Yes, I agree.  All ED copper foils are produced to a 10% tolerance of
these nominal numbers cited.  We take discrete measurements of all foil
thickness and these vary little from nominal.  I believe the weight
metric was derived from a costing standpoint rather than a thickness; we
merely applied a conversion to allow for verification of the weight
parameter to the circuit thickness which is critical in many
applications.

Jeffrey Bush
Director, Quality Assurance and Technical Support

                   76 Technology Drive - POB 1890
                       Brattleboro, Vermont 05302
                            802.257.4571.21
                             http://www.vtcircuits.com
 

-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]] 
Sent: Friday, November 05, 2004 1:54 PM
To: [log in to unmask]
Subject: Re: [TN] copper weight

Hi Jeffrey and all,
Things are not quite as simple as has been portraied--the density of ED
copper is not a fixed number, it varies depending on the plating details
of a given
batch.
This is the reasopn ED Cu foil is given as a weight per area, not as a
fixed
thickness. The situation is further muddies, because many of these foils
have
a variety of adhesion "tooth" geometries.
Thus, to say "copper weights in oz - 1/4, 3/8, 1/2, 1.0, 2.0, 3.0, 4.0
are as
follows in microns - 9, 12, 18, 35, 71, 107, 142" is not correct. The
micron
numbers are only the metric equivalents of the mil numbers, BUT the
mil-thicknesses are only NOMINAL values with significant +/- ranges.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com


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