Title: Heat sink material and method of manufacturing the heat sink material
Abstract: Graphite is placed in a case, and the case is set in a furnace. The interior of the furnace is subjected to sintering to produce a porous sintered member of graphite. After that, the case with the porous sintered member therein is taken out of the furnace, and is set in a recess of a press machine. Subsequently, molten metal of metal is poured into the case, and then a punch is inserted into the recess to forcibly press the molten metal in the case downwardly. Open pores of the porous sintered member are infiltrated with the molten metal of the metal by the pressing treatment with the punch.
Patent Number: 6,933,531 Issued on 08/23/2005 to Ishikawa, et al.
| Inventors:
|
Ishikawa; Shuhei (Nagoya, JP);
Mitsui; Tsutomu (Nagoya, JP);
Suzuki; Ken (Nagoya, JP);
Nakayama; Nobuaki (Nagoya, JP);
Takeuchi; Hiroyuki (Nagoya, JP);
Yasui; Seiji (Nagoya, JP)
|
| Assignee:
|
NGK Insulators, Ltd. (Nagoya, JP)
|
| Appl. No.:
|
913353 |
| Filed:
|
December 22, 2000 |
| PCT Filed:
|
December 22, 2000
|
| PCT NO:
|
PCT/JP00/09133
|
| 371 Date:
|
August 13, 2001
|
| 102(e) Date:
|
August 13, 2001
|
| PCT PUB.NO.:
|
WO01/48816 |
| PCT PUB. Date:
|
July 5, 2001 |
Foreign Application Priority Data
| Dec 24, 1999[JP] | 11-368108 |
| Mar 22, 2000[JP] | 2000-080833 |
| Current U.S. Class: |
257/76; 428/307.7; 428/312.2; 428/408; 428/469; 428/472 |
| Intern'l Class: |
H01L 023/12 |
| Field of Search: |
257/76,77
428/408,469,472,307.7,312.2,325,698,457
|
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Other References
Wei et al "Improvement of wear resistance of pulsed laser deposited diamond-like
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U.S. patent application Ser. No. 10/279,959, Ishikawa et al., filed Oct. 24, 2002.
U.S. patent application Ser. No. 10/245,999, Ishikawa et al., filed Sep. 18, 2002.
|
Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Burr & Brown
Claims
1. A heat sink material comprising carbon or graphite and metal which is at least
one selected from Cu, Al, and Ag, said metal having one or more of Te, Bi, Pb,
Sn, Se, Li, Sb, Tl, Ca and Cd added thereto for improving wettability at an interface
between said carbon or graphite and said metal,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/°
C.
2. The heat sink material according to claim 1, wherein an additive is added
to said carbon or said graphite for decreasing a closed porosity when said carbon
or said graphite is sintered.
3. The heat sink material according to claim 2, wherein said additive for decreasing
said closed porosity is at least one selected from SiC and Si.
4. The heat sink material according to claim 1, wherein a closed porosity is
not more than 12% by volume.
5. The heat sink material according to claim 1, wherein said carbon or said graphite
has a coefficient of thermal conductivity of not less than 100 W/mK.
6. The heat sink material according to claim 1, wherein as for volume ratios
between said carbon or said graphite and said metal, said volume ratio of said
carbon or said graphite is within a range from 20 to 80% by volume, and said volume
ratio of said metal is within a range from 80 to 20% by volume.
7. A heat sink material comprising carbon or graphite and metal which is at least
one selected from Cu, Al, and Ag, said metal having one or more of Nb, Cr, Zr,
Be, Ti, Ta, V, B and Mn added to improve reactivity with said carbon or graphite,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/°
C.
8. The heat sink material according to claim 7, wherein an additive is added
to said carbon or said graphite for decreasing a closed porosity when said carbon
or said graphite is sintered.
9. The heat sink material according to claim 8, wherein said additive for decreasing
said closed porosity is at least one selected from SiC and Si.
10. The heat sink material according to claim 7, wherein a closed porosity is
not more than 12% by volume.
11. The heat sink material according to claim 7, wherein said carbon or said
graphite has a coefficient of thermal conductivity of not less than 100 W/mk.
12. The heat sink material according to claim 7, wherein as for volume ratios
between said carbon or said graphite and said metal, said volume ratio of said
carbon or said graphite is within a range from 20 to 80% by volume, and said volume
ratio of said metal is within a range from 80 to 20% by volume.
13. A heat sink material comprising carbon or graphite and metal which is at
least one selected from Cu and Ag, said metal includes an element added thereto
to improve molten metal flow performance, said element added to said metal has
a temperature range of solid phase/liquid phase of not less than 30° C.,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6to 10×10
-;6/°
C.
14. The heat sink material according to claim 13, wherein said element added
to said metal comprises Si.
15. The heat sink material according to claim 13, wherein an additive is added
to said carbon or said graphite for decreasing a closed porosity when said carbon
or said graphite is sintered.
16. The heat sink material according to claim 15, wherein said additive for decreasing
said closed porosity is at least one selected from SiC and Si.
17. The heat sink material according to claim 13, wherein a closed porosity is
not more than 12% by volume.
18. The heat sink material according to claim 13, wherein said carbon or said
graphite has a coefficient of thermal conductivity of not less than 100 W/mK.
19. The heat sink material according to claim 13, wherein as for volume ratios
between said carbon or said graphite and said metal, said volume ratio of said
carbon or said graphite is within a range from 20 to 80% by volume, and said volume
ratio of said metal is within a range from 80 to 20% by volume.
20. A heat sink material comprising carbon or graphite and metal which is at
least one selected from Cu, Al, and Ag, said metal having an element added thereto
for lowering a melting point of said metal,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/°
C.
21. The heat sink material according to claim 20, wherein said element to be
added is Zn.
22. The heat sink material according to claim 20, wherein an additive is added
to said carbon or said graphite for decreasing a closed porosity when said carbon
or said graphite is sintered.
23. The heat sink material according to claim 22, wherein said additive for decreasing
said closed porosity is at least one selected from SiC and Si.
24. The heat sink material according to claim 20, wherein a closed porosity is
not more than 12% by volume.
25. The heat sink material according to claim 20, wherein said carbon or said
graphite has a coefficient of thermal conductivity of not less than 100 W/mK.
26. The heat sink material according to claim 20, wherein as for volume ratios
between said carbon or said graphite and said metal, said volume ratio of said
carbon or said graphite is within a range from 20 to 80% by volume, and said volume
ratio of said metal is within a range from 80 to 20% by volume.
27. A heat sink material comprising carbon or graphite and metal which is at
least one selected from Cu, Al, and Ag, said metal having an element added thereto
for improving a coefficient of thermal conductivity of said heat sink material,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein said added element being alloyed with said met to obtain an alloy which
is deposited on the surface of said metal after heat treatment and reaction with
carbon, and wherein said alloy has an initial coefficient of thermal conductivity
of not less than 10 W/mk.
wherein an average coefficient of thermal conductivity of said heat sink material
in directions of orthogonal three axes, or a coefficient of thermal conductivity
in a direction of any axis is not less than 180 W/mK, and a ratio of coefficient
of thermal conductivity is not more than 1:5 between a direction in which said
coefficient of thermal conductivity is minimum and a direction in which said coefficient
of thermal conductivity is maximum, and wherein a coefficient of thermal expansion
is 1×10
-;6 to 10×10
-;6/° C.
28. The heat sink material according to claim 27, wherein an additive is added
to said carbon or said graphite for decreasing a closed porosity when said carbon
or said graphite is sintered.
29. The heat sink material according to claim 28, wherein said additive for decreasing
said closed porosity is at least one selected from SiC and Si.
30. The heat sink material according to claim 27, wherein a closed porosity is
not more than 12% by volume.
31. The heat sink material according to claim 27, wherein said carbon or said
graphite has a coefficient of thermal conductivity of not less than 100 W/mK.
32. The heat sink material according to claim 27, wherein as for volume ratios
between said carbon or said graphite and said metal, said volume ratio of said
carbon or said graphite is within a range from 20 to 80% by volume, and said volume
ratio of said metal is within a range from 80 to 20% by volume.
33. A heat sink material comprising carbon or graphite and metal which is at
least one selected from Cu, Al, and Ag,
wherein a carbide layer is formed on a surface of said carbon or said graphite,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/°
C.
34. The heat sink material according to claim 33, wherein an element for forming
a carbide layer is added to said metal, and wherein said carbide layer is formed
on the basis of a reaction at least between said carbon or said graphite and the
element to be added.
35. The heat sink material according to claim 34, wherein said element to be
added is one or more of those selected from Ti, W, Mo, Nb, Cr, Zr, Be, Ta, V, B,
and Mn.
36. A heat sink material comprising carbon or graphite and metal which is at
least one selected from Cu, Al, and Ag,
wherein said heat sink material is constructed by infiltrating a porous sintered
member with said metal, said porous sintered member being obtained by sintering
said carbon or said graphite to form a network,
wherein an element which has a temperature range of solid phase/liquid phase
of not less than 30° C. is added to said metal in order to improve molten
metal flow performance,
wherein an average coefficient of thermal conductivity of those in directions
of orthogonal three axes, or a coefficient of thermal conductivity in a direction
of any axis is not less than 180 W/mK, and a ratio of coefficient of thermal conductivity
is not more than 1:5 between a direction in which said coefficient of thermal conductivity
is minimum and a direction in which said coefficient of thermal conductivity is
maximum, and
wherein a coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/°
C.
37. The heat sink material according to claim 36, wherein said element to be
added is one or more of those selected from Sn, P and Mg.
38. The heat sink material according to claim 37, wherein said element to be
added is Si.
Description
TECHNICAL FIELD
The present invention relates to a heat sink material for construction a heat
sink which efficiently releases heat generated, for example, from an IC chip, and
a method of producing the same.
BACKGROUND ART
In general, heat is an enemy for the IC chip and it is necessary that the internal
temperature thereof does not exceed the maximum allowable junction temperature.
The electric power consumption per operation area is large in the semiconductor
device such as a power transistor or a semiconductor rectifier element. Therefore,
the generated heat amount cannot be sufficiently released with only the heat amount
released from a case (package) and a lead of the semiconductor device. It is feared
that the internal temperature of the device may be raised to cause thermal destruction.
This phenomenon also occurs in the same manner in the IC chip which carries
a CPU. The amount of heat generation is increased during the operation in proportion
to the improvement in clock frequency. It is an important matter to make the thermal
design in consideration of the heat release.
In the thermal design for preventing the thermal destruction or the like, element
design or package design is made on condition that a heat sink having a large heat
release area is secured to a case (package) of the IC chip.
In general, a metal material such as copper and aluminum, which has a good thermal
conductivity, is used as a material for the heat sink.
Recently, the IC chip such as CPU and memory is in a trend that the IC
chip itself has a large size in accordance 10, with the high degree of integration
of the element and the enlargement of the element-forming area, while it is intended
to drive the IC chip at low electric power for the purpose of low electric power
consumption. When the IC chip has such a large size, it is feared that the stress
caused by the difference in thermal expansion between the semiconductor substrate
(silicon substrate or GaAs substrate) and the heat sink is increased, and that
the peeling-off phenomenon and the mechanical destruction occur in the IC chip.
In order to avoid such an inconvenience, for example, it may be pointed out that
the low electric power driving of the IC chip should be realized, and the heat
sink material should be improved. The low electric power driving of the IC chip
is realized in the level of not more than 3.3 V at present and the TTL level (5
V) which has been hitherto used as the power source voltage becomes obsolete.
As for the constitutive material for the heat sink, it is insufficient to consider
only the thermal conductivity. It is necessary to select a material which has a
coefficient of thermal expansion approximately identical with those of silicon
and GaAs, which are used as the semiconductor substrate, while having a high thermal
conductivity at the same time.
A variety of reports have been made in relation to the improvement of the heat
sink material, including, for example, a case in which aluminum nitride (AlN) is
used and a case Cu (copper)-W (tungsten) is used. AlN is excellent in balance between
the thermal conductivity and the thermal expansion. Especially, the coefficient
of thermal expansion of AlN is approximately coincident with the coefficient of
thermal expansion of Si. Therefore, AlN is preferred as a heat sink material for
a semiconductor device in which a silicon substrate is used as the semiconductor substrate.
Cu-W is a composite material having both of the low thermal expansion of W and
the high thermal conductivity of Cu. Further, Cu-W is mechanically machined with
ease. Therefore, Cu-W is preferred as a constitutive material for a heat sink having
a complicated shape.
Other instances have been suggested, wherein metal Cu is contained in a ratio
of 20 to 40% by volume in a ceramic base material containing a major component
of SiC (conventional technique 1, see Japanese Laid-Open Patent Publication No.
8-279569), and wherein a powder-sintered porous member of an inorganic substance
is infiltrated with Cu by 5 to 30% by weight (conventional technique 2, see Japanese
Laid-Open Patent Publication No. 59-228742).
The heat sink material concerning the conventional technique 1 is produced in
the powder formation in which a green compact of SiC and metal Cu is formed to
produce a heat sink. Therefore, the coefficient of thermal expansion and the coefficient
of thermal conductivity represent only theoretical values. It is impossible to
obtain the balance between the coefficient of thermal expansion and the coefficient
of thermal conductivity required for actual electronic parts etc.
The conventional technique 2 uses a low ratio of Cu with which the powder-sintered
porous member composed of the inorganic substance is infiltrated. It is feared
that a limit may arise to enhance the thermal conductivity thereby.
On the other hand, a composite material, which is obtained by combining carbon
and metal, has been developed and practically used. However, such a composite material
is used, for example, as an electrode for the discharge machining when the metal
is Cu. When the metal is Pb, such a composite material is used, for example, as
a bearing material. No case is known for the application as a heat sink material.
That is, in the present circumstances, the coefficient of thermal conductivity
is at most 140 W/mK for the composite material obtained by combining carbon and
metal, which cannot satisfy the value of not less than 160 W/mK required for the
heat sink material for the IC chip.
DISCLOSURE OF THE INVENTION
The present invention has been made taking the foregoing problems into consideration,
and an object thereof is to provide a heat sink material which makes it possible
to obtain characteristics adapted to the balance between the coefficient of thermal
expansion and the coefficient of thermal conductivity required for actual electronic
parts (including semiconductor devices) etc.
Another object of the present invention is to provide a method of producing
with ease a heat sink material having characteristics adapted to the balance between
the coefficient of thermal expansion and the coefficient of thermal conductivity
required for actual electronic parts (including semiconductor devices) etc., and
the method for improving the productivity of a high quality heat sink.
According to the present invention, there is provided a heat sink material
comprising carbon or allotrope thereof and metal. An average coefficient of thermal
conductivity of those in directions of orthogonal three axes, or a coefficient
of thermal conductivity in a direction of any axis is not less than 160 W/mK. Accordingly,
it is possible to obtain the heat sink material in which the coefficient of thermal
expansion is approximately coincident with those of the ceramic substrate (such
as silicon or GaAs), and the semiconductor substrate (such as silicon or GaAs),
etc., and the thermal conductivity is satisfactory.
It is also possible to obtain the heat sink material wherein the average coefficient
of thermal conductivity of those in the directions of the orthogonal three axes,
or the coefficient of thermal conductivity in the direction of any axis is not
less than 180 W/mK, and wherein a coefficient of thermal expansion is 1×10
-;6
to 10×10
-;6/° C.
It is preferable that the allotrope is graphite or diamond. Further, it is preferable
that the carbon or the allotrope thereof has a coefficient of thermal conductivity
of not less than 100 W/mK.
The heat sink material can be constructed by infiltrating a porous sintered member
with the metal, the porous sintered member being obtained by sintering the carbon
or the allotrope thereof to form a network.
In this case, it is preferable that a porosity of the porous sintered member
is
10 to 50% by volume, and an average pore diameter is 0.1 to 200 μm. It is
preferable that as for volume ratios between the carbon or the allotrope thereof
and the metal, the volume ratio of the carbon or the allotrope thereof is within
a range from 50 to 80% by volume, and the volume ratio of the metal is within a
range from 50 to 20% by volume.
It is preferable that an additive is added to the carbon or the allotrope thereof
for decreasing a closed porosity when the carbon or the allotrope thereof is sintered.
The additive may be exemplified by SiC and/or Si.
It is also preferable that the heat sink material is constructed by infiltrating
a preformed product with the metal, the preformed product being prepared by mixing
water or a binder with powder of the carbon or the allotrope thereof, and forming
an obtained mixture under a predetermined pressure. In this case, it is preferable
that an average powder particle size of the powder is 1 to 2000 μm, and a
length ratio is not more than 1:5 between a direction in which the powder has a
minimum length and a direction in which the powder has a maximum length. In this
case, although there is no strong network, it is possible to make an arbitrary shape.
It is preferable that as for volume ratios between the carbon or the allotrope
thereof and the metal, the volume ratio of the carbon or the allotrope thereof
is within a range from 20 to 80% by volume, and the volume ratio of the metal is
within a range from 80 to 20% by volume.
It is also preferable that the heat sink material is constructed by mixing powder
of the carbon or the allotrope thereof with the metal dissolved into a liquid state
or a solid-liquid co-existing state to obtain a mixture, and casting the obtained mixture.
It is preferable that a closed porosity of the produced heat sink material is
not more than 12% by volume.
It is preferable that an element for improving wettability at an interface is
added to the metal. It is possible to adopt one or more of those selected from
Te, Bi, Pb, Sn, Se, Li, Sb, Tl, Ca, Cd, and Ni as the element to be added. Especially,
Ni has an effect that carbon is easily dissolved and easily infiltrated.
It is preferable that the metal is added with an element for improving reactivity
with the carbon or the allotrope thereof. It is possible to adopt one or more of
those selected from Nb, Cr, Zr, Be, Ti, Ta, V, B, and Mn, as the element to be added.
It is preferable that an element, which has a temperature range of solid phase/liquid
phase of not less than 30° C., desirably not less than 50° C., is added
to the metal in order to improve molten metal flow performance. Accordingly, it
is possible to reduce the dispersion during the infiltration, the residual pores
are decreased, and it is possible to improve the strength. The equivalent effect
can be also obtained by increasing the infiltration pressure. It is possible to
adopt one or more of those selected from Sn, P, Si, and Mg as the element to be
added. Further, it is preferable that an element for lowering a melting point is
added to the metal. The element to be added is Zn, for example.
It is preferable that an element for improving the coefficient of thermal conductivity
is added to the metal. In this case, it is preferable that an element for improving
the coefficient of thermal conductivity is added to the metal, and an alloy of
the element and the metal is obtained by segregation or the like after a heat treatment,
processing, and reaction with carbon, the alloy has a coefficient of thermal conductivity
of not less than 10 W/mK. It is preferable that the coefficient of thermal conductivity
is desirably not less than 20 W/mK, more desirably not less than 40 W/mK, and most
desirably not less than 60 W/mK.
It is the known effect brought about by the heat treatment that the coefficient
of thermal conductivity is improved by combining aging of the added element, annealing,
and processing. The feature described above is based on the use of this effect.
It is also known that the reaction with carbon decreases the added element of copper,
aluminum, and silver, resulting in improvement in coefficient of thermal conductivity.
Further, it is also known that the added element is deposited on the surface etc.
owing to the segregation or the like when the infiltrated metal is solidified,
and the coefficient of thermal conductivity as a whole is improved. Therefore,
it is possible to utilize such an effect as well.
The heat sink material can be also constructed such that powder of the carbon
or the allotrope thereof is mixed with powder of the metal to obtain a mixture,
and the obtained mixture is formed under a predetermined pressure. In this case,
it is preferable that an average powder particle size of the powder of the carbon
or the allotrope thereof and the powder of the metal is 1 to 500 μm.
The heat sink material can be also constructed such that a pulverized cut material
of the carbon or the allotrope thereof is mixed with powder of the metal to obtain
a mixture, and the obtained mixture is formed at a predetermined temperature under
a predetermined pressure.
When the heat sink material is constructed by the forming process as described
above, it is preferable that as for volume ratios between the carbon or the allotrope
thereof and the metal, the volume ratio of the carbon or the allotrope thereof
is within a range from 20 to 60% by volume, and the volume ratio of the metal is
within a range from 80 to 40% by volume. Accordingly, it is possible to obtain
the heat sink material in which the coefficient of thermal conductivity is not
less than 200 W/mK, and a coefficient of thermal expansion is 3×10
-;6
to 14×10
-;6/° C.
It In this case, it is preferable that an additive making it possible to perform
re-sintering after forming process is added to the carbon or the allotrope thereof.
The additive may be exemplified by SiC and/or Si.
It is preferable that a low melting point metal for improving wettability at
an
interface is added to the metal. It is possible to adopt one or more of those selected
from Te, Bi, Pb, Sn, Se, Li, Sb, Se, Tl, Ca, Cd, and Ni as the low melting point metal.
It is preferable that an element for improving reactivity with the carbon or
the
allotrope thereof is added to the metal. It is possible to adopt one or more of
those selected from Nb, Cr, Zr, Be, Ti, Ta, V, B, and Mn as the element to be added.
It is preferable that an element, which has a temperature range of solid phase/liquid
phase of not less than 30° C., desirably not less than 50° C., is added
to the metal in order to improve molten metal flow performance. Accordingly, it
is possible to reduce the dispersion during the infiltration, the residual pores
are decreased, and it is possible to improve the strength. The same or equivalent
effect can be also obtained by increasing the infiltration pressure. It is possible
to adopt one or more of those selected from Sn, P, Si, and Mg as the element to
be added. Further, it is preferable that an element for decreasing a melting point
is added to the metal. The element to be in added is Zn, for example.
It is also preferable that a carbide layer is formed on a surface of the carbon
or the allotrope thereof by means of a reaction at least between the carbon or
the allotrope thereof and the element to be added. In this case, it is possible
to adopt one or more of those selected from Ti, W, Mo, Nb, Cr, Zr, Be, Ta, V, B,
and Mn as the element to be added.
It is possible to adopt at least one selected from Cu, Al, and Ag, as the metal
to be combined with the carbon or the allotrope thereof. Each of the metals Cu,
Al, and Ag has high conductivity.
In the present invention, a ratio of coefficient of thermal conductivity is not
more than 1:5 between a direction in which the coefficient of thermal conductivity
is minimum and a direction in which the coefficient of thermal conductivity is
maximum. Accordingly, the coefficient of thermal conductivity has a characteristic
approximately equal to the isotropic characteristic. Therefore, the heat is diffused
in a well-suited manner. Thus, the heat sink material is preferably used for a
heat sink. Further, it is unnecessary to consider the direction of installation
case by case, thereby advantageous on the practical mounting.
According to another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: sintering
carbon or in allotrope thereof to form a network for obtaining a porous sintered
member; infiltrating the porous sintered member with metal; and cooling the porous
sintered member infiltrated with at least the metal.
Accordingly, it is possible to easily produce the heat sink material
having a coefficient of thermal expansion approximately coincident with those of
a ceramic substrate (such as silicon or GaAs), a semiconductor substrate (such
as silicon or GaAs), etc., and having good thermal conductivity. It is possible
to improve the productivity of a heat sink having a high quality.
It is also preferable that in the sintering step, the carbon or the allotrope
thereof is placed in a vessel, and an interior of the vessel is heated to produce
the porous sintered member of the carbon or the allotrope thereof.
It is also preferable that in the infiltrating step, the porous sintered member
is immersed in molten metal of the metal introduced into a vessel, and the porous
sintered member is infiltrated with the molten metal by introducing infiltrating
gas into the vessel to pressurize an interior of the vessel. In this case, it is
preferable that the force of the pressurization is four to five times as strong
as a compressive strength of the porous sintered member of the carbon or the allotrope
thereof or less than four to five times the compressive strength of the porous
sintered member. Alternatively, the force of the pressurization is preferably 1.01
to 202 MPa (10 to 2000 atmospheres). In the cooling step in this case, the infiltrating
gas in a vessel may be vented, and cooling gas may be quickly introduced to cool
an interior of the vessel.
The following method is exemplified as another production method. The sintering
step includes a step of setting the carbon or the allotrope thereof in a case,
and a step of preheating an interior of the case to prepare the porous sintered
member of the carbon or the allotrope thereof. The infiltrating step includes a
step of setting the case in a mold of a press machine, a step of pouring molten
metal of the metal into the case, and a step of forcibly pressing the molten metal
downwardly with a punch of the press machine to infiltrate the porous sintered
member in the case with the molten metal.
In this case, it is preferable that a pressure of the forcible pressing by the
punch is four to five times as strong as a compressive strength of the porous sintered
member of the carbon or the allotrope thereof or less than four to five times the
compressive strength of the porous sintered member. Alternatively, the preferable
pressure is 1.01 to 202 MPa (10 to 2000 atmospheres). It is preferable that a mold
formed with a gas vent hole for venting any remaining gas in the porous sintered
member or formed with a gap for venting gas.
It is also preferable that in the cooling step, the heat sink material, in which
the porous sintered member is infiltrated with the metal, is cooled by cooling
gas blown thereagainst or by using a cooling zone or a cooling mold where cooling
water is supplied.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing water
or a binder with powder of carbon or allotrope thereof to obtain a mixture; forming
the obtained mixture into a preformed product under a predetermined pressure; and
infiltrating the preformed product with metal.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing powder
of carbon or allotrope thereof with metal dissolved into a liquid state or a solid-liquid
co-existing state to obtain a mixture; and casting the obtained mixture.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing powder
of carbon or allotrope thereof with powder of metal to obtain a mixture; and pressurizing
the obtained mixture placed in a mold of a hot press machine at a predetermined
temperature under a predetermined pressure to form into the heat sink material.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing powder
of carbon or allotrope thereof with powder of metal to obtain a mixture; preforming
the obtained mixture to prepare a preformed product; and pressurizing the preformed
product placed in a mold of a hot press machine at a predetermined temperature
under a predetermined pressure to form into the heat sink material.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing a pulverized
cut material of carbon or allotrope thereof with powder of metal, and preforming
to prepare a mixture; and pressurizing the mixture placed in a mold of a hot press
machine at a predetermined temperature under a predetermined pressure to form into
the heat sink material.
According to still another aspect of the present invention, there is provided
a method of producing a heat sink material, comprising the steps of: mixing a pulverized
cut material of carbon or allotrope thereof with powder of metal to obtain a mixture;
preforming the obtained mixture to prepare a preformed product; and pressurizing
the preformed product placed in a mold of a hot press machine at a predetermined
temperature under a predetermined pressure to form into the heat sink material.
In the production methods described above, it is preferable that the predetermined
temperature is relatively -;10° C. to -;50° C. with respect to a melting
point of the metal, and it is preferable that the predetermined pressure is 10.13
to 101.32 MPa (100 to 1000 atmospheres).
In the production methods described above, it is also preferable that the heat
sink material is heated to a temperature of not less than a melting point of the
metal after the pressurizing step.
Further, it is also preferable that the metal is at least one selected from
Cu, Al, and Ag.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view illustrating construction of a heat sink material
according to a first embodiment;
FIG. 2A shows, with partial cutaway, a front of a high pressure vessel to be
used in a first production method;
FIG. 2B shows, with partial cutaway, a side of the high pressure vessel;
FIG. 3 shows a block diagram illustrating steps of the first production method;
FIG. 4 shows a block diagram illustrating steps of a first modified method of
the first production method;
FIG. 5 shows a block diagram illustrating steps of a second modified method
of the first production method;
FIG. 6 shows an arrangement of a furnace to be used in a second production method;
FIG. 7 shows a press machine to be used in the second production method;
FIG. 8 shows a block diagram illustrating steps of the second production method;
FIG. 9 shows a perspective view illustrating construction of a heat sink material
according to a second embodiment;
FIG. 10 shows an arrangement of a preforming machine to be used in a third production method;
FIG. 11 shows an arrangement of a hot press machine to be used in the third
production method;
FIG. 12 shows a block diagram illustrating steps of the third production method;
FIG. 13 shows a block diagram illustrating steps of a fourth production method;
FIG. 14 shows an arrangement of a hot press machine to be used in the fourth
production method;
FIG. 15 shows a perspective view illustrating construction of a heat sink material
according to a third embodiment;
FIG. 16 shows a block diagram illustrating steps of a fifth production method;
FIG. 17 shows a table illustrating characteristics of the heat sink material
according to the fifth production method;
FIG. 18 shows a block diagram illustrating steps of a sixth production method;
FIG. 19 shows a table illustrating results of an exemplary experiment concerning
a carbon P;
FIG. 20 shows a table illustrating results of an exemplary experiment concerning
a carbon M;
FIG. 21 shows a table illustrating results of an exemplary experiment concerning
a carbon N;
FIG. 22 shows a table illustrating characteristics of carbons P, M, and N;
FIG. 23 shows a table in which representative examples concerning a case based
on a mold press and a case based on gas pressurization are extracted from the experimental results;
FIG. 24 shows characteristic curves illustrating the change of the porosity
and the density with respect to the infiltration pressure;
FIG. 25 shows characteristic curves illustrating the relationship between the
measured density and the average density for respective lots;
FIG. 26 shows a characteristic curve illustrating the change of the coefficient
of thermal conductivity with respect to the infiltration pressure;
FIG. 27 shows a characteristic curve illustrating the change of the compressive
strength with respect to the infiltration pressure;
FIG. 28 shows a characteristic curve illustrating the change of the density
with respect to the infiltration pressure;
FIG. 29 shows a characteristic curve illustrating the change of the coefficient
of thermal expansion with respect to the infiltration pressure;
FIG. 30 shows a table illustrating the difference of the reaction situation
of SiC/Cu and the infiltration situation of Cu when appropriate change is made
for the porosity of SiC, the pore diameter, the presence or absence of Ni plating,
the presence or absence of Si infiltration, the infiltration temperature, the pressurization,
the pressurization time, and the cooling speed;
FIG. 31 shows characteristic curves illustrating the change of the residual
pore with respect to the infiltration pressure;
FIG. 32 shows characteristic curves illustrating the change of the residual
pore with respect to the additive element;
FIG. 33 shows a schematic arrangement of a hot press machine to be used in a
seventh production method;
FIG. 34 shows a block diagram illustrating steps of the seventh production method;
FIG. 35A shows a plan view illustrating a packing member;
FIG. 35B shows a sectional view taken along a line XXIVB-XXIVB shown in FIG. 35A;
FIG. 36 shows a schematic arrangement of another exemplary hot press machine
to be used in the seventh production method;
FIG. 37 shows a schematic arrangement of a hot press machine to be used in a
modified method of the seventh production method;
FIG. 38 shows a block diagram illustrating steps of the modified method of the
seventh production method;
FIG. 39 shows a schematic arrangement of a hot press machine to be used in an
eighth production method; and
FIG. 40 shows a block diagram illustrating steps of the eighth production method.
DETAILED DESCRIPTION OF THE INVENTION
Illustrative embodiments of the heat sink material and the method of
producing the same according to the present invention will be explained below with
reference to FIGS. 1 to
40.
As shown in FIG. 1, a heat sink material
10A according to the first embodiment
comprises a porous sintered member
12 obtained by sintering carbon or allotrope
thereof to form a network, in which the porous sintered member
12 is infiltrated
with metal
14.
In this case, the carbon preferably used or the allotrope thereof has a coefficient
of thermal conductivity of not less than 100 W/mK, desirably not less than 150
W/mK (estimated value in a state in which no pore exists), and more desirably not
less than 200 W/mK (estimated value in a state in which no pore exists).
This embodiment is illustrative of a case of the heat sink material in which
open pores of the porous sintered member
12 of graphite having a coefficient
of thermal conductivity of not less than 100 W/mK are infiltrated with copper.
Those usable as the metal
14 of infiltration other than copper include aluminum
and silver.
As for the volume ratios of the porous sintered member
12 and the metal
14, the volume ratio of the porous sintered member
12 is within a
range from 50 to 80% by volume, and the volume ratio of the metal
14 is
within a range from 50 to 20% by volume. Accordingly, it is possible to obtain
the heat sink material in which the average coefficient of thermal conductivity
of those in the directions of the orthogonal three axes, or the coefficient of
thermal conductivity in the direction of any axis is 180 to 220 W/mK or more, and
in which the coefficient of thermal expansion is 1×10
-;6 to 10×10
-;6/° C.
The porosity of the porous sintered member
12 is desirably 10 to 50% by
volume, for the following reason. That is, if the porosity is not more than 10%
by volume, it is impossible to obtain the average coefficient of thermal conductivity
of those in the directions of the orthogonal three axes, or the coefficient of
thermal conductivity in the direction of any axis of not less than 180 W/mK (room
temperature). If the porosity exceeds 50% by volume, then the strength of the porous
sintered member
12 is lowered, and it is impossible to suppress the coefficient
of thermal expansion to be not more than 15.0×10
-;6/° C.
It is desirable that the value of the average open pore diameter (pore diameter)
of the porous sintered member
12 is 0.1 to 200 μm. If the pore diameter
is less than 0.1 μm, then it is difficult to infiltrate the interior of the
open pores with the metal
14, and the coefficient of thermal conductivity
is lowered. On the other hand, if the pore diameter exceeds 200 μm, then
the strength of the porous sintered member
12 is lowered, and it is impossible
to suppress the coefficient of thermal expansion to be low.
As for the distribution (pore distribution) in relation to the average open pores
of the porous sintered member
12, it is preferable that not less than 90%
by volume of the pores having diameters from 0.5 to 50 μm are distributed.
If the pores of 0.5 to 50 μm are distributed by less than 90% by volume,
then the open pores, which are not infiltrated with the metal
14, are increased,
and the coefficient of thermal conductivity may be lowered.
As for the closed porosity of the heat sink material
10A obtained by infiltrating
the porous sintered member
12 with the metal
14, it is preferable
that the closed porosity is not more than 12% by volume. If the closed porosity
exceeds 5% by volume, the coefficient of thermal conductivity may be lowered.
An automated porosimeter (trade name: Autopore 9200), which is produced by Shimadzu
Corporation, was used to measure the porosity, the pore diameter, and the pore distribution.
In the heat sink material
10A according to the first embodiment, it is
preferable that the graphite is added with an additive which reduces the closed
porosity when the graphite is sintered. The additive is exemplified by SiC and/or
Si. Accordingly, it is possible to decrease the closed pores upon the sintering,
and it is possible to improve the infiltration ratio of the metal
14 with
respect to the porous sintered member
12.
It is also preferable that an element, which reacts with the graphite, may be
added to the graphite. The element to be added is exemplified by one or more of
those selected from Ti, W, Mo, Nb, Cr, Zr, Be, Ta, V, B, and Mn. Accordingly, a
reaction layer (carbide layer) is formed on the surface of the graphite (including
the surface of the open pore) during the sintering of the graphite. The wettability
is improved with respect to the metal
14 with which the open pores of the
graphite are infiltrated. The infiltration can be performed at a low pressure.
Further, fine open pores can be also infiltrated with the metal.
On the other hand, it is preferable that one or more of those selected from Te,
Bi, Pb, Sn, Se, Li, Sb, Tl, Ca, Cd, and Ni are added to the metal
14 with
which the porous sintered member
12 is infiltrated. Accordingly, the wettability
is improved for the interface between the porous sintered member
12 and
the metal
14. The metal
14 easily enters the open pores of the porous
sintered member
12. Especially, Ni makes carbon easily dissolved and subject
to the infiltration.
It is preferable that one or more of those selected from Nb, Cr, Zr, Be, Ti,
Ta,
V, B, and Mn are added to the metal
1
