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PCB Fabrication

Countersink VS Counterbore Hole

Weller delivers precision-machined countersink and counterbore holes in PCBs – available in plated or non-plated finishes – for flush-mounted fasteners and secure component seating.

Countersink and Counterbore Hole in PCB

When your electronic circuit board need to be locked together with other equipment by some cone shape or T shape screws, the related mounting holes need to be designed on PCB accordingly so as that the PCB manufacturer can manufacture them purposely.

Generally, two types of shapes crews are widely used by designer, countersink hole or counterbore hole.

PCB Counterbore Hole design guidelines
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Plated Counterbore Holes in PCB Drilling

Countersink hole

A countersink hole is a hole with cone-shape drilled by printed circuit board manufacturer on the printed circuit board in PCB manufacturing process. Typically it is used to mount the tapered head screws.

Counterbore hole

Typically a counterbore hole is used when the mounting fastener is required to mount flush with or below the level of the circuit board surface. Counterbore hole drilling including creating a flat-bottomed hole and a cylindrical-shaped hole. The sides of these flat-bottomed holes are parallel and vertically straight. And the cylindrical-shaped counterbore can allow a hex-headed screw to sit under the drilled hole. This hole is the bigger version size of a coaxial hole.

PCB Counterbore Depth Requirements

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Countersink and Counterbore Hole, How to Choose it for Your PCB Design?

PCB Counterbore Depth Requirements
Nuts and screws mounted into countersink hole
What is PCB Counterbore Hole
Screws inserted in counterbore hole
Countersink hole is the first choice when the design is compacted in a critical constraint space. The planarized surface can release space for more surface area. These are widely used in tight-fitting, compact applications to improve flexibility and provide space for installation. For example, they are incorporated in smartwatches, smartphones, and other smart IOT devices.

Counterbore holes generally is to provide enough space to fix the fastener. They are ideal choice when your design is required strong mounting quality rather than space-saving or surface finishes. These holes can be used in washers and other electronic products where required highly secured fitting.

Drilling Requirements for Countersink and Counterbore

PCB Counterbore Hole design guidelines
Various angles of countersinks holes

Countersink

Cone shape countersink holes require extreme precision to match the screws with a flat head. These types of holes a drill into a printed circuit board, therefore, it is vital to have correct angle. There are a wide range of drill bites with different angles is suitable for creating countersinks holes. Generally, 82°and 90°is mostly commonly applied angles. Other angles like 60°, 100°, 110°, and 120 °are also available for design requirements. It is essential to have the angle of the larger hole matched with the tapered angle of the fastener.
What is PCB Counterbore Hole
The depth of the sink is subject to the major hole diameter and the angle of the sink. The depth varies inversely with the sinking angle If the major diameter remains unchanged.

To mostly accurately drill your countersunk holes in printed circuit board, we will need the following information below:

  • 1. Angle of the drill bit.
  • 2. Major Diameter (finished diameter of the hole at the surface)
  • 3. Depth the countersink is to be drilled
  • 4. On which side of the board is the sink? Top or Bottom?
  • 5. The finished diameter of the shaft of the hole
  • 6. Is the sink and shaft to be plated(metalised) or non-plated?
What is PCB Counterbore Hole
Metallized countersink hole

Counterbore

Because the sides of the counterbore hole are always in parallel to each other and do not require any tapering. Therefore the designer do not need to specify any angle to manufacture this.
PCB Drilling: Counterbore Specifications
To build your counterbored holes, we need to know the below information:
  • 1. Major Diameter (or finished diameter of the hole at the surface).
  • 2. Depth the countersink is to be drilled.
  • 3. On which side of the circuit board is the sink? Top or Bottom?
  • 4. The finished diameter of the shaft of the hole.
  • 5. Whether the bore and shaft are to be plated (metalised) or non-plated?
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Don’t hesitate, contact us to start discussing your projects. We prioritize your inquiries and aim to respond within 12 hours.

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CAD Symbolic Definition

The countersink hole is typically defined by the letter “V”, with the value of the diameter size beside that. Why using this symbol to represent that because the side view of the hole looks like the letter “V”. From a countersink symbol below where you will see that: through hole diameter size is 104mil, and countersink diameter and angle are 170mils and 100° respectively.
Counterbore Holes in PCB Manufacturing
Countersink hole symbol
The countersink hole is typically defined by the letter “V”, with the value of the diameter size beside that. Why using this symbol to represent that because the side view of the hole looks like the letter “V”. From a countersink symbol below where you will see that: through hole diameter size is 104mil, and countersink diameter and angle are 170mils and 100° respectively.
The counterbore like a square with opening from top side. These are respectively representing the drilling diameter, depth, and diameter size of the counterbore. If the material thickness below the cunterbore is significant, it is a must to define the material thickness instead of the hole depth.
What is PCB Counterbore Hole
Counterbore hole symbol
Above is two types of counterbore symbols illustration. You can see from two pictures that the major diameter is 375mil, counterbore diameter is 375mil, and the drill depth is 312mil.

Countersink VS Counterbore, Similarities and Differences

CharacteristicsCountersinkCounterbore
ShapeConical holeCylindrical, flat-bottomed hole
Angle 82°, 90°, 60°, 100°, 110°, and 120°No angle required

Countersink & Counterbore Holes in PCBs | Weller Manufacturing

Weller specializes in precision PCB manufacturing, offering both plated and non-plated countersink and counterbore holes for advanced circuit board applications. Our capabilities include high-tolerance countersunk holes (for flush-mounted fasteners) and counterbored holes (for bolt head seating), ensuring reliable performance in aerospace, automotive, and industrial electronics.

Request a quote for custom PCB solutions with machined holes today.