What are Test Points in PCB design?

A fabricated printed circuit board (PCB) generally goes through an automated test cycle. These tests check for component pins that are not connected to the board through a proper solder joint. Test points are placed on the board during the PCB design process and are used to ensure that the integrity of the component assembly process has not been compromised. A system of probes is used to touch the test points added during the PCB design process. Several different techniques are commonly used for this type of testing:

  • In-circuit test (ICT)

The in-circuit test is a system designed to test all of the nets on the PCB at the same time. To test all the nets at once, in-circuit testing (ICT) employs a test fixture that has probes in a position that correlates to the position of all the test points on the board and will contact each test point on the board simultaneously. The fixture will have one probe for each test point in a position that correlates to the position of each test point on the PCB. This allows the testing to be completed very quickly. These fixtures are typically set up to test the bottom of the board, but they can also be set up to test the top or both sides of the board simultaneously, at a higher cost.

  • Flying probe

As you might guess from the name, these probes "fly" around the board, touching each specific test point in the order they are programmed to test. The flying probe is different from in-circuit testing in that it only utilizes between two and six probes to check all the test points on the board. Due to the more specific type of testing, the flying probe takes a lot more time to test the same board going through an ICT. As opposed to ICT, flying probe testing cannot conduct any functional testing of the board because there are not enough probes available for each test point.

Other available tests:

  • Manufacturing Defect Analyzer, MDA

This type of testing employs a basic in-circuit test for resistance, continuity, and insulation. As the name suggests, MDA is only used for identifying manufacturing defects such as short circuits across traces and open trace connections.

  • Cableform tester

This type of test fixture is used to test cables. It employs the same essential functions as an MDA, but often some form of high voltage may need to be used to test for insulation optimization. The cableform tester operation is optimized specifically for the testing of cables.

A screenshot of a PCB with test points

These testing methods come up both in PCB Design and PCB Manufacturing.