Laser Drilling PCB Boards – How Does It Work?

Laser drilling PCB boards involves using a beam of high-energy and focused light to create holes. To learn how it works, continue below. We will take you through the drilling process, the various types of laser used, and everything else you need to know. Let’s get started!

What is PCB Drilling?

It means creating holes on a printed circuit board. The holes serve various purposes and have different diameters. They may also be shallow or through holes for varying functions, such as:

• Vias for interlayer communication by electrically connecting the layers and traces
• Component placement holes for assembling through-hole electronic and other devices
• Mounting holes to install the board in its application device or system
• Openings to attach the board to a fixture for testing

PCB drilling involves two main techniques: mechanically using physical drills and drill bits or with the help of the heat created by a high-energy light beam when focused on a spot on the substrate’s surface.

Laser PCB Drilling

PCB laser drilling is a way of circuit board holes, such as vias, by concentrating a beam of high-energy light onto a spot. The resulting heat melts the spot, vaporizing the circuit board material and creating an opening.

A narrow beam produces narrow holes, and vice versa. On the other hand, varying the exposure period controls how far the opening goes into the board. That way, it becomes possible to make different types of holes.

CO2 vs. UV PCB Laser Drill

A PCB laser drilling machine is typically one of these two types: CO2 or UV-based. Sometimes, the process requires the use of both. Here’s how each works.

CO2 Laser

CO2 means it uses CO2 and other gases for the light-amplification process. A CO2 type works in the higher infrared band. Being a longer wavelength beam, it best suits larger diameter holes. It also only works on dielectrics. However, it costs less to drill with and is relatively fast.

UV Laser

A UV drill uses the ultraviolet band. It drills smaller diameter holes less than 100 microns wide, making it a more precise type. It also works with a wide range of materials, including metals, but costs more to use.

What are the Advantages of Laser Drilling PCB Boards?

Laser drilling PCB boards presents more advantages over the mechanical method. These make it a preferred technique for most circuit board cavities, especially microvias. Here’s a list of the most significant benefits

• The drill doesn’t physically contact the board. That reduces wear problems and the possibility of cracking or delamination.
• Laser drilling PCB boards offer a higher aspect ratio or depth-to-hole diameter.
• Light drills smaller homes than mechanical bits. Cavities as small as 3mil or 0.075 mm are possible.
• It has a high speed. In higher production runs, it means a significant reduction in costs
• It produces precise holes, making it a preferred method for small-diameter cavities.
• It’s a clean way of making holes; unlike the mechanical method, it doesn’t produce chips.

Laser PCB drilling has its downsides. For example, it doesn’t work well if the material is too reflective. It’s also more expensive than the mechanical method and may not suit low-budget projects or lower production runs.

PCB Laser Drilling Process

The PCB laser drilling process involves a few steps. First, the beam requires shaping and directing using high-precision optics. The rest of the process, from when the beam hits the board surface to when it creates the required hole, happens as follows.

1. Heating

The beam contains electromagnetic energy. The circuit board material absorbs this energy when hit by the light. The absorbed energy excites the atoms.

2. Melting

The resulting kinetic energy causes a sudden and sharp increase in temperature, leading to a breakdown of the chemical bonds and melting the spot.

3. Vaporization

The melted material instantly vaporizes, creating a hole. Controlling the beam energy, exposure, and size determines the hole diameter and depth.

4. Material Ejection

The sudden increase of material volume in the cavity causes the pressure to increase abruptly. The resulting recoil pressure ejects any molten materials. Drilled holes pass through an inspection process to determine their quality.

PCB Laser Drilling Methods

PCB drilling using laser can take various forms depending on the required hole characteristics and cost, among other considerations. The methods include single pulse, trepanning, percussion, and helical drilling.

Single Pulse Drilling

The drill sends a single high-energy pulse to the board surface. The single pulse method creates larger holes and is typically less precise. When deeper and higher dimensional tolerance holes are necessary, the multi-pulse method called percussion is preferred.

Percussion

Instead of one long pulse, the light beam hits the board with relatively low-power and short-lived pulses. Each pulse results in a part of the material melting and vaporizing.

This hole-production method produces smaller civilities (smaller than the beam itself, making it more precise. Percussion also makes deeper holes more quickly than when using a single pulse beam.

Trepanning

In trepanning, the beam cuts around the hole diameter and is helpful if the required opening is larger than the beam. Although less accurate, a trepanning PCB laser drill makes larger holes. It also requires a carefully controlled beam motion or the hole quality may not be high.

Helical Laser

The beam traces a helically shaped path. At the same time, it also spins on its axis and uses a Dove prism (learn more about it here) to control the movement. Like trepanning, helical drilling produces quality holes but has a low speed.

Conclusion

Laser PCB drilling uses the energy of concentrated light to produce circuit board holes, from vias to mounting or component assembly holes. This method has many advantages, with many circuit board manufacturers preferring to use it over mechanical bits. We hope this article has helped you understand how it works and its benefits.