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February 1997

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Subject:
From:
sam mccorkel <[log in to unmask]>
Date:
Thu, 13 Feb 1997 11:10:17 -0500
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My previous posting did not yield any suggestions. I'm submitting again and
hope to have responses.

>Date: Fri, 07 Feb 1997 10:25:09 -0500
>To: TECHNET
>From: sam mccorkel <[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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