Hi Tim,
>Werner,
>I was a bit confused by your explanation of why copper barrel cracks occur
>where they do.
>First, the center of a construction is not necessarily B-stage. If I build a
>four layer board with foil construction the center is C-stage and the outer
>layers are prepreg.
The cracks will typically occur at the layer interface region (regions if the
center layer is a laminate) between the laminate and prepreg layers closest
to the PCB center. So in a four layer board with  the center C-stage you are
likely to get cracks at both the interfaces of the center laminate layer with
the adjacent prepreg layers.
>Second, why do you say that prepreg always has higher
>resin content than C-stage? What if I use only 7628 prepreg? I know, on
>average your statement is probably true, but you said "always". Couldn't
>that lead someone to a bad conclusion?
Perhaps always was to much, 'typically' (and in all cases I have seen) may
have been better since there are ways to make it otherwise. Any bad
conclusions are not serious since if you got cracks anywhere, they have to be
dealt with.
Werner Engelmaier

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
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
##############################################################