What are types of PCB test points, its uses, and design guidelines?

By Mer-Mar Electronics Date posted: Last updated: February 28, 2023
PCB Test Points

With the PCB being a crucial component of an electronic appliance, it is extremely important to verify the PCBs function during its development. This is a job that it done with the help of test points. PCB test point ensures that you can improve processes involved in the various stages of production.

What are PCB test points?

A PCB test point is a small wire loop through which you can inject test signals and monitor the board’s circuitry. The output of the test signal as compared to the desired results will help you make any optimal changes. Typically, these PCB test points need to be located on the outer layer of the board. The test probe tips can be of various shapes to cater to different testing surfaces.

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Types of circuit board test points

PCB Test points are usually of the following types:

1. Probe PCB Test Point

This is an accessible point that can be accessed with a handheld device. It comes handy to conduct surface level testing, for instance to do with current supply and ground values.

2. Automated PCB Test Points

As its name suggests, this is used for automated test equipment. These automated test points include vias, through-hole pins, metal landing pads, and more. In turn automated testing is of 3 types:

I. Bare board testing

This is undertaken before components are assembled. The prime purpose of this is to ensure that electrical conductivity on the board is consistent.

II. In-circuit Testing (ICT)

In circuit testing reveals if all the components on the board are working flawlessly.

III. Flying Probe Testing (FPT)

This test comes in extremely handy to detect issues such as:

  • Shorts
  • Opens
  • Resistance Values
  • Component Orientation, and more.

List of signal which should have test points

The following signals benefit from having test points:

  • Power supply rails
  • Ground
  • Programming connections
  • JTAG ports
  • Serial communications busses
  • Reset lines
  • UARTs
  • Programmable references
  • Interrupt lines

How to use test points on PCB?

For a PCB test point to work well, it is important that the point should be an exposed metal spot on the outer layer of the board. That way, the probes of the test equipment will make contact with it. The designer can then designate thru-hole pins & vias as test points.

Next up, it is important to identify the right locations as test points. The PCB design software tool will allow you to do this basis the requirements or parameters you set up.

Once this is done, the information can be exported into a test point file. With the right PCB design system test point generation is easy. Additionally, there are several other features that will enhance quality.

Advantages of adding test points to your PCB

The major advantages that come from adding test points to the PCB include:

  • Their profile is similar to that of surface mount components hence they fit well and are versatile.
  • Since they help identify issues in the early phases of design, they ensure that there aren’t costly errors to pay for in the later stages.
  • They ensure easy error detection without compromising on the PCB design.

PCB Test Point Guidelines

When it comes to proper test point placement, the following PCB test point guidelines need to be kept in mind:

  • All test points should be placed on the same side of the board.
  • To ensure testing efficacy, the minimum test point distance needs to be 0.100 inches.
  • Uniform distribution of test points is ideal.
  • Keeping all tall components in a designated area will ensure the access to test points isn’t blocked.
  • It is important to keep manufacturing tolerances in mind while accommodating test points and probes.

To sum up

Adding test points to the PCB help with easy error detection and leads to huge savings in terms of time and cost. While test points are essential in verifying the integrity of a PCB, the various guidelines need to be kept in mind in implementing them. For instance, limiting the test points on a PCB board go a long way in ensuring that there are no chances of accidental shorts & therefore damage to the circuit.

To avoid such future problems and to save time and money hiring Mermar Electronics is the best decision. Mermar Electronics provides PCB assembly, PCB fabrication, and PCB design services under one roof. Fill out form below to request a free quote or send mail at sales@mermarinc.com

PCB Test Point FAQs

1. How big should a test point be?

Larger test points work well as it makes it easier for the probe tips. Ideally a 0.050-inch test point works well.

2. How do you know if your PCB is shorted?

There are several indicators of a short. You could witness visual damage such as a cracked IC, blown capacitor or more. There could also be an acrid smell.

3. How do you choose a PCB test point?

The guidelines to follow when it comes to choosing a test point include placing test points on the same side of the PCB, distributing them evenly, and having a minimum distance of 0.100 inches between them.

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