A method for manufacturing an embedded PCB heat spreader

Abstract

This invention relates to the field of PCB board processing technology and discloses a method for fabricating an embedded PCB heat sink, comprising the following steps: welding copper blocks and metal materials to the upper and lower surfaces of a ceramic substrate, and performing stepped processing on the copper blocks and metal materials to form a stepped morphology; mounting a chip on the copper blocks to form a chip-copper block-ceramic composite structure; preparing a copper-containing substrate, wherein the copper-containing substrate is formed by laminating and pressing metal materials and insulating materials, and processing grooves adapted to the composite structure on the copper-containing substrate; placing the composite structure in the grooves, and stacking insulating materials and metal materials for single-sided lamination and fixation. The purpose of this method for fabricating an embedded PCB heat sink is to solve the problems in the prior art where the heat sink and PCB have an independent assembly interface, which introduces contact thermal resistance, artificially prolongs the heat transfer path, reduces heat conduction efficiency due to material discontinuity at the interface, and fails to fully utilize the direct heat conduction advantages of the embedded structure.

Description

Technical Field

[0001] This invention relates to the field of PCB board processing technology, specifically to a method for preparing an embedded PCB heat sink. Background Technology

[0002] As electronic products evolve towards miniaturization, high density, and high performance, embedded PCB technology has emerged. This technology directly embeds bare chips within the PCB board, effectively reducing package size and improving signal transmission efficiency. To achieve chip heat dissipation, existing technologies primarily employ two methods: one is to attach an independent heatsink to the back of the PCB using thermally conductive adhesive or mechanical fixation; the other is to prefabricate the heatsink using 3D printing technology and then assemble it onto the PCB. These methods have addressed the heat dissipation problem of embedded PCBs to some extent, but with the continuous increase in chip power consumption, the limitations of existing heat dissipation solutions are becoming increasingly apparent.

[0003] However, in existing technologies, there is an independent assembly interface between the heat sink and the PCB, which introduces a significant contact thermal resistance. Specifically, when external heat sinks are fixed with thermally conductive adhesive or screws, the uneven thickness of the thermally conductive adhesive layer and the difficulty in completely eliminating the interface air gaps result in a significant thermal resistance bottleneck at the assembly interface during the heat flow from the chip through the ceramic substrate and metal layer to the heat sink. Pre-fabricated 3D-printed heat sinks also need to be connected to the metal layer on the back of the PCB by welding or bonding. The presence of the solder layer or adhesive layer artificially prolongs the heat transfer path, and the material discontinuity at the interface leads to a significant decrease in heat conduction efficiency. This fails to fully utilize the advantages of direct heat conduction between the ceramic substrate and the back metal layer in the embedded structure, severely restricting the overall heat dissipation performance. Summary of the Invention

[0004] The purpose of this invention is to solve the problems in the prior art where the heat sink and PCB have an independent assembly interface, which introduces contact thermal resistance, artificially prolongs the heat transfer path, reduces the heat conduction efficiency due to material discontinuity at the interface, and fails to fully utilize the direct heat conduction advantages of the embedded structure. Therefore, this invention proposes a method for preparing an embedded PCB heat sink.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for manufacturing an embedded PCB heat sink includes the following steps: S1: Weld copper blocks and metal materials to the upper and lower surfaces of a ceramic substrate, and perform a stepped processing on the copper blocks and metal materials to form a stepped morphology. S2: The chip is mounted on the copper block to form a chip-copper-ceramic composite structure; S3: Prepare a copper-containing substrate, wherein the copper-containing substrate is formed by laminating and pressing metal materials and insulating materials, and grooves adapted to the composite structure are processed on the copper-containing substrate; S4: Place the composite structure in the groove, and press and fix it on one side by stacking insulating material and metal material; S5: Laser technology is used to remove the metal and insulating materials on the chip, forming through holes and electroplating to fill them to form metal conductive pillars; S6: 3D printing is performed directly on the surface of the metal material under the ceramic substrate to form a metal heat sink that is integrally connected with the metal material.

[0006] Based on the above technical solution, the present invention can be further improved as follows.

[0007] Furthermore, the stepped processing in S1 adopts a combination of chemical etching and mechanical processing. By controlling the etching depth and mechanical processing precision, at least two stepped structures are formed between the side of the copper block and the edge of the metal material. The step height of the stepped structure matches the thickness of the insulating material, ensuring that the insulating material can completely fill the step gap during the subsequent pressing process, thereby achieving electrical isolation between the chip and the external metal layer.

[0008] Furthermore, in S2, the chip and the copper block are connected by a thermally conductive solder layer with a thickness of 20-100μm. The welding process adopts reflow soldering or sintering process, with a welding temperature of 250-350℃ and a holding time of 30-180 seconds, to ensure that the solder fully melts and fills the tiny gap between the chip and the copper block, forming a low thermal resistance heat conduction channel.

[0009] Furthermore, the copper substrate in S3 is prepared by: firstly, stacking metal materials on the upper and lower sides of the insulating material, and then pressing them together using a hot pressing process. The pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 60-120 minutes. The groove is processed by milling or laser cutting. The depth of the groove is adapted to the total thickness of the chip-copper block-ceramic composite structure, and the flatness of the bottom of the groove is controlled within ±0.05mm.

[0010] Furthermore, the parameters of the single-sided pressing process in S4 are: pressing temperature of 170-210℃, pressure of 1.5-4MPa, and holding time of 50-100 minutes; during the pressing process, the insulating material flows under the action of hot pressing, filling all the gaps between the ceramic substrate, copper block, chip and copper-containing substrate, and forms an integral structure after curing. The insulating material simultaneously realizes the functions of mechanical support, electrical insulation and gap filling.

[0011] Furthermore, in S5, the laser process uses a CO2 laser or an ultraviolet laser with a laser power of 10-50W and a scanning speed of 100-500mm / s. Through multiple scans, the metal and insulating materials above the chip are removed layer by layer. The electroplating filling process uses chemical copper plating or electrolytic copper plating. First, a chemical copper seed layer is formed on the inner wall of the through hole, and then the through hole is completely filled by electroplated copper. The formed metal conductive pillar provides a vertical electrical connection channel for the chip.

[0012] Furthermore, prior to S6, a circuit patterning step is included: coating a photoresist onto the surface of a metal material, followed by exposure, development, and chemical etching to form conductive lines. These conductive lines are electrically connected to the electrodes of the chip via metal conductive posts, thus constructing a signal transmission path and power distribution network between the chip and external circuits.

[0013] Furthermore, before 3D printing in S6, ink solder resist treatment is applied to areas where heat sinks are not needed to form a protective layer. The 3D printing uses selective laser melting or electron beam melting technology, and the printing material is copper alloy or aluminum alloy powder with a particle size of 15-53μm. The powder is melted and stacked layer by layer to form a metal heat sink. The metal heat sink forms a metallurgical bond with the metal material under the ceramic substrate, eliminating the need for additional welding or bonding processes and removing contact thermal resistance.

[0014] Furthermore, the internal structure of the metal radiator is a densely arranged microchannel structure, which includes an inlet region, a middle flow region, and an outlet region. The cross-sectional area of ​​the channels in the inlet and outlet regions is larger than that of the channels in the middle flow region. The middle flow region adopts a honeycomb or rhomboid staggered array of microchannels. The wall thickness of the microchannels is 0.3-1.0 mm, the channel spacing is 0.5-2.0 mm, and the microchannels in adjacent layers are staggered to form a turbulence-promoting structure, thereby enhancing the heat exchange efficiency between the cooling medium and the radiator wall.

[0015] Furthermore, the ceramic substrate is made of aluminum nitride ceramic or alumina ceramic with a thermal conductivity ≥150W / (m·K); the insulating material is at least one of polyimide resin, epoxy resin or BT resin; the metal material is copper foil or copper alloy foil with a thickness of 18-105μm; when the heat sink is working, a liquid cooling medium is circulated inside, which is one of deionized water, ethylene glycol aqueous solution or fluorinated liquid, with a flow rate of 0.5-3.0L / min.

[0016] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: This invention eliminates the need for thermally conductive adhesive, solder, or any bonding agent as an intermediate connecting layer. During the 3D printing process, the metal powder melts under the high energy of a laser or electron beam, undergoing metallurgical bonding with the surface of the metal material beneath the ceramic substrate to form an atomic-level interface connection. This completely eliminates the thermal resistance bottlenecks caused by uneven adhesive layer thickness, interface gaps, solder layers, or bonding agent layers in traditional assembly methods. After heat is generated from the chip, it passes sequentially through the copper block, ceramic substrate, and back metal material, directly transferring to the integrated 3D-printed heat sink. There are no discontinuous material interfaces in the entire heat transfer path, ensuring smooth and efficient heat flow. This fully leverages the direct thermal conductivity advantage of the ceramic substrate and the back metal layer in the embedded structure. Furthermore, 3D printing technology allows for flexible design of the heat sink's internal microchannel structure based on the chip's heat flow distribution characteristics, achieving a high degree of integration between heat sink structure design and manufacturing process. Compared to prefabricated heat sinks and subsequent assembly, this not only improves heat dissipation efficiency but also simplifies the manufacturing process, reduces process accumulation errors introduced by multiple assembly operations, and significantly improves the overall performance and reliability of the embedded PCB heat dissipation system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the fabrication of the ceramic substrate structure of the present invention; Figure 2 This is a schematic diagram of the chip mounting structure of the present invention; Figure 3 This is a schematic diagram of the machining process of the copper-containing substrate of the present invention; Figure 4 This is a schematic diagram of the resin copper plate pressing process of the present invention; Figure 5 This is a schematic diagram of the windowed electroplated copper pillar of the present invention; Figure 6 This is a schematic diagram of the surface etching pads of the present invention; Figure 7 This is a schematic diagram of the 3D printed heat sink of the present invention.

[0018] In the diagram: 1. Ceramic substrate; 2. Copper block; 3. Metal material; 4. Chip; 5. Insulating material; 6. Groove; 7. Conductive circuit; 8. Metal heat sink. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Combination Figures 1-7As shown, a method for manufacturing an embedded PCB heat sink according to the present invention includes the following steps: S1: Weld copper blocks 2 and metal materials 3 on the upper and lower surfaces of ceramic substrate 1, and perform step processing on copper blocks 2 and metal materials 3 to form a step morphology. S2: Attach chip 4 onto copper block 2 to form a chip-copper block-ceramic composite structure; S3: Prepare a copper-containing substrate, which is made by laminating metal material 3 and insulating material 5, and process grooves 6 adapted to the composite structure on the copper-containing substrate. S4: Place the composite structure in the groove 6, and press and fix the insulating material 5 and the metal material 3 on one side; S5: Use laser technology to remove the metal material 3 and insulating material 5 above the chip 4, form a through hole and electroplating to fill it to form a metal conductive pillar 6; S6: 3D printing is performed directly on the surface of the metal material 3 below the ceramic substrate 1 to form a metal heat sink 8 that is integrally connected with the metal material 3.

[0021] First, in step S1, a ceramic substrate 1 with high thermal conductivity is selected as the heat dissipation intermediate layer. A copper block 2 is welded to its upper surface using active metal brazing or eutectic welding technology, and a metal material 3 is welded to its lower surface. After welding, the copper block 2 and the metal material 3 are processed in a stepped manner to form a three-dimensional morphology with multiple steps. This stepped morphology provides a structural basis for the subsequent filling of insulating materials and electrical isolation.

[0022] In step S2, the chip 4 is attached to the upper surface of the copper block 2 using thermally conductive solder or thermally conductive adhesive to form a three-layer composite structure of chip-copper block-ceramic. This structure forms the core channel for conducting heat downward from the chip 4. The copper block 2 acts as a diffusion layer to uniformly diffuse the high-density heat flow generated by the chip 4 to the ceramic substrate 1, and then quickly transfers it to the metal material 3 below through the high thermal conductivity of the ceramic substrate 1.

[0023] Step S3 prepares a copper-containing substrate, which is made of metal material 3 and insulating material 5 laminated by hot pressing. According to the shape and size of the composite structure, a matching groove 6 is processed on the copper-containing substrate. The depth, width and positional accuracy of the groove 6 directly affect the alignment accuracy and surface flatness of the subsequent embedding.

[0024] Step S4: The chip-copper block-ceramic composite structure is precisely placed in the groove 6, and the insulating material 5 and metal material 3 are superimposed on it. The whole structure is fixed by a single-sided pressing process. During the pressing process, the insulating material 5 flows fully and fills all gaps under the combined action of heat and pressure. After curing, a void-free whole structure is formed.

[0025] Step S5 uses a laser process to precisely remove the cover layer above chip 4, forming a through-hole. This is then filled with an electroplating process to form a metal conductive pillar 6, achieving vertical electrical interconnection between chip 4 and the PCB surface circuitry. Step S6 is the most crucial innovative step of this invention: 3D printing is performed directly on the surface of the metal material 3 below the ceramic substrate 1. Additive manufacturing technology is used to melt and deposit metal powder layer by layer, forming a metal heat sink 8 that is metallurgically bonded to the metal material 3.

[0026] This integrated molding method eliminates the contact thermal resistance of traditional assembly interfaces, establishes an unobstructed heat conduction path from chip 4 to heat sink 8, and significantly improves the overall heat dissipation efficiency of the embedded PCB system.

[0027] The stepped processing in S1 employs a combination of chemical etching and mechanical machining. By controlling the etching depth and machining precision, at least two stepped structures are formed between the side of the copper block 2 and the edge of the metal material 3. The step height matches the thickness of the insulating material 5, ensuring that the insulating material 5 can completely fill the step gaps during subsequent lamination, achieving electrical isolation between the chip 4 and the external metal layer. Figure 1 As shown, a copper block 2 is welded to the upper surface of the ceramic substrate 1, and a metal material 3 is welded to the lower surface. The copper block 2 and the metal material 3 are processed in a stepped manner by a combination of chemical etching and mechanical processing.

[0028] The stepped processing technology first uses photoresist as an etching mask. The area to be retained is determined by ultraviolet light exposure and development. Then, the ceramic substrate 1 is immersed in ferric chloride or ammonium persulfate solution for chemical etching. The etching depth is precisely controlled by the immersion time and solution concentration. Generally, the etching depth of the first step is 50-80μm, and the etching depth of the second step is 100-150μm, so that at least two stepped structures are formed between the side of the copper block 2 and the edge of the metal material 3.

[0029] For parts requiring precision that are difficult to achieve with chemical etching, CNC milling or precision grinding is used for machining to ensure that the verticality and surface roughness of the steps meet the requirements of subsequent pressing.

[0030] The stepped structure design allows the insulating material 5 to flow fully along the stepped shape and fill all gaps during the subsequent lamination process, avoiding the formation of a conductive path between the copper block 2 and the external metal layer, and achieving electrical isolation between the chip 4 and the external metal layer. This is a key design to ensure the reliability of the electrical performance of the embedded PCB.

[0031] In S2, chip 4 and copper block 2 are connected by a thermally conductive solder layer with a thickness of 20-100μm. The soldering process employs reflow soldering or sintering, with a soldering temperature of 250-350℃ and a holding time of 30-180 seconds to ensure the solder fully melts and fills the tiny gap between chip 4 and copper block 2, forming a low-thermal-resistance heat-conducting channel. Figure 2 As shown, the connection between chip 4 and copper block 2 is made of thermally conductive solder layer. The solder layer is preferably made of SAC305 lead-free solder or high thermal conductivity silver-copper solder. The thickness of the solder layer is strictly controlled within the range of 20-100μm. If the thickness is too thin, it will cause poor local contact between chip 4 and copper block 2. If the thickness is too thick, it will increase thermal resistance and reduce heat dissipation efficiency.

[0032] The welding process can be reflow soldering or sintering. When reflow soldering, a vapor phase reflow oven or an infrared reflow oven is used. The temperature profile is set as follows: preheating section 150-180℃ for 60-90 seconds, heating section heating to peak temperature 250-350℃ at a rate of 1-3℃ per second, holding time 30-180 seconds, to ensure that the solder melts fully and fills the tiny gap between chip 4 and copper block 2 under capillary action. Cooling section uses natural cooling or forced air cooling to solidify the solder.

[0033] The sintering process uses nano-silver paste or nano-copper paste as the connecting material. It is held at a temperature of 200-300℃ and a pressure of 1-10MPa for 10-30 minutes. The nanoparticles sinter under high temperature and high pressure to form a dense intermetallic compound layer. The heat conduction channel formed by this method has lower thermal resistance and excellent high temperature resistance.

[0034] The copper substrate in S3 is prepared as follows: First, metal materials 3 are stacked on the upper and lower sides of insulating material 5, and then pressed together using a hot-pressing process. The pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 60-120 minutes. The groove 6 is processed using milling or laser cutting. The depth of the groove 6 is adapted to the total thickness of the chip-copper block-ceramic composite structure, and the flatness of the bottom of the groove 6 is controlled within ±0.05mm. Figure 3 As shown, the copper-containing substrate is prepared using the standard copper-clad laminate manufacturing process. An insulating material 5 with a thickness of 100-200μm is selected as the core layer, and copper foil with a thickness of 18-105μm is stacked on its upper and lower sides as the metal material 3. After forming a sandwich structure, it is sent into a vacuum hot press for pressing. The pressing temperature is set at 180-220℃. This temperature range allows the resin system in the insulating material 5 to reach a molten flow state without thermal decomposition. The pressure is set at 2-5MPa to ensure that the resin fully wets the surface of the copper foil and removes interlayer bubbles. The holding time is 60-120 minutes to allow the resin system to completely cure and form a strong copper-resin-copper laminate structure.

[0035] The processing of groove 6 is based on the external dimensions of the chip-copper block-ceramic composite structure. It is processed using a high-speed CNC milling machine or ultraviolet laser cutting equipment. The milling process uses a carbide end mill with a speed of 15,000-30,000 rpm and a feed rate of 500-1,500 mm / min. The depth is gradually reached through multiple passes. The depth tolerance of groove 6 is controlled within ±0.03 mm. The flatness of the bottom is ensured to be within ±0.05 mm by measuring with a coordinate measuring machine. The verticality deviation of the sidewall is no more than 0.1 mm. These precision requirements ensure that the subsequent composite structure can be accurately positioned and that the surface flatness after pressing meets the requirements of circuit processing.

[0036] The parameters for the single-sided lamination process in S4 are: lamination temperature 170-210℃, pressure 1.5-4MPa, and holding time 50-100 minutes. During lamination, the insulating material 5 flows under hot pressure, filling all the gaps between the ceramic substrate 1, copper block 2, chip 4, and the copper-containing substrate. After curing, it forms an integral structure. The insulating material 5 simultaneously performs the functions of mechanical support, electrical insulation, and gap filling. Figure 4 As shown, the single-sided lamination process involves placing the chip-copper block-ceramic composite structure in the groove 6, then sequentially stacking an insulating material 5 and a metal material 3 of appropriate thickness on top of it. The entire assembly is then fed into a single-sided lamination device for hot pressing and fixing. The lamination temperature is set to 170-210℃, which is slightly lower than the preparation temperature of the copper substrate to avoid warping and deformation of the lower structure due to overheating. The pressure is set to 1.5-4MPa, which ensures that the insulating material 5 can fully flow and fill all gaps without causing the ceramic substrate 1 to be subjected to excessive stress and crack.

[0037] The pressing process adopts staged heating control. First, the temperature is raised to the set temperature at a rate of 5-10°C per minute. After reaching the set temperature, the pressure is maintained for 50-100 minutes. During this process, the epoxy resin or polyimide resin system in the insulating material 5 flows under the action of hot pressing. The resin fully fills the stepped gaps of the ceramic substrate 1, the side gaps of the copper block 2, the peripheral area of ​​the chip 4, and all the tiny cavities between the copper substrates under the pressure drive. After curing, a gapless integral structure is formed.

[0038] The insulating material 5 plays multiple functions in this structure. It serves as a mechanical support skeleton to support the chip 4 and the ceramic substrate 1, as an electrical insulating medium to isolate metal layers with different potentials, and as a void filler to eliminate voids and cracks inside the structure. This integrated pressing and fixing method significantly improves the mechanical strength and thermal cycling reliability of the embedded PCB.

[0039] The laser process in S5 uses a CO2 laser or an ultraviolet laser with a laser power of 10-50W and a scanning speed of 100-500mm / s. Multiple scans are used to remove the metal material 3 and insulating material 5 layer by layer above the chip 4. The electroplating filling process uses chemical copper plating or electrolytic copper plating. First, a chemical copper seed layer is formed on the inner wall of the via, and then electroplated copper is used to fill the via completely. The resulting metal conductive pillars 6 provide a vertical electrical connection channel for the chip 4. Figure 5 As shown, the laser process uses a CO2 laser with a wavelength of 10.6μm or an ultraviolet laser with a wavelength of 355nm to selectively remove the metal material 3 and insulating material 5 on the chip 4. The laser power is set to 10-50W. Too low a power will result in low processing efficiency, while too high a power may damage the pads or passivation layer on the surface of the chip 4. The scanning speed is controlled within the range of 100-500mm / s. The precise ablation of different materials is achieved by adjusting the pulse frequency and duty cycle of the laser.

[0040] The processing adopts a strategy of multiple scans and layer-by-layer removal. First, the surface metal material 3 is removed with a low energy density. The copper material is instantly vaporized under the action of the laser to form steam and is discharged. Then, the energy density is increased to remove the lower insulating material 5. The organic resin undergoes thermal decomposition and carbonization under laser irradiation. The carbonization products are removed by high-pressure gas purging. This scanning is repeated until all the cover layers above the chip 4 are completely removed, forming a through-hole structure with a diameter of 100-300μm. The inner wall of the through-hole has a conical or cylindrical profile.

[0041] The electroplating filling process first involves desmearing and roughening the through-holes. Residual resin carbides on the hole walls are removed using potassium permanganate solution or plasma bombardment, increasing surface roughness. Then, a 0.5-2 μm thick chemical copper seed layer is deposited on the inner wall of the through-hole using a chemical copper plating process. This seed layer provides a conductive basis for subsequent electroplating. Following this, electrolytic copper plating is performed using an acidic copper sulfate solution, with the current density controlled at 1-3 A / dm³. 2 The electroplating time is determined based on the depth of the through hole and the target filling thickness, generally 30-120 minutes. The electroplated copper gradually grows from the hole wall to the hole center until it completely fills the through hole. The formed metal conductive pillar 6 provides a vertical electrical connection channel for the electrodes of chip 4, realizing the electrical interconnection between chip 4 and the PCB surface circuit.

[0042] Before S6, a circuit patterning step is also included: a photoresist is coated on the surface of metal material 3, and after exposure and development, chemical etching is performed to form conductive lines 7. The conductive lines 7 are electrically connected to the electrodes of chip 4 through metal conductive posts 6, constructing the signal transmission path and power distribution network between chip 4 and external circuits. The circuit patterning step is performed before S6. This step uses photolithography etching process to create conductive lines 7 on the surface of metal material 3. First, a positive or negative photoresist with a thickness of 5-15μm is coated on the surface of metal material 3 by spin coating or roll coating. After drying, ultraviolet light is used for selective exposure through a photomask, with an exposure energy of 100-200mJ / cm. 2 After exposure, the resist is developed in the developer. Positive resists are dissolved in the exposed areas while the unexposed areas are preserved, while negative resists are the opposite. After development, a resist mask layer corresponding to the circuit pattern is formed.

[0043] The PCB board is then immersed in ferric chloride or alkaline etching solution for chemical etching. The metal material 3 not protected by the resist is etched away, while the area covered by the resist is retained. The etching time is determined according to the thickness of the metal material 3, generally 3-10 minutes. After etching, the residual resist is removed with alkaline solution or organic solvent to form conductive lines 7 with specific patterns.

[0044] The conductive lines 7 include signal traces, power planes, and ground planes. The line width and spacing are determined according to the electrical design requirements. Typically, the signal line width is 50-200μm, and the power line width is 200-1000μm. These conductive lines 7 are electrically connected to the corresponding electrodes of the chip 4 through the metal conductive posts 6, thus constructing the signal transmission path and power distribution network between the chip 4 and the external circuit, and completing the circuit function integration of the embedded PCB.

[0045] Before 3D printing in S6, ink solder resist is applied to areas where heat sink printing is not required to form a protective layer. 3D printing employs selective laser melting or electron beam melting technology, using copper or aluminum alloy powder with a particle size of 15-53μm as the printing material. The powder is melted and deposited layer by layer to form the metal heat sink 8. The metal heat sink 8 forms a metallurgical bond with the metal material 3 beneath the ceramic substrate 1, eliminating the need for additional welding or bonding processes and thus removing contact thermal resistance. Figure 6 and Figure 7As shown, before 3D printing, the PCB board needs to undergo selective area protection treatment. Solder resist ink is applied to areas where heat sinks do not need to be printed, such as the edge areas of copper substrates, dense circuit areas, and component pad areas. This ink uses a thermosetting epoxy resin system and is applied by screen printing or inkjet printing. The coating thickness is 20-50μm. After UV pre-curing and thermo-curing, a high-temperature resistant protective layer is formed. This protective layer prevents laser or electron beam from causing thermal damage to non-printing areas during 3D printing, and also prevents metal powder from adhering to non-printing areas.

[0046] 3D printing processes employ selective laser melting or electron beam melting technologies. The working chamber of the printing equipment is evacuated or filled with an argon protective atmosphere to prevent oxidation of the metal powder. The printing material is selected from copper alloy powders such as CuCrZr alloy or aluminum alloy powders such as AlSi10Mg alloy. The powder is prepared by gas atomization or plasma rotating electrode process, and the particle size is controlled within the range of 15-53μm. The narrower the particle size distribution, the higher the printing accuracy.

[0047] During the printing process, the powder spreader evenly spreads a metal powder layer with a thickness of 30-50μm on the surface of the metal material 3 below the ceramic substrate 1. The laser beam or electron beam scans on the powder layer according to the preset scanning path. The laser power is 200-400W, the scanning speed is 800-1500mm / s, and the laser spot diameter is 80-150μm. The metal powder melts instantly under the action of the high-energy beam to form a molten pool. The molten pool and the surface of the metal material 3 below melt and mix at the same time. After cooling and solidification, a metallurgical bonding interface is formed. At this interface, metal atoms diffuse into each other to form a continuous metal lattice structure. The bonding strength can reach more than 80% of the strength of the matrix material.

[0048] By repeating the powder spreading and melting process layer by layer, the metal heat sink 8 grows layer by layer from the bottom up, eventually forming a three-dimensional complex structure that is integrated with the metal material 3 below the ceramic substrate 1. The whole process does not require additional welding, brazing or bonding processes, completely eliminating the contact thermal resistance introduced by traditional assembly methods, so that heat can be transferred directly from the chip 4 through the copper block 2, ceramic substrate 1 and metal material 3 to the cooling medium inside the heat sink 8 without any obstacles.

[0049] The internal structure of the metal radiator 8 is a densely arranged microchannel structure, which includes an inlet area, a middle flow area, and an outlet area. The cross-sectional area of ​​the channels in the inlet and outlet areas is larger than that of the channels in the middle flow area. The middle flow area adopts a honeycomb or rhomboid staggered microchannel array. The wall thickness of the microchannel is 0.3-1.0 mm, and the channel spacing is 0.5-2.0 mm. The microchannels in adjacent layers are staggered to form a turbulence-promoting structure, which enhances the heat exchange efficiency between the cooling medium and the radiator wall. The internal structure of the metal radiator 8 is designed as a densely arranged microchannel structure, which is precisely constructed by 3D printing technology and includes three functional areas: an inlet area, a middle flow area, and an outlet area.

[0050] The water inlet area is located at one end of the radiator 8. The cross-sectional area of ​​the channel in this area is designed to be 2-4 times that of the middle flow area. The channel gradually narrows and transitions to the middle flow area. This design allows the flow rate of the cooling medium to gradually increase when it enters the radiator 8 from the external pipe, while keeping the pressure loss within a reasonable range.

[0051] The intermediate flow area is located in the high heat flux density region directly below chip 4. It adopts a honeycomb or diamond-shaped staggered microchannel array. Each microchannel in the honeycomb structure has a regular hexagonal cross-section with a side length of 0.8-1.5mm, a wall thickness of 0.3-1.0mm, and a channel height of 2-5mm. The diamond-shaped staggered structure arranges the diamond-shaped cross-section microchannels by rotating them 45 degrees between adjacent layers. The channel spacing is controlled within the range of 0.5-2.0mm. The staggered arrangement of microchannels in adjacent layers generates a turbulent effect when the cooling medium flows through. The fluid constantly changes its flow direction and impacts the channel wall in the microchannel, destroying the laminar boundary layer and enhancing convective heat transfer. The heat transfer coefficient is improved by 30-50% compared to the straight channel structure.

[0052] The outlet area is located at the other end of the radiator 8. The cross-sectional area of ​​the channel gradually expands and converges to the outlet interface, discharging the cooled medium from the radiator 8.

[0053] The design of the entire microchannel structure takes into account flow resistance, heat transfer efficiency, and mechanical strength. The geometric parameters of the channel are determined by a topology optimization algorithm to minimize pumping power consumption while ensuring heat dissipation performance, thereby achieving efficient and energy-saving liquid cooling.

[0054] The ceramic substrate 1 is made of aluminum nitride ceramic or alumina ceramic with a thermal conductivity ≥150W / m·K; the insulating material 5 is made of at least one of polyimide resin, epoxy resin or BT resin; the metal material 3 is copper foil or copper alloy foil with a thickness of 18-105μm; when the heat sink 8 is working, a liquid cooling medium is introduced into it, which is one of deionized water, ethylene glycol aqueous solution or fluorinated liquid, with a flow rate of 0.5-3.0L / min. The choice of material for the ceramic substrate 1 is crucial to the performance of the entire heat dissipation system. Aluminum nitride ceramic is preferred, with a thermal conductivity as high as 150-230W / m·K, close to that of copper. It also has excellent electrical insulation properties and a thermal expansion coefficient similar to that of silicon chips, resulting in low thermal stress and high reliability. Alumina ceramic, which has a lower cost, can also be used, with a thermal conductivity of 20-35W / m·K, which is lower than that of aluminum nitride but still significantly higher than that of organic substrate materials.

[0055] Insulation material 5 is selected according to the working temperature and electrical performance requirements. Polyimide resin has a temperature resistance of up to 260℃ and a low dielectric constant, making it suitable for high-frequency and high-speed signal transmission. Epoxy resin is inexpensive and has good processing performance, making it suitable for general industrial applications. BT resin is between the two, with good thermal stability and dimensional stability. In practical applications, a single resin or a mixed resin system can be selected according to performance and cost requirements.

[0056] Metal material 3 uses electrolytic copper foil or rolled copper foil, with thickness specifications including 18μm, 35μm, 70μm and 105μm and other options. The greater the thickness, the stronger the current carrying capacity, but the more difficult the etching becomes. In practical applications, the signal layer usually uses 18-35μm copper foil, while the power layer and ground layer use 70-105μm copper foil.

[0057] When the heat sink 8 is working, a liquid cooling medium is circulated inside. Deionized water has the advantages of high specific heat capacity and low cost, but its operating temperature range is limited. Ethylene glycol aqueous solution can work in the range of -30℃ to 110℃ and has anti-corrosion properties. Fluorinated liquids such as FC-72 or FC-77 have excellent insulation properties and chemical stability, but their cost is high. The flow rate of the cooling medium is controlled in the range of 0.5-3.0L / min. If the flow rate is too low, the heat exchange will be insufficient, and if the flow rate is too high, the pumping power consumption and flow noise will increase. The flow state of the cooling medium is monitored and adjusted in real time through flow control valves and pressure sensors to ensure that the heat dissipation system operates under optimal conditions, and the junction temperature of chip 4 is stably controlled within the design range to ensure the long-term reliable operation of the embedded PCB system.

[0058] The embedded PCB heat sink manufacturing method of the present invention first welds copper blocks 2 and metal materials 3 to the upper and lower surfaces of a ceramic substrate 1. Step processing is performed by combining chemical etching and mechanical processing. A two-stage step structure is formed by etching in ferric chloride or ammonium persulfate solution using a photoresist mask. The depth of the first step is 50-80μm and the depth of the second step is 100-150μm. For parts with high precision requirements, CNC milling is used to trim them to ensure that the subsequent insulating material 5 can be fully filled along the steps to achieve electrical isolation.

[0059] Chip 4 and copper block 2 are connected by a thermally conductive solder layer with a thickness of 20-100μm. The welding process can be either reflow soldering or sintering. The peak temperature of reflow soldering is 250-350℃ and the holding time is 30-180 seconds. The sintering process uses nano silver paste or nano copper paste and holds it at a temperature of 200-300℃ and a pressure of 1-10MPa for 10-30 minutes to form a low thermal resistance thermal conductive channel.

[0060] The copper-containing substrate is prepared by hot-pressing insulating material 5 and metal material 3 at 180-220℃ and 2-5MPa pressure for 60-120 minutes. The groove 6 is processed by CNC milling or laser cutting, with a depth tolerance of ±0.03mm and a bottom flatness of ±0.05mm. The single-sided lamination process involves holding the pressure at 170-210℃ and 1.5-4MPa for 50-100 minutes, allowing the insulating material 5 to fully flow, fill all gaps, and solidify to form an integral structure. The laser process uses a CO2 laser or ultraviolet laser with a power of 10-50W and a scanning speed of 100-500mm / s to remove the cover layer above the chip 4 layer by layer. The electroplating filling uses a chemical copper seed layer followed by electrolytic copper plating to form the metal conductive pillars 6.

[0061] Before 3D printing, solder resist ink is applied to the non-printing area for protection. Selective laser melting or electron beam melting technology is used, with copper alloy or aluminum alloy powder with a particle size of 15-53μm. The laser power is 200-400W and the scanning speed is 800-1500mm / s. The powder is melted and deposited layer by layer to form a metal heat sink 8 that is metallurgically bonded with the metal material 3 below the ceramic substrate 1.

[0062] The radiator 8 is designed with a microchannel structure, including three functional zones: inlet, intermediate flow zone and outlet. The intermediate flow zone adopts a honeycomb or diamond-shaped staggered microchannel array with a microchannel wall thickness of 0.3-1.0mm and a channel spacing of 0.5-2.0mm. The staggered arrangement of adjacent microchannel layers forms a turbulence-promoting structure, which improves the heat transfer coefficient by 30-50%.

[0063] In terms of material selection, the ceramic substrate 1 is preferably aluminum nitride ceramic or alumina ceramic with a thermal conductivity ≥150W / m·K. The insulating material 5 can be polyimide resin, epoxy resin or BT resin. The metal material 3 is copper foil with a thickness of 18-105μm. When the heat sink 8 is working, deionized water, ethylene glycol aqueous solution or fluorinated liquid is introduced as the cooling medium, and the flow rate is controlled in the range of 0.5-3.0L / min. The heat dissipation system is ensured to operate under optimal conditions through flow control and pressure monitoring, so that the junction temperature of the chip 4 is stably controlled within the design range, ensuring the long-term reliable operation of the embedded PCB system.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing an embedded PCB heat sink, characterized in that, Includes the following steps: S1: Weld copper blocks (2) and metal materials (3) on the upper and lower surfaces of the ceramic substrate (1), and perform step processing on the copper blocks (2) and metal materials (3) to form a step morphology; S2: The chip (4) is mounted on the copper block (2) to form a chip-copper block-ceramic composite structure; S3: Prepare a copper-containing substrate, which is formed by laminating a metal material (3) and an insulating material (5), and process a groove (6) adapted to the composite structure on the copper-containing substrate. S4: Place the composite structure in the groove (6), and press and fix it on one side by superimposing the insulating material (5) and the metal material (3); S5: Use laser technology to remove the metal material (3) and insulating material (5) above the chip (4), form a through hole and electroplating to fill it to form a metal conductive pillar (6). S6: 3D printing is performed directly on the surface of the metal material (3) below the ceramic substrate (1) to form a metal heat sink (8) that is integrally connected with the metal material (3).

2. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, The stepped processing in S1 adopts a combination of chemical etching and mechanical processing. By controlling the etching depth and mechanical processing precision, at least two steps are formed between the side of the copper block (2) and the edge of the metal material (3). The step height of the step structure matches the thickness of the insulating material (5), ensuring that the insulating material (5) can completely fill the step gap during the subsequent pressing process, thereby achieving electrical isolation between the chip (4) and the external metal layer.

3. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, In S2, the chip (4) and the copper block (2) are connected by a thermally conductive solder layer. The thickness of the thermally conductive solder layer is 20-100μm. The welding process adopts reflow soldering or sintering process, the welding temperature is 250-350℃, and the holding time is 30-180 seconds to ensure that the solder is fully melted and fills the tiny gap between the chip (4) and the copper block (2) to form a low thermal resistance thermal conductive channel.

4. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, The copper substrate in S3 is prepared by stacking metal materials (3) on the upper and lower sides of the insulating material (5) and pressing them together by hot pressing. The pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 60-120 minutes. The groove (6) is processed by milling or laser cutting. The depth of the groove (6) is adapted to the total thickness of the chip-copper block-ceramic composite structure. The flatness of the bottom of the groove (6) is controlled within ±0.05mm.

5. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, The parameters of the single-sided pressing process in S4 are: pressing temperature is 170-210℃, pressure is 1.5-4MPa, and holding time is 50-100 minutes. During the pressing process, the insulating material (5) flows under the action of hot pressing, filling all the gaps between the ceramic substrate (1), copper block (2), chip (4) and copper substrate. After curing, it forms an integral structure. The insulating material (5) simultaneously realizes the functions of mechanical support, electrical insulation and gap filling.

6. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, The laser process in S5 uses a CO2 laser or an ultraviolet laser with a laser power of 10-50W and a scanning speed of 100-500mm / s. The metal material (3) and insulating material (5) above the chip (4) are removed layer by layer through multiple scans. The electroplating filling process uses chemical copper plating or electrolytic copper plating. First, a chemical copper seed layer is formed on the inner wall of the through hole, and then the through hole is filled with electroplated copper until it is completely filled. The metal conductive pillar (6) formed provides a vertical electrical connection channel for the chip (4).

7. The method for manufacturing an embedded PCB heat sink according to claim 6, characterized in that, Before S6, a circuit patterning step is also included: a photoresist is coated on the surface of the metal material (3), and after exposure and development, chemical etching is performed to form a conductive line (7). The conductive line (7) is electrically connected to the electrode of the chip (4) through the metal conduction post (6), thereby constructing a signal transmission path and power distribution network between the chip (4) and the external circuit.

8. The method for manufacturing an embedded PCB heat sink according to claim 6, characterized in that, Before 3D printing in S6, ink solder resist treatment is performed in areas where heat sinks do not need to be printed to form a protective layer; the 3D printing adopts selective laser melting technology or electron beam melting technology, and the printing material is copper alloy or aluminum alloy powder with a particle size of 15-53μm. The powder is melted and stacked layer by layer to form a metal heat sink (8). The metal heat sink (8) forms a metallurgical bond with the metal material (3) under the ceramic substrate (1), without the need for additional welding or bonding processes, thus eliminating contact thermal resistance.

9. A method for manufacturing an embedded PCB heat sink according to claim 8, characterized in that, The internal structure of the metal radiator (8) is a densely arranged microchannel structure, which includes an inlet area, a middle flow area and an outlet area. The cross-sectional area of ​​the channels in the inlet area and the outlet area is larger than that of the channel in the middle flow area. The middle flow area adopts a honeycomb or rhomboid staggered microchannel array. The wall thickness of the microchannel is 0.3-1.0 mm and the channel spacing is 0.5-2.0 mm. The microchannels in adjacent layers are staggered to form a turbulence-promoting structure, which enhances the heat exchange efficiency between the cooling medium and the radiator wall.

10. The method for manufacturing an embedded PCB heat sink according to claim 1, characterized in that, The ceramic substrate (1) is made of aluminum nitride ceramic or alumina ceramic with a thermal conductivity ≥150W / (m·K); the insulating material (5) is made of at least one of polyimide resin, epoxy resin or BT resin; the metal material (3) is copper foil or copper alloy foil with a thickness of 18-105μm; when the heat sink (8) is working, a liquid cooling medium is introduced into it, which is one of deionized water, ethylene glycol aqueous solution or fluorinated liquid, with a flow rate of 0.5-3.0L / min.

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