I am soldering a series of spring like high carbon steel wires to flat copper plates, for example like on a set of snares on the bottom of a musical snare drum. I am using gas flames and soldering paste/flux material and this requires a large puddle of solder to fully encompass the springs. One issue is that since I need so much solder a lot of it wicks around onto the back of the copper plates and requires a good amount of cleaning. Does anyone know if there is anything I can apply to the back of the copper plates that would prevent the solder from sticking? I see some solder masks on-line but they seem to be for electrical soldering and I suspect they could not handle direct flame but maybe? Or some kind of paste I can paint on that cleans of more easily? Any ideas are greatly appreciated.

 

First, I would spot weld the steel onto the copper. It's quicker and much neater than trying to solder steel. You can apply Kapton tape anywhere you don't want solder to stick.

 

The reason that the solder flows to the back of the plate is you are applying too much heat.
You would have a better chance of success if you used a larger sized soldering iron.
A soldering iron would allow better heat control and for you to build up the solder.
This is why they are used for certain types of tin work.

.........or, you could use a wire wheel to remove the solder from the back then a cloth wheel with abrasive grit to polish it.

 

try marking what you do not want the solder to stick to with soapstone, the kind of soapstone you would use to mark steel with