On 07/05/2017 03:42 PM, Rob Jarratt via cctalk wrote:
I bought some ChipQuik recently and managed to successfully remove a 74LS125
with little trouble. Today I have come to trying to desolder another similar
sized chip, but try as I might I just cannot get it to work. The ChipQuik
just balls up and won't "take" to the pins. I applied plenty of the flux
supplied with the ChipQuik, but I wonder if I applied too much?
The solders may be incompatible. What are you trying to do,
replace a defective chip to make an old board work?
You DON'T need ChipQuik. If the board was soldered with
lead-free solder, diluting the solder with PbSn solder makes
it easier. If it is already done with leaded solder, then
you just need a little technique. For surface mount parts,
use an Xacto knife under the pins, and lift them one at a
time while touching with the iron. Generally, I remove as
much solder as I can with solder wick first, then lift the
pins. When one row of pins are lifted, the chip can be
flexed a few times and the other row of pins break off. The
remaining pins can be swept off with the soldering iron.
Then, the solder can be removed with solder wick and the new
chip installed.
For through hole chips, the safest way is to snip the pins
off at the chip body with tiny diagonal cutters, remove the
body and then pick each lead out with tweezers while heating
the pad with the soldering iron. Also, with good
desoldering tools, you can remove the chip without
destroying it. The best desolderers have a vacuum pump (or
air venturi pump) and a hollow desoldering tip. You apply
the tip to the lead for about 5 seconds, then apply the
vacuum while "swirling" the tip around the component lead.
This works amazingly well, and the parts generally fall off
the board when all leads are done, even on multi-layer
boards. The solder suckers that are used with a standard
iron are FAR inferior to the units described above.
Jon
