Chip and heat sink self-adaptive connecting structure based on shape memory alloy phase change driving and connecting method

Abstract

The application discloses a chip and heat sink self-adaptive connecting structure and connecting method based on shape memory alloy phase change driving, and belongs to the technical field of semiconductor packaging and heat dissipation structure. The application comprises a heat sink, a shape memory alloy connecting component, a flexible buffer layer and a metallization layer. The shape memory alloy connecting component comprises a fixed section, an elastic transition section and a clamping section. The elastic transition section comprises a first connecting section, a second connecting section and an intermediate connecting section. According to the difference in thermal expansion coefficients and temperature changes of the chip and the heat sink, the structure parameters of the shape memory alloy connecting component can be calculated, and the shape memory alloy connecting component can be controlled quantitatively. The application is suitable for the connecting scene of the chip and the heat sink. The restoring force generated by the shape memory alloy connecting component in the phase change process matches the stress generated by thermal expansion, so that the thermal stress compensation is realized, and the technical effects of improving the heat conduction stability and the stability of the chip connection can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device packaging and heat dissipation connection technology, and particularly relates to an adaptive connection structure and method between a chip and a heat sink based on shape memory alloy phase change driven. Background Technology

[0002] With the rapid development of high-power semiconductor devices, laser chips, radio frequency power devices, and power electronic modules towards higher power density, miniaturization, and higher reliability, chips generate a significant amount of heat during operation. If this heat cannot be effectively conducted to external heat dissipation structures and dissipated quickly, it will lead to increased chip junction temperature, performance degradation, and even device failure. Therefore, modern semiconductor packaging structures place higher demands on the thermal conductivity, mechanical stability, and long-term reliability of the connection structure between the chip and the heat sink.

[0003] To improve heat dissipation, high thermal conductivity materials are typically used as heat sinks, such as diamond, aluminum nitride, silicon carbide, copper-tungsten alloys, and high thermal conductivity ceramics. These materials have high thermal conductivity, but their coefficients of thermal expansion (COPs) often differ significantly from those of semiconductor chip materials (such as silicon, gallium arsenide, and silicon carbide). For example, diamond has a much lower COP than silicon or gallium arsenide, while copper-tungsten alloys and aluminum nitride have COPs that differ from those of silicon carbide chips. During chip assembly and subsequent operation, devices typically undergo repeated temperature cycles from room temperature to higher operating temperatures. Due to the mismatch in COPs, significant thermal stress is generated at the interface between the chip and the heat sink. This thermal stress easily leads to stress concentration at the interface, causing interface cracking, delamination, chip warping, and even connection failure, severely impacting the long-term reliability of the device. This is especially true in high-power-density devices, where the chip size is small and the heat flux density is high, making localized stress concentration at the interface even more likely, rendering traditional connection structures inadequate for meeting high reliability requirements.

[0004] Currently, common connection methods between chips and heat sinks mainly include soldering, brazing, screw clamping, thermally conductive adhesive, and metal interlayer connections. While soldering and brazing offer good thermal conductivity, they are typically rigid connections, making it difficult to release interfacial stress caused by thermal expansion differences during temperature changes. This can easily lead to fatigue cracks or interfacial delamination after repeated thermal cycles. Thermally conductive adhesive connections offer some flexibility, but their low thermal conductivity can result in insufficient heat dissipation in high-power devices due to excessive thermal resistance, and they also exhibit poor long-term reliability at high temperatures. Screw clamping or ordinary metal spring connections provide some mechanical clamping force, but this force is usually fixed after assembly and difficult to adjust automatically with temperature changes. Furthermore, ordinary metal elastic elements are prone to stress relaxation or elastic decay at high temperatures, leading to reduced interfacial pressure and affecting thermal stability. In addition, as semiconductor devices become increasingly miniaturized and chip sizes continue to shrink, higher demands are placed on the volume, assembly methods, and clamping precision of the connection structures. Traditional screw or spring structures are difficult to achieve precise clamping under small size conditions, and it is also difficult to ensure the stability of interface pressure and the controllability of thermal stress while ensuring the convenience of assembly.

[0005] Shape memory alloys possess both shape memory and superelasticity effects, enabling them to generate controllable restoring or elastic forces during temperature changes and maintain different mechanical properties at different temperatures. These materials have the ability to output restoring or elastic forces during temperature variations, thus showing potential for use in temperature-adaptive connection structures. However, in existing technologies, shape memory alloys are primarily used in actuators, fasteners, connectors, or medical devices, typically for shape recovery or actuation functions, without specifically addressing the interface issues between semiconductor chips and high thermal conductivity heat sinks. Especially in scenarios requiring simultaneous high thermal conductivity connections, thermal expansion mismatch compensation, interface pressure stability, and miniaturized assembly, existing technologies lack effective solutions.

[0006] In other words, in the field of connecting chips and high thermal conductivity heat sinks, existing technologies struggle to simultaneously achieve the following objectives: ensuring high thermal conductivity while enabling the connection interface to automatically adjust the clamping force during temperature changes and compensate for stress caused by differences in thermal expansion coefficients, while ensuring that the connection structure remains stable and reliable under repeated thermal cycling conditions.

[0007] Therefore, there is an urgent need to provide a new connection structure that can adaptively adjust the connection pressure between the chip and the heat sink by utilizing the controllable mechanical response generated by temperature changes, thereby reducing thermal stress concentration, improving the stability of the thermal interface, and meeting the needs of high power density and miniaturized semiconductor devices.

[0008] To address the above problems, this invention proposes a solution. Summary of the Invention

[0009] The purpose of this invention is to address the problem that existing technologies cannot simultaneously achieve high thermal conductivity connection, thermal stress compensation, adaptive adjustment of interface pressure, and thermal cycling stability, and to provide an adaptive connection structure and method for chip and heat sink based on shape memory alloy phase change driven.

[0010] To achieve the above objectives, the invention employs the following technical solution: An adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven structure includes: a heat sink; a shape memory alloy connecting member disposed on the upper surface of the heat sink, the shape memory alloy connecting member including a fixed section, an elastic transition section, and a clamping section connected in sequence; the fixed section is connected to the upper surface of the heat sink; the elastic transition section is used to generate controllable deformation in temperature change, so that the shape memory alloy connecting member generates a restoring force or elastic force, thereby applying at least one of clamping force, pressing force, supporting force or pre-tightening force to the chip placed on the upper surface of the heat sink, so as to realize the adaptive connection between the chip and the heat sink.

[0011] The controllable deformation generated by the elastic transition section at temperature, together with the phase transformation recovery force of the shape memory alloy connecting component, works to compensate for the thermal expansion mismatch between the chip and the heat sink. This enables an adaptive connection between the chip and the heat sink without the need for screws or rigid clamping structures, and maintains a stable clamping state during thermal cycling.

[0012] Preferably, the elastic transition section includes a first connecting section, an intermediate connecting section, and a second connecting section connected in sequence, with the first connecting section connected to the end of the fixed section and the end of the second connecting section connected to the clamping section.

[0013] Preferably, a flexible buffer layer is provided at the end of the clamping section, and the flexible buffer layer material is at least one of indium, gold, silver, tin, and gold-tin alloy.

[0014] Preferably, the upper surface of the heat sink is provided with a metallization layer, and the metallization layer material is at least one of titanium, platinum, nickel, and gold.

[0015] Preferably, the heat sink material is at least one of diamond, silicon carbide, aluminum nitride, copper-tungsten alloy or high thermal conductivity ceramic.

[0016] Preferably, the shape memory alloy connecting component material is at least one of nickel-titanium shape memory alloy, copper-based shape memory alloy, or iron-based shape memory alloy.

[0017] Preferably, the austenite termination temperature A of the shape memory alloy connecting member is... fThe temperature ranges from 60℃ to 150℃.

[0018] Preferably, the elastic transition section adopts a sheet-like structure, and its shape is one of corrugated, serpentine, arc-shaped, S-shaped, multi-level bending, or periodic curved surface structure, and the thickness of the shape memory alloy connecting component is 0.05mm~0.2mm.

[0019] Preferably, the structural parameters of the elastic transition section include: the length of the elastic transition section before deformation, the effective bending length L, the radius of curvature R, the effective width b, and the thickness t. Given that at least two structural parameters of the elastic transition section are known, the remaining unknown structural parameters of the sheet-like, curved, or corrugated elastic transition section are determined using the following expression: , , , Where: k is the target stiffness of the elastic transition section, and E is the elastic modulus of the material.

[0020] Preferably, a method for adaptive connection between a chip and a heat sink based on shape memory alloy phase change driven includes the following steps: S1: Connect the fixed section to the heat sink. During the connection process, the assembly temperature T a Austenite termination temperature of shape memory alloy connecting components f <Chip operating temperature T w ; S2: Open the clamping section, place the chip at the preset position on the upper surface of the heat sink, and align the clamping section with the chip; S3: Heat the shape memory alloy connecting component to a temperature higher than its austenite termination temperature A. f The shape memory alloy connecting component undergoes a phase change and enters the clamping working state. The clamping section applies clamping force to the chip to achieve a fixed connection between the chip and the heat sink. S4: During chip operation, maintain the temperature above the austenite termination temperature A of the shape memory alloy connecting components. f This keeps the shape memory alloy connecting components in an austenitic state, ensuring a stable clamping force.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Using an alloy with shape memory effect as the clamping connection component, by adjusting the austenite termination temperature A of the shape memory alloy... fBy positioning the shape memory alloy connectors between the chip assembly temperature and the chip operating temperature, the connectors can generate shape recovery force as the temperature rises, thereby applying clamping pressure to the chip. This allows the pressure at the connection interface to automatically adjust with temperature changes. Compared to traditional rigid connection methods, this maintains stable interface pressure during thermal cycling, improving connection reliability. 2. By setting an elastic transition section with elastic deformation capability, the phase transformation recovery force of the shape memory alloy and the elastic deformation work together to buffer and compensate the thermal stress at the connection interface when there is a difference in the coefficient of thermal expansion between the chip and the heat sink material. This reduces stress concentration, reduces the risk of interface cracking, delamination or chip damage, and improves the stability of the shape memory alloy connection component under thermal cycling conditions. 3. By utilizing the properties of shape memory alloys that can deform at low temperatures and automatically recover at high temperatures, shape memory alloy connecting components can be opened by external force during assembly and automatically return to the clamped state after heating. This eliminates the need for solder or screws to fix the chip, enabling reversible assembly and facilitating chip installation, replacement, and maintenance. 4. The present invention is an integral structure and can be prepared by additive manufacturing or precision forming process, so that the thickness, curvature and stiffness of the connecting components can be controlled, thereby making it suitable for chip connection scenarios with small size and meeting the requirements of high power density semiconductor devices for miniaturized connection structure. 5. By setting a flexible buffer layer between the clamping section and the chip, the local contact stress between the clamping section and the chip can be reduced, avoiding damage to the chip surface, while ensuring the uniform distribution of clamping force, thereby improving the stability of the connection interface. 6. The present invention is applicable to the connection between semiconductor chips such as silicon, gallium arsenide, and silicon carbide and heat sinks with high thermal conductivity such as diamond, aluminum nitride, silicon carbide, or copper tungsten. While ensuring thermal conductivity, it can compensate for the interface stress caused by thermal expansion differences. It is suitable for application scenarios that require high-reliability heat dissipation structures, such as high-power semiconductor devices, laser chips, and radio frequency power devices. 7. Since the clamping force is provided by the phase transformation recovery force of the shape memory alloy and can be automatically adjusted with temperature changes, the shape memory alloy connecting component of the present invention is not prone to elastic decay or loosening in high temperature environment. Compared with ordinary metal spring or spring structure, it can maintain a stable clamping state in a wider temperature range, thereby improving long-term working reliability. 8. Chip fixation can be achieved without relying on large-area welding or rigid bonding, which can reduce interface thermal resistance and reduce residual stress generated during welding, thereby improving the thermal conductivity stability between the heat sink and the chip. 9. Temperature-responsive clamping is achieved through phase change driving of shape memory alloy, giving the shape memory alloy connecting component thermo-mechanical coupling adaptive characteristics. It can automatically adjust the interface pressure during temperature changes, thus taking into account thermal conductivity, mechanical stability and thermal cycling reliability, and is suitable for packaging structures of high power density electronic devices. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention in its open state; Figure 2 This is a side view of the structure of the present invention in its open state; Figure 3 This is a schematic diagram of the clamping working state of the present invention; Figure 4 This is a schematic diagram of the structure of multiple clamping working states of the present invention; Figure 5 This is a side view of the clamping structure of the present invention in its working state; Figure 6 This is a schematic diagram of the structure of multiple array-type clamping working states of the present invention; Figure 7 This is a flowchart of the connection method of the present invention.

[0023] In the diagram: 1. Heat sink; 2. Fixed section; 3. Elastic transition section; 31. First connecting section; 32. Second connecting section; 33. Intermediate connecting section; 4. Clamping section; 5. Chip; 6. Flexible buffer layer; 7. Metallization layer; 8. Combination unit. Detailed Implementation

[0024] The embodiments of the present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited to the following embodiments. Various changes or substitutions can be made by those skilled in the art without departing from the spirit of the present invention, and all such changes or substitutions should fall within the protection scope of the present invention.

[0025] In the description of this invention, it should be noted that the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] like Figures 1-3As shown, an adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driving includes: a heat sink 1; a shape memory alloy connecting member disposed on the upper surface of the heat sink 1, the shape memory alloy connecting member including a fixed section 2, an elastic transition section 3, and a clamping section 4 connected in sequence; the fixed section 2 is connected to the upper surface of the heat sink 1; the elastic transition section 3 is used to generate controllable deformation in temperature changes, so that the shape memory alloy connecting member generates a restoring force or elastic force, thereby applying at least one of clamping force, pressing force, supporting force or pre-tightening force to the chip 5 placed on the upper surface of the heat sink 1, so as to realize the adaptive connection between the chip 5 and the heat sink 1.

[0027] Shape memory alloy (SMI) connecting components exhibit elasticity in the austenitic state and maintain continuous restoring force within the operating temperature range. These SMI components provide a durable and stable clamping force for chip 5, avoiding performance degradation caused by material creep and aging in traditional rigid or adhesive connections. The three-segment structure (fixed segment 2, elastic transition segment 3, and clamping segment 4) employed in this invention offers excellent design freedom. The clamping segment 4 acts on chip 5 through the deformation of the elastic transition segment 3. The fixed segment 2, elastic transition segment 3, and clamping segment 4 are integrally formed and fabricated using additive manufacturing, selective laser melting, electron beam melting, precision stamping, or micromachining processes. These processes allow for precise control of the thickness, curvature, and stiffness of the SMI components, reducing assembly errors and structural weaknesses caused by multi-component connections, meeting the connection requirements of chips of different sizes, and improving overall strength and reliability. The fixed section 2 is connected to the heat sink 1 by welding, brazing, diffusion bonding, or metal bonding to ensure connection strength and improve interface thermal conductivity. The elastic transition section 3 acts as an elastic hinge, absorbing deformation and adjusting stiffness. The clamping section 4 directly acts on the chip 5, ensuring tight contact between the chip 5 and the heat sink 1 through precisely designed clamping force. The clamping section 4 also effectively reduces interface contact thermal resistance, improves thermal conductivity, and protects the edges of the chip 5 from mechanical damage. The chip 5 can be a semiconductor laser chip, a power device chip, a radio frequency device chip, or a high-power electronic chip.

[0028] Furthermore, the elastic transition section 3 includes a first connecting section 31, an intermediate connecting section 33, and a second connecting section 32 connected in sequence. The first connecting section 31 is connected to the end of the fixed section 2, and the end of the second connecting section 32 is connected to the clamping section 4.

[0029] The three-segment bending structure of the first connecting segment 31, the intermediate connecting segment 33, and the second connecting segment 32 forms a flexible arm structure. The first connecting segment 31 is a bent structure and connects to the fixed segment 2, while the second connecting segment 32 is a wave-shaped or curved structure and connects to the clamping segment 4, forming an elastic transition region with different stiffness, thereby improving the thermal stress compensation capability. When the chip 5 and the heat sink 1 experience relative displacement due to the difference in their thermal expansion coefficients, this structure absorbs the thermal mismatch displacement through the bending deformation of the elastic transition segment 3, reducing the thermal stress at the corners of the chip 5 and preventing the chip 5 from cracking due to stress concentration. The three-segment design can optimize the geometric parameters of each segment separately, independently satisfying the often contradictory requirements of "providing sufficient clamping force" and "adapting to thermal deformation." This structure ensures that after the shape memory alloy connecting component undergoes phase transformation recovery, the resultant force applied by the clamping segment 4 is closer to being perpendicular to the surface of the chip 5. Compared to the lateral force that is easily generated by a single-bend structure, the three-section design effectively reduces the tangential force component that pushes the chip 5 away from the preset position, ensuring the long-term stability of the chip 5's positioning accuracy and contact state on the heat sink 1.

[0030] Furthermore, a flexible buffer layer 6 is provided at the end of the clamping section 4, and the flexible buffer layer 6 is made of at least one of indium, gold, silver, tin, and gold-tin alloy.

[0031] A flexible buffer layer 6 is provided at the end of the clamping section 4. The connection methods include, but are not limited to: physical attachment, welding, diffusion bonding, electroplating deposition, vapor deposition or sputtering deposition, and adhesive bonding. The materials selected for the flexible buffer layer 6 all possess excellent thermal conductivity. These high thermal conductivity materials can fully fill the microscopic gaps between the chip 5 and the clamping section 4, forming an efficient heat conduction path, significantly reducing interfacial contact thermal resistance, and ensuring that the heat generated by the chip 5 can be quickly dissipated. The contact between the chip 5 and the clamping section 4 is a solid-solid contact, with numerous microscopic gaps. Under the action of clamping force, the flexible buffer layer 6 can also undergo micro-plastic deformation, actively filling the microscopic unevenness of the contact interface, significantly increasing the effective contact area, and avoiding gaps or stress concentrations that may occur at rigid contact interfaces during thermal cycling. The flexible buffer layer 6 can also absorb some micro-displacement, maintaining a stable contact interface over a long period and extending the service life of the shape memory alloy connecting components.

[0032] Furthermore, a metallization layer 7 is provided on the upper surface of the heat sink 1, and the metallization layer 7 is made of at least one of titanium, platinum, nickel, and gold.

[0033] The connection methods between the metallization layer 7 and the heat sink 1 include, but are not limited to: physical vapor deposition (PVD), chemical vapor deposition (CVD), magnetron sputtering, evaporation deposition, electroplating deposition, and electroless plating. As an intermediate transition layer, the metallization layer 7 improves the stability of welding or diffusion connections and prevents oxidation of the surface of high thermal conductivity materials from affecting thermal conductivity. The metallization layer 7 also forms an active interface on the upper surface of the heat sink 1, achieving a strong bond with the fixing section 2, solving the problem of direct connection between dissimilar materials. The metallization layer 7 also provides a stable working position for the chip 5. The metallization layer 7 forms a continuous and dense metal-metal interface with the heat sink 1, eliminating microscopic gaps, significantly reducing the thermal resistance of the connection interface, and ensuring efficient heat transfer from the chip 5 through the clamping section 4, the elastic transition section 3, and the fixing section 2 to the heat sink 1.

[0034] Titanium has extremely strong chemical activity and excellent adhesion, which can form a strong chemical bond or mechanical anchor with the surface of heat sink 1, ensuring that the metallization layer 7 will not peel off or delaminate during subsequent welding, brazing or bonding processes, thus providing a stable and reliable connection foundation for the fixed section 2.

[0035] Both platinum and nickel have dense crystal structures and low diffusion coefficients, which can maintain the stability of the interface microstructure, avoid connection failure caused by interface embrittlement, and significantly improve the long-term reliability of shape memory alloy connecting components.

[0036] The gold surface does not readily form a dense oxide film, allowing for direct welding, brazing, hot-press bonding, or ultrasonic bonding under normal atmospheric conditions without special treatment. This provides significant process convenience for the connection between shape memory alloy connecting components and heat sink 1, while ensuring low contact resistance and low thermal resistance at the connection interface.

[0037] Furthermore, the heat sink 1 material is at least one of diamond, silicon carbide, aluminum nitride, copper-tungsten alloy or high thermal conductivity ceramic.

[0038] The materials selected for heat sink 1 all possess extremely high thermal conductivity, enabling rapid conduction of heat generated by chip 5 to the external heat dissipation system, effectively reducing the junction temperature of chip 5 and improving its efficiency and reliability. Using these materials fundamentally reduces the difference in thermal expansion coefficients between chip 5 and heat sink 1, lowering thermal stress generated during thermal cycling and enhancing the structure's resistance to thermal fatigue. Furthermore, these materials are excellent electrical insulators. When chip 5 requires electrical isolation from heat sink 1, these materials simplify the insulation design, eliminating the need for additional insulation layers and avoiding the introduction of additional thermal resistance.

[0039] Furthermore, the shape memory alloy connecting component material adopts at least one of nickel-titanium shape memory alloy, copper-based shape memory alloy, or iron-based shape memory alloy.

[0040] The preferred material is a nickel-titanium shape memory alloy, with a Ni atomic percentage of 49 at.% to 51 at.%. All selected materials for the shape memory alloy connecting components exhibit reversible martensitic phase transformation characteristics, enabling them to generate significant shape recovery rates and recovery stresses upon temperature changes, thus providing a strong and stable clamping force for chip 5. Shape memory alloys possess excellent mechanical properties, including high tensile strength, high fatigue strength, and good ductility, maintaining a stable mechanical response during repeated thermal cycling. After appropriate heat treatment, the selected materials maintain stable phase transformation characteristics and recovery force output during multiple phase transformation cycles, without easily experiencing performance degradation. This thermal cycling stability is particularly important for applications where chip 5 requires repeated power-on / off cycles and temperature cycling, ensuring that the shape memory alloy connecting components continuously provide reliable clamping force throughout their entire service life.

[0041] Furthermore, the austenite termination temperature A of the shape memory alloy connecting component... f The temperature ranges from 60℃ to 150℃.

[0042] Different austenite termination temperatures A can be obtained by selecting different materials for shape memory alloy connecting components. f Different austenite termination temperatures A can also be achieved through at least one of the following methods. f Changing the alloy composition, heat treatment state, prestress state, structural dimensions, and structural stiffness. The temperature of shape memory alloy connecting components is above their austenite termination temperature A. f When in the austenitic state, it generates shape recovery force and maintains a stable clamping force. The shape memory alloy connecting component maintains a reversible clamping state during cooling or reheating, thereby achieving a reversible assembly connection between chip 5 and heat sink 1, and maintaining a stable clamping force under repeated thermal cycling conditions. The temperature range of 60℃ to 150℃ is controllable, and in existing technologies, it can be heated by a heating wire to keep it in the austenitic state.

[0043] Furthermore, the elastic transition section 3 adopts a thin sheet structure, and its shape is one of corrugated, serpentine, arc, S-shaped, multi-level bending, or periodic curved surface structure. The thickness of the shape memory alloy connecting component is 0.05mm~0.2mm.

[0044] The shape memory alloy connecting component includes a fixed section 2, an elastic transition section 3, and a clamping section 4, all three having the same width and thickness. The curved shape of the elastic transition section 3 compensates for the difference in thermal expansion between the chip 5 and the heat sink 1. More specifically, the side of the first connecting section 31 near the middle connecting section 33 has a larger curvature wave structure, while the side of the second connecting section 32 near the clamping section 4 has a smaller curvature wave structure, thus forming elastic regions with different stiffnesses to improve the thermal stress compensation capability. The combination of the L-shaped bending structure of the first connecting section 31 and the wave-shaped curved surface structure of the elastic transition section 3 allows the elastic transition section 3 to deform in multiple directions, thereby effectively absorbing the thermal stress generated between the chip 5 and the heat sink 1 due to the difference in thermal expansion coefficients, reducing the risk of cracking, delamination, and interface failure. The thin sheet structure has a smaller moment of inertia in the thickness direction, resulting in lower equivalent stiffness in the horizontal direction. When absorbing the thermal mismatch displacement between chip 5 and heat sink 1, the elastic transition section 3 mainly relies on its own elastic bending deformation to significantly reduce the mechanical stress transmitted to the corners of chip 5, effectively protecting chip 5 from thermal cycling damage. The sheet-like structure has a large surface area to volume ratio, which can quickly absorb heat and uniformly heat up during the heating process, enabling the shape memory alloy connecting components to complete the martensitic to austenitic phase transformation in a short time. The sheet-like structure uses very little material, making it suitable for weight-sensitive applications such as aerospace and mobile terminals.

[0045] Furthermore, the structural parameters of the elastic transition segment 3 include: the length of the elastic transition segment 3 before deformation, the effective bending length L, the radius of curvature R, the effective width b, and the thickness t. Given at least two known structural parameters of the elastic transition segment 3, the remaining unknown structural parameters of the sheet-like, curved, or corrugated elastic transition segment 3 are determined using the following expression: , , , Where: k is the target stiffness of the elastic transition section 3, and E is the elastic modulus of the material; More specifically, the calculation process for elastic transition segment 3 is as follows: Based on the difference in thermal expansion coefficients between chip 5 and heat sink 1 Temperature changes Calculate thermal strain Thermal mismatch displacement : Thermal deformation:

[0046] in: and These are the coefficients of thermal expansion of chip 5 and heat sink 1, respectively. Thermal mismatch displacement for:

[0047] Where: L c The feature length of chip 5; Based on the equivalent elastic modulus E eq Calculate the thermal stress at the connection interface : Corresponding thermal stress:

[0048] To achieve thermal stress compensation, the restoring force generated in the elastic transition section 3 during the phase transition must satisfy:

[0049] The recovery stress generated in the elastic transition section 3 during the phase transition is:

[0050] Where: C is the material constant, T is the current temperature, and A f This is the austenite termination temperature; Phase transition restoring force of elastic transition segment 3:

[0051] in: Let be the effective force-bearing area of ​​clamping segment 4. Since the thickness and width of clamping segment 4 are the same as the effective width b and thickness t of elastic transition segment 3, we can obtain:

[0052] To verify the equivalent force caused by thermal mismatch, the effective load area corresponding to a single clamping segment 4 is taken as the same force-bearing area, and the equivalent force of thermal mismatch is calculated. Thermal mismatch equivalent effect is:

[0053] like This indicates that the restoring force generated by the clamping section 4 during the phase transition can compensate for the thermal mismatch caused by the difference in thermal expansion. The clamping force of clamping segment 4:

[0054] Where: A is the chip contact area, P is the interface contact pressure, and P should satisfy: Pmin ≤ P ≤ Pmax, where Pmin is determined based on thermal conductivity requirements, and Pmax is determined based on the chip material strength. To ensure that the elastic force and phase transition restoring force of clamping segment 4 work together, the total force of clamping segment 4 must satisfy: 。

[0055] Furthermore, based on the above structure, a method for adaptive connection between a chip and a heat sink driven by shape memory alloy phase change is provided, comprising the following steps: S1: Connect the fixed section 2 to the heat sink 1. During the connection process, the assembly temperature T a Austenite termination temperature of shape memory alloy connecting components f <Chip operating temperature T w ; S2: Put the clamping section 4 in the open state, place the chip 5 on the preset position on the upper surface of the heat sink 1, and make the clamping section 4 correspond to the chip 5; S3: Heat the shape memory alloy connecting component to a temperature higher than its austenite termination temperature A. f The shape memory alloy connecting component undergoes a phase change and enters the clamping working state. The clamping section 4 applies a clamping force to the chip 5 to achieve a fixed connection between the chip 5 and the heat sink 1. S4: During the operation of chip 5, maintain the temperature above the austenite termination temperature A of the shape memory alloy connecting component. f This keeps the shape memory alloy connecting components in an austenitic state, ensuring a stable clamping force.

[0056] Based on the above structure and connection method, the present invention provides two specific embodiments.

[0057] Example 1: In this example, chip 5 is a SiC power chip, and heat sink 1 is a diamond heat sink. Due to the significant difference in thermal expansion coefficients between the SiC power chip and the diamond heat sink, large thermal stresses are easily generated at the connection interface during temperature changes. To improve the reliability of the connection interface, this example quantitatively designs the structural parameters of the shape memory alloy connecting component, ensuring that the restoring force generated during the phase transformation of the shape memory alloy connecting component matches the stress generated by thermal expansion, thereby achieving thermal stress compensation.

[0058] The coefficient of linear expansion of SiC chips is The coefficient of linear expansion of a diamond heat sink is . Assume the chip assembly temperature is... =25℃, chip operating temperature is =125℃, the temperature change is The thermal strain caused by the difference in thermal expansion is Substituting the values, we get: .

[0059] In this embodiment, the feature length of chip 5 is... The displacement due to thermal mismatch caused by the difference in thermal expansion is 2.0 mm. Substituting the values, we get: .

[0060] Equivalent elastic modulus This is the equivalent parameter under the combined action of chip 5, heat sink 1, and the connection interface. Its value can be estimated by engineering based on the elastic modulus range of the material or obtained through finite element analysis. It is preferably taken as 50 GPa to 300 GPa. In this embodiment, it is taken as... The thermal stress generated at the connection interface is: Substituting the values, we get: .

[0061] To achieve thermal stress compensation, the recovery stress generated by the elastic transition section 3 within the operating temperature range must satisfy the following: .

[0062] In this embodiment, a NiTi shape memory alloy is selected, and its austenite termination temperature is set as follows: Satisfy: T a f <T w The recovery stress generated during the phase transformation of shape memory alloy connecting components can be expressed by the following engineering approximation: Where C is a material constant, representing the proportionality between the recovery stress of the shape memory alloy and the temperature change. Its value can be obtained experimentally or by referring to material performance data, and is typically taken as 1–5 MPa / ℃; in this embodiment, it is taken as 2.5 MPa / ℃. The operating temperature is T = 125℃. Substituting these values, we get: .

[0063] In this embodiment, the width of the clamping segment 4 is the effective width of the elastic transition segment 3: b = 2.0 mm, and the thickness of the clamping segment 4 is the thickness of the elastic transition segment 3: t = 0.10 mm. Therefore, the effective force-bearing area is: The restoring force generated in the elastic transition section 3 during the phase transition is: Substituting the values, we get: .

[0064] To verify the equivalent force caused by thermal mismatch, the effective load area corresponding to a single clamping segment 4 is taken as the same force-bearing area. The thermal mismatch equivalent effect is: Substituting the values, we get: =9 N.

[0065] Therefore, it can be seen that: This demonstrates that the restoring force generated during the phase transformation of shape memory alloy connecting components can compensate for the thermal mismatch caused by differences in thermal expansion.

[0066] To ensure that the elastic force and phase transition restoring force of clamping segment 4 work together, the total force of clamping segment 4 must satisfy the following: .

[0067] ​Where k is the equivalent stiffness of the elastic transition section 3. For the thin-plate elastic connector, its bending stiffness is: k = 3EI / L 3 .

[0068] Where E is the elastic modulus of NiTi in the austenitic state, and in this embodiment, E = 70 GPa.

[0069] L is the effective length of the elastic transition section 3, which is taken as L = 3.0 mm in this embodiment. Its moment of inertia is: I = bt 3 / 12, substituting it in, we get: .

[0070] Substituting this into the stiffness formula, we get: k≈1.30 N / mm. Therefore, the elastic force contributed by the elastic transition section 3 is: kδ=0.00078 N. Thus, the total clamping force is: F=0.00078+22.5≈22.5 N.

[0071] In this embodiment, the chip contact area between chip 5 and the chip clamping structure 4 is: A = 25 mm. 2 The average contact pressure at the connection interface is: P = F / A = 22.5 / 25 = 0.90 MPa.

[0072] The average contact pressure P should satisfy: Pmin ≤ P ≤ Pmax, where Pmin is determined based on thermal conductivity requirements and Pmax is determined based on the chip material strength. In this embodiment, Pmin is preferably 0.3 MPa and Pmax is preferably 5 MPa. The average contact pressure P in this embodiment is within the preferred range, ensuring thermally conductive contact without causing localized damage to the chip.

[0073] For the corrugated or curved elastic transition segment 3, its equivalent stiffness and radius of curvature R can be approximated by the following relationship: REt 3 / 12kL.

[0074] Substituting E=70000 MPa, t=0.10 mm, k=1.30 N / mm, and L=3.0 mm, we get: R≈1.50 mm.

[0075] Therefore, in this embodiment, the elastic transition section 3 can be designed as a corrugated structure with a curvature radius of approximately 1.5 mm.

[0076] Furthermore, in this embodiment, multiple shape memory alloy connecting components can constitute a combined unit 8, and different combined units 8 can have different austenite termination temperatures A. f ,For example: Central Unit: A f1 =70°C Intermediate Unit: A f2=80°C Edge unit: A f3 =90°C Satisfy: A f1 f2 f3 When multiple combined units 8 have different austenite termination temperatures A f During the heating process, each of the combined units 8 deforms sequentially and generates restoring force, causing the clamping force to be gradually applied according to the temperature. The total clamping force can be expressed as:

[0077] Among them, each component It is gradually activated within different temperature ranges.

[0078] With the single austenite termination temperature A f Compared to other structures, this phased loading method can effectively reduce the instantaneous growth rate of clamping force, reduce sudden changes in interface pressure, thereby reducing local stress concentration and impact stress, improving the uniformity of stress distribution at the connection interface, and enhancing the reliability of the structure under thermal cycling conditions.

[0079] The preferred material for shape memory alloy connecting components is nickel-titanium shape memory alloy, but it can also be any of copper-based or iron-based shape memory alloys. Its austenite termination temperature A... f Preferably, the temperature is between 60℃ and 150℃, and the austenite termination temperature A of the shape memory alloy connecting member is... f Satisfy: Assembly temperature T a Austenite termination temperature A f <Chip operating temperature T w The elastic transition section 3 is below the austenite termination temperature A. f When in the martensitic state, it can undergo reversible deformation under external force to facilitate chip 5 assembly; when the temperature rises to the austenite termination temperature A... f At this point, the elastic transition section 3 undergoes a phase transition and generates a shape recovery force, causing the clamping section 4 to move toward the chip 5, thereby applying a stable and continuous clamping pressure to the chip 5.

[0080] The phase change driven clamping method described above enables an adaptive connection between chip 5 and heat sink 1 without the need for screws or rigid clamping structures, and maintains a stable clamping state during thermal cycling. The fixing segment 2 is preferably connected to heat sink 1 by welding, brazing, diffusion bonding, or metal bonding to ensure a strong connection and improve interface thermal conductivity.

[0081] ​​In this embodiment, the elastic transition section 3 is used to generate elastic deformation during temperature changes to compensate for the difference in thermal expansion between the chip 5 and the heat sink 1. The elastic transition section 3 can be at least one of a curved structure, a corrugated structure, a serpentine structure, an arc structure, an S-shaped structure, or a curved surface structure.

[0082] The first connecting section 31 has an L-shaped bend structure. The side of the first connecting section 31 closest to the middle connecting section 33 has a wave structure with a larger curvature, while the side of the second connecting section 32 closest to the clamping section 4 has a wave structure with a smaller curvature. This creates elastic regions with different stiffnesses to improve thermal stress compensation capabilities. The combination of the L-shaped bend structure and the wave-shaped curved surface structure allows the elastic transition section 3 to deform in multiple directions, effectively absorbing the thermal stress generated between the core 5 and the heat sink 1 due to the difference in thermal expansion coefficients, thus reducing the risk of cracks, delamination, and interface failure.

[0083] The aforementioned process enables precise control over the structural thickness, curvature, and stiffness to meet the connectivity requirements of chips 5 of different sizes. The unibody structure reduces assembly errors and structural weaknesses caused by connecting multiple components, thereby improving overall strength and reliability.

[0084] like Figure 7 As shown, after the shape memory alloy connecting component is connected to the heat sink 1, the chip 5 is clamped and connected through the following steps: (1) The connection structure provided by the present invention is placed at a temperature lower than its austenite termination temperature A. f In this environment, the shape memory alloy connecting component is in a martensitic state. Utilizing its elastic and reversible deformation characteristics, the clamping section 4 is gently pried open by external force, leaving enough space to place the chip 5. The chip 5 to be clamped is placed at the preset clamping position on the surface of the metallization layer 7, ensuring that the lower surface of the chip 5 is tightly attached to the metallization layer 7. At the same time, the position of the chip 5 is adjusted so that the flexible buffer layer 6 of the clamping section 4 corresponds to the upper surface or edge of the chip 5. (2) Release the external force applied to the clamping section 4, and gradually increase the temperature until it is higher than the austenite termination temperature A of the shape memory alloy connecting component. f The shape memory alloy connecting component transforms from martensitic to austenitic state, entering the clamping working state and applying a continuous and stable clamping force to chip 5; (3) After clamping, check the clamping status of chip 5 to confirm that chip 5 is not offset, the clamping force is uniform, the fixed section 2 is firmly connected to the heat sink 1, and there is no stress concentration in the elastic transition section 3. Maintain the temperature above the austenite termination temperature A. f This allows the shape memory alloy connecting components to be in an austenitic state, thus achieving stable clamping of chip 5.

[0085] Using the above method, a stable connection between chip 5 and heat sink 1 can be achieved without the need for screws or solder to fix chip 5, and reliable clamping can be maintained during thermal cycling.

[0086] Example 2: Based on the above examples, this example provides a multi-connection unit array-type shape memory alloy adaptive connection structure, which is suitable for thermal management connections of large-size chips, multi-chip packages, or high-power-density devices.

[0087] like Figures 4-6 As shown, this embodiment includes: heat sink 1, combination unit 8, chip 5 or multiple chips 5a, 5b, 5c, flexible buffer layer 6, and metallization layer 7. Multiple assembly units 8 are fixed to the surface of the metallization layer 7 and are arranged in an array along the edge of the chip 5 or around the chip 5. The multiple assembly units 8 work together to apply uniform clamping force to the chip 5 from multiple directions, thereby improving connection stability. By setting multiple assembly units 8, the deformation of a single assembly unit 8 can be reduced, improving structural reliability.

[0088] (1) Multi-spring array structure: In this embodiment, the combined unit 8 can be multiple independent shape memory alloy connecting components. The multiple combined units 8 can be distributed in the following ways: ring array, rectangular array, symmetrical distribution, four-corner distribution, and polygonal distribution. Preferably, the combined units 8 are arranged around the chip 5 to make the clamping force distribution uniform. When the chip 5 is large, 6, 8 or more combined units 8 can be arranged around the chip 5. Through multi-point clamping, the stress concentration at a single point can be significantly reduced.

[0089] (2) Multi-chip packaging structure: In this embodiment, multiple chips 5a, 5b, and 5c can be disposed on the heat sink 1. For example... Figure 6 As shown, multiple chips 5 are mounted on the heat sink 1, and each chip 5 is held by multiple corresponding combination units 8. The multiple combination units 8 can be set independently or integrated into a single structure. This structure enables multi-chip packaging. This structure is suitable for: power modules, laser arrays, RF modules, and multi-chip packaging systems.

[0090] (3) Three-dimensional elastic structure: In this embodiment, the elastic transition segment 3 is not limited to a planar bending structure, but can also be a three-dimensional elastic structure. The three-dimensional structure can be: a spatial bending structure, a three-dimensional curved surface structure, a mesh structure, a porous structure, or a TPMS structure. The three-dimensional structure can improve the deformation capacity and reduce local stress concentration.

[0091] (4) TPMS Structure: In this embodiment, the elastic transition section 3 can also be a TPMS porous structure. The TPMS structure can be selected as: Gyroid structure, Schwarz P structure, Schwarz D structure, Diamond structure, or IWP structure. The TPMS structure has continuous curved surface characteristics, which can provide low stiffness and high elastic stroke. The TPMS structure also has a large specific surface area, which is beneficial for heat dissipation. Through the TPMS structure, elastic buffering, thermal management, structural lightweighting, and uniform stress distribution can be achieved, thereby further improving the connection reliability of chip 5.

[0092] (5) Gradient stiffness structure: In this embodiment, the elastic transition section 3 can also be a gradient structure. The gradient may include: thickness gradient, curvature gradient, porosity gradient, and composition gradient. Preferably, the stiffness is greater near the fixed section 2 and less near the clamping section 4. This arrangement can improve the deformation capacity. Thermo-mechanical matching can be achieved through the gradient structure.

[0093] In this embodiment, the multiple combined units 8 can be a single-piece structure. For example, an integral frame structure, an integral ring structure, an integral mesh structure, or an integral TPMS structure. Single-piece molding can reduce assembly errors. The single-piece molding method can be additive manufacturing, selective laser melting, electron beam melting, precision stamping, or micromachining. Additive manufacturing preferably uses a NiTi structure.

[0094] In this embodiment, the temperature of the multiple combined units 8 is higher than their austenite termination temperature A. f At this time, multiple combined units 8 undergo phase transitions and generate clamping forces, thereby achieving adaptive clamping connection of chip 5. Through multi-unit coordinated phase transition driving, a stable and uniform clamping force can be obtained, enabling the shape memory alloy connecting components to remain reliable under thermal cycling conditions.

[0095] In this embodiment, different combination units 8 can have different austenite termination temperatures A. f Different austenite termination temperatures A f This can be achieved through the following methods: different alloy compositions, different heat treatment states, different prestressing states, different geometric dimensions, and different structural stiffness. When the temperature increases, each combined unit 8 can be configured according to different austenite termination temperatures A. f Phase transformations occur sequentially, thus achieving a staged clamping process. This is achieved by setting different austenite termination temperatures A. f The combined unit 8 enables gradual loading of the clamping force, thereby reducing instantaneous stress concentration and improving the stability of the shape memory alloy connecting component under large temperature difference conditions. Preferably, the combined unit 8 located near the center of the chip 5 has a lower austenite termination temperature A. f The combined unit 8 located near the edge of chip 5 has a higher austenite termination temperature A.f This creates a clamping mode that gradually activates from the inside out during temperature changes, further improving the thermo-mechanical matching capability of the combined unit 8. This is achieved by setting different austenite termination temperatures A... f The multi-unit array structure enables distributed phase change driving, adaptive clamping, and stress gradient control, thereby improving the reliability of the chip 5 package connection structure.

[0096] In this embodiment, by setting multiple combined units 8 and adopting at least one of array structure, TPMS structure or three-dimensional elastic structure, the elastic buffering capacity of the combined units 8 can be significantly improved, the thermal stress concentration can be reduced, the packaging reliability of chip 5 can be improved, and it is suitable for multi-chip and high power density devices.

[0097] Although embodiments of the present invention have been shown and described, those skilled in the art will be able to make various modifications, alterations or substitutions to the above embodiments without departing from the principles and spirit of the present invention. All such modifications, alterations or substitutions should fall within the protection scope of the present invention, which is defined by the appended claims.

Claims

1. A chip-heat sink adaptive connection structure based on shape memory alloy phase change driven, characterized in that, include: Heat sink (1); Shape memory alloy connecting member, the shape memory alloy connecting member is disposed on the upper surface of the heat sink (1), the shape memory alloy connecting member includes a fixed section (2), an elastic transition section (3), and a clamping section (4) connected in sequence; the fixed section (2) is connected to the upper surface of the heat sink (1); the elastic transition section (3) is used to generate controllable deformation in temperature change, so that the shape memory alloy connecting member generates restoring force or elastic force, thereby applying at least one of clamping force, pressing force, supporting force or pre-tightening force to the chip (5) placed on the upper surface of the heat sink (1) to achieve adaptive connection between the chip (5) and the heat sink (1).

2. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The elastic transition section (3) includes a first connecting section (31), an intermediate connecting section (33), and a second connecting section (32) connected in sequence. The first connecting section (31) is connected to the end of the fixed section (2), and the end of the second connecting section (32) is connected to the clamping section (4).

3. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The end of the clamping section (4) is provided with a flexible buffer layer (6), and the material of the flexible buffer layer (6) is at least one of indium, gold, silver, tin, and gold-tin alloy.

4. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The upper surface of the heat sink (1) is provided with a metallization layer (7), and the metallization layer (7) is made of at least one of titanium, platinum, nickel and gold.

5. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The heat sink (1) material is at least one of diamond, silicon carbide, aluminum nitride, copper-tungsten alloy or high thermal conductivity ceramic.

6. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The shape memory alloy connecting component is made of at least one of nickel-titanium shape memory alloy, copper-based shape memory alloy, or iron-based shape memory alloy.

7. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The austenite termination temperature A of the shape memory alloy connecting component f The temperature ranges from 60℃ to 150℃.

8. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The elastic transition section (3) adopts a thin sheet structure, and its shape is one of corrugated, serpentine, arc, S-shaped, multi-level bending, or periodic curved surface structure. The thickness of the shape memory alloy connecting component is 0.05mm~0.2mm.

9. The adaptive connection structure between a chip and a heat sink based on shape memory alloy phase change driven according to claim 1, characterized in that, The structural parameters of the elastic transition segment (3) include: the length of the elastic transition segment (3) before deformation, the effective bending length L, the radius of curvature R, the effective width b, and the thickness t. Given that at least two structural parameters of the elastic transition segment (3) are known, the remaining unknown structural parameters of the sheet-like, curved, or corrugated elastic transition segment (3) are determined by the following expression: ， ， ， Where: k is the target stiffness of the elastic transition segment (3), and E is the elastic modulus of the material.

10. A method for adaptive connection between a chip and a heat sink based on shape memory alloy phase change driven, characterized in that, Using the chip-heat sink adaptive connection structure based on shape memory alloy phase change driven as described in any one of claims 1 to 9, the method includes the following steps: S1: Connect the fixed section (2) to the heat sink (1). During the connection process, the assembly temperature T a Austenite termination temperature of shape memory alloy connecting components f <Chip operating temperature T w ; S2: Put the clamping section (4) in the open state, place the chip (5) on the preset position on the upper surface of the heat sink (1), and make the clamping section (4) correspond to the chip (5); S3: Heat the shape memory alloy connecting component to a temperature higher than its austenite termination temperature A. f The shape memory alloy connecting component undergoes a phase change and enters the clamping working state. The clamping section (4) applies clamping force to the chip (5) to achieve a fixed connection between the chip (5) and the heat sink (1). S4: During the operation of the chip (5), the temperature is maintained above the austenite termination temperature A of the shape memory alloy connecting member. f This keeps the shape memory alloy connecting components in an austenitic state, ensuring a stable clamping force.

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