piclist 1997\09\07\193930a >
Thread: SMT soldering
face BY : fastfwd@spam_OUTix.netcom.com

Mike Keitz wrote:

> > Removal of ICs is difficult.  Start by using solder braid to remove as
> > much solder as possible.  If the IC is under 20 pins it may be possible
> > to use two soldering irons and braid to distribute the heat to melt all
> > the pins free at once.  If not, heat each pin and use a dental pick or
> > large sewing needle to bend it slightly so it is clear of the board.
> > When the part is off, clean the remaining little bumps of solder off the
> > pads.

and Eric van Es <spam_OUTPICLISTspam_OUTspamspamMITVMA.MIT.EDU> replied:

> I once spoke to a guy who had to desolder and solder smt componenets
> without the special equipment for the componenets. Apparently you
> get a soldering iron tip that fit over an ic, ie one for 20, 40 pin
> etc. Only very expensive....
> He ended up using a scalpel to lift the IC's from their pads. It
> sounded like it worked pretty good.


Here's another way that often works better AND doesn't bend the IC
leads (a necessary requirement if, for instance, you're removing a
surface-mount PIC for the purpose of putting it in a programmer and
verifying its contents):

   1.  DON'T use solder braid to "remove as much solder as
       possible".  Instead, ADD solder:  Lay down a thick bridge of
       solder across all the leads on each side of the IC.

   2.  Turn the board upside-down.  Gravity is your friend.

   3.  Heat the leads on one side of the IC a little, then heat the
       leads on the other side.  Switch back and forth between the
       two sides, heating each a little at a time, until both sides
       melt more-or-les simultaneously.

   4.  The IC will drop off the board onto your bench.  The force of
       the impact will knock nearly all the molten solder off the
       IC's leads... The small amount that remains can be removed
       with solder braid.

If the chip is glued to the board, of course, you'll need to break
the adhesive bond... A dental pick or small screwdriver GENTLY wedged
under one side of the chip (AFTER the solder is melted) will snap
the chip free from the board without bending the leads.


P.S.  Wear safety glasses.

=== Andrew Warren - spam_OUTfastfwdspamBeGonespamix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

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