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Dry bones
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PerranOak:
I was soldering a board yesterday and everything was going fine. Then, for no reason I could see, one joint would not solder! All the joints before it were OK as were all the joints after it.

It was a manufactured PCB and the component was a through-hole T092 tranny - this happened on only one lead - with quality multicore solder and a Hakko FX-888D.

The solder simply "climbed-up" the lead, away from the pad as if allergic to it! Neither flux nor masses of solder helped.  |O

Eventually, it worked after trying time and time again.

Why on Earth does this happen and what should one do about it?
taydin:
Must have been covered with some kind of oxidation. Those will be really hard to remove with heat, because oxides have a very high melting point. There are acid based fluxes for this type of situation, but those do cause corrosion themselves if the copper traces are exposed.
amyk:
Was the pad connected to a large ground plane or similar?
PerranOak:
taydin: ah, I see.

amyk: no but the lead was quite long.
MosherIV:
Hi. I agree with amyk. Most likely a pad with high thermal mass.
You mentioned you eventually did it.
It just takes a long time to get enough heat into the pad to get the solder to melt onto it.
Even the best brand irons will take time.
My personel preference is for Metcal irons, they handle high thermal mass the best, easily out perform other brands.
Just look up the Metcal penny trick. Not many irons can solder together pennies or 2 nuts!
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