Joe,
Good question.
Measling or delamination could contribute to conductive filaments forming by providing areas of poor PTH quality, entrapped ionic contamination, moisture accumulation, and weak epoxy-fiberglass bonding. Although not a true "CAF" failure, these defects could significantly reduce the spacing that a CAF filament would have to bridge to cause a failure.
Electrochemical Migration:
The growth of conductive metal filaments across or through a dielectric material in the presence of moisture and under the influence of voltage bias.
Conductive Anodic Filament (CAF) Formation:
The growth of metallic conductive salt filaments by means of an electrochemical migration process involving the transport of conductive chemistries across or through a nonmetallic substrate under the influence of an applied electric field, producing Conductive Anodic Filaments (CAF). [AT&T Labs, Lando and Mitchell, 1979]
Regards,
Karl Sauter
Jeffrey Bush wrote:
>
> I would say no - CAF is seen on packages that have good drilling,
> lamination and glass wet-out. Tight designs with pin placed close to
> utilities should be reviewed closely for minimum spacings and the use of
> CAF resistent materials (some other than FR4 also) may also be needed to
> be evaluated.
>
> Jeffrey Bush
> Director, Quality Assurance and Technical Support
>
> 76 Technology Drive - POB 1890
> Brattleboro, Vermont 05302-1890
> Tel. 802.257.4571.21 Fax. 802.257.0011
> [log in to unmask]
> http://www.vtcircuits.com
>
> -----Original Message-----
> From: Kane, Joseph E [mailto:[log in to unmask]]
> Sent: Wednesday, March 24, 2004 10:09 AM
> To: [log in to unmask]
> Subject: [TN] CAF And PWB Subsurface Imperfections
>
> Does anything we know now about conductive anodic filaments indicate
> that we should rethink acceptance of measles, or reconsider criteria for
> delamination?
>
> -Joe
>
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