EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Swake on August 17, 2024, 01:31:09 pm
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Hi,
What is your preference in terms of testpoints on PCB's?
What should it look like physically?
- Just a copper pad.
- A pad with a hole (so the test lead does not slip).
- A hole with a pin soldered in it.
- Single hole with colored bead and a loop (see attachment for styles).
- 2 holes with a wire bridge allowing to hook some test lead?
- Surface mount style loop.
- Something else?
Where do you like to find them?
- - All grouped in the middle of the board.
- - Near the border of the board.
- - Anywhere as long as they are all on the same side.
- - I hate them and don't want any.
How do you like them visually?
- - No label at all just the pad.
- - Labeled 'tp#'.
- - labeled with the expected value.
- - Just a big arrow pointing to it.
What makes you happy about testpoints?
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For the last category, I would add 5. labeled with the signal name or function.
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A wire loop of some format and a label of what should be there (and a schematic!) would be ideal, but honestly for most signals, a pad is plenty, especially if in a production unit you don't expect people to be poking around in. The one place the wire loop (or edge accessible pad to hook onto) really pays off is for circuit ground(s).
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Depends - for development boards I use normal pads, but also THT pads and pin headers.
For production PCBs I used almost exclusively simple round pads. The exception was a special device that was very low volume and required a lot of measurements to set up and calibrate - there I used test poles for specific signals (something like this: https://uk.farnell.com/vero/18-1658/pcb-terminal-pin-single-sided/dp/2113939 ). This allowed me to hook up the probes for everything. The price of the device justified it, and just a few pieces were made per year.
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All of the above.
If board space permits, I always put 0.1in type (45mil hole) through holes on the board edge with anything I need to test/debug the board. With this configuration you can directly clip a scope probe or ezhook right to the board edge hole without any connector/pin/testpoint soldered in. So main power supply rails, lots of grounds, inputs, etc. You can also use these holes for pogo pins. These almost always get silkscreen labels. You always need more ground clip points than you think, so put a lot of these around the edge.
For space constrained sections I'll use 2mm through holes (30mil hole). The exhooks don't work as well with these, but they work great for scope probe tips. You can still solder in a wire or small testpoint loop in these.
For other points I might need access to on internal circuits I have a 50mil square smt pad that I'll put on the bottom layer. Usually no silk labels on these. Just the pads. You can solder a kynar wire to these, it's just more of a pain.
I have a big stash of through hole test pins that I can add if I need a clip point on a hole that's not on the board edge:
https://www.digikey.com/en/products/detail/keystone-electronics/1040/315157 (https://www.digikey.com/en/products/detail/keystone-electronics/1040/315157)
(https://mm.digikey.com/Volume0/opasdata/d220001/medias/images/4849/36_1040.jpg)
Any of these points can be used for pogo pins and other fixturing. Just make sure you keep a reasonable spacing between points. Don't put them too close together.
You should be thinking of test point allocation and locations throughout the whole design, but I usually end up adding most of these near the end. It's always satisfying when you need a signal and you actually remembered to put a test point for it and it's right there and easy to get to.
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I use Keystone (or equivalent) loop test points. For ground(s) I use their 5011 which uses a 0.063 hole and has a large loop for multiple connections. For the signals I use the smaller types that have a 0.040 hole and smaller loop. For production I do not populate the test points, leaving the holes in case debugging is needed. I label the test points using the same size font used for the designators where possible, simple names GND for ground for example. I do not usually use the test point designator unless there is room for them on all test points. The keystone test points are available in at least 10 colors.