Solid-state chip cooling by use of microchannel coolant flow

Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents

Reexamination Certificate

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C257S714000, C257S721000

Reexamination Certificate

active

06388317

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to cooling arrangements for semiconductor devices, and more particularly to cooling arrangements using circulating fluid coolant.
BACKGROUND OF THE INVENTION
The history of communications and of computing is a continuing saga of increasing power densities as increased transmitted power is sought in conjunction with shorter and shorter wavelengths, and as the path lengths in microprocessors are reduced in conjunction with increasing numbers of processing elements.
In the field of communications and radar, it is desirable to reduce the cost, size, and weight of antennas. In general, antenna gain is a function of its size measured in wavelengths, so that, at a given frequency, antenna gain decreases as antenna size decreases. A corollary is that antenna the gain of a physically small antenna may be increased by increasing the operating frequency. In an array antenna, the inter-element spacing decreases as the operating frequency increases. In general, the effective range of a radar or communication system depends upon how much power can be transmitted toward the target or receiver, since the designers of radar and communications systems attempt to use the best transistors or other signal amplifiers, namely those capable of transmitting the highest power, and for reception, those providing the lowest noise.
In an array antenna associated with a ground plane, the interelement spacing of the radiating elements defines the area behind the ground plane which can be devoted to electronics associated with a particular antenna element. The drive toward smaller antennas tends to result in higher frequencies, at which electronic equipment tends to be less efficient that at lower frequencies. Thus, array antennas for modern systems tend to operate at high frequencies and high power, with small antenna inter-element spacing. This, in turn, means a tendency toward higher power dissipation in the associated equipment. U.S. Pat. No. 5,013,997, issued May 7, 1991 in the name of Reese, describes a phase shifter for an array antenna in which a ferrite phase shifter coupled directly to the horn antenna element is immersed in liquid, and the hot liquid is made available to the radome for deicing. Other systems, such as that described in U.S. Pat. No. 5,017,927, issued May 21, 1991 in the name of Agrawal et al., make use of transmit-receive (TR) modules using one module associated with each antenna element. These TR modules include phase shifters, power amplifiers, low-noise amplifiers, and various types of filtering. In such an arrangement, the high frequency operation and high power results in large heat generation by transmitting transistors associated with each antenna element TR module, coupled with relatively small spacing between adjacent ones of the modules.
The performance of transistors and solid-state devices is closely linked to the operating temperature, and the reliability of such transistors and solid-state devices is linked to the long-term or historic operating temperature. Both of these considerations require keeping operating temperatures as low as possible. In the context of the high packing densities of array antennas, maintaining a low temperature of at least some portions of a transmitter is a significant problem.
Various options present themselves, such as reducing the heat generated so that conventional thermal conduction suffices. However, this tends to reduce the electromagnetic signal power available for transmission. If the amount of heat is given as a constant, other techniques can be used, such as cooling air flow in conjunction with finned heat sinks for the transistors or other solid-state devices, thermal management materials having extremely low thermal impedance, heat pipes, and liquid-filled cold plates. The problem of temperature control is much exacerbated by the need to make all the antenna element modules identical to reduce the manufacturing cost, and the need for such modules to be field-interchangeable. In the context of computer microprocessors, the drivers are the need for increased numbers of logic elements within confines which maintain short signal path lengths for high-speed operation.
U.S. Pat. No. 5,999,407, issued Dec. 7, 1999 in the name of Meschter et al. describes a scheme for conductively heat-sinking a heat-generating device mounted on a printed-circuit board through a thermally conductive structure to a module mounting rail, and thence to an ultimate heat sink. U.S. Pat. No. 5,552,633, issued Sep. 3, 1996 in the name of Sharma, describes the transfer of heat in a multilayer interconnect structure by way of thermally conductive posts extending through the multilayer structure. U.S. Pat. No. 5,459,474 issued Oct. 17, 1995 in the name of Mattioli et al. describes an active array antenna in which the antenna element modules, together with portions of the elemental antennas themselves, are mounted in side-by-side racks which slide from their operating position for maintenance.
Improved solid-state device cooling is desired for removable modules in closely spaced arrays and for chips having a high elemental packing density.
SUMMARY OF THE INVENTION
In the most general terms, a cooling arrangement according to various aspects of the invention is useful for semiconductors or solid-state assemblages which mount the semiconductor or other solid-state device directly onto a first surface of a thermally conductive “heat spreader.” The heat spreader contains microchannels which open into coolant fluid ports on the second side of the heat spreader. The heat spreader, in turn, is mounted on a coolant fluid distribution or circulation plate. In one embodiment, the coolant fluid distribution plate also includes a micropump for circulating coolant fluid through the microchannels of the heat spreader. In another embodiment, the coolant fluid distribution plate simply distributes coolant applied to its fluid input port to those heat spreaders mounted thereon, and a plurality of coolant fluid distribution plates are mounted on a coolant fluid circulation plate, which uses a micropump to circulate coolant fluid to the various distribution plates and ultimately to the heat spreaders. Thus, coolant fluid is communicated directly into the support for the semiconductor chip or other solid-state device, for good heat transfer with low temperature drop.
In another general aspect of the invention, a solid-state device, such as, for example, a transistor, a laser, phase shifter or the like, is mounted on a supporting thermally conductive piece. The piece on which the solid-state device is mounted contains microchannels through which a flow of coolant fluid is established. The coolant flow originates, in a preferred embodiment of the invention, with a “cold” plate to which the thermally conductive piece is mounted, and in which a micropump causes coolant fluid to circulate.
More particularly, a monolithic solid-state chip includes a planar dielectric substrate defining first and second broad surfaces. For purposes of this invention, the planar dielectric substrate may include a semiconductor substrate which is not doped, or doped so as to be relatively nonconductive. The solid-state chip also defines electrical conductors lying on the first surface. The solid state chip produces heat during operation. According to an aspect of the invention, a thermally conductive plate including a first broad surface is directly connected to the second surface of the solid-state chip. The thermally conductive plate also includes a second broad surface substantially parallel with the first broad surface, at least sufficiently for mounting convenience. The thermally conductive plate includes at least one microchannel extending between coolant fluid input and output ports and between the first and second broad surfaces of the thermally conductive plate. The microchannel has a cross-sectional area smaller than about 0.001 square inch. In a preferred embodiment, the coolant fluid input and output ports are located on the second broad surface of th

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