US 20050056403 A1
The present invention relates to thermosyphons, in particular for use in the cooling of electronic components. In a first embodiment a thermosyphon is manufactured by extruding a base (1) and milling a channel structure in the base to produce a plurality of fins (5) extending vertically from the base. A lid (3) comprising a number of fins (4) extending vertically from the lid is placed over the heat sink channel structure so that a thermosyphon of an expanding channel system is formed. In a second embodiment the evaporator and condenser sections are separated and connected by pipes. To form a leak proof seal between the lid and the base, joining is preferably done by friction stir welding. By providing an extruded thermosyphon, heat transfer is made more efficient than when junctions are used. The present invention provides a new way of efficiently manufacturing an integrated structure, while keeping the heat transfer of the structure high.
1. A thermosyphon comprising a base, a condenser section and an evaporator section conducting heat from a heat source by the use of a working fluid, wherein the evaporator and/or the condenser section has an internal structure providing an extended surface area, where at least a part of the internal structure has been produced by extrusion.
2. The thermosyphon according to
3. The thermosyphon according to
4. A The thermosyphon according to
5. The thermosyphon according to
6. The thermosyphon according to
7. The thermosyphon according to
8. The thermosyphon according to
9. A method of producing a thermosyphon structure according to
10. The method of producing a thermosyphon according to
11. Use of a thermosyphon according to
The present invention relates to thermosyphons, in particular for use in the cooling of electronic components.
Thermal management is a key issue in the design of the electronic package. The proper design insures that the peak temperatures remain within a specified operating range to produce a reliable module. The main objective is to maintain the semiconductor device junction temperature below the maximum operating temperature of the module. Design challenges included in heat removal are higher circuit densities, close proximity of adjacent devices or components, low thermal conductivity substrates, inner layers of metal forming the interconnect, and the thermal resistance of heat sink systems.
The purpose of any heat transfer design is to allow the flow of thermal energy from heat source to heat sink within the constraints of specified temperature levels. The current trend towards miniaturisation of electronic devices, greater functionality and faster processor results in a steady increase in heat dissipated per unit area. Multi-chip modules having an increasingly close placement of components having high heat fluxes means that the various thermal resistances, from the internal heat sources to the external final heat sink, must be reduced. This puts new demands on cooling and heat spreading technology.
As air cooling is approaching it's limits a lot of researchers have re-focused upon liquid cooling techniques with phase-change in a closed channel. Two known types of devices in particular employ this phase-change mechanism for heat transfer from electronic circuit components: thermosyphons and heat pipes. These components take advantage of the heat of vaporisation of the fluid by transporting heat from an evaporator to a condenser through the liquid-vapour phase change.
A thermosyphon has an evaporator section, an adiabatic section, and a condenser section. In operation, electronic devices produce heat which is absorbed in the evaporator section of the thermosyphon which causes evaporation into vapour of a working fluid that is in the evaporator section. Working fluid in the form of vapour moves through the adiabatic section to the condenser section where it gives up its latent heat and condenses into liquid. The condensed liquid returns to the evaporator section from the condenser section with the aid of gravity. Therefore, in a thermosyphon the evaporator should always be placed lower than condenser.
Heat pipes are known from U.S. Pat. No. 6,216,343.
U.S. Pat. No. 6,418,017 describes an integrated heat pipe/heat sink manufactured by mechanically scribing grooves length-wise in a channel drilled into a chassis for electronic components. The chassis is cast or moulded and may comprise fins to more effectively dissipate heat. The use of extrusion as a manufacturing method is not mentioned.
From GB-2151769 it is known to manufacture extruded heat sinks having internal cavities acting as thermosyphons (see
In “Thermosyphon concept for cooling of PCB”, Rahmatollah, K et al, 8th THERMINIC Workshop, 1-4 October 2002, Madrid, a concept of cooling PCB:s by using an aluminium sheet having a milled channel system. The thermosyphon is attached to the heat sink, and thus not integrated with it as in the present invention.
Bearing in mind the problems and deficiencies of the prior art, It is an object of the present invention to provide a method suitable for mass production of the thermosyphon of the present Invention.
It is another object of the present invention to provide a thermosyphon with a more efficient heat transfer than could be obtained by the thermosyphons of the prior art.
The fins of the evaporator and/or condenser section, at least partially produced by extrusion, form an Internal structure with an extended surface area, providing a more efficient heat transfer between the working fluid and the thermosyphon.
By integrating the lid and the evaporator fins into one part, the contact thermal resistance between the lid and the fins is eliminated, which makes the thermosyphon more efficient. The heat dissipating fins are integrated in the thermosyphon, which eliminates the contact thermal resistance between the condenser fins and the outer heat dissipating fins.
To form a leak proof seal between the lid and the heat sink, joining is preferably done by, but not limited to, friction stir welding. This joining technique is described in EP-A-615480. Typically, a friction welding tool (a probe), inserted into a joint region to be welded, undergoes a cyclic motion to generate a plastizised material and is typically traversed along the joint region. When the material cools a joint of high quality is produced.
By providing an integrated heat sink/thermosyphon, heat transfer is made more efficient than when junctions are used. The present invention provides a new way of efficiency manufacturing an Integrated structure, while keeping the heat transfer of the structure high.
The material selection for the base and lid depends on application requirements for ease of fabrication and service reliability. Aluminum is preferred because of its ease of machinability and lower density compared to other metals, but other materials may also be used.
A lid is extruded from an aluminium billet so that a plate is formed having fins extending from one side along the centre of the plate. The fins extending beyond the area dedicated to the evaporator are removed by milling to form the evaporator section, E, according to
While the present Invention has been particularly described in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. The evaporator may for example be a part of the base and the condenser a part of the lid. All parts may be extruded including the fins of the condenser and the fins removed from areas used for joining of the parts. In the latter case all of the fins may be produced integrally with either the lid or the heat sink base or as parts of either the lid or the base.
By extruding parts or all of the parts of the thermosyphon manufacturing is simplified and heat transfer improved.