If there is some micro short circuit in PCB copy. Short-circuit phenomenon of the finished PCB, using ordinary low-voltage computer board testing machine test can not ensure that it does not flow into the hands of customers to customers complaints. Usually pcb copy board manufacturers push this problem to the computer board testing machine suppliers, thus promoting the development of high voltage computer board testing machine. However, it is also impossible to guarantee 100% pass rate with high voltage board testing machine. Shenzhen RayMing how to solve this problem, through work experience we came up with the following methods for your study.
Sometimes the first time with low-voltage test line PCB board test all OK, the second time with 300V high-voltage test test has a short circuit. The third time and re-test with ordinary low-voltage, the second measurement of the short-circuit board is also measured as a short circuit. Using a multimeter resistance file to measure the short circuit point between the two lines solder plate point for short circuit, the average resistance value of 6.7 ohms. So it should be identified as a complete short circuit rather than a micro-short circuit. Then use a high magnification lens to check the short circuit phenomenon can not accurately check the short circuit point (should be the reason for the finished product has solder resist ink).
From the test process and its resistance value can be identified as: etching side etching generated by the edge, and then by the process of grinding the board so that the edge breaks down in the formation of bridging between the wires, and then printed on the green oil to make its bridge is not a complete short circuit bridging. So the first test for low voltage naturally can not measure the bridging short circuit. The second time for high-voltage first measured its micro-short circuit, and then high-voltage breakdown welding (because the copper wire is very small so do not need a lot of power to do the welding to form a short circuit. (If the test machine manufacturers can improve its short-circuit test current of the allowed power to burn off the bridge, we will be difficult to see this phenomenon). So the third low-voltage computer test board machine will be able to test the short-circuit point, and its resistance value is only an average of 6.7 ohms.
As mentioned before, the 300V high-voltage board testing machine also has complaints about short-circuit phenomenon, check the return of bad short circuit board to see the third measurement of bad short circuit board is the same reason. Because resist soldering (green oil) screen printing will make the lifting copper wire insulation aggravated, resulting in the use of high-voltage computer board testing machine also can not be measured, and in the handling, assembly, wave soldering and semi-finished products in the test process to make its bridge to form a short circuit. Sometimes we use low-voltage board testing machine to measure this short circuit board with bending and tapping sometimes the short circuit will disappear. In the absence of a high-voltage computer board testing machine, due to the uneasy, measured OK board and then re-tested there is a short circuit bad board. Most of the problems are in the etching side etching and graphics production and solder resist ink pretreatment line, to solve this aspect of the problem of the first two processes to solve the more difficult, mainly in the production of graphics to ensure the line width and line distance to prevent part of the line too close, etching to ensure the quality of the side etching. Reduce the phenomenon of micro-short circuit during high-voltage testing.
The simplest and most economical method is to purchase a new mill or improve the existing mill, using a swinging brush and volcanic ash brush or low mesh nylon brush, and then rinse with high pressure, especially the water wash section is best to have a filtering device to prevent foreign objects that can cause a short circuit to pollute the board again, the mill can remove the side of the formation of copper wire and abrupt edge (sticky dust machine also has a certain role in removing). At the same time, the new purchase of computer test machine should be selected for high pressure machine, can reduce the copy board micro-short circuit and short circuit occurred. This short-circuit phenomenon Y is also very ordinary in the single panel and high-density pcb copy board.