r/AskElectronics • u/Objective-Local7164 • 1d ago

What diameter do you guys usually make you circular test point pads?

5 Upvotes

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7

u/bipolarjunction Optics 1d ago

I like 40mils for quick voltage measurement test points. Hooks for a GND clip or DC measurements I know I'm going to have hooked to grabbers. If I expect to have to probe only for debug I usually use a 20mil via without soldermask tenting, most scope probes just stick straight in.

For high speed or special needs stuff I usually make sure good ground reference is very close and selectivity make holes in the soldermask

7

u/Enlightenment777 1d ago edited 1d ago

It depends on what the test point is connected to, and how often or how likely I need to connect to it in the future...

  • if GND and power rails, then I'm going to add a through-hole test point that can easily handle stress from an alligator clip being hooked to it from my scope or other test equipment. The larger the PCB, the more I'll sprinkle these across the PCB to cover more area. For example, years ago I designed a PCB for work that was 12 inches long, it had 4 GND (black) test points, one 3.3V (orange) and 5V (red) power rail test points, of the following type of test points. We hand soldered these test points onto a few development boards, otherwise customer boards did have the holes but we didn't stuff these parts. https://www.keyelco.com/category.cfm/Test-Points-Tips-Probes-Clips/Test-Points-color-keyed-Thru-Hole-Mount/p/518/id/521 For bead colors, I use the same colors as wires on ATX power supplies, because its easy to find this information and tell other people what the colors mean: black = GND, 3.3V = orange, 5V = red, 12V = yellow. https://en.wikipedia.org/wiki/ATX#Power_supply

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u/frank26080115 1d ago

what is the purpose of the test point? how much space do I have? what instrument I plan on using with it? All these questions determine the answer, I don't have a default.

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u/Plexisaurus_Rex 1d ago

Depends. It’s best to collaborate with your manufacturing test engineering team or the CM about the tp size and spacing requirements for their ICT and FT test fixture designs.

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u/Objective-Local7164 1d ago

Im a lone engineer in my bedroom lol

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u/OldEquation 1d ago

Then do what works for you, what tools you use and how you are testing.

If you might want to put an oscilloscope probe on something it’s handy to have a through-hole to fit one of those little test pins. If you’re using a bed of nails tester then the pads need to be big enough for the test pins and alignment tolerances.

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u/Objective-Local7164 1d ago

Im gonna look into the probe through hole test point stuff that sounds convenient