If you are sourcing precision thin metal components, prototyping intricate planar parts, or comparing subtractive manufacturing technologies, you must have encountered the term photo etching. In the global precision machining industry, photo etching is the most commonly used short name for Photochemical Machining (PCM), also referred to as photo chemical etching, metal photo etching, wet chemical etching or industrial acid etching. It is a mature room-temperature cold processing technology that combines photolithographic pattern transfer and controlled liquid chemical corrosion to selectively remove excess metal materials from flat thin sheets.

Different from laser cutting’s thermal ablation and stamping’s mechanical extrusion force, photo etching completes material dissolution at the molecular level via chemical reactions, delivering stress-free, 100% burr-free finished parts. Since it was derived from PCB photolithography technology in the 1960s, photo etching has become the preferred production solution for high-precision micro-components in high-end manufacturing sectors, widely adopted by electronics, medical devices, aerospace, new energy and precision instrument industries worldwide. This article systematically explains the definition, complete production steps, compatible metal materials, competitive advantages, inherent limitations and real-world application scenarios of photo etching.

The underlying logic of photo etching can be summarized into three core links: pattern masking via photosensitive resist, selective chemical dissolution, and post-process surface finishing. First, digital CAD drawings are made into high-precision photo tool negative films; UV-sensitive photoresist is attached to the flat metal surface, and ultraviolet light cures the reserved areas into an acid-resistant protective mask after alignment exposure. The unprotected bare metal is then sprayed with customized etching solution and dissolved into soluble metal ions through redox reaction, retaining the preset geometric outlines, dense micro-hole arrays and controllable half-depth grooves on the workpiece.

A typical technical feature of photo etching is isotropic wet etching: vertical downward corrosion is accompanied by horizontal lateral undercut (side erosion). Professional engineers will add dimensional compensation on design drawings according to metal thickness to offset the tolerance brought by side etching and ensure finished product dimensional accuracy, which is a standard operation in mass photo etching production lines.

The whole automatic production line adopts closed-loop parameter control, with pre-treatment standards and etchant formulas adjusted based on the passive film characteristics of different metals.

Pre-treatment determines the final yield rate of photo etching. Operators straighten warped metal plates first, then use ultrasonic alkaline cleaning to eliminate rolling oil, fingerprints and surface attachments. For stainless steel, aluminum and titanium with dense inert oxide passive films, weak acid micro-etching is carried out to roughen the surface slightly, enhancing the bonding force between the substrate and photoresist. Multi-stage pure water rinsing and hot air drying follow to completely remove residual acid liquor.

Dry film photoresist hot roller double-sided lamination is the mainstream choice for rigid stainless steel and copper alloy plates, featuring strong acid resistance and stable graphic resolution. For ultra-thin fragile foils below 0.05mm, liquid photoresist roller coating is applied to avoid wrinkling and deformation during pressing. No bubbles or gaps are allowed between the resist and metal surface to prevent etching liquid penetration and pattern damage.

The CAD-designed photo negative film is tightly fixed on the resist-coated plate through vacuum adsorption. UV light penetrates the transparent area of the negative film to polymerize and cure the corresponding photoresist into a protective layer, while the shaded part remains soluble for subsequent development. Symmetrical through-hole components require synchronous double-sided exposure to guarantee upper and lower pattern consistency.

Alkaline developer sprays wash away uncured soft photoresist to expose the metal areas waiting for etching. Full visual inspection removes defects such as broken lines and micro-hole blockage, followed by low-temperature baking curing to strengthen the mask’s anti-corrosion ability against long-time high-temperature etching liquid scouring.

This is the decisive procedure for product quality. Different metals use matched etchants: ferric chloride mixed solution for stainless steel, brass and nickel alloys; phosphoric-nitric acid mixed acid for aluminum alloy; special hydrofluoric-nitric acid mixed acid for titanium alloy with strict safety management requirements. By adjusting the conveyor running speed, manufacturers realize full penetration through-cut or unique partial-depth half etching, a core exclusive capability of photo etching. Constant temperature and balanced double-side spray pressure ensure uniform material removal and reduce surface pitting.

Alkaline stripping agent thoroughly removes all residual protective photoresist. Workpieces pass through multi-tank overflow pure water washing to eliminate chemical residues, avoiding delayed oxidation, rust spots and surface discoloration after processing.

Mandatory passivation treatment is conducted on stainless steel, aluminum and titanium parts to rebuild anti-corrosion passive films. Optional surface finishes include blackening, wire brushing, sandblasting and anti-fingerprint coating. Quality inspection uses 2D optical measuring instruments to test dimensional tolerance and half-etched depth, and checks edge smoothness and flatness for ultra-thin foils. Qualified products are packed with anti-static and moisture-proof materials for delivery.

Photo etching has wide material compatibility for flat thin plates with thickness ranging from 0.01mm ultra-thin foil to 2.0mm sheet:

First, photo etching is zero-stress cold processing. The whole reaction occurs in liquid at room temperature without mechanical force or thermal damage, completely retaining the original elasticity, conductivity and corrosion resistance of metals, perfectly fitting elastic shrapnels and fatigue-sensitive micro-parts. Second, it delivers naturally burr-free smooth edges without secondary deburring or polishing, eliminating the hidden risk of circuit short circuit caused by falling metal debris. Third, one-step integrated half-depth etching can form bending indentations and positioning steps on a single part, which cannot be achieved by stamping, CNC or laser cutting. Fourth, it requires no expensive hard stamping molds, only low-cost photo film, supporting rapid prototyping within 24–48 hours with obvious cost advantages for small batches and frequent design revisions. Fifth, the whole plate is etched simultaneously with excellent batch dimensional consistency, meeting strict traceability standards of medical and automotive industries. In addition, mainstream ferric chloride etching liquid can be filtered, recycled and reused, matching modern green closed-loop production requirements.

Photo etching also has inherent technical constraints: it is only applicable to planar thin metal sheets, unable to process 3D solid blocks and curved surfaces; isotropic wet etching brings inevitable slight undercut, limiting the production of ultra-high aspect ratio deep micro blind holes; special metals like titanium need hazardous mixed acid, demanding standardized wastewater treatment; for ultra-large-volume simple structural parts, progressive stamping has better unit cost competitiveness.

In the electronics and semiconductor industry, photo etched parts include stainless steel EMI shielding cans, copper alloy lead frames, connector spring contacts, heat dissipation grids and wafer carrier fixtures, the largest downstream market for this technology. In medical device manufacturing, medical-grade 316L stainless steel filter meshes, cell culture sieves and titanium micro implant accessories are widely used, with smooth edges preventing tissue scratching and resisting repeated high-temperature sterilization. For aerospace and precision optoelectronic instruments, ultra-thin adjusting shims, hydraulic filter screens, encoder grating discs and optical slits rely on photo etching’s micron-level stability under extreme temperature and vibration environments. New energy industry adopts photo etched lithium battery collector nets and fuel cell flow field plates to satisfy long-term reliability standards for automotive electronics. Besides, industrial filter screens, metal nameplates and hollow decorative panels are also mature application products of photo etching technology.

In short, photo etching (Photochemical Machining/PCM) is a cost-effective, high-precision subtractive metal manufacturing technology integrating photolithography and wet chemical corrosion. Its irreplaceable strengths of stress-free processing, burr-free edges, controllable half etching and flexible digital customization solve many processing bottlenecks of ultra-thin foils and complex planar micro-components that traditional machining cannot overcome efficiently. With the continuous miniaturization and high-reliability upgrading of downstream products, photo etching will maintain steady market growth. Future technical optimization directions focus on reducing undercut ratio, improving surface finish precision and developing low-pollution recyclable etching formulas, continuously providing reliable precision processing solutions for global advanced manufacturing industries.