Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With provision for cooling the housing or its contents
Reexamination Certificate
1990-02-28
2001-02-06
James, Andrew J. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With provision for cooling the housing or its contents
C257S713000, C257S728000, C361S702000, C361S704000, C361S709000, C361S711000, C361S310000
Reexamination Certificate
active
06184578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to heat pipes for conducting heat away from electronic circuitry and, more particularly, to heat pipes which are particularly well adapted to airborne avionics and to the radar systems used therein.
2. Description of Related Art
As is well known, electronic circuitry often generates heat. For maximum efficiency and longevity, means are often provided to remove or reduce this heat.
Devices called heat pipes have been used for this purpose. Traditionally, heat pipes consist of a wick and fluid housed in a sealed chamber. One end is subjected to heat; the other to a cold wall. The liquid at the heated end boils, the vapor travels to the cold end and condenses, and the capillary action of the wick causes the condensed fluid at the cold end to travel back to the heated end for re-vaporization.
The vapor pressure, unfortunately, is often quite high. For example, the internal working pressure of ammonia at 70 degrees centigrade is approximately 900 pounds per square inch. The chamber, therefore, must be quite strong in order to contain this pressure. Aluminum and copper, for example, typically must have a wall thickness of approximately 0.035 inches. Stainless steel typically must have a wall thickness of approximately 0.023 inches.
These great thicknesses, in turn, add substantial weight to the heat pipe. In many applications, such as airborne avionics, this weight is highly undesirable.
The materials which are typically used for the outer cylinder of the heat pipes, moreover, conduct electricity. As a consequence, interfaces are usually required to electrically isolate the heat pipe from the circuitry. This adds further bulk and weight to the system and reduces heat transfer efficiency.
SUMMARY OF THE INVENTION
It is a principle object of the present invention to obviate these as well as other problems in prior art heat pipes.
It is a further object of the present invention to provide a heat pipe which is light in weight, has great strength and efficiency, is compact, which has a wall thickness of only 0.015 inches, which can remove heat from electronic circuitry without additional electrical isolation in interfaces, and which can be directly integrated in the printed wiring board.
These as well as other objects, features and advantages of the present invention are facilitated by wrapping a thin-walled heat pipe, i.e. one which could not normally withstand the internal pressure, with a composite graphite fiber having high thermal conductivity and tensile strength.
In the preferred embodiment, the composite graphite fiber is THORNEL, a trademark of Union Carbide, model P-120 2K. It is first wrapped longitudinally around the core of the heat pipe at a very low angle, preferably at approximately 15 degrees. Three to four additional layers of it are then tightly wrapped in hoops around the longitudinal wrap.
These two cross-directional wraps give the heat pipe great strength, thereby allowing the inner core to be made of aluminum having a wall thickness of only 0.010 inches. Compared to a traditional aluminum heat pipe, the subject invention has superior thermal conductivity with twenty-five percent less weight.
When utilized with circuit card applications, the subject invention will permit direct integration of the heat sink with the printed wiring board. The result is a single integral assembly of the heat sink and printed wiring board. Additional inefficient and bulky thermal interfaces are therefore eliminated.
These as well as other objects, features and benefits of the present invention will now become apparent from a review of the following description of the preferred embodiments, taken in conjunction with the drawings.
REFERENCES:
patent: 4631636 (1986-12-01), Andrews
patent: 4724901 (1988-02-01), Munekawa
patent: 4867235 (1989-09-01), Grapes et al.
patent: 4912548 (1990-03-01), Shanker et al.
Gardner William T.
Sohn Kiho D.
Gudmestad Terje
Hughes Electronics Corporation
James Andrew J.
Whitehead, Jr. C
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