Thomi-
Yes, I think you've located a CAF failure. Michael Pecht of CALCE/Univ. of
Maryland may have written about these recently, but I can't any references
from him.
2 articles in IEEE's Proceedings, CPMT Part B are:
1) Use of surface insulation resistance and contact angle measurements to
characterize the interactions of three water soluble fluxes with FR-4
substrates
- Jachim, J.A.; Freeman, G.B.; Turbini, L.J
Air & Radiat. Technol. Branch, Environ. Protection Agency, Atlanta, GA,
USA
in
Components, Packaging, and Manufacturing Technology, Part B:
Advanced Packaging, IEEE Transactions on [see also Components,
Hybrids, and Manufacturing Technology, IEEE Transactions on]
Volume: 20 4 , Page(s): 443 -451
{November 1997 issue}
and,
2) Reliability of the laminate from advanced COPNA-resin/E-glass fabrics
system
- Nawa, K.; Ohkita, M.
Res. & Dev. Center, Sumitomo Metal Ind. Ltd., Amagasaki, Japan
in
Components, Packaging, and Manufacturing Technology, Part B:
Advanced Packaging, IEEE Transactions on [see also Components,
Hybrids, and Manufacturing Technology, IEEE Transactions on]
Volume: 20 1 , Page(s): 78 -86
{February 1997 issue}
You should also look at web page below, which lists a CAF paper from Dr.
Turbini:
1997 TMS Annual Meeting: Wednesday PM Session
Abstracts
{found this CAF info on web page...}
http://www.tms.org/Meetings/Annual-97/Program/AM97-WednesdayPM.html
DESIGN AND RELIABILITY OF SOLDERS AND SOLDER INTERCONNECTS:
Session VI: Interconnect Design and Reliability in Electronic Packages II,
RELIABILITY CONSIDERATIONS WHEN CHOOSING WATER SOLUBLE FLUX FOR ELECTRONIC
ASSEMBLY: Laura Turbini,
Georgia Institute of Technology, School of Materials Science and
Engineering, 778 Atlantic Drive, Atlanta, GA 30332
There is a need for a fundamental understanding of the interaction of
processing chemicals such as fusing fluids, soldering fluxes and cleaning
agents with printed wiring board substrates. This need is driven by two
factors: (1) the increased density of today's electronic products creates
voltage gradients which are high enough to enhance degradation modes which
are not important for less dense circuitry, and (2) the elimination of
chlorofluocarbons CFCs) and other ozone depleting cleaning agents due to
their destructive effect on the stratospheric ozone layer has lead to a
proliferation of new soldering fluxes and cleaning agents whose interactions
with the printed wiring board (PWB) are not well characterized. Water
soluble fluxes have been effectively used in high volume electronic
manufacturing operations for a number of years. Their use has increased
dramatically as they provided an opportunity to eliminate CFCs in the
cleaning process. They provide excellent soldering with low defect levels
and with a proper cleaning process can produce highly reliable electronic
circuits. However, some water flux and fusing fluid formulations contain
ingredients which can have deleterious effects on the reliability of a
product under certain operating and use conditions. There is a failure
mechanism known as conductive anodic filament formation (CAF) which has been
observed in PWBs boards treated with certain water soluble fluxes. This
failure mode involves a debonding of the epoxy-glass interface and the
formation of a conductive filament which grows along this interface from
anode to cathode. This paper will report on those chemicals which tend to
enhance this failure mode and will make recommendations on assuring the
reliability of electronic assemblies.
========================================
Finally, you can download a 22 page presentation [Adobe Acrobat] from Dr.
Laura Turbini [photos, chemical background, and description of Experiments]
at this page,
http://smaplab.ri.uah.edu/lce/proceedl.htm
Presented at:
Proceedings for Life Cycle Systems Engineering Workshop
"Conductive Anodic Filament Formation: A Potential Reliability Problem for
Fine-Line Circuits"
Good luck!
Michael Alderete
Aerojet, Azusa CA, USA
-----Original Message-----
From: Thomi [mailto:[log in to unmask]]
Sent: Thursday, February 03, 2000 5:46 PM
Subject: electrical shorts in RCC (resin coated copper) build up layer
Dear Technetters,
has anyone come across a root cause for electric shorts between neighboring
copper lines of different potential within a layer laminated with RCC (resin
coated copper)? We have carefully ground away layers 1+2 from one side, and
layer 4 from the other, to find a (ca.) 1 micrometer diameter filament
connecting two neighboring lines in layer 3. Cross sectioning this further,
we could analyse this filament by using SEM/EDX and found copper. The
surrounding resin shows peaks of Bromium (probably from flame retardants)
and Aluminum (??Al2O3 filler material??). The electric short was not
detected during bare board testing, but occured within one week of
functional testing of the full assembly in an environmental chamber
operating at 120°C (I wouldn't believe it!).
Is there a certain resin condition under which copper migration is enhanced
within the RCC-resin (however close to the interface with the core to which
the RCC is laminated)? There is a recommendation to ensure driving/baking
out humidity from the multilayer, which makes me somewhat suspicious, but I
don't know enough about the constituents (resin, hardener, flame retardant,
maybe filler material) to try and explain what happens electrochemically.
Best regards,
Thomas Ahrens, Memellandstr. 8, D-24598 Boostedt
Tel. ++(49) (0) 4393 97769 e-mail [log in to unmask]
<mailto:[log in to unmask]>
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