What is Laser Etching?
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.
Lasers for etching
Because of the wide range of materials involved and the diversity of the requirements, many different types of lasers are used for etching. Typical examples include:
The near infrared output of fiber lasers is well-matched to the absorption characteristics of most metals, generally making them the first choice for etching these materials. They can also etch ceramics and some polymer materials. Fiber lasers for etching deliver the same benefits as in other applications. These include low cost of ownership, high reliability, long lifetime, excellent beam quality, and flexibility of implementation.
CO2 lasers output in the far infrared, which is well absorbed by virtually all organic materials. This makes them ideal for etching materials such as wood and most polymers. CO2 lasers are also universally used for etching natural stone.
Diode-pumped solid-state lasers can deliver high power output in the green or ultraviolet and have excellent beam quality. This makes them a desirable source for two specific types of etching applications. The first is with materials that simply don’t absorb well at longer wavelengths. This is true of some polymer materials.
The second class of applications are those involving thin or heat sensitive materials. The typically higher absorption of most materials at shorter wavelengths (especially the UV) means that the laser light is completely absorbed over a relatively shallow depth. The result is less heating of the surrounding area. Because of this, DPSS laser etching is used throughout semiconductor fabrication and packaging, other electronics component manufacturing, medical products, and displays.
Diode lasers are available at wavelengths from the blue through the near infrared, making them capable of etching a variety of metals and non-metals. Their unique combination of beam quality and cost characteristics makes them mostly suitable for inexpensive etching systems primarily directed at small job shops, plaque and award makers, and hobbyists.
Coherent laser etching products
We also provide etching sub-systems. In particular, our PowerLine Series combine a laser with high-performance scanning and beam delivery optics, drive electronics, and powerful control software. This yields a fast, flexible, and accurate etching, marking, and engraving platform. PowerLine Series products can be supplied with nearly any type of laser source, making them ideal for system builders and production line integration in a wide range of applications.
Finally, Coherent has an extensive range of complete tools for laser etching. These integrate a laser engine into an enclosure, provide a user interface, and can incorporate a range of other capabilities including part handling, vision, connectivity options, process monitoring, and more. They can reduce even complex laser etching tasks to nothing more than pressing a button.