Stainless steel heat plate and preparation method and application thereof

Abstract

The application provides a stainless steel heat plate and a preparation method and application thereof. The stainless steel heat plate comprises a shell and a capillary core in the shell. The shell comprises a stainless steel base material and a chromium-copper alloy layer embedded in the stainless steel base material. The mass content of chromium in the chromium-copper alloy layer is greater than or equal to 30%. The stainless steel heat plate of the application is alloyed in the region close to the surface of the stainless steel, so that the alloy material becomes part of the stainless steel and forms an integrated structure with the stainless steel base material, thereby effectively avoiding problems such as peeling of the plating layer. The generated alloy layer is resistant to high temperature, and the high temperature generated by subsequent welding has little effect on it. In the application, a high-chromium copper alloy layer is generated on the surface of the stainless steel, a dense chromium passivation film can be formed, the compatibility problem of the stainless steel and water is solved, and the problems such as hydrogen evolution existing in the current process are greatly reduced.

Description

Technical Field

[0001] This application relates to the field of stainless steel heat spreader technology, specifically to a stainless steel heat spreader, its preparation method, and its application. Technical Background

[0002] With the increasing integration of electronic devices, heat dissipation within small spaces becomes a crucial issue, making vapor chambers a popular choice for electronic product cooling. Currently, vapor chambers are primarily made of copper or copper alloys. However, these materials result in vapor chambers with relatively low hardness, and their thickness is rarely less than 0.25mm. As mobile phones and other electronic products become increasingly ultra-thin, even thinner vapor chambers are needed to meet these demands. Furthermore, copper or copper alloys have poor corrosion resistance, causing the vapor chamber to oxidize after a period of use, leading to further corrosion of the copper or alloy and ultimately resulting in liquid leakage and the failure of the electronic product.

[0003] Compared to copper, stainless steel not only has higher hardness, strength, and corrosion resistance, but also offers a significant cost advantage. However, stainless steel reacts with water in a vapor chamber to produce hydrogen evolution gas, leading to the generation of non-condensable gases. This significantly reduces the vacuum level inside the vapor chamber, causing it to fail. Traditional methods for addressing the compatibility of stainless steel with water include copper or copper alloy electroplating and surface passivation. However, due to the poor plating properties of stainless steel, electroplating is prone to problems such as plating peeling; and the passivation film formed by surface passivation is difficult to withstand the high temperatures of subsequent welding. Summary of the Invention

[0004] To address the aforementioned technical limitations, this application proposes a stainless steel heat spreader and its preparation method. Unlike traditional stainless steel surface treatment techniques, the stainless steel heat spreader of this application involves alloying the stainless steel near the surface, making the alloy material an integral part of the stainless steel and forming a unified structure with the stainless steel substrate. This effectively avoids problems such as coating peeling, and the resulting alloy layer is heat-resistant, with minimal impact from the high temperatures generated during subsequent welding. This application also generates a high-chromium copper alloy layer (chromium content ≥30wt%) on the stainless steel surface, forming a dense chromium passivation film. This solves the compatibility problem between stainless steel and water, significantly reducing hydrogen evolution and other issues present in current processes. Simultaneously, copper provides excellent hydrophilicity and weldability.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] The inventive point of this application is to provide a stainless steel heat spreader, including a shell and a capillary core located inside the shell. The shell includes a stainless steel substrate and a chromium-copper alloy layer covering the stainless steel substrate. In the chromium-copper alloy layer, the mass content of chromium is ≥30%.

[0007] Optionally, by weight, the chromium-copper alloy layer comprises: 30-60% chromium, 10-40% copper, 2-10% iron, 2-10% nickel, and 0-3% trace metal elements.

[0008] Optionally, the thickness of the chromium-copper alloy layer is 0.1 μm to 20 μm.

[0009] The capillary wick can be made of stainless steel and / or copper.

[0010] When the capillary wick is made of stainless steel, the capillary wick comprises a stainless steel substrate and a chromium alloy embedded in the stainless steel substrate.

[0011] Another inventive point of this application is to provide a method for preparing a stainless steel heat spreader.

[0012] Optionally, the preparation method includes: (1) obtaining a stainless steel upper cover, a stainless steel lower cover, and a capillary core; (2) mixing the stainless steel upper cover and the stainless steel lower cover with chromium alloy material under vacuum to alloy them, thereby obtaining an upper cover containing a chromium-copper alloy layer and a lower cover containing a chromium-copper alloy layer; (3) combining the lower cover containing the chromium-copper alloy layer with the capillary core, and then sealing and welding it with the upper cover containing the chromium-copper alloy layer to obtain a shell containing a capillary core; (4) injecting liquid into the shell containing the capillary core and evacuating it to obtain the stainless steel heat spreader.

[0013] Optionally, the stainless steel upper cover and stainless steel lower cover being mixed with chromium alloy material means that the stainless steel upper cover and stainless steel lower cover are completely embedded in chromium alloy material.

[0014] Optionally, by weight, the chromium alloy material comprises: 20-60 parts chromium, 8-40 parts copper, 30-70 parts dispersant, 0.1-5 parts reducing agent, and 0.5-5 parts activator.

[0015] Optionally, the vaporization temperature of the reducing agent is lower than the alloying temperature; the vaporization temperature of the activating agent is lower than the alloying temperature; and the activating agent contains halogen.

[0016] Preferably, the reducing agent comprises metallic magnesium; the activating agent comprises zinc chloride; and the dispersant comprises at least one of aluminum oxide, silicon oxide, and magnesium oxide.

[0017] Optionally, the vacuum refers to a vacuum degree of less than 13 Pa; the alloying conditions are: temperature 917~1050℃, time greater than 2 hours.

[0018] Another inventive point of this application is to provide an application of the stainless steel heat spreader as described above in electronic products.

[0019] Compared with the prior art, this application has the following advantages:

[0020] (1) The stainless steel heat spreader of this application is alloyed in the area of ​​stainless steel near the surface, so that the alloy material becomes part of the stainless steel and forms an integrated structure with the stainless steel substrate. There is no interface problem between different metals that exists in other methods, thus effectively avoiding problems such as coating peeling; the generated alloy layer is resistant to high temperature, and the high temperature generated by subsequent welding has little effect on it, avoiding the problem of damage to the alloy layer caused by subsequent preparation processes, thus failing to effectively protect it; this application generates a high chromium copper alloy layer (chromium content ≥30wt%) on the surface of stainless steel, which can form a dense chromium passivation film, solving the compatibility problem between stainless steel and water, and greatly reducing the hydrogen evolution problem existing in the current process.

[0021] (2) The method for preparing the stainless steel heat spreader in this application involves vacuum infiltration, where chromium alloy material and the upper and lower covers of the stainless steel heat spreader are alloyed. The reducing agent in the chromium alloy material vaporizes under specific vacuum and temperature conditions. The vaporized reducing agent vapor rapidly reacts with chromium powder (granules), removing oxygen from the chromium oxide film on the surface of the chromium powder (granules) to form oxides. These oxides are then removed under continuous vacuum, promoting the conversion of chromium from a solid to a gaseous state, laying the foundation for subsequent high-content chromium infiltration. The activator also vaporizes under these conditions, becoming a gas. The gaseous activator provides a large number of active chloride ions, accelerating the reaction and promoting the formation of intermetallic compounds between chromium and stainless steel, resulting in a tighter bond. Furthermore, the preparation method in this application produces a dense and smooth chromium-infiltrated layer. Attached Figure Description

[0022] Figure 1 A finished drawing of the stainless steel heat spreader provided in Test Example 1 of this application;

[0023] Figure 2 A light mirror image of the cross-section of the stainless steel heat exchange plate provided in Test Example 1 of this application;

[0024] Figure 3 A high-magnification scanning electron microscope image of the surface of the stainless steel heat spreader provided in Test Example 1 of this application;

[0025] Figure 4 High-temperature test diagrams of stainless steel heat exchange plates provided for experimental examples and comparative examples in this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, a more detailed description is provided below. However, it should be understood that the description herein is merely for explaining this application and is not intended to limit its scope.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. All materials and instruments used herein are commercially available, and the characterization methods involved can be found in relevant descriptions in the prior art, which will not be repeated here.

[0028] To further understand this application, the following detailed description is provided in conjunction with the preferred embodiments.

[0029] Example 1

[0030] This embodiment provides a stainless steel heat spreader, including a shell and a capillary core located inside the shell. The shell includes a stainless steel substrate and a chromium-copper alloy layer covering the stainless steel substrate; in the chromium-copper alloy layer, the mass content of chromium is ≥30%.

[0031] The chromium content in stainless steel is generally less than 30%. When the chromium content is less than 30%, it is difficult to form a sufficiently dense chromium passivation film, thus failing to provide adequate protection. However, in the stainless steel heat spreader of this application, there is a chromium-copper alloy layer on the surface of the stainless steel. The chromium content in this alloy layer is ≥30%, making it the main element in the alloy layer. This prevents the breakage between chromium elements, thereby forming a sufficiently dense and continuous chromium passivation film. This chromium passivation film does not react with water, solving the problem of hydrogen evolution from iron-nickel ions in stainless steel. Furthermore, this passivation film has high corrosion resistance in acidic or alkaline environments, extending the service life of the heat spreader. In addition, the infiltration of chromium can also improve the high-temperature resistance of the heat spreader, maintaining its original shape and preventing deformation during subsequent welding or use in electronic equipment.

[0032] In the chromium-copper alloy layer, the mass content of chromium is preferably 30% to 60%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value between any two values.

[0033] By weight, the chromium-copper alloy layer comprises: 30-60% chromium, 10-40% copper, 2-10% iron, 2-10% nickel, and 0-3% trace metal elements.

[0034] Trace metal elements include any one of molybdenum, manganese, vanadium, titanium, aluminum, cobalt, and barium.

[0035] The thickness of the chromium-copper alloy layer is 0.1μm to 20μm, for example, it can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any value between any two values.

[0036] If the thickness is less than 0.1 micrometers, it is difficult to form a completely continuous alloy layer. Once the alloy layer is discontinuous, the stainless steel heat exchange plate will react with water and the substrate during use, causing the stainless steel heat exchange plate to fail.

[0037] If the thickness exceeds 20 micrometers, on the one hand, the surface brittleness will increase rapidly, leading to a decrease in the overall material toughness. On the other hand, an excessively thick alloy layer will affect the sealing performance of subsequent laser welding.

[0038] The capillary wick can be made of stainless steel and / or copper.

[0039] When the capillary wick is made of stainless steel, the capillary wick comprises a stainless steel substrate and a chromium alloy embedded in the stainless steel substrate.

[0040] Example 2

[0041] This embodiment provides a method for preparing a stainless steel heat spreader plate, which is the same as the stainless steel heat spreader plate in Embodiment 1, so it will not be described in detail here.

[0042] The preparation method includes: (1) obtaining a stainless steel upper cover, a stainless steel lower cover and a capillary core; (2) mixing the stainless steel upper cover and the stainless steel lower cover with chromium alloy material under vacuum and alloying them to obtain an upper cover containing a chromium-copper alloy layer and a lower cover containing a chromium-copper alloy layer; (3) combining the lower cover containing the chromium-copper alloy layer with the capillary core and then sealing and welding it with the upper cover containing the chromium-copper alloy layer to obtain a shell containing a capillary core; (4) injecting liquid and evacuating the shell containing the capillary core to obtain the stainless steel heat spreader.

[0043] The preparation methods of the stainless steel top cover, stainless steel bottom cover and capillary core in step (1) are not limited. They can be conventional methods or commercially available finished products. This application does not limit them here.

[0044] Since the stainless steel top cover and the stainless steel bottom cover have the same composition and size, and are only distinguished as top cover and bottom cover during assembly, the preparation methods of the top cover containing the chromium copper alloy layer and the bottom cover containing the chromium copper alloy layer in step (2) are exactly the same.

[0045] The phrase "the stainless steel top cover and the stainless steel bottom cover are respectively mixed with chromium alloy material" means that the stainless steel top cover and the stainless steel bottom cover are completely embedded in chromium alloy material.

[0046] Step (2) includes: under vacuum, embedding the stainless steel upper cover and the stainless steel lower cover in chromium alloy material and alloying them to obtain an upper cover containing a chromium-copper alloy layer and a lower cover containing a chromium-copper alloy layer; or under vacuum, covering all surfaces of the stainless steel upper cover and the stainless steel lower cover with chromium alloy material and alloying them to obtain an upper cover containing a chromium-copper alloy layer and a lower cover containing a chromium-copper alloy layer.

[0047] Further, it can be a step-by-step alloying process. Under vacuum conditions, one or more surfaces of the stainless steel top and bottom covers are first coated with a chromium alloy material for alloying. Then, the remaining surfaces of the stainless steel top and bottom covers are coated with the same chromium alloy material and alloyed again, ultimately resulting in a top cover and a bottom cover containing chromium-copper alloy layers. This step-by-step alloying can be a one-step, two-step, or multi-step alloying process, depending on specific requirements.

[0048] The chromium alloy material is in powder form. If there are lumps or large particles in the alloy material, they need to be ground into powder before use. Small powder particles help to occur more uniformly during the alloying process and can promote the fusion of the alloy with the stainless steel more quickly and effectively.

[0049] The particle size of the alloy material is preferably less than 50 mesh, and more preferably 80-200 mesh. This particle size ensures that the powder can fully contact the stainless steel surface to react, while avoiding the sintering and agglomeration of the powder itself, which would affect its use.

[0050] By weight, the chromium alloy material comprises: 20-60 parts of chromium or ferrochrome, 8-40 parts of copper, 30-70 parts of dispersant, 0.1-5 parts of reducing agent, and 0.5-5 parts of activator. The chromium or ferrochrome can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, or any value between any two of these numbers; the dispersant can be 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, or any value between any two of these numbers; the reducing agent can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, or any value between any two of these numbers; the activator can be 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, or any value between any two of these numbers.

[0051] Optionally, the vaporization temperature of the reducing agent is lower than the alloying temperature; the vaporization temperature of the activating agent is lower than the alloying temperature; and the activating agent contains halogen.

[0052] Preferably, the vaporization temperature of the reducing agent is not less than the vaporization temperature of the activating agent.

[0053] More preferably, the vaporization temperature of the reducing agent is lower than that of the activating agent.

[0054] Preferably, the reducing agent comprises metallic magnesium; the activating agent comprises zinc chloride; and the dispersant comprises at least one of aluminum oxide, silicon oxide, and magnesium oxide.

[0055] Optionally, the vacuum refers to a vacuum degree of less than 13 Pa; the alloying conditions are: temperature 917~1050℃, time 2~10 hours.

[0056] Under a vacuum of 13 Pa, chromium vaporizes at a temperature of 917°C. Chromium will vaporize when the alloying temperature is greater than or equal to 917°C. Preferably, the alloying temperature is between 917°C and 1150°C, and the time is greater than 2 hours.

[0057] Chromium metal has a body-centered cubic lattice structure with an atomic radius of 0.1249 nm. Stainless steel is primarily composed of iron. Iron has a body-centered cubic lattice structure with an atomic radius of 0.1241 nm at temperatures below 912℃; and a face-centered cubic lattice structure with an atomic radius of 0.1288 nm at temperatures between 912℃ and 1394℃.

[0058] The chromium diffusion process is carried out at temperatures above 917℃. At this temperature, chromium has a body-centered cubic structure with an atomic radius of 0.1249 nm, while free iron ions have a face-centered cubic structure with an atomic radius of 0.1288 nm. Since the atomic radii of chromium and iron are relatively close at high temperatures, chromium and iron readily form a substitutional solid solution. As the holding time increases, chromium continuously diffuses in, and the chromium content also increases. Simultaneously, copper can be partially carried away by the vaporized chromium and adhere to the stainless steel surface. Furthermore, copper has a face-centered cubic crystal structure with an atomic radius of 0.1278 nm, which is similar to that of chromium and iron, enabling it to undergo diffusion alloying with stainless steel.

[0059] After chromium infiltration, during the cooling process, the iron undergoes a transformation from a face-centered cubic structure to a body-centered cubic structure, resulting in volume expansion. Due to the "anchoring" effect of chromium and copper atoms, this volume expansion during cooling is limited, resulting in a uniform and dense infiltrated layer. This prevents water and water vapor from penetrating into the matrix and reacting with free iron ions. Simultaneously, the addition of copper increases compatibility with the capillary core. Since most capillaries are currently made of copper mesh, the copper in the bottom cover allows for faster integration with the capillary core, reducing potential interface problems.

[0060] Preferably, the alloying process is divided into three stages: the first stage is the vaporization of the reducing agent, that is, the temperature of the first stage needs to reach or exceed the vaporization temperature of the reducing agent; the second stage is the vaporization of the activator, that is, the temperature of the second stage needs to reach or exceed the vaporization temperature of the activator; and the third stage is the alloying temperature, that is, it needs to reach or exceed the vaporization temperature of chromium.

[0061] The preferred temperature for the first stage is 450–500℃, and the holding time is 30–60 min; the temperature for the second stage is 732–850℃, and the holding time is 30–60 min; the temperature for the third stage is 917–1050℃.

[0062] By increasing the temperature in stages, the reducing agent can be vaporized first, breaking the oxide film and generating byproducts, which are then removed by vacuuming. In the second stage, the activator vaporizes, generating active ions and activating chromium. The third stage is alloying, which alloys the activated chromium, copper, and stainless steel to form a dense alloy layer.

[0063] The first stage of heating is a slow heating process, preferably with a heating rate of less than 5°C / min. During the slow heating process, the reducing agent can fully react with the oxide film layer, remove the oxide film formed in the foamed nickel or raw materials, and promote the faster penetration of subsequent alloys.

[0064] The second stage is the vaporization temperature of the activator, with a heating rate of less than 10℃ / min, to prevent the activator from being rapidly removed, maximizing contact with chromium and promoting its activation.

[0065] Under these vacuum conditions and temperature ranges, the reducing agent has already vaporized; that is, the vaporization temperature of the reducing agent is lower than the aforementioned temperature under the vacuum conditions. The activator is a substance capable of releasing active chloride ions, preferably a substance capable of vaporizing within the aforementioned vacuum conditions and temperature range, thereby releasing active chloride ions.

[0066] The dispersant includes at least one of alumina, silicon dioxide, and magnesium oxide; the reducing agent includes magnesium; and the activating agent includes zinc chloride.

[0067] Chromium has a vaporization temperature of 917℃ under a vacuum of 13 Pa, which can be used for chromium diffusion under vacuum. However, due to the dense chromium oxide film on the surface of chromium powder (particles), it cannot vaporize under these conditions. Even with further increases in vacuum and temperature, vaporization of the chromium powder (particles) remains difficult. Magnesium, on the other hand, has a vaporization temperature of 439℃ under a vacuum of 13 Pa. The vaporized magnesium vapor reacts rapidly with the chromium powder (particles), removing oxygen from the chromium oxide film on the surface to form magnesium oxide, which is then removed under continuous vacuum. Zinc chloride has a boiling point of 732℃, and gaseous zinc chloride provides a large amount of active chloride ions, accelerating the reaction.

[0068] More preferably, by performing a staged temperature treatment on the alloy, the temperature is first raised to 450°C, then slowly raised to 732°C (the vaporization temperature of zinc chloride), and then slowly raised to 917°C to 1150°C, to avoid the rapid removal of zinc chloride and magnesium vapors.

[0069] The capillary wick can be made of stainless steel and / or copper.

[0070] When the capillary wick is made of copper, it can be a porous metal material such as copper or copper alloy mesh, foam metal, or copper powder sintered porous copper foil.

[0071] Both the upper and lower cover alloy layers contain copper, which can improve the welding wettability between the capillary wick and the lower cover.

[0072] When the capillary core is made of stainless steel, the capillary core includes a stainless steel substrate and a chromium alloy embedded in the stainless steel substrate; that is, the stainless steel capillary core is also alloyed, so that it has the same alloy layer as the lower cover. When the two are welded, the instability of the interface is reduced, it is easier to fuse into one, reduce gaps, avoid leakage, reduce poor sealing and other problems, and extend the service life of the heat spreader.

[0073] The stainless steel top cover, bottom cover, and capillary core can be made of 304, 304L, 316, or 316L. The capillary core can be made of stainless steel wire mesh with a mesh size of less than 80, copper wire mesh, or foamed copper, etc.

[0074] Step (3) involves bonding the capillary core to the lower cover. Furthermore, to improve the bonding strength, a welding process can be used.

[0075] The welding in step (3) is laser welding; laser welding is efficient, reliable and low cost, and is convenient for large-scale use.

[0076] The bottom cover, after being alloyed with chromium copper, is then bonded with copper alloy capillaries such as copper mesh or copper foam. Alternatively, stainless steel capillaries alloyed with chromium copper can be used. Further, the top and bottom covers are sealed together using laser welding. Laser welding process parameters: power 60–120W, speed 50–200m / s.

[0077] Currently, brazing is another welding method, but it is a complex and costly process, drastically increasing overall expenses. Furthermore, the bond strength at the brazed joint is the weakest point in the entire heat spreader, making it highly susceptible to leaks and reactions during long-term use. Laser welding, on the other hand, does not introduce new materials and boasts significantly higher weld strength than brazing. In addition, laser welding offers numerous advantages, including faster speed, lower cost, and higher yield.

[0078] Currently, most stainless steel is made of copper-plated stainless steel, which means that one or more layers of copper are plated on the surface of stainless steel to avoid water contact with stainless steel. However, laser welding cannot be used on copper-plated materials, meaning that laser welding cannot weld substances with a high copper content on the surface, which greatly increases the welding cost to a certain extent.

[0079] After laser welding, the stainless steel heat spreader undergoes high-temperature shaping at temperatures between 880℃ and 1000℃ for more than 10 minutes. The resulting flatness of the shaped stainless steel heat spreader is less than 0.2. Shaping improves the bonding between chromium and copper and the stainless steel, enhances weldability, and strengthens the weld joint. Furthermore, welding damages the alloy layer at the weld joint, while shaping allows for the uniform redistribution of the damaged alloy elements, reforming the alloy layer.

[0080] Next, the rat tail is attached, water is injected, and a vacuum seal is created.

[0081] The process involves injecting water, vacuuming, and sealing using a liquid injection pipe; subsequent shaping and other processes yield the final stainless steel heat spreader.

[0082] Example 3

[0083] Based on the content of this application, the preparation methods of the stainless steel heat spreader in Example 1 and Example 2 are described in detail below:

[0084] Experimental Example 1

[0085] (1) The upper and lower covers are obtained by stamping 60-micron thick 316 stainless steel, and 400-mesh stainless steel capillary cores of specific shapes are cut.

[0086] (2) The stainless steel top cover, stainless steel bottom cover, and stainless steel capillary core prepared above were placed together with 80-mesh alloy material (25 parts chromium powder, 10 parts copper, 40 parts silicon oxide, 1 part magnesium powder, and 2 parts zinc chloride) in a furnace. The alloy material was used to embed the entire surface of the stainless steel top cover, stainless steel bottom cover, and stainless steel capillary core. Then, a vacuum was drawn. When the vacuum reached 13 Pa (this vacuum was maintained throughout the process), the temperature was raised at a rate of 2 °C / min. When the temperature reached 450 °C, it was held for 30 min. The temperature was raised at a rate of 4 °C / min. When the temperature reached 732 °C, it was held for 30 min. Then, the temperature was raised again at a rate of 6 °C / min. When the temperature reached 930 °C, the temperature was stopped and maintained for 4 h. The top cover and the bottom cover contained chromium-copper alloy layers.

[0087] (3) After the lower cover containing the chromium copper alloy layer is assembled with the capillary core, it is sealed and welded with the upper cover containing the chromium copper alloy layer to obtain a shell containing the capillary core. The stainless steel heat spreader plate after laser welding is subjected to high-temperature shaping at a temperature of 880℃ for 20 minutes. The flatness of the stainless steel heat spreader plate after shaping is less than 0.2.

[0088] (4) The shell containing the capillary core is injected with liquid and vacuumed to obtain a stainless steel heat exchange plate.

[0089] The average content of elements in the alloy layer is as follows: chromium 48%, copper 36%, iron 8.8%, nickel 4.5%, and trace elements (molybdenum) 2.7%. Figure 1 As shown, the stainless steel prepared in this experimental example is copper-colored because it is doped with copper. Figure 2 The image shows the cross-sectional optical microstructure of the stainless steel heat exchanger. It can be seen that the formed alloy layer is relatively dense and the elements in the alloy layer are evenly distributed. The thickness of the chromium-copper alloy layer in the stainless steel heat exchanger is 2.8 micrometers.

[0090] Elemental analysis was performed on the alloy layer of the stainless steel heat exchanger, such as... Figure 3 As shown in the figure, the scanning electron microscope image is shown. Two regions were randomly selected (region I has an area of ​​16 μm × 16 μm; region I has an area of ​​22 μm × 22 μm) for elemental analysis. The results are shown in Table 1.

[0091] Table 1

[0092] Cr (wt%) Cu (wt%) Fe (wt%) Ni (wt%) Mo (wt%) Area I 48.2 36.5 8.6 3.9 2.8 Area II 47.8 35.6 9.1 4.8 2.7

[0093] As shown in Table 1, the component content in different regions is relatively consistent, indicating good consistency of the infiltration layer. This ensures high reliability during use.

[0094] Experimental Example 2

[0095] (1) The upper and lower covers are obtained by stamping 60-micron thick 316 stainless steel, and the capillary core of 350 mesh copper mesh of a specific shape is cut.

[0096] (2) The stainless steel upper cover, stainless steel lower cover, copper mesh capillary core and alloy material 80 mesh (50 parts chromium powder, 30 parts copper, 60 parts alumina powder, 3 parts magnesium powder, 4 parts zinc chloride) prepared above were placed in a furnace pot. The alloy material was used to embed the entire surface of the stainless steel upper cover and stainless steel lower cover. Then, a vacuum was drawn. When the vacuum degree reached 13 Pa (this vacuum degree was maintained throughout the process), the temperature was raised at a rate of 5℃ / min. When the temperature reached 450℃, it was held for 40 min. The temperature was raised at a rate of 3℃ / min. When the temperature reached 732℃, it was held for 40 min. Then, the temperature was raised again at a rate of 8℃ / min. When the temperature reached 950℃, the temperature was stopped and maintained for 3 h. The upper cover and the lower cover containing the chromium-copper alloy layer were then prepared.

[0097] (3) After the lower cover containing the chromium copper alloy layer is assembled with the capillary core, it is sealed and welded with the upper cover containing the chromium copper alloy layer to obtain a shell containing the capillary core; the stainless steel heat spreader plate after laser welding is subjected to high-temperature shaping at a temperature of 880℃ for 20 minutes, and the flatness of the stainless steel heat spreader plate after shaping is less than 0.2.

[0098] (4) The shell containing the capillary core is injected with liquid and vacuumed to obtain a stainless steel heat exchange plate.

[0099] The average content of elements in the alloy layer is as follows: chromium 55%, copper 38%, iron 3%, nickel 2%, and other elements (molybdenum) 2%.

[0100] In this stainless steel heat exchanger, the thickness of the chromium-copper alloy layer is 4.2 micrometers.

[0101] Experimental Example 3

[0102] (1) 304 stainless steel was used for etching to obtain a 120-micron thick top cover and a 100-micron thick bottom cover, and a 350-mesh copper mesh capillary core of a specific shape was cut.

[0103] (2) The stainless steel upper cover and stainless steel lower cover prepared above are placed together with 80 mesh alloy material (40 parts chromium powder, 35 parts copper, 50 parts magnesium oxide powder, 4 parts magnesium powder, and 4 parts zinc chloride) in a furnace. The alloy material is used to embed the entire surface of the stainless steel upper cover and stainless steel lower cover. Then, a vacuum is drawn. When the vacuum reaches 13 Pa (this vacuum is maintained throughout the process), the temperature is raised at a rate of 5 °C / min. When the temperature reaches 450 °C, it is held for 60 min. The temperature is raised at a rate of 2 °C / min. When the temperature reaches 732 °C, it is held for 40 min. Then, the temperature is raised again at a rate of 6 °C / min. When the temperature reaches 1050 °C, the temperature is stopped and maintained for 2.5 h. The upper cover and the lower cover contain chromium-copper alloy layers.

[0104] (3) After the lower cover containing the chromium copper alloy layer is assembled with the capillary core, it is sealed and welded with the upper cover containing the chromium copper alloy layer to obtain a shell containing the capillary core; the stainless steel heat spreader plate after laser welding is subjected to high-temperature shaping at a temperature of 880℃ for 20 minutes, and the flatness of the stainless steel heat spreader plate after shaping is less than 0.2.

[0105] (4) The shell containing the capillary core is injected with liquid and vacuumed to obtain a stainless steel heat exchange plate.

[0106] The average content of elements in the alloy layer is as follows: chromium 50%, copper 6%, iron 9%, nickel 4%, and other elements (molybdenum) 1%.

[0107] In this stainless steel heat exchanger, the thickness of the chromium-copper alloy layer is 6.9 micrometers.

[0108] Comparative Example 1

[0109] The stainless steel heat spreader contains only steps (1), (3) and (4) of Example 1, that is, it does not contain step (2), and the upper and lower covers of the obtained stainless steel heat spreader do not contain a chromium-copper alloy layer.

[0110] Performance testing

[0111] (1) To test the temperature difference between the two furthest points of the stainless steel heat spreader plate prepared above after high-temperature aging, the stainless steel heat spreader plate was placed in an environment of 110℃ for 1000 hours, and the temperature difference between the two points of the heat spreader plate was measured. The specific test method is as follows: 8W test power, before the aging test, the test temperatures of the two points are T1 and T2 (the heat source is below the heat spreader plate, and the test thermocouple is above the heat spreader plate, such as...). Figure 4 As shown in Table 2), after aging at 110℃ for 1000 hours, the test temperatures at two points are T1' and T2'. If the differences between T1 and T1', T2 and T2', and T1 and T2 are not significantly different from the difference between T1' and T2', then the performance of the heat spreader is considered to have remained basically unchanged, i.e., no internal reaction has occurred.

[0112] The purpose of high-temperature aging is to determine whether a reaction has occurred between water vapor and the inner cavity material. If a reaction has occurred, the performance after aging will be significantly degraded, resulting in large temperature variations in the heat spreader before and after aging. As the temperature decreases, its heat conduction performance will be significantly reduced.

[0113] Table 2. Performance test results of stainless steel heat exchange plates in the experimental and comparative examples.

[0114] T1(℃) T2(℃) T1-T2 (°C) T1’(℃) T2’(℃) T1'-T2' (°C) Experimental Example 1 68.62 67.25 1.37 68.66 67.26 1.40 Experimental Example 2 67.45 66.36 1.09 67.42 66.10 1.32 Experimental Example 3 68.12 66.88 1.24 68.25 66.92 1.33 Comparative Example 1 68.09 66.87 1.22 71.47 47.39 24.08

[0115] As shown in Table 2, for the test examples T1' and T2', if the differences between T1 and T1', T2 and T2', and T1 and T2 are not significantly different from the difference between T1' and T2', it indicates that the performance of the heat spreader remains essentially unchanged, meaning no internal reaction occurs. However, in Comparative Example 1, after 1000 hours of aging, the temperatures at both points decreased significantly, and a large temperature difference was observed between them. This indicates that the heat spreader reacted with water vapor to varying degrees. Therefore, heat spreaders without a chromium-copper alloy layer cannot avoid reaction with water, leading to aging and reduced service life.

[0116] (2) The state of iron in the alloy layer was also tested. When free iron is present, it readily reacts with water. The test method was the blue spot test, specifically: 5 grams of potassium ferricyanide K3[Fe[CN]6] was added to 1 ml of 98% sulfuric acid and 5 ml of 36% hydrochloric acid, along with an appropriate amount of distilled water to prepare a solution with a total volume of 100 ml (prepared fresh before use); the solution was directly applied or dropped onto the top cover of the test example and comparative example, and the appearance of blue spots was observed, i.e., whether blue spots appeared and the time it took for them to appear. It should be noted that this test should be performed after the acid-washed and passivated surface has basically dried. The test liquid should be rinsed clean after the test.

[0117] The basic principle of the blue dot test is that if the surface passivation film is imperfect or there is ferrous ion contamination, ferrous ions will be present, and the following reaction will occur.

[0118] 3Fe2 + +2[Fe[CN6]]-=Fe3[Fe[CN]6]2 precipitate is a dark blue precipitate, which can be used to check whether passivation treatment has been performed and to check the passivation effect.

[0119] In Comparative Example 1, the cover without a chromium-copper alloy layer showed blue spots after 5 minutes, indicating the presence of a certain amount of free iron. However, in Test Examples 1-3 of this application, the cover containing a chromium-copper alloy layer did not show blue spots after 24 hours, indicating that the amount of free iron in the alloy layer was almost non-existent, forming an alloy layer with chromium and copper, thus exhibiting better corrosion resistance.

[0120] (3) Based on the experience of life prediction of traditional heat pipe aging accelerated test, if the temperature difference performance can still meet the requirements after aging at 150℃ for 48 hours, its equivalent service life is 2.8 years. The heat spreader prepared in test examples 1 to 3 of this application has no performance degradation after aging at 150℃ for 500 hours. Therefore, the heat spreader of this application can not only be used in mobile phones, but also in other heat dissipation components with long service life requirements.

[0121] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A stainless steel heat spreader, comprising a shell and a capillary wick located inside the shell, characterized in that, The housing comprises a stainless steel substrate and a chromium-copper alloy layer embedded in the stainless steel substrate; The chromium-copper alloy layer has a chromium content of ≥30% by mass; the chromium-copper alloy layer is formed by alloying a stainless steel substrate with a chromium alloy material.

2. The stainless steel heat spreader according to claim 1, characterized in that, By weight, the chromium-copper alloy layer comprises: 30-60% chromium, 10-40% copper, 2-10% iron, 2-10% nickel, and 0-3% trace metal elements.

3. The stainless steel heat spreader according to claim 1, characterized in that, The thickness of the chromium-copper alloy layer is 0.1μm to 20μm.

4. The stainless steel heat spreader according to claim 1, characterized in that, The capillary wick can be made of stainless steel and / or copper; When the capillary wick is made of stainless steel, the capillary wick comprises a stainless steel substrate and a chromium alloy embedded in the stainless steel substrate; the chromium alloy is formed by alloying the stainless steel substrate by embedding it in the chromium alloy material.

5. A method for preparing a stainless steel heat spreader as described in any one of claims 1 to 4, characterized in that, include: (1) Obtain a stainless steel top cover, a stainless steel bottom cover, and a capillary core; (2) Under vacuum, the stainless steel upper cover and the stainless steel lower cover are respectively mixed with chromium alloy material and alloyed to obtain an upper cover containing a chromium-copper alloy layer and a lower cover containing a chromium-copper alloy layer; (3) After the lower cover containing the chromium-copper alloy layer is laminated with the capillary core, it is sealed and welded with the upper cover containing the chromium-copper alloy layer to obtain a shell containing the capillary core; (4) The shell containing the capillary core is injected with liquid and vacuumed to obtain the stainless steel heat spreader; The mixing of the stainless steel upper cover and the stainless steel lower cover with chromium alloy material means that the stainless steel upper cover and the stainless steel lower cover are completely embedded in the chromium alloy material.

6. The preparation method according to claim 5, characterized in that, By weight, the chromium alloy material comprises: 20-60 parts chromium, 8-40 parts copper, 30-70 parts dispersant, 0.1-5 parts reducing agent, and 0.5-5 parts activator.

7. The preparation method according to claim 6, characterized in that, The vaporization temperature of the reducing agent is lower than the alloying temperature; the vaporization temperature of the activating agent is lower than the alloying temperature; the activating agent contains halogen; Preferably, the reducing agent comprises metallic magnesium; the activating agent comprises zinc chloride; and the dispersant comprises at least one of aluminum oxide, silicon oxide, and magnesium oxide.

8. The preparation method according to claim 5, characterized in that, The vacuum refers to a vacuum degree of less than 13 Pa; the alloying conditions are: temperature 917~1050℃, time 2~10 hours.

9. The application of the stainless steel heat spreader according to any one of claims 1 to 4 in electronic products.

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