We took our 18W CO2 machining laser and tried some selective soldering
with it.  CO2 is IR and it will preferentially heat the surrounding
dielectric.  There was some potential, but we figured out another way of
solving the problem.  For through hole selective soldering, a machine
using a tip that aims a small stream of solder at the joint seems to
work well, although you don't have the kind of control available to the
electric iron style of soldering system, so, particularly with Pb-free,
there is a significant risk of over-eroding pads with low thermal mass
while under-flowing pads with high thermal mass.  I've done a lot of
selective soldering of SMT parts with a "hot foot":  You machine an
aluminum fixture to have a "finger" which contacts the area you want to
solder, providing a fairly high pre-heat.  Usually we use vacuum to hold
our typically thin boards down to this "finger", then use hot air on top
to do the job.  But that is obviously a re-work mode, and can't be done
with components in the way of the "finger".

Wayne Thayer 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ray, Carl (GE
Indust, GE Fanuc)
Sent: Thursday, December 06, 2007 8:57 AM
To: [log in to unmask]
Subject: [TN] Laser Soldering vs Selective Soldering

Hi All,
 How many of you "out there" have any experience with laser soldering
machines verse selective soldering machines? Currently we have several
types of selective soldering equipment but due to our designs we are
having significant issues with adjacent components. 
 I have seen some equipment but do not have experience with the venders
or process.

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