Anyone encountered black coating like material under plating of heatsink ?
The package is TO 220. Upon desoldering the package or plying off the board
with a nose plier, it sheared off at plating. A portion of plating stayed on the
board while remaining on heatsink plate. The surface on parts' heatsink where
plating peeled off is black in color. On scratching with sharp tool, it appears to
have copper under.
The surface is tin lead plated. Any guesses what this black surface could be ?
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