I agree with Werner's description of the cost relationship between the
foil manufacturers and the laminate makers. The margins in that business
are increasingly thin, and like it or not shaving the foil weight to the
low end of the spec. has often helped keep things reasonable for them.
(The same applies to polyimide films for flex.)

From a design/user perspective if the foil was specified with an
absolute thickness tolerance, rather than by percentage, the electrical
performance variation would be more consistent through all the foil
weights. The same is true for the copper removed in circuit processing
by the fabricators. Their processes don't typically remove more copper
just because the foil is thicker, so the percentage approach is a gift
when working with thick copper.

If the politics behind the IPC specs. don't allow for a more practical
approach for the ultimate customer, then consider creating a new
standard by being a more demanding customer. Just keep in mind that
nothing comes for free.

Andy Magee
[log in to unmask]
(937) 435-3629

################################################################
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
################################################################