Hey, my method works beautifully on TTL chips:
get a #1 cannula (needle) and remove the sharp edge so that
you simply have a very small steel pipe. Turn board around
and heat pins to remove one by one. As soon as the soldering
melts push the cannula over the pin and through the hole in
the board. That's very gentle to the chip and the board.
I have moved the C64 SID that way and it worked very well.
-Gunther
Ethan Dicks wrote:
> --- Andreas Freiherr <Andreas.Freiherr_at_Vishay.com> wrote:
>
>>On the risk of getting OT, but desoldering ICs is certainly on-topic...
>>
>>
>>>>Good luck! Meanwhile, I'll try to get that blown 74123 out of my
>>>>RX211
>>>>
>>>Best method for replacing chips is to cut the pins of the broken
>>>part and then take out the single pins with a desoldering pump.
>>>Works good even on multilayers with a good soldering iron.
>>>
>>Yes, I have not only heard this hint, but also tried to follow it. At
>>least with my tools, I always have trouble getting to the pins to cut.
>>There is not much room between a pin, the board, and the IC body.
>>
>
> I have a set of very sharp-nosed diagonal cutters - Xcelite, ISTR. They
> are not available at the hardware store or Radio Shack. You can get them
> at places like Greybar and such that sell electrical components.
>
> The IC-to-board clearance shouldn't matter. The best way to cut the pins
> is to hold the dikes so they point straight-up-and-down and cut right
> where the pin goes into the package (not possible for side-bonded ceramic,
> but those are rare and frequently socketed anyway). From the description
> of your problem, it sounds like you are trying to hold the dikes parallel
> to the board.
>
> The goal is not to eliminate an semblance of a pin above the board, but
> to free it from its neighbors so it can be removed on its own. I've
> found that the severed pin can frequently be lifted out by heating at
> the base, then lifting up when the solder flows - the severed shoulder
> snags on the tip of the iron and lifts right out.
>
> On multi-layer boards, it can be difficult to desolder the power and
> ground pins because the power and ground plane acts as a heat-sink. The
> best technique I've found is to apply the right temperature (too hot can
> blister off the traces) and flow in a lot of solder (1-2cm) Having a
> set of heat-resistant nonmetalic tweezers can be a help in pulling on
> the severed pin. It can take a while to get things flowing. Cleaning
> out the hole can be difficult, but it's much easier with the pin out
> of the way. I've found that mopping up can be aided with solder wick,
> but the actual hole needs to be suctioned out, sometimes from the other
> side (while heating the first side).
>
>
>>I think if I use not too high a temperature, I can save the copper leads
>>from getting off the epoxy, and it wouldn't matter if desoldering takes
>>a bit longer: the bug is dead anyway.
>>
>
> Right. The point here is that the chip is known dead (or you don't
> care because you have a replacement) and the most important thing
> is to preserve the circuit board.
>
> -ethan
>
>
>
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--
Gunther Schadow, M.D., Ph.D. gschadow_at_regenstrief.org
Medical Information Scientist Regenstrief Institute for Health Care
Adjunct Assistant Professor Indiana University School of Medicine
tel:1(317)630-7960 http://aurora.regenstrief.org
Received on Fri Mar 08 2002 - 20:39:44 GMT