What are Test Points in PCB Design?

What are Test Points in PCB design?

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 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. There are. a system of probes used to touch the test points that were added during the PCB design process. There are sevedal different systems that are commonly used for this type of testing:

  • In-circuit test (ICT)

This is a system that is designed to test all of the nets on the PCB at the same time. In order to do test all the nets at once, in-circuit testing (ICT) employs the use of 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 normally 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 at the same time, at a higher cost. 

  • Flying probe

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. 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. 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 tests that are available:

  • Manufacturing Defect Analyser, 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 fixtures is used to test cables. It employs the same basic 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.