I am going to try and make my own mechanical USB cable. For soldering the wires to the usb plug, what is the recommended Solder tip type/size and also what is a good temp to use?
I would use a fine tip, very thin.
Also some very thin solder. The tip & the solder should be about the size of those pads or less. I would also set my soldering gun to about 700°F ( ≈ 370°C) (Lead solder, not RoHS)
First touch the tip to the pad, then touch the solder. This will leave a little blob of solder on the pad.
Next using multi-strand wire of AWG26 or 28, I would remove about 3mm of insulation, and tin the wire with more solder. Not a big blob here, just wet it.
Last, place the wire on the pad, then place the soldering tip on the wire. Push down very lightly. After a second or two, the solder blob will melt, the wire will move down. Remove the soldering tip. Hold the wire steady for about 3 second, and you're done :)
I would then look at it REALLY CLOSE with a magnifying lens or some such, to see the quality of my work.
Last - After I'd tested it, I would cover the entire area with hot melt glue, so I don't break the wires later or accidentally rip off the pads.