Hi Hillel,
The problem with copper foil that you mention is nothing new. The cost of
producing copper foil is in the copper weight provided to the customer as well
as the electrical energy required for the plating; with some additional cost
for the other plating chemicals consumed as well. A 5 to 10% thinner (lighter)
foil translates directly into a 5 to 10% higher production capacity as well as
an increased profit margin. In most cases, copper foil is, however, bought by
weight. Thus, the direct customers of foil manufacturers, the laminators, not
only get what they pay for, but get more foil in terms of area received,
increasing their profit margin as well. The real users of foils, the customers
of the laminators, however, get a thinner foil on the laminates they buy.
However, not all foil manufacturers are the same, and measuring actual foil
thickness is not a totally straightforward process (that is why weight is
specified) (see IPC-TR-484, Results of IPC Copper Foil Ductility Round Robin
Study).

But thickness of plated copper foil is only a relatively minor problem. When
ANSI/IPC-MF-150F, issued in October 1991, was produced, I was the chairman of
the copper foil committee. I and the few other users of copper foil—not
counting the laminators, who are part of the problem—tried very hard to have a
specification that would give the users some protection. Our efforts were
unsuccessful, since  we were unable to get sufficient user participation in
the committee to balance the overwhelming presence of the copper foil
manufacturers on this committee. I resigned the chairmanship in protest prior
to the completion of ANSI/IPC-MF-150F; one can play Don Quixote only so long.

The foil thickness (weight) issue is, however, only a small part of the
issue—and at least it is consistent for a given foil manufacturer. Thus, the
user can adjust the current carrying trace cross-section by designing wider
traces. For a real problem issue, take a look at the Elongation values for all
CU-E (plated) foils. The foil manufacturers labeled  Fatigue Ductility, which
is a much better measure than Elongation for the ductility of foils for which
elongation is a notoriously bad measure, "NA" (Not Applicable). How can a real
ductility measure of an ASTM test method specifically developed for foils be
"Not Applicable"? The minimum Elongation values listed are for the most used
foils in the 2 to 3% range. Most of the foil produced has significantly higher
elongation values.

The foil product getting close to the specification minimums are in the 2 to
3-sigma tail of the production. Thus, it does not happen very often and may
not be used in a product that runs into trouble at those values. Low
elongation (ductility)  values like that are produced when the plating
chemistry goes off-balance. Not only will the ductility be lower, but also the
tensile strength and perhaps also the density, the etch rate will be higher as
will be the electrical resistivity.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]


################################################################
TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for additional information.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
################################################################