FR2707383A1 - Device improving thermal and/or electrical contact between opposing surfaces - Google Patents

Abstract

In order to make it possible to fix a casing (9) containing elements giving rise to significant release of heat in a cavity (5), shape-memory alloy rings (13) are, for example, arranged inside the casing. In one of the states memorised by this alloy, the rings do not exert pressure on the casing and, in the other state, they firmly apply the casing against the walls of the cavity, thus establishing good thermal contact between them.

Description

THERMAL CONTACT IMPROVING DEVICE
AND / OR ELECTRICAL BETWEEN LOOKING SURFACES
The present invention relates to a device improving the thermal and / or electrical contact between facing surfaces.

 In certain fields, in particular in that of electronic equipment, mechanical structures are used to support a large number of removable housings which must be grouped in a high density assembly to ensure a common function. The elements contained in these boxes often dissipate great thermal energy that each box is responsible for removing. Each box taken separately can be able to evacuate the thermal energy produced by the components which it contains, if it is ventilated or if it is placed in a flow of heat-transfer liquid. On the other hand, when a large number of such boxes are densely grouped in a support structure, and these boxes must be removable (for example for the adjustment, maintenance or repair of the components which they contain), known means offer only unsatisfactory solutions.

 For example, in the case of an electronic scanning antenna comprising a large number of active modules in a small volume, we are dealing with a set of modules of the same dimensions, generally parallelepiped or cylindrical, arranged side by side, their front faces being coplanar and defining the emission surface of the antenna. The outline of this surface is often circular or square. The supporting structure has a generally cylindrical shape with a circular or square section depending on the shape of the antenna's emission surface. This cylinder is closed by two parallel plates pierced with corresponding holes in which tubes are fixed, the section of which has the same dimensions as the cross section of the housings. A heat transfer fluid circulates in the volume thus delimited in the support structure. The main drawback of this type of structure lies in the quality of the thermal contacts between the housings and the cooling circuit of the structure.

 The present invention relates to a device which makes it possible to improve the thermal and / or electrical contact, in particular between devices which one must be able to disassemble without damaging them, even when it is difficult to access them, and that these devices are assembled without play, and risk being mutually blocked during their operation as a result of thermal expansion, this device making it possible, in the case of thermal contact, to improve this contact between a device giving rise to a significant thermal release and a cooling device, without requiring fixing between the cooling surfaces and the device to be cooled, making it possible to produce the simplest cooling device possible, and allowing easy disassembly of the device to be cooled.

 The present invention more particularly relates to a support structure for modules requiring cooling, this structure comprising means ensuring good thermal contact and, where appropriate, good electrical contact, with these modules, while making assembly and installation easy. disassembly of these modules, this structure being easy to produce, rigid, resistant to mechanical forces, in particular to vibrations, and accepting high pressures (10 bars or more) of the coolant, if necessary, without the need for a pressure regulator , the modules can have a wide variety of shapes.

 The device according to the invention improving the thermal and / or electrical contact between at least a first and at least a second facing surface, is characterized by the fact that it comprises at least one piece of shape memory alloy associated with at least one of the surfaces, this part practically exerting no stress on said surfaces for a first memorized form of the alloy, and exerting stress on at least one of said first surfaces to apply it against at least one of said seconds surfaces, for a second memorized form of the alloy.

 In the case where the cooling device is a supporting structure, of the type with cells of shapes and dimensions corresponding to those of the housings which they are intended to receive, the external faces of these cells being, where appropriate, in contact with a refrigerant, the shape memory alloy part is formed either by the cells themselves, or by the boxes, or by an intermediate part disposed between each case and its cell, this intermediate part can be associated with alloy springs with shape memory, either by springs.

The present invention will be better understood on reading the detailed description of several embodiments, taken by way of nonlimiting examples and illustrated by the appended drawing, in which:
- Figure 1 is a simplified perspective view of a carrier structure with circular section cells, according to the prior art;
- Figure 2 is a simplified perspective view of a circular section module provided with interface elements according to the invention;
- Figure 3 is a partial explanatory front view of a structure according to the invention showing, theoretically, the operation of the elements of Figure 2;
- Figure 4 is a simplified sectional view of a rectangular section module, provided with interface elements according to the invention;
FIG. 5 is a simplified sectional view of a variant, according to the invention, of the device of FIG. 4;
- Figure 6 is a partial sectional view of a support structure, the cells of which are provided with interfaces according to the invention; and
FIG. 7 is a partial sectional view of a structure similar to that of FIG. 6, showing details of the cooling fluid circulation circuit.

 The invention is described below with reference to electronic modules, in particular to modules forming part of an electronic scanning antenna, but it is understood that the invention is not limited to such an application, and that it can be implemented to cool modules other than electronic modules, and in general, to cool very diverse devices, in particular those which must be removable and on which it is difficult to fix cooling radiators, for example printed circuit boards. Cooling can be ensured by air circulation (by convection or by forced circulation), or by circulation of an appropriate fluid. It is also understood that the number of elements to be cooled can vary in large proportions: either a single element, or several, even in large numbers, and when there are several, these can be grouped or not, and can have different forms within the same group.

 FIG. 1 shows an antenna 1 with electronic scanning having the general shape of a cylinder with a section, for example circular. The carrying structure of this antenna 1 essentially comprises an anterior plate 2 and a posterior plate 3, both circular and connected at their periphery by a tube 4. There are holes in the plates 2 and 3 opposite, having a circular shape (suitable for the shape of the electronic modules used, described below), and they are connected by metal tubes of the same section, to form cells 5 substantially parallel to each other and to the axis of the tube 4.

The tube 4 has at its upper part a tubular end piece 6, and at its lower part a tubular end piece 7, these two end pieces being connected to a circuit (not shown) for circulating coolant. Electronic modules 8 with a metallic envelope are housed in the cells 5 parallel to each other and to the axis of the tube 4. Thus, the fluid is circulated inside the volume delimited by the plates 2, 3, the tube 4 and the alveoli 5.

This fluid cools the cells 5, and therefore the modules 8 which are in close contact with the cells 5. As specified above, such a device ensures correct cooling of the modules, if there is good mechanical contact between the of the modules and the internal walls of the cells. However, this good mechanical contact makes it very difficult to extract the modules from their cells after an initial period of operation of the modules.

There is shown in Figures 2 and 3 an embodiment of the invention more particularly suitable for modules with circular or substantially circular section (elliptical, oblong ...). These modules are for example inserted into cells such as cells 5 of the support structure 1 of FIG. 1. According to this embodiment
The tubular casing 9 of the modules 10 has a longitudinal slot 11.

The slot 11 is rectilinear in the present case, but is not necessarily so. The thickness of the slot 11 can be very small (a few tenths of a millimeter for example), and it is closed off by an elastic seal 12, for example made of silicone material. Inside the envelope 9, there are several rings 13 made of shape memory alloy. These rings can have a shape corresponding to the shape of the section of the envelope 9 (circular for example) or an approximate shape (polygonal for example). The rings 13 can be fixed on the inner face of the envelope 9 or simply be held in place by elements contained in the envelope, in contact with the inner face of the envelope 9 or at a short distance from the latter. When there are several rings 13, they are preferably regularly spaced.

 Numerous studies have been carried out worldwide on the production of shape memory alloys (see in particular the articles "Shape Memory Alloys: materials in action" and "General discussion: the use of Shape Memory Actuators" of the University Catholic of Louvain).

 The materials mainly used are of NiTi type or copper alloys of Cu-Al-Ni or Cu-Al-Zn type and the memory effect is based on a transition of martensitic-austenitic type obtained by varying the temperature of the alloy studied associated with a change in shape of the alloy.

 The temperature range varies from one type of alloy to another and is generally between -100 and +200 "C approximately. Two types of memory effect are to be distinguished: The one-way memory effect and the effect double sense memory The double sense memory effect corresponds to the reversible transition from a high temperature form to a low temperature form by a simple temperature change.

 The production of springs, wires, plates in shape memory alloys has found numerous applications in all fields ranging from dental surgery to the automobile passing by household appliances (the potential applications identified are grouped in the article by M. Van Humbeek: "From a seed to a need: thetgrowth of shape memory applications in Europe").

Some studies, in particular in Japan and in the United States, have been dedicated to the use of shape memory alloys for the realization of interconnections of electronic chips (Raychem Corporation: "Shape
Memory effect alloys as an interconnection technology for IC packages an
PC boards ") or PGA type electronic component boxes (Pin Grid
Array - Japanese).

 The envelope 9 has a section of dimensions such that when the slot 11 has its minimum width (state which is called here "state of rest" of the module), it can be easily introduced into the corresponding cell. In this state (FIG. 3, diagram on the left), the rings 13 are in a state, which is called here "contracted state", for which their section has minimum dimensions. This contracted state corresponds to one of the two forms memorized during the learning of the AMF material constituting the rings 13. This form corresponds for example to a temperature of the material below its transition temperature, this transition temperature is chosen to be less than the operating temperature range of the modules in question.

 In the so-called "working" state of the modules, when they are placed in their respective cells, they are naturally brought to a temperature which makes the AMF material of the rings 13 cross its transition temperature (this rise in temperature is due to ambient temperature and overheating caused by the operation of the module circuits). This material then takes its second stored form which corresponds to the so-called "expanded" state of the rings 13 (FIG. 3, diagram on the right). In this state, the section of the rings 13 increases, and they exert a pressure on the envelope 9. This pressure firmly applies the envelope against the wall of the cell in which the module is placed, which establishes a good thermal contact. between the envelope 9 and the cell. This expansion of the envelope 14 is made possible by the slot 11. Of course, this expansion is limited, so that the seal 12 disposed in this slot can ensure the proper sealing of the module. It is also understood that in the module the elements with high heat dissipation are in good thermal contact with the casing 9 and that the variations in cross-sectional dimensions of this casing practically do not affect the quality of this thermal contact. It is also understood that good thermal contact is not the only physical effect obtained thanks to the AMF elements, and that one also obtains, in addition to good mechanical contact, good electrical contact, which is valid for all. the other embodiments described below.

 There is shown in Figure 4 an embodiment of the invention more particularly suitable for modules whose housing has a rectangular or polygonal section. The housing of the module 14 in FIG. 4 is formed by two half-shells 15, 16 on each of which, or on one of which, are fixed the electrical and electronic circuits 17, 18 of the module. These half-shells are almost in mutual contact before the module is inserted into its socket and the dimensions of these half-shells are such that the module can be easily inserted into its socket.

The longitudinal gap 19 which separates them is filled with an elastic sealant 20, for example made of silicone material. Inside the housing 15, 16, there are springs 21 made of AMF. The springs 21 can have various shapes: helical shape, in the shape of curved blades (in "S" or in "C" for example), or any other shape that can act as a spring. The number of these springs depends on the dimensions of the housing, the space available inside this housing and the characteristics of the springs used. In the "contracted" state of these springs (for which they have their minimum learned length) the gap 19 and of minimum width, while in their "expanded" state (corresponding to their second learned form), the half shells 15, 16 are firmly applied against the corresponding walls of the cell in question, which establishes good thermal contact between the housing 15, 16 and the corresponding cell, and consequently, good refrigeration of the circuits 17, 18.

 There is shown in Figure 5 a variant of the device shown in Figure 4. This -variante suitable for boxes of any shape (rectangular, polygonal, circular ...), and avoids the practice of slots in the housing of each module. Is fixed on one of the outer faces of the housing 22 of each module elements 23 in AMF.

In the present case, these elements are helical springs, but it is understood that they can be in many other forms, for example in the form of corrugated plates, cushions, etc.

 According to the embodiment of Figures 6 and 7, the AMF interface is at least one of the walls of each cell of the supporting structure. This embodiment is particularly advantageous in the case of modules with rectangular or polygonal section. In the case shown in the drawing, the lower 24 and upper 25 walls of the cell 26 are made of AMF. For one of the memorized forms of AMF, the walls 24 and 25 are planar (in this case this form is memorized for a temperature of the walls lower than the transition temperature of the material in AMF of the walls, the transition temperature being lower than the temperature range of use of the cells). Under these conditions, it is easy to introduce each module 27 into its cell (FIG. 7), the dimensions (in this case, the height) of the section of the modules being slightly smaller than the dimensions of the internal section of the cells. The other memorized form of AMF (for temperatures above its transition temperature) is a curved shape towards the inside of the cell (shown in broken lines in Figure 6). This shape is such that in the absence of a module in the cell, at least part of the inner section of the cell has dimensions slightly smaller than those of the module section. Thus, when the module is in place in the cell, and the temperature of the walls of the cell rises above said transition temperature, this module is strongly held in the cell.

Of course, the pressure then exerted by the AMF walls of the cell on the module is high enough to keep it firmly in place to ensure good thermal contact and, if necessary to allow the modules to resist vibrations, without being too large in order not to damage the modules. To remove each module, it suffices to refrigerate the cells below said transition temperature. This refrigeration can be done by any appropriate means: by placing the entire structure in a refrigerating cabinet, by circulating in the cooling circuit of the structure a fluid brought to very low temperature, etc.

 According to an advantageous characteristic of the invention, applicable in particular to cell structures for a large number of modules dissipating a large amount of heat, and in order to avoid temperature gradients in the refrigerant (coolanol for example) circulating in the structure, the circulation of this fluid is forced in the longitudinal direction of the modules, from front to rear or vice versa, the direction depending on the part (anterior or posterior) of the modules which heats up the most. For this purpose, there are inside the structure of the deflector plates 28, 29 parallel to the front and rear faces of the structure. These plates are pierced with holes corresponding to the various cells, the dimensions of which are greater than those of the outer section of the cells, in order to leave sufficient passage for the refrigerant fluid around the outer faces of the cells. These holes can be centered with respect to the cells, or else be off-center so as to favor the circulation of the fluid along a determined face of the cells, for example their upper face, which is generally the warmest. The plates 28, 29 are fixed for example to the tube 30 forming the outer wall of the structure, near the plates 31, 32 forming the front and rear faces of the structure. The inlet (33) and outlet (34) ends of the coolant are fixed to the tube 30, near the faces 31 and 32.

Of course, the number of deflector plates can be greater than two or even equal to 1 (near the arrival of fluid). In the present case, the refrigerant arrives near the rear plate 32, and is distributed among all the holes drilled in the plate 29. Thus, this fluid cools in parallel all the alveoli 1 from back to front, and consequently all the modules, which are in very good thermal contact with the walls of their respective cells. This thermal contact is obtained thanks to the material
AMF of the cell walls which exerts a stress on the module housings. It is assumed in this case that the greatest thermal release of the modules occurs at their rear part. Of course, if this greater clearance occurred at their anterior part, it would be necessary to reverse the inlet and outlet of refrigerant fluid. It is also clearly understood that if this higher thermal release occurs in the central part of the modules, provision should be made for an inlet for refrigerant fluid towards the middle of the tube 30, an outlet at the front and another at the rear, and have a deflector plate on each side of the fluid inlet, in order to channel it both towards the front and towards the rear of the structure, along the alveoli
The invention has been described above with a view to using good mechanical contact to ensure good thermal contact1 but it is understood that the good mechanical contact, easily suppressable without requiring access to the surfaces in contact, can be used for itself (for example for fixing parts that are difficult to access, for locking slide drawers in a certain position, etc.) or for ensuring good electrical contact (for example, ground contact between a housing and the structure which encloses it , or between male and female parts of connectors that are difficult to access and / or fragile, ...).

Claims (8)

 1. Device improving the thermal and / or electrical contact between at least a first and at least a second surface with a look, characterized in that it comprises at least one piece of shape memory alloy (13, 21, 23, 24 -25) associated with at least one of the surfaces (9, 15-16, 22, 24-25), this part practically exerting no stress on said surfaces for a first memorized form of the alloy, and exerting a stress on at least one of said first surfaces to apply it against at least one of said second surfaces, for a second memorized form of the alloy.  2. Device according to claim 1, characterized in that the first surfaces are exterior surfaces of a housing (10, 14), and that the second surfaces are the interior faces of a cell (5) in which must be inserted the housing.  3. Device according to claim 2, characterized in that the housing comprises at least one longitudinal slot (11, 19), and that this housing contains at least one part (13, 21) of shape memory alloy.  4. Device according to claim 3, characterized in that the part (s) in shape memory alloy is (are) annular (s) (13).  5. Device according to claim 3, characterized in that the part (s) of shape memory alloy has (have) a spring form.  6. Device according to claim 2, characterized in that the part (s) of shape memory alloy constitutes at least one of the walls of the cell (24, 25).  7. Device according to one of the preceding claims, characterized in that the first surfaces are the external lateral surfaces of modules (27) grouped in a support structure (1), and that the second surfaces are the internal surfaces of cells (5) intended to receive the modules.  8. Device according to claim 7, characterized in that the supporting structure is cylindrical, and is connected to a device for circulating coolant, that the cells are substantially parallel to each other and to the axis of the cylinder, and that the structure includes deflector means (28, 29) circulating the coolant along the external faces of the cells.