Could you clarify what iMac you have?
The Early 2012 iMac does not exist.
The Unibody iMacs (thicker) last release was the Mid 2011 iMacs and the next iMac was the Late 2012 Thin Unibody iMacs.
Either way, I am almost positive that neither are soldered, but it would probably be worth it for you to make sure what iMac you have before you start buying stuff that may not work with it.