Electrode terminal connection structure of semiconductor module

Details Electrode terminal connection structure of semiconductor module Electrode terminal connection structure of semiconductor module

1999-09-03

2002-04-30

Graybill, David E. (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Housing or package

With contact or lead

C257S724000, C257S735000, C257S787000, C257S694000, C257S723000, C257S695000, C257S706000

Reexamination Certificate

active

06380617

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrode terminal connection structure for connecting a non-insulated semiconductor module to a dual inverter structure used in the motor control apparatus for industrial vehicles.
2. Description of the Prior Art
Conventionally, a semiconductor module with a large current capacity is used as the switching device of an inverter directly supplying a main motor with electric power in a motor control apparatus used in battery-powered vehicles, such as a battery forklift, etc. A semiconductor module is obtained by incorporating a plurality of power semiconductor chips into one insulated package, and there are modules with a variety of internal compositions, such as a module in which the current capacity is increased by simply incorporating chips of the same kind in parallel, a module in which a simple circuit is composed of a plurality of kinds of chips, a module in which a drive circuit composed of semiconductor chips is embedded, etc. Usually the package is made of plastic, and the concavity inside the package is filled with a gel and epoxy insulating agent from the bottom to prevent a chip peripheral circuit from oxidizing.
Since a semiconductor module is used to control a large current, a semiconductor module generates a lot of heat. For this reason, a non-insulated type is generally used in which semiconductor chips, being the current control circuit of a heat source, are directly mounted on a heat-radiating substrate with both a high thermal capacity and a high heat-radiation efficiency (highly heat-conductive) and in which the heat-radiating substrate itself is used as one electrode. Usually the heat-radiating substrate of a semiconductor module having such a structure is provided with a heat sink made of aluminum, etc., and is highly heat-conductive as a heat-radiating material to improve the radiation efficiency, which also serves to secure the semiconductor module itself.
A switching frequency usually used in a semiconductor module structured in this way, for example, in the above-described battery vehicle, is approximately 10 kHz.
When a semiconductor module structured as described above is actually used at the above-described switching frequency, the occurrence of a large inductance in the wiring of an internal circuit and the wiring connecting the semiconductor module to the outside cannot be avoided, and the occurrence of a large inductance causes a fairly large loss of switching power (hereinafter called a “switching loss”) when a switching element is turned off. When the switching element is turned off, a fairly large surge voltage also occurs, which electrically damages the internal circuit.
This switching loss is an electric power loss occurring inside the semiconductor module when a device with a control electrode like the above-described semiconductor switch performs switching, and since usually many (5 or 6) semiconductor switches are used in the above-described motor control apparatus, the total switching loss occurring in these switches becomes a serious problem. This large loss, for example, greatly affects the drive and operation of the above-described battery vehicle, etc., and thermally damages the semiconductor switches since the lost electric power is converted into heat.
Conventionally, the reduction of the wiring inductance, that is, the reduction of both the switching loss and surge voltage has been realized by arranging two pieces of electrode wiring for the main current (for example, in the case of a MOS FET, source electrode wiring and drain electrode wiring) through which a large current flows in and out of the semiconductor module in opposite directions as input and output, in parallel and as close as possible to each other as much as possible and by causing an electro-magnetic effect which offsets (cancels) the two pieces of wiring inductance due to a reciprocal induction function.
FIG. 1
is the circuit diagram of an inverter used in the above-described semiconductor module, and each of the switching elements Q
1
through Q
6
shown in
FIG. 1
correspond to one semiconductor module.
Then, the rotation of a three-phase motor M can be controlled by inputting a control signal from a drive circuit, which is not shown in
FIG. 1
, to the gate electrode of each switching element (semiconductor module).
Two of the above-described inverters, that is, one for driving and the other for lifting are needed in industrial vehicles, such as a battery-powered forklift, etc. Recently, a dual inverter structure
1
in which a small size, light weight and low cost can be realized by arranging two inverters
2
and
3
in parallel, making the inverters share common power capacitors, bus electrodes, etc., and thereby realizing a single module, as shown in
FIGS. 2A and 2B
(
2
A and
2
B are a top view and side view, respectively), is proposed.
FIG. 3
is a side view in which the conventional connection structure of a pair of modules corresponding to a pair of upper and lower arms in the case where Q
1
and Q
2
shown in the circuit diagram (
FIG. 1
) are paired, are extracted and enlarged. Since the current flowing in the circuit is relatively small and thereby gate electrodes are not affected much by the wiring inductance, the gate electrodes are omitted in FIG.
3
.
As shown in
FIG. 3
, the semiconductor modules used have a non-insulated structure in which base substrates
6
a
and
6
b
are also used as drain electrodes and in which source electrodes
7
a
and
7
b
are vertically installed along the inner sides of packages
8
a
and
8
b
from the joint part mounted on the upper surfaces of package
8
a
and
8
b
, as shown in dotted lines.
The semiconductor module has a sandwich structure in which a sufficiently thin insulation sheet
9
is inserted. The two extensions of a positive electrode
10
beneath the lower surface and a negative electrode
11
of a bus electrode plate
5
located above inverters
2
and
3
are used as a positive electrode terminal
12
and a negative electrode terminal
13
, respectively, are extended to the drain electrode
6
a
of the Q
1
module and the source electrode
7
b
of the Q
2
module, respectively, and are connected and secured using screws
14
.
The source electrode
7
a
of the Q
1
module and the drain electrode
6
b
are connected using an inter-electrode terminal
15
made of copper plate, and a part of the terminal constitutes the output part to a drive motor M.
The positive electrode terminal
12
is divided into two parts in the longitudinal direction, and the inter-module electrode terminal
15
is positioned between the divided terminals.
However, according to the conventional semiconductor module connection structure in the above-described dual inverter structure
1
, the electrode terminals
12
,
13
and
15
connected to each semiconductor module correspond to the two extensions of the electrode plates
10
and
11
of the bus electrode plate
5
and a single copper plate, respectively, and as shown as D in
FIG. 3
, gaps are provided between the packages
8
a
and
8
b
in order to make tools, such as a driver, etc., easy to access if they are secured with screws
14
, and the source electrodes
7
a
and
7
b
inside the packages
8
a
and
8
b
of the semiconductor module and the vertical portions of the electrode terminals
12
and
15
, respectively, are separated and geometrically parallel. For this reason, the offset effect of the wiring inductance due to the reciprocal induction function in the vertical portions cannot be expected and thereby both surge voltage and switching loss are proportional.
Since many electrolytic capacitors are mounted as power capacitors
4
on the bus electrode plate
5
, the weight of the semiconductor module becomes large, and thereby according to the conventional structure, reinforcing materials, such as a bracket
16
, etc., must be installed in order to support the bus electrode plate
5
above the entire circuit.
SUMMARY OF THE INVENTION
An object of the present invention

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