Preparation method of stainless steel vapor chamber and stainless steel vapor chamber thereof

Abstract

The invention relates to the field of heat dissipation devices, in particular to a preparation method of a stainless steel vapor chamber and the stainless steel vapor chamber thereof.The preparation method comprises the following steps that a liquid absorption core is welded and fixed in a groove of a bottom shell to obtain a bottom shell assembly, and surface modification treatment is conducted on the bottom shell assembly to enable the surface contact angle of the bottom shell assembly to be smaller than or equal to 10 degrees; the upper cover plate and the modified bottom shell assembly are subjected to passivation treatment through a citric acid solution, and ultrasonic cleaning is conducted after passivation; the upper cover plate covers the bottom shell assembly, sealing welding is conducted along the periphery in a laser welding mode, and a vapor chamber shell is obtained; deionized water is poured into the vapor chamber shell, vacuumizing is conducted after freezing solidification, secondary degassing and sealing are conducted, and the stainless steel vapor chamber is obtained; by means of surface modification and active passivation, hydrogen evolution caused by reaction of stainless steel and water is avoided, wettability between the stainless steel and cooling liquid after passivation is improved, and the prepared vapor chamber does not generate hydrogen after being used for a long time, capillary backflow is smooth, and gas tightness of a cavity is stable.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation devices, and in particular to a method for preparing a stainless steel heat spreader and the stainless steel heat spreader thereof. Background Technology

[0002] A vapor chamber is a highly efficient phase change heat-conducting element that is widely used in thermal management fields such as laptops, servers, mobile phones, LED lighting, and power batteries. Due to the excellent thermal conductivity of copper, traditional vapor chambers mostly use copper as the main material. However, copper has high cost, low strength, and limited machinability and microstructure manufacturing capabilities, making it difficult to meet the current requirements of thinner and smaller devices for structural strength and manufacturing integration.

[0003] Stainless steel possesses excellent strength, corrosion resistance, and formability, and its relatively low cost makes it a promising alternative material. However, stainless steel suffers from surface passivation and a reaction with water. Passivation of the stainless steel wire mesh or braided strip wicking core within the heat spreader cavity not only creates oxide particles that remain inside the cavity, hindering coolant circulation and increasing the risk of pore blockage, but also reduces wettability with the coolant, weakening capillary suction. Furthermore, the reaction of the stainless steel wire mesh or braided strip wicking core with water produces hydrogen gas, leading to increased internal pressure, performance degradation, and even failure. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a method for preparing a stainless steel heat spreader and the stainless steel heat spreader itself. By performing surface modification treatment on the bottom shell assembly, combined with active passivation and cleaning treatment on the bottom shell assembly and the top cover plate, the oxide film formed by passivation effectively avoids hydrogen evolution from the reaction between stainless steel and water. The surface modification treatment improves the wettability between the passivated stainless steel surface and the coolant, ensuring suitable capillary suction capacity. The heat spreader prepared does not evolve hydrogen during long-term use, and the capillary return flow is smooth and the airtightness of the cavity is stable.

[0005] The technical solution of the present invention is achieved in the following ways: A method for preparing a stainless steel heat spreader, the heat spreader comprising a bottom shell, a top cover plate, and a liquid-absorbing core made of stainless steel, wherein the bottom shell has a groove, and the liquid-absorbing core is fixed in the groove; the method for preparing the heat spreader includes the following steps: The liquid-absorbing core is welded and fixed in the groove to obtain the bottom shell assembly; The bottom shell assembly is subjected to surface modification treatment so that the surface contact angle of the bottom shell assembly is ≤10°; The upper cover plate and the modified bottom shell assembly were passivated with citric acid solution, and then ultrasonically cleaned. The upper cover plate is placed on the bottom shell assembly and sealed along the periphery by laser welding to obtain the heat spreader shell. Deionized water is injected into the heat spreader shell, frozen and solidified, then vacuumed for secondary degassing, and finally sealed to obtain the stainless steel heat spreader. The method for preparing the stainless steel heat spreader of the present invention involves surface modification of the bottom shell assembly, combined with active passivation and cleaning of the bottom shell assembly and the top cover plate. The oxide film formed by passivation effectively prevents hydrogen evolution from the reaction between stainless steel and water. The surface modification improves the wettability between the passivated stainless steel surface and the coolant, ensuring suitable capillary suction capacity. The heat spreader prepared does not evolve hydrogen during long-term use, and has smooth capillary reflux and stable cavity airtightness.

[0006] Furthermore, the surface modification treatment includes the following steps: heating the bottom shell assembly at 500~700℃ for 1~4 hours.

[0007] Furthermore, the surface modification treatment includes the following steps: scanning the surface of the wick using a pulsed laser, with a laser output power of 20~40W, a wavelength of 1064nm, a pulse width of 10~200ns, a repetition frequency of 20~100kHz, a scanning speed controlled at 200~400mm / s, and a scanning line spacing controlled at 20~40μm; the scanning includes one of network scanning and parallel line scanning.

[0008] Furthermore, the citric acid solution has a mass fraction of 1% to 5%, the passivation treatment temperature is 40 to 90°C, and the treatment time is 1 to 4 hours.

[0009] Furthermore, the volume of deionized water injected into the heat spreader shell accounts for 20-40% of the effective volume of the heat spreader shell, the freezing and solidification temperature is -30 to -10℃, the pressure inside the heat spreader shell after vacuuming is 0-5Pa, and the temperature during secondary degassing is 60-100℃.

[0010] Furthermore, the inventors discovered through practice that the welding and fixing of stainless steel wire mesh or braided strip liquid absorbent cores in the heat spreader also constitutes a key bottleneck restricting its large-scale application. Current processes mostly rely on high-temperature sintering or diffusion welding, which usually requires heating the entire structure to above 1200°C to break the dense oxide film on the surface and form a reliable intermetallic bond. Such high temperatures not only place extremely high demands on atmosphere control, heating uniformity, and fixture materials, but also result in huge energy consumption and expensive equipment, leading to slow production cycles and significant fluctuations in yield, making it difficult to meet the needs of consumer electronics heat spreaders for large-scale, low-cost manufacturing.

[0011] Furthermore, the liquid-absorbing core is fixed in the groove by intermittent resistance welding. The intermittent welding methods include roll welding and spot welding. The spot welding pressure is 1.0 to 3.0 kgf / cm2, the roll welding pressure is 1.0 to 2.0 kgf / cm2, the roll welding speed is 50 to 150 mm / s, the welding power is 200 to 400 W, and the distance between adjacent welds or weld points is ≤10 mm.

[0012] Furthermore, the liquid-absorbing core is fixed in the groove by resistance welding. The continuous welding method includes roll welding, with the thickness of the roll welding electrode wheel being 1~2mm, the roll welding pressure being 1.0~2.0kgf / cm2, the roll welding speed being 50~150mm / s, and the welding power being 200~400W.

[0013] Compared to high-temperature sintering processes that require temperatures exceeding 1200°C, resistance welding can achieve reliable metal bonding at lower temperatures and in shorter cycles. This not only avoids problems such as grain coarsening and pore structure collapse of the wire mesh at high temperatures, but also significantly reduces energy consumption and equipment costs. Furthermore, it is particularly beneficial for thin-walled heat spreaders, improving yield and providing a more stable substrate for subsequent capillary processing.

[0014] Furthermore, before performing surface modification treatment on the bottom shell assembly, the bottom shell assembly is immersed in an acidic solution formed by pure water, 20-30 wt% nitric acid, and 5-10 wt% hydrofluoric acid, and ultrasonically treated for 5 minutes, followed by immersion in deionized water and ultrasonic treatment for 5 minutes. Oxides and metal residues in the welding area are removed by pickling.

[0015] Furthermore, both the bottom shell and the top cover are manufactured using a stamping process, and the liquid-absorbing core comprises one or both of stainless steel wire mesh and stainless steel braided strip. Stainless steel material has high yield strength and work hardening tendency, making it difficult to obtain precise cavity contours and stable shapes on thin plates using traditional cutting or mechanical bending. Stamping allows for high-consistency, large-area forming at a lower cost, ensuring stable cavity depth, boundary height, and contour dimensions, thereby guaranteeing the fitting accuracy of subsequent welding and packaging processes. In addition, stamping is efficient, produces high-strength finished products, and allows for controllable deformation, significantly improving the structural integrity and production yield of the heat spreader, making it suitable for large-scale manufacturing requirements.

[0016] The present invention also provides a stainless steel heat spreader, which is prepared by any of the above-described methods for preparing stainless steel heat spreaders.

[0017] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the heat spreader according to an embodiment of the present invention; Figure 2 This is a schematic diagram showing the weld seam distribution of the bottom shell according to Embodiment 2 of the present invention; The components include a bottom shell 1, a groove 11, a first liquid injection groove 12, a support column 13, an upper cover plate 2, a second liquid injection groove 21, and a liquid suction core 3. Detailed Implementation

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of the embodiments of this application.

[0020] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0021] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0022] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] It should be understood that the embodiments of this application are not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from their scope. The scope of the embodiments of this application is limited only by the appended claims.

[0024] This invention only exemplifies a heat spreader made of preferred 316L stainless steel. It should be noted that the stainless steel applicable to the preparation method provided by this invention is not limited to 316L stainless steel.

[0025] This invention only exemplifies the use of a liquid-absorbing core composed of stainless steel wire mesh. As an optional embodiment, the liquid-absorbing core can also be composed of stainless steel braided strip, for example, stainless steel braid with a braiding density of 20 braids / 10mm. As an optional embodiment, the liquid-absorbing core can also be composed of both stainless steel wire mesh and stainless steel braided strip.

[0026] Example 1 This embodiment provides a method for preparing a stainless steel heat spreader, including the following steps: Select size 171mm A 101mm thick 316L stainless steel plate with a thickness of 0.2mm is used to form a bottom shell 1 and a top cover plate 2 through a stamping process. Specifically, the bottom shell 1 is provided with a groove 11 and a first liquid injection groove 12. One end of the first liquid injection groove 12 is connected to the groove 11, and the other end extends to the outer periphery of the bottom shell 1. The groove 11 has a depth of 1.8mm. Several support columns 13 protruding from the bottom to the top of the groove 11 are also formed in the groove 11. The height of the support columns 13 is 1.8mm. The top cover plate 2 is provided with a second liquid injection groove 21. After the top cover plate 2 is placed on the bottom shell 1, the top cover plate 2 covers the upper side of the bottom shell 1. The support columns 13 just abut against the top cover plate 2. The second liquid injection groove 21 and the first liquid injection groove 12 are positioned correspondingly and together form a liquid injection hole that connects the groove 11 to the outside of the heat spreader plate. Cut the graded stainless steel wire mesh of 300 mesh, 250 mesh and 200 mesh to match the groove 11, and make through holes according to the distribution position of the support column 13 so that the support column 13 can be set after the stainless steel wire mesh is laid. The graded stainless steel wire mesh of 300 mesh, 250 mesh and 200 mesh is laid into the groove 11 in sequence as the liquid absorption core 3. Stainless steel wire mesh is welded and fixed to the bottom of groove 11 by intermittent spot welding using a resistance welding machine to obtain bottom shell 1 assembly; the welding power is 300W, the spot welding pressure is 2.0kgf / cm2, and short-term power can be applied during welding as needed to ensure full fusion of the weld points; the weld point spacing is controlled within 10mm, which helps to ensure uniform stress, high fit, and no local warping or delamination of the composite liquid absorbent core 3 structure; The bottom shell 1 component is immersed in an acidic solution composed of pure water, 25wt% nitric acid and 7wt% hydrofluoric acid, and ultrasonically treated for 5 minutes to remove oxides and metal residues in the welding area. Then the bottom shell 1 is immersed in deionized water and ultrasonically treated for 5 minutes to clean its surface. Next, the bottom shell 1 component was modified: the bottom shell 1 component was heated at 600℃ for 3 hours to form a uniform rough structure and microporous structure on the stainless steel surface, which serves as a continuous and stable capillary reflux channel; after the heat modification treatment, the surface contact angle of the stainless steel can reach 0°, and the capillary liquid can spread rapidly on its surface, significantly improving the capillary reflux capacity of the wick 3; according to actual measurement, when the surface contact angle of the stainless steel is ≤10°, the passivated wick 3 has a suitable capillary reflux capacity, and the capillary liquid can spread rapidly on the wick 3. The top cover plate 2 and the modified bottom shell 1 were respectively immersed in deionized water and ultrasonically treated for 5 minutes. Then, they were immersed together in a 2% citric acid solution for passivation treatment at a temperature of 90°C for 3 hours. The purpose of the passivation treatment is to form a uniform and dense chromium-rich passivation film on the surface of the modified stainless steel. On the one hand, this significantly improves the corrosion resistance and chemical stability of the inner wall of the heat exchange plate under the action of deionized water, and avoids hydrogen evolution. On the other hand, since the passivation treatment method in this embodiment is relatively mild, it can maintain the micro-rough structure and capillary channels formed during surface modification, and will not cause pore blockage or surface smoothing. Overall, it takes into account both capillary performance and long-term reliability. After the passivated bottom shell 1 and top cover 2 are dried, they are aligned and assembled. Laser welding equipment is used to perform sealing welding along the periphery of the groove 11 and the first injection groove 12 to obtain the heat spreader shell. Specifically, a spiral scanning path is used for welding, the weld width is controlled at 0.5 mm, and the welding speed is 1000 mm / s. Laser welding can achieve rapid and stable metal fusion in a small heat-affected zone without damaging the formed capillary structure and passivation film. At the same time, it can ensure that the heat spreader has good airtightness and structural strength after welding, providing a reliable sealed environment for subsequent vacuuming and filling. Deionized water is injected into the heat spreader shell through the pre-reserved injection port on the upper cover plate 2, so that the deionized water occupies 20~40% of the effective volume of the heat spreader shell. After injection, it is placed at -20℃ to freeze and solidify the deionized water. After solidification, it is connected to the vacuum system to evacuate the vacuum and reduce the internal pressure of the heat spreader shell to below 5Pa. Then, the injection hole is turned upward and placed in a 90℃ water bath for heating to perform secondary degassing. When the lost deionized water reaches 5% of the effective volume of the heat spreader shell, the secondary degassing is considered to be completed. The injection hole is then sealed by laser or resistance welding to obtain the heat spreader product.

[0027] Example 2 This embodiment provides a method for preparing a stainless steel heat spreader. The parts of the preparation method that are the same as in Example 1 will not be described again. The difference between the preparation method in this embodiment and that in Example 1 is: In this embodiment, a resistance welding machine is used to weld and fix stainless steel wire mesh and stainless steel braided strip to the bottom of the groove 11 using a continuous roll welding method. The welding power is controlled between 200 and 400W, the welding pressure is controlled between 1 and 2 kgf / cm2, and the welding speed is controlled between 50 and 150 mm / s. Specifically, a 2 mm thick roll welding electrode wheel is used for welding. The diameter of the roll welding electrode wheel can be selected according to the size of the heat spreader. In this embodiment, the heat spreader can use a roll welding electrode wheel with a diameter of 20 to 30 mm. Roll welding is a type of continuous welding, which forms a continuous linear weld. On the one hand, it has a higher bonding strength than spot welding, and on the other hand, it can also produce fine indentations and microgrooves in the local area of ​​the wire mesh. In essence, it extends and connects the original pore network of the wire mesh, and builds a continuous capillary channel in the weld area, which has advantages in the preparation of medium and large heat exchange plates.

[0028] Example 3 This embodiment provides a method for preparing a stainless steel heat spreader. The parts of the preparation method that are the same as in Example 1 will not be described again. The difference between the preparation method in this embodiment and that in Example 1 is: In this embodiment, laser etching is used to modify the bottom shell 1 component: a pulsed laser is used to perform a network scan along the screen surface, with a laser output power of 20~40W, a wavelength of 1064nm, a pulse width of 10~200ns, a repetition frequency of 20~100kHz, a scanning speed controlled at 200~400mm / s, and a scanning line spacing controlled at 20~40μm; in other embodiments, parallel line scanning can be performed; Under the parameter conditions of this embodiment, the laser can form a uniform micron-level rough texture on the surface of the stainless steel wire mesh, and form local nanoscale erosion pits or molten resolidification layers, thereby significantly improving the surface specific surface area and wettability. After laser etching, the contact angle of the bottom shell 1 component surface can be maintained at 0°, and the working fluid can be continuously spread between the wire mesh pores and the weld indentation, further improving the consistency of the reflow path and capillary transport efficiency. Overall, without damaging the strength of the wire mesh structure, a higher degree of surface activation and stable capillary reflow performance are achieved.

[0029] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing a stainless steel heat spreader, characterized in that, The heat spreader includes a bottom shell, a top cover plate, and a liquid-absorbing core made of stainless steel. The bottom shell has a groove, and the liquid-absorbing core is located within the groove. The method for preparing the heat spreader includes the following steps: The liquid-absorbing core is welded and fixed in the groove to obtain the bottom shell assembly; The bottom shell assembly is subjected to surface modification treatment so that the surface contact angle of the bottom shell assembly is ≤10°; The upper cover plate and the modified bottom shell assembly were passivated with citric acid solution, and then ultrasonically cleaned. The upper cover plate is placed on the bottom shell assembly and sealed along the periphery by laser welding to obtain the heat spreader shell. Deionized water is injected into the heat spreader shell, and after freezing and solidification, a vacuum is drawn to perform secondary degassing and sealing to obtain the stainless steel heat spreader.

2. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The surface modification treatment includes the following steps: heating the bottom shell assembly at 500~700℃ for 1~4 hours.

3. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The surface modification treatment includes the following steps: scanning the surface of the wick with a pulsed laser, the laser output power is 20~40W, the wavelength is 1064nm, the pulse width is 10~200ns, the repetition frequency is 20~100kHz, the scanning speed is controlled at 200~400mm / s, and the scanning line spacing is controlled at 20~40μm; the scanning includes one of network scanning and parallel line scanning.

4. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The citric acid solution has a mass fraction of 1% to 5%, the passivation treatment temperature is 40 to 90°C, and the treatment time is 1 to 4 hours.

5. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The volume of deionized water injected into the heat spreader shell accounts for 20-40% of the effective volume of the heat spreader shell. The freezing and solidification temperature is -30 to -10℃. After vacuuming, the pressure inside the heat spreader shell is 0-5Pa. The temperature during secondary degassing is 60-100℃.

6. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The liquid-absorbing core is fixed in the groove by intermittent resistance welding. The intermittent welding methods include roll welding and spot welding, with a spot welding pressure of 1.0–3.0 kgf / cm². 2 The rolling welding pressure is 1.0~2.0 kgf / cm. 2 The rolling welding speed is 50-150 mm / s, the welding power is 200-400 W, and the spacing between adjacent welds or weld points is ≤10 mm.

7. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, The liquid-absorbing core is fixed in the groove by resistance welding. The continuous welding method includes roll welding, with the thickness of the roll welding electrode wheel being 1~2mm and the roll welding pressure being 1.0~2.0kgf / cm. 2 The rolling welding speed is 50-150 mm / s, and the welding power is 200-400 W.

8. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, Before performing surface modification treatment on the bottom shell assembly, the bottom shell assembly is immersed in an acidic solution formed by pure water, 20-30 wt% nitric acid and 5-10 wt% hydrofluoric acid, and ultrasonically treated for 5 minutes, and then immersed in deionized water and ultrasonically treated for 5 minutes.

9. The method for preparing a stainless steel heat spreader according to claim 1, characterized in that, Both the bottom shell and the top cover are manufactured using a stamping process, and the liquid-absorbing core includes one or both of stainless steel wire mesh and stainless steel braided strip.

10. A stainless steel heat spreader, characterized in that, The stainless steel heat spreader is prepared according to any one of claims 1 to 9.

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