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Browse Prior Art Database

Coaxial Leads for TAB And Flex

IP.com Disclosure Number: IPCOM000121422D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 36K

Publishing Venue

IBM

Related People

Goldblatt, RD: AUTHOR [+4]

Abstract

TAB and flex are being used in high performance applications where good electrical properties are essential. With the addition of a ground plane to the traditional TAB structure, controlled impedance, low loop inductance, and low coupled noise are all achieved. This invention provides a structure that will improve that signal line density and the electrical properties of TAB and flex.

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This is the abbreviated version, containing approximately 100% of the total text.

Coaxial Leads for TAB And Flex

      TAB and flex are being used in high performance applications
where good electrical properties are essential. With the addition of
a ground plane to the traditional TAB structure, controlled
impedance, low loop inductance, and low coupled noise are all
achieved. This invention provides a structure that will improve that
signal line density and the electrical properties of TAB and flex.

      A four-step process using standard lithographic techniques is
used to fabricate a TAB frame having each lead enveloped by a
dielectric layer and a common ground. The initial structure would be
a three-layer TAB frame consisting of individual copper leads, an
insulating polyimide film, and a blanket ground plane of copper. By
allowing the existing copper leads to be a mask, the polyimide layer
is removed by wet etch or by RIE process steps.  This structure would
then be flooded with a polyimide precursor at a level equal to twice
the original polyimide film. After cure of the polyamic acid, the
structure is photoprocessed to provide a uniform coating of
dielectric around each signal trace. To complete the desired coaxial
structure, the polyimide is seeded, followed by electroplating of
copper to a suitable thickness.

      Disclosed anonymously.