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.

We’ll discuss 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

 

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

It would be best to have 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.  

 

Further, you can create holes via mechanical means or chemical milling (electrochemical etching).

The automated method involves punching, drilling, or laser cutting.

However, today's most popular production method combines 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

 

We have two significant types of drilling technologies: mechanical and laser drilling.  

Mechanical Drills

 

This drilling technology is relatively easy to execute.

But it has less precision, and it uses drill bits.

The minor hole diameter with this drill is about 0.006” (6 mils).

Further, using the mechanical drills on soft materials like the FR4 can get 800 hits.

But for more rigid materials like Rogers, the lifespan of the mechanical exercises reducreduced00 counts.  

Laser Drills

 

This technology is a non-contact process.

That is, the tool and the workpiece don’t contact each other.

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., each with varying optical properties.

Hence, it’s difficult for the laser beam to burn through a board effectively.  

What Are the PCB Drill Types?

The typical drill bits used on PCBs include the following.

Twist Drill Bits

These drill bits are the most common, and as the name suggests, they have a twisted, spiral design that channels the drilled material out of the hole when drilling.

Micro Drill Bits

Micro drill bits have tiny diameters that range from 0.1mm to 1mm. This size makes them ideal for creating narrow drill bits for components with fine pitches.

A set of color-coded micro drill bits

Diamond-Coated Drill Bits

Diamond is known for being tough. The tips of these drill bits have industrial-grade diamond particles, making them capable of drilling through hard substrate materials like ceramic. You can also use them to drill through multilayer PCBs.

Carbide Drill Bit

Solid carbide drill bits are highly durable and heat resistant, and they can create clean, precisely drilled holes.

PCB Miniature Drill Bit

These drill bits are similar to the micro type because their diameter ranges from 0.2mm to 1mm. They are ideal for delicate hole drilling through tiny pads or high-precision copper traces.

A set of tiny, high-precision drill bits

Type of PCB Drill Holes

 

You can classify PCB drill holes based on their ability to carry current.

However, the classification doesn’t show the importance of drilling holes between circuit board structures.

Hence, here’s 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

 

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

Mounting Holes

 

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

Fasteners

 

This type of hole is ideal when you need to do mechanical justification.

Alternatively, you can use fasteners to confirm that you correctly installed a component that needed extra support.  

Plated Through-holes

 

Here are the types of holes in this category:  

Thermal Vias

 

First off, the thermal vias don’t conduct current.

However, these 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

 

These are connections that occur between internal layers.

And it doesn’t spread to the top or bottom surfaces.  

Blind Vias

 

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

 

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 include the following:  

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.

This factor plays a significant role in drilling 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 depends on 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 must 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. 

 

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 besmearing process.  

Entry and Exit Burrs

 

Burrs may occur after a drilling process.

You’ll see an unwanted part of the copper protruding from the hole.

This defect can arise in the PCB’s highest and lowest-stacked top surfaces.  

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.

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.

When this happens, the wax will stick to the hole walls (resin smear).

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.  

PCB Drilling Validation Checks

Check these factors to validate the drilling process.

• Keep the through-hole aspect ratio low to prevent drill wear.
• Confirm if you must reduce the via-hole size to attain the minimum aspect ratio requirements with drill tolerance in mind.
• Check whether the drill hole is plated or non-plated.
• Confirm if the non-plated holes have electrical connections.
• Remember that plated holes have a tolerance of +/-0.002, while non-plated holes have half that.
• Check the hole count and the size between the holes in the drill file and the fabrication print.
• Reduce the varying drill-hole sizes to keep the required drill bits for the project low.
• Increase the space between holes with a diameter of less than 0.007mm or delete some.
• Confirm if the drills and other copper layer features are outside the circuit board’s profile.
• Keep a minimum distance of 0.01mm between the hole’s edge and the PCB profile.
• Check if you have mouse bits to create a line of holes because they have better grip.
• Indicate the via-hole sizes that require filling.
• Check whether the fab drawing indicates the cut-out points or non-plated through holes while lacking the drill file.

 

 

PCB drilling

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 miles
• 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

How To Drill Holes in PCBs at Home

If you manage to fabricate a PCB at home or want to modify an existing one by adding holes, you can drill it using the following steps.

Step 1: Drill the Pilot Holes

Pilot holes keep the bit stuck in position when drilling. Without them, the bit will walk and damage other board parts. We recommend laser drills for tiny holes and mechanical twist drills to punch large holes (0.1mm to 4mm). The former doesn’t need pilot holes.

Step 2: Pick The Most Suitable Drill Bit and Consider the Size

You can use any straight drill bit to punch an angled hole. But wire gauge drill bits are ideal for holes ranging from 0.8 to 1mm. Flat or round small drill bits have a wider range of 0.7-2mm, and any hole 2mm or wider requires a large drill bit.

Also, electroplated bits are ideal for creating holes through thick PCBs using a high-frequency air hammer.

High-speed bits are handy for drilling through metals like copper but can get hot when used for long periods. But, high-speed steel bits can withstand more heat, making them suitable for making wider holes through one or multiple thin boards.

Step 3: Use a Drill Press

Instead of holding a drill manually, we recommend using a drill press to maximize accuracy.

A drill press

Step 4: Clean the PCB After Drilling

Clean the holes and board surface using a brush and solvent to remove the shavings.

Shavings (debris) from the drilling process

Step 5: Solder the Drilled Holes

Insert the component’s lead into the hole, then melt just enough solder above to attach the pin. The joint should be solid after cooling and drying. Validate this by squeezing the component slightly and checking if it shakes.

How To Minimize the PCB Drilling Cost

Consider drilling via holes instead of through holes. But if you must drill through holes, go for the non-plated type. They don’t require copper on the sides, making them cheaper. Lastly, optimize the hole design and reduce their number.

Advancements in PCB Drilling Technology

The PCB drilling process has advanced to include the following developments over the years.

• Plasma drilling, which has achieved high aspect ratios up to 10:1.
• Laser drilling for creating narrow microvias (up to 0.008mm) in high-density interconnect boards.
• Lubrication spindles that require up to 75% less lubricant (for mechanical drills).

A CNC machine working on a PCB

• Multi-drill machines (multi-station) that can accommodate up to 152 spindles.
• Automated drill wear compensation to keep the hole size constant.
• In-process cleaning systems for removing shavings and other debris.
• Automated optical inspection for analyzing the drilled hole quality.
• Predictive tool condition monitoring using acoustic and power sensors to help maintain the work tools.

Final Thoughts

 

PCB drilling is a vital step in producing quality PCBs.

Hence, following our tips is 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.