PCB and FPC composite wiring structure and radial motor stator manufacturing method based on the structure

Abstract

The application relates to the technical field of motors, in particular to a PCB and FPC composite wiring structure and a method for manufacturing a radial motor stator based on the wiring structure, which comprises a plurality of rigid PCB coil units, an FPC flexible interconnection layer, a depth-controlled milling flexible transition area and an interlayer electrical conduction structure, the rigid PCB coil unit is made of a multilayer base material to manufacture a spiral power coil, and a center is provided with a core matching area; the FPC flexible interconnection layer is made of a high-temperature-resistant PI base material to connect adjacent coil units; the depth-controlled milling flexible transition area removes a rigid base material and only retains an FPC layer to form a flexible hinged section. The manufacturing method comprises layout coordination design, separately manufacturing a multilayer rigid PCB power coil and an FPC flexible interconnection circuit, PCB and FPC precise alignment and pressing, interlayer metallization electrical conduction, separate milling and forming and annular nesting assembly and shaping. The design has the advantages of rigid PCB high-strength heat dissipation and FPC flexible bending assembly, and the power density, operation stability and mass production consistency are improved.

Description

Technical Field

[0001] This invention relates to the field of motor technology, specifically to a composite wiring structure of PCB and FPC and a method for manufacturing a radial motor stator based on this structure. Background Technology

[0002] Radial flux brushless motors, as one of the important development directions of modern motor technology, are widely used in many fields such as robotics, drones, gimbals, medical devices, and small servo mechanisms. The design and manufacturing quality of the motor stator winding structure directly determines the motor's power density, operational reliability, wiring convenience, and overall assembly efficiency, thus becoming a key aspect of motor core technology research and development.

[0003] Traditional radial motor stator manufacturing primarily employs the method of stacking silicon steel sheets and then winding enameled wire. While this method is technically mature and widely used, it suffers from several insurmountable drawbacks in practical production and application. Firstly, the enameled wire winding process is cumbersome and highly dependent on operator skills, leading to high labor costs and low production efficiency. Secondly, limited by the spatial constraints of the winding mechanism, slot fill factor is difficult to further improve, and the consistency of winding distribution is hard to guarantee, resulting in significant performance fluctuations between product batches. More importantly, traditional winding processes face increasing technical bottlenecks in the manufacturing of small-sized micro-motors, making it difficult to meet the miniaturization and lightweighting trends of modern electronic products.

[0004] To address the shortcomings of traditional processes, the industry has proposed a technical solution using a flexible circuit board wound into a ring to fabricate stator windings. While this solution simplifies the winding process and improves automation to some extent, deeper analysis reveals more significant technical limitations. When the flexible circuit board is used as a whole as the stator winding, its substrate is primarily made of polymer materials such as polyimide film. In applications involving large-size motors or high-current motors, its rigidity is severely insufficient to withstand the interaction forces between the stator core and the windings. Simultaneously, the heat dissipation performance of flexible materials is far inferior to that of metal substrates, making it difficult to effectively dissipate the heat generated during high-frequency operation. This leads to a continuous increase in winding temperature and accelerated insulation aging. Furthermore, the flexible board is prone to plastic deformation and even fatigue failure under continuous thermal cycling and mechanical vibration, severely impacting the motor's lifespan and operational stability. These inherent defects limit the application of the flexible circuit board solution to specific micro- and low-power applications, making it difficult to promote its use across a wider power range.

[0005] In summary, how to achieve reliable application of rigid PCBs on radial motor stators while ensuring sufficient structural strength and excellent heat dissipation performance of the stator windings, and at the same time taking into account the flexibility of wiring and assembly, has become an urgent technical challenge to be solved in this field.

[0006] Furthermore, when rigid PCBs and flexible circuit boards are directly combined for use in motor stators, the significant difference in the linear expansion coefficients of the two materials leads to substantial thermal stress concentration at the interface under the cyclic thermal cycling conditions caused by the high-frequency alternating current of the motor. This shear stress, over time, can easily cause interface cracking or delamination, ultimately resulting in electrical insulation failure and posing a significant threat to the reliable operation of the motor. Therefore, effectively overcoming the thermal stress mismatch between rigid and flexible materials and achieving a reliable and stable electrical connection between them is a core technological challenge in exploring the composite application of PCBs and FPCs in motor stators. Summary of the Invention

[0007] In view of this, the problem to be solved by the present invention is to provide a composite wiring structure of PCB and FPC and a method for manufacturing a radial motor stator based on the structure.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The advantages and positive effects of this invention are: This invention, by setting a controlled-depth milling flexible transition zone, precisely removes the rigid substrate, leaving only the FPC flexible layer as the bending area. This concentrates bending deformation in the purely flexible region, avoiding stress concentration at the rigid-to-flexible interface and fundamentally eliminating the risk of interface cracking or delamination caused by differences in thermal expansion coefficients. Simultaneously, the use of a multi-layer rigid substrate PCB to fabricate the power coil body significantly improves mechanical strength, enabling it to withstand electromagnetic forces under high current conditions. The rigid PCB can utilize a thicker copper foil layer, providing excellent heat dissipation and effectively controlling the motor's operating temperature rise. The FPC flexible interconnect layer can fill the gaps at the coil ends, adapting to the spatial requirements of ring assembly and improving assembly flexibility. The entire system employs mature PCB and FPC manufacturing processes, ensuring good process compatibility and facilitating mass production. The multi-layer PCB structure uses photolithography to precisely fabricate the coil pattern, resulting in good product consistency and a low scrap rate. Attached Figure Description

[0009] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0010] In the attached diagram: Figure 1 This is a schematic diagram of a rigid PCB coil unit assembly; Figure 2 A schematic diagram of an integrated flexible and rigid winding strip; Figure 3 A schematic diagram of the FPC flexible interconnect layer; Figure 4This is a schematic diagram of the interface between the rigid PCB coil unit and the FPC flexible interconnect layer; Figure 5 This is a schematic diagram of a ring stator structure; In the diagram: 10. Rigid PCB coil unit; 11. Spiral power coil circuit; 12. Core mating area; 13. Metallized connection pad; 20. FPC flexible interconnect layer; 21. High-temperature resistant PI substrate layer; 22. Metal conductor; 23. Butt pad; 24. Three-phase lead-out pad; 30. Controlled-depth milling flexible transition area; 40. Interlayer electrical conduction structure; 41. Metallized through-hole; 50. Integrated flexible and rigid winding strip; 60. Annular stator structure. Detailed Implementation

[0011] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0012] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is considered "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is considered "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0014] like Figures 1 to 5As shown in the figure, the core of the PCB and FPC composite wiring structure and the method for manufacturing a radial motor stator according to an embodiment of the present invention lies in using a multi-layer rigid PCB coil unit 10 as the main body of the power coil to bear the mechanical load and heat dissipation requirements under high current conditions. A flexible interconnect layer 20 of FPC is used to achieve flexible connection and lead-out routing between the coil units. By controlling the depth of milling the flexible transition area 30, the rigid substrate is removed, leaving only the FPC layer as a bending area. This allows the integrated rigid-flexible winding strip 50 to be bent into a ring structure along a predetermined path at the flexible hinge section, and then embedded in the slot of the radial motor stator core to form a complete ring stator structure 60. This structure fundamentally eliminates the risk of interface cracking or delamination caused by the difference in thermal expansion coefficients in traditional rigid-flexible composite solutions, while combining the high strength and high heat dissipation characteristics of rigid PCBs with the flexible bending assembly advantages of FPCs.

[0015] Example 1; like Figure 1 As shown, the integrated rigid-flexible winding strip 50 of this embodiment of the invention has an elongated structure in its unfolded state, with multiple rigid PCB coil units 10 arranged sequentially along its length. Adjacent rigid PCB coil units 10 are connected by a section of FPC flexible interconnect layer 20. Specifically, the number of rigid PCB coil units 10 is determined according to the number of slots in the radial motor stator. For example, for a twelve-slot stator, twelve rigid PCB coil units 10 are provided, with each coil unit corresponding to one stator slot. The rigid PCB coil units 10 are arranged at equal intervals along the length of the winding strip, and a metallized connection pad 13 is reserved on the same side of each coil unit for electrical connection with the adjacent FPC flexible interconnect layer 20.

[0016] Three-phase lead-out pads 24 are reserved at one or both ends of the winding strip, corresponding to the terminals of phase U, phase V and phase W respectively. The three-phase lead-out pads 24 are etched and formed in the end area of ​​the FPC flexible interconnect layer 20, and their area and line width are designed according to the rated current parameters to ensure that they can reliably withstand the maximum phase current when the motor is running.

[0017] like Figure 3 As shown, the integrated rigid-flexible winding strip 50 of this embodiment of the invention is bent into a ring structure along the circumferential direction. The ring structure is a complete circular ring shape, with multiple rigid PCB coil units 10 evenly distributed along the circumferential direction. The FPC flexible interconnect layer 20 between each coil unit fills the gap between the ends of adjacent coils, forming a complete ring stator winding. The bending operation is completed in one go only at the controlled-depth milling flexible transition zone 30, and mechanical fixation is achieved by magnetic boots after bending.

[0018] Example 2; Each rigid PCB coil unit 10 is made of FR-4 rigid substrate to form a multilayer PCB structure with two to eight layers. The specific number of layers is determined according to the number of turns and current carrying capacity requirements of the coil. Taking a four-layer rigid PCB coil unit 10 as an example, it includes the following layers from top to bottom: a top copper layer for etching to form the first layer of the spiral power coil circuit 11; a first prepreg layer for bonding the top circuit board to the second circuit board; a second copper layer for etching to form the second layer of the spiral power coil circuit 11; a second prepreg layer for bonding the second circuit board to the third circuit board; a third copper layer for etching to form the third layer of the spiral power coil circuit 11; a third prepreg layer for bonding the third circuit board to the bottom circuit board; and a bottom copper layer for etching to form the fourth layer of the spiral power coil circuit 11.

[0019] The spiral power coil lines 11 on each layer are etched to form a predetermined number of turns and linewidth pattern. The copper foil thickness ranges from 35 to 70 micrometers to meet the requirements of different current carrying capacities. The coils between layers are electrically connected in series through metallized vias to form a complete multi-turn power coil structure. For example, the starting point of the coil in the top layer is connected to the starting point of the coil in the second layer through a metallized via, the ending point of the coil in the second layer is connected to the starting point of the coil in the third layer through another metallized via, and so on, until a complete multi-layer series winding is formed.

[0020] A core mating area 12 is provided at the center of the rigid PCB coil unit 10, the shape and size of which match the slot structure of the radial motor stator core. In this embodiment, the core mating area 12 adopts a rectangular hollow structure, the width of the hollow area is slightly larger than the width of the core slot, and the height matches the depth of the core slot, so that the rigid PCB coil unit 10 can be locked and fixed in the core slot by interference fit or clearance fit. In other embodiments, the core mating area 12 may also adopt a circular hollow structure or other structural forms adapted to the geometry of the stator core. A metallized connection pad 13 is provided at the connection end between the rigid PCB coil unit 10 and the FPC flexible interconnect layer 20.

[0021] Example 3; The FPC flexible interconnect layer 20 is a long, flexible circuit structure disposed on the same side of multiple rigid PCB coil units 10. Its total length is equal to the sum of the widths of all rigid PCB coil units 10 plus the sum of the gaps between adjacent coil units. The FPC flexible interconnect layer 20 is made of high-temperature resistant PI substrate with a substrate layer thickness of 12 to 25 micrometers. Polyimide film is used as the matrix material. This material has excellent heat resistance and maintains stable physical and electrical properties within the temperature rise range of motor operation. At the same time, it has good flexibility and can withstand one-time bending deformation without breaking.

[0022] Metal wires 22 are formed on the PI substrate layer 21 by etching. The path planning of the metal wires 22 follows the following principles: connecting the metallized connection pads 13 of two adjacent rigid PCB coil units 10 to form an electrical conduction path between adjacent coil units; ensuring that the U / V / W three-phase lines each form an independent closed loop, and maintaining sufficient electrical insulation distance between adjacent phases, with an insulation distance of not less than 0.5 mm; and keeping the overall wiring path short to reduce resistance loss caused by the wire length.

[0023] A mating pad 23 is provided at the end of the metal conductor 22, and its position corresponds to the metallized connection pad 13 on the rigid PCB coil unit 10. Three-phase lead-out pads 24 are reserved at one or both ends of the FPC flexible interconnect layer 20, respectively corresponding to the wiring terminals of the U phase, V phase and W phase. The area design of the three-phase lead-out pads 24 meets the following conditions: the pad area is not less than three square millimeters to ensure that overheating and aging do not occur under the rated current condition of the motor; solder mask openings are provided around the pads, and the distance between the edge of the opening and the edge of the pad is 0.3 mm to 0.5 mm to prevent solder overflow from causing short circuits between adjacent pads.

[0024] Example 4; The controlled-depth milling flexible transition area 30 is set at the connection between each rigid PCB coil unit 10 and the FPC flexible interconnect layer 20. Its width is one millimeter to five millimeters. The lower limit of the width ensures that the FPC substrate layer retained after CNC controlled-depth milling has sufficient mechanical strength and will not break during bending. The upper limit of the width ensures that the transition area can fill the gap between the ends of adjacent rigid PCB coil units 10 after being bent into a ring, without occupying too much axial space.

[0025] The machining process of controlled-depth milling of the flexible transition area 30 is as follows: the FR-4 rigid substrate layer in the rigid PCB coil unit 10 is removed by CNC controlled-depth milling process, leaving only the underlying FPC flexible substrate and metal wires exposed, forming a flexible hinge segment composed only of the FPC layer. After milling, only the metal wires 22 of the FPC layer and the high-temperature resistant PI substrate layer 21 of the FPC layer are left in this area. The metal wires 22, which were originally covered by the rigid substrate, are completely exposed. The surface of the metal wires 22 is insulated and protected by a solder mask layer to prevent the wires from contacting the external conductors during bending and causing a short circuit.

[0026] By controlling the depth of the milling process to create a flexible transition zone 30, the originally rigid long winding strip has the ability to bend into a ring along a preset path at the flexible hinge section. The bending radius is determined by the following formula based on the size of the stator: the bending radius R equals the inner radius of the stator minus the thickness of the winding strip. Since the bending in this invention is a one-time bending operation, and the wire is fixed by a magnetic shoe after bending, there is no dynamic bending fatigue problem. Therefore, there is no need to strictly limit the minimum value of the bending radius, as long as the metal wire 22 does not break during the bending process.

[0027] Example 5; The interlayer electrical conduction structure 40 is disposed at the mating pad 23 between the rigid PCB coil unit 10 and the FPC flexible interconnect layer 20, including a metallized through-hole 41 penetrating the rigid substrate and the FPC substrate, and a hole wall metal layer formed by copper plating and electroplating. The metallized through-hole 41 is a PTH electroplated through-hole structure.

[0028] After the rigid PCB and FPC are precisely aligned and laminated, a CNC drilling machine is used to drill through holes at the mating pads 23. Chemical copper plating and electroplating are performed after drilling. First, the hole wall is activated using a palladium catalyst to give it the catalytic activity required for chemical copper plating. Then, chemical copper plating is performed, depositing a seed copper layer with a thickness of 0.5 to 1 micrometer on the hole wall surface. Finally, electroplating is performed, thickening the copper layer on top of the chemical copper plating layer using an acidic copper sulfate electroplating solution, resulting in a plating thickness of 20 to 30 micrometers. Through the aforementioned metallized vias 41, the metallized via wall layer connects the copper foil of the rigid PCB windings and the FPC circuitry to the inner ring. The inner ring connection refers to the electroplated copper layer simultaneously covering the annular area of ​​the rigid PCB copper foil, the annular area of ​​the FPC copper conductors, and the interface between them, forming a continuous low-impedance electrical path from the rigid PCB copper layer to the FPC copper layer. This ensures reliable current conduction between the rigid coil and the flexible interconnect during motor operation.

[0029] Example 6; This embodiment takes a three-phase radial brushless motor stator with twelve slots and a rated current of five amps as an example; During the collaborative design phase of the winding layout, the number of slots in the radial stator core was first determined to be twelve, with an inner diameter of twenty millimeters, a rated current of five amperes, and three phases. The regional layout design included: designing the layout of twelve independent rigid PCB coil units (10 units), each using a four-layer PCB structure. The top and bottom copper foil thicknesses were seventy micrometers, the middle layer copper foil thickness was thirty-five micrometers, and the coil turns were six turns per layer, totaling twenty-four turns. The line width was 0.5 millimeters, and the line spacing was 0.3 millimeters to meet the five-ampere rated current requirement and reserve a 50% current margin; designing the FPC interconnection routing layout between units, with the connecting wires between adjacent coil units having a line width of one millimeter. The U-phase, V-phase, and W-phase wires were independently routed along different paths of the winding strip. The minimum insulation distance between conductors is 0.8 mm; four sets of metallized hole alignment reference holes are set, with a diameter of 2.0 mm, and their positions are distributed in the area with the highest alignment accuracy requirements, for subsequent multilayer PCB interlayer alignment and FPC-PCB alignment; the twelve coil units are divided into three groups, corresponding to the U phase, V phase and W phase respectively, each phase contains four coil units, which are connected in series, and the preset series connection points are the start and end points of each phase; the boundary line position of the controlled depth milling area is designed, and the boundary line width is 2 mm to ensure that the electrical insulation distance between adjacent lines is not less than 0.5 mm after bending.

[0030] In the fabrication stage of the multilayer rigid PCB power coil, a four-layer PCB is made using FR-4 rigid substrate. The specific process is as follows: A spiral power coil circuit pattern 11 is formed on each copper-clad laminate using dry film lithography and etching. The etching process uses acidic copper chloride etching solution, with the etching temperature controlled at 50°C to 55°C, and the lateral etching amount controlled within 10% of the line width. The etched circuit boards and prepregs are then stacked in the designed order: from top to bottom, the first circuit board, the first prepreg, the second circuit board, the second prepreg, the third circuit board, the third prepreg, and the fourth circuit board. The resin flow rate is 30% to 45%. The hot-press curing process parameters are: a pressing temperature of 175°C to 185°C, a pressing pressure of 30 kg / cm², and a pressing time of 120 to 180 minutes. A segmented temperature and pressure curve is used to avoid bubble formation. After drilling, chemical copper plating and electroplating are used to form metallized holes, achieving electrical interconnection of multiple single coils. The hole wall plating thickness is 25 micrometers.

[0031] In the FPC flexible interconnect fabrication stage, a high-temperature resistant PI substrate with a thickness of 25 micrometers is selected to fabricate the FPC flexible interconnect. The specific process is as follows: connecting wires between each PCB unit and three-phase lead-out pads 24 are formed on the PI copper-clad foil material through etching. The etching process parameters are similar to those of rigid PCB etching, but considering the temperature resistance limitations of the PI substrate, the etching solution temperature is controlled at 40 to 45 degrees Celsius. The pad area to be connected to the PCB is reserved and subjected to solder mask insulation treatment. Photosensitive solder mask ink is covered on the non-soldering area, exposed, developed, and cured. The thickness of the solder mask layer is 15 to 25 micrometers. Reinforcing sheet pretreatment is performed. A PI reinforcing sheet with a thickness of 0.2 millimeters is attached to the support area of ​​the three-phase lead-out pads 24 to avoid stress concentration and breakage in this area during subsequent bending and assembly.

[0032] During the PCB and FPC alignment and lamination stage, the PCB coil unit and the FPC interconnect layer are aligned and bonded using positioning reference holes. A low-temperature lamination process is used for pre-fixation, with the lamination temperature controlled between 120 and 130 degrees Celsius, the lamination pressure controlled at 10 kg / cm², and the lamination time between 15 and 30 minutes. Areas for subsequent metallization drilling are reserved, and a rigid-flex lamination process is used to achieve a reliable bond between the two. The characteristic of rigid-flex lamination is that it simultaneously utilizes the adhesive strength of the rigid area and the flexibility of the flexible area, ensuring the integrity of the entire laminated structure during subsequent processing and assembly.

[0033] During the interlayer metallization electrical conduction stage, an interlayer electrical conduction structure 40 is formed at the mating pad 23. The specific process is as follows: through-holes are drilled at the mating pads of the rigid PCB and FPC, and a metallization layer is formed on the hole wall through chemical copper plating and electroplating processes to achieve reliable conduction of the PTH metallized hole. The metallized through-hole 41 ensures that the copper foil of the rigid PCB winding and the FPC circuit achieve inner ring connection. The series and parallel networking of multi-unit coils is completed to form a complete three-phase stator winding circuit. In this embodiment, the four coil units of each phase are connected in series. The starting point of phase U is connected to terminal U1 and the ending point is connected to terminal U2. The starting point of phase V is connected to terminal V1 and the ending point is connected to terminal V2. The starting point of phase W is connected to terminal W1 and the ending point is connected to terminal W2.

[0034] In the partitioned CNC milling forming stage, CNC milling equipment is used for partitioned milling processing. The entire process is divided into three stages. The first stage is the whole board milling stage: milling is performed along the boundary of each rigid PCB coil unit 10 to separate the contours of adjacent coil units and form independent rigid coil units. The second stage is the controlled depth milling flexible release stage: at the connection between the rigid PCB coil unit 10 and the FPC flexible interconnect layer 20, i.e., the coil connection end area, controlled depth milling is performed using CNC depth control function to accurately remove the rigid PCB substrate, leaving only the lower FPC flexible layer to form a flexible hinge section. The third stage is the slot precision milling stage: in the iron core mating area 12 of each rigid PCB coil unit 10, positioning slots that match the stator iron core slots are milled. The slot depth is determined according to the actual depth of the iron core slot to ensure that the PCB unit can be firmly locked and fixed in the iron core slot.

[0035] In the annular nested assembly and shaping stage, the integrated flexible and rigid combined winding strip 50 is assembled into a radial motor stator. The specific process is as follows: First, the annular bending radius is calculated. For a twelve-slot stator with an inner diameter of 20 mm, the bending radius is calculated as the stator inner radius minus the total thickness of the winding strip. The total thickness of the winding strip is approximately 1.6 mm (including four layers of PCB and FPC), so the bending radius is approximately 8.2 mm. Then, the winding strip is bent into an annular structure along the circumferential direction. The bending operation is completed in one go along the flexible hinge section without preheating or auxiliary forming tools. Each rigid PCB coil unit 10 is inserted one-to-one into the slot of the radial motor stator core. The slots formed by precision milling are interference fit or clearance fit with the core slots. The interference is controlled within the range of 0.05 mm to 0.1 mm. The process involves: filling the gaps between adjacent coil units with FPC connecting sections, filling the gaps between rigid units with flexible material to ensure efficient space utilization of the ring structure; performing adhesive bonding and fixing by injecting epoxy resin adhesive into the interface between the core slot and the PCB coil unit, with the adhesive curing conditions being room temperature for 20 minutes followed by heating to 100 degrees Celsius and holding for 30 minutes; performing insulation potting by using polyurethane or epoxy resin potting compound to pot the entire stator winding, which then cures to form an insulating protective layer at a temperature of 80 to 100 degrees Celsius for 2 to 4 hours; and finally, leading out the three-phase terminals to complete the radial stator assembly.

[0036] Example 7: In traditional rigid-flex PCB composite designs, the rigid region typically uses FR-4 substrate, while the flexible region usually uses PI substrate. When the rigid and flexible regions are directly bonded, their coefficients of thermal expansion differ significantly, leading to thermal stress at the interface under varying temperature conditions. More critically, during motor operation, high-frequency alternating current flows through the stator windings, generating periodically changing electromagnetic forces and causing periodic temperature fluctuations in the windings. Under high-frequency thermal cycling conditions, shear stress continuously accumulates at the interface. When this shear stress exceeds the bonding strength of the interface, it causes cracking or delamination, resulting in electrical insulation failure.

[0037] This invention utilizes a controlled-depth milling flexible transition zone 30 at the connection between each rigid PCB coil unit 10 and the FPC flexible interconnect layer 20. This precisely removes the FR-4 rigid substrate in this area, leaving only the FPC flexible layer as the bending region. The physical effect of this design is that bending deformation is concentrated in the purely flexible region, rather than at the rigid-flexible interface. During the subsequent thermal cycling of the motor, when temperature changes cause material expansion or contraction, the rigid PCB coil unit 10 and the FPC flexible interconnect layer 20 undergo independent thermal expansion deformation. Electrical connection is achieved between them through a metallized via 41. Because the metal layer of the via wall 41 has sufficient flexibility, it can absorb most of the deformation caused by the relative displacement between the rigid and flexible regions, thereby avoiding excessive shear stress at the interface.

[0038] Meanwhile, the one-time bending assembly method adopted in this invention ensures that the FPC flexible interconnect layer 20 is in a constrained state after bending. Both ends of the bent FPC are fixed to the rigid PCB coil unit 10, and the flexible area itself no longer undergoes relative displacement, thus eliminating the problem of dynamic bending fatigue. The stator is fixed above by magnetic shoes, and the mechanical constraint of the magnetic shoes further limits the deformation space of the FPC layer, ensuring its stability under the vibration environment of the motor operation.

[0039] Example 8; The rigid PCB coil unit 10 adopts a multi-layer FR-4 substrate structure and achieves efficient heat dissipation through the following design: the spiral power coil circuit 11 in the rigid PCB coil unit 10 is directly formed from copper foil, and the copper foil layer is in direct contact with the FR-4 substrate. Heat can be conducted to the PCB surface through the copper foil layer, and then exchanged with the surrounding air or stator core through the PCB surface; in the multi-layer PCB structure, the copper foil layers are insulated by prepreg. Although the prepreg material has low thermal conductivity, by appropriately increasing the thickness of the copper foil layer in the high current region, the thermal conductivity cross-sectional area can be effectively increased and the thermal resistance reduced; the surface of the rigid PCB coil unit 10 can be in direct contact with the stator core or fixed by thermally conductive adhesive. Heat can be directly transferred to the core through conduction. The core is usually made of stacked silicon steel sheets, which can serve as an effective heat dissipation channel.

[0040] Although the FPC flexible interconnect layer 20 is relatively thin, its metal conductors 22 are also etched from copper foil. The heat generated when current passes through can be conducted along the length of the conductors to the rigid PCB coil units 10 on both sides, and then dissipated through the rigid area. The FPC connection segment fills the gap at the end of the coil. This flexible material itself does not carry a large current and only serves as a connecting conductor and mechanical filler, so the heat it generates is minimal.

[0041] Compared to existing flexible circuit board solutions, this invention uses a rigid PCB as the main body of the power coil, which greatly improves mechanical strength and can withstand electromagnetic forces under high current conditions, making it less prone to creep deformation. The rigid PCB can use a thicker copper foil layer to meet the high current carrying capacity requirements. At the same time, the thick copper layer itself serves as a heat conduction channel, providing excellent heat dissipation performance and effectively controlling the temperature rise of the motor during operation.

[0042] Example 9; In terms of structural design, the main difference between this invention and the prior art is that in the prior art, the interface between the rigid PCB and the FPC is usually located in the middle area of ​​the circuit board. That is, under normal working conditions, this interface is simultaneously subjected to multiple loads such as thermal stress, vibration stress and electromagnetic force, which is prone to fatigue failure. In contrast, this invention sets the rigid-to-flexible interface at the controlled-depth milling flexible transition zone 30. This area becomes a flexible hinge section after assembly and does not bear any dynamic load. It only undergoes one-time deformation during assembly bending, thus completely eliminating the risk of fatigue failure under dynamic load.

[0043] In terms of process implementation, the PCB and FPC manufacturing processes adopted in this invention have good process compatibility and do not require the development of dedicated rigid-flex bonding equipment and materials. The multilayer rigid PCB is manufactured using standard PCB processes, including mature procedures such as inner layer etching, prepreg lamination, and metallized via fabrication. The FPC is manufactured using standard FPC processes, including PI copper etching, solder mask treatment, and reinforcing sheet bonding. The rigid-flex lamination process uses a low-temperature lamination process to avoid thermal damage to the FPC substrate caused by high temperatures. These characteristics make this invention suitable for large-scale production, resulting in good product consistency and a low scrap rate. The multilayer PCB structure uses photolithography to precisely fabricate coil patterns, achieving high consistency in coil turns and shape. Compared to the traditional manual operation of enameled wire winding, product consistency and repeatability are significantly improved.

[0044] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0046] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is 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 second feature can mean that the first feature is 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.

[0047] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0049] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A composite wiring structure of PCB and FPC, characterized in that, include: Rigid PCB coil units (10) are arranged in an array on an integrated flexible and rigid winding strip (50); The FPC flexible interconnect layer (20) is disposed on the same side of the rigid PCB coil unit (10) and connects the adjacent rigid PCB coil units (10). A controlled-depth milling flexible transition area (30) is provided at the connection between each of the rigid PCB coil units (10) and the FPC flexible interconnect layer (20); An interlayer electrical conduction structure (40) is provided at the connection end between the rigid PCB coil unit (10) and the FPC flexible interconnect layer (20).

2. The PCB and FPC composite wiring structure as described in claim 1, characterized in that, Each of the rigid PCB coil units (10) includes a multilayer rigid substrate, a spiral power coil line (11) etched on each layer of the multilayer substrate, a prepreg and metallized holes disposed between each layer of the power coil line (11), a core mating area (12) disposed at the center of the rigid PCB coil unit (10), and a metallized connection pad (13) disposed at one end of the rigid PCB coil unit (10).

3. The PCB and FPC composite wiring structure as described in claim 2, characterized in that, The multilayer rigid substrate has a structure of two to eight layers, and each layer is fixed by pressing together with a prepreg to form an integral rigid power coil bearing substrate.

4. The PCB and FPC composite wiring structure as described in claim 2, characterized in that, The core mating area (12) is a hollow structure, and its shape and size match the slot structure of the radial motor stator core.

5. The PCB and FPC composite wiring structure as described in claim 1, characterized in that, The FPC flexible interconnect layer (20) includes a high-temperature resistant PI substrate layer (21), metal wires (22) etched on the PI substrate layer (21), mating pads (23) disposed at the ends of the metal wires (22), and reserved three-phase lead-out pads (24).

6. The PCB and FPC composite wiring structure as described in claim 1, characterized in that, The interlayer electrical conduction structure (40) includes a metallized through-hole (41) penetrating the rigid substrate and the FPC substrate, and a hole wall metal layer formed by copper plating and electroplating.

7. A method for fabricating a radial motor stator based on a PCB and FPC composite wiring structure, characterized in that, Includes the following steps: S1 is divided into zones based on the number of slots, inner diameter, rated current, and number of phases of the radial stator core; S2 uses a rigid substrate to make a multi-layer PCB, and forms a spiral power coil circuit pattern on each copper-clad board through an etching process. S3 uses high-temperature resistant PI substrate to make FPC flexible interconnect circuits. The connecting wires between each PCB unit and the three-phase lead-out pads are formed on the PI copper foil material by etching process. S4 achieves precise alignment and bonding between the PCB coil unit and the FPC interconnect layer through positioning reference holes; S5 involves drilling through holes at the mating pads of the rigid PCB and FPC, and forming a metallization layer on the hole wall through chemical copper plating and electroplating processes. S6 uses CNC milling equipment for partitioned milling, including the whole plate milling stage, the controlled depth milling flexible release stage, and the slot fine milling stage; S7, the winding tape is bent into a ring structure along the circumferential direction, and each rigid PCB coil unit is inserted into the slot of the radial motor stator core one by one.

8. The method for manufacturing a radial motor stator as described in claim 7, characterized in that, In S6, the connection between the rigid PCB coil unit and the FPC flexible interconnect layer retains only the lower FPC flexible layer, forming a flexible hinge segment.

9. The method for manufacturing a radial motor stator as described in claim 7, characterized in that, The high-temperature resistant PI substrate layer (21) uses polyimide film as the substrate material, with a thickness of 12 micrometers to 25 micrometers; the width of the controlled-depth milling flexible transition area (30) is 1 millimeter to 5 millimeters.

10. The method for manufacturing a radial motor stator as described in claim 7, characterized in that, The metallized through-hole (41) is a PTH electroplated through-hole structure with a diameter of 0.3 mm to 0.8 mm.

Images