U.S. patent number RE35,721 [Application Number 07/451,761] was granted by the patent office on 1998-02-03 for cooling device of semiconductor chips.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Noriyuki Ashiwake, Takahiro Daikoku, Keizo Kawamura, Fumiyuki Kobayashi, Tadakatsu Nakajima, Wataru Nakayama, Motohiro Sato.
United States Patent |
RE35,721 |
Daikoku , et al. |
February 3, 1998 |
Cooling device of semiconductor chips
Abstract
A cooling device for providing cooling of integrated circuit
semiconductor chips is so arranged as to transfer a heat via thin
fin members which are fitted with each other with a small
clearance. The bottom surface of one of thermal conductive members
which is provided integrally with the fin members is made greater
in surface area than a back planar surface of the semiconductor
chip, and the thermal conductive member and the semiconductor chip
are kept at all times in plane contact with each other, thereby
enhancing the cooling performance.
Inventors: |
Daikoku; Takahiro (Ushikumachi,
JP), Nakajima; Tadakatsu (Shimoinayoshi,
JP), Ashiwake; Noriyuki (Shimoinayoshi,
JP), Kawamura; Keizo (Shimoinayoshi, JP),
Sato; Motohiro (Minoriomachi, JP), Kobayashi;
Fumiyuki (Sagamihara, JP), Nakayama; Wataru
(Kashiwa, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
27332097 |
Appl.
No.: |
07/451,761 |
Filed: |
December 18, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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680927 |
Dec 21, 1984 |
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Reissue of: |
873304 |
Jun 9, 1986 |
04770242 |
Sep 13, 1988 |
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Foreign Application Priority Data
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Dec 14, 1983 [JP] |
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58-234219 |
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Current U.S.
Class: |
165/185;
165/80.3; 165/80.4; 361/702; 361/704; 361/715; 361/716;
361/719 |
Current CPC
Class: |
H01L
23/4338 (20130101); H01L 2224/16 (20130101) |
Current International
Class: |
H01L
23/34 (20060101); H01L 23/433 (20060101); F28F
007/00 () |
Field of
Search: |
;165/185,80.3,80.4,80.2
;361/386,383,702,704,715,716,719 ;357/81 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
IBM Technical Disclosure Bulletin, vol. 24, No. 5, Oct. 1981, p.
2540. .
Kammerer, HC Thermal Conduction Button, IBM Technical Disclosure
Bulletin, vol. 19, No. 12, pp. 4622-4623, May 1977. .
Dombroski et al, El Thermal Conduction Stud, IBM Technical
Disclosure Bulletin, vol. 19, No. 12, pp. 4683-4685, May
1977..
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Primary Examiner: Ford; John K.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP.
Parent Case Text
This application is a continuation of application Ser. No. 680,927,
filed Dec. 12, 1984, now abandoned.
Claims
What is claimed is:
1. A cooling device for providing cooling of integrated circuit
semiconductor chips by effecting transfer of heat generated in a
plurality of semiconductor chips mounted on a circuit substrate to
a housing so as to dissipate said heat, comprising a housing; a
plurality of separate thermal .Iadd.one piece .Iaddend.conductive
members each positioned with one side thereof in contact with a
back planar surface of a respective semiconductor chip and having
the other side thereof positioned in spaced relationship with the
housing so as to provide a small clearance between the other side
of each thermal conductive member and said housing, each of said
thermal conductive members including a base portion having a bottom
surface in contact with a back planar surface of the semiconductor
chip, the area of said bottom surface being greater than the
surface area of said back planar surface of the semiconductor chip,
and a plurality of first .Iadd.non-flexible .Iaddend. fins
.[.integral.]. .Iadd.being of one piece construction .Iaddend.with
said base portion and extending in a direction perpendicular to
said bottom surface; a plurality of second fins each .[.integrally
provided.]. .Iadd.being of one piece construction .Iaddend.with
said housing in fitted relation to said plurality of first fins and
each of said second fins extending continuously substantially over
an entire length of the housing in parallel with each other, each
of said plurality of second fins fitting with said first fins of
several of said thermal conductive members; and a plurality of
resilient members in the form of springs, each of said springs
being mounted between a respective one of said thermal conductive
members and said housing, each of said springs being inserted in a
gap .Iadd.circumferentially .Iaddend.surrounded by .Iadd.at least
portions of .Iaddend.the first and second fins and fixedly held
.[.in a recess formed in.]. between said housing and .[.a recess
formed in the center of.]. the base portion of said thermal
conductive member; said first and second fins forming a plurality
of parallel plate-like members, wherein said plurality of first
fins are telescopically movable with respect to said plurality of
second fins with a small clearance existing therebetween .Iadd.so
as to enable the base portion to be maintained in substantially
planar surface contact with the back planar surface of the
semiconductor chip even if the semiconductor chip is
tilted.Iaddend..
2. A cooling device for cooling semiconductor chips as claimed in
claim 1, wherein said gap is formed by cutting away a portion of
said second fins.
3. A cooling device for cooling semiconductor chips claimed in
claim 1, wherein said housing comprises a ceiling member being
integrally provided with said plurality of second fins, and a side
frame member. .[.
4. A cooling device for providing cooling of integrated
semiconductor chips by effecting transfer of heat generated in a
plurality of semiconductor chips mounted on a circuit substrate to
a housing so as to dissipate said heat, comprising a housing; a
plurality of separate thermal conductive members each contacting at
one side thereof a back planar surface of a respective one of said
plurality of semiconductor chips and having another side thereof
positioned in spaced relationship with the housing so as to provide
a small clearance between the other side of each thermal conductive
member and said housing, each of said thermal conductive members
including a base portion having a bottom surface in contact with
the back planar surface of the respective semiconductor chips the
area of said bottom surface being greater than the surface area of
said back planar surface of the semiconductor chip, and a plurality
of first fins integral with said base portion and extending in a
direction perpendicular to said bottom surface; a plurality of
second fins each integrally provided with said housing in fitted
relation to said plurality of first fins and extending continuously
substantially over an entire length of the housing and being
disposed in parallel with each other, each of said plurality of
second fins fitting with said first fins of several of said thermal
conductive members; and a plurality of resilient members in the
form of springs, each of said springs being mounted between a
respective one of said thermal conductive members and said housing,
each of said springs being respectively members and said housing,
inserted in a gap surrounded by the first and second fins and
fixedly held in a recess formed in said housing and a recess formed
in the center of the base portion of said thermal conductive
members; said first and second fins respectively including a
plurality of parallel plate-like members of a thickness in a range
of 0.2-2.6 mm, and wherein said plurality of first fins are
telescopically movable with respect to said plurality of second
fins with a small clearance existing therebetween..]..Iadd.5. A
cooling device for providing cooling of integrated circuit
semiconductor devices mounted on a circuit substrate, the cooling
device comprising:
a housing;
a plurality of separate one piece thermal conductive members each
positioned at a back planar surface of the respective semiconductor
device and having the other side thereof positioned in spaced
relationship with the housing so as to provide a small clearance
between the other side of each thermal conductive member and said
housing, each of said thermal conductive members including a base
portion having a bottom surface in contact with a back planar
surface of the semiconductor device, the area of the bottom surface
of said base portion being greater than the surface area of said
back planar surface of the semiconductor device, and a plurality of
first non-flexible fins being of one piece construction with said
base portion and extending in a direction perpendicular to said
base portion; a plurality of second fins extending continuously
substantially over an entire length of the housing in parallel with
each other, each of said plurality of second fins being in fitted
relation to said first fins of several of said thermal conductive
members with a clearance therebetween, and a plurality of resilient
members, a respective one of said resilient members being disposed
between a respective one of said thermal conductive members and
said housing so as to be circumferentially surrounded by at least
portions of said first and second fins, said first and second fins
being telescopically movable with the clearance so as to enable the
base portion to be maintained in substantially planar surface
contact with the back planar surface of the semiconductor device
even if the semiconductor device is tilted. .Iaddend..Iadd.6. A
cooling device as claimed in claim 1, wherein said first and second
fins respectively include a plurality of parallel plate-like
members of a thickness in a range 0.2-2.6 mm. .Iaddend..Iadd.7. A
cooling device as claimed in claim 1, wherein each of said springs
is fixedly held in a recess formed in said housing and a recess
formed in the center of the base portion of said
thermal conductive member. .Iaddend..Iadd.8. A cooling device as
claimed in claim 5, wherein said first and second fins form a
plurality of parallel plate-like members. .Iaddend..Iadd.9. A
cooling device as claimed in claim 5, wherein each of said
resilient members is inserted in a gap surrounded by at least the
portions of said first and second fins between said housing and a
center part of the base portion of said thermal conductive members.
.Iaddend..Iadd.10. A cooling device as claimed in claim 9, wherein
said first and second fins form a plurality of parallel plate-like
members. .Iaddend..Iadd.11. A cooling device as claimed in claim 5,
where each of said resilient members is a spring.
.Iaddend..Iadd.12. A cooling device as claimed in claim 5, wherein
the clearance extends in a direction transverse to an extension
direction of said first and second fins. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a cooling device for dissipating
the heat generated by semiconductor elements or integrated circuit
chips.
In a large-sized electronic computer system, it is demanded that
the processing operation is performed at high speed. To this end, a
circuit chip on which a large number of semiconductor elements are
integrated has been developed in recent years. Further, in order to
make short the electric wiring for interconnecting such integrated
circuit chips, a method of mounting a large number of such
integrated circuit chips in a macropackage is developed.
A cooling device which is disclosed in U.S. Pat. No. 3,993,123 has
hitherto been proposed with regard, in particular, to a cooling
device for use in the large-sized electronic computer system. In
this cooling device, the heat generated by LSI chip is transferred
into piston via the helium-gas layer which exists around a portion
of contact between a spherical tip end of the piston and a back
planar surface of the LSI chip. The heat is then transferred from
the piston into the helium-gas layer which exists in the clearance
between this piston and a cylinder, thus transferred into a housing
of a macro package. The heat is thus finally introduced, for
dissipating, into a cooler which is provided on the housing and in
which cooling water or cooling air is circulated.
The above-mentioned prior art cooling device, however, involves the
following problems.
Thermal conductivity of helium-gas is relatively high as compared
with other gases, but its thermal conductivity is very low as
compared with that of a metallic body such as, for example, the
piston, cylinder or the like. Accordingly, in order to make the
thermal resistance of the layer of helium gas small, it is
necessary to make the clearance between the piston and cylinder
small. For this reason, the piston or cylinder is demanded to be
fabricated with high precision. If it is fabricated with low
precision, then, for example, the piston fails to be moved with
smoothness, or the temperature of each LSI chip is likely to vary
widely.
A cooling structure such as that disclosed in U.S. Pat. No.
4,263,965 has been proposed in order to solve the above-mentioned
problems. In this structure, a number of parallel grooves are
formed in a housing opposed to the LSI chips, and, in each groove,
a thin rectangularly shaped thermal conductive plate and a leaf
spring for applying a pressing force onto this thermal conductive
plate are inserted. This structure is improved in that the surface
area for effecting a heat exchange between the thermal conductive
plate and the side walls of the parallel grooves is large and
besides the thin planar surface of each thermal conductive plate is
kept in plane contact with the planar surface of LSI chip at its
one end surface.
The above-mentioned structure, however, involves the following
problems. Since each thermal conductive plate is independently
separated and inserted into its corresponding parallel groove, the
heat exchange between adjacent thermal conductive plates is little
effected. Since the integrated circuits on the LSI chip are
composed of a number of electric circuits, it is, generally, very
rare that such LSI chip generates neat uniformly. The distribution
of heat generation in the LSI chip varies from place to place as
well as with the lapse of time. Accordingly, only the thermal
conductive plate located near such peripheral portion serves to a
portion of heat generation on the LSI chip dissipate the heat
generated therefrom. In other words, the other thermal conductive
plates which are located away from such portion of heat generation
can serve to dissipate only the heat which has come via the LSI
chip having a very small thickness. Namely, even if a number of
thermal conductive plates are placed on the LSI chip, their
efficiency of heat dissipation is decreased because the good heat
transfer connection between these thermal conductive plates is
little effective.
Further, since the maximum size where the thermal conductive plates
can be mounted is limited by a width of the LSI chip, limitation is
imposed upon increasing the cooling performance.
Further, a cooling device which uses a thermal conductive metallic
plate bundle composed of laminated leaf springs is disclosed in
Japanese Patent Laid-Open No. 23463/83. This cooling device has a
drawback in that the thermal contact resistance between the leaf
springs is high.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned
drawbacks inherent in the prior art and the object of the present
invention is to provide a cooling device for semiconductor elements
or integrated circuit chips which is capable of exhibiting its high
cooling performance and absorbing various displacements which
include deformation of the substrate, displacements in connecting
the semiconductor chips, deformations made in assembling the
cooling structure, thermal deformations involved in the cooling
structure, etc without exceeding the acceptable level of force on
the semiconductor chip.
The present invention is characterized in that a plurality of first
fins are integrally provided on a thermal conductive member having
a bottom surface area which is greater than a surface area, i.e.,
heat dissipation area of a semiconductor chip; these first fins are
fitted with a plurality of second fins provided on the inner
surface of a housing with a small clearance; and the bottom surface
of the thermal conductive member is pressed onto the planar surface
of the semiconductor chip by means of a resilient member which is
mounted between the thermal conductive member and the inner surface
of the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned perspective view showing an
embodiment of the cooling device for providing cooling of
integrated circuit semiconductor chips according to the present
invention;
FIG. 2 is a vertical cross-sectional view of a main part of cooling
device for the semiconductor chip shown in FIG. 1;
FIG. 3 is a horizontal cross-sectional view of a main part of the
cooling device for semiconductor chips shown in FIGS. 1;
FIG. 4 is a plane view of a substrate on which semiconductor chips
are mounted;
FIGS. 5, 6 and 7 are vertically sectional views of main parts of
other embodiments of the present invention, respectively;
FIG. 8 is a perspective view, partially in section, of a detailed
structure of a housing member shown in FIG. 7;
FIG. 9 is a perspective view, partially in section, of a detailed
structure of a leaf spring shown in FIG. 7;
FIG. 10 is a perspective view of a cooling device for semiconductor
chips according to another embodiment of the present invention;
FIG. 11 is a vertical cross-sectional view of another embodiment of
the present invention;
FIGS. 12 and 13 are cross-sectional views of the housing of the
other embodiments of the present invention, respectively; and
FIGS. 14 to 16 are graphs showing the relationship of the
overlapped length of the fins in the vertical direction with
thermal resistance and the relationship of the number of first fins
with thermal resistance, for purpose of proving the performance of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will now be described by
referring to FIGS. 1 to 4.
In the Figures, a housing 15 is made of material having a high
thermal conductivity such as, for example, copper, aluminium, or
the like, and on the inner surface of the housing, a number of
plate-like fins 16 are provided in parallel with each other.
Further, thermal conductive members 17 each having a surface area
greater than the heat transfer arm constituted by a back planar
surface of an LSI chip 1, and have a base portion. On this base
portion, a number of plate-like fins 18 are integrally provided at
the same pitch as that at which the fins 16 are provided. The fins
16 of the housing 15 and the fins 18 of the base portion of the
thermal conductive member 17 are fitted with each other with small
clearances 19 provided therebetween. The base portion of the
thermal conductive member 17 is pressed onto the planar surface of
the LSI chip 1 by a spring 20 which has a small spring constant so
as not to have any effect upon solder balls 3 for connecting the
LSI chip 1. It thus is kept in plane-contact with the back planar
surface of the LSI chip 1. The spring 20 is inserted into a gap 23
formed in the fin 16 and is fixedly held in a recess 21 formed in
the housing 15 and a recess 22 formed in a center of the base
portion of the thermal conductive member 17. Since, in this case,
the points of action of the spring 20 reside in the respective
recesses 21 and 22 of the base portion of the thermal conductive
member 17 and the housing 15 respectively, the thermal conductive
member 17 can be stably pressed onto the planar surface of the LSI
chip 1 and, at the same time, the spring can have a sufficient
length. Further, it is also possible to prevent the base portion of
the thermal conductive member 17 from slipping off from the back
planar surface of the LSI chip 1, thus to keep the thermal
conductive member 17 at all times in plane-contact with the planar
surface of the LSI chip 1 at its central part.
Within a closed space 24 which is defined between the housing 15
and a substrate 2, there is filled a gas having high thermal
conductivity, such as, for example, helium gas, hydrogen gas, or
the like. It should be noted here that a fluid capable of high heat
conduction such as, for example, a heat conductive grease may be
filled only in the small clearance 19.
Since this embodiment has been constructed as stated above, the
heat which has been generated in the LSI chip 1 is once transferred
into the base portion of the heat conductive member 17 kept in
plane-contact with the planar surface of LSI chip 1 as a whole and
then is diffused uniformly within the base portion. Thereafter, the
heat is transferred into each fin 18 of the thermal conductive
member 17. Thereafter, it is transferred into the fins 16 of the
housing 15 through the gas layers of high thermal conductivity in
the small clearances between the fins 16 and 18. The heat is
finally carried away by a cooling device (not shown) which is
mounted on the housing 15.
Since the fins 18 of the thermal conductive member 17 are formed
integrally with the base portion thereof, the heat generated in the
LSI chip 1 can be uniformly diffused within the base portion even
when the distribution of the heat in the LSI chip 1 is non-uniform.
Accordingly, it is possible to maximize the heat transfer
efficiency in each fin 18 of the thermal conductive member 17. The
thermal conductive member 17 can have any size which is chosen such
that its area of projection of the thermal conductive member 17 on
the substrate 2 falls within the range of from the minimum area of
the back planar surface of the LSI chip 1 to the maximum area 51
which can be occupied by one LSI chip on the substrate 2, as shown
in FIG. 4. Where a total cross-sectional area of either the fins 16
of the housing 15 or the fins 18 of the thermal conductive member
17 is smaller than the heat transfer area which is the back planar
surface of the LSI chip 1, their heat transfer efficiency decreases
due to the thermal resistance which is produced due to the
reduction in the cross-sectional area. For this reason, it is
desirable that the size of the thermal conductive member 17 be not
smaller than the back-surface area of the LSI chip, or more
preferably not smaller than an area 50 which is two or more times
as large as the back-surface area. On the other hand, however, as
the size of the thermal conductive member 17 is increased, this
member 17 comes into contact with that of an adjacent LSI chip 1.
Therefore, the size of the thermal conductive member 17 is limited
to the minimum area 51 which can be occupied by one LSI chip 1 on
the substrate 2.
Since the spring 20 is so disposed as to prevent its force from
directly acting on the fins 16 and 18, there is no likelihood that
those fins 16, 18 are bent or buckled. Therefore, the fins 16 and
18 may be thin. Further, since the base portion 17B of the thermal
conductive member 17 is merely in contact with the LSI chip 1, it
can be freely moved while it is kept in contact with the LSI chip
1. Besides, the thermal conductive member 17 can be freely
separated from the LSI chip 1.
FIG. 5 shows another embodiment of the invention, in which each fin
25 integrally provided on the inner surface of the housing 15 and
each fin 27 similarly provided on the thermal conductive member 26
have a trapezoidal section which is tapered toward its tip end. The
other structure of this embodiment is the same as that of the
embodiment shown in FIG. 1, and its description is omitted. By
forming the vertical section of the fins 25 and 27 into such a
trapezoidal shape, an advantage of facilitating the operation of
shaping the fin is offered.
FIG. 6 shows another embodiment of the present invention, which is
characterized in that the lowest or bottom surface of the base
portion 28B of the thermal conductive member 28 is made into a
cylindrical surface 30. A center axis of this cylindrical surface
is extended to the same direction of the fin 29 of the thermal
conductive member 28. If the thermal conductive member 28 is
constructed as such, it is not only possible for the fins 29 of the
thermal conductive member 28 and the fin 16 of the housing 15 to
move freely in grooves between the corresponding fins but, even
when the LSI chip 1 is inclined in a direction which intersects the
fin 29, it is possible for the thermal conductive member 28 to
follow the movement of the LSI chip 1, easily.
By making the bottom surface into the cylindrical surface, the
thermal conductive member 28 comes into a line contact with the LSI
chip 1, not into a point contact therewith which occurs where the
bottom surface is made into a spherical surface, thereby making the
contact thermal resistance low. Further, since the thermal
conductive member 29 can follow the LSI chip 1 to an increased
degree, it is possible to make the clearance 19 between the fins 16
and 29 smaller, thus finally to enhance the cooling performance of
the heat conductive member.
A further embodiment of the present invention will now be described
with reference to FIGS. 7, 8 and 9.
A number of fins 32 which are provided on the inner surface of the
housing 15 are formed with protrusions 35 at their tip ends. On the
other hand, the surface of the thermal conductive member 40 which
contacts the LSI chip 1 is flattened. When a number of fins 31 have
been inserted between a number of the fins 32, it may be prevented
from moving in the longitudinal direction of the grooves between
the fins 32 and the thermal conductive member 40 is held in place
between the protrusions 35. Further, the thermal conductive member
40 is pressed, at its both sides, by leaf springs 33 integrally
formed with a number of springs 34, onto the LSI chip 1.
FIG. 10 shows another embodiment of the present invention, in which
a group of the fins 42 provided on the housing 41 is separately or
independently provided so as to correspond to each one LSI chip 1.
The other structure of this embodiment is the same as that of the
embodiment shown in FIG. 1. This mentioned structure offers as
advantage of preventing the fins 16 of the thermal conductive
member 17 and the fins 42 of the housing 41 from being intermeshed
with each other even when the housing 41 undergoes a thermal
deformation, or a deformation due to a stress produced by
application of, for example, an external force.
FIG. 11 shows another embodiment of the present invention, in which
the fins 45 of the housing 43 are formed in the fins of a thermal
conductive member 44 which is provided on the housing 43 side in
the same manner as the thermal conductive member 17 on the LSI chip
1 side, and then this thermal conductive member 44 is joined to the
inner surface of the housing 43. Since, in this embodiment, both
the thermal conductive members 17 and 44 can be manufactured in the
same process of manufacture, it is possible easily to manufacture
the fins 16 and 45 with the same precision. Further, the
productivity of the housing which is achieved by fabricating fins
separately from housing is higher than that which is achieved by
fabricating fins integrally.
FIG. 12 shows another embodiment of the present invention, in which
the top surface area of each thermal conductive member 44 is made
equal to the maximum area 51 shown in FIG. 4 which can be occupied
by one LSI chip 1, and the thermal conductive member 44 is formed
as a separate member from the housing 43 and made slidable with
respect thereto. According to this embodiment, since the two
adjacent of the thermal conductive members 44 come into contact
with each other, each thermal conductive member 44 is prevented
from being horizontally moved, so that the portion of this member
44 within the housing 43 is automatically fixed. Accordingly, the
housing 43, thermal conductive member 44, and thermal conductive
member 17 can respectively be independently formed, with the result
that their respective productiveness are enhanced.
FIG. 13 shows another embodiment of the present invention, in which
the housing 46 is divided into a ceiling portion 47 and a side
frame portion 49. When the fins 48 of the housing 46 are
fabricated, if the side frame portion 49 is separated beforehand
from the ceiling portion of the housing 46, said fins 48 become
easy to fabricate particularly by cutting working. Further, the
substrate 2 on which a large number of wiring pattern are
distributed is generally low in mechanical strength and, therefore,
a flange for sealing the housing is provided as a separate member.
In this embodiment, since the ceiling portion 47 is made of the
same material as that of the substrate 2, their coefficients of
thermal expansion can be made the same. Furthermore, it is also
possible to use the materials of the same mechanical strength with
respect to the side frame portion 49 and the sealing flange,
respectively. By using different materials with respect to the
ceiling portion 47 and the side frame portion 49 as mentioned
above, it is possible to obtain various advantages including
enhancement in the sealing performance, reduction in the thermal
stress, rise in the productivity, etc., of the housing.
In each of the above-mentioned embodiments, description was made on
the assumption that the height of the fins of each thermal
conductive member, or the number of such fins, is the same with
respect to each LSI chip 1. Since the operating condition or
electric circuit of each SLI chip 1 differ, the amount of heat
generated therein also differs. Therefore, in order to increase the
reliability of the LSI chip in respect of its operation, it is
necessary to keep the LSI chip's temperature constant. In this
connection, if the height of the fins of the thermal conductive
member, or the height of the fins of the housing, or the number of
such fins is adjusted in accordance with the operating condition of
the corresponding LSI chip 1, then it will be possible to easily
control that LSI chip's temperature. Note here in this connection
that even when the height of the fins of the thermal conductive
member is made low, the length of the spring for pressing the
thermal conductive member is not required to be varied.
The material of which the thermal conductive member or housing is
made, generally, of copper of aluminum having high thermal
conductivity. On the other hand, the back planar surface of the LSI
chip is electrically conductive unless it is subjected to a special
electrical insulation. For this reason, if the thermal conductive
member made of copper or aluminium is pressed onto such back planar
surface of the LSI chip, each LSI chip will be mutually shortened.
Accordingly, when the thermal conductive member or housing is made
of a Si-C material which has an electrical insulation property and
at the same time has a high thermal conductivity, it is possible
not to cause the thermal conductive member or housing to have a
high thermal conductivity between the thermal conductivity of
copper and that of aluminium but also to make small the difference
in thermal coefficient of expansion between the thermal conductive
member or housing and the substrate of LSI chip.
It is to be noted here that the number of fins and the number of
LSI chips may be changed without departing from the spirit and
scope of the invention.
Further, it will be appreciated that a change from semiconductor
chips shown in FIGS. 1 to 12 to multi-chip module package in which
a number of semiconductor chips are contained may be made without
departing from the scope of the invention, in the preferred
embodiment.
Examination was made of the performance of the cooling device
according to the present invention, the results being presented in
FIGS. 14 to 16.
The examination was performed under the following conditions:
wherein the LSI chip has a size of 4 mm square; the maximum area
occupied by one LSI chip is 9 mm square; the material of which the
thermal conductive member and the housing are respectively made is
aluminum; and the gas which is sealed into the housing is helium.
Further, the base portion of the thermal conductive member is not
over the maximum size of 8 mm square so as to prevent the two
adjacent thermal conductive members from abutting against each
other.
FIG. 14 shows the thermal resistance between the thermal conductive
member and the housing, with respect to the overlapped length of
the fins in the vertical direction, which was measured when the
thickness of each of the first fins of the thermal conductive
member and that of the second fins of the housing are respectively
1 mm which is a fixed value; and the number and the depth of the
first fins is 4 and 8 mm, respectively, which are fixed values, and
when, under these conditions, the respective heights of the first
fins and the second fins are made high and the overlapped length of
these first and second fins in the vertical direction is increased
up to 10 mm, the clearance between the first and the second fins
being used as a parameter. In the Figure, curves A, B, C and D
correspond to the clearances of 25 .mu.m, 50 .mu.m, 100 .mu.m, and
100 .mu.m, respectively. If the clearance is fixed, there exists an
overlapped length of the fins which makes the thermal resistance
minimum. For example, if the clearance is 25 .mu.m, the optimum
overlapped length is approximately 5 mm. As the clearance increases
up to 50 .mu.m, 100 .mu.m and 200 .mu.m in the order mentioned, the
optimum overlapped length increases accordingly. The reason for
this is as follows. That is, when the overlapped length is small or
short, the thermal resistance to heat conduction in each of the
first and the second fins is decreased. However, the whole thermal
resistance between the thermal conductive member and the housing is
increased in the long run due to a decrease in the overlapped area
between the first and the second fins. On the other hand, when the
overlapped length is large or long, although the overlapped area is
increased, the whole thermal resistance is increased due to an
increase in the thermal resistance to heat conduction in each of
the first and the second fins.
On the other hand, FIG. 15 shows the thermal resistance between the
thermal conductive member and the housing, with respect to the
overlapped length, which was measured under the condition of which
the clearance between the first fin and the second fin is made 50
.mu.m constant; the base portion of the thermal conductive member
is made 8 mm square; and the thicknesses of the first and the
second fins are made as a parameter. In the Figure, curves E, F, G
and H correspond to the thicknesses and the numbers of the fin
provided on the thermal conductive member, namely, (2.6 mm, 2),
(1.0 mm, 4), (0.4 mm, 8) and (0.2 mm, 16), respectively. As seen,
the thermal resistance is decreased as the fin numbers are
increased. It should be noted here that the sample represented by
the curve B of FIG. 14 is the same as that which is represented by
the curve F of FIG. 15.
As will be understood from FIGS. 14 and 15, if the fin thickness is
decreased; the fin numbers are increased; the clearance between the
fins is decreased; and yet an optimum overlapped length is
selected, then it will be possible to make the thermal resistance
small.
FIG. 16 shows the thermal resistance between the thermal conductive
member and the housing, with respect to the number of the first
fins, which was measured when the thickness of the first fin is 1
mm; the height thereof is 4 mm; the overlapped length is 3 mm; and
the clearance between the first and second fins is 50 .mu.m, and,
under these conditions, the number of the first and the second fins
is increased sequentially by decreasing only the thickness of the
second fins. As seen, as the number of the first fins is increased,
the thermal resistance is decreased. However, when the first-fin
number increases over certain numbers, the thermal resistance
increases because of a reduction in thickness of the second fins.
When it is desired to increase the fin numbers, it is sufficient to
make the thicknesses of the first and the second fins small and at
the same time make the overlapped length short as shown in FIG.
15.
* * * * *