U.S. patent application number 10/872548 was filed with the patent office on 2005-01-06 for production method for sintered metal-ceramic layered compact and production method for thermal stress relief pad.
This patent application is currently assigned to HITACHI POWDERED METALS CO., LTD.. Invention is credited to Ichikawa, Jun-ichi, Ishihara, Chio, Iwakiri, Makoto, Saito, Shigeyuki, Shibata, Masaki, Shikata, Hideo.
Application Number | 20050002818 10/872548 |
Document ID | / |
Family ID | 33556553 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050002818 |
Kind Code |
A1 |
Ichikawa, Jun-ichi ; et
al. |
January 6, 2005 |
Production method for sintered metal-ceramic layered compact and
production method for thermal stress relief pad
Abstract
The present invention provides a production method for a
sintered metal-ceramic layered compact, comprising steps of:
filling and layering a metal powder and a ceramic powder, or
filling and layering a metal powder, a mixed powder of a metal
powder and a ceramic powder, and a ceramic powder; forming a green
compact of the layered powders by compacting the layered powders;
and sintering a layer including the metal of the green compact at a
temperature of lower than a melting point of the metal by heating
by irradiation of microwaves in a non-oxidizing atmosphere.
Inventors: |
Ichikawa, Jun-ichi;
(Matsudo-shi, JP) ; Shikata, Hideo; (Matsudo-shi,
JP) ; Saito, Shigeyuki; (Matsudo-shi, JP) ;
Ishihara, Chio; (Matsudo-shi, JP) ; Shibata,
Masaki; (Matsudo-shi, JP) ; Iwakiri, Makoto;
(Matsudo-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
HITACHI POWDERED METALS CO.,
LTD.
Matsudo-shi
JP
|
Family ID: |
33556553 |
Appl. No.: |
10/872548 |
Filed: |
June 22, 2004 |
Current U.S.
Class: |
419/6 |
Current CPC
Class: |
B22F 7/02 20130101; B22F
2998/10 20130101; H01L 35/08 20130101; B22F 7/02 20130101; B22F
1/0096 20130101; B22F 3/105 20130101; H01L 35/34 20130101; B22F
2998/10 20130101 |
Class at
Publication: |
419/006 |
International
Class: |
B22F 007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2003 |
JP |
2003-270872 |
Jul 7, 2003 |
JP |
2003-271256 |
Jul 9, 2003 |
JP |
2003-272143 |
Jul 10, 2003 |
JP |
2003-272735 |
Claims
What is claimed is:
1. A production method for a sintered metal-ceramic layered
compact, comprising steps of: filling and layering a metal powder
and a ceramic powder, or filling and layering a metal powder, a
mixed powder of a metal powder and a ceramic powder, and a ceramic
powder; forming a green compact of the layered powders by
compacting the layered powders; and sintering a layer including the
metal of the green compact at a temperature of lower than a melting
point of the metal by heating by irradiation of microwaves in a
non-oxidizing atmosphere.
2. The production method for a sintered metal-ceramic layered
compact according to claim 1, wherein the production method uses a
microwave heating furnace provided with a cooling device, and a
side of the metal layer of the compact is contacted to the cooling
device of the microwave heating furnace in the step of sintering
the green compact.
3. The production method for a sintered metal-ceramic layered
compact according to claim 1, wherein the metal is selected from a
group consisting of copper, aluminum, silver, and nickel, or a
mixture thereof, and the ceramic is alumina or aluminum
nitride.
4. The production method for a sintered metal-ceramic layered
compact according to claim 1, wherein the ceramic powder includes
at least one low melting point powder selected from a group
consisting of boric acid, anhydrous borax, sodium triboric acid,
sodium pentaboric acid, and soda-lime glass, and the low melting
point powder is mixed in a ratio of not more than 50 mass % in the
ceramic powder.
5. The production method for a sintered metal-ceramic layered
compact according to claim 1, wherein the ceramic powder includes
at least one binder selected from a group consisting of methyl
cellulose (MC), polyvinyl alcohol (PVA), ammonium alginic acid,
carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and
polyvinyl pyrrolidone (PVP), and the binder is mixed in a ratio of
not more than 1 mass % in the ceramic powder.
6. The production method for a sintered metal-ceramic layered
compact according to claim 5, wherein the mixed powder of the
ceramic powder and the binder is granulated to have a particle
diameter of not more than 150 .mu.m.
7. The production method for a sintered metal-ceramic layered
compact according to claim 1, wherein the mixed powder of the metal
powder and the ceramic powder has two or more mixed powders which
have different compositions from each other, wherein the metal is
mixed in a volume not less than that of the ceramic powder in the
mixed powder disposed on the side of the metal layer, and the
ceramic powder is mixed in a volume not less than that of the metal
powder in the mixed powder disposed on the side of the ceramic
layer.
8. A production method for a sintered metal-ceramic layered
compact, comprising steps of: filling and layering a metal powder
and a ceramic powder, or filling and layering a metal powder, a
mixed powder of a metal powder and a ceramic powder, and a ceramic
powder; forming a green compact of the layered powders by
compacting the layered powders; presintering a layer including the
metal of the compact at a temperature lower than a melting point of
the metal by heating by irradiation of microwaves in a
non-oxidizing atmosphere; and resintering the presintered compact
at a temperature lower than a melting point of the metal in a
non-oxidizing atmosphere.
9. The production method for a sintered metal-ceramic layered
compact according to claim 8, wherein the production method uses a
microwave heating furnace provided with a cooling device, and a
side of the metal layer of the compact is contacted to the cooling
device of the microwave heating furnace in the step of sintering
the compact.
10. The production method for a sintered metal-ceramic layered
compact according to claim 8, wherein the metal is selected from a
group consisting of copper, aluminum, silver, and nickel, or a
mixture thereof, and the ceramic is alumina or aluminum
nitride.
11. The production method for a sintered metal-ceramic layered
compact according to claim 8, wherein the ceramic powder includes
at least one low melting point powder selected from a group
consisting of boric acid, anhydrous borax, sodium triboric acid,
sodium pentaboric acid, and soda-lime glass, and the low melting
point powder is mixed in a ratio of not more than 50 mass % in the
ceramic powder.
12. The production method for a sintered metal-ceramic layered
compact according to claim 8, wherein the ceramic powder includes
at least one binder selected from a group consisting of methyl
cellulose (MC), polyvinyl alcohol (PVA), ammonium alginic acid,
carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and
polyvinyl pyrrolidone (PVP), and the binder is mixed in a ratio of
not more than 1 mass % in the ceramic powder.
13. The production method for a sintered metal-ceramic layered
compact according to claim 12, wherein the mixed powder of the
ceramic powder and the binder is granulated to have a particle
diameter of not more than 150 .mu.m.
14. The production method for a sintered metal-ceramic layered
compact according to claim 8, wherein the mixed powder of the metal
powder and the ceramic powder has two or more mixed powders which
have different compositions from each other, wherein the metal is
mixed in a volume not less than that of the ceramic powder in the
mixed powder disposed on the side of the metal layer, and the
ceramic powder is mixed in a volume not less than that of the metal
powder in the mixed powder disposed on the side of the ceramic
layer.
15. A production method for a sintered metal-ceramic layered
compact, comprising steps of: filling and layering a metal powder
and a ceramic powder, or filling and layering a metal powder, a
mixed powder of a metal powder and a ceramic powder, and a ceramic
powder; forming a green compact of the layered powders by
compacting the layered powders; and sintering the compact at a
temperature lower than a melting point of the metal in a
non-oxidizing atmosphere.
16. The production method for a sintered metal-ceramic layered
compact according to claim 15, wherein the metal is selected from a
group consisting of copper, aluminum, silver, and nickel, or a
mixture thereof, and the ceramic is alumina or aluminum
nitride.
17. The production method for a sintered metal-ceramic layered
compact according to claim 15, wherein the ceramic powder includes
at least one low melting point powder selected from a group
consisting of boric acid, anhydrous borax, sodium triboric acid,
sodium pentaboric acid, and soda-lime glass, and the low melting
point powder is mixed in a ratio of not more than 50 mass % in the
ceramic powder.
18. The production method for a sintered metal-ceramic layered
compact according to claim 15, wherein the ceramic powder includes
at least one binder selected from a group consisting of methyl
cellulose (MC), polyvinyl alcohol (PVA), ammonium alginic acid,
carboxymethyl cellulose (CMC), hydroxyethyl cellulose (EC), and
polyvinyl pyrrolidone (PVP), and the binder is mixed in a ratio of
not more than 1 mass % in the ceramic powder.
19. The production method for a sintered metal-ceramic layered
compact according to claim 18, wherein the mixed powder of the
ceramic powder and the binder is granulated to have a particle
diameter of not more than 150 .mu.m.
20. The production method for a sintered metal-ceramic layered
compact according to claim 15, wherein the mixed powder of the
metal powder and the ceramic powder has two or more mixed powders
which have different compositions from each other, wherein the
metal is mixed in a volume not less than that of the ceramic powder
in the mixed powder disposed on the side of the metal layer, and
the ceramic powder is mixed in a volume not less than that of the
metal powder in the mixed powder disposed on the side of the
ceramic layer.
21. A production method for a thermal stress relief pad for
thermoelectric conversion elements, comprising steps of: filling
and layering an electrical insulating powder (30C) and a mixed
powder (30B) of a metal powder and an electrical insulating powder
in turn in a cavity of a die, and forming a green compact (31) of
the layered powders by compacting the layered powders, or filling
and layering an electrical insulating powder (30C), a mixed powder
(30B) of a metal powder and an electrical insulating powder, and a
metal powder (30A) in turn in a cavity of a die, and forming a
green compact (32) of the layered powders by compacting the layered
powders; and contacting an electrical insulating layer, which is
made of the electrical insulating powder (30C) in either the green
compact (31) or the green compact (32), to a surface of an
electrical insulating layer of the electrical insulating powder
(30C) in either the green compact (31) or the green compact (32);
or filling a mixed powder (30B) of a metal powder and a ceramic
powder in a cavity of a die, and forming a green compact (33) by
compacting the powder, and contacting an electrical insulating
layer, which is made of the electrical insulating powder (30C) in
either the green compact (31) or the green compact (32), to a
surface of the green compact (33), or filling and layering a metal
powder (30A) and a mixed powder (30B) of a metal powder and an
electrical insulating powder in turn in a cavity of a die, and
forming a green compact (34) of the layered powders by compacting
the layered powders, and contacting an electrical insulating layer,
which is made of the electrical insulating powder (30C) in either
the green compact (31) or the green compact (32), to a surface of
the green compact (34); and sintering the green compacts, which are
in the above contacting state to each other, at a temperature lower
than a melting point of the included metal in a non-oxidizing
atmosphere.
22. The production method for a thermal stress relief pad for
thermoelectric conversion elements, according to claim 21, wherein
the electrical insulating powder is a mixed powder (30C1), a mixed
powder (30C2), or a glass frit powder (30C3), wherein the mixed
powder (30C1) is composed of one of an alumina powder and an
aluminum nitride powder, and one low melting point electrical
insulating powder selected from a group consisting of boric acid,
sodium boric acid, and soda-lime glass, the low melting point
electrical insulating powder being mixed in a ratio of not more
than 50 mass %, the mixed powder (30C2) is composed of one of an
alumina powder and an aluminum nitride powder and a glass frit
which is mixed in a ratio of not less than 0.1 mass %, and the
metal powder (30A) is selected from a group consisting copper,
aluminum, silver, and nickel, or a mixture thereof.
23. A production method for a thermal stress relief pad for
thermoelectric conversion elements, comprising steps of: filling
and layering a mixed powder (30B) of a metal powder and an
electrical insulating powder, an electrical insulating powder
(30C), and a mixed powder (30B) of a metal powder and an electrical
insulating powder in turn in a cavity of a die, or filling and
layering a metal powder (30A), a mixed powder (30B) of a metal
powder and an electrical insulating powder, an electrical
insulating powder (30C), a mixed powder (30B) of a metal powder and
an electrical insulating powder, and a metal powder (30A) in turn
in a cavity of a die; forming a green compact of the layered
powders by compacting the layered powders; sintering the green
compact at a temperature lower than a melting point of the included
metal powder in a non-oxidizing atmosphere; and removing a side
surface portion of the sintered compact by cutting or by
polishing.
24. The production method for a thermal stress relief pad for
thermoelectric conversion elements, according to claim 23, wherein
the electrical insulating powder is a mixed powder (30C1), a mixed
powder (30C2), or a glass frit powder (30C3), wherein the mixed
powder (30C1) is composed of one of an alumina powder and an
aluminum nitride powder, and one low melting point electrical
insulating powder selected from a group consisting of boric acid,
sodium boric acid, and soda-lime glass, one low melting point
electrical insulating powder being mixed in a ratio of not more
than 50 mass %, the mixed powder (30C2) is composed of one of an
alumina powder and an aluminum nitride powder and a glass frit
which is mixed in a ratio of not less than 0.1 mass %, and the
metal powder (30A) is selected from a group consisting copper,
aluminum, silver, and nickel, or a mixture thereof.
25. A production method for a thermal stress relief pad for
thermoelectric conversion elements, comprising steps of: filling
and layering an electrical insulating material powder (40A) for an
electrical insulating layer and a mixed powder (40B) of a metal
powder and an electrical insulating material powder in a die, or
filling and layering an electrical insulating material powder (40A)
for an electrical insulating layer, a mixed powder (40B) of a metal
powder and an electrical insulating material powder, and a metal
powder (40C) in a die; forming a green compact of the layered
powders by compacting the layered powders; and sintering the green
compact at a temperature lower than a melting point of the included
metal powder in a non-oxidizing atmosphere, wherein the metal
powder is selected from a group consisting of copper, aluminum,
silver and nickel, or a mixture thereof, the electrical insulating
material powder (40A) is selected from a group consisting of a
glass frit (40A1) and a mixed powder (40A2) of a ceramic powder and
a glass frit, the ceramic powder being composed of alumina or
aluminum nitride, the electrical insulating material powder (40A)
included in the mixed powder (40B) is selected from a group
consisting of a ceramic powder, the glass frit (40A1), and a mixed
powder (40A2) of a ceramic powder and a glass frit, the ceramic
powder being composed of alumina or aluminum nitride.
26. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the electrical insulating material powder (40A) is a mixed powder
(40A2) of the ceramic powder and the glass frit, and the glass frit
is mixed in a ratio of not less than 0.1 mass % in the mixed powder
(40A2).
27. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the mixed powder (40B), the electrical insulating material powder
(40A) and the mixed powder (40B) are layered in turn in the die in
the step of filling and layering powders, or the metal powder
(40C), the mixed powder (40B), the electrical insulating material
powder (40A), the mixed powder (40B), and the metal powder (40C)
are layered in turn in the die in the step of filling and layering
the powders, and the layered compact of the powders are integrally
compacted in the step of compacting.
28. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the mixed powder (40B) and the electrical insulating material
powder (40A) are layered in turn in the die in the step of filling
and layering powders, or the metal powder (40C), the mixed powder
(40B) and the electrical insulating material powder (40A) are
layered in turn in the die in the step of filling and layering
powders, the layered compact of the powders are integrally
compacted in the step of compacting, whereby two green compacts are
obtained, and the green compacts are sintered in a state in which
surfaces of layers of the electrical insulating material powder
(40A) are contacted to each other in the sintering step, thereby
being connected.
29. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the electrical insulating material powder (40A) includes at least
one binder selected from a group consisting of methyl cellulose
(MC), polyvinyl alcohol (PVA), ammonium alginic acid, carboxymethyl
cellulose (CMC), hydroxyethyl cellulose (HEC), and polyvinyl
pyrrolidone (PVP), wherein the binding agent is mixed in a ratio of
not more than 1 mass %.
30. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the binder is mixed into the electrical insulating material powder
(40A) in a middle portion layer in a thickness direction, and the
mixed powder is granulated so as to have a particle diameter of not
more than 150 .mu.m.
31. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 25, wherein
the mixed powder (40B) has two or more mixed powders which have
different composition from each other, wherein the metal powder
(40C) is mixed in a volume not less than that of the electrical
insulating material powder (40A) on the side of the metal layer
formed on an end face, and the electrical insulating material
powder (40A) is mixed in a volume more than that of the metal
powder (40C) in a electrical insulating layer formed at a middle
portion in a thickness direction.
32. A production method for a thermal stress relief pad for
thermoelectric conversion elements, comprising steps of: filling a
mixed powder (40B) of a metal powder and an electrical insulating
material powder in a die, or filling and layering a mixed powder
(40B) of a metal powder and an electrical insulating material
powder, and a metal powder (40C) in turn in a die; forming a green
compact of the layered powders by compacting the layered powders,
whereby two green compacts of the layered powders are obtained;
coating an electrical insulating material powder (40A) on a surface
of a layer of the mixed powder (40B) of one of the green compacts;
and connecting the green compacts via the electrical insulating
material powder (40A) by sintering.
33. The production method for a thermal stress relief pad for
thermoelectric conversion elements, according to claim 32, wherein
the electrical insulating material powder (40A) coated on a surface
of a layer of the mixed powder (40B) is dispersed in a liquid so as
to be made into slurry.
34. The production method for a thermal stress relief pad for
thermoelectric conversion elements according to claim 32, wherein
the mixed powder (40B) has two or more mixed powders which have
different composition from each other, wherein the metal powder
(40C) is mixed in a volume not less than that of the electrical
insulating material powder (40A) on the side of the metal layer
formed on an end face, and the electrical insulating material
powder (40A) is mixed in a volume more than that of the metal
powder (40C) in an electrical insulating layer formed at a middle
portion in a thickness direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a production method for
producing metal-ceramic layered compacts by using a powder
metallurgy technique, and relates to a production method for
producing thermal stress relief pads for thermoelectric conversion
elements by using a powder metallurgy technique. The metal-ceramic
layered compact is heat resistant and thermally conductive, or is
electrically insulated at one portion thereof and electrically
conductive and thermally conductive at another portion thereof, and
has a required thermal stress relief function. The thermal stress
relief pad has a structure in which metal and ceramic are layered
and which is electrically conductive and electrically
insulated.
[0003] 2. Description of the Related Art
[0004] A metal-ceramic layered compact which is heat resistant and
heat dissipating is disclosed in, for example, Japanese Unexamined
Patent Application Publication No. 5-286776, as described below.
That is, a metal-ceramic layered compact has an intermediate layer
between a metal layer and a ceramic layer. The metal layer is made
of copper, nickel, or tungsten. The ceramic layer is made of
alumina, aluminum nitride, or boron nitride. The intermediate layer
is made of metal and ceramic such that the mixing ratio of metal
and ceramic varies gradually or continuously in a thickness
direction. This layered compact is produced as follows. That is, a
metal included layer is layered by thermal spraying on a ceramic
substrate or is layered by paste printing thereon, and is then
sintered by hot pressing, by hot isostatic pressing (HIP), or by an
electrization heating method in which voltage is directly applied
thereto so that plasma discharge is generated among grains
thereof.
[0005] A metal-ceramic layered compact is disclosed in, for
example, Japanese Unexamined Patent Application Publication No.
6-329480, as described below. The metal-ceramic layered compact has
an intermediate layer between an alumina substrate and a copper
plate. The intermediate layer is composed of tungsten,
silver-copper alloy, and titanium. The composition of the
intermediate layer is set such that the silver-copper alloy is
included more on the copper plate side. The intermediate layer is
laminated by paste printing, and is then sintered in a vacuum or in
an atmosphere of nitrogen gas, hydrogen gas, or argon gas.
[0006] In the above conventional techniques, the metal-ceramic
layered compact is obtained such that metal layers are layered by
thermal spraying or by paste printing on a presintered ceramic
substrate, and the metal layers are then sintered. The ceramic has
high strength and the metal-ceramic layered compact has good
thermal conductivity since the metal layers have fine structures.
However, in the above production methods, after the ceramic is
sintered at high temperatures, the following processes are
repeatedly performed. That is, a thermal spraying process is
sequentially performed on metal containing powders which have
different compositions from each other, or pasted materials are
printed, and a drying process is performed. Due to this, the above
techniques require numerous processes, are time consuming, and are
troublesome. As a result, it is desired that a metal-ceramic
layered compact be more easily produced.
[0007] A thermal stress relief pad for a thermoelectric conversion
element is disclosed in, for example, Japanese Unexamined Patent
Application Publication No. 10-229224 as described below. That is,
the thermal stress relief pad has an electrical insulation layer
made of ceramic at the intermediate portion in a thickness
direction, and metal layers are formed via a mixed layer of ceramic
(electrical insulation material) and metal (thermal stress relief
material and thermal conductivity compact) on both sides of the
electrical insulating layer. In this case, the mixed layer is a
graded function layer having a gradient component in which the
ceramic is included more on the electrical insulating layer and the
metal is included more on the metal layer. This thermal stress
relief pad is used such that one end face thereof is contacted to
an electrode side of the thermoelectric element and the other end
face is contacted to a side of a heat source or to a side of a
cooling device. As a result, thermal stress relief pad has good
thermal conductivity, is prevented from leaking electricity to the
heat source side or to the cooling device by the electrical
insulating layer, and yield a thermal stress relief function by
having the graded composition in a thickness direction. For
example, the mixture of the electrical insulating material and the
metal is composed of alumina and copper, and is produced such that
powder filling is performed by injecting each powder from a nozzle
into a die while controlling the injecting ratio thereof so as to
have a graded composition in a thickness direction, and then
compacting and sintering are performed on the layered powders in
the die.
[0008] In the production method disclosed in the Japanese
Unexamined Patent Application Publication No. 10-229224, when a
multilayered structure having a graded composition layer is
produced, a method as described below can be used instead of the
multilayered filling method by the above powder spraying. That is,
one or more kinds of a mixed powder and a metal powder are layered,
are filled by using a powder feeder, and are formed by compacting
in turn in a die. The mixed powder is composed of an electrical
insulating powder (for example, alumina powder) and a metal powder
(for example, copper powder). However, since a thermal stress
relief pad for thermoelectric conversion elements generally has a
structure such that a conductive metal-ceramic mixed layer and a
metal layer are formed on both sides of the electrical insulating
layer (for example, alumina simple substance) which is at a middle
portion in a thickness direction thereof, when the powders are
sequentially filled and layered, the metal powder enters an outer
face of the electrical insulating layer via an inner wall surface
of the die. In this case, metal foil is formed on the outer face of
the electrical insulating layer, and causes a short circuit in the
thermal stress relief pad.
[0009] In addition, in the production method disclosed in Japanese
Unexamined Patent Application Publication No. 10-229224, a green
compact has a structure such that the electrical insulating layer
made of, for example, alumina powder, and is disposed between the
mixed powder of alumina and copper. However, since this green
compact is sintered at a temperature at which copper does not melt,
an alumina compact of the electrical insulating layer is not
sintered well, and cracks thereby occur at the electrical
insulating layer portion. As a result, the sintered compact
requires care in the use thereof.
SUMMARY OF THE INVENTION
[0010] An object of the present invention according to an aspect of
the invention is to provide a production method for a sintered
metal-ceramic layered compact, which can reduce the number of
processes and can be performed efficiently.
[0011] An object of the present invention according to another
aspect of the invention is to provide a production method for
thermal stress relief pads for thermoelectric conversion elements,
in which, however, compacting is performed on the powders by using
a die, can prevent a short circuit which is caused by metal
materials and can yield reliable performance of an electrical
insulating layer.
[0012] An object of the present invention according to another
aspect of the invention is to provide a production method for
thermal stress relief pads for thermoelectric conversion elements,
which can reduce the number of processes and can be performed
efficiently.
[0013] The present invention provides a production method for a
sintered metal-ceramic layered compact, comprising steps of:
filling and layering a metal powder and a ceramic powder, or
filling and layering a metal powder, a mixed powder of a metal
powder and a ceramic powder, and a ceramic powder; forming a green
compact of the layered powders by compacting the layered powders;
and sintering a layer including the metal of the green compact at a
temperature of lower than a melting point of the metal by heating
by irradiation of microwaves in a non-oxidizing atmosphere.
[0014] The present invention further provides a production method
for a sintered metal-ceramic layered compact, comprising steps of:
filling and layering a metal powder and a ceramic powder, or
filling and layering a metal powder, a mixed powder of a metal
powder and a ceramic powder, and a ceramic powder; forming a green
compact of the layered powders by compacting the layered powders;
presintering a layer including the metal of the green compact at a
temperature lower than a melting point of the metal by heating by
irradiation of microwaves in a non-oxidizing atmosphere; and
resintering the presintered compact at a temperature lower than a
melting point of the metal in a non-oxidizing atmosphere.
[0015] According to the present invention, the step of compacting
the powders and the step of sintering the green compact by using
powder metallurgy are performed when the sintered metal-ceramic
layered compact is produced. As a result, the number of processes
can be reduced and the production is performed efficiently.
[0016] The production method can use a microwave heating furnace
provided with a cooling device, and a side of the metal layer of
the compact may be contacted to the cooling device of the microwave
heating furnace in the step of sintering the green compact.
[0017] In the production method of the present invention, the metal
may be selected from a group consisting of copper, aluminum,
silver, and nickel, or a mixture thereof, and the ceramic may be
alumina or aluminum nitride.
[0018] In the present invention, the following embodiments can be
used. The ceramic powder may include at least one low melting point
powder selected from a group consisting of boric acid, anhydrous
borax, sodium triboric acid, sodium pentaboric acid, and soda-lime
glass, and the low melting point powder may be mixed in a ratio of
not more than 50 mass % in the ceramic powder. The ceramic powder
may include at least one binder selected from a group consisting of
methyl cellulose (MC), polyvinyl alcohol (PVA), ammonium alginic
acid, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC),
and polyvinyl pyrrolidone (PVP), and the binder may be mixed in a
ratio of not more than 1 mass % in the ceramic powder. The mixed
powder of the ceramic powder and the binder may be granulated to
have a particle diameter of not more than 150 .mu.m. The mixed
powder of the metal powder and the ceramic powder may have two or
more mixed powders which have different compositions from each
other, wherein the metal may be mixed in a volume not less than
that of the ceramic powder in the mixed powder disposed on the side
of the metal layer, and the ceramic powder may be mixed in a volume
not less than that of the metal powder in the mixed powder disposed
on the side of the ceramic layer.
[0019] The present invention further provides a production method
for a sintered metal-ceramic layered compact, comprising steps of:
filling and layering a metal powder and a ceramic powder, or
filling and layering a metal powder, a mixed powder of a metal
powder and a ceramic powder, and a ceramic powder; forming a green
compact of the layered powders by compacting the layered powders;
and sintering the green compact at a temperature lower than a
melting point of the metal in a non-oxidizing atmosphere.
[0020] According to the present invention, the step of compacting
the powders and the step of sintering the green compact by using
powder metallurgy are performed when the sintered metal-ceramic
layered compact is produced. As a result, the number of processes
can be reduced and the production is performed efficiently.
[0021] The present invention further provides a production method
for a thermal stress relief pad for thermoelectric conversion
elements, comprising steps of: filling and layering an electrical
insulating powder (30C) and a mixed powder (30B) of a metal powder
and an electrical insulating powder in turn in a cavity of a die,
and forming a green compact (31) of the layered powders by
compacting the layered powders, or filling and layering an
electrical insulating powder (30C), a mixed powder (30B) of a metal
powder and an electrical insulating powder, and a metal powder
(30A) in turn in a cavity of a die, and forming a green compact
(32) of the layered powders by compacting the layered powders; and
contacting an electrical insulating layer, which is made of the
electrical insulating powder (30C) in either the green compact (31)
or the green compact (32), to a surface of an electrical insulating
layer of the electrical insulating powder (30C) in either the green
compact (31) or the green compact (32); or filling a mixed powder
(30B) of a metal powder and an electrical insulating powder in a
cavity of a die, and forming a green compact (33) by compacting the
powder, and contacting an electrical insulating layer, which is
made of the electrical insulating powder (30C) in either the green
compact (31) or the green compact (32), to a surface of the green
compact (33), or filling and layering a metal powder (30A) and a
mixed powder (30B) of a metal powder and an electrical insulating
powder in turn in a cavity of a die, and forming a green compact
(34) of the layered powders by compacting the layered powders, and
contacting an electrical insulating layer, which is made of the
electrical insulating powder (30C) in either the green compact (31)
or the green compact (32), to a surface of the green compact (34);
and sintering the green compacts, which are in the above contacting
state to each other, at a temperature lower than a melting point of
the included metal in a non-oxidizing atmosphere.
[0022] According to the present invention, the metal powder, the
mixed powder of the metal powder and the electrical insulating
powder, and the electrical insulating powder are filled and layered
in an appropriate multilayered structure, two green compacts are
thereby obtained, are appropriately combined with each other, and
then are sintered at a temperature lower than the melting point of
the included metal in a non-oxidizing atmosphere. As a result,
short-circuiting caused by metal materials can be prevented and the
electrical insulating layer can function reliably although
compacting is performed on the powders by using the die in the
production method of the present invention.
[0023] The present invention further provides a production method
for a thermal stress relief pad for thermoelectric conversion
elements, comprising steps of: filling and layering a mixed powder
(30B) of a metal powder and an electrical insulating powder, an
electrical insulating powder (30C), and a mixed powder (30B) of a
metal powder and an electrical insulating powder in turn in a
cavity of a die, or filling and layering a metal powder (30A), a
mixed powder (30B) of a metal powder and an electrical insulating
powder, an electrical insulating powder (30C), a mixed powder (30B)
of a metal powder and an electrical insulating powder, and a metal
powder (30A) in turn in a cavity of a die; forming a green compact
of the layered powders by compacting the layered powders; sintering
the green compact at a temperature lower than a melting point of
the included metal powder in a non-oxidizing atmosphere; and
removing a side surface portion of the sintered compact by cutting
or by polishing.
[0024] In the present invention, the electrical insulating powder
may be a mixed powder (30C1), a mixed powder (30C2), or a glass
frit powder (30C3), wherein the mixed powder (30C1) may be composed
of one of an alumina powder and an aluminum nitride powder, and one
low melting point electrical insulating powder selected from a
group consisting of boric acid, sodium boric acid, and soda-lime
glass, the low melting point electrical insulating powder being
mixed in a ratio of not more than 50 mass %, the mixed powder
(30C2) may be composed of one of an alumina powder and an aluminum
nitride powder and a glass frit which is mixed in a ratio of not
less than 0.1 mass %, and the metal powder (30A) may be selected
from a group consisting copper, aluminum, silver, and nickel, or a
mixture thereof.
[0025] The present invention further provides a production method
for a thermal stress relief pad for thermoelectric conversion
elements, comprising steps of: filling and layering an electrical
insulating material powder (40A) for an electrical insulating layer
and a mixed powder (40B) of a metal powder and an electrical
insulating material powder in a die, or filling and layering an
electrical insulating material powder (40A) for an electrical
insulating layer, a mixed powder (40B) of a metal powder and an
electrical insulating material powder, and a metal powder (40C) in
a die; forming a green compact of the layered powders by compacting
the layered powders; and sintering the green compact at a
temperature lower than a melting point of the included metal powder
in a non-oxidizing atmosphere, wherein the metal powder is selected
from a group consisting of copper, aluminum, silver and nickel, or
a mixture thereof, the electrical insulating material powder (40A)
is selected from a group consisting of a glass frit (40A1) and a
mixed powder (40A2) of a ceramic powder and a glass frit, the
ceramic powder being composed of alumina or aluminum nitride, the
electrical insulating material powder (40A) included in the mixed
powder (40B) is selected from a group consisting of a ceramic
powder, the glass frit (40A1), and a mixed powder (40A2) of a
ceramic powder and a glass frit.
[0026] According to the present invention, the step of compacting
the powders and the step of sintering the green compact by using
powder metallurgy are performed when the sintered metal-ceramic
layered compact is produced. As a result, since the electrical
insulating layer and the metal layer can be sintered simultaneously
when the thermal stress relief pad for thermoelectric conversion
elements is produced, the number of processes can be reduced and
the production is performed efficiently.
[0027] In the present invention, the electrical insulating material
powder (40A) may be a mixed powder (40A2) of the ceramic powder and
the glass frit, and the glass frit may be mixed in a ratio of not
less than 0.1 mass % in the mixed powder (40A2). The following
concrete methods can be used in the present invention. That is, the
mixed powder (40B), the electrical insulating material powder (40A)
and the mixed powder (40B) may be layered in turn in the die in the
step of filling and layering powders, or the metal powder (40C),
the mixed powder (40B), the electrical insulating material powder
(40A), the mixed powder (40B), and the metal powder (40C) may be
layered in turn in the die in the step of filling and layering the
powders, and the layered powders may be integrally compacted in the
step of compacting. Alternatively, the mixed powder (40B) and the
electrical insulating material powder (40A) may be layered in turn
in the die in the step of filling and layering powders, or the
metal powder (40C), the mixed powder (40B) and the electrical
insulating material powder (40A) may be layered in turn in the die
in the step of filling and layering powders, the layered powders
are integrally compacted in the step of compacting, whereby two
green compacts are obtained, and the green compacts may be sintered
in a state in which surfaces of layers of the electrical insulating
material powder (40A) are contacted to each other in the sintering
step, thereby being connected.
[0028] The following concrete methods can be used in the present
invention. That is, the electrical insulating material powder (40A)
may include at least one binder selected from a group consisting of
methyl cellulose (MC), polyvinyl alcohol (PVA), ammonium alginic
acid, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC),
and polyvinyl pyrrolidone (PVP), wherein the binder may be mixed in
a ratio of not more than 1 mass %. The binder may be mixed into the
electrical insulating material powder (40A) in a middle portion
layer in a thickness direction, and the mixed powder may be
granulated so as to have a particle diameter of not more than 150
.mu.m.
[0029] The present invention further provides a production method
for a thermal stress relief pad for thermoelectric conversion
elements, comprising steps of: filling a mixed powder (40B) of a
metal powder and an electrical insulating material powder in a die,
or filling and layering a mixed powder (40B) of a metal powder and
an electrical insulating material powder, and a metal powder (40C)
in turn in a die; forming a green compact of the layered powders by
compacting the layered powders, whereby two green compacts of the
layered powders are obtained; coating an electrical insulating
material powder (40A) on a surface of a layer of the mixed powder
(40B) of one of the green compacts; and connecting the green
compacts via the electrical insulating material powder (40A) by
sintering. In this case, the electrical insulating material powder
(40A) coated on a surface of a layer of the mixed powder (40B) may
be dispersed in a liquid so as to be made into slurry.
[0030] In the both methods of the present invention, the mixed
powder (40B) can have two or more mixed powders which have
different composition from each other, the metal powder (40C) can
be mixed in a volume not less than that of the electrical
insulating material powder (40A) on the side of the metal layer
formed on an end face, and the electrical insulating material
powder (40A) can be mixed in a volume more than that of the metal
powder (40C) in a electrical insulating layer formed at a middle
portion in a thickness direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIGS. 1A to 1E are cross sectional views showing examples of
a multilayered structure of a sintered ceramic-metal layered
compact according to the first and the second embodiments.
[0032] FIGS. 2A and 2B are cross sectional views showing examples
of a sintered ceramic-metal layered compact applied to a
thermoelectric conversion module according to the first and the
second embodiments.
[0033] FIG. 3 is a cross sectional view showing an example of a
multilayered structure of a thermal stress relief pad according to
the third embodiment.
[0034] FIG. 4 is a cross sectional view for explaining that a
copper foil portion causing a short-circuit is formed at an
electrical insulating layer of a sintered compact obtained by
integrally compacting all powders.
[0035] FIGS. 5A to 5D are cross sectional views showing examples of
a compressed material.
[0036] FIGS. 6A to 6G are cross sectional views showing examples of
a thermal stress relief pad.
[0037] FIG. 7 is a cross sectional view showing an example of a
thermal stress relief pad applied to a thermoelectric conversion
module according to the third embodiment.
[0038] FIGS. 8A to 8C are cross sectional views showing examples of
a multilayered structure for thermal stress relief pads according
to the fourth embodiment.
[0039] FIGS. 9A to 9C are cross sectional views showing examples of
a thermal stress relief pad.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Preferred embodiments of the present invention will be
described hereinafter with reference to the Figures.
[0041] (A) First Embodiment
[0042] Desirable materials and production method in which the
desirable materials are used according to the first embodiment will
be described in detail hereinafter.
[0043] (1) Ceramic Powder
[0044] A Ceramic powder is composed of alumina or aluminum nitride,
which has good electrical insulation and good thermal conductivity.
In this case, in particular, alumina has better powder compression
compactibility than that of aluminum nitride, and has a lower
melting point than that of aluminum nitride, thereby being
favorably used. A ceramic powder as a component of a ceramic layer
is favorably densified as high as possible by compacting, and has
good sinterability, thereby favorably having fine grain size. When
a ceramic powder has low flowability due to fine grain size
thereof, the ceramic powder is favorably granulated by using a
binder such as carboxymethyl cellulose (CMC) so as to have a
particle diameter of about 50 to 150 .mu.m, and the flowability
thereof is thereby improved. As a result, powder filling into a die
is easily performed and the ceramic powder compact has high
strength. As compared with a fine ceramic powder, a coarse powder
is mixed with the fine ceramic powder, and the sinterability and
flowability can thereby be improved. A ceramic powder which is
mixed with a mixture of metal and ceramic and which is component of
an intermediate layer favorably has the grain size approximate to
that of the metal powder so that the ceramic powder is equally
dispersed in the metal powder and the metal powder is sintered.
[0045] (2) Low Melting Powder Added to Ceramic Powder
[0046] A ceramic layer of only alumina can be sintered by
irradiation of microwaves. A electrical insulating material, which
is softened or has a liquid phase at temperatures at which layered
metal does not melt, is formed into a powder and is mixed into a
ceramic layer, whereby liquid phase sintering is performed on the
ceramic layer at relatively low temperatures, thereby having high
strength.
[0047] This low meting point powder is as follows.
[0048] a) boric acid (H.sub.3BO.sub.3): melting point of
577.degree. C. in a state of anhydrous boric acid
[0049] b) anhydrous borax (Na.sub.2B.sub.4O.sub.7): melting point
of 741.degree. C.
[0050] c) sodium pentaboric acid (NaB.sub.5O.sub.8.5H.sub.2O):
melting point of 750.degree. C.
[0051] d) sodium triboric acid (NaB.sub.3O.sub.5): melting point of
694.degree. C.
[0052] e) soda-lime glass
(SiO.sub.2--Na.sub.2O--CaO--Al.sub.2O.sub.3--MgO- ): softening
point of 500 to 700.degree. C.; melting point of about 725.degree.
C.
[0053] In the low melting point powder, plural low melting point
materials and high melting point materials can be added to a
ceramic layer. When the adding ratio of the low melting point
powder is about 0.1 mass % in the ceramic layer, the strength of
the ceramic layer is improved. When the adding ratio of the low
melting point powder is larger, the liquid phase of the low melting
point powder may possibly bubble to the surface of the ceramic
layer in the case of sintering the ceramic layer or in the case in
which the temperature range of a sintered metal-ceramic layered
compact is high, whereby the adding ratio of the low melting point
powder is not more than 50 mass % in the ceramic layer.
[0054] (3) Binder for Ceramic Powder
[0055] A green compact of a ceramic layer has predetermined
strength so as to be easily handled by adjusting the grain size
distribution of a ceramic powder. A binder such as methyl cellulose
(MC), polyvinyl alcohol (PVA), ammonium alginic acid, carboxymethyl
cellulose (CMC), or polyvinyl pyrrolidone (PVP) is mixed into a
ceramic layer, or is mixed into a ceramic powder for granulating,
whereby the green compact can have higher strength. As a result,
when the green compact is transferred in processes of powder
compacting and of sintering, cracks and defects can be prevented
from forming therein. Although the green compact can be produced
without the above binder, it is desirable that flowability of the
ceramic powder be improved by granulating the ceramic powder so
that filling to a die is improved.
[0056] The above binder dissipates when heated during the sintering
of the ceramic layer. Since the density of the ceramic layer is
reduced and the thermal conductivity thereof is deteriorated when
too much of the above binder is added much, the mixing ratio of the
above binder into the ceramic layer is favorably not more than 1
mass %.
[0057] (4) Powder of Metal Layer
[0058] A metal layer which is electrically conductive and thermally
conductive is made of a metal powder. The metal powder is composed
of one of copper, aluminum, silver, and nickel, or mixture of at
least two of copper, aluminum, silver, and nickel. For example, the
mixture may be composed of copper and aluminum. Although these
powders have good compressibility, these powders favorably have
predetermined grain sizes so as to pass through a 100-mesh sieve,
thereby facilitating filling into a die. When a fine powder is
used, flowability can be improved by granulating.
[0059] (5) Powder of Intermediate Layer
[0060] An intermediate layer is made of a metal powder and a
ceramic powder. The volume ratio of the metal powder to the ceramic
powder is about 1:1. Alternatively, when plural intermediate layers
of the metal powder and the ceramic powder are formed, the
component ratio of the metal powder to the ceramic powder increases
as the intermediate layers approach the metal layer, and the
component ratio of the ceramic powder to the metal powder increases
as the intermediate layers approach the ceramic layer. The mixed
powders are made such that the ceramic powder is mixed into the
metal powder without granulation so that these powders are equally
dispersed.
[0061] (6) Lubricant
[0062] It is not necessary to mix a lubricant into the metal powder
because the metal powder has good compressibility. A lubricant such
as a metal stearate is favorably coated on an inner wall of a die
so that the green compact is easily ejected from the die. The
lubricant is coated by electrostatic coating. Alternatively, the
lubricant dispersed in a liquid is used.
[0063] (7) Multilayered Structure
[0064] A multilayered structure has a metal layer and a ceramic
layer, has a metal layer, an intermediate layer and a ceramic
layer, has a metal layer, an intermediate layer, a ceramic layer
and an intermediate layer, or has a metal layer, an intermediate
layer, a ceramic layer, an intermediate layer and a metal layer in
turn on an end face of a layered direction. The intermediate layer
has at least one layer. The ceramic layer has relatively low
thermal conductivity, thereby being favorably thinly formed.
However, when the ceramic layer is formed very thinly, the layers
which are adjacent thereto and which include metal are easily
mixed, and the electrical insulation may be possibly reduced.
Therefore, the thickness of the ceramic layer is favorably about
0.5 to 2 mm.
[0065] (8) Multilayered Filling of Powders
[0066] A powder feeder can be used for filling each powder in a die
having a die for forming an outer portion of a green compact, an
upper punch and a lower punch. The powder feeder can be moved
forward or backward on a die cavity. Plural powder boxes are
connected to the powder feeder in a powder feeder moving direction.
For example, when a multilayered structure has a metal layer, an
intermediate layer, a ceramic layer, an intermediate layer and a
metal layer, the powder feeder has three boxes. In this case, a
metal powder is filled in the front box, an intermediate layer
powder is filled in the middle box, and a ceramic powder is filled
in the rear box. The powder feeder is moved forward in a state in
which the lower punch is flush with the upper face of the die, so
that the powder box having the metal powder is stopped on the lower
punch, and then the lower punch or the die is moved so as to form a
cavity, whereby the metal powder is filled therein. Next, the box
having the intermediate layer powder is moved on the die cavity,
and then the intermediate layer powder is filled in the same manner
as that of the metal powder. After the ceramic powder is filled in
the same manner as that of the metal powder, the powder feeder is
moved in turn backward, and multilayered filling of five layers can
be performed. A powder feeder has a structure such that spaces are
provided between plural powder boxes. In this case, after one kind
of powder is filled in the cavity, in a state in which the space is
stopped on the cavity, the filled powder is dropped, the cavity is
formed, and the filled powder adhered on the wall surface of the
die cavity is scratched and dropped by using a simple punch. As a
result, a green compact having a multilayered structure which is
distinctively divided can be obtained.
[0067] Since surfaces of the filled powders have microscopic rough
portions, the powders adjacent to each other have slightly mixed
portions of each other. The intermediate layer and the ceramic
layer have slightly mixed portions in the same manner. As a result,
the compositions of the layers are not distinctively divided from
each other, and the layers adjacent to each other are mixed so as
to be connected to each other, and each layer is difficult to peel
off from the green compact.
[0068] (9) Compacting of Powders
[0069] Compacting is performed on the metal powders of the above
metal powders as described below. That is, compacting is performed
on the copper powder, the silver powder, and the aluminum powder at
a compacting pressure of about 100 to 300 MPa, and is performed on
the nickel powder at a compacting pressure of about 400 MPa of the
above metal powders, whereby the green compacts of these metal
powders have the relative density of not less than 95% and thereby
have good electrical conductivity and good thermal conductivity. On
the other hand, when compacting is performed on the ceramic powder
of alumina at a compacting pressure of about 600 MPa, the green
compact of the ceramic powder of alumina has a relative density of
about 50%. When compacting is performed on the ceramic powder of
alumina at a compacting pressure of 700 MPa, the green compact of
the ceramic powder of alumina has a relative density of about 60%.
The compacting pressure of the multilayered powder is favorably
about 700 to 1000 MPa since the relative density of the green
compact of the ceramic powder gradually increases when compacting
is performed on the ceramic powder of alumina at a compacting
pressure of more than 700 MPa.
[0070] (10) Microwave Sintering
[0071] A microwave sintering furnace is used for sintering. For
example, as disclosed in Japanese Unexamined Patent Application
Publication No. 6-345541, a microwave sintering furnace provided
with a heater at an inner wall portion of a heating chamber can
control preheating and cooling, thereby being favorably used. The
inside of the heating chamber contains a non-oxidizing gas or is a
vacuum when the green compacts are sintered. The non-oxidizing gas
may be hydrogen, nitrogen, or argon, or may be a mixed gas of
hydrogen and nitrogen. When the metal powder is composed of silver,
sintering can be performed in air. The furnace is constructed such
that a supporting pedestal and a holding plate on which a sintered
compact held is are provided in the heating chamber, and heat
discharging and cooling are performed thereon by a water cooling
device provided apart therefrom so that the green compact can be
sintered at a high temperature at which the ceramic is sintered
well without melting metal of the green compact, thereby being
favorable when a metal powder of aluminum having a low melting
point is used.
[0072] When microwaves are irradiated on a multilayered green
compact of metal and ceramic, the ceramic is heated and the
temperature thereof is increased so that the degree of sintering of
the ceramic is progressed. Since the metal portion of the
multilayered green compact reflects microwaves, the metal portion
is not significantly heated by the microwaves. However, the
temperature of the metal portion is increased by Joule heat, by
heat conducted from the ceramic, and/or by radiant heat, so that
the degree of sintering of the metal portion is progressed. Since
the shape thereof is collapsed when the intermediate layer
including the metal and the metal layer is melted, the output of
the microwaves and processing time thereof are appropriately
determined by experience in accordance with the kind of metal and
quantity of the green compact.
[0073] The lubricant and the binder are dissipated by microwave
sintering, and the ceramic layer, the intermediate layer, and the
metal layer are sintered. When a low melting point powder such as a
soda-lime glass is included in the ceramic layer, the low melting
point powder is melted without heating the ceramic layer to a high
temperature, and the ceramic layer is sintered and the interface
portion between the ceramic layer and the intermediate layer has
high bonding strength. In particular, a method in which a low
melting point powder is added to the ceramic powder and aluminum
having low melting point is used is favorable since the ceramic
layer is sintered at a low temperature without melting the
aluminum.
[0074] When microwave sintering is performed, the metal layer is
electrically conductive and thermally conductive, and wettability
is ensured when brazing or adhering by an adhesive agent is
performed in using the sintered multilayered compact.
[0075] (11) Resintering
[0076] Although in the above microwave sintering, a sintered
multilayered compact of metal and ceramic can be obtained, when
boric acid or anhydrous borax is included in the ceramic layer, a
two step sintering method can be adopted as described below. That
is, microwave sintering is briefly performed on the ceramic
portion, the microwave sintering is stopped so that the metal
portion is incompletely sintered, and then the presintered compact
is heated at a temperature at which the metal is not melted in a
non-oxidizing atmosphere. This sintering can be performed in a
typical continuous sintering furnace, and is thereby suitable for
mass production. In the apparatus provided with the heater in the
inner wall of the heating chamber as disclosed in the above
Japanese Unexamined Patent Application Publication No. 6-345541,
resintering can be performed on the presintered compact by heating
by the heater after stopping microwave irradiation.
[0077] Next, the first embodiment of the present invention will be
described with reference to the Figures.
[0078] FIGS. 1A to 1E are cross sectional diagrams showing sintered
metal-ceramic layered compacts. In the sintered metal-ceramic
layered compacts, the metal layer is made of copper and the ceramic
layer is made of alumina.
[0079] A sintered layered compact 105A shown in FIG. 1A has a
two-layered structure having a copper layer 103 and a ceramic layer
101 layered on the copper layer 103. The copper layer 103 is made
of an electrolytic copper powder, and the ceramic layer 101 is made
of a powder in which anhydrous borax (Na.sub.2B.sub.4O.sub.7) is
mixed into alumina powder in a ratio of 1 mass %. In producing the
sintered layered compact 105A, the above powders are filled and
layered in turn at a predetermined thickness in a die, and then
compacting is performed on the filled layered powders at a
compacting pressure of 800 MPa, whereby a green compact is
obtained. Next, this green compact is provided in the microwave
sintering furnace, nitrogen gas is charged therein, and microwaves
are irradiated on the green compact so that the ceramic layer 101
is heated for five minutes at a temperature of about 900.degree. C.
and is then cooled. The primary sintered compact is resintered at a
temperature of 800.degree. C. under a dissociated ammonia
atmosphere in a mesh belt-type furnace, whereby the sintered
layered compact 105A is obtained.
[0080] For example, this sintered layered compact is used as a heat
discharging member. In this case, the ceramic layer 101 is
contacted to a ceramic product or a ceramic member of which the
temperature is increased, and heat dissipating fins are provided to
the copper layer 103. When the copper layer is needed having
thermal conductivity and electrical conductivity and the ceramic
layer 101 is needed having electrical insulation, the copper layer
103 is contacted to a side which must be electrically conductive
and the ceramic layer 101 is contacted to a side which must be
electrically insulating. Since this sintered layered compact 105A
has the copper layer 103 and the ceramic layer 101, the interlayer
therebetween is peeled off due to thermal expansion differences
therebetween when this sintered layered compact 105A is used in a
high temperature atmosphere. Therefore, this sintered layered
compact 105A is used at a relatively low temperature at which the
above phenomenon does not occur.
[0081] Sintered layered compacts 105B to 105E shown in FIGS. 1B to
1E will be described hereinafter. Production methods for these
sintered layered compacts 105B to 105E are the same as that for the
sintered layered compact 105A. The following intermediate layer is
made of a alumina powder and a copper powder.
[0082] The sintered layered compact 105B is constructed such that
two intermediate layers 121 and 123 having different composition
from each other are sandwiched between the copper layer 103 and the
ceramic layer 101. The intermediate layer 123 on the side of the
copper layer 103 is composed of a mixed powder of an alumina powder
and a copper powder. The mass ratio of the alumina powder to the
copper powder is 15 to 85 in the mixed powder of the intermediate
layer 123. That is, the volume ratio of the alumina powder is about
30% in the mixed powder of the intermediate layer 123. The
intermediate layer 121 on the side of the ceramic layer 101 is
composed of a mixed powder of an alumina powder and a copper
powder. The mass ratio of the alumina powder to the copper powder
is 30 to 70. That is, the volume ratio of the alumina powder is
about 50%. That is, the content of copper is large in the
intermediate layer 123 on the side of the copper layer 103, and the
content of ceramic is large in the intermediate layer 121 on the
side of the ceramic layer 101. This sintered layered compact 105B
has a more advantageous structure than the sintered layered compact
105A in relieving thermal stress caused by heat cycling causing
surrounding temperature changes and/or repeated thermal
stresses.
[0083] The sintered layered compact 105C shown in FIG. 1C is
constructed such that the ceramic layer 101 is sandwiched between
two copper layers 103a and 103b. The copper layers 103a and 103b
are thermally conductive and electrically conductive, and the
ceramic layer 101 therebetween is electrically insulating.
Therefore, the copper layers 103a and 103b are electrically
insulated therebetween by the ceramic layer 101. In this sintered
layered compact 105C, for example, heating is performed on the
copper layer 103a and heat dissipation is performed on the copper
layer 103b so as to have a cooling action. Since the ceramic layer
101 directly contacts the copper layers 103a and 103b, heat
resistance characteristics are inadequate, and the sintered layered
compact 105C is favorably used at a relatively low temperature or
in an environment having low temperature differences.
[0084] The sintered and layered compact 105D as shown in FIG. 5D is
constructed such that an intermediate layer 122a is sandwiched
between the ceramic layer 101 and the copper layer 103a and an
intermediate layer 122b is sandwiched between the ceramic layer 101
and the copper layer 103b in the sintered layered compact 105C. The
volume ratio of alumina is about 50% in the intermediate layers
122a and 122b. The sintered and layered compact 105E as shown in
FIG. 5E is structured such that an intermediate layer 121a is
sandwiched between the intermediate layer 122a and the ceramic
layer 101, an intermediate layer 121b is sandwiched between the
intermediate layer 122b and the ceramic layer 101, an intermediate
layer 123a is sandwiched between intermediate layer 122a and the
copper layer 103a, and an intermediate layer 123b is sandwiched
between intermediate layer 122b and the copper layer 103b in the
sintered layered compact 105D. The volume ratio of alumina is about
70% in the intermediate layers 121a and 121b. The volume ratio of
alumina is about 30% in the intermediate layers 123a and 123b. As
the above, three layers as intermediate layers are disposed between
the ceramic layer 101 and the copper layer 103a and between the
ceramic layer 101 and the copper layer 103b. In these sintered
layered compacts 105D and 105E, intermediate layers are disposed
between the ceramic layer 101 and the copper layer 103a and between
the ceramic layer 101 and the copper layer 103b, and these sintered
layered compacts 105D and 105E have thermal stress relief, thereby
giving good heat shock resistance characteristics.
[0085] Next, use examples of the above sintered layered compacts
105A to 105E will be described with reference to FIGS. 2A and 2B.
In FIGS. 2A and 2B, reference numeral 105 shows one of the sintered
and layered compacts 105A to 105E.
[0086] FIG. 2A shows a cross sectional diagram of a thermoelectric
conversion module 106A. The thermoelectric conversion module 106A
is constructed such that plural N-type elements and plural P-type
elements (thermoelectric elements 108) are positioned so as to
alternate with each other, the thermoelectric elements 108 are
connected to each other in a line by the sintered layered compacts
105, and the both ends of the sintered layered compacts 105 are
sandwiched by metal plates 107 having good thermal conductivity so
as to fix the members to each other. For example, the metal plates
107 may be copper plates. The sintered layered compact 105 may be
used as a connecting pad. In this thermoelectric conversion module
106A, electricity is generated from a terminal mounted on the end
of the thermoelectric element 108 by heating one side thereof and
cooling the other side thereof. This thermoelectric conversion
module 106A is mounted and used in a state of being disposed
between a heat discharging portion of a furnace and a cooling
device such as a water jacket.
[0087] In the thermoelectric module 106A as shown in FIG. 2A, the
thermoelectric elements 108 and the sintered layered compacts 105
are connected to each other by using solder or graphite coating, so
that electrical conductivity and thermal conductivity therebetween
are ensured. The sintered layered compacts 105 and the copper
plates 107 are connected to each other by using solder or graphite
coating, water glass, or high melting point glass, so that thermal
conductivity therebetween is ensured. A thermoelectric conversion
module 106B shown in FIG. 2B has the same fundamental structure as
that of the thermoelectric conversion module 106A, and bolt 110 and
nut 111 for fastening two copper plates 107 hold such that the
members thereof are layered and contacted to each other in the
thermoelectric conversion module 106B.
[0088] The above sintered layered compacts 105A to 105E can be used
as a sintered layered compact 105 used in these thermoelectric
conversion modules 106A and 106B. In particular, the sintered
layered compacts 105D and 105E are favorably used since the copper
layers 103a and 103b have good electrical conductivity and thermal
conductivity, the ceramic layer electrically insulates between the
copper layers 103a and 103b, thermal stress, which is caused by
thermal expansion differences between the high temperature side and
the low temperature side and by heat cycling, can be relieved by
the intermediate layers 121a, 122a, and 123a, and generation
performance and reliability of these thermoelectric conversion
modules 106A and 106B are improved.
[0089] (B) Second Embodiment
[0090] Desirable materials and production method in which the
desirable materials are used according to the second embodiment
will be described hereinafter. In the second embodiment,
description of the same materials and structures as that of the
first embodiment are omitted.
[0091] (1) Ceramic Powder
[0092] The same ceramic powder as that of the first embodiment is
used.
[0093] (2) Low Melting Powder Added to Ceramic Powder
[0094] A ceramic powder composed of only ceramic powder is hardly
sintered when heated to a temperature in which the metal layer is
sintered. Due to this, the ceramic layer may possibly collapse when
a strong impact is imparted thereto although the ceramic layer may
be handled. Therefore, the same low melting point powder as that of
the first embodiment is used so as to improve the strength of the
ceramic layer.
[0095] (3) Binder for Ceramic Powder
[0096] The same binder for the ceramic powder as that of the first
embodiment is used.
[0097] (4) Powder of Metal Layer
[0098] The same powder of the metal layer as that of the first
embodiment is used.
[0099] (5) Powder of Intermediate Layer
[0100] The same powder of the intermediate layer as that of the
first embodiment is used.
[0101] (6) Lubricant
[0102] The same lubricant as that of the first embodiment is
used.
[0103] (7) Multilayered Structure
[0104] The same multilayered structure as that of the first
embodiment is used.
[0105] (8) Multilayered Filling of Powder
[0106] The same multilayered filling of the powders as those of the
first embodiment are performed.
[0107] (9) Compacting of Powders
[0108] The same compacting of the powders as those of the first
embodiment are performed.
[0109] (10) Sintering
[0110] Temperatures of metal-ceramic green compact are about 700 to
950.degree. C. when the metal is copper, about 500 to 600.degree.
C. when the metal is aluminum, about 700 to 850.degree. C. when the
metal is silver, and about 800 to 1150.degree. C. when the metal is
nickel. The inside of the heating chamber is in a non-oxidizing gas
or in a vacuum when the green compact is sintered. The
non-oxidizing gas may be hydrogen, nitrogen, or argon, or a mixed
gas of hydrogen and nitrogen. When the metal powder is composed of
silver, the green compact can be sintered in air. The lubricant and
the binder are dissipated by sintering, and the ceramic layer, the
intermediate layer, and the metal layer are sintered. When a low
melting point powder such as a soda-lime glass is included in the
ceramic layer, the low melting point powder is melted without
heating the ceramic layer to a high temperature, and the ceramic
layer is sintered and the interface portion between the ceramic
layer and the intermediate layer has high bonding strength. In
particular, a method in which a low melting point powder is added
to the ceramic powder and aluminum having a low melting point is
used is favorable since the ceramic layer is sintered at a low
temperature without melting the aluminum.
[0111] When sintering is performed, the metal layer is electrically
conductive and thermally conductive, and wettability when brazing
or adhering by an adhesive agent is performed when using the
sintered multilayered compact is ensured.
[0112] Next, the second embodiment of the present invention will be
described with reference to the Figures.
[0113] In the second embodiment, a production method of the
sintered layered compact 105A shown in FIG. 1A is different from
that of the first embodiment. That is, the green compact in the
same manner as that of the first embodiment is provided in a
sintering furnace, and is sintered at a temperature of 820.degree.
C. under a dissociated ammonia atmosphere in a mesh belt-type
furnace. As a result, the sintered layered compact 105A is
constructed in the above manner such that anhydrous borax is melted
and alumina is thereby sintered, thereby being integrally sintered
and connected. The above second embodiment can be applied to the
sintering methods for the sintered layered compacts 105B to 105E
shown in FIGS. 1B to 1E.
[0114] (C) Third Embodiment
[0115] Desirable materials and production method in which the
desirable materials are used according to the third embodiment will
be described hereinafter.
[0116] (1) Metal Powder
[0117] A metal layer having electrical conductivity and thermal
conductivity is made of a metal powder. The metal powder is
composed of one of copper, aluminum, silver, and nickel, or mixture
of at least two of copper, aluminum, silver, and nickel. For
example, the mixture is composed of copper and aluminum. These
powders have good compressibility, and these powders favorably have
predetermined grain sizes so as to pass through a 100-mesh sieve,
thereby being easily filled into a die. When a fine powder is used,
flowability can be improved by granulating. These metal powders
used in a mixed powder with an electrical insulation powder are
selected so that the mixed powder has low segregation degree and
good flowability in consideration of grain size distribution of the
electrical insulation powder, and commercial and common types used
in producing sintered alloy products can be used.
[0118] (2) Electrical Insulating Powder
[0119] A ceramic powder composed of alumina or aluminum nitride
which has good electrical insulation characteristics and thermal
conductivity characteristics can be used as a simple substance as a
powder for forming an electrical insulating layer. Since a
sintering of green compacts is performed at temperatures lower than
the melting point of included metal therein, a material which is
softened or is melted at a sintering temperature and has electrical
insulation is favorably mixed into a ceramic powder in the form of
a powder, the electrical insulating layer has high strength, and
connecting layers thereto is reliably performed. For example, this
low melting point powder is boric acid (melting point of
577.degree. C. in a state of anhydrous boric acid), anhydrous borax
(melting point of 741.degree. C. in a state of anhydrous borax), or
soda-lime glass (softening point of 500 to 700.degree. C.; melting
point of about 725.degree. C.). When the adding ratio of the low
melting point powder is about 0.1 mass % in the ceramic layer, the
strength of the ceramic layer is improved. When the adding ratio of
the low melting point powder is larger, the liquid phase of the low
melting point powder may possibly bubble to the surface of the
ceramic layer in a case of sintering the ceramic layer, whereby the
adding ratio of the low melting point powder is not more than 50
mass % in the ceramic layer. In the low melting point powder,
plural low melting point materials and high melting point materials
can be added to a ceramic layer. When the adding ratio of the low
melting point powder is about 0.1 mass % in the ceramic layer, the
strength of the ceramic layer is improved. When the adding ratio of
the low melting point powder is larger, the liquid phase of the low
melting point powder may possibly bubble to the surface of the
ceramic layer in a case of sintering the ceramic layer, whereby the
adding ratio of the low melting point powder is favorably not more
than 50 mass % in the ceramic layer.
[0120] The other low melting point material is a glass frit. The
glass frit as a glaze for enamel has a vitreous structure composed
of SiO.sub.2 as a main component, B.sub.2O.sub.3, MgO,
Al.sub.2O.sub.3, and BaO. In the present invention, other
commercial kinds of glass frit can be used. The glass frit is
melted at temperatures of about 500 to 900.degree. C., and is
selected depending on the metal powder used. When the glass frit is
added to a ceramic powder at a ratio of 0.1 mass %, the ceramic
powder is sintered by melting of the glass frit. As the ratio of
the glass frit contained increases, the content of the liquid phase
thereof increases in sintering the electrical insulating layer at
melting temperatures of the glass frit. In a case in which the
content of the liquid phase of the glass frit is extensively
generated much, the ceramic powder functions as a frame of the
layer, whereby distortion of the layer is inhibited. The electrical
insulating layer can be made of only the glass frit in a case in
which the sintering temperature is relatively low, the glass frit
having a relatively high melting point is used, or the electrical
insulating layer is formed thinly.
[0121] Since the glass frit and the mixed powder of the glass frit
and the ceramic powder are hard and have low compactibility, a
binder such as methyl cellulose (MC), polyvinyl alcohol (PVA),
ammonium alginic acid, carboxymethyl cellulose (CMC), or polyvinyl
pyrrolidone (PVP) is mixed into an electrical insulating layer,
whereby the green compact can have higher strength. As a result,
when the green compact is transferred in processes of powder
compacting and of sintering, cracks and defects can be prevented
from occurring therein. The above binder dissipates when heated in
sintering the electrical insulating layer. Since the density of the
electrical insulating layer is reduced and the thermal conductivity
thereof is deteriorated when too much of the above binder is added,
the mixing ratio of the above binder in the electrical insulating
layer is favorably not more than 1 mass %.
[0122] Since the glass frit and the ceramic powder have relatively
low flowability, the flowability can be improved by granulating so
that powder filling to a die is improved. When the above powders
have low flowability due to fine grain size thereof, the above
powders are favorably granulated by using a binder such as
carboxymethyl cellulose (CMC) so as to have a particle diameter of
about 50 to 150 .mu.m, and flowability thereof is thereby improved.
As a result, powder filling to a die is easily performed and a
green compact has high strength. As compared with a fine ceramic
powder, a coarse powder is mixed with the fine powder,
sinterability and flowability can thereby be improved.
[0123] (3) Mixed Powder of Metal Powder and Electrical Insulating
Powder
[0124] A mixed powder is formed into a functionally gradient layer.
For example, the mixed volume ratio of the electrical insulating
powder to the metal powder is 1 to 1 in the functionally gradient
layer. Alternatively, when the mixed layer is made to have plural
layers, a mixed powder including the electrical insulating powder
is substantially positioned on the electrical insulating layer, and
a mixed powder including the metal powder is substantially
positioned away from the electrical insulating layer. For example,
when the mixed layer has three layers, the mixed volume ratio of
the electrical insulating powder to the metal powder is 75 to 25 in
the layer on the side of the electrical insulating layer, is 50 to
50 in the intermediate layer, and is 25 to 75 in the layer on the
side of the metal layer.
[0125] (4) Lubricant
[0126] Since the electrical insulating powder is hard, a lubricant
such as a metal stearate is favorably added to the electrical
insulating powder by not more than about 0.5 mass %, or is coated
on an inner wall of a die so that the green compact is easily
ejected from the die. The lubricant is coated by electrostatic
coating. Alternatively, a lubricant dispersed in liquid is
used.
[0127] (5) Filling and Layering of Powders
[0128] A powder feeder can be used for filling each powder in a die
having a die for forming an outer portion of a green compact, an
upper punch and a lower punch. The powder feeder can be moved
forward or backward on a die cavity. Plural powder boxes are
connected to the powder feeder in a powder feeder moving direction.
For example, when a multilayered structure has a metal layer, a
mixed layer, an electrical insulating layer, a mixed layer, and a
metal layer, the powder feeder has three boxes. In this case, a
metal powder is filled in the front box, a mixed layer powder is
filled in the middle box, and an electrical insulating powder is
filled in the rear box. The powder feeder is moved forward in a
state in which the lower punch is flush with the upper face of the
die, so that the powder box having the metal powder is stopped on
the lower punch, and then the lower punch or the die is moved so as
to form a cavity, whereby the metal powder is filled therein. Next,
the box having the mixed layer powder is moved on the die cavity,
and then the mixed powder is filled in the same manner as that of
the metal powder. After the electrical insulating powder is filled
in the same manner as that of the metal powder, the powder feeder
is moved in turn backward, and multilayered filling of five layers
can be performed.
[0129] A powder feeder has a structure such that spaces are
provided between plural powder boxes. In this case, after one kind
of powder is filled in the cavity, in a state in which the space is
stopped on the cavity, the filled powder is dropped, the cavity is
formed, and the filled powder adhered on the wall surface of the
die cavity is scratched and dropped by using a simple punch. As a
result, a green compact having a multilayered structure which is
distinctively divided can be obtained.
[0130] Since surfaces of the filled powders have microscopic rough
portions, the powders adjacent to each other have slightly mixed
portion with each other. As a result, the compositions of the
layers are not distinctively divided from each other, and the
layers adjacent to each other are mixed so as to be connected to
each other, and each layer is difficult to peel off from the green
compact.
[0131] (6) Compacting of Powders
[0132] Compacting is performed on the metal powders of the above
metal powders as described below. That is, compacting is performed
on the copper powder, the silver powder, and the aluminum powder at
a compacting pressure of about 100 to 300 MPa, and is performed on
the nickel powder at a compacting pressure of about 400 MPa of the
above metal powders, whereby the green compacts of these metal
powders have a relative density of not less than 95% and thereby
have good electrical conductivity and good thermal conductivity. On
the other hand, when compacting is performed on the electrical
insulating powder of alumina at a compacting pressure of about 600
MPa, the green compact of the electrical insulating powder of
alumina has a relative density of about 50%. When compacting is
performed on the electrical insulating powder at a compacting
pressure of 700 MPa, the green compact of the electrical insulating
powder has a relative density of about 60%. The compacting pressure
of the multilayered powders is favorably about 700 to 1000 MPa
since the relative density of the green compact of the electrical
insulating powder gradually increases when compacting is performed
on the electrical insulating powder at a compacting pressure of
more than 700 MPa.
[0133] (7) Multilayered Structure
[0134] A multilayered structure of a thermal stress relief pad has
an electrical insulating layer which is at a middle portion in a
thickness direction and mixed layers which are formed on the both
sides of the electrical insulating layer. The electrical insulating
layer has a thickness of 0.5 to 2 mm so that thermal conductivity
and electrical insulation of the electrical insulating layer are
ensured. The mixed layer is layered such that the content of the
electrical insulating powder is large on the side of the electrical
insulating layer and the content of the metal powder is large on
the side away from the electrical insulating layer. Alternatively,
a thermal stress relief pad has a multilayered structure such that
the metal layer is provided on at least one of the outsides of the
mixed layer. One metal layer is used as an electrode which connects
thermoelectric conversion elements. When electrodes are separately
produced and thermoelectric conversion elements are assembled, the
multilayered structure may have no metal layer.
[0135] (8) Sintering
[0136] The same continuous sintering furnace as that used in
producing sintered metal products is used in sintersing.
Alternatively, microwave sintering or plasma sintering can be
performed. A typical mesh belt-type continuous furnace is favorable
since sintering can be performed efficiently. Sintering is
performed in a non-oxidizing gas or in a vacuum when the green
compacts are sintered. The non-oxidizing gas is hydrogen, or
nitrogen, argon, or a mixed gas of hydrogen and nitrogen. When the
metal powder is composed of silver, the green compact can be
sintered in air. The temperatures of sintering is about 700 to
950.degree. C. when the metal is copper, is about 500 to
600.degree. C. when the metal is aluminum, is about 700 to
950.degree. C. when the metal is silver, and is about 800 to
1150.degree. C. when the metal is nickel. The kind of enamel frit
for sintering or for melting is selected in accordance with the
above temperature range.
[0137] The lubricant and the binder are dissipated by sintering,
the metal layer, the mixed layer, and the electrical insulating
layer are sintered, and each interlayer therebetween is strongly
connected to each other. The glass frit of the electrical
insulating layer is sintered or melted, is enameled and is adhered
closely to the mixed layer. When the electrical insulating powder
of the mixed layer is only the ceramic powder, the ceramic
dispersed sintered metal composite material is formed. When only
glass frit is included in the electrical insulating powder in the
mixed layer, the glass frit is softened or melted, whereby
sintering the mixed layer can be performed more quickly.
[0138] Next, the third embodiment of the present invention will be
described hereinafter with reference to Figures. FIG. 3 is a cross
sectional diagram showing a thermal stress relief pad 301A for
thermoelectric conversion elements. The thermal stress relief pad
301A has an electrical insulating layer 302 and mixed layers 303
having plural mixed layers layered on the both sides of the
electrical insulating layer 302, metal layers 304 which are made of
only copper and are layered as an outermost layer thereof. The
mixed layer 303 has a structure such that a first mixed layer 331,
a second mixed layer 332, and a third mixed layer 333 are layered
in turn on the side of the electrical insulating layer 302. The
content volume ratio of copper is small in the first mixed layer
331, the content ratio of copper to electrical insulating material
is 1:1 in the second mixed layer 332, and the content of copper is
large in the third mixed layer 333.
[0139] The following powders are used for producing this thermal
stress relief pad 301A.
[0140] (a) copper powder (for forming the metal layer 304)
[0141] (b) mixed powder (for forming the first mixed layer 331) of
a copper powder and an alumina powder (ratio of the copper powder
to the alumina powder is 50:50, that is, the volume ratio of
alumina is about 70%)
[0142] (c) mixed powder (for forming the second mixed layer 332) of
a copper powder and an alumina powder (ratio of the copper powder
to the alumina powder is 30:70, that is, volume ratio of alumina is
about 50%)
[0143] (d) mixed powder (for forming the second mixed layer 333) of
a copper powder and an alumina powder (ratio of the copper powder
to the alumina powder is 15:85, that is, volume ratio of alumina is
about 30%)
[0144] (e) ceramic powder (for forming the electrical insulating
layer 302) composed of an electrical insulating powder of an
alumina powder and an enamel frit; the electrical insulating powder
including methyl cellulose at ratio of 0.1 mass % (weight ratio of
the alumina powder to the enamel frit powder is 1:1)
[0145] A vitreous powder composed of SiO.sub.2 and/or
B.sub.2O.sub.3 as a main component is used as an enamel frit.
SiO.sub.2 and/or B.sub.2O.sub.3 start melting at a temperature of
700.degree. C., and show a melted state in which they are wet and
spread on the copper plate when heated on the copper plate under a
dissociated ammonia gas.
[0146] Next, the above powders are filled in turn into a cavity for
a die in a layering direction, and then compacting is performed on
the multilayered powders at a compacting pressure of 700 to 1000
MPa, whereby a green compact is obtained. In this case, when the
above powders are filled into the die, a zinc stearate powder is
coated by electrostatic coating on an inner wall of the cavity, and
then the above powders are filled thereto in turn by using a
feeder. After compacting is simultaneously performed on all the
multilayered powders in the above manner, the green compact is
ejected from the die, and is then sintered. For example, the
sintering is performed on the green compact by heating at a
temperature of 800.degree. C. under a dissociated ammonia gas.
[0147] When the above processes of multilayered filling,
compacting, and sintering are performed, a sintered compact shown
in FIG. 4 is often obtained. That is, a thin copper foil portion
305 is formed in this sintered compact on a surface of a side of
the electrical insulating layer 302 (on a side of the inner wall
face of the die). The mixed layers 303 are electrically
short-circuited by the copper foil portion 305, and the electrical
insulating layer 302 does not perform an electrical insulating
function. The reason that the copper foil portion 305 is formed is
thought to be that, when multilayered filling is performed on the
above powders in the die in turn, the metal of the metal powder
containing layer, which is filled before the electrical insulating
powder is filled therein, is adhered to the inner wall face of the
die, and then the electrical insulating layer is moved thereto,
whereby the side of the electrical insulating layer 302 is covered
with the metal powder.
[0148] Therefore, the following stepwise production method is used
for maintaining the electrical insulating function of the
electrical insulating layer 302.
[0149] FIGS. 5A and 5B show raw materials 310a and 310b of the
green compact, which are referred to simply as "compressed
materials 310a and 310b". The electrical insulating powder, the
various mixed powders, and the copper powder are layered, are
filled, and are compacted, whereby the compressed material 310a is
obtained. The compressed material 310a is a green compact having
the electrical insulating layer 302 and the mixed layer 303 which
has the first mixed layer 331, the second mixed layer 332 and the
third mixed layer 333 in turn from the bottom, and the metal layer
304. Since compacting is performed in a state in which the
electrical insulating layer 302 is positioned at bottom, the side
of the electrical insulating layer 302 is not contaminated by the
mixed powders and/or the metal powders and is not adhered thereby
when the above compacting is performed, whereby forming the copper
foil portion 305 shown in FIG. 4 is prevented and the side of the
electrical insulating layer 302 is exposed. Next, the mixed layer
303 of the compressed material 310b is contacted to the side of the
electrical insulating layer 302 of the compressed material 310a,
and then sintering is performed thereon while maintaining the state
of contact thereof. As a result, contacting interfaces of the mixed
layer 303 of the compressed material 310b and the electrical
insulating layer 302 of the compressed material 310a are connected
to each other, and the thermal stress relief pad 301A shown in FIG.
6A is produced. According to this thermal stress relief pad 301A,
the electrical insulating function of the electrical insulating
layer 302 is ensured and electrical short-circuiting does not occur
since forming the copper foil portion 305 shown in FIG. 4 is
prevented on the side of the electrical insulating layer 302 of the
compressed material 310a.
[0150] The other method for securing the electrical insulating
characteristics of the electrical insulating layer 302 is as
follows. That is, as shown in FIG. 4, a surface portion P-P'which
is thicker than the copper foil portion 305 on a side of the
sintered compact is removed by cutting or by polishing. As a
result, the copper foil portion 305 causing a short-circuit is
removed, and the electrical insulating layer 302 is exposed on the
side of the thermal stress relief pad 301A.
[0151] The thermal stress relief pad 301A shown in FIGS. 3 and 5A
is one example of the present invention, and FIGS. 6B to 6G show
thermal stress relief pads 301B to 301G. FIGS. 5C and 5D show other
compressed materials 310c and 310d.
[0152] The electrical insulating powder and the various mixed
powders are filled, are layered, and are compacted, whereby the
compressed material 310c is obtained. The compressed material 310c
shown in FIG. 5C is a green compact having the electrical
insulating layer 302 and the mixed layer 303 which has the first
mixed layer 331, the second mixed layer 332, and the third mixed
layer 333 in turn from the bottom. The electrical insulating powder
and the various mixed powders are filled, are layered, and are
compacted, whereby the compressed material 310d is obtained. The
compressed material 310d shown in FIG. 5D is a green compact having
only the mixed layer 303 which has the first mixed layer 331, the
second mixed layer 332 and the third mixed layer 333 in turn from
the bottom.
[0153] Two kinds of compressed materials are appropriately selected
from the compressed materials 310a to 310d shown in FIGS. 5A to 5D,
and sintering is performed on the selected kinds of compressed
materials, whereby the thermal stress relief pads 301B to 301G
shown in FIGS. 6B to 6G can be produced. The thermal stress relief
pad 301B shown in FIG. 6B is produced such that two compressed
materials 310c are stacked so that the electrical insulating layers
302 thereof contact each other and are sintered. The thermal stress
relief pad 301C shown in FIG. 6C is produced such that compressed
materials 310a and 310c are stacked so that the electrical
insulating layers 302 thereof contact each other and are sintered.
The thermal stress relief pad 301D shown in FIG. 6D is produced
such that the electrical insulating layer 302 of the compressed
material 310c and the compressed material 310d are stacked on each
other and are sintered. The thermal stress relief pad 301E shown in
FIG. 6E is produced such that the electrical insulating layer 302
of the compressed material 310c and the mixed layer 303 of the
compressed material 310b are stacked and are sintered. The thermal
stress relief pad 301F shown in FIG. 6F is produced such that the
electrical insulating layers 302 of the compressed materials 310a
are stacked and are sintered. The thermal stress relief pad 301F
shown in FIG. 6F is produced such that the electrical insulating
layer 302 of the compressed material 310a and the compressed
material 310d are stacked and are sintered.
[0154] In the thermal stress relief pads 301B to 301G, two of the
compressed materials 310a to 310d which are compacted beforehand
are appropriately selected and sintered in the same manner as the
case of the thermal stress relief pad 301A, whereby formation of
the copper foil portion 305 which may cause a short-circuit is
prevented, and the electrical insulating function of the electrical
insulating layer 302 is secured.
[0155] A use example of the above thermal stress relief pad 301A
will be described hereinafter with reference to FIG. 7. The thermal
stress relief pads 301B to 301G can be used appropriately instead
of the thermal stress relief pad 301A.
[0156] FIG. 7 shows a cross sectional diagram of a thermoelectric
conversion module 307. The thermoelectric conversion module 307 is
constructed such that plural N-type elements and plural P-type
elements (thermoelectric elements 305) are positioned so as to
alternate with each other, the thermoelectric elements 305 are
connected to each other in series by the metal layers 304 of the
thermal stress relief pads 301A, and the both ends of the thermal
stress relief pads 301A are sandwiched by metal plates 306 having
good thermal conductivity so as to fix the members to each other.
For example, the metal plates 306 are copper plates.
[0157] The thermal stress relief pads 301A are connected to the
thermoelectric conversion elements 305 by using solder or a
graphite coating so that electrical conductivity and thermal
conductivity therebetween are ensured, and are connected to the
copper plates 306 by using solder or a graphite coating, water
glass, or high melting point glass, so that thermal conductivity
therebetween is ensured. Alternatively, instead of using the above
adhesive agents, a bolt and a nut for fastening two copper plates
306 hold such that the members thereof are layered and contacted to
each other in the thermoelectric conversion module 307. In this
thermoelectric conversion module 307, electricity is generated from
a terminal mounted on the end of the thermoelectric element 305 by
heating one side thereof and cooling the other side thereof. This
thermoelectric conversion module 307 is mounted and used in a state
of being disposed between a heat discharging portion of a furnace
and a cooling device such as a water jacket.
[0158] When the thermoelectric conversion module 307 is used, the
metal layer 304 contacting the thermoelectric conversion element
305 of the thermal stress relief pad 301A is an electrode member
and a heat conducting member. The electrical insulating layer 302
prevents electrical leakage to the sides of the copper plates 306.
The thermal expansion coefficient of the mixed layer 303 is
different from that of the metal layer 304 or the copper plates
306. As a result, thermal stress, which is caused by thermal
expansion difference between the high temperature side and the low
temperature side and by heat cycling, can be relieved and
generation performance and reliability of the thermoelectric
conversion module 307 is improved.
[0159] (D) Fourth Embodiment
[0160] Desirable materials and production method in which the
desirable materials are used according to the fourth embodiment
will be described hereinafter. In the fourth embodiment,
description of the same materials and structures as that of the
third embodiment are omitted.
[0161] (1) Metal Powder
[0162] The same metal powder as that of the third embodiment is
used. The same powder, which is mixed into an electrical insulating
material powder as that of the third embodiment, is used. The
electrical insulating material powder is composed of the following
ceramics powder and the following glass frit, and is used instead
of the electrical insulating powder, which is composed of the
ceramics and the low melting point material such as boric acid or
is composed of the ceramics and the glass frit, of the third
embodiment.
[0163] (2) Ceramic Powder
[0164] A ceramic powder is composed of alumina or aluminum nitride,
which has good electrical insulation and good thermal conductivity.
In this case, in particular, alumina has better powder compression
compactibility than that of aluminum nitride, and has a lower
melting point than that of aluminum nitride, thereby being
favorably used. The ceramic powder is used as a mixed powder with a
metal powder or as described below glass frit. When the ceramic
powder is added to the mixed powder, the ceramic powder favorably
has a grain size approximate to that of the metal powder so that
the ceramic powder is equally dispersed in the metal powder and the
metal powder is sintered.
[0165] (3) Glass Frit
[0166] The glass frit has a vitreous structure composed of
SiO.sub.2, B.sub.2O.sub.3, P.sub.2O.sub.5, Al.sub.2O.sub.3, or ZnO
as a main component, and includes MgO, TiO.sub.2, BiO.sub.2, or CaO
if necessary. The glass frit does not have electrical conductivity.
For example, the glass frit may be an oxide glass which is widely
used as a glass in practice, special glass such as an oxidized
glass in which a part of oxygen is substituted by nitrogen, glaze
used for enamel, cloisonn and ceramic, solder glass used for
sealing or adhering, or binder for a baking finish. Various kinds
of the above glass frits are sold commercially. For example, a
glass frit for a porcelain covering is disclosed in Japanese
Unexamined Patent Application Publication No. 61-297, and glass
frits for enamel substrates are disclosed in Japanese Unexamined
Patent Application Publication No. 3-63162, in Japanese Unexamined
Patent Application Publication No. 58-104042, in Japanese
Unexamined Patent Application Publication No. 3-73158, in Japanese
Unexamined Patent Application Publication No. 6-56923 and in
Japanese Unexamined Patent Application Publication No. 7-30463 in
which component of enamel is disclosed.
[0167] The glass frits have softening points of not less than about
350.degree. C. In consideration of viscosity of the glass frit when
softened and melted, wettability of the glass frit with metal and
thickness of the electrical insulating layer, the kind of the glass
frit is selected from glass frits having softening points of about
500 to 900.degree. C., and whether or not only glass frit is used
and whether a ceramic is mixed into the glass frit are determined
depending on sintering temperature of the metal for thermal stress
relief pads. Borate glass or glaze for enamel is favorably used
from a standpoint of adhesiveness thereof with metal.
[0168] (4) Powder for Forming Electrical Layer
[0169] A glass frit as a simple substance or a mixture of a ceramic
powder and a glass frit is used as a powder for forming the
electrical insulating layer. When the glass frit as a simple
substance is used, the electrical insulating layer is sintered at a
temperature at which the glass frit is melted and flowed freely,
whereby the glass frit is flowed out of the outer portion of the
multilayered compact so that the electrical insulating layer is
made much thinner. In this case, since there may be a case in which
the electrical insulating layer breaks, the sintering temperature
thereof is not more than the softening point thereof. When the
electrical insulating layer is sintered at a temperature in which
the glass frit is melted, the glass frit is favorably mixed with a
ceramic powder such as an alumina powder or aluminum nitride. As a
result, the ceramic powder functions as a frame of the electrical
insulating layer so as to maintain the melted glass frit, the
electrical insulating layer is sintered, and the electrical
insulating layer and the layers adjacent thereto are connected
reliably. When the glass frit is added to the ceramic powder at a
ratio of 0.1 mass %, the green compact of the ceramic powder is
sintered in a state in which the glass frit is in a liquid phase.
When the included ratio of the glass frit is larger, the liquid
phase of the glass frit increases by sintering, the electrical
insulating layer is sintered well and is strongly adhered to the
composite layers adjacent thereto.
[0170] (5) Binder for Forming Electrical Insulating Layer and
Granulating Thereof
[0171] Since the glass frit and the mixed powder of the glass frit
and the ceramic powder are hard and are relatively fine, these
materials have low strength in the green compact, and care in
handling is needed. Therefore, the same binder as that of the third
embodiment is used, and the same method of granulation as that of
the third embodiment is used so that the green compact has high
strength.
[0172] (6) Mixed Powder of Metal Powder and Electrical Insulating
Powder
[0173] A mixed powder is formed as an graded function layer. The
mixed powder is a mixed powder of the metal powder and the ceramic
powder, a mixed powder of the metal powder and the glass frit, or a
mixed powder of the metal powder, the ceramic powder and the glass
frit. For example, the mixed volume ratio of the metal powder to
the electrical insulating powder is 1 to 1 in the mixed layer.
Alternatively, when the mixed layer is made to have plural layers,
a mixed powder including the electrical insulating material powder
is substantially positioned on the electrical insulating layer, and
a mixed powder including the metal powder is substantially
positioned away from the electrical insulating layer. For example,
when the mixed layer has three layers, the mixed volume ratio of
the electrical insulating material powder to the metal powder is 75
to 25 in the layer on the side of the electrical insulating layer,
is 50 to 50 in the intermediate layer, and is 25 to 75 in the layer
on the side of the metal layer.
[0174] (7) Lubricant
[0175] Since the electrical insulating material powder is hard, a
lubricant such as a metal stearate is favorably coated on an inner
wall of a die so that the green compact is easily ejected from the
die. The lubricant is coated by electrostatic coating.
Alternatively, the lubricant dispersed in a liquid is used.
[0176] (8) Filling and Layering of Powders
[0177] The same filling and layering of powders as those of the
third embodiment are used other than using the electrical
insulating material powder instead of the electrical insulating
powder of the third embodiment.
[0178] (9) Compacting of Powders
[0179] The same compacting of powders as those of the third
embodiment are used.
[0180] (10) Multilayered Structure
[0181] The multilayered structure is shown in (a) to (f). The mixed
powder of the metal powder and the electrical insulating material
powder includes a powder having one kind of component or more kinds
thereof.
[0182] (a) mixed layer
[0183] (b) metal layer-mixed layer
[0184] (c) mixed layer-electrical insulating layer
[0185] (d) metal layer-mixed layer-electrical insulating layer
[0186] (e) mixed layer-electrical insulating layer-mixed layer
[0187] (f) metal layer-mixed layer-electrical insulating
layer-mixed layer-metal layer
[0188] A thermal stress relief pad is produced by appropriately
using the structures shown in (a) to (f). For example, a thermal
stress relief pad is produced such that an electrical insulating
material powder is coated on surfaces of mixed layers of two green
compacts and the green compacts are sintered and connected in a
state in which the electrical insulating layer is disposed
therebetween. In this case, the structure shown in (a) or (b) is
used as the green compact. For example, a thermal stress relief pad
is produced such that two green compacts, which have half thickness
including the electrical insulating material powder, are sintered
and connected in a state in which the electrical insulating layer
is disposed therebetween. In this case, the structure shown in (c)
or (d) is used as the green compact. The structures shown in (a) or
(b) can be used as one of the above green compacts. A thermal
stress relief pad can be produced by sintering in a state of green
compact having the structure shown in (e) or (f).
[0189] (11) Coating of Electrical Insulating Material Powder on
Green Compact of powders
[0190] Coating an electrical insulating material powder to the
green compact of only the mixed powder shown in the above (a) or on
the green compact of the metal layer and the mixed layer shown in
the above (b) can be performed in a state of a powder or slurry
thereof. A method in which the electrical insulating material
powder is dropped from a sieve to the side of the mixed layer of
the green compact which is mounted at top and then the other green
compact is mounted thereon so that the electrical insulating
material powder is disposed therebetween is used. Alternatively, a
method in which pasted liquid of the above CMC or the above PVA is
coated on the mixed layer of the green compact and then the other
green compact is mounted thereon so that the electrical insulating
material powder is disposed therebetween is used. The slurry of the
electrical insulating material powder is commercial enamel liquid
(glaze slurry), organic solvent such as mineral oil, liquid
paraffin, alcohol, or acetone, or mixed dispersed liquid of PVA or
CMC.
[0191] (12) Sintering
[0192] The same sintering as that of the third embodiment is
used.
[0193] Next, the fourth embodiment of the present invention will be
described with reference to the Figures.
[0194] FIGS. 8A to 8C are cross sectional diagrams showing thermal
stress relief pads 401A to 401C for thermoelectric conversion
elements. In the thermal stress relief pads 401A to 401C, the metal
is copper, and the ceramic is alumina and/or enamel frit.
[0195] The thermal stress relief pad 401A shown in FIG. 8A has an
electrical insulating layer 402 at a center portion in a thickness
direction, and mixed layers 403 having plural mixed layers on both
sides of the electrical insulating layer 402. The mixed layer 403
has a structure such that a first mixed layer 431, a second mixed
layer 432, and a third mixed layer 433 are layered in turn on the
side of the electrical insulating layer 402. The content ratio of
copper is small in the first mixed layer 431, the volume content
volume ratio of copper to electrical insulating material is 1:1 in
the second mixed layer 432, and the content of copper is large in
the third mixed layer 433. The thermal stress relief pad 401B shown
in FIG. 8B has a structure such that metal layers 404 made only of
copper are layered on both surfaces of thermal stress relief pad
401A shown in FIG. 8A. The thermal stress relief pad 401C shown in
FIG. 8C has a structure such that a metal layer 404 made only of
copper is layered on one of the surfaces of the thermal stress
relief pad 401A shown in FIG. 8A. In FIG. 8C, the metal layer 404
made only of copper is layered on the bottom surface of thermal
stress relief pad 401A shown in FIG. 8A.
[0196] The powders used for producing the above thermal stress
relief pads 401A to 401C are the same as those of the third
embodiment.
[0197] For example, three method, as shown in FIGS. 9A to 9C, are
used as a compacting of powders. In all cases, a zinc stearate
powder is coated by electrostatic coating on an inner wall of the
cavity, the above powders are filled thereto in turn by using a
feeder, and then are compacted at a pressure of 700 MPa. These
methods can be used for compacting the thermal stress relief pads
401A and 401C shown in FIGS. 8A and 8C instead of the thermal
stress relief pad 401B shown in FIG. 8B.
[0198] FIG. 9A shows a method in which, when compacting is
performed on powders, all used powders are filled and layered so
that the powders are simultaneously and integrally compacted, and
then are sintered. FIG. 9B shows a method in which, when compacting
is performed on powders, two green compacts having the electrical
insulating layer 402, the mixed layer 403 and the metal layer 404
are obtained and then sintered in a state in which the electrical
insulating layers 402 are contacted to each other. In this case,
one of the green compacts may not have the electrical insulating
layer 402. FIG. 9C shows a method in which, after two green
compacts having the mixed layer 403 and the metal layer 404 are
obtained, the electrical insulating layer 402 is formed by coating
the electrical insulating material powder on the surface of the
mixed layer 403 of one green compact, the other green compact is
mounted on the electrical insulating layer 402 of one green
compact, and then they sintered.
[0199] The above thermal stress relief pads 401A to 401C can be
applied to the thermoelectric conversion module 307 in the same
manner as thermal stress relief pads 301A to 301E of the third
embodiment.
[0200] When the thermal stress relief pads 401A and 401C are used,
the thermoelectric conversion elements 305 are connected by a
conductive member corresponding to the metal layer 404, and the
surface of the mixed layer 403 is contacted to the conductive
member.
* * * * *