Hi, I'm searching a way of test to identify cracked condensers on a production line. We use X7R ceramic with nickel electrodes condenser (size 0805) which are molded with epoxy resin. I need a test I can insert on the production line (EM constraints and fast time of test). Can somebody advise me ?
Ultrasound often used for composites. Don't know speed of current testers and think you have to immerse in water.
The best you can do is have your production line follow the manufacturer's rules very closely with respect to time/temperature soldering profile and the size and position of the lands.
The only why I could identify cracked capacitors that caused a short was with a curve tracer and only when I compared it to a known good one. the only way you can truely verify fractures is to cross-section the capacitor in place and you have to destroy the PCB. Often the fractures are at the bottom near the solder line. And now with the new non-lead solders you may have many more.
Good luck.
Al
Ultrasound is a good way to test ceramic. You can compare it to ceramics that do not have cracks in a short period of time. I do believe you do not have to use water to test them. You will just need two transducer and an ultrasonic tester.
When I worked in the capacitor industry they used a SLAM - Scaning laser acustic microscope. It was not fast enough for 100% testing, but enough parts were tested to ensure < a given PPM defect rate existed. You might also try an impedance analyizer to determine the resinonce frequency of the capacitor. A cracked capacitor should have an offset the res. frequency (but the potting and or mounting could cause problems with that measurement)
Good Luck! Gregg
Dear Eole, I don't know how much you're willing to spend, but I know of a company in Pittsburgh called Solid State Measurements. A few years ago they developed a contact probe method to determine C-V and I-V curves for the semiconductor industry. I'm not sure what your EM constraints are, but I suppose you could ramp the voltage to under some critical voltage and see if you get leakage currents or a drop in capacitance. If this isn't viable, then ultrasonics is the way to go. The airline industry uses ultrasonics to determine crack sizes, as do most structural engineering NDT methods. As far as insterting into your production line, there's really no "fast" way to do it, and I doubt it would be cheap. From what I understand, the method involves random sample statistics from every "heat". Hope that clears up mud for you, although it probably only mucked up the clear.
-SrvClapton
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