Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With large area flexible electrodes in press contact with...
Reexamination Certificate
1998-08-26
2001-09-04
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With large area flexible electrodes in press contact with...
C257S726000
Reexamination Certificate
active
06285076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a press-connection semiconductor device and a press-connection semiconductor assembly, and more particularly to a press-connection power semiconductor device with reliability improved in terms of a temperature cycle test and a power cycle test.
2. Description of the Related Art
Conventionally, a high-power semiconductor device is used for an inverter which is used to control the running speed of a drive motor in an electric vehicle, an air conditioner, various types of machine tools and the like.
FIG.
8
and
FIG. 9
show a configuration of such a conventional power semiconductor device.
In the drawings, reference numeral
1
denotes a ceramic wiring substrate, which has a wiring layer
1
a
of a copper foil formed on both faces of a ceramic substrate such as aluminum nitride or aluminum oxide (alumina). Two types of semiconductor elements
2
of IGBT (insulated gate bipolar transistor) and FRD (fast recovery diode) are die-bonded by soldering at predetermined positions on the main face of the ceramic wiring substrate
1
. The ceramic wiring substrate
1
having the semiconductor elements
2
is soldered onto a copper radiator plate
3
. The ceramic wiring substrate
1
mounted onto the copper radiator plate
3
is accommodated into a casing
8
of insulating resin having an anode member
4
, a cathode member
5
, a common electrode member
6
, and a plurality of signal terminals
7
. Electrode pads of the semiconductor elements
2
and the wiring layer
1
a
of the ceramic wiring substrate
1
, said wiring layer
1
a
and the electrode members mounted on the casing
8
are wire-bonded with an Al wire
9
. It is not shown but the wire-bonded portion is covered with a sealing layer of insulating resin and further covered with a cap.
When such a semiconductor device is subjected to a thermal cycling or power cycling, a stress is applied to the semiconductor device due to a difference in thermal expansion coefficient among the different materials used. This thermal stress has a possibility of causing a fatigue failure or breakage in a solder connection or a connection of the bonding wire.
Specifically, in the conventional semiconductor device, the ceramic wiring substrate
1
and the semiconductor element
2
are bonded with Sn—Pb solder, and the electrode pads of the semiconductor element
2
and, the wiring layer
1
a
of the ceramic wiring substrate
1
, said wiring layer
1
a
and the electrode member are connected by wire bonding. Accordingly, a temperature of the device as the whole rises and drops repeatedly because of heating generated when the semiconductor element
2
is operating, leading to a fatigue in the solder connecting portions or the joint of the Al wire
9
, and possibly resulting in breaking the device.
SUMMARY OF THE INVENTION
The present invention was achieved to remedy the problems described above. It is an object of the invention to provide a power semiconductor device and a semiconductor assembly, which excel in electrical characteristics, and especially have improved reliability in terms of temperature cycle and power cycle.
A press-connection semiconductor device, comprises a semiconductor unit, which has a plurality of semiconductor elements, the element having two main faces with electrode pads, arranged on the same plane so to enable parallel connection; heat buffer layers, which are arranged in contact with both the main faces of the semiconductor elements; electrode plates, which interpose the semiconductor unit between them and are electrically in contact with the electrode pads of the semiconductor elements; spring members, which push the electrode plates in the direction of normal line of the main faces of the semiconductor elements; a engaging rod, which is disposed to pierce through the centers of the semiconductor unit and also the electrode plates; and a clamping member, which is joined to the engaging member to control the pushing force of the spring members.
The press-connection semiconductor device of the invention may have a heat sink disposed on the outside of the spring members. The heat sink can be a supporting member made of aluminum, copper or ceramic. Otherwise, the heat sink can be an aluminum supporting member having fins.
The semiconductor element configuring the semiconductor unit can have, for example, a plurality of IGBTs (insulated gate bipolar transistors) and a plurality of diodes in combination.
The semiconductor device having the semiconductor unit configured by combining the plurality of IGBTs and the plurality of diodes may further comprises a gate extending structure, having a probe pin, a spring fixed to the rear end of the probe pin, a printed circuit board having necessary wiring on its main face, connected to the gate electrodes of the IGBTs.
The semiconductor device having the IGBTs and the diodes in the semiconductor unit preferably has the IGBTs and the diodes alternately arranged around the engaging rod, and the IGBTs positioned at corners. Besides, the gate electrode of the IGBT is preferably located at corner near a direction that the gate electrode is extended.
A press-connection semiconductor assembly of the invention has three of the press-connection semiconductor devices described above, which are arranged in a direction parallel to the axial direction of the engaging rod, and all the electrode plates of the semiconductor devices being extended in the same direction.
A single set (unit) or a plural sets of semiconductor units having a plurality of semiconductor elements such as IGBTs and FRDs arranged on the same plane are disposed in series, intervened between two electrode plates. These electrode plates are pushed by spring members in a direction perpendicular to the main faces of the semiconductor elements so to be press-contacted to the electrode pads of the respective semiconductor elements through a heat buffer layer.
Thus, in the semiconductor device and assembly of the present invention, the semiconductor elements configuring the respective semiconductor units are connected in parallel through the means of electrode plates, and the semiconductor units are connected in series to one another. Thus, the required electrical connection is made without soldering or wire bonding. Therefore, the connecting portion does not suffer from a fatigue failure or breakage caused due to a difference in thermal expansion coefficient among the members used even if a cyclic temperature change, such as heating and cooling caused when the semiconductor elements are operating, is repeated. Connection reliability is thus improved substantially.
Inductance is also small because the respective electrode plates are closely arranged with the semiconductor elements intervened between them and an electrode-to-electrode distance is small. Besides, when the semiconductor elements are operating, mutual inductance operates because of the short electrode-to-electrode distance, so that total inductance of the elements is also lowered substantially as compared with the conventional device.
In addition, the spring member serves to press the respective electrode plates in a direction perpendicular to the main faces of the semiconductor elements. A pushing force of the spring member is controlled by a clamping member, so that it is applied uniformly to each part of the electrode plates without being dispersed, and the electrode plates are pushed against the semiconductor elements by a necessary and sufficient force.
REFERENCES:
patent: 5483103 (1996-01-01), Blickhan et al.
patent: 5544038 (1996-08-01), Fisher et al.
patent: 5610439 (1997-03-01), Hiyoshi et al.
patent: 5956231 (1999-09-01), Yamada et al.
Chaudhuri Olik
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Weiss Howard
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