Anil,

FR-4 is composed of several layers of epoxy coated fiberglass fabric. 

The fabric has a warp and weft not unlike cloth.

When the material is coated with the "B" stage epoxy it is subjected to 
strains from the conveyor.
When the layers are added between copper there may be as many as three 
different fiberglass fabrics, all will have different strains.
Heat up and cooling rates from the pressing or lamination cause additional 
strains to be applied.

Movement during your processing are a product of the fabric, for instance 
the thicker glass (ie 7628) moves less, the thinner and higher resin 
content fabrics move more.

There is no one standard for movement.  Work with your suppler technical 
support to find the best dimensional product but this may be a tradeoff 
for other factors.

hope this helps,

Chuck


Charles W. Brummer | 3M Manufacturing Engineer
3M Electronic Solutions Division
3M Canoga Park, 8357 Canoga Ave. | Canoga Park, CA 91304
Office: 818 734 4930
[log in to unmask] | www.3M.com


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From:   "Anil Kher" <[log in to unmask]>
To:     <[log in to unmask]>
Date:   12/30/2014 12:33 AM
Subject:        [TN] Fr4 panel distortion
Sent by:        TechNet <[log in to unmask]>



We have yield issues in production of 500 mm size panels in pattern to 
hole
alignment within 50 microns.
Never thought fr4 panel will distort.
Can anyone guide me on distortion of panel - 0.2 and 0.4 mm thick h/h
Thanks a lot
Anil Kher


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