Do you know how PCB circuit boards are tested?
In general, all circuit boards should be 100% open for short circuit test before shipment. Automatic detection of circuit board is not only basic, but also necessary. What are the common test methods in complex circuit board testing?
Needle bed test method
The open circuit and short circuit test of PCB circuit board is to put a test pin at the end of the line and power on. If the resistance of the same network (line) is greater than the minimum on resistance, it is displayed as open circuit. If the resistance of different networks (lines) is less than the minimum insulation resistance, it is displayed as short circuit.
The probe with spring is connected to each detection point on the circuit board. The spring makes each probe have a pressure of 100 – 200g to ensure good contact at each detection point. Such probes are arranged together, which is called “needle bed”. The equipment of needle bed tester is expensive and difficult to maintain. The probes are arranged differently according to their specific application.
Flying probe test
Flying probe test is a program-controlled moving probe. Flying needle test has two test methods: capacitance method and resistance method.
The principle is: capacitance method: a capacitance can be formed between two conductors, and the standard capacitance value can be obtained through the “learning” of the software on the “standard board”. If it is lower than the standard, it is a short circuit, and if it is higher than the standard, it is an open circuit; Resistance method: similarly, the resistance between two conductors can be regarded as a resistance, and the standard resistance value can be obtained through the “learning” of the software on the “standard board”. If it is lower than the standard, it is open circuit and higher than the standard, it is short circuit.
The flying probe tester does not depend on the pin pattern mounted on the fixture or bracket.Based on this system, two or more probes are mounted on tiny magnetic heads that can move back and forth on the X-Y plane, and the test points are directly controlled by CADI Gerber data.
The double probes can move within a distance of 4mil from each other. The flying pin tester is based on the measurement of capacitance. The circuit board is tightly pressed on the insulating layer on a metal plate as another metal plate of the capacitor. If there is a short circuit between lines, the capacitance will increase; If there is an open circuit, the capacitance will decrease.
Using observation instruments
The circuit board has small volume and complex structure, so the observation of the circuit board must also use professional observation instruments.
Generally, we use a portable video microscope to observe. Using a video microscope camera, we can clearly see the very intuitive microstructure of the circuit board. In this way, it is easier for us to design and test the circuit board.
Now many circuit board manufacturers use portable video microscopes msa200 and vt101, which can realize “observation, detection and discussion at any time”, which is more convenient than traditional microscopes.