PCB Drilling Explained: Everything You Need to Know

PCB drilling is a critical stage of its manufacturing process. As such, engineers must use the right drilling methods and steps. Because these may vary based on the situation, this article will take you through the different options when drilling a PCB. The most important considerations too, and tips that can help perfect the entire process.

What is PCB Drilling?

PCB drilling means the process where holes (or slots) are created on bare printed circuit boards. These can be small holes to mount components, holes that connect the different layers, registration holes, or holes for installing the board and connecting mechanical features to it, also called mechanical holes. Typically, PCB drills are either mechanical or laser-based.

Mechanical PCB Drilling

With mechanical drilling, physical parts are used to pierce the board. A mechanical PCB drill is made up of these crucial components; the bit, chuck, and the upper section called the spindle, and which connects to the feed mechanism.

A PCB drilling bit must be strong enough to go through the material being drilled. So it is mostly made from carbide, although high-strength steel is also a common option. Other than material, the drill bit size also matters, usually depending on the required hole diameter.

Professional PCB manufacturers use computerized drills. These offer greater accuracy and time savings, plus they’re simpler and less costly to use. With mechanical PCB drilling, holes as small as up to 6 mils or 0.006” are possible.

Laser PCB Drilling

Despite being a more expensive method, laser PCB drilling is a revolutionary way of making holes on printed circuit boards. It essentially uses a concentrated beam of high-power laser. When shone onto a PCB, the light vaporizes the material to create the required opening.

Drilling PCB boards using laser offers several advantages: being a non-contact process, it means reduced chances of mechanical damage. This makes it a preferred method when dealing with delicate circuit board materials or substrates.

With PCB laser drilling, it’s also possible to create more precise holes, an advantage when drilling boards that are too small. Additionally, using laser allows tinier holes that are as small as 2 mils to be made, or about 0.002 inches.

PCB back drilling process illustrated
PCB back drilling process illustrated
Resource: https://www.researchgate.net

How to Drill PCB

When drilling PCB holes, proper steps must be followed. That’s because drilling is one of the most time-consuming stages of the PCB manufacturing process, and errors when executing it costly. Engineers must, therefore, ensure correctness in the following.

PCB Drill Hole Size

Based on the specific function, different holes are created. Typically, these are either plated or non-plated. Plated holes (vias) are electrically conductive and used to carry signals, while the non-plated types are basically registration or part mounting holes.

By changing the PCB drilling bit size (or beam opening if using laser), different holes may be created. The following standards apply when it comes to standard sizes for both plated and non-plated holes.

  • Plated PCB Holes: a minimum diameter of 0.006” is recommended and 0.004” for annular ring size.
  • Non Plated PCB Holes: for non-plated holes, it’s required to ensure no less than 0.006” diameter and 0.005” edge-to-edge clearance.

PCB Drill Speed

PCB drills are basically high-speed machines that can spin at thousands of RPM. Setting the right speed ensures not only greater precision, but also minimal damage to the board being drilled. In automatic PCB drilling machine, the speed varies according to the type of hole drilled, among other factors such as bit size.

PCB Back Drilling

Back drilling is the process where unused via portions (called stubs) are reduced using a drill bit. If left alone, these can cause signal reflections in the PCB during, often leading to interference that affects its performance during use. PCB back drilling to remove via stubs involves re-drilling the already drilled holes using larger bits that the original.

Automatic PCB drilling machine
Automatic PCB drilling machine
Resource: https://www.youtube.com/watch?qw3KdM6khk

PCB Drilling Process

The PCB drilling process, owing to its critical role in ensuring board quality and performance, must be properly executed. This stage comes immediately after the board’s lamination or cutting steps, and involves the following: the drilling software, the drilling bit or laser, and the drilling action itself.

Step 1: Preparations

First, the PCB drilling software is loaded with the required drilling file. The file contains hole-positions based on the X and Y coordinates. Other prepping activities include the following.

  • The board is placed on the drilling table, either manually or automatically.
  • To minimize costs and increase manufacturing efficiency, several boards are often stacked together.
  • A backup panel is placed underneath the PCB. This panel that serves to prevent the formation of exit burr. It also protects the drilling board against the drill bit.
  • On the topside, the PCB is covered with a sheet of aluminum. In addition to preventing entry burr, this sheet serves to dissipate the heat generated by the drill bit.
  • To prevent unwanted movements and displacements, it’s also common practice to secure the boards with pins.

Step 2: PCB Drilling

After the necessary preparations, the PCB drilling process can now begin. Depending on the specified steps, this may start with positioning or registration holes being drilled along the board’s edges. These serve as reference openings during the board’s manufacturing or testing steps.

  • In a mechanical drill, a system of actuators move the rapidly spinning spindle and bit, creating holes at the appropriate positions.
  • In the PCB laser drilling process, a high-density beam of light passes through a controlled window and hits the PCB board at the desired locations.
  • The heat generated by the laser beam removes material from the board, creating a hole that can be as tiny as 200 microns and less.
  • By controlling the beam’s size (varying an opening), different PCB hole diameters are achieved. On the other hand, the depth of the hole is dependent on the duration of the beam’s exposure.

Step 3: Polishing the Drilled PCB

Drilled PCB boards are taken to the next stage where they are de-burred and de-smeared. To de-burr drilled boards, the manufacturer may either plasma-clean or brush them to remove excess copper that may have been left on the hole edges. The de-smearing process involves the use of chemicals to remove resin smear from the holes.

Step 4: Inspecting Drilled PCB

Finally, the boards are checked for accuracy and missing holes, among other specifications. This is aimed at ensuring their utmost quality. Accurately drilled PCB circuit boards are sent to the other stages of the board’s manufacturing process.

PCB controlled depth drilling
PCB controlled depth drilling
Resource: https://www.semanticscholar.org

PCB Drilling Tips & Tricks

With the continued miniaturization of electronic products and the need for even smaller holes, drilling of PCB substrates is no longer the simple process that it was before. Today, there’s even a greater need for precision and board protection, among other requirements. These PCB drilling tips and tricks tips can help you ensure a job well done.

1. When drilling in PCB material, the ratio of hole depth to hole diameter, also called the Aspect Ratio, is a crucial factor. Industry rules recommend an aspect ratio of 10:1 for thru-holes, and 0.75:1 when it comes to micro vias.

2. Always leave enough space between the drilled holes and nearby copper traces or any other copper area on the PCB being drilled. Ideally, a clearance of 8 mils is recommended.

3. The PCB drill bit, due to its rapid spinning action, can heat make the resin in the PCB material to melt and cover the holes, leading to plating problems and conductivity issues. To help prevent that from occurring, use lubrication and adjust the drilling speed.

4. Worn bits can cause damage to the board being drilled. Ensure that these are changed in time, or new bit cartridges loaded if the drilling machine is designed to replace them automatically.

5. Using standard PCB drill holes sizes reduces the need for frequent changes of the drill bit. This is important since using too many differently sized bits can lead to tolerance errors and increase drilling costs

Conclusion

PCB drilling is one of the most important steps when manufacturing printed circuit boards, and ensuring its proper execution a crucial requirements. That in turn, requires PCB designers and fabricators to understand the various requirements that can help them achieve optimal drilling results. These have been outlined in this article.

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