If you want to improve registration between layers you need to start way
sooner than the press.

Here are a few quick pointers to improving registration/stability.

Choose cores and pre-pregs carefully. Cores with a high glass to resin ratio
will be better for stability.
Some pre-pregs give better results than others. I've always found 2116
better than 2125 for instance.
If you use compensation factors on inner layer artwork make sure they
reflect what the laminate is doing. (Signal layers will need more
compensation than ground layers).
Brushing can stretch inners. Chemical clean is better.
Always have copper around tooling holes in inner cores.
Make sure the heat up rate in the press is not too fast. If it's too fast it
will give too much flow and "stretch" the inner cores.
Make sure the pressure is not too high use a vacuum press if possible.
Make sure the cure time is long enough to fully cure the resin.
Cool down rate should be the same as the heat up rate. (This affects bow &
twist more than stability.

Hope this helps

Geoff Layhe
Lamar UK Ltd

-----Original Message-----
From: [log in to unmask]
[mailto:[log in to unmask]]
Sent: 29 October 2002 09:34
To: [log in to unmask]
Subject: [TN] Dimensional stability


Fellow Technetters,

Pls suggest a way out of this problem

      1. If I want to reduce the dimensional instability after Multilayer
pressing, what all the variables I should consider

      2. By reducing the rate of cool down, will I be able to achieve the
required stability


Thanx in advance.

Warm regards,

      Madhu




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