Blog  /  PCB Drilling: Definition, Types, and How It Works

PCB Drilling: Definition, Types, and How It Works

Are you new to PCB engineering? Then, you should know that PCB drilling is one of the critical factors contributing to a board’s quality.

After all, properly drilling your board creates a secure base for excellent plating on the hole walls. Also, the general rule of thumb is to prepare each hole individually and carefully.

That said, we’ll talk more about this topic later in this article by explaining the process, types, tips & tricks, and more.

Let’s proceed!  

What is PCB Drilling?

 

PCB drilling tool

PCB drilling tool

 

Printed circuit board drilling is a procedure that involves crafting cavities, slots, or holes on an electronic circuit board before you mount components.

That said, you need an automated machine or PCB drill bit to execute the process.

How do you drill the electronic board layers? In reality, you can do PCB drilling the same way you use a regular drill bit. The only difference is that you need to add a slight twist.  

PCB Drill bits

Source: Wikimedia Commons  

Further, you can create holes via mechanical means or chemical milling (electrochemical etching). The automated method involves punching, drilling, or laser cutting. But the most popular production method today is combining electrochemical etching and chemical processes.

Also, before you start drilling a series of small holes, it’s vital to consider the design of your board contour first. That way, you’ll get a more precise hole size.  

The PCB Drilling Tech

 

The two significant types of drilling technologies we have are: mechanical and laser drilling.  

Mechanical Drills

 

Mechanical PCB Drill

Source: Flickr  

This drilling technology is relatively easy to execute. But it has less precision, and it uses drill bits. That said, the minor hole diameter you can get with this drill is about 0.006” (6 mils).

Further, if you use the mechanical drills on soft materials like the FR4, you can get 800 hits. But for more rigid materials like Rogers, the lifespan of the mechanical exercises reducreduced00 counts.  

Laser Drills

 

Laser Drill PCBs

Source: Wikimedia Commons  

This technology is a non-contact process. That is, the tool and the workpiece don’t have contact with each other. And this process is effective for drilling small holes. Plus, you can control the drill depth effortlessly.

In addition, you can drill buried and blind vias with laser technology. And the minimum hole diameter you can get from the laser drills with precision is about 0.002” (2 mils).

But the snag of this technology revolves around PCB materials. We have different PCB materials like resin, copper, glass fiber, etc., and each of them has varying optical properties. Hence, it’s difficult for the laser beam to burn through a board effectively.  

Type of PCB Drill Holes

 

You can classify PCB drill holes based on their ability to carry current or not. But the classification doesn’t show the importance of drill holes between circuit board structures. Hence, here’s is a more comprehensive way of sorting or differentiating between drill holes based on their usage:  

Non-Plated Through-holes

 

In this category, we have the following types of drill holes:  

Countersink Holes

 

Tool for creating Countersink Holes

Source: Wikimedia Commons  

You can use these non-plated through-holes or NPTHs to mount boards that the bold head requires lowering below the surface.  

Mounting Holes

 

Mounting Holes on PCB

Source: Wikimedia Commons  

These holes help install mechanical fasteners where you don’t need vertical clearance.  

Fasteners

 

PCB Fasteners

Source: Wikimedia Commons  

This type of hole is ideal when you need to do mechanical justification. Alternatively, you can use fasteners to confirm that you installed a component that needed extra support correctly.  

Plated Through-holes

 

Here are the types of holes in this category:  

Thermal Vias

 

Thermal Vias on PCB

Source: Researchgate  

First off, the thermal vias don’t conduct current. But this vital PTHs remove excess heat by controlling the high transfer rate of copper. And the thermal vias usually do this from a high-power component on its surface.  

Through-hole vias

 

This plated hole helps route traces from the surface (top to bottom). But when these conductors spread throughout your board stackup, you can use them to route signals within any layer.  

Buried Vias

 

Illustration showing buried Vias Process

Source: Wikimedia Commons  

These are connections that occur between internal layers. And it doesn’t spread to the top or bottom surfaces.  

Blind Vias

 

Blind Vias Structure

Source: Wikimedia Commons  

You can use blind vias when you need an electrical connection between a stack-up internal and surface layers. And these PTHs only extend to targeted layers.  

Microvias

 

Microvias Structure

 

You can have buried or blind microvias. And they stand out with their small size, which makes them useful in high-density signal routing.  

Press-fit

 

Press-Fit schematic structure

Source: Researchgate  

As the name suggests, these PTHs fit the leads of through-hole components. Hence, you don’t need to solder or fill press-fit holes.  

Considerations in the PCB Drilling Process

 

The two vital things to consider in a drilling process includes:  

Drill to Copper Clearance

 

The drill to copper is the space or land clearance from a drilled hole’s edge to the closest copper feature.

That said, the closest copper feature can be an active copper region or copper trace. And this factor plays a significant role in the drilling process because a slight deviation can cause circuit disruption.

Furthermore, the typical value of the drill to copper is about 0.008” (8 mils).

Minimum clearance = width of annular ring + solder dam clearance  

Aspect Ratio

 

The aspect ratio has to do with how well the holes can plate copper effectively. No doubt, it’s pretty tricky for a hole’s interior part to have copper plating when you increase its depth and reduce the diameter.

So, if you have an issue like this, you need to do a plating bath. And while you’re at it,  use a higher throwing power. Consequently, the liquid will force its way through the tiny holes.

That said, the aspect ratio for microvias is 0.75:1 while the through-holes is 10:1. Also, if you have a 62 mil PCB, your smallest drill size can be six miles.

AR (Aspect Ratio) = hole’s depth/ diameter of your drilled hole  

Drilling Disasters

 

When you use drilling tools repeatedly, they tend to wear and break. Consequently, it results in the following problems:  

Compromise of the Hole Location’s Precision

 

When your drill bit doesn’t hit a specific spot, it may deviate in the same axis. Hence, the shift in the drilled hole will cause a breakout or tangency in annular rings.  

The light passes through the holes 

The light passes through the holes. 

 

Delamination

 

This problem occurs when PCB layers separate partially. But you can avoid this by using laser drills. Also, you can remedy this problem by a deburring or desmearing process.  

Entry and Exit Burrs

 

Burrs may occur after a drilling process. That is, you’ll see an unwanted part of the copper protruding from the hole. And this defect can arise in the PCB’s highest stacked top surface and lowest-stacked bottom surface.  

Drilled Hole with Roughness Internally

 

When your drilled holes are rough internally, you’ll have deviating plating of copper. Consequently, you may notice barrel cracks and blowholes. And it can also cause lower insulation resistance.  

Resin smear

 

When you drill your board, the process produces a lot of heat. As a result, the resin in your board may melt. The wax will stick to the hole walls (resin smear) when this happens. Consequently, you’ll have conductivity failure between the circuit’s internal layers and the via. Hence, there will be poor copper plating.  

Nailhead

 

During drilling, your inner layers of exposed copper on through-holes may form a nail head shape. As a result, you may experience conductivity failure of plating.  

Tips and Tricks

 

Here are a few tips and tricks that will improve your PCB drilling results:

  • Ensure that your aspect ratio is low to prevent drill wear
  • Start with pilot holes for appropriate drilling
  • Confirm that you have a defined drill type (NPTH/ PTH)
  • Address any close gap that is less than six mils
  • Clean your PCB after drilling
  • Ensure that your non-plated drills have a connection
  • Verify your size or drill count between the drill file and Fab print
  • When you’re drilling at an angle, use only a straight PCB drill
  • Add solder to drilled holes
  • Use a drill press for precise drilling holes

 

PCB drilling

PCB drilling

 

Final Thoughts

 

PCB drilling is a vital step in producing quality PCBs. Hence, following the tips we listed are essential to get the best results (a functional electronic board). Also, you need to use the right skills and tools.

Are you going to try using a drilling machine? Or do you need help getting the best PCBs for your project? Please feel free to contact us.