Re: conductive adhesive as alternative to solder?

Jon,

I agree with you entirely. I would not trust any joining method that
did not include solder. It takes as you say a very tiny (temp
controlled) iron, .020 multicore solder, good eyes, a steady hand and
good soldering techinque.

About solder paste. Unless you have a stencil and an SMT oven, don't
bother. Solder paste does not adhere well when applied manually,
balls easily when used with a soldering iron and results in wildly
non-uniform solder joints.

A much better (and easier) bet is to use multicore solder and
soldering iron for fine-pitch hand-mounted SMT devices.

The trick is to intentionally have solder bridges between pins as
long as the joints are of a good quality (shiny, no stalagtites or
dross). Then take a good quality, fine pitch solder wick and use it
as a brush.

Place the iron on top of the wick and sweep the wick along the SMT
pins. If you keep the wick fresh (not burned or saturated with
solder, clip it frequently just ahead of the wicked solder), you will
get joints that would be the envy of any automated SMT line product.
It's fast also, with experience, it takes 15 sec for a perfectly
soldered SO-16 package.

All it takes is just a little practice and a sense of what is right.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> urstest wrote:
>
> > I hate soldering smt chips. Have anyone try using conductive
> > adhesive to glue these chips to a broad?
>
> Broad? Hmm, we're getting VERY far off topic, here.
>
> Well, I don't know of anyone who uses conductive epoxy for attaching
> electronics. I have some conductive epoxy with silver in it, that
we use
> for grounding very fragile detectors. Sometimes it becomes non-
conductive
> when it sets. Then, you have to start over. It has a shelf life
(by the time
> I get it) of about 6 months before it turns hard in the tube
(whether the tube
> has ever been opened or not). It costs $19.00 for two TINY tubes
with
> about 1 CC each!
>
> I really don't recommend such a thing. I have perfected hand
soldering SO
> and even SSOP and high density quad flat packs down to .5 mm
> pin spacing. A VERY small soldering iron, very fine solder wire and
> a strong magnifier are needed, plus a good collection of tweezers.
> I put heat shrink tubing on the handles of the tweezers to give them
> a better grip. Nothing like having the tweezers flip sideways
between
> your fingers and fling a $30 chip across the room! When the
inevitable
> solder bridge ocurrs, you need some fine solder wick.
>
> Jon