Method for improving milling groove burrs of embedded copper block circuit board

Abstract

The invention relates to a method for improving milling groove burrs of a copper-block-embedded circuit board. The method comprises the following steps: preprocessing a substrate; performing first-time depth control milling, and milling two groove walls in an area, corresponding to the copper block, on the inner-layer core plate; carrying out surface metallization treatment, carrying out metallization treatment on the surface of the groove wall and manufacturing a preset circuit pattern on the surface of the outer circuit; second-time depth control milling is carried out, and two side areas are milled in the areas of the two ends of the two groove walls respectively; burr removal treatment: carrying out micro-etching treatment on the joints of the side areas and the tank walls by adopting alkaline etching liquid; third-time depth control milling is carried out, and a first installation groove used for containing a first electronic element is milled; and fourth-time depth control milling is carried out, deepening milling is carried out on the two side areas, and a second installation groove used for containing a second electronic element is milled. According to the method, through combination of staged depth-controlled groove milling and alkaline etching liquid micro-etching treatment, burrs generated in the milling process can be accurately removed, and the problem of surface damage or residue caused by a traditional mechanical polishing or single etching process is avoided.

Description

Technical Field

[0001] The present invention relates to the field of printed circuit board processing, and more particularly to a method for improving the burrs on the grooving of buried copper block printed circuit boards. Background Art

[0002] With the rapid progress of the new generation of information technology and new energy fields, the heat dissipation requirements of electronic products are becoming increasingly urgent. Printed circuit boards with buried copper blocks are widely used in fields such as 5G communication and automobiles due to their high thermal conductivity characteristics. In order to make full use of the high heat dissipation characteristics of copper blocks, mounting grooves for placing electronic components are usually opened at positions corresponding to the copper blocks on the printed circuit board. And in order to improve the space utilization rate to install more electronic components, multiple consecutive mounting grooves are often opened. Currently, the method for opening the mounting grooves is usually to first mill a groove connecting multiple layers of circuits and perform copper plating on the groove to form conductive columns, and then successively mill the mounting grooves for installing different electronic components according to the positions of the conductive columns. However, it is found in the actual operation process that burrs will be concentrated in the area where the conductive columns are connected to the mounting grooves during the process of milling the mounting grooves, thus affecting the product quality. Summary of the Invention

[0003] In view of this, the present invention provides a method that can effectively reduce the burrs generated during the grooving of buried copper block printed circuit boards.

[0004] The object of the present invention is achieved through the following technical solutions: A method for improving the burrs on the grooving of buried copper block printed circuit boards, comprising the following steps: S1: Substrate pretreatment, providing an inner core board that has completed the processes of copper block embedding, lamination, and via hole processing; S2: First depth control milling, milling two groove walls in the area corresponding to the copper block on the inner core board, and the two groove walls are spaced apart; S3: Surface metallization treatment, performing surface metallization treatment on the groove walls to form a metallized hole wall structure, and fabricating a predetermined circuit pattern on the outer layer circuit surface; S4: Second depth control milling, respectively milling two side areas at both ends of the two groove walls, and the two side areas and the two groove walls together form a closed surrounding area, and the surrounding area is completely located within the copper block; S5: Burr removal treatment, using an alkaline etching solution to perform micro-etching treatment on the connection between the side area and the groove wall to remove the copper burrs generated by milling; S6: Third depth control milling, milling a first mounting groove for placing a first electronic component within the surrounding area; S7: Fourth depth control milling, performing deep milling on the two side areas to mill a second mounting groove for placing a second electronic component.

[0005] In the above technical solution, the grooved wall formed by the first controlled-depth milling and the metallization treatment on the surface of the grooved wall can form a terminal for conducting the multi-layer board circuit, facilitating the electrical connection of subsequent electronic components; the second controlled-depth milling is to pre-mill the second mounting groove for mounting the second electronic component. The second mounting groove is located at the end of the grooved wall, and the burrs will concentrate on the edge of the grooved wall, that is, the burrs appear in advance, and then the burrs are removed through the burr removal treatment process. Finally, the first mounting groove for mounting the first electronic component and the second mounting groove for mounting the second electronic component are milled through the third controlled-depth milling and the fourth controlled-depth milling respectively.

[0006] Therefore, through the combination of staged controlled-depth milling grooves and alkaline etching solution micro-etching treatment, the present invention can accurately remove the burrs generated during the milling process, avoiding surface damage or residue problems caused by traditional mechanical grinding or single etching processes. And through the second controlled-depth milling and the burr removal treatment process, the burrs generated by the controlled-depth milling in the area where the metallized wall groove is connected to the non-metallized wall groove during the controlled-depth milling of the buried copper block circuit board can be effectively improved, thereby improving the quality of the buried copper block circuit board and increasing the product yield.

[0007] Optionally, in a possible implementation manner, in step S3, the process of metallization treatment on the surface of the grooved wall includes sequentially implementing electroless copper plating treatment, electroplated copper layer formation, and selective surface treatment process.

[0008] In the above technical solution, the electroless copper plating treatment forms a uniform copper deposition layer on the non-conductive resin substrate surface of the grooved wall. The electroplated copper layer further thickens the copper layer thickness on the basis of the electroless copper plating, improving the conductive performance and mechanical stability of the grooved wall. The selective surface treatment process can adjust the surface performance of the grooved wall according to different functional requirements. Therefore, through staged treatment, the bonding force, conductive performance, and functional requirements between the metallized layer and the substrate are taken into account, ensuring the long-term reliability of the grooved wall processing.

[0009] Optionally, in a possible implementation manner, the selective surface treatment process includes forming a solderable metal coating on the surface of the metallized grooved wall.

[0010] In the above technical solution, the solderable metal coating can protect the metallized grooved wall, and through the deposition of solderable coatings such as tin-based alloys or pure tin, the wettability and welding bonding strength of the metallized area of the grooved wall can be significantly improved. In addition, the selective treatment is only applied to the areas that need to be welded, avoiding the waste of precious metals caused by full-board electroplating.

[0011] Optionally, in a possible implementation manner, in step S7, the milling depth of the fourth controlled-depth milling is increased by 0.1 - 0.3 mm based on the milling depth of the second controlled-depth milling.

[0012] In the above technical solution, staged controlled-depth milling avoids local stress concentration on the substrate caused by single deep cutting. By gradually increasing the milling depth, the cutting force can be evenly dispersed, reducing the risk of substrate deformation, ensuring that the formed second mounting groove can match the second electronic component, thereby improving the machining accuracy and ensuring the mechanical stability and electrical contact reliability after the component is embedded.

[0013] Optionally, in a possible implementation manner, an anti-solder mask treatment process for the outer layer circuit is further included between the step S5 and the step S6. The anti-solder mask treatment process includes photosensitive anti-solder ink coating, exposure and development, and curing treatment.

[0014] In the above technical solution, the process of ink coating combined with exposure and development can accurately control the thickness of the anti-solder mask layer and the pattern accuracy, avoid problems such as bubbles or uneven filling caused by coating, reduce the rework rate at the same time, and significantly shorten the production cycle. The cured anti-solder mask layer forms a dense protective film, effectively isolating moisture, electrolytes, and mechanical damage, and preventing circuit oxidation and short circuits between conductors.

[0015] Optionally, in a possible implementation manner, the copper block is embedded in the insulating substrate of the inner core board, and the copper block is fixed by conductive adhesive or high-temperature epoxy resin.

[0016] In the above technical solution, the fitting design of the copper block and the insulating substrate combined with the fixing method of conductive adhesive or high-temperature epoxy resin can significantly increase the contact area between the copper block and the substrate. The high thermal conductivity of the conductive adhesive or epoxy resin can effectively establish a heat conduction path, quickly export the heat of the components to the copper block, and improve the overall heat dissipation performance.

[0017] Optionally, in a possible implementation manner, the two groove walls are arranged at intervals and in parallel, and the two side regions are respectively located at the ends of the two groove walls and extend in a direction perpendicular to the groove walls.

[0018] In the above technical solution, the design of parallel and spaced double groove walls realizes a compact arrangement. The extended part of the side region can be embedded in the connection space of adjacent functional modules, especially suitable for high-density integration scenarios. This layout saves a large amount of planar floor area compared with the traditional single groove structure while ensuring the structural strength.

[0019] Optionally, in a possible implementation manner, the surrounding area is a rectangular structure, and rounded corner transition structures are provided at the four corners of the rectangular structure.

[0020] In the above technical solution, the rounded corner transition effectively disperses the mechanical stress and thermal stress in the sharp corner area, avoids crack propagation or structural fatigue failure caused by stress concentration at the right angle, and significantly improves the impact resistance and long-term reliability of the component. Description of the Drawings

[0021] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a flowchart of an embodiment.

[0023] Figure 2 It is a schematic structural diagram of a first mounting groove and a second mounting groove in an embodiment. Specific embodiments

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the present application to be protected, but only represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0026] Please refer to Figure 1 and Figure 2 , this embodiment provides a method for improving the burr of the milling groove of the buried copper block circuit board, including the following steps: S1: Substrate pretreatment. Provide an inner core board that has completed the processes of copper block embedding, lamination, and via hole processing, and the copper block is embedded in the insulating substrate of the inner core board; S2: First depth-controlled milling. Mill out two groove walls 1 in the area corresponding to the copper block on the inner core board, and the two groove walls 1 are arranged at intervals; specifically, use a numerical control milling machine to perform the first depth-controlled milling in the area corresponding to the copper block, and the two groove walls 1 match the opposite boundaries of the electronic components to be installed; S3: Surface metallization treatment. Perform surface metallization treatment on the surface of the groove wall 1 to form a metallized hole wall structure, and make a predetermined circuit pattern on the surface of the outer layer circuit; S4: Second depth-controlled milling. Perform the second depth-controlled milling in the two end regions of the two groove walls 1 to mill out two side regions respectively. The two side regions and the two groove walls 1 together form a closed surrounding area, and the surrounding area is completely located within the copper block; S5: Burr removal process. Use an alkaline etching solution to micro-etch the connection between the side area and the groove wall 1 to remove the copper burrs generated by milling. S6: The third depth-controlled milling. Conduct the third depth-controlled milling within the enclosed area to mill out the first mounting groove 2 for placing the first electronic component. Among them, when milling, the first mounting groove 2 with a depth reaching the preset standard is formed. The size of the first mounting groove 2 is adapted to the packaging specification of the first electronic component, and the first electronic component can be electrically connected to the metallized groove wall 1. S7: The fourth depth-controlled milling. Conduct the fourth depth-controlled and deepened milling on the two side areas to mill out the second mounting groove 3 for placing the second electronic component. Among them, the depth of the second mounting groove 3 is greater than that of the first mounting groove 2. The size of the second mounting groove 3 is adapted to the packaging specification of the second electronic component, and an insulating substrate layer is reserved at the bottom of the second mounting groove 3. The second electronic component can also be electrically connected to the metallized groove wall 1.

[0027] In this embodiment, the groove wall 1 formed by the first depth-controlled milling and the metallization treatment on the surface of the groove wall 1 can form a wiring post for conducting the multi-layer board circuit, so as to facilitate the electrical connection of subsequent electronic components. The second depth-controlled milling is to pre-mill the second mounting groove 3 for installing the second electronic component. The second mounting groove 3 is located at the end of the groove wall 1, and the burrs will concentrate on the edge of the groove wall 1, that is, the burrs appear in advance, and then the burrs are removed through the burr removal process. Finally, the first mounting groove 2 for installing the first electronic component and the second mounting groove 3 for installing the second electronic component are milled out through the third depth-controlled milling and the fourth depth-controlled milling respectively.

[0028] Therefore, through the combination of staged depth-controlled grooving and micro-etching treatment with an alkaline etching solution in this embodiment, the burrs generated during the milling process can be accurately removed, avoiding surface damage or residue problems caused by traditional mechanical grinding or single etching processes. And through the second depth-controlled milling and the burr removal process, the burrs generated by the depth-controlled milling in the area where the metallized wall groove and the non-metallized wall groove are connected during the depth-controlled milling of the buried copper block circuit board can be effectively improved, thereby improving the quality of the buried copper block circuit board and increasing the product yield.

[0029] In step S3 of this embodiment, the process of metallizing the surface of the groove wall 1 includes sequentially implementing electroless copper plating treatment, electroplated copper layer formation, and selective surface treatment processes.

[0030] The electroless copper plating process forms a uniform copper deposition layer on the surface of non-conductive substrates through the catalytic reaction of a colloidal palladium activator, realizing the construction of the initial conductive layer on the inner wall 1 of the groove. This process uses an alkaline solution system to ensure the electrical connection basis between the hole wall and the copper block. The electroplated copper layer further thickens the copper layer on the basis of electroless copper plating, forming a dense copper layer through an acidic electroplating solution system. In this stage, the copper layer thickness is increased to 15 - 25 μm, enhancing the electrical conductivity and mechanical strength, and compensating for the copper loss during subsequent micro-etching treatment. The selective surface treatment process can implement differential treatment for different functional areas, adjusting the surface performance of the inner wall 1 according to different functional requirements. Therefore, through the staged treatment, the bonding strength, electrical conductivity, and functional requirements between the metallization layer and the substrate are taken into account, ensuring the long-term reliability of the processing of the inner wall 1.

[0031] In this embodiment, the selective surface treatment process includes forming a solderable metal coating on the surface of the metallized inner wall 1. Among them, the solderable metal coating can be a tin-based alloy or pure tin.

[0032] The solderable metal coating can protect the metallized inner wall 1, and through the deposition of a solderable coating, such as a tin-based alloy or pure tin, the wettability and welding bonding strength of the metallized area of the inner wall 1 can be significantly improved. In addition, the selective treatment is only applied to the areas that need to be welded, avoiding the waste of precious metals caused by full-panel electroplating.

[0033] In step S7 of this embodiment, the milling depth of the fourth controlled-depth milling is increased by 0.1 - 0.3 mm based on the milling depth of the second controlled-depth milling.

[0034] The staged controlled-depth milling avoids the local stress concentration of the substrate caused by single deep cutting. By gradually deepening the milling, the cutting force can be evenly dispersed, reducing the risk of substrate deformation, ensuring that the formed second mounting groove 3 can match the second electronic component, thereby improving the processing accuracy and ensuring the mechanical stability and electrical contact reliability after the component is embedded. In addition, the incremental depth design allows the tool to cut layer by layer under a smaller load, significantly reducing the tool wear rate compared with milling to the final depth at one time. At the same time, the layered processing combined with the previous micro-etching treatment can reduce the abnormal tool wear caused by burrs or residues.

[0035] It should be noted that between step S5 and step S6, there is also an anti-soldering treatment process for the outer layer circuit. The anti-soldering treatment process includes photosensitive anti-soldering ink coating, exposure and development, and curing treatment.

[0036] By using the ink coating combined with the exposure and development process, the thickness and pattern accuracy of the anti-soldering layer can be precisely controlled, avoiding problems such as bubbles or uneven filling caused by coating, reducing the rework rate, and significantly shortening the production cycle. The cured anti-soldering layer forms a dense protective film, effectively isolating moisture, electrolytes, and mechanical damage, preventing circuit oxidation and short circuits between conductors.

[0037] In this embodiment, the copper block is embedded in the insulating substrate of the inner core board, and the copper block is fixed by conductive adhesive or high-temperature epoxy resin.

[0038] The fitting design of the copper block and the insulating substrate combined with the fixing method of conductive adhesive or high-temperature epoxy resin can significantly increase the contact area between the copper block and the substrate. The high thermal conductivity of the conductive adhesive or epoxy resin can effectively establish a heat conduction path, quickly export the heat of the components to the copper block, and improve the overall heat dissipation performance. Using conductive adhesive or high-temperature epoxy resin as the bonding medium, the mechanical properties after curing can compensate for the difference in thermal expansion coefficients between the copper block and the substrate, and reduce the interfacial stress concentration caused by temperature changes.

[0039] The two groove walls 1 of this embodiment are arranged at intervals and in parallel, and the two side areas are respectively located at the ends of the two groove walls 1 and extend in a direction perpendicular to the groove walls 1.

[0040] The design of the parallel and spaced double groove walls 1 realizes a compact layout. The extended part of the side area can be embedded in the connection space of adjacent functional modules, which is especially suitable for high-density integration scenarios. While ensuring the structural strength, this layout saves a large amount of planar floor area compared with the traditional single groove structure.

[0041] Specifically, the surrounding area is a rectangular structure, and rounded corner transition structures are provided at the four corners of the rectangular structure. The rounded corners effectively disperse the mechanical stress and thermal stress in the sharp corner area, avoid crack propagation or structural fatigue failure caused by stress concentration at the right angles, and significantly improve the impact resistance and long-term reliability of the component. The first installation groove 2 and the second installation groove 3 of this embodiment are continuous groove body structures, so that the space occupation can be further reduced and the heat dissipation characteristics of the copper block can be fully utilized.

[0042] In the description of the present invention, it should be understood that terms such as "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0043] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0044] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the flash of the gong groove of a buried copper block circuit board, characterized in that: The following steps are involved: S1: Substrate pretreatment, providing inner core board with copper block embedding, pressing process and through-hole processing completed; S2: Firstly, the depth of the gong is controlled to mill two groove walls in the area corresponding to the copper block on the inner core plate, and the two groove walls are arranged at intervals; S3: Surface metallization treatment: metallization treatment is performed on the surface of the groove wall to form a metallized hole wall structure, and a predetermined circuit pattern is made on the surface of the outer circuit layer; S4: a second depth control gong, milling out two side areas at the two end areas of the two groove walls respectively, the two side areas and the two groove walls together form a closed enclosing area, and the enclosing area is completely located in the copper block; S5: burr removal treatment, using alkaline etching solution to perform micro-etching treatment on the connection between the side area and the groove wall to remove copper burrs generated by milling; S6: a third depth control gong is performed to mill a first mounting groove for placing a first electronic component in the enclosed area; S7: The fourth depth control gong is used to deepen the milling of the two side areas to mill out a second mounting groove for placing a second electronic component.

2. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 1 is characterized in that: In the step S3, the process of metallizing the groove wall surface includes sequentially performing chemical copper deposition, forming an electroplated copper layer, and selective surface treatment processes.

3. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 2 is characterized in that: The selective surface treatment process includes forming a solderable metal plating layer on the surface of the metallized groove wall.

4. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 1 is characterized in that: In step S7, the milling depth of the fourth depth-controlled gong is increased by 0.1-0.3 mm based on the milling depth of the second depth-controlled gong.

5. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 1 is characterized in that: The step between step S5 and step S6 also includes a solder mask treatment process for the outer layer circuit, and the solder mask treatment process includes photosensitive solder mask ink coating, exposure and development, and curing treatment.

6. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 1 is characterized in that: The copper block is embedded in the insulating base material of the inner core board, and the copper block is fixed by conductive glue or high-temperature epoxy resin.

7. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 1, characterized in that: The two groove walls are spaced apart and arranged in parallel, and the two side areas are respectively located at the ends of the two groove walls and extend in a direction perpendicular to the groove walls.

8. The method for improving the flash of the gong groove of the buried copper block circuit board according to claim 7 is characterized in that: The enclosed area is a rectangular structure, and rounded transition structures are arranged at the four corners of the rectangular structure.

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