Browse Prior Art Database

Anti-Curl Backer Sheet for Act IV Stiffener

IP.com Disclosure Number: IPCOM000122245D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Gall, TP: AUTHOR [+2]

Abstract

Disclosed is a method of controlling the warpage of an asymmetric composite circuit panel during lamination. A polymer composite panel that is laminated onto a low expansion metal plate (stiffener and heat spreader) will tend to warp in the direction of the polymer since the polymer has a higher coefficient of thermal expansion (CTE) than the stiffener. Because the composite structure is not symmetric, it warps upon cooling from the lamination temperature. The stiffener acts as a mechanical support, a ground plane, and as a cooling plate, so putting polymer on both sides to make a symmetric structure would reduce the ability to cool the panel and make grounding more difficult.

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Anti-Curl Backer Sheet for Act IV Stiffener

      Disclosed is a method of controlling the warpage of an
asymmetric composite circuit panel during lamination.  A polymer
composite panel that is laminated onto a low expansion metal plate
(stiffener and heat spreader) will tend to warp in the direction of
the polymer since the polymer has a higher coefficient of thermal
expansion (CTE) than the stiffener.  Because the composite structure
is not symmetric, it warps upon cooling from the lamination
temperature.  The stiffener acts as a mechanical support, a ground
plane, and as a cooling plate, so putting polymer on both sides to
make a symmetric structure would reduce the ability to cool the panel
and make grounding more difficult.

      Laminating a temporary layer of a high expansion metal, such as
aluminum, to the back of the panel will balance the shrinkage of the
polymer and thus minimize (or eliminate) the warpage (see the
figure).  After the panel has cooled to room temperature, the
anti-curl layer can be removed without causing the panel to warp
because the tensile stress in the polymer relaxes over a short time.
1.   The panel is laid up with an aluminum (or other high CTE metal)
sheet on the bottom of the stiffener instead of the normal copper
release sheet.
2.   The thickness of the aluminum sheet has been calculated to match
the force put on the stiffener by the polymer panel due to CTE
mismatch.
3.   The aluminum sheet is pressed into the stiffe...