OK, so this is basically emulating the reflow process. The only issue with
this is that there is no real temperature control and you can damage both
the board and the components if you are not careful (as is the case with all
soldering).

The technique I use is lots of flux and a soldering iron. It is key to use
flux so that the solder flows properly. Sometimes a microscope is required
and then occasional washing to remove the solidified gunky flux [wash in
ethyl alcohol]. However if you want to solder an IC you can run the
soldering iron along the side of the IC. Slope the board and then run the
soldering iron down the board from the top most pin to the bottom most one
and the solder meniscus will stick/flow with the soldering iron. You will
end up with the last 2 or 3 pins with a bridge which can easily be removed
with solder braid. You do however need to tack the IC down to start off
with so that it doesn't move whilst soldering. I learned this from a very
skilled tech and it works incredibly well. Especially for 25-50mil pitch
QFPs. For Passives, it's a lot of work and the technique given in the link
below may be better if you have lots of them.

**FLUX** is always key though! Water soluble if possible as it's easier to
clean off. Just wash it and wait for it to dry. Don't try and heat it dry
since this can cause steam to form under the solder joints (and the ICs) and
cause adverse pressure. The pressure can cause joints to fail and parts to
crack.

I would also like to point out something else about the technique given in
the link below. Bake out! One real issue in SMT soldering is that IC's
have to be baked out if they've been sitting in a normal environmnet
(humidity) since the epoxy absorbs water. The water then gets heated by the
IR reflow process/oven and can cause the IC to crack. The way around this
is to heat the IC/components gently to above 100 deg C (125 deg C is OK).
This bkes out the water. USually in an industrial process this is done for
about an hour or 2. The IC's are then sealed in a waffle tray and bag with
anhydrous silicone crystals to make sure no water gets reabsorbed. You
shoudl only be wary of this if your IC's have been lying around in a damp
warm atmosphere for a few days. For normal prototyping this is not so much
of a problem.



You can also get the reflow "hairdryer" kinds of devices. These work well
also and are a little bit more controllable than an oven. If you paste as
described by the link below, just heat around the IC/components until the
solder goes shiny. It'll reflow at that point. Let it cool off and check
it.



"w9gb" wrote in message
news:Q_vrd.178384$HA.36082@attbi_s01...
Have you seen my new soldering iron?
http://www.seattlerobotics.org/encod...6/oven_art.htm

w9gb


"Tim Wescott" wrote in message
...
Airy R. Bean wrote:
That certainly matches my experience, which I had
put down to being supplie dfrom a reject batch.

So, what can we do as Radio Hams to prevent such
a problem?

How hot does the whole board have to be raised before
applying a solfering iron? Would a hairdryer do?

"Terry Given" wrote in message
...

Larry Brasfield wrote:

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly

--snip--



Folks are starting to experiment with reflow soldering in toaster ovens.
I've read good reports on the web, but have absolutely no personal
experience nor have I even talked to someone who's done it, so I can't
vouch for it. One of these days I'll give it a try, in the meantime you
can search on toaster oven reflow and get a slew of pages.

There's at least one company (www.pcbexpress.com) who'll even make
prototype stencils for your solder paste, although for stuff that's not
too fine you can dispense paste from a syringe.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com