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How PCB Laser Drilling Works

The PCB drilling process is pretty expensive, time consuming process that is very crucial. For a PCB to function correctly, PCB manufacturers must execute this step carefully, minimizing the number of errors that might occur. That is because even a tiny error in this process can render a Print Circuit Board useless. Therefore, most manufacturers refer to this process as the bottleneck and the most crucial process of the PCB manufacturing phase.

PCB manufacturers utilize the drilling phase to generate multiple holes, which are good to create continuity between the bottom surface and the top surface or to a mid-PCB layer. The drilled holes also act like mounting holes and allow the connection of copper polygons, pads, and traces to the PCB for it to function as required. Whether the Printed Circuit Board design is single-layered or multi-layered, it has to go through this phase before it hits the market.

To get the perfect holes you find in PCB, manufacturers utilize two methods: mechanical and laser drilling. Both of these methods work efficiently. However, when it comes to accuracy and generating smaller holes, the laser technique beats mechanical drilling without a doubt. But this is not the only reason laser drilling has been outshining mechanical drilling over time. Hence let us look at laser Drilling and why you should opt to use it.

Laser Drilling in a Nutshell

laser-cut-pcb

Laser drilling generates precise tiny holes on PCBs which are useful in creating connections between various layers. Almost all sleek devices you can think of have undergone laser drilling to help them function optimally. Laser drilling is pretty popular because it ensures excellent accuracy even when generating microscopic holes.

LASER (light amplification by simulated emission of radiation) drilling is a process that utilizes lasers that are highly concentrated to drill hole on PCBs.

Mechanical Drilling in a Nutshell

Mechanical drilling, on the other hand, relies on drill bits to effectively cut through various laminate components. The drill bits used in this process comprise micro-grain carbide, which allows them to keep on drilling holes for an extended period. Moreover, you can resharpen these bits when they go blunt, although this only happens thrice in the bit’s lifespan to increase its productivity.

But what exactly is PCB Drilling Process?

Print Circuit Board Drilling is a crucial process of generating holes on Printed circuit boards. The holes generated become useful in:

–         Mounting holes

–          Interconnecting different layer

For these feats to be achieved, PCB manufacturers should utilize different types of holes, which include:

–          Blind and buried vias

–          Microvias

–          Thru holes

Regarding generating electrical connections between different layers, manufacturers mostly prefer to utilize blind and buried vias instead of through-hole vias. That is because blind vias provide a larger space that you can use for wiring purposes.

Is Laser Drilling needed for PCBs to Work?

When utilizing PCB designing and HDI technology, you will work with many microvias. These tiny vias, which mostly appear like blind structures, require a lot of precision to get right. To achieve this precision, the manufacturers should utilize laser drilling.

Why is it impossible to utilize mechanical drilling to generate Microvias?

You can’t use mechanical drilling to generate microvias because of the following reasons:

  • Using mechanical drilling, you cannot drill a hole that is less than six millimeters in diameter. You hence can’t drill out micro-holes using this technique
  • Mechanical drilling involves a lot of vibrations and since the drill bit is in contact with the PCB, it sometimes ends up harming the boards integrity
  • When using mechanical drilling, you can’t get the precisely controlled depth needed for microvias

What is the smallest Diameter you can achieve when working with a Laser Drill?

When utilizing the laser drilling process on a flat glass reinforcement, you can achieve a diameter that is between 2.5 to 3.5 millimeters. However, when working on an unreinforced dielectric, you can achieve a diameter as small as 1 millimeter. That is why manufacturers prefer to utilize laser drilling to generate microvias.

Advantages of Laser Drilling

It is a Non-contact Process

The laser drilling process is non-contact. Therefore, you get rid of the damage that usually occurs on a PCB due to drilling vibrations.

Precise Control

You can easily control the heat output, beam intensity, and the laser beam’s duration when utilizing the laser PCB drilling process to drill your PCB. By controlling these aspects, you can achieve high accuracy while at the same time generating vias of varying shapes to suit your PCB design.

Higher Aspect Ratio

Aspect ratio is simply the ratio of the hole’s drilled depth to its diameter. Since laser drilling can generate drill holes with tiny diameters, it offers a higher aspect ratio.

Multi-tasking

Machines utilized for laser drilling can also be utilized to undertake other processes such as cutting, welding, et cetera.

How can you achieve Micro drilled holes via Laser Drilling?

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To achieve microvias, you must first project the beam onto the PCB using various beam shaping methods. After doing this, the PCB will absorb the laser beam’s energy, breaking the Printed Circuit Board material’s chemical bonds. The process then creates vapors which generate a recoil pressure. The recoil force, in turn, places downward pressure on the molten component forcing the molten parts of the Printed Circuit Board to slowly flow out of the PCB.

The removal of the now molten parts of the PCB is called melt ejection. On the other hand, the rate of absorption usually depends on the type of components used to produce the PCB. Primarily, manufacturers utilize non-homogenous components, for example, FR4, to create their PCBs.

Different Techniques used to Drill holes using the Laser Drilling

Percussion

When utilizing the percussion technique, manufacturers repeatedly shoot laser pulses on the PCB to generate a hole on the PCB. However, during this incredibly effective process, no relative motion occurs between the PCB and the laser beam, which makes the process achieve great precision.

PCB manufacturers utilize the percussion technique to generate deeper holes with better precision and smaller diameters.

Single-pulse

As its name dictates, the single-pule technique utilizes a single beam to generate vias on a PCB. During this process, manufacturers fire one shot of laser on the PCB to create a hole. The process is then repeated until all the required holes are made.

When this process is taking place, both the PCB and the laser’s source must be kept static.

Trepanning

Trepanning is simply a process whereby the laser beam used to drill holes on the PCB is directed to move around a specific predefined locus. The locus is simply the hole’s center. Hence the laser can maneuver around the via’s center, developing a perfect hole.

The trepanning technique is usually utilized when the laser beam’s diameter is smaller than that of the via.

Helical

The helical laser technique involves moving the beam along a helical path on the PCB while rotating it about its axis according to the PCB’s position. Manufacturers control the laser beam using a dove prism to achieve precision and greater accuracy.

Which Laser Beams are best for Drilling Micro-Holes?

Many different laser machines exist, and all of them serve various purposes. For example, some are good for etching purposes, depaneling, etc. However, for a drilling machine to qualify in terms of carrying out laser PCB drilling, it has to be able to generate tiny holes on various components utilized to make PCBs.

The most popular laser machines utilized for micro-hole drilling are:

–          Nd: YAG laser drilling machine

–          CO2 laser drilling machine

Carbon dioxide (CO2) lasers utilize gases as their lasing medium. They then emit light with a wavelength of about 10.6μm on the IR spectrum. These laser beams can create holes bearing a diameter that falls between 50μm to 70μm.

Carbon dioxide beams fall under the high-power beam category. They are hence great in terms of drilling polymers. What’s more, these beams bear high metal surface reflectivity. We use them mainly when drilling speed is of at most importance.

On the other hand, Nd: YAG lasers utilize a solid lasing. They have a fundamental emission that lies in the IR spectrum bearing a wavelength of 1064nm.

The Nd: YAG beam can efficiently emit up to one hundred thousand pulses in one second. What’s more, these beams are more versatile, and hence they can be useful drilling through different components, for example:

–          Metals

–          Glass

–          Polymers

In some cases, manufacturers utilize a combination of carbon dioxide and Nd: YAG lasers to gain specific customized results.

What you should significantly consider during the Laser PCB Drilling Process

When undertaking laser drilling, you should greater consider the following aspects concerning your PCB:

The copper thickness

You should ensure that the copper layer you are targeting is twice as thick as the PCB’s top copper layer. Though plain and simple, this simple aspect is actually an important thumb rule.

Stack-up Materials Non-Homogeneity

Different components absorb energies at varying rates. For instance, glass fibers absorb light at a rate that equals that of FR4 resins. On the other hand, BT epoxy resins tend to vaporize faster than regular glass. In such situations, obtaining great precision when working with laser beams becomes an issue. Therefore, to prevent such incidences, try to maintain your PCB’s stack-up homogeneity as much as possible.

If you utilize components that bear different thermal and optimal properties, then the beam will react with these components differently hence breeding inaccurate drills.

Conclusion

Apart from some challenges that might come up when utilizing laser drilling to make holes in your PCB, we can easily conclude that this process is excellent for developing micro-holes. And given how the current market is trying to reduce the size of the PCB while at the same time increasing its wiring density, it’s no wonder this technique has become pretty popular. Generating minuscule holes with great precision without harming the PCB’s integrity is not an easy task to achieve. However, manufacturers have not just been able to accomplish this feat using laser drilling, but they can now utilize it to mass produce small gadgets.