Wires and such

[Paul E. Campbell]

>         [ snip ]
> 
> >Like David said, soldering don't cut it when you are talking about wires
> >that move around. Even wires that attach to a circuit board are (gasp)
> >wrapped, not soldered, when used in high vibration environments.
> 
>         [ snip ]
> 
> Soldered connections are still the standard for the majority of hi-
> reliability connections.  Mil-Spec (I mention this, because mil-spec
> and NASA specs are some of the toughest in the world) and NASA allow
> crimp only under very stringent guidelines (of course, the same could
> be said for soldering).  Wire wrap is NOT COOL for anything.  It's only
> for temporary connections or for connections which are in a non-hostile
> environment (i.e. no humidity or temperature extremes, no vibration, etc.
> -- essentially in a building).

[the rest of the discussion of wire wrap vs. soldering vs. crimping deleted
for brevity]

I've recently started doing things totally different.

The thing that scared the willys out of me is altering or repairing surface
mount circuits. They are quite literally NO FUN to solder to. However, there's
a new way of doing it...

You simply use conductive inks to construct your circuit. You can do this on
plastic, cardboard, paper, mylar (my favorite), wood, or whatever useful
surface you have. Some inks require a heated curing to make them really
solid/dry, some don't. Some have much better conductivity than others. And
some can actually be soldered to when you get done. Only problem with most
of them is they have problems with the suspension settling and problems with
shelf lives.

But the REALLY nifty material is electrically conductive adhesives like two
part epoxies and some thermally sensitive adhesives (use a heat gun to make
the adhesive loosen up enough to replace a component).

In both cases, silver, gold, copper, or nickel powders are added to ordinary
inks/adhesives for conductivity. One company even sells the inks in a ball
point pen arrangement so you can literally sketch/print the circuit out on
paper and then simply trace it out with the pen.

This stuff isn't limited to surface mount only. For example, buy a piece of
fiberglass. Draw out your circuit using conductive inks. Drill out the
appropriate holes and mount the chips to it using conventional soldering.
Glue the wires on using a two-part conductive epoxy. And if you REALLY need
to make traces cross each other, whack off a piece of plastic, glue it down
using "normal" nonconductive epoxy, draw your traces across the "bridge",
and make little adhesive "bridges" down onto the main board with conductive
epoxy (not necessary but just in case the ink cracks along the edge of the
plastic/fiberglass gap). Course it's probably easier to just glue a piece of
insulated copper wire down using a combination of conductive and nonconductive
epoxy. I've also heard of people using the "green stuff" that's usually used
over the top of conventional circuit boards as the insulator. Since you can
get photosensitive versions, they used several layers to make channels and
then built multilayer boards completely out of conductive inks and insulator
material.

With surface mount components, you simply make a little pool of adhesive on
a piece of scrap cardboard. Dip the edges of the surface mount chip in the
adhesive and stick it on the board where it belongs.

Another point (though not a major one to me anyways...) is that most of
the "base" inks and adhesives are usually polymers, acrylics, etc., so they
are about as "environmentally friendly" as you can get...most of them are
safe to flush down the drain even with a septic tank for instance.

Also look for some of the carbon-based paints. They don't do diddly for
conductivity but you can enclose any RF sensitive/interfering components
in a cardboard cover (glue it on) and then paint it with the RF shielding
paint. Makes building those faraday cages trivial.