BLF188XR Smoked

jisoo

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Jan 3, 2017
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My amplifier's BLF188XR was recently replaced (think a voltage spike took out the original).

The mounting was done with the "Arctic Silver 5" thermal compound. It is non-conductive according to the specification, but it may not be non-conductive enough. The following problem may have been caused by the chemical.

I noticed a brief spark and a small puff of smoke when I connected 48 volts to the drain(s). I was unable to locate the exact source.

After that, I used a 14 MHz RF drive to deliver 400 watts to a dummy load. I got arcs, smoke, and even a little fire at the drain tabs almost quickly! One drain tab was destroyed and the other tab burnt to the package casing before I could turn off the power. There is no longer a lead tab. I was able to scrape and grind away the char/carbon from the burned adjacent circuit board.

A new BLF188XR is on the way. Plan on replacing the next one (pain!) with an old-school alumina-based thermal compound and hoping for a better result.

Is there anyone who has dealt with a scenario like this before?
 
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