Hey there. Still looking for some tin for myself.
Circuit boards made 2006 & newer use (by law) lead free solder - so the solder on newer CBs use tin/antimony 95% tin 5% antimony solder (mostly) --- or solders of (around plus/minus a few percent) 95% tin with copper or silver making up (plus/minus a few percent) the other 5% of the solder
HCl dissolves tin but not antimony/copper/silver
Therefore the solder on CBs made after 2006 will work perfectly fine for making stannous
HCl will dissolve the tin - the antimony/copper/silver will then settle (as a black powder) to the bottom of your beaker (you now have your stannous testing solution)
Take some newer CBs - put them on a hot plate (or use a heat gun) when the solder becomes molten bang the CB on a hard surface (work bench) pick up the blobs of solder & use them to make your stannous
I use a small 50 ml beaker for making my stannous
AND - for what it is worth - the solder from CBs will also contain small amounts of gold - the gold comes from the gold plated pads on the CBs - when they solder the component to the CB - the solder dissolves the gold (plating) & the gold ends up alloyed with the solder
One kilo of solder recovered from (newer) CBs will yield 1.5 - 2.5 grams of gold - the gold will be in the black antimony/copper/silver powder that settles after dissolving the tin solder with HCl
That is why I use HCl for depopulating RAM (for the IC chips) after cutting the fingers off (10 - 20 pound batches) the black powder that settles to the bottom of the bucket has gold in it
The tin (in solution) can then be cemented out with zinc - after washing & drying the tin cement you can then "smelt" the tin cement with carbon/borax/soda ash flux to recover the tin
If you want more details on the process I can post that
Kurt