[NLRS] DB6NT assembly soldering tools

[Doug Reed]

At 07:35 AM 2/12/2003 -0600, you wrote:
>Doug, what type of soldering iron(s) are you using for the little work and
>for the big work ?
>Jon.

I was using a Metcal soldering station for everything. I'd never have
thought that such a small tip could do such a good job on the big stuff......

For the big stuff I would normally have used a soldering gun or iron with a
wide tip so it is easier to drag the solder to mount the PCB to the tin
plate box and faster to heat the pipe caps. But I used what I had at work.  

My usual home choice would be a Weller or Ungar soldering station. For the
surface mount work you need a small CLEAN tip and be sure to flux the
joints for best solder flow. The common suggestion at work is to use a 600
degree tip rather than anything hotter. But most of that is so non-expert
solderers can do the work without lifting PCB traces. I use a 700 degree
tip for everything since it heats big ground pads better. I don't even own
any 800 degree tips and wouldn't use one for this kind of work anyway. 

I'll also note that many of the parts are wrapped in tin foil because they
are static sensitive. That means you should be working on a anti-static mat
or a conductive surface such as steel or aluminum foil. Your soldering iron
should be one with a grounded tip or at least you need to check that there
is no voltage leakage path from the tip to ground. If you don't have a
ground strap for yourself, you can make sure you always have one hand or
elbow on the conductive surface. Another option would be a home made wrist
strap with a wire wrapped around your wrist watch band and a 100K to 1 meg
resistor in series to the conductive surface. (The resistance is enough to
drain static but high enough for safety in case you contact something with
voltage on it.) 

For SMT work, if you can see the solder on the tip of the iron, you
probably have too much! One of the details they warn you about in the
directions is getting too much solder on the joint. You want just enough to
flow and wick up the side of the lead. If you have a blob or ball of solder
on the lead, it will change the RF characteristics of the trace and bugger
the tuning. 

The best tip is the smallest one you have. You want the point or at least a
corner of the tip to be down around 1/32". I've done a lot of SMT soldering
on fine-pitch IC leads with a standard round nose tip but it is a LOT
easier with a truly fine point tip. If you don't have a fine tip it is even
more important to use lots of flux and absolute minimum solder and the
thinnest, finest solder you can find. 

When you are done work for the day, be sure to wash off any excess flux.
Don't let it stand over night or it may corrode things.... (At least it
would if there was bare copper around.) I use 98% alcohol and an "acid
brush" for cleaning things. A soft worn-out tooth brush will work too but
the "acid brush" is about 25 cents at the hardware store. Regular household
alcohol is 30-40% water. You can get the better stuff at the hardware store
in gallons or over the counter at a pharmacy in smaller quantities. Just
don't brush hard enough to break anything.... When assembly is complete be
sure to go over everything and clean it again. I've had a lot of high
impedance circuits fail because of "non-conductive" flux between the leads
of an IC....

And as I mentioned at breakfast, you REALLY want some sort of magnification
while doing SMT work. I consider a stereo microscope around 7 power to be
about perfect. 10 power is about as high as practical while anything less
than 5 power is getting kind of weak for best results. But I'll also say
that 1206 size parts can be done by eye if you are careful and many of the
rework people at work don't have stereo microscopes..... But when you look
at their work under the scope, the difference in quality is obvious. 

The big magnifying lens in a florescent lamp is about 2 or 3 power and is
better than nothing. For about $10 you can get a 5 or 8 power eye loupe
such as jewelers and hobbyists use. And Ax-Man has a few fold-up magnifying
stands such as they use for stamp collecting. Any of these are better than
trying to solder without magnification..... A hand-held lens is suitable
for inspecting joints but probably not practical for the soldering task. 

All the soldering I've done on this project so far could easily be handled
by any competent person. Soldering the can and the top side components is
just like working on any old Heathkit, except the directions are almost
nonexistent. The tricky soldering will be the SMT stuff on the other side
of the board. It will probably be next week before I get time for that. 

Hope this is what you wanted.

73, Doug Reed, N0NAS.