Phil,

I did some early development work with sputtered copper way back in
1991. I'm sure the current suppliers can answer this better than I can,
but here goes.

1) Yes, standard plated through holes are fine.

2) The original products were pretty ethereal, and had just enough pin
holes to ruin pattern plating yield. I've had the sputtered copper
dissolve in a copper plating tank during a delay before the current came
on. Too much current applied before the copper plated up and the
sputtered layer would just vaporize around the contact point. Adhesion
after moisture exposure used to be a real problem too, but the modern
versions have an improved tie layer between the copper and the polyimide
so this is not as great of a concern. We used the GouldFlex sputtered
and electroplated product to produce some very fine featured circuits
for CTS in 1997 and had no trouble at all. The EP layer provided a nice
matte texture for adhesion and solved all the pin hole, plating
initiation problems.

3) Most all flex fabricators can work with conventional 1 mil materials.
Many have even been using 1/2 mil polyimide for the last five years or
so. The shops with any real experience with the sputtered products are
pretty limited. Contact Sheldahl or Gould for a current list.

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

Phil Hersey wrote,

I would like to laminate a sheet of "adhesiveless" (sputtered) polyimide
flex material within an FR4 PCB.  The copper on the flex is very thin,
just a couple thousand angstroms, and also very very smooth.

1)  Can I connect to this thin copper with plated through holes?  What
is the minimum copper thickness for reliable PTH connection?

2)  Will "black oxide" treatment of the copper be sufficient to ensure
good lamination/adhesion of this inner layer?  Will it wipe out my 3000
Angstroms of copper?  (if not, how are polyimide multilayers held
together with good adhesion- they just use an acrylic adhesive of some
kind don't they?). Is there a way to "etch" the smooth copper to
increase surface roughness?

3)  This flex material is one mil thick.  What percentage of PCB
fabricators out there can pattern both sides of such thin material
before lamination?

Resp.
Phil Hersey, Carson City Nevada USA

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