Laser drilling small holes

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David Gillen, managing director, Blueacre Technology

Advances in industrial technology require ever-smaller holes in electronic, medical and related devices. Laser drilling achieves strict size and tolerance requirements in an economically viable process. Numerous small hole creation methods exist, with chemical etching, mechanical drilling and laser machining among the more widely used. However, as the dimension of the hole decreases, the choice of process is more limited, and the interaction of the material and the hole forming process becomes more critical. This article looks at various small hole drilling methods and examines the use of laser drilling techniques to create repeatable, high-aspect ratio holes that have <10 μm diameters.

Traditional methods such as mechanical drilling allow for the creation of features on the order of 50 to 100 μm, which is roughly the diameter of a human hair. By modern standards, these holes can no longer be described as small. Refined, repeatable, high-speed laser processes can machine holes as small as 1 μm in diameter with specialised configurations and can easily drill below the 10 μm diameter mark in a variety of materials. Comparative examples of how small laser drilled holes can be made, including a human hair and an aerosol spray droplet, are shown in figure 1.

Small hole creation methods

There is a number of small hole drilling methods for creating holes in the sub 100 μm range. The table below outlines some of the key characteristics

The comparative cost of different drilling methods is shown in figure 2. In general, the cost of producing a small hole rises exponentially as the hole diameter decreases. Laser drilling is the one method that can be used to cover a broad range of diameters.

The advantages of laser drilling

Using lasers to drill small holes has many advantages, the main ones being listed below.

  1. Lasers are non-contact and therefore do not require the use of additional coolants or lubricants. The noncontact nature of laser drilling is especially advantageous if machining very thin materials that are too flexible or fragile to undergo a contact machining process. 
  2. It is possible to choose a laser source that will achieve optimal results for a given material. Different materials absorb different wavelengths of light in different proportions, as shown in figure 3. 
  3. Lasers can be operated in different modes, such as pulsed or continuous wave, to suit various applications. For very fine applications, short-pulsed lasers in the nanosecond range and below tend to provide optimal results because heat build-up during the machining process is minimised.
  4. The optics of a laser can be changed in order to change the shape of the via. By controlling how the laser beam is delivered, it is possible to achieve a range of hole shapes. Although this can add to the cost per hole, it is a key method when using the hole to deliver fluids or vapour since the shape of the hole can control the size of the droplet formed.

Laser drilling applications

Medical devices

The ability to drill small holes in polymer and metal materials is important in medical device design. These holes can be used for collecting fluids from the body or delivering localised medicine into the blood stream. As the laser is a highly repeatable process, it is ideally suited to medical device applications, where process control is key to ensuring patient safety.

Leak testing

In safety critical industries such as pharmaceutical, it is necessary to ensure the integrity of packaging. The manufacturers of blister packs need to ensure that their in-house test systems can detect any leaks. To do this, Blueacre Technology laser drills holes as small as 5 μm into the packs to simulate the tiniest of defects. Detecting these small holes gives the manufacturers confidence in their products’ integrity. 

Filters

The laser process can be used to machine fast and repeatable arrays of micro holes in a range of materials from metal through to ceramics and polymers. These can then be used as filters in process critical applications in industries such as aerospace, automotive and oil and gas. Chemically resistant polymers such as polyether ether ketone (PEEK) and polyimide (PI), which can withstand both high temperatures and chemical attack, are routinely laser drilled by Blueacre Technology.

Conclusion

Current manufacturing trends are driving the need to drill smaller holes with increased repeatability and process yield. Although there are several suitable drilling methods, such as EDM and mechanical drilling, laser drilling outperforms them in many applications. As it is a noncontact process, there is less need for post processing of the drilled parts, and there is no mechanical tooling wear to consider. Lasers afford the user the possibility to drill holes smaller than can be achieved using other techniques while maintaining high throughput and economic viability.

Blueacre Technologyhttps://blueacretechnology.com