Re: gEDA-user: hotplate DEsoldering

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Sat, Nov 10, 2007 at 04:10:43PM -0800, Dave N6NZ wrote:
> 
> 
> DJ Delorie wrote:
> > I just had an occasion to remove a bunch of SMT parts from a proto
> > board (so they can be moved to the production board).  I used the
> > hotplate, because many of them had solder under the part, not next to.
> 
> What are you using for a hot plate?
> 
> The SparkFun site talks about using a cheap US$20 hot plate from Target. 
>   They mention uneven heating. A friend who happens to be a Mech E with 
> a specialty in heat transfer suggested using one of the "liquid filled" 
> hot plates, which are more expensive, but have a hollow core filled with 
> oil or something that distributes the heat more evenly by convection.

I recently used a very cheap aluminum-core stainless steel skillet on
my stovetop to do some soldering.  (Cheap knock-off of the All-Clad
style tri-ply cookware.)  This was to handle a chip that had an
exposed pad on the bottom, not accessible to a soldering iron.  I only
did that chip that way, not the whole board, so it wasn't really a
great test of evenness of heating, but I suspect it wasn't too bad.
Anyway, that was a 4-layer board with two inner planes, which should
have augmented the aluminum core of the skillet somewhat in spreading
heat.

I am a little nervous about the SparkFun suggestion, since it involves
a non-stick coating.  Don't those start to break down at right around
the same temperature that solder melts, leading to the release of
toxic fumes?

Anyway, if you have a skillet that you trust to distribute heat evenly
for cooking, give it a try.  Just be sure to avoid getting any lead
solder on something you intend to cook with in the future.
Double-sided boards that come from a real fab will have solder coating
on any exposed copper on the bottom.  I used some parchment paper
between the board and the skillet.  The paper got a bit blackened, but
never actually smoked or caught fire.  (The stuff is meant to go in
the oven, after all.)  I wonder if the paper improved or degraded the
evenness of heating?

-- 
Randall


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