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Soldermask and "leakage"

I have been testing small FR-4 PCBs with different color soldermasks at temperature (177C). Firstly, there is a big difference between "leakage" of green,red, black and blue soldermask (red best, blue close second and black crappy). Then i got sneaky thinking i could show the "leakage" acts as a constant current source, so i switched my GR1862B to the 50V position and WOW! measured almost the same exact resistance. What??? Had the impression the stuff would act like a FET at pinchoff.

So, a few questions: Why resistive and not current limited? Which color is best for 1000 hours, 10,000 hours? Color change over time? Resistance change over long periods of time (first 2 hours they seem to "settle" in)?

Reply to
Robert Baer
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Beware black solder mask.... especially with fets on baord!

Reply to
TTman

FR4 will look very brown after 1000 hours at 350F. The Tg for that stuff in in the 285F range.

It wouldnt' matter which color the solder mask was.

Reply to
mook johnson

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black

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Why?

I am thinking about switching from green to black. Problem is that green soldermask turns to black with hot air. So, black would hid the burns. I have two batches of boards. One works fine and the other pops and burns.

Reply to
linnix

And what is the difference between the batches?

Reply to
Robert Baer

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