Re: [CAD_CAM_EDM_DRO] Re: conductive adhesive as alternative to solder?

Mariss, I don't agree with your solder paste comments. I've been soldering
SMT components since there were SMT components and I have great luck with
solder paste. However, I do almost always just hand solder with fine solder
as you recommended unless I'm doing the really fine pitch stuff or high pin
counts over 128 pins, then I'll almost always use paste. For SO-16 type
components I wouldn't even bother with paste. I don't often use hot air with
the paste either as I find hot air just too slow. I use a small butane torch
or a soldering iron most of the time. The toaster oven works great for doing
a complete board at a time.

Stencils aren't needed for solder paste for prototype work. What is needed
is a GOOD paste and a GOOD applicator. Most people make the mistake in using
the typical JUNK tip that comes with many paste syringes. Get your paste in
a bottle and fill your own syringes with paste. Or, replace the applicator
tip with a metal blunt point tip on the prefilled syringes. Most people also
seem to lay down a bead of paste that is too wide.
If you are getting bad results with paste, you either have bad paste, the
wrong temperatures or too much / too little paste.

One downside of good paste is it'll leave behind a lot of flux. The water
soluable flux doesn't seem to work as nice as the flux that won't wash off
in water. A little ammonia / alcohol mix will usually do the trick though.
There are a lot of 'no clean flux' pastes but I still clean it off as it
looks bad to leave it on the board.

Radio Shack has a good fine silver bearing solder that works well that is
easy to find. Part# 64-035 it's .015 diameter and is a 62/36/2 mix.

If you don't already wear glasses, then a pair of the strongest reading
glasses you can find at the discount store that won't make you dizzy is a
great tool for SMT work.

If you do wear glasses, then a magnafying lamp is mandatory. I still have
perfect vision, but there are a lot of things you just can't see clearly on
fine pitch surface mount without magnification!

A GREAT! not just good ESD safe temperature controlled soldering iron is as
important as the vision system too. Hakko, Metcal and Pace are some of the
names to look for.

You 'can' do fine pitch SMT with Radio Shack irons, but it's a LOT more
difficult. I keep a butane powered Radio Shack soldering iron in my desk at
work. I do a fair amount of fine pitch soldering with it as it's quicker
than taking a board to the lab. But you won't do this without a lot of
experience!

For folks that are new to soldering components, get some old junk boards,
remove the chips with a butane or propane torch and practice putting them
back on instead of practicing on your new components and valuable boards!

I also agree that there's just no reason to use conductive adhesive when you
can solder.

Oh, by the way, don't be afraid of BGA devices either. They aren't as
difficult as the BGA inspection equipment vendors want you to think they
are!

later,
Larry E.

----- Original Message -----
From: "mariss92705" <mariss92705@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, March 23, 2002 1:14 AM
Subject: [CAD_CAM_EDM_DRO] 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