I need a test for microcracking in diodes
I need a test for microcracking in diodes
(OP)
We are having major problems with rectifier diodes (70 amp 200 volt DO5 devices). We are testing for solder voids by measureing heat retained in the diode after a power pulse, contamination and general construction by a biased temperature cycle. However we do not have a good test to detect microcracking that was found by an analisys house. Does anyone know of a good fast test?
RE: I need a test for microcracking in diodes
TTFN
RE: I need a test for microcracking in diodes
RE: I need a test for microcracking in diodes
If you're insistent on testing, then you'll need to run an accelerated life/thermal cycle and measure the appropriate indicator, presumably the leakage current.
This would most likely chew up a sizeable number of otherwise good parts to refine the test process. You'll most likely also cause premature failure on parts that would have otherwise been fine in normal service.
TTFN
RE: I need a test for microcracking in diodes
Inject a high frequency signal on the trace and run a scope probe along the trace. The signal supposedly attenuates or alters in some way down stream of the crack.
Maybe some permutation on that will work.
RE: I need a test for microcracking in diodes
I will keep the idea in mind, but it is not practical in this case since the diode is about 3/8 inch square and sealed inside a metal hermetic housing.
IR stuff,
I know we shouldn't have to do this much sorting, however there are not many manufacturers that make big power diodes in metal cases anymore, and even fewer we have not had problems with. We are working with the supplyer and attempting to qualify new suppliers to meet our needs. As a matter of fact the thermal cycle testing you mention is part of our qualification process and is done on a production basis for a couple of products, so far with no decrease in product life.
RE: I need a test for microcracking in diodes
kontiki99
Your approch might have sense, hoever I will use reflectometry or reflection in time domain. You shoud see some dicontinuity in the time /distance from the source.
So some network analyzer with time domain could be used for that.
You will used good unit as a standart how the time domain signal should look like and compare that to demage component. The demage component will propably have a lot of more spiks a dips then the good one.