What is a test point?

A test point is, actually, a site on an electronic circuit which is either utilized for checking out the state of the circuitry or to shoot some test signals. Majorly, there are two uses of test points which are outlined below:

• The first use falls under the manufacturing part. Once the device is assembled; test points are utilized to check out the working of the concerned device. If any device fails this testing process then it is simply abandoned and discarded or assigned to the concerned department to repair the defects detected.
• Even when a device is sold to a customer; it can malfunction, anytime, later on. At this stage, these test points are utilized to repair the device. Also, if repairing is not feasible and the device requires entire components to be replaced, then these test points are very useful to re-calibrate the device.

Test points are usually labeled on the printed circuit board and include pins or connectors for the attachment of clips used for testing.

PCB Layout & Test Points Always Come Together

The concept of test points is not something which is different or apart from PCB designing process. In fact, placing test points on a PCB is an integral part of PCB designing process and contributes significantly to the reliability factor of the final product. Testing is done either by the technician, also called bench testing, or is done in an automated way as a part of manufacturing process. There are two types of automated tests i.e. bare board testing for fabrication and in-circuit testing for assembly. In almost all the cases, boards are designed to maximize in-circuit testing.

If you are a circuit board designer then it is very important for you to learn about the concept of test points. Secondly, simply having knowledge is not enough. You must work closely with your personal testing team as well when designing a printed circuit board so that the test points can be placed effectively. If the required amount of care is not given to the test points while designing a PCB; it can lead to the development of varying types of complexities in the printed circuit board in later stages of manufacturing or fabrication. Following are some tips to efficiently place the test points for an electronic circuit.

• Prefer secondary side of the board to place test points and try to encompass test points for each node. If you don’t provide test points for each electrical node then internal or external shorts cannot be detected completely.
• Whenever it is likely; please utilize devices which are boundary-scan conformable. This way even if the board has fixed and limited test points; accessibility to the device can be ensured through a boundary scan.
• In circuit control lines mustn’t be attached directly to power or ground. Instead, resistors must be added. This way the tester can easily check out these control lines as and when required during the testing phase.
• Test points must not be cluttered at one single place on the board. In fact, they must be tagged as evenly as possible on the board.

Conclusion

A good design with evenly distributed test points ensures the reliability of the product. A PCB Designer must have complete knowledge of test points so as to avoid any kind of complexity in the design or the later process of fabricating, manufacturing and assembly of PCBs.