Together, in particular, to be integrated into an electronic device
The assembly with flexible thermal interface material and embedded hooks addresses thermal contact resistance and mechanical instability in power electronic devices, providing reliable mechanical support and efficient cooling by accommodating differential thermal expansion.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- VALEO SYST THERMIQUES SAS
- Filing Date
- 2024-12-04
- Publication Date
- 2026-06-05
AI Technical Summary
Existing methods for attaching power modules to heat sinks in power electronic devices face issues with high thermal contact resistance and mechanical instability due to differential thermal expansion, leading to interface cracks and component breakage.
An assembly comprising first and second components with different thermal expansion coefficients, anchored by flexible thermal interface material with embedded hooks, providing mechanical locking and thermal bridging to accommodate differential deformations.
The solution ensures reliable mechanical support and efficient heat transfer by allowing components to adapt to thermal cycling, preventing interface deterioration and ensuring effective cooling performance.
Smart Images
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Abstract
Description
Title of the invention: Assembly, in particular for integration into an electronic device
[0001] The present invention relates in particular to an assembly, in particular for integration into an electronic device.
[0002] Generally speaking, power electronic devices such as inverters, DC-DC converters, and on-board chargers contain electronic components that have significant cooling requirements. This is the case, for example, with power modules (or "Power Modules") which include SiC chips that generate a considerable amount of heat during operation (for example, on the order of 80-100 W / cm²). To dissipate this heat, power modules (of the IGBT, switching cell, or other type) are mounted on dedicated heat sinks (or "Coolers"), for example, made of aluminum. This mounting is most often achieved using a thermal interface material (TIM) or by brazing / sintering.
[0003] The solution with thermal interface material or TIM (including a thermal cushion also called "Gap pad", thermal grease, or a filling material also called "Gap filler") presents high thermal contact resistances at the interfaces and does not ensure mechanical support.
[0004] The brazing / sintering solution, on the other hand, is very thermally efficient, but its reliability in thermal cycling is low due to differential thermal expansion stresses (differences in the coefficient of thermal expansion at the interfaces), which can generate cracks at the interfaces. Indeed, electronic chips have a silicon-based substrate with a very low coefficient of thermal expansion, and when the substrate is brazed onto an aluminum heat sink with a very high coefficient of thermal expansion, deformations can occur, leading to breakage in the substrate of the electronic components.
[0005] The invention aims in particular to provide an assembly which at least partially overcomes the aforementioned drawbacks.
[0006] The invention thus relates to an assembly, in particular for integration into an electronic device, this assembly comprising: - a first component comprising a first assembly face exhibiting a first coefficient of thermal expansion, - a second component comprising a second assembly face having a second coefficient of thermal expansion different from the first coefficient of thermal expansion, - the first attachment elements formed on a first attachment face linked to the first component, - second attachment elements formed on a second attachment face linked to the second component, - a flexible thermal interface material interposed, with contact, between the first attachment face linked to the first assembly face of the first component and the second attachment face linked to the second assembly face of the second component, and in which the first and second attachment elements are anchored.
[0007] In the invention, the first and second fastening elements are anchored in the flexible thermal interface material, in particular by means of their insertion into the mass of the flexible thermal interface material, specifically by two opposite faces of this flexible thermal interface material. This provides mechanical locking on each upper and lower face of the flexible thermal interface material.
[0008] It should be noted that the first and second fastening elements are anchored in the flexible thermal interface material and do not necessarily interlock with each other. Mechanical locking is achieved primarily through the bonding of the fastening elements with the flexible thermal interface material, and not through the bonding of the fastening elements to each other.
[0009] This mechanical assembly by the first attachment elements and the second attachment elements anchored in the flexible thermal interface material allows, in the event of differential deformations of the first component and the second component, to take up these differential deformations because the attachment elements and the flexible thermal interface material can accompany the variations in dimensions.
[0010] The invention thus makes it possible to avoid deterioration or breakage at the interfaces between the first component and the second component which have very different coefficients of thermal expansion.
[0011] Furthermore, the flexible thermal interface material ensures good thermal contact, allowing heat transfer from one component to the other. The flexible thermal interface material also provides flexibility to the interface, enabling it to withstand potential deformations during thermal cycling (tension, compression, shear of the interface).
[0012] According to one aspect of the invention, the first attachment elements and the second attachment elements are made of metal.
[0013] According to one aspect of the invention, the first attachment elements and the second attachment elements are hooks.
[0014] Advantageously, the first attachment elements and the second attachment elements are made of material with their respective attachment face.
[0015] Each hook is formed in particular by a strand of curved material, in particular metal. In particular, the hooks are made from the material that forms the hooking face.
[0016] According to one aspect of the invention, the hooks are made by points which scratch a surface to raise the material on the surface and form these hooks.
[0017] The first attachment face with the first attachment elements defines a structured surface, which is different from a smooth surface.
[0018] The second attachment face with the second attachment elements defines a structured surface, which is different from a smooth surface.
[0019] According to one aspect of the invention, at least some of the first attachment elements and the second attachment elements can be deformed, in particular by being compressed in the flexible thermal interface material.
[0020] For example, some of the first attachment elements may come against the opposite face, namely the second attachment face linked to the second component, and possibly curl up.
[0021] For example, some of the second attachment elements may come against the opposite face, namely the first attachment face linked to the first component, and possibly curl up.
[0022] These first and second attachment elements, which are in contact with the opposite face, act as thermal bridges between the two components, allowing good heat transfer from one component to the other. This ensures good cooling performance, for example.
[0023] Advantageously, the first and second fastening elements are irreversibly anchored in the flexible thermal interface material. In other words, if the fastening elements are removed, they and / or the flexible thermal interface material are destroyed.
[0024] According to one aspect of the invention, the density of hooks per unit area is between 30,000 and 100,000 hooks / m2, in particular being substantially 65,000 hooks / m2.
[0025] According to one aspect of the invention, the length of the hooks is between 0.25 and 0.7 mm, in particular being substantially 0.5 mm.
[0026] According to one aspect of the invention, the flexible thermal interface material comprises a thermal cushion, also called a "Gap pad" in English. In particular The fasteners are anchored in the flexible thermal interface material by penetrating (or piercing) the flexible thermal interface material already in solid form.
[0027] According to one aspect of the invention, the flexible thermal interface material is silicone-based, optionally with a ceramic or metallic filler.
[0028] According to one aspect of the invention, particularly for high-temperature applications, the flexible thermal interface material can be based on laminated expanded graphite, for example in the form of a flexible graphite sheet. This type of material exhibits resistance to high temperatures.
[0029] According to another embodiment of the invention, the attachment elements are placed opposite each other and the thermal interface material in the form of liquid resin (or "Gap filler" in English) is deposited which encompasses the attachment elements, this material is then polymerized to form the flexible thermal interface material in which the attachment elements are anchored.
[0030] According to one aspect of the invention, the first attachment face on which the first attachment elements are present is formed by an intermediate plate connected by brazing to the first component.
[0031] In other words, the first attachment elements are not directly made on the first component.
[0032] According to one aspect of the invention, the second attachment face on which the second attachment elements are present is formed by an intermediate plate bonded by brazing to the second component.
[0033] In other words, the second attachment elements are not directly made on the second component.
[0034] These intermediate plates are for example made of strips with a structured surface formed by the fastening elements.
[0035] Each intermediate plate thus comprises a face with the attachment elements and a face for brazing onto the component.
[0036] According to one aspect of the invention, the intermediate plates are made of different materials.
[0037] The material of the intermediate plate can be chosen according to the material of the first assembly face of the first component when the intermediate plate is brazed onto this first assembly face, these materials being in particular identical or with identical or close coefficients of thermal expansion.
[0038] The material of the intermediate plate can be chosen according to the material of the second assembly face of the second component when the intermediate plate is brazed onto this second assembly face, these materials being in particular identical or with identical or close coefficients of thermal expansion.
[0039] For example, an intermediate aluminum plate can be brazed onto an aluminum heat sink and a copper intermediate plate can be brazed onto a copper base plate of an electronic component.
[0040] According to one aspect of the invention, the intermediate plates are made of a material selected from a metal or a metal alloy, in particular selected from the following list: - Note: Niobium - Cr: Chrome - Mo: Molybdenum - W: Tungsten - Ta: Tantalus - Cu: copper - Co: cobalt - a FeNi type alloy - an aluminum alloy.
[0041] For the FeNi type alloy, the coefficient of thermal expansion (also called CTE for "Coefficient of Thermal Expansion" in English) depends strongly on the Ni (Nickel) content.
[0042] According to another aspect of the invention, the first attachment face on which the first attachment elements are present is formed on a first wall of the first component which forms the first assembly face of the first component.
[0043] In other words, the first attachment elements are made directly on the first component, namely the first attachment elements came from the material with the first component.
[0044] According to one aspect of the invention, the second attachment face on which the second attachment elements are present is formed on a second wall of the second component which forms the second assembly face of the second component.
[0045] In other words, the second attachment elements are made directly on the second component, namely the second attachment elements are made of material with the second component.
[0046] According to one aspect of the invention, the first component comprises a direct bonded copper substrate (or DBC for "Direct Bonded Copper" in English) on which the first attachment elements are formed, or a copper base plate on which the first attachment elements are formed.
[0047] According to one aspect of the invention, the second component comprises a cooler, in particular made of metallic material, for example aluminium, on which the second attachment elements are formed.
[0048] In this embodiment of the invention, each of the first component and second component have a structured surface.
[0049] In this example, there is no brazing operation because the assembly is done mechanically by the fastening elements.
[0050] According to another aspect of the invention, only one of the first and second components has a structured surface, and the other of the first and second components has a structured surface formed on an intermediate plate brazed onto this component.
[0051] The present invention further relates to a method for manufacturing an assembly as described above, comprising the following steps: - provide the flexible thermal interface material which includes a thermal cushion, also called a "Gap pad" in English, - anchor the fastening elements in the flexible thermal interface material by making them penetrate the flexible thermal interface material already in solid form.
[0052] The present invention further relates to a method for manufacturing an assembly as described above, comprising the following steps: - Place the fastening elements opposite each other, - deposit the thermal interface material in the form of a liquid resin which encapsulates the fastening elements, this material is then polymerized to form the flexible thermal interface material in which the fastening elements are anchored.
[0053] The process may include a preliminary step of brazing an intermediate plate with attachment elements onto one of the first and second components.
[0054] Brazing is in particular soft brazing, preferably using a brazing alloy having a melting point below 250 °C, for example, composed of a mixture of tin, silver, and copper. Generally speaking, soft brazing is carried out at a lower melting temperature than that of the metals of the first and second components. Furthermore, brazing can be performed in a furnace or on an ad hoc basis, using a blowtorch, soldering lamp, or induction heating, for example.
[0055] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:
[0056] [Fig-1] The [Fig. 1] is a perspective representation of an example of an embodiment of an assembly according to the invention, configured to be integrated into an electronic device;
[0057] [Fig.2] The [Fig.2] is a perspective representation of different elements of the whole of the [Fig.1];
[0058] [Fig.3] The [Fig.3] is a cross-sectional representation of an electronic device according to another embodiment of the invention;
[0059] [Fig.4] Fig.4 represents a curve which shows that the coefficient of thermal expansion depends on the Ni (Nickel) content.
[0060] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.
[0061] In the following description, identical elements or elements with identical function bear the same reference numeral. For the sake of brevity, only the differences between the embodiments presented are described.
[0062] Figure 1 shows an assembly 100 configured for integration into an electronic device 200, such as a DC-AC converter, a DC-DC converter, or an on-board charger.
[0063] This assembly 100 comprising: - a first component 1 comprising a first assembly face 10 having a first coefficient of thermal expansion, - a second component 2 comprising a second assembly face 20 having a second coefficient of thermal expansion different from the first coefficient of thermal expansion, - the first attachment elements 11 formed on a first attachment face 12 linked to the first component 1, - second attachment elements 21 formed on a second attachment face 22 linked to the second component 2, - a flexible thermal interface material 300 interposed, with contact, between the first attachment face 12 linked to the first assembly face 10 of the first component 1 and the second attachment face 22 linked to the second assembly face 20 of the second component 2, and in which the first attachment elements 11 and the second attachment elements 21 are anchored.
[0064] In the invention, the first attachment elements 11 and the second attachment elements 21 are anchored in the flexible thermal interface material 300 because they are inserted into the mass of the flexible thermal interface material 300, respectively by two opposite faces of this flexible thermal interface material. This results in a mechanical lock on each upper and lower face of the flexible thermal interface material 300.
[0065] It should be noted that the first attachment elements 11 and the second attachment elements 21 are anchored in the flexible thermal interface material 300 and do not necessarily interlock with each other. Mechanical locking is achieved primarily through the bonding of the attachment elements 11, 21 with the flexible thermal interface material 300, and not through the bonding of the attachment elements to each other. The first attachment elements 11 and the second attachment elements 21 are formed from material with their respective attachment faces.
[0066] This mechanical assembly by the first attachment elements 11 and the second attachment elements 21 anchored in the flexible thermal interface material 300 allows, in the event of differential deformations of the first component 1 and the second component 2, to take up these differential deformations because the attachment elements 11, 21 and the flexible thermal interface material 300 can accompany the variations in dimensions.
[0067] The invention thus makes it possible to avoid deterioration or breakage at the interfaces between the first component 1 and the second component 2 which have very different coefficients of thermal expansion.
[0068] Furthermore, the flexible thermal interface material 300 ensures good thermal contact, allowing heat transfer from one component 1, 2 to the other. The flexible thermal interface material 300 also provides flexibility to the interface, enabling it to withstand potential deformations during thermal cycling (tension, compression, shear of the interface).
[0069] The first attachment elements 11 and the second attachment elements 21 are made of metal, and are hooks.
[0070] Each hook is formed in particular by a strand of curved material, in particular metal. Here, the hooks are made from the material that the attachment face 12, 22.
[0071] The hooks are made by points which scratch a surface to raise the material on the surface and form these hooks.
[0072] The first attachment face 12 with the first attachment elements 11 defines a structured surface, which is different from a smooth surface.
[0073] The second attachment face 22 with the second attachment elements 21 defines a structured surface, which is different from a smooth surface.
[0074] At least some of the first attachment elements 11, in the form of hooks, and of the second attachment elements 21, in the form of hooks, can be deformed, in particular by being compressed in the flexible thermal interface material 300.
[0075] For example, some of the first attachment elements 11 may come against the opposite face, namely the second attachment face 22 linked to the second component 2, and possibly curl up.
[0076] For example, some of the second attachment elements 21 may come against the opposite face, namely the first attachment face 12 linked to the first component 1, and possibly curl up.
[0077] These first attachment elements 11 and these second attachment elements 21, which are in contact with the opposite face, serve as thermal bridges between the two components 1, 2, thus allowing good heat transfer from one of the components to the other. This ensures good cooling performance, for example.
[0078] Advantageously, the first fastening elements 11 and the second fastening elements 21 are irreversibly anchored in the flexible thermal interface material 300. In other words, if the fastening elements are removed, the fastening elements 11, 21 and / or the flexible thermal interface material 300 are destroyed.
[0079] The density of hooks per unit area is between 30,000 and 100,000 hooks / m2, in particular approximately 65,000 hooks / m2.
[0080] The length of the hooks is between 0.25 and 0.7 mm, in particular approximately 0.5 mm.
[0081] As illustrated in [Fig. 2], the flexible thermal interface material 300 comprises a thermal pad, also called a "Gap pad". In particular, the attachment elements 11, 21 are anchored in the flexible thermal interface material 300 by penetrating (or piercing) the already solid flexible thermal interface material.
[0082] The flexible thermal interface material 300 is silicone-based, optionally with a ceramic or metallic filler.
[0083] For high-temperature applications, the flexible thermal interface material 300 can be based on laminated expanded graphite, for example in the form of a flexible graphite sheet. This type of material exhibits resistance to high temperatures.
[0084] In one embodiment of the invention, the attachment elements 11, 21 are placed opposite each other and the thermal interface material in the form of a liquid resin (or "Gap filler") is deposited, which encloses the attachment elements. This material is then polymerized to form the flexible thermal interface material 300 in which the attachment elements are anchored.
[0085] In the example described with reference to [Fig.1] and 2, the first attachment face 12 on which the first attachment elements 11 are present is formed by an intermediate plate 13 connected by brazing to the first component 1.
[0086] In other words, the first attachment elements 11 are not directly made on the first component 1.
[0087] The second attachment face 22 on which the second attachment elements 21 are present is formed by an intermediate plate 23 connected by brazing to the second component 2.
[0088] In other words, the second attachment elements 21 are not directly made on the second component 2.
[0089] These intermediate plates 13, 23 are for example made of strips with a structured surface formed by the fastening elements 11, 21.
[0090] Each intermediate plate 13, 23 thus comprises a face with the attachment elements and a face for brazing on the component 1, 2.
[0091] The intermediate plates 13, 23 are made of different materials.
[0092] The material of the intermediate plate 13 can be chosen according to the material of the first assembly face 10 of the first component 1 when the intermediate plate 13 is brazed onto this first assembly face, these materials being in particular identical or with identical or close coefficients of thermal expansion.
[0093] Similarly, the material of the intermediate plate 23 can be chosen according to the material of the second assembly face 20 of the second component 2 when the intermediate plate 23 is brazed onto this second assembly face, these materials being in particular identical or with identical or close coefficients of thermal expansion.
[0094] For example, an intermediate plate 13 made of aluminum can be brazed onto an aluminum heat sink and an intermediate plate 23 made of copper can be brazed onto a copper base plate of an electronic component.
[0095] The intermediate plates 13, 23 are made of a material selected from a metal or a metal alloy, in particular selected from the following list: - Note: Niobium - Cr: Chrome - Mo: Molybdenum - W: Tungsten - Ta: Tantalus - Cu: Copper - Co: Cobalt - a FeNi type alloy - an aluminum alloy.
[0096] For the FeNi type alloy, the coefficient of thermal expansion (also called CTE for "Coefficient of Thermal Expansion" in English) depends strongly on the Ni (Nickel) content, as illustrated in the curve of [Fig.4].
[0097] On this graph of [Fig.4], the x-axis represents the Ni (Nickel) content relative to the Iron content, and the y-axis represents the coefficient of thermal expansion (in units of 10-6 K-1).
[0098] The FeNi alloy is a particularly interesting alloy because its coefficient of thermal expansion can be adjusted according to the proportion of nickel.
[0099] We will now describe, with reference to [Fig.3], another example of implementation of the invention.
[0100] In this example of implementation of the invention, the first attachment face 12 on which the first attachment elements 11 are present is formed on a first wall 32 of the first component 1 which forms the first assembly face 10 of the first component.
[0101] In other words, the first attachment elements 11 are made directly on the first component 1.
[0102] The second attachment face 22 on which the second attachment elements 21 are present is formed on a second wall 33 of the second component 2 which forms the second assembly face 20 of the second component.
[0103] In other words, the second attachment elements 21 are made directly on the second component 2.
[0104] In the example described, the first component 1 comprises a direct bonded copper substrate 35 (or DBC for "Direct Bonded Copper" in English) on which the first attachment elements 11 are formed.
[0105] For example, the copper substrate 35 is the last layer in a stack of three layers: - a thin layer of copper on which the chips are assembled (by sintering, brazing for example), - a thicker layer of ceramic (AIN or A12O3 for example), - the last thin layer of copper 35.
[0106] The second component 2 includes a cooler, in particular made of metallic material, for example aluminium, on which the second attachment elements 21 are formed.
[0107] In this embodiment of the invention, each of the first component 1 and second component 2 has a structured surface.
[0108] In this example, there is no brazing operation because the assembly is done mechanically by the fastening elements 11,21.
[0109] The process for manufacturing an assembly 100 as described above comprises the following steps: - to supply the flexible thermal interface material 300 which includes a thermal cushion, also called a "Gap pad" in English, - anchor the fastening elements 11,21 in the flexible thermal interface material 300 by making them penetrate the flexible thermal interface material already in solid form.
[0110] Alternatively, the process comprises the following steps: - place the fastening elements 11, 21 opposite each other. - deposit (e.g., pour / inject) the thermal interface material 300 in the form of a liquid resin that encapsulates the fastening elements. This material is then polymerized to form the flexible thermal interface material 300 in which the fastening elements are anchored.
[0111] In the example of figures 1 and 2, the process includes a preliminary step of brazing on one of the first component 1 and second component 2, an intermediate plate 13, 23 with attachment elements 11, 21.
[0112] Brazing is in particular soft brazing, preferably using a brazing alloy having a melting point below 250 °C, for example composed of a mixture of tin, silver, and copper. Generally speaking, soft brazing is carried out at a lower melting temperature than that of the metals of the first component 1 and second component 2. Furthermore, brazing can be carried out in a furnace or occasionally, using a blowtorch, a soldering lamp, or by induction.
Claims
Demands
1. Assembly (100), in particular for integration into an electronic device (200), said assembly (100) comprising: - a first component (1) comprising a first assembly face (10) having a first coefficient of thermal expansion, - a second component (2) comprising a second assembly face (20) having a second coefficient of thermal expansion different from the first coefficient of thermal expansion, - first attachment elements (11) formed on a first attachment face (12) linked to the first component (1), - second attachment elements (21) formed on a second attachment face (22) linked to the second component (2), - a flexible thermal interface material (300) interposed, with contact, between the first attachment face (12) linked to the first assembly face (10) of the first component (1) and the second attachment face (22) linked to the second assembly face (20) of the second component (2),and in which the first attachment elements (11) and the second attachment elements (21) are anchored.
2. Assembly (100) according to the preceding claim, wherein the first attachment elements (11) and the second attachment elements (21) are made of metal.
3. Assembly (100) according to any one of the preceding claims, wherein the first attachment elements (11) and the second attachment elements (21) are hooks, and each hook is formed in particular by a strand of curved material, in particular of metal.
4. Assembly (100) according to any one of the preceding claims, wherein some of the first attachment elements (11) butt against the opposite face, namely the second attachment face (22) linked to the second component (2), and may curl up, and these first attachment elements (11) and these second attachment elements (21) which are in contact with the opposite face serve as thermal bridges between the two components.
5. Assembly (100) according to any one of the preceding claims, wherein the density of hooks per unit area is between 30,000 and 100,000 hooks / m2, in particular being substantially 65,000 hooks / m2.
6. Assembly (100) according to any one of the preceding claims, wherein the first attachment face (12) on which the first attachment elements (11) are present is formed by an intermediate plate (13) bonded by brazing to the first component (1) and / or the second attachment face (22) on which the second attachment elements (21) are present is formed by an intermediate plate (23) bonded by brazing to the second component (2).
7. Assembly (100) according to the preceding claim, wherein the intermediate plates (13, 23) are made of a material selected from a metal or a metal alloy, in particular selected from the following list: - Nb: Niobium - Cr: Chromium - Mo: Molybdenum - W: Tungsten - Ta: Tantalum - Cu: Copper - Co: Cobalt - an FeNi type alloy - an aluminum alloy.
8. Assembly (100) according to any one of claims 1 to 5, wherein the first attachment face (12) on which the first attachment elements (11) are present is formed on a first wall (32) of the first component (1) which forms the first assembly face (10) of the first component (1), and / or the second attachment face (22) on which the second attachment elements (21) are present is formed on a second wall (33) of the second component (2) which forms the second assembly face (20) of the second component (2).
9. Assembly (100) according to any one of the preceding claims, wherein the first component (1) comprises a directly bonded copper substrate (35) on which the first elements are formed attachment (11), or a copper base plate on which the first attachment elements (11) are formed.
10. Assembly (100) according to any one of the preceding claims, wherein the second component (2) comprises a cooler, in particular made of metallic material, for example aluminium, on which the second attachment elements (21) are formed.
11. A method for manufacturing an assembly (100) according to any one of the preceding claims, comprising the following steps: - providing the flexible thermal interface material (300) which includes a thermal cushion, also called a "Gap pad" in English, - anchoring the fastening elements in the flexible thermal interface material (300) by making them penetrate the flexible thermal interface material (300) already in solid form.
12. A method for manufacturing an assembly (100) according to any one of the preceding claims, comprising the following steps: - placing the fastening elements opposite each other, - depositing the thermal interface material (300) in the form of a liquid resin which encompasses the fastening elements, this material then being polymerized to form the flexible thermal interface material (300) in which the fastening elements are anchored.