this is a very long thread over at home brew talk (USA)
it's an excellent read and it also discusses the SS -> copper soldering and has a good method
it shows a method of dimpling the keg / boiler that creates a very strong joint
http://www.homebrewtalk.com/f51/solderi ... el-155782/
a good video of the dimpling process
http://www.youtube.com/watch?v=OpMFQFi6 ... r_embedded
thought it might be use for some of us,
never having much success in soldering stainless to copper i made a great joint after looking at the thread this afternoon.
i think i will be using it a bit more in my brew rig i am working on