Integrated preparation process of copper paste of high-heat-dissipation multilayer printed circuit board

Abstract

The application relates to the technical field of printed circuit boards, in particular to a copper paste integrated preparation process of a high-heat-dissipation multilayer printed circuit board. The process comprises the following steps: S1, providing a core plate formed with inner-layer circuits, and laminating and pressing a plurality of core plates and a semi-cured sheet to form a multilayer circuit board; S2, performing controlled-depth milling processing on a predetermined heat-dissipation area of the multilayer circuit board to form a groove with a specific depth and shape; S3, performing hole metallization processing on the multilayer circuit board to form a continuous metallization layer on the whole inner surface; S4, filling high-heat-conducting copper paste into the groove after metallization by using a printing process, and ensuring that the filling is compact and bubble-free; S5, curing the copper paste and performing surface grinding processing on the cured copper paste; and S6, performing outer-layer circuit manufacturing, solder mask and surface treatment on the copper paste to obtain a finished printed circuit board integrated with a copper paste heat-dissipation module. The application solves the problems of large interface thermal resistance, difficult flatness control and glue overflow pollution in the traditional copper block embedding process.

Description

Technical Field

[0001] This application relates to the field of printed circuit board technology, and in particular to a copper paste integration fabrication process for a high heat dissipation multilayer printed circuit board. Background Technology

[0002] As electronic devices in fields such as 5G communication, high-performance computing, automotive electronics, and aerospace develop towards higher power, higher density, and miniaturization, the heat dissipation problem of printed circuit boards (PCBs) is becoming increasingly prominent. Localized overheating has become a key factor affecting the reliability, stability, and lifespan of equipment.

[0003] Currently, the industry commonly uses the method of embedding solid copper blocks in certain parts of the PCB to enhance heat dissipation. However, this traditional copper coin embedding process has a series of inherent technical defects, such as interface gaps, excess adhesive contamination, and a single heat dissipation path, resulting in low production yield, high cost, and ultimately limited heat dissipation performance. Summary of the Invention

[0004] This application provides a copper paste integration fabrication process for a high-heat-dissipation multilayer printed circuit board to solve the above-mentioned problems. The method includes:

[0005] S1. Provide a core board with inner layer circuitry, and laminate multiple core boards with prepreg to form a multilayer circuit board;

[0006] S2. Perform controlled-depth milling on the predetermined heat dissipation area of ​​the multilayer circuit board to form a groove of specific depth and shape. The minimum groove width is 0.6 mm, and the groove depth is controlled to expose the target heat dissipation conductive layer.

[0007] S3. The multilayer circuit board is subjected to hole metallization treatment. A continuous metallization layer is formed on the entire inner surface of the through holes, blind holes and grooves through chemical copper plating and electroplating processes.

[0008] S4. Using a printing process, high thermal conductivity copper paste is filled into the metallized groove under vacuum or reduced pressure to ensure dense filling without air bubbles.

[0009] S5. Curing the copper paste, and performing surface grinding treatment on the cured copper paste so that the surface of the cured copper paste is flush with the surface of the substrate surrounding the circuit board.

[0010] S6. After the copper paste has been ground, the outer layer circuitry, solder mask, and surface treatment are performed to obtain the finished printed circuit board with the copper paste heat dissipation module integrated.

[0011] The above technical solution, employing a combination of controlled-depth milling and vacuum printing filling, solves the problems of high interfacial thermal resistance, difficulty in controlling flatness, and adhesive overflow contamination inherent in traditional embedded copper block processes. High thermal conductivity copper paste achieves molecular-level close contact with the metallization layer, significantly reducing interfacial thermal resistance. Precise controlled-depth milling exposes the target heat-dissipating conductive layer, ensuring effective connectivity of the heat dissipation path. Curing and polishing processes guarantee the coplanarity of the cured copper paste module surface with the surrounding substrate, facilitating reliable mounting of subsequent components (such as core heat-generating chips) and significantly improving the overall heat dissipation performance and manufacturing precision of the multilayer board structure.

[0012] Optionally, in step S2, the groove formed by controlled depth milling has a three-dimensional microstructure designed on its bottom and wall to enhance thermal connection and mechanical interlocking.

[0013] The three-dimensional microstructure is formed synchronously during the controlled depth milling process, and is used to increase the contact area between the metallization layer and the filling copper paste and the target heat dissipation and conductive layer in subsequent steps.

[0014] The above technical solution enhances the bonding strength and reliability between the cured copper paste module and the multilayer board structure by integrating a three-dimensional microstructure within the groove. The three-dimensional microstructure provides additional anchoring points, effectively resisting delamination stress that may occur during thermal cycling or mechanical vibration, especially for large-size or deeply embedded heat dissipation modules. Furthermore, the three-dimensional microstructure increases the effective cross-sectional area for heat transfer from the copper paste to the target heat dissipation conductive layer, improving heat conduction efficiency.

[0015] Optionally, the three-dimensional microstructure is an array of multiple micro-blind holes distributed at the bottom of the groove and extending to the target heat dissipation and conductive layer;

[0016] Each micro-blind hole in the array has a diameter of 0.2 mm to 0.5 mm and a depth extending at least to the insulating medium above the target heat dissipation conductive layer.

[0017] By defining the three-dimensional microstructure as a micro-blind via array using the above technical solution, the high-precision drilling technology in existing PCB processes can be utilized to the maximum extent to achieve a high degree of structural integration. The via diameter is controlled between 0.2mm and 0.5mm, ensuring both sufficient copper paste filling under vacuum or low pressure and consistent metallization layer thickness on the via walls. The micro-blind vias directly connect to the target heat dissipation conductive layer, forming a highly thermally conductive "copper pillar" structure and providing an additional vertical heat dissipation path.

[0018] Optionally, in step S2, the groove is a contoured groove.

[0019] The planar contour of the contoured groove is designed to match the layout, shape and hot spot distribution of one or more heat-generating electronic components within the predetermined heat dissipation area, so as to achieve directional and efficient heat dissipation coverage of dispersed or concentrated heat sources.

[0020] The contoured groove includes at least one main groove area that matches the projected shape of the core heating chip, and one or more branch grooves extending from the main groove area and pointing to the positions of the surrounding auxiliary heating elements.

[0021] The width of the branch channel is less than or equal to the width of the main channel area.

[0022] The aforementioned technical solution, employing a contoured, irregularly shaped slot design, allows the high thermal conductivity copper paste module to conform maximally to the heat source, achieving precise thermal management by "dissipating heat wherever it's generated." The main slot area ensures rapid heat conduction from the core heat source, while the branch slots collect heat from dispersed auxiliary heat sources and guide it to the main heat sink, achieving efficient thermal expansion and diffusion through the copper paste module. This customized structure significantly improves the overall efficiency and flexibility of the cooling system.

[0023] Optionally, in step S3, the electroplating copper process includes performing a thickening electroplating treatment after forming the basic conductive layer to increase the thickness of the metallization layer formed on the inner surface of the groove.

[0024] The thickening electroplating treatment employs a pulse electroplating process or a DC electroplating process to achieve a copper metallization layer thickness of 50 μm to 100 μm on the inner surface of the groove, with the surface of the copper metallization layer exhibiting a micro-rough morphology.

[0025] The above technical solution, through a thickened and roughened metallization layer, ensures effective heat conduction within the groove, providing a robust and low-thermal-resistance foundation for the copper paste module. The thickened copper layer enhances the mechanical stability of the structure, while the micro-roughened morphology significantly improves the bonding strength between the high thermal conductivity copper paste and the metallization layer.

[0026] Optionally, in step S4, the high thermal conductivity copper paste is composed of the following components: a polymer binder matrix, 85% to 95% by weight of metallic copper filler, and an interface bonding agent.

[0027] The metallic copper filler comprises a compound mixture of micron-sized flake copper powder and micron-sized or nano-sized spherical copper powder;

[0028] The polymer binder matrix is ​​a high thermal conductivity epoxy resin, silicone, or polyimide;

[0029] The interface bonding aid is a silane or titanate coupling agent;

[0030] The compound mixture is used to construct a dense three-dimensional thermally conductive network in the polymer binder matrix.

[0031] By employing the aforementioned technical solution, and through precise control of the compounding morphology of copper powder (flake and spherical / nanoscale) and high filling volume, the cured copper paste module achieves extremely high thermal conductivity. The high thermal conductivity polyimide matrix provides excellent heat resistance and mechanical strength. This optimized composition of the copper paste ensures that heat is rapidly and effectively conducted from the heating element to the target heat dissipation conductive layer, significantly improving heat dissipation efficiency.

[0032] Optionally, in step S4, the high thermal conductivity copper paste is composed of the following components: a polymer binder matrix, 85% to 95% by weight of metallic copper filler, and an interface bonding agent.

[0033] The metallic copper filler comprises a compound mixture of micron-sized flake copper powder and micron-sized or nano-sized spherical copper powder;

[0034] The polymer binder matrix is ​​a high thermal conductivity epoxy resin, silicone, or polyimide;

[0035] The interface bonding aid is a silane or titanate coupling agent;

[0036] The compound mixture is used to construct a dense three-dimensional thermally conductive network in the polymer binder matrix.

[0037] The above technical solution, which involves printing in a vacuum or low-pressure environment and using atmospheric pressure for assisted densification, effectively solves the problems of incomplete filling and residual air bubbles in the micro-grooves of high-viscosity copper paste. This ensures that the cured copper paste module has an extremely low porosity, thereby guaranteeing maximum heat transfer efficiency and improving the module's mechanical reliability.

[0038] Optionally, in step S5, the curing process employs a multi-stage heating procedure, including:

[0039] First, a pre-curing stage at a lower temperature is carried out to allow the copper paste to initially take shape and maintain a certain stress relaxation ability. Then, a final curing stage at a higher temperature is carried out to achieve complete cross-linking and reach the final mechanical and thermal properties.

[0040] The above technical solution employs a multi-stage heating and curing process, effectively controlling the generation and release of internal stresses during curing, particularly thermal and shrinkage stresses. This significantly reduces the risk of delamination or cracking between the cured copper paste module and the groove wall, ensuring the long-term reliability of the interface and maintaining excellent heat dissipation performance.

[0041] Optionally, the temperature of the pre-curing stage is 80°C to 100°C, and the time is 20 to 40 minutes;

[0042] The final curing stage is performed at a temperature of 150°C to 180°C for 50 to 70 minutes.

[0043] By precisely controlling the curing temperature and time parameters using the above technical solution, the high thermal conductivity copper paste can be fully cured to achieve the highest thermal conductivity and mechanical strength, while minimizing the residual stress generated during the curing process. This is crucial for ensuring the reliability of the cured copper paste module under long-term thermal cycling.

[0044] Optionally, in step S5, the surface grinding process employs a closed-loop control mechanism;

[0045] The closed-loop control mechanism dynamically adjusts the feed rate, rotation speed, or pressure of the grinding tool by monitoring the height difference between the grinding area and the surface of the surrounding substrate in real time, until the height difference between the surface of the cured copper paste and the surface of the outer substrate of the circuit board is less than 0.02mm.

[0046] By employing the above technical solution and a closed-loop control mechanism for surface grinding, the consistency and precision of the surface flatness of the cured copper paste module are greatly improved, controlling the final flatness tolerance within ±0.01mm. This high flatness makes subsequent outer layer circuit fabrication and component mounting more reliable, avoiding soldering defects caused by surface unevenness, thereby improving the overall yield and reliability of the finished printed circuit board. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart illustrating a copper paste integration fabrication process for a high-heat-dissipation multilayer printed circuit board, as provided in one embodiment of this application. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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 this application.

[0050] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0051] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0052] The industry commonly uses the method of embedding solid copper blocks in certain parts of the PCB to enhance heat dissipation. However, this traditional copper coin embedding process has a series of inherent technical defects, such as interface gaps, excess adhesive contamination, and a single heat dissipation path, resulting in low production yield, high cost, and ultimately limited heat dissipation performance.

[0053] Based on this, this application provides a copper paste integration fabrication process for high heat dissipation multilayer printed circuit boards, including technical solutions and effects.

[0054] For specific implementation details, please refer to the following examples.

[0055] Figure 1 A flowchart illustrating a copper paste integration fabrication process for a high-heat-dissipation multilayer printed circuit board, as provided in one embodiment of this application, is shown below. Figure 1 As shown, the process includes:

[0056] S1. Provide a core board with inner layer circuitry, and laminate multiple core boards with prepreg to form a multilayer circuit board;

[0057] S2. Perform controlled-depth milling on the predetermined heat dissipation area of ​​the multilayer circuit board to form a groove of specific depth and shape. The minimum groove width is 0.6 mm, and the groove depth is controlled to expose the target heat dissipation conductive layer.

[0058] S3. The multilayer circuit board is subjected to hole metallization treatment. A continuous metallization layer is formed on the entire inner surface of the through holes, blind holes and grooves through chemical copper plating and electroplating processes.

[0059] S4. Using a printing process, high thermal conductivity copper paste is filled into the metallized groove under vacuum or reduced pressure to ensure dense filling without air bubbles.

[0060] S5. Curing the copper paste, and performing surface grinding treatment on the cured copper paste so that the surface of the cured copper paste is flush with the surface of the substrate surrounding the circuit board.

[0061] S6. After the copper paste has been ground, the outer layer circuitry, solder mask, and surface treatment are performed to obtain the finished printed circuit board with the copper paste heat dissipation module integrated.

[0062] Existing high-power electronic devices place extremely high demands on the heat dissipation capabilities of printed circuit boards. Traditional embedded solid copper block solutions suffer from issues such as dimensional tolerances, interface voids, and bonding stress, making it difficult to guarantee the reliability and flatness of thermal connections. This implementation aims to solve the interface thermal resistance problem between the copper block and the cavity in traditional solutions. Its working principle is as follows: First, through S2 controlled deep milling, the insulating medium is precisely removed to expose the target heat dissipation conductive layer, forming a groove with a conductive inner surface; second, through S3 metallization, a continuous metallization layer is formed on the inner surface of the groove to ensure the continuity of electrical and thermal connections; subsequently, in the S4 vacuum filling step, a high-flowability, high-thermal-conductivity copper paste is densely filled into the metallized groove under vacuum conditions using a printing process, eliminating interface voids; finally, in S5 curing and grinding, the cured copper paste module is flush with the board surface, providing a highly flat surface for subsequent component mounting.

[0063] The process begins in step S1, stacking, where a high-Tg FR4 copper-clad laminate is used as the core board and laminated with prepreg (e.g., type 1080 or 7628) to form a multilayer board structure. In step S2, controlled-depth milling, a CNC milling machine precisely mills the predetermined heat dissipation areas of the multilayer board structure to form grooves, ensuring a minimum groove width of 0.6 mm and precise control of the milling depth to expose the target heat-dissipating conductive layer (e.g., ground layer). In step S3, metallization, chemical copper plating and DC electroplating are performed on the inner surfaces of the grooves to thicken them, forming a continuous metallization layer on all internal surfaces, with a thickness of, for example, 25 μm. In step S4, copper paste filling, the circuit board is placed in a vacuum chamber, the pressure is reduced to below 10 Pa, and high thermal conductivity copper paste with an average thermal conductivity greater than 200 W / mK is filled into the grooves using a stencil printing method. The plate is then left to stand to ensure adequate wetting and air bubble removal. In the S5 curing and polishing step, the copper paste is cured at 170℃ for 70 minutes, followed by surface polishing using a precision grinding wheel to ensure that the surface of the cured copper paste module is flush with the surface of the outer substrate of the circuit board, with a flatness tolerance of less than 0.02mm. Finally, in the S6 final processing step, the subsequent outer layer circuitry, solder mask patterning, and Ni / Au or OSP surface treatment are completed on the surface of the cured copper paste module to obtain the finished printed circuit board.

[0064] By employing a combination of controlled-depth milling and vacuum printing filling techniques, this implementation method solves the problems of high interfacial thermal resistance, difficulty in controlling flatness, and adhesive overflow contamination inherent in traditional embedded copper block processes. High thermal conductivity copper paste achieves molecular-level close contact with the metallization layer, significantly reducing interfacial thermal resistance. Precise controlled-depth milling exposes the target heat-dissipating conductive layer, ensuring effective connectivity of the heat dissipation path. Curing and polishing processes guarantee the coplanarity of the cured copper paste module surface with the surrounding substrate, facilitating reliable mounting of subsequent components (such as core heat-generating chips) and significantly improving the overall heat dissipation performance and manufacturing precision of the multilayer board structure.

[0065] In some embodiments, in step S2, the groove formed by controlled-depth milling has a three-dimensional microstructure designed on its bottom and wall to enhance thermal connection and mechanical interlock; the three-dimensional microstructure is formed synchronously in the controlled-depth milling step and is used to increase the contact area between the metallization layer and the filling copper paste and the target heat dissipation conductive layer in subsequent steps.

[0066] In existing technologies, even when a high thermal conductivity copper paste is connected to the target heat dissipation conductive layer via a metallization layer, the interfacial bonding between the two may still suffer from stress concentration or potential delamination risks due to mismatched coefficients of thermal expansion. This embodiment aims to significantly improve the interfacial bonding strength and thermal conductivity efficiency by constructing a three-dimensional microstructure within the groove. Its working principle is that the formation of the three-dimensional microstructure expands the interfacial contact area, allowing the metallization layer and the high thermal conductivity copper paste to be "anchored" to the insulating medium, forming a mechanical interlock. Simultaneously, it provides more thermal conduction paths for heat transfer from the copper paste module to the target heat dissipation conductive layer.

[0067] In the S2 controlled-depth milling step, while using a CNC milling machine to perform controlled-depth machining on the multilayer board structure, a laser drilling system or mechanical drilling is simultaneously used to design and form a three-dimensional microstructure on the bottom and walls of the groove. This three-dimensional microstructure extends to the target heat-dissipating and conductive layer by penetrating the insulating medium. In the S3 metallization step, the metallization layer covers the inner surface of the three-dimensional microstructure, forming a highly thermally conductive copper wall. In the S4 copper paste filling step, highly thermally conductive copper paste fills the interior of the three-dimensional microstructure, tightly bonding with the metallization layer to form a high-strength mechanically interlocking structure.

[0068] By integrating a three-dimensional microstructure within the groove, this implementation significantly enhances the bonding strength and reliability between the cured copper paste module and the multilayer board structure. The three-dimensional microstructure provides additional anchoring points, effectively resisting delamination stresses that may occur during thermal cycling or mechanical vibration, especially for large-size or deeply embedded heat dissipation modules. Furthermore, the three-dimensional microstructure increases the effective cross-sectional area for heat transfer from the copper paste to the target heat dissipation conductive layer, improving heat conduction efficiency.

[0069] In some embodiments, the three-dimensional microstructure is an array of multiple micro-blind holes distributed at the bottom of the groove and extending to the target heat dissipation and conductive layer; the diameter of each micro-blind hole in the array is 0.2 mm to 0.5 mm, and the hole depth extends at least to penetrate the insulating medium above the target heat dissipation and conductive layer.

[0070] In the foregoing embodiments, the specific geometry and size of the three-dimensional microstructure are crucial to the final bonding strength and thermal conductivity. This embodiment aims to achieve optimal mechanical interlocking and thermal conduction by precisely defining the three-dimensional microstructure as a micro-blind via array of specific sizes. The micro-blind vias, acting as thermal channels, can efficiently and vertically transfer heat from the copper paste module to the target heat-dissipating conductive layer, while their geometry facilitates the subsequent formation of the metallization layer and the dense filling of the copper paste.

[0071] In the S2 controlled-depth milling step, after or simultaneously with the formation of the groove, an array of micro-blind holes is drilled at specific intervals (e.g., a hole center-to-center distance of 0.8 mm) at the bottom of the groove using laser drilling or high-precision mechanical drilling equipment. The diameter of these micro-blind holes is precisely controlled between 0.2 mm and 0.5 mm, and the hole depth is designed to penetrate the insulating medium covering the target heat-dissipating conductive layer and extend to the surface of the target heat-dissipating conductive layer. In the S3 metallization step, chemical copper plating and electroplating processes ensure that the hole walls of the micro-blind holes are completely covered by the metallization layer, forming a robust heat-conducting channel.

[0072] By defining the three-dimensional microstructure as an array of micro-blind vias, the high-precision drilling technology in existing PCB processes can be utilized to the maximum extent to achieve a high degree of structural integration. The via diameter is controlled between 0.2mm and 0.5mm, ensuring both sufficient copper paste filling under vacuum or low pressure and consistent metallization layer thickness on the via walls. The micro-blind vias directly connect to the target heat dissipation conductive layer, forming a highly thermally conductive "copper pillar" structure that provides an additional vertical heat dissipation path.

[0073] In some embodiments, in step S2, the groove is a contoured groove; the planar contour of the contoured groove is designed to match the layout, shape and hotspot distribution of one or more heat-generating electronic components within the predetermined heat dissipation area, so as to achieve directional and efficient heat dissipation coverage of dispersed or concentrated heat sources; the contoured groove includes at least a main groove area that matches the projected shape of the core heat-generating chip, and one or more branch grooves extending from the main groove area and pointing to the positions of peripheral auxiliary heat-generating components; the width of the branch grooves is less than or equal to the width of the main groove area.

[0074] In applications such as high-performance computing and server motherboards, heat sources are often concentrated and unevenly distributed, making it difficult for traditional rectangular heat dissipation structures to accurately cover these scattered hotspots. This implementation aims to improve the efficiency of heat capture and conduction by using contoured slots to achieve a precise match between the heat dissipation structure and the distribution of heat sources.

[0075] Before the S2 controlled milling step begins, the planar contour of the contoured groove is designed within a predetermined heat dissipation area based on the position and shape of the core heat-generating chip's projected area and the positions of surrounding auxiliary heat-generating components. For example, for a compact server motherboard housing a core GPU chip and several peripheral power management ICs (PMICs), the main groove area is designed to match the projected shape of the core GPU chip, with a width set at 1.5mm. Simultaneously, one or more branch grooves extend from the main groove area, pointing towards the positions of auxiliary heat-generating components such as the PMICs. The width of the branch grooves is smaller than the width of the main groove area to accommodate smaller heat source sizes. The controlled milling process precisely mills the groove according to this contour.

[0076] The contoured slot design allows the high thermal conductivity copper paste modules to fit the heat source to the maximum extent, achieving precise thermal management by "dissipating heat where it's needed." The main slot area ensures rapid heat conduction from the core heat source, while the branch slots collect heat from dispersed auxiliary heat sources and guide it to the main heat sink, achieving efficient heat expansion and diffusion through the copper paste modules. This customized structure significantly improves the efficiency and flexibility of the overall cooling system.

[0077] In some embodiments, in step S3, the copper plating process includes performing a thickening electroplating treatment after forming the base conductive layer to increase the thickness of the metallization layer formed on the inner surface of the groove; the thickening electroplating treatment adopts a pulse electroplating process or a DC electroplating process to make the thickness of the metallization copper layer on the inner surface of the groove reach 50μm to 100μm, and the surface of the metallization copper layer has a micro-rough morphology.

[0078] In fabricating high heat dissipation structures, the metallization layer is not only the basis for subsequent copper paste filling, but also an important channel for heat conduction from the copper paste to the groove walls (insulating medium). This embodiment aims to improve the thermal conductivity and mechanical bonding of the interface by thickening the metallization layer and controlling its microstructure, especially for grooves with greater depth.

[0079] In the S3 metallization step, a basic conductive layer is first formed on the inner surface of the groove by chemical copper plating. Subsequently, a thickening electroplating process is performed. This thickening process can employ DC constant current electroplating or forward and reverse pulse electroplating processes. For example, using a pulse electroplating process, the copper layer thickness reaches 75 μm. Optimization of pulse electroplating parameters (e.g., forward current density 5 A / dm², pulse time 10 ms) results in a micro-roughened surface of the copper layer on the groove wall. This metallization layer, with a thickness of 50 μm to 100 μm, not only significantly reduces thermal resistance, but its micro-roughened morphology also provides a larger physical contact area and mechanical interlocking force for subsequent high thermal conductivity copper paste, further enhancing the interfacial bonding strength.

[0080] By employing a thickened and roughened metallization layer, this embodiment ensures effective heat conduction within the groove, providing a robust and low-thermal-resistance foundation for the copper paste module. The thickened copper layer enhances the mechanical stability of the structure, while the micro-roughened morphology significantly improves the bonding strength between the high thermal conductivity copper paste and the metallization layer.

[0081] In some embodiments, in step S4, the high thermal conductivity copper paste is composed of the following components: a polymer binder matrix, 85% to 95% by weight of metallic copper filler, and an interface bonding aid; the metallic copper filler comprises a compound mixture of micron-sized flake copper powder and micron-sized or nano-sized spherical copper powder; the polymer binder matrix is ​​a high thermal conductivity epoxy resin, silicone, or polyimide; the interface bonding aid is a silane or titanate coupling agent; the compound mixture is used to construct a dense three-dimensional thermally conductive network in the polymer binder matrix.

[0082] In the S4 copper paste filling step, the thermal conductivity of the copper paste is a key factor determining the final heat dissipation effect. This embodiment aims to optimize the composition of the copper paste, especially the morphology and content of the metallic copper filler, to ensure the formation of a highly dense copper / polymer composite material after curing, thereby achieving high thermal conductivity.

[0083] In the S4 copper paste filling step, the weight ratio of copper paste components is 92% metallic copper filler. The polymer binder matrix is ​​a high thermal conductivity polyimide resin. The metallic copper filler is a blend of micron-sized flake copper powder and nano-sized spherical copper powder. The flake copper powder helps form a continuous overlapping structure in the planar direction, while the spherical and nano-sized copper powders fill the tiny gaps between the flake copper powders, thereby constructing a highly efficient and dense three-dimensional thermally conductive network within the polyimide matrix. Simultaneously, an appropriate amount of silane coupling agent is added as an interfacial bonding aid to improve the wettability and adhesion between the copper powder and the polyimide matrix, reducing interfacial thermal resistance.

[0084] By precisely controlling the compounding morphology of the copper powder (flakes and spherical / nanoscale) and the high filling content (85% to 95%), this embodiment ensures that the cured copper paste module has extremely high thermal conductivity (e.g., greater than 200 W / mK). The high thermal conductivity polyimide matrix provides excellent heat resistance and mechanical strength. This optimized composition of the copper paste ensures that heat is quickly and efficiently conducted from the heating element to the target heat dissipation conductive layer, significantly improving heat dissipation efficiency.

[0085] In some embodiments, step S4 specifically includes: placing the multilayer circuit board in a vacuum chamber, reducing the vacuum level to below 10 Pa and maintaining it; injecting the high thermal conductivity copper paste into the groove using stencil printing or screen printing; allowing the copper paste to flow in the groove and completely wet the metallized inner surface while maintaining a vacuum or low pressure; slowly releasing the vacuum, using atmospheric pressure to assist in further densification of the copper paste and expelling residual gas.

[0086] During the S4 copper paste filling process, ensuring the density of the copper paste filling is crucial for eliminating internal air bubbles and reducing thermal resistance. This embodiment aims to maximize the filling quality of the copper paste by combining low-pressure filling under vacuum conditions with atmospheric pressure-assisted densification.

[0087] In the S4 copper paste filling step, the circuit board treated with S3 metallization is first placed in a vacuum chamber, and the vacuum level is reduced to below 5 Pa and maintained. Then, a thinning stencil printing method is used to inject high thermal conductivity copper paste into the grooves. Under low pressure, the fluidity of the copper paste is improved, allowing for better wetting of the inner surface of the grooves and the three-dimensional microstructure, while avoiding air entrapment during the filling process. After printing, the reduced pressure is maintained for a period of time (e.g., 5 minutes), followed by the slow introduction of nitrogen to atmospheric pressure. The additional pressure provided by the external atmospheric pressure forces the copper paste into the microstructure, further eliminating nanoscale bubbles and achieving efficient and dense filling.

[0088] By printing under vacuum or low pressure and using atmospheric pressure for assisted densification, this embodiment effectively solves the problems of incomplete filling and residual air bubbles in micro-grooves with high-viscosity copper paste. This ensures that the cured copper paste module has an extremely low porosity, thereby guaranteeing maximum heat conduction efficiency and improving the module's mechanical reliability.

[0089] In some embodiments, in step S5, the curing process is carried out using a multi-stage heating procedure, including: first, a pre-curing stage at a lower temperature to allow the copper paste to initially set and maintain a certain stress relaxation capability, and then a final curing stage at a higher temperature to achieve complete cross-linking and achieve the final mechanical and thermal properties.

[0090] High-fill-content copper paste generates significant curing shrinkage stress during the curing process. If a single-stage high-temperature curing method is used, stress concentration may lead to microcracks or delamination at the interface between the copper paste and the metallization layer. This implementation aims to effectively control curing stress through a multi-stage heating process, thereby improving the reliability and performance of the module.

[0091] In the S5 curing and polishing step, the copper paste curing process is divided into two stages. First, a low-temperature pre-curing stage is performed, for example, holding at 90°C for 30 minutes. During the pre-curing stage, the polymer binder matrix (e.g., high-performance epoxy resin) begins initial cross-linking, giving the copper paste a certain strength and shape stability. Simultaneously, the lower temperature allows sufficient time for stress relaxation, preventing rapid shrinkage. This is followed by a high-temperature final curing stage, for example, holding at 165°C for 60 minutes, to ensure complete cross-linking and curing of the polymer matrix, achieving the desired mechanical and thermal properties.

[0092] A multi-stage heating and curing process was employed to effectively control the generation and release of internal stresses during curing, particularly thermal and shrinkage stresses. This significantly reduced the risk of delamination or cracking between the cured copper paste module and the groove wall, ensuring long-term interface reliability and maintaining excellent heat dissipation performance.

[0093] In some embodiments, the temperature of the pre-curing stage is 80°C to 100°C and the time is 20 to 40 minutes; the temperature of the final curing stage is 150°C to 180°C and the time is 50 to 70 minutes.

[0094] This embodiment optimizes the copper paste curing process by precisely controlling the temperature and time during the pre-curing and final curing stages, thereby further improving the performance and reliability of the cured copper paste module.

[0095] In the S5 curing and polishing step, the multi-stage temperature program is specifically set as follows: the temperature of the pre-curing stage is controlled at 90°C and held for 30 minutes to achieve initial shaping and stress relaxation. The temperature of the final curing stage is set at 165°C and held for 60 minutes to achieve complete cross-linking of the polymer matrix. These parameters are optimized based on the curing kinetics curves of the selected high thermal conductivity epoxy resin or polyimide, aiming to balance curing speed and stress control.

[0096] Precise control of curing temperature and time parameters ensures that the high thermal conductivity copper paste can fully cure, achieving the highest thermal conductivity and mechanical strength, while minimizing residual stress generated during the curing process. This is crucial for ensuring the reliability of the cured copper paste module under long-term thermal cycling.

[0097] In some embodiments, in step S5, the surface grinding process adopts a closed-loop control mechanism; the closed-loop control mechanism dynamically adjusts the feed rate, rotation speed or pressure of the grinding tool by monitoring the height difference between the grinding area and the surface of the peripheral substrate in real time online, until the height difference between the surface of the cured copper paste and the surface of the peripheral substrate of the circuit board is less than 0.02mm.

[0098] In the S5 curing and polishing step, achieving high-precision coplanarity between the surface of the cured copper paste module and the surface of the substrate surrounding the circuit board is crucial to ensuring the subsequent soldering quality of SMD components. This implementation aims to control the polishing flatness tolerance within an extremely small range by employing a closed-loop control mechanism.

[0099] In the S5 curing and grinding step, a precision grinding wheel is used for surface grinding. During the grinding process, the height difference between the surface of the cured copper paste module and the surface of the surrounding substrate is monitored in real time using photoelectric sensors or displacement sensors. This height difference signal is fed back to the control system, which dynamically adjusts the feed rate and / or pressure of the grinding tool according to a preset flatness target (less than 0.02 mm). For example, when the detected height difference is greater than a preset threshold, the control system increases the feed rate or pressure; when it approaches the target value, it decreases the feed rate or rotation speed until the final height difference is less than 0.02 mm.

[0100] By employing a closed-loop control mechanism for surface grinding, the consistency and precision of the surface flatness of the cured copper paste module are greatly improved, controlling the final flatness tolerance within ±0.01mm. This high flatness makes subsequent outer layer circuit fabrication and component mounting more reliable, avoiding soldering defects caused by surface unevenness, thereby improving the overall yield and reliability of the finished printed circuit board.

Claims

1. A process for integrated preparation of copper paste of high heat dissipation multilayer printed circuit board, characterized in that, The method comprises the following steps: S1. providing a core board formed with inner layer circuits, and laminating a plurality of the core boards with prepreg to form a multilayer circuit board; S2. performing controlled depth milling processing on a predetermined heat dissipation area of the multilayer circuit board to form a groove with a specific depth and shape, the minimum groove width of the groove being 0.6 mm, and the groove depth being controlled to expose a target heat dissipation conductive layer; S3. performing hole metallization processing on the multilayer circuit board to form a continuous metallization layer on the entire inner surface of the through hole, blind hole and groove by chemical copper deposition and electroplating copper process; S4. filling high thermal conductivity copper paste into the groove after metallization by printing process in a vacuum or reduced pressure environment to ensure dense and bubble-free filling; S5. curing the copper paste and performing surface grinding treatment on the cured copper paste to make the surface of the cured copper paste flush with the surface of the peripheral substrate of the circuit board; S6. performing outer layer circuit manufacturing, solder mask and surface treatment on the copper paste after grinding treatment to obtain a finished printed circuit board integrated with a copper paste heat dissipation module; In step S2, the groove formed by the controlled depth milling processing is designed with a three-dimensional microstructure on the groove bottom and groove wall to enhance thermal connection and mechanical interlocking; The three-dimensional microstructure is formed synchronously in the controlled depth milling processing step to increase the contact area of the metallization layer and the filled copper paste with the target heat dissipation conductive layer in the subsequent steps; The three-dimensional microstructure is a plurality of micro blind hole arrays distributed on the groove bottom and extending to the target heat dissipation conductive layer; The aperture of each micro blind hole in the micro blind hole array is 0.2 mm to 0.5 mm, and the hole depth extends at least to penetrate the insulating medium above the target heat dissipation conductive layer; In step S2, the shape of the groove is a profiled special-shaped groove; The planar profile of the profiled special-shaped groove is designed to match the layout, shape and hot spot distribution of one or more heat generating electronic elements in the predetermined heat dissipation area to achieve directional and efficient heat dissipation coverage of dispersed or concentrated heat sources; The profiled special-shaped groove at least includes a main groove area matched with the projection shape of a core heat generating chip, and one or more branch groove channels extending from the main groove area and pointing to the positions of peripheral auxiliary heat generating elements; The width of the branch groove channel is less than or equal to the width of the main groove area.

2. The manufacturing process according to claim 1, characterized in that, In step S3, the electroplating copper process includes thickening electroplating processing after forming a basic conductive layer to increase the thickness of the metallization layer formed on the inner surface of the groove; The thickening electroplating processing adopts pulse electroplating process or direct current electroplating process to make the thickness of the metallized copper layer on the inner surface of the groove reach 50 μm to 100 μm, and the surface of the metallized copper layer is in a microscopically rough form.

3. The manufacturing process of claim 1, wherein, In step S4, the high thermal conductivity copper paste is composed of the following components: a high molecular binder matrix, 85% to 95% of metal copper filler based on the total weight, and an interface bonding aid; The metal copper filler includes a compounded mixture of micron-sized flaky copper powder and micron-sized or nano-sized spherical copper powder; The high molecular binder matrix is high thermal conductivity epoxy resin, silicone or polyimide; The interface bonding aid is a silane or titanate coupling agent; The compounded mixture is used to build a dense three-dimensional heat conduction network in the polymer binder matrix.

4. The manufacturing process of claim 1, wherein, Step S4 specifically includes: placing the multilayer circuit board in a vacuum chamber, reducing the vacuum degree to below 10 Pa and maintaining; The high-thermal-conductivity copper paste is injected into the groove by using template printing or screen printing; Under the condition of maintaining vacuum or low pressure, the copper paste flows in the groove and completely wets the inner metalized surface; Slowly release the vacuum, use atmospheric pressure to assist the copper paste to further densify and discharge residual gas.

5. The manufacturing process of claim 1, wherein, In step S5, the curing process adopts a multi-stage temperature program, including: First, a lower-temperature pre-curing stage is performed to make the copper paste preliminarily set and keep a certain stress relaxation ability, and then a high-temperature final curing stage is performed to realize complete crosslinking and achieve the final mechanical and thermal properties.

6. The manufacturing process of claim 5, wherein, The temperature of the pre-curing stage is 80-100℃, and the time is 20-40 minutes; The temperature of the final curing stage is 150-180℃, and the time is 50-70 minutes.

7. The manufacturing process of claim 6, wherein, In step S5, the surface grinding treatment adopts a closed-loop control mechanism; The closed-loop control mechanism dynamically adjusts the feed amount, rotation speed or pressure of the grinding tool by online real-time monitoring the height difference between the grinding area and the surface of the peripheral substrate until the height difference between the surface of the cured copper paste and the surface of the peripheral substrate of the circuit board is less than 0.02 mm.

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