Introduction
Drilling is a critical process in the manufacture of printed circuit boards (PCBs). The holes drilled in the PCB, known as vias, interconnect the conductive layers to form electrical connections between components. High precision drilling machines equipped with specialized drill bits are used to make the thousands of via holes required on a typical multilayer PCB.
This article provides a detailed overview of PCB drilling. It covers the drill bits – their materials, geometries, features and selection criteria. The machines used for drilling along with their capabilities are explained. The sequence of steps followed in the automated drilling of vias and through holes in PCB fabrication is also described.
Drill Bits for PCB Drilling
High speed steel, tungsten carbide and diamond drill bits are used for drilling holes in PCBs. The choice depends on factors such as hole size, board stackup, accuracy needs, and material type.
Materials Used for Drill Bits
1. High Speed Steel (HSS)
- Alloy tool steel with high hardness and wear resistance
- Cobalt HSS offers better performance than M2 HSS
- Used for drilling holes above 0.4 mm diameter
- Lower cost compared to carbide and diamond
2. Tungsten Carbide
- Dense metal-ceramic composite of tungsten carbide grains in cobalt matrix
- Hard, heat resistant, maintains sharp cutting edge
- Used for micro-via drilling ≤ 0.25 mm diameter
- More wear resistant than HSS with 5-10x tool life
3. Industrial Diamond
- Polycrystalline diamond (PCD) or single crystal diamond used
- Excellent hardness, thermal conductivity and wear resistance
- Allows high drill speeds and feed rates
- Used for holes < 0.15 mm and multilayer drilling > 16 layers
- Most expensive drill bit option
Drill Bit Geometries
Various physical geometries used for PCB drill bits:
- Standard straight flute – For general purpose drilling
- Double flute/angle flute – Reduced thrust, good debris ejection
- Core drills – Hollow inside for laminate debris extraction
- Step drills – Different diameters along length for various hole sizes
- Conical shape – Entry taper for ease of drilling multilayer stacks
Specialized drill point geometries like screw point, dust core point and diamond point are also used for specific applications.
Key Drill Bit Features
| Feature | Description |
|---|---|
| Diameter tolerance | ±10 μm for holes > 0.15 mm; ±5 μm for microvias |
| Suited for stack height | Max PCB thickness it can drill, typically 1.5x bit diameter |
| Point angle | Typically 118°-140°; higher for HSS and diamond |
| Surface coating | TiAlN, diamond coatings for wear resistance and lubricity |
| Shank type | Cylindrical or 3 faceted shank with tolerance |
| Tool life | Number of holes drilled before noticeable wear |
| Rotational speed | Optimum drill spindle RPM for smooth cutting |
Drill Bit Selection Criteria
Considerations for choosing right drill bit:
- Hole size – Smaller microvias need carbide/diamond, larger holes use HSS
- Material type – HSS for epoxy glass PCBs, diamond for exotic boards
- Accuracy – Carbide/diamond bits have less than ±5 μm tolerance
- Plated or non-plated – Avoid clogging with plated hole specific geometries
- Blind or through holes – Conical bits easier for multilayer blind vias
- Stage count – Diamond used for PCBs above 16 layer thickness
- Drilling machine – Match shank, precision and speed requirements
- Budget – Diamond is most expensive, HSS lowest cost per bit
Proper drill selection ensures high hole quality, diameter consistency and productivity in PCB drilling.
PCB Drilling Machines
Automated precision drilling machines are used in PCB fabrication for making the hundreds to thousands of holes required on each board.
Types of Drilling Machines
1. High Speed Drilling
- Uses air bearing spindles for precision and speed
- Capable of >100,000 RPM rotational speed
- For holes ≥ 0.2 mm diameter
- Ideal for high throughput
2. Micro-Drilling
- Precise drilling of holes ≤ 0.3 mm
- Spindles with ceramic bearings used
- Rotation speed is 40,000 – 60,000 RPM
- Lower material removal rate
- Uses laser micromachining to ablate material
- For microvias ≤ 0.10 mm diameter
- High accuracy of ± 25 μm achievable
- Low taper and high circularity
- Compatible with sensitive materials
4. Plasma Drilling
- Uses oxygen plasma to etch micro holes
- For multilayer microvias down to 0.015 mm
- High densities of 107 holes/m2 achieved
- Limited by aspect ratio of holes
Machine Capabilities
| Feature | Capability |
|---|---|
| Hole size range | 0.01 mm to 6.5 mm |
| Hole tolerance | ±0.025 mm |
| Hole position accuracy | ±0.03 mm |
| Minimum pitch | 0.2 mm |
| Hit ratio | Up to 99% |
| Depth control | ± 0.05 mm |
| Spindle power | Up to 10 kW |
| Spindle speed | Up to 200,000 RPM |
Advanced drilling machines can drill a large range of via sizes with excellent accuracy at high speeds.
Automation Features
Modern PCB drilling machines offer extensive automation:
- Automatic tool changing with multi-spindle heads
- Automated drill wear monitoring and compensation
- Intelligent tool life management
- Automatic depth setting and breakthrough detection
- Automatic fiducial and pattern recognition
- Integration with upstream and downstream processes
- Programmable drilling parameters
- Troubleshooting and diagnostics capabilities
This enables optimized, continuous and unmanned operation with minimal human intervention.
The PCB Drilling Process
Drilling forms an integral step in the overall PCB fabrication sequence. Here are the typical stages:
1. Program Generation
- CAD drilling data is converted to machine instructions
- Optimal tool selection and hole grouping applied
- Programs generated for each drill tool size
2. Setup
- The prepared inner layer PCB panel is loaded in the drilling machine
- Drill bits are loaded in the spindles based on sequence
- Machining parameters, offsets, and tool registers set
3. Fiducial Recognition
- Fiducials on the PCB used to align it correctly under the spindles
- Optical alignment mechanism recognizes fiducial pattern
- Alignment accuracy of under 25 μm achieved
4. Stage Drilling
- Different tool sizes used in sequence from smallest to largest holes
- Multiple hits used for deeper multilayer boards
- Depth limit set for each tool to avoid breakthrough
5. Deburring
- Light deburring between drilling stages using same tool
- Prevents debris buildup and clogging while drilling
6. Breakthrough
- Last hits drill fully through the PCB thickness
- Automatic breakthrough detection to stop at exit
- Prevents damage to sensitive exit side layers
7. Cleaning
- PCB panel cleaned in chemical baths
- Removes burrs, drilling debris and lubricants
- Ensures good plating quality of holes
8. Inspection
- Drilled holes examined for any defects
- Checks for diameter, circularity, burrs, hole position accuracy
- Aids in tool wear analysis and correction
The drilled panels then undergo metallization and plating of the holes before further PCB fabrication.
Key Quality Metrics in PCB Drilling
Maintaining hole quality is critical for reliable functioning of the PCB. Some key metrics evaluated:
1. Hole Position Accuracy
- Difference between designed and drilled hole center
- Influenced by drill guide precision
- Tolerance ±0.05 mm typical requirement
2. Hole Diameter
- Check against specified hole size
- Affected by tool wear, machine parameters
- Tolerance ±0.025 mm standard requirement
3. Circularity
- Measure of hole roundness
- Ratio of max and min hole diameter in perpendicular axes
- Value close to 1 indicates high circularity
4. Barrel Hole Wall
- Taper or hourglass shape of plated hole
- Due to non-uniform plating thickness
- Can affect hole resistance
5. Hole Breakout
- Separation around hole exit on outer layer
- Due to drill penetrating the last laminate
- Can impact pad connection quality
6. Drill Smear
- Resin debris redeposited on hole wall post drilling
- Impacts copper plating adhesion and conductivity
By optimizing the drilling process, high quality holes with correct size, placement and profile can be reliably produced.
Advancements in PCB Drilling Technology
Some recent developments in drilling technology are:
- Laser drilling capable of microvias down to 0.008 mm for HDI boards
- Plasma drilling with higher aspect ratios up to 10:1
- Automated optical inspection systems for fast in-line hole quality analysis
- In-process cleaning systems to remove debris during drilling
- Predictive tool condition monitoring through power and acoustic sensors
- Multi-station machines with up to 152 spindles for high throughput
- Reduced lubrication spindles that require 75% less lubricant
- Automated drill wear compensation to maintain hole size
These innovations allow drilling more precisely at higher densities and through greater PCB thicknesses.
Conclusion
Drilling is a critical fabrication process that determines the structural integrity of the PCB. The specialized drill bits and precise drilling machines along with optimized operating parameters enable manufacture of high density PCBs with thousands of high quality microvias. As PCB complexity increases, innovations in drilling technology will be vital to achieve the hole placeability, accuracy and surface finish required. Adopting automated drilling machines with advanced inspection and tool control capabilities offers electronics manufacturers a competitive edge.
Frequently Asked Questions
Q1. How are the optimal drill bit and operating parameters selected for a particular PCB design?
The key considerations for selecting drill bit and optimum drilling conditions are:
- Hole size distribution – Choose right tool sizes
- Board material type – Determines drill material
- Board layer count – Indicates rigidity, hits required
- Hole tolerance – Guides drill precision needs
- Plating requirements – Influences bit geometry
- Target productivity – Drives drill speed and feed rates
- Drill life needs – Tool material and coatings
- Drilling machine capabilities – RPM, power, fixture type
Q2. What are some best practices to improve PCB drilling quality and productivity?
Some best practices for high performance PCB drilling are:
- Frequent drill sharpening and replacement for dimensional consistency
- Proper drill point geometries for different hole types
- Optimized programming to minimize tool changes
- Adjusting parameters based on wear measurements
- Regular maintenance and cleaning of machine
- In-process cleaning to prevent debris buildup
- Dedicated drilling machines for different hole sizes
- Quality inspection feedback into process settings
- Taking full advantage of drill automation capabilities
Drill Types
The types of drills used for PCB drilling are different from what you would find for normal drilling. Most people only know about regular drills being used in the drilling process, but there are also other drills present. The most commonly used drill is the twist drill which can be found in the sizes of 0.1-2.0mm and 0.3-4.0mm, as well as slotting drills that are usually found in sizes of 1.5mm and 2.5mm, as well as both various wood drills that are usually found to be wood files around 5-8cm long (of which some have been made specifically for PCB drilling). There are also twist drills used specifically for drilling PCBs as they are milled to have better stability than regular twist drills.
A few essential parts of a drill machine, including a drill chuck or clamp, are used to hold the bit in place. It is also responsible for having the bit spin when power is applied. The arbor, also known as the spindle, does just what it says; it allows the chuck to attach the bit through a shaft. The chuck and arbor are usually found in the same drill machine to make it easier for the user.
PCB Hand Drill
A PCB hand drill is a drill for use on printed circuit boards. The PCB hand drill generally has a chuck, which is a part of the hand drill that holds the drill bit in place. The chuck on a PCB hand drill can be tightened by using either an Allen key or an Allen wrench. A PCB hand drill comes with its own set of instructions and package contents.
A Back Drill PCB
A back drill PCB is a kind of drill designed to drill holes in a printed circuit board. The holes are then used for soldering or inserting wires or component leads into the holes by hand, hence the name. The PCB’s surface is cut away with a blade, exposing the copper layer. Then the exposed copper is removed using a tool called a burr cutter. Once this has been done, a back drill PCB can be fitted with components and connected electrically to its power supply circuit board.
The circuit board drill bit
The circuit board drill bit is a type of drill bit with a sharp point at one end and a flat face. The circuit board drill bit can create holes through which wires can be inserted or soldered into place. A good tip in using the circuit board drill bit is to ensure that the flat face is held firmly against a surface to stop moving in any direction. This will ensure that holes are drilled in the PCB at right angles.
Tips and Tricks
Circuit boards are created by drilling holes into a sheet of copper or other metal. The process requires careful precision and accuracy for each hole and detailed planning of where each drill bit will go to avoid damaging any components. Here are some tips to make the process of drilling PCBs foolproof:
1. Drill Pilot Holes for Proper Drilling
The first step before any drilling is performed is to drill a pilot hole. This is used to keep the drill bit from “walking,” which means the bit starts in one location and moves towards an unintended direction while drilling. It can be done by hand using a small drill bit or can be done with an automatic tool called a drill press.
If the pilot hole is made using a drill press, the drill bit heads are pulled out one by one from the tool. The number of bits used in this process depends on the size of the PCB to be drilled. For example, if a 0.2 mm drill bit is used, four of these can be pulled out for one hole. This process will usually leave a small metal mark on the PCB as each head gets removed.
2. Use a Straight PCB Drill Bit When Drilling at an Angle
It is a great practice when drilling at an angle. Drill bits are usually sold in sets and come in different sizes. The sizes include the following:
Wire gauge drill bit: This is used for wires that are 0.8 to 1 mm thick.
Small drill bit: This size is for holes between 0.7 to 2 mm thick or diameter and includes flat and round shapes.
Medium drill bit: This type is used for holes ranging from 2 to 10 mm thick or diameter and usually includes flat and round shapes.
Large drill bit: This size is used for holes that are 5 mm or greater. It can be flat or round, depending on the manufacturer.
3. Use a Correctly Sized Drill Bit
It is very important to make sure the drill bit you use for your PCBs is the right size. If the bit is too big, it can damage the components in your circuit board drill. On the other hand, if it is too small, you will not pass wires through the holes you drill.
4. Use a Drill Bit of Appropriate Speed and Power
The power and speed of your drill determine how fast or slow a hole is drilled in metal. The most common options are:
High-speed bit: This type of bit drills through metal quickly and efficiently but can also cause problems if used for too long at a time.
High-speed steel bit: This type is used for larger drill holes and works well to drill multiple PCBs that are not too thick.
Electroplated bit: These bits are used in the process of drilling circuit boards and plating, as well as when making holes in the thick board or for use with a high-frequency air hammer.
5. Use a Drill Press
A drill press is the best choice for making sure that you have the best chance of drilling accurate holes. They can drill at least four times more efficiently than a hand-held drill and usually use industry-standard bits. The only option is to buy a new one if you decide to go with this option.
6. Understand the Operation of a Drill Press
Drill presses vary depending on their cost and capabilities, but they all work by simply injecting the right amount of pressure needed to drill through metal. The more pressure applied, the faster a hole is drilled. There are also different types of drilling such as “cross drilling,” “plunge drilling,” “ventilated holes,” and “inclined ends.” The most commonly used type of drill press has perpendicular faceplates (a metal plate with drill holes facing up at an angle). When using this type, ensure that the drill bit is facing up and the angle matches that of the holes in the PCB.
7. Use a Drill Press to Drill PCBs
A drill press can be used in every phase of drilling PCBs. It is a great help, especially when you need to drill holes with precision and accuracy. Although it takes a while for your drill press to get adjusted, it will pay off in the end as long as you use it properly.
8. Be Careful When Drilling
Drilling holes in a circuit board can be challenging if you don’t have the right tools and materials. It is important to take your time and be patient when drilling holes because rushing through the process can cause damage to the board. When drilling, always ensure that your drill bit is not spinning too fast or too slow. It is also important to use goggles while drilling so that you don’t damage your eyesight.
9. Clean a PCB After Using a Drill
Once you are finished drilling your board, you must clean the holes with a brush and solvent. The solvents will remove any metal shavings that may have been created during drilling holes in PCBs. This will ensure that your board is ready for use when you are finished.
10. Apply Solder to the Drilled Holes
Once you are done drilling your PCB, you must apply solder to the new holes and use a soldering iron with a small tip to melt them. To ensure that the solder sticks properly, run a wire from one of the holes and apply heat. This will prevent the solder from dripping through the holes. Then lightly press it down to make sure that it is firmly attached.
Once you have the right drill bits, all you need to do is to make sure that they are free of small chips and debris when making a hole or a slot on your PCB. If there are any chips or debris found on the bit, this could cause problems with the drilling process and produce some unwanted results.
When it comes to PCB drilling, it can be accomplished without risking damaging your drill bit if you do it correctly. These tips will help you to easily drill your PCBs.
Your mechanical parts can be damaged if they come in contact with the bit while the machine is working. There are just too many factors that can make a PCB drilling process go wrong. You should always remember to wear protective clothing, such as gloves, goggles, and masks, as certain toxic fumes could be produced during your drilling session.
To those who are unaware, there is some small dust that comes out from the drill bit when you use it. This might not seem like much, but if you bring this into contact with your body and inhale it, it can lead to complications such as respiratory problems. Therefore, it is essential that you make sure that there is no dust left on your machine after each drilling session. You can do this by having a wet cloth handy whenever you finish drilling a hole on your PCB.
Conclusion:
With the right tools and materials, anyone can make their PCBs. It is a very useful skill that you can learn quickly and easily. It is important to have the right equipment by your side at all times so that you can complete your circuit boards in time for your projects. Some of the best equipment to use for drilling holes in PCBs include drills, drill presses, saws, and PCB solder stencils.
