[DSP-10] Bench setup

Sun, 17 Mar 2002 18:43:13 -0700

John,

My SMT solder technique was taught to me by Chuck Green N0ADI at the P3D lab
in Orlando, FL.  Chuck uses two fine time solder irons in a tweezer fashion
to solder components such as resitors and capacitors in place.  The
proceedure goes something like this:

- flux the solder pads on the PCB
- place component with tweezers
- using one soldering iron in each hand, touch the iron tip to the PCB pads
- the solder coating on the pads will melt and the component will spring
into position from surface tension
- remove the solder iron

This technique I use often.  It works best when there's sufficent solder on
the pads.  If there's little solder the part will not spring into position.
So you may need to add a little bit of solder prior to step 1 above.

SMT parts with more that two leads (such SOT-23 or SOICs) I have found
require a different technique because you can't heat all the pads at once
and make the part settle onto the PCB.  So I make sure there is not a lot of
solder on the pads except one.  Then I flux the pads and place the part.
Then I solder the one pad with solder.  The part will not spring into place,
so you will have to take care in positioning it.  Sometimes they stay
because they are large enough, other times you have to hold them down.  Once
you have the one pin soldered the part will stay in place when you solder
the remaining pins.  You may need to hold the part down against the PCB
pads, but this is rare in my experience.

You need to be careful with ceramic capacitors.  If you over heat them they
will crack.  The worst part is that you will not see the cracks!  So if you
find yourself clutzing with a cap and feel you have overheated it, then you
should seriously consider throwing it away and insert another one.

As with through hole parts, make sure you have enough solder fillet when
done.  The solder should be shiney.

Take a look at application notes of many surface mount parts.  They explain
the soldering process.  Read the warnings.  They usually have nice drawings
showing what the final solder joint should look like.  Put up a book on SMT
soldering is a plus.

Try your hand on a old SMT PCB with parts.  Remove the parts, clean the pads
with solder braid and try the above technique with a new part.

Good luck!

73,

- Steve, N7HPR
  ([email protected])

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Clark, John
> Sent: Sunday, March 17, 2002 4:39 PM
> To: '[email protected]'
> Subject: [DSP-10] Bench setup
>
>
> The DSP-10 box arrived last week. I am doing the customary inventory.
>
> I can see that I will need recommendations to update my bench.
>
> I'm looking for a new iron. Small enough to work on these SMT.
> Please send in your comments, Good & Bad.
>
> The big Radio Shack store closed ere in Denver and I still need a
> non-ferrous tweezers and
> a desk pad to work on.
>
> Being over 50, I have had the magnification lams for some time.
>
> Any other tools that anyone has found helpful?
>
> This looks to be much more of a challenge than the Elecraft K2,
> last years project.
>
> 73  N�URE
> John
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