PCB drilling is a very delicate process, as creating the right holes to get a circuit board to function is not an easy task. Complex circuits often have multiple layers to allow the mechanism to function. In those situations, a circuit board will have vias, or small holes that allow circuits to connect through different layers on the PCB.
Vias are very important for complex electrical systems, which is why it is vital that you use the right methods to drill them. The two most popular methods are mechanical drilling and laser drilling. They’re both widely used in PCB manufacturing, but which one is better?
This article will give you a detailed insight into which of these drilling methods is better for electrical circuit vias.
Mechanical Drilling: Pros and Cons
Mechanical drilling uses a rotating bit to drill small holes into a PCB. Here are the advantages and disadvantages of this method.
Pros
Mechanical drilling gives you perfect control over the depth of the hole that you drill. The drills also penetrate deeper than laser drilling does. This is great, especially if you have multiple layers in your circuit board and need to get your vias through the layers.
Another advantage of using mechanical drilling is consistency. Mechanical drilling uses a carbide drill bit that is replaced after you resharpen it three times. The bits create the same size holes with the same quality every time. You don’t have to worry about matching up holes of different sizes, chipped walls, or holes tapering off toward the bottom.
Finally, mechanical drilling is faster and more efficient than other methods, increasing your production per minute. That is perfect, especially if you have a circuit board with dense vias.
Cons
While mechanical drilling has many advantages, in many ways it is an outdated technology.
With mechanical drilling, you are limited in terms of the size of the via by the size of the drill bit. You cannot make very small holes because the bits are too large, which is a problem as PCBs are getting smaller and more complex.
Mechanical drilling also causes burrs, or little fragments of metal, usually copper, that stick out from the wall of the hole. You have to deburr each via to ensure smooth walls, which is a time-consuming process. Once you add in the time (and money) you spend preparing the drill for creating vias, you cancel out any advantages in efficiency you gained from the drill working faster.
Laser Drilling: Pros and Cons
Laser drilling doesn’t use a traditional drill bit but rather a highly focused laser beam to create holes in the PCB. Different types of lasers are used for laser drilling, depending on the material you are working with.
Pros
Laser drilling allows you to drill much smaller holes than you can with a mechanical drill. Lasers are extremely focused, so you are not constrained by the bit size. As circuit boards get smaller and more complex, microdrilling is becoming more and more important, so laser drilling has its definite advantages in manufacturing.
Laser drilling also gives you more choices in terms of materials. You can use it to work with PCBs made out of pretty much anything.
Finally, laser drilling is a more efficient process. While mechanical drilling can drill more holes per minute, you lose a lot of time during set-up and deburring. Laser drilling is an entirely hands-off process, which makes the production of vias much easier. Plus, the hands-off nature of the job makes it easier for workers to get through their tasks.
Cons
The biggest disadvantage of laser drilling is how it performs on depth. It has a lower depth range than mechanical drilling, so if you are trying to align a via through multiple layers, you will struggle a bit with laser drilling. It is also harder to control the laser through multiple layers. Sometimes, you need to add a metal stop layer to give yourself control over the depth, which adds a step to the process.
Laser drilling yields vias and holes that are less consistent than mechanical drilling. The size might be slightly off, or the vias might taper. You have to be careful when adjusting your settings to make sure that you are maintaining consistency, while for mechanical drilling, it stays the same no matter what you do, as long as you are using a bit of the same size.
Finally, vias created with laser drilling don’t always look the best. Laser drilling carbonizes or burns the edges of the holes it creates. While it shouldn’t affect the performance, be ready for vias that have singed edges or blackened bits.
Considerations When Deciding Between Mechanical and Laser Drilling
As you can see, both types of drills have their advantages and disadvantages. Which type you choose comes down to the specifics of the drilling situation you have going on.
Size of the Vias
One of the most important factors that determines which type of PCB drilling you will use is the size of the vias. As we established, laser drilling allows you to drill much smaller holes than mechanical drilling. If you are drilling tiny vias, then laser drilling is better because it gives you better control of the diameter of the whole via.
You need to consider two measurements when you discuss the size of the vias: the pad-to-hole ratio, which is similar to the diameter, and the aspect ratio, which determines the depth. If the boards are thicker, you need either a mechanical drill or a metal plate with your laser drill.
Through-Hole Vias
Through-hole vias are vias that go all the way through a PCB board. These vias are the easiest to manufacture because you just drill all the way through the circuit board. You don’t have to calculate which layers to drill through and which ones to leave untouched.
You can use both laser and mechanical drilling for through-hole vias. Mechanical drills go deeper and give you better control over the depth. If you want a smaller via or you need to knock out a bunch of vias, then you can use laser drilling which is more efficient.
Blind and Buried Vias
Blind and buried vias are vias that don’t go all the way through all the layers of the circuit. Blind vias are visible from the outside but only go through a few layers. Buried vias connect two or more inner layers and are not visible from the outside at all.
Blind and buried vias are shallower and more precise drills. You need extra control over the depth of the drill, which is why mechanical drilling is sometimes easier for this type of drilling. You can also use laser drilling, but you will have to be very careful and add an extra step of etching.