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Novel Footprint Design for TAB Assembly

IP.com Disclosure Number: IPCOM000107621D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Adams, L: AUTHOR [+4]

Abstract

Disclosed is a unique idea whereby more solder can be deposited at the corner pads of Surface Mount Technology (SMT) components. For Tape Automated Bonding (TAB) devices, this practice can compensate for bonding misregistration and tape stretch. Due to the copper wet etch process, corner pads are usually narrower than the rest of the pads, resulting in lower solder height for those corner pads. The low solder height at the corner pads, in conjunction with bonding misregistration and tape stretch, often cause poor solder joints during bonding.

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Novel Footprint Design for TAB Assembly

       Disclosed is a unique idea whereby more solder can be
deposited at the corner pads of Surface Mount Technology (SMT)
components.  For Tape Automated Bonding (TAB) devices, this practice
can compensate for bonding misregistration and tape stretch.  Due to
the copper wet etch process, corner pads are usually narrower than
the rest of the pads, resulting in lower solder height for those
corner pads.  The low solder height at the corner pads, in
conjunction with bonding misregistration and tape stretch, often
cause poor solder joints during bonding.

      The figure depicts an implementation of this disclosure for a
TAB device with a 0.0125" pitch.  The same technique can be applied
to any other SMT footprints.  The figure shows that the corner pads
are 0.010" wide while the rest of the internal pads are 0.007" wide.
The spacings between the pads are kept at 0.0055".  In general, all
eight of the corner pads are to be made wider than the internal pads
while keeping the spacings constant.

      It has been shown in an experiment that a solder height of
0.0005" can be deposited on a 0.007" wide internal pad. However, a
solder height of 0.0009" can be achieved on a 0.010" wide corner pad.
Wider corner pads also allow the corner TAB leads to be properly
registered on the pads for good bonding.