"clifto" wrote in message
...
Tim Wescott wrote:
Mike Young wrote:
(Yell if a quick primer on SMT
construction will be useful. I reflow boards in a skillet on the kitchen
range.)

I am aware of toaster oven reflow, but I haven't seen skillet reflow.
If you have the time and inclination to prepare a little web site --
particularly if you could do pictures -- that would be cool.

What's to figure out? A little olive oil, fresh-ground pepper...

Tune in Thursday when Emeril demonstrates reflow in a boil-in bag, with
pesto.

That's not too far off. We're all somewhat mislead by the assumed
complexity. After all that we've read and thought, it's not easy to accept
on faith that reflowing doesn't have to require carefully controlled
equipment and expensive stencils. For now, consider only that hand soldering
is much more stressful to the parts than almost any other (mis)treatment.
Uneven heating; uncertain temperature rise; solder bridging and subsequent
rework and more heat stress; ... on and on. On that basis alone, stir-frying
is already a huge improvement. At its best, it isn't very far from a more
stringently controlled process.

A few pictures of it working will help make the point. I had every intention
at the onset of taking a few, and plotting temperatures taken with an IR
thermometer. After doing the first board, though, the whole process seemed
as obvious as noting that a rock will indeed drive nails. Or something like
that. Bear with me.

The temperature profile is likely the major concern in your mind. Here's an
example of a profile: http://www.stencilsunlimited.com/solder_products.php.
Click on the link for "SynTECH Technical Data Sheet". The profile is on page
2. (Incidentally, their prices are among the lowest I found for small
quantities. Less than $25 for a 35g syringe shipped. I use their 63/37
paste.)

There are two important control points: flux activation at 140^C, and reflow
at 220^C. Flux activation is easily recognizable by the gray crud that forms
on the paste. Reflow is also obvious from visual cues: the paste turns
silvery and looks like molten solder. All that's needed now is to control
the time.

Medium flame on my kitchen range is just about right for my thick bottomed
aluminum skillet. Flux activation "happens" in a little less than 2
minutes. Reflow starts about 2 minutes later. When the last bit of paste
turns silvery, cover the skillet, count to ten slowly, and then turn off the
flame. Let it cool undisturbed.

The rest of it is putting on the paste and populating the board. You don't
need a stencil to do that. Just draw a neat bead along the pads. The parts
center themselves when it reflows. Compare that to the contortions of
holding an SOT23 in place to solder by hand.

There is a difference in how you plan your work. Since you can reflow only
once without special pastes and finer control, everything has to go on in
the 6 hours the paste remains workable. The NorCal 2030 probably shouldn't
be your first project.

Anyway, stir frying works well and easily with very few critical details.
Try it on a scrap board first to "calibrate" the stove. Within reason, a
little too hot is better than not hot enough, and a little too much paste is
better than not enough.