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June 2006

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Subject:
From:
Lee parker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Lee parker <[log in to unmask]>
Date:
Thu, 22 Jun 2006 11:48:35 -0400
Content-Type:
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text/plain (182 lines)
Ramon

I would not say your theory is wrong, but generally the ions plate to the
cathode which of course has a negative charge due to a net loss of
electrons. This is why it attracts ions of course. If your theory is correct
then what is the nature of the deposit on the anode?

Best regards

Lee

J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389

----- Original Message -----
From: "Dehoyos, Ramon" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Lee parker" <[log in to unmask]>
Sent: Thursday, June 22, 2006 10:51 AM
Subject: RE: [TN] Board material





The reason is simple. Current travels from Cathode to Anode and
as the electron flow enters the anode, it deposits conductors at the
anode side, so the anode grows towards the Cathode. An analogy would be,
several rivers coming to a one river bottle neck. Each river brings
debris and the obstruction builds from the bottle neck to the feeding
rivers. In the case of CAFs, they probably start growing slowly and the
growth speeds up as the distance between anode and cathode is curtailed.
It is only my theory.
Ramon



\

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
Sent: Thursday, June 22, 2006 9:34 AM
To: [log in to unmask]
Subject: Re: [TN] Board material

Richard

Actually CAF was first identified by Dave Lando who was in the same Bell
Laboratories organization as Werner and myself. This was in 1974, just
after we opened the new and world's largest PCB shop in Richmond.
Probably the most important attribute of CAF is as the name suggest, the
filaments grow from the anode to the cathode which is the opposite of
what one would anticipate.

Best regards

Lee

J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389


----- Original Message -----
From: "Stadem, Richard D." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 22, 2006 9:06 AM
Subject: Re: [TN] Board material


In about 1978, when CAF was realized as a problem in standard PTH power
supply boards, the strands were continuous through the pre-preg. It was
then that the fab shops started to used chopped fiberglass mat weave, in
order to provide shorter strand lengths so CAF formation was less likely
to happen. However, because of circuitry being so close together
sometimes with fairly high potential, CAF has become more of an issue
again.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Thursday, June 22, 2006 7:36 AM
To: [log in to unmask]
Subject: Re: [TN] Board material

        Hi Werner, could you expand on "Having PCB materials without
continuous glass fibers makes them immune to internal CAFs"?  I was
under the impression that the continuous glass fibers were the strength
of the board.
        Regards,
        Ramon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, June 21, 2006 3:58 PM
To: [log in to unmask]
Subject: Re: [TN] Board material

Hi George,
CAF stands for 'Conductive Anodic Filament'-CAFs are capillary paths,
typically from PTH to PTH, along the glass fibers of the PCB glass fiber
reinforcements. The get started by damage done during PTH drilling with
a dull drill, propagate further depending on internal vapor pressures,
and on application of a potential difference transport metallic ions
forming a conductive path. Now, this conductive path does not give you a
dead open, but lowers insulation resistance by couple of orders of
magnitude.
Having PCB materials without continuous glass fibers makes tham imune to
internal CAFs.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com

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