Have you considered using the smooth side of the foil against this thin
core?  Sound to me like you might be getting the rough foil side dendrites
opposite each other on the foil somewhere and getting very reduced
dielectric as a result. This gives the condition you describe.

> -----Original Message-----
> From: Marti Tully [SMTP:[log in to unmask]]
> Sent: Thursday, September 21, 2000 7:42 PM
> To:   [log in to unmask]
> Subject:      [TN] High Resistance Shorts
>
> Thank you for confirming my position on dppm and AQL.
>
> We make a number of different rigid board part numbers using 0.0025 inch
> core material with 1 or 2 ounce copper on both sides.  We use two plies
> of prepreg (usually 106) between the cores.  We periodically have
> manufacturing lots where there is very significant loss due ot high
> resistance shorts.  Our success rate in locating the source of the short
> is around 10% or less and it requires 8 to 16 hours of effort ... not
> cost effective.    Those that we have found were either foreign material
> in the core or laminate voids in the core.   We do hi pot testing of
> these thin cores before we use them.
>
> Is there any data, articles, research available on the root cause of
> high resistance shorts and/or how to prevent their occurrence?
>
> Marti Tully
> Quality Manager
> Sanmina-Phoenix
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################