Method for assembling at least two parts

Abstract

The invention relates to a method for assembling at least two parts, the method comprising the following steps: - preparing a first element (4) comprising a first surface (8) having a general shape provided with a cavity (6); - preparing a second element (14) having a main surface (16) that has the same shape as at least one portion of the general shape of the first surface (8) of the first element (4); - applying a coating (26) to the first surface (8) of the first element (4) and to the main surface (16) of the second element (14); - placing the second element (14) on the first surface (8) of the first element (4) so that it fully covers the cavity (6); - placing the first element (4) and the second element (14) in a chamber (28) containing a fluid (30); and - pressurising the fluid (30) contained in the chamber (28).

Description

Method of assembling at least two parts together

[0001] The invention relates to an assembly technique. More particularly, the invention relates to a method for assembling at least two parts together and a device obtained by implementing such a method.

[0002] Microfluidic technology has been embraced by biologists and engineers in academia and industry. The expansion of its applications has been accompanied by an explosion in the range of materials and processes used to fabricate these devices. Early microfluidic devices were made of silicon and glass and borrowed processes directly from semiconductor and microelectromechanical systems manufacturing. Today, many researchers have abandoned silicon and glass and instead use cast elastomers such as polydimethylsiloxane (PDMS), which is ideal for rapid prototyping and is well-suited to inexpensive manufacturing.

[0003] However, there are still many applications where silicon offers advantages over polymer materials, such as chemical microreactors and the cooling of silicon electronic chips. Indeed, numerous studies aimed at cooling high-power electronic chips have shown that silicon microchannel devices are a very efficient cooling system. In recent years, silicon microchannel cooling has been successfully applied to the cooling of devices such as particle detectors. Thanks to their high thermal efficiency, they can guarantee the cooling of silicon tracers for particle physics, which is fundamental for reducing radiation damage from particle detectors. With the electrification of vehicles, it is very likely that the issue of cooling electronics will become increasingly important.

[0004] The fabrication of a silicon microchannel device begins by etching channels into a first element formed by a silicon wafer, followed by the assembly of a second silicon element to close the channels. The channels are then closed and openings must then be made, generally by etching or mechanical machining, to allow the circulation or injection of the fluid. These openings can be made before or after the assembly of the second element.

[0005] To fix the second element on the first element to close the channels in a watertight manner, it is known to carry out an assembly by thermocompression with filler material. This consists of inserting, between the first element and the second element, a layer allowing the assembly of these two elements. For this purpose, a gold deposit is used, for example, on each of these elements, for example by physical vapor deposition. The assembly is carried out by bringing the gold layers into contact under pressure, the adhesion then taking place by reciprocal migration of the gold atoms.

[0006] For adhesion to occur, it is necessary to apply pressure to the first element against the second element. For this purpose, it is known to use a platen press allowing mechanical contact and compression. However, the force that must be applied by the press is significant and increases proportionally with the surface to be assembled, and perfect flatness of the first element and the second element is a necessary condition to allow assembly by thermocompression. The larger the size of these elements, the more difficult and expensive it is to have a flatness compatible with good adhesion of the substrates. Even when taking all possible precautions, the manufacturing yield of such assemblies remains poor, which makes the cost prohibitive and industrial exploitation unviable.Furthermore, to ensure proper assembly and, above all, non-destruction of the first and second elements, the compression must be applied very evenly across the contact surface. However, if you want to assemble two parts with complex shapes, it becomes difficult, if not impossible, to do so with a simple platen press, otherwise you risk having very uneven contact pressure, potentially leading to destruction of the first and second elements.

[0007] Furthermore, beyond the specific field of microfluidic technology, these same problems can arise when assembling one part onto another. Therefore, a solution to these problems in the specific field of microfluidic technology could be implemented in a more general field involving the assembly of two parts onto each other.

[0008] The invention aims in particular to remedy these problems by proposing a method for assembling at least two parts together which can be implemented even if the two parts have relatively complex shapes, without risking damaging these two parts.

[0009] For this purpose, the invention provides a method for assembling at least two parts together, in which the following steps are implemented:

[0010] - preparation of a first element comprising a first surface having a predefined general shape and provided with a cavity,

[0011] - preparation of a second element having a main surface of the same shape as at least part of the predefined shape of the first surface of the base,

[0012] - applying a coating, comprising a first material chosen from titanium, chromium and nickel and a second material chosen from gold, copper, aluminum and lead, on the first surface of the first element and on the main surface of the second element,

[0013] - placing the second element on the first surface of the first element so as to completely cover the cavity so that the latter forms at least one cavity delimited by the first and second elements,

[0014] - placing the first element and the second element in a box containing a fluid, and

[0015] - pressurizing the fluid contained in the box until it reaches a predetermined pressure value.

[0016] Thus, the first element and the second element are pressurized by means of a fluid. Since the cavity forms, after placement of the second element on the first element, a cavity delimited by the first and second elements, that is to say an isolated volume inside the assembly of the first element and the second element, this volume contains air at atmospheric pressure approximately equal to one bar which remains constant during the pressurization of the fluid contained in the box. In this way, the fluid applies a uniform pressure on the first element and the second element which has the effect of pressing the second element against the first element, whatever the geometric shape of the first element and the second element.It is therefore understood that this method guarantees the application of a homogeneous pressure for the adhesion of the second element to the first element, without risking mechanically damaging the first element and the second element, unlike the press of the prior art, in a reliable and easily reproducible manner. This allows for better assembly of the second element on the first element.

[0017] Furthermore, since the pressure is applied homogeneously to the first element and the second element regardless of their geometric shape, the invention makes it possible to design the first element and a second element with relatively complex shapes. This contributes to improving the integration capability of the cooling member in a given electronic chip system.

[0018] Advantageously, the cavity of the first element is prepared by etching, by depositing material, by generating roughness or by a combination of these.

[0019] The cavity is thus created with great precision while benefiting from great freedom in the shape and dimensions given to it.

[0020] Advantageously, the fluid contained in the box is water, oil or a gas.

[0021] The invention is thus simple to implement and inexpensive.

[0022] Advantageously, the predetermined pressure value is greater than 200 bars, preferably equal to 400 bars.

[0023] Advantageously, during the pressurization step, the pressure of the fluid is maintained at a value greater than or equal to the predetermined pressure value for at least 1 hour, preferably for at least several hours.

[0024] These pressure and duration values ​​allow for particularly rigid and watertight adhesion of the second element to the first element.

[0025] Advantageously, the first element and the second element are made of silicon, metal, carbon or ceramic.

[0026] The assembly method can thus be implemented in a large number of technical fields, which contributes to the easily implementable nature of the invention.

[0027] Advantageously, the additional step is implemented in which a third element, having a main surface of the same shape as at least part of the second surface of the first element and having a cavity, is placed on the second surface of the first element.

[0028] Preferably, before the step of placing the third element, a coating is applied, comprising a first material selected from titanium, chromium and nickel and a second material selected from gold, copper, aluminum and lead, on the second surface of the first element and on the main surface of the third element.

[0029] The invention can thus be applied for the assembly of more than two parts together, which makes it possible to produce particularly complex assemblies and contributes to broadening the scope of applications of the invention. The third element can, for example, form a connector configured to receive means for supplying cooling fluid.

[0030] Advantageously, during the pressurization step, the fluid contained in the box is left at room temperature.

[0031] The invention is therefore particularly simple to implement and inexpensive.

[0032] Advantageously, the first element comprises several textured parts identical to each other.

[0033] The invention thus makes it possible to assemble parts in batches, which is generally referred to by the English expression “batch-making”. After implementing the assembly method, the first element and the second element can be cut into elementary parts each comprising a cavity, each of these parts forming a device in its own right.

[0034] According to an alternative embodiment of the invention, the cavity opens onto an external surface of the first element via several openings, and the openings are sealed with as many removable plugs, for example made of elastomer, before placing the first and second elements in the box.

[0035] The invention is thus suitable for the production of cooling micro-channels in the assembly.

[0036] The invention also provides a device comprising a first element and a second element obtained by implementing an assembly method as defined above.

[0037] The invention also makes it possible to assemble parts with surfaces that are not completely identical. The uniform pressure applied to the assembly deforms the different surfaces in order to bring them into contact. The difference in shape between the different surfaces must be small enough to be filled by deformation without damaging the materials being bonded. Brief description of the figures

[0038] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0039] is a sectional view illustrating a cooling member for an electronic chip according to an embodiment of the invention,

[0040] is a perspective view of a first element and a second element of the cooling member of the, before application of a coating thereto,

[0041] is a perspective view of a first element and a second element of the cooling member of the, after application of a coating thereon,

[0042] is a schematic view illustrating a fluid-filled box used when implementing a method for manufacturing a cooling member for an electronic chip according to an embodiment of the invention, and

[0043] is a succession of sectional views illustrating a method of manufacturing cooling members for electronic chips according to an alternative embodiment of the invention. Detailed description

[0044] A device 2 comprising at least two parts according to an embodiment of the invention has been shown. In the following, the device 2 forms a cooling member for an electronic chip. The cooling member 2 comprises a first element 4, made of silicon, carbon or ceramic, comprising a cavity 6. The cavity 6 is open on a first surface 8 of the first element 4, thus taking the form of a groove, and here has an opening 10 on a second surface 12 of the first element opposite the first surface 8. In other words, the cavity 6 passes through the first element 4 from the first surface 8 to the second surface 12. The cavity 6 is here produced by etching the first element, for example by means of laser radiation or chemical or physicochemical etching, but it can be provided that it is produced by deposition of material or by generation of roughness, in combination or not with the etching.

[0045] The cooling member 2 comprises a second element 14, made of silicon, carbon or ceramic, having a main surface 16 in contact with the first surface 8 of the first element 4. The main surface 16 of the second element 14 and the first surface 8 of the first element 4 are of identical shapes so that the main surface 16 of the second element 14 matches the first surface 8 of the first element 4. Here, this shape is flat, but it is possible to provide for this shape to be curved or of more complex geometry.

[0046] The cooling member 2 comprises a third element 18, which here forms a connector, made of silicon, metal, carbon or ceramic, having a main surface 20 in contact with the second surface 12 of the first element 4. The main surface 20 of the third element 18 and the second surface 12 of the first element 4 are of identical shapes so that the main surface 20 of the third element 18 matches the second surface 12 of the first element 4. Here, this shape is flat, but it is possible to provide for this shape to be curved or of more complex geometry. The third element 18 forming a connector comprises a cavity 22 forming a through micro-channel communicating with the opening 10 of the micro-channel 6 of the first element. The cavity 22 of the third element 18 has an inlet orifice sealed in a sealed manner by a removable plug 24. The inlet orifice is sized to be able to be connected to fluid supply means.

[0047] We will now present a method of assembling the device 2 according to an embodiment of the invention.

[0048] Steps of this method are shown. First, the first element 4 and the second element 14 are prepared separately as described above. By "preparing", it is meant that they are manufactured or that they are already manufactured or that they are simply made available for the implementation of the invention.

[0049] A following step of the method is shown in which a coating 26 comprising a first material chosen from titanium, chromium and nickel and a second material chosen from gold, copper, aluminum and lead is applied to the first surface 8 of the first element 4 and to the main surface 16 of the second element 14. Preferably, gold is chosen because this material has the advantage of not oxidizing, of having good diffusion capacity and is an electrical conductor, which may be useful depending on the nature of the device 2. More precisely, a layer of the first material, here titanium, is first deposited on the first surface 8 of the first element 4 and on the main surface 16 of the second element 14, then a layer of the second material, here gold, is deposited above the layer of first material, on the first surface 8 of the first element 4 and on the main surface 16 of the second element 14.The titanium layer prevents gold from diffusing into the first element 4 or the second element 14. The first material can thus be described as a “barrier material” and the second material as an “adhesion material”. The titanium layer generally has a thickness of 5 to 50 nanometers while the gold layer generally has a thickness of 100 to 500 nanometers. In the same way, the coating 26 comprising a first material chosen from titanium, chromium and nickel and a second material chosen from gold, copper, aluminum and lead is applied to the second surface 12 of the first element 4 and to the main surface 20 of the third element 18.

[0050] The second element 14 is then placed on the first surface 8 of the first element 4 so as to completely cover the cavity 6 of the first element 4, such that the layer of second material of the main surface 16 of the second element 14 is in contact with the layer of second material of the first surface 8 of the first element 4. This allows the second element to completely cover the cavity 6 so that the latter forms at least one cavity delimited by the first 4 and second 14 elements. The third element 18 is also placed on the second surface 12 of the first element 4 so as to completely cover the opening 10 of the cavity 6 of the first element 4, such that the layer of second material of the main surface 20 of the third element 18 is in contact with the layer of second material of the second surface 12 of the first element 4.

[0051] A chamber 28 is shown containing a fluid 30 used to implement a following step of the method. The chamber 28 is a device commonly referred to as a "hyperbaric chamber" and is configured to be able to put the fluid 30, here water, oil or a gas, under high pressure. For this purpose, the chamber 28 is equipped with a hydraulic pump 32. After implementing the steps of applying the coating 26 described above, the first element 4, the second element 14 and the third element 18 are placed in the chamber 28, immersed in the fluid 30. The fluid 30 is then pressurized until the pressure of the fluid reaches a predetermined pressure value. Here, this predetermined value is chosen at 200 bars, or even 400 bars. The fluid 30 is maintained at a pressure higher than the predetermined value for at least one hour, preferably for several hours.During all these steps, the fluid 30 is left at room temperature.

[0052] The pressure difference between that of the fluid 30 and that prevailing inside the cooling member 2, in the cavity formed by the cavity 6 between the first 4 and second 14 elements, is of the order of the pressure of the fluid 30 since the pressure inside the cooling member (in the cavity) remains at 1 bar. This significant pressure difference makes it possible to increase the pressure force around the cavity 6 and presses the second element 14, the first element 4 and the third element 18 against each other. This allows the gold to migrate between the gold layers, on the one hand, between the main surface 16 of the second element 14 and the first surface 8 of the first element 4, and, on the other hand, between the main surface 20 of the third element 18 and the second surface 12 of the first element 4, to achieve adhesion by thermocompression.The second element 14, the first element 4 and the third element 18 are thus assembled rigidly and in a sealed manner. The cooling member 2 can then be removed from the box 30 and dried.

[0053] 5a to 5d show, more precisely, an assembly method according to an alternative embodiment of the invention. According to this alternative, the first element 4 differs from that of the embodiment previously described in that it comprises several textured parts 6 identical to each other, each similar to the cavity of the first element of the. As shown in Figure 5a, the second element 14 covers all of the textured parts 6 of the first element 4, while the third element 18 covers all of the openings of the textured parts 6 of the first element 4.

[0054] The assembly method according to this embodiment variant comprises the same steps as those described above in relation to the previously described embodiment, with the difference that the ends of the second element 14, the first element 4 and the third element 18 are placed in sealed enclosures 34, here made of elastomer, to prevent fluid 30 contained in the box 28 from infiltrating between the second element 14 and the first element 4 or between the first element 4 and the third element 18, as illustrated in FIG. 5b. The assembly is placed in the box 28, as illustrated in FIG. 5c, in a similar manner to the previously described embodiment.The method further comprises an additional step at the end thereof, and after removing the sealed enclosures 34, consisting of cutting the second element 14, the first element 4 and the third element 18, assembled, according to elementary parts as illustrated in figure 5d, each of these elementary parts comprising one of the textured parts 6 of the first element 4. Each of these elementary parts forms a cooling member 2 for an electronic chip. It is thus understood that this variant embodiment of the invention makes it possible to assemble devices in batches, which makes it possible to greatly increase the assembly rate.

[0055] An assembly method according to another alternative embodiment of the invention consists of not depositing a coating 26 on the third element 18 so that after pressurizing the fluid 30 in the box 28, the third element 26 is not glued and can be removed. This allows the gluing to be carried out and the openings 10 to be preserved.

[0056] The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art.

[0057] The device may be of a nature other than a cooling member for an electronic chip. For example, the assembly method according to the invention may be implemented to produce a stack of electronic chips.

[0058] It is possible to increase the temperature of the fluid in the box when pressurizing the fluid, which would accelerate the creation of adhesion by thermocompression.

[0059] It may be provided that the cavities provided in the first element and / or in the third element form micro-channels opening respectively onto the external surfaces of the first and third elements via several openings not covered by any of the elements. If necessary, these openings are sealed by as many removable plugs, for example made of elastomer, during the assembly step before placing the elements in the box. Once the elements are removed from the box, the plugs are removed. List of references

[0060] 2: cooling element for electronic chip4: first element6: cavity of the first element8: first surface of the first element10: opening12: second surface of the first element14: second element16: main surface of the second element18: third element20: main surface of the third element22: cavity of the third element24: removable plug26: coating28: box30: fluid32: hydraulic pump34: sealed enclosures

Claims

Method for assembling at least two parts together, characterized in that it comprises the following steps: - preparation of a first element (4) comprising a first surface (8) having a predefined general shape and provided with a cavity (6), - preparation of a second element (14) having a main surface (16) of the same shape as at least part of the predefined general shape of the first surface (8) of the first element (4), - application of a coating (26), comprising a first material chosen from titanium, chromium and nickel and a second material chosen from gold, copper, aluminum and lead, on the first surface (8) of the first element (4) and on the main surface (16) of the second element (14), - placement of the second element (14) on the first surface (8) of the first element (4) so ​​as to completely cover the cavity (6),- placing the first element (4) and the second element (14) in a box (28) containing a fluid (30), and - pressurizing the fluid (30) contained in the box (28) until it reaches a predetermined pressure value., Method according to the preceding claim, in which the cavity (6) of the first element (4) is prepared by etching, by deposition of material, by generation of roughness or by a combination of these. A method according to any preceding claim, wherein the fluid (30) contained in the housing (28) is water, oil or a gas. Method according to any one of the preceding claims, wherein the predetermined pressure value is greater than 200 bars, preferably equal to 400 bars. Method according to any one of the preceding claims, in which during the pressurization step, the pressure of the fluid (30) is maintained at a value greater than or equal to the predetermined pressure value for at least 1 hour, preferably for at least several hours. A method according to any preceding claim, wherein the first element (4) and the second element (14) are made of silicon, metal, carbon or ceramic. A method according to any preceding claim, wherein the further step is carried out of placing a third element (18), having a main surface (20) of the same shape as at least part of the second surface (12) of the first element (4) and having a cavity (22), on the second surface (12) of the first element (4). Method according to the preceding claim, in which, before the step of placing the third element (18), a coating (26) is applied, comprising a first material chosen from titanium, chromium and nickel and a second material chosen from gold, copper, aluminum and lead, on the second surface (12) of the first element (4) and on the main surface (20) of the third element (18). Method according to any one of the preceding claims, in which during the pressurization step, the fluid (30) contained in the box (28) is left at room temperature. Method according to any one of the preceding claims, in which the first element (4) comprises several textured parts (6) identical to each other. Method according to any one of the preceding claims, in which the cavity (6) opens onto an external surface of the first element (4) via several openings, and in which the openings are sealed with as many removable plugs, for example made of elastomer, before placing the first (4) and second (14) elements in the box (28).

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