Learn about PCB tooling holes.
Find out what’s the right size for PCB tooling holes.
Figure out where to place PCB tooling holes in a design.
My photography skills, or the lack thereof, often invite their fair share of criticism. While I know about the “rule of thirds” in composing a photograph, something happens in that last split second before I press the button where I just can’t seem to maintain the desired camera angle. The result is always either a blurry picture or a composition that just looks “off” even though I could have sworn I was holding the camera higher. At least, that’s what happened until I invested in a tripod. Once I bought a tripod, I was finally able to keep the camera still and nail each angle with precision.
Fixing anyone’s awkward photography skills with a tripod is easy. However, correctly aligning a PCB design is a bit trickier. If you fail to include PCB tooling holes to ensure alignment in your design, you could be in for an earful from the PCB fabricator or assembler. Worse, you may need to rework and produce a whole new batch. To understand how to prevent these potential issues, let’s take a closer look at PCB tooling holes.
What Are PCB Tooling Holes?
PCB tooling holes ensure alignment accuracy in manufacturing
If you’ve ever visited a PCB production facility, you’ll find that it’s filled with machines for the entire manufacturing flow. These machines turn a PCB manufacturing file into a physical PCB, and later, populate it with components. Precision is key to ensure that the final product is free from issues—PCB tooling holes design plays an important role in this.
PCB tooling holes, or mounting holes, are circular openings made at the edge of a PCB. Tooling holes are non-plated, and they are used by machines to hold the PCB down for alignment. During the fabrication process, it’s imperative that the PCB be kept still and properly aligned for drilling. If the PCB is not kept still, it will be impossible to deliver precisely-drilled holes.
When the fabricated PCB is sent for assembly, the tooling holes will be needed again if there are SMD components in the design. The machines will use the tooling holes for stencil alignment when applying solder paste and placing SMD components with the pick-and-place machines.
It is important to note that PCB tooling holes should not be confused with fiducial markers. Fiducial markers are pads that are created on the PCB to provide a reference for optical pick-and-place machines. However, both are equally important when designing a PCB with SMD components.
PCB Tooling Holes Design
What’s the Right Size for PCB Tooling Holes?
Common drill sizes are acceptable for PCB tooling holes
Usually, common sizes like 1mm, 1.5mm, and 2mm are acceptable tooling hole sizes for most manufacturers. If you’re unsure, make sure to consult with your PCB manufacturer. For uniformity, you’ll want to stick with a common size for all tooling holes on a PCB.
Besides size, you’ll also need to ensure that the PCB tooling hole isn’t plated. A non-plated hole is better in terms of accuracy compared to a plated one. Also, ensure that there is a solder mask expansion that slightly extends over the hole.
Where Should You Place PCB Tooling Holes?
Place PCB tooling holes on a tooling strip to save space
Now here’s the tricky part: The textbook advice on PCB tooling hole placement is to have them at the edge of the board. Having the holes at the edge of the board ensures stability, as long as the center of gravity is covered by the perimeter of the tooling holes. There should also be a clearance between the tooling hole and adjacent traces or components.
However, the demand for smaller-sized PCBs is greater than ever. Even an additional four tooling holes can take up precious space for a compact PCB. Thankfully, there are no rules stating that the tooling holes need to be part of the actual design. You can have both the tooling holes and space for a compact design by adding tooling strips on the PCB. A tooling strip is an extension that is V-scored to the main PCB. It can be depanelized after production is complete.
Instead of squeezing your design around the PCB tooling holes, you can place the holes on the tooling strip. The additional cost of V-scoring is not significant compared to freeing up precious PCB spaces from the tooling holes and might be an addition worth considering.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.