Back To Basics: PCB Test Points

Let’s talk about something simple yet incredibly crucial – PCB test points. If you’ve ever wondered what those tiny little exposed pads scattered across a PCB are doing there, this one’s for you.

Test points are essentially designed spots on a PCB where you can easily connect probes or testing equipment during manufacturing for troubleshooting. Think of them as small entry points giving you direct access to the board’s inner workings without messing up the traces.

Why use them? Without test points, you’d have to solder wires by scratching off the solder mask. It’s OK for larger tracks but it’s a strict No-No for thinner ones. They can be used for functional board testing during production, debugging in your development cycle, or even repairing/diagnosing faults in the field. In production, you might use a test jig with spring-loaded probes or even use the fly probe technique to probe the test points to see continuity, measure voltage, or even inject voltage to see a response at another test point.

How do you design them? Good test points should be accessible and preferably all on the same side of the PCB. Placement and size matter, where it should be accessible for probing and the size larger than the probe tip. If in a pinch, you can even use a PCB via as a test point if it’s untented(solder mask removed), although I won’t recommend it as a sharp probe can damage a via. The only place you need to be super careful is when you are adding vias for high-speed signals. I try to not provide a test point and usually try to probe them at the IC/connector end because adding a test point can introduce a stub or disturb the spacing in high-speed differential lines. If absolutely needed, I will stagger them in a way to not affect the spacing between them or expose the solder mask.

Check images above for different types of test points. These are metal parts that can be soldered on the PCB to give a place for a probe to hook onto.

Test points might not get the spotlight as some other things on the PCBs, but they are as crucial as anything else on the board. Any PCB manufacturer will attest to that.

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