Hi! First time poster on RG!

I would like to solder (ball grid array reflow) onto a Platinum/Iridium alloy without the use of special Platinum soldering fluxes. Can copper be sputtered onto Platinum/Iridium to provide a solderable interface? I've read that a film of ~5um should provide a sufficient diffusion barrier, is this correct? And would an adhesion layer be recommended, or is copper adhesion to Pt/Ir good enough without? I've used Ti as an adhesion layer in the past.

Thanks for any help!