Hi Laura,
Sorry it took so long to get back to you about this.
I thought that CAF was copper or copper salts that bridge the two
different conductors. What I saw was a dark grey scale like growth
between the two conductors. What we found was that a coupon that we had
been testing was showing variable resistances between the power and
sense circuits when we put the coupon over a coffee cup. Don't ask me
why we put the coupon over of coffee cup but that is what we did. We
determined that the resistance change was due to the humidity as this
resistance change did not vary due to heating. We then split the coupon
in half and added a drop of distilled water between the power and sense
PTHs. What I saw was some blue coloring coming into the solution. I
applied 6 volts between the two holes and the conductive fiber grew
before my eyes (using a scope). I assumed that this was a conductive
anodic filament. I assumed the blue was from plating solution that was
trapped behind the gross hole wall pull away.
So what your saying is that it is only Cu(OH)3Cl or CU(OH)3Br that can
be classified at CAF? What color are these filaments when we find them
in cross section. We think the CAF can be a copper filament. What we
have found is copper filaments that propagate down spaces between the
epoxy and glass. Is this not CAF?
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
-----Original Message-----
From: Laura J Turbini [mailto:[log in to unmask]]
Sent: November 16, 2012 3:18 PM
To: 'TechNet E-Mail Forum'; Paul Reid
Subject: RE: [TN] Root cause for measling-crazing
CAF, conductive anodic filament, is a copper salt which grows from the
anode
to the cathode. The salt is either Cu(OH)3Cl or Cu(OH)3Br in cases
where a
high bromide-containing HASL fluid has been used. In the case where
excessive plating salts were found, did you verify that the filament was
not
just copper metal growing from the cathode? Do plating salts contain
halides, or only sulfate? Has anyone run SEM/EDX on the filament?
The presence of a bias voltage, moisture, and an easy path can be
conducive
to copper dendrite formation along the glass fibers as well as CAF. The
close spacing between mechanically drilled holes on the some board
designs
causes cracks between the anode and cathode holes. When the holes are
plated, plating salts can get into the holes and become conductive in a
humid environment - but that is not CAF.
Regards,
Laura
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: November-16-12 2:10 PM
To: [log in to unmask]
Subject: Re: [TN] Root cause for measling-crazing
Exactly.
What you need is a path, a potential, moisture, ionic contamination or a
source for ionic contamination and time.
I found CAF once when a Teflon board had hole wall pull away that was
filled
with plating solution.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: November 16, 2012 2:03 PM
To: TechNet E-Mail Forum; Paul Reid
Subject: RE: [TN] Root cause for measling-crazing
Paul,
That is correct. Most CAF incidents I have seen were associated with
some
type of abscess within the PWB that allowed water and flux or other
impurities to become entrapped. When that is combined with a significant
difference of electrical potential, the CAF begins and grows over time
until
its resistance reduction reaches the point where catastrophic failure
takes
place.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Friday, November 16, 2012 12:55 PM
To: [log in to unmask]
Subject: Re: [TN] Root cause for measling-crazing
The problem is that crazing is a path for conductive anodic filament
(CAF) growth. The gap is so small you can get water to wick up the gap
due
to capillary action. If the water wicks up between two conductors with a
potential between them then you can have conductive anodic filament
formed
between the two adjacent conductors. The resulting short occurs over
time.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: November 16, 2012 1:29 PM
To: [log in to unmask]
Subject: Re: [TN] Root cause for measling-crazing
Folks,
If the resin system fails to adhered/bond to the surface of the woven
glass weave bundle I can see where one could see an anomaly on the
exterior of some thicknesses of raw boards, measling/crazing. This may
not hold true for very thick HDI boards. In a cross section one can
see a torn artifact involving the glass rod. My concern is when the
glass rod is not damage and a gap/space is visible. What then?
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Friday, November 16, 2012 11:53 AM
To: [log in to unmask]
Subject: Re: [TN] Root cause for measling-crazing
Interesting. 610 seems to offer different criteria, but criteria which
I
have always struggled to understand and agree with. 610 reads that both
measling and crazing are externally observable, with the primary
differentiator being that measling is thermally induced and crazing is
mechanically induced. But the photos don't seem to match what I have
seen
in reality. I have seen instances where it is absolutely known the
condition was caused by mechanical means, but the condition looks more
like
the photos 610 offers for measling, and I have seen solder related
conditions that look more like the 610 photos for crazing.
-----Original Message-----
From: Paul Reid [mailto:[log in to unmask]]
Sent: Friday, November 16, 2012 11:54 AM
To: [log in to unmask]
Subject: Re: [TN] Root cause for measling-crazing
Hi Victor,
In my mind they are different failure mechanisms.
Measling is small blisters that are a separation of the epoxy and the
glass
fibers as a group. In a cross section you can see a blister type of
separation. Measling is usually found by a visual examination of the
board
so it is on the outer layers of the dielectric.
Crazing is a separation of the epoxy from individual glass fibers. In a
cross section you can see long silver air gaps running the length of
fibers
viewed form the side or half moon cracks around fibers when you look at
the
fibers on end. Crazing is most often found in cross sections and is not
visible by visual inspection.
Both can be enhanced by mechanical stress (thermal stress).
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: November 16, 2012 11:07 AM
To: [log in to unmask]
Subject: [TN] Root cause for measling-crazing
Fellow TechNetters:
Are the above artifact cause by the wettability of the resin to yarn,
woven glass cloth rods, interface? Then this artifact is enhance by
mechanical stress. I am trying to understand the terminology so that
it is not misused.
"X"
From: Hernandez, Victor G
Sent: Friday, November 16, 2012 7:14 AM
To: TechNet E-Mail Forum ([log in to unmask])
Cc: Hernandez, Victor G
Subject: Laminate, Resin recession-dry glass bundle
Fellow TechNetters:
Can any of the gurus out there comment on the above terminology and
perhaps share a photo. What is the worse than can occur within the
laminate with such artifacts.
"X"
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