Browse Prior Art Database

Control Or Elimination of Flex Lead Bending

IP.com Disclosure Number: IPCOM000120487D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 46K

Publishing Venue

IBM

Related People

Feger, C: AUTHOR [+4]

Abstract

Disclosed is an approach to prevent leads from excessive bending during the operation and thermal cycling of an electronic system containing partially supported conductor leads joined to a substrate with matching pads. The disclosed approach makes use of encapsulation/coating of the leads by a material that exhibits a high modulus at, and at least 50~C above, the use temperature where thermal mismatch stresses are highest. Preferably the material softens below the highest process temperature so that the encapsulant does not exert a stress of its own onto the lead joint.

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Control Or Elimination of Flex Lead Bending

      Disclosed is an approach to prevent leads from excessive
bending during the operation and thermal cycling of an electronic
system containing partially supported conductor leads joined to a
substrate with matching pads.  The disclosed approach makes use of
encapsulation/coating of the leads by a material that exhibits a high
modulus at, and at least 50~C above, the use temperature where
thermal mismatch stresses are highest.  Preferably the material
softens below the highest process temperature so that the encapsulant
does not exert a stress of its own onto the lead joint.

      Lead bending control is required to avoid cracking/shorting of
conductor leads for component-to-component interconnection during
machine operation.  The coating preferred is a polymer with a high
modulus similar to that typical of epoxy resins.  In contrast to the
latter, the preferred polymer can be removed cleanly with solvents to
facilitate component repair.  The polymer can be a neat resin or a
resin containing filers (e.g., ceramic) for control of thermal
expansion mismatch.

      In the application at hand, the conductor leads are partially
held by a flexible substrate, such as du Pont's Kapton film, and are
attached to a central die via solder bonds.  The free standing leads,
which are separated from each other by a few mils, are coated by a
pre-imidized silicone containing polyimide (e.g., GE's SP129, but
polyimides with hi...