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[DPRG] SMT Soldering
Subject: [DPRG] SMT Soldering
From: Erik Petrich
epetrich at ivorytower.norman.ok.us
Date: Fri Jun 6 13:29:14 CDT 2008
On Fri, 6 Jun 2008, Eric Sumner wrote:
> I am working on laying out one of the boards for my thesis, and I have
> no experience with surface-mount soldering. The processor that I am
> using is available in DIP, TQFP, or MLF; how hard will it be to
> hand-solder either the TQFP or MLF package? Also, which size of
> resistors and such would you recommend?
It's not on your list of available packages (and quickly disappearing from
production in general), but PLCC and SOIC are very nice to work with for
surface mount; the 50 mil pitch is very tolerant of slight misalignment.
TQFP isn't hard to hand solder as long as you have a fine tipped soldering
iron and small diameter solder. The hardest part is to get the pins lined
up properly with the pads. Focus on getting two opposite corners lined up
and soldered down; the rest should fall into place (but you need to really
get the first two lined up properly; don't try to bend the first pin to
make the second line up). If you are in the position of designing the
board yourself, it is helpful to have the pads extend out further from the
chip than usual. This lets you draw out the solder from the pins if you
accidently get too much on them. Solder wick can also be helpful, but be
sure to inspect carefully with a magnifier; I've had more than one short
caused by a strand of the solder wick that's been too small to see
with my naked eye.
MLF scares me, so I haven't attempted it.
I usually go with 0805 sized discretes if I know I have to assemble the
board myself. In general, 0603 seem to be a bit more economically priced,
but take me longer to solder since they are harder to manipulate, so I
don't use then unless I really need the miniaturization. The 1206 sized
parts are even easier than 0805 to work with, but cost enough more than I
usually stick with the 0805. I haven't had much luck using tweezers, but I
hear others like then. I usually use some sort of stylus (often an X-acto
knife) to nudge the parts around and hold them in place while soldering.
Erik
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