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July 1998

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Subject:
From:
"Gerald G. Gagnon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 15 Jul 1998 08:18:44 -0400
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text/plain
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text/plain (70 lines)
Hello KK

Although I'm not 100% sure, I believe the Laminate data convention is
the X is the warp (i.e. grain or machine direction of the treated
fabric) and the Y is the fill (i.e. weft or cross grain direction of the
treated fabric).

If you know the lay-up construction detail, you will know which is
which. Most board shops specify grain orientation for their laminates
and prepregs. Most board shops would be happy to tell you.

If it is not known, the only way I know to determine  the fabric warp
direction, assuming the lay-up does not cross-ply prepregs, is to burn
the resin & copper layers off in a vacuum furnace. This should leave the
glass fabric layers only. Using a "linen tester" you would then count
the number of threads per inch in both sample directions. You would then
compare the numbers to a fabric chart (either IPC spec or glass fabric
vendors can provide) which will tell you the thread count in warp and
fill directions.

Hope this helps.

Gerry

-----Original Message-----
From:   KK Chin [mailto:[log in to unmask]]
Sent:   Tuesday, July 14, 1998 7:29 PM
To:     [log in to unmask]
Subject:        [TN] CTE of PCB Laminates

Specs from laminate manufacturers show a substantial difference in
coefficient of thermal expansion between X-axis and Y-axis for FR4, FR2,
CEM3, CEM1, etc. Is there any way I can tell from a finished PCB which
is X
and which is Y? How can I specify in my PCB drawing such that a fab.
house
always orientates my PCB in a particular axis? I consider this as a mean
to
match with the CTE of certain components on that PCB.

Thanks!
K.K.Chin

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