U.S. patent application number 10/548723 was filed with the patent office on 2006-07-20 for method for producing a composite material.
This patent application is currently assigned to Plansee Aktiengesellschaft. Invention is credited to Gerhard Leichtfried, Arndt Ludtke.
Application Number | 20060157884 10/548723 |
Document ID | / |
Family ID | 32967982 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157884 |
Kind Code |
A1 |
Ludtke; Arndt ; et
al. |
July 20, 2006 |
Method for producing a composite material
Abstract
The invention relates to a process for producing a
diamond-containing composite material. Diamond grains having a mean
particle size of from 5 to 300 .mu.m are infiltrated under
atmospheric pressure or with the aid of pressure with a eutectic or
near-eutectic alloy which has a solidus temperature of
<900.degree. C. and comprises at least one element or an alloy
from the group consisting of Cu, Ag, Au and at least one element
from the group consisting of Si, Y, Sc, rare earth metals or
densified by hot pressing. The components produced in this way have
a high thermal conductivity and low thermal expansion and are
particularly useful as heat sinks for semiconductor components.
Inventors: |
Ludtke; Arndt; (Reutte,
AT) ; Leichtfried; Gerhard; (Reutte, AT) |
Correspondence
Address: |
LERNER GREENBERG STEMER LLP
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Plansee Aktiengesellschaft
|
Family ID: |
32967982 |
Appl. No.: |
10/548723 |
Filed: |
January 20, 2004 |
PCT Filed: |
January 20, 2004 |
PCT NO: |
PCT/AT04/00017 |
371 Date: |
October 3, 2005 |
Current U.S.
Class: |
264/122 ;
257/E23.11; 257/E23.111; 264/128; 423/446 |
Current CPC
Class: |
C04B 2235/9607 20130101;
C04B 2235/3279 20130101; H01L 2924/0002 20130101; C04B 35/528
20130101; C04B 2235/80 20130101; H01L 23/3732 20130101; C04B
2235/422 20130101; C04B 35/634 20130101; C22C 1/1036 20130101; C04B
2235/3826 20130101; C04B 35/653 20130101; C04B 2235/402 20130101;
C04B 2235/608 20130101; C22C 26/00 20130101; C04B 2235/40 20130101;
H01L 23/373 20130101; C04B 2235/604 20130101; C04B 2235/428
20130101; C22C 21/02 20130101; H01L 2924/0002 20130101; C04B
2235/407 20130101; H01L 2924/00 20130101; C04B 2235/408 20130101;
C04B 2235/427 20130101 |
Class at
Publication: |
264/122 ;
264/128; 423/446 |
International
Class: |
D04H 1/00 20060101
D04H001/00; D04H 1/64 20060101 D04H001/64; B01J 3/06 20060101
B01J003/06; B29C 59/00 20060101 B29C059/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2003 |
AT |
GM 164/2003 |
Claims
1-21. (canceled)
22. A method of producing a diamond-containing composite material,
which comprises the following steps: shaping, in a pressureless or
pressure-aided shaping process, an intermediate product containing
diamond grains having a mean particle size of from 5 to 300 .mu.m
and, optionally, metallic components of high thermal conductivity
and/or binder, and setting a proportion of diamond after shaping
from 40 to 90%, based on a total volume of the intermediate
product; heating, in a pressureless or pressure-aided heating
process, the intermediate product and a eutectic or near-eutectic
infiltrate alloy having a solidus temperature of <900.degree. C.
and containing at least a metallic component of high thermal
conductivity with an element or an alloy from the group consisting
of Cu, Ag, Au and at least one element from the group consisting of
Si, Y, Sc, rare earth metals, and optionally <3 atom % of one or
more elements from the group consisting of Ni, Cr, Ti, V, Mo, W,
Nb, Ta, Co, Fe that promote wetting, wherein near-eutectic alloys
encompass compositions having a liquidus temperature of
<950.degree. C., to a temperature above a liquidus temperature
of the infiltrate alloy but below 1000.degree. C., causing an
infiltration of the intermediate product by the infiltrate alloy
and a filling of pores of the intermediate product to an extent of
at least 97%.
23. The method according to claim 22, wherein the eutectic or
near-eutectic infiltrate alloy is a two-component alloy comprising
a first component selected from the group consisting of Cu, Ag, and
Au and a second component selected from the group consisting of Si,
Y, Sc, and a rare earth metal.
24. The method according to claim 23, wherein the infiltrate alloy
comprises the components Ag and Y.
25. The method according to claim 23, wherein the infiltrate alloy
comprises the components Ag and Si.
26. The method according to claim 23, wherein the infiltrate alloy
comprises the components Au and Si.
27. The method according to claim 23, wherein the infiltrate alloy
comprises the components Cu and Y.
28. The method according to claim 23, wherein the infiltrate alloy
comprises the components Cu and one or more elements of the rare
earth metals.
29. The method according to claim 22, wherein the eutectic or
near-eutectic infiltrate alloy is a multicomponent alloy having a
solidus temperature of <800.degree. C.
30. The method according to claim 22, wherein the eutectic or
near-eutectic infiltrate alloy is a multicomponent alloy having a
solidus temperature of <700.degree. C.
31. The method according to claims 22, wherein the infiltrate alloy
is a eutectic alloy.
32. The method according to claim 22, wherein the intermediate
product comprises a binder based on polymer or wax.
33. The method according to claim 32, which comprises setting a
proportion of binder from 1 to 20% by weight.
34. The method according to claim 32, which comprises, subsequent
to shaping the intermediate product, heating the intermediate
product to a temperature from 300.degree. C. to 900.degree. C. in a
protective gas atmosphere to at least partially pyrolyze the
binder.
35. The method according to claim 22, which comprises carrying out
the infiltration at an elevated pressure p between 5 MPa and 200
MPa.
36. The method according to claim 35, which comprises carrying out
the infiltration in a squeeze casting process.
37. The method according to claim 22, which comprises subjecting
the infiltrated or hot-pressed intermediate product to a heat
treatment step at a temperature in a range of 300.degree.
C.<T<900.degree. C., forming phases corresponding to
equilibrium.
38. The method according to claim 22, which comprises forming the
composite material with 40 to 90% by volume of diamond having a
mean particle size of from 5 to 300 .mu.m, from 0.005 to 12% by
volume of a silicon-carbon compound, from 7 to 49% by volume of an
Ag-rich or Au-rich phase, and less than 5% by volume of a further
phase, wherein a volume ratio of the Ag-rich or Au-rich phase to
the silicon-carbon compound is greater than 4, and at least 60% of
a surface of the diamond grains is covered by the silicon-carbon
compound.
39. The method according to claim 38, wherein the silicon-carbon
compound is SiC.
40. The method according to claim 22, which comprises forming the
composite material with 40 to 90% by volume of diamond having a
mean particle size of from 5 to 300 .mu.m, from 0.001 to 5% by
volume of a Y-carbon compound or rare earth metal-carbon compound,
from 7 to 49% by volume of an Ag-rich, Au-rich, or Cu-rich phase,
and less than 5% by volume of a further phase, wherein a volume
ratio of the Ag-rich, Au-rich, or Cu-rich phase to the Y-carbon
compound or rare earth metal-carbon compound is greater than 4, and
at least 60% of a surface of the diamond grains are covered by the
Y-carbon compound or rare earth metal-carbon compound.
41. The method according to claim 22, which further comprises
forming the composite material as a heat sink.
42. A method of producing a diamond-containing composite material,
which comprises the following steps: mixing or milling an
intermediate product containing from 40 to 90% by volume of diamond
grains having a mean particle size from 5 to 300 .mu.m and from 10
to 60% by volume of a eutectic or near-eutectic infiltrate alloy
having a solidus temperature of <900.degree. C. and comprising
at least a metallic component with high thermal conductivity and
including an element or an alloy from the group consisting of Cu,
Ag, Au and at least one element from the group consisting of Si, Y,
Sc, rare earth metals, and optionally <3 atom % of one or more
elements from the group consisting of Ni, Cr, Ti, V, Mo, W, Nb, Ta,
Co, Fe that promote wetting, wherein the near-eutectic infiltrate
alloy encompasses compositions having a liquidus temperature of
<950.degree. C.; filling a die of a hot press with the
intermediate product, heating to a temperature T between
500.degree. C. and 1000.degree. C., and hot-pressing the
intermediate product.
43. The method according to claim 42, wherein the eutectic or
near-eutectic infiltrate alloy is a two-component alloy comprising
a first component selected from the group consisting of Cu, Ag, and
Au and a second component selected from the group consisting of Si,
Y, Sc, and a rare earth metal.
44. The method according to claim 43, wherein the infiltrate alloy
comprises the components Ag and Y.
45. The method according to claim 43, wherein the infiltrate alloy
comprises the components Ag and Si.
46. The method according to claim 43, wherein the infiltrate alloy
comprises the components Au and Si.
47. The method according to claim 43, wherein the infiltrate alloy
comprises the components Cu and Y.
48. The method according to claim 43, wherein the infiltrate alloy
comprises the components Cu and one or more elements of the rare
earth metals.
49. The method according to claim 42, wherein the eutectic or
near-eutectic infiltrate alloy is a multicomponent alloy having a
solidus temperature of <800.degree. C.
50. The method according to claim 42, wherein the eutectic or
near-eutectic infiltrate alloy is a multicomponent alloy having a
solidus temperature of <700.degree. C.
51. The method according to claims 42, wherein the infiltrate alloy
is a eutectic alloy.
52. The method according to claim 42, wherein the intermediate
product comprises a binder based on polymer or wax.
53. The method according to claim 52, which comprises setting a
proportion of binder from 1 to 20% by weight.
54. The method according to claim 52, which comprises, subsequent
to shaping the intermediate product, heating the intermediate
product to a temperature from 300.degree. C. to 900.degree. C. in a
protective gas atmosphere to at least partially pyrolyze the
binder.
55. The method according to claim 42, which comprises carrying out
the infiltration at an elevated pressure p between 5 MPa and 200
MPa.
56. The method according to claim 55, which comprises carrying out
the infiltration in a squeeze casting process.
57. The method according to claim 42, which comprises subjecting
the infiltrated or hot-pressed intermediate product to a heat
treatment step at a temperature in a range of 300.degree.
C.<T<900.degree. C., forming phases corresponding to
equilibrium.
58. The method according to claim 42, which comprises forming the
composite material with 40 to 90% by volume of diamond having a
mean particle size of from 5 to 300 .mu.m, from 0.005 to 12% by
volume of a silicon-carbon compound, from 7 to 49% by volume of an
Ag-rich or Au-rich phase, and less than 5% by volume of a further
phase, wherein a volume ratio of the Ag-rich or Au-rich phase to
the silicon-carbon compound is greater than 4, and at least 60% of
a surface of the diamond grains is covered by the silicon-carbon
compound.
59. The method according to claim 58, wherein the silicon-carbon
compound is SiC.
60. The method according to claim 42, which comprises forming the
composite material with 40 to 90% by volume of diamond having a
mean particle size of from 5 to 300 .mu.m, from 0.001 to 5% by
volume of a Y-carbon compound or rare earth metal-carbon compound,
from 7 to 49% by volume of an Ag-rich, Au-rich, or Cu-rich phase,
and less than 5% by volume of a further phase, wherein a volume
ratio of the Ag-rich, Au-rich, or Cu-rich phase to the Y-carbon
compound or rare earth metal-carbon compound is greater than 4, and
at least 60% of a surface of the diamond grains are covered by the
Y-carbon compound or rare earth metal-carbon compound.
61. The method according to claim 42, which further comprises
forming the composite material as a heat sink.
Description
[0001] The invention relates to a process for producing a
diamond-containing composite material.
[0002] Diamond-containing composite materials have been used for a
long time as cutting tool materials. In addition, owing to the high
thermal conductivity and low thermal expansion of diamond, they are
also potentially interesting materials for heat sinks. Thus, the
thermal conductivity of diamond is from 1000 to 2000 W/(m.K), with
the content of nitrogen and boron atoms on lattice sites being of
special importance for determining the quality.
[0003] Heat sinks are widely used in the production of electronic
components. Apart from the heat sink, semiconductor components and
a mechanically stable encapsulation are the essential constituents
of an electronic package. The terms substrate, heat spreader or
support plate are frequently also used for the heat sink. The
semiconductor component comprises, for example, single-crystal
silicon or gallium arsenide. This is connected to the heat sink,
usually using soldering methods as joining technique. The heat sink
has the function of conducting away heat produced during operation
of the semiconductor component. Semiconductor components which
produce a particularly large quantity of heat are, for example,
LDMOS (laterally diffused metal oxide semiconductor), laser diodes,
CPU (central processing unit), MPU (microprocessor unit) or HFAD
(high frequency amplify device).
[0004] The geometric configurations of the heat sink are specific
to the application and may vary widely. Simple forms are flat
plates. However, substrates having a complex configuration with
recesses and steps are also used. The heat sink itself is in turn
joined to a mechanically stable encapsulation. The coefficients of
thermal expansion of the semiconductor materials used are low
compared to other materials and are reported in the literature as
from 2.1.times.10.sup.-6 K.sup.-1 to 4.1.times.10.sup.-6 K.sup.-1
for silicon and from 5.6.times.10.sup.-6 K.sup.-1 to
5.8.times.10.sup.-6 K.sup.-1 for gallium arsenide.
[0005] Other semiconductor materials which are not yet widely used
in industry, e.g. Ge, In, Ga, As, P or silicon carbide, also have
similarly low coefficients of expansion. Ceramic materials,
material composites or plastics are usually used for the
encapsulation. Examples of ceramic materials are Al.sub.2O.sub.3
with a coefficient of expansion of 6.5.times.10.sup.-6 K.sup.-1 or
aluminum nitride having a coefficient of expansion of
4.5.times.10.sup.-6 K-.sup.-1.
[0006] If the expansion behavior of the participating components is
different, stresses are incorporated in the composite, and these
lead to distortion, to detachment of material or to fracture of the
components. Stresses can arise during manufacture of the package,
specifically during the cooling phase from the soldering
temperature to room temperature. However, temperature fluctuations
also occur during operation of the package, and these can extend,
for example, from -50.degree. C. to 200.degree. C. and lead to
thermal mechanical stresses in the package.
[0007] In recent years, the process speed and degree of integration
of semiconductor components have increased greatly, which has also
led to an increase in the evolution of heat in the package.
[0008] These factors determine the requirements for
diamond-containing composite materials for heat sinks. Firstly,
these should have a very high thermal conductivity in order to keep
the temperature rise of the semiconductor component during
operation as low as possible. Secondly, it is necessary for the
coefficient of thermal expansion to be matched as well as possible
to that of the semiconductor component and also that of the
encapsulation.
[0009] EP 0 521 405 describes a heat sink which has a
polycrystalline diamond layer on the side facing the semiconductor
chip. The absence of plastic deformability of the diamond layer can
lead to cracks in the diamond layer even during cooling from the
coating temperature.
[0010] U.S. Pat. No. 5,273,790 describes a diamond composite
material having a thermal conductivity of >1700 W/(m.K) in the
case of which loose diamond particles brought to shape are
converted into a stable shaped body by means of subsequent diamond
deposition from the gas phase. The diamond composite produced in
this way is too expensive for commercial use in mass-produced
parts.
[0011] WO 99/12866 describes a process for producing a
diamond-silicon carbide composite material. It is produced by
infiltration of a diamond skeleton with silicon or a silicon alloy.
Owing to the high melting point of silicon and the resulting high
infiltration temperature, diamond is partly converted into carbon
or subsequently into silicon carbide. Owing to the high
brittleness, the mechanical forming of this material is highly
problematical and costly, so that this composite material has
hitherto not yet been used for heat sinks.
[0012] U.S. Pat. No. 4,902,652 describes a process for producing a
sintered diamond material. An element from the group of transition
metals of groups 4a, 5a and 6a, boron and silicon are deposited
onto diamond powder by means of physical coating methods in this
process. The coated diamond grains are subsequently joined to one
another by means of a solid-state sintering process. Disadvantages
are that the product formed has a high porosity and a coefficient
of thermal expansion which is too low for many applications.
[0013] U.S. Pat. No. 5,045,972 describes a composite material in
which diamond grains having a size of from 1 to 50 .mu.m and also a
metallic matrix comprising aluminum, magnesium, copper, silver or
an alloy thereof are present. A disadvantage is that the metallic
matrix is bound only unsatisfactorily to the diamond grains, so
that, as a result, the thermal conductivity and mechanical
integrity are not sufficient.
[0014] The use of finer diamond powder, for example diamond powder
having a particle size of <3 .mu.m, as is described in U.S. Pat.
No. 5,008,737, also does not improve diamond/metal adhesion.
[0015] U.S. Pat. No. 5,783,316 describes a process in which diamond
grains are coated with W, Zr, Re, Cr or titanium, the coated grains
are subsequently compacted and the porous body is infiltrated, for
example, with Cu, Ag or Cu--Ag melts. The high coating costs limit
the uses of composite materials produced in this way.
[0016] EP 0 859 408 describes a material for heat sinks whose
matrix is made up of diamond grains and metal carbides, with the
interstices of the matrix being filled by a metal. As metal
carbides, mention is made of the carbides of metals of groups 4a to
6a of the Periodic Table. TiC, ZrC and HfC are particularly
emphasized in EP 0 859 408. Ag, Cu, Au and Al are said to be
particularly advantageous filler metals. A disadvantage is that the
metal carbides have a low thermal conductivity, which in the case
of TiC, ZrC, HfC, VC, NbC and TaC is in range from 10 to 65
W/(m.K). A further disadvantage is that the metals of groups 4a to
6a of the Periodic Table have a degree of solubility in the filler
metal, for example silver, as a result of which the thermal
conductivity of the metal phase is greatly reduced.
[0017] EP 0 893 310 describes a heat sink comprising diamond
grains, a metal or a metal alloy having a high thermal conductivity
from the group consisting of Cu, Ag, Au, Al, Mg and Zn and a metal
carbide of the metals of groups 4a, 5a and Cr, with the metal
carbides covering at least 25% of the surface of the diamond
grains. EP 0 898 310 also describes techniques, for example an
infiltration process, for producing a heat sink. Alloys comprising
a metal having a high thermal conductivity and a carbide-forming
metal from the group of the elements of groups 5a, 6a and Cr are
used for this purpose. However, two-component alloys of these
components require infiltration temperatures of above 1000.degree.
C., as a result of which unacceptably high decomposition of diamond
into graphite occurs. The examples of EP 0 898 310 therefore
describe three-component alloys consisting of Cu--Ag--Ti. Even when
Ti reacts completely with diamond to form TiC, the metallic region
surrounding the diamond or carbide regions consists of an Ag--Cu
alloy and therefore has a significantly lower thermal conductivity
than pure Ag. In addition, in the three-component system Ag--Cu--Ti
or in systems in which Ti has been replaced by Zr, Hf, Mo, W, V or
Cr, the solidus or liquidus temperature is increased compared to
the eutectic temperature of an Ag--Cu alloy. Thus, the liquidus
temperature of a eutectic Ag--Cu alloy (Ag-30% by weight of Cu) is
780.degree. C., while the Cu--Ag--Ti alloys mentioned in EP 0 898
310 have a liquidus temperature of from 830 to 870.degree. C.
[0018] It is therefore an object of the present invention to
provide a process which makes it possible to produce
diamond-containing composite materials having a high thermal
conductivity and a low coefficient of expansion in an inexpensive,
reliable manner.
[0019] This object is achieved by a process as claimed in claim 1
or claim 2 of the present invention.
[0020] The process of the invention comprises a shaping step
carried out under atmospheric pressure or with the aid of pressure
to produce an intermediate. The intermediate comprises diamond
powder having a mean particle size of the diamond grains of from 5
to 300 .mu.m. A preferred particle size range is from 60 to 250
.mu.m. Fine diamond grains and thus a large interfacial area to
adjoining neighboring phases reduce the thermal conductivity.
Pressureless processes are, for example, pouring processes,
vibratory introduction processes or slip casting. Pressure-aided
techniques are, for example, die pressing, isostatic pressing and
powder injection molding. Depending on the technique chosen, the
proportion of diamond after the shaping process is from 40 to 90%,
based on the total volume. The remainder comprises pores and/or
binder and/or metallic components having a high thermal
conductivity. An incorporated binder makes it possible to increase
the density of the green body or reduces the die friction. Diamond
powder and binder are for this purpose mixed in customary mixers or
mills. Suitable binders are, for example, those based on polymer or
wax. Advantageous proportions of binder are in the range from 1 to
20% by weight. It is advantageous to remove at least part of the
binder by means of a chemical or thermal process prior to the
infiltration step. In the case of a thermal process, it can be
advantageous to carry out the process so that residues of pyrolized
carbon remain on the diamond surface and react with part of the
infiltrate to form a carbide. Thermal binder removal can also be
integrated into the infiltration process. Metallic components
having a high thermal conductivity which may be mentioned are Cu,
Al, Au and alloys thereof.
[0021] The infiltration process can be carried out under
atmospheric pressure or with the aid of pressure. The latter is
usually referred to as squeeze casting. The infiltrate alloy has a
eutectic or near-eutectic composition. Near-eutectic alloys
encompass compositions which have a liquidus temperature below
950.degree. C. The infiltrate alloy comprises at least one metallic
component having a high thermal conductivity and comprising an
element or an alloy from the group consisting of Cu, Ag, Au and at
least one element from the group consisting of Si, Y, Sc, rare
earth metals. It has been found that the use of infiltrate alloys
according to the invention leads to very good wetting of the
diamond grains and to a high interface strength between the diamond
grains and the surrounding phases. In addition, the infiltrate
alloys according to the invention have the advantage that their
solidus temperatures are significantly below those of Cu, Au or Ag
alloys with the metals of groups 4a/5a of the Periodic Table or Cr,
as can be seen from Table 1. This makes it possible to use
two-component alloys instead of multicomponent alloys, which has a
favorable effect on the thermal conductivity. The solidus
temperatures of the infiltrate alloys according to the invention
are below 870.degree. C. This ensures that unacceptably high
reaction of the diamond does not occur during the infiltration
process. TABLE-US-00001 TABLE 1 Con- centration Boundary Solubility
at Solubility Eutectic at the system eutectic at tem- eutectic
Cu--, Au-- temperature 400.degree. C. perature point System or
Ag-rich [atom %] [atom %] [.degree. C.] [atom %] Cu--Ti peritect.
-- 0.8 -- -- Cu--Zr eutect. 0.12 <0.1 972 8.6 Cu--Hf eutect. 0.4
<0.1 988 7.75 Cu--Mo eutect. <0.1 <0.1 1083 <0.5 Cu--W
eutect. <0.1 <0.1 1084 <0.5 Cu--Cr eutect. ca. 1 <0.1
1077 ca.2 Cu--V peritect. -- <0.1 -- -- Cu--Nb eutect. <0.1
<0.1 1080 <0.5 Cu--Ta eutect. <0.1 <0.1 1083 <0.5
Cu--Y eutect. <0.4 <0.1 860 9.3 Cu--La eutect. 0 0 865 9
Cu--Nd eutect. 0 0 865 9 Cu--Pr eutect. 0 0 870 7.5 Cu--Si
peritect. -- 9 -- -- Ag--Ti peritect. -- 1.5 -- -- Ag--Zr eutect.
<0.1 <0.1 940 2.5 Ag--Mo eutect. <0.1 <0.1 959 <0.5
Ag--Cr eutect. <0.1 <0.1 961 <0.5 Ag--V eutect. <0.1
<0.1 961 <0.5 Ag--Y eutect. 1.31 <0.5 799 11.5 Ag--La
eutect. 0.05 <0.1 792 10 Ag--Nd eutect. 0.2 <0.1 806 10.5
Ag--Pr eutect. 0.05 <0.01 802 9.2 Ag--Si eutect. 0 0 835 11
Ag--Ti peritect. -- 1.5 -- -- Au--Hf peritect. -- 5 -- -- Au--Mo
eutect. 1.25 ca. 1 1054 2.1 Au--W eutect. <0.1 <0.1 1063
<0.5 Au--Cr peritect. -- 25 -- -- Au--V peritect. -- 15 -- --
Au--Nb peritect. -- ca. 8 -- -- Au--Ta peritect. -- ca. 8 -- --
Au--La eutect. 0 0 808 9 Au--Nd eutect. 0 0 796 9.5 Au--Pr eutect.
0 0 808 12 Au--Si eutect. 0 0 363 19
[0022] This reaction can be reduced still further by the use of
multicomponent alloys corresponding to the composition ranges
indicated in the claims. These multicomponent alloys are
particularly advantageous when the infiltration times are long
because of the process. However, the use of multicomponent alloys
leads to a reduced thermal conductivity.
[0023] Table 1 also shows that the infiltrate alloys according to
the invention have a very low solvent capability for Y, Si and rare
earth metals at the eutectic temperature or at 400.degree. C. This
has the advantage that the Cu--, Ag-- or Au-rich phase formed by
the eutectic conversion has a very high purity and thus thermal
conductivity. Alloys of Ag or Au with Cu or up to 3 atom % of Ni
likewise have a sufficiently high thermal conductivity which is not
reduced to an unacceptable extent by small amounts of undissolved
Si, Y, Sc or rare earth metal. Proportions of graphite also do not
reduce the thermal conductivity to an unacceptable extent.
[0024] Y, Sc, Si and the rare earth metals not only reduce the
solidus temperature of Cu, Au and Ag but also produce good wetting
and bonding of the Cu--, Au-- or Ag-rich phase to the diamond
grains. In the case of Ag--Si, an Si--C compound having a thickness
in the nanometer range was able to be found. Owing to the low
proportion, these phases do not produce any significant
deterioration in the thermal conductivity. Also deserving of
mention is the thermal conductivity of Si--C of about 250 W/(m.K),
which is very high compared to the metal carbides of the elements
of groups 4a and 5a of the Periodic Table and chromium carbide. The
good wetting behavior ensures that the pores of the intermediate
are filled to an extent of at least 97%.
[0025] The wetting behavior can be improved still further by
addition of Ni, Cr, Ti, V, Mo W, Nb, Ta, Co and/or Fe, but the
total content of these elements must not exceed 3 atom %, since
otherwise they result in an unacceptably large reduction in the
thermal conductivity. The advantages of the infiltrate alloy
according to the invention also become apparent when hot pressing
is used as densification process. Here, an intermediate comprising
from 40 to 90% by volume of diamond grains having a mean particle
size of from 5 to 300 .mu.m and from 10 to 60% by volume of a
eutectic or near-eutectic infiltrate alloy which has a solidus
temperature of <900.degree. C. and comprises at least one
metallic component of high thermal conductivity which comprises an
element or an alloy from the group consisting of Cu, Ag, Au and at
least one element from the group consisting of Si, Y, Sc, rare
earth metals and optionally <3 atom % of one or more elements
from the group consisting of Ni, Cr, Ti, V, Mo, W, Nb, Ta, Co, Fe
which promote wetting, with near-eutectic alloys encompassing
compositions which have a liquidus temperature of <950.degree.
C., is homogenized by mixing or milling. A die of a hot press, e.g.
a graphite die, is filled with the intermediate. The intermediate
is subsequently brought to a temperature which is above the solidus
temperature of the infiltrate alloy but below 1000.degree. C., for
example by conductive heating of the die, and densified, with the
pressure being applied by moving the punch. The advantages
according to the invention can likewise be achieved when the
infiltrate alloy is in the liquid or partially liquid range, i.e.
between the solidus temperature and the liquidus temperature.
[0026] Depending on the infiltration or hot pressing apparatuses
used, it can be advantageous, particularly when a high cooling rate
occurs during solidification of the infiltrate alloy, to subject
the infiltrated intermediate to a heat treatment so that
constituents which have been trapped in solution are precipitated,
as a result of which the thermal conductivity is improved. This
heat treatment can also have a favorable effect on the interface
strength between the diamond particles and the surrounding
constituents. This heat treatment step can also be integrated into
the cooling process of the infiltration step.
[0027] Diamond-containing composite materials produced according to
the invention have a sufficiently good mechanical formability due
to the very ductile Ag, Au or Cu microstructure constituents. It is
also advantageous for inexpensive production that the high thermal
conductivity of the Ag--, Au-- or Cu-rich microstructure
constituents enables the diamond content to be reduced.
[0028] Variation of the diamond and metal phase content make it
possible to produce heat sinks for a variety of requirements to be
tailored in respect of thermal conductivity and thermal
expansion.
[0029] Further microstructure constituents do not worsen the
property to an unacceptable degree as long as their content does
not exceed 5% by volume. Here, mention may be made of free Si, C,
Y, Sc and rare earth metals. Although these microstructure
constituents increase the thermal conductivity slightly, they in
the case of C and Si have a favorable effect on the coefficient of
thermal expansion by reducing the latter. In addition, they can
sometimes only be avoided completely with a relatively high degree
of difficulty in terms of the production process.
[0030] Particularly advantageous contents of Ag--, Au-- or Al-rich
phase are from 7 to 30% by volume. Experiments have shown that
diamond powder can be processed within a wide particle size
spectrum. Apart from natural diamonds, it is also possible to
process more inexpensive synthetic diamonds. Excellent processing
results have also been achieved using the customary coated diamond
types. As a result, the most inexpensive type in each case can be
employed. In the case of applications in which the thermal
conductivity has to meet extremely high requirements and cost is
not critical, it is advantageous to use a diamond fraction having a
mean particle size in the range from 50 to 250 .mu.m. Furthermore,
the highest thermal conductivity values can be achieved by the use
of Ag at contents of from 7 to 30% by volume.
[0031] Apart from the particularly advantageous use of the
components for conducting away heat in semiconductor components,
the composite material of the invention can also be used as heat
sink in other applications, for example in the aerospace field or
in engine construction.
[0032] The invention is illustrated below by means of production
examples.
EXAMPLE 1
[0033] Natural diamond powder of the grade IIA (Micron+SND from
Element Six GmbH) having a mean particle size of 80-150 .mu.m was
introduced into a graphite mold having the dimensions 35
mm.times.35 mm.times.5 mm. The bulk density was brought to 65% by
volume by mechanical shaking. The diamond powder was subsequently
covered with a film composed of a eutectic Ag--Si alloy having an
Si content of 11 atom % and, to carry out the infiltration, was
heated in a furnace to a temperature of 860.degree. C. under
reduced pressure, with the hold time being 15 minutes. The
subsequent gas pressure infiltration using helium was carried out
at 1 bar for 15 minutes. After cooling to room temperature with a
hold point at 400.degree. C. for about 10 minutes, the volume
contents of the phases present were determined by means of
quantitative metallography.
[0034] The value for silicon carbide was about 1% by volume, with
the silicon carbide mostly enveloping the diamond grains uniformly.
Owing to the low thickness of this silicon carbide shell, the
modification of the silicon carbide phase could not be determined.
Apart from diamond and silicon carbide, the microstructure
comprises an Ag-rich phase with embedded Si precipitates which have
been formed by the eutectic reaction. The proportion by volume of
the Ag-rich phase was about 12%, and that of Si was about 1%. No
further constituents apart from Ag could be detected in the Ag-rich
phase by means of EDX, so that it can be assumed on the basis of
the applicable detection limit that the proportion of Ag is greater
than 99 atom %.
[0035] To determine the thermal conductivity and the coefficient of
thermal expansion, the plate was processed by means of a laser and
erosion. A mean value of 500 W/(m.K) was measured for the thermal
conductivity at room temperature. The determination of the
coefficient of thermal expansion gave a mean value of 8.5 10.sup.-6
K.sup.-1.
EXAMPLE 2
[0036] In a further experiment, synthetic diamond powder of the
grade Micron+MDA from Element Six GmbH having a mean particle size
of 40-80 .mu.m was processed. Processing was carried out as
described in Example 1. The mean thermal conductivity at room
temperature of the composite material produced in this way was 410
W/(m.K), and the mean coefficient of thermal expansion was
9.0.times.10.sup.-6 K.sup.-1.
EXAMPLE 3
[0037] In a further experiment, synthetic diamond powder of the
grade Micron+MDA from Element Six GmbH having a mean particle size
of 40-80 .mu.m was processed. Processing was carried out as
described in Example 1. The infiltration of the bed of diamond
powder with a eutectic Ag--Si melt was carried out at a gas
pressure of about 40 MPa in a conventional squeeze casting
apparatus whose hot forming steel mold had been preheated to
150.degree. C. The temperature of the Ag--Si melt was about
880.degree. C. The subsequent, slow cooling to room temperature was
carried out with a hold point at 400.degree. C. for about 15
minutes. The mean thermal conductivity at room temperature of the
composite material produced in this way was 480 W/(m.K).
EXAMPLE 4
[0038] Synthetic diamond powder of the grade Micron+MDA from
Element Six GmbH having a mean particle size of 40-80 .mu.m was
processed as described in Example 3, but without a hold phase at
about 400.degree. C. for 15 minutes being carried out during
cooling from the infiltration temperature. The mean thermal
conductivity at room temperature of the composite material produced
in this way was 440 W/(m.K), and the mean coefficient of thermal
expansion was 8.5.times.10.sup.-6 K.sup.-1.
EXAMPLE 5
[0039] Natural diamond powder of the grade IIA (Micron+SND from
Element Six GmbH) having a mean particle size of 40-80 .mu.m was
mixed with 7% by volume of a binder based on epoxy resin. The
precursor or intermediate produced in this way was pressed by means
of die pressing at a pressure of 200 MPa to give a plate having the
dimensions 35.times.35 mm.times.5 mm. The porosity of the plate was
about 15% by volume.
[0040] This plate was subseq uently covered with a film composed of
a eutectic Cu--Y alloy having a Y content of 9.3 atom % and, to
carry out the infiltration, was heated in a furnace to a
temperature of 900.degree. C. under reduced pressure, with the hold
time being 15 minutes. To determine the thermal conductivity and
the coefficient of thermal expansion, the plate was processed by
means of a laser and erosion. A mean value of 410 W/(m.K) was
measured for the thermal conductivity at room temperature. The
determination of the coefficient of thermal expansion gave a mean
value of 7.7 10.sup.-6 K.sup.-1.
* * * * *