What Is Industrial Laser Ablation? | Laserax

Laser ablation is the physical reaction that occurs when a laser removes material through sublimation—going from solid to gas almost instantly. It is used to selectively remove layers of material. Laser ablation most commonly refers to laser cleaning, but it is also used for marking, texturing, and cutting.

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Here is how it is used more specifically:

• Laser cleaning removes contaminants, oxides, and coatings without removing material from the substrate.
• Laser marking creates permanent marks like 2D codes and logos by etching into the surface.
• Laser texturing modifies a part’s roughness by digging patterns into the surface.
• Laser cutting cuts through a surface by removing layers of material.

Laser ablation was discovered in when Gordon Gould proposed the Q-switching method to produce pulsed laser beams. The key characteristic of pulsed lasers is that they can reach the high peak power typically required to remove material.

Table of Content

• How Does the Process Work?
• What Are the Ablation Parameters?
• What Are the Industrial Applications?
• What Are the Benefits and Drawbacks?

How Does the Laser Ablation Process Work?

In today’s manufacturing, CO2 and fiber laser systems are widely used for laser ablation. Although these lasers are used with different materials, they achieve laser ablation in the same way.

Here’s how:

All materials have an ablation threshold. It is a property that is unique to each material. When the intensity generated by a laser is above the material’s ablation threshold, the material is ablated. If the intensity is below the ablation threshold, nothing happens, except a slight increase in temperature.

Materials expelled from the surface are vaporized into fumes. Although these fumes are minimal, a fume extraction system is usually required near the laser for safety and to avoid accumulation and obstruction of the laser beam.

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What Are the Ablation Parameters?

Laser parameters are key to mastering laser ablation. By adjusting them, experts can optimize the laser process for different applications. You will find the most important laser parameters to consider below. Take note that for laser cutting, different parameters need to be adjusted.

Wavelength

When laser light hits a surface, it is partly reflected, partly absorbed. The absorbed laser energy is converted into heat which ablates the material.

Due to their different laser source, each type of laser emits a different wavelength. The laser that emits the wavelength that is the least reflected by the material should be favored. Fiber lasers, for example, work more efficiently with metals whereas CO2 lasers with plastics and organic materials.

Beam Diameter

The larger the diameter of the focused beam, the more dispersed the laser energy—up to a point where laser ablation is impossible. By reducing the beam diameter (also known as the spot size), the same amount of energy can be transferred to a smaller area. This results in a higher energy density and hence more efficient ablation.

Beam Quality

The beam quality (also known as M2) measures how well a laser beam can be focused. The closer the laser beam tends towards M2= 1, the more efficient the laser will be for ablation.

Beams with a high M2 factor are unfocused and fail to generate the high energy required for ablation. However, they are often ideal for laser welding.

Focal Distance

Laser Power

Pulse Length

Pulse Repetition Rate

The pulse repetition rate (also known as pulse frequency) is the number of pulses per second. For example, the default setting for our 100W pulsed lasers is 100,000 pulses per second, each containing 1 mJ of energy. Similarly, our 50W lasers have a nominal repetition rate of 50,000 pulses per second.

Increasing the number of pulses per second reduces the amount of energy per pulse. Our 50W laser could generate 100,000 pulses per second instead of 50,000, but each pulse would contain 0.5 mJ instead of 1.

If the energy per pulse is too low, ablating materials will be impossible.

Scanning Speed

Pulse Spacing

The pulse spacing is a direct result of the scanning speed. If laser pulses are closer to one another, more energy is sent to the same area. This parameter is used to ablate materials in different ways. For instance, laser engraving requires a very tight pulse spacing to dig deep into materials.

Number of Passes

A single laser pass is usually enough for a material to be ablated. This is the case when etching permanent marks or removing paint from a surface.

Sometimes, several laser passes deliver better results as it avoids overheating an area, such as when engraving deep marks into a material or when removing thick mill scale layers from a surface.

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What Are the Industrial Applications?

Laser Cleaning

It is possible to remove thin films of materials like rust, oxide and paint from surfaces with laser cleaning by breaking the chemical bond that holds them together.

As explained earlier, every material has an ablation threshold. Since the ablation threshold of rust, paint and oxide is lower than that of metals, the laser parameter can be set so that the beam’s intensity ablates them without impacting the base material.

The vaporization of contaminants and coatings from metals usually requires a high-power laser (100W and more). You can watch the following videos for examples of laser cleaning applications.

Laser Paint Removal

Laser Oxide Removal

Laser Rust Removal

Laser Marking

Laser marking creates permanent markings directly onto part surfaces. It is often used to implement part traceability by creating identifiers such as data matrix codes, QR codes, alphanumerical characters and serial numbers. It is also used to identify products with logos. 

Laser marking can be performed on most metals, several plastics as well as organic materials.

The most common laser marking processes, laser etching and laser engraving, use laser ablation at different intensities. For typical barcodes, ablation is performed within 100 microns of the surface, but deep engraving can also be used for more resistant codes.

Not all laser marking processes use laser ablation. Laser annealing, for instance, does not ablate materials; it marks metals like stainless steel by inducing a color change under the surface, which preserves the material’s corrosion resistance.

Laser Texturing

Laser ablation can be used to texture surfaces before subsequent manufacturing steps. By modifying their roughness, surfaces can be prepared for adhesive bonding, painting, thermal spray coating, and other processes.

In the following picture, you can see a textured and non-textured surface up close.

What Are the Benefits and Drawbacks?

Like all technologies, laser ablation has advantages and disadvantages. We’ve summed them up here to help you understand if it is right for you, whether you need it for laser cleaning, marking or texturing.

• Non-contact process that minimizes wear & tear for more consistent results
• Functions without consumables to replace technologies that use chemicals, abrasive media, and other types of consumables
• Reduces maintenance & operative costs
• Helps manufacturers reduce their environmental footprint and meet environmental protection regulations
• Easy to automate in production lines to reduce manual labor

• When enclosed properly, laser technology is completely safe. But to achieve this, you must follow laser safety standards. Ideally, laser ablation is performed in a Class-1 laser safety enclosure.
• Material processing could release fumes and particles into the air. A fume extraction system is almost always needed near the laser system.
• Laser technology typically requires a higher initial investment than its alternatives.

What Industrial Laser Experts Can Do for You

If you’re looking at integrating laser ablation for an industrial application, our experts are there for you. They can:

• Offer you turnkey solutions, including laser marking and laser cleaning machines
• Run tests to optimize the laser parameters for your application
• Help you manage laser safety and fumes properly
• Answer all your questions

Process and laser optimization are key for high throughput and precise clean scribes

Arecent article presented an overview of how lasers can play a key role in the development and production of solar devices, delivering twin benefits of lower fabrication costs and superior performance (see ILS, August , p. 24). Laser scribing is rapidly emerging as one of the most significant of all these processes as it is critically enabling high-volume production of next-generation thin-film devices, surpassing mechanical scribing methods in quality, speed, and reliability.

These thin-film solar cells are important because they lend themselves to streamlined, high-volume manufacturing and greatly reduced silicon consumption. This results in dramatically lower fabrication costs per unit of power output compared to traditional silicon-wafer-based solar cells.

Fabrication steps

As implied by their name, “thin-film” devices typically consist of multiple thin layers of material deposited on sheet glass. While other formats and materials are at early stages of development, initial volume production of thin-film solar cells is being dominated by devices based on amorphous silicon (a-Si) in a so-called single-junction configuration (see Fig. 1). Multijunction a-Si variants such as the tandem ‘micromorph’ structure are expected to follow soon. But the laser-scribing processes described here are applicable to all other thin-film systems under development, including those based on CdTe (cadmium telluride) and cigs (copper indium gallium selenide).

Each panel starts off as a sheet of glass with a typical thickness of 3 mm. This is called a glass superstrate, because sunlight will enter through this support glass. The first step is to deposit a continuous, uniform layer of tco (transparent conductive oxide) with a typical thickness of a few hundred nanometers, which will form the front electrodes. This is followed by a scribe process called P1, which scribes through the entire layer thickness. The next step is vapor deposition of p- and n-type silicon with a total thickness of 2-3 µm, again followed by a scribing step, called P2, which completely cuts through the silicon layer. The final deposition is the thin (submicron) metal (Al or Mo) layer that forms the rear electrodes. These are patterned using a third scribe process, called P3. The panel is then sealed with a rear surface glass lamination.

Scribing requirements

To attain economic viability, thin-film devices must be produced in high volumes for low unit costs. Fast process throughput (short takt times) is critical to minimizing scribing costs. But high-quality scribes with very low defect counts are also necessary to deliver a high yield of final product with the highest possible electrical-conversion efficiency.

As with many other laser micromachining applications, both resolution and precision are important. Specifically, the area between P1 and P3 is a nonactive (that is, wasted or ‘dead’) area. Scribe lines are currently on the order of several tens of microns in width, with an offset separation between P1 and P3 of tens to hundreds of microns. But given that each cell has a total width of less than 10 mm, together with the importance of maximizing the inherently low conversion efficiency (6%-10% versus 15%-20% for bulk Si devices), it is vital to further minimize this already small scribe area. That means narrow scribes that are placed as close to each other as possible, with minimum offset. (Next-generation product is projected to use line widths in the 25-30-µm range.) The use of more closely spaced scribes requires very straight cuts that don’t wander out of alignment. Scribe narrowing also must be accomplished without increasing scribe defects.

Cut quality in terms of edge roughness and layer peeling is another important consideration, because solar conversion efficiency is substantially reduced by microcracks, and other types of surface and subsurface thermal damage. Therefore, it is vital to create scribes with a minimal haz (heat affect zone), smooth edges, and no recast debris.

However, this application is somewhat unique in that it must combine this precision, resolution, and edge quality with very high speed. Panels are produced in a continuous-flow production line. The typical amount of time a panel spends in a specific process step is widely considered to be in the range of only a few tens of seconds for small panels and a few minutes for larger sized panels. Yet each panel requires literally hundreds of meters of scribing. Even in workstations that utilize several lasers, scribe rates have to be in the range of 2 m/s, and each scribe has to be accomplished in a single pass. Moreover, active depth control is not realistic-each laser scribe depth must be naturally limited by material selectivity.

This does not represent a significant obstacle for the P1 scribe, which only needs to remove a few hundred nanometers of tco. Although quite demanding on certain laser parameters, it can be performed using conventional techniques with the near-infrared (1.06 µm) output of a Q‑switched dpss (diode-pumped solid-state) laser. But the P2 and P3 scribes must remove a few microns of thickness of silicon, plus the overlaying metal film in the case of P3. Conventional (thermal) materials processing cannot deliver the combination of single-pass speed, as well as cut quality and spatial resolution. Photoablation with a fast-pulsed UV laser is not an option, as this application would not sustain the cost of the laser and, more important, such a laser would provide no material selectivity and, hence, depth control: it would ablate all the materials and could damage the glass.

The solution is a laser lift-off process that has been developed in different forms for other applications. Instead of melting, vaporizing, or atomizing all the target material, this lift-off process vaporizes a small amount of material at the film interface, removing the overlaying layers entirely in a microexplosive effect. This is the principal reason that these scribes are performed through the glass (see Fig. 3). Specifically, P2 and P3 scribes are accomplished using a fast-pulsed green (532 nm) dpss laser.

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