Countersink and Counterbore Holes in PCBs

Printed Circuit Boards (PCBs) are foundational to modern electronics, and their design includes numerous mechanical features to ensure optimal performance and assembly. Among these are countersink and counterbore holes—two critical types of mechanical drillings that support hardware mounting. These features are essential for applications where flush surfaces or secure fastener placement is needed.

What are countersink and counterbore holes in PCBs?

A countersink hole is a cone-shaped hole that is notched or drilled into a PCB laminate. This tapered hole allows a flat-head socket screw head to be inserted in the drilled hole. Countersinks are designed to allow the bolt or screw to stay tucked inside with a planarized board surface.

A counterbore hole involves creating a flat-bottomed hole. The sides of these holes are parallel and vertically straight. Cylindrical-shaped counterbore allows a hex-headed screw to fit under the drilled hole. This hole is the bigger version of a coaxial hole.

Both types of holes serve mechanical purposes but differ in shape, application, and manufacturing requirements.

PCB Material Design Guide

When designing PCBs with countersink or counterbore holes, material selection plays a vital role in ensuring structural integrity and manufacturability. Key considerations for choosing PCB materials include basic properties of the dielectric material, signal loss characteristics, copper foil selection, and thermal properties. Common materials used for such designs include FR-4, aluminum-based substrates, ceramics, and PTFE composites.

PCBAStore offers fabrication capabilities using materials like FR-4 / PI / ALU / Ceramic / PTFE etc., making it suitable for custom mechanical features like countersink and counterbore holes.

When to use countersink and counterbore holes

Countersink holes are implemented in compact designs where space is a critical constraint. The planarized surface makes room for more surface area. These are largely used in tight-fitting, compact applications to enhance flexibility and provide space for installation. Devices such as smartphones, smartwatches, or compact medical instruments often employ this feature.

Counterbore holes provide enough room to fix the sockets. They are the appropriate choice when your design requires strong attachment rather than space-saving and even surface finishes. Applications include washers, industrial controllers, automotive modules, or any scenario requiring robust mechanical fastening.

Drilling requirements for countersink and counterbore

Countersink

Conical countersink holes require great precision to accommodate screws with a flat head. These types of holes are bored into a PCB; hence, determining the correct angle is vital. Standard angles include 82° and 90°, while other options such as 60°, 100°, 110°, and 120° may be used depending on design specifications.

The depth of the sink depends on the major hole diameter and the angle of the sink. If the major diameter remains unchanged, the depth varies inversely with the sinking angle.

To fabricate an accurate countersink hole, designers must specify:

· Drill bit angle

· Major (countersink) diameter

· Through-hole diameter

· Side (top or bottom) requiring countersinking

· Depth

· Plated or non-plated status

Counterbore

The sides of the counterbore hole are parallel to each other and do not require any tapering. Hence, designers need not mention an angle to manufacture this.

Details required for proper fabrication include:

· Major (surface) diameter

· Drilling depth

· Bore location (top/bottom)

· Shaft diameter

· Plating requirement

These specifications help ensure compatibility with mounting hardware during final assembly.

Symbolic representation

Standardized symbols simplify documentation across engineering teams.

The countersink hole is represented by the letter ‘V’ with the numerical value of the diameter beside that. For example: Ø0.25 mils through-hole with Ø0.50 mils countersink at an angle of 82°.

The counterbore resembles a square, opened from the top. These are specified with drilling diameter, depth, and shaft diameter. If material thickness below the bore is significant, it should be mentioned instead of just depth.

Countersink Vs. Counterbore

This comparative table helps engineers decide which type best fits their application based on functional priorities such as space constraint or strength.

Manufacturing Equipment at Sierra Circuits

While many facilities offer standard PCB fabrication services, advanced features like countersinks and counterbores demand precision tooling.

Our factory have been offering full spec electronic manufacturing solutions for 16 years to meeting the needs of our customers from different industries in terms of cost-effectiveness, quality , delivery and any other requests.

We can fabricate Buried & Blind holes heavy copper up to 30 oz Rigid-flex board and others with our state-of-the-art PCB equipments.

This includes high-speed CNC drilling machines capable of producing complex geometries required by both conical (countersinks) and cylindrical (counterbores) structures.

Turn-times as fast as 1 day

Speed matters when prototyping or addressing market demands quickly.

PCBAStore offers rapid PCB prototyping services for quick-turn PCB at high quality and low cost that no only makes your PCBs quick, but also makes your job right as well as cost-effective.

For instance:

· 2-layer PCBs can be delivered within 24 hours

· Multilayer boards take only 2–4 days

Such timelines enable engineers to iterate faster without compromising on quality—even when complex mechanical features like countersinks/counterbores are involved.

Talk to PCBAStore Expert today：get instant online PCBA quote from PCBAStore

When your project demands precision mechanical drilling along with reliable assembly services under one roof:

PCBAStore offers full Turn-Key and partial Turn-Key Circuit Board Assembly Services Our experienced team enable us to meet all your PCBA needs under one roof in an inexpensive way

Whether you're developing consumer electronics requiring flush-mounted screws via countersinks or industrial devices needing secure fasteners via counterbores,

You can get a PC board price instantly after a few option selections All PCBs will be electrically tested
and
You can get the labour assembly cost in seconds

Simply visit our website or email us at svc@pcbastore.com for personalized support on your next project involving advanced PCB drilling techniques like countersinks and counterbores.