Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
1999-10-08
2004-01-06
Wille, Douglas A. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C361S689000
Reexamination Certificate
active
06674164
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to devices for interconnecting and/or cooling electrical components and, more particularly, to a power bus and heatsink for electrically connecting and cooling electrical devices, along with related methods.
Presently, power switching devices such as the insulated Gate Bipolar Transistor (“IGBT”) are commercially packaged as both “discrete” and “modular” parts. Discrete parts, as typified by the popular TO-247 package, as sold by International Rectifier, Inc., have advantages of low packaging cost, compact size and low termination inductance. A typical manufacturing cost of the TO-247 package (less die and lead bonds) is about $0.12, while the typical termination (lead) inductance for this package is approximately 6 nH. Limitations of discrete packaged parts include a lack of electrical isolation and limited current capabilities. The maximum lead current capability for the TO-247 package is approximately 60 A.
Modular packaging has not become standardized to the degree that discrete parts have. An example of a popular modular package is the Powerex CM—DY package. One advantage of this type of packaging is the capability of packaging large total die areas so that high current ratings (more than 1000 A) can be achieved. Other advantages of the modular package include electrical isolation between the semiconductors and the heat-transfer surface and the capability of combining multiple semiconductor die so that several functions can be achieved within a single module.
Compared with discrete packaging, modular packaging has a number of disadvantages, including increased package cost and increased termination inductance. For modular devices, typical packaging costs are approximately equal to the bare Silicon die costs, whereas for the discrete packaged devices, the package cost is frequently less than 5% of the die cost. Accordingly, the manufacturing cost per VA for modular devices is nearly twice that of discrete devices. Furthermore, as die costs continue to fall more rapidly than packaging costs, this cost ratio between modular and discrete parts is expected to increase with time.
The termination inductance associated with modular packaging is also an increasing problem, as both die current ratings and die switching speeds are increasing with time. The net result is that for modular parts, voltage ratings must be reduced significantly below the die voltage rating—often more than 20%. In contrast, the required voltage derating for discrete packaged parts is negligible. This, in turn, adds to the cost advantage for discrete parts—and particularly to the cost average over time.
While discrete packaged parts have the stated inherent economic advantage over their modular counterparts, this advantage is presently more than offset by the costs associated with heatsinking, mounting and terminating these parts. In particular, where multiple discrete parts must be paralleled, suitable means must be used to insure current balancing and uniform die temperatures in order to ensure viable operation. Accordingly, a situation exists where the manufacturing costs for complete power systems could be significantly reduced if a technically and economically viable means were at hand for simultaneously interconnecting, heatsinking and mechanically supporting discrete semiconductor devices.
FIGS. 1
a
-
1
c
illustrate a prior art design for power processing that is based on the use of semiconductor modules
50
. Semiconductor modules
50
are mounted in thermal contact with heatsink
51
which has fluid inlet
53
and fluid outlet
52
; semiconductor modules
50
are electrically connected to capacitors
56
via circuit board
57
; electrical input termination is provided by buses
54
and
55
; and semiconductor modules
50
are controlled by terminals
57
. Advantages of this design include a low impedance interconnection between capacitors
56
and semiconductor modules
50
, and an efficient use of space. However, the semiconductor modules themselves cost approximately twice the cost of equivalently rated discrete semiconductor parts.
FIGS. 2
a
and
2
b
illustrate a prior art design for power processing that is based on the use of discrete semiconductor devices
10
. Discrete semiconductor devices
10
are horizontally mounted in thermal contact with heatsink
51
; and discrete semiconductor devices
10
are electrically connected to capacitors
56
(and other components that are not shown) via circuit board
11
. The advantages of this design include the low cost associated with the discrete semiconductor devices
10
, the low impedance interconnections between capacitors
56
and discrete semiconductor devices
10
, and the design's compatibility with commercially available heatsinks. However, this design is subject to high assembly costs, current limitations imposed by the circuit board foil resistance, high repair cost and inefficient use of space. The assembly cost is particularly high due to the fact that components are located on both sides of the circuit board, which makes automated soldering difficult or impossible. Included in the cost is the securing of each semiconductor device to the heatsink with individual hardware.
FIGS. 3
a
and
3
b
illustrate a prior art design for power processing that is based on the use of discrete semiconductor devices
10
. Discrete semiconductor devices
10
are vertically mounted in thermal contact with heatsink
51
; and they are electrically connected to capacitors
56
(and other components not shown) via circuit board
11
. The advantages of this design include the low costs associated with discrete semiconductor devices
10
, a low impedance interconnection between capacitors
56
and discrete semiconductor devices
10
, and a moderately efficient use of space. The disadvantages of this design include a high assembly cost, the current limitations imposed by the circuit board foil resistance; and a high repair cost. The assembly costs are particularly high due to the fact that components are located on both sides of the circuit board, which makes automated soldering difficult or impossible.
Accordingly, there has existed a definite need for an energizing and cooling system, and related methods, for simultaneously interconnecting, heatsinking and mechanically supporting discrete semiconductor devices. The present invention satisfies these and other needs, and provides further related advantages.
SUMMARY OF THE INVENTION
The present invention provides an energizing and cooling system, a related method of cooling, and related methods of producing and installing such a system. It advantageously provides for devices, such as electrical components, to be efficiently and economically installed and used, with uniform power levels and uniform cooling.
In accordance with the present invention, a structure is defined which provides for the electrical interconnection, cooling and mechanical support of discrete semiconductor parts. Key elements of this structure include a conventional circuit board, a fluid-cooled heatsink which mounts on the component side of the circuit board, a spring clip which forces semiconductor devices installed in the circuit board into thermal contact with both front and rear surfaces of the heatsink, and electrically conductive buses which interconnect the circuit board with various components. Assembly of this structure may be fully automated using conventional fabrication means such as automated component insertion and wave soldering equipment.
The heatsink is typically an extruded aluminum tube having a rectangular outer cross-section and two liquid-filled interior chambers separated by a common wall. Interior surfaces of the heatsink may contain fins which protrude into the liquid to enhance heat transfer. At one end of the heatsink, the two chambers are made contiguous, thus establishing fluid counter-flow with respect to the common wall. The interior fluid is circulated by an external pump while heat contained in the fluid is transferred to ambient air by an ext
Buchanan Darrell
Rippel Wally E.
Aerovironment Inc.
Law Office of John A. Griecci
Wille Douglas A.
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