Frank,
How the hell are you - long time no speak.

In answer to your question on warp & weft, there is usually more movement in
the warp direction since this is under tension during pre-preg manufacture,
however most shops have the warp in the long because the movement is more
predictable than the movement in the weft.

Some average figures I had for artwork compensation from a few years ago
were:-

Signal/Signal layers    + 400 to 600 ppm Warp
                        + 50 to - 50 ppm   Weft

Ground                          0             Warp
                                0             Weft.

A few other considerations on registration problems:-
Laminate.
The more glass in a thin laminate the less movement.
Baking to "stress relieve" before processing may help.
Leaving as much copper on the layers will help (cross hatching, border
patterns, etc)
Mixed thicknesses in a build will give mis-registration, thinner core move
more than thin cores.
Pre-preg.
I've always found that 2116 pre-preg gives better results than 2125 or 2113.
(That's a personal opinion).
Too high a flow or too high a resin will give more movement.
Too high a pressure will give more movement.
Separator plates,
You may get better registration with steels separators than aluminium
because the TCE of steel is closer to FR4 than is aluminium.
Processing
Thin cores can be stretched if you brush or pumice clean, chemical clean
gives less movement.
Tooling
Is the tooling consistent for the whole package.
Artwork
Is the artwork expanding/contracting during use.

OK Frank that's it for now time to go home for the weekend.
Hope this helps.
Keep in touch I'm sure you owe me a Guinness from some time past.

Geoff Layhe
www.lamar-uk.co.uk

> ----------
> From:         Frank Davies[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Frank Davies
> Sent:         07 April 2000 14:09
> To:   [log in to unmask]
> Subject:      [TN] Mis-registration of Multilayer PCBs
>
> We are having problems with mis-registration with multilayers 8 layer and
> above. Information given to me to work on stretch factors of the printing
> films. One thing our Warp is in the short direction and Waff is in the
> long direction, and few people work this way. Could I get some help with
> this problem
> Thank You
> Frank
>

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