>
> I was a little bemused to receive Jerry's comment and have re-read my
> posting.
>
> Perhaps I should have worded it more clearly, particularly in view of
> Karen's reply. As I conduct this correspondence late in the evening, so
my
> communications are sometimes not as I would intend

Maybe Jerry was playing internet in the late evening, also.

> of course RF
> circuits use AC not DC and that the real issue with flux residues will be
> dielectric influences.

I would think so.

>
> I do not agree that AC will not cause dendrites. You have gazillions of
> reverse biasing going on at any moment which will certainly limit the
> ability of dendrites to form but over time they surely will, particularly
if
> there is something present to help them.

I am very doubtful that purely AC voltage will allow electrochemical
migration.
However, I am willing to change my opinion if decent experimental proof
is given.  AC on top of appropriate DC may indeed allow electrochemical
migration and dendrite formation to occur.  I also doubt that there would
be a
synergy of AC and DC combined, I would guess that the DC voltage will grow
dendrites like the AC voltage wasn't there.
>
> Many examples of RF circuitry that I have seen, are incorporated near to
DC
> inputs and other DC circuitry.

Such as power inputs for IC's etc., which are prime sites for
electrochemical
migration to occur.

> I am not sure how or why, one would
> selectively leave solder residues on an RF circuit where they would
> certainly compromise performance and not on the other areas (if present)
> where dendrites will form more readily.

Gloppy RMA residues (like good old Reliacore 15 (if Graham can do it, so
can I))
are not particularly "dendro-genic", nor do they degrade DC and low
frequency SIR,
like certain no-clean, organic-acid-type residues.  They tend to be
hydrophobic and
act like quasi conformal coatings.  However, their residues have dielectric
properties
that may have a deleterious affect on RF circuits.  Adding another layer of
dielectric
material near a stripline, resonator, etc., may mess up its designed
function.

>
> As to the application of SIR testing, we are looking at developing the
> measurement aspects of our system to include for AC circuitry testing
which
> Karen asked about in an earlier posting.
>

AC measurements could be a very interesting way of studying SIR and
electrochemical reactions in the thin moisture film on circuit board with
hygroscopic residues at high humidities.

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