THERMAL DIFFUSION INTERFACE

Description

[0001] The present invention relates to a thermal diffusion interface, such as an electronic component package base or a heat sink.

[0002] US 2005 / 013119 discloses a thermal diffusion interface made of isotropic thermal diffusion material, comprising a cross-shaped graphite insert.

[0003] Diffusion or thermal conduction is a mode of heat transfer caused by a temperature difference between two regions of the same medium, or between two media in contact, and occurring without overall movement of matter (on a macroscopic scale) as opposed to convection which is another heat transfer. It can be interpreted as the transmission of thermal agitation from one place to another: an atom or molecule gives up part of its kinetic energy to the neighboring atom.

[0004] For example, in the field of electronic component packaging, internal chips must dissipate a very high power over a very small surface area, for example a few square millimeters.

[0005] In this field, it is known to use Cu / Mo (Copper / Molybdenum) alloy cases with a thermal conductivity between 200 Wm -1< .K -1< and 400 Wm -1< .K -1< depending on the proportion of Cu and Mo.

[0006] It is also known to use Cu / D (Copper / Diamond) with conductivity performances of the order of 500 Wm -1< .K -1< but whose cost is of the order of 60 times higher than the Cu / Mo solution.

[0007] There figure 1 schematically illustrates an example of an embodiment of a known thermal diffusion interface 1, in this case a sole 1 of an electronic component housing 2. In this case, the sole 1 is made of Cu / Mo alloy, and must diffuse the thermal power or heat supplied by a chip 3. The sole 1 is fixed, for example by brazing, welding or gluing to a structure 4, for example made of aluminum Al of a system such as a transmitter and / or receiver.

[0008] An aim of the invention is to overcome the problems mentioned above, and in particular to provide a thermal diffusion interface having improved diffusion or conductivity, based on a material that is easy to produce, and at reduced cost.

[0009] According to one aspect of the invention, there is provided a thermal diffusion interface made of isotropic thermal diffusion material, comprising an insert made of anisotropic thermal diffusion material comprising graphite comprising at least one preferred plane of thermal conduction perpendicular to the mean plane of the interface, the upper surface of the insert opening onto the upper surface of the interface, and the lower surface of the insert being covered by the isotropic thermal diffusion material of the interface; the insert being cross-shaped with a raised central portion corresponding to the upper surface of the insert opening onto the upper surface of the interface.

[0010] Graphite, generally supplied in the form of bars or sheets, is anisotropic, and has a thermal conduction essentially in the directions of the mid-plane of the sheet and almost zero in the direction orthogonal to this mid-plane of the sheet. The presence of such an insert makes it possible to reduce the thermal resistance of the sole and therefore to limit the heating of the element mounted in contact with the upper part of the latter, the heat supplied from which must be dissipated.

[0011] The lower surface of the insert is covered by the isotropic heat diffusion material of the interface, thus the crumbling of the anisotropic heat diffusion material comprising graphite which can generate pollution is avoided, and the latter is protected. In addition, the thermal conduction between the anisotropic heat diffusion material comprising graphite and the isotropic heat diffusion material is improved because the assembly can be carried out by molding.

[0012] Such an insert shape allows the drainage of heat from the source to be channeled via its graphite composition, to then promote thermal diffusion in the volume of the matrix. This involves taking advantage of the significant thermal diffusion capacity of graphite, by seeking to overcome its orthotropy using the isotropic matrix. Thermal diffusion in the structure (insert+graphite) can then be improved and thus the electronic components protected.

[0013] In one embodiment, the bottom surface of the insert is larger than the top surface of the insert.

[0014] The thermal power origin zone defines the size of the upper surface of the insert, and the lower surface is determined to maximize the diffusion of this power in the isotropic matrix of the thermal diffusion interface, such as copper or a Cu / Mo (Copper / Molybdenum) alloy. This makes it possible to make the best use of the orthotropic properties of graphite, by minimizing the need for diffusion in the unfavorable direction and maximizing this thermal diffusion in the favorable plane, while promoting heat exchange with the isotropic matrix of the thermal diffusion interface.

[0015] According to one embodiment, the isotropic thermal diffusion material comprises copper.

[0016] Copper is commonly used in electronic component carriers for its thermal diffusion properties combined with its ease of use and isotropy, and the properties of copper are well known and understood.

[0017] According to one embodiment, the raised central portion has edges inclined at an angle of between 30 and 60° relative to an axis perpendicular to the mean plane of the interface, for example 45°.

[0018] Such inclined edges improve heat diffusion from the insert to the rest of the thermal diffusion interface, with an optimum for an inclination of 45°. The inclination of the edges improves heat diffusion by taking advantage of a larger contact surface between the graphite and the matrix.

[0019] For example, the thermal diffusion interface is configured to be an electronic component package sole.

[0020] For example, the Thermal Diffusion Interface is configured to be a heat sink, the principle being to position the element for which heat must be dissipated in contact in order to benefit from heat exchange by conduction, such as aluminum radiators on chips or power transistors.

[0021] In one embodiment, the upper surface of the insert is lower than that of the surface of the heat-delivering element, intended to be in contact with said upper surface of the insert.

[0022] This improves heat diffusion by taking advantage of a larger contact surface with the copper matrix.

[0023] The invention will be better understood by studying a few embodiments described as non-limiting examples and illustrated by the appended drawings in which: there figure 1 schematically illustrates an example of the embodiment of a known thermal diffusion interface, in this case a sole 1 of a housing 2 of an electronic component according to the state of the art; figure 2a schematically illustrates a thermal diffusion interface according to one aspect of the invention; the figure 2b schematically illustrates a thermal diffusion interface, configured to be an electronic component package sole, according to one aspect of the invention; and the figure 3 schematically illustrates a cross-shaped graphite insert, according to one aspect of the invention; the figure 4 schematically illustrates a plurality of rod-shaped graphite inserts, in this case four, according to one aspect of the invention; and the figure 5 schematically illustrates a thermal diffusion interface comprising a plurality, in this case four, graphite inserts in the form of bars, according to the figure 4 , according to one aspect of the invention.

[0024] Throughout the figures, elements with identical references are similar.

[0025] In the present description, the embodiments described are in no way limiting, and the characteristics and functions well known to those skilled in the art are not described in detail.

[0026] There figure 2a schematically represents a thermal diffusion interface 1 with a graphite insert 5, according to one aspect of the invention. The graphite insert 5 comprises at least one preferred plane of thermal conduction perpendicular to the mean plane of the interface 1, the upper surface of the insert 5 opening onto the upper surface of the interface 1, and the lower surface 5a of the insert 5 being covered by the isotropic thermal diffusion material of the interface 1.

[0027] The thermal conduction of graphite in a privileged plane of thermal conduction perpendicular to the average plane of interface 1 is essential. It can be ensured during the manufacture of graphite by annealing at very high temperature which makes it possible to obtain a conduction of the order of 1000 Wm -1< K -1< .

[0028] The isotropic thermal diffusion material is preferably based on copper Cu, because it has a fairly high thermal conductivity value, and its use in the field of electronics and thermal diffusion is well known.

[0029] The process of integrating the pyrolytic graphite insert 5 into the isotropic thermal diffusion material such as copper Cu consists of coating copper brought to its melting temperature in a furnace in a graphite mold for example. After cooling the copper, the graphite insert is coated in the copper and taken up for example mechanically to have an optimal contact surface on one side by surfacing the copper and on the other by revealing the active part of the insert 5.

[0030] On the figure 2b schematically represents a thermal diffusion interface 1 in an exemplary embodiment of a known thermal diffusion interface 1, in this case a sole 1 of an electronic component housing 2. In this case, the sole 1 comprises copper Cu, and the graphite insert 5 must diffuse the thermal power or heat supplied by a chip 3. The sole 1 is fixed, for example by brazing, welding or gluing, to a structure 4, for example made of aluminum Al of a system such as a transmitter and / or receiver.

[0031] The lower surface 5a of the insert may be larger than the upper surface of the insert, to maximize the heat exchange between the graphite and its copper matrix.

[0032] There figure 3 schematically represents a graphite insert 5 in the shape of a cross with a raised central part 6 corresponding to the upper surface of the insert 5 opening onto the upper surface of the interface 1.

[0033] Due to the strong orthogonality of the thermal conductivity of graphite, a cross shape is determined to allow better dissipation of the heat flux in the copper coating.

[0034] The raised central portion 6 of the graphite insert 5 has edges 7 inclined at an angle of between 30 and 60° relative to an axis perpendicular to the mean plane of the interface, ideally 45°. This provides the largest exchange surface of graphite with copper.

[0035] Alternatively, the thermal diffusion interface may be a heat sink, such as fingers or any other means to increase the heat exchange surface between the graphite and the copper.

[0036] There figure 4 schematically represents a plurality of graphite inserts 5, in this case 4, in the form of parallel bars, with a raised central part 6 corresponding to the upper surface of the insert 5 opening onto the upper surface of the interface 1.

[0037] There figure 5 schematically illustrates a thermal diffusion interface 1 comprising a plurality, in this case four, graphite inserts in the form of bars, according to the figure 4 , according to one aspect of the invention.

[0038] The thermal anisotropy of graphite reduces heat conduction perpendicular to the (x,y) plane of the graphite sheet of the insert. This property makes it possible to limit thermal exchanges between two heat-providing elements, such as electronic components such as microwave chips, placed next to each other on the z axis on two separate inserts.

[0039] In microwaves, we try to bring the chips closer together to limit parasitic elements such as inductors. But inter-chip diffusion with an isotropic thermal diffusion material limits this proximity and therefore the maximum operating frequency. With the inserts of the figures 4 And 5 in anisotropic thermal diffusion material including graphite, it is possible to reduce this conduction and therefore bring the chips closer together and increase the maximum operating frequency of the microwave circuit.

Claims

1. Thermal diffusion interface (1) made from a material with isotropic thermal diffusion, comprising an insert (5) made from a material with anisotropic thermal diffusion comprising graphite comprising at least one favoured plane of thermal conduction perpendicular to the mean plane of the interface (1), the upper surface of the insert (5) opening onto the upper surface of the interface (1), and the lower surface (5a) of the insert (5) being covered with the isotropic thermal diffusion material of the interface (1); the insert (5) being in the shape of a cross with a raised central part (6) corresponding to the upper surface of the insert (5) opening onto the upper surface of the interface (1).

2. Thermal diffusion interface (1) according to claim 1, wherein the lower surface (5a) of the insert (5) is larger than the upper surface of the insert (5).

3. Thermal diffusion interface (1) according to one of the preceding claims, wherein the isotropic thermal diffusion material comprises copper.

4. Thermal diffusion interface (1) according to one of the preceding claims, wherein the raised central part (6) has edges (7) inclined by an angle between 30 and 60° with respect to an axis perpendicular to the mean plane of the interface (1).

5. Thermal diffusion interface (1) according to claim 4, wherein the raised central part (6) has edges (7) inclined by an angle of 45° with respect to an axis perpendicular to the mean plane of the interface (1).

6. Thermal diffusion interface (1) according to one of claims 1 to 5, configured to be a base of a housing of an electronic component.

7. Thermal diffusion interface (1) according to one of claims 1 to 5, configured to be a heat sink.

8. Thermal diffusion interface (1) according to one of the preceding claims, wherein the upper surface of the insert (5) is smaller than that of the surface of the element delivering the heat, which is intended to be in contact with said upper surface of the insert (5).