From the sound of the problem description, I must agree with Mark. It sounds
like resin spots on the copper surface are the most probable cause. I assume
that you are using foil lamination.

You could pass a black light over the panels before etching and determine
whether there are fluorescent "blobs" on the surface prior to etching. Etch
the panels and see whether the copper spot locations coincide with the
original "blob" locations. This would be pretty conclusive evidence of
epoxy. If you have access to an SEM, EDAX would confirm the presence of
Bromine at the surface, again confirming resin. If this is true, I would
also suspect that you would have a lot of outer layer shorts that are
repaired at final electrical testing due to the same failure mode. You would
also have a lot of pits and dents after lamination.

I would recommend that you evaluate the use of CAC from JJA or SC3 from RES.
Both products will eliminate the possibility of prepreg glass/epoxy dust
contacting the foil during the layup operation. Single ply would be more
likely to cause the problem only because thicker glass fabrics are used, and
these are more likely to fracture when punched or cut, resulting in larger
and probably higher numbers of uncured epoxy contaminated particles. You
would have the same failure mode using 1080 or other thin glass fabrics,
however, the resulting spots are much smaller and are probably etched off
during the outer layer etch process.

Dave Rooke
Viasystems Canada
= = = = =

>        We have been laminating with single ply construction at our Buffalo
>facility for three months now and have not experienced any problems. We
>have recently started to laminate with single ply at our Maple Grove
>facility and have run into a problem. I was wondering if anyone has come
>across this same problem. What we are seeing is copper spots in the oxide
>after lamination. We etched the foil off of several panels and to one
>degree or another we have seen these spots. We ran several test lots with
>the single ply 7628 high resin layup and our standard 1080/2116. The copper
>spots did not show with the 1080/2116 layup. We are using Electrochemicals
>oxide and we go into a post dip(reducer). Our laminate supplier seems to be
>leaning toward the oxide as the problem. If anyone has experienced this
>problem let me know.
>
>Anthony Carfagna
>Engineering Manager
>Universal Circuits, Inc. - Buffalo
>
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