John
Rather than putting the illness onto the designers, AT&T chose to change
materials.
For sometime, product that was considered at risk for CAF was built on BT.
This obviously was a very expensive solution.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "John Burke" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, June 23, 2006 12:58 AM
Subject: Re: [TN] Board material
> Use anti CAF materials and give proper design clearances fom hole to
> internal copper on the through holes and vias. Be particularly careful on
> boards having 48V (or other higher voltages) on the internal power planes
> as
> they are more at risk.
>
> John
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Huynh Thanh Nhan
> Sent: Thursday, June 22, 2006 8:08 PM
> To: [log in to unmask]
> Subject: Re: [TN] Board material
>
> Hi,
>
> How to improve CAF (or anti-CAF)?
> Change glass cloth or resin system?
>
> Best regards,
> Nhan
> ----- Original Message -----
> From: "Stadem, Richard D." <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, June 22, 2006 10:40 PM
> Subject: Re: [TN] Board material
>
>
> Totally understand, Ramon. After doing that job for a couple of years,
> it prepared me for anything. Office politics pale in comparison to those
> conditions.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
> Sent: Thursday, June 22, 2006 10:04 AM
> To: [log in to unmask]
> Subject: Re: [TN] Board material
>
> I knew there was some Indiana Jones in you, Richard. In my
> barrios I had to jump over fences, dodge bullets and bite dogs back to
> stay alive too. So when I joined the Army it was easy. Do not want to
> relive them, I like peace.
>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Thursday, June 22, 2006 9:57 AM
> To: [log in to unmask]
> Subject: Re: [TN] Board material
>
> Hi, Lee
> Good enough. My experience with it began in 1977 on telephone network
> circuit cards used in Saskatchewan, Canada. I was a telephone tech at
> that time and ran into CAF when attempting to troubleshoot the boards
> while straddling the pole. I eventually had to pull the entire network
> cards out and replace them. Nobody could figure out why the boards were
> "leaking" current from the power supply to the signal lines, disrupting
> the service. They finally figured it out that with the extremely cold
> mornings turning into extremely hot days, the condensation was actually
> infiltrating the pwb along the power supply buss terminal (not conformal
> coated), and over time CAF formed.
> I ran into CAF again in 1979 at Honeywell, and this time I recognized
> it. When the pwb supplier changed to the different pre-preg, no more
> problems.
>
> Those were the good old days, straddling the pole and trying to debug
> the network while simultaneously shooting the brown bears trying to
> climb the pole to eat me for breakfast, all in a howling sandstorm on
> the God-forsaken wide open sand prairies near Saskatoon. Nobody around
> for several hundred miles, and sometimes I would not see another person
> for three or four days while I worked. The last thing I needed was CAF.
> Impossible to see or detect using standard troubleshooting tools of the
> time.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
> Sent: Thursday, June 22, 2006 8:34 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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