Difference: Countersink vs. Counterbore Holes in PCBs

The printed circuit boards (PCB) have several features that contribute to its function and aesthetics. Some standard features we focus on are substrates used, finishing, layers, and so on. Features like holes are often overlooked. Do you know – a printed circuit board may have two types of screw holes – countersink and counterbore! These holes help screws to be fixed to the board surface. These holes may not be generally visible to us, but they differ lot in terms of application or designs. Are you intrigued to learn more about it? If so, stay tuned to this post.

An Overview of Countersink and Counterbore Holes

This section offers you a brief overview of countersink and counterbore holes.

• Counterbore Hole: A counterbore hole is a cylindrical-shaped hole that has two parts: a small, deep hole and a larger, shallow hole on top. Imagine drilling a regular hole, but then widening the top part to make it flat and larger. The purpose of a counterbore hole is to hide the head of a screw or bolt inside the hole so that it sits flush with the surface of the material (like the surface of a PCB). This makes the surface smooth and prevents the screw from sticking out, which is useful when you want everything to be even or if you plan to put something else over it.

• Countersink Hole: A countersink hole is a canonical-shaped hole that is more complex than a standard hole because it takes more effort to drill. This type of hole is shaped to fit a screw, allowing the screw cap to sit below the surface of the board. The depth of the hole can vary. This depends on whether you want the screw to be visible on top of the board or if you want to drive it deeper to hide it. The term "countersink" refers to both the hole made in the board and the tool used to create that hole. This tool allows a countersunk screw to sit below the surface of the board. Countersinks can be made at six angles: 60°, 82°, 90°, 100°, 110°, and 120°. The most commonly used angles are 82° and 90°.

Making a hole on a bare circuit board may look simple and easy. However, certain considerations must be made to ensure the selected hole offers the right function. 

1. Shape: A countersink hole has a conical shape, tapered to fit flat-head screws, while a counterbore hole has cylindrical shape with a flat bottom, designed for round or socket-head screws.
2. Screw head fit: Countersink allows the screw head to sit flush with or below the surface. Counterbore recesses the screw head deeper into the material, making it sit below the surface.
3. PCB thickness and material: Countersink holes work well on thinner boards; deeper angles may not suit thicker or multi-layer PCBs. Counterbore holes can also be used on thicker boards, but precise drilling is needed to avoid damaging inner layers.
4. Aesthetics and surface considerations: Countersink creates a smooth, flush finish and is ideal for clean-looking designs. While counterbore results in a recessed area but maintains a flat surface around the screw.
5. Structural integrity and load distribution: Countersink hole may not handle high mechanical stress as evenly. While, counterbore distributes load better, providing stronger support for heavier components.

Countersink and counterbore holes differ in shape and many other things. The following pointers will help you understand it better. 

1. Vertical walls: Countersinks have slanted side walls, while counterbores have straight walls. Straight walls give fasteners more strength against shearing.
2. Top opening size: The size of the top opening differs for the two types of holes. A countersink has a gentle taper from the full width of the hole. A counterbore has a larger, concentric cut on top that matches the diameter of the fastener.
3. Material removal: More material is removed to make a countersink in the PCB. In contrast, counterbores keep more material and strength in the PCB.
4. Bottom opening width: The bottom opening of a counterbore is wider than that of a similarly-sized countersink. This gives you more options when choosing fastener sizes. 

Here are some use-case scenarios for countersink and counterbore holes: 

1. Countersink Holes

• Flush mounting components
• Electronics with slim profiles
• Aesthetic PCB designs
• Vibration reduction

2. Counterbore Holes

• Heavy component mounting
• Thicker PCBs
• Mechanical assemblies
• Mixed material devices 

Countersink and counterbore holes serve distinct purposes in PCB design, each offering unique benefits depending on the application. Understanding their differences helps ensure optimal component placement, structural integrity, and aesthetics in PCB projects. For professional PCB design and manufacturing services or more information about selecting the right hole type for your project, contact Accelerated Assemblies today! The experts at the company will guide you through the process to achieve the best results.