The goal of both counterbores and countersinks is to enable the head of a screw or other fastener to rest flush with or slightly below the surface of the material they are placed into. The angle at which the bigger hole is drilled separates them from one another. A counterbore is drilled straight into the material, leaving a level bottom between it and the narrower inner shaft, while a countersink’s bigger hole tapers at an angle.

Counter Bore

Except for a handful, the information required for each class is nearly the same. Since a counterbore is always drilled straight down without a taper, the angle is not necessary to know.

counterbore and countersink bits differences

Countersink

We need to know the intended angle because a countersink is not drilled straight into the material. For those who are interested in mathematics, you have probably noticed that the angle and the major hole diameter make a triangle. The angle, major, and main diameters dictate the depth to which the countersink will be drilled, yet stating your anticipated depth is a useful way to verify your expectations.

  • Which way around is the sink on the board? Above or Below?
  • Is plating or not plating appropriate for the hole walls?
  • The hole’s small inner shaft’s completed diameter. (First Drill)
  • Major Diameter: the hole’s final surface diameter
  • The tapered drill’s angle.
  • Depth at which the countersink should be drilled.

Differences between counterbore and counterskink drills in PCB

Important Distinctions Between Counterbore and Countersink Holes

Although hardware can be positioned flush on the board surface with both hole types, there are some significant variations that affect how they are used:

1. Shape of a Hole

The form of the hole is the main distinction. Counterbores have straight cylindrical walls, whereas countersinks have conical shapes. This affects the fastener’s flushness against the board.

2. Size of Top Opening

In a similar vein, the two holes differ in the size of the top opening. A countersink’s top taper gradually from the entire hole width. A counterbore is matched in diameter to the fastener and has a broader concentric cut on top.

3. Walls That Are Vertical

Counterbores have vertical walls, and countersinks have inclined side walls. Fasteners have greater shear strength when the walls are vertical.

4. Width of Bottom Opening

A counterbore’s bottom hole aperture is larger than a countersink’s of equivalent size. This increases the design’s versatility in terms of fastener size selection.

5. Material Elimination

In order to make a countersink, more material is removed from the PCB. Counterbores preserve the strength and substance of PCBs.

When to Use PCB Counterbore and Countersink?

Now that we have a fundamental understanding of counterbore and countersink holes, let’s examine their applications in printed circuit boards.  These fittings can be used on a printed circuit board, even though they are typically meant for stronger materials like metal and wood.  A PCB has holes, just as most circuit boards, and how each hole is drilled counts.
 There are screw holes in some of these holes that are utilized to attach the PCB to an application.
 The sort of screw you can use to drill countersunk or counterbore holes into the PCB depends on what kind of screw is available. Instead of saving space or choosing a smoother design, use counterbore holes if you need a more stable PCB installation.  The screws from them will provide a more stable attachment because these holes are typically big enough to fit socket fixtures.  However, if you’re looking to save space, opt for a countersink hole.

For PCBs, which is better?

Knowing the main distinctions between counterbore and countersink holes is essential to determining when to utilize one over the other during PCB assembly.

The substance you’re drilling into frequently determines which technique you should use. As previously noted, countersinking is frequently recommended when working with wood to prevent overtightened screws from damaging the material.

Most manufacturers will utilize the counterbore approach instead of countersinking during PCB assembly to prevent needless damage to the PCB since countersinking necessitates using an angle and additional depth from the drill. Additionally, countersinking necessitates greater tools and materials, which could prolong the production process and endanger the board.

A ground or earth terminal, which is essentially a physical connection to the earth and serves as a secure return point to drain excess current, can be used to establish a connection through counterboring.  Counterbore holes are also the finest option if you need to mount your PCB more securely. The screws from them will provide a more stable attachment because these holes are typically big enough to fit socket fixtures.

Principal Uses for Each Type of Hole

Countersink and counterbore holes have distinct uses because of their characteristics.

  • Typical Applications for Countersunk Holes
  • Installing flush screws on PCBs’ outside surfaces
  • Allowing low-profile bolt heads that must be flush with the surface of the board
  • Creating a sleek surface for aerodynamics on exposed external PCB layers
  • PCB mounting on thin aluminium covers or panels

Usage of Counterbored Holes in Common:

  • Fasteners for mounting machines that require a high shear strength
  • Letting spacers or washers rest flush against the PCB surface
  • Allowing bigger fastener heads to be accommodated with less material removal
  • Supplying the highest strength possible for screw connections at heavy load
  • Properly assembling internal PCB layers while reducing surface defects

Counterbores offer stronger screw joints, especially for internal PCB layers that are hidden, but countersinks are often better for applications where aerodynamics and aesthetics are important considerations.

Design Factors to Consider When Choosing a Hole Type

Engineers should consider the following aspects when designing a PCB layout and choose between countersunk and counterbored holes:

Sizes of Fasteners

More fastener heads can be used in counterbores than in countersinks of the same size.

Board Space Available

Because of their tapering design, countersinks require extra space.

Location of the PCB Layer

Counterbores work better for internal layers, whereas countersinks maximize outward layers.

Requires Shear Strength

Compared to countersunk holes, counterbores offer stronger screw joints.

Exposure to Environment

For external PCBs, countersunk holes enhance weatherproofing.

Priorities for Aesthetics

The surface finish is smoother with countersunk holes.  It will be easier to guarantee that the hole type chosen offers the appropriate functionality for the application if these factors are considered early in the design process.

 Drilling and completing Compare Counterbored vs. Countersunk Holes

  A functional, dependable PCB requires appropriate drilling and finishing procedures after the hole type has been chosen. The following are some recommended procedures:

Cutting Countersink Holes

  • Use a countersink drill bit that is specifically designed for the screw size. The correct angled hole cannot be created with standard twist bits.
  • To prevent breaking through the bottom layer or tapering too shallowly, precisely adjust the drilling depth.
  • When you get close to the bottom, don’t push too hard to prevent drill walking. Reposition and back off if there is a walk.

How Counterbores Are Drilled

  • A normal straight hole should be drilled first using a twist bit with a minor diameter.
  • Next, cut the shallow counterbore ledge to the required depth using a bigger bit.
  • When counterboring, support the board with a stiff backer to avoid a tear-out.

Finishing  Holes

After drilling, gently deburr the margins of both types of holes to prevent solder mask damage. Further polishing of countersinks with abrasive cones may be necessary to enhance fastener fit.

Proper drilling and finishing will result in smooth holes sized exactly right for the specified fasteners. This eliminates screw damage during assembly and offers reliable performance.

How to take dimensions for a Counterbore and Countersink

To account for the head of the flathead fixtures—which may be bolts, rivets, screws, or other similar objects—the angular sides of a countersink are recessed.

When drawing, the diameter, depth, and included rise of a counter-drilled hole are also provided, together with the surface diameter and angle.  The head of the fastener can rest in the recessed area of the counterbore’s flat-bottomed, cylindrical section.  When drawing and dimensioning this, the diameter, depth, and corner radius are provided and specified. In certain cases, the center can be substituted for the remaining shaft’s thickness when determining dimensions.  Either a rectangular or polar coordinate form could be used to size both holes.

Conclusion

To attach to various materials, counterbore and countersink holes are used with matching screws. It is possible, albeit uncommon, to use this as a print circuit board fixture. As we’ve seen, a counterbore is more cylindrical than a countersink, which is a hole with a cone form. This article has emphasized the distinctions between a counterbore and a countersink, as well as the parallels between them, their definitions, and how both holes function. Since the terms counterbore and countersinks can be used interchangeably, they refer to the same kind of screws that fit into both a counterbore and a countersunk hole. Additionally, we have seen how they differ in their manufacturing process by employing distinct drill bits for every kind of hole.

 FAQs

  • What minimum angle do we need to maintain for Countersink?

The hardware being used determines the countersink’s angle. Although it doesn’t have to match precisely, the hardware should have at least 50% contact with the countersunk hole. For hardware that is metric, the usual countersink angle is 90°, and for hardware that is imperial, it is 82°. We provide both perspectives in our sizes.

  • Can counter holes be plated for ground connections?

Plated is the best option if the screw is used to ground the board (such as PC motherboards) since it has numerous tiny vias radially surrounding the hole and the top, bottom, and internal ground plane connected together. The vias don’t have any heat relief. The vias make sure that the top and bottom pads are firmly attached to the ground plane, even in the event that the screw thread damages the hole plating. If not, it isn’t really important.

  • Does it cost extra in manufacturing?

However, as Scott Seidman points out, it can increase the cost of the board if there aren’t any other unplated holes in it. The type of lock washer or screw you put on the PCB may depend on whether or not there is a pad and how the pad is finished after assembly because solder has a propensity to flow cold. If the board is multilayer, there should be a lot of space between unplated holes and non-connected internal planes because you don’t want the screw shorting to (say) an internal power plane and the thread can damage the internal surface (people sometimes drill out holes that don’t quite match the mating surface).

Read More: How To Solve The Common Problems During Edge Plating In PCB Assembly? An Expert Guide

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