Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
1997-03-12
2001-06-05
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C257S724000, C257S696000
Reexamination Certificate
active
06242800
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to semiconductor devices and, more specifically, to a novel device in which the die is fixed to the bottom surface of a lead frame within a package or housing and in which the lead frame serves to remove heat from the die in an improved manner.
BACKGROUND OF THE INVENTION
Numerous electrical circuits, for example, dc to dc converters, synchronous converters, and the like, require a number of semiconductor components, such as MOSFETs. These components typically generate heat which can increase the on-resistance or forward voltage drop of the MOSFET. If the MOSFET is located near other components, such as a microprocessor, the heat generated can also interfere with their operation.
Typically, the components are each housed in a surface mount package which normally consists of the semiconductor component die mounted with its back surface in contact with the surface of a lead frame and with its front surface including wires extending from connection pads to the lead extensions of the lead frame. The bottom of the lead frame is then typically located atop a heat-conducting slug whose bottom surface is to be connected to a flat surface which is to receive the surface mount package. The assembly, consisting of the die, lead frame and heat-conducting slug, is then encapsulated so that the flat bottom surface of the slug is exposed for surface connection and so that the lead frames extend out of the molded housing for external connection.
Surface mounted packages typically have a large plastic insulation portion located beneath the main pad area of the lead frame, namely between the lead frame and the board to which the device is mounted, that is unused. Also, the semiconductor device die is mounted to the top of the lead frame, which necessitates increasing the thickness of plastic at the top of the package to protect the die, thereby increasing the height of the package. It is also desirable to reduce the height of the surface mount package.
Principally, however, it is desired that heat be removed from the package as efficiently as possible.
SUMMARY OF THE INVENTION
In accordance with the present invention, a conductive lead frame in a semiconductor device includes a main pad area. At least two pins extend from one edge of the main pad area, and at least two pins extend from another edge of the main pad area. The at least four pins are integral with the main pad area to more efficiently remove heat from the main pad area. Additional pins are separated from the main pad area as well as from one another.
A semiconductor die has a surface that is disposed in contact with the main pad area of the lead frame and has one or more electrodes in electrical contact therewith. An opposing surface of the die also has one or more electrodes which are electrically connected to respective pins.
A molded housing encapsulates the lead frame in the semiconductor die. The pins extend outside the molded housing for external connection. The at least four pins that are integral with the main pad area thus serve to remove heat from the surface of the semiconductor die.
According to this aspect of the invention, the surface that is disposed to the main pad area may contact the bottom surface of the main pad area, and may electrically contact the in-line pins that are integral with opposing edges of the main pad area. The semiconductor die may include a MOSFET die that has source, drain and gate electrodes. The die surface that contacts the main pad area includes the drain electrode, and the opposing surface includes the source and gate electrodes which are connected to respective pins. The drain electrode may contact the bottom surface of the main pad area and may electrically contact the two pairs of in-line pins that are integral with opposing edges of the main pad area.
At least one electrode may be wire bonded to a respective pin by one or more bonding wires. The pins may be bent downwardly along the side edges of the housing to define a surface-mount device. The pins may be arranged in a line and may include an enlarged bonding pad area which are coplanar with one another and with the main pad area.
The package may include six pins. The pins may include a plated bond post.
The electrode of the surface that contacts the main pad area may be soldered to the main pad area or conductively bonded using a conductive epoxy. The molded housing may be a plastic transfer mold compound.
According to another aspect of the present invention, a surface mount package includes a conductive lead frame and a MOSFET die.
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: 4891686 (1990-01-01), Krausse, III
patent: 5521429 (1996-05-01), Aono et al.
patent: 5521431 (1996-05-01), Tahara
patent: 5530284 (1996-06-01), Bailey
patent: 5583372 (1996-12-01), King et al.
patent: 5625226 (1997-04-01), Kinzer
patent: 5719435 (1998-02-01), Davis et al.
patent: 5757070 (1998-05-01), Fritz
patent: 3-286558 (1991-12-01), None
PTO 99-2220—Translation of Japanese Kokai Patent Application No. Hei 3-286558 Dec. 1991.
Cheah Chuan
Kinzer Daniel M.
Munos Jorge
Chaudhuri Olik
International Rectifier Corp.
Ostrolenk Faber Gerb & Soffen, LLP
Weiss Howard
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