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An Interposer Approach to Enhanced Wire Bondability

IP.com Disclosure Number: IPCOM000121418D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 57K

Publishing Venue

IBM

Related People

Furman, BK: AUTHOR [+6]

Abstract

Wire bonding is a common method of interconnecting chips to carriers and effecting engineering changes and repairs in substrates used in electronic packages. To achieve reliable wire bonds it is necessary to provide a thick layer (several microns) of a noble metal like Au on the bonding pads. Further, if a given site is to be bonded to a number of times, requiring removal of an existing bond, then the pad can be subjected to the stresses of the wire removal and dresssing operations which can lead to unbondable pad surfaces. In this article we describe an alternate method to achieve reliable wire bonding to substrates including the option to allow multiple repairs of a given pad site.

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An Interposer Approach to Enhanced Wire Bondability

      Wire bonding is a common method of interconnecting chips to
carriers and effecting engineering changes and repairs in substrates
used in electronic packages.  To achieve reliable wire bonds it is
necessary to provide a thick layer (several microns) of a noble metal
like Au on the bonding pads. Further, if a given site is to be bonded
to a number of times, requiring removal of an existing bond, then the
pad can be subjected to the stresses of the wire removal and
dresssing operations which can lead to unbondable pad surfaces.  In
this article we describe an alternate method to achieve reliable wire
bonding to substrates including the option to allow multiple repairs
of a given pad site.

      The method involves adding a bonding pedestal to those sites
that require to be bonded.  Depending on the number of such sites,
two approaches can be used.  If all or a large number of pads are
involved, one would use a gang addition approach wherein pedestals
are placed on all the pads and attached by a soldering or brazing
process en masse.  The pedestal material in this case can be suitably
selected to provide thermal expansion match to the substrate and
stress relief during bonding, in addition to providing a bondable
surface.  In cases where the bonding is needed only at a few pad
sites, one can add a pedestal of pure Au by Au ball bonding to the
pad and flattening to achieve a pedestal of several tens of micr...