ASM-1 problems/solder flux

[Stopp,Gene]

I'm pretty sure that all of the solder I have is water-based. I get the
feeling that much of the solder used today in manufacturing facilities
is water-based, so that the companies don't have to deal with the hassle
of environmental agency fines for their cleaner disposal. Since all of
my solder came from my old job, it's probably water-based. It could well
be that the leakage characteristics of residual flux is different
between water-based and non-water-based. I distinctly remember *not*
having so many flux-related problems years ago, so there's a little
evidence right there.

What I find is that solder flux residue on a circuit board causes
leakage currents between components. In analog circuits where precise
charges across capacitors are depended upon for proper operation, this
leakage will really mess things up. In VCO's, it can cause distorted
waveshapes, stoppage of oscillation, non-linear (or non-exponential!)
voltage-to-frequency tracking, etc. In VCF's, it can cause the same
tracking problems as well as lock-up and distortion. In Sample & Hold
circuits, it can cause excessive held voltage droop. In general audio
paths, it can cause crosstalk, distortion, offsets, and other nasties.
In other words, flux sucks.

 - Gene

 ----------
From: Brett Duggan
To: synth-diy at mailhost.bpa.nl
Subject: Re: ASM-1 problems/solder flux
Date: Friday, May 29, 1998 1:38PM


You guys must be using water soluble flux solder.  The flux left by
rosin
core solder should not have to be cleaned, even though I suppose it is a
good idea.

The point is emphasized when you look at the solder side of a 20-year
old
PCB that is still working perfectly and notice the layer of brown crud
that covers it.  I assume that this is rosin core flux...could someone
please correct me if I'm wrong?

Brett D

> > Oh yes - clean the circuit board to remove *any* solder flux. When
you
> > think it's clean, clean it again!
> >
> > [Luke:] I've heard people stress this point before. What exactly is
the
> > reason for this ?
>
> Coz otherwise it won't work, doh!   :-)
>
> No, seriously, seems like solder flux is somewhat conductive, which
> means that you'll get small leaking currnets through the flux between
> points that should not be connected. That is Not Good. Granted, it's
> not very big currents at all, but then again our ears are very
> sensitive to very small differences in, say, pitch, so...
> /Moxie (At least that's what I think)