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Re: Surface Mount Techniques



At 08:40 AM 3/28/98, you wrote:
>For once I have to agree with laura! (... girlish naivete?)
>
>More desirable is some sort of hot air source in place of a soldering iron.
>I use a reverse engineered desoldering iron of the old "squeeze the bulb"
>style. Air is blown through with one of those otherwise useless 12v
>minicompressors from your auto store. you have to mess around to get the

I've used a Portasol butane soldering iron for SMT work;  it has a hot air
attachment available.

>flow just right but it's no big deal. I use a "Maggylamp"(t) 'cause I have
>one, but a pair of manifying glasses on a headband work just fine.

Or if you already have glasses, one of those magnifying lamps that you can
find for $50 if you shop around and which you should probably have anyway.

A timesaver for desoldering chips is ChipQuik.  This is a kit with a flux,
braid and a special solder.  After applying the flux, you melt just a bit
of the solder, melting it into the existing joints.  Then pull.  The chip
comes right off (most of the time);  that special solder reduces the
strength of the solder joint to zero.  The flux, of course, is to remove
all the solder before replacing the part.  It's available at MCM among
other places.

>A vacuum pickup tool would be handy but I haven't got that figured yet,
>maybe someone else has.

I've seen handheld pickup tools for cheap at MCM;  their really-cheap model
goes for $8, their more expensive for $21 or so.  If I were hacking one,
I'd buy the cheap one for the tips and the nozzle, and put a pump on the
other end with a foot switch.  Perhaps Bernoulli's principles would let you
use your pump with a tee connector so that it does double duty as a vacuum
pickup.

The real trick is to have a cheap SMT oven for reflow.  Toaster ovens
*almost* work but not quite.

But Laura is right as usual:  SMT is not hard as such.  It is just
different.  Myself, I'll be happy if I never have to drill holes in PC's
again.

73's, Dave N1KGH





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