Detailed introduction to the different processing methods of laser micromachining technology

The development of pulsed laser technology has made it possible to use micromachining on tiny devices, such as medical equipment, with minimal damage to surrounding materials. With rapid scientific advances in the field of lasers, laser micromachining expertise is essential.

Leiser Laser specializes in complex processes utilizing infrared and ultraviolet lasers. Infrared lasers focus a beam onto the surface of a material, which then converts it into heat and melts the material. Ultraviolet lasers operate using ablation, instantly removing material by directly breaking bonds. This process instantly vaporizes the material with minimal thermal effects. High-precision micromachining requires precise coordination. Both the laser pulse sequence and the linear stage must be synchronized to ensure precise control of the target.

Laser micromachining is the use of lasers to cut, drill, weld, or otherwise modify materials to achieve features in the single or double-digit micron range. Laser processing can be accomplished in three ways: direct write, mask projection, and interferometry.

Pulse vs. Continuous Wave Mode

An important part of optical micromachining is the transfer of heat to the substrate area adjacent to the micromachining material. Lasers can be operated in either pulsed mode or continuous wave mode. In continuous wave mode, the laser output is essentially constant over time.

In pulsed mode, the laser output is concentrated in small pulses. Pulsed mode laser devices provide pulses of sufficient energy and small pulse duration for micromachining of a given material. Small pulse durations minimize heat flow to the surrounding material. The length of laser pulses can vary from milliseconds to femtoseconds.

Peak power is related to the duration of the laser pulse, so pulsed lasers can achieve much higher peaks than continuous waves.

Laser processing primarily involves interactions that result in ablation of the substrate material. The energy transfer that occurs depends on the material and laser characteristics. Laser characteristics that are influencing factors include peak power, pulse width, and emission wavelength. The material consideration is whether it can absorb the laser energy through thermal and/or photochemical processes.

Why is pulse width important?

Laser cutting is clean and precise. The need to make smaller, faster, lighter, and lower cost devices requires lasers to meet the challenge. Pulsed lasers are used for precision micromachining of a wide variety of materials. The ability to generate different pulse widths is key to precision, throughput, quality and cost-effectiveness.

Nanosecond lasers have higher material removal rates and therefore higher throughput than picosecond and femtosecond lasers using the same average power.

Picosecond and femtosecond lasers melt material to remove it through a process of evaporation and expulsion of the molten material. This melting affects the precision and quality of the process because the removed material adheres to the edges and re-solidifies.

Nanos, Picos, Femtoseconds (Power vs. Precision vs. Price)

In many cases, the purpose of laser processing is to selectively remove material. Laser technology allows us to focus a lot of energy into a small area. This is what leads us to precision machining. When removing material, we must first exceed a material threshold. Each pulse of the laser must overcome this threshold. Advances in diode technology have allowed lasers to reach such energy levels with shorter pulses. These can be loosely divided into groups named nanosecond, picosecond, and femtosecond lasers. These names represent the units used to measure the pulse period.

Why is there such a benefit?

There are several reasons. One of the main issues is that with longer pulses, the laser spends more time below threshold. Thus adding more energy without doing any removal work. This excess energy can change the state of the material. This could be grain structure, physical state (solid or liquid), shape, flatness, and more. These changes can cause differences in reflectivity and absorptivity that can greatly affect the laser process.

As the cycles decrease, the frequency increases. This means there are more pulses at this high energy level. This generally results in improved quality when cutting, but it does mean a relatively higher cost due to advanced technology.

Laser Ablation

Laser processing primarily involves interactions that result in ablation of substrate material. The energy transfer that occurs depends on the material and laser characteristics. Laser characteristics that are influencing factors include peak power, pulse width, and emission wavelength. A material consideration is whether it can absorb the laser energy through thermal and/or photochemical processes.

In thermal ablation, absorption of the laser energy results in rapid heating. This temperature increase causes the material to melt and/or vaporize. Thermal ablation can result in large heat-affected zones, which are commonly observed with long wavelength and continuous wave lasers.

When the laser photon energy is greater than the bond energy of the substrate material, photochemical processes are observed. This occurs when the substrate material evaporates due to bond dissociation caused by photon absorption.

The laser ablation process is more efficient if the substrate material is able to absorb more of the laser energy. Materials microprocessed with shorter (femtosecond) laser pulses show less thermal effects than those processed with longer pulse lasers.

Why Choose a LASER Laser?

Lasers are effective because they are versatile and accurate, which allows our laser systems to achieve unprecedented precision and clean cuts. Pulse widths are also important because they affect throughput and quality. Our lasers are capable of delivering speeds up to hundreds of features per second. Before designing a tool, we conduct research to ensure the best laser energy density is achieved. We are able to determine the ideal speed for each material and design while reducing carbon redeposition. Our unique laser tool designs are unique to each material to ensure cleanliness and accuracy of every cut.