Chemical etching, commonly termed photochemical machining (PCM), is a non-contact, stress-free subtractive manufacturing technology tailored for ultra-precision thin-gauge metal components, widely adopted in aerospace, medical devices, 5G electronics, new energy and precision instrumentation industries. Different from CNC milling, stamping and laser cutting, this technology relies on photoresist masking and controlled redox reactions to remove unwanted metal materials selectively, delivering burr-free, heat-damage-free and distortion-free micro-parts with micron-level dimensional tolerance. This paper elaborates basic chemical principles, standard industrial workflow, applicable metal substrates, critical process parameters, comparative advantages over conventional machining, inherent defects and optimization solutions, as well as global industrial applications of precision metal chemical etching. Meanwhile, it analyzes green manufacturing upgrades and future technical trends of photochemical etching. Research shows that optimized chemical etching achieves ±1 μm dimensional accuracy for thin alloy parts, retains original mechanical properties of metal substrates, and cuts mass production costs for complex micro-structure components. As high-end manufacturing pursues miniaturization and high integration, chemical etching has become an irreplaceable core process for precision metal component batch fabrication, overcoming bottlenecks of traditional mechanical processing on ultra-thin sheets, dense micro-holes and irregular profiled parts.

1. Introduction

The booming development of intelligent manufacturing and microelectronic technology raises stringent requirements for precision metal components, including ultra-tight tolerance, ultra-smooth surface, zero residual stress and stable corrosion resistance. Typical precision metal parts cover electromagnetic shielding sheets, medical micro gaskets, battery current collectors, aerospace thin shims, micro filter meshes and sensor alloy substrates, mostly made of 304/316L stainless steel, oxygen-free copper, aluminum alloy, titanium alloy and nickel-based alloy with thickness ranging from 0.02 mm to 2 mm. Traditional manufacturing methods face prominent limitations in processing such sophisticated components. Mechanical stamping generates extrusion stress, edge burrs and work hardening, causing component warpage and shortened service life. Laser cutting produces thermal-affected zones, surface oxidation and micro-cracks, damaging fatigue performance of finished parts. CNC micro-milling suffers tool wear, high die cost and low efficiency for tiny array structures.

As a low-temperature cold machining process, chemical etching eliminates mechanical force and thermal radiation during the whole production cycle. It uses digital photolithography to transfer CAD patterns onto metal surfaces, isolates reserved areas via polymer photoresist, and dissolves exposed metal with matched etchants. This process features low mould cost, fast pattern iteration and excellent batch consistency, suitable for both mass production and customized small-batch orders. Currently, over 65% of ultra-precision thin metal components in medical and 5G communication fields adopt photochemical etching. This paper comprehensively discusses the whole technical system of precision metal chemical etching, providing practical process references for industrial production and academic research.

2. Fundamental Reaction Mechanism

The core mechanism of precision metal chemical etching is controllable selective isotropic chemical corrosion. Most engineering alloys form a dense chromium or aluminum oxide passivation film in the air, preventing spontaneous chemical corrosion. The whole etching process breaks this passivation layer of unmasked zones and realizes quantitative metal dissolution, while photoresist film protects finished component contours completely without chemical reaction.

Ferric chloride (FeCl₃) acidic solution is the dominant industrial etchant for stainless steel, copper and nickel alloy components, with adjustable hydrochloric acid additives to stabilize reaction rate. Chloride ions in etchant first erode the dense passive film on metal surfaces; then ferric ions oxidize metallic atoms into soluble metal ions, which diffuse into circulating etching liquid to complete material removal. For high-strength titanium and aluminum precision parts, buffered fluoride etchants replace iron chloride solutions to avoid over-corrosion and surface roughness rise.

Conventional precision metal etching belongs to isotropic corrosion, where vertical depth etching and horizontal lateral undercut proceed at the same speed, forming smooth vertical side walls of components. Different from thermal machining, the reaction temperature is controlled below 55℃, without metal phase transition, grain structure change or residual internal stress. This core advantage ensures etched precision components maintain original hardness, toughness and anti-corrosion performance, meeting long-term assembly and service requirements of high-end industrial equipment.

3. Standard Manufacturing Process

Industrial mass production of chemically etched precision metal components follows nine standardized, quality-controlled procedures, optimized for micron precision and industrial cleanliness standards.

First, substrate pretreatment. Raw metal coils are cut into standard sheets, followed by alkaline degreasing and weak acid pickling to eliminate surface oil, dust and uneven oxide layers. This step improves photoresist adhesion and avoids uneven etching defects. Second, double-sided dry film lamination. Alkali-resistant, food-safe and electronic-grade photoresist is hot-laminated on metal bilaterally to fit ultra-fine pattern exposure. Third, UV alignment exposure. Digital component drawings are typeset, and double-sided aligned ultraviolet exposure cures photoresist to form anti-corrosion masks.

Fourth, alkaline development. Sodium carbonate developer washes uncured photoresist away, exposing metal areas to be etched with 1:1 pattern reduction. Fifth, constant-temperature spray etching. Closed circulating spray equipment replaces static immersion etching to guarantee uniform reaction across the whole plate, stabilizing size tolerance. Sixth, photoresist stripping. Alkaline stripper removes polymerized resist without scratching polished metal base surface.

Seventh, multi-stage neutralization and ultrapure water cleaning. Residual acid etchant is neutralized to prevent post-production rust and chemical residue. Eighth, electrolytic passivation. Surface passive film is repaired to enhance oxidation and acid resistance of finished components. Ninth, die cutting and full inspection. Finished parts are separated, and optical dimension detection, residue test and surface defect screening are conducted before delivery.

4. Material Selection and Key Process Parameters

4.1 Common Precision Metal Substrates

316L stainless steel is the top choice for medical and food-grade precision components with superior acid and alkali resistance; 304 stainless steel balances cost and performance for electronic industrial parts. Oxygen-free copper applies to electromagnetic shielding and thermal conductive components with fast etching speed. 5052 aluminum alloy is adopted for lightweight aerospace precision gaskets, while titanium alloy serves implant medical components with ultra-high chemical stability. Metal thickness for etched components is limited within 0.02 mm–2 mm for optimal forming effect.

4.2 Core Parameter Optimization

Etchant concentration, liquid temperature and spray pressure dominate component precision and yield. For stainless steel precision parts, 42–46 °Bé ferric chloride solution, 48–52 ℃ constant temperature and 0.26–0.30 MPa spray pressure are optimal industrial parameters. Excessively high temperature accelerates lateral undercut and causes dimensional out-of-tolerance; low temperature leads to incomplete penetration and low productivity. For micro-hole components below 50 μm aperture, circulating filtration of etching slag is mandatory to prevent micropore blockage. After parameter optimization, batch dimensional tolerance can be stably controlled within ±1 μm for high-precision industrial components.

5. Process Advantages, Defects and Optimization

5.1 Technical and Industrial Advantages

Firstly, zero-stress and burr-free forming. No mechanical extrusion or thermal burn guarantees flat parts without post-processing deformation. Secondly, ultra-high pattern reproducibility. Complex contours, dense micro holes and array grooves can be fabricated without secondary polishing. Thirdly, low manufacturing cost. No hard metal mould is needed, cutting customized part development cost by 40% compared with stamping. Fourthly, universal material adaptability. All alloy thin sheets available for precision manufacturing can be processed via matched etchants. Fifthly, outstanding batch consistency, improving equipment assembly matching rate greatly.

5.2 Defects and Improvement Strategies

Primary drawbacks include limited processing thickness for thick metal plates, inevitable minor lateral undercut, and traditional etching wastewater containing heavy metal and chloride ions. Targeted optimizations are widely applied in modern factories: organic corrosion inhibitors reduce side etching to lift precision; membrane filtration technology regenerates waste etchant to cut 60% chemical discharge; combined chemical etching and micro-polishing upgrade surface finish. These solutions solve environmental pollution and precision bottlenecks simultaneously.

6. Industrial Applications and Future Trends

At present, chemically etched precision metal components are widely deployed in three high-end sectors. Medical industry uses etched titanium and stainless steel micro-parts for surgical gaskets and implant device accessories. New energy industry adopts etched copper and stainless steel substrates for lithium battery pole pieces and fuel cell micro flow plates. 5G electronic communication applies ultra-thin etched shielding sheets and heat dissipation components to miniaturized communication modules.

Future development directions of precision metal chemical etching focus on three aspects. First, nano-scale ultra-precision composite etching for semiconductor micro-components. Second, full closed-loop green production lines to realize zero discharge of etching waste liquid. Third, one-step etching and super-hydrophobic surface integrated modification to enhance component service performance. With the iteration of miniaturized industrial equipment, photochemical etching will further replace traditional cutting processes and expand market share in high-end precision metal manufacturing.

7. Conclusion

Chemical etching is a high-efficiency, eco-optimizable and high-precision subtractive manufacturing technology for precision metal components, solving core processing pain points of ultra-thin alloy sheets, micro array structures and complex profiled parts that traditional machining cannot overcome. Supported by photolithography masking and controllable redox reactions, this process retains intrinsic metal mechanical properties, realizes micron-level dimensional accuracy and zero-burr surface quality, and reduces batch production and customization costs effectively. Rational matching of metal substrates, etchant formulas and process parameters improves product yield and industrial applicability greatly. Although the technology has limitations on thick metal processing, green regeneration equipment and parameter optimization have compensated core defects. Driven by high-end precision manufacturing demands, chemical etching of precision metal components will keep technical upgrading and maintain dominant status in micro-precision metal machining industry in the next decade.