A test point in a PCB is an exposed copper pad that can be used to check whether a circuit is functioning to specification. During production, users can inject test signals via probes through the test points to detect potential issues. The test signals output determines if a given signal is low/high when compared with the desired result and optimal changes can be made to achieve the same.
The PCB Test point must be located on the exterior layer of the board. This allows the test equipment probes to make contact with it and conduct the test. The test probe tips are available in a variety of shapes for different testing surfaces (flat, spherical, conical, etc) which allows for each test point on the board to be matched with the probe that is best suited to it. This allows the designers to designate the existing thru-hole pins and vias on the boards as a test point.
Types Of Test Points
Probe Test Point
The First type of test point is an easily accessible point that can be accessed by a technician using a handheld device or a probe. These test points can be easily identified such as “GND”, “PWR” etc. The probe test is done to perform surface level testing i.e. verify proper current supply and ground values.
Automated Test Points
The Second type of test point is used for automated test equipment. The automated test points on the PCB are vias, thru-hole pins, and small landing pads of metal that are designed to accommodate the probes of automated test systems. Automated test points allow for Automated testing procedures that make use of Automated test probes. They are of three types:
1. Bare board testing: The bare board testing is done prior to assembly of the components to ensure that there is good electrical connectivity throughout the board.
2. In-circuit testing (ICT): The ICT test is performed to ensure all the components present on the board are working as they should. Probes from the testing fixture will come in contact with the test points on the circuit boards to perform the test.
3. Flying Probe Testing (FPT): Flying Probe Testing (FPT) is an automated test used to evaluate the proper operation of components on a PCB board. In this test, two or more probes are programmed to move across the board in the air and access various component pins one by one to detect faults like Opens, Shorts, Resistance values, Capacitance values, and Component Orientation.
Things to Consider while implementing a test point on a PCB:
● Test Point Distribution: Test Points must be distributed evenly throughout the PCB so that multiple tests can be carried out simultaneously.
● Board Side: Test points must be placed on the same side of the PCB which helps in saving time and money.
● Minimal Test point distance: Test points must have a minimum distance of 0.100 inches between them to improve testing effectiveness,
Advantages of adding test points to the PCB:
● Easy Error Detection
● Time and Cost Savings
● Easy to implement
Test Points are essential in verifying the integrity of a PCB. The number of test points on a PCB board must be limited as they are an exposed copper area that could accidentally short to another test point in its close proximity and damage the circuit.