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October 2006

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From:
"valerie St. Cyr" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 3 Oct 2006 10:46:12 -0400
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All,

There are materials whose properties' data sheets have the values that 
would indicate high thermal stability, and so one might conclude they 
could pass a lead free reflow or reflows. But it is not so simple. As the 
laminators load up on fillers to restrain the Z-axis CTE to mitigate 
against the higher temperature at reflow, the interlaminar strength can be 
compromised. We are seeing an x-y sheer phenomena. The delamination is not 
prepreg to copper, or adhesive failure, it can be within a core, or 
prepreg to glass - a cohesive failure. 

Also, regardless of the above, your particular design might survive a lead 
free reflow process while another design on the same material fabricated 
by the same supplier will not. Some of these materials have design 
dependencies only now being understood.

OK, if that isn't problematic enough, these materials aren't drop-in 
replacements in the fabricator's processes despite any claims to the 
contrary from the laminators. So, for the same design on the same material 
if you switch fabricators you could then experience delamination or 
massive hole wall pullaway (which we haven't seen in a very long time).

What else ? Oh yeah, for non-phenolic systems better prebake before 
assembly ...

What else ? Oh yeah, some (not all, but some) are still being tweaked and 
what worked last month may not work next month.

We are not done learning yet... all the answers aren't in. In fact, some 
of the experiments have even been thought of yet.

my 42 cents.

Valerie




Werner Engelmaier <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
10/02/2006 06:29 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
Re: [TN] #3 laminate Qualification






Hi Dave,
Well, I spoke too soon. I did come across numbers similar to these: Tg=210 
C, 
Td=365 C, just not in this combination.
There are: 
N4000-13     200°C     365°C     3.5%     STII=247
TU-832             210°C     340°C     2.5%     STII=250
IS620          ~205°C     353°C     2.8%     STII=251

Werner

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