Wet Chemical Etching Process

Wet chemical etching (commonly shortened to wet etching) is a subtractive manufacturing technology that uses liquidphase chemical etchant to dissolve and remove unwanted material from workpiece surfaces. In metal component production, wet chemical etching is the core procedure of photochemical machining (PCM / photoetching). Different from dry etching which adopts plasma or reactive gas, wet etching relies entirely on liquid chemical reaction to achieve material removal. It is widely applied for fabricating burrfree, stressfree precision thinmetal parts across electronics, automotive, medical device and newenergy industries.

In industrial metal wet etching, ferricchloridebased etchant is the most widely used solution for stainless steel, copper, brass, nickelbased alloys and titanium. Workpiece areas protected by photoresist mask remain intact, while exposed bare metal contacts etchant and dissolves through redox reaction. Wet etching can be divided into immersion wet etching and spray wet etching. Immersion soaking puts panels into static or circulating chemical bath, while spray wet etching pressurizes etchant and sprays solution onto metal surfaces. For highprecision mass production, automatic spray wet chemical etching is the mainstream industrial solution, delivering more uniform etching rate and better dimensional consistency compared with simple immersion mode.

Wet chemical etching shows isotropic etching characteristics. Material dissolves both vertically in depth and horizontally sideways, resulting in unavoidable sideetch (undercut). This lateral undercut effect must be calculated and compensated in advance during phototool artwork design to meet final drawing dimensional tolerances. Isotropic property makes wet etching excellent for thinsheet microhole meshes, gaskets and complex planar profiles, yet brings limitations for ultrahighaspectratio deepwall structures.

StepbyStep Wet Chemical Etching Process Workflow

Step 1: DFM Review and Artwork Compensation

Before wet etching production starts, engineering teams review CAD / DXF drawings. According to target metal material and sheet thickness, engineers calculate isotropic sideetch value. Corresponding compensation is added onto phototool graphic size to offset horizontal undercut caused by wetetch isotropic nature. Minimum aperture, slot width and feasible tolerance are confirmed; optimization suggestions are provided for unreasonable design parameters.

Step 2: Sheet Cutting and Surface PreTreatment

Raw thinmetal sheets are cut into productionready panels. Surface pretreatment largely determines wet etching yield. Oil, fingerprint, oxidation scale and passive film must be fully eliminated:

Alkaline degreasing removes grease and antirust contaminants.

Multistage water rinsing washes alkaline residues away.

Acid activation removes surface oxide and passive layer, ensuring uniform chemical reaction between bare metal and liquid etchant in subsequent wet etching stage.

Rinsing and lowdust drying obtain clean, stainfree metal substrate for lamination. Residual contamination will trigger uneven wet etching, mask lifting and pinhole defects.

Step 3: DryFilm Photoresist Lamination

Lightsensitive dryfilm photoresist is hotlaminated onto single side or double sides of cleaned metal panels under stable temperature and pressure. Doublesided lamination is essential for throughhole parts to realize synchronous doublesided wet chemical etching. Operators eliminate bubbles and wrinkles between resist and metal surface. Bubbles will allow etchant to seep underneath photoresist mask during wet etching, causing pattern damage.

Step 4: UV Exposure for Mask Pattern Transfer

Highprecision phototool films are closely aligned against laminated panels. Controlledintensity UV light cures photoresist in transparent graphic regions to form chemicalresistant protective mask. Unexposed photoresist under opaque areas stays unpolymerized. Doublesided exposure equipment guarantees alignment accuracy for dualsided wetetched components.

Step 5: Developing

Panels travel through dilute sodiumcarbonate developer tank. Uncured photoresist is dissolved and rinsed off, exposing bare metal regions to be removed by wet chemical etching. UVcrosslinked photoresist remains firmly adhered as mask. Parameters including developer concentration, temperature and conveyor speed are strictly controlled. After developing, panels are rinsed, dried and inspected for pattern integrity.

Step 6: Core Wet Chemical Etching (SprayType)

Patterncovered panels enter continuous automatic spray wet etching production line. Liquid etchant with functional additives is pressurized and sprayed onto both panel surfaces. Exposed bare metal continuously dissolves under isotropic wet chemical reaction.

Key process parameters are monitored in realtime: etchant baumé degree, liquid temperature, PH value, spray pressure, solution circulation flow and conveyor speed. Conveyor travelling speed directly controls vertical etching depth and throughcut status. Since wet etching rate is highly sensitive to solution condition, parameter drift will cause uneven etching depth across panel surface. Firstarticle inspection is compulsory; massproduction can only proceed after dimension verification passes.

Note: In immersion wet chemical etching, panels are fully soaked inside circulating etchant bath without spray force. Immersion equipment costs lower, yet suffers slower etching rate, poorer uniformity and higher risk of residue accumulation, mostly used for lowrequirement smallbatch samples.

Step 7: Rinsing and Photoresist Stripping

Once target depth or full throughcut is achieved, panels go through intensive multistage water rinsing to wash off residual liquid etchant thoroughly. Remaining etchant must be eliminated to prevent overetching after parts exit wetetching tank. Afterwards, panels pass through hot alkaline stripping tank to hydrolyse and strip all photoresist protective mask. Finished components stay tabconnected on carrier frame. Final full rinsing removes chemical residues to avoid surface discoloration or corrosion.

Step 8: PostTreatment and Quality Inspection

Available postprocessing includes passivation, deburring, polishing, antirust treatment, color filling and electroplating. Parts can be separated by breaking, punching or laser singulation. Finished panels are measured by 2D vision instrument and metallurgical microscope for dimension, hole consistency and surface defects. Batch inspection reports and material certificates can be supplied for highreliability industries.

Main Advantages of Wet Chemical Etching Process

Burrfree & stressfree: Pure liquid chemical dissolution without mechanical contact, no mechanical stress, no burr, no heataffected zone. Original metal material performance remains unchanged.

Highcomplexity planar geometry: Suitable for largearray microholes, fine meshes, intricate contours and ultrathin foil components which are difficult for mechanical cutting.

Flexible material compatibility: Works for most conductive thin metals: stainless steel, copper, brass, nickel alloy, titanium, Kovar, Invar and more.

Lowcost prototyping & revision: No hard stamping dies required; only phototool film is needed. Design modification only updates artwork, low iteration cost.

Scalable for massproduction: Automatic spray wetetching lines support stable output from smallbatch prototype to highvolume orders.

Limitations of Wet Chemical Etching Process

Isotropic sideetch effect: Horizontal undercut is inherent feature of wet etching, restricting minimum wall thickness and highaspectratio structures.

Thickness limitation: Best performance for material thickness 0.01 mm2.0 mm; efficiency drops sharply for thicker metal plates.

Strict liquidwaste treatment requirement: Wet chemical etching consumes large volume of corrosive liquid etchant, demanding professional wasteliquid treatment for environmental compliance.

Typical Industrial Applications for Wet Chemical Etching

Automotive: horn meshes, precision shims, spring contact plates, sensor metal parts

Medical: 316L stainlesssteel nebulizer plates, sanitary filter meshes, thin surgical accessories

Electronics & semiconductor: encoder discs, EMI shielding gaskets, microstencils, aperture masks

Newenergy: hydrogenenergy flowfield sheets, filter elements, custom thinmetal gaskets

General industry: microporous filter mesh, metal nameplates, precision thinsheet components

Wet Chemical Etching VS Dry Etching

Wet chemical etching: Liquid etchant, isotropic, high throughput, lower unit cost, ideal for thin planar metal parts; sideundercut exists. Mainstream for industrial photochemical metal manufacturing.

Dry etching: Plasma / reactive gas, anisotropic, minimal sideetch, highaspectratio microstructure capability; expensive equipment, low throughput, mainly used for semiconductor wafer processing.

Conclusion

The wet chemical etching process is a mature isotropic subtractive manufacturing method using liquid corrosive solution for material removal. Spraymode wet etching dominates modern highvolume precision metal production. Pretreatment quality, etchant parameter stability and sideetch artwork compensation jointly determine final part quality. Though constrained by isotropic undercut characteristics, wet chemical etching remains a costeffective solution for burrfree complex thinmetal components serving automotive, medical, electronics and newenergy industries.