Determining Plated-Thru-Hole Size for Round and Rectangular Leads
Getting the size of your plated-thru-hole right is critical to having your design be manufacturable. The IPC organization has some suggested guidelines that, when followed, will result in making your design as easy to manufacture as possible.
There are 3 steps to getting your footprint correct for a given lead size.
Determine the density of your design
Determine the maximum lead diameter
Calculate the plated-thru-hole diameter
Calculate the pad diameter
1. Determine the Density of Your Design
IPC suggests 3 different density levels you can choose to design with. The less dense your design, the more wiggle room you can have to make your design easier to manufacture. The more dense your design, the more difficult it might be to manufacture. These are defined as
Density Level A (lease dense, easiest to manufacture)
Density Level B (moderately dense, moderately easy to manufacture)
Density Level C (most dense, most difficult to manufacture)
2. Determine the Maximum Lead Diameter
This one is easy. Your datasheet should define your maximum lead diameter for you. If the lead is square or rectangular, then your maximum diameter in this case would just be from one corner to the opposite corner.
3. Calculate the Minimum Plated-Thru-Hole Diameter
Using your maximum lead diameter, just add 0.25mm and that will end up being your plated-thru-hole diameter. Granted, this won’t work in every circumstance and sometimes the position and alignment of the component is critical and so giving it that much wiggle room is not always a good thing.
So for example if your lead diameter is 0.5mm then your minimum plated-thru-hole diameter should be 0.75mm.
Remember, this is just a minimum. Going larger usually won’t hurt anything.
4. Calculate the Minimum Pad Diameter
You’ll want the annular ring to be large enough so that your PCB shop doesn’t struggle fabricating your PCB. The minimum annular ring for many shops is around 0.05mm. So we’ll need to take that minimum annular ring and add 0.3mm to it to come up with our overall width of the annular ring. Then we’ll double that and add the hole size to it.
So if we’re following along with our previous example, with your lead being 0.5mm and your PTH diameter being 0.75mm then you’ll want your pad to be 1.45mm.
We hope you find this information helpful. As always, please feel free to reach out to us any time with any questions you may have about how to design your assembly so that it’s as easy to manufacture as possible.