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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power module device and, more
particularly, to a power module device which combines a power element such
as a MOSFET, and a control element therefor into one piece.
2. Description of the Related Art
FIG. 11 is a top view of a known power module device with the exterior
cover removed. FIG. 12 and FIG. 13 are a side view and a perspective view,
respectively, of the power module device of FIG. 11 which has been mounted
so as to be used practically. As shown in FIG. 11, the whole surface of a
metallic substrate 1 is covered with an insulating resin layer (not shown)
made of epoxy resin or the like, and wiring patterns 5 are provided on the
insulating resin layer. Provided on the wiring patterns 5 are a heat sink
2 on which a MOSFET 3 constituting a power element is mounted. The MOSFET
3 is electrically connected to the wiring pattern 5 on the metallic
substrate 1 through a bonding wire 6 or the like made of a fine metallic
wire as illustrated. Mounted on the metallic substrate 1 is a control
element 4 for controlling the MOSFET 3, the control element 4 being
electrically connected to the MOSFET 3 through the wiring pattern 5 and
the bonding wire 6. The MOSFET 3, the heat sink 2, etc. are covered with
gel-like resin (not illustrated) to protect them against humidity. A
relatively viscous gel-like resin is suitable for this purpose so that it
does not spread too much because it is only locally used for the MOSFET 3
on the metallic substrate 1. Further, since lead wires 9, which are
electrically connected to the wiring patterns 5 on the metallic substrate
1, are connected to electrodes 106 (see FIG. 12), etc. provided on a
printed circuit board 100 (see FIG. 12) at the time of mounting;
therefore, the lead wires 9 are provided so that it extends outward in a
cantilever-manner. The metallic substrate 1 is mounted on a radiator 102
(see FIG. 12) such as a heat sink and therefore the metallic substrate 1
is provided with a plurality of mounting holes 7 for installing it on the
radiator 102.
In the case of the known power module device having the structure described
above, as illustrated in FIG. 12 and FIG. 13, a box-shaped cover 108 made
of resin is provided on the metallic substrate 1 for mechanically
protecting the MOSFET 3 and other mounted components including the control
element 4 at the time of packaging. The box-shaped cover 108 is installed
in such a manner that only both ends of the metallic substrate 1, where
the mounting holes 7 of the metallic substrate 1 are provided, are
exposed. The metallic substrate 1 is attached to the radiator 102, such as
a heat sink, by screws 70 installed through the mounting holes 7. The
radiator 102 is attached on the printed circuit board 100, such as a
glass-epoxy substrate, by screws 22 as illustrated. Furthermore, a
partitioning plate 108b is provided within the box-shaped cover 108 as
illustrated in FIG. 12 to mechanically protect the lead wires 9 which
extend in a cantilever-manner. The wirings 5 extend under the partitioning
plate 108b (see FIG. 11) and ends thereof are soldered to the lead wires
9. The lead wires 9 extend in parallel to the metallic substrate 1, pass
through the printed circuit board 100, and are electrically connected,
with solder 16, to for example the electrodes 106 mounted on the printed
circuit board 100. For the purpose of reinforcing the lead wires 9, the
space which is enclosed by the box-shaped cover 108, the partitioning
plate 108b, and the metallic substrate 1, is filled with resin 104.
As stated above, the known power module device has the MOSFET 3 and the
control element 4 which are mounted two-dimensionally on the single
metallic substrate 1. Further, the conductor constituting the wiring
pattern 5 needs to be relatively thick because a relatively large current
must be supplied to the wiring pattern 5, this results because it is
difficult to provide the wiring pattern 5 with a high-density wiring. For
these reasons, the known metallic substrate 1 has a problem in that it
needs to be made large for the wiring and therefore it is extremely
difficult to make the device smaller.
In addition, there are problems related to the lead wires. The lead wires
9, which extend outward in a cantilever manner, require the box-shaped
cover 108 and the resin 104 or the like filled in the box-shaped cover 108
to provide the lead wires 9 with a mechanical protection. Further,
protection of the components including the MOSFET 3 and the wiring pattern
5 mounted on the metallic substrate 1 from mechanical damage requires the
provision of the box-shaped cover 108 made of resin or the like to cover
the surface of the metallic substrate 1. Therefore, numerous assembly
steps are required, resulting in a high cost production.
There is still another problem with the conventional power module device
namely, the heat generated by the MOSFET 3 constituting the power element
is transmitted to the whole metallic substrate 1 through the heat sink 2,
and the control element 4 is unavoidably subjected to the heat, causing
the control element 4 to malfunction.
SUMMARY OF THE INVENTION
The present invention has been made with a view toward solving the problems
described above and it is therefore an object of the present invention to
provide a power module device which permits a simplified assembly process,
reduced cost, and a smaller size and which is also capable of preventing
the heat generated by a power element from being transmitted to a control
element.
To this end, in a preferred form of the invention, a power module device is
equipped with a metallic substrate constituted by a recessed portion,
which houses a power element, and a flat portion which extends outward
from the recessed portion, a circuit board which is fixed onto the
metallic substrate in a manner that it covers the recessed portion and
which has a control element mounted on a surface facing against the bottom
surface of the recessed portion, and an electrical connection means for
providing the electrical interconnection between the power element and the
control element and for the electrical connection with an outside system,
the metallic substrate and the circuit board constituting a package.
With this arrangement, the size of the metallic substrate can be reduced
with a consequent reduced size of the entire power module device and the
assembly process can be therefore simplified since the power element is
mounted in the recessed portion provided in the metallic substrate and the
circuit board with the control element mounted on the bottom surface
thereof is placed over the recessed portion. Further, since the power
element and the control element are mounted in the recessed portion
provided in the metallic substrate, they can be protected against
mechanical damage without the need for providing a special armor.
Moreover, the wiring conductor provided on the metallic substrate and the
circuit board can be mechanically and electrically connected when placing
the circuit board over the recessed portion, thus permitting easier
connection between the metallic substrate and the circuit board. Further,
it is possible to prevent the heat produced by the power element from
being transmitted to the control element.
In another preferred form of the invention, the recessed portion of the
metallic substrate has a bottom surface section and a side wall section
which extends continuously from the bottom surface section.
With this arrangement, since the side wall section of the recessed portion
is provided continuously, it is possible to securely protect the mounted
components including the power element and control element and the wiring
conductor, etc. from mechanical damage. Further, as necessary, the side
wall section, which is continuously provided, allows resin for protecting
the power element from humidity to be charged easily in the recessed
portion without causing the resin to spread.
In a further preferred form of the invention, the recessed portion of the
metallic substrate has a bottom surface section and a pair of opposing
side wall sections which extend upward from the opposing sides of the
bottom surface section.
With this arrangement, the size of the metallic substrate can be further
reduced since the recessed portion has only one pair of opposing side
walls.
In a still further preferred form of the invention, the metallic substrate
has a bent portion which functions as a connector.
With this arrangement, since the metallic substrate is equipped with a bent
section which serves as a connector, there is no longer the need for
providing a separate connector on the metallic substrate, thus permitting
a further reduced size of the substrate, a simplified assembly, and
reduced cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a power module device according to a
first embodiment of the present invention;
FIG. 2 is a perspective view of a metallic substrate of the first
embodiment;
FIG. 3 is a partial perspective view of the junction or connecting portion
between a circuit board and the metallic substrate according to the first
embodiment of the present invention;
FIG. 4 is a front view of an example of the power module device of the
first embodiment which has been mounted;
FIG. 5 is a perspective view of the metallic substrate of the power module
device according to a second embodiment of the present invention;
FIG. 6 is a perspective view of the metallic substrate of the power module
device according to a third embodiment of the present invention;
FIG. 7 is a partial cross-sectional view illustrative of a bent section
connected with an external connector in the third embodiment;
FIG. 8 is a partial perspective view illustrative of the junction or
connecting portion between the circuit board and the metallic substrate
according to a fourth embodiment of the present invention;
FIG. 9 is a front view illustrative of an example of the power module
device of the fourth embodiment which has been mounted;
FIG. 10 is a side view of FIG. 9;
FIG. 11 is a top view of a privately known but unpublished power module
device with an armor removed;
FIG. 12 is a side view of the privately known but unpublished power module
device of FIG. 11 which has been mounted; and
FIG. 13 is a perspective view of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
The following describes the embodiments of the present invention in
conjunction with the accompanying drawings. FIG. 1 is the cross-sectional
view illustrating the power module device according to the first
embodiment. FIG. 2 is the perspective view illustrating the metallic
substrate shown in FIG. 1. As shown in FIG. 1 and FIG. 2, a metallic
substrate 11 has a flat section 11a and a box-shaped recessed section 11b
which is formed by drawing or the like to provide a predetermined depth
from the flat section 11a and which has an opening 11e. The recessed
section 11b has a bottom surface section 11c and a side wall 11d which
continuously extends upward from the circumference of the bottom surface
section 11c. The side wall 11d may be provided with a predetermined slope
as illustrated in FIG. 1 or it may be provided substantially
perpendicularly to the bottom surface section 11c. The opening 11e of the
recessed section 11b opens upward as illustrated and the flat section 11a
is provided in such a manner that it extends, from the opening 11e of the
recessed section 11b, outward horizontally to be nearly parallel to the
bottom surface section 11c. The flat section 11a of the metallic substrate
11 may be provided as a pair on both sides as in the case of the
embodiment shown in FIG. 5 to be discussed later, or it may be provided in
four directions as shown in FIG. 2, or it may be provided in three
directions.
Provided on the surface of the metallic substrate 11 is an insulating resin
layer 12 as shown in FIG. 1, and provided on the insulating resin layer 12
are wiring patterns 13 comprised of a conductor such as copper. A
heat-resistant resin such as polyimide which has flexibility to permit
easy bending is suitably used for the insulating resin layer 12. As
illustrated, the wiring patterns 13 are formed, beginning from the bottom
surface section 11c of the recessed section 11b of the metallic substrate
11 up to the flat section 11a of the metallic substrate 11 along the side
wall 11d of the recessed section 11b. The wiring patterns 13 should be
made as thin as possible, provided it is strong enough to survive the
forming step of the recessed section 11b and also survive the operating
currant to which it will be subjected because the wiring patterns 13 are
produced before the recessed section 11b of the metallic substrate 11 is
formed by drawing or the like.
A first heat sink 2 is provided on the wiring patterns 13 which are mounted
on the bottom surface section 11c of the recessed section 11b of the
metallic substrate 11. The MOSFET 3, which is the power element, is fixed
onto the first heat sink 2 with solder or the like. The MOSFET 3 is
electrically connected to the wiring patterns 13 through fine metallic
wires 14 such as a bonding wire. Input/output terminals 13a of the MOSFET
3 are formed integrally with the wiring patterns 13 on the end of the flat
section 11a of the metallic substrate 11 of the wiring patterns 13, the
MOSFET 3 being electrically connected to the input/output terminals 13a
through the fine metallic wirings 14 and the wiring patterns 13. The
input/output terminals 13a may not be formed integrally with the wiring
pattern 13; it may alternatively be made in a discrete form and then
electrically connected to the wiring pattern 13. The recessed section 11b
is filled with a predetermined amount of resin 8 such as silicone resin to
fully seal the MOSFET 3 to protect the MOSFET 3 from humidity. The resin 8
to be used for this purpose should be a resin which is close to a liquid
and which has a relatively low viscosity for less bubbles produced inside.
Thus, filling the recessed section 11b with the resin 8 protects the
MOSFET 3 from humidity and also prevents a short circuit between the wires
of the wiring pattern 13 or other similar component due to humidity or the
like, enabling the protection of the insulation between the wires.
Furthermore, in the power module device according to the present invention,
as shown in FIG. 1, the circuit board 15, composed of the glass-epoxy
substrate or the like, bridges the flat sections 11a over the recessed
section 11b in such a manner that it covers the recessed section 11b of
the metallic substrate 11. Hence, in the power module device according to
the present invention, the metallic substrate 11 and the circuit board 15
constitute the package of the power module device. Electrodes 18 are
provided on ends of the circuit board 15 and the electrodes 18 are
electrically and mechanically connected, with the solder 16, to the
input/output terminals 13a of the MOSFET 3 provided on the flat section
11a of the metallic substrate 11. FIG. 3 is the perspective view of the
electrode 18 which has been connected to the input/output terminal 13a. As
illustrated in FIG. 3, the electrode 18 is constituted by an electrode
main body 18b mounted on the bottom surface of the circuit board 15 and a
connecting surface 18a which is provided on the end of the circuit board
15 which electrically connected to the electrode main body 18b. The
connecting surface 18a can be formed for example by first providing a
notch 15a in the end of the circuit board 15, then providing the surface
of the exposed surface of the notch 15a with an appropriate conductor by
plating or the like. The circuit board 15 is positioned so as to couple
the connecting surface 18a of the electrode 18 thus configured to the
input/output terminal 13a of the MOSFET 3, and it is mounted on the flat
sections 11a of the metallic substrate 11. The connecting surface 18a of
the electrode 18 is then electrically and mechanically connected with the
solder 6 to the input/output terminal 13a of the MOSFET 3 as mentioned
above. Thus, the wiring pattern 13 and the input/output terminal 13a
provided on the metallic substrate 11, the electrode 18 provided on the
circuit board 15, and the solder 16 which connects between the
input/output terminal 13a and the electrode 18, constitutes an electrical
connection means for providing the electrical interconnection between the
MOSFET 3 and the control element 4 to be discussed later and also the
electrical connection with an external system. This embodiment shows an
example wherein the electrode main body 18b is mounted on the bottom
surface of the circuit board 15; it is not, however limited thereto. The
electrode main body 18b may alternatively be provided on the top surface
of the circuit board 15. In such a case, the electrical connection with
the control element 4 may be accomplished by providing the circuit board
15 with a through hole (not illustrated).
Furthermore, in the power module device according to the present invention,
as shown in FIG. 1, the molded control element 4 is mounted to the bottom
surface of the circuit board 15, the control element 4 being spaced away
from the MOSFET 3 in the recessed section 11b of the metallic substrate
11. As illustrated, the control element 4 must be provided in such a
manner that it does not touch the aforesaid resin 8 charged in the
recessed section 11b. For this reason, only a predetermined amount of the
aforesaid resin 8 is charged so that the area where the control element 4
is mounted is left in the recessed section 11b. The control element 4 is
electrically connected to the MOSFET 3 through the electrode 18 provided
on the circuit board 15 and the wiring pattern 13 or the like on the
metallic substrate 11. The flat section 11b of the metallic substrate 11
is provided with a plurality of mounting holes 17 as illustrated, and the
power module device is installed with screws through the mounting holes
17.
The following describes the mounting method for the power module device in
this embodiment. As shown in FIG. 4, a recessed device mounting section
20a, which has a complementary shape with respect to the external shape of
the recessed section 11b of the metallic substrate 11, is provided on a
radiator 20 such as a heat sink, then the recessed section 11b of the
metallic substrate 11 is fitted in the device mounting section 20a. In the
next step, the metallic substrate 11 is installed onto the radiator 20
with the screws 19 through the mounting holes 17 provided in the flat
section 11b of the metallic substrate 11. As necessary, a printed circuit
100 composed of a glass-epoxy board may be prepared and the radiator 20
with the power module device mounted on may be screwed onto the printed
circuit board 100 with screws 22. Thus, the power module device according
to the present invention is fitted in and housed in the device mounting
section 20a of the radiator 20 at the time of mounting; therefore, it is
protected by the radiator 20 from external mechanical damage.
In the power module device in this embodiment thus constructed, the MOSFET
3, i.e. the power element, is mounted in the recessed section 11b formed
on the metallic substrate 11 and the circuit board 15 with the control
element 4 mounted thereon is rested over the recessed section 11b. This
makes it possible to considerably reduce the size of the finished power
module device in comparison with the known power module device which has
the MOSFET 3 and the control element 4 mounted on the same board at the
same level. Moreover, in the known power module device, the wiring is
provided in a two-dimensional manner on the same board on which the MOSFET
3 and the control-element 4 are mounted, so that an area for the wiring
must be provided, leading to the need of a significantly large board. In
the power module device according to this embodiment, the control element
4 is mounted on a separate circuit board 15 and the wiring is provided in
a three-dimensional manner on the bottom surface section 11c and the side
wall 11d of the recessed section 11b of the metallic substrate 11 and on
the flat section 11a of the metallic substrate 11, thereby laying out the
metallic substrate 11 and the circuit board 15 in a three-dimensional
manner. This permits a substantially smaller bottom area of the device.
Furthermore, the three-dimensional wiring eliminates the need for curving
the wires to bypass other wiring as in the case of the known device
illustrated in FIG. 11. This linear wiring allows the wiring pattern 13 to
be shorter.
Further, the known power module inevitably ends up with a great total
height since the resinous box-shaped cover 108, which is made relatively
thick for the mechanical protection of the components mounted on the
metallic substrate 1, is provided on the metallic substrate 1. In the
power module device according to this embodiment, the metallic substrate
11, which is thinner than the known resinous box-shaped cover 108, serves
as the board and also as the package, thereby allowing the overall height
of the device to be reduced.
According to the embodiment, the input/output terminal 13a of the MOSFET 3
is provided on the flat section 11a of the metallic substrate 11 and the
electrode 18 of the circuit board 15 mounted on the flat section 11a is
provided along the surface of the circuit board 15 to correspond to the
input/output terminal 13a and the input/output terminal 13a of the MOSFET
3 and the electrode 18 are electrically and mechanically connected with
the solder 16 when installing the circuit board 15. This method eliminates
the need for the lead wire 9 employed in the known power module device and
enables a simpler connecting process. In addition, the embodiment no
longer requires the protecting means such as the box-shaped cover 108 and
the resin 104 charged in the box-shaped cover 108 for protecting the lead
wire 9 shown in the known device.
The arrangement, where the metallic substrate 11 is provided with the
recessed section 11b and the wiring pattern 13, the MOSFET 3, and the
control element 4 are mounted in the recessed section 11b, enables easier
mechanical protection of the wiring pattern 13, the MOSFET 3, etc. from
mechanical damage and eliminates the need of the special protection such
as the box-shaped cover 108 for protecting the wiring pattern 13, the
MOSFET 3, etc. from mechanical damage, thus achieving a further simplified
assembly process and lower cost.
Still further, in this embodiment, the MOSFET 3 which generates heat, is
installed on the metallic substrate 11 and the control element 4 is
mounted on the circuit board 15. This design prevents the heat produced by
the MOSFET 3 from being transferred to the control element 4 via the
metallic substrate 11, thereby preventing the control element 4 from
malfunctioning due to the heat.
Furthermore, in this embodiment, since the MOSFET 3 and the control element
4 are mounted on separate boards before they are assembled, it is possible
to subject the MOSFET 3 and the control element 4 separately to
reliability testing.
Second Embodiment
FIG. 5 is the perspective view illustrative of the metallic substrate of
the power module device according to the present invention in another
embodiment of the invention. The description of the part of the structure
which is identical to that of the first embodiment will be omitted. The
second embodiment refers to the case where a pre-packaged MOSFET 23 is
employed. As illustrated in FIG. 5, a metallic substrate 21 is composed of
a recessed section 21b and a pair of flat sections 21a which extend
horizontally outward from both ends of the opening in the recessed section
21b. The recessed section 21b is composed of a bottom surface section 21c
which is provided nearly in parallel to the flat section 21a and a side
wall 21d which extends upward nearly vertically or with a predetermined
slope up to the flat section 21a from the two opposing sides of the bottom
surface section 21c. The metallic substrate 21 can be formed by bending
both ends of a nearly rectangular metal plate into a reversed-L shape by,
for example, pressing or the like by using a metal mold or the like.
As in the first embodiment, the second embodiment also has the wiring
pattern 13 provided along the bottom surface section 21c, the side wall
21d, and the flat section 21a of the metallic substrate 21. Formed on the
end of the flat section 21a of the wiring pattern 13 is the input/output
terminal 13a of the MOSFET 23 which is made integral with the wiring
pattern 13. In the bottom surface section 21c of the metallic substrate
21, an end 21cc of the bottom surface section 21c, on which the side wall
21d is not provided, extends outward with respect to the side wall 21d,
the input/output terminal 13a being provided on the end 21cc as an
integral part of the wiring pattern 13. In the bottom surface section 21c,
the heat sink 2 is provided on the wiring pattern 13 and the MOSFET 23 is
mounted on the heat sink 2. In this second embodiment, the MOSFET 23 is
packaged in advance and an appropriate known method can be employed for
the packaging. Molding with resin or the like, for example, may be
employed, or the mounted components may be housed in a package case made
of resin or metal or the like.
As in the first embodiment, the power module device according to the second
embodiment is constructed by resting the circuit board 15, which has the
control element 4 mounted on the bottom surface thereof (see FIG. 1), on
the flat sections 21a of the metallic substrate 21. The second embodiment
uses the packaged MOSFET 23 and therefore it does not require the resin 8
(see FIG. 1), which protects the MOSFET 3 from humidity as shown in the
first embodiment, be charged in the recessed section 21 of the metallic
substrate 21. Hence, just providing the recessed section 21b with a pair
of opposing side walls 21d is adequate, eliminating the need for the box
shape with two pairs of opposing side walls as in the first embodiment.
The second embodiment provides the same advantages as those of the first
embodiment and it makes it possible to make the metallic substrate 21 even
smaller than that in the first embodiment.
Further, the second embodiment refers to the case where the packaged MOSFET
23 is employed. The present invention, however, is not limited thereto; an
unpackaged MOSFET 3 (see FIG. 1) as in the first embodiment may
alternatively be used. When such an unpackaged MOSFET is used, resin,
which is relatively viscous, may be used to protect the MOSFET 3 against
humidity as in the known device.
Third Embodiment
FIG. 6 is the perspective view showing the structure of a metallic
substrate 31 in the third embodiment. FIG. 7 is the partial
cross-sectional view taken along line VII--VII. The description of the
basic structure of the third embodiment will be omitted because it is
identical to that of the second embodiment shown in FIG. 5. As
illustrated, the third embodiment has a bent section 32 which is formed by
bending about 180 degrees downward the end of the bottom surface section
21c of the metallic substrate 31, which end does not have the flat section
21a. As shown in FIG. 7, the bent section 32 is formed by bending 180
degrees one end of the metallic substrate 31 together with the wiring
pattern 13 and the insulating resin layer 12 provided on the metallic
substrate 31. The end of the wiring pattern 13 is provided with the
input/output terminal 13a of the MOSFET 23 (see FIG. 5) as in the
embodiments described above; therefore, as illustrated in FIG. 7, simply
by inserting the bent section 32 into a known appropriate female connector
39 which is provided externally, the input/output terminal 13a can be
easily connected electrically to the external female connector 39.
In the known power module device shown in FIG. 11, the aforesaid box-shaped
cover 108, which protects the lead wire 9 (see FIG. 11), must be provided
on the metallic substrate 1 to form the male connector. In this third
embodiment, however, since the bent section 32 of the metallic substrate
31 serves as the male connector, it is no longer necessary to provide a
separate male connector on the metallic substrate 31. This makes it
possible to further reduce the size of the metallic substrate 31 and
simplify the assembly process with consequent lower cost.
The third embodiment describes the example which is applied to the same
basic structure as that of the second embodiment; it is not, however,
limited thereto. The same can be applied also to the metallic substrate 11
of the first embodiment shown in FIG. 2. In this case, the same advantages
can be obtained by forming the bent section 32 (see FIG. 7) by bending 180
degrees the end of the flat section 11a of the metallic substrate 11.
The third embodiment also provides the same advantages obtained in the
first and second embodiments. In addition, since the metallic substrate 31
of the third embodiment is equipped with the bent section 32 serving as
the male connector, no separate male connector is required as stated
above, thus achieving a power module device which features a simplified
assembly process and reduced cost.
Fourth Embodiment
FIG. 8 is the perspective view of a metallic substrate 41 which has been
connected to the circuit board 15 (see FIG. 1) in the fourth embodiment.
This embodiment can be applied to any of the above first to third
embodiments. The description of the part of the structure of the fourth
embodiment will be omitted because it will be the same as any of the
aforesaid embodiments. The connection between the metallic substrate 41
and the circuit board 15 in the fourth embodiment shown in FIG. 8 will be
described.
The metallic substrate 41 is provided with the similar flat section 41a to
that in any of the first to third embodiments. The circuit board 15 is
rested over the flat section 41a as illustrated. In this embodiment, the
circuit board 15 is equipped with a through-hole electrode 48 which has a
through hole 48a, the through-hole electrode 48 being installed so that it
matches the wiring pattern 13 and the input/output terminal 13a at the end
thereof provided on the metallic substrate 41. The inner wall of the
through hole 48a of the through-hole electrode 48 is provided with a
conductor by plating or the like and the through-hole electrode 48 is
electrically connected to the input/output terminal 13a and the wiring
pattern 13 with solder (not shown) or the like which is supplied in the
through hole 48a. An electrode main body 48b of the through-hole electrode
48 may be provided on the top surface of the circuit board 15 as shown in
FIG. 8 or it may be provided to the bottom surface of the circuit board 15
as in the case of the first embodiment.
According to the fourth embodiment, the power module device is composed by
providing tapped holes 15A and 17A (see FIG. 9) in both the circuit board
15 and the flat section 41a of the metallic substrate 41, then
mechanically fixing and connecting the circuit board 15 and the metallic
substrate 41 by screws 19. To mount the power module device on the
radiator 20 or the like as shown in FIG. 9, the circuit board 15 and the
metallic substrate 41 are fixed on the radiator 20 or the like by using
the common screws 19 to install the power module device. According to the
fourth embodiment, the screws 19 are used to connect the circuit board 15
and the metallic substrate 41, enabling firm connection and fixation.
In this embodiment, as in the case of the first embodiment, a printed
circuit board 100 may be prepared, if necessary, as shown in FIG. 9 and
FIG. 10 and the radiator 20 with the power module device mounted on is
fixed onto the printed circuit board 100 with screws 22. To fix the
radiator 20 on the printed circuit board 100, as shown in FIG. 10, one of
the flat sections 41a of the metallic substrate 41 may be let pass through
the printed circuit board 100 and the circuit (not shown) provided on the
printed circuit board 100 and the input/output terminal 13a on the flat
section 41a may be electrically and mechanically connected and fixed with
the solder 16 or the like.
The fourth embodiment provides the same advantages as those of the first to
third embodiments and it also permits reinforced connection between the
metallic substrate 41 and the circuit board 15.
Thus, in a preferred embodiment of the present invention, the size of the
metallic substrate can be reduced with a consequent reduced size of the
entire power module device since the power element is mounted in the
recessed portion provided in the metallic substrate and the circuit board
with the control element mounted on the bottom surface thereof is placed
over the recessed portion. Further, since the power element and the
control element are mounted in the recessed portion provided in the
metallic substrate, they can be protected against mechanical damage
without the need for providing a special armor. Moreover, the wiring
conductor provided on the metallic substrate and the circuit board can be
mechanically and electrically connected when placing the circuit board
over the recessed portion, thus permitting easier connection between the
metallic substrate and the circuit board. Further, it is possible to
prevent the heat produced by the power element from being transmitted to
the control element, thus preventing the malfunctioning of the power
element due to the heat. Still further, the size of the metallic
substrate, which is relatively expensive, can be reduced since the lead
wire and the armor shown in the known device are no longer necessary, thus
enabling the achievement of lower cost. Furthermore, since the power
element and the control element are mounted on separate boards, they can
be subjected to reliability testing separately.
In another preferred form of the invention, since the side wall section of
the recessed portion is provided continuously, it is possible to securely
protect the mounted components including the power element and control
element and the wiring conductor, etc. from mechanical damage. Further, as
necessary, the side wall section, which is continuously provided, allows
resin for protecting the power element from humidity to be charged easily
in the recessed portion without causing the resin to spread.
In a further preferred form of the invention, the size of the metallic
substrate can be further reduced since the recessed portion has only one
pair of opposing side walls.
In a still further preferred form of the invention, since the metallic
substrate is equipped with a bent portion which serves as a connector,
there is no longer the need for providing a separate connector on the
metallic substrate, thus permitting a further reduced size of the
substrate, a simplified assembly, and reduced cost.
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