SMT soldering questions

Ethan Dicks ethan.dicks at gmail.com
Thu Jun 24 12:36:52 CDT 2010


On 6/24/10, Keith M <keithvz at verizon.net> wrote:
> I've got a Xytronic 137ESD
> (http://www.howardelectronics.com/xytronic/137ESD.html).

Looks nice.

> Which of these tips, keeping in mind I have the 137ESD, would be
> appropriate for surface mount work?
>
> http://www.howardelectronics.com/xytronic/tips.html

That would depend on your style.  I've used larger (1/32") tips with
success, but occasionally I've needed a smaller tip for touch-up work.

For the flux-wet-then-drag technique for QFPs, you want a larger tip.
The same size tip can probably be used successfully with 1206-sized
parts, but if you intend to do a lot of work with 805s or smaller, a
finer tip might be recommended, or if your parts density is so tight
that you are lifting your iron in the air to clear adjacent parts.

> What temperature should I be set at for soldering?  The number 630F
> comes to mind, but I'm not sure.

That depends on your solder type, and how much mass you'll be heating
up, but for leaded solder, that's not a bad place to start.  If you
need more heat, add more heat, though over 700F and you are probably
boiling off your flux or risking lifting your pads.  If you are
working on ultra-low-cost PCBs (like dark brown case resin), don't get
too hot or you will definitely have lifting issues.  For SMT projects,
you are probably using modern, high-quality FR-4 boards, so that's
less of an issue.

> What type of solder?  I think I'm using 63/37, I think .015 OD.

That's one form.  Injectable solder paste can also be handy.  I also
use larger solder, but apply it carefully to avoid overflowing the
joint.

> Should I use flux?  In what form? A pen? A syringe? A brush?

I have a flux pen.  It does 90% of what I need.  I keep thinking about
a flux syringe but haven't bothered buying one yet.

> Any other standard accessories that might help?

A solder sucker, solder wick, magnification with lots of light if you
can't read the numbers on the parts, fine-point tweezers, optionally a
vacuum picker to collect parts, and scotch tape (I've been known to
tape down one end of 1206 parts so they don't move while I solder the
other end - that was a tip given in the Heathkit SMT course I did 20
years ago).

-ethan



More information about the cctalk mailing list