A multi-layer heat plate and a manufacturing process thereof

Abstract

The present application relates to the field of electronic equipment thermal management and packaging technology, and particularly relates to a multilayer heat plate and a manufacturing process thereof, the heat plate comprising an upper cover plate, a lower cover plate, a capillary layer and an intermediate support layer arranged between the upper cover plate and the lower cover plate, and a heat transfer working medium packaged inside the upper cover plate and the lower cover plate; the intermediate support layer comprises support columns arranged in an array, the top and bottom of the support columns are provided with inverted conical protrusions; the inner side surfaces of the upper cover plate and the lower cover plate are provided with grooves matching the geometric shapes of the inverted conical protrusions, the inverted conical protrusions are embedded in the grooves to form a composite mortise and tenon structure. The purpose of the present application is to provide a multilayer heat plate and a manufacturing process thereof, by combining the mortise and tenon structure on the micro geometric morphology and the transient liquid phase bonding process, high-strength metallurgical bonding is realized without high temperature and high pressure, the capillary structure inside the heat plate is effectively protected, and better heat conduction performance and yield are obtained.

Description

Technical Field

[0001] This invention relates to the field of thermal management and packaging technology for electronic devices, specifically to a multilayer heat sink and its manufacturing process. Background Technology

[0002] Vapor chambers (VCs) are indispensable advanced heat dissipation components in modern high-power electronic systems. With the development of 5G / 6G communication terminals, foldable screen phones, and high-performance computing chips towards extreme thinness and high heat flux density, vapor chambers with ultra-thin, multi-layered structures have become the mainstream trend in the industry.

[0003] However, traditional ultra-thin multilayer heat exchange plates have inherent limitations in their manufacturing process:

[0004] Traditional multi-layer heat spreaders typically employ diffusion bonding during encapsulation, a process that requires high temperature and high pressure. Because the shell of an ultra-thin heat spreader is extremely thin and its internal capillary structure is tiny and fragile, under the macroscopic physical compression of high temperature and pressure, the central support pillars can easily pierce through the upper and lower shells. Simultaneously, the internal micro-capillary structure can be severely flattened or even destroyed, causing the heat spreader to lose its capillary suction force, resulting in dry-burning failure.

[0005] To address these issues, the industry has attempted to reduce the temperature and pressure of diffusion welding, but this often results in insufficient bonding strength and poor airtightness between multilayer structures, making them highly susceptible to delamination and leakage in subsequent high-temperature working environments or drop impacts.

[0006] Therefore, how to resolve the technological contradiction between high-strength support connections and non-destructive protection of capillary structures while maintaining the multi-layered, ultra-thin physical form of the heat spreader is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies of the existing technology, the present invention aims to provide a multi-layer heat spreader and its manufacturing process. By combining the tenon and mortise structure in the micro-geometry with the transient liquid phase bonding process, a high-strength metallurgical bond is achieved without high temperature and high pressure, which effectively protects the capillary structure in the heat spreader and obtains better thermal conductivity and yield.

[0008] This invention is achieved through the following technical solution: In a first aspect, the present invention discloses a multilayer heat exchange plate, which includes an upper cover plate, a lower cover plate, a capillary layer and an intermediate support layer disposed between the upper cover plate and the lower cover plate, and a heat transfer medium encapsulated inside the upper cover plate and the lower cover plate. The intermediate support layer includes support columns arranged in an array, and each support column has an inverted conical protrusion at its top and bottom. The inner surfaces of the upper cover plate and the lower cover plate are provided with grooves that match the geometry of the inverted conical protrusion. The inverted conical protrusion is embedded in the groove to form a composite tenon and mortise structure. The inner wall of the groove is provided with an array of copper wires grown in situ; An intermetallic compound layer is bonded between the contact interface between the inverted conical protrusion and the groove. The intermediate support layer is metallurgically bonded to the upper and lower cover plates through the intermetallic compound layer. The melting point of the intermetallic compound layer is higher than the maximum design operating temperature of the multi-layer heat spreader.

[0009] In conjunction with the first aspect, furthermore, the intermetallic compound layer is an all-intermetallic compound interface generated by a transient liquid-phase bonding reaction, and its phase composition is at least [missing information]. It does not contain tin-based solid solutions.

[0010] In conjunction with the first aspect, further, the diameter of a single copper wire in the copper wire array is 50nm to 200nm, and the length is 1μm to 5μm; The copper wire array is interconnected with the capillary layer and is used to apply suction force to the micro-composite tenon-and-mortise structure region.

[0011] In conjunction with the first aspect, further, the maximum outer diameter of the inverted conical protrusion is greater than the neck diameter at its connection with the main body of the support column; the bottom width of the groove is greater than its opening width.

[0012] Secondly, the present invention discloses a manufacturing process for a multilayer heat exchange plate, which includes the following steps: S100. On the inner surfaces of the upper and lower cover plates, grooves distributed in an array are processed by laser etching or wet chemical etching, and then copper wire arrays are grown in situ on the inner walls of the grooves by chemical bath deposition. S200. A middle support layer with inverted conical protrusions is fabricated using photolithography mask and anisotropic etching process; S300. A tin-containing alloy intermediate layer is deposited on the surface of an inverted conical protrusion or inside a groove by magnetron sputtering. S400. The upper cover plate, capillary layer, intermediate support layer, and lower cover plate are stacked in predetermined positions, so that the inverted conical protrusion is embedded in the groove; under vacuum or inert gas protection, pressure is applied and heated to a set bonding temperature, and the temperature is held for a set time, so that the tin-containing alloy intermediate layer melts and undergoes an isothermal solidification reaction with the copper substrate to generate the intermetallic compound layer; wherein, the set bonding temperature is higher than the melting point of the tin-containing alloy intermediate layer and lower than the melting point of the generated intermetallic compound layer; S500. After cooling, a vacuum is drawn inside the heat transfer medium, and the heat transfer medium is injected and sealed with an airtight seal.

[0013] In conjunction with the second aspect, further, in step S300, the tin-containing low-melting-point alloy intermediate layer is a tin-silver alloy layer, the mass percentage of silver is 2% to 5%, and the thickness of the tin-silver alloy layer ranges from 1 μm to 3 μm.

[0014] In conjunction with the second aspect, furthermore, in step S400, the specific process parameters for the transient liquid phase bonding are as follows: The bonding temperature is 250℃ to 300℃, the applied micro pressure is 0.5MPa to 2.0MPa, and the holding time is 30 minutes to 120 minutes.

[0015] In conjunction with the second aspect, further, in step S100, the step of in-situ growth of the copper wire array by chemical bath deposition includes: The cover plate with etched microgrooves is immersed in an alkaline solution containing copper salt, reducing agent and surfactant, and reacted at a temperature of 60°C to 90°C for a set time. It is then washed with deionized water and dried.

[0016] In conjunction with the second aspect, further, in step S400, the heating method is induction heating or hot plate conduction heating.

[0017] The beneficial effects of this invention are: This invention discloses a multi-layer heat spreader and its manufacturing process. By combining a micro-composite tenon and mortise design with a transient liquid phase bonding process, it solves the problems of capillary collapse and shell puncture that are easily caused by traditional high-temperature and high-pressure diffusion welding. Under low-temperature and low-pressure process conditions, a metal compound layer generated by melting a tin-containing alloy intermediate layer is used to achieve a strong high-temperature metallurgical bond between the multi-layer structures. At the same time, the copper wire array grown in situ on the inner wall of the micro-groove, in conjunction with the tenon and mortise structure, not only enhances the mechanical anchoring force of the interface but also provides additional capillary suction force, enabling the product to maintain excellent heat dissipation performance while possessing extremely high structural reliability. Attached Figure Description

[0018] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0019] Figure 1 This is a cross-sectional view of a heat spreader plate in one embodiment of the present invention.

[0020] Figure 2 This is a flowchart of the manufacturing process of the heat spreader in one embodiment of the present invention.

[0021] Figure Labels Upper cover plate--1, lower cover plate--2, capillary layer--3, intermediate support layer--4, support column--41, inverted conical protrusion--42, groove--5. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used 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.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0025] Example 1 like Figure 1 As shown, this embodiment discloses a multi-layer heat spreader, which has an extremely thin, flat structure and is mainly used for heat dissipation of high heat flux density electronic components (such as CPUs, GPUs, or 5G RF chips). The multi-layer heat spreader mainly includes an upper cover plate 1, a lower cover plate 2, and a capillary layer 3 and an intermediate support layer 4 sandwiched between the upper cover plate 1 and the lower cover plate 2. Within the sealed cavity formed by the upper cover plate 1 and the lower cover plate 2, a suitable amount of heat transfer medium (such as pure water, methanol, or refrigerant) is also encapsulated. The heat transfer medium achieves efficient heat transfer through vapor-liquid phase change circulation within the heat spreader.

[0026] To address the issues of traditional ultrathin vapor chambers easily deforming and bulging under internal steam pressure, and the tendency of traditional high-temperature welding to damage capillary structures, this embodiment features a completely redesigned internal connection and support structure: First, the intermediate support layer 4 serves to maintain the thickness of the steam chamber inside the heat spreader and resist external compression and internal steam pressure. This support layer includes an array of support columns 41. Unlike traditional cylindrical or cuboid columns with flush end faces, in this embodiment, the top and bottom of each support column 41 are provided with micron-sized inverted conical protrusions 42. This inverted conical design is narrower at the root (i.e., where it connects to the main body of the support column 41) and wider at the top.

[0027] To complement this, microgrooves 5 are pre-fabricated on the inner surfaces of the upper cover plate 1 and the lower cover plate 2 (i.e., the side facing the internal cavity), precisely matching the geometry of the aforementioned inverted conical protrusion 42. During assembly, the inverted conical protrusion 42 is embedded into the microgrooves 5, thereby forming a micro-composite mortise and tenon structure at the microscale. This mortise and tenon joint provides extremely strong lateral restraint and vertical mechanical anti-loosening locking force in its physical structure, effectively preventing relative sliding and interlayer peeling of the multi-layer structure during thermal expansion.

[0028] Furthermore, an in-situ grown array of copper nanowires is provided on the inner wall of the microgroove 5. This microstructure has a dual function: on the one hand, the dense copper nanowires greatly increase the specific surface area of ​​the inner wall of the microgroove 5, providing extremely rich reaction attachment points for subsequent metallurgical bonding and significantly enhancing the bonding strength of the interface; on the other hand, when the heat spreader is working, these copper nanowire arrays located in the bonding area of ​​the support column 41 can communicate with the adjacent capillary layer 3. Due to their extremely high porosity and nanoscale gaps, they can provide extremely strong additional capillary suction force in this area, effectively preventing the working fluid from dry burning in the area around the support column 41 and improving the overall ultimate thermal conductivity.

[0029] Finally, an intermetallic compound layer is bonded between the contact interface of the inverted conical protrusion 42 and the microgroove 5. The intermediate support layer 4 achieves a strong metallurgical bond with the upper cover plate 1 and the lower cover plate 2 through this intermetallic compound layer, rather than a simple physical contact or organic adhesive bonding.

[0030] More importantly, the melting point of the intermetallic compound layer is higher than the maximum design operating temperature of the multilayer heat spreader. This means that although the intermetallic compound layer is formed through a liquid-phase reaction at a relatively low temperature (avoiding damage to the capillary layer 3 at high temperatures), once it is formed and solidified, it transforms into a high-melting-point alloy phase. Therefore, when the heat spreader is subsequently installed (such as undergoing SMT reflow soldering) or operates under extreme high-power conditions, this metallurgical bonding layer will not melt or soften again, thus completely ensuring the structural reliability and airtightness of the multilayer heat spreader under high-temperature environments.

[0031] As a preferred embodiment of the present invention, the microstructure composition and reaction mechanism of the intermetallic compound layer are further described in detail: Based on the above embodiments, the intermetallic compound layer between the contact interfaces is an all-metallic compound interface generated based on a transient liquid phase (TLP) bonding reaction.

[0032] Specifically, during the bonding heating stage, the tin-containing alloy intermediate layer deposited at the bonding interface first melts to form a liquid phase. Subsequently, during the holding process at the bonding temperature, the liquid tin undergoes intense atomic interdiffusion and isothermal solidification reactions with the copper substrates on both sides (i.e., the inverted conical protrusions 42 on the support pillars 41 and the pure copper or copper alloy at the bottom of the microgrooves 5). As the reaction progresses, the liquid tin continuously combines with copper, and its microstructure composition ultimately transforms into... These are two intermetallic compound phases.

[0033] The core technology of this embodiment lies in the fact that by precisely controlling the bonding temperature, holding time and the thickness of the initial tin-containing alloy intermediate layer, the liquid tin is completely consumed during the isothermal solidification process, thereby ensuring that the final bonding interface does not contain any tin-based solid solution residue.

[0034] In traditional soldering processes using tin-containing solder, a large amount of unreacted pure tin or tin-based solid solution is typically retained at the center of the solder joint. Because pure tin has an extremely low melting point (around 232°C), when traditional heat spreaders undergo downstream SMT reflow soldering processes (typically reaching peak temperatures of 260°C) after leaving the factory, or are used for extended periods in high-heat-flux-density, extremely hot devices, this residual low-melting-point tin-based solid solution is highly susceptible to secondary melting or softening. This can instantly compromise the internal seal, causing the heat spreader to bulge, delaminate, leak the working fluid, or even fail completely due to internal vapor pressure.

[0035] In contrast, the all-metal intermetallic compound interface constructed in this embodiment fundamentally eliminates the aforementioned risks. The reaction produces... The melting point of the phase is approximately 415℃, while the phase growing closer to the copper substrate... The melting point of the phase is as high as 800°C or more. This means that although the multilayer heat spreader of the present invention is assembled and bonded at a relatively low temperature (e.g., 250°C to 300°C), once its interface is transformed into an all-metal intermetallic compound phase, its withstand temperature jumps directly to over 400°C. This not only endows the heat spreader with extremely high interlayer tensile and shear strength, but also gives it excellent high-temperature thermodynamic stability, making it perfectly compatible with the complex thermal processes of modern semiconductor packaging.

[0036] As a preferred embodiment of the present invention, the specific parameter settings and hydrodynamic effects of the nano-copper wire array are further described in detail: In the above embodiments, the geometric dimensions of the single copper nanowire array grown in situ on the inner wall of the microgroove 5 are strictly controlled within a specific range: the diameter is 50nm to 200nm and the length is 1μm to 5μm.

[0037] First, regarding the diameter of the nanowires, if the diameter of a single nanowire is less than 50 nm, its mechanical strength is too weak, and it is very easy to break or collapse over a large area when micro-pressure is applied during subsequent transient liquid phase bonding, thus failing to play a good micro-anchoring role. On the other hand, if the diameter is greater than 200 nm, the specific surface area of ​​the nanowire array will decrease significantly, which not only reduces the contact area for reaction with the tin alloy interlayer, but also leads to excessively large pores between the nanowires, thereby reducing the micro-capillary force.

[0038] Secondly, regarding the length of the nanowires, if the length is less than 1 μm, the nanowires cannot effectively penetrate the bonding interface and it is difficult to form a three-dimensional network interlocking structure of sufficient depth; if the length is greater than 5 μm, during the liquid phase growth process of chemical bath deposition, the excessively long nanowires are prone to agglomeration and adhesion due to the surface tension, thereby blocking the micropores and hindering the flow of liquid.

[0039] In addition to serving as an interface material for enhanced bonding, the nano-copper wire array also plays an indispensable role as a micro-fluidic channel in the gas-liquid circulation within the heat exchanger. Structurally, the nano-copper wire array extends spatially and achieves physical interconnection and fluid conduction with the main capillary layer 3 inside the heat exchanger.

[0040] In traditional vapor chamber designs, the contact area where the support column 41 meets the upper and lower cover plates 2 is often a solid blind zone lacking capillary structure. When the vapor chamber is operating at its limit under high heat flux density, condensate has difficulty penetrating these blind zones, causing localized dry burning to easily occur around the support column 41, which in turn leads to a sharp increase in overall thermal resistance.

[0041] In the structure of this invention, thanks to the high density and superhydrophilic properties of the aforementioned specific-sized nano-copper wire array, the condensed heat transfer fluid is strongly drawn into the gaps of the micro-composite tenon and mortise structure as it flows through the main capillary layer 3. This is equivalent to adding a layer of nanoscale additional capillary suction force to the solid blind area around the support column 41 within the macroscopic capillary network, greatly delaying the occurrence of local dry burning and significantly improving the critical heat flux density and ultimate heat dissipation power of the multilayer heat sink.

[0042] As a preferred embodiment of the present invention, the specific morphology and tensile resistance mechanism of the mechanical anti-loosening locking structure are further described in detail: In the above embodiments, in order to resist the severe steam pressure fluctuations inside the heat spreader, the present invention employs a special reverse locking design for the geometric cross-section of the micro-composite tenon structure.

[0043] Specifically, the inverted conical protrusion 42 at the end of the support column 41 has a cross-sectional shape similar to a dovetail or mushroom head. Its structural feature is that the maximum outer diameter of the inverted conical protrusion 42 (i.e., the diameter at its furthest and widest point) is greater than the neck diameter at its connection with the main body of the support column 41. Correspondingly, the microgrooves 5 formed by etching on the inner surfaces of the upper and lower cover plates 2 have a cavity-like cross-section that is wider at the inside and narrower at the outside; that is, the bottom width of the microgroove 5 is greater than the opening width of its surface.

[0044] During assembly and bonding, when the inverted conical protrusion 42 is embedded in the microgroove 5, the wider top of the protrusion is firmly locked into the wider bottom cavity of the groove 5, while the narrower opening of the groove 5 tightly binds the thinner neck of the protrusion. After the two are precisely engaged, a physical interference is formed on the Z-axis (i.e., the direction perpendicular to the cover plate surface), constructing an extremely stable mechanical anti-loosening locking structure.

[0045] This unique geometric design allows the internal heat transfer medium to rapidly boil and vaporize when the heat spreader is used for cooling high-power chips, generating enormous internal vapor pressure within the sealed cavity. This pressure forces the upper and lower cover plates 2 to undergo elastic deformation outward, resulting in extremely strong vertical tensile stress at the interface between the support layer and the cover plates.

[0046] In traditional flush-face welding, this vertical tensile stress acts directly on the fragile weld plane, easily leading to weld fatigue fracture and heat spreader bulging failure. However, in the mechanical anti-loosening locking structure of this invention, the vertically outward tensile force is transformed into the mutual compressive stress between the inclined surface of the inverted conical protrusion 42 and the chamfered inner wall of the micro-groove 5. This purely mechanical interlocking mechanism, like thousands of miniature anchors, greatly reduces the stress load on the underlying intermetallic compound layer.

[0047] Tests show that this composite structure improves the peel strength of the multi-layer heat exchanger by several times. It can not only withstand higher internal saturated vapor pressure, but also ensure that the ultra-thin heat exchanger can maintain perfect surface flatness and airtightness when subjected to harsh temperature shock cycles or external mechanical bending.

[0048] Example 2 like Figure 2 As shown, this embodiment discloses a processing technology for manufacturing the multilayer heat spreader in Embodiment 1. This process abandons the traditional high-temperature, high-pressure diffusion welding and instead adopts a low-temperature micro-pressure molding technology based on micro / nano structures and transient liquid phase bonding. Specifically, it includes the following steps: Step S100, Cover plate preparation: First, pure copper or copper alloy foil meeting the thickness requirements is obtained as the upper cover plate 1 and the lower cover plate 2. On the inner surfaces of both, microgrooves 5 distributed in an array are fabricated using high-precision laser mask etching or wet chemical etching processes. To form the aforementioned microgrooves 5 with a wider inner surface and a narrower outer surface, a wet etching solution combining isotropic and anisotropic properties is preferably used, achieved by controlling the lateral drilling rate.

[0049] Subsequently, the cover plate with microgrooves 5 was placed in the reactor, and an array of copper nanowires was grown in situ on the inner wall of the grooves 5 using a chemical bath deposition method. The in-situ growth process ensures that the roots of the copper nanowires and the copper substrate of the cover plate exhibit continuous lattice extension, thus possessing extremely high bonding strength and being less prone to detachment during subsequent assembly.

[0050] Step S200, preparation of the support layer: A copper foil substrate for the intermediate support layer 4 is obtained, and the pattern of the support pillar 41 is defined using double-sided photolithography. Subsequently, an anisotropic etching process (e.g., adjusting the concentration of certain additives in the etching solution to produce significant differences in etching rates on different crystal planes) is used to etch the substrate from top to bottom. By precisely controlling the etching time and the solution ratio, inverted conical protrusions 42, wider at the top and narrower at the bottom, are processed at the top and bottom of the support pillar 41, completing the fabrication of the intermediate support layer 4.

[0051] Step S300, intermediate layer deposition: In a vacuum environment, a very thin tin-containing alloy intermediate layer is deposited on the surface of the inverted conical protrusion 42 (or inside the microgroove 5) using a magnetron sputtering process. The magnetron sputtering process ensures high density, excellent thickness uniformity, and good initial adhesion between the alloy layer and the substrate.

[0052] Step S400, Assembly and transient liquid phase bonding: The processed upper cover plate 1, capillary layer 3 (such as sintered copper powder mesh or multi-layer woven mesh), intermediate support layer 4 and lower cover plate 2 are placed in a high-precision alignment fixture and precisely stacked in the predetermined position so that the inverted conical protrusion 42 on the intermediate support layer 4 is completely embedded in the micro-groove 5 on the cover plate to form a physical fastening.

[0053] The assembled components are then placed in a vacuum heating furnace or an inert gas protected furnace. Under micro-pressure (which is only used to ensure tight bonding between layers and is much lower than that of conventional diffusion bonding, so as not to cause collapse of the capillary layer 3 pores), the components are heated to the set bonding temperature and held at that temperature for the set time.

[0054] The thermodynamic control logic for this step is as follows: the set bonding temperature is higher than the melting point of the tin-containing alloy intermediate layer and lower than the melting point of the generated intermetallic compound layer.

[0055] When the furnace temperature rises above the melting point of the alloy interlayer, the interlayer melts to form an extremely thin liquid phase layer. This liquid phase layer is fully wetted by capillary force within the gap between the microgroove 5 and the inverted conical protrusion 42, and encapsulates the nano-copper wire array. During the subsequent isothermal holding process, the liquid tin undergoes atomic interdiffusion with the solid pure copper on both sides. Due to the metallurgical reaction at the solid-liquid interface, the liquid phase is continuously consumed and undergoes isothermal solidification, eventually transforming completely into a high-melting-point intermetallic compound layer. This process macroscopically achieves welding at low temperatures, yet generates a high-temperature resistant weld.

[0056] Step S500, Injection and Sealing: The bonded and cooled vapor chamber plate semi-finished product is removed from the heating furnace. The internal cavity of the vapor chamber plate is evacuated to a high vacuum state through the reserved liquid injection tail pipe to remove non-condensable gases. Then, a precise amount of heat transfer medium (such as ultrapure water) is injected. Finally, the tail pipe is sealed airtightly by mechanical cold pressure welding or laser pulse welding technology to complete the overall manufacturing of the multi-layer vapor chamber plate.

[0057] As a preferred embodiment of the present invention, a detailed mechanistic and mathematical description is provided regarding the selection of the intermediate layer material and its thickness parameters: In step S300 of the above embodiment, the deposited tin-containing alloy intermediate layer is defined as a tin-silver (Sn-Ag) alloy layer, wherein the mass percentage of silver is controlled between 2% and 5%, and the thickness of the tin-silver alloy layer is strictly controlled between 1 μm and 3 μm.

[0058] First, regarding the selection criteria for the material composition (2%-5% Ag): Pure tin has a melting point of 232°C and is highly prone to Kirkendal voids during solidification, which severely weakens the mechanical strength of the bonding interface. In this embodiment, by incorporating 2% to 5% by mass of silver, a microalloying effect is utilized to form an alloy structure close to the eutectic point (typical eutectic composition is Sn-3.5Ag, melting point reduced to 221°C). This not only further lowers the initial liquid phase formation temperature, but more importantly, during the isothermal solidification process of transient liquid phase bonding, silver atoms precipitate first to form nanoscale... Dispersed phases. These dispersed phases can effectively pin grain boundaries and prevent the aggregation of microscopic voids, thus giving the final intermetallic compound layer excellent fatigue resistance.

[0059] Secondly, regarding the collaborative control model of thickness parameters and core process algorithms: thickness of intermediate layer It is the decisive variable that determines the success or failure of TLP bonding process. If the thickness is less than 1μm, the amount of liquid phase after melting is insufficient to completely fill the gaps caused by the surface roughness of the substrate due to machining, and it is also insufficient to fully wrap the nano-copper wire array in the microgroove 5, which will lead to large-area poor soldering; if the thickness is greater than 3μm, it will lead to the time required for the liquid phase to be consumed, which will seriously slow down the industrial production cycle, and may even fail to complete complete isothermal solidification within the set process time, leaving fatal low-melting-point tin-based residue.

[0060] To achieve efficient industrial production, this embodiment incorporates a thickness-temperature-time dynamic coordinated control algorithm into the control system (such as the PLC control terminal of the heating furnace). This algorithm, based on Fick's second law and the Arrhenius equation, constructs an integral model of liquid phase consumption under non-isothermal heating conditions.

[0061] In the designed bonding process, to ensure that the liquid tin-silver alloy is completely consumed, the initial design thickness is [not specified]. Compared with the actual furnace temperature curve and bonding time The following integral inequality must be satisfied:

[0062] in, The initial thickness of the deposited tin-silver alloy layer (target thickness controlled between 1 μm and 3 μm). This is the stoichiometric volume conversion factor, due to the volume consumed by the liquid phase and the volume of solid intermetallic compounds generated (such as...). The volumes are different. Used to characterize the molar volume expansion or contraction compensation rate during solid-liquid phase transition processes; This refers to the total duration of the bonding process; The intrinsic pre-diffusion factor of copper atoms in liquid tin-silver alloy characterizes the basic diffusion activity of the material. This is the diffusion activation energy of the isothermal solidification reaction, and this value reflects the energy required for atoms to overcome the interfacial energy barrier. For an ideal gas constant, ; For heating furnace over time The temperature is a dynamically changing absolute temperature function (in K). In actual production, equipment includes heating slope, insulation platform, etc. Therefore, temperature is a function that changes with time. Time integration can accurately calculate the cumulative diffusion effect during the heating stage.

[0063] Through the aforementioned dynamic collaborative control algorithm, the production equipment can adjust its operation based on the actual deposition thickness measured at micrometers. (A specific value between 1μm and 3μm), by solving the integral inequality in reverse, the most economical heat preservation time is automatically matched and dynamically calculated. and temperature curve This ensures that, within an extremely thin physical space, perfect liquid-phase filling of nanoscale pores can be achieved, while guaranteeing that the liquid phase is 100% converted into high-melting-point intermetallic compounds in the shortest possible time, thus endowing the manufacturing process with extremely high yield and process robustness.

[0064] As a preferred embodiment of the present invention, the specific process parameter range of transient liquid phase bonding and its underlying multiphysics field collaborative control model are further described in detail: In step S400 of the above embodiment, in order to ensure the bonding quality and internal structure integrity of the multilayer heat spreader, the specific process parameters for transient liquid phase bonding are set as follows: bonding temperature is 250°C to 300°C, applied micro pressure is 0.5MPa to 2.0MPa, and heat preservation time is 30 minutes to 120 minutes.

[0065] The above parameter range is obtained by accurately solving a diffusion-creep multi-field coupling constraint algorithm built into the process control terminal of this invention. The purpose of this algorithm is to solve the problem in a three-dimensional parameter space ( The goal is to find a solution that simultaneously satisfies two opposing physical requirements: complete alloying of the intermediate layer (to prevent secondary melting) and zero collapse of the capillary structure (to maintain heat dissipation performance).

[0066] Specifically, the control algorithm consists of two mutually constraining high-order nonlinear integral-differential equations: 1. Metallurgical diffusion completeness model (lower bound constraint): To ensure the initial thickness is The tin-containing alloy intermediate layer is completely transformed into a high-melting-point intermetallic compound, and the parabolic growth integral consumed by the liquid phase must be greater than or equal to the initial thickness of the liquid phase. The first formula of the algorithm is:

[0067] 2. Capillary structure anti-creep collapse model (upper limit constraint): Heating and applying micro pressure During the process, the porous capillary layer 3 undergoes high-temperature viscoplastic creep, leading to a decrease in porosity. To ensure capillary suction force, its cumulative creep strain (pore collapse rate) must be strictly limited. Based on Norton's creep law, the second formula of the algorithm is:

[0068] in, The real-time growth thickness of the intermetallic compound layer; Bonding temperature over time The changing dynamic function (unit: K); The macroscopic micro-pressure (in MPa) applied to the surface of the heat exchange plate. This refers to the total time for heat preservation and pressurization; The growth rate constant of the interfacial reaction depends on the lattice matching degree between tin-silver and copper; The activation energy for inter-atomic diffusion characterizes the energy barrier that needs to be overcome to form an IMC. The phase change volume shrinkage coefficient; is the viscoplastic creep constant of the capillary layer 3 copper-based material; The creep stress index, typically for porous copper networks, is between 3 and 5, indicating that a slight increase in pressure leads to an exponential increase in the collapse rate. The deformation activation energy for high-temperature creep deformation of porous frameworks; This represents the cumulative loss due to the porosity of the capillary layer 3. The maximum allowable pore loss threshold for the system is, in this embodiment, limited to no more than 5% of the initial porosity; The control system, through joint solution of the above partial differential coupled equations, found that if the bonding temperature is below 250℃ or the time is less than 30 minutes, integral formula 1 cannot be satisfied, resulting in incomplete liquid phase conversion and leaving a potential low melting point; however, if a rapid response is desired, the pressure... Increase to above 2.0 MPa, or increase the temperature. Increase to above 300°C (even with shortened time) ), due to the pressure index in Formula 2 The power-law amplification effect and the exponential term The surge, the calculation result of integral formula 2 It will quickly break through the safety threshold. This causes the capillary network to be instantly flattened, completely losing its capillary suction ability.

[0069] Therefore, 250℃ to 300℃, 0.5MPa to 2.0MPa, and 30 minutes to 120 minutes are the optimal values ​​that the system has determined after countless iterations using this algorithm. Within this parameter range, the micro-pressure only serves to overcome surface tension and promote liquid phase wetting, without triggering macroscopic creep; at the same time, by extending the time integral in the low-temperature region, the transformation of all-metallic compounds within a micrometer-scale thickness is ultimately achieved.

[0070] As a preferred embodiment of the present invention, the in-situ growth process of the copper nanowire array and the reaction kinetics control algorithm are described in detail: In step S100 of the above embodiment, in order to controllably grow a nano-copper wire array with a specific aspect ratio (such as a diameter of 50nm-200nm and a length of 1μm-5μm as described in Example 1) on the inner wall of the microgroove 5, the present invention employs a chemical bath deposition method with a strictly controlled formulation.

[0071] The specific operational steps include: using the cover plate with the completed microgroove 5 etching as the deposition substrate, immersing it vertically or at an angle into a pre-prepared alkaline reaction solution. This solution system mainly comprises: Copper salts (such as copper nitrate or copper sulfate) provide the growth... Ion source; Reducing agents (such as hydrazine hydrate or ascorbic acid) are used to... Reduced to elemental copper atoms; Surfactants (such as ethylenediamine EDA or hexadecylamine HDA) are used not only as alkalinity regulators but also as crystal facet end-capping agents.

[0072] Set the reaction system to an alkaline environment (pH typically controlled between 10 and 12), and precisely control the reactor temperature between 60°C and 90°C, setting the reaction time. After the reaction is complete, quickly remove the lid, rinse repeatedly with deionized water to terminate the reaction, and dry under vacuum or inert gas.

[0073] Whether nanocrystals can grow into linear shapes (i.e., one-dimensional anisotropic growth) instead of spherical shapes depends entirely on the adsorption and capping ability of surfactants on specific crystal faces, as well as the reduction rate at a specific temperature.

[0074] To accurately target the desired nanowire length (1 μm to 5 μm), the fabrication apparatus of this invention incorporates a crystal plane-selective anisotropic growth integral model. This model abandons traditional linear estimation and employs high-order differential equations to calculate the dynamic growth length in real time as precursor concentration decays and temperature fluctuations occur.

[0075] Nano copper wires in axial cumulative growth length over time Satisfies the following integral equation:

[0076] in, For the set reaction time At the end, the final axial length of the copper nanowire; Let be the intrinsic reduction rate constant of copper ions under unimpeded conditions; This represents the molar concentration of the surfactant in the solution. Let be the Langmuir adsorption equilibrium constant of surfactant molecules on a specific crystal plane of copper, and the terms within square brackets be... The steric hindrance adjustment factor characterizes the effective fraction of active crystal faces that are not covered by surfactants and are available for continuous deposition of copper atoms. It is the apparent activation energy of a chemical reduction reaction; It is the ideal gas constant; The absolute temperature of the solution system is used as the reference temperature. In this embodiment, the target temperature is locked at 60°C to 90°C because... The exponential decay of the term results in an extremely slow reaction and a tendency to grow into amorphous particles; if If the reduction rate is too fast, the capping agent will not have enough time to be adsorbed, and the nanowires will undergo severe radial expansion and thickening. For a moment The ratio of the copper precursor concentration to the initial concentration. Since the reaction takes place in a closed bath, copper ions are continuously consumed, and this ratio decreases over time. This represents the reaction order of the redox reaction.

[0077] In actual mass production, this algorithm is compiled into the low-level control logic of the PLC. The equipment sensors collect the current concentration of the solution in real time. and temperature By performing definite integral calculations over time, the instantaneous length of the copper nanowire is accurately predicted. When the calculated integral value reaches the set target length (e.g., 3.5 μm), the system automatically issues a command to drain the reaction solution or inject a terminator. The introduction of this mathematical model completely eliminates batch-to-batch dimensional deviations caused by solution concentration decay or slight temperature fluctuations, ensuring that the in-situ grown nanocapillary structures have extremely excellent consistency and reliability.

[0078] As a preferred embodiment of the present invention, the heating method, parameter threshold limitation, and its protection mechanism for the porosity of the capillary layer 3 are described in detail: In step S400 of the above embodiment, the heating method for achieving transient liquid phase bonding is preferably induction heating or hot plate conduction heating.

[0079] When induction heating is used, eddy currents are generated in the metal shell of the heat exchanger using an alternating magnetic field, which can achieve an extremely high heating rate and localized heat concentration, reducing the overall heat load of the capillary layer 3. When heat exchanger conduction heating is used, it can provide excellent planar temperature uniformity, ensuring that the conversion rate of intermetallic compounds in each area of ​​the large-size heat exchanger is highly consistent.

[0080] Regardless of the heating method used, the core anti-collapse mechanism of this embodiment lies in the strict control of the thermodynamic and kinetic boundaries: since the set bonding temperature is strictly lower than the annealing temperature of the substrate (pure copper or copper alloy), and the macroscopic micro pressure applied to the surface of the cover plate is strictly less than 2.0 MPa, the porosity of the capillary layer 3 decreases by less than 5% after undergoing a complete bonding thermal cycle.

[0081] In traditional diffusion bonding processes, to facilitate the cross-interface diffusion of pure copper atoms, it is typically necessary to raise the temperature to over 800°C (far exceeding the recrystallization annealing temperature of copper at approximately 400°C) and apply a physical pressure exceeding 10 MPa. When the porous capillary layer 3 is in an annealed softened state and subjected to high pressure, its internal microscopic framework network undergoes catastrophic plastic compaction and collapse, resulting in the loss of capillary suction.

[0082] To accurately predict and avoid this failure mode in industrial mass production, the process control system of this invention incorporates a porous skeleton viscoplastic compaction integral model. This algorithm model combines a modified Shima-Oyane porous media yield criterion with a temperature-dependent thermal softening function, abandoning simple static stress checks and employing high-order differential equations to dynamically calculate porosity loss throughout the bonding cycle.

[0083] The cumulative decrease in porosity of capillary layer 3 The calculation formula is as follows:

[0084] in, To achieve the set bonding time The total loss rate of capillary porosity (process target limited to within 5%). The macroscopic compaction morphology coefficient of the porous medium is related to the weaving method of the capillary layer 3 or the particle size distribution of the sintered powder. The external micro-pressure applied dynamically over time (constrained by hardware, its maximum peak value is strictly limited to) MPa); For capillary layer 3 in Instantaneous porosity at time t, in the denominator The porosity strengthening factor indicates that as the porosity decreases slightly, the material becomes compacted, and its ability to resist further deformation is enhanced. (geometric index); For copper matrix framework at transient temperature The macroscopic yield strength function under the following conditions, when the bonding temperature is... Below the annealing temperature of copper At approximately 400°C, the matrix did not recrystallize. Maintain at a high level (e.g., hundreds of MPa); once the annealing temperature is exceeded, A precipitous drop is expected.

[0085] The stress sensitivity index for viscoplastic deformation; This is a thermally activated term for viscoplastic deformation. The higher the temperature, the easier it is for atomic dislocations to slip, and the easier it is for the skeleton to undergo creep compaction. In the above formula, the dimensionless stress ratio within the parentheses plays a decisive role. The control system of this invention is proven through this algorithmic logic that, due to the peak pressure... Locked in Extremely low threshold temperature, while limiting the maximum bonding temperature to below 300°C (ensuring...) ), so that the denominator Always remain much larger than molecules The magnitude.

[0086] Therefore, the stress fraction is extremely small, plus the exponent The attenuation effect causes the value of the integrand to approach zero throughout the bonding cycle. This, from a rigorous mechanical and materials science perspective, confirms that the micro-pressure TLP bonding process can achieve porosity reduction. This ensures the protection of the target, thus preserving the best working fluid reflux and heat dissipation performance in the finished vapor chamber.

[0087] In summary, the multilayer heat spreader and its manufacturing process of this invention, through the combination of micro-composite tenon and mortise design and transient liquid phase bonding process, solves the problems of capillary collapse and shell puncture that are easily caused by traditional high-temperature and high-pressure diffusion welding; under low-temperature and low-pressure process conditions, the intermetallic compound layer generated by melting the tin-containing alloy intermediate layer achieves a strong high-temperature metallurgical bond between the multilayer structures; at the same time, the copper wire array grown in situ on the inner wall of the micro-groove 5, in conjunction with the tenon and mortise structure, not only enhances the mechanical anchoring force of the interface, but also provides additional capillary suction force, so that the product maintains excellent heat dissipation performance while possessing extremely high structural reliability.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A multi-layer heat spreader, characterized in that, It includes an upper cover plate, a lower cover plate, a capillary layer and an intermediate support layer disposed between the upper cover plate and the lower cover plate, and a heat transfer medium encapsulated inside the upper cover plate and the lower cover plate; The intermediate support layer includes support columns arranged in an array, and each support column has an inverted conical protrusion at its top and bottom. The inner surfaces of the upper cover plate and the lower cover plate are provided with grooves that match the geometry of the inverted conical protrusion. The inverted conical protrusion is embedded in the groove to form a composite tenon and mortise structure. The inner wall of the groove is provided with an array of copper wires grown in situ; An intermetallic compound layer is bonded between the contact interface between the inverted conical protrusion and the groove. The intermediate support layer is metallurgically bonded to the upper and lower cover plates through the intermetallic compound layer. The melting point of the intermetallic compound layer is higher than the maximum design operating temperature of the multi-layer heat spreader.

2. The multi-layer heat spreader according to claim 1, characterized in that, The intermetallic compound layer is an all-intermetallic compound interface generated by a transient liquid-phase bonding reaction, and its phase composition is at least as follows: It does not contain tin-based solid solutions.

3. A multi-layer heat spreader according to claim 1, characterized in that, The diameter of a single copper wire in the copper wire array is 50nm to 200nm, and the length is 1μm to 5μm. The copper wire array is interconnected with the capillary layer and is used to apply suction force to the micro-composite tenon-and-mortise structure region.

4. A multi-layer heat spreader according to claim 1 or 2, characterized in that, The maximum outer diameter of the inverted conical protrusion is greater than the neck diameter at its connection with the main body of the support column; the bottom width of the groove is greater than its opening width.

5. A manufacturing process for a multi-layer heat spreader, characterized in that, Includes the following steps: S100. On the inner surfaces of the upper and lower cover plates, grooves distributed in an array are processed by laser etching or wet chemical etching, and then copper wire arrays are grown in situ on the inner walls of the grooves by chemical bath deposition. S200. A middle support layer with inverted conical protrusions is fabricated using photolithography mask and anisotropic etching process; S300. A tin-containing alloy intermediate layer is deposited on the surface of an inverted conical protrusion or inside a groove by magnetron sputtering. S400. The upper cover plate, capillary layer, intermediate support layer, and lower cover plate are stacked in predetermined positions, so that the inverted conical protrusion is embedded in the groove; under vacuum or inert gas protection, pressure is applied and heated to a set bonding temperature, and the temperature is held for a set time, so that the tin-containing alloy intermediate layer melts and undergoes an isothermal solidification reaction with the copper substrate to generate the intermetallic compound layer; wherein, the set bonding temperature is higher than the melting point of the tin-containing alloy intermediate layer and lower than the melting point of the generated intermetallic compound layer; S500. After cooling, a vacuum is drawn inside the heat transfer medium, and the heat transfer medium is injected and sealed with an airtight seal.

6. The manufacturing process of a multi-layer heat spreader according to claim 5, characterized in that, In step S300, the tin-containing low-melting-point alloy intermediate layer is a tin-silver alloy layer, with a silver mass percentage of 2% to 5%, and the thickness of the tin-silver alloy layer ranges from 1 μm to 3 μm.

7. The manufacturing process of the multi-layer heat spreader according to claim 5, characterized in that, In step S400, the specific process parameters for the transient liquid phase bonding are as follows: The bonding temperature is 250℃ to 300℃, the applied micro pressure is 0.5MPa to 2.0MPa, and the holding time is 30 minutes to 120 minutes.

8. The manufacturing process of the multi-layer heat spreader according to claim 5, characterized in that, In step S100, the in-situ growth of the copper wire array by chemical bath deposition includes: The cover plate with etched microgrooves is immersed in an alkaline solution containing copper salt, reducing agent and surfactant, and reacted at a temperature of 60°C to 90°C for a set time. It is then washed with deionized water and dried.

9. The manufacturing process of the multi-layer heat spreader according to claim 5, characterized in that, In step S400, the heating method is induction heating or hot plate conduction heating.

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