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Date: Fri, 11 Apr 1997 09:41:12 -0400 (EDT)
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Subject: Re: DES: HTE Copper
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Hi Randy,
On the HTE (E3) vs. the Standard (E1) copper foil, the issues are not as
clean-cut as one would like.
FIRST, because the minimum property values in IPC-MF-150 are so low, there is
from a spec point little difference with the exception of elevated
temperature behavior.
SECOND, because the copper foil vendors stonewalled the users' efforts, the
ED foils do not have a ductility requirement, only a minimum elongation which
for foils is a lousy ductility indicator (spec minimums of 2 and 3%). As a
consequence the foils from the different vendors differ significantly (see
IPC-TR-484, Results of IPC Copper Foil Ductility Round Robin Study), where in
some cases the E1 foil from one vendor was better than the E3 foil from
another.
THIRD, these commercial foils are plated at very high plating current
densities requiring lots of exotic additives; these plating solutions are
rather precariously balanced. These solutions do however occasionally go
off-balance, resulting in large distributions of properties such as strength,
ductility, electrical resistivity, etchability, density, etc., all however
within MF-150, because these same vendors kept the spec numbers down. The
means of these distributions are significantly above the minimum spec values,
however. Thus, the only foils that will hurt a customer are the tail ends of
the distributions coming close to the minimum spec values. When these plating
solutions go off-balance, apparently more of the additives (mostly organics)
are co-deposited at the copper grain boundaries. The result is reduced
strength and ductility and increased electrical resistivity and etch rates.
The difference between E1 and E3 is that the distribution apparently is moved
to a higher level. I say 'apparently', because no hard data exist except at
the foil manufacturers. Further, no hard data exist as to the improvements
obtained with a switch from E1 to E3 (there are strength, ductility and
fatigue data in IPC-TR-484); the available information is all anecdotal, but
positive except perhaps for drilling. I would also suspect, that there are
large differences between copper foils from different vendors.
Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ 07945 USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]
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