Some micro-short circuit, short-circuit the finished plate, with an ordinary low pressure computer test Board test can not guarantee that it does not flow into the hands of customers to customer complaints. Typically PCB manufacturers have pushed the issue to the computer test board machine supplier, thus promoting the development of high-voltage computer test board machine. But with high-pressure test board machine also can not guarantee 100% pass rate.
Sometimes the first low-voltage test circuit board test all OK, second and then 300V high voltage test test a short circuit. The third and ordinary low pressure retest, the second measured short circuit board is also determined to be short-circuited. Measured with a multimeter resistance profile short circuit between two points is a short circuit wire pads, average resistance of 6.7 ohms. It should be regarded as a dead short rather than micro-short circuit. And can not accurately check inspection loupe short circuit short circuit point (should be finished solder resist ink for a reason).
It can be identified from the testing process and its resistance value is: etched side etching produces ledge, and then by the grinding plate process causes sudden break down along the bridge is formed between the conductor, and then printed on green oil to make the bridge is not completely short circuit bridge. Thus the first test of the low-pressure natural bridge short circuit can not be measured. The second measure is that it is the first high-pressure micro-short circuit, high voltage breakdown then welded (because copper is very small so do not need a lot of power can do welding a short circuit. If the test machine manufacturers to improve their short-circuit test current Xu sufficient power can blow bridging point, we can hardly see this phenomenon). So the third low pressure computer test board machine will be able to test out the short circuit, but its resistance is only average of 6.7 ohms.
The easiest and most economically feasible way is to purchase a new or modified existing grinding plate grinding plate machine, grinding brush with swinging and throwing using a brush or low ash mesh nylon brush, then rinse with a high pressure, especially water segment preferably a filter device to prevent foreign objects can cause a short circuit recontamination board, copper and sudden grinding plates can be formed along the side etching removal (Sticky machine also has some effect removal). While newly purchased computer testing should use high-pressure machine, can reduce circuit board micro-short circuit and short circuit. This short circuit phenomenon usually occurs in single-panel and high-density circuit boards.