Laser Drill for Flex PCB: The Ultimate Guide

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Oakley Mae

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What is a laser drill for flex PCB? Is it necessary for flexible circuit boards, and if yes, what are the laser drilling methods available?

We guarantee you’re in the right place if you ask yourself these questions. 

Generally, laser drilling is a critical step of flexible PCB fabrication and involves making precise holes on the board to create a link between layers.

Laser in full stands for light amplification by stimulated emission of radiation.

Therefore, the technology employs laser energy to drill holes in a circuit board. 

In this article, we help you understand laser drilling for flex PCB by focusing on the benefits, drilling methods, drilling machines, and considerations during drilling. Let’s get started!

Table of Contents

What’s Laser Drilling?

(A laser cut stainless)

Flex circuit board drilling involves drilling holes in the circuit board to provide interconnection between layers.

Additionally, it creates holes for component placement.

The result is the creation of different via types, including microvias, buried vias, blind vias, and through-hole vias. 

Therefore, laser drilling involves using laser energy to create holes in your circuit board. It’s known as laser ablation and guarantees great accuracy even when dealing with tiny holes.

Laser drilling is an excellent alternative to manual circuit board drilling. 

Why Is Laser Drilling Necessary for Flex PCB?

A PCB drilling machine

(A PCB drilling machine)

When you employ HDI technology for your flex circuit design, you’ll include many microvias.

Surprisingly, the microvias are tiny and need precision-controlled depth drilling.

And such a task is only possible if you use laser drilling technology.

In such cases, you can’t use mechanical drilling since it can’t drill holes under 6 mils. 

Benefits of flexible PCB Laser Drilling

Check out the benefits of flexible circuit board laser drilling below: 

  • Non-contact drilling: Generally, no contact is involved when drilling flex PCB with a laser. Therefore, there is no creation of unnecessary vibrations and consequently limited damage to the board. 
  • Precise control: With laser drilling technology, it becomes easy to control the laser beam duration, beam intensity, and heat output. Therefore, it becomes possible to generate vias of different sizes and shapes. Also, it guarantees a more accurate drilling process. 
  • High aspect ratio: The aspect ratio is a very important parameter of a circuit board hole. It represents the ratio of drilled hole depth to diameter. As we highlighted, laser technology can drill holes with a very small diameter, thus translating into a high aspect ratio. Surprisingly, a normal flex board micro via boasts a ratio of 0.75:1. 
  • Multi-tasking capabilities: We know this will surprise you, but you can use a laser for drilling holes to carry out additional manufacturing tasks like cutting and welding. Consequently, it’ll reduce the production cost. 

Flexible PCB Laser Drilling Methods

A circuit board that has undergone drilling

(A circuit board that has undergone drilling)

Percussion technique

During the percussion technique application, you frequently shoot laser pulses on your circuit board to create holes.

However, the process doesn’t involve relative motion between the circuit board and laser pulses.

Therefore, it achieves greater precision. 

Surprisingly, manufacturers employ this method to create deeper holes with smaller diameters and high precision. 

Single-Pulse Technique

This technique uses a single laser beam to make holes in a circuit board.

Therefore, the manufacturer fires a single laser shot to generate a hole and repeats the process until they meet the required holes.

This method requires no motion between the laser source and the circuit board, just like the percussion technique. 

Trepanning

With this technique, the laser beam is designed and directed to move in a specific locus.

Generally, the locus, in this case, is the center of the hole.

Therefore, the laser moves around the via’s center to generate a perfect hole. 

Manufacturers use the trepanning technique when the via is larger than the laser beam’s diameter. 

Helical

Finally, this technique lets you move the laser beam along a helical path on your board.

At the same time, you rotate the beam about its axis relative to the circuit board position.

And to achieve precision and accuracy, use a dove prism to control the laser beam. 

Flexible PCB Laser Drilling Machine

A laser machine

(A laser machine)

A flex PCB laser drilling machine is a machine that drills PCB holes as per the data and parameters you provide.

In most cases, the parameters include the number of holes and the hole position. 

There are two primary drilling machines based on the operation principle. Therefore, we’ll discuss them below:

CO2 Lasers

These lasers employ carbon dioxide as the lasing medium.

Also, they emit light wavelengths of about 10.6 microns in the IR spectrum.

And the lasers can create holes with a diameter of about 50-70 microns. 

Surprisingly, carbon dioxide lasers are very popular with a significant application in polymer drilling.

Moreover, the lasers present a high refractivity from a metal surface.

If the drilling speed concerns you, count on these lasers.

Nd: YAG Lasers

Unlike the carbon dioxide laser, which uses gas, the ND: YAG laser employs a solid medium.

Also, they emit in the IR spectrum with a wavelength of about 1064 nm.

However, for the non-linear crystal, emission happens at 532 nm and 266 nm or 355 nm for the visible and UV spectrum, respectively. 

Surprisingly, this laser machine can emit 100,000 pulses each second, creating hole diameters between 12 to 25 microns.

However, use the trepanning method to make holes with a larger diameter.

Lastly, you can use ND: YAG laser to drill on metals, glass, and polymers. 

Considerations During Laser Drilling

When drilling your board using a laser, there are certain considerations to remember:

Copper Thickness

The copper you’re targeting should be twice as thick as the top copper layer you intend to penetrate.

This will enhance accuracy and improve precision. 

Stack-up Non-homogeneity

The stack-up non-homogeneity should be your top priority when drilling your circuit board with a laser.

Normally, different materials will absorb laser energy at different rates.

In some cases, you’ll get materials like FR-4 and glass fibers that absorb lasers at the same rate. Moreover, these materials will leave behind a clean hole. 

However, BT epoxy resin might vaporize faster than glass and leave behind glass fibers.

Therefore, the drilling won’t be accurate and precise in this case. For the best result, you must keep the circuit board stack-up homogeneity. 

FAQ

Which materials aren’t suitable for laser cutting?

Certain materials with chemical makeup might generate dangerous dust and gas when you drill with a laser. They include: 

What is the maximum thickness a laser can drill?

The maximum thickness you can drill using a laser is 20 mm to 25 mm.

Beyond this limit, you’ll have to use very high-power CO2 lasers.

In most cases, the shorter the wavelength of the laser, the smaller the hole diameter you can drill with precision. 

Why can’t you use mechanical drilling for microvias?

Avoid mechanical drilling for microvias because of the following reasons: 

  • First, mechanical drilling causes vibrations
  • Secondly, it can’t drill holes having less than 6 mil
  • Finally, it doesn’t offer the required precise and accurate micro via controlled depth drilling

Conclusion

Despite the few challenges, laser drilling is the best microvia drilling option.

Generally, it offers very accurate and precise drilling, something you won’t get with mechanical drilling.

Surprisingly, mechanical drilling causes dangerous vibration that affects the drilling precision. 

Moreover, laser drilling facilitates non-contact drilling, enables multi-tasking capabilities, and offers a high aspect ratio.

Lastly, when drilling with laser energy, consider the copper thickness and stack-up non-homogeneity.