A high-density mounting thin circuit board for mini LEDs and its manufacturing method

Abstract

A method for manufacturing a high-density mounting thin circuit board for mini LEDs and the circuit board itself are disclosed to solve the problem of board warping caused by significant differences in copper content on both sides. The method includes: providing a core board layer; sequentially stacking a first copper foil, a first prepreg, the core board layer, a second prepreg, and a second copper foil, and then pressing them together to form a multilayer board; wherein the adhesive content of the first prepreg is greater than that of the second prepreg, and the thickness of the first prepreg is less than that of the second prepreg; and fabricating the outer layer circuitry of the multilayer board, wherein: the first copper foil is fabricated into an LED bead surface pattern; the second copper foil is fabricated into a control surface pattern, the control surface pattern including pads and signal lines, and the continuous copper foil on the second copper foil, excluding the pads and signal lines, is replaced with a grid pattern. This invention improves product flatness and reliability.

Description

Technical Field

[0001] This invention relates to the field of circuit board processing, and more particularly to a method for manufacturing a high-density mounting thin circuit board for mini LEDs, as well as a high-density mounting thin circuit board for mini LEDs. Background Technology

[0002] With the rapid development of display technology, mini LED (miniature light-emitting diode) has become an important choice for the next generation of high-definition displays. It uses smaller LEDs and more partitions to achieve image quality close to that of OLED (organic light-emitting diode) on the LCD (Liquid Crystal Display) architecture, while retaining the advantages of LCD such as long lifespan, no burn-in, and controllable cost.

[0003] As a circuit board supporting mini LED mounting, its design tends towards high-density interconnect (HDI), multi-layer (≥4 layers), and ultra-thin (0.3mm~1.0mm) technologies, resulting in high integration per unit area and significant manufacturing challenges. Due to increasingly enhanced functionality, the circuitry on its upper and lower surfaces is typically designed as follows: the first surface (LED bead surface) has smaller pads and a smaller overall copper retention rate (i.e., the area of ​​copper remaining on the board after circuit pattern fabrication divided by the total board area); the second surface (control surface) requires the mounting of control chips and has a large area of ​​ground copper, resulting in a higher copper retention rate. After the outer layer circuitry is fabricated, a significant difference in copper retention rates appears between the first and second surfaces. When this thin circuit board is subjected to high-temperature shocks during subsequent processing or mini LED chip mounting (e.g., reflow soldering temperatures can reach 255℃), the significant difference in copper retention rates between the two surfaces leads to inconsistent thermal expansion and contraction behavior, resulting in problems such as board warping, bending, and buckling.

[0004] In existing technologies, board warping can be improved by selecting a substrate with a higher Tg (Glass Transition Temperature). Using a substrate with a higher Tg can withstand higher temperatures and increase the ability to withstand pressure deformation caused by high temperatures, but the cost will increase accordingly. Board warping can also be improved by optimizing the reflow soldering temperature profile and performing baking and re-pressing processes before packaging and shipping. However, these methods do not change the actual materials and structure of each layer of the board, and the efficiency of warping improvement is low. Baking and re-pressing can also cause adverse effects such as wear and damage to the surface treatment layer and solder mask layer of the board.

[0005] Therefore, how to fundamentally solve the warping problem of thin circuit boards during post-processing and high-temperature reflow soldering by improving material selection, circuit pattern design and structural layout has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to solve the problem of warping, bending, and buckling of mini LED circuit boards during processing and reflow soldering due to significant differences in copper content on both sides after circuit fabrication. It provides a high-density mounting thin circuit board for mini LEDs and its manufacturing method. By using prepregs with differentiated adhesive content and thickness, and pre-setting reverse internal stress during the lamination stage, and by replacing the large continuous copper area on the control surface with a grid-like circuit, the difference in copper content on both sides is significantly reduced, making thermal expansion and contraction at high temperatures more consistent. These two methods work synergistically to balance stress release from both material and graphic design perspectives, effectively suppressing warping deformation of the thin circuit board during processing and reflow soldering, and improving product flatness and reliability.

[0007] This invention provides a method for manufacturing a high-density mounting thin circuit board for mini LEDs, comprising the following steps: Provide core layer; The first copper foil, the first prepreg, the core board layer, the second prepreg, and the second copper foil are stacked in sequence and pressed together to form a multilayer board; wherein the adhesive content of the first prepreg is greater than that of the second prepreg, and the thickness of the first prepreg is less than that of the second prepreg. The outer layer circuitry is fabricated on the multilayer board, wherein: The first copper foil is made into an LED bead surface pattern; The second copper foil is fabricated into a control surface pattern, which includes pads and signal lines, and the continuous copper foil on the second copper foil, excluding the pads and signal lines, is replaced with a grid pattern.

[0008] Furthermore, the first semi-cured sheet has an adhesive content of 60% to 75%, the second semi-cured sheet has an adhesive content of 52% to 63%, and the adhesive content of the first semi-cured sheet is at least 5% higher than that of the second semi-cured sheet.

[0009] Furthermore, the thickness of the first prepreg is 0.068 mm to 0.080 mm, and the thickness of the second prepreg is 0.098 mm to 0.110 mm.

[0010] Furthermore, the first prepreg is a 1080 prepreg, and the second prepreg is a 2113 prepreg.

[0011] Furthermore, the angle between the lines of the grid-like circuit and the edge of the thin circuit board is 30° to 60°.

[0012] Furthermore, during the fabrication of the outer layer circuitry, the tool edge area on the first copper foil is made into a complete copper foil, leaving copper entirely in the tool edge area; and the tool edge area on the second copper foil is made into a grid-like circuitry.

[0013] Furthermore, after completing the outer layer circuit fabrication, the process also includes drilling multiple through holes in the blank area on the thin circuit board where the spacing between adjacent mini LED beads is greater than 2mm.

[0014] Furthermore, after drilling the through hole, the method further includes: attaching a black light-shielding film, which is a black PET film, above the through hole on the side where the first copper foil is located.

[0015] Furthermore, In the outer layer circuit fabrication step, when the spacing between adjacent mini LED beads on the LED bead surface is ≥1mm, the blank area on the LED bead surface located between adjacent beads is also fabricated into a grid-like copper circuit.

[0016] Secondly, the present invention also provides a mini LED high-density mounting thin circuit board, which is manufactured using the manufacturing method of mini LED high-density mounting thin circuit board as described in any of the preceding claims.

[0017] The main beneficial effects of this technical solution are: The present invention relates to a high-density mounting thin circuit board for mini LEDs and its manufacturing method. By setting the first prepreg on the LED bead side to have a higher adhesive content than the second prepreg on the control side, and the first prepreg being thinner than the second prepreg, the resin flow and curing shrinkage direction are actively controlled during the lamination stage. This results in greater shrinkage on the LED side and less shrinkage on the control side, thereby pre-setting internal stress within the board that is opposite to the subsequent warping direction, forming a stress pre-compensation mechanism. Simultaneously, the thicker, low-adhesion-content prepreg improves the bending stiffness of the control side, enhancing its resistance to deformation. Furthermore, by replacing the large area of ​​continuous copper on the control side (excluding pads and signal lines) with a grid-like pattern, the copper retention rate on the control side is significantly reduced, decreasing the difference in copper retention rate between the two sides. This significantly reduces the expansion and contraction differences caused by the mismatch in the coefficient of thermal expansion (CTE) during high-temperature reflow soldering, fundamentally alleviating the warping driving force. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for manufacturing a high-density mounting thin circuit board for mini LEDs according to Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of a stacked structure of a circuit board that supports mini LED mounting in the prior art; Figure 3 A schematic diagram of the structure of a circuit board that supports mini LED mounting in the prior art after the outer layer circuit pattern has been fabricated; Figure 4 This is a schematic diagram of the stacking structure of a mini LED high-density mounting thin circuit board during lamination, provided in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the structure of a mini LED high-density mounting thin circuit board after the surface circuit pattern has been formed, as provided in Embodiment 2 of the present invention. Figure 6 This is a schematic diagram of a mini LED high-density mounting thin circuit board with through holes in the blank area of ​​the reserved area, as provided in Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of a mini LED high-density mounting thin circuit board with a black light-shielding film attached to the through holes on the LED bead surface, as provided in Embodiment 2 of the present invention. Figure 8 This is a photograph of a product manufactured using the method for fabricating a high-density mini LED mounting thin circuit board according to Embodiment 2 of the present invention. Figure 9 A physical image of a circuit board that supports mini LED mounting, generated using existing technology.

[0020] Explanation of reference numerals: 11. First copper foil; 12. First curing sheet; 13. Core board layer; 14. Second curing sheet; 15. Second copper foil; 21. Molding line; 22. LED bead surface; 23. Control surface; 24. Tool edge; 25. In-board reserved area; 221. LED bead pad; 231. Control pad; 232. Mesh circuit; 30. Black light-shielding film.

[0021] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0024] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0025] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0026] To better understand the above technical solution, a detailed explanation of the technical solution is provided below with reference to the accompanying drawings.

[0027] Example 1

[0028] Figure 1 This is a flowchart illustrating a method for manufacturing a high-density mounting thin circuit board for mini LEDs according to Embodiment 1 of the present invention. Figure 1 As shown, the method includes: Step S100: Provide the core board layer; Step S200: The first copper foil, the first prepreg, the core board layer, the second prepreg, and the second copper foil are stacked sequentially and pressed together to form a multilayer board; wherein, the adhesive content of the first prepreg is greater than that of the second prepreg, and the thickness of the first prepreg is less than that of the second prepreg. Step S300: Fabricate the outer layer circuitry of the multilayer board, wherein: The first copper foil is made into an LED bead surface pattern; The second copper foil is fabricated into a control surface pattern, which includes pads and signal lines, and the continuous copper foil on the second copper foil, excluding the pads and signal lines, is replaced with a grid pattern.

[0029] This invention provides a method for manufacturing a thin circuit board for high-density mini LED mounting. It aims to solve the deformation problems of existing thin circuit boards during post-processing of the circuit fabrication and subsequent mini LED mounting reflow soldering, caused by the significant difference in copper content between the two sides after circuit fabrication (approximately 18% for the LED bead side and approximately 72% for the control side), leading to warping, bending, and buckling of the board. The technical solution of this invention starts with material selection and stacking structure. By using prepregs with differentiated adhesive content and thickness, it actively controls the internal stress distribution during the lamination stage and presets reverse stress compensation. Starting with the circuit pattern design, it replaces the large continuous copper area on the control side (excluding pads and signal lines) with a grid-like circuit, reducing the copper content on the control side and minimizing the difference in the coefficient of thermal expansion (CTE) between the two sides, thereby suppressing warping during high-temperature reflow soldering. Without adding complex post-processing steps, it improves the flatness and reliability of the thin circuit board while avoiding damage to the surface treatment layer and solder mask layer.

[0030] The finished thickness of the thin circuit board described in this embodiment of the invention is 0.2mm to 1.2mm, used to support high-density mounting of mini LED chips. The manufacturing method specifically includes the following steps: Step S100: Provide the core board layer.

[0031] Select the pre-fabricated core board layer. This core board layer can be a single-layer double-sided core board or a multi-layer core board that has been pre-pressed together (such as 2 layers, 4 layers, etc.). The thickness of the core board layer is selected according to design requirements, for example, 0.1mm to 0.8mm. In this embodiment, a double-sided copper-clad laminate with a thickness of 0.4mm is used, and its copper foil thickness is 1oz (approximately 35μm).

[0032] Step 200: Stack and press the materials together.

[0033] The first copper foil, the first prepreg, the core board layer, the second prepreg, and the second copper foil are stacked sequentially, in the following order: the outermost layer is the first copper foil (used to form the LED bead surface); the first prepreg is stacked below the first copper foil; the core board layer is placed below the first prepreg; the second prepreg is stacked below the core board layer; and the second copper foil (used to form the control surface) is placed below the second prepreg. Of course, the stacking order can be reversed, as long as it conforms to the stacking sequence. The first prepreg has a higher adhesive content than the second prepreg, and the thickness of the first prepreg is less than the thickness of the second prepreg. For example, the first prepreg may be a 1080 prepreg with a higher adhesive content (approximately 65%–75% adhesive content, approximately 0.068 mm–0.080 mm thickness), and the second prepreg may be a 2113 prepreg with a lower adhesive content (approximately 52%–63% adhesive content, approximately 0.098 mm–0.110 mm thickness). This differentiated material selection results in stronger resin flow and greater shrinkage on the LED bead side during subsequent lamination, while the resin on the control side exhibits weaker flow and less shrinkage. This pre-sets internal stress within the board, opposite to the direction of subsequent warping. The stacked materials are then fed into a press for lamination. The lamination process uses standard PCB lamination parameters, such as a heating rate controlled at 2℃ / min~5℃ / min, a lamination temperature reaching 180℃~200℃, and a holding time of 60min~90min, allowing the prepreg to fully melt, flow, and solidify. During lamination, the first prepreg, with its high resin content and thinness, exhibits more significant resin flow and curing shrinkage; the second prepreg, with its low resin content and thickness, experiences less shrinkage and a higher modulus after curing. This difference causes a slight pre-bending of the board towards the control side after lamination, providing pre-compensation for the main warping towards the LED bead side during subsequent processing and reflow soldering.

[0034] Step S300: Outer layer circuit fabrication.

[0035] After lamination, the outer layer circuit pattern of the multilayer board is fabricated. Specifically, this includes: LED bead surface (first copper foil): The first copper foil is patterned into an LED bead surface using conventional processes such as dry film application, exposure, development, etching, and film removal. This pattern includes multiple pads for mounting mini LED beads and signal lines (such as row scan lines and column data lines) connecting these pads. Due to the large number and small spacing of the LED beads, the pad size is typically 100μm–200μm, and the line width is 25μm–50μm. Control surface (second copper foil): Similarly, the second copper foil is patterned into a control surface using pattern transfer and etching processes. This pattern includes: pads for the control chip (for mounting the driver IC), signal lines (for inter-chip communication and connection to the LED surface), and all continuous copper foil (i.e., the original solid copper surface used for grounding) except for the pads and signal lines is replaced with a grid-like circuit. The line width and spacing of the mesh-like wiring can be designed, for example, to be 0.1mm / 0.1mm, reducing the copper retention rate in this area from 100% to approximately 30%–60%, thereby reducing the overall copper retention rate of the control surface from approximately 72% to below 68%. The mesh-like wiring still maintains its grounding function and does not affect electromagnetic shielding or signal integrity.

[0036] After etching is completed, subsequent processes such as AOI inspection, surface treatment (such as electroless gold plating, OSP, etc.) and solder mask layer fabrication are performed to complete the circuit board fabrication.

[0037] The thin circuit board manufactured by the above method in this invention embodiment can significantly reduce warpage: during the lamination stage, pre-stressed reverse stress is preset using prepregs with differentiated adhesive content and thickness; during the circuit fabrication stage, the difference in copper retention ratio between the two sides is significantly reduced by controlling surface meshing. The synergistic effect of these two methods significantly improves the warpage of the board during subsequent processing and reflow soldering. This invention embodiment does not change the conventional PCB manufacturing process (lamination, pattern transfer, etching, etc.), only adjusting the prepreg selection and pattern design, making it easy to implement on existing production lines without adding special equipment or post-processing correction steps. It eliminates the need for post-processing methods such as baking and re-pressing, thereby avoiding wear and component damage to surface treatment layers (such as electroless gold layers) and solder mask layers, ensuring product reliability and appearance quality.

[0038] Furthermore, the first semi-cured sheet has an adhesive content of 60% to 75%, the second semi-cured sheet has an adhesive content of 52% to 63%, and the adhesive content of the first semi-cured sheet is at least 5% higher than that of the second semi-cured sheet.

[0039] The adhesive content of the first prepreg (LED bead side) is controlled between 60% and 75%, preferably 65% ​​to 70%. This adhesive content range ensures sufficient resin flow during lamination to fill the gaps between circuits and bond the layers, while also generating appropriate curing shrinkage to form a pre-bend towards the control surface. If the adhesive content is below 60%, the amount of resin is insufficient, which may lead to a decrease in interlayer bonding strength, and the pre-bend amplitude is too small, failing to effectively compensate for subsequent reflow soldering warpage. If the adhesive content is above 75%, excessive adhesive overflow may contaminate the board surface or affect dimensional accuracy, and the pre-bend amplitude may be too large, potentially leading to excessive reverse warpage.

[0040] The adhesive content of the second prepreg (on the control side) is controlled between 52% and 63%, preferably 55% to 60%. This relatively low adhesive content range results in less resin flow and curing shrinkage during lamination, thereby reducing stress accumulation on the control side. Simultaneously, a lower adhesive content means a higher proportion of glass fiber, leading to a larger modulus after curing, which helps improve the flexural stiffness of the control surface. If the adhesive content is below 52%, the bonding reliability is insufficient, and delamination is likely to occur; if it is above 63%, the advantage of low stress release is lost, and the stress on both sides cannot be effectively balanced.

[0041] In the prior art, the high copper retention rate on the control surface restricts the release of internal stress in the second prepreg, causing the internal stress to be released towards the LED chip surface, resulting in buckling. This embodiment uses a material selection and stacking method with a lower adhesive content for the prepreg adjacent to the second copper foil side. When processing or mounting LED chips after lamination, the low adhesive flow characteristics of the second prepreg will not cause excessive expansion and contraction, thereby reducing the release of internal stress and balancing to some extent the uneven release of internal stress caused by the high copper retention rate on the control surface.

[0042] Resin Content Difference Condition: The resin content of the first prepreg is at least 5 percentage points higher than that of the second prepreg. For example, if the first prepreg has a resin content of 68% and the second prepreg has a resin content of 58%, the difference is 10 percentage points; or if the first prepreg has a resin content of 62% and the second prepreg has a resin content of 57%, the difference is 5 percentage points. This difference ensures that the LED surface shrinkage is significantly greater than the control surface during the lamination stage, thus producing a sufficient pre-bending effect. If the difference is less than 5 percentage points, the pre-bending effect is not significant and may not be able to completely offset the warpage during subsequent reflow soldering.

[0043] For the first prepreg with a high resin content, the heating rate should be appropriately reduced during lamination (e.g., 2℃ / min~3℃ / min) to prevent excessive resin flow and severe overflow. For the second prepreg with a low resin content, the pressure can be appropriately increased (e.g., 350psi~400psi) to ensure tight interlayer bonding. A holding time of 70min~90min is recommended to allow the high resin content layer to fully cure and prevent residual stress from being released later.

[0044] Under the premise that the difference in adhesive content meets the requirements, the control surface grid circuit further reduces the copper retention rate, which greatly reduces the difference in CTE between the two sides during the reflow soldering stage, and the pre-bending and main warping are more accurately offset, and the final board warping can be stably controlled within 0.5%.

[0045] Furthermore, the thickness of the first prepreg is 0.068 mm to 0.080 mm, and the thickness of the second prepreg is 0.098 mm to 0.110 mm.

[0046] The thickness of the first prepreg (on the LED bead side) is controlled between 0.068 mm and 0.080 mm, preferably 0.075 mm. This thickness range is within the range of thin prepregs commonly found in the market (e.g., the typical thickness of a 1080-type prepreg is 0.068 mm to 0.080 mm). The thinner thickness combined with a higher resin content allows the resin to heat up quickly and flow fully during lamination, resulting in greater curing shrinkage and thus creating a significant pre-bending driving force on the LED side. If the thickness is less than 0.068 mm, the absolute amount of resin is insufficient, which may affect interlayer bonding and result in too small a pre-bending amplitude; if the thickness is greater than 0.080 mm, it contradicts the design intention of "thickness less than the second prepreg," and an excessively thick prepreg will reduce the bending deformation sensitivity on the LED side.

[0047] The thickness of the second prepreg (control side) is controlled between 0.098 mm and 0.110 mm, preferably 0.105 mm. This thickness range falls within the category of thicker prepreg specifications (e.g., the typical thickness of type 2113 prepreg is 0.098 mm to 0.110 mm). The combination of this greater thickness and lower adhesive content results in the following triple benefits: Increased bending stiffness: The increased thickness on one side of the control surface significantly improves the bending stiffness of that side (proportional to the cube of the thickness), thus more effectively resisting the bending moment caused by the shrinkage of the LED surface.

[0048] Increased stress buffering: The thicker low-resin content layer acts as a high-modulus buffer layer, which can absorb and disperse the residual stress transmitted from the core board and the opposite side, and prevent the stress from being directly transmitted to the copper foil on the control surface, causing local deformation.

[0049] Compensating for absolute resin content: Although the resin content is relatively low (52%–63%), the thickness is relatively large, and the absolute resin content per unit area is still sufficient to ensure the reliability of interlayer bonding. For example, a prepreg with a thickness of 0.105 mm and a resin content of 55% has an absolute resin content that is basically equivalent to that of a prepreg with a thickness of 0.075 mm and a resin content of 70%.

[0050] If the thickness is less than 0.098mm, the bending stiffness of the control surface will not be improved enough, the stress buffering effect will be weakened, and the absolute resin content may be too low, leading to the risk of adhesion. If the thickness is greater than 0.110mm, the overall plate thickness will increase, which is not conducive to thin design (the finished product thickness requirement is 0.3mm to 1.0mm), and may cause difficulties in resin flow during pressing.

[0051] In this embodiment, the thickness difference between the first and second prepreg sheets is controlled to be at least 0.018 mm (i.e., 0.098 mm minus 0.080 mm), preferably 0.025 mm to 0.035 mm. This thickness difference, together with the difference in adhesive content (≥5 percentage points), ensures a clear pre-bending direction (towards the control surface) and a moderate amplitude. During the lamination process, because the first prepreg sheet (LED bead side) has a high adhesive content and is thin, its resin fluidity and curing shrinkage are greater than that of the second prepreg sheet (control surface side). Therefore, after lamination, the board will have a slight pre-bending towards the control surface. The direction of this pre-bending is opposite to the main warping (towards the LED bead side) caused by the difference in copper retention on both sides during the subsequent reflow soldering stage. By controlling the material parameters (adhesive content difference, thickness difference), the amplitude of the pre-bending is matched with the amplitude of the subsequent main warping, and the two cancel each other out during the reflow soldering process, so that the final board remains flat.

[0052] Furthermore, the first prepreg is a 1080 prepreg, and the second prepreg is a 2113 prepreg.

[0053] The adhesive content of type 1080 prepreg is typically between 65% and 75%, type 2113 prepreg is typically between 52% and 63%, type 106 is approximately 70% to 80%, and type 3313 is approximately 55% to 65%. In this embodiment, type 1080 is preferred as the first prepreg and type 2113 as the second prepreg, naturally satisfying the aforementioned adhesive content range and difference requirements. If other models are selected due to special design requirements, the adhesive content should be confirmed through the supplier's specifications, ensuring a difference of ≥5 percentage points.

[0054] Furthermore, the angle between the lines of the grid-like circuit and the edge of the thin circuit board is 30° to 60°.

[0055] Alternatively, the grid lines (lines of the copper mesh) are at an angle of 30° to 60° to the edge of the board, preferably 40° to 50°, or 45°.

[0056] The fiberglass cloth in the prepreg is distributed in the warp (0°) and weft (90°) directions, and there are differences in the coefficient of thermal expansion (CTE) and modulus of elasticity between these two directions (the warp direction is generally more rigid). When a large area of ​​continuous copper foil is retained on the control surface, the CTE of copper (approximately 17 ppm / ℃) does not match the CTE of the fiberglass cloth (approximately 6 ppm / ℃ in the warp and approximately 15 ppm / ℃ in the weft), resulting in anisotropic deformation during thermal cycling.

[0057] After changing the continuous copper sheet to a 45° inclined grid: the grid lines are no longer parallel or perpendicular to the warp / weft of the fiberglass cloth, making the equivalent CTE of the control surface more even in the X and Y directions, reducing directional differences; at the same time, the 45° grid allows the stress of the plate to be distributed and transmitted along the 45° direction when heated, rather than concentrated along the length / width direction of the plate edge, thereby reducing overall warping.

[0058] Based on current requirements, the width and spacing of the mesh lines are designed to be 0.2mm / 0.2mm-1mm / 1mm, reducing the copper content on the control surface. This not only provides a more uniform stress distribution and reduces local warping, but also ensures electrical performance, optimizes the current path, reduces power consumption, and improves overall energy efficiency.

[0059] Furthermore, the large copper surface on the side of the core board layer that contacts the second prepreg can be changed into a grid pattern.

[0060] When prepreg is used in circuit board manufacturing, the internal fiberglass cloth is distributed in both warp and weft directions. The fiberglass cloth is parallel or perpendicular to the edge of the board. If the grid lines (copper mesh) are also parallel or perpendicular to the edge of the board, the adhesive (mainly epoxy resin) of the prepreg will concentrate and flow towards the length and width of the board edge. This results in a larger flow at the edge of the board and a smaller flow of adhesive towards the center of the board because it is difficult to "squeeze" it outward. Therefore, the copper mesh is made at an angle to balance and restrain the orientation distribution of the internal fiberglass mesh, thereby improving the balance of adhesive flow.

[0061] Furthermore, during the fabrication of the outer layer circuitry, the tool edge area on the first copper foil is made into a complete copper foil, leaving copper entirely in the tool edge area; and the tool edge area on the second copper foil is made into a grid-like circuitry.

[0062] In mass production of circuit boards, to improve production efficiency, a panel approach is typically used. This involves fabricating multiple unit circuit boards simultaneously on a large copper-clad board. Tool edges (process edges) are reserved between unit boards and between unit boards and the board edges. These tool edges are used to arrange auxiliary graphics such as alignment marks, test points, and clamping areas. They are removed by a milling cutter during the final forming process and are not part of the finished product.

[0063] During lamination and subsequent processing (such as reflow soldering), the copper retention rate of the tool edge, as a component of the panel, also affects the stress distribution and warpage behavior of the entire panel. Existing technologies typically do not specifically control the copper retention rate of the tool edge. The copper foil on the tool edge may be partially etched away (e.g., only the alignment target is retained), completely etched away, or left randomly.

[0064] To address the issue of a significant difference in copper retention rates between the LED bead side (first copper foil) and the control side (second copper foil) of thin circuit boards with high-density mini LED mounting, where the copper retention rate is lower (approximately 18%) in the finished product area and higher (approximately 72%) in the finished product area, this embodiment employs an asymmetrical tooling edge copper retention design, as detailed below: For the tool edge of the LED bead surface (first copper foil): it is made as a complete copper foil, meaning the entire copper layer in this area is retained without etching. In this way, in the panelized state, the copper retention rate of the LED bead surface tool edge is 100%, far higher than the copper retention rate of the finished product area (approximately 18%). This increases the copper retention rate of the LED bead surface in the board edge area, making the copper retention rate of this surface tool edge closer to that of the control surface tool edge, thus reducing the difference in copper retention rate between the two surfaces in the board edge area. The high rigidity of the complete copper foil at the board edge resists warping deformation of the board edge during lamination and reflow soldering.

[0065] For the tool edge of the control surface (second copper foil): It should be fabricated as a grid pattern (same as or similar to the grid pattern in the finished product area). The grid line width / spacing can be designed to match the finished product area (e.g., 0.1mm / 0.1mm), reducing the copper retention rate in this area to approximately 30%–50%. Its function is: The copper retention rate of the control surface tool edge is reduced to form an appropriate difference with the copper retention rate (100%) of the LED lamp bead surface tool edge. Moreover, the grid structure itself is conducive to the uniform release of stress and avoids the generation of concentrated thermal stress at the edge of the solid copper sheet.

[0066] This asymmetrical design achieves a rebalancing of copper retention rates on both sides of the panel edge: the copper retention rate on the tool edge of the LED side is increased to 100%, while the copper retention rate on the tool edge of the control side is reduced to about 30% to 50%. The difference between the two brings the overall copper retention rates of the LED bead side and the control side closer, thereby reducing the overall warping caused by the difference in copper retention rates.

[0067] It is important to note that during graphic design, the tool edge area of ​​the panel should be defined in the CAM software (usually a ring-shaped area with a panel edge width of 5mm to 15mm). For the LED bead surface (first copper foil), no etched patterns should be designed in this area; the entire copper sheet should be retained. For the control surface (second copper foil), a grid pattern should be designed in this area, with the grid line width / spacing consistent with the finished product area (e.g., 0.1mm / 0.1mm), and the grid line direction is preferably at a 45° angle.

[0068] The tool edge may contain auxiliary graphics such as alignment targets, test points, and partition slots between unit boards. These graphics should be fabricated additionally on top of the full copper foil or grid (e.g., opening windows in the full copper foil to expose the targets, or retaining pads on the grid). The tool edge is removed by a milling cutter during final shaping, so the above design does not affect the electrical performance and appearance of the shipped product.

[0069] Furthermore, after completing the outer layer circuit fabrication, the process also includes drilling multiple through holes in the blank area on the thin circuit board where the spacing between adjacent mini LED beads is greater than 2mm.

[0070] For some low-to-medium resolution or large-size display products, the spacing between LED chips may reach 2mm or more (e.g., 2.5mm, 3.0mm or even larger). In this case, a large blank area will be formed between adjacent chips—that is, an exposed dielectric area without copper foil, solder pads, or signal lines.

[0071] In this embodiment, multiple through-holes, typically non-metallized through-holes (NPTH), are drilled in blank areas with a spacing greater than 2 mm. These through-holes disrupt the continuity of the plate surface: they divide the originally complete dielectric layer into several smaller regions, blocking the long-distance transmission path of stress in the continuous medium. This prevents local stress from accumulating throughout the blank area; instead, it is "interrupted" by the through-holes and dispersed to various smaller regions. They also provide stress relief points: the edge (hole wall) of each through-hole is a free boundary. When thermal stress occurs, the hole wall can undergo slight elastic deformation (such as slight expansion or contraction), thereby absorbing and releasing local stress and preventing stress concentration at the macroscopic level of the plate. Furthermore, they increase surface area to buffer deformation: the through-holes increase the surface area (hole wall area) of the region. Under the same thermal expansion, the strain per unit area decreases, thus reducing the local warping amplitude.

[0072] Through-holes should preferably be placed at the geometric center or stress concentration peak point of the blank area (which can be determined through finite element simulation). For larger blank areas (such as those with a spacing of more than 3 mm), multiple through-holes can be drilled. The safe distance between the through-hole and the adjacent LED chip pads should be at least 0.2 mm to avoid damaging the pads or causing short circuits during drilling.

[0073] The diameter of the through hole is preferably 0.2mm to 0.5mm. If the diameter is too small (<0.2mm), drilling will be difficult and the stress release effect will be limited; if the diameter is too large (>0.5mm), it may weaken the structural strength of the board and occupy too much blank area, affecting the aesthetics or subsequent application of the light-shielding film.

[0074] After the outer circuitry and solder mask layers are fabricated, a CNC drilling machine can be used for drilling. Drilling parameters (rotation speed, feed rate) should be set according to standard non-metallized hole processing procedures, taking care to avoid off-center drilling or burrs at the hole opening. After drilling, desmearing should be performed to clean the hole walls, ensuring no residual resin or fiberglass burrs remain.

[0075] Through-holes divide the continuous dielectric layer region, preventing thermal stress from being transmitted over long distances and significantly reducing peak stress. The dispersion of local stress directly reduces the driving force for overall plate bending.

[0076] Furthermore, after drilling the through hole, the method further includes: attaching a black light-shielding film, which is a black PET film, above the through hole on the side where the first copper foil is located.

[0077] Mini LED display technology has extremely stringent requirements for optical performance, especially in terms of black level and contrast. When through-holes are drilled in the blank areas of the LED chips, these through-holes physically form windows that penetrate the entire board. Although the through-holes themselves are non-conductive (non-metallized), their light transmittance can lead to problems such as light leakage and poor appearance.

[0078] In this embodiment, after drilling the through holes, a layer of black light-shielding film is attached to one side of the LED bead surface. This film covers the top of all the through holes (i.e., the openings on the LED bead surface side), completely concealing the through holes. The specific material used is black PET film.

[0079] Color: Pure black, with a high light absorption rate (>98%), effectively blocking visible light transmission.

[0080] Thickness: Typically 25μm to 75μm, preferably 50μm. This thickness provides sufficient light-blocking capability without significantly increasing the overall thickness of the plate.

[0081] Temperature resistance: The glass transition temperature (Tg) of PET film is approximately 70–80°C. It can withstand temperatures above 150°C for short periods, making it suitable for post-reflow soldering processes (such as testing and assembly). However, it cannot directly withstand the high temperatures of reflow soldering. Therefore, the bonding process should be performed after reflow soldering.

[0082] Adhesion: One side of the black PET film is coated with pressure-sensitive adhesive (PSA) or thermosetting adhesive, which can be firmly attached to the surface of the circuit board and has good adhesion to the solder mask and copper surface.

[0083] Flexibility: PET film has a certain degree of extensibility, which allows it to slightly sink into the through-holes to form a mechanical anchor, further improving the reliability of the adhesion.

[0084] Insulation: PET is an excellent insulating material and will not cause electrical short circuits.

[0085] Application Location: The black light-shielding film should only be applied to the LED bead side, as the light originates from this side. No film is needed on the control side (second copper foil side), as the main light leakage direction is from the LED surface.

[0086] Black shading film should be applied after all high-temperature processes are completed, including reflow soldering and aging tests. Because PET film is not resistant to high temperatures (long-term operating temperature <120℃), premature application may cause the film to melt, bubble, or discolor.

[0087] Application Process: Cutting Openings: For areas requiring exposed LED chip pads (such as above the pads), the film needs to be cut open using laser cutting or die punching to expose the pads for subsequent LED chip mounting. The opening size should be slightly larger than the pads (e.g., 0.1mm larger on each side) to ensure reliable soldering. Clean the Surface: Before applying the film, the LED chip surface needs to be plasma cleaned or wiped with alcohol to remove oil and dust, ensuring a strong bond between the film and the board. Use a CCD alignment system to align the black PET film with the positioning marks on the circuit board. Due to the large number and wide distribution of through-holes, a full-board film application method (i.e., covering the entire LED chip surface) is usually used, rather than just covering the through-hole area. This simplifies the process and protects the entire LED surface from scratches and contamination. Use a laminator or roller laminator to evenly apply the film to the board surface, applying pressure of 0.2–0.5 MPa to remove air bubbles. Curing (if required): If using thermosetting PET film, it needs to be baked at 80-100°C for 30-60 minutes to allow the adhesive layer to fully cross-link.

[0088] Heat resistance test: Simulates reflow soldering after LED mounting (peak temperature approximately 255℃). Since the PET film softens and shrinks at high temperatures, the film application process should be scheduled after reflow soldering. If there is a subsequent second reflow soldering (e.g., for mounting other components), a high-temperature resistant black light-shielding film (such as a polyimide PI substrate) should be used, but this is more expensive. In typical mini LED production, the circuit board first mounts the LED chips (reflow soldering), then mounts other components (which may also be reflow soldered). Therefore, it is recommended to apply the film after the final reflow soldering. If this cannot be avoided, a high-temperature resistant black PI film can be used.

[0089] The optical density (OD) of black PET film can reach over 3.0 (i.e., light transmittance <0.1%), which can completely block through-holes, ensuring no stray light leakage when mini LEDs are working, and improving display contrast and black level performance. As a protective layer, PET film can prevent scratches and contamination of pads and circuits during subsequent processes (such as handling and assembly), thereby improving product yield.

[0090] Furthermore, In the outer layer circuit fabrication step, when the spacing between adjacent mini LED beads on the LED bead surface is ≥1mm, the blank area on the LED bead surface located between adjacent beads is also fabricated into a grid-like copper circuit.

[0091] In high-density mini LED mounting applications, the spacing between LED chips (pixel pitch) varies depending on the product resolution. For high-resolution products, the spacing can be as small as 0.5mm to 0.8mm. In this case, the chip pads and signal lines are densely packed, and the copper distribution across the entire LED chip surface is relatively uniform. The copper coverage is mainly contributed by the pads and lines, with very small blank areas. However, for medium-to-low resolution or large-size display products, the LED chip spacing may reach 1mm or more (e.g., 1.2mm, 1.5mm, 2.0mm, etc.). In this case, a certain area of ​​blank space will be formed between adjacent chips—that is, an exposed dielectric area without pads or signal lines.

[0092] Create a grid-like copper trace within blank areas with a spacing of ≥1mm. This grid-like copper trace is not connected to the existing pads and signal lines (or is grounded as needed), and mainly serves the following functions: Increase the copper retention rate of the LED bead surface: By adding grid copper, the blank areas that were originally without copper are partially covered with copper, increasing the overall copper retention rate of the LED surface from about 18% to 25% to 40% (depending on the grid density), thereby reducing the difference in copper retention rate with the control surface and reducing warping caused by thermal expansion mismatch.

[0093] Uniform local thermal expansion: The presence of copper mesh makes the thermal expansion behavior of the blank area more similar to that of the surrounding copper area, reducing the local strain gradient and lowering the probability of micro-torsion.

[0094] Improved heat dissipation: The copper mesh can serve as an auxiliary heat dissipation path, spreading the heat generated by the LED chip laterally, reducing the chip junction temperature, and improving reliability.

[0095] In the outer layer fabrication process, the copper mesh, pads, and signal lines are designed together in the photoplot file. After exposure and development, the mesh area and the pad area are etched simultaneously, requiring no additional steps.

[0096] By fabricating the blank areas (spacing ≥1mm) of LED beads into grid-like copper circuits, the copper retention rate of the LED surface can be increased, the difference between the two sides can be reduced, and the local stress distribution can be improved. The grid copper divides the continuous blank area into multiple small copper / dielectric composite units, making the thermal expansion behavior more similar to the surrounding copper areas.

[0097] This invention systematically eliminates the warping driving force of thin circuit boards during lamination and high-temperature reflow soldering by using prepregs with differentiated adhesive content and thickness. This is achieved by replacing the large continuous copper area on the control surface with a grid pattern to reduce the copper retention rate, leaving all copper on the tool edges of the LED bead surface and gridding the tool edges of the control surface to balance edge stress, tilting the grid lines to optimize isotropic thermomechanical behavior, adding grid copper in the mid-spacing blank areas to improve the copper retention rate and heat dissipation capacity of the LED surface, drilling through holes in the large-spacing blank areas to disperse local stress, and attaching a black light-shielding film to prevent light leakage. This systematically eliminates the warping driving force of thin circuit boards during lamination and high-temperature reflow soldering from the three levels of materials, graphics, and structure, significantly improving the flatness of the board while ensuring optical performance and process compatibility. It can meet the requirements of high flatness and high reliability of circuit boards for high-density mini LED mounting without additional post-processing correction.

[0098] Example 2

[0099] The general manufacturing process for existing circuit boards supporting Mini LED mounting is as follows: First, fabricate the core layer (which can be a double-sided or multi-layer core layer) → Take the first prepreg, second prepreg, first copper foil, and second copper foil → Stack, arrange, and laminate → Fabricate the outer layer circuit pattern → Subsequent processes (which may include: fabricating solder mask patterns, surface treatment, and shaping). Its stacked structure is as follows: Figure 2 As shown, from top to bottom, the layers are: first copper foil 11, first prepreg 12, core layer 13, second prepreg 14, and second copper foil 15. The first prepreg 12 and the second prepreg 14 are identical (optionally: 2113 prepreg, 1080 prepreg, 106, 2116, 3313). After lamination, the outer layer pattern is fabricated. The structure after fabricating the outer layer circuit pattern is as follows. Figure 3 As shown, the LED bead surface 22 has pads for attaching the LED beads, the control surface 23 has control pads and grounding copper, the edge of the board outside the forming line 21 is the tool edge 24, and the area between the forming lines is the in-board reserved area 25. Because the copper retention rate of the LED bead surface (generally around 18%) is much smaller than that of the control surface (generally around 72%), after the circuit is fabricated and the mini LED bead chips are processed or mounted, such as... Figure 3 As shown, the board will bend toward the LED bead surface (as shown). Figure 3 The diagram shows a curved curve, with the control surface forming a "bow back" and the LED bead surface forming a "bow belly".

[0100] To address this issue, this embodiment provides a method for manufacturing a thin circuit board using high-density mounting of mini LEDs.

[0101] For details, please refer to Figure 4 , Figure 4 In this embodiment of the invention, the stacking structure during lamination is modified so that the adhesive content of the first semi-cured sheet 12 is greater than that of the second semi-cured sheet 14 (the adhesive content of the first semi-cured sheet can optionally be 60% to 75%, and the adhesive content of the second semi-cured sheet can optionally be 52% to 63%). This embodiment employs a material selection and stacking method with a lower adhesive content for the prepreg adjacent to the second copper foil 15. After lamination or LED chip mounting, the low adhesive flow characteristics of the second prepreg 14 prevent excessive expansion and contraction, thereby reducing the release of internal stress and balancing the uneven release of internal stress caused by the high copper retention rate on the control surface. Optionally, the thickness of the first prepreg 12 is less than that of the second prepreg 14, with the first prepreg thickness ranging from 0.068 mm to 0.080 mm and the second prepreg thickness ranging from 0.098 mm to 0.110 mm. The increased thickness of the second prepreg 14, based on the aforementioned reduced adhesive content, can reduce the unbalanced stress within the board caused by differences in copper retention rate during subsequent processing.

[0102] Optionally, the first prepreg 12 is a 1080 prepreg and the second prepreg 14 is a 2113 prepreg.

[0103] In addition, the outer layer circuit pattern has been redesigned and processed in this embodiment.

[0104] The large copper area on the control surface, excluding the original pads, was replaced with a mesh circuit to reduce the copper content of the control surface.

[0105] Alternatively, the grid lines (lines of the copper mesh) are at an angle of 30° to 60° to the edge of the board (preferably 40° to 50°, or 45°).

[0106] Meanwhile, when making the inner core board, the large copper foil on both sides of the core board can be changed into a grid pattern, and the angle with the board edge can be controlled to be 30° to 60°.

[0107] When prepreg is used in circuit board manufacturing, the internal fiberglass cloth is distributed in both warp and weft directions. The fiberglass cloth is parallel or perpendicular to the edge of the board. If the grid lines (copper mesh) are also parallel or perpendicular to the edge of the board, the adhesive (mainly epoxy resin) of the prepreg will concentrate and flow towards the length and width of the board edge. This results in a larger flow at the edge of the board and a smaller flow of adhesive towards the center of the board because it is difficult to "squeeze" it outward. Therefore, the copper mesh is made at an angle to balance and restrain the orientation distribution of the internal fiberglass mesh, thereby improving the balance of adhesive flow.

[0108] Furthermore, the tool edge on the LED bead side (the ineffective area of ​​the board edge, which needs to be milled away and discarded after molding) was changed to be entirely copper-retained (the tool pattern is made on the copper surface of the retained copper), and the tool edge on the control side was changed to a grid pattern. On the one hand, this further balances the overall copper retention rate on both sides after the outer layer pattern. On the other hand, the asymmetrical copper retention design on the upper and lower sides releases the internal stress on the control side, while the internal stress on the LED bead side is released towards the control side, thus utilizing the board edge to form a structural internal stress balance effect on the board.

[0109] The structural diagram after the surface circuit pattern is formed is shown in Figure 5. Since the LED chip pads 221 on the LED chip surface 22 are small, while the control pads 231 on the control surface 23 are large, and grounding copper needs to be retained, the residual copper on the control surface will be much larger than that on the LED chip surface. By designing the tool edge 24 of the LED chip surface 22 as a large copper sheet, designing the tool edge 24 of the control surface 23 as a grid-like circuit, and also changing the large copper sheet on the control surface 23 to a grid-like circuit 232 (black dotted lines in the figure), the copper retention rate of the two sides is balanced.

[0110] Furthermore, the blank area (non-copper area) of the reserved area on one side of the LED lamp bead (that is, the area to be retained and shipped after molding) is also made into a copper mesh pattern.

[0111] When the distance between adjacent LED beads is relatively large (e.g., ≥1mm) and the space is relatively large, this method can further balance the copper retention rate on both sides. After the above design and processing, the copper retention rate on one side of the LED lamp bead is increased to >55%, while the copper retention rate on the control side is reduced to below 70%, which significantly reduces the difference in copper retention rate between the two sides.

[0112] Furthermore, in this embodiment, through holes are also machined in the blank areas of the reserved area.

[0113] When the distance between adjacent LED beads is large, meaning the blank space is significant (e.g., greater than 2mm), through holes are machined in the blank area. These through holes break up the otherwise intact board surface, allowing stress to be released more widely and preventing stress concentration in a single area, which can lead to localized expansion and contraction imbalances and warping. The design method is as follows: Figure 6 As shown (where Figure 6 Figure (a) is a schematic diagram of the planar structure, and Figure (b) is a schematic diagram of the AA section structure in Figure (a). The dashed line running from (a) to (b) indicates the corresponding cross-sectional positions in the two figures. At this point, it is designed as a metal through-hole. After lamination, through-holes are formed through drilling and electroplating. Then, the outer layer pattern and subsequent processes are fabricated, and further, such as... Figure 7 As shown, after the surface treatment is completed, a black light-shielding film 30 (optionally: black PET film) is attached to the through hole on the LED lamp bead surface to prevent light leakage.

[0114] The comparison results of the flatness of the board surface produced by the embodiments of the present invention and the prior art are as follows: Figure 8 and Figure 9 As shown.

[0115] It can be observed that the warping of the board surface produced by existing technology is very obvious. Figure 9 The improved manufacturing method in this embodiment produces a flatter circuit board that supports Mini LED mounting. Figure 8 ).

[0116] Example 3

[0117] Embodiment 3 of the present invention also provides a mini LED high-density mounting thin circuit board, which is manufactured using the manufacturing method of mini LED high-density mounting thin circuit board as described in any of the above embodiments.

[0118] The mini LED high-density mounting thin circuit board of the present invention is manufactured by the mini LED high-density mounting thin circuit board manufacturing method in method embodiment one or two, so the description is relatively simple. For details, please refer to the relevant descriptions in the previous method embodiments, which will not be repeated here.

[0119] It is worth noting that the processing technology of this embodiment does not involve the processing technology of the positive and negative electrode pads for mini LED mounting. Therefore, the positive and negative electrode pads are not distinguished or marked in the accompanying drawings, which will not cause doubts or misleading those skilled in the art about "insufficient disclosure" or "unclear".

[0120] It should be noted that, due to the high precision of circuit board processing, the high density of circuit distribution, and the thinness of the stacked structure, all reaching the micron level, such as the thickness of the cover film being 25μm to 75μm, and the line width being 25μm, 50μm, etc., if the actual stacked structure is drawn, some layers or some patterns are difficult to represent; therefore, the accompanying drawings in this embodiment are graphic concepts that highlight the technical features, and do not represent the actual circuit board structure in the processing process, nor do they represent a scaled-up enlarged view of the processing structure.

[0121] This embodiment adopts a description method based on technical features as key nodes, and the existing technology in the processing process may not be described in detail. For example, the existing technology for circuit pattern making generally assumes "dry film application → exposure → development → etching → film removal", and the basic process of lamination generally assumes "core board layer extraction → prepreg extraction → stacking → fusion / riveting → layout → lamination → X-ray targeting → burr removal". Therefore, the understanding of this embodiment is mainly the understanding of the process of forming technical features during processing.

[0122] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made under the inventive concept of the present invention using the description and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for manufacturing a high-density mounting thin circuit board for mini LEDs, characterized in that, Includes the following steps: Provide core layer; The first copper foil, the first prepreg, the core board layer, the second prepreg, and the second copper foil are stacked in sequence and pressed together to form a multilayer board; wherein the adhesive content of the first prepreg is greater than that of the second prepreg, and the thickness of the first prepreg is less than that of the second prepreg. The outer layer circuitry is fabricated on the multilayer board, wherein: The first copper foil is made into an LED bead surface pattern; The second copper foil is fabricated into a control surface pattern, which includes pads and signal lines, and the continuous copper foil on the second copper foil, except for the pads and signal lines, is replaced with a grid pattern.

2. The manufacturing method according to claim 1, characterized in that, The first prepreg has an adhesive content of 60% to 75%, the second prepreg has an adhesive content of 52% to 63%, and the adhesive content of the first prepreg is at least 5% higher than that of the second prepreg.

3. The manufacturing method according to claim 2, characterized in that, The thickness of the first prepreg is 0.068 mm to 0.080 mm, and the thickness of the second prepreg is 0.098 mm to 0.110 mm.

4. The manufacturing method according to claim 2, characterized in that, The first prepreg is a 1080 prepreg, and the second prepreg is a 2113 prepreg.

5. The manufacturing method according to claim 1, characterized in that, The angle between the lines of the grid-like circuit and the edge of the thin circuit board is 30° to 60°.

6. The manufacturing method according to claim 1, characterized in that, When fabricating the outer layer circuit, the tool edge area on the first copper foil is also made into a complete copper foil, so that the entire tool edge area is left with copper; and the tool edge area on the second copper foil is made into a grid-like circuit.

7. The manufacturing method according to claim 1, characterized in that, After the outer circuit is fabricated, the process also includes drilling multiple through holes in the blank area on the thin circuit board where the spacing between adjacent mini LED beads is greater than 2mm.

8. The manufacturing method according to claim 7, characterized in that, After drilling the through hole, the method further includes: attaching a black light-shielding film, which is a black PET film, to the side where the first copper foil is located and above the through hole.

9. The manufacturing method according to claim 1, characterized in that, In the outer layer circuit fabrication step, when the spacing between adjacent mini LED beads on the LED bead surface is ≥1mm, the blank area on the LED bead surface located between adjacent beads is also fabricated into a grid-like copper circuit.

10. A high-density mounting thin circuit board for mini LEDs, characterized in that, It is manufactured using the manufacturing method described in any one of claims 1 to 9.

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