Photo chemical etching, also commonly referred to as photochemical machining (PCM), photoetching or chemical blanking, is a subtractive precision metal manufacturing technology that combines photolithography and controlled chemical dissolution. It transfers digital CAD patterns onto metal sheets through photographic masking, then selectively dissolves unprotected metal areas with etchant to produce complex, burrfree, stressfree flat metal components. Unlike stamping, laser cutting or CNC milling, photo chemical etching does not apply mechanical force or thermal energy to the workpiece. Thin metal sheets retain original material properties without deformation, microcracks or heataffected zones. This mature highvolumeready process is widely adopted across automotive, medical device, aerospace, electronics, semiconductor and newenergy industries for custom thingauge metal parts.

The core principle of photo chemical etching relies on isotropic chemical corrosion. A lightsensitive photoresist mask protects required part geometry. Exposed bare metal reacts with sprayed etchant and dissolves away. Since etching progresses both vertically through material thickness and horizontally under the edge of resist mask, sideetch (undercut) will inevitably occur. Engineers compensate sideetch value at the artwork design stage to achieve final dimensional tolerances. Material thickness, etchant concentration, temperature and spray parameters directly determine undercut magnitude and overall part quality.

Suitable Materials for Photo Chemical Etching

Photo chemical etching works well on most rolled thinsheet conductive metals and alloys. Material thickness typically ranges from 0.01 mm to 2.0 mm.

Stainless steel (304, 304L, 316L, 301 spring grade): most popular for meshes, gaskets, spring plates and medical components

Copper, brass, bronze: EMI shielding, conductive shims, decorative nameplates

Nickel, nickelcobalt alloy: hightemperature spring elements

Titanium and titanium alloys: hydrogenenergy bipolar plates, medical implant accessories

Special alloys: Kovar, Invar, Hastelloy for aerospace and semiconductor packaging

Metals forming dense passive oxide films demand adjusted pretreatment and modified etchant formulas to guarantee uniform etching performance. Very thick metal plates are generally not costeffective for PCM processing.

StepbyStep Photo Chemical Etching Process

Step 1: Sheet Cutting & Surface Preparation

Raw metal coil or flat sheet is cut into productionsize working panels according to panellayout nesting. Surface preparation is the foundation of consistent yield. Alkaline degreasing removes oil, grease and fingerprints. Acid pickling and activation eliminate oxidation scale and passive surface films. Any residual contamination causes photoresist delamination, pattern lifting, pinholes or incomplete etching defects. Panels go through multistage rinsing and are fully dried inside a dustfree environment before next operation. Dust particles on metal surface will create pattern flaws.

Step 2: DryFilm Photoresist Lamination

Dryfilm photoresist, a lightsensitive polymer film, is hotrolled and laminated onto one or both sides of clean metal panel under controlled temperature and pressure. Doublesided lamination enables simultaneous etching from top and bottom surfaces, which is essential for microporous mesh and throughhole components. Lamination must avoid bubbles, wrinkles and uneven pressure. Bubbles trapped between film and metal will lead to pattern failure during subsequent exposure and etching.

Step 3: UV Exposure & Pattern Transfer

A highaccuracy phototool (film mask) generated from customer CAD / DXF drawing is closely registered against the photoresistcovered metal panel. Highintensity ultraviolet light passes through transparent areas of the phototool and crosslinks (cures) corresponding photoresist. Opaque black regions on the mask block UV light, leaving underlying photoresist unpolymerized. For parts requiring strict topbottom alignment, doublesided exposure equipment performs precise registration between frontside and backside patterns. After exposure, latent image of the component geometry is stored inside photoresist layer.

Step 4: Developing

Panels are conveyed through developer tank filled with dilute alkaline sodiumcarbonate developer solution. Developer washes away unexposed, uncured photoresist, fully exposing bare metal areas intended for removal. UVcured crosslinked photoresist remains firmly bonded as an antietch protective mask. Operators strictly control developer concentration, temperature and conveyor speed to prevent overdeveloping or underdeveloping. Overdeveloping erodes resist edges and increases sideetch; insufficient developing leaves resist residue covering metal and blocks etching action. After developing, panels are rinsed, dried and visually inspected for pattern integrity before entering etching chamber.

Step 5: Spray Etching (Core Process Stage)

Patterned panels travel into continuous automatic spray etching machine. Pressured etchant (mostly ferricchloridebased for general metals) is evenly sprayed onto both panel surfaces. Etchant chemically dissolves exposed bare metal. Key production parameters including etchant baumé / specific gravity, liquid temperature, spray pressure, circulation flow rate and conveyor speed are continuously monitored and adjusted. Etching depth and throughcut are controlled by conveyor speed. Sideetch compensation which was builtin during artwork design offsets horizontal undercut effect to hit drawing tolerance requirements. Firstarticle inspection is mandatory for every new batch to verify dimension, aperture, edge quality and etching completeness before massproduction run.

Step 6: Resist Stripping

After etching finishes, panels are thoroughly rinsed to wash off residual etchant liquid. Panels then pass through stripping tank with hot alkaline stripping solution. Hot alkali hydrolyses cured photoresist polymer and strips protective resist layer completely from metal substrate. Only the finished metal part structures remain on the sheet frame. Complete rinsing removes stripping chemical residues to avoid subsequent surface discoloration or premature rusting.

Step 7: PostTreatment & Surface Finishing

Multiple posttreatment options are available based on customer specifications: passivation for stainlesssteel corrosion resistance, deburring, polishing, sandblasting, antirust treatment, color filling for nameplates, electroplating or surface coating. Parts can stay attached to the carrier frame for easy handling during assembly, or be separated by breaking, punching or laser singulation.

Step 8: Comprehensive Quality Inspection

Finished panels undergo multilevel quality control. Twodimensional vision measuring systems check critical dimensions, hole diameters, slot widths and overall tolerances. Microscope inspection detects pinholes, partial etching, pattern distortion and surface blemishes. For highreliability applications in medical, aerospace and newenergy industries, additional tests for flatness, hardness and corrosion resistance can be performed. Qualified components are packed for shipment.

Key Advantages of Photo Chemical Etching

Burrfree & stressfree parts: Material removal purely by chemical dissolution, no mechanical contact, no clamping deformation. Ideal for thin springtempered metal sheets.

Lowcost tooling & fast prototyping: No expensive hard stamping dies. Only lowcost phototool film is required. Design revisions are completed simply by updating CAD artwork, greatly reducing iteration cost and leadtime. Supports prototype, smallbatch and massproduction seamlessly.

Excellent capability for intricate microfeatures: Produce dense microholes, narrow slots, complex planar contours that are difficult or uneconomical for traditional machining. Minimum feature size can approach material thickness.

Consistent flatness: No mechanical compression during processing; ultrathin metal sheets keep good flatness after etching.

Uniformity across full panel: Hundreds of parts on one production panel maintain consistent dimensional performance.

Process Limitations

Photo chemical etching is optimized for thinwall sheet metal. As material thickness increases, sideetch effect becomes more significant, limiting achievable aspect ratio for deep narrow structures. The isotropic etching nature cannot achieve perfectly vertical side walls. Production consumes industrial etchant chemicals, requiring professional wasteliquid treatment system for environmental compliance. For very thick metal workpieces, PCM is not competitive compared with CNC or laser cutting.

Photo Chemical Etching VS Competing Manufacturing Technologies

Vs Stamping: Stamping delivers highspeed mass output but creates burrs and mechanical stress; die modification cost is high. Photo chemical etching excels at complex thinsheet prototypes and frequent design changes.

Vs Laser Cutting: Laser cutting is thermal processing, generating heataffected zone, slag and edge oxidation. For largearray microhole mesh products, photo chemical etching achieves better edge quality and higher overall efficiency.

Vs Electroforming: Electroforming is additive manufacturing building parts by metal deposition. It can achieve higher aspect ratio structures without sideetch, yet longer leadtime and higher prototype cost compared with photo chemical etching.

Typical Industrial Applications

Automotive: precision shims, horn grille meshes, spring contact plates, sensor metal components

Medical devices: stainlesssteel filter meshes, nebulizer plates, surgical instrument thinmetal parts

Aerospace: special alloy gaskets, lightweight thinwall structural components

Electronics & semiconductor: EMI shielding sheets, encoder discs, aperture masks, lead frames

Newenergy: flowfield components, filter elements, custom gaskets for energystorage and hydrogen equipment

General hardware: metal nameplates, microporous filter elements, mechanical thinsheet components

Conclusion

Photo chemical etching (PCM) combines photolithography and controlled chemical corrosion to manufacture highprecision thinmetal components. The complete workflow covers sheet preparation, photoresist lamination, UV exposure, developing, spray etching, resist stripping, postfinishing and quality inspection. Thanks to burrfree, stressfree output, lowcost tooling and strong microfeature capacity, photo chemical etching fills an irreplaceable position across automotive, medical, aerospace, electronics and newenergy industries. Understanding sideetch compensation, material characteristics and process boundaries helps engineers make full use of this proven precision manufacturing technology.