Integrated circuit package

Details Integrated circuit package Integrated circuit package

1999-08-05

2001-05-01

Picard, Leo P. (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S702000, C361S704000, C361S710000, C257S707000, C029S840000, C029S841000

Reexamination Certificate

active

06226187

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an improved integrated circuit package including a semiconductor chip, a metal heat sink and an electrically-insulating adhesive bonding the chip to the metal heat sink.
Modern integrated circuit packages oftentimes include semiconductor dies or chips bonded to a metal heat sink. Typically, the metal heat sink is carried on or by an electrically insulating carrier made from an epoxy resin or other plastic. In order to secure the chip in place, a glob of another epoxy or other resin is used to encapsulate the chip as well as any metal wires present for electrically connecting the chip to leads on the carrier.
In order to securely bond the chip to the metal heat sink, an electrically-insulating adhesive is used. Since the function of the metal heat sink is to absorb heat generated in the chip, this adhesive must exhibit a high thermal conductivity. In addition, this adhesive must also exhibit a high bond strength to the material forming the chip, most typically silicon, as well as a high bond strength to the metal forming the metal heat sink.
As modern chips become larger and larger, both in terms of size as well as power consumed, the stresses put on the chip/heat sink bond become greater and greater. As a result delamination of the chip from the heat sink is a growing problem in the industry today.
Accordingly, there is a need for a new bonding system for bonding a semiconductor chip to a metal heat sink which can accommodate the high stresses and heat involved in modern integrated circuit package designs and yet is still simple and inexpensive to carry out.
SUMMARY OF THE INVENTION
In accordance with the present invention, a new bonding system is provided for bonding a metal heat sink to a semiconductor chip, this adhesive system comprising a first adhesive layer bonded to the chip and a second adhesive layer bonded to the metal heat sink, the second adhesive exhibiting a higher bonding strength to the metal of the heat sink than the first adhesive, a lower modulus of elasticity than the first adhesive, or both.
In accordance with the present invention, it has been determined that the normal cause for rupture of the chip/heat sink bond in conventional integrated circuit packages is delamination at the metal/adhesive interface. In addition, it has been further determined that this problem can be avoided by interposing between the heat sink and the thermal adhesive normally used for bonding the chip to the heat sink another adhesive exhibiting a higher bonding strength for the metal of the heat sink, a lower modulus of elasticity, or both.
Because two layers of adhesive are used in accordance with the present invention, these adhesives can be tailored for adhesion to the chip and adhesion to the metal heat sink, respectively. This enables superior bonding systems to be produced, since the constraint characterizing adhesives used in prior art packages—namely that they bond well to both the chip and the metal sink—has been avoided. Furthermore, use of a second adhesive with a lower modulus of elasticity introduces greater flexibility in the overall chip/heat sink bond, thereby allowing larger stresses to be accommodates without rupture. Each of these features results in significantly reduced costs, since a much broader range of adhesives can be used in formulating the inventive bonding system than in prior art systems.


REFERENCES:
patent: 4759970 (1988-07-01), Seeger, Jr. et al.
patent: 4975761 (1990-12-01), Chu
patent: 5026748 (1991-06-01), Adams et al.
patent: 5369058 (1994-11-01), Burns et al.
patent: 5691567 (1997-11-01), Lo
patent: 5749988 (1998-05-01), Leibovitz et al.
patent: 6084299 (2000-07-01), Quastad et al.

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