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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