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From: jhs@disunix.UUCP.UUCP
Newsgroups: net.micro.atari16
Subject: Re: 520 AND BLITTER
Message-ID: <8607161601.AA21826@mitre-bedford.ARPA>
Date: Wed, 16-Jul-86 12:01:35 EDT
Article-I.D.: mitre-be.8607161601.AA21826
Posted: Wed Jul 16 12:01:35 1986
Date-Received: Wed, 16-Jul-86 22:56:22 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The MITRE Corp., Bedford, MA
Lines: 55

Shudder, horrors!  You don't want to CUT THE PINS OFF  the 68000, just
unsolder them carefully, remove it, and solder in the socket in its place.

Removing an IC is not a picnic, but it can be done successfully with the right
equipment.  One needs a low-wattage soldering iron such as an Ungar, designed
for PC board soldering.  Also a "Solder Sucker" or "Solda-Pullt" or some such
device which acts as a micro vacuum cleaner to suck the solder out of each PC
board hole into which a pin of the IC to be removed is inserted and soldered.
You heat each "pad" as the area around the hold is called, and often it
paradoxically helps to add fresh solder, mostly for the effect of the fresh
flux.  If the exhortation "strike while the iron is hot" ever applied, it does
here.  While the solder is freshly melted, and helped along by the fresh
solder flux, apply and activate the vacuum device and slurp out all the solder
you can get.  Remove the heat as quickly as possible.  If it didn't work, let
it cool a bit before trying again.


Another method that can be used is a "solder wick".  This is a tiny strip of
woven copper wire which has lots of surface area for its size.  Melt the
solder and touch it to the pad and it will soak up an amazing amount of solder
by capillary action.  I have found that solder wick works best for final
removal of solder, after getting the bulk of it with  a vacuum device.

Yet another trick that is often useful is to clean off your soldering iron
and apply heat with it from BELOW the board, with the soldering tip offering
a downhill path for solder to flow away on.  This seems to work best for
removing excess solder from the pad if it is NOT TOUCHING the IC pin.

The final trick that sometimes helps is heating and blowing through the hole,
either just with your lips or with some kind of tube or -- best of all --
compressed air gun.  The problem with this is that it causes little blobs of
solder to fly all over the place -- that's why the vacuum approach is better
if it works.

When you have cleaned out all the solder you can, you can usually start prying
the IC out gently.  Sometimes a few pins will still be sticking to the board
with a light coat of solder.  You may need to re-heat these, or you may be
able to free some of them with tweezers or an Exacto knife.  At this point,
you are on your own, but you will probably be able to work out a solution.
Heating a pin and prying the IC usually gains you more ground each time than
you realize until the IC finally pops out easily.

My advice to anyone attempting to remove an IC for the first time, especially
a big one like the 68000, is to follow the Golden Rule: "Never Force Anything"
-- following this will probably enable you to get the 68000 out intact and in
a reasonable amount of time.  Also, be sure you have the right equipment
--a rule which will save you a lot of grief not only in this situation but
many others involving electronic equipment as well.   Don't attempt to do such
a task until you have the right equipment (solder sucker and solder wick and
low-wattage iron and fresh roll of Ersin 60/40 solder and tweezers etc.)
Don't apply heat too freely.  Do all of this and you will probably do OK.


-John Sangster
jhs@mitre-bedford.arpa