U.S. patent application number 11/910460 was filed with the patent office on 2009-06-04 for heat sink device.
This patent application is currently assigned to Kabushiki Kaisha Toyota Jidoshokki. Invention is credited to Yuichi Furukawa, Ryoichi Hoshino, Masahiko Kimbara, Eiji Kono, Hidehito Kubo, Shintaro Nakagawa, Kota Otoshi, Nobuhiro Wakabayashi, Shinobu Yamauchi.
Application Number | 20090139704 11/910460 |
Document ID | / |
Family ID | 37086936 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090139704 |
Kind Code |
A1 |
Otoshi; Kota ; et
al. |
June 4, 2009 |
HEAT SINK DEVICE
Abstract
A heat radiator 1 includes an insulating substrate 3 whose first
side serves as a heat-generating-element-mounting side, and a heat
sink 5 fixed to a second side of the insulating substrate 3. A
metal layer 7 is formed on a side of the insulating substrate 3
opposite the heat-generating-element-mounting side. A stress
relaxation member 4 intervenes between the metal layer 7 of the
insulating substrate 3 and the heat sink 5. The stress relaxation
member 4 is formed of an aluminum plate 10 having a plurality of
through holes 9 formed therein, and the through holes 9 serve as
stress-absorbing spaces. The stress relaxation member 4 is brazed
to the metal layer 7 of the insulating substrate 3 and to the heat
sink 5. This heat radiator 1 is low in material cost and exhibits
excellent heat radiation performance.
Inventors: |
Otoshi; Kota; (Kariya-shi,
JP) ; Kono; Eiji; (Kariya-shi, JP) ; Kubo;
Hidehito; (Kariya-shi, JP) ; Kimbara; Masahiko;
(Kariya-shi, JP) ; Furukawa; Yuichi; (Oyama-shi,
JP) ; Yamauchi; Shinobu; (Oyama-shi, JP) ;
Hoshino; Ryoichi; (Oyama-shi, JP) ; Wakabayashi;
Nobuhiro; (Oyama-shi, JP) ; Nakagawa; Shintaro;
(Oyama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Toyota
Jidoshokki
Aichi-ken
JP
Showa Denko K.K.
Minato-ku Tokyo
JP
|
Family ID: |
37086936 |
Appl. No.: |
11/910460 |
Filed: |
April 6, 2006 |
PCT Filed: |
April 6, 2006 |
PCT NO: |
PCT/JP2006/307307 |
371 Date: |
October 2, 2007 |
Current U.S.
Class: |
165/185 |
Current CPC
Class: |
H01L 23/367 20130101;
H05K 1/0306 20130101; H05K 2201/09681 20130101; H05K 3/341
20130101; H01L 23/3677 20130101; H05K 2201/0969 20130101; Y02P
70/50 20151101; H05K 3/0061 20130101; H01L 23/473 20130101; H01L
2924/0002 20130101; H05K 3/4015 20130101; H05K 2201/0373 20130101;
H01L 23/3735 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
165/185 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 2005 |
JP |
2005 110175 |
Claims
1. A heat radiator comprising an insulating substrate whose first
side serves as a heat-generating-element-mounting side, and a heat
sink fixed to a second side of the insulating substrate; wherein a
stress relaxation member formed of a high-thermal-conduction
material and having a stress-absorbing space intervenes between the
insulating substrate and the heat sink, and the stress relaxation
member is metal-bonded to the insulating substrate and to the heat
sink.
2. A heat radiator according to claim 1, wherein the stress
relaxation member is brazed to the insulating substrate and to the
heat sink.
3. A heat radiator comprising an insulating substrate whose first
side serves as a heat-generating-element-mounting side, and a heat
sink fixed to a second side of the insulating substrate; wherein a
metal layer is formed on a side of the insulating substrate
opposite the heat-generating-element-mounting side; a stress
relaxation member formed of a high-thermal-conduction material and
having a stress-absorbing space intervenes between the metal layer
and the heat sink; and the stress relaxation member is metal-bonded
to the metal layer of the insulating substrate and to the heat
sink.
4. A heat radiator according to claim 3, wherein the stress
relaxation member is brazed to the metal layer of the insulating
substrate and to the heat sink.
5. A heat radiator according to claim 1, wherein the insulating
substrate is formed of a ceramic.
6. A heat radiator according to claim 1, wherein the stress
relaxation member is formed of an aluminum plate having a plurality
of through holes formed therein, and the through holes serve as the
stress-absorbing spaces.
7. A heat radiator according to claim 6, wherein the through holes
are formed in at least a portion of the aluminum plate which
corresponds to a perimetric portion of the insulating
substrate.
8. A heat radiator according to claim 6, wherein the through holes
are of a non-angular shape and have a circle-equivalent diameter of
1 mm to 4 mm.
9. A heat radiator according to claim 6, wherein a percentage of a
total area of all of the through holes to an area of one side of
the aluminum plate is 3% to 50%.
10. A heat radiator according to claim 3, wherein the stress
relaxation member is formed of an aluminum plate having a plurality
of recesses formed on at least either side, and the recesses serve
as the stress-absorbing spaces.
11. A heat radiator according to claim 10, wherein the recesses are
formed on at least a portion of the aluminum plate which
corresponds to a perimetric portion of the insulating
substrate.
12. A heat radiator according to claim 10, wherein openings of the
recesses are of a non-angular shape and have a circle-equivalent
diameter of 1 mm to 4 mm.
13. A heat radiator according to claim 10, wherein a percentage of
a total area of openings of all of the recesses to an area of a
side of the aluminum plate on which the recesses are formed is 3%
to 50%.
14. A heat radiator according to claim 1, wherein the stress
relaxation member is formed of an aluminum plate having a plurality
of recesses formed on at least either side and a plurality of
through holes formed therein, and the recesses and through holes
serve as the stress-absorbing spaces.
15. A heat radiator according to claim 6, wherein a thickness of
the aluminum plate used to form the stress relaxation member is 0.3
mm to 3 mm.
16. A heat radiator according to claim 1, wherein the stress
relaxation member is formed of a corrugate aluminum plate
comprising wave crest portions, wave trough portions, and
connection portions each connecting the wave crest portion and the
wave trough portion, and spaces present between the adjacent
connection portions serve as the stress-absorbing spaces.
17. A heat radiator according to claim 16, wherein a thickness of
the corrugate aluminum plate is 0.05 mm to 1 mm.
18. A heat radiator according to claim 16, wherein at least one
cutout portion extending in a direction perpendicular to a
longitudinal direction of the wave crest portions and the wave
trough portions is formed at the wave crest portions, the wave
trough portions, and the connection portions of the corrugate
aluminum plate.
19. A heat radiator according to claim 16, wherein a plurality of
the corrugate aluminum plates are disposed in a longitudinal
direction of the wave crest portions and the wave trough portions
while being spaced apart from one another.
20. A heat radiator according to claim 19, wherein the adjacent
corrugate aluminum plates are disposed such that the wave crest
portions and the wave trough portions of one corrugate aluminum
plate are shifted from those of the other corrugate aluminum plate
in a lateral direction of the wave crest portions and the wave
trough portions.
21. A heat radiator according to claim 6, wherein the aluminum
plate is formed of pure aluminum having a purity of 99% or
higher.
22. A heat radiator according to claim 6, wherein the stress
relaxation member is formed of a brazing sheet which comprises a
core, and brazing-material layers covering respective opposite
sides of the core, and the stress relaxation member is brazed to
the insulating substrate or the metal layer of the insulating
substrate and to the heat sink by use of the brazing-material
layers of the brazing sheet.
23. A heat radiator according to claim 6, wherein the stress
relaxation member is brazed to the insulating substrate or the
metal layer of the insulating substrate and to the heat sink by use
of a sheetlike brazing material.
24. A power module comprising a heat radiator according to claim 1,
and a semiconductor device mounted on the insulating substrate of
the heat radiator.
Description
TECHNICAL FIELD
[0001] The present invention relates to a heat radiator, and more
particularly to a heat radiator which includes an insulating
substrate whose first side serves as a
heat-generating-element-mounting side, and a heat sink fixed to a
second side of the insulating substrate and which radiates, from
the heat sink, heat generated from a heat-generating-element, such
as a semiconductor device, mounted on the insulating substrate.
[0002] The term "aluminum" as used herein and in the appended
claims encompasses aluminum alloys in addition to pure aluminum,
except for the case where "pure aluminum" is specified.
BACKGROUND ART
[0003] In a power module which uses a semiconductor device, such as
an IGBT (Insulated Gate Bipolar Transistor), the semiconductor
device must be held at a predetermined temperature or lower by
means of efficiently radiating heat generated therefrom.
Conventionally, in order to meet the requirement, a heat radiator
is used. The heat radiator includes an insulating substrate which
is formed of a ceramic, such as Al.sub.2O.sub.3 or AlN, and whose
first side serves as a heat-generating-element-mounting side, and a
heat sink which is formed of a high-thermal-conduction metal, such
as aluminum or copper (including copper alloys; hereinafter, the
same is applied), and is soldered to a second side of the
insulating substrate. A semiconductor device is soldered to the
heat-generating-element-mounting side of the insulating substrate
of the heat radiator, thereby forming the power module.
[0004] A power module used in, for example, a hybrid car must
maintain the heat radiation performance of a heat radiator over a
long term. The above-mentioned conventional heat radiator involves
the following problem. Under some working conditions, thermal
stress arises from a difference in thermal expansion coefficient
between the insulating substrate and the heat sink and causes
cracking in the insulating substrate, cracking in a solder layer
which bonds the insulating substrate and the heat sink together, or
warpage of a bond surface of the heat sink bonded to the insulating
substrate. Such cracking or warpage impairs heat radiation
performance.
[0005] A proposed heat radiator in which the above problem is
solved includes an insulating substrate whose first side serves as
a heat-generating-element-mounting side, a heat radiation member
which is soldered to a second side of the insulating substrate, and
a heat sink which is screwed on the heat radiation member. The heat
radiation member includes a pair of platelike heat-radiation-member
bodies formed of a high-thermal-conduction material, such as
aluminum or copper, and a low-thermal-expansion material, such as
an Invar alloy, intervening between the platelike
heat-radiation-member bodies. (Refer to Patent Document 1)
[0006] However, the heat radiator described in Patent Document 1
must use the heat radiation member formed of a
high-thermal-conduction material and a low-thermal-expansion
material; thus, material cost is increased. Furthermore, since the
heat radiation member and the heat sink are merely screwed
together, thermal conduction therebetween is insufficient,
resulting in a failure to provide sufficient heat radiation
performance.
Patent Document 1: Japanese Patent Application Laid-Open (kokai)
No. 2004-153075
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] An object of the present invention is to solve the above
problem and to provide a heat radiator whose material cost is low
and which exhibits excellent heat radiation performance.
Means for solving the Problems
[0008] To achieve the above object, the present invention comprises
the following modes.
[0009] 1) A heat radiator comprising an insulating substrate whose
first side serves as a heat-generating-element-mounting side, and a
heat sink fixed to a second side of the insulating substrate;
[0010] wherein a stress relaxation member formed of a
high-thermal-conduction material and having a stress-absorbing
space intervenes between the second side of the insulating
substrate and the heat sink, and the stress relaxation member is
metal-bonded to the insulating substrate and to the heat sink.
[0011] 2) A heat radiator according to par. 1), wherein the stress
relaxation member is brazed to the insulating substrate and to the
heat sink.
[0012] 3) A heat radiator comprising an insulating substrate whose
first side serves as a heat-generating-element-mounting side, and a
heat sink fixed to a second side of the insulating substrate;
[0013] wherein a metal layer is formed on a side of the insulating
substrate opposite the heat-generating-element-mounting side; a
stress relaxation member formed of a high-thermal-conduction
material and having a stress-absorbing space intervenes between the
metal layer and the heat sink; and the stress relaxation member is
metal-bonded to the metal layer of the insulating substrate and to
the heat sink.
[0014] 4) A heat radiator according to par. 3), wherein the stress
relaxation member is brazed to the metal layer of the insulating
substrate and to the heat sink.
[0015] 5) A heat radiator according to any one of pars. 1) to 4),
wherein the insulating substrate is formed of a ceramic.
[0016] 6) A heat radiator according to any one of pars. 1) to 5),
wherein the stress relaxation member is formed of an aluminum plate
having a plurality of through holes formed therein, and the through
holes serve as the stress-absorbing spaces.
[0017] 7) A heat radiator according to par. 6), wherein the through
holes are formed in at least a portion of the aluminum plate which
corresponds to a perimetric portion of the insulating
substrate.
[0018] 8) A heat radiator according to par. 6) or 7), wherein the
through holes are of a non-angular shape and have a
circle-equivalent diameter of 1 mm to 4 mm.
[0019] The term "non-angular" as used herein and in the appended
claims refers to a shape which does not have a mathematically
defined acute angle, obtuse angle, or right angle; for example, a
circle, an ellipse, an elongated circle, or a substantially
polygonal shape whose corners are rounded. The term
"circle-equivalent diameter" as used herein and in the appended
claims refers to the diameter of a circle whose area is equal to
that of a shape in question.
[0020] In the heat radiator of par. 8), the through holes have a
circle-equivalent diameter of 1 mm to 4 mm, for the following
reason. If the circle-equivalent diameter of the through holes is
too small, deformation of the stress relaxation member may become
insufficient when thermal stress arises in the heat radiator from a
difference in thermal expansion coefficient between the insulating
substrate and the heat sink, with the potential result that the
stress relaxation member fails to exhibit sufficient
stress-relaxing performance. If the circle-equivalent diameter of
the through holes is too large, thermal conductivity may drop.
Particularly, in the case where the stress relaxation member is
brazed to the insulating substrate and to the heat sink, if the
circle-equivalent diameter is too small, the through holes may be
filled with a brazing material, with the potential result that the
stress relaxation member is not deformed at all even when thermal
stress arises in the heat radiator.
[0021] 9) A heat radiator according to any one of pars. 6) to 8),
wherein a percentage of a total area of all of the through holes to
an area of one side of the aluminum plate is 3% to 50%.
[0022] In the heat radiator of par. 9), the percentage of the total
area of all of the through holes to the area of one side of the
aluminum plate is 3% to 50%, for the following reason. If the
percentage is too low, deformation of the stress relaxation member
may become insufficient when thermal stress arises in the heat
radiator from a difference in thermal expansion coefficient between
the insulating substrate and the heat sink, with the potential
result that the stress relaxation member fails to exhibit
sufficient stress-relaxing performance. If the percentage is too
high, thermal conductivity may drop.
[0023] 10) A heat radiator according to any one of pars. 1) to 5),
wherein the stress relaxation member is formed of an aluminum plate
having a plurality of recesses formed on at least either side, and
the recesses serve as the stress-absorbing spaces.
[0024] 11) A heat radiator according to par. 10), wherein the
recesses are formed on at least a portion of the aluminum plate
which corresponds to a perimetric portion of the insulating
substrate.
[0025] 12) A heat radiator according to par. 10) or 11), wherein
the openings of the recesses are of a non-angular shape and have a
circle-equivalent diameter of 1 mm to 4 mm.
[0026] In the heat radiator of par. 12), the openings of the
recesses have a circle-equivalent diameter of 1 mm to 4 mm, for the
following reason. If the circle-equivalent diameter of the openings
of the recesses is too small, deformation of the stress relaxation
member may become insufficient when thermal stress arises in the
heat radiator from a difference in thermal expansion coefficient
between the insulating substrate and the heat sink, with the
potential result that the stress relaxation member fails to exhibit
sufficient stress-relaxing performance. If the circle-equivalent
diameter of the openings of the recesses is too large, thermal
conductivity may drop. Particularly, in the case where the stress
relaxation member is brazed to the insulating substrate and to the
heat sink, if the circle-equivalent diameter is too small, the
recesses may be filled with a brazing material, with the potential
result that the stress relaxation member is not deformed at all
even when thermal stress arises in the heat radiator.
[0027] 13) A heat radiator according to any one of pars. 10) to
12), wherein a percentage of a total area of openings of all of the
recesses to an area of a side of the aluminum plate on which the
recesses are formed is 3% to 50%.
[0028] In the heat radiator of par. 13), the percentage of the
total area of openings of all of the through holes to the area of
the side of the aluminum plate on which the recesses are formed is
3% to 50%, for the following reason. If the percentage is too low,
deformation of the stress relaxation member may become insufficient
when thermal stress arises in the heat radiator from a difference
in thermal expansion coefficient between the insulating substrate
and the heat sink, with the potential result that the stress
relaxation member fails to exhibit sufficient stress-relaxing
performance. If the percentage is too high, thermal conductivity
may drop.
[0029] 14) A heat radiator according to any one of pars. 1) to 5),
wherein the stress relaxation member is formed of an aluminum plate
having a plurality of recesses formed on at least either side and a
plurality of through holes formed therein, and the recesses and
through holes serve as the stress-absorbing spaces.
[0030] 15) A heat radiator according to any one of pars. 6) to 14),
wherein the aluminum plate used to form the stress relaxation
member has a thickness of 0.3 mm to 3 mm.
[0031] In the heat radiator of par. 15), the aluminum plate used to
form the stress relaxation member has a thickness of 0.3 mm to 3
mm, for the following reason. If the aluminum plate is too thin,
deformation of the stress relaxation member may become insufficient
when thermal stress arises in the heat radiator from a difference
in thermal expansion coefficient between the insulating substrate
and the heat sink, with the potential result that the stress
relaxation member fails to exhibit sufficient stress-relaxing
performance. If the aluminum plate is too thick, thermal
conductivity may drop.
[0032] 16) A heat radiator according to any one of pars. 1) to 5),
wherein the stress relaxation member is formed of a corrugate
aluminum plate comprising wave crest portions, wave trough
portions, and connection portions each connecting the wave crest
portion and the wave trough portion, and spaces present between the
adjacent connection portions serve as the stress-absorbing
spaces.
[0033] 17) A heat radiator according to par. 16), wherein a
thickness of the corrugate aluminum plate is 0.05 mm to 1 mm. In
the heat radiator of par. 17), the thickness of the corrugate
aluminum plate is 0.05 mm to 1 mm, for the following reason. If the
corrugate aluminum plate is too thin, difficulty is involved in
processing for obtaining the corrugate aluminum plate, and buckling
may arise. If the corrugate aluminum plate is too thick, difficulty
is involved in processing for obtaining the corrugate aluminum
plate. In either case, difficulty is involved in finishing for
obtaining a predetermined shape.
[0034] 18) A heat radiator according to par. 16) or 17), wherein at
least one cutout portion extending in a direction perpendicular to
a longitudinal direction of the wave crest portions and the wave
trough portions is formed at the wave crest portions, the wave
trough portions, and the connection portions of the corrugate
aluminum plate.
[0035] 19) A heat radiator according to par. 16) or 17), wherein a
plurality of the corrugate aluminum plates are disposed in a
longitudinal direction of the wave crest portions and the wave
trough portions while being spaced apart from one another.
[0036] 20) A heat radiator according to par. 19), wherein the
adjacent corrugate aluminum plates are disposed such that the wave
crest portions and the wave trough portions of one corrugate
aluminum plate are shifted from those of the other corrugate
aluminum plate in a lateral direction of the wave crest portions
and the wave trough portions. 21) A heat radiator according to any
one of pars. 6) to 20), wherein the aluminum plate is formed of
pure aluminum having a purity of 99% or higher.
[0037] 22) A heat radiator according to any one of pars. 6) to 21),
wherein the stress relaxation member is formed of a brazing sheet
which comprises a core, and brazing-material layers covering
respective opposite sides of the core, and the stress relaxation
member is brazed to the insulating substrate or the metal layer of
the insulating substrate and to the heat sink by use of the
brazing-material layers of the brazing sheet.
[0038] 23) A heat radiator according to any one of pars. 6) to 21),
wherein the stress relaxation member is brazed to the insulating
substrate or the metal layer of the insulating substrate and to the
heat sink by use of a sheetlike brazing material.
[0039] 24) A power module comprising a heat radiator according to
any one of pars. 1) to 23), and a semiconductor device mounted on
the insulating substrate of the heat radiator.
Effects of the Invention
[0040] According to the heat radiator of par. 1), the stress
relaxation member formed of a high-thermal-conduction material and
having a stress-absorbing space intervenes between the insulating
substrate and the heat sink, and the stress relaxation member is
metal-bonded to the insulating substrate and to the heat sink.
Thus, excellent thermal conductivity is established between the
insulating substrate and the heat sink, thereby improving heat
radiation performance for radiating heat generated by a
semiconductor device mounted on the insulating substrate.
Furthermore, even when thermal stress arises in the heat radiator
from a difference in thermal expansion coefficient between the
insulating substrate and the heat sink, the stress relaxation
member is deformed by the effect of the stress-absorbing space;
thus, the thermal stress is relaxed, thereby preventing cracking in
the insulating substrate, cracking in a bond zone between the
insulating substrate and the stress relaxation member, or warpage
of a bond surface of the heat sink bonded to the insulating
substrate. Accordingly, heat radiation performance is maintained
over a long term. Also, use of the stress relaxation member
described in any one of pars. 6) to 20) lowers cost of the stress
relaxation member, thereby lowering material cost for the heat
radiator.
[0041] According to the heat radiator of par. 2), the stress
relaxation member is brazed to the insulating substrate and to the
heat sink. Thus, bonding of the stress relaxation member and the
insulating substrate and bonding of the stress relaxation member
and the heat sink can be performed simultaneously, thereby
improving workability in fabrication of the heat radiator.
According to the heat radiator described in Patent Document 1,
after the insulating substrate and the heat radiation member are
soldered together, the heat radiation member and the heat sink must
be screwed together; therefore, workability in fabrication of the
heat radiator is poor.
[0042] According to the heat radiator of par. 3), the metal layer
is formed on a side of the insulating substrate opposite the
heat-generating-element-mounting side; the stress relaxation member
formed of a high-thermal-conduction material and having a
stress-absorbing space intervenes between the metal layer and the
heat sink; and the stress relaxation member is metal-bonded to the
metal layer of the insulating substrate and to the heat sink. Thus,
excellent thermal conductivity is established between the
insulating substrate and the heat sink, thereby improving heat
radiation performance for radiating heat generated by a
semiconductor device mounted on the insulating substrate.
Furthermore, even when thermal stress arises in the heat radiator
from a difference in thermal expansion coefficient between the
insulating substrate and the heat sink, the stress relaxation
member is deformed by the effect of the stress-absorbing space;
thus, the thermal stress is relaxed, thereby preventing cracking in
the insulating substrate, cracking in a bond zone between the metal
layer of the insulating substrate and the stress relaxation member,
or warpage of a bond surface of the heat sink bonded to the
insulating substrate. Accordingly, heat radiation performance is
maintained over a long term. Also, use of the stress relaxation
member described in any one of pars. 6) to 20) lowers cost of the
stress relaxation member, thereby lowering material cost for the
heat radiator.
[0043] According to the heat radiator of par. 4), the stress
relaxation member is brazed to the metal layer of the insulating
substrate and to the heat sink. Thus, bonding of the stress
relaxation member and the metal layer of the insulating substrate
and bonding of the stress relaxation member and the heat sink can
be performed simultaneously, thereby improving workability in
fabrication of the heat radiator. According to the heat radiator
described in Patent Document 1, after the insulating substrate and
the heat radiation member are soldered together, the heat radiation
member and the heat sink must be screwed together; therefore,
workability in fabrication of the heat radiator is poor.
[0044] With the heat radiator of any one of pars. 6) to 20), cost
of the stress relaxation member is lowered, thereby lowering
material cost for the heat radiator.
[0045] According to the heat radiator of any one of pars. 6) to 9),
the stress relaxation member is deformed by the effect of the
stress-absorbing spaces in the form of the through holes; thus,
thermal stress is relaxed.
[0046] The heat radiator of par. 7) exhibits excellent
thermal-stress relaxation effect. A largest thermal stress or
strain is likely to arise in a perimetric portion of the insulating
substrate of the heat radiator. However, by virtue of the
configuration of par. 7), a portion of the aluminum plate
corresponding to the perimetric portion of the insulating substrate
is apt to be deformed by the effect of the through holes, thereby
relaxing the thermal stress.
[0047] According to the heat radiator of par. 10), the stress
relaxation member is deformed by the effect of the stress-absorbing
spaces in the form of the recesses, thereby relaxing the thermal
stress.
[0048] The heat radiator of par. 11) exhibits excellent
thermal-stress relaxation effect. A largest thermal stress or
strain is likely to arise in a perimetric portion of the insulating
substrate of the heat radiator. However, by virtue of the
configuration of par. 11), a portion of the aluminum plate
corresponding to the perimetric portion of the insulating substrate
is apt to be deformed by the effect of the recesses, thereby
relaxing the thermal stress.
[0049] According to the heat radiator of par. 14), the stress
relaxation member is deformed by the effect of the stress-absorbing
spaces in the form of recesses and through holes, thereby relaxing
the thermal stress.
[0050] According to the heat radiator of par. 16) or 17), the
stress relaxation member is deformed by the effect of the
stress-absorbing spaces of the corrugate aluminum plate, thereby
relaxing the thermal stress.
[0051] According to the heat radiator of par. 18), the cutout
portion enhances the thermal-stress relaxation effect.
[0052] According to the heat radiator of par. 19), the spaces
between the adjacent corrugate aluminum plates enhance the
thermal-stress relaxation effect.
[0053] According to the heat radiator of par. 20), the
thermal-stress relaxation effect is enhanced in different
directions.
[0054] According to the heat radiator of par. 21), wettability of a
molten brazing material on the stress relaxation member becomes
excellent when the stress relaxation member and the insulating
substrate or the metal layer of the insulating substrate are to be
brazed together and when the stress relaxation member and the heat
sink are to be brazed together, thereby improving brazing
workability. Furthermore, when brazing heat causes a drop in the
strength of the stress relaxation member and generation of thermal
stress in the heat radiator, the stress relaxation member is apt to
be deformed, thereby yielding excellent stress relaxation
effect.
BEST MODE FOR CARRYING OUT THE INVENTION
[0055] Embodiments of the present invention will next be described
with reference to the drawings. The upper and lower sides of FIG. 1
will be referred to as "upper" and "lower," respectively. In all
the drawings, like features or parts are denoted by like reference
numerals, and repeated description thereof is omitted.
[0056] FIG. 1 shows a portion of a power module which uses a heat
radiator of a first embodiment of the present invention. FIG. 2
shows a stress relaxation member.
[0057] In FIG. 1, the power module includes a heat radiator (1) and
a semiconductor device (2); for example, an IGBT, mounted on the
heat radiator (1).
[0058] The heat radiator (1) includes an insulating substrate (3)
which is formed of a ceramic and whose upper side serves as a
heat-generating-element-mounting side; a stress relaxation member
(4) bonded to the lower side of the insulating substrate (3); and a
heat sink (5) bonded to the lower side of the stress relaxation
member (4).
[0059] The insulating substrate (3) may be formed of any ceramic so
long as it satisfies requirements for insulating characteristics,
thermal conductivity, and mechanical strength. For example,
Al.sub.2O.sub.3 or AlN is used to form the insulating substrate
(3). A circuit layer (6) is formed on the upper surface of the
insulating substrate (3), and the semiconductor device (2) is
soldered onto the circuit layer (6). The solder layer is not shown.
The circuit layer (6) is formed of a metal having excellent
electrical conductivity, such as aluminum or copper. Preferably,
the circuit layer (6) is formed of a pure aluminum having high
purity, which exhibits high electrical conductivity, high
deformability, and excellent solderability in relation to a
semiconductor device. A metal layer (7) is formed on the lower
surface of the insulating substrate (3). The stress relaxation
member (4) is brazed to the metal layer (7). The brazing-material
layer is not shown. Preferably, the metal layer (7) is formed of a
metal having excellent thermal conductivity, such as aluminum or
copper. Preferably, the metal layer (7) is formed of a pure
aluminum having high purity, which exhibits high thermal
conductivity, high deformability, and excellent wettability in
relation to a molten brazing material. The insulating substrate
(3), the circuit layer (6), and the metal layer (7) constitute a
power module substrate (8).
[0060] The stress relaxation member (4) is formed of a
high-thermal-conduction material and has stress-absorbing spaces.
As shown in FIG. 2, the stress relaxation member (4) is formed of
an aluminum plate (10) in which a plurality of non-angular holes;
herein, circular through holes (9), are formed in a staggered
arrangement, and the through holes (9) serve as stress-absorbing
spaces. The circular through holes (9) are formed in at least a
portion of the aluminum plate (10) which corresponds to a
perimetric portion of the insulating substrate (3); i.e., in the
entire region of the aluminum plate (10), including a perimetric
portion corresponding to the perimetric portion of the insulating
substrate (3). Preferably, the aluminum plate (10) is formed of a
pure aluminum having a purity of 99% or higher, desirably 99.5% or
higher, which exhibits high thermal conductivity, high
deformability induced by a drop in strength caused by brazing heat,
and excellent wettability in relation to a molten brazing material.
The thickness of the aluminum plate (10) is preferably 0.3 mm to 3
mm, more preferably 0.3 mm to 1.5 mm. The circle-equivalent
diameter of the through holes (9) (here, the diameter of the
through holes (9), because the through holes (9) are circular) is
preferably 1 mm to 4 mm. Preferably, the percentage of the total
area of all of the through holes (9) to the area of one side of the
aluminum plate (10) is 3% to 50%.
[0061] Preferably, the heat sink (5) assumes a flat, hollow shape
in which a plurality of cooling-fluid channels (11) are formed in
parallel, and is formed of aluminum, which exhibits excellent
thermal conductivity and is light. A cooling fluid may be either
liquid or gas.
[0062] Brazing between the stress relaxation member (4) and the
metal layer (7) of the power module substrate (8) and brazing
between the stress relaxation member (4) and the heat sink (5) are
performed, for example, as follows. The stress relaxation member
(4) is formed of an aluminum brazing sheet which is composed of a
core formed of pure aluminum, and aluminum brazing-material layers
covering respective opposite sides of the core. Examples of an
aluminum brazing-material include an Al--Si alloy and an Al--Si--Mg
alloy. Preferably, the thickness of the aluminum brazing-material
layer is about 10 .mu.m to 200 .mu.m. When the thickness is too
small, lack of supply of the brazing material arises, potentially
causing defective brazing. When the thickness is too large, excess
supply of the brazing material arises, potentially causing
generation of voids and a drop in thermal conductivity.
[0063] Next, the power module substrate (8), the stress relaxation
member (4), and the heat sink (5) are arranged in layers and
restrained together by use of an appropriate jig to thereby apply
an appropriate load to bond surfaces. The resultant assembly is
heated to 570.degree. C. to 600.degree. C. in a vacuum or an inert
gas atmosphere. Thus, brazing of the stress relaxation member (4)
and the metal layer (7) of the power module substrate (8) and
brazing of the stress relaxation member (4) and the heat sink (5)
are performed simultaneously.
[0064] Alternatively, brazing of the stress relaxation member (4)
and the metal layer (7) of the power module substrate (8) and
brazing of the stress relaxation member (4) and the heat sink (5)
may performed as follows. The stress relaxation member (4) is
formed of a bare material of the above-mentioned pure aluminum. The
power module substrate (8), the stress relaxation member (4), and
the heat sink (5) are arranged in layers. In this arrangement, a
sheetlike aluminum brazing-material of, for example, an Al--Si
alloy or an Al--Si--Mg alloy intervenes between the stress
relaxation member (4) and the metal layer (7) of the power module
substrate (8) and between the stress relaxation member (4) and the
heat sink (5). Preferably, the thickness of the sheetlike aluminum
brazing-material is about 10 .mu.m to 200 .mu.m. When the thickness
is too small, lack of supply of the brazing material arises,
potentially causing defective brazing. When the thickness is too
large, excess supply of the brazing material arises, potentially
causing generation of voids and a drop in thermal conductivity.
Subsequently, brazing is performed as in the above-mentioned case
of use of the aluminum brazing sheet. Thus, brazing of the stress
relaxation member (4) and the metal layer (7) of the power module
substrate (8) and brazing of the stress relaxation member (4) and
the heat sink (5) are performed simultaneously.
[0065] FIG. 3 shows a second embodiment of the heat radiator
according to the present invention.
[0066] In the case of a heat radiator (15) shown in FIG. 3, the
metal layer (7) is not formed on the lower surface of the
insulating substrate (3) of the power module substrate (8); i.e.,
the stress relaxation member (4) is directly brazed to the
insulating substrate (3). This brazing is performed in a manner
similar to that of the first embodiment described above.
[0067] FIGS. 4 to 21 show modified embodiments of the stress
relaxation member.
[0068] A stress relaxation member (20) shown in FIG. 4 is formed of
the aluminum plate (10) in which a plurality of rectangular through
holes (21) are formed in a staggered arrangement, and the through
holes (21) serve as stress-absorbing spaces. The through holes (21)
are formed in at least a portion of the aluminum plate (10) which
corresponds to a perimetric portion of the insulating substrate
(3); i.e., in the entire region of the aluminum plate (10),
including a perimetric portion corresponding to the perimetric
portion of the insulating substrate (3). Preferably, as in the case
of the stress relaxation member (4) shown in FIG. 2, the percentage
of the total area of all of the through holes (21) to the area of
one side of the aluminum plate (10) is 3% to 50%.
[0069] A stress relaxation member (22) shown in FIG. 5 is formed of
the aluminum plate (10) in which a plurality of the circular
through holes (9) are formed only in a perimetric portion; i.e., in
a portion corresponding to a perimetric portion of the insulating
substrate (3). Also, in this case, preferably, as in the case of
the stress relaxation member (4) shown in FIG. 2, the percentage of
the total area of all of the through holes (9) to the area of one
side of the aluminum plate (10) is 3% to 50%.
[0070] A stress relaxation member (23) shown in FIG. 6 is formed of
the aluminum plate (10) in which a plurality of the circular
through holes (9) are formed in two inner and outer rows only in a
perimetric portion; i.e., in a portion corresponding to a
perimetric portion of the insulating substrate (3). Also, in this
case, preferably, as in the case of the stress relaxation member
(4) shown in FIG. 2, the percentage of the total area of all of the
through holes (9) to the area of one side of the aluminum plate
(10) is 3% to 50%.
[0071] In the stress relaxation members (22) and (23) shown in
FIGS. 5 and 6, respectively, the rectangular through holes (21) may
be formed in place of the circular through holes (9). In either
case, the through holes (9) and (21) serve as stress-absorbing
spaces.
[0072] A stress relaxation member (25) shown in FIG. 7 is formed of
the aluminum plate (10) in which a plurality of spherical recesses
(26) are formed in a staggered arrangement on one side, and the
recesses (26) serve as stress-absorbing spaces.
[0073] A stress relaxation member (30) shown in FIG. 8 is formed of
the aluminum plate (10) in which a plurality of the spherical
recesses (26) are formed in vertical and horizontal rows on
opposite sides, and the recesses (26) serve as stress-absorbing
spaces. The recesses (26) formed on one side of the aluminum plate
(10) differ from the recesses (26) formed on the other side in
position as viewed in plane.
[0074] A stress relaxation member (31) shown in FIG. 9 is formed of
the aluminum plate (10) in which a plurality of
truncated-cone-shaped recesses (32) are formed in a staggered
arrangement on one side, and the recesses (32) serve as
stress-absorbing spaces.
[0075] A stress relaxation member (34) shown in FIG. 10 is formed
of the aluminum plate (10) in which a plurality of the
truncated-cone-shaped recesses (32) are formed in vertical and
horizontal rows on opposite sides, and the recesses (32) serve as
stress-absorbing spaces. The recesses (32) formed on one side of
the aluminum plate (10) differ from the recesses (32) formed on the
other side in position as viewed in plane.
[0076] In the stress relaxation members (25), (30), (31), and (34)
shown in FIGS. 7 to 10, respectively, the recesses (26) and (32)
are formed in the entire region of the aluminum plate (10),
including at least a perimetric portion corresponding to a
perimetric portion of the insulating substrate (3). However, as in
the case of the stress relaxation members (22) and (23) shown in
FIGS. 5 and 6, respectively, the recesses (26) and (32) may be
formed only in the perimetric portion corresponding to the
perimetric portion of the insulating substrate (3). In the stress
relaxation members (25), (30), (31), and (34) shown in FIGS. 7 to
10, respectively, since the openings of the recesses (26) and (32)
are circular, the recesses (26) and (32) preferably have a
circle-equivalent diameter; i.e., a diameter, of 1 mm to 4 mm.
Preferably, the percentage of the total area of openings of all of
the recesses (26) or (32) to an area of the side of the aluminum
plate (10) on which the recesses (26) or (32) are formed is 3% to
50%.
[0077] A stress relaxation member (36) shown in FIG. 11 is formed
of the aluminum plate (10) in which a plurality of
quadrangular-pyramid-shaped recesses (37) are formed in a staggered
arrangement on one side, and the recesses (37) serve as
stress-absorbing spaces.
[0078] A stress relaxation member (38) shown in FIG. 12 is formed
of the aluminum plate (10) in which a plurality of the
quadrangular-pyramid-shaped recesses (37) are formed in vertical
and horizontal rows on opposite sides, and the recesses (37) serve
as stress-absorbing spaces. The recesses (37) formed on one side of
the aluminum plate (10) differ from the recesses (37) formed on the
other side in position as viewed in plane.
[0079] A stress relaxation member (40) shown in FIG. 13 is formed
of the aluminum plate (10) in which a plurality of
rectangular-parallelepiped-shaped recesses (41) are formed in
vertical and horizontal rows on one side, and the recesses (41)
serve as stress-absorbing spaces. Herein, the adjacent recesses
(41) in each of the vertical rows are arranged such that their
longitudinal directions are oriented 90 degrees different from each
other. Similarly, the adjacent recesses (41) in each of the
horizontal rows are arranged such that their longitudinal
directions are oriented 90 degrees different from each other.
[0080] A stress relaxation member (42) shown in FIG. 14 is formed
of the aluminum plate (10) in which a plurality of the
rectangular-parallelepiped-shaped recesses (41) are formed in a
staggered arrangement on opposite sides, and the recesses (41)
serve as stress-absorbing spaces. The recesses (41) formed on one
side of the aluminum plate (10) differ from the recesses (41)
formed on the other side in position as viewed in plane. Also, the
recesses (41) formed on a first side of the aluminum plate (10) are
arranged such that their longitudinal directions are oriented in
the same direction, and the recesses (41) formed on a second side
of the aluminum plate (10) are arranged such that their
longitudinal directions are oriented perpendicularly to those of
the recesses (41) formed on the first side.
[0081] A stress relaxation member (45) shown in FIG. 15 is formed
of the aluminum plate (10) in which a plurality of through holes
(46) and (47) are formed, and the through holes (46) and (47) serve
as stress-absorbing spaces. In four corner portions of the aluminum
plate (10), a plurality of slit-like through holes (46) are formed
on a plurality of diagonal lines which are in parallel with one
another and intersect with two sides that define each of the corner
portions, while the slit-like through holes (46) are spaced apart
from one another along the diagonal lines. In a portion of the
aluminum plate (10) other than the four corner portions, a
plurality of arcuate through holes (47) are formed on a plurality
of concentric circles while being circumferentially spaced apart
from one another. Also, in this stress relaxation member (45),
preferably, the percentage of the total area of all of the through
holes (46) and (47) to the area of one side of the aluminum plate
(10) is 3% to 50%.
[0082] A stress relaxation member (50) shown in FIG. 16 is formed
of the aluminum plate (10) in which a plurality of groove-like
recesses (51) are formed on one side, and the recesses (51) serve
as stress-absorbing spaces. Some recesses (51) assume the form of
connected letter Vs, and other recesses (51) assume the form of a
letter V.
[0083] A stress relaxation member (53) shown in FIG. 17 is formed
of the aluminum plate (10) in which a plurality of V-groove-like
recesses (54) and (55) are formed on opposite sides, and the
recesses (54) and (55) serve as stress-absorbing spaces. The
recesses (54) formed on a first side of the aluminum plate (10)
extend along the longitudinal direction of the aluminum plate (10)
and are spaced apart from one another in the lateral direction of
the aluminum plate (10). The recesses (55) formed on a second side
of the aluminum plate (10) extend along the lateral direction of
the aluminum plate (10) and are spaced apart from one another in
the longitudinal direction of the aluminum plate (10). The total of
the depth of the recesses (54) formed on the first side of the
aluminum plate (10) and the depth of the recesses (55) formed on
the second side of the aluminum plate (10) is less than the
thickness of the aluminum plate (10).
[0084] A stress relaxation member (57) shown in FIG. 18 is formed
of the aluminum plate (10) in which a plurality of V-groove-like
recesses (58) and (59) are formed on opposite sides and in which a
plurality of through holes (60) are formed, and the recesses (58)
and (59) and the through holes (60) serve as stress-absorbing
spaces. The recesses (58) formed on a first side of the aluminum
plate (10) extend along the longitudinal direction of the aluminum
plate (10) and are spaced apart from one another in the lateral
direction of the aluminum plate (10). The recesses (59) formed on a
second side of the aluminum plate (10) extend along the lateral
direction of the aluminum plate (10) and are spaced apart from one
another in the longitudinal direction of the aluminum plate (10).
The total of the depth of the recesses (58) formed on the first
side of the aluminum plate (10) and the depth of the recesses (59)
formed on the second side of the aluminum plate (10) is greater
than the thickness of the aluminum plate (10), whereby the through
holes (60) are formed at intersections of the recesses (58) and
(59).
[0085] The aluminum plate (10) used to form the stress relaxation
members shown in FIGS. 4 to 18 is identical with that used to form
the stress relaxation member (4) shown in FIG. 2. Each of the
stress relaxation members shown in FIGS. 4 to 18 is brazed to the
power module substrate (8) and to the heat sink (5) in a manner
similar to that of the first and second embodiments.
[0086] A stress relaxation member (63) shown in FIG. 19 is formed
of a corrugate aluminum plate (67) which includes wave crest
portions (64), wave trough portions (65), and connection portions
(66) each connecting the wave crest portion (64) and the wave
trough portion (65), and spaces present between the adjacent
connection portions (66) serve as stress-absorbing spaces. A cutout
portion (68) which extends at a laterally central portion of the
corrugate aluminum plate (67) in a direction perpendicular to the
longitudinal direction of the wave crest portions (64) and the wave
trough portions (65) is formed at the wave crest portions (64), the
wave trough portions (65), and the connection portions (66).
Accordingly, the corrugate aluminum plate (67) is divided into two
portions except for its opposite end portions.
[0087] A stress relaxation member (70) shown in FIG. 20 is
configured as follows. A plurality of the cutout portions (68) are
formed at the wave crest portions (64), the wave trough portions
(65), and the connection portions (66) of the corrugate aluminum
plate (67) similar to that of FIG. 19, in such a manner as to
extend in a direction perpendicular to the longitudinal direction
of the wave crest portions (64) and the wave trough portions (65)
and to be juxtaposed to one another in the lateral direction of the
corrugate aluminum plate (67). Accordingly, the corrugate aluminum
plate (67) is divided into a plurality of portions except for its
opposite end portions.
[0088] A stress relaxation member (72) shown in FIG. 21 is
configured as follows. A plurality of; herein, two, corrugate
aluminum plates (67) in which no cutout is formed are disposed in
the longitudinal direction of the wave crest portions (64) and the
wave trough portions (65) while being spaced apart from one
another. No particular limitation is imposed on the number of the
corrugate aluminum plates (67). The adjacent corrugate aluminum
plates (67) are disposed such that the wave crest portions (64) and
the wave trough portions (65) of one corrugate aluminum plate (67)
are shifted from those of the other corrugate aluminum plate (67)
in the lateral direction of the wave crest portions (64) and the
wave trough portions (65).
[0089] In some cases, the stress relaxation member (72) shown in
FIG. 21 may be configured as follows: the adjacent corrugate
aluminum plates (67) are disposed such that the wave crest portions
(64) and the wave trough portions (65) of one corrugate aluminum
plate (67) coincide with those of the other corrugate aluminum
plate (67) with respect to the lateral direction of the wave crest
portions (64) and the wave trough portions (65).
[0090] In the stress relaxation members (63), (70), and (72) shown
in FIGS. 19 to 21, respectively, the thickness of the corrugate
aluminum plate (67) is preferably 0.05 mm to 1 mm. As in the case
of the stress relaxation member (4) shown in FIG. 2, preferably,
the corrugate aluminum plate (67) is formed of a pure aluminum
having a purity of 99% or higher, desirably 99.5% or higher, which
exhibits high thermal conductivity and high deformability induced
by a drop in strength caused by brazing heat. As in the case of the
above-described first and second embodiments, each of the stress
relaxation members (63), (70), and (72) shown in FIGS. 19 to 21 is
brazed to the power module substrate (8) and to the heat sink
(5).
INDUSTRIAL APPLICABILITY
[0091] The heat radiator of the present invention includes an
insulating substrate whose first side serves as a
heat-generating-element-mounting side and a heat sink fixed to a
second side of the insulating substrate, and is preferably used for
radiating, from the heat sink, heat generated from a
heat-generating-element, such as a semiconductor device, mounted on
the insulating substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0092] FIG. 1 Vertical sectional view of a portion of a power
module which uses a heat radiator, showing a first embodiment of a
heat radiator according to the present invention.
[0093] FIG. 2 Perspective view showing a stress relaxation member
used in the heat radiator of FIG. 1.
[0094] FIG. 3 View equivalent to FIG. 1, showing a second
embodiment of the heat radiator according to the present
invention.
[0095] FIG. 4 Perspective view showing a first modified embodiment
of the stress relaxation member.
[0096] FIG. 5 Partially cutaway perspective view showing a second
modified embodiment of the stress relaxation member.
[0097] FIG. 6 Partially cutaway perspective view showing a third
modified embodiment of the stress relaxation member.
[0098] FIG. 7 Partially cutaway perspective view showing a fourth
modified embodiment of the stress relaxation member.
[0099] FIG. 8 Partially cutaway perspective view showing a fifth
modified embodiment of the stress relaxation member.
[0100] FIG. 9 Partially cutaway perspective view showing a sixth
modified embodiment of the stress relaxation member.
[0101] FIG. 10 Partially cutaway perspective view showing a seventh
modified embodiment of the stress relaxation member.
[0102] FIG. 11 Partially cutaway perspective view showing an eighth
modified embodiment of the stress relaxation member.
[0103] FIG. 12 Partially cutaway perspective view showing a ninth
modified embodiment of the stress relaxation member.
[0104] FIG. 13 Perspective view showing a tenth modified embodiment
of the stress relaxation member.
[0105] FIG. 14 Perspective view showing an eleventh modified
embodiment of the stress relaxation member.
[0106] FIG. 15 Perspective view showing a twelfth modified
embodiment of the stress relaxation member.
[0107] FIG. 16 Perspective view showing a thirteenth modified
embodiment of the stress relaxation member.
[0108] FIG. 17 Perspective view showing a fourteenth modified
embodiment of the stress relaxation member.
[0109] FIG. 18 Perspective view showing a fifteenth modified
embodiment of the stress relaxation member.
[0110] FIG. 19 Perspective view showing a sixteenth modified
embodiment of the stress relaxation member.
[0111] FIG. 20 Perspective view showing a seventeenth modified
embodiment of the stress relaxation member.
[0112] FIG. 21 Perspective view showing an eighteenth modified
embodiment of the stress relaxation member.
* * * * *