Desoldering Chips, was Re: Can someone,

[Tony Duell]

> > The easiest way to not damage the board is to cut the leads to the
> > chip, and then use a solder sucker to remove the solder in the hole
> > along with the remnants of the chip leads. Hopefully if one or more of
> > the leads is soldered to the ground plane, those pads used thermal
> > isolation to separate them from the ground plane.
> 
> Tools are important.  A good temperature-controlled iron (I use my 
> trusty Weller WTCPT with a 600 degree tip for through-hole stuff) and 

That sounds a bit cool to me. I normally use a #8 tip (800 Fahrenheit) on 
my TCP for such work.

> a BIG solder sucker (the Edsyn DS017 is appropriate).  Add solder to 
> the pin if it's a little thin on solder, use the solder pump to suck 

Adding a bit of solder will genrally improve the heat conduction and make 
it a lot easier to get the solder in the hole molten.

Also, if it deosn't cleaer the first time you use the sucker, it's 
notmally a wast of time to just try again. Resolder the joing with fresh 
solder and then suck it off.

> the solder  out of the hole.  You should be able to see light through 
> the via; then wiggle the pin if necessary to free it from the sides 
> of the via.

My method for removing ICs inteact without damaing the PCB is to suck off 
the oslder (as above), then free the pins on the solder side. They will 
normally be against ones side of the hole, use pliers or a small 
screwdrive to foce them towards the centre of the hole. You need ot know 
how much force you can reasonably apply without wreckign the via, this, 
alas, comes with experiece. If the pin won;t move, reolder it, resuck, 
and try again.

Then on the component side of the board, use a small screwdriver to fuch 
the IC pins inwards (towards the body of the IC). Place the scrrewever as 
close to the PCB as posible. When they've all 'moved' the IC will normlly 
just lift out with no damage to PCB or chip.
 
> Every once in awhile, I'll get a pin that doesn't free--I'll use a 
> #70 wire drill in a Foredom handset to clear out the via.  Use low 
> speed and you'll usually end up with the via intact.

I've never had a hole/via that won't clear if heated wirh an adequate 
soldering iron from one side and sucked from the other.

-tony