"We know what we know", followed by: "we know what we think we know", then
there is: "we know what we don't know" and finaly: "we don't know what we
don't know".
Yuk,
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of valerie St. Cyr
Sent: Tuesday, 03 October, 2006 7:46
To: [log in to unmask]
Subject: Re: [TN] #3 laminate Qualification
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 [log in to unmask]
To
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cc
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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