Photochemical etching, also widely named photochemical machining (PCM) or photoetching, is a noncontact subtractive metal manufacturing technology that combines photolithography and controlled chemical dissolution to fabricate intricate, highprecision metal components. Different from stamping, laser cutting and CNC machining which rely on mechanical force or thermal energy, photochemical etching transfers digital CAD patterns onto metal surface via photosensitive photoresist, then selectively dissolves unprotected metal by etchant solution. This process produces stressfree, burrfree parts without heataffected zones, and becomes a preferred solution for thingauge metal microcomponents across electronics, semiconductor, medical, filtration, aerospace and newenergy industries.

Photochemical etching is compatible with numerous metal materials, including stainless steel, copper, brass, nickel, alloy steel, kovar, 4J42 and other special alloys. Applicable material thickness normally ranges from 0.01 mm to 1.5 mm. General dimensional tolerance follows ±10% of sheet thickness. Under strict process control, minimum feature size can reach 0.03 mm. Besides full throughetching for separate parts, it also supports halfetching to create recessed marks, bend lines, positioning grooves and multilevel structures on one single metal sheet. Since tooling is digital phototool rather than expensive hard metal dies, design modification only needs updating CAD files, which greatly shortens prototype cycle and lowers setup cost for lowtomedium volume production.

The core logic of photochemical etching process can be summarized as: metal surface cleaning → photoresist lamination → UV exposure → developing → chemical etching → resist stripping → posttreatment → quality inspection. Every single procedure directly influences final dimension, edge quality and batch consistency. Tiny defects in pretreatment or imaging phase will be amplified in etching stage and lead to scrap parts. Below is the detailed stepbystep workflow of photochemical etching process with key control notes.

Step 1: Material selection and surface preparation & cleaning. According to customer CAD specifications, confirm metal alloy grade, thickness, temper state and grain condition. Grain orientation shall be considered for highprecision thin foil parts. Raw metal sheets go through multistage cleaning procedures including alkaline degreasing, water overflow rinsing and microetch activation. This step thoroughly removes oil, grease, dust, oxide layer and surface contamination, to guarantee firm adhesion between photoresist and metal substrate. Poor cleaning will cause photoresist peeling, blistering, local underetching or pitting defects in subsequent procedures. Cleaned panels must be fully dried without water stains before entering cleanroom for lamination.

Step 2: Photoresist dryfilm lamination. Inside dustcontrolled cleanroom environment, heatsensitive dryfilm photoresist is hotlaminated onto one or both sides of cleaned metal sheet under stable temperature and pressure. Doubleside lamination is standard for throughetched parts such as filter meshes and metal stencils. The photoresist serves as protective masking layer resisting corrosive etchant. Operators must eliminate all bubbles, wrinkles and tiny gaps between film and metal. Micro gaps will allow etchant liquid to creep sideways and damage fine microholes, narrow slots and delicate patterns.

Step 3: UV exposure with compensated phototool. Preoptimized phototool (photomask) which integrates undercut compensation data is closely aligned against laminated photoresist surface. For doublesided parts, accurate topbottom registration is critical to ensure pattern coincidence on two faces. Highintensity ultraviolet light passes through transparent areas of photomask. Exposed photoresist areas occur crosslinking chemical reaction and get hardened, while regions covered by opaque mask remain soft and soluble. Exposure energy must be precisely calibrated. Overexposure makes photoresist brittle and easy to crack; underexposure results in insufficient polymerization, causing mask swelling or peeling during etching cycle.

Step 4: Developing process. Exposed metal panels are transported through circulating alkaline developer bath. The unexposed, nonpolymerized soft photoresist is dissolved and washed away, exposing bare metal zones that need to be removed by etching. Hardened crosslinked photoresist stays intact and forms complete protective masking pattern. Developer concentration, temperature and conveyor speed require strict monitoring. After developing, visual inspection verifies full pattern opening. Even tiny residual photoresist spots will leave unetched metal islands on finished components, damaging part function and appearance.

Step 5: Core chemical etching. Panels enter closedloop etching machine chamber. Heated etchant solution (commonly ferric chloridebased formula) is uniformly sprayed from upper and lower nozzles onto workpiece surface. Unprotected bare metal gets dissolved by redox chemical reaction, while regions covered by hardened photoresist remain unchanged. Key process parameters including etchant concentration, temperature, spray pressure, circulation flow rate and conveyor speed are calibrated according to metal material type and sheet thickness. Continuous filtration system removes accumulated metal ions inside circulating etchant, preventing ion buildup from slowing etching rate and causing uneven depth across batches. Adjust conveyor speed to realize full throughetch for standalone components or controlleddepth halfetch for recessed features. Lateral undercut is unavoidable during material removal, which is why undercut compensation has been added at phototool design phase in advance.

Step 6: Photoresist stripping and multistage rinsing. Once target etching depth and feature dimension are achieved, sheets move to stripping tank. Alkaline stripping liquid completely strips off remaining hardened photoresist mask. Multilevel overflow water rinsing is compulsory to wash away residual corrosive etchant thoroughly. Residual chemical trapped on metal surface will trigger postdelivery discoloration, spot corrosion and surface staining, so sufficient rinsing is essential for longterm part quality stability.

Step 7: Posttreatment operations. Multiple optional postprocessing can be implemented according to application requirements. For stainless steel parts, passivation treatment rebuilds passive oxide film to restore corrosion resistance. Other common options include pickling, electrolytic polishing, deburring, antifingerprint coating, electroplating, forming and bending. Posttreatment eliminates minor surface discoloration generated during etching process and improves component service performance and appearance quality.

Step 8: Comprehensive quality inspection and packaging. QC technicians adopt optical comparator, digital microscope and dimension measuring equipment to inspect dimensional tolerance, edge verticality, microhole roundness, slot width and overall surface appearance. All finished parts are crosschecked against original engineering drawings. Defects including pitting, underetching, overetching, misregistration and discoloration are screened out. Qualified photochemical etched components are separated from carrier frame, counted and packed for shipment.

Photochemical etching process brings prominent manufacturing advantages. It delivers completely burrfree and stressfree parts, no mechanical deformation even for ultrathin fragile metal foil. Complex outlines, dense microhole arrays and intricate meshes can be manufactured without extra cost. Digital phototool supports fast design revision and rapid prototyping. No heataffected zone preserves original metal material properties. The process suits both smallbatch sampling and massvolume production with excellent repeatability.

Nevertheless, photochemical etching also has practical limitations. It is most economical for thingauge metal, not ideal for thick workpieces above 1.5 mm. Inherent lateral undercut exists, so pattern compensation is mandatory. Different metal alloys need customized etchant formula and parameter tuning. Waste liquid generated from etching procedure must be disposed complying with local environmentalprotection regulations.

Major application sectors cover hightech industries worldwide. Filtration industry manufactures precision filter meshes and microperforated screens. Medical device sector produces surgical auxiliary components and microfluidic parts. Semiconductor and electronics produce EMI shielding sheets, precision metal stencils, thin shims and optical slit components. Aerospace and newenergy industries adopt etched thinwall structural parts and flowfield plates.

To sum up, photochemical etching process is a mature, reliable photochemical machining solution for thingauge metal precision manufacturing. Through strict fullprocess control from cleaning, imaging, etching to posttreatment, manufacturers can produce intricate burrfree microcomponents that are difficult or costly to achieve via traditional mechanical processing methods.