So I'm trying to solder a power button onto my RPi 0. My issue is simple actually. I can't get the solder to melt onto the board. I've watched several videos all say the same. Basically to touch the pad with the iron then the solder to the iron tip and slide down fast. I tried this and either the solder just like evaporates or it beads up onto the iron or onto itself. I'm using lead-free rosin core solder 2.2% flux at about 350 C. I've basically melted the back of the pi which is fine since I bought about 15 because I assumed I'd mess up. Any insight as to why this is happening? I thought about maybe picking up some flux gel but in all of the videos I seen, none of those people used them nor had this type of trouble. Could it be my temps? I tried lowering them but it just doesn't melt the solder in that case.
EDIT: I've never actually had an issue soldering but I've also never soldered anything so tiny. Usually soldering for me was big boards for RC stuff.
Possible reasons for not being able to melt solder:
Small footprint for the pad makes it harder to transfer heat.
Crappy solder iron.
Too small solder tip.
Pad is efficient in dissipating heat. It could be that it is part of a bigger copper pool which can consume the heat applied and and radiate it elsewhere. Perhaps it is connected to GND?
Oxide on the solder tip will make it hard to transfer heat.
When manufacturing a board in a fab, you cannot and should not use any lead based solder. Non-lead solder does have a much higher melting point and makes it difficult to melt.
Advice that could help you:
Get an smd hot air gun or similar and pre-heat the board before trying to solder.
Get a good soldering iron and a pretty large tip and set it to about 400C.
Make sure that the tip is free from oxide by using a metal wire steel ball.
Before soldering put some 60/40 on the tip itself so that you get a better connection between the two surfaces. Also if you are lucky you will get the lead into the joint itself and act as a catalyst to the melting process.