Jim Adney wrote:

I've never managed to do well at this, so I've given up and clip the
leads so I can remove one leg at a time. Most of what I work on has
been HP boards, and the holes are so tight that I can't get a leg to
come completely loose by any amount of solder sucking. I have to pull
them while hot.

I find that different manufacturers use widely varying hole sizes for
their PTHs. That would make a big difference.

Does your desoldering iron allow you to heat up the whole chip at one
time? I've often thought that I should make some modified tips for my
Weller WTCP iron so I could do this. If I had that option, I'm sure it
would be easy to remove complete ICs.


Jim, I remove all the solder, one pin at a time. After the pin
cools, I put the side of the tip to the edge of the pin so the remaining
solder will let go without heating the PTH and pull the pin to the
center of the hole, where I let go an let it cool. Sometimes I have to
take a small pick and press gently against the pin on the top side to
free it from the wall of the PTH. if I have trouble pulling all the
solder out of a hole, I add fresh 63/37 solder to the 80/20 that was
used for wave soldering. It now has a lower melting point, and will
come out easier.

If the pin is soldered to a large trace on top I either use a
soldering iron to heat the top side and the desoldering iron to pull the
solder out of the bottom, or I use solder wick on the top side first and
finish from the bottom with the desoldering iron. Its a judgment call
that you soon learn which way to go.

One tip: Use liquid RMA flux with the solder wick to reduce heat
damage, and leave about 1/16" of the wick filled with solder when you
clip off the used portion. The solid part allows you to transfer the
heat to the pin, rather than the board so it flows into the braid a lot
quicker.

Another thing, use a board holder to position the PTHs horizontally
so you can get the solder out easier. When you do it from the top you
don't always get it on the first try because gravity is trying to pull
it back down. That allows an air leak and that's the end of the proper
solder flow. A little practice on scrapped double sided (or more
layers) will give you a feel for the way to do it.

I am trying to scrape up the money to buy a Fuji Finepix S5100 camera
that does excellent close-up shots. If I do get it I will try to take a
series of pictures and create a tutorial on CDROMs for those who are
interested. I have plenty of boards to take example shots of, a decent
workbench and good lighting, but none of my digital cameras will take a
decent close-up shot.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida