Dark deposit on pins near leaking SMD electrolytic caps


Does anyone know the chemical composition of the dark deposits on IC pins that are close to leaking SMD caps? What is the best way to clean them? Litmus paper shows base (hard to tell because it gets stained by the deposit). I couldn't find a good solvent for it.

Here is a picture from a TDS520A

Interestingly sometimes one or two pins are covered but neighboring pins are OK (maybe voltage at the pin making a difference?). I have seen this in CPU card of 2467B, both acquisition and CPU cards of TDS520 and TDS520A.

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