The Tech Blog

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.

I was playing around with PCB conformal coating for a client project. Wanted to share my takeaways.
Conformal coating is a thin, non-conductive layer applied to the surface of a PCB. It conforms (hence the name) to the board’s contours, including components and traces, forming a protective barrier. This coating acts as the PCB’s protection armor against environmental damages like humidity, dust, or chemical exposure.

Why use it? It provides humidity protection. When your device needs to work in high-humidity areas, condensation can happen on the PCB surface to short the circuits and can even erode the tracks with continuous exposure. In industrial or automotive environments, exposure to chemicals like solvents or oils can degrade PCBs. Coatings provide a barrier against that. Some coatings are done all around the PCB not just as a thin layer to make it mate with an enclosure to be a temperature insulator and to provide vibrational rigidity to the PCBs. Also used as a high-voltage insulation barrier.

Conformal Coatings are of a few types:
Acrylic: Affordable, easy to apply, and repairable. Good for hobby projects. You can solder/rework them if needed. Usually transparent and comes with and without UV glow. UV glow is a cool feature that will allow you to see where the coating has been applied under UV light(Check pics).
Epoxy: Strong and durable, but rigid when hardened. They are often seen as black material covering bare dies or chips, commonly used to prevent reverse engineering of PCBs as they are difficult to remove without aggressive chemicals and significant effort. You will see them a lot in defense products.
Silicone: Great for extreme temperatures and flexible surfaces. Common in automotive or aerospace applications.
Common methods of applying it include spray coating, brush application, dipping, or selective dispensing by machines for large volumes. The application really depends on the type, MoQ volume, thickness and precision needed.

Feel free to try them out on your next projects. They can make or break a product in the right environmental conditions!