Try bonding a single ply of, say, 1080 or 106 no flow prepreg, which you
can pre-machine holes and apertures for access to vias and PTH holes. This
should have no problems as far as the adhesion of the PI. Bonded thickness
of the 1080 is likely to be around 0.05mm (0.002")

Material is available from Cookson Electronics PC Fab Ltd in Livingston,
Scotland. Telephone number 01506 412812

Regards,

Colin McVean
Cookson Electronics Technical Services UK


At 10:06 12/07/99 +0000, you wrote:
>I am attempting to screen print resistive carbon ink over a large area of
a PCB, for reasons I will not go into now. Under the carbon ink are tracks
and via's which must be insulated from the ink, this is currently being
achieved by plugging the via's with an epoxy and printing two layers of
photo imageable soldermask.
>
>The reason I am posting this question to the sig is that the process
described above is producing low yields. Does anyone in sig land have any
innovative suggestions to resolve this problem.
>
>TIA
>
>Steve
>
>P.S. Ideas currently under consideration
>
>Use dry soldermask instead of photo imageable (out of favour, at least in
the UK)
>
>Replace the soldermask with a polymide covercoat (as used on flexible
PCB's) - not sure that the carbon ink will adhere to its shiny surface.
>
>Use a thicker carbon ink to reduce the risk of the carbon ink getting into
where it shouldn't.
>
>Any ideas welcomed !!
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