Earl,

The IPC Surface Insulation Resistance Task Group is 5-32b.

The IPC Electrochemical Migration Task Group is 5-32e.
This may seem confusing, but there is not much linkage
between (surface) ionic cleanliness and (sub-surface) "CAF."

Perhaps what you are calling for is a new IPC board cleanliness
task group, say 5-32-??

My own interest in CAF (not necessarily a "cleanliness"
issue) started when my company needed to understand much better
the reasons for the following and similar requirements:

  GR-78-CORE, Issue 1, Sept. 1997, Section 6.1.2.3 (page 6-4),
  item O6-18 states:
    "[188] Plated-through holes in PWBs separated by less than
     a nominal 0.035 inch, (i.e., drilled hole wall to drilled
     hole wall distance), shall be used only when supported
     with reliability data."

Note that 06-18 is a X-Y plane requirement, not a Z-axis or
"two ply minimum requirement" issue.

Telcordia (GR-78) type temperature/humidity/bias testing does
demonstrate an increase in failure rates (shorts) at closer X-Y
spacings and at higher voltages even when boards are "dry when
assembled".  Earlier work has attributed this internal board
failure mechanism to "conductive anodic filament (CAF) growth"
where the first reaction step is a breakdown (hydrolysis) at
the resin and glass fiber interface.

The increasing use of finer pitch through-hole connectors and
perhaps higher voltage makes the assignment of adjacent power
and ground pins on such devices a more risky business, one for
which a standard CAF resistance test method needs to be developed.
Dense via grid arrays such as large I/O fine pitch BGA can also
represent an increased risk of CAF.

Factors affecting "CAF-resistance" include the ease of drilling
the laminate material used (ex: how brittle vs drill feed and speed
which affects the extent of fracturing extending out from the
drilled and plated hole wall) and the chemical bonding and possible
contaminates present at the epoxy-fiberglass interface.

Regarding CAF, there will be a meeting of 5-32e at the next IPC
annual meeting (November 2002).

Regards,
Karl Sauter

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------