The situation of short circuit/micro short circuit on the PCB circuit board is relatively common. There are several ways to deal with the circuit board micro short circuit/short circuit. Let me give you a detailed explanation below.
Some finished boards with micro-shorts and short-circuit phenomena cannot be tested with ordinary low-voltage computer board testers to ensure that they will not flow into the hands of customers to complain to customers. Usually this problem is pushed to the computer testing machine supplier, thus promoting the development of high-voltage computer testing machine. However, 100% pass rate cannot be guaranteed with a high-pressure testing machine.
Sometimes the circuit board test is all OK when the low voltage test circuit is used for the first time, and the 300V high voltage test is used for the second time to test for a short circuit. For the third time, it was re-tested with ordinary low voltage, and the short-circuit board measured for the second time was also determined to be short-circuited. Use the resistance profile of a multimeter to measure that the pad point between the two wires of the short-circuit point is a short circuit, and the average resistance value is 6.7 ohms. Therefore, it should be regarded as a complete short circuit instead of a micro short circuit. Then use a high-power magnifying glass to check the short-circuit phenomenon, and the short-circuit point cannot be accurately detected (it should be the cause of the solder mask ink in the finished product).
From the test process and its resistance value, it can be determined that the edge is etched by the side etching, and then the edge is broken by the grinding process to form a bridge between the wires, and then printed with green oil to make the bridge not a complete short-circuit bridge. In this way, the first test is a low voltage and it is naturally impossible to detect a bridge short circuit. For the second time, the high voltage is first detected as a micro short circuit, and then the high voltage breakdown welding (because the copper wire is very small, it can be welded to form a short circuit without high power. If the test machine manufacturer can increase its short circuit test current The bridge contact can be blown if the power is sufficient, and it is difficult for us to see this phenomenon). So the third low-voltage computer tester can test the short-circuit point, and its resistance value is only an average of 6.7 ohms.
The simplest and most economically feasible method is to purchase a new plate grinding machine or to improve an existing plate grinding machine, adopt swing brushing and use volcanic ash buffing or nylon brush with low mesh, and then use high-pressure washing, especially in the water washing section. It is better to have a filter device to prevent foreign matter that can cause a short circuit from contaminating the board surface again. The board grinding machine can remove the copper wire and the protruding edge formed by the side erosion (the dust sticking machine also has a certain removal effect). At the same time, a high-voltage machine should be used for the newly purchased computer test machine, which can reduce the occurrence of micro short circuits and short circuits. This short-circuit phenomenon usually occurs in single-sided boards and high-density circuit boards.
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