I would have to agree with Werner, and add that ED Cu foil from the material
suppliers tends to be at the lower end of the tolerance range - if the
process control is accurate enough then why would they want to supply more
than the least amount of expensive copper. Never come across anything at the
higher end yet, but maybe one day...
Other considerations are the removal of copper from the inner layer foils
that are a natural and necessary result of the fabrication processes.
Usually best to ask your target fabs for the expected final weight, and they
should be sentient of this for impedance controlled jobs.
At least you can have some control over the finished outer layer copper
weights by forcing you fabricator to supply to your tolerance requirements
on this.
Best Regards
David Greig
_________________________________________
Director
GigaDyne Ltd
Buchan House
Carnegie Campus
Dunfermline KY11 8PL
United Kingdom
Tel. +44 (0) 1383 62 49 75
_________________________________________
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: 05 November 2004 18:54
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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