No such thing as too much solder. You HAVE to use too much, then you HAVE to wick it off. This has to be your plan up front. Wicking it off should be done carefully, as should the initial flooding. Never persist for a long time in a single session. If it's not going well, let it fully cool, then start again.
Depending on which pins and traces got fucked by severe overheating you may want to order a new CPU and PCB and start again, transferring what you can salvage. Traces only lift when you get things very very hot. Pins only bend when you apply physical force to them with the tip while the solder is soft enough to allow movement. Neither of these things should ever happen.
If you put that much heat into the FTDI IC it will die. They have strong thermal conductivity to the core from the legs and need to be soldered correctly quickly. The CPU is more tolerant, but don't push your luck.
How I do it:
- Wash the board with alcohol if it has been corrupted by fingerprints etc. Must be perfectly clean and dry.
- Carefully position and align the CPU such that all four sides are correct and have no more than 10% or so misalignment.
- Tack a pin or two on opposite corners, ideally just two pins, one on one corner, the other on the diagonally opposite corner
- If necessary, carefully melt one at a time and walk it around to align it better. Step by step. One corner, one rotation around the other. Repeat, carefully. This step should be avoided by nailing step 2 the first time.
- Once happy with alignment, flood one side that has no solder on it (so as to not free it up to move). I don't use flux, just the rosin cored solder is enough to wet it out with a fresh clean CPU straight out of dry packaging and a gold plated board that has not been contaminated by fingerprints etc.
- Let it cool
- Flood the opposite side.
- Let it cool
- Flood one of the remaining two sides
- Let it cool
- Flood the remaining side
- Let it cool
- Using the side of a medium tip to get maximum length per heat cycle, wick away the excess solder from one side only. This takes 3 or 4 or 5 passes, trimming the soaked wick off in between each.
- Let it cool
- If you are left with a few bridged pins, reflood them so there's plenty of solder, don't be afraid to wet out the ones around them, either. Not an issue. If it's doable afterward in one pass, this is better, if not, no big deal anyway.
- You guessed it, let it cool
- Wick away the reflooded bridged section.
- Let it cool
- Repeat for other sides, I typically do opposites in pairs with cooling in between.
When flooding a side, do it with thicker solder, 0.7mm or more, and use the heat to wet it out, don't try to spread the solder forcefully with the tip, move the tip and flow the solder in, and repeat. This way you avoid raping/bending pins. Be sure to do this quickly, though, to keep core temperatures low.
Hopefully this makes some sense in the context of your recent experiences?
Now, post up some macro shots of the mess and let's see if you can get away with keeping this PCB, or not.
Fred.