Werner,
It is with some trepidation that I respond to your
comments. I do not want to start an email war so take
these comments as an explanation to my earlier mail...


> >The fact that the cracks are on the prepreg not
> core may be a red herring.

Please note the words 'may be'.  I didn't indicate
that it is a red herring just that it might be.  We
don't have any details about this failure the the lab
may be differentiating prepreg from inner foils.  So
the pupose of my red herring comment is only to
caution Robert from jumping to the prepreg  as the
cause and eliminating all other factors.

> >A couple things I would check out...
> >  1. Do the cracks appear near the outer layers
> (Layer 1 and n)?  You will
> tend to get >more movement towards the outside of
> the board.
> Also not likely. Failures at layers 1, 2, n-1 and n
> are typically inner layer
> separations (see results of Post Separation
> committee) because those are the
> locations with the most land rotation; barrel
> cracking occurs near the PCB
> center because that is where the loads are highest
> for the barrel.

I've learned something new, Thanks.


> >  3. Have your laminate supplier run Tg on the
> board to verify cure.  Be careful here, the Tg >
numbers will include the core
> material and the prepreg.
> The core material will
> almost certainly be cured
> but since your testing both
> core and prepreg together the
> cured core will
> affect the prepreg numbers. (I
> hope this made sense) You might try
> pressing some
> prepreg together (no core)
> and having this tested.  Use the exact
> same press
> parameters used for the
> failed panel.  (Slip a few sheets of prepreg in a
> book, don't just press the
> prepreg by itself)

> No need for this; it is clear that the load on the
> PTH barrel was too large
> giving the construction details. One thing that
> should be looked at is
> whether the product saw manual solder operations
> (typically the highest
> thermal excursions by far) near the failed PTHs.
> I hope this helps, Robert.
> Werner Engelmaier


Maybe I missed an email stating the construction
details but the original message that I responded to
was that the board is a multilayer, polyimide board.

I still think its very important to know the Tg's of
the material and I would also throw in a time to delam
test.  (I don't know what the equivalent to a T-260 or
T-288 test is for polyimide). I think it is critical
to know the condition of the prepreg.

Let's say for illustration purposes that you typically
get 1 to 2 degree deltas in your Tg tests and the time
to delam is 7 minutes.  Again for illustration let's
imagine you experiance a failure (cracks) in the
plating - you verify your Tg's and Time to delam are
normal - then I am going to start looking at my
plating chemistry much harder.

Finally, we are talking about Polyimide material.  In
my experience polyimide is going to move much less
than FR-4 material.  From the TD-579 report (GF
material) there were some failures of less than 100
Mil-T cycles but if I remember correctly the average
failure occured in the 200 cycle area. (Depending on
factors such as hole size)  For a polyimide material
failure to occur in the 100 cycle range I would think
that the board would not have been cured at all or
something else is causing the defect.

This is just my two cents worth.

pete menuez



##############################################################
> 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
>
##############################################################


__________________________________________________
Do You Yahoo!?
Yahoo! Mail - Free email you can access from anywhere!
http://mail.yahoo.com/

##############################################################
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
##############################################################