【 Weak current College 】 micro-shorts/short and countermeasures 】

Some micro-short short circuit of finished products-plates, with ordinary low pressure computer measuring machine test cannot guarantee that it will not flow into the hands of the customer to customer complaints. Usually printed circuit board manufacturers have put this question to computer measuring machine suppliers, thereby promoting a high-voltage measuring machine computer. But with high pressure measurement plate machine also cannot guarantee 100% pass rate.
Sometimes the first low voltage test circuit circuit board test all OK, second reuse 300V high-pressure test test with short-circuit. The third and with a normal low-weight measurement, a second measure of short circuit board determination as short as well. Multimeter resistance measurement circuit two stalls line welding inventory to short-circuit, average resistance to 6.7 ohm. It should be identified as completely short-circuit instead of micro-shorts. Then use power Magnifier check short circuit could not accurately check out short point (should be finished with solder mask ink).

From the testing process and its resistance value can be identified as: etched side erosion caused by the sudden along and then brushing process so that the process of breaking down along the wires between the bridge and then printed on green oil makes its bridge is not fully meet the short road bridge. This first test to detect low-voltage nature cannot bridge circuit. The second is the high voltage is first detected and then micro-short circuit of welding of high voltage breakdown (as copper wire is very small so it doesn't require much power can do short circuit of welding formation. If the test machine manufacturers can improve their short circuit testing current allowed power to blow the bridge contact, we would be very difficult to see this phenomenon). So the third LP computer measuring machine will be able to test out the short point, and its resistance value only average 6.7 ohm.
The aforementioned high pressure measurement plate 300V machine also have complaints, check return to short circuit the adverse short circuit board see a third measure adverse short circuit board is the same reason. Because solder mask (green oil) will make the screen printing received copper wire insulation aggravate bridge?, resulting in the use of high pressure computer logging machine cannot detect, handling, Assembly, soldering and semi-finished products for the testing process to bridge formed a short circuit. Sometimes we use low voltage measuring machine measured this short circuit board with bending and slapped sometimes short-circuit will disappear. In the absence of pressure measurement plate machine because the computer is not assured that measure good ok Board then re-test a short side plate. Problems most of the etched side erosion and graphic production and solder mask ink pre-treatment line, addressing this aspect of the problem before the second process of solving difficult, mainly in the graphics production guarantee the line width and line spacing, too close to prevent some line, etching, guarantee the quality of the side erosion. Reduction in the high-voltage tests produce micro-short circuit.
The simplest and most economical feasible method is newly purchased grinding machine or modified existing grinding machine, using abrasive brush and adopted swings volcanic ash throw brush or brush nylon mesh size low, and high pressure washing, particularly the washing of the best has filter to prevent foreign objects can cause a short circuit board surface again pollution, grinding machine to the side erosion formation of copper wire and process along the removal (sticking machine also has certain removal). At the same time new computer testing machine should use high pressure machine, can reduce PCB micro-shorts and short circuit occurs. This short circuit usually appear in single-panel and high-density printed circuit boards.