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February 1997

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Subject:
From:
Ed Cosper <[log in to unmask]>
Date:
Fri, 7 Feb 1997 15:44:06 -0600
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Dear technetters,

This is an FYI.  Last week I posted a concern regarding what I have perceived as in increase in dimensional stability problems on FR4 rigid laminates. It may interest many board fabricators to know that since that posting, the submission below has been the 7th response noting the same problems from 7 different manufacturers across the country. It does not seem to be limited to one supplier. I have notified my suppliers of the concern and strongly recommended they evaluate the glass fabric and glass tensions during treating. I would therefore recommend to anyone else seeing this problem they notify there suppliers and let them know that we are aware it is not limited to one shop. There appears to be something going on in the laminate industry  that maybe their not even aware of. If it is not addressed, it may get worse.

Ed Cosper
Director, Quality Assurance and Engineering
Graphic Electronics Inc.
Tulsa, OK   

----------
From:  sam mccorkel[SMTP:[log in to unmask]]
Sent:  Friday, February 07, 1997 9:25 AM
To:  [log in to unmask]
Subject:  FR-4 material movement

We experience up to .020" material movement on FR-4 materials.We ran some
tests and measured after each operation and found that it began to move
after etch, and moved a lot more after screen bakes and hot air leveling.We
have not seperated panels by grain direction in our tests so far. We've
tried baking before drilling and have not seen a significant difference from
those not baked. The movement we experience causes major problems when we
rout or score. We have to internally pin each piece to hold a ± .005"
tolerance between a drilled hole and the edge of the part.We used to be able
to pin externally with 4 pins to rout our boards and had no problems.
Internally pinning adds a lot of labor with panels that have many parts on
them. This problem cropped up on us about 10 months ago. Before that it
wasn't a problem. Are other fabricators out there experiencing this same
problem? Is there anything we can do to reduce the amount of movement?
Should the material move this much with "normal" processing of 2-sided
boards that are .062" thick? Do you have to internally pin each part on your
panels?

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