Laser etching is a broad term covering various marking and  shallow engraving processes. It is used on products as diverse as auto  parts, medical devices, wine barrels, microelectronic components, and  tombstones.

Laser etching is a method for producing visible marks or patterns  on a wide variety of materials. In fact, the exact definition of what  constitutes “etching” (as opposed to marking or engraving) varies by  material and application.

In general,  laser etching is distinct from marking; it involves  altering the surface profile of the part, rather than simply producing a  change in surface color or texture. But this change in profile, which  can be either a raised or sunken area, is generally much shallower than  those associated with laser engraving.

Laser etching is implemented in the same way as many other marking,  engraving, and cutting processes. In fact, it’s not at all unusual for a  single laser tool to perform all these functions.

To create the desired pattern, the laser beam scans across the part  surface while it is being modulated (having its power varied). One way  to create this motion is with a galvanometer scanning system. In this  case, the beam motion is achieved with moving mirrors. This method is  often used with small parts because of its high speed. Also, this  technique lends itself to etching curved parts (often in combination  with rotary movement of the part).

Alternately, the beam delivery optics (or even the part itself) can  be moved using linear motion stages to trace out the mark pattern.  Larger parts, like signs and monuments, are virtually always etched  using this approach.

A material difference

Almost any type of material can be laser etched. This includes  metals, plastics, glass and ceramics, natural stone, and  semiconductors.

Laser etching of metal parts is performed in many industries,  including automotive, aerospace, medical products, oil and gas, and  more. It can be applied to nearly any metal, including aluminum, steel,  brass, copper, and titanium.

Laser etching of metals usually involves heating the material until  it melts and slightly expands. After this brief laser heating cycle is  performed, the material cools almost immediately. It resolidifies into a  raised area which has a rougher texture than previously.

For metals, laser etching usually changes the surface height by less  than about 25 µm. In contrast, laser engraving is often ten times that  deep. Because engraving deeper marks requires removing much more  material, laser etching can typically be performed much quicker.

Another advantage of laser etching is that the marks it produces can  appear dark, light, or even a shade of gray. Laser engraving typically  only makes dark marks. However, the shallower etched marks aren’t as  durable and abrasion resistant as engraved marks.

Glass is laser etched for both decorative and commercial purposes.  Drinking glasses, mugs, bottles, award plaques, mirrors, and more can be  etched with text, designs and other complex patterns, even including  images. In the industrial sector, many products that are supplied in  glass containers, such as beverages or pharmaceuticals, are etched with  information like lot numbers and expiration dates. Similarly, glass  substrates used in microelectronics and display fabrication can be  etched with serial numbers and tracking codes.

The laser etched area on glass appears “frosted” – that is  translucent, but not transparent. This is accomplished by removing a  very small amount of material, typically less than 25 µm. And  importantly, the etching process creates a much rougher surface  texture.

Laser etching is advantageous over other mechanical and chemical  methods because it is fast, clean, and easily adapted for use on curved  surfaces (which are commonplace on wine glasses, bottles, and the  like).

Laser etching of natural stone – such as granite or marble – is  widely used for tombstones, plaques, and architectural purposes. Like  glass etching, it involves removing a very small layer of material and  altering the surface texture.

Laser etching is almost always used to produce a light-colored mark  on a dark stone surface. The laser etched pattern consists of numerous  small dots placed close together, in the same way that photos are  reproduced in newspapers. This allows virtually any pattern to be  etched, and even makes grayscale marks possible. So, photos, drawings,  and other designs can readily be etched, in addition to just text.

Laser etching on stone typically provides better mark visibility than  sandblasting or mechanical engraving. It’s also much faster than these  other methods.

Polymers are laser marked in an extremely broad range of commercial,  medical, and consumer products, as well as for signage and novelty  items. Because of the tremendous diversity of materials and processes  involved, it’s more difficult to define exactly what constitutes laser  etching of polymers, and how this process is distinct from marking or  engraving. The commonly used technique of “foaming” – which delivers a  light mark on a dark plastic, could rightly be considered a form of  etching, since it produces only small amount of surface relief (less  than 50 µm).

Because laser etching allows high contrast marks to be produced in  polymers without introducing a significant amount of heat into the part,  it’s also very popular in semiconductor fabrication and  microelectronics production. For example, flip-chips and other  semiconductor packaging types can be marked without damaging the  circuitry they contain.

Laser etching of semiconductors themselves is used throughout  microelectronics fabrication. This is because the shallow mark depth –  often 10 µm or less – produces a high contrast mark which doesn’t cause  any damage to surrounding or underlying circuitry. Laser etching is  particularly useful for marking serial numbers and other identifiers on  the backside of wafers. It’s also used on thin mold caps of packaged  devices.