Metal chemical etching, also widely known as photochemical machining (PCM), photo etching or chemical milling, is a subtractive precision manufacturing technology that selectively removes unwanted metal material through controlled chemical dissolution. Different from stamping, CNC machining and laser cutting which rely on mechanical force or thermal energy to shape metal parts, chemical etching uses chemical etchant to dissolve unprotected metal regions, while preapplied photoresist mask preserves the geometry of finished components. This unique processing method produces burrfree, stressfree thinmetal parts with intricate microfeatures, without introducing mechanical deformation or thermal distortion. It has become a mainstream production solution for aerospace, automotive, medical device, semiconductor, optoelectronics and newenergy industries for custom thinsheet metal components.

The fundamental working principle of metal chemical etching lies in selective chemical corrosion. A lightsensitive photoresist layer is laminated onto flat metal substrate. After UV exposure and developing procedure, the target pattern is transferred onto photoresist: protected areas remain covered by cured resist, while areas requiring material removal expose bare metal surface. Under preciselycontrolled temperature, pressure, concentration and spraying circulation, etchant (most commonly ferric chloride solution) continuously reacts with exposed metal and dissolves metal atoms into liquid phase. By adjusting etching duration and fluid parameters, manufacturers achieve consistent depth and dimensional tolerance for micro holes, slots, meshes, gaskets and encoder structures.

One critical phenomenon in chemical etching is isotropic sideetch. While etchant attacks vertically down into metal thickness, it also corrodes horizontally underneath the edge of photoresist mask. Sideetch value is closely related to material thickness, etchant formula and processing parameters, and must be fully considered during artwork design to guarantee final dimensional accuracy.

Compatible Metals for Chemical Etching

Chemical etching works for most common industrial thinsheet metals and alloys, though each material requires customized etchant formula and process tuning.

Stainless steel (304, 316 series): The most popular material, widely used for filter mesh, gaskets, spring sheets and medical components. Thickness range typically from 0.02 mm to 1.5 mm.

Copper, brass, bronze: Fast etching response, ideal for EMI shielding parts, conductive shims and decorative nameplates.

Nickel, nickelcobalt alloy: Applied for spring components and hightemperature resistant precision parts.

Titanium and titanium alloy: Demands special etchant system, for hydrogenenergy bipolar plates and medical implant accessories.

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

Materials with dense, stable native oxide film need enhanced pretreatment steps to achieve uniform etching effect.

StepbyStep Metal Chemical Etching Process

Step 1: Metal Sheet Cutting & Surface PrePreparation

Raw metal coil or sheet is cut to required working panel size according to production layout. Surface preparation is the foundation of stable etching quality. Operators perform thorough degreasing, alkaline cleaning and pickling to eliminate oil stains, fingerprints, dust and oxidation layer on metal surface. Any residual contamination will cause poor photoresist adhesion, resist lifting, pinholes or broken patterns in subsequent stages. After cleaning, sheets are fully dried under dustfree environment.

Step 2: Photoresist Lamination

Dryfilm photoresist is hotrolled and laminated uniformly onto both sides of cleaned metal sheet under controlled temperature and pressure. The photoresist is lightsensitive polymer material that forms antietching protective mask after UV curing. Doublesided lamination enables simultaneous twosided etching for symmetrical parts such as microporous mesh sheets. Lamination quality directly determines pattern fidelity; bubbles, wrinkles or uneven film thickness will lead to defective finished products.

Step 3: UV Exposure & Pattern Transfer

Highprecision phototool (film mask) carrying customer CADderived patterns is closely aligned against photoresistcovered metal panel. Highintensity ultraviolet light penetrates transparent zones of phototool and cures corresponding photoresist, making these regions chemically resistant to developer solution. The opaque areas on mask block UV light, keeping underlying photoresist unpolymerized for later removal. For highprecision microcomponents, doublesided alignment equipment ensures pattern consistency on top and bottom surfaces.

Step 4: Developing

Panels go through developer tank, where alkaline developer washes away unexposed, uncured photoresist, completely exposing bare metal areas to be etched. Cured photoresist stays firmly bonded to metal surface as protective mask. Operators monitor developing speed, solution concentration and temperature to avoid overdeveloping or underdeveloping defects. After developing, panels are rinsed and dried, and visual inspection checks pattern integrity before entering etching chamber.

Step 5: Core Etching Procedure

The patterned metal panels are transported into continuous spray etching machine. Pressurized etchant solution is sprayed evenly onto top and bottom surfaces. Etchant reacts chemically with exposed bare metal and dissolves metal material gradually. Key process parameters including etchant concentration, liquid temperature, spray pressure, circulation flow rate and conveyor speed are strictly monitored and adjusted throughout production run to control etching depth and sideetch amount. Isotropic sideetch effect is compensated in artwork design phase to hit target dimensional tolerances.

Step 6: Stripping (Resist Removal)

After etching reaches target depth and geometry, panels are thoroughly rinsed to remove residual etchant liquid. Then sheets pass through stripping tank with strong alkaline solution, stripping off all remaining cured photoresist protective layer. Only the final metal component structures are retained on the metal panel frame. Complete rinsing removes stripping chemical residues to prevent postprocess corrosion.

Step 7: PostTreatment

According to customer requirements, multiple posttreatment options are available: deburring, passivation, polishing, surface sandblasting, antirust treatment, filling color for nameplates, or electroplating. For mass production, parts can remain attached to original sheet frame for easy handling; final separation can be done by manual breaking or stamping.

Step 8: Comprehensive Quality Inspection

Finished panels undergo multilevel quality control. Twodimensional vision measuring instruments verify critical dimensions, microhole aperture, slot width and overall tolerance. Microscope inspection checks for pinholes, incomplete etching, pattern distortion and surface defects. Hardness, flatness and corrosionresistance tests are executed for highreliability components for medical, aerospace and newenergy fields. Only parts complying with drawing specifications can be approved for delivery.

Core Advantages of Metal Chemical Etching

First, zero burr and zero mechanical stress. Since material removal relies purely on chemical dissolution without mechanical contact or impact, etched parts contain no burrs, deformation or internal mechanical stress, which is extremely valuable for thin spring sheets and sensitive microcomponents.

Second, lowcost tooling for complex geometry. Unlike stamping requiring expensive custom hard dies, chemical etching only needs lowcost phototool film. Design modification can be completed rapidly by updating CAD artwork, supporting fast prototype iteration and flexible smallbatch to massbatch production.

Third, outstanding capability for ultrafine intricate features. Microholes, narrow slots, dense mesh and complex planar outlines that are difficult for traditional machining can be realized precisely. Feature size can be close to material thickness.

Fourth, consistent part flatness. Workpiece will not suffer compression deformation during processing; flatness performance remains stable for thingauge metal sheets.

Process Limitations of Metal Chemical Etching

Chemical etching also has clear technical boundaries. It is best suited for thinwall metal sheets; as material thickness increases, sideetch effect becomes more significant, raising difficulty for ultrasmall microfeatures. The isotropic etching nature restricts aspect ratio of deep narrow structures. Besides, the process consumes large volumes of chemical etchant liquid; manufacturers must equip professional wasteliquid treatment system to satisfy environmentalprotection regulations. For very thick metal plates, chemical etching is usually not economically competitive compared with CNC or laser cutting.

Chemical Etching vs Other Conventional Metal Processing

Compared with stamping: stamping excels at highvolume thickpart production, yet generates burr and mechanical stress; die modification cost is high. Chemical etching delivers burrfree results and easy design revision, more competitive for thinsheet complex microparts.

Compared with laser cutting: laser cutting applies thermal ablation, may produce heataffected zone, slag and edge oxidation. Chemical etching avoids thermal damage, delivers smoother edge quality for largearray microhole and mesh products.

Compared with electroforming: chemical etching is subtractive manufacturing starting from raw metal sheet. Electroforming belongs to additive manufacturing, growing metal atombyatom on mandrel. Electroforming achieves higher aspectratio microstructures free from sideetch limitation, but has longer leadtime and higher cost for prototype development.

Typical Industrial Applications

In automotive industry: precision shims, horn mesh grilles, sensor metal components, automotive spring contact plates. In medical devices: stainlesssteel filter meshes, nebulizer atomizer plates, surgical instrument thinmetal parts. In optoelectronics: encoder discs, aperture masks, optical slits, shielding cans. In newenergy & aerospace: flowfield components, special alloy gaskets, micro filter elements. In electronics: EMI shielding sheets, leadframe components, PCBrelated precision metal accessories.

Conclusion

Metal chemical etching is a mature and reliable subtractive precision manufacturing technology built on photolithography and controlled chemical corrosion. Through sequential workflow including sheet preparation, photoresist lamination, UV exposure, developing, spray etching, stripping, posttreatment and inspection, it produces burrfree, stressfree complex thinmetal components. Although constrained by isotropic sideetch and thickness limitations, its advantages of lowcost tooling, fast prototyping and capability for dense microfeatures make it irreplaceable across automotive, medical, semiconductor and newenergy sectors. With continuous optimization of etchant formula and automatic production equipment, metal chemical etching keeps expanding its application scope for nextgeneration microprecision metal parts.