Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Outside periphery of package having specified shape or...
Reexamination Certificate
1998-02-13
2001-08-28
Williams, Alexander O. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Outside periphery of package having specified shape or...
C257S673000, C257S687000, C257S678000, C257S731000, C257S666000, C257S712000, C257S704000, C257S698000, C257S696000, C257S692000, C257S693000, C257S690000
Reexamination Certificate
active
06281579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a high power semiconductor module and, more particularly, to an insert-molded leadframe which optimizes and improves the interface between a power stage and a driver board of the high power module.
2. Description of the Related Art
Conventional power control modules include a power train circuit which comprises two main components—a power stage and a driver board.
FIG. 1
schematically illustrates a prior art power stage consisting of power conductors and a component board
2
which operates in conjunction with a module/heat sink assembly
4
. The component board
2
includes power components such as diodes, MOSFETs, IGBTS, bipolar transistors, etc. which are connected to form various kinds of circuits such as half bridges, full wave bridges, voltage doublers, and the like.
The power components on component board
2
are controlled by a driver board
6
which contains control circuits such as logic circuitry, microprocessors, and the like to control the power provided from the power elements
2
and
4
to be delivered to a motor or a light ballast, for example.
Another known power control module arrangement is illustrated schematically in
FIG. 2
, in which driver board
6
interfaces with power components (diodes, MOSFETs, IGBTs)
8
installed on an IMS (insulated metal substrate) board
10
. Interconnection between IMS board
10
and driver board
6
is effected through vertical pins
12
that are received in through-holes
14
on the driver board
6
. The IMS board
10
is mounted directly to a heat sink
16
. The heat sink
16
and IMS board
10
make up the power portion
18
of the module.
IMS substrates such as IMS board
10
are known in the art. Such substrates have semiconductor chips or die thermally secured thereto. The substrate has a relatively thick aluminum body covered by a very thin insulation layer which, in turn, carries a copper pattern that is electrically insulated from the aluminum. Typically, chips are mounted on one or more heat spreaders, to improve thermal management of the heat generated by the chips during operation of the device.
The IMS substrate also includes conductor patterns for receiving bonding wires and effecting connection to the main device terminals. Thus, the die and chips may be internally interconnected to one another on the IMS substrate by stitch-bonding of parallel lead wires. These wires ultimately are connected to pins
12
, which extend externally of the casing comprising the power package.
For some time, the industry has been searching intensively for improvements which reduce the cost of circuitry of this type, result in circuits which have a smaller footprint, and deliver improved connectivity between the power circuitry and the driver board.
SUMMARY OF THE INVENTION
The present invention overcomes the deficiencies of the prior art by providing an insert-molded leadframe for a high power semiconductor module package. The insert-molded leadframe includes a conductive leadframe partially encased in a plastic casing. The conductive leadframe has device pins extending vertically on an outer portion thereof, wire bonding posts formed on an inner portion, and a central portion connecting between the inner and outer portions. Plastic encases the central portion of the conductive leadframe, such that the bonding posts and the device pins are exposed at inner and outer edges, respectively, of the plastic casing.
The wire bonding posts are exposed along the inner edge of the leadframe for attachment of an IMS substrate, for example. The device pins extend vertically from the leadframe to receive a circuit board, as described more fully below.
According to a preferred method of manufacturing the insert-molded leadframe, the conductive leadframe first is clamped into a molding tool. The conductive leadframe is clamped such that the bonding posts and the device pins advantageously remain exposed at the inner and outer edges of the plastic casing, respectively. Plastic is injected into the mold around the conductive leadframe.
To facilitate the injection molding process, the conductive leadframe bonding posts preferably are formed in a first plane and the device pins are formed in a second plane, the first and second planes being substantially mutually parallel. Subsequently, the device pins are bent vertically along the outer edge of the plastic casing for attachment to a circuit board. The circuit board preferably has holes that align with and accept the device pins for attachment.
A power package according to the present invention is assembled by inserting the IMS substrate into a central opening of the leadframe, and physically bonding the IMS substrate (populated with components) to the inner edge of the leadframe using liquid adhesive, for example. Adhesive bonds are formed directly between each of the exposed bonding posts and the IMS substrate. Electrical connections between the bonding posts and the substrate are made by wire bonding.
The IMS substrate then is potted, and the leadframe is trimmed prior to testing of the substrate/leadframe assembly. After successful testing, the device board is received over, and soldered to, the device pins.
Power packages manufactured using the insert-molded leadframe of the present invention provide a powertrain circuit which has a smaller footprint and is less expensive than prior art modules. The present invention also provides improved connectivity and support for the driver board. In addition, the present invention provides a device and methodology which improve physical and electrical connectivity to the IMS power board, reducing or eliminating the need for providing electrical take-outs on the IMS power board. The present invention also provides a configuration of a power train circuit that permits obtaining higher operating voltages in smaller packages.
In addition, the invention obviates the need for manual steps in bonding the circuit components to one another. That is, the electrical connection terminals on the device board advantageously can be located to align automatically with the device pins at the outer edge of insert-molded leadframe. Also, because virtually the entire body of the conductive leadframe is embedded in plastic, the individual power pins can be located closer to one another, since the plastic material of the board provides a higher dielectric insulation as compared to the more conventional use of air as a dielectric insulator.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4868638 (1989-09-01), Hirata et al.
patent: 5102829 (1992-04-01), Cohn
patent: 5172215 (1992-12-01), Kobayashi et al.
patent: 5517058 (1996-05-01), Temple
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patent: 5633530 (1997-05-01), Hsu
patent: 5646445 (1997-07-01), Masumoto et al.
patent: 5686758 (1997-11-01), Arai et al.
patent: 5753971 (1998-05-01), Miller et al.
patent: 5767579 (1998-06-01), Kanazawa et al.
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patent: 5920119 (1999-07-01), Tamba et al.
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R. Rutter, B. Pinder, J. Kimball, M. Kalfus, Cost Effective Power Package Handles Up to 3HP Motor Drives, Motion Power, pp. 24-25, 27, 30-32, Jan. 1997.
Motorola Semiconductor Technical Data Sheet, MHPM7A15A60A, 9 pages, (1995).
Motorola Semiconductor Technical Data Sheet, MHPM7A8A120A, Systems Design Guide, pp. 91-93 (1995).
International Rectifier Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Williams Alexander O.
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