Cursitor Doom wrote:

Hi all,

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.
OY! It depends a lot on the quality of the board, and then how much heat it
has been exposed to, over its life.

If the chip is no good, I scribe the leads with an X-acto knife, running
down the whole row, and then JUST BARELY snap the leads off from the body.
You only have to do this on one side of a SOIC. Then scribe the other side
and bend the IC up and down a few times, until it breaks off completely.
Then, the individual leads can be removed in a much more gentle fashion.
Avoid pressing down on the pads, they will tend to "crumple" and the edges
pull up from the board.

Since you say OVER 25 years, I'm guessing none of this is SMT? If it has
plated through holes, these generally are quite robust. The worst are some
old paper-phenolic one-sided boards. You just look at them and the pads
start coming off.

There are mass desoldering tools for DIP and SOIC standard sizes that work
pretty well to melt the solder on all leads simultaneously. These work
great if you have the right size. I've even made some custom ones out of
solid copper bar when I had a bunch of chips to pull.

And, of course, a temperatur-controlled soldering iron, run at the minimum
temperature possible, is a big help.

Jon