Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-08-02
2001-08-07
Picard, Leo P. (Department: 2811)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S704000, C361S719000, C361S713000, C361S752000, C174S050510, C174S050510, C165SDIG119, C165S185000, C257S706000, C257S717000
Reexamination Certificate
active
06272015
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to semiconductor device power modules and more specifically relates to a novel structure for such devices which simplifies their manufacturing cost and reliability.
BACKGROUND OF THE INVENTION
Semiconductor modules are well known, in which a plurality of power semiconductor die are fixed to a ceramic based substrate support such as an insulation metal substrate (IMS) or the like to interconnect the devices and are carried in a main support shell which also supports a printed circuit board (PCB) which carries control circuits for controlling the power die. Power terminals extend from the IMS for connection to a load, such as a motor and the PCB carries a terminal connector for connection to an external source of control signals. Such devices, as shown in aforementioned application Ser. No. 09/197,078 are usually arranged so that the IMS is secured within a small opening in the shell (so that the area of the expensive IMS can be minimized) and the bottom surface of the IMS can be pressed into contact with the top flat surface of a heatsink.
The PCB is generally supported in a plane above the plane of the IMS and is laterally removed from the IMS area. The bottom of the PCB is spaced above the top surface of the support shell so that components can be mounted on the bottom surface of the PCB as well as on its top surface.
In general ceramic based substrates are frequently employed to carry the various semiconductor die. These substrates usually have the construction shown in
FIGS. 13 and 14
for substrate
320
and have a bottom copper layer
321
, a central insulation ceramic
322
, which may be Al
2
O
3
or AlN, and a top copper layer which has been patterned into various areas, such as the six insulated areas
323
,
324
,
325
,
326
,
327
and
328
shown. Any other pattern could be formed for the top copper layer. Each of areas
323
to
328
have a respective power semiconductor device die
330
to
335
secured thereto, as by soldering or conductive epoxy, or the like. The bottom electrodes of die
330
to
335
are insulated, but could be connected together as desired by conductive traces or by wire bonds. Substrate
320
of
FIGS. 13 and 14
may also be a direct bonded copper (DBC) substrate.
In order to insure the mechanical integrity of such substrates, and to prevent the ceramic from cracking, their length is usually limited to less than about 2 inches. Thus, when a power module requires a larger substrate, two or more shorter separate substrates must be used. Thus, as shown in
FIG. 15
, two identical substrates
320
and
340
are attached to a common base plate
341
which is of copper or of AlSiC for higher performance applications.
Substrates
320
and
340
are conventionally attached to a common baseplate
341
by solder reflow techniques, or by a conductive epoxy. The subassembly of substrates
320
,
340
and base plate
341
is then secured within a plastic support shell
350
with the base plate
341
bottom exposed for connection to a flat heatsink
351
. A suitable printed current board and terminals are then provided, for example as described in copending application Ser. No. 09/197,078 (IR-1520). The silicon die and substrate are wire bonded or otherwise connected to the PCB and terminal and the substrates are enclosed in a suitable potted volume.
The above described structure has a number of drawbacks. These include:
1. Tooling and material cost for base plate
341
.
2. The additional processing required for the use of base plate
341
.
3. The added thermal resistance between the silicon die and the heatsink
351
due to the added interfaces at the top and bottom of plate
341
.
4. Degradation of power and temperature cycling capability due to the added interfaces.
It would be desirable to employ multiple substrates in a power module without the disadvantages brought about by the added common base plate.
In the known prior art structure and as described above, the entire module is attached to a single unitary heatsink as by screws or the like. The individual devices are electrically isolated from one another against conduction through the common heatsink by the use of the expensive IMS or DBC. The use of the IMS or DBC or the like substrate increases the thermal resistance between the die and heatsink.
It would be desirable to provide a power module which is a self contained circuit, as for a motor control circuit, and which does not require expensive single or multiple insulation substrate(s) and which does not impede heat flow from the die to the heatsink.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with a first aspect of the present invention, multiple substrates are mounted in respective openings in a plastic shell, and the intermediate common conductive base is eliminated. A PCB is disposed above the substrates and contains openings to provide access to the tops of each substrate for the necessary interconnect and wire bonding between the silicon die, the substrates and the PCB and terminals.
If desired, the PCB may include additional interconnects such as solderable or snap mount pins, terminals, connectors, etc. for connecting another PCB, or other components or wires to other equipment.
In another implementation, the PCB can be eliminated and the insulation shell can contain an insert molded lead frame with wire bond connections being made to the lead frame. The leads may be soldered to a PCB external of the module for making the interconnects.
In still another implementation of the invention, the internal PCB may be replaced by an external PCB and the substrate may contain terminal pins (connected to the substrate by reflowed solder), which pins are connected to the external PCB.
In a yet further implementation of the invention, the separate substrates can be aligned longitudinally to reduce the number of mounting screws needed to mount the PCB to the insulation support shell.
In accordance with second aspect of the invention the single heatsink of the prior art is divided into a plurality of separate heatsinks which are fixed to the main support insulation shell of the module and are spaced from one another and are insulated from one another by the insulation shell. The die may be attached to their respective heatsinks by solder reflow or conductive epoxy techniques or the like. Thus, one or more die, the bottom electrodes of which are at the same potential, are fixed directly to the top bare conductive surface of the respective heatsinks. Thus, no IMS is needed for the isolation of die at different potentials and the die are intimately thermally connected to their respective heatsink. Note that any mixture of power die such as diodes, Power MOSFETs, IGBTs, thyristors and the like can be used.
REFERENCES:
patent: 4899256 (1990-02-01), Sway-Tin
patent: 4965710 (1990-10-01), Pelly et al.
patent: 5031069 (1991-07-01), Anderson
patent: 5373418 (1994-12-01), Hayasi
patent: 5398160 (1995-03-01), Umeda
patent: 5521437 (1996-05-01), Oshima et al.
patent: 5536972 (1996-07-01), Kato
patent: 5606487 (1997-02-01), Yasukawa et al.
patent: 5625536 (1997-04-01), Soyano et al.
patent: 5747876 (1998-05-01), Majumdar et al.
Chervinsky Boris L.
International Rectifier Corp.
Ostrolenk Faber Gerb & Soffen, LLP
Picard Leo P.
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