After all the manufacturing processes of the circuit board have been completed, the electrical test is carried out to check the board for open circuits and short circuits. The two most commonly used test methods are the flying probe test and the bed-of-nails test.
Flying probe test
Flying probe test uses removable probes with the drive devices to contact test pads and vias of the board. The probes move in three directions - X, Y, and Z. Before testing, the engineer needs to convert the CAD data into the test data files that can be identified by the tester. These files contain the coordinates (x, y) of each solder joint to be tested and the grid values of the solder joint on the board. The flying probe test does not require the production of the test fixture, and it is very convenient to directly install the PCBs on the tester and then run the test program. So it not only saves the test cost, reduces the time to make test fixture, but also improve the delivery efficiency. Also, flying probe test can be applied to high-density boards. However, as it is a kind of endpoint test, the speed is relatively slow, so it is more suitable for prototypes and small-scale production. While for mass production, the bed-of-nails test is required.
Bed-of-nails test
Unlike flying probe test, Bed-of-nails test needs to prepare specified fixed test fixtures for different boards to achieve rapid testing of all test points simultaneously. The test has a faster testing speed and is suitable for testing the mass production of boards. However, there are also drawbacks. The test fixture needs to be individually customized and takes time to produce; The programming is often complex and the price is also sort of higher; And mostly, the original test fixture will not be used after the PCB design has been changed.
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