxide passive film. Ferric‑chloride‑dominated composite etchant is adopted for mass manufacturing. Typical thickness 0.02 mm‑1.5 mm, used for filter meshes, gaskets, spring plates and medical components.

• Copper & brass: Good etching performance, suitable for EMI shielding parts, lead frames and decorative components. Anti‑oxidation control is critical during post‑treatment.

• Phosphor bronze: Favoured for elastic spring contacts and conductive shims; demands careful etch‑rate adjustment to preserve material elasticity.

• Nickel and nickel‑based alloys: Applied for battery components, electrode meshes and high‑temperature functional parts. Custom‑mixed etchant prevents uneven corrosion.

• Titanium: Common in hydrogen‑energy bipolar plates and medical implants. Specialised etching chemistry is essential due to its highly stable surface passivation layer.

• Kovar / Invar: For semiconductor packaging components; tight process control minimises dimensional drift.

Materials that are extremely thick or contain large non‑metallic inclusions are generally not suitable for photo etching on metal. Most industrial applications focus on sheet thickness ranging from 0.02 mm up to 1.5 mm.

2. Full Process Workflow of Photo Etching on Metal

The whole production sequence consists of design optimisation, surface preparation, photoresist masking, UV imaging, developing, spray etching, stripping, post‑treatment and final inspection.

Step 1: DFM Design Review & Phototool Fabrication

CAD drawings are evaluated by process engineers. Key parameters including minimum feature width, hole‑to‑thickness ratio, feature spacing and target etching depth are analysed. Since photo etching follows isotropic corrosion behaviour, lateral undercut compensation is calculated and embedded into the phototool film before manufacturing starts. Unreasonable design proposals will be fed back for revision to lower scrap risk.

Step 2: Metal Surface Pre‑Treatment

Raw metal sheets go through alkaline degreasing to eliminate rolling oil, grease and organic contaminants. Acid activation removes oxide and passive surface films. Multi‑stage de‑ionised‑water rinsing plus hot‑air drying follow. A uniformly clean micro‑rough surface is mandatory for reliable photoresist adhesion. Poor pre‑treatment causes photoresist lifting, pattern peeling and spot‑type etching defects.

Step 3: Dry‑Film Photoresist Lamination

Light‑sensitive dry‑film photoresist is hot‑roll laminated onto metal surfaces. Double‑sided lamination is required for through‑etched components such as micro‑porous meshes. Lamination temperature, roller pressure and feeding speed are precisely controlled to eliminate bubbles and wrinkles. Any trapped air will permit etchant to seep underneath the resist and create random defective patterns. Laminated panels rest for thermal stabilisation.

Step 4: UV Exposure

The pre‑compensated phototool is precisely aligned against the photoresist‑covered metal. High‑intensity UV light passes through transparent regions of the film and cures corresponding sections of dry‑film resist. Cured photoresist becomes chemically resistant and forms the protective mask for final‑part geometry. Areas under opaque parts of the phototool remain soluble. Double‑sided exposure is utilised for high‑precision through‑etching to achieve top‑bottom pattern alignment.

Step 5: Developing

Panels pass through dilute alkaline developer solution. Un‑exposed photoresist dissolves completely, opening clear etching windows on the metal substrate, while UV‑cured masking resist stays firmly attached. In‑line AOI automatic optical inspection screens out semi‑finished goods with broken traces, residual resist or blocked micro‑holes.

Step 6: Spray Etching (Core Material‑Removal Stage)

Panels travel horizontally through a conveyor‑type spray etching chamber. Pressured, continuously‑circulated etchant is sprayed onto both sides of workpieces. Etchant chemistry varies according to metal alloy. Conveyor speed, liquid temperature, spray pressure and accumulated dissolved‑metal‑ion concentration are strictly monitored. For through‑etching, balanced double‑sided spraying ensures uniform material removal. Etching continues until holes are fully penetrated or specified half‑etch depth is obtained. Isotropic corrosion takes place both vertically and laterally, which is why pre‑calculated undercut compensation is indispensable.

Step 7: Photoresist Stripping

After etching is completed, panels are conveyed into hot‑alkali stripping tanks to remove all cured photoresist mask. Complete stripping avoids resist residue‑related surface staining. Workpieces are thoroughly rinsed afterwards.

Step 8: Post‑Treatment

Neutralisation removes residual corrosive chemicals. Stainless‑steel parts usually undergo passivation to rebuild protective chromium‑oxide passive film and restore corrosion resistance. Optional secondary processes include electropolishing, plating, bending, colour filling, laser marking and panel separation into individual finished components.

Step 9: Quality Inspection

Dimensional measurements are performed with video‑measuring equipment to verify hole size, slot width, outer contour and flatness. AOI scanning detects pinholes, nicks and pattern distortion. Visual appearance screening and batch‑record archiving complete the workflow.

3. Key Advantages of Photo Etching on Metal

1. Zero burrs & zero mechanical stress: No mechanical contact during material removal. Thin, elastic components retain original material properties without deformation.

2. No hard‑tooling costs: Pattern modifications only require updated phototool film. Fast design iteration supports quick prototyping and flexible product upgrading.

3. Excellent capability for dense complex features: Hundreds of micro‑holes, fine slots and intricate outlines can be formed in one single etching cycle; no extra time cost for increasing feature quantity.

4. Dual‑mode processing: Supports both through‑etching and controlled‑depth half‑etching for marking, texturing and structural weakening.

5. Consistent batch repeatability: Automated spray‑etching lines deliver stable part‑to‑part dimensional performance for mass‑volume orders.

4. Inherent Process Limitations

Isotropic etching inevitably generates lateral undercut; achievable feature dimensions are closely linked to raw‑material thickness. Ultra‑high depth‑to‑width‑ratio structures cannot be manufactured. Photo etching on metal is most economical for thin‑gauge sheets; thick metal workpieces become cost‑inefficient. Different metal alloys demand dedicated etchant and pre‑treatment parameters.

5. Typical Industrial Applications

Photo etching on metal produces micro‑porous filter meshes, test sieves, encoder discs, optical apertures, EMI shielding sheets, precision gaskets, spring contacts, automotive horn grilles, medical nebulizer plates, new‑energy functional metal components, decorative metal nameplates and badges. It serves prototype verification, small‑batch trial‑run and large‑scale automated manufacturing scenarios.

Conclusion

Photo etching on metal is a mature precision subtractive manufacturing solution for thin‑sheet metallic materials. Supported by DFM optimisation, standardised pre‑treatment, photolithographic masking and controlled isotropic chemical dissolution, it delivers burr‑free, low‑stress complex metal parts for diverse industries. Understanding compatible‑material scope, isotropic‑etching rules and process boundaries helps engineers optimise CAD drawings and maximise the value of photo‑etched metal components.