Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-03-20
2001-10-30
Tolin, Gerald (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C165S185000, C257S719000, C361S719000, C428S901000
Reexamination Certificate
active
06310775
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power module to be used in semiconductor devices for controlling high voltages and large electric current for use in electric vehicles such as electric automobiles and electric trains. In more detail, the present invention relates to a power module substrate having a heat sink for dissipating the heat generated from heating elements such as semiconductor chips.
2. Description of the Related Art
In the conventional power modules as described above, an insulation substrate
2
has been made of a material such as AlN, a circuit layer
6
and a metallic layer
7
have been laminated and bonded on the insulation substrate
2
via a brazing foil, and the metallic layer
7
has been bonded to a heat spreader
8
of a heat sink
3
formed of AlSiC via a first solder layer
5
a
as shown in
FIG. 5. A
semiconductor chip
4
is bonded to the circuit layer
6
via a second solder layer
5
b
, while a water cooled sink
9
is attached to the radiator
8
using external threads
9
c
(such as pan-head screws). A cooling water flow path
9
b
for flowing cooling water to flow through is provided within the water cooled sink
9
.
Relatively a large amount of heat is generated from the semiconductor chip
4
in the power module substrate having the construction as described above. However, the power module substrates
1
are prevented from being overheated, because the heat generated in the semiconductor chip
4
is transferred to the water cooled sink
9
through the second solder layer
5
b
, the circuit layer
6
, the insulation substrate
2
, the metallic layer
7
, the first solder layer
5
a
and the heat spreader
8
; cooling water
9
a
flowing through the cooling water flow path
9
b
receives the heat and carries it out of the power module substrates
1
.
However, it was a problem that the production coast increases in the conventional power module substrates
1
since the large size heat spreader
8
is made of relatively expensive AlSiC.
It was also a problem in the conventional power module substrate
1
that heat cycle service life of the first solder layer
5
a
is shortened due to difference in deformation of the insulation substrate
2
and the radiator
8
caused by different thermal expansion coefficients between the insulation substrate
2
and the heat spreader
8
.
It was an another problem that man-hour for assembling was increased in the conventional power module substrate
1
, because the met allic layer
7
should be bonded to the radiator
8
via the first solder layer
5
a
in a separate process from lamination and bonding of the circuit layer
6
and the metallic layer
7
on the insulation substrate
2
.
For solving these problems, a power module substrate
1
as shown in
FIG. 6
has been disclosed, wherein the metallic layer
7
is bonded to the heat spreader
8
using the same brazing foil as the brazing foil (not shown) used for lamination and bonding of the circuit layer
6
and the metallic layer
7
on the upper face and lower faces of the insulation substrate
2
, respectively.
The problem of shortening the heat-cycle service life can be solved in the power module
1
having the construction as described above, since the first solder layer is not used for bonding the insulation substrate
2
and the heat spreader
8
, besides allowing the metallic layer
7
to be bonded to the heat spreader
8
simultaneously with lamination and bonding of the circuit layer
6
and the metallic layer
7
on the insulation substrate
2
.
However, manufacturing cost has been increased yet in the improved power module substrate as described above, because the large size radiator is formed using relatively expensive AlSiC.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a power module substrate that can reduce the load caused by heat stress on the insulation substrate, and is able to diminish the manufacturing cost, besides further improving productivity.
An another object of the present invention is to provide a power module substrate that can improve cooling efficiency by the heat sink, while preventing the solder layer for bonding semiconductor chips on the circuit layer from being degraded.
In a first aspect, the present invention provides a power module substrate in which a buffer layer
14
having a surface area one to three times as large as the surface area of an insulation substrate
12
is inserted with bonding between the insulation substrate
12
and a heat sink
13
as shown in
FIG. 1
, wherein the buffer layer
14
is formed using a material having a thermal expansion coefficient between the thermal expansion coefficient of the insulation substrate
12
and the thermal expansion coefficient of the heat sink
13
.
Since the difference in deformation between the insulation substrate
12
and the heat sink
13
due to difference of the thermal expansion coefficients between the insulation substrate
12
and the heat sink
13
is absorbed by the buffer layer
14
in the power module according to the first aspect of the present invention, internal stress generated in the insulation substrate
12
is reduced thereby to suppress the load caused by heat stress of the insulation substrate
12
.
Preferably, AlN, Si
3
N
4
or Al
2
O
3
is used for the insulation substrate
12
, Al or Cu is used for the heat sink
13
, and AlSiC, a carbon plate or an AlC composite material is used for the buffer layer
14
as shown in FIG.
1
.
Since the heat sink
13
is formed using Al or Cu in the power module substrate as described above, the production cost may be reduced as compared with the conventional power module in which the heat spreader is formed using expensive AlSiC.
The buffer layer
14
preferably has a thickness 1.5 to 50 times as large as the thickness of the insulation substrate
12
.
Since the difference of deformation between the insulation substrate
12
and the heat sink
13
caused by the difference of the thermal expansion coefficients between the insulation substrate
12
and the heat sink
13
is more securely absorbed by the buffer layer
14
, the load caused by the heat stress on the insulation substrate
12
is certainly suppressed.
Preferably, the insulation layer
12
, the buffer layer
14
and the heat sink
13
are laminated and bonded via a brazing foil as shown in FIG.
1
.
Productivity of the power module substrate
11
may be improved in the power module substrate as described above, because an integrated member of the insulation substrate
12
, the buffer layer
14
and the heat sink
13
is manufactured through one step heat treatment.
Preferably, the power module substrate comprises a heat spreader
48
in which the heat sink
13
is bounded to the buffer layer
14
, and a water-cooled sink
19
, which is attached to the radiator
48
and in which a cooling water flow path
19
b
for allowing the cooling water
19
a
to flow through, is formed as shown in
FIG. 2
, wherein a groove (or a recess)
48
a
capable of inserting the buffer layer
14
is formed on the surface of the heat spreader
48
, and the buffer layer
14
is bounded to the radiator
48
by being inserted into the groove
48
a.
The heat may be promptly transferred to the water cooled sink
19
from the buffer layer
14
through the heat spreader
48
in the power module substrate as described above, because the buffer layer
14
may be placed close to the water cooled sink
19
. Consequently, cooling efficiency by the heat sink
13
may be improved to prevent the power module substrate
41
from being overheated, because cooling water
19
a
flowing through the cooling water flow path
19
b
of the water cooled sink
19
receives the heat to take out it of the power module substrate
41
.
Preferably, the power module substrate comprises a water cooled heat sink
73
in which a cooling water flow path
73
b
for allowing cooling water
73
a
to flow through is formed; the buffer layer
14
being directly laminated on and bonded to the water cooled heat si
Kubo Kazuaki
Nagase Toshiyuki
Nagatomo Yoshiyuki
Shimamura Shoichi
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tolin Gerald
LandOfFree
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