Werner,

you put two thoughts in this message; I agree with both and want to
amplify.


All,

I totally agree that we absolutely NEED to have some sort of coupon that
would indicate if the board that it came from will be reliable at and
after
LF assembly temperatures. This need was discussed at the PCQR2 meeting
in Las Vegas (Werner, you  were there .... maybe you remember it) - the
standard PTH solder float coupon is no longer "good enough" - a material
can look OK at those hole sizes and that hole density for even 6x at
250C...
but we have seen the same material (same board) delaminate at a high I/O
BGA site with .010" interconnecting vias ... so, one part of a quality
coupon
would be to change the solder float section to a much higher density set
of PTHs - many many more holes in the area drawing heat into the center
of the board.

We have also seen delamination at sites with very very low density PTHS
but high density copper - so another part of the quality coupon could be
a segment of planes over each other; the only thing holding them
together being the copper bonds and oxide ...

We'll have to see if those changes are more predictive. The other thing I
would really like to see happen is that for LF coupon acceptance we
probably need to move away from "solder floats" in solder pots to actual
little reflow ovens where the fabricators will take the coupons and put
them through the LF reflow profile, the actual temperatures and dwells,
that the PCB is likely to see - I think that might be more indicative and
am
trying to start a ground swell for that ....

As for the second part of your email: the use of the term "suppliers" is
meant to mean Laminators, I think. In addition to the problems with the
IPC slash sheets which was illuminated earlier, the data sheets can also
be problematic and pose a big "buyer beware". Unfortunately you have
to know what test EXACTLY was done (TGA, TMA, DSC) to make sure
you have apples-to-apples comparisons; you need to read all the fine
print on every data sheet to see if the conditions of the test have been
changed (yes, I have found laminators citing standard IPC tests but
listing different conditions of test!!); you need to understand how the
tested
material relates to your finished multilayer (if they are testing a .031"
thick double sided board to get some property - and that is what the
IPC test asks for - then that property is likely to be very different in
your
multilayer package. But the IPC isn't wrong trying to standardize on a
test
that eliminates variables not attributable to the material ... it's no
easy
thing). So, many of these data should be consider "reference only" and
even taken with a large dose of skepticism. Yes, I could rail about this
for awhile also ....

Some laminators actually don't distort their data sheets - they are very
forthcoming; but others aren't. If you don't know how to read a
laminate data-sheet, or even if you do, talk to your most credible
fabricator and ask them to translate the property values into reality
based on their familiarity with the laminate and how it really does
compare to other laminates.

Valerie

wow! now I went on ...




Werner Engelmaier <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/13/2005 10:00 AM
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Re: [TN] Qualification of the Pb-free capable manufacturers






Hi Charlie,
Yes, that would serve. We have "PTH/PTV Reliability Coupons,"
"Registration
Coupons" and "SIR Coupons"--why not "Delamination Coupons." At this point,
it
is however not clear, at least to me, which PWB design features [lots of
Cu,
little Cu, coupon size, etc.] are the most critical in terms of
lamination.



But my question is as 'Why should the burden not be on the
suppliers?'--they
control the properties of their materials and it should be part of their
data
sheets. Unfortunately, data sheets are made of very uncomplaining paper--I
have found data sheets from large 'reputable' suppliers giving CTE values
of FR-4
material as low as 11 ppm/C when the true CTE when we measured it was
almost
double.

Why is it, that in our industry, most of the suppliers are part of the
problem rher than part of the solution? With this 'Lead-Free' insanity and
the
lack of resources, we had better all contribute or face the consequences.

Regards,
Werner Engelmaier
-


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