An aluminum VC vapor chamber applied to a VPX module and a preparation method thereof

Abstract

The application relates to an aluminum VC heat plate applied to a VPX module and a preparation method thereof, and belongs to the heat plate manufacturing field, and at least solves one of the technical problems that the existing aluminum VC heat plate preparation method has poor sealing reliability, high manufacturing cost and difficulty in considering the structural strength and heat dissipation efficiency in the limited space of the VPX module. The application comprises the following steps: processing a plate shell according to the VPX module standard and reserving a filling port; preparing a liquid absorbing core by laser wire cutting with a foamed metal profile as raw material; vacuum brazing the plate shell and the liquid absorbing core to form a heat plate main body; flattening and low-temperature brazing a thin-walled hollow aluminum pipe to be installed in the filling port; sequentially performing first air tightness detection, vacuumizing and 100% liquid filling rate acetone filling; sealing the filling port by adopting a two-step sealing method of cold pressure welding temporary sealing and friction stir welding complete sealing; and obtaining a finished product through finishing and second air tightness detection. The aluminum VC heat plate prepared by the application has good heat dissipation efficiency and good sealing performance.

Description

Technical Field

[0001] This invention relates to the field of heat spreader manufacturing technology, and in particular to an aluminum VC heat spreader for use in VPX modules and its preparation method. Background Technology

[0002] VPX is an open, modular electronic system architecture. In modern electronics, the application scenarios of VPX modules are constantly expanding and deepening, especially in key areas such as high-performance computing, aerospace, communications, and complex industrial control, where its importance is increasingly prominent. However, as electronic technology develops towards higher integration, higher computing speed, and higher power, the heat dissipation problem of VPX modules has become a key factor limiting their performance improvement and stable operation. From an internal structure perspective, VPX modules integrate numerous high-performance chips and electronic components. These components consume enormous power during operation, resulting in a sharp increase in heat flux density per unit area. Traditional heat dissipation methods, such as simple metal heat sinks combined with air cooling, have relatively low heat dissipation efficiency and cannot effectively address the uneven heat distribution problem under high power density. They fail to meet the stringent temperature control requirements of VPX modules, leading to excessively high chip junction temperatures. This not only degrades chip performance but also severely affects chip reliability and lifespan, causing system failures and downtime.

[0003] A vapor chamber (VC) utilizes the phase change cycle of its internal working fluid for efficient heat transfer. Through the evaporation and condensation of the working fluid, heat can be rapidly transferred from high heat flux regions to low temperature regions, achieving rapid heat diffusion and uniform distribution. Its unique capillary structure design ensures smooth reflux of the working fluid during the phase change cycle, further enhancing the heat transfer effect and making it an ideal method for solving heat dissipation problems in VPX modules. However, successfully applying vapor chambers to VPX modules faces a series of technical challenges: Firstly, the VPX module has standardized board size, fixed mounting holes, and thin-walled areas, resulting in extremely limited internal height space. It must accommodate a sufficiently thick wick to ensure capillary force while also reserving enough space for the vapor chamber to ensure phase change heat transfer efficiency. These two aspects encroach on each other's space. At the same time, the mounting holes and thin-walled areas are ineffective heat dissipation areas. Maintaining the temperature uniformity of the entire board under the condition that the effective heat dissipation area is compressed is the main challenge faced by the structural design.

[0004] Secondly, VPX modules are commonly used in critical mission scenarios such as aerospace and communications, where extremely high sealing reliability is required. Existing filling port seals mostly employ single fusion welding processes such as electron beam welding. The welding process is prone to introducing defects such as thermal stress, microcracks, and porosity in the weld area. Under the long-term effects of temperature cycling and mechanical vibration, these defects may expand into leakage channels, leading to the failure of the heat spreader.

[0005] Third, existing liquid wicks are mostly prepared using powder sintering processes, which have narrow process windows, long cycles, and high costs. Furthermore, the limited porosity results in insufficient driving force for the recirculation of the working fluid, making it difficult to further improve the heat dissipation efficiency of the heat exchange plate.

[0006] In summary, there is an urgent need to systematically optimize the preparation method of the aluminum VC heat sink used in VPX modules. Summary of the Invention

[0007] Based on the above analysis, the present invention aims to provide an aluminum VC heat spreader for VPX modules and its preparation method, at least to solve one of the following problems in the preparation of existing aluminum VC heat spreaders for VPX modules: 1. Existing sealing methods easily lead to insufficient long-term sealing reliability of the heat spreader; 2. The preparation and liquid injection process of the liquid wick in existing aluminum VC heat spreaders for VPX modules is complex and the manufacturing cost is high; 3. The heat dissipation efficiency of existing aluminum VC heat spreaders for VPX modules is insufficient.

[0008] The objective of this invention is mainly achieved through the following technical solutions: This invention provides a method for preparing an aluminum VC heat sink for use in VPX modules, comprising the following steps: S1: Using aluminum alloy sheet as raw material, CNC machining and pickling are used to obtain a clean VPX module shell; S2: Foam metal profiles are used as raw materials, and foam metal liquid absorbent cores are obtained through laser wire cutting, cleaning and drying; S3: Vacuum brazing the plate shell and the liquid absorption core and post-weld heat treatment are performed to obtain a heat spreader body with a closed cavity; S4: The thin-walled hollow aluminum tube is flattened and brazed at low temperature and installed at the filling port to obtain a heat spreader semi-finished product. S5: Fill the heat spreader semi-finished product with test gas and maintain pressure to monitor, completing the first airtightness test; S6: After evacuating the inner cavity of the shell through the filling tube, acetone working fluid is filled in, with a filling rate of 100%; S7: After filling, the heat-soaked plate semi-finished product is temporarily sealed by cold pressure welding and then completely sealed by friction stir welding. S8: Perform CNC precision machining and conductive oxidation surface treatment on the sealed heat spreader semi-finished product to obtain the finished aluminum VC heat spreader; S9: Perform a secondary airtightness test on the finished aluminum VC heat exchange plate.

[0009] Furthermore, in step S2, the foamed metal profile is foamed aluminum or foamed nickel, the laser wire cutting processing speed is 30~70mm / s, the spot size is 60~100μm, the scanning interval is 0.1~0.5mm, and the jump speed is 800~1200mm / s.

[0010] Furthermore, in step S3, the brazing filler metal used in vacuum brazing is an Al-Si based filler metal with a magnesium content of 0.1% to 0.5%.

[0011] Furthermore, in step S3, the welding temperature of the vacuum brazing is 595℃~610℃, and the vacuum degree is ≤10. - ²Pa; A multi-stage heating and stepped heat preservation program is adopted: the temperature is increased to 350~420℃ at 8~15℃ / min and held for 20~60min, then increased to 480~520℃ at 3~8℃ / min and held for 20~60min, then increased to 550~590℃ at 3~8℃ / min and held for 20~60min, and finally increased to 595~610℃ at 3~8℃ / min and held for 5~20min.

[0012] Further, in step S3, the post-weld heat treatment includes solution treatment and aging treatment: the post-weld workpiece is heated to 520℃~530℃ and held for 1~2 hours, then quenched and cooled, and then artificially aged by heating to 165℃~175℃ and holding for 6~10 hours.

[0013] Further, in step S4, the outer diameter of the filling tube is 0.8mm~1.2mm, the thickness after flattening is 0.8mm~1.2mm, and an assembly gap of 0.05mm~0.15mm is left between the two sides of the flattened tube wall and the inner wall of the filling port. The low-temperature brazing uses low-temperature solder paste, which is heated to 220℃~240℃ and held for 1~2 minutes.

[0014] Further, in step S5, the airtightness test includes: filling the inner cavity of the shell with dry air at 0.5~1.0MPa, maintaining the pressure for 30~40 minutes, and if the pressure does not drop, it indicates that the shell's sealing performance meets the requirements; If the pressure drops, use epoxy resin adhesive or UV-cured adhesive to reseal the leaking area, and then test again until the airtightness is satisfactory.

[0015] Further, in step S7, the downward pressure of the cold pressure welding is 0.5~2.0MPa; the stirring head rotation speed of the friction stir welding is 1000~2000rpm, the feed speed is 200~500mm / min, and the downward pressure is 5~15MPa.

[0016] The present invention also provides an aluminum VC heat spreader for use in VPX modules, which is prepared by the above preparation method and includes an upper shell (1), a lower shell (2), a foam metal liquid absorbent core (3), a liquid filling tube (5) and a sealing joint (4). The upper shell (1) and the lower shell (2) are connected by vacuum brazing to form a heat-spreading plate shell with a sealed cavity inside. The upper shell (1) or the lower shell (2) is provided with a filling port that penetrates the shell. The foam metal absorbent core (3) is fixed to the inner surface of the upper shell (1) and / or the lower shell (2) by vacuum brazing; The filling tube (5) is installed on the filling port, and its end is sealed by cold pressure welding. The sealing joint (4) is located at the filling port and is welded to the filling port by friction stir welding. It covers the sealed end of the filling tube (5) to form a second seal. The sealing joint (4) and the filling tube (5) together constitute a composite sealing structure of the filling port.

[0017] Furthermore, the foamed metal absorbent core (3) is made of foamed aluminum or foamed nickel, with a thickness of 0.5 mm to 2.0 mm and a porosity of 85% to 97%. The sealing joint (4) is stepped and has a groove inside to accommodate the end of the filling tube (5), with rounded edges. The upper shell (1), lower shell (2) and sealing joint (4) are made of aluminum alloy 6063.

[0018] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. This invention provides a complete method for preparing an aluminum VC vapor chamber heat exchanger suitable for VPX modules. Starting from structural adaptability design, this method forms a complete process system through the coordinated cooperation of a series of steps, including laser wire cutting of the foam metal liquid absorbent core, vacuum brazing, low-temperature brazing installation of the liquid filling tube, air tightness testing, vacuuming and 100% liquid filling, two-step sealing, fine machining and surface treatment, and secondary air tightness testing. This enables the vapor chamber heat exchanger to achieve efficient heat dissipation within the limited space of the VPX module, while solving the shortcomings of existing aluminum VC vapor chamber heat exchangers in terms of sealing reliability and manufacturing cost.

[0019] 2. This invention employs a two-step composite sealing method of "cold pressure welding for temporary sealing + friction stir welding for complete sealing". The two solid welding processes are sequentially connected and complement each other, which fundamentally eliminates the thermal defects (thermal stress, microcracks, porosity) that may be caused by traditional fusion welding. This gives the heat spreader excellent long-term sealing reliability and service life, and fully meets the stringent requirements of VPX module for zero tolerance of failure.

[0020] 3. This invention prepares the liquid-absorbing core by laser wire cutting using foam metal profiles as raw materials. Compared with the traditional powder sintering process, it does not require complex sintering temperature curves and long-term heat preservation, resulting in a shorter process flow and faster cycle. At the same time, it avoids the risks of limited porosity and sintering layer detachment during powder sintering, giving the liquid-absorbing core high porosity and high capillary force, which significantly improves the heat transfer performance of the heat spreader.

[0021] 4. This invention sets the filling rate to 100%, meaning the volume of the liquid working fluid is equal to the volume of the absorbing core cavity. This ensures that the working fluid completely fills the pore space of the absorbing core, creating a synergistic effect with the high porosity of the foam metal absorbing core. This ensures the continuity of capillary supply at the evaporation end, avoids localized drying, and fully leverages the high capillary force advantage of the foam metal. Furthermore, the invention employs a liquid injection method that involves vacuuming before filling, which, compared to filling before vacuuming, avoids working fluid loss and secondary degassing, simplifies the production process, and improves production efficiency.

[0022] 5. This invention, through customized structural design and precision CNC machining, takes into account the industry standards, mounting hole positions and thin-walled areas of the VPX module from the design source to avoid them, ensuring that the heat spreader meets the structural strength requirements within the limited space of the VPX module while achieving the maximum heat dissipation area, and is seamlessly integrated into the VPX system.

[0023] 6. The present invention also provides an aluminum VC heat spreader product, wherein the filling port forms a composite sealing structure consisting of a cold-pressed sealing part of the filling pipe and a friction-stirred sealing part of the plugging joint. This structural feature directly reflects the process advantages of the two-step sealing method in the preparation method, enabling the product to have excellent sealing reliability and long service life.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 is a schematic diagram of the structure of the aluminum VC heat spreader prepared in Example 1 of the present invention; Figure 2 This is a schematic diagram of the liquid filling pipe installation during the preparation of the aluminum VC heat spreader in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the temporary sealing process during the preparation of the aluminum VC heat spreader in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram illustrating the complete sealing process during the preparation of the aluminum VC heat spreader in Embodiment 1 of the present invention. Figure 5 This is a schematic diagram of the sealing joint in the aluminum VC heat spreader of Embodiment 1 of the present invention.

[0027] Figure label: 1-Upper shell; 2-Lower shell; 3-Foam metal liquid-absorbing core; 4-Sealing connector; 5-Filling tube; 6-Pressure head. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0029] This invention provides a method for preparing an aluminum VC heat sink for use in VPX modules, comprising the following steps: S1: Using aluminum alloy sheet as raw material, CNC machining and pickling are used to obtain a clean VPX module shell; Specifically, based on the industry standards and structural requirements of the specific model to be applied to the VPX module, the upper shell 1 and lower shell 2 are precision machined using CNC machine tools. Among them, aluminum 6063 is preferred as the shell material, which has high thermal conductivity and high strength, and plays a key supporting and heat transfer role.

[0030] Meanwhile, customized designs of bosses or recesses can be made on the outer surfaces of the upper shell 1 and / or lower shell 2 according to the relative height of the heating element, to adapt to the height of the heating element inside the module, facilitating the bonding of the heating element through the interface material, so that the heating element can achieve a tighter and more uniform contact with the heat spreader through the interface material, effectively reducing the contact thermal resistance. It should be noted that when designing bosses or recesses, the fixing holes and thin plate areas of the VPX module must be avoided, in order to maximize the heat transfer efficiency while meeting the strength requirements of the aluminum VC heat spreader. In addition, according to the structural strength requirements of the heat spreader, support columns can be set between the upper shell 1 and the lower shell 2 to prevent the shell from denting and deforming under vacuum negative pressure.

[0031] After processing, the shell plate needs to be pickled to remove grease, debris and oxide impurities from milling, and reduce the impact of oxide layer on welding strength and heat exchange of aluminum VC heat exchange plate.

[0032] In addition, according to the industry standards and structural requirements of the specific model to be applied to the VPX module, a filling port is reserved at a predetermined position on the board shell. The filling port is rectangular and is used for the subsequent installation of the filling tube.

[0033] Through the above processing and cleaning, an upper shell (1) and a lower shell (2) with clean surfaces and structural dimensions that meet the installation requirements of the VPX module are obtained.

[0034] S2: Foam metal profiles are used as raw materials, and foam metal liquid absorbent cores are obtained through laser wire cutting, cleaning and drying; Specifically, the foamed metal profile is either aluminum foam or nickel foam. Foamed metal is a novel multifunctional material containing a large number of pores, which is lightweight yet has a large specific surface area to increase heat dissipation area. The porosity of the molded foamed metal profile can be controlled by adjusting the powder particle size, thereby controlling the magnitude of capillary force and adapting to the heat dissipation requirements of different scenarios. In this invention, the foamed metal profile is preferably aluminum foam or nickel foam. As a preferred embodiment, nickel foam wicks prepared with nickel powder with a particle size <20μm have a porosity of up to 90% and a capillary force of over 5kPa, and are commonly used in medical imaging equipment. Aluminum foam wicks prepared with aluminum powder with a particle size of 300~500μm have a porosity that can be controlled at around 60% and a capillary force of up to 1.2kPa, and are suitable for aerospace thermal management systems.

[0035] The laser processing is wire cutting, which ensures material separation within a minimal heat-affected zone, avoiding the potential collapse or deformation of the porous structure of the foam metal due to mechanical stress during cutting. During wire cutting, a fiber laser is used with a processing speed of 30-70 mm / s, a spot size of 60-100 μm, a scanning interval of 0.1-0.5 mm, and a jump speed of 800-1200 mm / s, assisted by nitrogen for bidirectional reciprocating scanning. Sectional cutting is performed according to the design requirements of the heat spreader, and through holes are cut at predetermined positions. The cut workpiece is then ultrasonically rinsed with deionized water and vacuum dried. Through the coordinated control of these process parameters, the neatness and low roughness of the cutting edges are ensured, resulting in a kerf width ≤0.1 mm, perpendicularity ≤0.03 mm / m, surface roughness Ra ≤1.2 μm, and heat-affected zone ≤80 μm.

[0036] Through the above-mentioned laser wire cutting, cleaning and drying, a foam nickel liquid absorbent core 3 with target porosity, neat edges and well-preserved pore structure is obtained.

[0037] S3: Vacuum brazing the plate shell and the liquid absorption core and post-weld heat treatment are performed to obtain a heat spreader body with a closed cavity; Specifically, since the main component of the substrate of the upper shell 1, lower shell 2, and liquid absorber 3 of the aluminum VC heat exchanger plate is aluminum, the solidus temperature of the substrate is relatively low. In order to avoid the collapse of the foam structure of the liquid absorber 3 or the decrease in the bonding force between the shell and the plate due to excessive welding temperature, the vacuum brazing process of the present invention is as follows: The brazing filler metal used is an Al-Si based filler metal with a low liquidus temperature. Conventional Al-Si filler metals typically add magnesium (Mg) as an activator to remove the oxide film; however, excessive magnesium content significantly lowers the filler metal's liquidus temperature, exacerbating its penetration and erosion of the porous structure of the foamed metal. Therefore, this application controls the magnesium content in the filler metal to 0.1%~0.5% (preferably 0.2%~0.4%) to ensure filler metal activity while maximizing the protection of the microstructure integrity of the wicking core. The filler metal is a 0.10~0.20mm thick foil. For locations with support pillars, corresponding circular holes are pre-cut into the filler metal foil to prevent the filler metal from reaching the support pillar mounting area. During brazing, the silicon (Si) in the filler metal undergoes a eutectic reaction with the Al in the aluminum alloy substrate, generating an aluminum-silicon liquid eutectic phase. The liquid filler metal wets and spreads on the surface of the base material and diffuses into each other. After cooling and solidification, it forms a continuous metallurgical bonding layer, achieving a reliable connection between the wicking core and the shell.

[0038] Welding temperature controlled at 595℃~610℃, vacuum degree inside welding furnace ≤10 -2 Pa. The welding process employs multi-stage heating and stepped holding: heating begins after the vacuum level meets the requirements, with the furnace body heated to 350-420℃ at a rate of 8-15℃ / min and held for 20-60 minutes; then heated to 480-520℃ at a rate of 3-8℃ / min and held for 20-60 minutes; then heated to 550-590℃ at a rate of 3-8℃ / min and held for 20-60 minutes; finally, heated to 595-610℃ at a rate of 3-8℃ / min and held for 5-20 minutes before heating is stopped and the furnace is cooled. An air-cooling system is provided during the welding process for rapid cooling.

[0039] After welding, solution treatment and aging treatment are performed: the welded workpiece is heated to 520℃~530℃, held at that temperature for 1~2 hours, then removed and quenched in water at 35℃~40℃; subsequently, artificial aging treatment is performed, heating to 165℃~175℃ and holding for 6~10 hours, followed by air cooling. Through the above post-weld heat treatment, the strength, hardness, and fatigue resistance of the welded joint can be significantly improved, while eliminating residual stress generated during welding, ensuring the dimensional stability and structural reliability of the heat spreader during subsequent processing and long-term service.

[0040] Through the above-mentioned vacuum brazing and post-weld heat treatment, the upper shell (1), the lower shell (2) and the liquid-absorbing core (3) are welded together to form a heat-spreading plate main structure with an internal closed cavity. The cavity is formed by the inner wall of the shell and the surface of the liquid-absorbing core, providing a sealed space for subsequent working fluid filling.

[0041] S4: The thin-walled hollow aluminum tube is flattened and brazed at low temperature and installed at the filling port to obtain a heat spreader semi-finished product. The filling tube (5) is a thin-walled hollow aluminum tube, serving as a channel for vacuuming and filling the working fluid. Due to limited internal space within the VPX module, to reduce the height of the filling tube protruding from the board surface after installation, the pre-reserved filling port in S1 is designed as rectangular. The filling tube needs to be flattened before installation. Specifically, the outer diameter of the filling tube (5) is 0.8mm~1.2mm, the short side width of the rectangular filling port is 1.0mm~1.5mm, and the thickness of the flattened filling tube is 0.8mm~1.2mm, meaning the thickness after flattening is less than the short side width of the filling port, ensuring the filling tube can be smoothly inserted into the filling port. Simultaneously, a 0.05mm~0.15mm assembly gap is left between the flattened tube wall and the inner wall of the filling port for easy installation.

[0042] During installation, use low-temperature solder paste for welding and sealing. Clean the outer surface of the aluminum tube and the inner surface of the filling port; apply solder paste evenly to the outside of the aluminum tube insertion end, ensuring the application is at least 2mm above the tube end face to prevent the solder paste from liquefying and blocking the tube opening; insert the aluminum tube into the filling port to a depth of approximately 8-12mm and secure it, then place it in a muffle furnace and heat to 220℃-240℃, holding for 1-2 minutes. This allows the solder paste to flow and fill the gap between the tube wall and the filling port under capillary action. After cooling, a sealed connection is achieved. Using low-temperature solder paste for welding and sealing effectively prevents metal oxidation, ensures a beautiful and high-quality weld, and reduces the impact of localized thermal stress on the installation interface.

[0043] At this point, the upper shell (1), lower shell (2), liquid-absorbing core (3), and filling pipe (5) are assembled into one piece by welding to form a heat-spreading plate semi-finished product with a sealed cavity inside and connected to the outside through the filling pipe (5), which can be used for subsequent airtightness testing and working fluid filling.

[0044] S5: Fill the heat spreader semi-finished product with test gas and maintain pressure to monitor, completing the first airtightness test; For the first airtightness test of the heat spreader semi-finished product: fill the inner cavity of the shell with dry air at 0.5~1.0MPa, maintain the pressure for 30~40 minutes and monitor the pressure change. If the pressure does not drop, it indicates that the shell sealing meets the requirements; if the pressure drops, it indicates that there is a leak. Epoxy resin glue or light-curing glue can be used to seal the leaking part for a second time. After the glue cures, test again until the airtightness is qualified.

[0045] S6: After evacuating the inner cavity of the shell through the filling tube, acetone working fluid is injected. The inner cavity of the shell is evacuated through the filling tube (5) to remove air and non-condensable gases from the cavity, and then high-purity acetone is filled in as the working fluid. This application adopts the method of evacuating first and then filling, which can avoid the loss of working fluid and secondary degassing process caused by filling first and then evacuating.

[0046] It should be noted that the vacuum level and liquid filling rate inside the cavity have a significant impact on the heat dissipation effect and start-up time of the heat spreader: insufficient vacuum means that a large amount of non-condensable gas remains in the cavity, which will hinder the transport of gaseous working fluid from the evaporation end to the condensation end, reduce heat transfer efficiency, and delay the start-up response of the heat spreader. In this application, the liquid filling rate is defined as the ratio of the volume of injected liquid working fluid to the cavity volume of the wick (3). The liquid filling rate is 100%, that is, the liquid working fluid completely fills the pore space of the wick. The reason for adopting this liquid filling rate is based on the high porosity characteristics of the foam metal wick. The foam metal wick has a large number of interconnected micropores inside, which can accommodate sufficient liquid working fluid to maintain the evaporation-condensation cycle; the liquid working fluid completely fills the pores of the wick, which can ensure the continuity of capillary supply at the evaporation end and avoid local drying, thereby giving full play to the high capillary force advantage of the foam metal wick. Both excessively high and low filling ratios negatively impact heat transfer performance: an insufficient filling ratio may lead to inadequate working fluid supply at the evaporation end, resulting in drying out; an excessively high filling ratio may occupy too much space in the steam chamber, increasing steam diffusion resistance. A 100% filling ratio combined with a foamed metal wick ensures sufficient wetting of the capillary return path while reserving effective space for steam diffusion.

[0047] The working fluid is high-purity acetone. Acetone does not react chemically with aluminum alloy, and it has a moderate boiling point and high latent heat of vaporization, making it suitable for phase change heat transfer cycles in heat exchangers.

[0048] S7: After filling, the heat-soaked plate semi-finished product is temporarily sealed by cold pressure welding and then completely sealed by friction stir welding. After the working fluid is filled, the filling pipe 5 is sealed under internal vacuum (pressure < 10 Pa) to prevent the liquid inside the cavity from vaporizing and evaporating and to prevent the entry of external non-condensable gases, thus ensuring the reliability and long service life of the aluminum VC heat exchanger.

[0049] See Figure 3 A temporary seal is achieved using cold pressure welding on the filling tube 5. A downward pressure of 0.5~2.0 MPa is applied to the filling tube 5 through the pressure head 6, causing sufficient plastic deformation. Under pressure, the atoms of the tube wall metal approach each other to their lattice distance, achieving a strong atomic bond. This process is solid-state welding, with no heat input during welding, completely avoiding the risks of working fluid vaporization, performance degradation, and thermal shock to the interface materials that may be caused by thermal effects. This provides a good initial sealing condition for subsequent complete sealing.

[0050] Based on the temporary seal formed by cold pressure welding, a sealing joint (4) made of aluminum alloy 6063 was welded to the filling port by friction stir welding. During welding, the stirring head speed was 1000~2000rpm, the feed speed was 200~500mm / min, and the downward pressure was 5~15MPa.

[0051] The temporary seal achieved through cold pressure welding and the complete seal achieved through friction stir welding follow in sequence and complement each other: the former provides an immediate seal without heat-affected zone effects, while the latter achieves a high-strength, high-reliability permanent seal while maintaining the vacuum level of the cavity. Friction stir welding, as a solid-state welding process, has low heat input, and the material does not reach its melting point during welding. This results in minimal microstructural changes, low residual stress, and reduced susceptibility to cracks and porosity in the sealing joint 4, ensuring the long-term reliability of the sealing structure.

[0052] S8: Perform CNC precision machining and conductive oxidation surface treatment on the sealed heat spreader semi-finished product to obtain the finished aluminum VC heat spreader; The sealed vapor chamber plate semi-finished product is CNC precision machined to ensure that the machining dimensions meet the industry standards and structural design requirements of the VPX module, and the machining tolerances meet the national standards, ensuring that its external dimensions are precisely matched with the VPX module. Subsequently, a conductive anodizing surface treatment is performed to enhance corrosion resistance, wear resistance, and surface strength, resulting in the finished aluminum VC vapor chamber plate.

[0053] S9: Conduct a secondary airtightness test on the finished aluminum VC heat spreader to ensure that the airtightness of the finished aluminum VC heat spreader meets the requirements.

[0054] This invention also provides an aluminum VC heat spreader for use in VPX modules, prepared by the above-described method for preparing aluminum VC heat spreaders for VPX modules, such as... Figure 1 As shown, it includes an upper shell 1, a lower shell 2, a foam metal liquid-absorbing core 3, a sealing connector 4, and a filling tube 5; The external dimensions, mounting hole positions, and layout of the thin-walled areas inside the cavity of the upper shell 1 and lower shell 2 are all customized according to the industry standards and internal structural space of the VPX module. The upper shell 1 and lower shell 2 are vacuum-brazed together to form a heat spreader shell with a sealed cavity inside, which is filled with working fluid and maintained under vacuum. The shell material is aluminum alloy, preferably 6063 aluminum alloy. The upper shell 1 or lower shell 2 is provided with a through-hole filling port, which is rectangular and used to install the filling tube 5. The location of the filling port is determined according to the industry standards of the VPX module and the structural requirements of the specific model.

[0055] The foam metal absorbent core 3 is fixed to the inner surface of the upper shell 1, or the inner surface of the lower shell 2, or both the upper and lower shells by vacuum brazing; the thickness of the foam metal absorbent core 3 is determined according to the internal space allowed by the VPX module and the target thermal conductivity, preferably 0.5mm~2.0mm, and its porosity is determined by selecting foam metal profiles of different specifications, preferably 85%~97%, to ensure sufficient capillary force is generated; the absorbent core (3) is made of foam aluminum or foam nickel.

[0056] The sealing connector 4 is located at the filling port, and its external dimensions are larger than the opening size of the filling port to ensure complete coverage of the filling port and allowance for friction stir welding. The sealing connector 4 is stepped, with an internal groove to accommodate the end of the filling tube 5, and its edges are rounded. The sealing connector 4 is welded to the filling port by friction stir welding, covering the sealed end of the filling tube 5, and together with the filling tube 5, forms a composite sealing structure. The sealing connector 4 is made of aluminum alloy, preferably 6063 aluminum alloy.

[0057] The filling tube 5 is a thin-walled hollow aluminum tube, installed on the filling port of the upper shell 1 or the lower shell 2, serving as a channel for vacuuming and filling the working medium. The outer diameter of the filling tube 5 is 0.8mm~1.2mm. The portion installed at the filling port is flattened, and the thickness after flattening is less than the width of the short side of the filling port. A 0.05mm~0.15mm assembly gap is left between the two sides of the tube wall and the inner wall of the filling port. The filling tube (5) is sealed in the filling port by low-temperature solder paste.

[0058] After the working fluid is filled, the end of the filling tube 5 is sealed by cold pressure welding to form the first seal; the sealing joint 4 is sealed by friction stir welding over and onto the sealed end of the filling tube 5 and part of the surrounding filling port area to form the second seal. The sealing joint 4 and the filling tube 5 together constitute a composite sealing structure for the filling port.

[0059] This invention employs a two-step sealing method: "temporary sealing by cold pressure welding + complete sealing by friction stir welding." Cold pressure welding, as a solid-state welding process, involves no heat input throughout, avoiding the risks of working fluid vaporization and thermal shock to the interface materials, thus providing a non-destructive initial sealing state for the cavity. Friction stir welding, also a solid-state welding process, features low heat input, low residual stress, and a dense weld free of porosity and cracks. The two methods work sequentially and complement each other, fundamentally eliminating thermal defects such as thermal stress and microcracks introduced by material melting and resolidification in traditional fusion welding processes. This ensures the sealing reliability of the heat spreader under long-term temperature cycling and mechanical vibration service conditions.

[0060] This invention uses foamed metal profiles as raw materials and prepares the liquid-absorbing core through laser wire cutting. Compared with powder sintering, it eliminates the need for complex sintering temperature curve control and long-term heat preservation, resulting in a shorter process flow and faster cycle. Furthermore, this invention employs a liquid injection method of first vacuuming and then filling, avoiding the working fluid loss and secondary degassing process caused by filling first and then vacuuming, further simplifying the production process and reducing overall manufacturing costs.

[0061] This invention considers the VPX standard from the design stage: on the one hand, it avoids the mounting holes and thin-walled areas of the VPX module, and through customized structural design and precision machining, it ensures that the heat spreader meets the structural strength requirements within a limited space; on the other hand, it adopts a foam metal liquid absorbent core combined with a 100% liquid filling rate optimization design, giving full play to the advantages of high porosity and high capillary force of foam metal, so that the working fluid returns smoothly and the evaporation end is continuously replenished, achieving high heat conduction efficiency and temperature uniformity of the entire plate, thereby maximizing heat dissipation performance under the premise of structural adaptation.

[0062] The aluminum VC heat spreader prepared by this invention has an isothermal performance temperature difference ≤17℃ (e.g., 14.3~16.8℃) and a heat transfer performance temperature difference ≤30℃ (e.g., 26.4~29.6℃), exhibiting excellent isothermal and heat transfer performance.

[0063] Example 1 This embodiment provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The aluminum VC heat spreader to be prepared has dimensions of 233.4mm × 167.5mm × 24mm, and includes the following steps: S1: Using aluminum alloy sheet as raw material, CNC machining and pickling are used to obtain a clean VPX module shell; The aluminum substrate selected for processing the upper shell 1 and lower shell 2 is aluminum 6063. The outer surface of the shells can be designed with bosses and recesses according to the relative height of the heating elements, while avoiding the mounting holes of the VPX module and thin plate areas. Support columns are installed between the upper shell 1 and lower shell 2 according to structural strength requirements. After processing, the shells need to undergo acid pickling to remove grease, debris, and oxide impurities from milling. A rectangular filling port is pre-drilled at a predetermined location on the shell for subsequent installation of the filling tube.

[0064] Through the above processing and cleaning, the upper shell 1 and lower shell 2 with clean surfaces and structural dimensions that meet the installation requirements of the VPX module are obtained.

[0065] S2: Foam metal profiles are used as raw materials, and foam metal liquid absorbent cores are obtained through laser wire cutting, cleaning and drying; The liquid-absorbing core 3 is a nickel foam core prepared with nickel powder with a particle size <20μm and a porosity of 90%. A fiber laser is used to cut the 0.5mm thick nickel foam core at a processing speed of 50mm / s, a spot size of 80μm, a scanning interval of 0.2mm, and a jump speed of 1000mm / s. Nitrogen-assisted bidirectional reciprocating scanning is used for partitioned cutting, with 3mm diameter through-holes cut at 8mm intervals. The cut workpiece is then ultrasonically rinsed with deionized water and vacuum dried. The kerf width is 0.1mm, the perpendicularity is ≤0.03mm / m, the surface roughness Ra is 1.2μm, and the heat-affected zone is ≤80μm.

[0066] Through the above-mentioned laser wire cutting, cleaning and drying, a foam nickel liquid absorbent core 3 with target porosity, neat edges and well-preserved pore structure is obtained.

[0067] S3: The plate shell and the liquid absorption core are vacuum brazed and then heat-treated after welding to obtain a heat spreader body with a closed cavity.

[0068] Select Al-Si brazing filler metal with a thickness of 0.15mm (magnesium content 0.3%). For the location where support pillars are set, pre-cut corresponding round holes on the brazing filler metal sheet and lay it flat between the foam metal absorbent core and the lower shell.

[0069] Welding temperature controlled at 600℃, vacuum degree ≤10 -2 Pa. Once the vacuum level meets the requirements, start heating. Increase the temperature to 400℃ at 10℃ / min and hold for 30min. Then increase the temperature to 500℃ at 5℃ / min and hold for 30min. Next, increase the temperature to 570℃ at 5℃ / min and hold for 30min. Finally, increase the temperature to 600℃ at 5℃ / min and hold for 10min. Then stop heating and let the furnace cool.

[0070] After welding, solution treatment and aging treatment are performed: the specimen is heated to 525℃ and held for 1.5 hours, then removed and placed in water at 35℃~40℃ to cool; then artificial aging treatment is performed, heated to 170℃ and held for 8 hours, and then cooled in air.

[0071] Through the above-mentioned vacuum brazing and post-weld heat treatment, the upper shell 1, the lower shell 2 and the liquid absorption core 3 are welded together to form a heat spreader main structure with an internal closed cavity.

[0072] S4: The thin-walled hollow aluminum tube is flattened and brazed at low temperature and installed at the filling port to obtain a heat spreader semi-finished product. The outer diameter of the filling tube 5 is 1.0 mm, and its thickness is 0.9 mm after being flattened by mechanical pressure. The short side width of the filling port is 1.2 mm, and a 0.1 mm assembly gap is left between the two sides of the flattened tube wall and the inner wall of the filling port. After cleaning the outer surface of the aluminum tube and the inner surface of the filling port, low-temperature solder paste is evenly applied to the outside of the aluminum tube insertion end, with the application position more than 2 mm away from the tube end face. The aluminum tube is inserted into the filling port to a depth of 10 mm and fixed. It is then placed in a muffle furnace and heated to 230℃ and held for 1 minute, allowing the solder paste to flow and fill the gap between the tube wall and the filling port under the action of capillary force. After cooling, a sealed connection is achieved.

[0073] At this point, the upper shell 1, lower shell 2, liquid-absorbing core 3, and liquid-filling pipe 5 are assembled into one piece by welding, forming a heat spreader semi-finished product with a sealed cavity inside and connected to the outside world through the liquid-filling pipe 5.

[0074] S5: Fill the heat spreader semi-finished product with test gas and maintain pressure to monitor, completing the first airtightness test; Dry air at 0.8 MPa was introduced into the inner cavity of the shell, and the pressure was maintained for 30 minutes. The pressure change was monitored. The absence of pressure drop indicates that the shell sealing performance meets the requirements. The above tests confirmed that the sealing performance of the heat spreader semi-finished shell meets the requirements.

[0075] S6: After evacuating the inner cavity of the shell through the filling tube, acetone working fluid is injected. After reducing the pressure inside the shell to 10 Pa and maintaining it for 20 minutes, high-purity acetone working fluid was injected, with a working fluid filling rate of 100% (i.e., the volume of liquid working fluid is equal to the volume of the suction core cavity).

[0076] Through the above-mentioned vacuuming and filling, a heat exchanger plate with an internal vacuum and working fluid completely filling the pores of the wick is obtained.

[0077] S7: After filling, the heat-soaked plate semi-finished product is temporarily sealed by cold pressure welding and then completely sealed by friction stir welding. When the internal pressure is <10Pa, cold pressure welding is used to temporarily seal the filling tube 5. A downward pressure of 1.0MPa is applied through the pressure head 6 to cause sufficient plastic deformation of the filling tube 5 to achieve interatomic bonding. Based on the temporary seal formed by cold pressure welding, the sealing joint 4 made of aluminum alloy 6063 is welded to the filling port by friction stir welding. The welding head speed is 1500rpm, the feed speed is 300mm / min, and the downward pressure is 10MPa.

[0078] Through the above two sealing steps, the filling port is sealed sequentially by cold pressure welding and friction stir welding to form a composite sealing structure.

[0079] S8: Perform CNC precision machining and conductive oxidation surface treatment on the sealed heat spreader semi-finished product to obtain the finished aluminum VC heat spreader; The sealed heat spreader semi-finished product is machined using a CNC machine tool. The machining dimensions meet the industry standards and structural design requirements of the VPX module, and the machining tolerances meet national standards. After machining, a conductive oxidation surface treatment is performed.

[0080] Through the above-mentioned finishing and surface treatment, an aluminum VC heat spreader with dimensions that meet the installation requirements of the VPX module is obtained.

[0081] S9: Perform a secondary airtightness test on the finished aluminum VC heat exchange plate.

[0082] The processed aluminum VC heat spreader was placed in an electric drying oven and heated to 125°C for 30 minutes. The weight before and after heating was compared to confirm whether there was any leakage.

[0083] The above-mentioned secondary airtightness test confirmed that the airtightness of the finished aluminum VC heat spreader meets the requirements.

[0084] Example 2 This embodiment provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Embodiment 1, and the preparation method is similar to that in Embodiment 1, except that: S2: The liquid-absorbing core is made of aluminum powder with a particle size of 300~500μm, with a porosity of 60% and a thickness of 1.0mm. During laser wire cutting, the processing speed is 30mm / s, the spot size is 100μm, the scanning interval is 0.3mm, the jump speed is 800mm / s, and through-holes with a diameter of 4mm are cut at 10mm intervals. After cutting, the workpiece is ultrasonically rinsed with deionized water and vacuum dried. The kerf width is 0.12mm, the surface roughness Ra is 1.5μm, and the heat-affected zone is ≤100μm.

[0085] S3: The brazing filler metal thickness is 0.18mm, the magnesium content is 0.2%, and the welding temperature is controlled at 605℃; The multi-stage heating program consists of: heating at 12℃ / min to 400℃ and holding for 40 min, then heating at 6℃ / min to 500℃ and holding for 40 min, then heating at 6℃ / min to 570℃ and holding for 40 min, and finally heating at 6℃ / min to 605℃ and holding for 15 min. Solution treatment is performed at 525℃ for 2 hours, and artificial aging is performed at 170℃ for 10 hours.

[0086] S4: The outer diameter of the filling tube is 1.2mm, the short side width of the filling port is 1.4mm, and after flattening, a 0.15mm assembly gap is left between the two sides of the tube wall and the inner wall of the filling port. The insertion depth of the aluminum tube is 12mm. When soldering with low-temperature solder paste, heat to 240℃ and hold for 2 minutes. S5: Fill the inner cavity of the shell with 1.0 MPa of dry air and maintain the pressure for 40 minutes; S7: Cold pressure welding: 1.5MPa; Friction stir welding: 1200rpm, feed rate: 400mm / min, pressure: 12MPa; The remaining steps (S1, S6, S8, S9) and process parameters are the same as in Example 1.

[0087] Example 3 This embodiment provides an aluminum VC heat spreader for use in VPX modules, prepared using the method described in Embodiment 1 or 2, such as... Figure 1 As shown, the upper shell 1, lower shell 2, and foam are included. The external dimensions, mounting hole positions, and layout of the thin-walled areas inside the cavity of the upper shell 1 and lower shell 2 are customized according to the industry standards of VPX modules and their internal structural space. They are sealed together by vacuum brazing to form a heat spreader shell with a sealed cavity inside. The shell material is 6063 aluminum alloy.

[0088] The upper shell 1 or the lower shell 2 is provided with a rectangular filling port that penetrates the shell for installing the filling pipe 5.

[0089] The foamed metal absorbent core 3 is fixed to the inner surface of the upper shell 1, the inner surface of the lower shell 2, or both the upper and lower shells by vacuum brazing. The absorbent core is made of foamed nickel or foamed aluminum. In this embodiment, the absorbent core structure has dimensions of 206.9mm × 110.6mm × 0.5mm.

[0090] The filling tube 5 is a thin-walled hollow aluminum tube installed on the filling port, serving as a channel for vacuuming and filling the working medium. The end of the filling tube 5 is sealed by cold pressure welding.

[0091] The sealing connector 4 is located at the filling port, and its external dimensions are larger than the opening size of the filling port. It is stepped and has an internal groove to accommodate the end of the filling tube 5. The edges are rounded, and the material is aluminum alloy 6063. The sealing connector 4 is welded to the filling port by friction stir welding, covering the already sealed end of the filling tube 5 to form a second seal. The sealing connector 4 and the filling tube 5 together constitute a composite sealing structure for the filling port. In this embodiment, the external dimensions of the sealing connector are 11.5mm × 7.3mm × 4mm.

[0092] The overall dimensions of the prepared heat spreader are 233.4mm × 167.5mm × 24mm.

[0093] Comparative Example 1 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: After the working medium is filled, no temporary cold pressure welding is performed. Instead, friction stir welding is used to completely seal the filling port. All other steps and parameters are the same as in Example 1.

[0094] Comparative Example 2 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: The liquid suction core is cut and shaped by mechanical punching rather than laser wire cutting. The remaining steps and parameters are the same as in Example 1.

[0095] Comparative Example 3 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: The filling rate during working fluid filling is 25% (i.e., the volume of liquid working fluid accounts for 25% of the volume of the suction core cavity), instead of 100%. The remaining steps and parameters are the same as in Example 1.

[0096] Comparative Example 4 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: The liquid-absorbing core is prepared by powder sintering process (aluminum powder sintering, porosity of about 65%), instead of foam metal profiles formed by laser wire cutting. The remaining steps and parameters are the same as in Example 1.

[0097] Comparative Example 5 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: The magnesium content in the Al-Si brazing filler metal used for vacuum brazing is 1.0%, and the remaining steps and parameters are the same as in Example 1.

[0098] Comparative Example 6 This comparative example provides a method for preparing an aluminum VC heat spreader for use in a VPX module. The dimensions of the aluminum VC heat spreader to be prepared are the same as those in Example 1, and the preparation method is similar to that in Example 1, except that: Instead of using a multi-stage stepped heat preservation process, the furnace body is directly heated to the welding temperature (600℃) for welding during vacuum brazing. The remaining steps and parameters are the same as in Example 1.

[0099] The vapor chambers prepared in the examples and comparative examples were subjected to the following tests: Isothermal performance test: Under the condition of 20W central heat source power and natural heat dissipation, the temperature difference (temperature uniformity) between the center and far end of the evaporation end of the heat spreader is measured.

[0100] Heat transfer performance test: Under the conditions of total power of 94W and cold end temperature of 32℃, the temperature difference between the outer wall surface temperature at the heat source location and the average temperature of the outer wall surface at the heat sink location is measured (heat transfer performance).

[0101] Table 1 shows the performance of the aluminum VC heat exchangers in the embodiments and comparative examples. Under fixed heat source power and heat dissipation conditions, a smaller isothermal performance temperature difference indicates more uniform heat diffusion in the two-dimensional plane and lower local hot spot temperatures; a smaller heat transfer performance temperature difference indicates a smoother path for heat transfer from the heat source to the heat sink. Therefore, by comprehensively comparing the isothermal performance temperature difference and heat transfer performance temperature difference, the superiority of the heat dissipation effect between the embodiments and comparative examples can be directly evaluated: a smaller temperature difference indicates better overall heat dissipation performance of the heat exchanger.

[0102] Table 1 Performance Tests of Aluminum Heat Spreader in Examples

[0103] As can be seen from the test results in Table 1, the performance indicators of Examples 1 and 2 are superior to all comparative examples.

[0104] The difference between Comparative Example 1 and Example 1 is that the temporary seal of cold pressure welding was eliminated, and friction stir welding was used directly for complete sealing. Due to the lack of immediate sealing protection from cold pressure welding, the vacuum in the cavity was destroyed and the pressure increased during the friction stir welding process, resulting in a decrease in sealing quality; its performance was weaker than that of Example 1.

[0105] Comparative Example 2 uses mechanical punching instead of laser wire cutting to prepare the liquid-absorbing core. The mechanical stress generated during the mechanical punching process causes the edges of the foam metal pores to collapse and deform, the local capillary force to decrease significantly, the working fluid return channel to be blocked, and the isothermal performance and heat transfer performance to be significantly worse than those of Example 1.

[0106] Comparative Example 3 reduced the liquid filling rate to 25%. Due to the severely insufficient liquid filling rate, the working fluid supply at the evaporation end could not meet the needs of the phase change cycle, resulting in localized drying and a significant decrease in heat transfer performance, which was significantly weaker than in Example 1. This indicates that the 100% liquid filling rate and the high porosity characteristics of the foam metal wick created a synergistic effect, and the capillary force advantage of the foam metal could not be fully utilized when the liquid filling rate was insufficient.

[0107] Comparative Example 4 uses a powder sintering process to prepare a liquid wick. The porosity of the powder sintered core (approximately 65%) is much lower than that of the foam metal (90%), resulting in insufficient capillary force, limited working fluid reflux rate, and significantly inferior heat transfer performance compared to Example 1.

[0108] Comparative Example 5 increased the magnesium content in the brazing filler metal to 1.0%. Excessive magnesium content resulted in excessive fluidity of the brazing filler metal, causing excessive filler metal to penetrate into the pores of the foamed metal during welding. After cooling, the filler metal solidified and blocked some of the pores, reducing the effective porosity, impairing capillary properties, and making the isothermal and heat transfer properties inferior to those of Example 1.

[0109] Comparative Example 6 did not employ a multi-stage stepped heat preservation process during vacuum brazing; instead, the furnace body was directly heated to the welding temperature. The lack of stepped heat preservation resulted in uneven temperature distribution within the workpiece, generating significant thermal stress, causing localized deformation of the liquid-absorbing core and warping of the plate shell. This led to uneven welding quality, and the isothermal and heat transfer performance was inferior to that of Example 1.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum VC heat spreader for use in VPX modules, characterized in that, Includes the following steps: S1: Using aluminum alloy sheet as raw material, CNC machining and pickling are used to obtain a clean VPX module shell; S2: Foam metal profiles are used as raw materials, and foam metal liquid absorbent cores are obtained through laser wire cutting, cleaning and drying; S3: Vacuum brazing the plate shell and the liquid absorption core and post-weld heat treatment are performed to obtain a heat spreader body with a closed cavity; S4: The thin-walled hollow aluminum tube is flattened and brazed at low temperature and installed at the filling port to obtain a heat spreader semi-finished product. S5: Fill the heat spreader semi-finished product with test gas and maintain pressure to monitor, completing the first airtightness test; S6: After evacuating the inner cavity of the shell through the filling tube, acetone working fluid is filled in, with a filling rate of 100%; S7: After filling, the heat-soaked plate semi-finished product is temporarily sealed by cold pressure welding and then completely sealed by friction stir welding. S8: Perform CNC precision machining and conductive oxidation surface treatment on the sealed heat spreader semi-finished product to obtain the finished aluminum VC heat spreader; S9: Perform a secondary airtightness test on the finished aluminum VC heat exchange plate.

2. The preparation method according to claim 1, characterized in that, In step S2, the foamed metal profile is aluminum foam or nickel foam, the laser wire cutting processing speed is 30~70mm / s, the spot size is 60~100μm, the scanning interval is 0.1~0.5mm, and the jump speed is 800~1200mm / s.

3. The preparation method according to claim 1, characterized in that, In step S3, the brazing filler metal used in vacuum brazing is an Al-Si based filler metal with a magnesium content of 0.1% to 0.5%.

4. The preparation method according to claim 3, characterized in that, In step S3, the vacuum brazing temperature is 595℃~610℃, and the vacuum degree is ≤10. - ²Pa; A multi-stage heating and stepped heat preservation program is adopted: the temperature is increased to 350~420℃ at 8~15℃ / min and held for 20~60min, then increased to 480~520℃ at 3~8℃ / min and held for 20~60min, then increased to 550~590℃ at 3~8℃ / min and held for 20~60min, and finally increased to 595~610℃ at 3~8℃ / min and held for 5~20min.

5. The preparation method according to claim 1, characterized in that, In step S3, the post-weld heat treatment includes solution treatment and aging treatment: the post-weld workpiece is heated to 520℃~530℃ and held for 1~2 hours, then quenched and cooled, and then artificially aged by heating to 165℃~175℃ and holding for 6~10 hours.

6. The preparation method according to claim 1, characterized in that, In step S4, the outer diameter of the filling tube is 0.8mm~1.2mm, the thickness after flattening is 0.8mm~1.2mm, and an assembly gap of 0.05mm~0.15mm is left between the two sides of the flattened tube wall and the inner wall of the filling port. The low-temperature brazing uses low-temperature solder paste, which is heated to 220℃~240℃ and held for 1~2 minutes.

7. The preparation method according to claim 1, characterized in that, In step S5, the airtightness test includes: filling the inner cavity of the shell with dry air at 0.5~1.0MPa, maintaining the pressure for 30~40 minutes, and if the pressure does not drop, it indicates that the shell's sealing performance meets the requirements; If the pressure drops, use epoxy resin adhesive or UV-cured adhesive to reseal the leaking area, and then test again until the airtightness is satisfactory.

8. The preparation method according to claim 1, characterized in that, In step S7, the downward pressure of the cold pressure welding is 0.5~2.0MPa; the stirring head rotation speed of the friction stir welding is 1000~2000rpm, the feed speed is 200~500mm / min, and the downward pressure is 5~15MPa.

9. An aluminum VC heat spreader for use in VPX modules, characterized in that, Prepared by the preparation method according to any one of claims 1 to 8, comprising an upper shell (1), a lower shell (2), a foam metal liquid-absorbing core (3), a filling tube (5), and a sealing connector (4). The upper shell (1) and the lower shell (2) are connected by vacuum brazing to form a heat-spreading plate shell with a sealed cavity inside. The upper shell (1) or the lower shell (2) is provided with a filling port that penetrates the shell. The foam metal absorbent core (3) is fixed to the inner surface of the upper shell (1) and / or the lower shell (2) by vacuum brazing; The filling tube (5) is installed on the filling port, and its end is sealed by cold pressure welding. The sealing joint (4) is located at the filling port and is welded to the filling port by friction stir welding. It covers the sealed end of the filling tube (5) to form a second seal. The sealing joint (4) and the filling tube (5) together constitute a composite sealing structure of the filling port.

10. The aluminum VC heat spreader according to claim 9, characterized in that, The foamed metal absorbent core (3) is made of foamed aluminum or foamed nickel, with a thickness of 0.5 mm to 2.0 mm and a porosity of 85% to 97%. The sealing joint (4) is stepped and has a groove inside to accommodate the end of the filling tube (5), with rounded edges. The upper shell (1), lower shell (2) and sealing joint (4) are made of aluminum alloy 6063.

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