do you freeze good ICs before unsoldering?

[komodore comrade]

i wanted to ask around how you go about unsoldering ICs which might be
good and required in the future.

do you use freeze to cool the component down before starting? or is
this more likely to screw up the ic through stress?

thanks,
Konrad

 

[Arfa Daily]

Depends on what sorts of ICs we're talking about here. If you're wanting to
remove ordinary DILs, you don't need to take any special care providing
you're using the right tools to get them out of the board - a vacuum
desoldering station is best as it's quick and gets all the solder off the
pins very cleanly. Next best is a desoldering pump ( solder sucker ). Most
stressful to the device is solder wick, which does a very good job, but you
need a very hot iron with good tip thermal inertia, and you need to be
quick.

If you're talking surface mount ICs, then unless you have the right kit - at
least an iron with an appropriate shaped bit to heat all the device's pins
at once, and preferably a hot air pencil, then I wouldn't even bother trying
to remove such ICs. If you're very skilled, there are ways to get quadpack
ICs off boards without special tools, but they are very fiddly, and result
in distorted pins unless you're very careful. Ther's nothing worse than
trying to reuse a 100 pin quadpack where the pins are not perfectly aligned.

As far as heat stress goes, if you're not ridiculously over-long with your
heating, and not using a poker hotted up in a gas flame, don't worry too
much. Remember that when these things are originally pre-heated then flow
soldered or infra red soldered, and then heat cycled in a burn-in chamber,
the ICs are being subjected to a lot more stress than you're likely to be
putting them through when you remove them.

Geoff

 

[[email protected]]

Apply fresh solder to all the pins and use a good temp controlled iron
and a solder puller.
Apply heat for about 2 seconds per pin.
On occasion you may get a tough pin so reapply fresh solder. If you are
inexperienced you may want to let the chip cool after
pulling half of the pins.
If you are removing a lot of ic's this would be a good practice anyway.
I used to service commodore 64's and they would always
blow 8 rams at once.They used .028 holes which made removal withiut
pulling traces a pain.
When you get good you can pull 2 or 3 pins at once.
Also, you may want to use a small flat jewlers screwdriver to push the
pins inward (from the componant side of the PWB) to release them after
sucking.
You can also (if there is room) twist the chip a fiew deg with pliers
to release. This works great upto about 20 pin dips.

 

[James Sweet]

i wanted to ask around how you go about unsoldering ICs which might be
good and required in the future.

do you use freeze to cool the component down before starting? or is
this more likely to screw up the ic through stress?

thanks,
Konrad

No, that'd be going from one temperature extreme to another.

If you you're harvesting a junk board for parts, heat it up with a heat gun
until the solder melts then tap it with something to make the parts fall
out.

 

[Jim Adney]

do you use freeze to cool the component down before starting? or is
this more likely to screw up the ic through stress?

I would expect freezing first to juat make things worse via greater
thermal shock. I've never done it, though.

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