I know that this is a duplicate question, but I have read the other posts and tried the answers but none of them work. I have tried more heat, less heat, medium heat and even holding the iron to the same spot for two full minutes and it still wouldn’t stick. My solder has resin and plates on the pcb are starting to turn black. I have tried multiple different types and brands of solder. If it helps I think the contacts on the board are made of copper. EDIT: Many people have asked for clarification, so I will try to answer them as best as I can. The solder does stick to the iron and does melt, but will not stick to the pcb. I will include pictures of the me trying to solder and of the solder I am using. The temperatures I have used include: 300C 350C 390C 250C and 200C Excuse me for bad quality, my phone wouldn’t focus.
The key detail not previously present in your writeup is that this is an ESC, ie a motor controller for an RC vehicle like a car or aircraft.
Such high-current devices usually have very heavy traces and will require a powerful iron to solder. Your present tool may simply not be up to the task.
First tin the wires by melting some solder onto them when they are nowhere near the pads.
Next, tin the pads. You'll probably need to melt some solder with the iron to improve the heat transfer to the pads, and then as they come up to temperature try to spread a thin layer across the exposed surface of the pad.
Finally put the wire and the iron side by side on the pad, so that it contacts each. Again you will likely need to directly melt some solder to increase the contact area and thus heat flow.
Flux is not the cure for glazed copper pads.
Bare copper will suck up the solder. Otherwise not.
If the pad can be cleaned with an abrasive ( fine grit) so that it can be solder tinned with 64/36 Sn/Pb and brushed flux or resin core and the heat will suck up the solder.
A 65W iron may be necessary to maintain tip temp for phat pads and tracks. Keep tip clean with wet sponge and tinned. 315'C
If it was quality ENIG or gold plated, then it should not have oxidized.
Clean copper is your answer with a constant hot tip, short dwell (3~5s max ) should do it when its clean , tinned and fluxed.