[hpsdr] Atlas soldering hints

[Mike Naruta]

Thanks to the SDR group, I have done my first
foray into surface-mount soldering.  Here's
some hints that worked for me.


I use a lighted magnifying device like the
GC Electronics 22-423.  I can get up close,
there's lots of light, I can take my glasses
off to take advantage of my nearsightedness
without worrying about solder or flux
splashing into my eye, and it directs the
flux smoke away from my face.

I use a temperature-controlled soldering iron.
This is terrific.  My old irons were always too
hot.  And different heats are useful for the
different components.  The by-pass capacitors,
for example, work best for me at 325 C (620 F).
The DIN connector pins at 350 C (660 F).  The
LEDs below 315 C (600 F).  (Lead-Tin solder)

Thanks, guys, for the intro to the water-soluble
flux.  This made cleanup a dream.  I just held
the board under the faucet and scrubbed with a
toothbrush.  All the flux came off and it looks
professional.  The Kester solder I'm using is
24-6337-6422.  (63/37, 0.015, water-soluble).

I also hit the board and connector pins with a
felt-tip flux pen (Kester 2331-ZX).  Watch out
for the manufacture date on the flux pens; I got
a batch with about 2/3 of their shelf life gone.

Note:  This flux is flammable.  I excitedly
discovered the flame going up a piece of wire
that I was tinning.

Put a large sheet of blank paper under your work
area.  This helps when you drop a part.  You will
drop a part.  Oh, also clean the floor before you
start.  I gave up on a capacitor I dropped on the
floor.  Sure glad that I ordered extra parts for
my Atlas.  I lost two capacitors; one that hit the
floor and one that arced off towards the scopes.

For holding down the SMDs, I use an old push-pin.
I use tweezers to position the SMD, center the
point of the pin on the SMD and apply moderate
pressure to hold it while soldering.

Tweezers with a bent end are more comfortable.

A way to hold the circuit board stationary is a must.

I tried tinning the pad with a blob of solder first,
but that gave an uneven surface.  This caused more
of a Tiddlywinks effect on the SMD.  I tried my
dual-iron tweezer, but I had trouble getting a good
position on the SMD and looked like the SMD got
very hot.  The tweezer irons are great for removing
soldered SMDs.

I tried laying a small, cut piece of solder next to
the SMD while heating it, but spent a lot of time
fussing with the solder and SMD to get them lined-up
first.  I don't have access to soldering paste.

The technique I settled into is to use the residual
solder on the SMD to tack one end into place by
putting the iron against the pad and SMD.  Then,
after a cooling period, apply solder to the other
end of the SMD.

Note:  Too much heat and the other end de-solders
the tacked side and you have an SMD on the loose.

Note:  It takes LESS solder than you expect.

Note:  The LEDs just have Gold plating, no solder,
so you need to add some solder to the pad first.

After the soldered side cools, you can go back to
the original side and solder it.

Do not dwell on the connection with your iron.
It is tiny and you're putting a lot of heat on it.
That's why you turn down the temperature.  I saw no
signs of pads lifting.  For the DIN connector pins,
if you have the iron on the connection for more
than two seconds, you need to change something.

For the DIN connectors, I used a screw, lock washer,
and nut to attach them to the board first.  The plastic
of the DIN connector probably has enough yield to hold
the nut on, but why take chances.

I started on the center row of pins, soldering every
other pin, then came back and soldered the skipped pins.
This helped spread the heating effect, but probably
wasn't necessary.  Then I when down one side and
alternated pins again.  By having the alternating
pattern, it helped distract me from the tedious task.

Do not be in a hurry to solder the pins.  Take your
time with each one.  As I learned from manufacturing,
inspection is only about 50% effective.  It will be
much harder to diagnose an locate a faulty connection,
than to focus on each one the first time.  Give
yourself breaks.  This is supposed to be fun.

Thanks SO much to the great folks in the group who
developed this and encourage us to do it ourselves.
What an exciting time in amateur radio!


Check out photos of my soldering stuff at HamSDR.com
< http://www.hamsdr.com/profile.aspx?id=76 >

Mike - AA8K