High bending resistance flexible copper clad laminate for rigid-flex boards
Patent Information
- Application Number
- CN202521976381.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-15
- Publication Date
- 2026-10-30
- Estimated Expiration
- 2035-09-15
AI Technical Summary
柔性聚酰亚胺绝缘薄膜基层；
[0012] The beneficial effects of this invention are as follows: This invention adopts a glue-free multi-layer composite structure, fundamentally eliminating the creep risk of traditional adhesives under bending stress. Even in extreme environments such as vibration, high-temperature shock, and high humidity, it still exhibits excellent bending resistance, temperature stability, and damp-heat reliability; simultaneously, it achieves zero attenuation of conductive interconnects, ensuring signal integrity throughout its entire lifecycle. It possesses self-adhesive strength, eliminating the need for an adhesive layer, which not only reduces manufacturing costs but also completely eliminates the risk of adhesive layer aging; its flexible, ultra-thin design perfectly adapts to narrow spaces such as medical devices and micro-sensors, significantly improving space utilization in unilateral bending scenarios, and fully meeting the dual requirements of demanding installation and efficient space utilization.
Smart Images
Figure CN224915517U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of electronic materials, and in particular to a flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards. Background Technology
[0002] With the rapid development of electronic assembly technology, the requirements for "lightweight, thin, short, and small" electronic products in fields such as consumer electronics, medical devices, and aerospace are becoming increasingly stringent. Traditional rigid printed circuit boards (PCBs) are limited by their physical characteristics (inflexible, large installation space required), making it difficult to meet the needs of high-density three-dimensional installation and dynamic bending scenarios.
[0003] Flexible printed circuit boards (PCBs) have become an ideal choice for miniaturized electronic devices due to their thinness and flexibility. However, purely flexible substrates have weak mechanical support and are prone to deformation and failure under complex operating conditions. Therefore, rigid-flex PCBs have emerged—by selectively laminating rigid and flexible substrates, the rigid area provides mechanical support and high-density wiring, while the flexible area enables three-dimensional bending and optimized spatial installation.
[0004] Despite the significant advantages of rigid-flex panels, their core weakness lies in the reliability of the flexible area, particularly performance degradation in harsh environments, such as: 1. The flexible zone, acting as a connecting hub between rigid plates, is prone to delamination or fracture under vibration and repeated bending conditions. Current technologies generally have a bending resistance of less than 100,000 cycles, which cannot meet the long-life requirements of high-end equipment (such as foldable screen phones and aerospace sensors). 2. Temperature shock (-65℃~125℃) and damp heat cycling (humidity>90%) can easily lead to interface delamination, causing conductive interconnect failure (interconnect resistance fluctuation>5%, insulation resistance<100MΩ). 3. After bending or environmental stress, microcracks are prone to appear at the metallized hole connection, which increases the risk of open circuit / short circuit. 4. Existing flexible copper clad laminates mostly use adhesive bonding processes, which have inherent defects such as weak interfacial bonding and poor thermal stability.
[0005] Therefore, there is an urgent need to develop a new generation of highly reliable flexible copper-clad laminate materials, while overcoming the above-mentioned problems and meeting the needs of current high-end application scenarios, especially applications under harsh working conditions. Utility Model Content
[0006] The main technical problem solved by this utility model is to provide a flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards, which can withstand more than 100,000 bending cycles without open circuits or short circuits, thereby improving the overall reliability and durability of the circuit board and having high bonding strength and environmental adaptability.
[0007] To solve the above-mentioned technical problems, the present invention provides a flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards, comprising: Flexible polyimide insulating film base layer; A thermoplastic polyimide layer is disposed on both sides of the polyimide insulating film base layer, and is respectively a first thermoplastic polyimide layer and a second thermoplastic polyimide layer; At least one layer of conductive metal foil is directly composited with the first thermoplastic polyimide layer and the second thermoplastic polyimide layer to form a multilayer composite structure without adhesive bonding.
[0008] In a preferred embodiment of this invention, the thickness of the flexible polyimide insulating film substrate is 12.5 μm to 125 μm.
[0009] In a preferred embodiment of the present invention, the first thermoplastic polyimide layer and the second thermoplastic polyimide layer are symmetrical or asymmetrical structures with the same thickness and composition.
[0010] In a preferred embodiment of the present invention, the thickness of the first thermoplastic polyimide layer and the second thermoplastic polyimide layer ranges from 3 μm to 25 μm.
[0011] In a preferred embodiment of this utility model, the conductive metal foil is an electrolytic copper foil or a rolled copper foil.
[0012] The beneficial effects of this invention are as follows: This invention adopts a glue-free multi-layer composite structure, fundamentally eliminating the creep risk of traditional adhesives under bending stress. Even in extreme environments such as vibration, high-temperature shock, and high humidity, it still exhibits excellent bending resistance, temperature stability, and damp-heat reliability; simultaneously, it achieves zero attenuation of conductive interconnects, ensuring signal integrity throughout its entire lifecycle. It possesses self-adhesive strength, eliminating the need for an adhesive layer, which not only reduces manufacturing costs but also completely eliminates the risk of adhesive layer aging; its flexible, ultra-thin design perfectly adapts to narrow spaces such as medical devices and micro-sensors, significantly improving space utilization in unilateral bending scenarios, and fully meeting the dual requirements of demanding installation and efficient space utilization. Attached Figure Description
[0013] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic diagram of a preferred embodiment of the flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards of this utility model. Figure 2 This is a microscopic cross-section of the sample of the present invention at 50X magnification after a temperature shock test; Figure 3 This is a microscopic cross-section of the sample of this invention at 200X magnification after a temperature shock test. Detailed Implementation
[0014] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0015] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0016] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0017] In the description of this utility model, it should be noted that the terms "front," "rear," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the utility model product is in use. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this utility model. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0018] In the description of this utility model, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0019] In this invention, unless otherwise expressly specified and limited, "above or below" the first feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on" the first feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.
[0020] Please see Figure 1 The embodiments of this utility model include: A flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards includes: Flexible polyimide insulating film base layer 1 provides basic insulation and mechanical support; Thermoplastic polyimide layers are disposed on both sides of the polyimide insulating film base layer 1, namely a first thermoplastic polyimide layer 2 and a second thermoplastic polyimide layer 3, which are chemically bonded to the base layer.
[0021] At least one layer of conductive metal foil 4 is directly composited with the first thermoplastic polyimide layer 2 and the second thermoplastic polyimide layer 3 to form a multilayer composite structure without adhesive bonding.
[0022] Figure 1 As shown, it includes two layers of conductive metal foil 4, which are respectively composited with the first thermoplastic polyimide layer 2 and the second thermoplastic polyimide layer 3.
[0023] Alternatively, it may consist of only one layer of conductive metal foil 4, which is composited with a first thermoplastic polyimide layer 2 or a second thermoplastic polyimide layer 3, not shown in the figure.
[0024] This structure eliminates the traditional adhesive layer, with the thermoplastic polyimide layer serving as both an adhesive medium and a stress buffer. The thermoplastic polyimide layer melts and penetrates into the micropores of the conductive metal foil at high temperatures, forming a mechanically interlocked and chemically bonded composite interface upon cooling, significantly improving peel strength (>1.5 N / mm).
[0025] The thickness of the flexible polyimide insulating film base layer 1 is 12.5μm to 125μm. Too thin (<12.5μm) results in insufficient mechanical strength, while too thick (>125μm) reduces flexibility. The thickness of the base layer controls the balance between insulation and flexibility.
[0026] The first thermoplastic polyimide layer 2 and the second thermoplastic polyimide layer 3 are symmetrical or asymmetrical structures with the same thickness and different compositions. The thickness of the first thermoplastic polyimide layer 2 and the second thermoplastic polyimide layer 3 ranges from 3 μm to 25 μm. The interfacial stress distribution is adjusted by regulating the thickness of the thermoplastic polyimide layers, thereby suppressing the propagation of bending cracks.
[0027] Symmetrical structure, such as the first thermoplastic polyimide layer and the second thermoplastic polyimide layer both having a thickness of 5 μm and the same composition.
[0028] Asymmetric designs, such as a first thermoplastic polyimide layer with a thickness of 15μm and a second thermoplastic polyimide layer with a thickness of 5μm, or with different compositions, can be adapted to single-sided bending scenarios. During bending, the neutral axis is shifted to the thick side, reducing tensile stress on the thin side, extending fatigue life, and supporting bending resistance >100,000 cycles.
[0029] The conductive metal foil 4 is an electrolytic copper foil or a rolled copper foil, and different conductive metal foils of different materials are selected according to different application scenarios.
[0030] Electrolytic copper foil has the advantage of high bonding strength: when the rough surface is melted and bonded with the thermoplastic polyimide layer, a mechanical interlocking structure is formed, which significantly improves the peel strength (>1.5 N / mm); it is suitable for consumer electronics products (such as mobile phone battery boards) with moderate bending requirements (<50,000 times).
[0031] Rolled copper foil possesses high ductility (elongation > 15%) and low roughness, reducing stress concentration during bending and supporting > 100,000 dynamic bends (bending diameter 2.5mm). It maintains high-frequency signal fidelity: the smooth surface reduces skin effect loss, making it suitable for high-end applications and extreme environments such as 5G millimeter-wave radar.
[0032] The preparation method of the flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards includes the following steps: (1) The surface functional group treatment includes treating the thermosetting polyimide film with surface corona technology, and then using surface chemical functionalization modification technology to perform surface functionalization treatment on the polyimide film to form a surface-aminated polyimide insulating film base layer 1, which enhances the chemical bonding ability between the base layer and the thermoplastic layer and provides a uniform active surface for subsequent coating.
[0033] (2) A thermoplastic polyimide precursor solution is applied to both sides of the polyimide insulating film substrate 1 using high-precision surface controllable coating technology; the coating speed is 0.5 ~ 6 m / min, and the basis weight is 10 ~ 120 g / m². 2Low speed (e.g., 0.5 m / min) is used for ultra-thin layers (e.g., 3 μm), while high speed (e.g., 6 m / min) is used for thick layers (e.g., 25 μm). By controlling the linear speed and basis weight per unit area, the basis weight and thickness of the thermoplastic polyimide layers on both sides are precisely controlled and adjusted simultaneously to eliminate micropores / bubbles and ensure interlayer bonding strength.
[0034] (3) A first thermoplastic polyimide layer 2 and a second thermoplastic polyimide layer 3 are formed by gradient drying, solvent evaporation and dehydration ring-closed imidization, thereby obtaining a thermoplastic polyimide / thermosetting polyimide insulating film 5. The specific operation of gradient drying, solvent evaporation and dehydration ring-closed imidization is as follows: drying is carried out in three stages of temperature increase from 80℃ to 150℃ to 300℃, so that the solvent residue is <50ppm, and dehydration condensation is carried out under nitrogen protection to form a dense and defect-free thermoplastic polyimide layer (first thermoplastic polyimide layer 2 and second thermoplastic polyimide layer 3), which provides a chemical basis for glue-free composite structure.
[0035] (4) Under adhesive-free conditions, at least one layer of conductive metal foil 4 is hot-pressed onto at least one side of the thermoplastic polyimide / thermosetting polyimide insulating film 5 by continuous roll-to-roll thermoforming composite technology to obtain a flexible multilayer composite structure, which is a flexible copper-clad laminate with high bending resistance.
[0036] The peel strength of the composite is greater than 1.5 N / mm. The molten thermoplastic resin fills the micropores of the copper foil and forms a "claw" structure after cooling, realizing the micro-mechanical interlocking between the metal foil and the substrate. The peel strength is 300% higher than that of the adhesive system.
[0037] Based on rigorous industry standards and experimental verification, a systematic test was conducted on the high bending resistance flexible copper-clad laminate for the rigid-flexible composite board of this utility model. The results confirmed that its core performance far exceeds industry standards. I. Covering film adhesion test Test method: Standard based on: IPC-TM-650 2.4.9 (Test for peel strength of cover film on flexible printed circuit boards) Sample preparation: After etching the copper-clad laminate to expose the thermoplastic polyimide layer, stack 50μm polyimide cover films and hot press at 180℃ / 2MPa for 30 seconds.
[0038] Test procedure: Perform 90° peeling at a rate of 50 mm / min and record the mean of 5 sets of samples.
[0039] Test results: Peel strength range: 1.3~1.6 N / mm (average 1.5 N / mm), all samples > target value of 1.2 N / mm; Failure mode: 100% coverage membrane bulk tear (cohesive failure), no interfacial delamination.
[0040] II. Temperature Shock Stability Test Test methods: Standards based on: GJB 7548A-2021 3.10.3, 4.8.7.3 and 4.8.3 (Temperature shock test) Test conditions: -65℃ (30 min) → 125℃ (30 min) is 1 cycle, for a total of 100 cycles.
[0041] Monitoring indicators: Interconnection resistance is measured every 20 cycles (four-wire method), and delamination defects are detected by X-ray.
[0042] Test results: Resistance change rate ΔR: 0.21%~0.25% (≤0.25%).
[0043] Structural integrity: such as Figure 2 , 3 As shown, microscopic cross-section reveals tight interlayer bonding, and the sample showed no defects such as blistering, delamination, or cracks after temperature shock testing.
[0044] III. Reliability Testing During Damp Heat Cycling Test methods: Standards based on: GJB 7548A-2021 3.10.1 and 4.8.7.1 (damp heat cycling and insulation resistance test) Test conditions: 25℃ / 90% RH → 65℃ / 98% RH, 10 cycles (24h per cycle).
[0045] Monitoring indicators: insulation resistance after cycling (500V DC), and metal oxidation detected by colorimeter.
[0046] Test conclusion: Insulation resistance: 1.2×10¹¹~8.0×10¹¹ Ω, exceeding industry requirements (>100MΩ) by 1000 times; Appearance: The copper foil under the solder mask shows no discoloration (ΔE < 1.0) and no delamination defects.
[0047] IV. Bending resistance test Test method: Standard basis: GJB 7548A-2021 3.8.6 and 4.8.5.6 (bending resistance test) Test conditions: MIT flexural endurance tester, bending diameter 2.5mm, rate 60 times / min until failure.
[0048] Circuit design: Etching "comb" circuit (line width / spacing = 1.5 mm / 1.0 mm).
[0049] Test conclusion: Bending life: 105,000~138,000 cycles (average 120,000 cycles), all > 100,000 cycles target; Electrical performance: Interconnect resistance before and after bending test <10 Ω (fluctuation <20%) Insulation resistance: >100MΩ (maintaining more than 90% of the initial value), 0 cases of open circuit and short circuit. In summary, this utility model, through its glue-free multi-layer composite design, completely eliminates the risk of creep under bending stress associated with traditional adhesive layers.
[0050] The technical solution of this invention exhibits excellent environmental resistance under harsh working conditions such as vibration, temperature shock, and high humidity: Breakthrough in bending resistance: Achieves over 100,000 dynamic bends at a bending diameter of 2.5mm and a rate of 60 bends / min, with no open circuits, short circuits, or delamination throughout the process. The adhesive-free composite interface between the thermoplastic polyimide layer and the copper foil (peel strength > 1.5N / mm) disperses stress through mechanical interlocking, completely solving the problem of fatigue fracture in the flexible area.
[0051] Extreme temperature stability: After 100 high and low temperature cycles, the resistance change rate is ≤0.25%, and there are no defects such as bubbling, delamination, or cracks.
[0052] Reliability in humid and hot environments: After 10 humid and hot cycles, the insulation resistance is >100 MΩ, and the copper foil under the solder mask shows zero discoloration. The hydrophobic functional groups of the amino-modified polyimide base layer block the penetration path of water molecules, preventing electrochemical corrosion.
[0053] The technical solution of this utility model achieves zero attenuation of conductive interconnection and ensures signal integrity of the circuit throughout its entire life cycle by maintaining an interconnection resistance of <10 Ω and an insulation resistance of >100MΩ before and after bending tests.
[0054] The product of this utility model has a 90° peel force of >1.2 N / mm between the exposed thermoplastic layer and the cover film after etching, and has excellent self-adhesion. It eliminates the need for an additional adhesive layer, which not only reduces manufacturing costs but also completely avoids the risk of adhesive layer aging.
[0055] The flexible area of this invention can be compressed to an ultra-thin thickness, making it suitable for confined spaces such as medical devices and micro sensors. The asymmetric thermoplastic layer design significantly improves space utilization in single-sided bending scenarios, fully meeting the dual requirements of demanding installation and efficient space utilization.
[0056] The above description is merely an embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made using the content of this utility model specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.
Claims
1. A flexible copper-clad laminate with high bending resistance for rigid-flexible composite boards, characterized in that, include: Flexible polyimide insulating film base layer; A thermoplastic polyimide layer is disposed on both sides of the polyimide insulating film base layer, and is respectively a first thermoplastic polyimide layer and a second thermoplastic polyimide layer; At least one conductive metal foil is directly composited with the first thermoplastic polyimide layer and the second thermoplastic polyimide layer. The first and second thermoplastic polyimide layers penetrate into the micropores of the conductive metal foil to form a "claw" structure, thereby achieving micro-mechanical interlocking between the metal foil and the substrate, and forming a multi-layer composite structure without adhesive between the conductive metal foil and the thermoplastic polyimide layer. The first thermoplastic polyimide layer and the second thermoplastic polyimide layer have a symmetrical structure of equal thickness, or an asymmetrical structure with different thicknesses.
2. The high bending resistance flexible copper-clad laminate for rigid-flexible composite boards according to claim 1, characterized in that, The thickness of the flexible polyimide insulating film substrate is 12.5 μm to 125 μm.
3. The high bending resistance flexible copper-clad laminate for rigid-flexible composite boards according to claim 1, characterized in that... The first thermoplastic polyimide layer and the second thermoplastic polyimide layer are symmetrical or asymmetrical structures with the same thickness and composition.
4. The high bending resistance flexible copper-clad laminate for rigid-flexible composite boards according to claim 3, characterized in that, The thickness of the first thermoplastic polyimide layer and the second thermoplastic polyimide layer ranges from 3 μm to 25 μm.
5. The high bending resistance flexible copper-clad laminate for rigid-flexible composite boards according to claim 1, characterized in that... The conductive metal foil is an electrolytic copper foil or a rolled copper foil.