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Low Stress Heatsinkable Encapsulation Structure for Tape-Automated Bonding Packages

IP.com Disclosure Number: IPCOM000106236D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Related People

Mok, LS: AUTHOR [+3]

Abstract

This article describes a method of encapsulation that reduces the thermal tensile stresses inside the silicon chip of the tape automated bonding (TAB) package, thereby reducing susceptibility to stress failure.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Low Stress Heatsinkable Encapsulation Structure for Tape-Automated Bonding Packages

      This article describes a method of encapsulation that reduces
the thermal tensile stresses inside the silicon chip of the tape
automated bonding (TAB) package, thereby reducing susceptibility to
stress failure.

      The method commonly used to encapsulate a
tape-automated-bonding (TAB) package is to lay a layer of polymer
type of materials, such as epoxy, on one side of the silicon where
electronic circuits are accommodated.  The cross-sectional view of
this encapsulation is shown in Fig. 1.  Since the coefficient of
thermal expansion (CTE) of polymer is much larger than that of
silicon (e.g. the CTE of epoxy is about 10 times that of silicon),
stresses will be generated in the package when it is brought down to
room temperature from the curing temperature of the polymer which is
usually above 100degree C.  As a result, the silicon bends slightly
toward the polymer side at room temperature and backside tensile
stresses are created in the silicon.  If the tensile stresses are
high or the package goes through a wide temperature change,
catastrophic failure may occur or the thermal cyclic life of the
package will be shortened.

      The TAB encapsulation method disclosed herein that give
low-level residual stresses (thermally induced) inside the silicon
chip, consists of two layers, a layer of low CTE material with
appropriate thickness on top of a polymer layer.  The final structure
of the TAB package looks like a sandwich, as shown in Fig. 2.  The
polymer used must provide good adhesion to both the low CTE material
and the silicon.  The low CTE material can be silicon, Cu-Invar-Cu,
or silica glass.  Since some of these materials may be electrically
conductive, they can be coated with insulating materials to avoid
sho...