U.S. patent application number 10/923782 was filed with the patent office on 2005-02-03 for substrate material for mounting a semiconductor device, substrate for mounting a semiconductor device, semiconductor device, and method of producing the same.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Abe, Yugaku, Fukui, Akira, Hirose, Yoshiyuki, Imamura, Makoto, Takano, Yoshishige, Takikawa, Takatoshi, Yamagata, Shinichi.
Application Number | 20050025654 10/923782 |
Document ID | / |
Family ID | 27304691 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050025654 |
Kind Code |
A1 |
Yamagata, Shinichi ; et
al. |
February 3, 2005 |
Substrate material for mounting a semiconductor device, substrate
for mounting a semiconductor device, semiconductor device, and
method of producing the same
Abstract
To provide a substrate material made of an aluminum/silicon
carbide composite alloy which has a thermal conductivity of 100
W/m.times.K or higher and a thermal expansion coefficient of
20.times.10.sup.-6/.degree. C. or lower and is lightweight and
compositionally homogeneous. A substrate material made of an
aluminum/silicon carbide composite ally which comprises Al--SiC
alloy composition parts and non alloy composition part and
dispersed therein from 10 to 70% by weight silicon carbide
particles, and in which the fluctuations of silicon carbide
concentration in the Al--SiC alloy composition parts therein are
within 1% by weight. The substrate material is produced by
sintering a compact of an aluminum/silicon carbide starting powder
at a temperature not lower than 600.degree. C. in a non-oxidizing
atmosphere.
Inventors: |
Yamagata, Shinichi;
(Itami-shi, JP) ; Abe, Yugaku; (Itami-shi, JP)
; Imamura, Makoto; (Itami-shi, JP) ; Fukui,
Akira; (Itami-shi, JP) ; Takano, Yoshishige;
(Itami-shi, JP) ; Takikawa, Takatoshi; (Itami-shi,
JP) ; Hirose, Yoshiyuki; (Itami-shi, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
Osaka
JP
|
Family ID: |
27304691 |
Appl. No.: |
10/923782 |
Filed: |
August 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10923782 |
Aug 24, 2004 |
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09925427 |
Aug 10, 2001 |
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09925427 |
Aug 10, 2001 |
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09692162 |
Oct 20, 2000 |
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6388273 |
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09692162 |
Oct 20, 2000 |
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08874543 |
Jun 13, 1997 |
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6183874 |
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Current U.S.
Class: |
419/17 ;
257/E23.009 |
Current CPC
Class: |
H01L 2224/48247
20130101; H01L 2924/1517 20130101; Y10T 428/24975 20150115; Y10T
428/26 20150115; H01L 2224/16225 20130101; H01L 2924/00014
20130101; H01L 2924/15312 20130101; H01L 2924/01078 20130101; H01L
2224/73204 20130101; H01L 2924/15311 20130101; H01L 2924/16152
20130101; H01L 2924/01046 20130101; H01L 2924/01322 20130101; H01L
2924/15153 20130101; H01L 2224/73265 20130101; H01L 2924/1532
20130101; H01L 2224/16 20130101; H01L 2924/12042 20130101; H01L
2924/16152 20130101; H01L 2924/16195 20130101; H01L 2224/32245
20130101; H01L 2224/48091 20130101; H01L 23/15 20130101; H01L
2224/73253 20130101; H01L 24/48 20130101; H01L 2924/01079 20130101;
H01L 2224/73204 20130101; H01L 2924/00014 20130101; H01L 2924/00
20130101; H01L 2224/45099 20130101; H01L 2224/73253 20130101; H01L
2224/16225 20130101; H01L 2224/48247 20130101; H01L 2924/00
20130101; H01L 2224/85399 20130101; H01L 2224/05599 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; H01L 2224/73204 20130101;
H01L 2224/32245 20130101; H01L 2924/207 20130101; H01L 2224/32225
20130101; H01L 2924/00014 20130101; H01L 2224/45015 20130101; H01L
2224/32225 20130101; H01L 2224/16225 20130101; H01L 2924/00
20130101; H01L 2224/73265 20130101; H01L 2224/32225 20130101; H01L
2924/00014 20130101; H01L 2924/15311 20130101; C22C 32/0063
20130101; H01L 2924/15165 20130101; H01L 2924/00014 20130101; H01L
2224/48091 20130101; H01L 2924/181 20130101; Y10T 428/25 20150115;
H01L 2924/12042 20130101; H01L 2924/01012 20130101; H01L 21/4807
20130101; H01L 2924/09701 20130101; Y10T 428/31678 20150401; H01L
2924/00014 20130101; Y10T 428/252 20150115; H01L 2924/01019
20130101; H01L 2924/181 20130101; H01L 2224/32188 20130101 |
Class at
Publication: |
419/017 |
International
Class: |
B22F 003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 1996 |
JP |
P.HEI.8-175730 |
Apr 3, 1997 |
JP |
P.HEI.9-84906 |
May 9, 1997 |
JP |
P.HEI.9-136164 |
Claims
What is claimed is:
1) A substrate material for mounting a semiconductor device, of an
aluminum/silicon carbide (Al--SiC) composite alloy which comprises
Al--SiC alloy composition part and non alloy composition part,
wherein silicon carbide granular particles are dispersed from 10 to
70% by weight in the composite alloy, and silicon carbide is
distributed homogeneously in the Al--SiC alloy composition
part.
2) The substrate material for mounting a semiconductor device, as
set forth in claim 1, fabricated by the sintering method of
sintering a pre-formed mixed starting material powders, wherein the
fluctuation of the concentration silicon carbide in the Al--SiC
alloy composition part is within 1% by weight.
3) The substrate material for mounting a semiconductor device, as
set forth in claim 1, wherein the substrate material has a thermal
conductivity of 100 W/m.times.K or higher and a thermal expansion
coefficient of 20.times.10.sup.-6/.degree. C. or lower.
4) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the silicon carbide granular particles
are dispersed from 35 to 70% by weight.
5) The substrate material for mounting a semiconductor device, as
set forth in claim 4, wherein the substrate material has a thermal
conductivity of 180 W/m.times.K or higher.
6) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the composite alloy contains aluminum
carbide formed at an interface between aluminum or aluminum alloy
and silicon carbide.
7) The substrate material for mounting a semiconductor device as
claimed in claim 6, wherein the amount of the aluminum carbide is
lower than 5% by weight.
8) The substrate material for mounting a semiconductor device as
claimed in claim 7, wherein the silicon carbide composite alloy has
a thermal conductivity of 180 W/m.times.K or higher.
9) The substrate material for mounting a semiconductor device as
claimed in claim 6, wherein aluminum carbide is distributed at the
interface between the silicon carbide and the aluminum or aluminum
alloy in such an amount that the ratio of the peak intensity for
aluminum carbide (012) to that for aluminum (200) both determined
by X-ray analysis with CuK.sub.8 line is not more than 0.025.
10) The substrate material for mounting a semiconductor device as
claimed in claim 9, wherein the silicon carbide composite alloy has
a thermal conductivity of 180 W/m.times.K or higher.
11) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the composite alloy contains silicon as
a component of a solid solution therein or as a precipitate.
12) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the aluminum/silicon carbide composite
alloy contains nitrogen in an amount of from 0.01 to 1% by
weight.
13) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the aluminum/silicon carbide composite
alloy contains oxygen in an amount of from 0.05 to 0.5% by
weight.
14) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the aluminum/silicon carbide composite
alloy contains 3--SiC as the silicon carbide.
15) The substrate material for mounting a semiconductor device as
claimed in claim 1, wherein the silicon carbide granular particles
have an average particle diameter of from 1 to 100 .mu.m.
16) The substrate material for mounting a semiconductor device as
claimed in claim 14, wherein the silicon carbide granular particles
have an average particle diameter of from 10 to 80 .mu.m.
17) The substrate for mounting a semiconductor device, which
comprises a substrate made of the substrate material as claimed in
claim 1, and a coating layer coated on a surface of the
substrate.
18) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer is a plating layer.
19) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer is a chromate film.
20) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer is a layer of an oxide of
either aluminum or silicon.
21) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer is a multilayer structure
film comprising a first metal layer having a Young's modulus of
15,000 kg/mm.sup.2 or lower and a second metal layer formed on the
first metal layer, and the second metal layer is made of at least
one metal selected from nickel and gold.
22) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer is a multilayer structure
film comprising a first metal layer having a melting point of
600.degree. C. or lower and a second metal layer formed on the
first metal layer, and the second metal layer is made of at least
one metal selected from nickel and gold.
23) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer comprises a layer of at
least one organic resin selected from an epoxy resin, a silicone
resin, a polyimide resin, and the like each containing a metallic
filler or not.
24) The substrate for mounting a semiconductor device, as claimed
in claim 23, wherein the coating layer further comprises a second
metal layer made of at least one metal selected from nickel and
gold, formed on the layer of organic resin.
25) The substrate for mounting a semiconductor device, as claimed
in claim 17, wherein the coating layer comprises aluminum as the
main component.
26) The substrate for mounting a semiconductor device, as claimed
in claim 25, wherein the coating layer is made up of crystal grains
comprising aluminum and having a diameter of from 0.1 to 10
.mu.m.
27) The substrate for mounting a semiconductor device, as claimed
in claim 26, wherein the coating layer is further covered with an
oxide layer having a thickness of from 10 to 800 .ANG..
28) The substrate for mounting a semiconductor device, as claimed
in claim 25, wherein the substrate has a surface roughness of from
0.1 to 20 .mu.m in terms of R.sub.max.
29) The substrate for mounting a semiconductor device, as claimed
in claim 28, wherein the substrate has a surface roughness of from
0.1 to 8 .mu.m in terms of R.sub.max.
30) The substrate for mounting a semiconductor device, as claimed
in claim 28, wherein the substrate comprises holes having a depth
of 100 .mu.m or smaller on the surface thereof.
31) The substrate for mounting a semiconductor device, as claimed
in claim 28, wherein the aluminum coating layer has a purity of
99.9% or higher.
32) The substrate for mounting a semiconductor device, as claimed
in claim 25, wherein the coating layer has a thickness of from 1 to
100 .mu.m.
33) The substrate for mounting a semiconductor device, as claimed
in claim 32, wherein the coating layer has a thickness of from 1 to
20 .mu.m.
34) A semiconductor device, which comprises the substrate material
as claimed in claim 1 or the substrate as claimed in claim 17, and
a semiconductor chip mounted on the substrate.
35) A method of producing a substrate material of an
aluminum/silicon carbide composite alloy by the sintering method,
wherein the method comprises steps of: mixing an aluminum powder
and silicon carbide powder to form an aluminum/silicon carbide
starting powder mixed homogeneously; compacting the
aluminum/silicon carbide starting powder having a silicon carbide
content of from 10 to 70% by weight to form a compact; and
sintering the compact at a temperature of 600.degree. C. or higher
in a non-oxidizing atmosphere to thereby obtain an aluminum/silicon
carbide composite alloy.
36) The method of producing a substrate material as claimed in
claim 35, wherein the sintering step is conducted at the
temperature within a range of from 600 to 750.degree. C.
37) The method of producing a substrate material as claimed in
claim 35, wherein the sintering step is conducted in a nitrogen
atmosphere having a nitrogen concentration of 99% by volume or
higher.
38) The method of producing a substrate material as claimed in
claim 35, wherein the sintering step is conducted in an atmosphere
having an oxygen concentration of 200 ppm or lower.
39) The method of producing a substrate material as claimed in
claim 35, wherein the sintering step is conducted in an atmosphere
having a dew point of -20.degree. C. or lower.
40) A method of producing a substrate for mounting a semiconductor
chip as claimed in claim 35, further comprising the step of
repressing the aluminum/silicon carbide composite alloy obtained by
sintering the aluminum/silicon carbide starting powder, or
repressing them and then heating in a non-oxidizing atmosphere so
as to prevent from oxidizing aluminum.
41) A method of producing a substrate made of an aluminum/silicon
carbide composite alloy by the sintering method, comprising the
steps of: mixing an aluminum powder and silicon carbide powder to
form an aluminum/silicon carbide starting powder having a silicon
carbide content of from 10 to 70% by weight; compacting the
aluminum/silicon carbide starting powder to form a compact;
sintering the compact at a temperature of 600.degree. C. or higher
in a non-oxidizing atmosphere for aluminum to thereby obtain ed
substrate made of an aluminum/silicon carbide composite alloy; and
forming a coating layer on a surface of the pre-formed substrate to
thereby obtain the substrate.
42) The method of producing a substrate as claimed in claim 41,
wherein the step of forming a coating layer is: heating the
substrate in an oxidizing atmosphere; or exposing the substrate to
a steam atmosphere.
43) The method of producing a substrate as claimed in claim 41,
wherein the step of forming a coating layer comprises steps of:
forming a layer of a metal having a Young's modulus of 15,000
kg/mm.sup.2 or lower on the substrate material; polishing the metal
layer; and plating the polished metal layer with at least one metal
selected from nickel and gold.
44) The method of producing a substrate as claimed in claim 41,
wherein the step of forming a coating layer comprises steps of:
forming a layer of a metal having a melting point of 600.degree. C.
or lower on the substrate surface; heating the metal layer to a
temperature not higher than 600.degree. C.; and plating the metal
layer with at least one metal selected from nickel and gold.
45) The method of producing a substrate as claimed in claim 41,
wherein the step of forming a coating layer comprises steps of:
forming a layer of at least one organic resin selected from an
epoxy resin, a silicone resin, a polyimide resin, and the like each
containing a metallic filler or not on the substrate surface.
46) The method of producing a substrate as claimed in claim 45,
wherein the step of forming a coating layer further comprises steps
of: plating a metal layer made of at least one metal selected from
nickel and gold on the layer of organic resin.
47) The method of producing a substrate as claimed in claim 46,
wherein the forming step of a layer of a metal having a Young's
modulus of 15,000 kg/mm.sup.2 or lower on the substrate is
conducted by barrel plating.
48) The method of producing a substrate as claimed in claim 47,
whrein the barrel plating is conducted in a container which
contains metal spheres having a particle diameter of from 0.1 to 10
mm and having the same composition as the deposit to be formed.
49) The method of producing a substrate as claimed in claim 48,
wherein the spheres contained in the container for use in barrel
plating have a surface area which is at least two times that of the
corresponding true spheres.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a substrate material for
use as, e.g., a heat sink material in a semiconductor device, and
also to a substrate, a semiconductor device, and method of
producing the same.
[0003] 2. Discription of the Prior Art
[0004] With the recent remarkable increases of the processing rate
of semiconductor device and the degree of integration in
semiconductor device, the heat generated by semiconductor elements
has come to produce influences that are not negligible. As a
result, substrate materials for mounting semiconductor devices have
come to be required to have a high thermal conductivity for
efficiently removing the heat generated by semiconductor
elements.
[0005] Substrate materials are further required not to be deformed
by a thermal stress at the interface between the substrate
materials and other device members used in combination therewith.
Hence, substrate materials are required not to have a large
difference in thermal expansion coefficient with semiconductor
chips, packages, etc. used in combination therewith. Specifically,
since the thermal expansion coefficients of silicon and GaAs, both
used as semiconductor elements, are as low as
4.2.times.10.sup.-6/.degree. C. and 6.5.times.10.sup.-6/.degree.
C., respectively, and that of Al.sub.2O.sub.3, which is widely used
as a packaging material, is also as low as
6.5.times.10.sup.-6/.degree. C., substrate materials desirably have
low thermal expansion coefficients which are almost the same as the
above values.
[0006] In recent years, plastics have come to be increasingly used
as packaging materials in place of ceramics such as
Al.sub.2O.sub.3. In the case of using a plastic package, the
substrate material used therewith can have a higher thermal
expansion coefficient than in conventional semiconductor devices,
because the plastic has a high thermal expansion coefficient and a
semiconductor element is bonded there to with a resin. Namely, the
optimal range of the thermal expansion coefficients which
semiconductor substrate materials are required to have is from
7.times.10.sup.-6 to 20.times.10.sup.-6/.degree. C., although it
varies depending on combinations with other device members
including packaging materials; those values are high and that range
is wide as compared with the case of ceramic packages.
[0007] Conventionally in the case where a low thermal expansion
coefficient is necessary, substrate materials for carrying a
semiconductor device of a Cu--W composite alloy or a Cu--Mo
composite alloy have been frequently used. Since these alloys can
be regulated in thermal expansion so as to be suitable for use with
plastics by controlling the amount of copper or molybdenum, they
can be also applicable to with plastic packages. However, because
of their low rigidity, the plastics are apt to deform when used in
combination with materials having a high specific gravity, such as
Cu--W alloys and Cu--Mo alloys, and this limits the use of these
alloys as substrate materials in combination with plastic
packages.
[0008] For electrically connecting a semiconductor element to a
package, a technique of using solder bumps in place of wires (flip
chip bonding) and a technique of using solder balls in place of
pins for connection to a base substrate (ball grid array bonding)
have come to be widely used. These techniques also have
difficulties in application to substrate materials made of a Cu--W
alloy or a Cu--Mo alloy, because the use of such heavy substrate
materials may flatten the solder balls excessively. In addition,
the use of substrate materials made of these alloys is
disadvantageous in cost because tungsten and molybdenum are
relatively expensive metals.
[0009] On the other hand, in the case where a high thermal
expansion coefficient is desired, substrate materials made of Al or
Cu, which are inexpensive metals, or of an alloy of these have been
frequently employed. However, these semiconductor substrate
materials have the same problem as the Cu--W alloys or the like
because Cu also has a density as high as 8.9 g/cm.sup.3. Substrate
materials made of aluminum are free from the above problem when
used in combination with plastic packages and connected by ball
grid array bonding, since the density of aluminum is as low as 2.7
g/cm.sup.3. However, substrate materials made of aluminum have
problems that they can be used in only limited applications because
aluminum has a thermal expansion coefficient as high as
23.5.times.10.sup.-6/.degree. C., and that the substrates are apt
to warp or deform because of their low rigidity.
[0010] Under these circumstances, there is a desire for a substrate
material which not only can be regulated so as to have any thermal
expansion coefficient in the wide range of from 7.times.10.sup.-6
to 20.times.10.sup.-6/.degree. C., especially from
7.times.10.sup.-6 to 15.times.10.sup.-6/.degree. C., but also has
high heat dissipation properties and is lightweight. It is thought
that substrate materials should generally have a thermal
conductivity of at least 100 W/m.multidot.K. However, there are
increasing cases where the semiconductor substrate materials used
in combination with plastic packages, having a poor thermal
conductivity, are required to have a thermal conductivity of 180
W/m.multidot.K or higher when heat dissipation from the whole
package is taken in account.
[0011] Aluminum composite alloys were recently proposed as
materials which are lightweight and satisfy the above-described
requirements concerning thermal expansion coefficient and thermal
conductivity. Among these, use of an aluminum/silicon carbide
(Al--SiC) composite alloy as a substrate material is being
investigated because the starting materials, i.e., aluminum and
silicon carbide, both are relatively inexpensive and highly
thermally conductive, and because a wide range of thermal expansion
coefficients can be obtained by combining silicon carbide, having a
low thermal expansion coefficient of 4.2.times.10.sup.-6/.degree.
C., with aluminum, having a high thermal expansion coefficient of
23.5.times.10.sup.-6/.degree. C., in various proportions.
[0012] Conventionally employed processes for producing such an
aluminum/silicon carbide composite alloy include the casting method
disclosed, e.g., in Tokuhyo-Hei-1-501489 (unexamined published PCT
application), the impregnation method described, e.g., in
JP-A-2-243729 (the term "JP-A" as used herein means an "unexamined
published Japanese patent application"), and the pressure casting
method disclosed, e.g., in JP-A-61-222668.
[0013] For use in fields where high reliability is required, the
substrate materials obtained are generally subjected to a surface
treatment before being used as semiconductor substrates.
[0014] In order to use an aluminum/silicon carbide composite alloy
as a substrate material for mounting a semiconductor device, the
above-described production methods each has problems which should
be solved.
[0015] First, the casting method has a drawback that the deviation
of composition which is caused during cooling is difficult to
avoid. This is because since the Al--SiC alloy produced by the
casting method necessarily has a higher aluminum concentration in
the surface part, the difference in silicon carbide concentration
between the central and surface parts exceeds 1% by weight, making
it impossible to obtain a material having a homogeneous
composition. It is also difficult to completely eliminate voids.
Although the pressure casting method is effective in eliminating
most voids, the concentration of aluminum around the surface tends
to be high due to the pressure applied. It is hence difficult in
the pressure casting method to reduce the difference in silicon
carbide concentration between the central and surface parts to 1%
by weight or smaller.
[0016] On the other hand, the impregnation method in which a
preform of silicon carbide is impregnated with molten aluminum has
a drawback that aluminum should be infiltrated in an excess amount
in order to obtain a completely dense alloy. Consequently, the
alloy obtained has the excess aluminum on the periphery thereof and
cannot have the original shape of the preform before impregnation.
It is therefore difficult to obtain a substrate material having
satisfactory dimensional precision. For obtaining the desired
dimensions, it is necessary to conduct an operation for removing
the excess aluminum from the whole periphery. In the pressure
infiltration method, in which a preform of silicon carbide is
placed in a pressure vessel and molten aluminum is forced into the
vessel, the resulting alloy has an aluminum film corresponding to
the clearance between the preform and the pressure vessel. Since
this aluminum film is uneven in thickness, it not only impairs the
low thermal expansion coefficient of the alloy material, but is
causative of warpage, etc.
[0017] The casting method has another drawback that since the
method involves the step of casting a molten metal, the
concentration of aluminum in the melt should be at least 70% by
weight. In the pressure casting method also, a melt having a
silicon carbide concentration not lower than 30% by weight has poor
flowability and has been unsuitable for use in producing alloys of
complicated shapes, resulting in poor production efficiency. It has
been found that alloys which can be produced by the impregnation
method so as to retain the same dimensions as the preform and to be
optionally dense have compositions in which the concentration of
silicon carbide is around 70% by weight. This is because if an
alloy having a silicon carbide concentration lower than 70% by
weight is to be produced, the silicon carbide preform has a reduced
strength and is hence apt to deform or warp during impregnation
with aluminum or during subsequent cooling due to a difference in
thermal expansion coefficient. As a result, the alloy obtained
hardly retains the same dimensions as the preform.
[0018] Further drawbacks of the impregnation method are that since
the framework of the alloy produced is constituted of silicon
carbide, warpage correction by sizing after alloying is impossible,
and that the processing of the alloy is possible only by grinding
with a diamond wheel and is hence costly. The pressure casting
method has a further problem that it has a far higher equipment
cost than the casting and impregnation methods. Therefore, it has
been difficult to produce an aluminum/silicon carbide composite
alloy having a homogeneous composition in which the silicon carbide
concentration is higher than about 30% by weight but not higher
than about 70% by weight at low cost by any of those prior art
methods.
[0019] Substrate materials for use in plastic packages of
semiconductor devices are frequently required to have a thermal
expansion coefficient of about from 7.times.10.sup.-6 to
13.times.10.sup.-6/.degree. C. for the reasons as set forth above.
In order for an aluminum/silicon carbide composite alloy to meet
this requirement, the alloy should have a silicon carbide
concentration of from 50 to 70% by weight. It has however been
difficult to produce an alloy having such a composition at low cost
by any of the casting, impregnation, and pressure casting methods
described above. It has also been difficult to obtain an
aluminum/silicon carbide composite alloy having a thermal
conductivity of 180 W/m.multidot.K or higher by any of those prior
art methods, except in the case of alloys having silicon carbide
concentrations exceeding 70% by weight or below 10% by weight.
[0020] Although an aluminum/silicon carbide composite alloy as it
is can be used as a semiconductor substrate material, it is
desirably subjected to a surface treatment when the composite alloy
is to be used in fields where high reliability is required, e.g.,
in work stations. For use in these fields, semiconductor substrate
materials are required not to suffer any change in properties,
e.g., thermal conductivity, or in appearance, etc., through various
reliability tests such as a thermal cycling test in which the
substrate materials are repeatedly exposed to -65.degree. C. and
150.degree. C., a PCT (pressure cooker test) in which the substrate
materials are exposed to an atmosphere of 121.degree. C., 100% RH,
and 2 atm., and an HAST (highly accelerated stress test) in which
the substrate materials are exposed to an atmosphere of 125.degree.
C., 85% RH, and 2 atm. However, the exposed aluminum part on the
surface discolors through these tests. Discoloration is apt to
occur also at the Al/SiC interface. Hence, the substrate materials
undergo a considerable change in appearance through the above
tests. It is therefore necessary to perform a surface treatment
suitable for aluminum/silicon carbide composite alloys and to use a
technique for the treatment.
[0021] The surface state of a substrate material for mounting a
semiconductor device is important, because it influences the flow
of solder when a semiconductor chip or a package is fixed to the
substrate formed by the material by using solders. For use with
some solders, a surface treatment suitable therefore is necessary
in order to ensure reliability with respect to the strength and
other properties of soldering parts. The surface state is important
also in bonding with a resin, which technique is becoming the
mainstream recently. Since different surface states result in
different strengths of resin bonding, a surface treatment suitable
for the desired bonding strength is required.
[0022] And aluminum/silicon carbide composite alloys has a high
degree of hardness. Therefore it is very difficult to forme a
shape, especially a complex shape such as heatsink by using
aluminum/silicon carbide composite alloys. It is required to a
substrate material being able to be formed easily to be near net
shape precisely.
SUMMARY OF THE INENTION
[0023] In view of the current situation as described above, an
object of the present invention is to eliminate the problems
concerning precision in forming, cost, etc. to provide a substrate
material for mounting a semiconductor device, made of a lightweight
aluminum/silicon carbide composite alloy which has a homogenous
composition and has the properties required of a substrate
material, i.e., a thermal conductivity of 100 W/m.multidot.K or
higher and a thermal expansion coefficient of
20.times.10.sup.-6/.degree. C. or lower.
[0024] Another object of the present invention is to provide a
substrate for mounting a semiconductor device, having higher
reliability.
[0025] Another object of the present invention is to provide a
method of forming a substrate which is controlled a thermal
expansion coefficient thereof easily with a large range so as to be
appropriate to a semiconductor chip or a package to be fixed to the
substrate.
[0026] And another object of the present invention is to provide a
substrate formed easily to be near net shape precisely.
[0027] To accomplish the above objects, the present invention
provides a substrate material for mounting a semiconductor device,
made of an aluminum/silicon carbide composite alloy which comprises
Al--SiC alloy composition part and non alloy part and dispersed
homogeneously silicon carbide granular particles. Silicon carbide
granular particles are dispersed from 10 to 70% by weight in the
composite alloy, and silicon carbide is distributed homogeneously
in the Al--SiC alloy composition part. And the fluctuations of
silicon carbide concentration in the Al--SiC alloy composition
parts is within 1% by weight, and which has a thermal conductivity
of 100 W/m.multidot.K or higher and a thermal expansion coefficient
of 20.times.10.sup.-6/.degree. C. or lower.
[0028] This aluminum/silicon carbide composite alloy is produced by
a sintering method.
[0029] The aluminum/silicon carbide composite alloy constituting
the substrate material of the present invention preferably contains
aluminum carbide formed at the interface between the silicon
carbide and the aluminum or aluminum alloy. Preferably aluminum
carbide is comprised in such an amount that the ratio of the peak
intensity for aluminum carbide (012) to that for aluminum (200)
both determined by X-ray analysis with CuK.sub..alpha. line is not
more than 0.025 or its analytical amount is not more than 5% by
weight. This substrate material simultaneously further contains
silicon in the aluminum or aluminum alloy, and the silicon is
present as a component of a solid solution or as a precipitate.
[0030] This aluminum/silicon carbide composite alloy has a thermal
conductivity of 180 W/m.multidot.K or higher. It is especially
suitable for use as a semiconductor substrate material for a
ceramic package, etc.
[0031] The present invention further provides a process for
producing the substrate material which comprises compacting an
aluminum/silicon carbide starting powder having a silicon carbide
content of from 10 to 70% by weight, and sintering the compact at a
temperature of 600.degree. C. or higher in a non-oxidizing
atmosphere in order to prevent aluminum from oxidizing to produce
an aluminum/silicon carbide composite alloy. Preferably such
process is employed by sintering a power mixture compact contained
aluminum and silicon carbide, namely a sintering method which
differs from some conventional process above described. By this
process of the present invention, a substrate material can be
obtained which is made of a lightweight aluminum/silicon carbide
composite alloy having a homogeneous composition and having a
thermal-expansion coefficient of 20.times.10.sup.-6/.degree. C. or
lower and a thermal conductivity of 100 W/m.multidot.K or
higher.
[0032] Especially the sintering process of the present invention
for producing an aluminum/silicon carbide composite alloy, is
capable of yielding an aluminum/silicon carbide composite alloy
having a thermal conductivity of 180 W/m.multidot.K or higher by
regulating the sintering temperature especially- to a value in the
range of from 600 to 750.degree. C. to thereby control the
interfacial reaction which yields the aluminum carbide and the
silicon.
[0033] A preferred atmosphere for the sintering is a nitrogen
atmosphere having a nitrogen concentration of 99% by volume or
higher. It is also preferred to conduct the sintering in an
atmosphere having an oxygen concentration of 200 ppm or lower and a
dew point of -20.degree. C. or lower.
[0034] Especially when the aluminum/silicon carbide composite alloy
has a thermal expansion coefficient of from 7.times.10.sup.-6 to
15.times.10.sup.-6/.degree. C. and a thermal conductivity of 180
W/m.multidot.K or higher, it is suitable for use as a substrate
material for a semiconductor mounted on a plastic package or as a
substrate used for semiconductor devices in which the electrical
connection of a semiconductor element is conducted by flip chip
bonding or mounting on a package is conducted by ball grid array
bonding.
[0035] A substrate having higher reliability can be formed by
coating the surface of the material of the present invention with a
plating layer, chromate film, or oxide film, or by forming on the
surface thereof a layer of a metal having a Young's modulus of
15,000 kg/mm.sup.2 or lower, a layer of a metal having a melting
point of 600.degree. C. or lower, or a layer of an organic resin
and then forming thereon a layer of nickel or gold, or by forming
on the surface thereof a coating layer comprising aluminum as the
main component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 shows a block diagram illustrating a process for
producing an aluminum/silicon carbide composite alloy according to
the present invention.
[0037] FIG. 2 is a photomicrograph taken with an optical microscope
(100 times) showing the metal structure of the aluminum/silicon
carbide composite alloy obtained as sample 6 in Example 1.
[0038] FIG. 3 is a diagrammatic sectional view illustrating one
embodiment of an IC package using a substrate made of the substrate
material of the present invention.
[0039] FIG. 4 is a diagrammatic sectional view illustrating another
embodiment of the IC package using a substrate made of substrate
material of the present invention.
[0040] FIG. 5 is a diagrammatic sectional view illustrating still
another embodiment of the IC package using a substrate made of
substrate material of the present invention.
[0041] FIG. 6 is a diagrammatic sectional view illustrating one
embodiment of an IC package having solder balls and using a
substrate made of substrate material of the present invention.
[0042] FIG. 7 is a diagrammatic sectional view illustrating another
embodiment of the IC package having solder balls and using a
substrate made of substrate material of the present invention.
[0043] FIG. 8 is a diagrammatic sectional view illustrating still
another embodiment of the IC package having solder balls and using
a substrate made of substrate material of the present
invention.
[0044] FIG. 9 is a diagrammatic sectional view illustrating one
embodiment of an IC package of the mold type using a substrate made
of substrate material of the present invention.
[0045] FIG. 10 is a diagrammatic sectional view illustrating one
embodiment of an IC package having aluminum fins bonded to a
substrate made of substrate material of the present invention.
[0046] FIG. 11 is a diagrammatic sectional view illustrating a test
piece used for measuring a bonding strength between the substrate
material of the present invention and resin.
DESCRIPTION OF THE PREFEERED EMBODIMENTS
[0047] In the present invention, an aluminum/silicon carbide
composite alloy useful as a semiconductor substrate material is
produced by sintering to thereby provide a semiconductor substrate
material having the desired values of thermal conductivity and
thermal expansion coefficient and having a homogeneous Al--SiC
composition and a near-net shape, i.e., excellent dimensional
precision, the attainment of both of which has been difficult in
conventional processes. This substrate material is capable of
coping with, not only conventional ceramic package, metal package
but also in particular, plastic packages, flip chip bonding, and
ball grid array bonding.
[0048] That is, since the aluminum/silicon carbide composite alloy
according to the present invention is produced from an
aluminum/silicon carbide granular particle as starting powder
having a silicon carbide content of from 10 to 70% by weight by
compacting the powder and sintering the compact, the aluminum or
aluminum alloy constitutes a continuous metal structure, while the
silicon carbide is homogeneously dispersed as particles unlike the
silicon carbide in aluminum/silicon carbide alloys produced by the
infiltration method.
[0049] The crystal forms of silicon carbide include hexagonal
.alpha.-SiC form, which is formed at a high-temperature, and cubic
.beta.-SiC form, which is formed at a low-temperature. Although
these two forms do not differ in the thermal conductivity of an
alloy, .alpha.-silicon carbide is susceptible to cleavage. Due to
this property, use of .alpha.-silicon carbide in a starting powder
is apt to result in silicon carbide cleavage due to the pressure
applied during compaction into a desired substrate shape. As a
result of the cleavage, the compact may contain aggregates made up
of fine silicon carbide particles. Since the aggregates have poor
adhesion to aluminum in an alloy, they tend to suffer debonding of
particles when the alloy is subjected to processings such as
grinding, barrel, shot blasting, etc. in the final step. It is
therefore desirable to use .beta.-silicon carbide or a mixture of
.alpha.-silicon carbide and .beta.-silicon carbide. "Debonding of
particles" means that particles are desplaced from the position to
be in the alloy, and the surface of the alloy grow porous.
[0050] If debonding of particles occurs, the resulting rough
surface may have the problems of reduced solder flowability and
reduced adhesion strength in resin bonding. Since the degree of
surface roughness caused by the debonding of particles is equal to
the particle diameter of the silicon carbide used, it is preferred
to use silicon carbide having a smaller particle diameter in order
to prevent solder flowability and resin bonding strength from
decreasing. However, too small particle diameters are apt to cause
aggregation and may result in an enhanced surface roughness.
Consequently, the particle diameter of the silicon carbide is
preferably from 1 to 100 .mu.m, more preferably from 10 to 80
.mu.m.
[0051] On the other hand, by intentionally forming a surface
roughness, the bonding strength of a resin can be improved based on
the anchoring effect thereof. In this case, anchoring effect means
the state where bonded surfaces engaged physically each other owing
to their roughness. In this case also, a surface having too high a
roughness may have a reduced bonding strength because vacant spaces
not filled with a resin, can remain. A surface having too low a
roughness does not produce an anchoring effect. From this
standpoint also, the particle diameter of the silicon carbide is
preferably from 1 to 100 .mu.m, more preferably from 10 to 80
.mu.m.
[0052] As will be described later in detail, the sintering method,
in which granular particles as a starting powder comprising
homogeneously dispersed particles of aluminum and silicon carbide
are compacted and then sintered, yields an alloy having a
homogeneous structure because particle movement is little during
these steps. The alloy obtained by the sintering method therefore
can be exceedingly reduced in compositional difference between the
central and surface parts thereof, which difference has been a
problem in the conventional casting method, pressure casting method
and infiltration method. Specifically, the fluctuations of silicon
carbide concentration in the Al--SiC alloy composition parts can be
reduced to a value within 1% by weight. The expression
"fluctuations of silicon carbide concentration in Al--SiC alloy
composition parts" used herein means that the Al--SiC alloy
composition parts, i.e., the alloy excluding any oxide or nitride
layer usually formed on the alloy surface and further excluding any
aluminum layer such as that formed on the alloy surface in a
conventional method, are compared with one another in compositional
homogeneity with respect to silicon carbide concentration. For
determining that difference, central and surface parts of the alloy
composition parts are analyzed for SiC concentration by examining a
0.5 mm.sup.2 area for each part with an electron microscope. The
ratio of area SiC occupied to that of whole area corresponding to
each examined visual field by the electron microscope.
[0053] If the concentration of silicon carbide in the aluminum or
aluminum alloy is lower than 10% by weight, thermal expansion
coefficients exceeding 20.times.10.sup.-6/.degree. C. result. If
the concentration thereof exceeds 70% by weight, densification is
difficult in the sintering method because of the too small aluminum
proportion. In the present invention, the amount of silicon carbide
in the aluminum/silicon carbide composite alloy is hence regulated
to from 10 to 70% by weight. In particular, regulating the
concentration of silicon carbide to a value in the range of from 35
to 70% by weight is effective in obtaining an aluminum/silicon
carbide composite alloy having a thermal expansion coefficient in a
range which has not been attainable with any prior art technique,
i.e., from 7.times.10.sup.-6 to 15.times.10.sup.-6/.degree. C.
[0054] In the sintering of an aluminum/silicon carbide mixture, an
interfacial reaction which yields aluminum carbide
(Al.sub.3C.sub.4) and silicon plays an important role. It has
become clear that if this interfacial reaction proceeds
excessively, the resultant composite alloy has a reduced thermal
conductivity mainly because the aluminum carbide generated at the
interface in too large an amount inhibits thermal conduction
through the aluminum/silicon carbide interface, and because the
silicon generated and present in too large an amount as a component
of a solid solution in aluminum enhances heat dispersion.
[0055] In each of the conventional infiltration, casting, and
pressure casting methods, it is difficult to control the
interfacial reaction between aluminum and silicon carbide since
each method is intended to alloy aluminum in a completely melted
state. Because of the use of aluminum as a melt, the interfacial
reaction proceeds excessively to yield large amounts of aluminum
carbide and silicon, or proceeds insufficiently to result in poor
adhesion between the aluminum and silicon carbide and hence in
inefficient heat transfer. Consequently, the thermal conductivities
of the alloys obtained by those conventional methods are below 180
W/m.multidot.K. In contrast, in the present invention, the
interfacial reaction can be easily controlled by employing the
sintering method and, as a result, an aluminum/silicon carbide
composite alloy having a thermal conductivity of 180 W/m.multidot.K
or higher can be obtained.
[0056] Specifically, an alloy having a thermal conductivity of 180
W/m.multidot.K or higher can be obtained by regulating the
sintering temperature to from 600 to 750.degree. C. as described
later to thereby regulate the amount of the aluminum carbide formed
by the interfacial reaction so that the ratio of the peak intensity
for aluminum carbide (012) to that for aluminum (200) both
determined by X-ray analysis with CuK.sub..alpha. line is not more
than 0.025. An alloy having a thermal conductivity of 180
W/m.multidot.K or higher can be obtained also by regulating the
amount of the aluminum carbide not more than to 5% by weight. If
the amount of the aluminum carbide is below the lower limit of the
above range, the interfacial reaction is insufficient and
densification does not proceed. On the other hand, if the amount
thereof exceeds the upper limit, the thermal conductivity of the
alloy is below 180 W/m.multidot.K for the reason stated above.
[0057] The process of the present invention for producing a
semiconductor substrate material is then explained. As shown in
FIG. 1, an aluminum/silicon carbide starting powder is first
prepared which comprises aluminum or an aluminum alloy and from 10
to 70% by weight silicon carbide. Although various techniques may
be used for preparing the starting powder, it is necessary to
employ a technique which imparts to the starting powder
satisfactory suitability for compaction and sintering. For example,
a mixture of a powder of either aluminum or an aluminum alloy with
a powder of silicon carbide can be used as a starting powder.
Although this technique is the simplest and most inexpensive, the
two powders should be mixed until the mixture becomes homogeneous.
Since the particle sizes of the two powders strongly influence the
mixability thereof, the average particle diameter of the one powder
is desirably up to two times that of the other powder.
[0058] A rapidly solidified powder prepared by solidifying an
alloying melt comprising a mixture of aluminum or an aluminum alloy
with silicon carbide may also be used as a starting powder. The
starting powder obtained by this technique has exceedingly high
homogeneity and excellent suitability for compaction. It is also
possible to use a starting powder obtained by mechanically alloying
a powder of either aluminum or an aluminum alloy with a silicon
carbide powder. Either pure aluminum or an aluminum alloy may be
used as a material for a starting powder. Pure aluminum is useful
for easily obtaining a compact having an increased density because
of the high deformability thereof, and is the most effective in
heightening thermal conductivity. However, due to its high
deformability, pure aluminum may cause seizing in the mold
depending on the shape of the mold. This seizing can be prevented
by using an alloy of aluminum with, e.g., silicon to thereby keep
the particles hard.
[0059] Subsequently, the aluminum/silicon carbide starting powder
thus obtained is compacted into a desired substrate shape, as shown
in FIG. 1. This compaction serves to adhere the particles of the
starting powder to one another beforehand to thereby enable the
resulting compact to retain its shape during the subsequent
sintering without breaking and to give a dense sinter. Finally,
this compact is sintered in a non-oxidizing atmosphere in order to
prevent aluminum from oxidizing. The sintering should be conducted
at a temperature of 600.degree. C. or higher, because sintering
temperatures lower than 600.degree. C. result in insufficient
bonding among particles.
[0060] As stated above, the sintering in the process of the present
invention is conducted in a non-oxidizing atmosphere for aluminum.
A useful non-oxidizing atmosphere is a nitrogen atmosphere
preferably having a nitrogen concentration of 99% by volume or
higher. Such a nitrogen atmosphere serves not only to prevent
oxidation but to generate aluminum nitride (AlN) through the
reaction of nitrogen with aluminum, thereby yielding an
aluminum/silicon carbide composite alloy containing nitrogen. On
the other hand, in the case of using a non-oxidizing atmosphere
comprising hydrogen, carbon monoxide, or a rare gas such as argon,
the alloy obtained contains no nitrogen.
[0061] In ordinary sintering, densification is generally inhibited
by the gas remaining within the alloy. However, the use of nitrogen
as a non-oxidizing atmosphere was found to be effective in
densification because the nitrogen gas remaining within the alloy
turns into aluminum nitride through reaction with aluminum. An
alloy containing nitrogen especially in an amount of 0.01% by
weight or larger is advantageous for attaining a thermal
conductivity of 180 W/m.multidot.K or higher. However, if the
content of nitrogen exceeds 1% by weight, densification is
inhibited rather than enhanced. Therefore preferred range of the
nitrogen content in the aluminum/silicon carbide composite alloy is
henee from 0.01 to 1% by weight.
[0062] If a sintering atmosphere containing oxygen or steam is
used, aluminum is oxidized, resulting in impaired properties. It is
therefore desirable to conduct sintering in an atmosphere having an
oxygen concentration of 200 ppm or lower and a dew point of
-20.degree. C. or lower. When this non-oxidizing atmosphere is used
to conduct sintering, no oxidation reaction proceeds during the
sintering, and the resultant alloy contains the same amount of
oxygen as the starting powder used. Namely, the aluminum/silicon
carbide composite alloy obtained has an oxygen content of from 0.05
to 0.5% by weight.
[0063] In the present invention, the interfacial reaction between
aluminum and silicon carbide can be controlled by regulating the
sintering temperature to from 600 to 750.degree. C. as described
above. If the sintering temperature exceeds 750.degree. C., the
carbonization of aluminum proceeds due to the interfacial reaction.
As a result, the amount of aluminum carbide yielded at the
interface exceeds the upper limit of the 5 wt % range, and the
aluminum or aluminum alloy contains silicon as a component of a
solid solution therein or as a precipitate in an amount larger than
the upper limit of the 3 wt % range. Such too large amounts of
aluminum carbide and silicon contained in the aluminum/silicon
carbide composite alloy reduce the thermal conductivity of the
alloy. It is therefore necessary to use a sintering temperature of
from 600 to 750.degree. C. for attaining a thermal conductivity of
180 W/m.multidot.K or higher.
[0064] Liquid-phase sintering can be conducted in the process of
the present invention, in which the compact is heated to or above
the melting point of aluminum or the aluminum alloy. It has been
thought that in a liquid-phase sintering system in which the
proportion of the liquid phase is 30% or larger, shape retention is
generally difficult because of the outflow or foaming of the liquid
phase. However, the compact according to the present invention can
retain its shape even in liquid-phase sintering because silicon
carbide has exceedingly high wettability by aluminum. In
particular, a compact having a silicon carbide content of from 35
to 70% by weight well retains its shape with high precision even in
liquid-phase sintering.
[0065] The aluminum/silicon carbide composite alloy thus produced
through sintering can be used as a substrate material without
conducting any treatment. However, the composite alloy may be
repressed in a non-oxidizing atmosphere, or may be repressed and
then heated in an non-oxidizing atmosphere. Since the composite
alloy has a structure comprising a matrix of aluminum, which is
highly deformable, and hard silicon carbide particles dispersed
therein, repressing is effective not only in attaining a further
improvement in precision, but also in removing residual voids and
densifying the composite alloy to thereby greatly change the shape
thereof. Although the alloy may develop fine cracks during this
repressing, the cracks can be eliminated by heating the repressed
alloy in a non-oxidizing atmosphere.
[0066] And according to aluminum/silicon carbide composite alloys
formed as above, a substrate can be formed precisely to be near net
shaped or in net shaped without warp or deform. In this case it is
not required to machine-processing with respect to whole
surface.
[0067] For use as a substrate such as workstation having higher
reliability, the substrate material should be subjected to a
surface treatment. Possible techniques for surface treatment
include plating, chromating, anordic oxidation to form an alumite
film, other oxidation treatment, and organic resin coating
[0068] In plating, the substrate material is plated with nickel or
Ni--Au to thereby protect the aluminum parts, which are susceptible
to oxidation. Chromate treatment is preferred in that film
formation on the surface of the semiconductor substrate material is
easy and a film can be homogeneously formed even when the surface
is highly rough. A plated substrate material can be made to have
further improved reliability by conducting chromating as a final
step. Oxidation treatment such as anodic oxidation is also
preferred in that film formation is easy and a film can be evenly
formed even when the surface of the substrate material is rough.
This oxidation can be accomplished by exposing the substrate
material to the air at a temperature of about from 200 to
600.degree. C. or exposing the same to a steam atmosphere heated to
about from 200 to 600.degree. C. Further subjecting the oxidized
semiconductor substrate material to chromate treatment is effective
in ensuring even higher reliability. Further coating a surface of
the substrate with a film made of organic resin such as an epoxy
resin, a silicone resin, a polyimide resin, or the like, is more
effective in ensuring even higher reliability.
[0069] A rough surface resulting from the debonding of particles
may have the problems of impaired solder flowability and reduced
resin bonding strength. These problems can be significantly
mitigated by sealing the surface with an organic or metallic
material prior to plating.
[0070] In a technique for the sealing treatment with an organic
material, the surface is coated with an epoxy resin, a silicone
resin, a polyimide resin, or the like by screen printing, dipping,
spinner coating, or another means. The electrical conductivity of
the surface may be maintained by using a resin containing silver or
copper as a filler. The organic film thus formed on the surface is
cured and then polished to complete the sealing treatment.
[0071] One possible technique for the sealing treatment with a
metallic material is plating. A metal film is formed by plating in
a thickness larger than depth of the depressions, and the metal
layer on the surface of the substrate is polished. Thus, the
surface roughness of the substrate material can be completely
eliminated. Preferred examples of the metal plated include those
having a Young's modulus of 15,000 kg/mm.sup.2 or lower, e.g.,
copper. Metals having such a low Young's modulus can be easily
polished, and are capable of readily filling up the depressions
because they are drawn out by polishing. On the other hand, if a
metal having a Young's modulus higher than 15,000 kgf/mm.sup.2,
e.g., nickel, is formed by plating, the metal is not drawn out by
polishing and cannot completely fill up the depressions. A
substrate material plated with copper alone readily rusts in
reliability tests. Hence, by subjecting the copper-plated and then
polished substrate material to plating with nickel, the resultant
substrate can satisfy not only the requirement concerning solder
flowability and resin bonding strength but also reliability.
[0072] Barrel plating is desirably used for forming a layer of a
metal having a Young's modulus of 15,000 kg/mm.sup.2 or lower on
the semiconductor substrate material. Barrel plating has an
advantage that the plated objects have no jig marks since the works
are plated in a suspended state in the container. During the barrel
plating operation, the works repeatedly collide with one another in
the plating bath. When dummy particles are introduced into the
container, the works collide also with the dummy particles. Upon
the collisions, the dummy particles are abraded and the resultant
debris of the dummy particles adhere to the works being plated.
This adhesion is more apt to occur in the depressions of the
surface, thereby mitigating the surface roughness. The dummy
particle debris adherent to the works preferably are easily drawn
out. Namely, the dummy particles are preferably made of a material
having a low Young's modulus, specifically 15,000 kgf/mm.sup.2 or
lower, e.g., copper. Metals having such a low Young's modulus can
be easily drawn out and are capable of readily filling up the
depressions. If a material having a Young's modulus higher than
15,000 kgf/mm.sup.2, e.g., nickel, is used, it is not drawn out and
cannot completely fill up the depressions. The dummy particles
desirably have a particle diameter of from 0.1 to 10 mm. If dummy
particles smaller than 0.1 mm are used, they undergo insufficient
collisions during barrel plating and are hence unable to completely
fill up the depressions. Dummy particles larger than 10 mm are
undesirable in that the works being plated are damaged by the
particles. The dummy particles desirably have such a shape that the
surface area thereof is large. By regulating the dummy particles so
as to have a surface area at least two times that of the
corresponding spheres, the dummy particles can exhibit their effect
in a reduced time period for barrel plating.
[0073] A further technique for eliminating a surface roughness is
to use a metal which melts at low temperatures, for example, to
plate the surface with tin. The semiconductor substrate material
plated with tin is heated to at least 240.degree. C., which is the
melting point of tin, whereby the tin melts and flows into the
depressions. As a result, a surface free from roughness can be
formed. The molten tin takes up aluminum, silicon, etc. as
impurities to come to have an increased melting point. The
solidified tin layer therefore does not melt again even in a later
soldering operation. Metals usable in this technique are those
having a melting point not higher than the sintering temperature
for the aluminum/silicon carbide composite alloy, i.e., not higher
than 600.degree. C.
[0074] Formation of a coating layer comprising aluminum as the main
component is effective in improving the bonding strength of a
resin.
[0075] In forming an aluminum layer by vapor deposition or the
like, polygonal crystal grains generate. Although there are minute
differences in level of 1 .mu.m or smaller among the crystal
grains, these level differences are not detected in a surface
roughness measurement. A combination of the diameter of the crystal
grains with those level differences among the crystal grains
produces a sufficient anchoring effect.
[0076] By regulating the diameter of the crystal grains
constituting of the coated aluminum layer to from 0.1 to 10 .mu.m,
a sufficient anchoring effect can be produced. If the crystal
grains have a diameter smaller than 0.1 .mu.m, a resin used for
bonding cannot sufficiently infiltrate into spaces among the
crystals and this often results in vacant holes, which are apt to
lead to a bonding failure. If the crystal grains have a diameter
larger than 10 .mu.m, a sufficient bonding strength cannot be
obtained because the number of grains per unit area which
contribute to an anchoring effect is small, although a resin can
infiltrate into spaces among the crystals.
[0077] In the case of a substrate for mounting a semiconductor
device, having such a structure in which a sufficient anchoring
effect is obtained, there is no particular need of forming an oxide
film. Namely, this substrate desirably has a native oxide layer
having a thickness of from 10 to 800 .ANG.. If there is no native
oxide layer, no hydrogen bonds are formed between the substrate and
a resin, so that sufficient bonding strength cannot be maintained.
If the substrate has an oxide film having a thickness exceeding 800
.ANG., the bonding strength between the oxide film and the base
metal cannot be maintained because of the brittleness of the metal
oxide film, although the bonding strength between the oxide film
and a resin is satisfactory.
[0078] The thickness of the aluminum layer formed is preferably
from 1 to 100 .mu.m. If the thickness thereof is smaller than 1
.mu.m, there are cases where a structure sufficient to produce an
anchoring effect cannot be formed. On the other hand, if the
thickness thereof is larger than 100 .mu.m, breakage is apt to
occur within the film. Since the formation of an aluminum film
thicker than 20 .mu.m may require much time, the more preferred
range of aluminum film thickness is from 1 to 20 .mu.m.
[0079] The aluminum film formed may be made of either aluminum or
an aluminum alloy. However, use of an aluminum alloy is
disadvantageous in that compositional control during film formation
is difficult and the adhesion thereof to the base is apt to
unstable. An aluminum film having a purity of preferably 99.9% by
weight or higher, more preferably 99.99% by weight or higher, is
desirable because of its diminished fluctuations in adhesion to the
base.
[0080] The surface state of the base on which an aluminum film is
to be formed is desirably regulated so as to have a surface
roughness in the range of from 0.1 to 20 .mu.m in terms of
R.sub.max as provided for in JIS. If the surface roughness,
R.sub.max, thereof is lower than 0.1 .mu.m, a sufficient anchoring
effect is difficult to obtain even when an aluminum film having the
structure described above is formed. If the R.sub.max thereof is
higher than 20 .mu.m, the amount of adsorbed gas increases, so that
the base releases an increased amount of oxygen during film
formation thereon. For example, if an aluminum film is formed on
such a rough surface by vapor deposition at a degree of vacuum
higher than 10.sup.-3 Torr, the resulting aluminum film
disadvantageously is made of crystal grains having a diameter
smaller than 0.1 .mu.m or has impaired adhesion to the base. For
bases having an R.sub.max higher than 20 .mu.m, it is difficult to
attain a degree of vacuum of 10.sup.-3 Torr or lower. Values of
R.sub.max higher than 8 .mu.m are usually undesirable in that after
the base surface is bonded with a resin, vacant spaces are apt to
remain between the resin and the surface, resulting in enhanced
fluctuations of bonding strength. Therefore, the R.sub.max of the
base is more desirably regulated to 8 .mu.m or lower. For
satisfying the above requirement, the base surface is desirably
regulated so as not to have holes having a depth exceeding 100
.mu.m. If the base surface has holes having a depth exceeding 100
.mu.m, not only gas adsorption occurs in a larger amount as stated
above, but also a film having a uniform thickness is difficult to
form on the base. In this case, the film formed is apt to have
pits. In addition, a resin used for bonding is less apt to
sufficiently infiltrate into the spaces, resulting in insufficient
bonding strength.
[0081] A possible technique for forming an aluminum film is vapor
deposition. First, a test piece is introduced into a chamber for
vacuum deposition. Prior to deposition, the chamber is evacuated.
The degree of vacuum in this stage influences the quality of the
aluminum film to be formed. A vacuum of 10.sup.-5 Torr or lower is
desirable. If a higher degree of vacuum is used, the test piece
releases an adherent gas during deposition and the aluminum grains
formed tend to have a reduced diameter. After evacuation, aluminum
is deposited. A preferred deposit source is aluminum having a
purity of 99.9% by weight or higher. If a source consisting of
aluminum having a purity up to around 99% by weight is used,
compositional control is difficult and enhanced fluctuations of
adhesion to the base are apt to result. During the deposition, the
degree of vacuum is preferably regulated to 10.sup.-1 Torr or
lower. If a higher degree of vacuum is used, the aluminum grains
formed have a diameter smaller than the desired value. During the
deposition, the test piece may be or may not be kept heated. Even
without heating, the temperature of the surface of the test piece
usually rises to about 100 to 200.degree. C.
[0082] An aluminum film can also be obtained by applying a
dispersion of aluminum particles in an organic solvent by screen
printing and then sintering the coating in an inert, vacuum, or
reducing atmosphere. In this technique also, the atmosphere for
sintering is crucially important for obtaining an aluminum film
having the desired grain diameter.
[0083] Still another technique which can be used for obtaining an
aluminum film comprises applying a dispersion of aluminum particles
in an organic solvent by dipping and then sintering the coating in
an inert, vacuum, or reducing atmosphere. A further technique
usable for obtaining an aluminum film comprises forming an aluminum
coating by flame spraying under an inert or reducing gas
atomosphere and then sintering the aluminum coating in an inert,
vacuum, or reducing atmosphere. In each technique, the atmosphere
for sintering is crucially important for obtaining an aluminum film
having the desired grain diameter. When the sintering is employed
in vacuum, it is allowable to control the sintering atmosphere in
the same manner of the above-described upper deposition
process.
[0084] However, in the case using an inert gas or reducing gas, an
impurity gaseous content in such gas is necessary to be controlled
lower than 500 ppm, because the grain diameter of the aluminum film
is apt to become smaller by adhering a gas such as oxygen, which
generates from the substrate, on the aluminum film surface.
[0085] The aluminum/silicon carbide composite alloy thus obtained
can be used as a semiconductor substrate material having a thermal
expansion coefficient of 20.times.10.sup.-6/.degree. C. or lower
and a thermal conductivity of 100 W/m.multidot.K or higher. It is
also possible to obtain an alloy having a thermal expansion
coefficient of 15.times.10.sup.-6/.degree. C. or lower and a
thermal conductivity as high as 180 W/m.multidot.K or higher, which
values have not been attained with any prior art technique. This
alloy is suitable for use as a semiconductor substrate material for
a plastic package. Since the alloy is lightweight, it is also
suitable for flip chip bonding for electrically bonding a
semiconductor element to a package or for ball grid array bonding
to a base substrate. Furthermore, by subjecting the alloy to a
surface treatment, it can be used as a substrate for mounting a
semiconductor device, having higher reliability.
EXAMPLE 1
[0086] An aluminum powder having an average particle diameter of 25
.mu.m was mixed in various proportions with a silicon carbide
powder consisting of a mixture of .alpha.-crystals and
.beta.-crystals and having an average particle diameter of 50 .mu.m
to prepare sample powders 1 to 9 respectively having silicon
carbide contents of 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 75%
by weight. These sample powders each was homogenized with a kneader
for 1 hour to obtain aluminum/silicon carbide starting powders.
[0087] The starting powders obtained were compacted at a pressure
of 7 t/cm.sup.2 to obtain tablet test pieces having a diameter of
20 mm and a height of 30 mm. These compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a results,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0088] However, the alloy of sample 9 was not dense and had voids
in a surface layer thereof; this alloy was hence not subjected to
the following measurements.
[0089] Each sinter was examined for SiC content, density after
sintering, thermal conductivity, thermal expansion coefficient,
nitrogen content, oxygen content, aluminum carbide content, and the
ratio of the peak intensity for aluminum carbide (012) to that for
aluminum (200) both determined by X-ray analysis with
CuK.sub..alpha., line. The results obtained are shown in Table 1.
Density was determined by the Archimedes' method. Thermal
conductivity was determined by the laser flash method. Thermal
expansion coefficient was determined by averaging found values
obtained with a push rod type apparatus in the temperature range of
from 20 to 200.degree. C. Nitrogen content was determined by gas
analysis. Content of SiC was determined by pulverizing an alloy,
removing all components excluding SiC and silicon with an acid,
dissolving the silicon in hydrofluoric acid, and calculating the
SiC content from the resulting weight change. Aluminum carbide
content was determined by pulverizing an alloy, dissolving aluminum
carbide with sodium hydroxide, and calculating the aluminum carbide
content from the amount of the methane gas generated. Further, each
alloy was examined by x-ray analysis with CuK.sub..alpha. line to
determine the ratio of the peak intensity for aluminum carbide
(012) to that for aluminum (200).
[0090] A photomicrograph taken with an optical microscope
(.times.100) of a metal structure of the alloy of sample 6 is shown
in FIG. 2. As apparent from FIG. 2, the aluminum/silicon carbide
composite alloy of the present invention had a micro structure
comprising aluminum (light gray parts) and silicon carbide granular
particles (black parts) dispersed therein. Furthermore, with
respect to each of samples 1 to 8, the surface layers thereof,
i.e., the oxide layer, the nitride layer, and the SiC-free
aluminum, were removed and the remaining Al--Sic alloy composition
parts were examined for difference in SiC content as follows.
Central and surface parts of the Al--SiC alloy composition parts
were compositionally analyzed with an electron microscope with
respect to an area of 0.5 mm.sup.2 for each part to determine the
SiC contents thereof. As a result, the difference in SiC content
was within 1% by weight in each alloy. From the compositional
electron microscopy, it was ascertained that in each of samples 1
to 8, aluminum carbide was present at the interface between the
aluminum and the silicon carbide and silicon was present mainly as
a component of a solid solution in aluminum and partly as a
precipitate.
[0091] In order to compare with the examples, following were
examined. Firstly, a silicon carbide powder having an average
particle diameter of 35 .mu.m and a silicon carbide powder having
an average particle diameter of 5 .mu.m were mixed in a weight
ratio of 3:1, and added a binder. These sample powders homogenized
with a kneader for 1 hour to obtain silicon carbide starting
powders.
[0092] The starting powders obtained were compacted at a pressure
of 7 t/cm.sup.2 to obtain tablet test pieces having a diameter of
20 mm and a height of 30 mm. These compacts were sintered in a
nitrogen atmosphere to remove a binder. Then after degassing the
tablet test pieces in a pressured chamber, they were
pressure-infiltrated in an aluminum melt. As a result,
aluminum/silicon carbide composite alloy having silicon carbide
contents of 71% by weight were obtained. It was difficult to obtain
aluminum/silicon carbide composite alloy having silicon carbide
contents of less than 70% by weight by similar method. Because more
porosity in the formed silicon carbide compact is required, and the
formed silicon carbide compact is not stiff enough to keep it
shape.
[0093] Secondly, a silicon carbide powder having an average
particle diameter of 35 .mu.m and a silicon carbide powder having
an average particle diameter of 5 .mu.m were mixed in a weight
ratio of 3:1, further added 5 weight % of Al-1 wt % Mg powder, and
added a binder. These sample powders were homogenized with a
kneader for 1 hour to obtain silicon carbide starting powders.
[0094] The starting powders obtained were compacted at a pressure
of 7 t/cm.sup.2 to obtain tablet test pieces having a diameter of
20 mm and a height of 30 mm. After compacting, Al-1 wt % Mg alloy
pellets were set, as infiltrating agent, on one side surface of
silicon carbide compacts and then these compact assemblies were
heated to 800.degree. C. in a nitrogen atmosphere to infiltrate the
molten infiltrating agent. Then as a result, aluminum/silicon
carbide composite alloy having silicon carbide contents of 71% by
weight were obtained. It was difficult to obtain desire-shaped
aluminum/silicon carbide composite alloy having silicon carbide
contents of less than 70% by weight by similar method, because of
large deformation of compacts during the infiltration. Thirdly, 30%
by weight of a silicon carbide powder having an average particle
diameter of 35 .mu.m is added to molten aluminum and then this
mixture is pressure-casted to obtain tablet test pieces having a
diameter of 20 mm and a height of 30 mm. It was difficult to obtain
aluminum/silicon carbide composite alloy having silicon carbide
contents of more than 35% by weight by similar method, because an
amount of aluminum is so much that it cannot be pressure-casted.
Further in order to compare with the examples, aluminum/silicon
carbide composite alloy having silicon carbide contents of 38% by
weight equal to the sample 5, were produced by the method of
infiltration and the method of casting. After removing an aluminum
layer and melted out part, central and surface parts of the Al--SiC
alloy composition parts were compositionally analyzed with an
electron microscope with respect to an area of 0.5 mm.sup.2 for
each part to determine the SiC contents thereof. As a result, the
difference in SiC content excesses 2% by weight in each alloy.
1TABLE 1 Thermal SiC Thermal expansion Nitrogen Oxygen
Al.sub.4C.sub.3 Al.sub.4C.sub.3 content Density conductivity
coefficient content content content (012)/ Sample (wt %)
(g/cm.sup.3) (W/m .multidot. K) (.times.10.sup.-6/.degree. C.) (wt
%) (wt %) (wt %) Al(200) 1* 3 2.69 238 21.9 0.28 0.42 0.7 0.001 2*
8 2.71 235 20.2 0.28 0.40 1.8 0.003 3 18 2.75 229 17.3 0.27 0.31
2.2 0.005 4 28 2.79 224 15.8 0.27 0.23 2.7 0.009 5 38 2.78 215 14.0
0.25 0.20 2.8 0.015 6 48 2.76 201 12.5 0.24 0.18 2.7 0.020 7 58
2.75 192 9.4 0.23 0.16 1.7 0.021 8 67 2.72 185 7.5 0.24 0.15 1.1
0.019 9* -- not -- -- -- -- -- -- densified (Note) The samples
indicated by * are comparative examples.
[0095] Table 1 shows that the aluminum/silicon carbide composite
alloys having a silicon carbide content in the range of from 10 to
70% by weight satisfied the requirement that the thermal
conductivity be 100 W/m.multidot.K or higher and the thermal
expansion coefficient be 20.times.10.sup.-6/.degree. C. or lower.
It was further understood that the alloys having a silicon carbide
content in the range of from 35 to 70% by weight had a thermal
expansion coefficient of 15.times.10.sup.-6/C or lower.
EXAMPLE 2
[0096] An aluminum powder having an average particle diameter of 25
.mu.m was mixed in a weight ratio of 1:1 with a silicon carbide
powder consisting of a mixture of .alpha.-crystals and
.beta.-crystals and having an average particle diameter of 50
.mu.m. This mixture was homogenized with a kneader for 1 hour to
obtain an aluminum/silicon carbide starting powder. The starting
powder obtained was compacted at a pressure of 7 t/cm.sup.2 to
obtain tablet test pieces having a diameter of 20 mm and a height
of 30 mm. These compacts were sintered in a nitrogen, hydrogen, or
argon atmosphere under the conditions shown in Table 2. As a
result, aluminum/silicon carbide composite alloy sinters were
obtained which retained the original shape of the compacted test
pieces.
[0097] Each sinter was examined for density, thermal conductivity,
thermal expansion coefficient, nitrogen content, oxygen content,
aluminum carbide content, and the ratio of the peak intensity for
aluminum carbide (012) to that for aluminum (200) both determined
by X-ray analysis with CuK.sub..alpha. line. The results obtained
are shown in Table 2. These properties were determined by the same
methods as in Example 1. The results given in Table 2 show that
alloys having a thermal conductivity of 100 W/m.times.K or higher
could be obtained by conducting sintering at temperatures not lower
than 600.degree. C. The results further show that alloys having a
thermal conductivity of 180 W/m.times.K or higher could be obtained
by conducting sintering at 600 to 750.degree. C. to regulate the
amount of the aluminum carbide yielded by an interfacial reaction
to such a value that the ratio of the peak intensity for aluminum
carbide (012) to that for aluminum (200) both determined with
CuK.sub..alpha. line was equal to or lower than 0.025 or that the
aluminum carbide content was equal to or lower than 5% by weight.
The results furthermore show that the alloys obtained through
sintering in the atmospheres other than nitrogen had a nitrogen
content lower than 0.01% by weight and a thermal conductivity lower
than 180 W/m.times.K.
2TABLE 2 Thermal Sintering Thermal expansion Nitrogen Oxygen
Al.sub.4C.sub.3 Al.sub.4C.sub.3 conditions Sintering Density
conductivity coefficient content content content (012)/ Sample
(.degree. C. .times. h) atmosphere (g/cm.sup.3) (W/m .times. K)
(.times.10.sup.-6/.degree. C.) (wt %) (wt %) (wt %) Al(200) 10 900
.times. 2 nitrogen 2.72 118 12.3 0.32 0.20 8.3 0.060 11 850 .times.
2 nitrogen 2.75 161 12.3 0.30 0.20 7.9 0.053 12 800 .times. 2
nitrogen 2.75 173 12.5 0.29 0.19 7.5 0.051 13 800 .times. 8
nitrogen 2.75 175 12.5 0.31 0.19 7.7 0.053 14 750 .times. 2
nitrogen 2.76 185 12.5 0.28 0.19 4.0 0.023 15 700 .times. 2
nitrogen 2.76 201 12.5 0.24 0.18 2.7 0.020 16 700 .times. 8
nitrogen 2.75 203 12.6 0.28 0.19 2.8 0.024 17 650 .times. 2
nitrogen 2.77 221 12.7 0.20 0.18 1.2 0.013 18* 550 .times. 2
nitrogen 2.78 46 18.0 0.08 0.18 0 0 19 700 .times. 2 hydrogen 2.70
162 12.3 <0.01 0.17 2.4 0.02 20 700 .times. 2 argon 2.70 165
12.3 <0.01 0.17 2.5 0.02 (Note) The sample indicated by * is a
comparative example. Sample 15 is the same as sample 6 in Example
1.
EXAMPLE 3
[0098] Some of the aluminum/silicon carbide composite alloy sinters
obtained as sample 6 in Example 1 were repressed at a pressure of 7
t/cm.sup.2 in a nitrogen atmosphere (sample 6-1). Part of the
repressed sinters were sintered again at 700.degree. C. for 2 hours
in a nitrogen atmosphere (sample 6-2).
[0099] These sinter samples were examined for density, thermal
conductivity, thermal expansion coefficient, nitrogen content,
oxygen content, aluminum carbide content, and the ratio of the peak
intensity for aluminum carbide (012) to that for aluminum (200)
both determined by X-ray analysis with CuK.sub..alpha. line, in the
same manner as in Example 1. The results obtained are shown in
Table 3. It is understood from Table 3 that repressing and
resintering were effective in heightening the density and improving
the thermal conductivity.
3TABLE 3 Thermal Sintering Thermal expansion Nitrogen Oxygen
Al.sub.4C.sub.3 Al.sub.4C.sub.3 conditions Density conductivity
coefficient content content content (012)/ Sample (.degree. C.
.times. h) (g/cm.sup.3) (W/m .times. K) (.times.10.sup.-6 .degree.
C.) (wt %) (wt %) (wt %) Al(200) 6 700 .times. 2 2.76 201 12.5 0.24
0.18 2.7 0.02 sintering 6-1 sintering .fwdarw. 2.80 203 12.9 0.24
0.18 2.7 0.02 repressing 6-2 repressing .fwdarw. 2.82 225 12.9 0.26
0.18 2.8 0.02 resintering
EXAMPLE 4
[0100] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with each of silicon carbide powders-having average
particle diameters ranging from 0.1 to 150 .mu.m, in such a
proportion as to result in a silicon carbide content of 50% by
weight. These mixtures each was homogenized with a kneader for 1
hour to obtain aluminum/silicon carbide starting powders.
[0101] The starting powders obtained were compacted at a pressure
of 7 t/cm.sup.2 to obtain test pieces having dimensions of 50 mm by
25 mm by 2 mm (thickness). These compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0102] The samples thus produced were evaluated for resin bonding
strength in accordance with JIS K 6850 as follows. A liquid epoxy
resin containing 70% by weight silver filler was applied to a
sample piece in a resin thickness of 25 .mu.m. This sample piece
was placed on another Al--SiC sample piece in the manner shown in
FIG. 11. The resultant structure was heated at 180.degree. C. for 1
hour to cure the resin, and then dried at 150.degree. C. for 24
hours.
[0103] The test pieces thus obtained according to JIS K 6850 were
examined for bonding strength after the drying and after each of
the thermal cycling test, PCT, and HAST. In the thermal cycling
test, the strength was measured after 100 cycles each consisting of
30-minute exposure to a 150.degree. C. atmosphere and 30-minute
exposure to -65.degree. C. atmosphere. In the PCT, the strength was
measured after a 100-hour treatment under the partial-saturation
conditions of 121.degree. C., 100% RH, and 2 atm. In the HAST, the
strength was measured after a 100-hour treatment under the
conditions of. 125.degree. C., 85% RH, and 2 atm. The measurement
of bonding strength was made with a precision universal tester
(Autograph). In the manner shown in FIG. 11, a test piece bonded to
which two test substrates A are bonded, was held by the holding
regions C with the grips of the tester. The test piece was pulled
at a rate of 50 mm/min while taking care to keep the major axis of
the test piece and the center line of the grips on the same
straight line. The maximum load at the time of test piece breakage
was recorded, and this value was divided by the area of the resin
bonding region of the test piece. This quotient was taken as the
bonding strength. The test piece breakage occurred in the resin
bonding region. The results obtained are shown in Table 4.
[0104] For the purpose of comparison, the tensile strength of the
resin alone used for bonding was measured as follows. The liquid
resin was formed into a sheet, cured at 180.degree. C. for 1 hour,
and then dried at 150.degree. C. for 24 hours. The strength thereof
after the drying was 2 kgf/mm.sup.2. The strength thereof after 100
thermal cycles was 1.6 kgf/mm.sup.2, that after the 100-hour PCT
was 1.2 kgf/mm.sup.2 and that after the 100-hour HAST was 1.3
kgf/mm.sup.2.
4TABLE 4 Strength Particle Initial after Strength Strength SiC
diameter strength thermal after after Sam- content of SiC (kgf/
cycling PCT HAST ple (wt %) (mm) mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) *21 50 0.1 1.0 0.6 0.3 0.4 22 50 1
1.2 0.8 0.5 0.6 23 50 10 1.5 1.0 0.8 0.9 24 50 50 1.5 1.0 0.8 0.9
25 50 80 1.4 0.9 0.7 0.8 26 50 100 1.2 0.8 0.5 0.6 *27 50 150 1.0
0.8 0.3 0.4
[0105] The results show that the Al--SiC sinters obtained using SiC
powders each having an average particle diameter of from 1 to 100
.mu.m could retain satisfactory bonding strengths not lower than
1.0 (kgf/mm.sup.2) at the initial stage and not lower than 0.5
(kgf/mm.sup.2) after the reliability tests.
EXAMPLE 5
[0106] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m in such a proportion as to result in
a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Example 4. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0107] One of the alloys as sample 28 obtained was treated with an
alkaline solution for 1 minute to etch the aluminum. The resultant
surface was subjected to zincate conversion and then electroless
nickel-phosphorus plating. Thus, sample 28 was obtained. The
deposit formed by the plating had a thickness of 5 .mu.m.
[0108] Another alloy as sample 29 was subjected to alumite
treatment in a sulfuric acid bath at a current density of 1.5
.ANG./dm.sup.2, and then boiled in ion-exchanged water to seal the
holes. Thus, sample 29 was obtained. The sample had a 5-mm alumite
layer on the aluminum, but had no alumite layer on the SiC.
[0109] Still another alloy as sample 30 was subjected to a
chromating, in which the alloy was immersed in a phosphate-chromate
treating liquid at 50.degree. C. for 1 minute, immediately washed
with water, and then dried at 80.degree. C. Thus, sample 30 was
obtained. The chromate layer deposited had a thickness of 500
.ANG..
[0110] A further alloy as sample 31 was plated with
nickel-phosphorus in a thickness of 5 .mu.m by the same method as
the above. A 500-.ANG. chromate layer was then formed thereon by
the same method as the above. Thus, sample 31 was obtained.
[0111] Still a further alloy sample as sample 32 was subjected to
an oxidation treatment, in which the sample was heated in the air
at 300.degree. C. for 1 hour. Thus, sample 32 was obtained. Still a
further alloy as sample 33 was heated in a steam atmosphere at
300.degree. C. for 1 hour to obtain sample 33 The test pieces
obtained above were subjected to the PCT to evaluate corrosion
resistance. In the PCT, the appearance of each test piece was
examined after a 100-hour treatment under the partial-saturation
conditions of 120.degree. C., 100% RH, and 2 atm. The results
obtained are shown in Table 5.
[0112] The sample 28 treated only by nickel-phosphorus plating had
uncovered parts where the deposit was not present, and these parts
were found after the PCT to have stained. In the sample 29 which
had undergone the alumite treatment, the surface SiC parts remained
uncovered with alumite, and staining was observed at the interface
between the alumite parts and the SiC parts. No change in
appearance was observed in the other samples even after the
PCT.
5 TABLE 5 Sample 28 staining occurred Sample 29 staining occurred
at alumite layer/SiC particle interface Sample 30 .largecircle.
Sample 31 .largecircle. Sample 32 .largecircle. Sample 33
.largecircle.
EXAMPLE 6
[0113] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m in such a proportion as to result in
a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Examples. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters, sample 34, were
obtained which retained the original shape of the compacted test
pieces. The dimensions of each sinter were 50 mm by 25 mm by 2 mm
(thickness).
[0114] One of the alloys obtained was subjected to a chromate
treatment, in which the alloy was immersed in a phosphate-chromate
treating liquid at 50.degree. C. for 1 minute, immediately washed
with water, and then dried at 80.degree. C. Thus, sample 35 was
obtained. The chromate layer deposited had a thickness of 500
.ANG..
[0115] Another alloy sample was subjected to an oxidation
treatment, in which the sample was heated in the air at 300.degree.
C. for 1 hour. Thus, sample 36 was obtained. Still another alloy
was heated in a steam atmosphere at 300.degree. C. for 1 hour to
obtain sample 37.
[0116] The samples thus produced were evaluated for resin bonding
strength in accordance with JIS K 6850 in the same manner as in
Example 1. The bonding strength of each sample was measured after
the drying, after 100 cycles in the thermal cycling test, and after
each of the 100-hour PCT and the 100-hour HAST. The results
obtained are shown in Table 6.
[0117] The test pieces (sample 35-37) which had undergone any of
the surface treatments described above had higher shear strengths
than the test pieces (sample 34) which had undergone no surface
treatment.
6TABLE 6 Strength Particle Initial after Strength Strength SiC
diameter strength thermal after after Sam- content of SiC (kgf/
cycling PCT HAST ple (wt %) (mm) mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) 34 50 40 1.5 1.0 0.8 0.9 35 50 40 1.7
1.2 1.0 1.1 36 50 40 1.6 1.2 1.0 1.0 37 50 40 1.6 1.1 1.0 1.0
EXAMPLE 7
[0118] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m in such a proportion as to result in
a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Examples. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original flat-plate shape of the compacted test
pieces.
[0119] One of the alloys obtained was treated with an alkaline
solution for 1 minute to etch the aluminum. The resultant surface
was subjected to zincate conversion and then electroless plating to
deposit a 100-.mu.m copper layer. Thereafter, the plated alloy was
polished on each side with a lap to remove a surface layer in a
thickness of 50 .mu.m. The surface roughness, R.sub.max, of the
plated alloy prior to the polishing was 60 .mu.m, which decreased
to 2 .mu.m through the polishing. A 5-.mu.m Ni--P layer was further
deposited thereon by electroless plating. Thus, sample 38 was
obtained.
[0120] Another alloy was treated with an alkaline solution for 1
minute to etch the aluminum. The resultant surface was subjected to
zincate conversion and then electroless plating to deposit a
100-.mu.m Ni--P layer. Thereafter, the plated alloy was polished on
each side with a lap to remove a surface layer in a thickness of 50
.mu.m. The surface roughness, R.sub.max of the plated alloy prior
to the polishing was 60 .mu.m, which decreased only to 30 .mu.m
through the polishing. A 5-.mu.m Ni--P layer was further deposited
thereon by electroless plating. Thus, sample 39 was obtained.
[0121] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm. Furthermore, a solder flow test was conducted as follows using
a eutectic solder preform having dimensions of 10 mm by 10 mm by
0.2 mm (thickness). The preform was put on a sample and placed in a
solder reflow at 215.degree. C. for 1 minute, and the flow state of
the solder was then examined. The results obtained are shown in
Table 7.
[0122] The sample 38 plated with copper underwent no change in
appearance through the PCT and was satisfactory also in solder
flow. The sample 39 which had undergone Ni--P plating alone was
found after the PCT to have stained. In the solder flow test, part
of the solder did not flow on this sample.
7 TABLE 7 After PCT Solder flow Sample 38 .largecircle.
.largecircle. Sample 39 staining partly underwent no solder
flow
EXAMPLE 8
[0123] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m m in such a proportion as to result
in a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Examples. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0124] The alloy obtained was treated with an alkaline solution for
1 minute to etch the aluminum. The resultant surface was subjected
to zincate conversion and then plated with tin in a thickness of 50
.mu.m. The plated alloy was heated in an infrared oven at
250.degree. C. for 10 minutes, upon which the tin deposit melted
and flowed into the depressions of the Al--SiC surface. The surface
roughness, R.sub.max, of the plated alloy prior to the heating was
60 .mu.m, which decreased to 5 .mu.m through the heating. A 5-.mu.m
Ni--P layer was further deposited thereon by electroless plating.
Thus, sample was obtained.
[0125] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm. Furthermore, a solder flow test was conducted as follows using
a eutectic solder preform having dimensions of 10 mm by 10 mm by
0.2 mm (thickness). The preform was put on the sample and placed in
a solder reflow at 215.degree. C. for 1 minute, and the flow state
of the solder was then examined. The results obtained are shown in
Table 8.
[0126] This sample underwent no change in appearance through the
PCT and was satisfactory also in solder flow.
8 TABLE 8 After PCT Solder flow Sample .largecircle.
.largecircle.
EXAMPLE 9
[0127] An aluminum powder having an average particle diameter of 25
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m in such a proportion as to result in
a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Example 5. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0128] The surface of the alloy obtained was coated with an epoxy
resin in a thickness of 100 .mu.m by screen printing. The epoxy
resin contained 70% by weight copper filler having an average
particle diameter of 5 .mu.m. After the screen printing, the alloy
was heated at 180.degree. C. for 1 hour in a nitrogen atmosphere to
cure the resin. Further another sample was also prepared by
dip-coating with the same kind of epoxy resin vontaining no filler
in a thickness of 10 .mu.m. This sample was also heated in the same
manner as the above to cure the resin. Thereafter, the coated alloy
samples were polished on each side with a lap to remove a surface
layer in a thickness of 50 .mu.m. The surface roughness, R.sub.max,
of the alloy samples prior to the epoxy resin application were both
60 .mu.m, which decreased to 2 .mu.m through the coating and the
polishing. The polished surfaces were subjected to lead conversion,
and a 5-.mu.m Ni--P layer was further deposited thereon by
electroless plating. Thus, two kinds of samples were obtained.
[0129] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm. Furthermore, a solder flow test was conducted as follows using
a eutectic solder preform having-dimensions of 10 mm by 10 mm by
0.2 mm (thickness). The preform was put on a sample and placed in a
solder reflow at 215.degree. C. for 1 minute, and the flow state of
the solder was then examined. The results obtained are shown in
Table 9.
[0130] These samples underwent no change in appearance through the
PCT and was satisfactory also in solder flow.
9 TABLE 9 After PCT Solder flow Sample 1 using a resin
.largecircle. .largecircle. contained filler Sample 2 using a
filler- .largecircle. .largecircle. free resin
EXAMPLE 10
[0131] An aluminum powder having an average particle diameter of 40
.mu.m was mixed with a silicon carbide powder having an average
particle diameter of 35 .mu.m in such a proportion as to result in
a silicon carbide content of 50% by weight. The mixture was
homogenized with a kneader for 1 hour in the same manner as in the
above Example 5. Thus, an aluminum/silicon carbide starting powder
was obtained. The starting powder obtained was compacted at a
pressure of 7 t/cm.sup.2. The resultant compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a result,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces. The
dimensions of each sinter were 40 mm by 40 mm by 2 mm
(thickness).
[0132] This sample was treated with an alkaline solution for 1
minute to etch the aluminum, and the resultant surface was
subjected to zincate conversion. About ten pieces of the
thus-treated sample were placed in a jig for barrel plating, and
this jig was introduced into an electroless copper plating bath.
Ten copper spheres having any of particle diameters ranging from
0.05 to 15 mm were simultaneously placed in the jig for barrel
plating. Barrel plating was conducted for 1 hour in the jig in that
state. A 5-.mu.m Ni--P layer was then deposited by electroless
plating.
[0133] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm.
[0134] The samples 41, 42, 43 obtained through barrel plating using
the copper spheres having partial diameters ranging from 0.1 to 10
mm had a satisfactory appearance both in the initial stage and
after the PCT. The sample 40 obtained using the copper spheres
having a particle diameter of 0.05 mm stained through the PCT. The
sample 44 obtained using the copper spheres having a particle
diameter of 15 mm had many collision marks in the initial
stage.
10 TABLE 10 Diameter of Time for copper barrel spheres plating
Initial Apperance (mm) (min) appearance after PCT *40 0.05 60
.largecircle. staining 41 0.1 60 .largecircle. .largecircle. 42 1
60 .largecircle. .largecircle. 43 10 60 .largecircle. .largecircle.
*44 15 60 collision marks collision marks
[0135] Barrel plating was conducted for 30 minutes in the same
manner as the above, except that the copper spheres having a
particle diameter of 1 mm used above were replaced with copper
particles having a surface area two times that of those copper
particles. A 5-.mu.m Ni--P layer was then deposited by electroless
plating. As a result sample 45 was obtained. For the purpose of
comparison, 30-minute barrel plating was conducted using the copper
spheres having a particle diameter of 1 mm, and a 5-.mu.m Ni--P
layer was then deposited by electroless plating to produce a
comparative sample 46.
[0136] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm. The sample 45 obtained using the copper particles having a
two-fold surface area had a satisfactory appearance both in the
initial stage and after the PCT. However, the sample 46 obtained
using the copper spheres having a smaller surface area stained
through the PCT. And in order to refer to the samples, the samples
46, 47 obtained through barrel plating for 1 hour or 2 hours using
the copper spheres having diameter of 1 mm instead of the copper
spheres.
11 TABLE 11 Diameter of Time for copper barrel spheres plating
Initial Apperance (mm) (min) appearance after PCT 45 1.0 30
.largecircle. .largecircle. *46 1.0 30 .largecircle. staining *47
1.0 60 .largecircle. staining *48 1.0 120 collision marks collision
marks staining
[0137] The test pieces obtained above were subjected to the PCT to
evaluate corrosion resistance. In the PCT, the appearance of each
test piece was examined after a 100-hour treatment under the
partial-saturation conditions of 121.degree. C., 100% RH, and 2
atm.
[0138] The sample 47 obtained through 1-hour barrel plating stained
through the PCT. The sample 48 obtained through 2-hour barrel
plating had many collision marks in the initial stage, and stained
through the PCT.
EXAMPLE 11
[0139] An aluminum powder having an average particle diameter of 25
.mu.m was mixed in various proportions with a silicon carbide
powder having an average particle diameter of 35 .mu.m to prepare
sample powders 49 to 55 respectively having silicon carbide
contents of 10%, 20%, 30%, 40%, 50%, 60%, and 70% by weight as
shown Table 12. These sample powders each was homogenized with a
kneader for 1 hour to obtain aluminum/silicon carbide starting
powders.
[0140] The starting powders obtained were compacted at a pressure
of 7 t/cm.sup.2 to obtain test pieces having dimensions of 100 mm
by 25 mm by 2 mm (thickness). These compacts were sintered at
700.degree. C. for 2 hours in a nitrogen atmosphere having a
nitrogen concentration of 99% by volume or higher. As a results,
aluminum/silicon carbide composite alloy sinters were obtained
which retained the original shape of the compacted test pieces.
[0141] A section of each sinter obtained was examined with an SEM
to measure the depth of the holes. The results obtained are shown
in Table 12. The surface roughness of each sinter was measured with
a surface roughness tester. In each sinter, the R.sub.max was found
to be almost directly proportional to the depth of the holes and be
within the range of from 0.1 to 20 .mu.m.
[0142] One side of each sinter obtained was subjected to aluminum
vapor deposition as follows. The Al--SiC sinter was placed in a
vacuum chamber for vapor deposition. After the chamber was
evacuated to a vacuum of 10.sup.-5 Torr or lower, vapor deposition
was conducted using aluminum having a purity of 99.9% by weight or
higher as a deposit source. During the vapor deposition, the degree
of vacuum was from 10.sup.-3 to 10.sup.-5 Torr and the temperature
of the Al--SiC surface was from 100.degree. to 200.degree. C.
[0143] The thickness of the aluminum film deposited on each Al--SiC
sinter and the crystal grain diameter thereof are shown in Table
12. The thickness of the native oxide film on the aluminum film was
measured by micro-Auger electron spectroscopy. The results obtained
are shown in Table 12.
[0144] The samples thus produced were evaluated for resin bonding
strength in accordance with JIS K 6850 as follows. A liquid epoxy
resin containing 70% by weight silver filler was applied to a
sample piece in a resin thickness of 25 .mu.m. This sample piece
was placed on another Al--SiC sample piece in the manner shown in
FIG. 11. The resultant structure was heated at 180.degree. C. for 1
hour to cure the resin, and then dried at 150.degree. C. for 24
hours.
[0145] The test pieces thus obtained according to JIS K 6850 were
examined for bonding strength after the drying and after each of
the thermal cycling test, PCT (pressure cooker test), and HAST
(highly accelerated stress test). In the thermal cycling test, the
strength was measured after 100 cycles each consisting of 30-minute
exposure to a 150.degree. C. atmosphere and 30-minute exposure to
-65.degree. C. atmosphere. In the PCT, the strength was measured
after a 100-hour treatment under the partial-saturation conditions
of 121.degree. C., 100% RH, and 2 atm. In the HAST, the strength
was measured after a 100-hour treatment under the conditions of
125.degree. C., 85% RH, and 2 atm. The results obtained are shown
in Table 12. The measurement of bonding strength was made with a
precision universal tester (Autograph). A test piece to which two
test substrates A are bonded, was held by the holding regions with
the grips of the tester. The test piece was pulled at a rate of 50
mm/min while taking care to keep the major axis of the test piece
and the center line of the grips on the same straight line. The
maximum load at the time of test piece breakage was recorded, and
this value was divided by the area of the resin bonding region of
the test piece. This quotient was taken as the bonding strength.
The test piece breakage occurred in the resin bonding region.
[0146] The results show that all the samples retained satisfactory
bonding strengths of 0.5 (kgf/mm.sup.2) or higher both in the
initial stage and after the reliability tests.
[0147] For the purpose of comparison, the tensile strength of the
resin alone used for bonding was measured as follows. The liquid
resin was formed into a sheet, cured at 180.degree. C. for 1 hour,
and then dried at 150.degree. C. for 24 hours. The strength thereof
after the drying was 2 kgf/mm.sup.2. The strength thereof after 100
thermal cycles was 1.6 kgf/mm.sup.2, that after the 100-hour PCT
was 1.2 kgf/mm.sup.2, and that after the 100-hour HAST was 1.3
kgf/mm.sup.2. The strength of the cured resin after 1,000 thermal
cycles was 1.0 kgf/mm.sup.2, that after the 300-hour PCT was 0.7
kgf/mm.sup.2, and that after the 300-hour HAST was 0.9
kgf/mm.sup.2. It should be noted that the resin bonding strength
basically required is the strength at the time of bonding with a
resin. In general, bonding strengths not lower than 0.5
kgf/mm.sup.2 in terms of shear strength are sufficient. Also
important besides the above is the shear strength in initial stages
in a thermal cycling test, PCT, and HAST, for example, after
initial 100 thermal cycles or after initial 100 hours in an PCT or
HAST. In such initial stages in these tests, shear strengths not
lower than 0.5 kgf/mm.sup.2 are sufficient. Substrates which
satisfy the requirement concerning shear strength in this stage
generally withstand long-term practical use.
[0148] However, in few applications, substrates should satisfy a
requirement concerning shear strength after 1,000 thermal cycles or
after 300 hours in a PCT or HAST. Since the bonding resin itself
has deteriorated, the shear strength level required at such a stage
is lower than the above level and is usually higher than 0.3
kgf/mm.sup.2.
[0149] To sum up, the properties required of a substrate for
mounting a semiconductor device are initial resin bonding strength
and bonding strength in initial stages in a thermal cycling test,
PCT, and HAST. It is however desirable that the shear strength
requirement be met even after 1,000 thermal cycles and after 300
hours in a PCT or HAST.
12TABLE 12 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
native of 100 100 100 1000 300 300 SiC Depth of of oxide crystal
Initial thermal hours hours thermal hours hours content holes Al
film film grains strength cycles in PCT in HAST cycles in PCT in
HAST Sample (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) 49 10 40 2 500 1.0 2.1 1.5 1.2 1.2
0.9 0.5 0.7 50 20 40 2 500 1.0 2.1 1.5 1.2 1.2 0.9 0.6 0.7 51 30 40
2 500 1.0 2.0 1.5 1.2 1.2 0.9 0.6 0.7 52 40 40 2 500 1.0 2.0 1.5
1.2 1.2 0.9 0.6 0.7 53 50 60 2 500 1.0 1.9 1.4 1.1 1.2 0.9 0.5 0.7
54 60 60 2 500 0.8 1.9 1.3 1.1 1.2 0.8 0.5 0.7 55 70 70 2 500 0.7
1.8 1.3 1.0 1.1 0.8 0.5 0.6
COMPARATIVE EXAMPLE 1
Crystal Grain Diameter Below 0.1-mm
[0150] Al--SiC sinters were produced in the same manner as in
Example 11. An aluminum film was formed by vapor deposition in the
same manner as in Example 11, except that the degree of vacuum for
the deposition was changed to 10.sup.-2 to 10.sup.-3 Torr. The
resin bonding strength of each sample 49'-55' obtained as above was
measured in accordance with JIS K 6850 using the same resin as in
Example 11. The results obtained are shown in Table 13.
[0151] The diameters of the crystal grains formed were from 0.04 to
0.05 .mu.m. After the reliability tests, all the samples had resin
bonding strengths sufficient for practical use. In particular, the
bonding strengths thereof were 0.5 (kgf/mm.sup.2) or higher after
the reliability tests, including after 300 hours in the PCT and
HAST.
13TABLE 13 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
native of 100 100 100 1000 300 300 SiC Depth of of oxide crystal
Initial thermal hours in hours in thermal hours hours content holes
Al film film grains strength cycles PCT HAST cycles in PCT in HAST
Sample (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) 49' 10 40 2 500 0.05 1.5 0.7 0.3 0.3
0.5 0.1 0.2 50' 20 40 2 500 0.05 1.5 0.7 0.3 0.3 0.5 0.1 0.2 51' 30
40 2 500 0.05 1.4 0.7 0.3 0.3 0.5 0.1 0.2 52' 40 40 2 500 0.05 1.4
0.7 0.3 0.3 0.5 0.1 0.2 53' 50 60 2 500 0.04 1.4 0.7 0.2 0.3 0.5
0.1 0.2 54' 60 60 2 500 0.04 1.3 0.5 0.2 0.3 0.4 0.1 0.2 55' 70 70
2 500 0.04 1.2 0.5 0.2 0.3 0.4 0.1 0.1
EXAMPLE 12
Influence of Crystal Grain Diameter
[0152] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. In producing the
sinters, the oxygen atmosphere for sintering was regulated so as to
result in a hole depth of 10 .mu.m to thereby facilitate the
control of vacuum during aluminum vapor deposition. In aluminum
film deposition, the degree of vacuum was varied in the range of
from 10.sup.-2 to 10.sup.-6 Torr to form aluminum films varying in
crystal grain diameter. Except the above, an aluminum film was
formed on each sinter in the same manner as in Example 11. The
resin bonding strength of each sample was measured in accordance
with JIS K 6850 using the same resin as in Example 11. The results
obtained are shown in Table 14. The results show that the samples
having crystal grain diameters in the range of from 0.1 to 10 .mu.m
retained sufficient resin bonding strengths of 0.5 (kgf/mm.sup.2)
or higher even after the reliability tests. However, the samples
having crystal grain diameters outside that range considerably
deteriorated in resin bonding strength through the reliability
tests. In particular, these comparative samples had bonding
strengths below 0.5 (kgf/mm.sup.2) after the PCT and HAST, and were
unable to retain a sufficient bonding strength.
14TABLE 14 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
native of 100 100 100 1000 300 300 SiC Depth of of oxide crystal
Initial thermal hours in hours in thermal hours hours content holes
Al film film grains strength cycles PCT HAST cycles in PCT in HAST
Sample (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) *56 50 10 2 500 0.05 1.4 0.7 0.2 0.3
0.5 0.1 0.2 57 50 10 2 500 0.1 1.5 1.2 0.9 1.0 1.0 0.7 0.9 58 50 10
2 500 1.0 1.9 1.4 1.1 1.2 1.2 0.9 1.0 59 50 10 2 500 10 1.4 1.0 0.8
0.9 0.8 0.6 0.7 *60 50 10 2 500 20 1.4 0.7 0.2 0.3 0.6 0.1 0.1
*comparative example
EXAMPLE 13
[0153] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. In producing the
sinters, the oxygen atmosphere for sintering was regulated so as to
result in a hole depth of 10 .mu.m. Thereafter, blasting was
conducted to form holes having the depths shown in Table 15. An
aluminum film was formed on each sinter in the same manner as in
Example 11. However, with respect to the sample having a hole depth
of 200 .mu.m or larger, it was impossible to maintain a vacuum of
from 10.sup.-3 to 10.sup.-5 Torr during film formation because of
gas diffusion from the holes of the Al--SiC substrate into the
vacuum system, so that a vacuum of 10.sup.-2 to 10.sup.-3 Torr was
used.
[0154] The resin bonding strength of each sample was measured in
accordance with JIS K 6850 using the same resin as in Example 11.
The results obtained are shown in Table 15. The results show that
the samples having hole depths not larger than 100 .mu.m retained
sufficient resin bonding strengths of 0.5 (kgf/mm.sup.2) or higher
even after the reliability tests. However, the sample having a hole
depth exceeding 100 .mu.m considerably deteriorated in resin
bonding strength through the long-term (300-hours) reliability
tests. In particular, its bonding strengths were not higher than
0.3 (kgf/mm.sup.2) after the PCT and HAST; this sample was unable
to attain the most desirable reliability level, although it
satisfied the reliability level required after the initial
reliability tests and were capable of withstanding ordinary
practical use.
15TABLE 15 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
native of 100 100 100 1000 300 300 SiC Depth of of oxide crystal
Initial thermal hours in hours in thermal hours hours content holes
Al film film grains strength cycles PCT HAST cycles in PCT in HAST
Sample (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) 61 50 10 2 500 1.0 1.9 1.4 1.1 1.2
0.9 0.7 0.8 62 50 50 2 500 1.0 1.9 1.4 1.1 1.2 0.8 0.7 0.8 63 50 70
2 500 2.0 1.7 1.2 1.0 1.1 0.8 0.6 0.7 64 50 100 2 500 0.1 1.4 1.0
0.8 0.9 0.8 0.4 0.5 65 50 200 2 500 0.1 1.4 0.7 0.6 0.7 0.6 0.2
0.3
EXAMPLE 14
[0155] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. In producing the
sinters, the oxygen atmosphere for sintering was regulated so as to
result in a hole depth of 10 .mu.m. Thereafter, blasting was
conducted to form holes having the depths shown in Table 16. On the
other hand, polishing was conducted to form holes having the depths
shown in Table 16. The values of R.sub.max determined with a
surface roughness tester are also shown in Table 16. An aluminum
film was formed on each sinter in the same manner as in Example 11.
The resin bonding strength of each sample was measured in
accordance with JIS K 6850 using the same resin as in Example
11.
[0156] The results obtained show the following. The sample having a
crystal grain diameter of 1.0 mm but having an R.sub.max lower than
0.1 .mu.m considerably deteriorated in resin bonding strength
through the reliability tests. In particular, this sample had
bonding strengths not higher than 0.3 (kgf/mm.sup.2) after the
long-term (300-hour) PCT and HAST and was unable to retain a
sufficient bonding strength, although the resin bonding strengths
thereof in the initial stages in the PCT and HAST (up to 100 hours)
were not lower than 0.5 kgf/mm.sup.2, which values are sufficient
for practical use. On the other hand, the sample having a crystal
grain diameter of 0.1 .mu.m but having an R.sub.max higher than 20
.mu.m also considerably deteriorated in resin bonding strength and,
in particular, came to have bonding strengths not higher than 0.3
(kgf/mm.sup.2) through the long-term PCT and HAST, although the
bonding strengths thereof were sufficient for practical use. Thus,
these two samples were unable to attain the most desirable
reliability level.
16TABLE 16 Thickness Di- Strength Strength Strength Strength
Strength Strength Thick- of ameter after after after after after
after Depth ness native of 100 100 100 1000 300 300 SiC of of oxide
crystal Initial thermal hours in hours thermal hours hours
R.sub.max content holes Al film film grains strength cycles PCT in
HAST cycles in PCT in HAST Sample (.mu.m) (wt %) (.mu.m) (.mu.m)
(.ANG.) (.mu.m) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) 66 0.08
2 500 1.0 1.4 0.7 0.6 0.7 0.5 0.2 0.3 67 0.12 2 500 1.0 1.4 1.0 0.8
0.9 1.0 0.6 0.7 68 10 2 500 1.0 1.9 1.4 1.1 1.2 1.2 0.7 0.8 69 20 2
500 0.1 1.4 0.9 0.7 0.8 0.7 0.5 0.6 70 30 2 500 0.1 1.4 0.7 0.6 0.7
0.5 0.2 0.3 *71 50 60 2 1500 1.0 0.8 0.4 0.1 0.2 72 50 60 2 500 1.0
1.8 1.4 1.1 1.2 0.9 0.7 0.8
COMPARATIVE EXAMPLE 2
Influence of the Thickness of Native Oxide Film on Aluminum
Film)
[0157] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. An aluminum film of
thickness of 2 .mu.m, was formed on each sinter in the same manner
as in Example 11. Holes of depth of 60 .mu.m were formed on a
surface of the sinters. The diameter of the crystal grains formed
was 1.0 .mu.m. Thereafter, the sinters were heated to 300.degree.
C. in the air with a furnace to form an oxide film in a thickness
of 1500 .ANG. on the aluminum film. The resin bonding strength of
the sample was measured in accordance with JIS K 6850 using the
same resin as in Example 11. The results obtained are shown in
Table 16 under No. 71.
[0158] The sample 71 considerably deteriorated in resin bonding
strength through the reliability tests. In particular, its bonding
strengths after the PCT and HAST were lower than 0.5
(kgf/mm.sup.2), and the sample 71 was unable to retain a sufficient
bonding strength. The breakage of the test pieces occurred at the
interface between the aluminum oxide film and the aluminum film, in
contrast to the test pieces in other Examples in which breakage
occurred at the interface between the resin and the aluminum
film.
COMPARATIVE EXAMPLE 3
Influence of the Alumite Treatment of Aluminum Film
[0159] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. An aluminum film was
formed on each sinter in the same manner as in Example 11.
Thereafter, an alumite layer was formed in a thickness of 500
.ANG.. The resin bonding strength of the sample was measured in
accordance with JIS K 6850 using the same resin as in Example 1.
The results obtained are shown in Table 16 under No. 72.
[0160] The results show that the sample was capable of retaining
satisfactory bonding strengths not lower than 0.5 (kgf/mm.sup.2)
both in the initial stage and after the reliability tests. However,
the electrical conductivity of the Al--SiC was impaired due to the
alumite treatment.
EXAMPLE 15
Influence of Film Thickness
[0161] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. An aluminum film was
formed on the sinters in the same manner as in Example 11 in
various thicknesses as shown in Table 17. The resin bonding
strength of each sample was measured in accordance with JIS K 6850
using the same resin as in Example 1. The results obtained are
shown in Table 17. The results show the following. The sample
having an aluminum layer thickness smaller than 0.1 .mu.m
considerably deteriorated in resin bonding strength through the
reliability tests. In particular, its bonding strengths after the
PCT and HAST were lower than 0.5 (kgf/mm.sup.2) and the sample was
unable to retain a sufficient bonding strength. On the other hand,
the sample having an aluminum film thickness larger than 100 .mu.m
had resin bonding strengths after 100-hour treatments in the PCT
and HAST of 0.5 kgf/mm.sup.2 or higher, which values are sufficient
for practical use. However, this sample considerably deteriorated
in resin bonding strength especially through the long-term (up to
300-hour) PCT and HAST to come to have a bonding strength of 0.3
(kgf/mm.sup.2), and was unable to attain the most desirable
reliability level. In this sample having an aluminum layer
thickness larger than 100 .mu.m, the breakage of the test pieces
occurred within the aluminum layer. It is required more than 10
hours to form the aluminum layer thickness larger than 100 .mu.m by
vapor deposition. Further as another sample, the sinters having
aluminum film of 20 .mu.m thickness was formed on in the same
manner as in Example 11. In the case of this it is required more
than 1 hour to form the aluminum layer thickness of 20 .mu.m. In
considering a productivity, it is sufficient to form the aluminum
layer thickness of 20 .mu.m.
17TABLE 17 Thick- Strength Strength Strength Strength ness of
Diameter after after after after Strength Strength Depth Thick-
native of 100 100 100 1000 after after SiC of ness of oxide crystal
Initial thermal hours in hours in thermal 300 300 content holes Al
film film grains strength cycles PCT HAST cycles hours in hours in
Sample (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) PCT
HAST 73 50 60 0.08 500 1.0 1.0 0.5 0.2 0.3 0.6 0.3 0.3 74 50 60 0.1
500 1.0 1.2 0.9 0.7 0.8 0.7 0.5 0.5 75 50 60 2 500 1.0 1.9 1.4 1.1
1.2 0.8 0.6 0.7 76 50 60 100 500 1.0 1.4 1.0 0.8 0.9 0.7 0.5 0.6 77
50 60 150 500 1.0 1.0 0.8 0.5 0.6 0.6 0.3 0.3
EXAMPLE 16
Influence of Film Composition
[0162] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same manner as in Example 11. Thereafter, an
aluminum film was formed on the sinters so as to produce samples 78
to 82 in which sample 78 had an Al--Mg alloy film having an
aluminum content of 99 wt % or higher, sample 79 had an Al--Mn
alloy film having an aluminum content of 99 wt % or higher, sample
80 had an Al--Si alloy film having an aluminum content of 99 wt %
or higher, sample 81 had an Al--Cu alloy film having an aluminum
content of 99 wt % or higher, and sample 82 had an Al--Cu--Si alloy
film having an aluminum content of 99 wt % or higher. The resin
bonding strength of each sample was measured in accordance with JIS
K 6850 using the same resin as in Example 11. The results obtained
are shown in Table 18 under No. 78 to 82. The results show that
these samples were capable of retaining satisfactory bonding
strengths not lower than 0.5 (kgf/mm.sup.2) both in the initial
stage and after the reliability tests. On the other hand, samples
83 to 87 were produced by forming aluminum-based films having
various compositions by vapor deposition on Al--SiC sinter
substrates having an SiC content of 50% by weight produced by the
same method as the above. Sample 83 had an Al--Mg alloy film having
an aluminum content of 90 wt %; sample 84 had an Al--Mn alloy film
having an aluminum content of 90 wt %; sample 85 had an Al--Si
alloy film having an aluminum content of 90 wt %; sample 86 had an
Al--Cu alloy film having an aluminum content of 90 wt %; and sample
87 had a duralmin film consisting of 94.5 wt % aluminum, 4 wt %
copper, 0.5 wt % magnesium, 0.5 wt % manganese, and 0.5 wt % Fe and
Si.
[0163] Although fifty pieces were prepared for each sample, they
fluctuated in film composition. For each sample, the ten pieces
whose compositions were the most close to the composition shown
above were selected and subjected to the same evaluation as the
above. The results obtained are shown in Table 18 under No. 83 to
87. The results show that samples 83 to 87 were capable of
retaining strengths not lower than 0.5 kgf/mm.sup.2, although
inferior in bonding strength after the long-term tests to samples
78 to 82, in which the deposited films had an aluminum content of
99% by weight or higher.
18TABLE 18 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
naturally of 100 100 100 1000 300 300 SiC Depth of of Al formed
crystal Initial thermal hours hours thermal hours hours Sample
content holes film oxide grains strength cycles in PCT in HAST
cycles in PCT in HAST No. (wt %) (.mu.m) (.mu.m) film (.ANG.)
(.mu.m) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) 78 50 60 2 500 1.0 1.8
1.3 1.0 1.1 0.9 0.6 0.7 79 50 60 2 500 1.0 1.7 1.2 1.0 1.1 0.9 0.6
0.7 80 50 60 2 500 1.0 1.9 1.4 1.1 1.2 1.0 0.7 0.8 81 50 60 2 500
1.0 1.5 1.1 1.0 1.1 0.8 0.6 0.7 82 50 60 2 500 1.0 1.7 1.1 0.8 0.9
0.8 0.6 0.7 83 50 60 2 500 1.0 1.4 1.2 0.9 1.0 0.8 0.5 0.6 84 50 60
2 500 1.0 1.5 1.2 0.9 1.0 0.8 0.5 0.6 85 50 60 2 500 1.0 1.4 1.3
1.0 1.0 0.9 0.6 0.7 86 50 60 2 500 1.0 1.4 1.2 1.0 1.0 0.8 0.5 0.5
87 50 60 2 500 1.0 1.4 1.2 0.9 1.0 0.8 0.5 0.5
EXAMPLE 17
Other Methods for Aluminum Film Formation
[0164] Al--SiC sinters having an SiC content of 50% by weight were
produced in the same-manner as in Example 11. Thereafter, an
aluminum film was formed on these sinters by the following methods
to produce samples 88 to 90. That is, for sample 88, an aluminum
film was formed by applying a dispersion of aluminum particles in
an organic solvent by screen printing in a thickness of 50 mm and
sintering the coating at 600.degree. C. for 1 hour in a nitrogen
atmosphere. For sample 89, an aluminum film was formed by applying
a dispersion of aluminum particles in an organic solvent by dipping
in a thickness of 50 .mu.m and sintering the coating at 600.degree.
C. for 1 hour in a nitrogen atmosphere. For sample 90, an aluminum
film was formed by applying an aluminum powder in a thickness of 50
.mu.m by thermal spraying using an inert gas and sintering the
coating at 600.degree. C. for 1 hour in a nitrogen atmosphere. The
resin bonding strength of each sample was then measured in
accordance with JIS K 6850 using the same resin as in Example
11.
[0165] The diameter of crystal grains, the depth of holes, and the
thickness of a native oxide film for each sample are shown in Table
19. The results show that samples 88 to 90 were capable of
retaining satisfactory bonding strengths not lower than 0.5
(kgf/mm.sup.2) both in the initial stage and after the reliability
tests.
19TABLE 19 Thickness Strength Strength Strength Strength Strength
Strength of Diameter after after after after after after Thickness
native of 100 100 100 1000 300 300 SiC Depth of of oxide crystal
Initial thermal hours in hours in thermal hours in hours in Sample
content holes Al film film grains strength cycles PCT HAST cycles
PCT HAST No. (wt %) (.mu.m) (.mu.m) (.ANG.) (.mu.m) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2) (kgf/mm.sup.2)
(kgf/mm.sup.2) (kgf/mm.sup.2) 88 50 60 2 500 1.0 1.8 1.2 0.9 1.0
0.9 0.6 0.7 89 50 60 2 500 1.0 1.8 1.2 0.9 1.0 0.9 0.6 0.7 90 50 60
2 500 1.0 1.7 1.2 0.9 1.0 0.9 0.6 0.7
EXAMPLE 18
[0166] As application examples of the semiconductor substrate
material of the present invention, which comprises an
aluminum/silicon carbide composite alloy, IC packages shown in
FIGS. 3 to 10 are explained below.
[0167] The IC package illustrated in FIG. 3 employs an
aluminum/silicon carbide composite alloy according to the present
invention as a substrate 1. The substrate 1 was produced by a
process comprising forming a compact having a predetermined shape,
sintering the compact, polishing the surface of the resultant alloy
sinter, and then plating the surface with nickel by a known means.
This substrate 1 has been bonded to a main package body 2 with a
highly thermally conductive resin 3, e.g., an epoxy resin filled
with a metallic filler.
[0168] This main package body 2 has a die attachment part 6 in the
center thereof, and a semiconductor chip 4 has been bonded to the
part 6 with a bonding material 5, e.g., a resin. One end of a
bonding wire 7 has been connected to the pad of the semiconductor
chip 4 mounted on the die attachment part 6 for establishing an
electrical connection of the semiconductor chip 4 to an external
circuit. The other end of the wire 7 has been connected, via a
conductive layer formed on the main package body 2, to metallic
lead pins 8 attached to the main package body 2 for connection to
an external circuit. After the mounting of the semiconductor chip
4, a cover 9 is attached to the main package body 2.
[0169] The IC package illustrated in FIG. 4 differs from the
package of FIG. 3 in that a semiconductor chip 4 has been directly
mounted on a substrate 1 with a bonding material 5 such as a solder
or a resin. The surface of this substrate 1 has been plated with
Ni--Au by a known method. The main package body 2 has an opening in
its bottom part corresponding to a die attachment part 6. The
substrate 1 has been bonded to the body 2 with a bonding material
5, e.g., a resin, so that the opening is covered with the substrate
1 and that the semiconductor chip 4 directly mounted on the
substrate 1 is housed in the die attachment part 6.
[0170] In IC packages containing a semiconductor chip 4 directly
mounted on a substrate 1 as described above, the substrate 1 is not
particularly limited in its shape on the side on which the
semiconductor chip 4 is mounted. For example, a substrate 1 having
a projecting flat part as shown in FIG. 5 can be used. In the
package illustrated in FIG. 5, the other constitution is the same
as in FIGS. 3 and 4.
[0171] The material of the main package body 2 in FIGS. 3 to 5 is
not particularly limited. Examples thereof include ceramic
materials such as alumina ceramic multilayer substrates having an
alumina content around 90%, which are generally used currently, and
low-temperature-sintered glass ceramic multilayer substrates
containing a glass ceramic and obtained through sintering at around
1,000.degree. C., which cope with high-speed signal processing.
Examples thereof further include plastic materials such as plastic
multilayer substrates comprising an epoxy or polyimide resin, which
are inexpensive and suitable for general purposes.
[0172] Among the semi conductor substrate materials according to
the present invention, those having a thermal conductivity of 180
W/m.times.K or higher are especially capable of exhibiting an
exceedingly high heat dissipation effect when used in combination
with plastic package body materials, which have a low thermal
conductivity and have a problem concerning heat dissipation when
used as they are.
[0173] There also are IC packages having a structure in which
solder balls 10, in place of metallic lead pins 8, have been
attached to a main package body 2 for connection to an external
circuit, as shown in FIGS. 6 and 7. These IC packages employ as a
substrate 1 an aluminum/silicon carbide composite alloy of a
predetermined shape whose surface has been plated with nickel by a
known means. This substrate 1 has a semiconductor chip 4 bonded
thereto through a bonding material 5, e.g., an adhesive resin.
[0174] In the IC package illustrated in FIG. 6, the main package
body 2 has a polyimide tape 11 bearing a copper foil circuit wiring
12. The body 2 has, in the center thereof, a semiconductor chip 4
mounted thereon by TAB (tape automated bonding). Further, a support
ring 13 has been bonded to the main package body 2 for reinforcing
the same. On the other hand, the IC package illustrated in FIG. 7
comprises a semiconductor chip 4 bonded to a substrate 1 and a
wiring substrate 14 having solder balls 10 for connection to an
external circuit. The semiconductor chip 4 has been mounted by flip
chip bonding on the substrate 14 through solder balls 10 formed on
the pad of the semiconductor chip 4. The sides of this structure
have been sealed with a resin 15 to protect the semiconductor chip
4. Methods for mounting the semiconductor chip 4 in the IC packages
illustrated in FIGS. 6 and 7 are not limited to those shown above.
Furthermore, the shape of the substrate 1 is not limited to a
flat-plate, and a substrate in the form of, e.g., a cap as shown in
FIG. 8 may be used.
[0175] The IC package illustrated in FIG. 9 is of the resin mold
type. In this package, a substrate 1 having a predetermined shape
has been bonded to a lead frame 16 through an insulating film 17.
This substrate 1 comprises an aluminum/silicon carbide composite
alloy whose surface has been plated with Ni--Au by a known means. A
semiconductor chip 4 has been bonded to the substrate 1 through a
bonding material 5, e.g., a silver paste. The lead frame 16 has
been connected to the bonding pad of the semiconductor chip 4 with
a bonding wire 7. The connected semiconductor chip 4 has been
embedded, together with the bonding wire 7, with a molding resin 18
by transfer molding.
[0176] In the IC packages shown in FIGS. 3 to 10, aluminum fins
generally having an anodized surface may be bonded to the substrate
1 comprising an aluminum/silicon carbide composite alloy for the
purpose of improving heat dissipation properties. For example, in
the case of an IC package of the type shown in FIG. 3, aluminum
fins 19 are bonded to the substrate 1 of this IC package through a
silicone resin 20 or the like as shown in FIG. 10. Furthermore, the
IC packages shown in FIGS. 3 to 10, of course, are applicable to IC
packages of the MCM (multi-chip mold) type containing two or more
semiconductor chips.
[0177] The semiconductor substrate material of the present
invention for use as a substrate 1, which material comprises an
aluminum/silicon carbide composite alloy, has little difference in
thermal expansion coefficient with silicon for use in semiconductor
chips and with the materials of generally used main package bodies.
Consequently, the semiconductor substrate material is less apt to
suffer a thermal strain caused by a thermal stress in package
production processes and IC mounting processes. Since the
semiconductor substrate material of the present invention has high
thermal conductivity and excellent heat dissipation properties, it
can be used to fabricate IC packages having a long service life and
excellent reliability. Furthermore, because the semiconductor
substrate material is lightweight, it is presumed to be effective
in stably maintaining the shape of a remelted solder especially in
producing packages having solder balls for connection to an
external circuit.
[0178] The IC packages respectively shown in FIGS. 3 to 9, each
having a substrate 1 comprising the semiconductor substrate
material of the present invention and containing a semiconductor
chip 4, were actually subjected to a thermal cycling test
(-60.degree. C. .about.+150.degree. C.; 100 cycles). As a result,
no abnormal operation was observed at all. It was thus ascertained
that the substrate was less apt to suffer a thermal strain, which
is caused by a thermal stress.
[0179] The present invention can provide, through a simple
sintering process, a substrate material for monting a semiconductor
device comprising a homogenous aluminum/silicon carbide composite
alloy which has a silicon carbide content of from 10 to 70% by
weight, especially 35 to 70% by weight. And the material has a
thermal conductivity of 100 W/m.times.K or higher, and a thermal
expansion coefficient of 20.times.10.sup.-6/.degree. C. or lower
and is lightweight and is very easy to form. This substrate
material is usable in various IC packages and is useful especially
for plastic packages. Therefore we can form a complex shaped
substrate in a fine and near net shape. In addition, because of its
high thermal conductivity and excellent heat dissipation
properties, the substrate material can be used to fabricate an IC
package having a long service life and excellent reliability.
* * * * *