Ingemar
You ask an interesting question, why is CAF so rare? There is a good
explanations. CAF is generally observer on bare boards while those in the
field are loaded and powered. Consequently, the temperature of the board is
somewhat higher than ambient and the surface humidity (the principal driver)
is lower obviously reducing the likelihood of CAF or at least dramatically
reducing the growth rate.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "Hfjord" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, June 23, 2006 5:29 PM
Subject: Re: [TN] Board material
> was that a CAF phenomenon? If the experiment was performed on the board
> surface, I'm not surprised, because even if you add DI, there will always
> be
> free ions from the PTH or solder pads or the coating etc, ions ready to
> bridge. I've done similar experiments myself, will se if I can find the
> video sequences...beautiful scenes as you say. Again, was your experiment
> true CAF? I'm surprised that CAF is so rare, we have had just a few these
> last 20 years...
>
> Just recently, I spilled a cup of coffee on my keyboard, and it died after
> a
> few minutes, was that COFFEE-CAF?
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
> ----- Original Message -----
> From: "Paul Reid" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, June 23, 2006 11:01 PM
> Subject: Re: [TN] Board material
>
>
> Back in the '80s, when I was at Algorex, a PWB fab shop in Nashua NH, one
> of
> our customers brought in a consultant from Florida. I don't remember his
> name but he had a doctorate and was asked to trouble shoot surface
> contamination on boards we had fabricated. We pointed out that the boards
> were clean as per our Omega ionic contamination measurement.
>
> He said of ionic contamination method, "That's like looking at the diaper
> to
> see if the baby is dirty". "We have to look at the baby!"
>
> He then proceeded to find two surface pad about 40 mils apart and solder a
> wire to a trace going to each pad. He was careful not to contaminate the
> pads. He added 5 drops of triple distilled water to bridge the pads. He
> connected a power supply to the wires and applied about 6 volts DC and
> observed the water using a 100X stereoscope.
>
> What we saw was a large amount of gassing as soon as we applied power. It
> looked like boiling water for a few seconds. After about 3 minutes at 6
> volts he increased the power to 12 volts. On contaminated boards CAF
> formed
> while we watched. It looked like small branches that formed a tortuous
> pathway from one pad to the other. The result was a small flat dark gray
> bush that looked a lot like cedar; the branches had a sort of scaly
> appearance.
>
> The boards in fabrication did not propagate these filaments while boards
> after assembly all propagated the filaments. We were given a clean bill
> of
> health.
>
> The good Dr. said that jet planes in Vietnam would flight at high
> altitudes
> where the PCB were in a cold dry environment. The fighter would then
> drive
> to drop bombs in the humid atmosphere of the jungle. The hot, humid air
> would infiltration the board environment, condensation would occur. By
> repeated diving and climbing, thermal cycling in the presents of very
> humid
> air produced the equivalent of a molecular water pump inside the PWB.
> Humid
> air would infiltrate around the glass fibers and condense into water deep
> in
> the PCB. The water would travel as far as 12 inches into the board to
> cause
> failures. He suggested we seal the edges of boards with epoxy to prevent
> this phenomenon.
>
> That, it turns out, was my first experience with CAF. Though I did not
> know
> if at the time.
>
> Last year we found an IST coupon that showed changes in resistance due to
> steam (from a coffee cup). On the edge of this .250" coupon we found a
> line
> of delamination near the center. Using an utility knife split the coupon
> in
> half right along the delamination. We then preformed the experiment
> described above on an internal layer. We grew CAF in just a few minutes.
>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
> Sent: Friday, June 23, 2006 3:50 PM
> To: [log in to unmask]
> Subject: Re: [TN] Board material
>
>
> Dr. Lee
> It is not the size that matters but the volume. If a group of
> tiny droplets of water can move a ship, why not electrons move some
> atoms like it is done in arc welding. The elements beside carbon could
> also be metals such as copper, tin, lead...
> Regards,
> Ramon
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
> Sent: Friday, June 23, 2006 3:35 PM
> To: [log in to unmask]
> Subject: Re: [TN] Board material
>
> Ramon
>
> Your concept is interesting.
>
> The concept that electrons are providing enough momentum to move a
> carbon atom seems problematic though given that the carbon molecule is
> orders of magnitude larger than the electron and is part of an organic
> chain with with a very large bond energy.
>
> It would be interesting if someone performed an elemental analysis of
> the CAF residue and determine what elements are present. Obviously, this
> would be very difficult to do since the residue is thin. I doubt an SEM
> would be adequate, perhaps Augur.
>
>
> ----- Original Message -----
> From: "Dehoyos, Ramon" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, June 23, 2006 2:32 PM
> Subject: Re: [TN] Board material
>
>
>
> Dr. Lee:
>
> electron mass: Value 9.109 3826 x 10-31 kg
>
> It all starts with an ever increasing parasitic current. The
> insulation starts to break down. Electrons jump from atom to atom
> leaving a hole behind or a positive ion due to a voltage potential
> difference. Since electron have mass and the media they are going
> through is not a conductor nor a semiconductor, electrons start to
> carbonize the fibers and epoxy, and pushing those carbons to the anode.
> In simple terms electrons kick a.. Most of us have seen the traces of a
> high voltage shorts. Where there was nothing but clean white Teflon
> material, there is a black shadowy trace. I am going to say that it may
> be like DC arc welding ( AC arc welding is the same but only half of the
> cycle is used ). Electron flow creates heat and melts the rod metal
> which transfers the molten metal to the ground (anode) and solidifies as
> it cools. I am saying that this is similar but at a super turtle pace,
> Pico amps versus 100 amps.
>
>
> Best Regards,
> Ramon
>
>
>
>
> -----Original Message-----
> From: Lee parker [mailto:[log in to unmask]]
> Sent: Friday, June 23, 2006 11:23 AM
> To: TechNet E-Mail Forum; Dehoyos, Ramon
> Subject: Re: [TN] Board material
>
> Ramon
>
> I have a few questions about you hypotheses.
>
> What is the nature of the parasite mass. It must have a negative
> polarity which needs to be explained. Also, the only mass I am aware of
> that is associated with a current is an electron which will not leave a
> neutral mass behind, which is the case with CAF; I remember Dave Lando
> and his group showing mico sections of CAF that was in a formative
> state, but not yet bridging the anode and cathode. Dave later showed
> these to an IPC meeting, I believe it was in Boston.
>
> Best regards
>
> Lee
>
> J. Lee Parker, Ph.D.
> JLP Consultants LLC
> 804 779 3389
>
>
> ----- Original Message -----
> From: "Dehoyos, Ramon" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, June 23, 2006 8:57 AM
> Subject: Re: [TN] Board material
>
>
>
>
> Dr. Lee:
> We are talking about two different matter. The positive Ion
> charge atoms will deposit on the cathode (opposite charges attract ) and
> plate the cathode, while at the same time electrons will travel to the
> anode from the cathode. Those ion will loose their charge once they
> become part of the Cathode and become plain metal.
> In the case of CAF, a starting parasitic current will travel
> from cathode to anode and carry with it mass and accumulate at the anode
> and build up towards the cathode till it becomes a short.
> Respectful Regards,
> Ramon
>
>
> -----Original Message-----
> From: Lee parker [mailto:[log in to unmask]]
> Sent: Thursday, June 22, 2006 11:49 AM
> To: TechNet E-Mail Forum; Dehoyos, Ramon
> Subject: Re: [TN] Board material
>
> 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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