A circuit board for high-density small-pitch LED display screen and a preparation method thereof

Abstract

The application discloses a circuit board for high-density small-pitch LED display screens and a preparation method thereof, and the preparation method comprises the following steps: pretreating an epoxy resin ceramic powder composite substrate; performing pattern transfer and etching; forming a solder pad and a circuit pattern on the surface of the epoxy resin ceramic powder composite substrate by means of a laser-induced etching and dry etching combined process; sequentially performing lamination and drilling on the epoxy resin ceramic powder composite substrate to form a through hole; and mounting a display unit on the solder pad. The epoxy resin ceramic powder composite substrate is selected, the low CTE, high thermal conductivity and low dielectric loss characteristics can be considered, the signal transmission stability of the ultra-high-definition display is ensured, and the service life of the circuit board and the terminal display screen is prolonged; the solder pad and the circuit pattern are formed by means of the laser-induced etching and dry etching combined process, and the core pain points that the side etching is serious in the traditional etching process and the micro-line width precision cannot meet the standards are solved.

Description

Technical Field

[0001] This invention relates to the technical field of high-density small-pitch displays, and more particularly to a circuit board for high-density small-pitch LED displays and its manufacturing method. Background Technology

[0002] With the maturation and industrialization of Mini LED and Micro LED technologies, LED displays have entered the ultra-high-definition and micro-pitch stage, with pixel pitch reduced to below P1.0, and some reaching the P0.3 level. They are widely used in high-end fields such as monitoring and command, high-end cinemas, and medical displays. Their LED chip sizes range from 50-200μm, and the pad sizes are approximately 100μm × 125μm with a pad spacing of ≤60μm, placing stringent requirements on the wiring accuracy, heat dissipation, and electrical reliability of the circuit board.

[0003] As the electrical connection, mechanical support, and heat dissipation carrier for LED chips and driver ICs, the performance of the circuit board directly determines the accuracy, stability, and lifespan of the display screen. Existing circuit board substrates use general-purpose FR-4 epoxy fiberglass copper-clad laminates, with a highly mature supply chain, low procurement costs, highly versatile production equipment throughout the process, high domestic production rate, and low barriers to mass production, enabling rapid large-scale production. Interlayer interconnection employs a metallized hole process of mechanical drilling + chemical copper plating + electroplating, which can stably achieve conventional interlayer interconnection for 2-8 layer boards. Mass production processing limits include a minimum line width and spacing of 60μm, a minimum mechanical drilling hole diameter of 0.2mm, and an interlayer alignment accuracy of ≥±25μm, fully meeting the basic usage requirements of conventional commercial LED displays.

[0004] However, existing processing technologies have reached their physical limits when the product dot pitch is reduced to P1.0 and below. The core shortcomings are concentrated in three points: First, the substrate performance is inherently insufficient. The expansion and contraction of the fiberglass cloth under temperature and humidity changes are inconsistent, which can easily lead to pad misalignment and cause poor soldering and dead LEDs. Second, there are physical limits to pattern processing. The side etching effect of subtractive etching can cause uneven lines and open / short circuits in line widths and spacings below 50μm, resulting in a sharp drop in mass production yield. Third, the interlayer interconnection capability is insufficient. The minimum hole diameter of mechanical drilling is 0.2mm, which occupies wiring space and cannot meet the interconnection requirements of high-density driving. Summary of the Invention

[0005] This invention aims to at least partially address one of the problems in related technologies. Therefore, one objective of this invention is to provide a method for fabricating circuit boards for high-density, small-pitch LED displays. This method utilizes an epoxy resin-ceramic powder composite substrate, which balances low CTE, high thermal conductivity, and low dielectric loss characteristics, ensuring signal transmission stability for ultra-high-definition displays and extending the lifespan of the circuit board and the terminal display. By employing a combination of laser-induced etching and dry etching processes, pads and circuit patterns are formed, solving the core pain points of traditional etching processes, such as severe side etching and inability to achieve micro-linewidth accuracy.

[0006] A method for fabricating a circuit board for a high-density, small-pitch LED display screen includes: Pretreatment of epoxy resin ceramic powder composite substrate; Pattern Transfer and Etching: Pads and circuit patterns are formed on the surface of an epoxy resin ceramic powder composite substrate through a combination of laser-induced etching and dry etching processes; The epoxy resin ceramic powder composite substrate is sequentially laminated and drilled to form through holes; Install the display unit on the pads.

[0007] Furthermore, the epoxy resin ceramic powder composite substrate undergoes pretreatment, specifically including: First, the epoxy resin ceramic powder composite substrate is baked at a low temperature of 120-130℃ for 1.5-2 hours, and then heated to 150-160℃ for 0.5-1.5 hours to cure. By using plasma surface modification treatment, the oxide layer and impurities on the surface of the epoxy resin ceramic powder composite substrate are removed, so that the surface roughness of the epoxy resin ceramic powder composite substrate is controlled at 0.8-1.2μm.

[0008] Furthermore, pattern transfer and etching specifically include: Photoresist is coated onto the copper layer on the surface of an epoxy resin ceramic powder composite substrate; The laser power is controlled at 80-100W and the scanning speed is 300-400mm / s. The epoxy resin ceramic powder composite substrate is selectively scanned and irradiated according to a preset trajectory to form the circuit outline and the pad outline. Development removes areas outside the circuit pattern and pads; Using photoresist as a mask, a dry etching process is employed. In a vacuum environment at 45-50℃, a mixed plasma of chlorine and argon is used as the etching medium for 8-12 minutes. After etching, the material is rinsed with deionized water.

[0009] Furthermore, the gas volume ratio of chlorine and argon in the chlorine and argon mixed plasma is (3:1) to (5:1).

[0010] Furthermore, during the dry etching process using a mixed plasma of chlorine and argon as the etching medium, the etching endpoint was determined by monitoring the attenuation of the CuCl2 signal using mass spectrometry.

[0011] Furthermore, during the lamination of the epoxy resin ceramic powder composite substrate, dual cameras are used to position the circuitry of each layer; and during lamination, the lamination temperature is controlled at 170-180℃, the lamination pressure at 2.0-2.5MPa, the lamination heating rate at 5℃ / min, and the lamination time at 60-90 minutes.

[0012] Furthermore, the epoxy resin ceramic powder composite substrate is drilled to form through holes, specifically including: Drilling using femtosecond lasers; Through-hole filling is performed using a pulse electroplating process, with the pulse current controlled at 1.5-2.5 A / dm. 2 The electroplating temperature of the pulse electroplating process is 35-40℃. The electroplating solution used in the pulse electroplating process includes a base electrolyte, chloride ions, accelerators, inhibitors and leveling agents. After the pulse electroplating process, a secondary curing process is carried out at 140-150℃.

[0013] Furthermore, before installing the display unit, the process includes: electroplating a high-purity nickel-gold plating layer on the surface of the circuit pattern; coating a semi-modified epoxy acrylate protective layer on the surface of the circuit board; the semi-modified epoxy acrylate protective layer contains a bifunctional structure, with one end of the molecular chain being an acrylate double bond and the other end being an epoxy group.

[0014] Furthermore, before installing the display unit, the process includes: precisely printing solder paste onto the pads using a stencil; and performing reflow soldering after installing the display unit.

[0015] The second objective of this application is to provide a circuit board for a high-density, small-pitch LED display screen, which is prepared based on the above-described method for preparing a circuit board for a high-density, small-pitch LED display screen.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for fabricating a circuit board for a high-density, small-pitch LED display. It utilizes an epoxy resin-ceramic powder composite substrate, which balances low CTE, high thermal conductivity, and low dielectric loss characteristics. The thermal conductivity of the epoxy resin-ceramic powder composite substrate can be increased to 50-200 W / m·K, highly matching the thermal expansion coefficient of the LED chip. This effectively solves the problems of insufficient heat dissipation of traditional FR-4 substrates and the difficulty in balancing heat dissipation and electrical performance in existing processes. Simultaneously, the epoxy resin-ceramic powder composite substrate can reduce high-frequency signal transmission loss and crosstalk, and control the dielectric constant below 3.0 and the dielectric loss below 0.008, ensuring... The signal transmission stability of ultra-high-definition displays extends the service life of circuit boards and terminal displays. This application uses a combination of laser-induced etching and dry etching processes to form pads and circuit patterns, ensuring that the line width and spacing are controlled within 10-30μm and the lateral etching amount is ≤5μm. This solves the core pain points of traditional etching processes, such as severe lateral etching and inability to meet micro-line width accuracy standards. It is perfectly compatible with the entire range of high-density small-pitch LED displays in the P0.3-P1.5 range, solving the problems of insufficient wiring accuracy in traditional processes and the difficulty in balancing accuracy and cost in existing high-end processes. It ensures precise interconnection between LED chips and driver ICs, avoiding the risk of cold solder joints and dead LEDs caused by pad misalignment.

[0017] This application also provides a circuit board for high-density, small-pitch LED displays, which uses a customized epoxy resin ceramic powder composite substrate. It takes into account the characteristics of low CTE, high thermal conductivity and low dielectric loss. The thermal conductivity can be increased to 50-200W / m·K, which is highly matched with the thermal expansion coefficient of LED chips. It effectively solves the problems of insufficient heat dissipation of traditional FR-4 substrates and the difficulty in balancing heat dissipation and electrical performance in existing processes. At the same time, it reduces high-frequency signal transmission loss and crosstalk, controls the dielectric constant (Dk@1GHz) below 3.0 and the dielectric loss (Df@1GHz) below 0.008, ensures the signal transmission stability of ultra-high-definition displays, and extends the service life of the circuit board and terminal display screen. Meanwhile, by optimizing the substrate system and manufacturing process, mass production of 10-30μm linewidth and line spacing can be stably achieved, with interlayer alignment accuracy controlled within ±10μm and the minimum aperture of vias reduced to below 30μm. This perfectly adapts to the full range of high-density small-pitch LED displays in the P0.3-P1.5 range, solving the problems of insufficient wiring accuracy in traditional processes and the difficulty in balancing accuracy and cost in existing high-end processes. It ensures precise interconnection between LED chips and driver ICs, avoiding the risk of cold solder joints and dead LEDs caused by pad alignment deviations. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] In the attached image: Figure 1 This is a schematic flowchart of the preparation method in Example 2 of this application. Detailed Implementation

[0021] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientations or positional relationships indicated by terms such as "front," "rear," "upper," "lower," "left," "right," "longitudinal," "horizontal," "vertical," "horizontal," "top," "bottom," "inner," "outer," "head," and "tail" are based on the orientations or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. They are only for the convenience of describing this technical solution and do not indicate that the referred mechanism or element must have a specific orientation; therefore, they should not be construed as limitations on this invention.

[0022] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "linking," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. When an component is referred to as being "on" or "below" another component, the component can be located "directly" or "indirectly" on the other component, or there may be one or more intermediary components. The terms "first," "second," "third," etc., are only for the convenience of describing this technical solution and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0023] In the following description, specific details such as particular system structures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, mechanisms, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0024] Example 1

[0025] This application provides a method for fabricating a circuit board for a high-density, small-pitch LED display screen, comprising: S1: Pretreatment of epoxy resin ceramic powder composite substrate.

[0026] The thermal conductivity of the epoxy resin ceramic powder composite substrate in this application can reach 50-200W / m·K, which is highly matched with the thermal expansion coefficient of the LED chip, effectively solving the problems of insufficient heat dissipation of traditional FR-4 substrate and difficulty in balancing heat dissipation and electrical performance in existing processes.

[0027] Pretreatment of epoxy resin ceramic powder composite substrate can significantly improve the adhesion and etching accuracy of subsequent circuits, solving the problems of circuit detachment and uneven etching caused by traditional pretreatment.

[0028] S2: Pattern Transfer and Etching: Pads and circuit patterns are formed on the surface of an epoxy resin ceramic powder composite substrate through a combination of laser-induced etching and dry etching processes.

[0029] This application uses laser-induced etching to precisely locate the line width, line spacing, and pad position and size, forming accurate circuit and pad outlines. Then, by controlling the parameters of the dry etching process, it can further ensure that the line width and line spacing are controlled within 10-30μm and the side etching amount is ≤5μm, solving the core pain points of traditional etching processes, such as severe side etching and inability to meet micro-line width accuracy (≤50μm).

[0030] S3: Lamination and drilling are performed sequentially on the epoxy resin ceramic powder composite substrate to form through holes; S4: Install the display unit on the pad.

[0031] This application provides a method for fabricating a circuit board for a high-density, small-pitch LED display. It utilizes an epoxy resin-ceramic powder composite substrate, which balances low CTE, high thermal conductivity, and low dielectric loss characteristics. The thermal conductivity of the epoxy resin-ceramic powder composite substrate can be increased to 50-200 W / m·K, highly matching the thermal expansion coefficient of the LED chip. This effectively solves the problems of insufficient heat dissipation of traditional FR-4 substrates and the difficulty in balancing heat dissipation and electrical performance in existing processes. Simultaneously, the epoxy resin-ceramic powder composite substrate can reduce high-frequency signal transmission loss and crosstalk, and control the dielectric constant below 3.0 and the dielectric loss below 0.008, ensuring... The signal transmission stability of ultra-high-definition displays extends the service life of circuit boards and terminal displays. This application uses a combination of laser-induced etching and dry etching processes to form pads and circuit patterns, ensuring that the line width and spacing are controlled within 10-30μm and the lateral etching amount is ≤5μm. This solves the core pain points of traditional etching processes, such as severe lateral etching and inability to meet micro-line width accuracy standards. It is perfectly compatible with the entire range of high-density small-pitch LED displays in the P0.3-P1.5 range, solving the problems of insufficient wiring accuracy in traditional processes and the difficulty in balancing accuracy and cost in existing high-end processes. It ensures precise interconnection between LED chips and driver ICs, avoiding the risk of cold solder joints and dead LEDs caused by pad misalignment.

[0032] This application also provides a circuit board for high-density, small-pitch LED displays, which uses a customized epoxy resin ceramic powder composite substrate. It takes into account the characteristics of low CTE, high thermal conductivity and low dielectric loss. The thermal conductivity can be increased to 50-200W / m·K, which is highly matched with the thermal expansion coefficient of LED chips. It effectively solves the problems of insufficient heat dissipation of traditional FR-4 substrates and the difficulty in balancing heat dissipation and electrical performance in existing processes. At the same time, it reduces high-frequency signal transmission loss and crosstalk, controls the dielectric constant (Dk@1GHz) below 3.0 and the dielectric loss (Df@1GHz) below 0.008, ensures the signal transmission stability of ultra-high-definition displays, and extends the service life of the circuit board and terminal display screen. Meanwhile, by optimizing the substrate system and manufacturing process, mass production of 10-30μm linewidth and line spacing can be stably achieved, with interlayer alignment accuracy controlled within ±10μm and the minimum aperture of vias reduced to below 30μm. This perfectly adapts to the full range of high-density small-pitch LED displays in the P0.3-P1.5 range, solving the problems of insufficient wiring accuracy in traditional processes and the difficulty in balancing accuracy and cost in existing high-end processes. It ensures precise interconnection between LED chips and driver ICs, avoiding the risk of cold solder joints and dead LEDs caused by pad alignment deviations.

[0033] Example 2

[0034] like Figure 1 As shown, a method for fabricating a circuit board for a high-density, small-pitch LED display includes: S1: Pretreatment of the epoxy resin ceramic powder composite substrate; specific pretreatment methods include: S11: Select an epoxy resin ceramic powder composite substrate with a thermal conductivity ≥50W / (m·K) and bake it at a low temperature of 120-130℃ for 1.5-2 hours to remove surface moisture. S12: Heat to 150-160℃ for 1 hour to cure at high temperature to improve the stability of the substrate; S13: Through plasma surface modification treatment, the surface oxide layer and impurities of the epoxy resin ceramic powder composite substrate are removed, so that the surface roughness of the epoxy resin ceramic powder composite substrate is controlled at 0.8-1.2μm, which greatly improves the adhesion and etching accuracy of subsequent circuits and solves the problems of circuit detachment and uneven etching caused by traditional pretreatment.

[0035] S2: Pattern transfer and etching. Through a combination of laser-induced etching and dry etching processes, pads and circuit patterns are formed on the surface of an epoxy resin ceramic powder composite substrate.

[0036] Laser-induced etching specifically includes: S21: Photoresist is coated on the copper layer on the surface of the epoxy resin ceramic powder composite substrate as a medium for pattern transfer. S22: Controls the laser power to 80-100W and the scanning speed to 300-400mm / s, selectively scanning and irradiating according to a preset trajectory to form a precise line outline; the irradiated area forms a latent image. S23: Development removes areas other than the circuit pattern and pads; S24: Using photoresist as a mask, a dry etching process is adopted. In a vacuum environment at 45-50℃, a mixed plasma of chlorine and argon is used as the etching medium for 8-12 minutes. After etching, deionized water is used for rinsing to ensure that the line width and line spacing are controlled at 10-30μm and the side etching amount is ≤5μm.

[0037] The dry etching process specifically includes: during the etching stage, a Cl2 / Ar mixed gas is introduced, with a Cl2 to Ar gas volume ratio of (3:1) to (5:1). Cl2 dissociates in the plasma to generate highly reactive chlorine radicals (Cl·), which react with copper to form volatile CuCl2, while exhibiting almost no chemical corrosion to organic materials such as epoxy resin and polyimide, achieving a selectivity ratio >50:1. + Ions bombard the copper surface vertically under radio frequency bias, breaking chemical bonds and helping to remove reaction products, inhibiting lateral drilling, achieving vertical sidewalls, and maintaining structural stability even when the depth-to-width ratio is >10:1.

[0038] During plasma etching, the completion of etching can be determined by monitoring the attenuation of the CuCl2 signal using mass spectrometry, thus avoiding over-processing.

[0039] S3: Lamination and drilling are performed sequentially on the epoxy resin ceramic powder composite substrate to form through holes and realize interlayer electrical connection.

[0040] Before lamination, dual cameras are used to precisely position the circuitry of each layer, with a positioning accuracy of ≤±2μm, ensuring accurate alignment of the multi-layer circuitry. During lamination, the temperature is controlled at 170-180℃ and the pressure at 2.0-2.5MPa, using a gradient temperature and pressure bonding method. The heating rate is controlled at 5℃ / min, and the bonding time is 60-90 minutes to avoid interlayer bubbles and delamination, while improving interlayer bonding strength, adapting to the high-density multilayer wiring requirements of 2-10 layers. This application adopts a "dual-camera positioning + constant temperature and pressure lamination" process to solve the problem of large interlayer alignment deviations. The two cameras are fixed to the bottom of the lamination stage and in the robotic arm, respectively. The camera fixed to the bottom of the lamination stage remains stationary and is used to identify the reference marks in each substrate layer. The camera fixed in the robotic arm moves with each substrate layer to capture the current position and angular deviation of the material to be laminated. The two cameras work together, and after calibration and algorithm calculation, sub-millimeter-level alignment accuracy is achieved.

[0041] The drilling process in this application specifically includes: S31: Blind holes are drilled using femtosecond lasers, with the hole diameter controlled at 0.08-0.15mm and the hole position deviation ≤±3μm, avoiding the hole diameter deviation and burr problems of mechanical drilling; S32: Hole filling uses a pulse electroplating process, with the pulse current controlled at 1.5-2.5A / dm. 2 The electroplating temperature is 35-40℃, and high-purity copper paste is used as filler.

[0042] The electroplating solution used in the pulse electroplating process of this application includes a base electrolyte, chloride ions, an accelerator, an inhibitor, and a leveling agent. The base electrolyte mainly consists of copper sulfate, sulfuric acid, and water, providing copper ions and maintaining the electroplating reaction environment. Chloride ions, derived from hydrochloric acid or sodium chloride, are maintained at a concentration of 50-90 ppm, acting as a bridge to promote the synergistic adsorption of the accelerator and inhibitor. The accelerator concentration is maintained at 0.8-1.2 mL / L, and sodium polydithiopropane sulfonate can be used. In the pulse electroplating process, the accelerator selectively adsorbs at the bottom of the hole, lowering the reduction site and accelerating copper ion deposition. The inhibitor concentration is maintained at 10-15 g / L, and polyethylene glycol can be used. In the pulse electroplating process, the inhibitor forms a complex with chloride ions, forming an inhibition layer at the hole opening to prevent premature sealing of the via. The concentration of the leveling agent should be maintained at 0.1-0.3 mg / L. Specifically, Janus Green B can be selected. In the pulse electroplating process, the leveling agent is preferentially adsorbed in the high current density area to inhibit the excessively rapid growth of local copper layers in the hole and improve the surface smoothness.

[0043] S33: After filling, it is cured for 2 hours at 140-150℃ to ensure that the filling is full without depressions or voids, and the conductivity reaches more than 99.9%, solving the pain points of insufficient filling and poor conductivity in existing systems.

[0044] The secondary curing here refers to the secondary curing of the epoxy resin in the epoxy resin-ceramic powder composite substrate, forming a denser three-dimensional network structure. This reduces the volume of micropores within the vias, strengthens the anchoring effect between the epoxy resin in the substrate and the copper layer on the via wall, reduces stress concentration points at the interface between the copper layer and the via wall, improves the adhesion of the copper plating layer, and prevents defects such as via wall separation and blistering. In this application, after pulse electroplating for copper plating, the secondary curing further ensures full via filling without depressions or voids, achieving a conductivity of over 99.9%, thus solving the problems of incomplete via filling and poor conductivity in existing systems.

[0045] This application, after pulse electroplating, utilizes the unique properties of the substrate to achieve adhesion between the hole wall and the substrate after pulse electroplating by secondary curing of the epoxy resin in the substrate, thereby further improving the hole filling advantage.

[0046] S4: Electroplating a 1-2μm thick high-purity nickel-gold plating layer on the surface of the circuit pattern to improve conductivity and oxidation resistance; A modified epoxy resin solder resist layer with a thermal conductivity ≥40W / (m·K) is coated on the surface of the circuit board. A UV curing + thermosetting composite method is used to ensure a uniform and dense solder resist layer with a thickness controlled at 15-20μm, preventing solder resist peeling and cracking. Simultaneously, it enhances heat dissipation, addressing the problems of weak protection and insufficient heat dissipation in existing surface treatments. The modified epoxy resin solder resist layer refers to a semi-modified epoxy acrylate protective layer. This semi-modified epoxy acrylate contains a bifunctional structure; one end of the molecular chain is an acrylate double bond (C=C), which can rapidly crosslink through free radical polymerization under UV irradiation; the other end is an epoxy group (-CH-O-CH-), which undergoes ring-opening polymerization with curing agents (such as acid anhydrides and amines) under heating conditions to form a dense three-dimensional network. The UV stage achieves instantaneous surface gelation, preventing sagging; the thermosetting stage completes deep internal crosslinking, eliminating microporous defects and significantly improving the coating's adhesion, chemical resistance, and thermal stability.

[0047] This application adopts a composite protection process of "high thermal conductivity coating + modified solder resist layer" to balance heat dissipation and protection performance.

[0048] S5: Use a stencil to precisely print solder paste onto the pads, with the thickness controlled at 100-150μm, to ensure the quality of subsequent soldering.

[0049] S6: Install the display unit; the display unit includes LED beads and a driver IC, and the driver IC is connected to the pins of the LED beads through copper foil leads; the display units are distributed in an array on the circuit board.

[0050] S7: Reflow soldering, which involves heating the solder paste in a reflow oven to melt it and wet the pads, and then cooling it to form a strong electrical connection.

[0051] In summary, the preparation method of this application has the following advantages; 1. This invention optimizes the substrate system and manufacturing process, enabling stable mass production of 10-30μm linewidths and spacings. The interlayer alignment accuracy is controlled within ±10μm, and the minimum aperture of vias can be reduced to below 30μm. It is perfectly compatible with a full range of high-density small-pitch LED displays in the P0.3-P1.5 range, solving the problems of insufficient wiring accuracy in traditional processes and the difficulty in balancing accuracy and cost in existing high-end processes. It ensures precise interconnection between LED chips and driver ICs, avoiding the risk of cold solder joints and dead LEDs caused by pad alignment deviations.

[0052] 2. Optimize heat dissipation and electrical performance to improve product reliability: This invention uses a customized epoxy resin ceramic powder composite substrate, which takes into account the characteristics of low CTE, high thermal conductivity and low dielectric loss. The thermal conductivity can be increased to 50-200W / m·K, which is highly matched with the thermal expansion coefficient of LED chips. This effectively solves the problems of insufficient heat dissipation of traditional FR-4 substrates and the difficulty in balancing heat dissipation and electrical performance in existing processes. At the same time, it reduces high-frequency signal transmission loss and crosstalk, with the dielectric constant (Dk@1GHz) controlled below 3.0 and the dielectric loss (Df@1GHz) below 0.008, ensuring the signal transmission stability of ultra-high-definition displays and extending the service life of circuit boards and terminal displays.

[0053] 3. Enhanced process compatibility and scalability: The manufacturing process of this invention balances high precision and versatility, enabling 2-10 layer multi-layer wiring and adapting to different integration levels of driver ICs and LED layouts. It can meet the needs of high-end ultra-fine pitch products as well as adapt to the large-scale production of mid-range small pitch products. There is no need to adjust the core process and equipment for different product types, thereby improving production efficiency and broadening the product compatibility range.

[0054] 4. Solving common technical pain points in the industry and enhancing product competitiveness: This invention effectively solves common problems in existing processes such as open / short circuits, poor conductivity of blind via metallization, interlayer expansion and contraction, and high-temperature delamination and aging. It improves the long-term working stability and environmental adaptability of circuit boards, meeting the stringent reliability requirements of high-end fields such as security monitoring and medical displays. At the same time, it takes into account cost and performance advantages, significantly enhancing the market competitiveness of end products and promoting the industrialization and popularization of Mini LED and MicroLED technologies.

[0055] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for fabricating a circuit board for a high-density, small-pitch LED display screen, characterized in that, include: Pretreatment of epoxy resin ceramic powder composite substrate; Pattern Transfer and Etching: Pads and circuit patterns are formed on the surface of an epoxy resin ceramic powder composite substrate through a combination of laser-induced etching and dry etching processes; The epoxy resin ceramic powder composite substrate is sequentially laminated and drilled to form through holes; Install the display unit on the pads.

2. The method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, Pretreatment of the epoxy resin ceramic powder composite substrate includes: First, the epoxy resin ceramic powder composite substrate is baked at a low temperature of 120-130℃ for 1.5-2 hours, and then heated to 150-160℃ for 0.5-1.5 hours to cure. By using plasma surface modification treatment, the oxide layer and impurities on the surface of the epoxy resin ceramic powder composite substrate are removed, so that the surface roughness of the epoxy resin ceramic powder composite substrate is controlled at 0.8-1.2μm.

3. The method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, Pattern transfer and etching, specifically including: Photoresist is coated onto the copper layer on the surface of an epoxy resin ceramic powder composite substrate; The laser power is controlled at 80-100W and the scanning speed is 300-400mm / s. The epoxy resin ceramic powder composite substrate is selectively scanned and irradiated according to a preset trajectory to form the circuit outline and the pad outline. Development removes areas outside the circuit pattern and pads; Using photoresist as a mask, a dry etching process is employed. In a vacuum environment at 45-50℃, a mixed plasma of chlorine and argon is used as the etching medium for 8-12 minutes. After etching, the material is rinsed with deionized water.

4. The method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 3, characterized in that, The volume ratio of chlorine to argon in the chlorine and argon mixed plasma is (3:1) to (5:1).

5. A method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 3, characterized in that, During dry etching using a mixed plasma of chlorine and argon as the etching medium, the etching endpoint is determined by monitoring the attenuation of the CuCl2 signal using mass spectrometry.

6. A method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, When laminating epoxy resin ceramic powder composite substrate, dual cameras are used to position the circuitry of each layer; and during lamination, the lamination temperature is controlled at 170-180℃, the lamination pressure at 2.0-2.5MPa, the lamination heating rate at 5℃ / min, and the lamination time at 60-90 minutes.

7. The method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, Drilling holes in an epoxy resin ceramic powder composite substrate to form vias specifically includes: Drilling using femtosecond lasers; Through-hole filling is performed using a pulse electroplating process, with the pulse current controlled at 1.5-2.5 A / dm. 2 The electroplating temperature of the pulse electroplating process is 35-40℃. The electroplating solution used in the pulse electroplating process includes a base electrolyte, chloride ions, accelerators, inhibitors and leveling agents. After the pulse electroplating process, a secondary curing process is carried out at 140-150℃.

8. A method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, Before installing the display unit, the process also includes: electroplating a high-purity nickel-gold plating layer on the surface of the circuit pattern; coating a semi-modified epoxy acrylate protective layer on the surface of the circuit board; the semi-modified epoxy acrylate protective layer contains a bifunctional structure, with one end of the molecular chain being an acrylate double bond and the other end being an epoxy group.

9. A method for manufacturing a circuit board for a high-density, small-pitch LED display screen according to claim 1, characterized in that, Before installing the display unit, the process includes: using a stencil to precisely print solder paste onto the pads; and reflow soldering after installing the display unit.

10. A circuit board for a high-density, small-pitch LED display screen, characterized in that, It is prepared based on the method for preparing a circuit board for a high-density small-pitch LED display screen according to any one of claims 1-9.

Images