It's a little old fashion, but I use rosin on almost everything I solder. I bought a little tube about 10 years ago at radio shack and still have it.

Clean both surfaces, wipe some rosin on them, heat the rosin briefly to affix it, then solder like normal. I do this even with rosin-core solder as it lets me put the rosin where I want it. Good luck.

jon

P.S. Great pic minnflyer