Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2000-04-20
2001-07-31
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S121000, C438S125000, C257S717000, C257S719000
Reexamination Certificate
active
06268239
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor chip cooling structure and a manufacturing method of a semiconductor chip cooling structure, and in particular, to a semiconductor chip cooling structure and a manufacturing method of a semiconductor chip cooling structure for a semiconductor chip which is mounted on a circuit board in “flip-chip” mounting.
DESCRIPTION OF THE PRIOR ART
A semiconductor chip cooling structure, that is, a structure for letting a semiconductor chip release its heat and thereby cooling the semiconductor chip, has generally been implemented by use of a heat sink and a thermal conduction material such as a rubber sheet.
FIG. 1
is a cross sectional view showing an example of a conventional semiconductor chip cooling structure. Referring to
FIG. 1
, a semiconductor chip (in “flip-chip” mounting) is mounted on a circuit board by means of solder balls etc. so that its surface will face downward onto the circuit board. A thermal conduction material such as a rubber sheet is attached to the back side of the semiconductor chip, and a heat sink is attached to the back of the thermal conduction material. The heat sink is fixed to the circuit board by means of fixation screws (bolts and nuts) etc. so as not to drop from the semiconductor chip and the circuit board.
In a “Semiconductor Package Structure for Promoting Heat Emission Effect” which has been disclosed in Japanese Patent Application Laid-Open No.HEI10-209348 (hereafter, referred to as a “second conventional semiconductor chip cooling structure”), a semiconductor chip is mounted on a circuit board so that its surface will face upward, and a heat emission piece is attached to the surface of the semiconductor chip, not to the back of the semiconductor chip. The heat emission piece is implemented by, for example, a metal plate which is substantially square. To the surface of the heat emission piece, convexity, concavity, holes, etc. are provided for some purposes including the prevention of damages to the surface of the semiconductor chip or bonding wires when the heat emission piece is attached. By such a structure, the heat of the semiconductor chip can be released not only from its back side but also from its upper surface, and thereby the heat emission effect is improved considerably.
In a “cooling structure for an integrated circuit package” which has been disclosed in Japanese Publication of Examined Patent Applications No.SHO61-42431 (hereafter, referred to as a “third conventional semiconductor chip cooling structure”), a heat sink is attached to a heat sink pad which has been formed on the back of a circuit board, and an IC chip is mounted on the surface of the circuit board in “flip-chip” mounting. Heat conduction channels are provided to the circuit board so as to penetrate the circuit board and thereby thermally connect the active surface of the IC chip and the heat sink on the back of the circuit board. A material (plastic, solder, etc.) having a thermoplastic/setting property and large thermal conductivity is filled in the heat conduction channels by heating the circuit board so as to lower thermal impedance between the IC chip and the heat sink. In conventional flip-chip packages, the active surface of the IC chip faces the circuit board and thus heat emission from the active surface tended to be disturbed by the existence of the circuit board and it has been difficult to successfully release the heat emitted by the IC chip or semiconductor chip especially when large scale IC chips emitting large amount of heat are used. The third conventional semiconductor chip cooling structure has been proposed in order to resolve the heat problems of the flip-chip packages.
However, the conventional techniques which have been described above involve the following problems or drawbacks. First, in the first conventional semiconductor chip cooling structure of
FIG. 1
, the heat sink is fixed to the circuit board by means of fixation screws (bolts and nuts) etc. so as to sandwich the semiconductor chip of flip-chip mounting. Due to such fixation of the heat sink, the load for the fixation of the heat sink to the circuit board is also applied to the semiconductor chip through the thermal conduction material, and thus damages to the semiconductor chip are easily caused due to the fixation load. Further, the first conventional semiconductor chip cooling structure of
FIG. 1
cools the semiconductor chip from its back side. The operations of the semiconductor chip occur in its diffusion layers, electrodes, lines, etc. which have been formed on the surface (0~a few &mgr;m in depth) of the semiconductor chip, and heat is evolved from the active surface layer of the semiconductor chip. The thickness of the semiconductor chip is as large as approximately 400 &mgr;m, and thus it is clear that the cooling from the back side is inefficient than cooling from the surface.
The second conventional semiconductor chip cooling structure cools the semiconductor chip from its surface by use of the heat emission piece (square metal plate etc.). However, the structure can not be applied to the flip-chip mounting having the advantage in miniaturization of the whole package.
The third conventional semiconductor chip cooling structure executes cooling of the semiconductor chip (IC chip) of flip-chip mounting from its surface. However, the cooling of the flip-chip is mainly done through the thermally conductive material (plastic, solder, etc.) which is filled in the heat conduction channels of the circuit board by heating. Thermal conductivity of the thermally conductive material (plastic etc.) is generally smaller than that of the metal heat sink itself and the length of the path of heat conduction through the thermally conductive plastic is longer than the thickness of the circuit board, therefore, it is difficult to attain a high cooling efficiency by the third conventional semiconductor chip cooling structure. Further, the thermal conductivity of the thermally conductive material (plastic, solder, etc.) which is filled in the heat conduction channels by heating is affected by flowing/setting statuses of the thermally conductive material in the heat conduction channels. If bubbles, interfaces, unevenness etc. are formed in the heat conduction channels in the setting of the thermally conductive material, the thermal conductivity through the heat conduction channels is easily deteriorated.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide a semiconductor chip cooling structure and a manufacturing method of a semiconductor chip cooling structure, by which cooling of a semiconductor chip mounted on a circuit board in flip-chip mounting can be executed from its surface with high cooling efficiency and without causing damages due to the fixation loads etc. to the semiconductor chip.
In accordance with a first aspect of the present invention, there is provided a semiconductor chip cooling structure comprising a semiconductor chip, a small-size circuit board, a large-size circuit board and a heat sink. The semiconductor chip is mounted on the small-size circuit board having a hole, in flip-chip mounting. The small-size circuit board is connected to the large-size circuit board so that the semiconductor chip will be placed between the small-size circuit board and the large-size circuit board and there will be a clearance between the semiconductor chip and the large-size circuit board. The heat sink is provided with a convex part for being inserted into the hole of the small-size circuit board to be thermally connected to the surface of the semiconductor chip through a thermal conduction material which is sandwiched between the convex part and the semiconductor chip. The heat sink is fixed to the large-size circuit board by means of fixation means so that the semiconductor chip and the small-size circuit board will be placed between the heat sink and the large-size circuit board.
In accordance with a second aspect of the present invention, in the first aspect, a
Foley & Lardner
NEC Corporation
Picardat Kevin M.
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