On Tue, 9 Feb 2016 21:10:14 -0000, "Ian Field"
wrote:



"Gareth Magennis" wrote in message
...


"Jon Elson" wrote in message
...

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.








I still use a similar method when it suits.
Get a new blade in your knife, and you can quite easily cut vertically
through all the pins on any sized DIL (or SMD) device with no damage to
the PCB, with a bit of practice of course.

There's a bit of a knack to it, you carve through the pins at a slight angle
and make sure the blade edge lands squarely on the PCB underneath without
any sliding/slicing motion.

If you avoided using too much force, any tracks underneath usually survive
unscathed.

One trick I've heard about, is to feed some thin wire under an SMD chip and
ease it out sideways while applying heat, lifting the pins as it goes - but
this doesn't exactly fit in with the advice to minimise the duration of
applied heat. It probably wouldn't help at all if the pads are fragile to
start with.

I used to use this technique. Usually on 64 pin or more chips at
least one trace would lift.

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