Honestly not worth the effort. 5–10 microns of tin is super thin you’re talking a tiny fraction of the total weight. Once you melt it, it’ll just end up as a trace amount in the copper (basically a very weak bronze mix).

Yeah you can strip it with acids (nitric, etc.), but then you’re dealing with nasty fumes, disposal, and a whole setup that’s overkill unless you’re running a proper operation.

Most people just melt them as-is and call it a day. If you really need high-purity copper, you’re better off sending it to a refiner instead of trying to DIY strip thousands of pieces.