Etching Process on Metal

Metal etching, also commonly referred to as chemical etching or photochemical machining (PCM), is a subtractive manufacturing process that creates precise 2dimensional patterns on thin metal sheets by selective chemical dissolution. Unlike mechanical stamping, CNC milling or laser cutting, metal etching removes material through controlled chemical reaction instead of physical force or hightemperature thermal ablation. There is no direct mechanical contact between tools and workpieces, so finished metal parts remain burrfree, stressfree and distortionfree, even for ultrathin metal foils and intricate microfeature designs. This mature industrial technology is widely adopted for producing precision metal components for semiconductor packaging, newenergy hydrogen fuel cells, medical devices, aerospace and consumer electronics.

Only wet chemical etching is commercially mainstream for sheetmetal processing. Dry plasma etching exists for metal materials, yet its high equipment cost and limited panel size make it uneconomical for massproduction metal parts. Therefore, when industry practitioners talk about etching process on metal, they almost always mean photochemical wet etching based on photoresist masking.

Core Principle of Etching Process on Metal

The fundamental logic of metal etching is simple: cover nonprocessing metal zones with acidresistant photoresist mask, expose target areas to corrosive etchant solution, and let chemical reagent dissolve away unprotected metal. Two materialremoval behaviours happen simultaneously during production: vertical downward etching that cuts through or carves depth into metal substrate, and lateral undercut that erodes metal under the edge of photoresist mask. Design engineers must calculate undercut compensation in advance on original CAD artwork to offset side erosion and guarantee final dimensional tolerances. Typical achievable tolerance for industrial metal etching can reach ±0.01 mm for suitable material thickness.

StepbyStep Etching Process on Metal

Step 1: Material selection and surface precleaning

The whole metal etching sequence starts with rawmetal sheet preparation. Available metals cover stainless steel, copper, brass, nickel, kovar 4J42, aluminium, titanium and various special alloy foils. Applicable thickness generally ranges from 0.01 mm to 2.0 mm. Toothick metal will generate excessive undercut and degrade finepattern accuracy.

Surface cleanliness directly determines final yield. Rolling oil, fingerprints, dust and oxide film must be fully eliminated. Manufacturers apply combined alkaline degreasing, ultrasonic washing and deionized water rinsing, followed by hotair drying. Any tiny contamination will cause photoresist delamination, resist lifting, random pitting or pattern shortcircuit. Clean metal panels are then transferred to dustrestricted workshop for subsequent procedures.

Step 2: Dryfilm photoresist lamination

UVsensitive dryfilm photoresist is thermally laminated onto both top and bottom surfaces of cleaned metal sheets under stable temperature and pressure. Lamination must exclude bubbles, wrinkles and foreign particles trapped between resist and metal substrate. Photoresist thickness is selected according to expected etching depth, mostly 15 μm35 μm for mass production. Poor lamination quality will become latent defect sources in later etching stages. After laminating, panels go through short conditioning time to stabilize polymer status of dryfilm resist.

Step 3: UV exposure for pattern transfer

Customer CAD files are converted into highprecision glass phototools with negative component patterns. The laminated metal sheet is sandwiched between two aligned phototools inside doublesided UV exposure equipment. 365 nm ultraviolet light passes through transparent areas of phototool and cures corresponding photoresist by crosslinking polymerization. Photoresist beneath opaque graphic regions remains uncured and chemically soluble.

Accurate topbottom alignment is critical for throughholes and symmetric profiles, especially for micro filter screens and semiconductor metal masks. Misalignment will produce skewed openings and asymmetric side walls. Exposure energy needs precise calibration: insufficient energy leads to incomplete curing; overexposure causes pattern swelling and blurred edges.

Step 4: Developing

Exposed metal panels are conveyed into spraytype developing chamber. Warm diluted alkaline developer solution is sprayed onto both sides to wash away all unpolymerized photoresist. Only UVcured photoresist stays firmly bonded on metal surface as anticorrosion protective mask, fully unveiling baremetal regions to be etched away.

Manufacturers strictly control developer concentration, liquid temperature, spray pressure and conveyor speed. Underdevelopment leaves residual resist blocking etching channels; overdevelopment attacks hardened resist edges and reduces graphic resolution. Operators perform frequent sample inspection to confirm sharp, clean pattern edges before moving to etching station.

Step 5: Chemical spray etching (core stage)

Panels travel horizontally through sealed etching tunnel. Heated ferricchloridebased etchant is highpressure sprayed from upper and lower nozzles onto exposed baremetal surface. Chemical reaction continuously dissolves unprotected metal in vertical and lateral directions. Realtime sensors monitor etchant concentration, temperature and liquid circulation status, keeping working temperature between 45 °C55 °C.

Adjustable conveyor speed controls total etching duration. The process can realize fullthrough etching to separate complete parts from panel frame, as well as partialdepth halfetching for engraved marks, cavities and positioning grooves. Doublesided synchronized spraying ensures uniform etching depth across the whole largesize metal sheet and prevents uneven depth between centre and edge positions.

Step 6: Rinsing and photoresist stripping

Once target etching depth is achieved, sheets exit etching tunnel and receive largeflow cascade deionized water rinsing to flush corrosive etchant quickly and stop overetching caused by residual chemical liquid. Workpieces are then sent into alkaline stripping bath, where stripper dissolves and peels off all hardened photoresist mask. Multistage rinsing removes stripping chemical residues, and filtered hotair knives dry etched metal parts thoroughly. Residual chemical contamination will trigger postprocess rust spots, which is unacceptable for highend semiconductor and medicalgrade metal components.

Step 7: Quality inspection and optional posttreatment

Finished metal panels enter qualitycontrol workflow. Automatic optical inspection checks dimensional accuracy, holeposition tolerance, edge condition and surface defects. Inspectors further measure critical dimensions using microscope and micrometre. Defective panels are screened out.

According to customer specifications, optional posttreatments include deburring, surface passivation, electroplating, polishing, adhesivetape laminating and part separation from carrier frame. Batchwise production parameter records are kept to guarantee repeatability from prototype development to highvolume mass manufacturing.

Main Advantages of Etching Process on Metal

First, zero mechanical force during processing. Metal etching produces burrfree, stressfree parts without material deformation. Original mechanical properties of alloys are fully preserved, no heataffected zones occur. Even ultrathin fragile foils can be processed reliably.

Second, no expensive hard stamping dies are required. Pattern modification only needs updating phototool artwork. Prototype cost is low and leadtime is short. Manufacturing cost does not rise significantly as graphic complexity increases, which makes metal etching ideal for dense microholes, slim slots and intricate outlines.

Third, doublesided simultaneous processing supports largeformat metal sheets, and stable process parameters deliver good batchtobatch consistency.

Every process has limitations. Metal chemical etching performs best within 0.012.0 mm thickness scope. Thicker metal brings serious undercut and loses finefeature precision. Designers should follow PCM DFM guidelines to optimise drawings before manufacturing.

Typical Industrial Applications

Etching process on metal supplies highprecision thinmetal parts for multiple hightech industries. In semiconductor packaging, it manufactures ball masks, flux masks and various metal shielding components. Newenergy hydrogen industry adopts etched metal flowfield plates for fuelcell stacks. Medical sector produces micro filter meshes and miniature surgical metal components. Consumer electronics uses etched EMI shielding sheets and spring contacts. Aerospace and sensor fields widely apply etched shims, fine meshes and complex thinmetal structural parts.

Conclusion

Etching process on metal, namely photochemical wet etching, is a reliable subtractive manufacturing solution for thinmetal components. Every procedure including cleaning, lamination, exposure, developing, etching, stripping and inspection jointly determines part accuracy, edge quality and production yield. By mastering undercut compensation and closedloop parameter control, manufacturers can convert complex CAD designs into qualified burrfree precisionmetal parts for prototype and massproduction demands.