Rigid-flex combined board manufacturing method, rigid-flex combined board and keyboard

Abstract

The application relates to the technical field of rigid-flexible composite printed circuit boards, and discloses a rigid-flexible composite board manufacturing method, a rigid-flexible composite board and application of the rigid-flexible composite board in a keyboard. The method comprises the following steps: providing a flexible substrate comprising a first substrate layer and a first circuit layer, and a rigid substrate comprising a second substrate layer and second and third circuit layers; forming an insulating glue with a through hole on the surface of the rigid substrate, and filling the through hole with conductive material; bending the flexible substrate reversely, so that one end of the first circuit layer is pressed against the position of the through hole, and the other end extends outward; realizing electrical connection with the second circuit layer through the conductive material; forming a protective layer covering the first circuit layer, and releasing the flexible area through local cutting. The rigid-flexible composite board formed by the method is stable in connection and suitable for high-density or thin keyboard devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rigid-flexible composite printed circuit board, and in particular to a rigid-flexible composite board applied to a keyboard and a manufacturing method thereof. BACKGROUND

[0002] With the development trend of increasingly thin and multi-functional integration of electronic devices, rigid-flexible composite boards (Rigid-Flex PCB) have been widely used in various high-end electronic products, such as smart phones, notebook computers, wearable devices, and keyboard modules, because they have the structural advantages of rigid circuit boards and flexible circuit boards. Such composite boards can effectively reduce the use of connectors and flat cables, improve electrical performance and structural reliability, and help to reduce the size and simplify the assembly process.

[0003] Traditional rigid-flexible composite board manufacturing methods mostly use a laminated structure, which stacks rigid and flexible materials in predetermined areas and combines them through high-temperature hot pressing. However, such methods have several technical challenges, such as stress concentration caused by the difference in the thermal expansion coefficient of the materials, insufficient reliability of the flexible area, and high process complexity and low yield caused by the multi-layer structure.

[0004] In addition, in some application scenarios, especially keyboard modules that need to be frequently operated and repeatedly bent, there are higher requirements for the stability and conduction quality of the flexible area. In traditional processes, the flexing area is usually located in the inner layer of the laminated structure, and the design for releasing and protecting the flexible substrate and conductor layer lacks flexibility, limiting the further optimization of product performance.

[0005] Therefore, the industry urgently needs a more simplified and reliable manufacturing method that can effectively release the flexible area of the rigid-flexible composite board to provide more stable electrical connections and longer bending life, and meet the development needs of high-density modular electronic products. SUMMARY

[0006] The present application provides a manufacturing method of a rigid-flexible composite board and a rigid-flexible composite board formed thereby, aiming to solve the problems of insufficient release of the flexible area, complex structure, high process difficulty, and insufficient electrical connection reliability in the prior art, and to improve the flexible structure performance and electrical performance stability of the rigid-flexible composite board in actual application.

[0007] According to an embodiment of the present application, a manufacturing method of a rigid-flexible composite board is provided, comprising: providing a flexible substrate, the flexible substrate comprising a first substrate layer and a first circuit layer formed on one side of the first substrate layer;

[0008] The rigid substrate includes a second substrate layer, and a second circuit layer and a third circuit layer formed on both sides of the second substrate layer respectively; an insulating adhesive is formed on the surface of the rigid substrate, the insulating adhesive has at least one through hole, and the through hole is filled with a conductive material; the flexible substrate is bent along the length direction thereof, one end of the first circuit layer is pressed on the position of the through hole, and the other end extends outward; the conductive material forms an electrical connection between the first circuit layer and the second circuit layer; a protective layer is formed on the surface of the second circuit layer and covers the exposed first circuit layer; the protective layer above the insulating adhesive is cut to form a cutting area and expose part of the insulating adhesive, so as to release the flexible area of the first circuit layer and expose the first substrate layer, thereby forming a rigid-flexible combination board.

[0009] Through the above structure and process design, the flexible substrate is bent and attached to the surface of the rigid substrate, and the conductive material is filled in the through hole to realize electrical connection, so that the flexible circuit can maintain bendability while ensuring stable overall electrical performance. In detail, by forming an insulating adhesive layer on the surface of the rigid substrate and setting a through hole, the first circuit layer of the flexible substrate and the second circuit layer of the rigid substrate are firmly electrically connected by filling the through hole with a conductive material. The formed conductive structure has stable contact area and covering property, and has more consistency and anti-interference ability than traditional plug-in or soft cable welding method, effectively reducing contact resistance and signal interference, thereby ensuring stable transmission of overall electrical performance. After completing the circuit connection and forming the protective layer, the extension area of the flexible substrate (i.e. the flexible area of the first circuit layer) is partially exposed and its restricted structure is released by locally cutting the protective layer. This design avoids the coverage and compression of the flexible area by the protective layer, so that the area restores the function of free bending. The released area can realize small bending radius and high degree of freedom of dynamic action, which is beneficial to flexible wiring or folding assembly of the product in limited space, thereby significantly improving the mobility of the flexible area. In addition, if the flexible area is covered by a hard protective layer, mechanical stress may accumulate at the boundary due to repeated bending during long-term use, thereby causing circuit open or short circuit failure. By locally cutting and releasing the flexible structure, the flexible substrate can be naturally bent, eliminating the forced compression of the structure, thereby effectively dispersing the stress concentration area, prolonging the flex life, and preventing reliability problems caused by stress accumulation. In summary, the present application adopts the process of "pre-bending + cutting release", which integrates the flexible circuit and the rigid structure, omits the traditional slot, connector or welding point structure, not only simplifies the assembly process and reduces the number of parts, but also eliminates the risk of poor contact caused by plugging or vibration, which helps to improve product durability and overall assembly convenience.

[0010] The application also provides a rigid-flexible combined board manufactured by the method, which comprises a rigid substrate, a flexible substrate, a through hole penetrating through the insulating adhesive and a conductive material; the flexible substrate is bent and adhered to the surface of the rigid substrate through the insulating adhesive, and an electrical connection is formed at the through hole; the surface of the second circuit layer is provided with a protective layer covering the flexible circuit part, and the protective layer is partially cut, and the first circuit layer retains the flexibility.

[0011] In addition, in order to further exert the advantages of the electrical connection and flexible wiring of the rigid-flexible combined board, the application also provides a keyboard which uses the rigid-flexible combined board as the main connection structure to realize the electrical connection and mechanical connection between the key module and the control circuit board, thereby improving the compactness and wiring flexibility of the overall structure. Therefore, the high-density signal path layout can be completed in a limited space, the use of traditional flexible flat cable and connector is avoided, and the assembly convenience, wiring reliability and structural durability are greatly improved. It is especially suitable for light and thin electronic equipment or high-integration input module.

[0012] In summary, the technical scheme of the application not only simplifies the manufacturing process of the traditional rigid-flexible combined board, but also improves the reliability of the flexible area and the overall usability of the product, and is especially suitable for modular electronic products (such as keyboards, wearable devices, etc.) with compact structure and frequent operation, and has good industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical scheme in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0014] Among them:

[0015] Figure 1 is a flow chart of the rigid-flexible combined board manufacturing method provided by the embodiment of the technical scheme;

[0016] Figure 2 is a sectional view of the flexible substrate provided by the embodiment of the technical scheme;

[0017] Figure 3 is a sectional view of the rigid substrate provided by the embodiment of the technical scheme;

[0018] Figure 4 is a sectional view of the rigid substrate after the insulating adhesive is formed on the rigid substrate of Figure 3

[0019] Figure 5 ​is a sectional view after the flexible substrate is bent and electrically connected to the rigid substrate;

[0020] Figure 6 is a sectional view of forming a protective layer on the first circuit layer and the second circuit layer of Figure 5 ;

[0021] Figure 7 is a sectional view after the protective layer of Figure 6 is cut;

[0022] Figure 8 is a top view of the cutting area of cutting the protective layer of Figure 6 ;

[0023] Figure 9 is a sectional view of the rigid-flex combined board provided by the technical solution embodiment.

[0024] Main component symbol explanation

[0025] DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0027] Please refer to Figure 1 , the flow chart of the rigid-flex combined board manufacturing method provided by the technical solution embodiment, mainly includes the following steps:

[0028] Step 1 S1, please refer to Figure 2, provide a flexible substrate 11, which includes a first substrate layer 111 and a first circuit layer 112 formed on one side of the first substrate layer 111. In a preferred embodiment, the material of the first substrate layer 111 is preferably a polyimide (PI) film with excellent flexibility, thermal stability and electrical insulation, and other high-performance flexible materials such as polyester (PET), liquid crystal polymer (LCP) or other high-performance flexible materials can also be selected according to application requirements. Specifically, the polyimide film has excellent flexibility, which can make the first substrate layer 111 remain stable deformation during repeated bending process, avoid cracks or delamination, and thus ensure the long-term bending reliability of the rigid-flexible combined structure; its high temperature resistance makes it not easy to deform or deteriorate during subsequent manufacturing processes such as hot pressing, welding or electroplating, which helps to improve process stability and product yield. In addition, polyimide has excellent dielectric strength and volume resistivity, which can effectively isolate signal interference between different conductive paths, further improving the electrical performance stability of the overall circuit layer. When applied to keyboards or other lightweight electronic devices, its lightweight characteristics also help to design the overall product to be thin and lightweight. Therefore, polyimide is preferred as the material of the first substrate layer 111, which not only improves process adaptability and mechanical properties, but also ensures the structural reliability and long-term performance of the finished product. The thickness of the first substrate layer 111 can be adjusted according to the structural requirements of the terminal product, and the common thickness range is 25μm to 100μm. Specifically, the first substrate layer 111 with a thickness of 25μm~50μm is suitable for terminal products with high flexibility and limited space, such as: (1) wearable devices (such as smart watches, health trackers), which can achieve small radius bending and skin structure fitting; (2) folding display terminals (such as folding phones, scroll screens), which need to have high flexibility and multiple dynamic bending capabilities; (3) ultra-thin keyboard modules, which have strict limitations on keycap height and substrate thickness, and need to control the overall thickness within a very small range. The first substrate layer 111 with a thickness of 75μm~100μm is more suitable for applications that emphasize mechanical support and thermal stability, such as: (1) vehicle control modules or soft and hard combined interfaces in industrial equipment, which need to resist external vibration and high temperature; (2) standard keyboards, laptop input modules, which have relatively low flexibility requirements but need to maintain certain structural stability and reliable electrical connection; (3) consumer electronic products that need to balance assembly efficiency and flex life interconnection components. Therefore, by selecting a first substrate layer 111 with an appropriate thickness according to the structural space, use situation and mechanical performance requirements of different terminal products, the compatibility, reliability and cost control ability of the rigid-flexible combined board in actual products can be improved. The first circuit layer 112 is formed on one side of the first substrate layer 111, that is, the surface of the flexible substrate 11.The first circuit layer 112 is usually made by etching a copper foil with a predetermined circuit pattern to realize subsequent signal transmission function. The thickness of the first circuit layer 112 can be selected as 12 μm, 18 μm, 35 μm, or increased to more than 35 μm according to the need of large current design, in other words, the thickness of the first circuit layer 112 can be determined according to the trade-off between current carrying capacity and bending performance. The circuit pattern is obtained by steps of exposure, development and etching, and can be further subjected to anti-oxidation treatment (such as OSP) or surface plating (such as ENIG) to enhance the soldering reliability. In the specific manufacturing process, the first circuit layer 112 can be directly subjected to pattern transfer by the flexible material of copper foil, or the required circuit structure can be formed by the method of "dry film, electroplating, stripping film, etching". In addition, in order to ensure the reliability of the circuit in the subsequent bending process, the minimum line width / line spacing (Line / Space) is recommended to be controlled above 75 μm to avoid the risk of micro-cracks or poor conduction.

[0029] In addition, in order to facilitate subsequent bending and pressing on the rigid substrate 12, the flexible substrate 11 should reserve sufficient length, and one end of the first circuit layer 112 is reserved with a connection pad, which will be used for conduction connection with the rigid substrate 12, and the other end of the first circuit layer 112 is reserved with an extension circuit as a circuit area for external electrical connection. Alternatively, in order to increase the mechanical strength and bending life, an insulating cover layer (not shown in the figure) such as cover glue, photosensitive polyimide or photosensitive solder resist ink can be formed on the first circuit layer 112, but the connection pad area should be avoided to facilitate subsequent electrical bonding. In summary, by providing the flexible substrate 11 with the above structure, good electrical performance, flexibility and processability are ensured in the subsequent processing process, which provides a structural basis for realizing high reliability of rigid-flex combination in the present application.

[0030] The second step S2, please refer to Figure 3, provide rigid substrate 12, the rigid substrate 12 includes the second substrate layer 121 and the second circuit layer 122 and the third circuit layer 123 formed on both sides of the second substrate layer 121. In a preferred embodiment, the second substrate layer 121 is a hard material with structural support and dimensional stability, used to provide mechanical strength and assembly base of the circuit board. The second substrate layer 121 can be selected from glass fiber reinforced epoxy (FR-4), aluminum substrate, or ceramic substrate, etc. Preferably, the thickness of the second substrate layer 121 can be adjusted according to the structural requirements of the end product, if the end product is a general consumer electronics, FR-4 material can be selected, the thickness can be 0.4mm to 1.6mm. If used in high heat dissipation requirements, for example: car lamp module, high-power electronic devices, then can be selected using aluminum-based or ceramic substrate, to improve the thermal conductivity and dimensional stability. The second circuit layer 122 and the third circuit layer 123 are formed on the upper surface and the lower surface of the second substrate layer 121, respectively, for providing double-sided circuit connection capability to meet the access requirements of multifunctional components. Similarly, the second circuit layer 122 and the third circuit layer 123 can be made by copper foil patterning process, the common thickness is 1 / 2 oz (about 18μm) or 1 oz (about 35μm), also can be selected according to the electrical design requirements. Among them, the second circuit layer 122 as the main interface connected with the flexible substrate 11, can reserve connection pads in the circuit pattern, the position corresponds to the through hole formed subsequently, to establish electrical connection relationship with the first circuit layer 112. The third circuit layer 123 is used to connect the control circuit or module, which can realize the intercommunication between upper and lower layers through through hole 131 or blind hole with the second circuit layer 122. Preferably, the second circuit layer 122 and the third circuit layer 123 can be differentially wired according to application requirements, and the ground layer / power layer design can be impedance controlled or heat spreading designed according to the design rules.

[0031] In the process of forming the rigid substrate 12, the circuit layer pattern process can include the following steps:

[0032] Copper coating → dry film coating → exposure and development → copper and tin electroplating → film removal etching → tin removal → surface treatment (such as OSP, ENIG, etc.); If multi-layer board structure is needed, laminated inner circuit and medium can be added, drilled and through hole 131 electroplated to form multi-layer interconnection. The rigid substrate 12 not only provides mechanical strength, but also serves as a functional circuit platform capable of carrying main control IC, power module, signal processor and other components. Through double-sided circuit design, the wiring density and space utilization are improved, and modular assembly is facilitated. The rigid substrate 12 formed by this structure provides a solid and reliable basic structure for the subsequent attachment, electrical connection and overall packaging of the flexible substrate 11, which helps to improve the overall performance and process yield of the rigid-flexible combined board.

[0033] Third S3, see Figure 4An insulating adhesive 13 is formed on the surface of the rigid substrate 12, and the insulating adhesive 13 has at least one through hole 131 filled with a conductive material 14. The insulating adhesive 13 is used for electrical isolation and structural fixation, and also serves as an intermediate medium for connecting the flexible substrate 11. The material of the insulating adhesive 13 can be a polyimide adhesive (PI adhesive), an epoxy resin adhesive, or a heat-pressed photosensitive insulating adhesive 13, etc. The insulating adhesive 13 can be formed by one of the following methods: dispensing, attaching a pre-made dry film, screen printing, etc., and has sufficient mechanical strength and electrical insulation after being heated or ultraviolet cured. At least one through hole 131 is formed in the insulating adhesive 13, and the through hole 131 is used to establish electrical connection between the rigid substrate 12 and the flexible substrate 11. The through hole 131 can be formed by the following methods: (1) laser drilling: suitable for high-precision and small-diameter layout, and the hole diameter can be controlled to be 50-150 μm; (2) mechanical drilling or punching: suitable for larger hole diameters and lower processing cost requirements; if the insulating adhesive 13 is a photosensitive material, the opening can also be formed by pattern exposure and development. After the through hole 131 is formed, the through hole 131 needs to be filled with a conductive material 14 to realize the conductive connection of the upper and lower circuit layers. In this embodiment, the conductive material 14 can be a filled conductor, specifically silver paste, conductive copper paste, or graphene-modified silver paste, which is filled into the through hole 131 by screen printing, dispensing, or doctor blade coating, and then solidified and conductive by heat curing or sintering process, has good contact performance and simple processing, and is suitable for flexible attachment structures. When the conductive material 14 is graphene-modified silver paste, the added graphene content is 0.5-3 wt%, which further enhances the comprehensive performance of the conductive material 14 on the basis of ensuring the conductivity of the silver paste body and the process adaptability. In particular, the ductility and flexibility of the silver paste can be effectively improved, so that it is not easy to crack during solidification or thermal cycling, which is very suitable for the bending requirement in this application, can improve the mechanical compliance and bending life of the through-hole conductive structure, and the resistance change rate is less than 5% after 500 times of bending. In another embodiment, the conductive material 14 can be a metal deposition conductor, that is, the conductive material 14 can be formed by electroplating or chemical plating. For example, chemical copper deposition can be performed on the inner wall of the through hole 131, and then electroplating thickening is performed to form a conductive column. Since this conductive column structure has the advantages of good conductivity, strong adhesion, and suitability for batch automatic process, it is particularly suitable for use in product structures requiring high reliability. No matter what method is used to form the conductive material 14, the filled conductive material 14 needs to ensure effective and reliable contact with the second circuit layer 122, and has good conductive impedance and thermal stability to ensure the long-term reliability of the electrical channel formed after the flexible substrate 11 is attached.

[0034] After this step, the rigid substrate 12 has an electrical connection via structure that can be used for subsequent pressing of the flexible substrate 11, laying the foundation for subsequent bending.

[0035] In the fourth step S4, please refer to Figure 5 The flexible substrate 11 is bent along its length direction, so that one end of the first circuit layer 112 is pressed on the position corresponding to the via hole 131, and the other end of the first circuit layer 112 extends outward.

[0036] In the fifth step S5, the first circuit layer 112 and the second circuit layer 122 are electrically connected by using the conductive material 14. Specifically, the so-called "extending outward" means that after the flexible substrate 11 is bent, the first substrate layer 111 is folded to stack, so that one end of the first circuit layer 112 not in contact with the conductive material 14 is exposed. In this embodiment, one end of the flexible substrate 11 includes the connection side 113 of the first circuit layer 112, so that the connection side 113 is in a bent state to be accurately positioned and pressed on the corresponding via hole 131 of the insulating glue 13 on the surface of the rigid substrate 12. In order to be flexible and accurate in positioning, the bending angle of the flexible substrate 11 is not greater than 180 degrees, preferably, the bending angle can be 180 degrees, that is, the flexible substrate 11 is in a U-shaped reverse folding state or an approximately folded state. Using this bending angle setting can help the first circuit layer 112 of the flexible substrate 11 to be accurately pressed on the corresponding position of the rigid substrate 12, avoiding problems such as contact deviation and abnormal conduction caused by insufficient or excessive bending. Among them, although the bending angle of 180 degrees reaches the maximum flexing state when deformed, since the first substrate layer 111 preferably uses a material such as polyimide (PI) that has flexibility, the mechanical compliance and bending durability of the flexible region are effectively ensured, avoiding the risk of material fatigue or short circuit. Therefore, the above-mentioned bending angle design not only ensures the structural matching precision, but also enhances the flexibility and reliability of the overall assembly, and is particularly suitable for terminal application scenarios with limited space or high requirements for circuit arrangement precision. At this time, the flexible substrate 11 is turned over from the original circuit layer downward to the circuit layer upward, so that the first circuit layer 112 and the second circuit layer 122 can form a vertical electrical connection path through the conductive material 14. The other end of the flexible substrate 11 remains in an outwardly extending state for connection with a subsequent control circuit board, a power module or an external connector. Further, as shown in Figure 5As shown, the flexible substrate 11 has been folded in half at this time, so that one end of the first circuit layer 112 directly contacts the conductive material 14 to form an electrical connection, while the other end of the first circuit layer 112 is folded upward to remain outwardly extending. Preferably, the pressing action can be performed by thermal bonding or lamination equipment to achieve good contact between the first circuit layer 112 and the conductive material 14. To ensure reliable bonding and conduction, an appropriate thermal pressure and temperature can be applied to the electrical connection area, for example, 150°C to 180°C, 12 MPa, and maintained for tens of seconds to facilitate the flow, solidification or bonding of the conductive adhesive or metal paste. In this step, the first substrate layer 111 acts as a structural support portion, providing flexible cushioning when bending to ensure that the circuit does not break due to stress concentration. The flexible material such as polyimide used has good flex life and is suitable for withstanding multiple or long-term bending operations. Through the structural design and reverse bending process of this step, not only is the electrical path effectively shortened, but also additional connectors or welding steps are omitted, improving electrical performance, saving space, and significantly improving the structural strength and manufacturability of the rigid-flexible bonding area. In this step, the so-called "rigid-flexible bonding area" refers to the composite connection site formed by the bending of one end of the flexible substrate 11 to the surface of the rigid substrate 12 and the electrical connection between the conductive material 14 and the second circuit layer 122.

[0037] In the sixth step S6, referring to Figure 6 A protective layer 15 is formed on the surface of the second circuit layer 122, covering the exposed first circuit layer 112. In this embodiment, the protective layer 15 not only covers the second circuit layer 122, but also extends to cover part of the first circuit layer 112 that has been pressed onto the via 131, providing the necessary mechanical fixation and electrical insulation functions. The protective layer 15 can be made of one of the following materials: (1) photosensitive solder mask - has excellent adhesion and insulation, and can be patterned after exposure and development; (2) coverlay - such as polyimide substrate with a hot melt adhesive layer, suitable for flexible circuit packaging; (3) photosensitive polyimide - can be precisely patterned and has high thermal stability and mechanical strength. In a preferred embodiment, the protective layer 15 can be formed by screen printing or dry film attachment, and appropriate openings or closed areas can be set according to the circuit pattern to ensure that it can effectively cover the circuit without affecting the electrical connection or subsequent processes.

[0038] In detail, the functions of the protective layer 15 include, but are not limited to: (1) preventing circuit oxidation or moisture, improving long-term stability of the circuit; (2) enhancing the mechanical stability of the circuit, especially at the reverse bending junction, preventing peeling or delamination; (3) avoiding short circuit welding, for solder mask protection, facilitating subsequent module assembly and welding operation; (4) providing insulation shielding for specific areas to prevent electromagnetic interference (EMI) or electrostatic discharge (ESD) problems.

[0039] After this step, the electrical connection part of the rigid-flexible junction area is well protected, providing a stable structural foundation for subsequent molding, cutting and functional integration.

[0040] Step 7 S7, please refer to Figures 7 to 9 Cut the protective layer 15 above the insulating glue 13 to form a cutting area A and reveal part of the insulating glue 13, release the flexible area B of the first circuit layer 112, and expose the first substrate layer 111, thereby forming a rigid-flexible combination board 10. In this embodiment, as shown in Figure 8 According to the cutting area A, the protective layer 15 is partially cut to cut through the protective layer 15 covering the flexible area, thereby releasing the flexible area B of the first circuit layer 112 (as shown in Figure 9 ), and finally forming a rigid-flexible combination board 10 with a freely bendable area. In detail, the partial cutting of this step can be implemented in one of the following ways: (1) Laser Ablation: using precise UV or CO2 laser to perform high-energy scanning on the preset area, accurately removing the protective layer 15, suitable for small area, high precision cutting; (2) Punching or knife die cutting: suitable for cutting off a large number of release areas in standardized production, mature technology, high efficiency; (3) If the protective layer 15 is made of photosensitive material, it can also be formed by local light shielding and developing to form a non-covered area, achieving the same effect.

[0041] In the design of the cutting region A, a sufficient flexible width and length can be reserved according to the wiring path of the first circuit layer 112 to ensure that the region can withstand repeated bending operations. Generally, the area of the cutting region A is not less than the flexible region of the first circuit layer 112, and sensitive structures such as electrical connection pads should be avoided. After the cutting step is completed, the extension section of the flexible substrate 11 (i.e. the flexible region B) will restore the original flexible state, which is beneficial for subsequent product folding, bending, plugging and other assembly actions. Through the structure formed by this step, not only the functional integrity of the flexible circuit is preserved, but also the protective layer 15 does not cause additional stress or mechanical restriction to the bending region, significantly improving the service life and dynamic reliability of the whole board. The finally formed rigid-flexible combination board 10 has both rigid bearing area and flexible active area, and is suitable for keyboard modules, electrical connection adapter boards, camera modules, medical probes and other scenes that need to be dynamically bent multiple times.

[0042] Please refer to Figure 9 The application also provides a rigid-flexible combination board 10, which includes a rigid structure part and a flexible structure part, thereby having the advantages of mechanical bearing capacity and flexible transmission capacity, and is suitable for electronic devices with limited space, multiple bending or module connection. In this embodiment, the rigid-flexible combination board 10 mainly includes the following components:

[0043] The rigid substrate 12 includes a second substrate layer 121, a second circuit layer 122 and a third circuit layer 123 formed on both sides of the second substrate layer 121. The second substrate layer 121 is a hard support structure for providing circuit board strength and shape stability, and can be selected from FR-4 fiberglass board, aluminum substrate, ceramic substrate, etc. Its thickness can be between 0.4mm and 1.6mm according to application requirements. The second circuit layer 122 and the third circuit layer 123 are formed on the upper and lower sides of the second substrate layer 121, respectively, for realizing double-sided circuit layout and device installation. Among them, the circuit layer can be formed by etching copper foil process, which has functional circuit pattern and ground / power layer.

[0044] The insulating glue 13 is formed above the second circuit layer 122, and is a bonding medium between the flexible structure and the rigid structure. The insulating glue 13 has the functions of electrical insulation, mechanical fixation, and processing stability. The insulating glue 13 is also provided with at least one through hole 131 for establishing electrical connection between the rigid substrate 12 and the flexible substrate 11. The through hole 131 penetrates the insulating glue 13 and is filled with conductive material 14, which can be silver paste, conductive copper paste, or graphene modified silver paste. When the conductive material 14 is graphene modified silver paste, the added graphene content is 0.5-3 wt%. In addition, in a variant, the conductive material 14 can be a metal column formed by electroplating / chemical plating. In the step of forming the metal column, the inner wall of the through hole is activated by palladium and then chemically plated with copper (thickness 0.3-0.8 μm), and then electroplated with copper to a thickness of 5-15 μm, wherein the current density can be controlled to 2-3 ASD and the temperature is 25±2 ℃.

[0045] The flexible substrate 11 includes a first substrate layer 111 and a first circuit layer 112 formed on one side of the first substrate layer 111. The first substrate layer 111 is composed of flexible polyimide, polyester, or LCP material, and is used to provide bendable characteristics. The thickness of the first substrate layer 111 is generally 25 μm-100 μm, which is determined according to specific applications and bending radius. The first circuit layer 112 is formed on one side of the first substrate layer 111 and has a circuit pattern. One end of the first circuit layer 112 is attached and pressed to the position of the through hole 131 of the insulating glue 13 by reverse bending, and is electrically connected to the second circuit layer 122 through the conductive material 14. The other end of the first circuit layer 112 is freely extended away from the rigid substrate 12, forming a bendable functional section, which is used to connect a control board, a power supply, or an external module.

[0046] The protective layer 15 is formed on the surface of the second circuit layer 122 and covers part of the first circuit layer 112, which is used to improve the insulation, environmental protection, and structural stability of the connection area. The area of the first circuit layer 112 covered by the protective layer 15 still has certain flexible characteristics, and even if it is a bonded area, it can also produce limited flexure with the bending of the whole board, which is suitable for dynamic bending applications.

[0047] Through the above structure combination, the rigid-flexible combination board 10 provided by the present application has the following characteristics:

[0048] Structure simplification: flexible and rigid integrated molding is achieved by reverse bending structure, and additional connectors are omitted. Stable electrical connection: through-hole and conductive filler are used to ensure good conduction of upper and lower layers. High flexibility reliability: flexible section is fully released to avoid stress concentration and prolong service life. Strong manufacturing process compatibility: each step is suitable for conventional PCB / FPC manufacturing process, facilitating mass production. In an embodiment of the application, a keyboard is provided, which includes a key module, a control circuit board, and the rigid-flexible combination board 10 for electrically connecting the key module and the control circuit board of the keyboard. The keyboard is mainly suitable for scenarios such as notebook computers, industrial control panels, wearable input devices, and game control terminals, and is particularly suitable for design architectures that require compact, thin, high-reliability, and flexible wiring.

[0049] Specifically, the keyboard includes a key module, a control circuit board, and the rigid-flexible combination board 10 provided by the application. The key module includes a plurality of mechanical or capacitive touch keys, thin film keys, or scissor structure keycaps, and each key module can form an independent signal output path. The control circuit board is used to receive key input signals and convert them into standard communication protocols such as USB, Bluetooth, I²C, etc. for recognition by the upper processing system. The rigid-flexible combination board 10 serves as an electrical connection bridge between the key module and the control circuit board. Preferably, the flexible structure at one end of the rigid-flexible combination board 10 can be connected to the output terminal of the key module, and the rigid structure at the other end is fixedly installed on the control circuit board and connected to the main control chip through welding, crimping, or buckling.

[0050] In this embodiment, the flexible area of the rigid-flexible combination board 10 not only serves as a space turning function, such as keyboard signals needing to bypass the frame, battery module, etc., but also has long-term flexibility durability, effectively avoiding the problems of traditional cable interface looseness, solder fatigue, or signal interference. In addition, compared with the traditional soft cable connector method, the structure of the application realizes module connection without additional connectors or sockets, significantly saving installation space, reducing component cost, and improving the structural reliability and assembly efficiency of the overall device.

[0051] The keyboard optimized by the application has the following advantages:

[0052] Ultra-thin structure: flexible area is closely combined with key layer, without high thickness stacked connector. High reliability connection: reduce connection points, improve electrical stability after long-term pressing. Flexible layout: cooperate with internal space changes, easily adapt to irregular distribution layout requirements. Suitable for large-scale modular production, easy to standardize process and automatic assembly. In summary, the rigid-flex combination board 10 not only has independent structural advantages, but also can be widely applied to keyboard module products that require thinness and flexible wiring, showing good industrial application prospects.

[0053] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for manufacturing a rigid-flexible composite plate, comprising: A flexible substrate is provided, the flexible substrate including a first substrate layer and a first circuit layer formed on one side of the first substrate layer; A rigid substrate is provided, the rigid substrate comprising a second substrate layer and a second circuit layer and a third circuit layer formed on both sides of the second substrate layer; An insulating adhesive is formed on the surface of the rigid substrate. The insulating adhesive has at least one through-hole, which is filled with a conductive material. The insulating adhesive serves as an intermediary medium for connecting the flexible substrate. The flexible substrate is bent along its length so that one end of the first circuit layer is pressed against the position corresponding to the through hole, and the other end of the first circuit layer extends outward. One end of the flexible substrate includes the connection side of the first circuit layer, and the connection side is bent so that it can be accurately aligned and pressed against the corresponding through hole of the insulating adhesive on the surface of the rigid substrate. The outward extension means that after the flexible substrate is bent, the first substrate layer is folded and stacked, so that the end of the first circuit layer that is not in contact with the conductive material is exposed. The conductive material is used to form an electrical connection between the first circuit layer and the second circuit layer; A protective layer is formed on the surface of the second circuit layer and the protective layer covers the exposed first circuit layer, wherein the protective layer not only covers the second circuit layer, but also extends to cover a portion of the first circuit layer that has been pressed onto the through hole to provide its necessary mechanical fixation and electrical insulation functions. The protective layer located above the insulating adhesive is cut to form a cutting area and expose a portion of the insulating adhesive, thereby releasing the flexible area of ​​the first circuit layer and exposing the first substrate layer, thus forming a rigid-flex board.

2. The method for manufacturing a rigid-flexible plate as described in claim 1, characterized in that: The bending angle of the flexible substrate is no greater than 180 degrees.

3. The method for manufacturing a rigid-flexible plate as described in claim 1, characterized in that: The area of ​​the cut region is not less than the area of ​​the flexible region of the first circuit layer.

4. The method for manufacturing a rigid-flexible plate as described in claim 3, characterized in that: In the step of cutting the protective layer, the protective layer is divided by laser ablation or punching.

5. The method for manufacturing a rigid-flexible plate as described in claim 1, characterized in that: The material of the first substrate layer is polyimide.

6. The method for manufacturing a rigid-flexible plate as described in claim 1, characterized in that: The material of the second substrate layer is one of fiberglass board, aluminum substrate and ceramic substrate.

7. The method for manufacturing a rigid-flexible plate as described in claim 1, characterized in that: The conductive material is silver paste, conductive copper paste, or graphene-modified silver paste.

8. The method for manufacturing a rigid-flexible plate as described in claim 7, characterized in that: When the conductive material is graphene-modified silver paste, the added graphene content is 0.5~3 wt%.

9. A rigid-flexible composite plate, characterized in that: The rigid-flexible bond plate is manufactured by the rigid-flexible bond plate manufacturing method according to any one of claims 1 to 8, and the rigid-flexible bond plate comprises: A rigid substrate includes a second substrate layer and a second circuit layer and a third circuit layer formed on both sides of the second substrate layer; An insulating adhesive is formed on the surface of the rigid substrate, the insulating adhesive having at least one through-hole penetrating the insulating adhesive, the through-hole being filled with a conductive material; A flexible substrate includes a first substrate layer and a first circuit layer formed on one side of the first substrate layer. One end of the first circuit layer is pressed onto the rigid substrate at a position corresponding to the through hole through the insulating adhesive, exposing the other end of the first circuit layer. The first circuit layer is electrically connected to a second circuit layer through the conductive material. The insulating adhesive serves as an intermediary medium for connecting the flexible substrate. The other end of the first circuit layer extends freely away from the rigid substrate, forming a bendable functional section. A protective layer is formed on the surface of the second circuit layer, the protective layer also extending to cover a portion of the first circuit layer, wherein the first circuit layer covered by the protective layer is flexible.

10. A keyboard, characterized in that: It includes a button module, a control circuit board, and a rigid-flex plate as described in claim 9, wherein the rigid-flex plate is used to electrically connect the button module and the control circuit board.

Images