A flying probe test is a type of ICT in which the probes advance seamlessly from one test point to the next without being part of an added physical fixture. This gives the illusion of “flying” probes that pass over the board from above and under the board from below.
While they were originally exclusively for bare board testing, these flying probes are now also used for PCB assemblies. Their needles are highly precise to ensure that no electrical defects on the board go undetected. A software program made for the FPT determines the pattern in which the needles make contact with specific test points.
Flying Probe Testing vs. ICT Testing
Typically, ICT involves what is called a “nail bed fixture”. The term refers to the pins on an added fixture specifically designed to work with a particular type of PCB. The spring-loaded pins link up with specific contact points on the board to search for electrical problems such as opens and shorts.
Because the added fixture for ICT has to be custom-made for a PCB, it requires additional production time, which can be up to several days. Due to the extra time and financial resources needed, this type of ICT only makes sense to produce larger magnitudes.
While traditional ICT involves a fixture, a flying probe test does not. Flying probe tests are thus often referred to as fixtureless ICTs.
How Does Flying Probe Testing Work?
To make an FPT, a software program with the instructions for it must be created, typically on an offline PC using a special FPT-programming application. The application will include files needed for the PCB assembly, such as a Gerber file, containing information on the board’s design and physical structure.
When the program is ready to go, it is loaded onto the FPT tester, and subsequently, the PCB assembly will be introduced into the tester via a conveyor belt. There, the program created will take over, instructing the needles on the FPT to move in a particular manner. If something is detected that does not match the design specified in the program, the test will return a failed result.
Advantages of Flying Probe Tests
There are several advantages of using FPTs, with the most obvious being lower costs and a lesser length of time for production. However, several other factors make the FPT a coveted test as well:
- Higher accuracy and sensitivity
- Automation allows more flexibility for test changes
- Requires no specifically created test points to be made
- High-tech features such as a Phasor Measurement Unit (PMU) eliminate the need for tests in isolation (such as determining the phase angle of voltage)
- FPTs include cameras that allow for performing additional tests, such as polarity inspection
Disadvantages of Flying Probe Tests
Though FPTs reduce test development and production time, it is also true that FPTs operate more slowly. Rather than being stationary in the correct positions like with a fixture, the probes must fly over to the proper points for testing. Because there is a limited number of probes, this can result in testing taking longer.
Another disadvantage of FPTs is that, despite being automated and possessing sophisticated features, they are not always suitable for every type of test. It is necessary to ensure that each flying probe test has the capabilities required for particularly complex testing. Additionally, tests requiring higher volumes may not be ideal for an FPT.