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Browse Prior Art Database

Encapsulation Scheme for Tab Product Utilizing Large Dimension Chips

IP.com Disclosure Number: IPCOM000102971D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 65K

Publishing Venue

IBM

Related People

Ameen, JG: AUTHOR [+3]

Abstract

When chips are solder attached to Tape Automated Bonding (TAB) tape, the requirement for the encapsulant are much different. This invention describes a method to reliably encapsulate such a package.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 69% of the total text.

Encapsulation Scheme for Tab Product Utilizing Large Dimension Chips

      When chips are solder attached to Tape Automated Bonding (TAB)
tape, the requirement for the encapsulant are much different.  This
invention describes a method to reliably encapsulate such a package.

      For aluminum bump chips that have been thermocompression bonded
to TAB tape, one of two families of encapsulants (for the chip) may
be used - epoxies or silicones.  A silicone is preferred due to its
low Young's modulus which provides for low stresses impressed upon
the chip and inner lead bonds.

      Previous experience with an epoxy encapsulant was not favorable
for the epoxy's higher modulus resulted in high stress concentrations
on the chip's periphery that actually lifted circuitry from the
surface of the chip.  In all but the smallest of chips, silicones
were made the encapsulants of choice.

      For solder attached tape, the chip's solder balls are partially
reflowed onto the tape's inner leads.  From work done previously on
sealing the tip layer of a Metallized Ceramic substrate, a stiffer,
harder encapsulant with a CTE that matches the solder (22-30 ppm) was
demonstrated to reliably increase solder life by holding the solder
in compression.

      To produce a similar structure as above, large TAB chips should
be encapsulated with an epoxy having a CTE in the 22-30 ppm range,
e.g., Hysol (Trademark of Hysol Electronic Chemicals, Olean, NY) CNB
520-34.  The epo...