Preparation method of multi-layer high-density flexible circuit board

Abstract

The invention belongs to the technical field of circuit boards, and discloses a preparation method of a multi-layer high-density flexible circuit board, which comprises the following steps: selecting polyimide (PI) as a base material, uniformly depositing a layer of copper foil on the surface of the flexible base material through a full-automatic plating line, and adopting high-performance polyimide (PI) as the base material to prepare the multi-layer high-density flexible circuit board. A femtosecond laser drilling machine is used for achieving connection of micro through holes with the diameter smaller than 20 micrometers and the precision as high as + / -1 micrometer, automatic laminating equipment and the micro through hole technology are combined, dozens of to hundreds of layers of circuits are accurately aligned and laminated, the bendability and adaptability of the circuit board are greatly improved through the design, and the cost is reduced. According to the flexible electronic device, the requirement for high flexibility of the flexible electronic device such as a wearable device and a flexible display screen is met, higher-density circuit integration is achieved, more circuits can be integrated in a limited space, and stronger functions are provided. The limitation that a traditional rigid circuit board cannot adapt to deformation requirements such as bending and folding is effectively overcome, and the electronic equipment can be further miniaturized and lightened.

Description

Technical Field

[0001] The present invention belongs to the technical field of circuit boards, and specifically relates to a method for preparing a multi-layer high-density flexible circuit board. Background Art

[0002] With the rapid development of information technology, electronic devices are evolving towards miniaturization, lightweight, and high performance. In this trend, as the core component of electronic devices, the manufacturing technology of circuit boards has become increasingly prominent. Flexible circuit boards, with their unique flexibility, lightweight, and bendability, have become an indispensable part of modern electronic devices and are widely used in portable electronic devices, medical devices, aerospace, and other fields.

[0003] A circuit board is a very important component in the electronics industry. Its basic function is to miniaturize and visualize circuits and play an important role in the mass production of fixed circuits and the optimization of electrical appliance layouts. A circuit board is a support for electronic components and provides circuit connections for electronic components.

[0004] Some invention patents in the technical field of circuit boards are disclosed in the prior art. Among them, the invention patent with the publication number CN112888165A discloses a method for preparing a flexible printed circuit board, including the following steps: S1. Prefabrication of the shielding layer: Before the heat-conducting resin layer solidifies, press the shielding layer between the protective layer and the heat-conducting resin layer to form the shielding layer of the flexible printed circuit board from the protective layer, the shielding layer, and the heat-conducting resin layer; S2. Cutting: Use a cutting device to preliminarily cut the circuit board substrate layer and the shielding layer, and the length and width ratios of the cut substrate layer and the shielding layer are 0.5 cm - 1.5 cm larger than the length and width of the flexible printed circuit board to be manufactured; S3. Pressing of the first processing board: Apply an adhesive on both sides of the cut substrate layer, and press the copper foil layer and the substrate layer through a pressing device to form a first processing board of copper foil - substrate - copper foil; Beneficial effects: The production process of this preparation method is simple and easy to implement, reducing the number of layers and processes for preparing the flexible printed circuit board, improving the preparation and processing efficiency, reducing the labor intensity, and then improving the product quality through this preparation method.

[0005] However, the above method still has the following defects in actual use: Traditional rigid circuit boards cannot meet the deformation requirements such as bending and folding, which limits their application in flexible electronic devices, and it is difficult to achieve high-density integration in a limited space, resulting in a large volume of electronic devices and unable to meet the miniaturization requirements. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a multi-layer high-density flexible circuit board to solve the problems raised in the above background art.

[0007] To achieve the above object, the present invention provides the following technical solution: A method for preparing a multi-layer high-density flexible circuit board, comprising the following steps:

[0008] Select polyimide (PI) as the substrate, and use a plasma processor to perform surface activation treatment on the substrate to improve the adhesion of the copper foil;

[0009] Deposit a layer of copper foil uniformly on the surface of the flexible substrate through a full-automatic electroplating line. The thickness of the copper foil can be adjusted between 5 μm and 100 μm according to the design requirements by a thickness monitoring system;

[0010] Use a lithography machine to form a high-precision circuit pattern on the copper foil, and remove the copper foil not protected by the photoresist through a chemical etching machine, leaving the required circuit pattern;

[0011] Use a laser drilling machine to form micro-vias with a diameter not exceeding 50 μm, and use a high-pressure water jet cleaning machine to clean the hole walls to ensure no residues;

[0012] Deposit copper uniformly in the micro-vias through high-precision electroplating equipment, and use an electroplating parameter control system to ensure the electrical connectivity and thickness consistency of the vias;

[0013] Stack multiple inner-layer circuit boards, and use a hot press to laminate them through a hot pressing process to form a multi-layer circuit board, and use epoxy resin to ensure the interlayer adhesion;

[0014] On the outer copper foil of the multi-layer structure, form an outer-layer circuit pattern through a lithography machine and a developer, and use a chemical etching machine to etch and remove the unprotected copper foil;

[0015] Form vias or micro-vias on the outer-layer circuit board, and use electroplating equipment for electroplating to ensure the electrical connectivity of different-layer circuits;

[0016] Coat a polyimide protective film on the surface of the circuit board, and perform metalization surface treatment to improve the solderability and stability of the circuit;

[0017] Cut the prepared multi-layer high-density flexible circuit board with a numerical control cutting machine and detect it with an electrical performance tester to ensure that the functions and quality meet the design requirements.

[0018] As a further solution of the present invention: The laser drilling technology uses a femtosecond laser drilling machine, which can achieve hole connections with a diameter less than 20 μm and a precision of up to ±1 μm, meeting the requirements of high-density circuit boards for small size and ultra-high precision.

[0019] As a further solution of the present invention: The high-precision electroplating technology precisely controls parameters such as the concentration, temperature, and current density of the electroplating solution through an automatic control system, uniformly deposits a copper layer with a consistent thickness in the micro-vias, uses an X-ray thickness gauge to detect the thickness, ensures the reliability of electrical connections, and improves the stability of the circuit board.

[0020] As a further solution of the present invention: The multi-layer high-density integrated design combines an automatic lamination device with micro-via technology to precisely align and stack dozens to hundreds of layers of circuits, and uses a hot press for lamination to integrate more circuits into a smaller space, providing a higher circuit density and stronger functions.

[0021] As a further solution of the present invention: The flexible substrate selects high-performance polyimide (PI), which improves the bendability and adaptability of the circuit board and meets the requirements of flexible electronic devices for high flexibility.

[0022] As a further solution of the present invention: The surface treatment is activated by a plasma processor, and the protective layer technology uses an automatic coater to coat a high-temperature and corrosion-resistant coating, which improves the oxidation resistance and corrosion resistance of the circuit board, ensures the welding performance, and is tested by a salt spray test machine and a high-temperature aging oven to ensure stability during long-term use.

[0023] As a further solution of the present invention: After the circuit pattern is formed, an automatic optical inspection device (AOI) is used to perform high-precision inspection on the circuit pattern to ensure the accuracy and integrity of the circuit pattern and reduce the defect rate.

[0024] As a further solution of the present invention: After the multi-layer circuit board is laminated, an X-ray detection system is used to perform non-destructive detection on the filling quality and electrical connectivity of the micro-vias to ensure the reliability of interlayer connections and the quality of the overall circuit board.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The present invention uses high-performance polyimide (PI) as the substrate and uses a femtosecond laser drilling machine to achieve micro-via connections with a diameter less than 20μm and a precision of up to ±1μm. Combining an automatic lamination device with micro-via technology, dozens to hundreds of layers of circuits are precisely aligned and stacked. This design not only greatly improves the bendability and adaptability of the circuit board, meets the requirements of flexible electronic devices such as wearable devices and flexible displays for high flexibility, but also realizes higher-density circuit integration, can integrate more circuits in a limited space, and provides stronger functions. This effectively overcomes the limitation that traditional rigid circuit boards cannot adapt to deformation requirements such as bending and folding, enabling electronic devices to be further miniaturized and lightweight.

[0027] 2. During the preparation process of the present invention, through high-precision electroplating technology and an automatic control system, the electroplating parameters are precisely controlled, and a copper layer with a uniform thickness is deposited in the micro-vias. The thickness is detected by an X-ray thickness gauge to ensure the reliability of electrical connection. At the same time, a plasma processor is used for surface activation to improve the adhesion of the copper foil, and a high-temperature and corrosion-resistant coating is applied to enhance the oxidation resistance and corrosion resistance of the circuit board. In addition, through an automatic optical inspection instrument (AOI), the circuit pattern is detected with high precision, and an X-ray detection system is used for non-destructive detection of the filling quality and electrical connectivity of the micro-vias, further ensuring the precision, integrity, and reliability of the interlayer connection of the circuit board. These measures jointly ensure the stability and quality of the circuit board during long-term use and meet the strict requirements of high-performance electronic devices for core components. Detailed implementation manners

[0028] The following will describe clearly and completely the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] The embodiment of the present invention provides a method for preparing a multi-layer high-density flexible circuit board, including the following steps:

[0030] Select polyimide (PI) as the base material, and use a plasma processor to perform surface activation treatment on the base material to improve the adhesion of the copper foil;

[0031] Deposit a layer of copper foil uniformly on the surface of the flexible base material through a fully automatic electroplating line. The thickness of the copper foil can be adjusted between 5 μm and 100 μm according to the design requirements through a thickness monitoring system;

[0032] Use a lithography machine to form a high-precision circuit pattern on the copper foil, and remove the copper foil not protected by the photoresist through a chemical etching machine to retain the required circuit pattern;

[0033] Use a laser drilling machine to form micro-vias with a diameter not exceeding 50 μm, and use a high-pressure water jet cleaning machine to clean the hole walls to ensure no residues;

[0034] Deposit copper uniformly in the micro-vias through high-precision electroplating equipment, and use an electroplating parameter control system to ensure the electrical connectivity and thickness consistency of the vias;

[0035] Stack multiple inner-layer circuit boards, and use a hot press to laminate them through a hot pressing process to form a multi-layer circuit board, and use epoxy resin to ensure the interlayer adhesion;

[0036] On the outer copper foil of the multi-layer structure, an outer circuit pattern is formed by a lithography machine and a developing machine, and an unprotected copper foil is etched away using a chemical etching machine;

[0037] Through holes or micro-vias are formed on the outer circuit board, and electroplating is carried out using electroplating equipment to ensure the electrical connectivity of circuits at different levels;

[0038] A polyimide protective film is coated on the surface of the circuit board, and a metallization surface treatment machine is used for treatment to improve the solderability and stability of the circuit;

[0039] The prepared multi-layer high-density flexible circuit board is cut by a numerical control cutting machine and tested by an electrical performance tester to ensure that the functions and quality meet the design requirements.

[0040] The laser drilling technology uses a femtosecond laser drilling machine, which can achieve hole connections with a diameter less than 20μm and a precision of up to ±1μm, meeting the requirements of high-density circuit boards for small sizes and ultra-high precision. Micro-holes with a diameter as small as 50μm can be processed with high precision using laser drilling technology to ensure that micro-vias in high-density circuit boards can be processed. The laser drilling technology has excellent precision and a small heat-affected zone, is suitable for processing flexible materials, and ensures the uniformity and high quality of the hole diameter. Through further cleaning treatment, contaminants in the holes are removed to ensure uniform deposition of the electroplated copper layer;

[0041] The high-precision electroplating technology precisely controls parameters such as the concentration, temperature, and current density of the electroplating solution through an automatic control system, and a copper layer with a uniform thickness is deposited uniformly in the micro-vias. The thickness is detected using an X-ray thickness gauge to ensure the reliability of electrical connections and improve the stability of the circuit board. The multi-layer high-density integrated design combines an automatic lamination device with micro-via technology to precisely align and stack dozens to hundreds of layers of circuits, and uses a hot press for lamination to integrate more circuits into a smaller space, providing higher circuit density and stronger functions. The flexible substrate selects high-performance polyimide (PI), which improves the bendability and adaptability of the circuit board and meets the requirements of flexible electronic devices for high flexibility. The surface treatment is carried out by a plasma treatment machine for activation, and the protective layer technology uses an automatic coating machine to coat a high-temperature and corrosion-resistant coating, which improves the oxidation resistance and corrosion resistance of the circuit board and ensures the welding performance;

[0042] In this method, polyimide (PI) is selected as the substrate of the circuit board. These materials are widely used in the production of flexible circuit boards due to their excellent mechanical strength, thermal stability, and good bendability, enhancing the adhesion between the substrate surface and the copper foil and ensuring uniform deposition of the electroplated copper foil on the substrate;

[0043] Through salt spray test machine and high-temperature aging oven tests, the stability during long-term use is ensured. After the circuit pattern is formed, an automatic optical inspection instrument (AOI) is used to perform high-precision inspection on the circuit pattern to ensure the accuracy and integrity of the circuit pattern, reduce the defect rate. After the multi-layer circuit board is laminated, an X-ray detection system is used to perform non-destructive inspection on the filling quality and electrical connectivity of the micro-vias to ensure the reliability of the interlayer connection and the quality of the overall circuit board;

[0044] Multiple inner-layer circuit boards are stacked and a multi-layer structure is formed through a hot pressing process. This process requires the use of high-performance adhesives or connection materials to ensure good adhesion between layers. The electrical connection between layers is achieved through precise micro-vias, ensuring that the multi-layer circuit board can provide a high circuit density within a limited space;

[0045] The formation of the outer-layer circuit pattern adopts the same photolithography and development processes as the inner-layer circuit, and the unprotected copper foil is removed through etching. The through-holes or micro-vias formed on the outer-layer circuit board are electrically connected to the internal layer through the electroplating process. The protective film coating technology for the outer layer, by coating a protective film, increases the antioxidant and corrosion resistance of the circuit board and improves the soldering performance to ensure stability during long-term use;

[0046] Through electroplating or chemical deposition technology, a layer of copper foil is deposited on the surface-treated flexible substrate. The thickness of the copper foil can be precisely adjusted according to design requirements to adapt to the current-carrying requirements of different application scenarios. The photolithography process is used to accurately transfer the circuit pattern onto the surface of the copper foil, and the formation of the protective layer is achieved by coating photoresist and exposing and developing it to ensure the accuracy of the circuit pattern. The etching process ensures the integrity of the conductive path of the circuit while removing the copper foil parts not protected by the photoresist;

[0047] Plasma treatment parameters: Oxygen and argon are mixed in a specific ratio, the chamber pressure is maintained at 0.5 - 1.0 Torr, the radio frequency power is set at 500 - 1000 W, the treatment time is controlled within 1 - 5 minutes, and the substrate temperature is maintained at 40 - 60 °C;

[0048] Details of the copper foil deposition process: Use a fully automatic electroplating line, copper sulfate, sulfuric acid, additives, etc., are mixed in a specific ratio, the current density is controlled at 10 - 50 A / dm2, and the electroplating speed is adjusted at 5 - 20 μm / min;

[0049] Process control of the chemical etching machine: Use acidic copper chloride solution, the concentration is controlled at 1.5 - 2.5 mol / L. The etching temperature is maintained at 40 - 60 °C, the etching time is set at 30 - 120 seconds, and the etching rate is controlled at 5 - 10 μm / min;

[0050] Technical details of the laser drilling machine: Use a femtosecond laser drilling machine, control the laser wavelength at 1030 - 1064 nm, control the pulse energy at 10 - 100 μJ, set the repetition frequency at 100 kHz - 1 MHz, and adjust the drilling speed at 100 - 1000 holes per second;

[0051] Processing details of the metallization surface treatment machine: Adopt the electroless nickel - gold plating process, use nickel sulfate as the chemical reagent, control the processing time at 10 - 30 minutes, and maintain the temperature at 40 - 60 °C.

[0052] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a multi-layer high-density flexible circuit board, characterized in that: The following steps are involved: Polyimide (PI) was selected as the substrate, and the surface of the substrate was activated by a plasma treatment machine to improve the adhesion of the copper foil; A layer of copper foil is evenly deposited on the surface of the flexible substrate through a fully automatic electroplating line. The thickness of the copper foil can be adjusted between 5μm and 100μm according to design requirements through a thickness monitoring system; A photolithography machine is used to form a high-precision circuit pattern on the copper foil, and a chemical etching machine is used to remove the copper foil not protected by the photoresist to retain the desired circuit pattern; A laser drilling machine is used to form micro-through holes with a diameter of no more than 50μm, and a high-pressure water jet cleaning machine is used to clean the hole wall to ensure that there is no residue; Copper is uniformly deposited in micro-vias using high-precision electroplating equipment, and the electroplating parameter control system is used to ensure the electrical connectivity and thickness consistency of the vias; Multiple inner-layer circuit boards are stacked and laminated into multi-layer circuit boards using a heat press machine through a heat press process, and epoxy resin is used to ensure interlayer adhesion; On the outer copper foil of the multi-layer structure, an outer circuit pattern is formed by a photolithography machine and a developer, and the unprotected copper foil is removed by etching using a chemical etching machine; Form through holes or micro-through holes on the outer circuit board and use electroplating equipment to ensure the electrical connectivity of different levels of circuits; Coat the circuit board with a polyimide protective film and perform metallization surface treatment to improve the solderability and stability of the circuit; The prepared multi-layer high-density flexible circuit boards are cut by CNC cutting machines and tested by electrical performance testers to ensure that their functions and quality meet the design requirements.

2. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: The laser drilling technology uses a femtosecond laser drilling machine, which can achieve channel connection with a diameter less than 20μm and an accuracy of up to ±1μm, meeting the requirements of high-density circuit boards for tiny size and ultra-high precision.

3. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: The high-precision electroplating technology uses an automatic control system to accurately control parameters such as the concentration, temperature, and current density of the electroplating solution, uniformly deposits a copper layer of consistent thickness in the micro-through holes, and uses an X-ray thickness gauge to detect the thickness, thereby ensuring the reliability of the electrical connection and improving the stability of the circuit board.

4. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: The multi-layer high-density integrated design combines automatic lamination equipment with micro-through-hole technology to precisely align and stack dozens to hundreds of layers of circuits, and uses a heat press to laminate them, integrating more circuits into a smaller space, providing higher circuit density and stronger functions.

5. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: The flexible substrate is made of high-performance polyimide (PI), which improves the bendability and adaptability of the circuit board and meets the demand for high flexibility of flexible electronic devices.

6. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: The surface treatment adopts a plasma treatment machine for activation, and the protective layer technology adopts an automatic coating machine to apply a high-temperature resistant and corrosion-resistant coating, which improves the oxidation resistance and corrosion resistance of the circuit board and ensures the welding performance. It passes the salt spray test machine and high-temperature aging box test to ensure stability in long-term use.

7. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: After the circuit pattern is formed, an automatic optical inspection device (AOI) is used to perform high-precision inspection on the circuit pattern to ensure the accuracy and integrity of the circuit pattern and reduce the defect rate.

8. The method for preparing a multi-layer high-density flexible circuit board according to claim 1, characterized in that: After lamination of multi-layer circuit boards, an X-ray inspection system is used to perform non-destructive inspection of the filling quality and electrical connectivity of micro-vias to ensure the reliability of inter-layer connections and the quality of the overall circuit board.