Subject:                              Time:  10:12 AM
  OFFICE MEMO         RE>Copper Thickness Designation...      Date:  1/24/96

Rich, we went through this about 2-years ago when we changed over from
MIL-Spec's and in-house spec's to industry (IPC) spec's.  The key is the
engineering data on your master drawing.

On the master drawing you need to reference one of the metal-clad laminate
spec's, IPC-L-108 or -115 and you must include the field discriptors for the
copper foil, such as C1/C1.  The IPC-RB-276 , in paragraph 3.9.2.3 "Minimum
Surface Conductor Thickness" states "Unless otherwise specified on the master
drawing, the minimum total (copper foil plus copper plating) shall be as
follows:"  It then in table gives the "Base Copper Foil" thickness and the
"Minimum Finished Conductor Thickness".  The IPC-A-600, Rev. "E" acceptance
requirements track the RB-276 requirements.

We have shared your experiences with some printed board manufacturers trying
to imply the specified foil thickness requirements in the material spec's
apply to the finished product (they do if the holes are not plated-through). 
We rejected the printed boards that did not meet the metal-clad base material
foil thickness requirements.  We have some designs that require 3-7 oz/sq.ft.
Cu laminated foil thickness.  These foil thickness are not readily available
(off-the-shelf) so the printed board manufacturer's will plate-up the
available material to meet the designated foil thickness per the material
spec. requirements, and then do the plated-through hole process.  In some
cases, the printed board manufacturer's have used "thinner" clad foil
thicknesses and increased the Cu plating thicknesses (both surface and
plated-through holes).  

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I am looking for information regarding the way various designers specify 
copper thickness for boards, and how this information is translated by the 
manufacturers. IPC-D-325A and IPC-D-275 are not clear on how this nformation
is to be stated or translated.

We have always indicated the copper weight as the starting weight, ie. 2oz,
1oz, 1/2oz, etc.. Some manufacturers translate this designation as finished
weight. They will start with a lighter copper and plate up to a finished
dimension, (start with 1oz, plate up to 2oz).

Tolerances are not stated in the IPC documents. IPC-RB-276 indicates that, in
the case of 2oz copper, the finished surface thickness should be .003".

What is the general direction of the industry? As indicated above, I have had
manufacturers indicate both ways.

Rich Ackerson
Sr. Industrial Engineer
Elsag Bailey Electronics
Voice 216-585-7646
Fax   216-585-8867
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