Laser Etching
Key Takeaways
- Etching affects only the upper surface layers, typically a few microns deep.
- It sits between marking and engraving — deeper than a colour change, shallower than material removal.
- Laser choice follows the material: CO2 for polymers, fiber for metals and plastics, UV for high resolution.
- Fume extraction is required, since surface melting and vaporisation release byproducts.
Laser Etching
Laser etching is a shallow surface process that melts and slightly displaces the top layer of a polymer, altering its texture and reflectivity to create a visible mark, typically to a depth under 0.025 mm. It sits between surface marking, which removes nothing, and engraving, which cuts a measurable recess.
The contrast in an etched mark comes largely from a change in surface finish rather than a change in colour. A glossy moulded surface, locally melted and resolidified, scatters light diffusely and reads as a lighter, matte or frosted area against the surrounding gloss. On transparent polymers the same effect produces a translucent, frosted appearance.
How It Differs in Practice
| Etching | Engraving | |
|---|---|---|
| Depth | Under ~0.025 mm | 0.05–0.5 mm and beyond |
| Dominant mechanism | Surface melting and micro-displacement | Vaporisation and removal |
| Speed | Fast — usually a single pass | Slow — multiple passes |
| Heat input | Low | High |
| Abrasion resistance | Moderate | High |
Where It Suits Plastics
- Transparent and clear polymers — acrylic, polycarbonate and clear PET, where a frosted mark is legible without any colourant or additive. This is the classic application.
- Anti-glare and tactile surface features, where a matte region is functional rather than decorative.
- Decorative and branding work on gloss-moulded consumer parts.
- Heat-sensitive components where the low energy input of a single shallow pass avoids the distortion that engraving would cause.
Its limitation follows directly from its shallowness: an etched mark can be polished, abraded or worn away more readily than an engraved one. For parts facing sustained abrasion, chemical attack or aggressive cleaning cycles, engraving or an additive-driven carbonized mark will outlast it.
Getting a Clean Etch
Because the process operates in a narrow band just above the melt threshold, it is more parameter-sensitive than either marking or engraving. Slightly too much energy tips it into engraving with the associated burr and haze; slightly too little produces an inconsistent, patchy mark. Practical guidance:
- Start with low power and high marking speed, then reduce speed incrementally rather than raising power.
- Use a high repetition rate so that pulses overlap and produce a uniform matte field rather than discrete pits.
- On transparent parts, confirm that the beam is focused at the intended surface — it is easy to focus through the material onto the far face.
- Watch for stress crazing on polycarbonate and acrylic, which can appear hours after processing rather than immediately.
For heat-sensitive and optically demanding work, a UV vanadate laser produces a finer, cleaner etched appearance than an infrared source because the interaction is largely photochemical — see cold laser marking.
Parameters That Control the Result
Etching lives in a narrow band just above the melt threshold, so the parameter set is
less forgiving than either marking or engraving. These are the levers, and the direction
each one pushes the result:
| Parameter | What it controls | Practical direction |
|---|---|---|
| Average power | Energy delivered per unit area | The blunt lever. Raise it last, not first — excess power tips etching into engraving and brings burr and haze with it. |
| Marking speed | Dwell time per spot | The preferred lever. Reducing speed deepens and whitens the etch far more controllably than adding power. |
| Pulse repetition rate | Spot overlap along a vector | High rates merge pulses into a uniform matte field. Low rates leave discrete pits that read as a dotted line. |
| Pulse duration | Peak power and heat diffusion | Shorter pulses concentrate energy before heat spreads, giving a crisper edge on thermally sensitive polymers. |
| Hatch spacing | Overlap between adjacent fill lines | Too wide leaves visible striping; too tight double-heats the surface and yellows it. Start near one spot diameter. |
| Defocus | Spot size at the surface | A deliberate small defocus enlarges the spot and softens the etch, which can even out a mottled field. |
| Number of passes | Cumulative depth | Two light passes usually give a more even matte than one heavy pass, and less bulk heating of the part. |
Troubleshooting Etched Marks on Polymers
| Symptom | Likely cause | Correction |
|---|---|---|
| Patchy, inconsistent whiteness | Operating at or below the melt threshold; energy varies across the field | Reduce speed in small steps before touching power. Check field flatness and clean the focusing optic. |
| Yellow or brown halo around the mark | Thermal degradation — the process has crossed from melting into carbonization | Cut power, raise speed, or split into several lighter passes. Consider a shorter wavelength source. |
| Raised burr at the mark edge | Too much energy; displaced melt is piling at the perimeter | Back off power. If a recess is genuinely wanted, specify engraving and accept its cycle time. |
| Visible line striping in filled areas | Hatch spacing wider than the effective spot | Tighten the hatch, or cross-hatch at 90° on a second pass. |
| Mark appears on the wrong surface of a clear part | Beam focused through the material onto the far face | Re-establish focus against the near surface, using a focus-finder rather than judging by eye. |
| Fine cracks appearing hours or days later | Stress crazing from residual moulding stress plus local thermal shock | Anneal or dry the mouldings before marking; reduce energy; avoid marking across a gate, weld line or other high-stress region. |
| Dull grey rather than bright white on a clear part | Soot redeposition from inadequate extraction | Improve fume extraction at the work point and clean the surface after processing. |
Specifying and Verifying an Etched Mark
Because an etched mark is a change in surface texture rather than colour, judging it by
eye under shop lighting is unreliable — the same mark reads bright under diffuse
light and nearly invisible under a directional source. Three measurements make the
specification objective:
- Depth. Stylus profilometry or confocal microscopy against a stated
maximum. Holding depth under roughly 0.025 mm is what keeps the process within
etching and out of engraving, and it matters on thin-walled parts where the mark
encroaches on the structural wall. - Contrast. Measure it. A spectrophotometer reading of L* inside and
outside the mark, against a stated minimum ΔL*, survives an audit; a judgement that
it looks good does not. Where the mark carries a code, grade it to ISO/IEC 15415 for
two-dimensional symbols or ISO/IEC 15416 for linear barcodes, and put the acceptance
grade in the control plan. - Durability. Etched marks are shallower than engraved ones and fail an
abrasion test sooner. Qualify against the actual service condition — a Taber
abrasion cycle, a solvent-rub schedule, or the specific autoclave, gamma or ethylene oxide
exposure the part will see.
Fix the lighting geometry in the inspection specification as well as the acceptance
numbers. A vision system that grades an etched code well at inspection and fails it on the
line is nearly always seeing a different angle of illumination, not a different mark.
Related Terms and Reading
- Laser marking clear and transparent plastics
- Acrylic laser marking
- Laser engraving
- Plastics laser marking solutions
Applying this in production
The Sabreen Group provides independent engineering support for laser etching parameter development for transparent and gloss-moulded plastics. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What is laser etching?
A marking technique that creates shallow, visible marks by controlled melting and vaporisation of the surface. It is non-contact and precise, typically producing marks a few microns deep for permanent text, logos and codes.
How is etching different from laser engraving?
Depth and material removal. Engraving removes material more deeply to create recessed features, while etching only affects the upper surface layers. Laser marking is shallower still, often producing a colour change or surface reaction with no material removal at all.
Which laser type suits which material?
CO2 at 10.6 μm for polymers, wood, glass and some ceramics, which absorb it strongly. Fiber at 1.06 μm for metals and plastics, offering high precision. UV at 355 nm where high resolution and minimal thermal impact are needed.
What parameters control etching quality?
Laser power controls the degree of surface melting and mark visibility. Pulse duration affects thermal damage and detail, with shorter pulses cleaner. Scan speed trades heat buildup against contrast. Focus position determines energy concentration at the surface.
What material properties affect the result?
Melting point, absorption at the laser wavelength, and thermal conductivity. Heat management matters to avoid distortion or discoloration, and adequate ventilation and fume extraction are needed to handle the byproducts generated.
How deep is a laser-etched mark, and how is that measured?
Typically under 0.025 mm — deep enough to change the surface texture, shallow enough that it is not a machined recess. Confirm it with stylus profilometry or confocal microscopy rather than by feel, particularly on thin-walled parts where mark depth eats into the structural wall thickness.
Does laser etching weaken the part?
Rarely on its own, because the affected depth is small. The risk is indirect: etching across a gate, weld line or other high residual stress region can nucleate crazing in polycarbonate and acrylic, sometimes hours after processing rather than immediately. Keep marks away from known stress concentrations, and anneal or dry mouldings beforehand if crazing appears.
Will an etched mark survive autoclaving and chemical cleaning?
Usually yes, since the contrast is a change in the polymer surface rather than an applied layer. But it is shallower than an engraved mark and therefore closer to being polished away by repeated aggressive cleaning. Qualify against the real cycle — the actual sterilisation method, the actual cleaning chemistry and the actual number of cycles — rather than assuming permanence.
