Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – For plural devices
Reexamination Certificate
2001-04-16
2003-02-18
Graybill, David E. (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
For plural devices
C257S587000, C257S777000, C257S666000, C257S135000, C257S151000, C257S690000, C257S691000, C257S728000, C257S177000
Reexamination Certificate
active
06521992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor apparatus used mainly as a switching device in, for example, a motor drive device in an inverter, an AC servomotor, an air conditioner, etc., or a power supply device in a vehicle, a welding machine, etc., and more specifically to the improvement of an electrode wiring structure in a semiconductor apparatus applicable as a power semiconductor module.
2. Description of the Related Art
Normally, a semiconductor module can be, for example, a plurality of semiconductor devices (semiconductor chips) connected in parallel to have a larger current capacity, a simple circuit of several types of semiconductor devices, semiconductor devices into which a drive circuit is incorporated, etc.
FIG. 1
is a plan view of an example of a conventional power semiconductor module.
In the semiconductor module shown in
FIG. 1
, an insulated substrate
2
is mounted on a base plate
1
for fixing. On the insulated substrate
2
, a plurality of (four as an example shown in
FIG. 1
) semiconductor devices (semiconductor chips)
4
are mounted in series through a conductive plate
3
. In this example, the semiconductor device
4
is a MOSFET (metal oxide semiconductor field-effect transistor) having a source electrode and a gate electrode on the top side, and a drain electrode on the reverse side.
The conductive plate
3
is electrically connected commonly to the drain electrode of each semiconductor device
4
by mounting the semiconductor device
4
directly on it, thereby functioning as a drain electrode of the entire module. On the insulated substrate
2
, a source electrode
5
and a gate electrode
6
of the entire module are mounted along the array of the semiconductor devices
4
and on either side of the conductive plate
3
.
The source electrode
5
is electrically connected commonly to the source electrode of each semiconductor device
4
through a wire (bonding wire)
7
, and the gate electrode
6
is electrically connected commonly to the gate electrode of each semiconductor device
4
through a wire (bonding wire)
8
. A gate resistor such as a silicon chip resistor, etc. can be provided on the gate electrode
6
, and the wire
8
can be connected thereto.
Furthermore, a drain terminal
9
is led outside the module as an external terminal from a portion of the conductive plate (drain electrode)
3
, a source terminal
10
is led outside the module as an external terminal from a portion of the source electrode
5
, and a gate terminal
11
is led outside the module as an external terminal from a portion of the gate electrode
6
.
Although not shown in the attached drawings, the entire module is normally put in a resin package, and the space in the package is filled with gel or epoxy resin, etc. The above mentioned external terminal is drawn in a two-dimensional array in
FIG. 1
, but it is appropriately bent and exposed on the top or side of the package.
The semiconductor module with the above mentioned configuration has a plurality of semiconductor devices
4
connected in parallel between the drain terminal
9
and the source terminal
10
. Therefore, in principle, the main current flowing between the drain terminal
9
and the source terminal
10
can be controlled by applying a control voltage between the gate terminal
11
and the source terminal
10
, and simultaneously setting all semiconductor devices
4
ON/OFF.
In the conventional semiconductor module as shown in
FIG. 1
, restrictions are placed by the gate electrode
6
especially on the wiring pattern from the drain electrode (conductive plate)
3
to the drain terminal
9
. That is, the drain terminal
9
is led outside through the path from the end portion of the conductive plate
3
without passing the gate electrode
6
.
Therefore, the lengths of the current paths are entirely long as indicated by the dot-and-dash line as shown in
FIG. 2
when the main current flows from the drain terminal
9
to the source terminal
10
through each semiconductor device
4
, and the lengths are uneven depending on the position of each semiconductor device
4
. Especially, the current path through the semiconductor device
4
shown in
FIG. 1
on the right is considerably longer than the current path through the semiconductor device
4
on the left.
Since the inductance generated in the current path is substantially proportional to the length of the path, the inductance increases correspondingly when the current path is long as described above. As a result, the surge voltage generated when the semiconductor device
4
is turned off rises, thereby possibly destroying the semiconductor device
4
.
In addition, when the lengths of current paths are not even, the wiring resistance also becomes uneven depending on the position of each semiconductor device
4
. As a result, the current value becomes unbalanced, thereby leading excess current through only a part of the semiconductor devices
4
, and also possibly destroying the semiconductor devices
4
. Therefore, with the problem of the above mentioned excess current to a part of the semiconductor devices
4
has prevented the maximum current through the module from largely increasing.
Furthermore, with the drain terminal
9
directly connected to the conductive plate
3
to be mounted on the insulated substrate
2
as the semiconductor module as shown in
FIG. 1
, there can easily be a crack in the joint (the portion encompassed by a circle A indicated by a dot-and-dash line) between the drain terminal
9
and the conductive plate
3
due to the expansion and contraction by the heat from the semiconductor devices
4
.
To prevent the above mentioned cracks, the drain terminal
9
can be connected through a plurality of wires (bonding wires) instead of directly connecting them. That is, in
FIG. 1
, the joint portion (indicated by the dot-and-dash circle A) can be separated and replaced with a plurality of wires.
With the above mentioned configuration, cracks can certainly be suppressed. However, the above mentioned problems of the lengths and unevenness of the current paths still remain unsolved. These problems become severer with an increasing number of semiconductor devices
4
mounted on one insulated substrate
2
.
SUMMARY OF THE INVENTION
An object of the invention is to solve the above mentioned problems with the conventional technology, and to provide a semiconductor apparatus capable of not only suppressing cracks, but also shortening and leveling the lengths of the current paths, reducing a surge voltage, and improving the maximum current in the apparatus.
To attain the above mentioned object, the present invention has the following configuration.
That is, the semiconductor apparatus according to the present invention includes: a plurality of semiconductor devices mounted in one or more arrays on a substrate; a first main current electrode mounted along the array(s) of the semiconductor devices, and commonly connected to each of the plurality of the semiconductor devices though the substrate; and a second main current electrode mounted along the array(s) of the semiconductor devices opposite the first main current electrode through the mounting area of the semiconductor devices, wherein the substrate is connected to the first main current electrode through a plurality of wires arranged at equal (or substantially equal) distances along the array(s).
The substrate can be a conductive plate or a conductive layer mounted on an insulated substrate. However, it is obvious that other configurations can be accepted only if a path of the main current flowing from the main current electrode to each of the semiconductor devices can be provided.
The above mentioned main current electrode is a drain electrode or a source electrode when the semiconductor device is, for example, a MOSFET. It also can be a collector electrode or an emitter electrode when the semiconductor device is, for example, a bipolar transistor. Although the second main current electrode is to be directly connected to each of
Graybill David E.
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Mitchell James
Woodcock & Washburn LLP
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