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

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.

Many examples of RF circuitry that I have seen, are incorporated near to DC
inputs and other DC circuitry. 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.

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.

Sorry if I upset you Jerry Cupples, though lord knows why.

Graham Naisbitt
__________________________________________________________________________

[log in to unmask]

Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK                        http://www.concoat.co.uk

Application Engineers in Chemical Compounds to the Electronics Industry

-----Original Message-----
From: Jerry Cupples <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 23 January 1998 15:25
Subject: Re: [TN] RF Circuitry and Rosin Core Solder


>Good morning, Karen; you said:
>
>
>>1.  Electromigration requires DC voltages and currents.
>>
>>        a. AC voltages and and current will not cause
>>           the electrodissolution of copper, silver,
>>           tin or lead.  The only materials that corrode
>>           with imposed AC (<~10 kHz). are amphoteric
>>           materials, like aluminum.
>>
>>        b. AC voltage and currents will not allow the
>>           the electrodeposition of any metal that I know.
>>           The metal deposited during one half wave will
>>           dissolved during the 2nd half wave.
>>
>>2.  Imposing a small AC voltage (5 to 50 mV) on top
>>    of a DC voltage and looking at the resulting
>>    small AC current is good way of studying
>>    electrochemical reactions like dissolution and
>>    deposition of metals.  The frequencies used range
>>    from 1 mHz to 100 kHz.  Frequencies over 100 kHz,
>>    such as RF, are not useful for looking at
>>    electrochemical reactions because the chemical
>>    kinetics of these reactions are too slow.
>
>1) I _love_ that kind of talk.
>2) Been waiting a long time for someone to techno-incinerate Graham
Naisbitt.
>
>
>thanks,
>
>
>Jerry
>
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