ARRANGEMENT FOR DISSIPATING THERMAL ENERGY GENERATED BY HEAT SOURCE

Abstract: The invention relates to an arrangement for dissipating thermal energy generated by a heat source (1), which arrangement comprises a heat conductor element (2) for conducting thermal energy generated by the heat source (1) away from the heat source (1), the heat conductor element (2) having at least one micro heat pipe module (3) attached to it for distributing thermal energy generated by the heat source (1) in the heat conductor element (2). The heat source (1) is attached to an element (4) which is made of a heat conducting material and which is in thermal contact with the heat conductor element (2) and which is arranged to conduct thermal energy from the heat source (1) to the heat conductor element (2) by means of the heat conducting ability of said heat conducting material.

Description: ARRANGEMENT FOR DISSIPATING THERMAL ENERGY GENERATED BY HEAT SOURCE BACKGROUND OF THE INVENTION The invention relates to an arrangement for dissipating thermal energy generated by a heat source, which arrangement comprises a heat conductor element for conducting thermal energy generated by the heat source away from the heat source, the heat conductor element having at least one micro heat pipe module attached to it for distributing thermal energy generated by the heat source in the heat conductor element. Cooling electronic components is an old problem which has become more and more pronounced with increasing integration intensities and power. New methods, such as heat pipes, have lately emerged along with conventional convection cooling. A standard heat pipe is typically a copper cylinder several millimetres in diameter and about nine inches in length, emptied of air and partly filled with a working fluid. A heat pipe conducts thermal energy generated by a heat source, such as an electronic component, from one end of the heat pipe to another as latent heat from the change of phase of a working fluid in the heat pipe. The thermal heat generated by the heat source makes the working fluid boil and vaporise in the hot end of the heat pipe, i.e. the vaporiser of the heat pipe. Due to a generated pressure difference, the vapour moves to the other, cold end of the heat pipe, i.e. the condenser of the heat pipe, where the vapour surrenders it latent heat and returns as fluid back to the vaporiser driven by capillary forces. A heat pipe is an extremely efficient heat conductor, its effective thermal conductivity is typically 10 to 100 times better than that of copper. Until now, heat pipes have usually been installed in such a manner that for each heat source, such as an electronic component, there is one separate heat pipe conducting heat to a condenser. If one circuit board has several electronic components requiring cooling, placing heat pipes in an efficient manner is difficult, awkward and requires space. This problem has been solved by means of micro heat pipe modules which comprise very small micro heat pipes placed side by side and a binding agent. These have been used to even out temperature distribution, especially when the heat source is a local one and surrounded by an area considerably cooler in temperature. The micro heat pipe modules are usually attached between the heat source, such as an electronic component generating thermal energy, and a heat conductor element, such as cooling plates or the body of an apparatus. Micro heat pipe modules have been disclosed in US patent 5,527,588, for instance. The method has its limitations, however. An extra layer between the component and the heat conductor element creates a new material interface. This interface creates a thermal contact resistance which impairs heat conduction from the heat source through the heat conductor element to the cooling air. In addition, the radial heat conductivity of the micro heat pipes in the micro heat pipe module is especially poor, because a micro heat pipe has an almost full vacuum and an axial heat flow dominates heat conduction completely. Achieving a good thermal contact when attaching the heat source to the micro heat pipe module is difficult, because through-drilled screws cannot be used as they would puncture the micro heat pipes. In addition, it is impossible to ground the heat source to the heat conductor element through the micro heat pipe module. BRIEF DESCRIPTION OF THE INVENTION It is thus an object of the invention to develop an arrangement for dissipating thermal energy generated by a heat source so as to solve the above problems. The object of the invention is achieved by an arrangement which is characterized in that the heat source is attached to an element which is in thermal contact with the heat conductor element and which is made of a heat conducting material and which is arranged to conduct thermal energy from the heat source to the heat conductor element by means of the heat conducting ability of said heat conducting material. Preferred embodiments of the invention are set forth in the dependent claims. The invention is based on the fact that since the heat source is installed on an element which is made of a heat conducting material and which is in thermal contact with a heat conductor element, thermal energy can directly conduct from the heat source to the heat conductor element. The solution of the invention provides the advantage that it improves the conduction of thermal energy from the heat source to directly the heat conductor element, because the micro heat pipe module, whose heat conductivity in the radial direction of the micro heat pipes is extremely poor, does not constitute an obstruction between the heat source and the heat conductor element. The solution of the invention provides the further advantage that with it, it is possible to minimize the maximum heat flow to the micro heat pipe modules, because a part of the heat load is directly conducted to the heat conductor element and the micro heat pipe module can function at a higher thermal energy generated by the heat source. The solution of the invention provides the yet further advantage that the heat source can easily be attached to the element with screws, for instance, because there is no danger of puncturing the micro heat pipes with the screws. The solution of the invention provides the yet further advantage that with it, it is possible to minimize the thermal contact resistance between the heat source and the heat conductor element, because the heat source can be attached with screws through holes drilled directly to the element. The solution of the invention provides the yet further advantage that with it, it is possible to even out the temperature distribution of the heat conductor element at maximum coverage, because the heat conductor element can be substantially entirely covered with micro heat pipe modules with the exception of the element at the heat source. The solution of the invention provides the yet further advantage that electronic components can be directly grounded through the element to the heat conductor element. BRIEF DESCRIPTION OF THE FIGURES In the following, the invention will be described in greater detail by means of preferred embodiments and with reference to the attached drawings in which Figure 1 shows a top view of an arrangement having two micro heat pipe modules, Figure 2 shows a side view of the arrangement of Figure 1 , and Figure 3 shows an arrangement having a hole in the micro heat pipe module. DETAILED DESCRIPTION OF THE INVENTION The figures show an arrangement of the invention for dissipating thermal energy generated by a heat source 1. The heat source 1 can be an electronic component, for instance. The arrangement comprises a heat conductor element 2 for conducting thermal energy generated by the heat source 1 away from the heat source 1. The heat conductor element 2 can be cooling plates or the body of an apparatus, for instance. A circuit board can also act as a heat conductor element 2. At least one micro heat pipe module 3 is attached to the heat conductor element 2 for distributing thermal energy generated by the heat source 1 in the heat conductor element 2. Since the micro heat pipe module 3 is known per se, it will not be described in more detail herein. A heat pipe module can be used instead of the micro heat pipe module 3, if there is enough space. The heat source 1 is attached to an element 4 which is in thermal contact with the heat conductor element 2 and which element 4 is made of a heat conducting material and which element 4 is arranged to conduct thermal energy from the heat source 1 to the heat conductor element 2 by means of the heat conducting ability of said heat conducting material. Figure 1 shows an arrangement having two micro heat pipe modules 3 with an intermediate space 5 between them. The element 4 which is in thermal contact with the heat conductor element 2 is installed in this intermediate space 5. Alternatively, there can be more than two micro heat pipe modules 3. In the arrangement shown in Figure 1 , the element 4 fills the intermediate space 5 substantially entirely. Such an arrangement provides good heat conductivity between the element 4 and the micro heat pipe modules 3. Figure 3 shows an arrangement where the micro heat pipe module 3 has a hole 6 and the element 4 which is in thermal contact with the heat conductor element 2 is installed in the hole 6. There can be more than one of these holes 6. In the arrangement shown in Figure 3, the element 4 fills the hole. 6 substantially entirely. Such an arrangement provides good heat conductivity between the element 4 and the micro heat pipe modules 3. It is also possible for the arrangement to have several micro heat pipe modules 3, as shown in Figure 1 , and that at least one of them has the hole 6 described in the arrangement shown in Figure 3. The element 4 which is in thermal contact with the heat conductor element 2 is preferably seamlessly attached to the heat conductor element 2, i.e. the element 4 and the heat conductor element 2 constitute one and the same part. Arrangements of this kind are presented in the figures. In such an arrangement, there is no interface between the element 4 and the heat conductor element 2 and consequently, heat conduction is good between the element 4 and the heat conductor element 2. It is entirely possible that the element 4 is a separate part which is in thermal contact with the heat conductor element 2, which means that heat can conduct from the element 4 to the heat conductor element 2. In such a case, thermal grease or a corresponding material improving heat conduction can be used between the element 4 and the heat conductor element 2. The heat conducting material is preferably a copper metal or an aluminium metal. The heat conductor element 2 shown in the figures is preferably equipped with cooling fins 7 which improves the cooling of the heat conductor element 2, i.e. the conduction of thermal energy from the heat conductor element 2 to the surrounding area. In the arrangements shown in the figures, the micro heat pipe modules 3 are sunk in recesses 8 in the heat conductor element 2. The recesses 8 can be machined, for instance, in the heat conductor element 2. The recesses 8 can, for instance, be made such that they correspond substantially to the dimensions and shape of the micro heat pipe modules 3, which provides good conductivity between the micro heat pipe modules 3 and the heat conductor element 2. In the figures, the heat source 1 is attached with screws 9 to the element 4. The heat source 1 can, if necessary, be grounded with the screws 9 to the heat conductor element 2 or through the element 4 to the heat conductor element 2. A good contact is also achieved between the heat source and the heat conductor element 2 by means of the screws. It is obvious to a person skilled in the art that while technology advances, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above, but can vary within the scope of the claims.

Claims: CLAIMS 1. An arrangement for dissipating thermal energy generated by a heat source (1), which arrangement comprises a heat conductor element (2) for conducting thermal energy generated by the heat source (1) away from the heat source (1), the heat conductor element (2) having at least one micro heat pipe module (3) attached to it for distributing thermal energy generated by the heat source (1) in the heat conductor element (2), characterized in that the heat source (1 ) is attached to an element (4) which is made of a heat conducting material and which is in thermal contact with the heat conductor element (2) and which is arranged to conduct thermal energy from the heat source (1) to the heat conductor element (2) by means of the heat conducting ability of said heat conducting material. 2. An arrangement as claimed in claim 1, characterized in that it has at least two micro heat pipe modules (3) having an intermediate space (5) between them, and that the element (4) which is in thermal contact with the heat conductor element (2) is installed in the intermediate space (5). 3. An arrangement as claimed in claim 2, characterized in that the element (4) fills the intermediate space (5) substantially entirely. 4. An arrangement as claimed in claim 1, characterized in that the micro heat pipe module (3) has a hole (6) and that the element (4) which is in thermal contact with the heat conductor element (2) is installed in the hole (6). 5. An arrangement as claimed in claim 4, characterized in that the element (4) fills the hole (6) substantially entirely. 6. An arrangement as claimed in claim 1, characterized in that the element (4) which is in thermal contact with the heat conductor element (2) is seamlessly attached to the heat conductor element (2). 7. An arrangement as claimed in claim 1, characterized in that the heat conductor element (2) is equipped with cooling fins (7). 8. An arrangement as claimed in claim 1, characterized in that the micro heat pipe module (3) is sunk in a recess (8) in the heat conductor element (2). 9. An arrangement as claimed in claim 1, characterized in that the heat conducting material is a copper metal. 10. An arrangement as claimed in claim 1, characterized in that the heat conducting material is an aluminium metal.

Inventors: HEIKKILAE TIMO, KABRELL CARL, LEHTINIEMI REIJO, RANTALA JUKKA, HEIKKILAE, TIMO, KABRELL, CARL, LEHTINIEMI, REIJO, RANTALA, JUKKA
Applicants: HEIKKILAE TIMO, KABRELL CARL, LEHTINIEMI REIJO, NOKIA NETWORKS OY, RANTALA JUKKA, HEIKKILAE, TIMO, KABRELL, CARL, LEHTINIEMI, REIJO, RANTALA, JUKKA
Application year: 2000
Main classification: H05K7
IPC codes: H01L23