Embedded micro-channel based on additive manufacturing and preparation method thereof

Abstract

The invention provides an embedded micro-channel based on additive manufacturing and a preparation method thereof, the embedded micro-channel is suitable for heat dissipation of a high-power electronic device, and the first scheme is single-substrate integrated electroplating: sequentially forming a seed layer and graphical photoresist on a substrate, controlling electroplating to enable copper to grow vertically and transversely, and forming an all-copper micro-channel cavity with a closed top in a self-closing manner; turbulent flow structures such as micro-columns, waves or fins are integrally formed; according to the second scheme, complementary half cavities are formed through electroplating, tin-silver-copper solder is applied after surface nickel plating, a complete flow channel is formed through reflow soldering bonding, photoetching and electroplating are utilized in the two schemes, an integrated structure which is high in precision and free of interface thermal resistance is achieved, the heat exchange efficiency is remarkably improved, and the heat exchange efficiency is improved. Moreover, the material utilization rate is high, and ceramic, silicon and glass substrates are compatible, and are respectively suitable for high-end power modules and low-cost consumer electronics scenes.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging and heat dissipation technology, and specifically relates to an embedded microchannel structure based on direct copper plating additive manufacturing process and its preparation method. The microchannel is integrally formed on a ceramic substrate by electroplating copper and has a built-in turbulence structure, which is mainly used for integrated heat dissipation of high power density electronic devices. Background Technology

[0002] With the rapid development of technologies such as fifth-generation mobile communication, artificial intelligence, and power electronics, electronic chips and modules are constantly evolving towards higher power density and smaller package size. However, this development trend has led to their heat flux density exceeding the limits of traditional heat dissipation technologies such as air cooling.

[0003] Therefore, microchannel cooling technology, with its large specific surface area and efficient liquid cooling heat exchange capability, is regarded as a key approach to solving the heat dissipation problem of high power density electronic devices.

[0004] In the field of microchannel manufacturing, existing technologies can be mainly divided into two categories:

[0005] The first category of technologies is represented by subtractive or equivalent manufacturing processes such as silicon etching, micro-milling, and laser processing.

[0006] However, such methods are usually complex in process, have low material utilization and high manufacturing costs. More importantly, the microchannels they process are often manufactured as independent components, making it difficult to achieve efficient and reliable integrated integration with the ceramic or metal substrates that carry the circuit.

[0007] Furthermore, subsequent assembly typically relies on processes such as brazing or gluing, which not only introduces additional interfacial thermal resistance, affecting overall heat dissipation performance, but also poses long-term reliability risks due to the mismatch in thermal expansion coefficients between materials.

[0008] The second category of technologies includes additive manufacturing processes, represented by 3D printing and stereolithography.

[0009] Although such technologies offer a degree of shape freedom, they still have significant limitations in microchannel fabrication. For example, the inherent high surface roughness of metal 3D printing increases flow resistance and inhibits heat transfer. At the same time, metal powder that is not completely melted or sintered during the printing process is difficult to remove completely from the closed channels, which can easily cause microchannel blockage.

[0010] Furthermore, when manufacturing microchannel structures with closed internal cavities, both metal and polymer 3D printing typically require the design and printing of support structures. Removing these supports after molding is extremely difficult and can easily damage or clog the delicate internal channels.

[0011] On the other hand, regardless of the manufacturing process used, the existing microchannel structures are mostly limited to simple rectangular or circular cross-sections, and the fluid is mostly in a laminar flow state, with fluid mixing and heat exchange efficiency approaching a bottleneck.

[0012] Although the industry has proposed to improve performance by setting up structures such as turbulence columns and fins inside the flow channel, most of these solutions rely on secondary processing or assembly of discrete components. Such non-integrated manufacturing methods not only increase the complexity and cost of the process, but also introduce contact thermal resistance between the turbulence structure and the flow channel wall, thus severely limiting the realization of its performance potential.

[0013] In the existing technology, direct copper plating technology, as a high-precision additive manufacturing process, has been maturely applied in the circuit wiring of electronic packaging substrates. However, at present, the application of this technology is mainly limited to two-dimensional circuit wires or 2.5-dimensional bump and pad structures. Its potential in three-dimensional molding has not been fully explored. There are no successful cases or clear technical inspirations of using direct copper plating technology to directly grow integrated microchannels with closed cavities and internal functional structures.

[0014] Therefore, the current microchannel manufacturing field urgently needs a new technical solution that can overcome the above limitations. The ideal solution should be able to achieve true three-dimensional integration of microchannels and electronic substrates, have the ability to form complex turbulence structures in one go inside the channel, and be compatible with the high-temperature processes required for subsequent electronic packaging, thereby providing an efficient, reliable and compact thermal management path for high power density electronic devices. Summary of the Invention

[0015] In view of the series of technical bottlenecks in the existing microchannel manufacturing process described in the background art, such as the difficulty in integrating with the circuit board and the introduction of thermal resistance by secondary processing of the internal turbulence structure, the present invention aims to provide an embedded microchannel based on additive manufacturing and its preparation method.

[0016] The core of this invention lies in utilizing a mature direct copper plating process to achieve high-precision integrated additive manufacturing of microchannels and electronic substrates, and incorporating an integrated turbulence structure with no interface thermal resistance, thereby providing an efficient, reliable and compact thermal management solution for high power density electronic devices.

[0017] To achieve the above objectives, this invention provides two core technical approaches, both based on the concept of additive manufacturing, which selectively grow copper through photolithography and electroplating processes to construct embedded microfluidic structures.

[0018] The first technical solution aims to provide an integrated microchannel that can withstand subsequent high-temperature packaging processes.

[0019] The method begins by providing a substrate and forming a seed layer on it as an electroplating conductive path. Then, photoresist is coated on the seed layer and patterned by a precise photolithography process, thereby revealing the patterned area of ​​the preset microchannels and their internal turbulence structures.

[0020] This step precisely defines the required three-dimensional structure in the form of a two-dimensional negative image.

[0021] The subsequent electroplating process is the key to this solution: during the selective growth of copper in the patterned area, by precisely controlling the electroplating parameters, the electroplated copper not only grows in the vertical direction until it exceeds the thickness of the photoresist, but also undergoes controllable lateral growth in the horizontal direction. Ultimately, the copper forming the flow channel sidewalls converges and closes above the photoresist mask, thus naturally forming a top-closed microchannel cavity.

[0022] At the same time, the turbulence structure defined in the photoresist pattern is also electroplated and formed simultaneously with the main flow channel, realizing the integrated manufacturing of the microchannel cavity and the internal functional structure, without any assembly interface.

[0023] Finally, by removing the photoresist and the excess seed layer it covers, a closed microchannel structure, integrally formed from all copper, can be obtained and embedded on the substrate.

[0024] Due to its pure copper material and interface-free characteristics, this structure has excellent thermal conductivity and mechanical strength, and can withstand subsequent high-temperature processes above 260°C, such as chip sintering or eutectic bonding, making it particularly suitable for high-temperature applications such as power semiconductors.

[0025] The second technical solution provides a more cost-effective and flexible flow channel design for bonded microchannels.

[0026] This approach breaks down the complete microchannel into two complementary half-cavities.

[0027] First, similar processes are performed on the first substrate and the second substrate respectively: seed layer is formed, photoresist is coated and patterned to expose the respective microchannel half-cavity patterns;

[0028] Copper is then selectively grown through an electroplating process to form a DPC substrate with a specific groove structure. In this process, the electroplated copper usually does not need to grow to a closed state, which reduces the extreme requirements for process control.

[0029] After removing the photoresist and excess seed layer, the surfaces of the microchannel semi-cavity structures on both substrates are nickel-plated to provide good solderability and oxidation resistance.

[0030] Subsequently, tin-silver-copper solder is applied to at least one nickel-plated surface, the two substrates are aligned by precise positioning, and bonded using a reflow soldering process.

[0031] During the melting and solidification of the solder, the two microchannel semi-cavities are firmly connected together to form a sealed, complete microchannel cavity.

[0032] The advantages of this solution are high process tolerance, controllable cost, and the ability to independently design more complex flow channel cross-sectional shapes for the upper and lower substrates.

[0033] However, due to the melting point limitation of tin-silver-copper solder, this structure is only suitable for low-temperature packaging environments where subsequent process temperatures are below 200°C.

[0034] Furthermore, the turbulence structure described in this invention can be flexibly designed as one or more combinations of micro-pillar arrays, wave-shaped flow channels, or fin structures to adapt to different fluid mixing and heat exchange requirements.

[0035] The substrate can be made of common insulating materials such as ceramics, silicon, or glass, ensuring broad compatibility with electronic packaging processes.

[0036] Corresponding to the above preparation method, the present invention also seeks protection for two embedded microfluidic structure products obtained therefrom.

[0037] The first type is a closed microfluidic cavity integrally formed on a single substrate by electroplating copper, with a turbulence structure integrated on its inner wall.

[0038] The second type is formed by bonding the first DPC substrate and the second DPC substrate together with tin-silver-copper solder. The microchannel semi-cavities of the two substrates together form a complete closed flow channel, and their inner walls are also integrally formed with a turbulence structure.

[0039] Compared with the prior art, the beneficial effects of this invention are significant and multifaceted:

[0040] 1. Achieve true additive manufacturing: Selective growth through electroplated copper eliminates the need for cutting / etching, increasing material utilization by over 60% (compared to traditional silicon etching).

[0041] 2. On the one hand, the all-copper unibody structure has extremely high thermal conductivity;

[0042] On the other hand, the turbulence structure, which is seamlessly connected to the inner wall of the flow channel, completely eliminates the contact thermal resistance caused by the additional interface, thereby greatly improving the turbulence intensity and heat exchange efficiency of the fluid.

[0043] The first option is better able to withstand high-temperature processes and meets the most demanding power application requirements.

[0044] 3. The two technical approaches proposed in this invention form a perfect complement.

[0045] Integrated high-temperature solutions are designed for the high-end market with extremely high requirements for performance and temperature resistance;

[0046] The low-cost dual-chip bonding solution is suitable for the cost-sensitive and mild-condition consumer electronics field. This flexibility allows the present invention to meet a wide range of diverse market needs.

[0047] 4. Thanks to the micron-level precision of photolithography, the microchannels and turbulence structures manufactured in this invention have precise dimensions and smooth surfaces, which is beneficial for achieving controllable fluid dynamics performance.

[0048] Meanwhile, the flexibility of photolithography mask design allows for almost arbitrary two-dimensional design of flow channels and turbulence structures, providing ample room for performance optimization. Attached Figure Description

[0049] Figure 1 This is a three-dimensional structural diagram of the integrated microchannel base in an embodiment of the present invention;

[0050] Figure 2 This is a three-dimensional structural schematic diagram of the bonded microchannel cover in an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of a microchannel base in the prior art;

[0052] Figure 4 This is a schematic diagram of a microchannel cover in the prior art;

[0053] Figure 5 This is a flowchart of the integrated electroplating molding process of the present invention;

[0054] Figure 6 This is a flowchart of the double bond synthesis process of the present invention. Detailed Implementation

[0055] To enhance understanding of the present invention, the invention will be further described in detail below with reference to embodiments and accompanying drawings. These embodiments are only for explaining the invention and do not constitute a limitation on the scope of protection of the invention.

[0056] For the implementation of the integrated electroplating molding high-temperature microchannel, a ceramic substrate, such as alumina or aluminum nitride, is first selected as the base material. The substrate thickness is preferably 0.5 mm to ensure sufficient mechanical strength and thermal conductivity.

[0057] An adhesion layer and a seed layer are deposited on the substrate surface by magnetron sputtering or evaporation. The adhesion layer is made of titanium or chromium and has a thickness of 0.1 micrometers. The seed layer is made of copper and has a thickness of 0.2 micrometers, providing a conductive basis for subsequent electroplating.

[0058] Subsequently, a dry film photoresist with a thickness of approximately 20 micrometers is spin-coated onto the seed layer, and ultraviolet exposure is performed through a mask to develop a negative image of the microchannels and internal turbulence structures.

[0059] In the integrated electroplating process (see flowchart) Figure 5 In the initial stage, a current density of 1 to 2 A / dm² is used to allow copper to grow vertically on the exposed seed layer.

[0060] Once the height of the copper pillar reaches the thickness of the photoresist, the current density is adjusted to 2 to 4 A / dm², causing the copper to grow laterally in a controlled manner. This results in the copper forming the sidewalls of the flow channel converging and closing above the photoresist mask, forming a closed microchannel cavity with an arched top. Simultaneously, a turbulence structure is integrally formed inside the microchannel.

[0061] After removing the photoresist, the seed layer not covered by copper is quickly etched away using dilute nitric acid or sodium persulfate etching solution to obtain a closed microchannel structure embedded in the substrate, which is made of all copper in one piece.

[0062] Once the structure is completed, it can undergo a high-temperature sintering process at 800℃ to enhance the bonding force between the copper and the ceramic substrate, enabling the structure to withstand subsequent high-temperature packaging processes.

[0063] For the implementation of the double-bonded synthesis type low-cost microchannel, a first substrate and a second substrate are first prepared separately, and the processing method is the same as that of the integrated solution, including the deposition of an adhesion layer and a seed layer.

[0064] Photoresist was coated on the seed layers of the two substrates, and the patterned areas of complementary microchannel semi-cavities and internal turbulence structures were revealed by photolithography.

[0065] In the bilayer bonding process (see flowchart), Figure 6 The lower half of the microchannel is designed as a rectangular groove with a width of 250μm and a height of 100μm, while the upper half is designed as a complementary shape. The design also includes interlocking positioning marks to ensure precise alignment during bonding.

[0066] Copper is selectively grown in the patterned area through electroplating to form a DPC substrate with a microchannel semi-cavity structure. The electroplating current density is controlled at 1 to 2 A / dm², and the copper growth height is about 100 micrometers. Lateral closed growth is not performed.

[0067] After removing the photoresist and uncovered seed layer, nickel plating is performed on the surface of the microchannel semi-cavity structure of the two substrates. The nickel layer thickness is controlled between 2 and 5 micrometers to provide good solderability and oxidation resistance.

[0068] Subsequently, tin-silver-copper solder is applied to at least one nickel-plated surface. The two substrates are aligned using precise positioning and bonded using a reflow soldering process. Figure 6 As shown.

[0069] During the melting and solidification of the solder, the two microchannel semi-cavities are firmly connected together to form a sealed, complete microchannel cavity.

[0070] The advantages of this solution are high process tolerance, controllable cost, and the ability to independently design more complex flow channel cross-sectional shapes for the upper and lower substrates.

[0071] Compared with the prior art, the two technical solutions of the present invention have significant advantages.

[0072] The integrated electroplating molding solution enables selective growth of copper in both vertical and horizontal directions by precisely controlling electroplating parameters, achieving natural closure of the microchannel cavity without the need for additional cover plates or encapsulation steps. This avoids the complex processes and material waste of traditional subtractive processes such as silicon etching and micromilling, while also achieving integrated integration of the microchannel and the substrate, eliminating interfacial thermal resistance.

[0073] The bilayer bonding synthesis scheme decomposes the microchannel into two half-cavities, which are electroplated on two substrates respectively. This reduces the control requirements of the electroplating process, improves the yield, and allows for more complex channel cross-sectional shapes to be designed independently on the upper and lower substrates. It is suitable for applications where temperature resistance requirements are not high.

[0074] The turbulence structure of this invention is flexible in design, and can be selected from micro-pillar arrays, wave-shaped flow channels or fin structures, or even combinations of multiple structures, according to the needs. It is integrally formed inside the micro-channel through photolithography, avoiding contact thermal resistance caused by secondary processing or assembly, and significantly improving fluid turbulence and heat exchange efficiency.

[0075] Implementation Example 1: Microchannel heat dissipation application for high power density IGBT modules

[0076] This embodiment aims to demonstrate the application of the present invention in high power density power semiconductor packaging, specifically in the heat dissipation of a 600V 100A IGBT module.

[0077] Aluminum nitride ceramic substrate is selected as the substrate material, with a thickness of 0.5 mm and an excellent thermal conductivity of approximately 170 W / m Kelvin.

[0078] First, a titanium-copper adhesion layer and a copper seed layer are deposited on the substrate surface by magnetron sputtering, such as... Figure 1 As shown.

[0079] Subsequently, dry film photoresist is spin-coated onto the seed layer, and ultraviolet exposure and development are performed through a mask to form a negative image of the microchannel and internal micropillar array turbulence structure.

[0080] In the electroplating process, the initial current density is 1.5A / dm². After the copper grows vertically to the thickness of the photoresist, the current density is adjusted to 3A / dm², so that the copper grows laterally in the horizontal direction and finally closes above the photoresist to form a top-arched microchannel cavity.

[0081] After removing the photoresist, the seed layer not covered by copper is etched away using dilute nitric acid to obtain a microchannel structure formed entirely of copper.

[0082] Finally, a high-temperature sintering process at 800℃ is performed to enhance the bonding strength between the copper and the aluminum nitride substrate.

[0083] After the microchannel heat dissipation structure is integrated with the IGBT chip, the heat flux density test shows that under the conditions of a coolant flow rate of 0.5 liters per minute and an inlet temperature of 25°C, the junction temperature of the IGBT chip is only 85°C, which is 35°C lower than the traditional silicon etching microchannel heat dissipation solution and the thermal resistance is reduced by 40%.

[0084] Meanwhile, this structure can withstand the high-temperature packaging process of IGBT modules, has no interface thermal resistance, and has high mechanical strength, effectively solving the heat dissipation problem of high power density power semiconductors.

[0085] Compared with the prior art, the microchannel structure of the present invention does not require additional bonding steps in the manufacturing process, avoids the interfacial thermal resistance introduced by the traditional brazing process, and adopts direct copper plating additive manufacturing process, which improves material utilization by more than 60% and significantly reduces manufacturing costs.

[0086] Implementation Example 2: Low-cost microchannel heat dissipation application for consumer electronics devices

[0087] This embodiment aims to demonstrate the application of the present invention in consumer electronic devices, specifically in the heat dissipation of smartphone processors.

[0088] Alumina ceramic substrate was selected as the substrate material, with a thickness of 0.5 mm, which has low cost and good insulation properties.

[0089] First, two alumina substrates were prepared, and a titanium-copper adhesion layer and a copper seed layer were deposited by magnetron sputtering.

[0090] Photoresist is coated on the seed layer of the first substrate, and patterned using photolithography to reveal the negative image pattern of the lower half-cavity of the microchannel, such as... Figure 3 As shown; photoresist is coated on the seed layer of the second substrate, and patterned using photolithography to reveal the negative image pattern of the upper half-cavity of the microchannel, as shown. Figure 4 As shown, the graphic design includes interlocking markers.

[0091] Copper was grown to a height of 120 micrometers on two substrates using an electroplating process at a current density of 1.5 A / dm², forming a microchannel semi-cavity structure.

[0092] After removing the photoresist and the uncovered seed layer, a nickel layer is electroplated on the surface of the microchannel semi-cavities of the two substrates.

[0093] Subsequently, tin-silver-copper solder paste was applied to the nickel-plated surface of the lower substrate. Using positioning marks, the upper and lower substrates were precisely aligned and placed in a reflow oven for bonding at a peak temperature of 240°C. Figure 6 As shown, a complete microchannel cavity is formed, with an integrally formed wave-shaped flow channel turbulence structure on the inner wall of the cavity.

[0094] After the microchannel heat dissipation structure is integrated with the smartphone processor, heat flux density tests show that, under the conditions of a coolant flow rate of 0.2 liters per minute and an inlet temperature of 25°C, the processor junction temperature is only 55°C, which is 15°C lower than the traditional brazing microchannel heat dissipation solution and the thermal resistance is reduced by 20%.

[0095] Meanwhile, this structure only requires a 240°C packaging process, which is compatible with the standard packaging process for smartphones and does not require additional high-temperature treatment steps.

[0096] Compared with the prior art, the bonded microchannel structure of the present invention does not require precise lateral electroplating control during the manufacturing process, has relatively relaxed process requirements, high yield, high surface smoothness of the microchannel, no residue in the channel, low flow resistance, and effectively improves heat dissipation efficiency.

[0097] Furthermore, the manufacturing cost of this invention is reduced by approximately 30% compared to traditional silicon etched microchannels, and it can be seamlessly integrated with existing consumer electronics packaging processes, giving it significant market competitiveness.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating embedded microfluidic channels based on additive manufacturing, characterized in that, Includes the following steps: S1: Provide a substrate, and form a seed layer on the substrate; S2: Photoresist is coated on the seed layer and patterned by photolithography to reveal the patterned area of ​​microchannels and internal turbulence structures; S3: Copper is selectively grown in the patterned area through electroplating until the height of the copper exceeds the thickness of the photoresist, and the electroplated copper grows laterally and closes above the photoresist, thereby forming a top-closed microchannel cavity. At the same time, a turbulence structure is integrally formed inside the microchannel. S4: Remove photoresist and uncovered seed layer.

2. The method according to claim 1, characterized in that, After step S3, a high-temperature process step is also included, wherein the temperature of the high-temperature process is higher than 260°C.

3. A method for fabricating embedded microchannels based on additive manufacturing, characterized in that, Includes the following steps: A1: Prepare a first substrate and a second substrate respectively, and form a seed layer on both substrates; A2: Photoresist is coated on the seed layers of the two substrates respectively, and patterned by photolithography to reveal the patterned areas of complementary microchannel semi-cavities and internal turbulence structures. A3: Copper is selectively grown in the patterned area by electroplating to form a DPC substrate with a microchannel semi-cavity structure. A4: Remove photoresist and uncovered seed layer; A5: Nickel plating is performed on the surface of the microchannel semi-cavity structure of the first substrate and the second substrate. A6: Apply tin-silver-copper solder to at least one of the nickel-plated surfaces, align and bond the first substrate and the second substrate, so that the two microchannel semi-cavities are closed to form a complete microchannel.

4. The method according to claim 3, characterized in that, The bonding process described in step A6 is reflow soldering, and the subsequent process temperature is a low-temperature process, which is below 200°C.

5. The method according to claim 1 or 3, characterized in that, The turbulence structure is one or more of the following: micro-pillar array, wave-shaped flow channel, and fin structure.

6. The method according to claim 1 or 3, characterized in that, The substrate is a ceramic, silicon, or glass substrate.

7. An embedded microchannel structure, manufactured using the method described in claim 1 or 2, characterized in that, include: The substrate and a closed microchannel cavity integrally formed by electroplating copper on the substrate, wherein a turbulence structure is integrally formed on the inner wall of the microchannel cavity.

8. An embedded microchannel structure, manufactured using the method described in claim 3 or 4, characterized in that, include: A first DPC substrate and a second DPC substrate are bonded together by tin-silver-copper solder. The first DPC substrate and the second DPC substrate each have a microchannel semi-cavity formed by electroplating. After the two are bonded together, a complete microchannel cavity is formed, and a turbulence structure is integrally formed on the inner wall of the microchannel cavity.

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