laser drilling Archive - Pulsar Photonics

What is Laser Drilling?

Joel Hafner — Tue, 01 Jul 2025 09:26:54 +0000

What is Laser Drilling?

Overview of Laser Drilling Methods & Guide for the Application of Laser Drilling

Dr. Stephan Eifel | 21. December 2023 ᛫ 10 Min.

Laser drilling has established itself as an important tool in the world of modern manufacturing methods. The process, which stands out with its high precision, large bandwidth of processable materials and great efficiency, has revolutionized a wide range of application areas such as the manufacturing of electronics (circuit boards), filter technology (microsieves) or the automotive field (injection nozzles).

Despite the large range of laser drilling as a method, many of our customers are facing a challenge in their product development: it is often difficult to determine, whether or not laser drilling is suitable for a specific application area or component. This pertains to both the general feasability as well as the economic viability of the method. The decision-making process is further complicated by the large number of applicable laser drilling methods and laser beam sources.

As experts with many years of experience in the field of laser drilling, in this article we provide you with a comprehensive overview of the prevalent laser drilling methods. The advantages of each method as well as typical achievable specifications will be listed. The goal is to establish an initial orientation guide to enable you do decide, whether or not the method of laser drilling is generally suitable for a given application and if so, which specific laser drilling method should ideally be utilized.

Application video on laser micro drilling

Basics of Laser Drilling

The principle of laser drilling is based on the targeted removal of material from a workpiece with a defined thickness through the use of laser radiation. Typically, a cylindrical or conical volume is removed from the workpiece, creating a borehole with an entry and an exit. The removal of material is achieved through the exposure to laser radiation. The laser radiation is focused on the workpiece and absorbed therein. Through the absorption and a high local heating, a phase change is created in the material, leading to the creation of a melt and a material vapor. The material vapor creates high pressure, thereby transporting the molten material out of the borehole. Thus, with increasing irradiation time, a borehole is created within the workpiece.

How is the quality of a laser borehole specified?

A laser drilled borehole comprises a number of attributes, which can be characterized by geometrically measurable metrics:

Borehole diameter and circularity
A borehole consists of an entry and an exit, the terminology is analogous to the entry and exit sides of the laser beam. For the typically circular boreholes, these diameters can easily be determined. Because the diameters D between laser entry and exit can differ, entry and exit diameters D_in und D_out are defined.
The shape of circular boreholes may deviate from the perfect circular shape, for example due to differences in the beam profile from the ideal form or due to the occurence of polarization effects. Thus, a borehole circularity is defined as a measure of form tolerance: circularity = (D_max-D_min) / 2, wherein D_max is the maximum diameter and D_min is the minimum diameter of the borehole.
Taper α
Depending on the drilling method, the walls of the borehole may not be perfectly perpendicular to the entry plane. They may have a slight taper, typically in the range of 80-90°. Due to the deviance of the wall angle from the vertical, the exit diameter is smaller than the entrance diameter.
Aspecr ratio A=D_in:t
The aspect ratio of a borehole is defined by the ratio of its entry diameter D_in and the material thickness t (depth of the borehole). The various laser drilling methods mainly differ in this metric. The aspect ratio of each drilling method is limited by the taper that occurs during drilling. For tapers α < 90°, the sidewalls of the borehole meet at a certain depth. This geometrical effect leads to an aborted drilling process and thus to a limitation in the achievable aspect ratio using percussion drilling. The typical aspect ratios of 1:3-1:5 for percussion drilling correspond to sidewall angles of α = 80-85°.

Synchroton capture of USP percussion drilling in metal (video still, borehole entry on the right, cross section). The maximum aspect ratio is limited to ca. 1:5 by the sidewall angle. (Source: Fraunhofer ILT, Aachen)
Tolerances
When producing a large number of holes, the average hole diameter and the variance of the hole diameters are particularly relevant. The drilling tolerances specify the achievable deviances from a target diameter.
Bulges
Due to the molten materical exiting from the borehole during the laser process, adhesions may occur on either side of the borehole. After the drilling process, these adhesions are visible as bulges. Typically a maximum bulging height is defined, which is determined by the distance between the unprocessed workpiece surface and the highest bulge around the borehole.
Heat-affected zone (HAZ)
Due to the heat input into the workpiece during laser drilling, a change in the structural conditions of the workpiece can occur in the region of the borehole walls. In metals, the heat-affected zone often shows itself through a discoloration around the borehole geometry (tempering color).

The achievable borehole qualities and drilling rates depend chiefly on the drilling method and laser beam source which are utilized. Hence, these are explained further in the following chapters.

Which Lasers are Applied in Laser Drilling?

Depending on use case and method, various laser beam sources can be applied in laser drilling. They mainly differ in the following attributes:

Pulse length (temporal length of a single laser pulse)
During laser drilling, unpulsed (so-called continuous wave lasers) and pulsed laser beam sources are applied. The pulse duration has an important impact on the distrubution of the laser energy introduced to the material volume and notably determines the ratio of molten material to material vapor and (for very short pulses) the plasma. A long pulse duration in the range of milliseconds and microseconds creates a large melt ratio and a large heat-affected zone because the energy that is introduced dissipates away into the workpiece through heat conduction within the time frame of the pulse duration. For short pulse durations in the range of nanoseconds and ultrashort pulse durations in the range of pico- and femtoseconds, the ratio of material vapor and plasma rises with decreasing pulse duration. The melt ratio decreases significantly, which is why there is no bulging when ultrashort pulse lasers are utilized. The heat-affected zone is also reduced.

Pulse energy
The pulse energy is the energy of an individual laser pulse. For long pulse lasers, the pulse energy typically lies in the single-digit Joules, which allows large volumes to be converted to melt. With short and ultrashort pulse lasers, the typical pulse energies range from 10-1000 µJ. In order to remove a certain volume, the drilling of a hole occurs through a multitude of laser pulses. For the drilling of high aspect-ratio boreholes, a large pulse energy is advantageous.

Repetition rate
The repetition rate quantifies the number of laser pulses per time unit. Typical repetition rates lie in the single- to double-digit Hertz range for single pulse drilling and in the range of 10-500.000 kHz for percussion drilling. An overly high rate for drilling is disadvantageous, as the energy is converted less effectively into material ablation due to the absorption of laser radiation in the removed material vapor/plasma and due to heat accumulation effects. These effects may lead to unfavorable deformations or damages to the workpiece.

Wavelength
The wavelength of the laser mainly influences the absorption of the laser radiation within the workpiece. Whereas metals can absorb laser radtiation well in the infrared range, UV-wavelengths are more suitable for the processing of polymers (linear absorption). An exception is the absorption of ultrashort laser pulses. In this case, wave lengths in the IR and visible (“VIS”) range can also be applied for ceramics and polymers (non-linear absorption).

Which Laser Drilling Methods Exist?

Single pulse drilling

Single pulse drilling applies a single long duration laser pulse to drill through the material.
The extraction of the melt is usually achieved with the support of a process gas nozzle. Workpieces with a material thickness of up to several millimeters can be drilled with high pulse energies and longer pulse durations (ms to µs range). The drilling time in relation to the material thickness is minimal but the achievable quality is limited due to the melt within the ablation.