The present invention is generally directed to heat sinks for dissipating heat from heat producing devices, and more specifically to modular apparatus for dissipating heat generated by electronic solid state devices.
Heat sinks are utilized for efficient removal of heat from solid state devices such as microprocessors and printed circuit boards (PCB) that can be populated with micro-electro-mechanical systems (MEMS). Such electronic devices generate considerable heat during operation, and failure to effectively remove this heat can result in failure of the devices.
These heat sinks are currently provided in various sizes that are selected based on the heat generated by the device. The heat sinks comprise one or more fins integrally formed with and extending from a core having a threaded base that is threaded into an adaptor that is assembled to the device so that the heat sink is thermally coupled to the device. The core conducts the heat away from the electronic device, and the fins integrally assembled to the core conduct heat away from the core, thereby keeping the device at an acceptable temperature. Of course, it would be a simple matter to overdesign heat sinks and provide a single size. However, aside from cost considerations, space restrictions usually limit the height of the core or the diameter of the fins, even when the heat dissipation requirements for two different applications are substantially the same, thereby requiring heat sinks having different configurations.
The heat sinks are formed by machining by machining from bar stock. Since the size of the heat sink will depend on the amount of heat that must be removed, it is necessary to manufacture heat sinks in different sizes in order to provide heat sinks for different applications. It is expensive and time consuming to machine these heat sinks, and it is expensive to maintain an inventory of heat sinks of different sizes for different applications.
It would be desirable to provide heat sinks that are assembled using a modular design that implements a plurality of interchangeable parts that can be used to provide heat sinks having different heat dissipation capabilities. If the machining of the interchangeable parts can be minimized, the cost of manufacturing the heat sinks can be significantly reduced. Similarly the cost of maintaining inventories of heat sinks of different sizes can be reduced.
The present invention provides a heat sink assembly and a method of fabricating a heat sink assembly. The heat sink assembly comprises a cylindrical core onto which are mounted a plurality of fin disks. The fin disks and cylindrical core are assembled to a threaded base. This assembly comprises the heat sink assembly. The heat sink assembly can be mounted onto a mounting clip or threaded directly onto a device having mating threads. The device can be a printed circuit board adapted to have threads or other electrical or electronic component that is adapted to have threads to receive the heat sink assembly.
The assembly is fabricated by providing a plurality of fin disks each having an aperture with a predetermined internal diameter. The plurality of fin disks are assembled over an alignment post on a fin disk assembly tool, the alignment post having an outer diameter that is larger than the internal diameter of the aperture on the fin disks. The cylindrical core, which is a pipe having an outer diameter that is sized to have an interference fit with the predetermined internal diameter of the fin disk apertures, that is, pipe outer diameter is slightly larger than the fin disk aperture internal diameters, and an inner diameter that is slightly larger than the outer diameter of the alignment post, is placed over the alignment post of the fin disk assembly tool. While on the fin disk assembly tool, the cylindrical pipe core is then press fit to the fin disks through the fin disk apertures to form a pipe core assembly. A threaded base having a first end with a projection and a second end with a threaded base is then placed onto a base insertion press that secures the base in position. The projection has a preselected size that allows it to be interference fit with the pipe. The pipe core assembly is secured in position and placed under the base insert press so that the projection end of the threaded base is press fit onto the pipe core assembly, forming the heat sink assembly, while leaving the threads in the threaded base exposed for additional assembly.
The heat sink assembly can then be assembled to well-known mounting clips. Alternatively, PCBs can be provided that include mating threads that permit the heat sink assemblies to be mounted directly to the PCBs. PCBs include motherboards to which are mounted VGA chips. Such chips draw a much as 5-15 watts of power, a large portion of which is dissipated by heat. Other electrical or electronic components can be provided with threads to permit direct mounting of the heat sink assemblies as well.
An advantage of the present invention is that the heat sinks are modular in design. Rather than having an inventory that involves machining of a large number of heat sinks, that is heat sinks having two, three, four or more fins, the heat sinks can be assembled in a modular fashion that eliminates most machining. The fin disks can be stamped and then assembled with the number of fins desired. Pipe cores can be provided in sizes required to accommodate a required number of fin disks that are assembled onto the pipe cores. The threaded bases can be provided in one or more standard thread sizes.
Another advantage is that modular heat sinks of the present invention, even though having different heat dissipation capacity, can utilize common components. These common components can be provided without the expense of custom machining, allowing for heat sink assemblies that are less expensive to fabricate while providing the same heat dissipation capability as current machined heat sinks.
Still another advantage is that heat sink assembly components can be made by processed such as stamping and maintained in inventory until ready for assembly. Only the threading operation requires machining.
Another advantage of the present invention is that the equipment required for assembling the heat sink assemblies is relatively inexpensive. This equipment can be used to provide heat sink assemblies over the entire range of fin disks required.
Finally, an inventory of modular heat sink assemblies can be maintained at a lower cost than machined heat sinks.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The heat sink assembly of the present invention can then be threaded into mating threads. The mating threads can be in a solid state device in which the heat sink bottoms against the device to provide intimate contact to provide thermal conduction away from the solid state device. Alternatively, the heat sink assembly can thread into adaptors identical to those currently in use that are mounted on electrical components to provide thermal conduction away from the solid state device to the heat sink assembly.
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The production of the heat sink assembly 10 of the present invention is accomplished by mechanical assembly. While the prior art heat sinks are machined from a single piece of material, the heat sinks of the present invention are somewhat different. Since the heat sink assemblies of the present invention comprise a number of different parts, the effectiveness of these assemblies is highly dependent on establishing good mechanical interfaces between these parts so that heat can be conducted across these interfaces. Failure to establish good mechanical interfaces could result in small air gaps, which actually have an insulative effect, resulting in exactly an opposite result from that desired. The desired mechanical interfaces are established by interference fits between the mating parts. While any method of establishing reliable mechanical interfaces between the mating parts is acceptable, such as, for example, shrink fitting of parts, which involves using the differential thermal expansion properties of materials when assembling different parts at different temperatures during assembly, a preferred method is press fitting.
Effective interference fits can be established between mating parts whose inner and outer dimensions differ by as little as a few tenths (of a mil), where one tenth is 0.0001 inches, to as much as 0.007 inches where 0.001 inches is a mil. The specific method to establish an interference fit between mating assemblies is not important.
After the heat sink assembly is formed from its component parts, the heat sink assembly can be matched with corresponding threads, here female threads and assembled onto an electronic component requiring cooling. Tool feature 46 is accessed through core aperture 26 with the appropriate tool so that heat sink assembly 10 can be properly torqued into place. The torque range for the most commonly used heat sink assemblies 10 is from about 1-in-lbs, the specified torque depending upon the actual size of the heat sing assembly package.
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While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.