Hi All,
Here is my two cents worth.
I am pretty sure this is crazing. It is a separation between the glass
and the epoxy. What you see is light refracted by the fine air gap
between the glass fiber and epoxy. Viewed on the glass fiber end this
condition looks like small half moon cracks. It is the path for CAF. It
is due to material or drilling problems 9 out of 10 times. On occasion
design can contribute to the condition. PTHs drilled on a .020" grid are
prone to this condition. Moisture or other volatiles in the separation
may be a contributor to propagation during assembly and in the end-use
environment. I have been told thermal cycling in a humid end-use
environment may cause water to be condensed in the air gaps. The
condition can be in the b-stage or c-stage epoxy layers but is mostly
found in the b-stage layers. This condition causes changes in
capacitance between copper planes in an IST test coupon with DELAM
circuits. We have found this condition is more common in lead-free
assembly and rework.
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] <mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Tuesday, May 20, 2008 11:43 AM
To: [log in to unmask]
Subject: Re: [TN] Blue Voids
Keith,
Can you share any information on CAF.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barbara Burcham
Sent: Tuesday, May 20, 2008 10:16 AM
To: [log in to unmask]
Subject: Re: [TN] Blue Voids
Interesting, very very interesting.
I received a technical presentation from Keith Larson at DDi this week
and when I saw this post and looked at the photos, I recalled a photo
that I had seen in the DDi paper by Gil White of a cross section of a
plated hole.
It was in the section about Conductive Anodic Filament Growth (CAF), and
I quote,
"Conditions that contribute CAF:
De-lamination of the glass polymer interface resulting from:
Excessive temperature (I.e. 260deg.C for standard FR-4)
Thermal cycling
CAF is accelerated by:
Moisture
Applied potential (higner potential accelerates the process)
Their photo shows the same smeared appearance across the hole and says
the smears are copper migration along glass fibers.
I have copied Keith into this email so that he can respond. I think they
may have the answer to this thread.
Or, contact Keith at this email address to get the paper or reach Gil
White.
[log in to unmask]
Regards,
Barbara Burcham
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Tuesday, May 20, 2008 9:36 AM
To: [log in to unmask]
Subject: Re: [TN] Blue Voids
Well, since our supplier hadn't seen this condition in their
microsections, and the independent lab used different equipment
(Scanning Electron Microscope and Differential Interference Contrast
photography), the question became whether the supplier's lab could even
see the condition if it was present.
The independent lab still has the sample panel with the known condition,
and they agreed to send back half of the panel so the supplier can
experiment with it.
In the meantime, our company issued a corrective action request so we
get some kind of follow-up on the results.
Thanks to everyone who looked at the evidence and sent their opinion.
http://frontdoor.biz/PCBportal/bluevoid.jpg
p.s. I think its kind of fun to do this (especially when it is not MY
company's sample) Maybe we should have more community "case studies", I
find the group feedback to be very educational, especially when the
descriptions in IPC-A-600 are vague.
Thanks again.
onward thru the fog,
Jack
-----Original Message-----
What became of this issue? I have not seen any more threads of e-mail.
Victor,
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Tuesday, April 29, 2008 9:59 PM
To: [log in to unmask]
Subject: Re: [TN] Blue Voids
Are the voids in the glass bundle or between the glass bundle and the
resin?
If the former, you have a glass supplier problem (not all the weaving
assistant burned off?)-- if the latter, then I would suspect incorrect
pH in the adhesion promoter application bath.
Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell: 970.980.6373
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