On Tue, 9 Feb 2016 11:23:24 -0000 (UTC), Cursitor Doom
wrote:

Anyone got any tips on how to avoid the unpleasant situation where you
try to de-solder a part on an elderly board and end up removing more than
just component leads? Most of the stuff I work on is at *least* 25 years
old and things start to get fragile.
thanks

My advice tends to go against conventional wisdom and some of the
other advice in this thread. The problem is that you're delivering
too many joules for too long a time (Joules = watt-seconds). To avoid
problems, you have to work fast. You can get the joint as hot as you
want, but not for very long.

Therefore, I suggest:
1. Don't use this type of soldering iron:
http://stellartechnical.com/images/213.jpg
2. Use an 850F solder tip, not 750F. Work fast.
3. Use a medium size tip. Too big and it will deliver too many
joules. Too small and de-soldering will take too long.
4. Don't mix lead free and Pb-Sn solder.
5. Don't use solder wick. A solder sucker works faster.
6. Hit the connection with some solder before unsoldering to make the
old solder flow. Slopping flux on the pad doesn't help because the
flux will vaporize before the solder melts.
7. If the PCB is phenolic, the pads always lift.

I'm undecided if hot air desoldering is any better than a soldering
sucker for through hole parts.

Conformal coatings such as urethane or acrylic, will either burn or
vaporize before the solder melts. Using these to glue down the pad
doesn't seem to work for me.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558