Beginner’s Guide to PCB Hole Drilling
PCB hole drilling is a necessary step for most electronic projects involving the creation of a new circuit board. Unless you plan to use surface-mount devices (SMDs), you will likely need to drill holes for through-hole components.
Holes are drilled into the printed circuit board (PCB) to accommodate through-hole components or to connect multiple layers of circuitry using plated-through holes.
In this beginner’s guide to PCB hole drilling, we’ll cover everything you need to know about the process. We’ll go over the type of hole in PCB board and the commonly used manufacturing technical.
Non-Plated Through-Hole
PCB holes are either plated or non-plated. Non-plated through-holes are holes drilled through the circuit board without copper plating around the perimeter or inside the hole. A non-plated through-hole (NPTH) is not connected to the conductive traces on the PCB.
These types of holes are mostly used for fastening the PCB to housing or mounting other components. You can mount hardware to non-plated through-holes that you do not want to connect to the circuitry of the PCB.
Fastener Holes
Fastener holes are drilled to accommodate fasteners, such as screws or stand-offs. Fasteners may be necessary for securing other components to the PCB that need to remain isolated from the conductive traces on the surface of the board.
For example, your PCB design may include a secondary board mounted to the main board. Fastener holes may also help secure hardware, such as a card reader or I/O port.
Mounting Holes
Mounting holes are used to secure PCBs to enclosures and flat surfaces. Most PCBs include at least four mounting holes, with one hole placed in each corner. Copper pads may sit around the holes on the outer layer of the PCB to help ground metal screws.
Countersink Holes
Countersink holes are mounting holes with a cone-shaped opening near the top. The cone shape allows screws with tapered heads to sit flush with the top of the PCB. In certain designs, you may need to keep a portion of the PCB completely flat, which is possible with countersink holes.
Instead of boring directly into the PCB, the countersink hole includes an angled cut-out. The angle of the chamber is typically between 82 and 100 degrees.
Plated Through-Hole
Plated through-holes include various types of vias, which are holes that connect layers of the PCB. The insides of the holes include copper plating, allowing the circuitry from one layer of the PCB to connect to another.
A plated through-hole (PTH) may include a press-fit design, a through-hole via, a blind via, a buried via, or a thermal via. Here is a closer look at each option.
Press-Fit
A press-fit hole is a through-hole that provides a tight fit for the metal pins on components that you want to connect to the board. Using press-fit holes may eliminate the need for soldering in certain instances, as the insides of the holes are plated with copper.
Through-Hole Via
Through-hole vias are holes that pass through each layer of the PCB. If the inside of the through-hole is plated, it can connect each layer in the PCB design.
Plated through-holes (PTHs) are typically used to connect the circuits on each layer of the board or to accommodate DIP components.
Blind Via
Blind vias are holes that extend from the surface layer of the PCB to one or more internal layers but do not pass through the other side of the board. For example, a blind via may be drilled into the top layer of the PCB, allowing you to connect the circuit to the layer underneath.
Buried Via
Buried vias are holes drilled through one or more internal layers of the PCB. The holes do not extend through the outer layers, making them buried inside the multilayer PCB.
Thermal Via
Thermal vias are small holes in the PCB designed to help with heat dissipation. The holes sit below components to decrease the risk of overheating. Thermal vias are most used with surface-mount devices (SMDs), as they often sit flush with the board.
Steps in the PCB Drill Hole Process
Preparing a circuit board may involve using premade copper-plated boards or multiple layers of material laminated together to create a board.
The individual layers of a board are called cores and may include copper foil or bare fiberglass.
Drilling Holes with Drill Bits
Drilling holes is one of the hardest steps in preparing a PCB, especially when making a press-fit PCB. You need to ensure that the hole size offers a tight fit with the pins of your components.
If you plan to use non-plated PCBs or a plated design with vias, you have greater tolerance when it comes to the hole size. You typically want to make the holes about 0.3 mm larger than the component’s leads. For example, if the pins measure 0.4 mm wide, the holes should measure about 0.7 mm wide.
Blind vias are often drilled with drill bits measuring 0.15 mm to 0.2 mm. After adding copper plating, the inside diameter may measure just 0.05 mm or slightly wider.
Buried vias must be drilled before laminating multiple board layers. The via is buried between layers. With blind vias, you can drill the holes before or after lamination. However, drilling the holes for blind vias before lamination is easier. You also need to drill blind vias before lamination if you need the circuitry on the bottom side of the layer to connect to other layers.
You can use a powered drill, drill press, or handheld manual drill to drill the holes in the PCB. A handheld drill offers greater precision, while a powered drill or press can save time, which is useful when drilling dozens of holes in a circuit board. A drill press can provide the most accurate results.
Adding Plated-Through Holes to the Walls of the Hole
The inside walls of the holes may include copper plating for increased conductivity. Plated-through holes are typically called “vias,” as they provide a way to connect multiple layers of circuitry.
A thin layer of copper is added using one of two chemical processes—electroless copper deposition and electroplating.
An electroless copper deposition involves several steps for depositing an even layer of copper across the entire surface of the board and the insides of the holes. The board is dipped in a chemical bath containing copper salts and other ingredients.
Manufacturers may also use electroplating instead of electroless plating. Electroplating involves applying an electric current to the board while soaking it in a chemical bath. However, both options require you to etch the circuit into one or both sides of the PCB afterward.
PCB etching typically involves the use of tin to protect the copper traces and hole plating. The unwanted copper is then dissolved by immersing the PCB in a chemical solution.
Checking Non-Connected Holes for Additional Copper Pads
Non-connected mounting holes may contain copper pads. Adding copper pads to mounting holes allows for mounting with metal screws and makes it easier to ground the circuit.
Grounding the metal screws helps eliminate electromagnetic interference (EMI). The mounting holes should only be left non-plated when using plastic screws or plastic standoffs.
Ensure that copper padding is included around non-connected holes before etching the outer layer of the PCB. If you have already removed copper from around the holes, you can add copper pads using adhesives and a soldering iron.
Inspecting the Surface Mounts on the PCB Surface
Along with through holes, your PCB design may include surface mounts for surface mount technology (SMT) components. Surface mounts do not require drilling, as the components are soldered to copper pads on the surface of the PCB.
Surface mount pads should connect with the rest of the circuit. If you notice any cracks or breaks in the traces, you may need to repair the pads. Using adhesive-backed copper pads is the easiest solution, as you can simply adhere the new pads in place and bond them using a soldering iron.
Finishing the PCB with a Solder Mask
A solder mask is used to protect the copper traces on your PCB. The solder mask is a lacquer-like material that protects against oxidation and other forms of damage.
After drilling, plating, and etching the PCB, clean it with a brush and a cleaning solvent. After the board dries, apply the solder mask.
Summary
The PCB hole drilling process depends on the types of holes that you need to drill. Non-plated through-holes (NPTHs) are often made using larger drill bits to accommodate screws and other fasteners.
Plated through-holes (PTHs) are added for through-hole components and feature copper plating on the inner walls. Your design may also include blind vias and buried vias, which are holes that do not go through each layer of the PCB. Vias typically need to be drilled before laminating multiple layers of a circuit board.
After drilling the holes, you can add copper plating using electroless copper deposition or electroplating. The PCB is then cleaned using a solvent and sealed using a solder mask.
Now that you understand how to drill a hole in a PCB, the next step is to try it yourself. You can also continue to learn more about PCB hole drilling and other topics by subscribing or joining our list. Join today!
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