Chemical Etching Process

Chemical etching, also widely referred to as photochemical machining (PCM) or photoetching, is a subtractive cold metalfabrication process. It uses photolithography and controlled chemical dissolution to selectively remove unwanted material from thinmetal sheets. Unlike stamping, laser cutting or CNC machining, chemical etching applies no mechanical force and generates no thermal impact on workpieces. The final parts are burrfree, stressfree and retain the original physical properties of base metals. This technology is ideal for producing complex contours, dense microholes, fine meshes, precision gaskets and ultrathin components from prototype sampling through to highvolume massproduction.

A wide range of conductive thingauge metals can be processed by chemical etching, typically ranging from 0.01 mm to 2.0 mm in thickness. Common materials include 304 / 301 / 316L stainless steel, copper, brass, phosphor bronze, nickel alloys, titanium, Kovar and Invar. Each metal has unique chemical activity. Some alloys such as titanium and highnickel grades easily form passive oxide films, requiring adjusted pretreatment and optimized etchant formulas to achieve uniform etching performance.

StepbyStep Chemical Etching Process Workflow

Step 1: Drawing Review & DFM Analysis

The whole process starts with manufacturability evaluation for customer CAD or DXF design files. Engineers calculate key technical parameters: minimum feature size, smallest aperture, narrow slot limit, wall thickness, achievable tolerance and sideetch compensation. Sideetch is unavoidable horizontal undercut during metal dissolution. Compensation values are embedded into phototool artwork in advance to guarantee finishedpart dimensional accuracy. Practical suggestions are provided if drawings contain nonmanufacturable features, preventing costly rework after production starts.

Step 2: Metal Sheet Cutting and Surface PreTreatment

Raw metal coils or flat sheets are nested and cut into standard productionsize panels. Surface pretreatment is one of the most decisive steps in the whole chemical etching process. Any contamination will cause subsequent photoresist delamination, pattern lifting, pinholes or partial etching failure.

Alkaline degreasing removes oil, grease, antirust agents and fingerprints from metal surfaces.

Multistage water rinsing washes away alkaline residues.

Acid activation eliminates oxidation scale and passive oxide films formed on alloy surfaces.

Further rinsing followed by lowdust hotair drying ensures perfectly clean, stainfree panels ready for lamination.

Step 3: DryFilm Photoresist Lamination

Lightsensitive dryfilm photoresist is hotrolled onto one or both sides of clean metal panels under stable temperature and pressure control. Doublesided lamination is required for throughhole mesh products to realize simultaneous etching from top and bottom surfaces. Operators strictly eliminate bubbles and wrinkles trapped between dryfilm and metal substrate. Tiny bubbles will lead to local leakage of etchant and pattern damage.

Step 4: UV Exposure for Pattern Transfer

Highprecision phototool films generated from customer drawings are closely aligned against laminated panels. Intensityregulated UV light passes through transparent graphic areas of the phototool, crosslinking and curing the underlying photoresist layer. Opaque areas on the phototool block ultraviolet rays so that the covered photoresist remains unpolymerized. Doublesided exposure equipment is adopted for dualsided etched components to maintain high registration accuracy between frontside and backside patterns. A latent image of target parts is formed within the photoresist after exposure.

Step 5: Developing

Panels are conveyed through a developer tank filled with dilute sodiumcarbonate solution. Unexposed, uncured photoresist is dissolved and rinsed away, exposing bare metal zones that need to be etched. UVcured photoresist stays firmly bonded as an anticorrosion protective mask. Process variables including developer concentration, temperature and conveyor speed must be precisely controlled. Overdeveloping erodes mask edges and increases sideetch; insufficient developing leaves photoresist residues blocking chemical reaction. After developing, panels are rinsed, dried and visually inspected for pattern completeness.

Step 6: Automatic Spray Etching (Core Stage)

Patternloaded panels enter continuous automatic spray etching production lines. Ferricchloridebased etchant mixed with functional additives is evenly sprayed onto panel surfaces. Exposed bare metal dissolves through redox chemical reactions.

Production staff continuously monitor etchant baumé degree, temperature, spray pressure, circulation flow rate and conveyor travelling speed. Conveyor speed directly governs etching depth and throughcut status. Precalculated sideetch compensation built into artwork offsets horizontal undercut effect to meet drawing tolerance requirements. Firstarticle inspection is mandatory for every new batch. Massproduction can only start after firstarticle dimensions pass full verification.

Step 7: Photoresist Stripping

Once target etching depth or full throughcut is achieved, panels go through thorough multistage rinsing to flush off residual etchant. Then panels pass through hot alkaline stripping tanks. Hot alkali hydrolyses crosslinked photoresist and completely strips away the protective mask layer. Finished components remain tabconnected on the carrier sheet frame. Complete poststripping rinsing is essential to remove all chemical residues and avoid surface discoloration, spots or premature corrosion.

Step 8: PostTreatment and Surface Finishing

Multiple secondary finishing processes can be performed according to application requirements: passivation, deburring, polishing, sandblasting, antirust treatment, color filling for nameplates, electroplating and coating. Parts can stay attached to the carrier frame for convenient assembly handling, or be separated by breaking, punching or laser singulation.

Step 9: MultiLevel Quality Inspection

Finished metal panels are measured with 2D vision measuring machines for critical dimensions, hole diameters, slot widths and overall tolerances. Metallurgical microscopes are used to check for pinholes, partial etching, pattern distortion and surface defects. Material certificates and batch inspection reports can be issued for automotive, medical, aerospace and newenergy highreliability projects.

Common Defects in Chemical Etching and Root Causes

Uneven etching depth: Caused by incomplete surface activation, unstable etchant parameters or residual oil contamination before lamination.

Pinholes: Resulting from substrate inclusions, dirt on photoresist film or insufficient cleaning in pretreatment section.

Excessive sideetch: Related to inadequate artwork compensation, improper exposure or overdeveloping parameters.

Photoresist lifting and delamination: Mostly triggered by insufficient degreasing and poor surface activation of raw metal sheets.

Key Advantages of Chemical Etching Process

Burrfree & stressfree: No mechanical deformation, no heataffected zones, original material performance is fully preserved.

High complexity capability: Supports intricate shapes, ultrafine slots and largearray microholes which are difficult for other manufacturing methods.

Lowcost iteration: No expensive hard stamping dies; only lowcost phototool film is needed. Design revisions simply require updating CAD artwork.

Consistent quality: Dimensional stability from prototype to largevolume production.

Broad material compatibility: Works for most thin conductive metals and various special alloys.

Typical Industrial Applications

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

Medical devices: nebulizer plates, filter meshes and thin surgical metal accessories.

Electronics & semiconductor: encoder discs, EMI shielding gaskets, aperture masks and microstencils.

Newenergy industry: hydrogenenergy bipolar plate flowfield sheets, filter elements and custom gaskets.

General industry: microporous filter mesh, metal nameplates and thinsheet mechanical parts.

Chemical Etching VS Competing Manufacturing Technologies

Stamping: Highspeed massproduction but creates burrs and mechanical stress; die modification brings high costs.

Laser cutting: Thermal processing with heataffected zones, slag and edge oxidation; inefficient for massive microhole arrays.

CNC machining: Suitable for thick solid metal blocks; high cost and low efficiency for ultrathin foils and dense microfeatures.

Conclusion

The chemical etching process integrates pretreatment, photolithography, spray etching, stripping, postfinishing and systematic quality control. Surface preparation and stable etchant parameter management determine final yield and product quality. As a mature cold subtractive manufacturing technology, chemical etching delivers reliable custom thinmetal components widely adopted across automotive, medical, electronics and newenergy sectors.