soldering
I am looking for the best solder type to connect a wire to a copper substrate. However, the wire is also a mechanical support as well as an electrical connection. Cost is not an issue.
The wire is Platinum/Iridium alloy.
Seems there is quite a variety of solder types
For things that require RoHS, I've been using a version of lead-free popular with assembly houses- Sn99.3/Cu0.7 2% flux, which seems to work okay.
The joints are not quite as shiny as the beloved Sn63/Pb37 with RMA flux, but quite acceptable.
Left two joints are lead-free, right joint is Sn63/Pb37.
You don't mention exactly what kind of resistors they are, but for "normal" through hole ones the best way is to first wrap one resistor's leg around the other resistor's leg, then wrap that resistor's leg around the first resistor's leg. So you end up with this:
The resistors hold themselves together and make it really easy to solder. It's a tough connection that won't easily break.
Depending on the kind of wire you're using you can use the same technique. It's also common to "insert" the resistor lead into the middle of the strands of stranded wire for soldering.
Best Answer
While there are lots of solders available, none of what you seem to be looking at are remotely suitable - they'll solder copper just fine, but platinum is a different matter. You need to start looking specifically at platinum solders. Since the melting point of copper (1085 C) is an obvious limit to your process, you should be aware that only the softest platinum solders melt below this temperature. While it's true that only local heating of the copper is necessary, this isn't much help due to a) the high thermal conductivity of copper, and b) the fact that you'll be heating with a torch or something like it.
Frankly, I'd suggest you look into spot welding or something similar.