What are proper techniques for soldering flat copper surfaces? (as opposed to ends of wires)?

If it was me I would use a propane torch and "sweat" the joint like it was pluming fittings. The first step is get both mating surfaces shiny clean with steel wool or fine sandpaper. Next apply flux or use rosin core solder. Finally with the parts held in position apply heat evenly to the parts and apply the solder to the seam (not the flame) When the parts are heated enough the metal will melt the solder and it will wick into the seam and flow smoothly. To make sure you get full penetration into the overlap for maximum strength you may want to "tin" (coat with solder) the mating surfaces by applying flux, heat and solder and wiping off the excess while it is still molten with a clean cotton cloth. This should leave a thin film of solder on the parts that will not interfere with the close mating of the parts. Then follow the instructions above for a strong neat looking joint. One last thing I should mention. If this joint is going to serve as an electrical connection you should not use paste flux or acid core solder, use rosin core solder.

in many cases, in accordance to code, you do not solder electric wiring. You twist the twine jointly and screw on a twine nut. the only place wiring may well be soldered is interior an digital device, including an amplifier or television set. in case you will possibly desire to solder, the wires might desire to be clean (no grease from hands) observe some flux, and heat the wires warm sufficient to soften the solder while touched to the twine, to not the soldering iron. till the wires are a stunning copper color they're oxidized and could be brownish; solder won't save on with this. Use metallic wool to scrub the twine.

Use a soldering iron tip that will most efficiently transfer heat to the contact (bigger is better) but not to any adjacent pads.

Use a solder that is right for the tempreture of your soldering iron.

Start by wiping the fully heated tip and cleaning off old solder on a MOIST sponge, and apply a small amount of new solder directly to the tip. then carefully place the iron on the pad while feeding solder to the connection. as the solder melts it should flow smoothly. once the connection is made, remove the iron, but DO NOT BLOW DIRECTLY ON THE CONTACT. this causes the solder to cool too quickly and can weaken it.

thats basically it.

watch for shorts and dont breathe in the solder smoke and have fun!