[Test-Equipment] Re-flowing solder joints

[DaveC]

I'm working on a Tek PCB that had electrolytic caps leak. The leaked 
electrolyte caused traces, pads, vias, and solder joints to oxidize 
or, at worst, corrode away.

The copper the easiest to deal with: brush up with a glass fiber 
brush and either solder or replace with some wire or copper (bridging 
vias to the flip side of the PCB if necessary).

It's the solder joints that I can't seem to fix. I brighten them up 
with the glass fiber brush, then put on some flux (no-clean in a 
dispenser pen), and apply heat and some new solder.

Well, the heat won't melt the solder. No matter the temperature I 
dial up, it won't melt. At best I've had it crumble, and at that 
temperature the pad is at risk of coming away from the board.

(This trouble is only with joints that are obviously oxidized. Normal 
joints will flow normally.)

I've trashed a couple of pads and SMD components trying to reflow joints.

What am I doing wrong? How can I get these joints to reflow without 
damaging pads or components?

Thanks,
Dave