Flexible printed circuit board large current transmission method in a weak magnetic environment

Abstract

The application discloses a flexible printed circuit board large current transmission method in a weak magnetic environment. The method comprises the following steps: designing a wiring structure, decomposing a current loop into an array form, and arranging in high symmetry; planning a flexible PCB laminated structure, designing a line width, a wiring spacing, a geometric size and the like according to the determined wiring structure, and connecting current conductors of different layers by using a via; and according to the structure and function of a transmission object, completing electrical connection, connecting the current connection of the completed wiring design to a solder pad, a connector and the like, forming electrical connection, and completing current transmission. The application can be applied to a large current in a weak magnetic environment, can reduce a magnetic field of a hundred-milliamperes current to a nanotesla order of magnitude, and has the functions of complex structure design and electrical connection.

Description

Technical Field

[0001] This invention relates to the field of precision magnetic field measurement, specifically to a method for reducing the magnetic field generated during the transmission of a hundred-milliampere current to the nanotesla level by designing the wiring method and lamination structure of flexible printed circuit board (PCB) cables, thereby enabling the application of large currents in weak magnetic environments. Background Technology

[0002] According to Biot-Savart's law, electric current and magnetic field are a deeply coupled pair of physical quantities. Therefore, in many environments requiring precise magnetic field measurements, the ambient current must be kept at a low level. For example, magnetoencephalography (MEG) studies brain function by detecting the weak picotesla-level magnetic field (approximately one billionth the strength of the Earth's magnetic field) generated by neuronal activity; magnetocardiography (MCC) captures the sub-nanotela-level magnetic field generated by cardiac electrical activity. In these measurements, active or passive shielding techniques are first required to shield against strong external magnetic field interference sources such as the Earth's magnetic field, reducing the background magnetic field to the nanotesla level.

[0003] Furthermore, the magnetic shielding device should avoid introducing new sources of interference, such as electronic components and power supply lines, to prevent problems like static magnetic fields or magnetic noise caused by strong power supply current. Therefore, apart from the magnetic field detector, other auxiliary equipment is difficult to introduce into the measurement environment. However, some weakly magnetic electronic components and optical chips can provide auxiliary functions for magnetic field measurement in weak magnetic detection environments, such as communication, electrophysiological data acquisition, and wearable medical monitoring sensors. For the magnetic compatibility requirements of these devices, in addition to the chip material itself, the chip's power supply usually requires a strong current; therefore, the power supply and signal current also need to be specifically designed for magnetic compatibility.

[0004] Current transmission occurs in a loop. Because the current travels in opposite directions, the resulting magnetic fields also have different directions. Therefore, when the current travels in the same direction, the smaller the distance between the two currents, the opposite the directions of the magnetic fields, and the better their mutual cancellation. Commonly used twisted-pair cables and coaxial cables both have the function of mutually canceling and suppressing magnetic field leakage. However, traditional coaxial cables and twisted-pair cables only have simple connection and transmission functions, rely on connectors, and are relatively small and inflexible. Flexible PCBs, on the other hand, can adapt to most deformation scenarios, and their routing schemes can be precisely designed. They can be specifically designed for magnetic fields, and their mounting with various chips is more flexible. They can accommodate wire bonding, on-chip packaging, and other process conditions while also considering magnetic fields.

[0005] In summary, the flexible design and application of flexible PCBs in weak magnetic environments, which allows for current transmission while minimizing magnetic field interference in measurements, can provide more application opportunities for electronic devices in precision magnetic field measurements. However, a complete and practical method for flexible PCB current transmission that simultaneously considers magnetic fields has not yet been proposed. Summary of the Invention

[0006] In view of the above, the purpose of this invention is to provide a method for transmitting a current of hundreds of milliamperes in a weak magnetic environment while reducing the magnetic field generated at close range to the nanotesla level (nT).

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for high current transmission on a flexible printed circuit board in a weak magnetic environment includes the following steps:

[0009] The back-and-forth conductors in the multilayer flexible PCB are divided into an even number of equal parts, namely conductors in the first current direction and conductors in the second current direction, wherein the first current direction is the opposite of the second current direction.

[0010] The conductors in the first current direction and the conductors in the second current direction are arranged in an N×N distribution pattern to cancel out the magnetic field, wherein the conductors in the first current direction and the conductors in the second current direction are arranged alternately in both the layer width direction and the layer thickness direction of the multilayer flexible PCB.

[0011] High current transmission and reduced magnetic field are achieved by using N×N distributed conductors in a multilayer flexible PCB.

[0012] Furthermore, the N×N distribution is a 2×2 distribution, representing two layers of flexible PCB, with two conductors laid on each layer.

[0013] Furthermore, the N×N distribution is a 4×4 distribution, representing a 4-layer flexible PCB with 4 conductors laid in each layer.

[0014] Furthermore, the 4×4 distribution can be one of the following three configurations, where “·” and “×” represent the first current direction and the second current direction, respectively:

[0015] Configuration A: The arrangement of the first layer of conductors is “·×·×”, the arrangement of the second layer of conductors is “×·×·”, the arrangement of the third layer of conductors is “·×·×”, and the arrangement of the fourth layer of conductors is “×·×·”.

[0016] Configuration B: The arrangement of the first layer of conductors is “·××·”, the arrangement of the second layer of conductors is “×··×”, the arrangement of the third layer of conductors is “·××·”, and the arrangement of the fourth layer of conductors is “×··×”.

[0017] C configuration: The arrangement of the first layer of conductors is “·××·”, the arrangement of the second layer of conductors is “×··×”, the arrangement of the third layer of conductors is “×··×”, and the arrangement of the fourth layer of conductors is “·××·”.

[0018] Furthermore, based on the requirements of the testing environment and factors such as cost and size, the number of layers, line width, layer width spacing, and layer thickness spacing of the flexible PCB are selected, and the electrical connection points are designed according to the transmission object, thereby forming a magnetically compatible current transmission scheme.

[0019] Furthermore, by setting multiple vias, the conductors of different layers of the flexible PCB are connected without interference. Each layer is bonded with insulating material, and a protective layer is laid on the surface to form a laminated structure, thereby determining the total thickness of the flexible PCB.

[0020] Furthermore, after the wires are interconnected through vias, mounting pads are placed on the flexible PCB to form an electrical connection with the wires, and then connected to the chip by wire bonding to complete the electrical connection.

[0021] The present invention also provides a flexible printed circuit board in a weak magnetic environment for implementing the above method, comprising a multilayer flexible PCB; the back-and-forth conductors in the multilayer flexible PCB are divided into an even number of equal parts, namely conductors in a first current direction and conductors in a second current direction, wherein the first current direction is the opposite direction of the second current direction; the conductors in the first current direction and the conductors in the second current direction are arranged in an N×N distribution pattern to cancel out the magnetic field, wherein the conductors in the first current direction and the conductors in the second current direction are arranged alternately in both the layer width direction and the layer thickness direction of the multilayer flexible PCB.

[0022] The high-current transmission method for flexible PCBs in a weak magnetic environment described in this invention has the following advantages:

[0023] 1. This method can reduce the magnetic field generated by transmitting a current of hundreds of milliamperes to the nT level over a short distance in a precision magnetic field measurement scenario, which is the same as the shielding level of general magnetic shielding devices and is compatible with the requirements of weak magnetic field detection.

[0024] 2. The flexible PCB used is suitable for most deformation scenarios and can adapt to different structures and systems;

[0025] 3. Flexible PCBs also support the mounting of chips and electronic components, enabling the realization of complex electronic functions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the principle of the present invention;

[0027] Figure 2This diagram illustrates the lamination structure of a flexible PCB and an example of chip current transmission. Coverlay represents the protective layer; Polyimide is the main material for flexible printed circuit boards; Top Layer represents the surface layer; Middle Layer 1 represents middle layer 1; Middle Layer 2 represents middle layer 2; and Bottom Layer represents the bottom layer. Detailed Implementation

[0028] In the following description, the flexible PCB current transfer method of the present invention is further described through specific embodiments to enable those skilled in the art to have a more thorough understanding of the features and advantages of the present invention. It should be noted that the following description is only a representative typical application. Obviously, the present invention is not limited to any specific structure, function, device, and method described herein, and may have other embodiments or combinations of other embodiments. The software / hardware modules described in the present invention or shown in the accompanying drawings can also be flexibly adjusted as needed.

[0029] This invention provides a method for high-current transmission on flexible printed circuit boards in a weak magnetic environment, which can achieve magnetic field cancellation on multilayer flexible PCBs. The technical solution is as follows:

[0030] Divide the round-trip current (wires) in a multilayer flexible PCB into even-numbered parts, creating wires in a first current direction and a second current direction, where the first current direction is the opposite of the second current direction. Rearrange these parts to obtain... Figure 1 The diagram shows various N×N distribution arrangements with offsetting current, where the conductors in the first current direction and the conductors in the second current direction are arranged alternately in both the layer width direction (lateral) and the layer thickness direction (vertical). Examples include 2×2 and 4×4 distributions. The 4×4 distribution can be further divided into three configurations: A, B, and C. 2×2 represents a 2-layer flexible PCB with 2 conductors per layer; 4×4 represents a 4-layer flexible PCB with 4 conductors per layer. "·" indicates that the current direction is perpendicular to the paper and outwards, while "×" indicates that the current direction is perpendicular to the paper and inwards.

[0031] like Figure 1 As shown, the three configurations of the 4×4 distribution are as follows:

[0032] Configuration A: The arrangement of the first layer of conductors is “·×·×”, the arrangement of the second layer of conductors is “×·×·”, the arrangement of the third layer of conductors is “·×·×”, and the arrangement of the fourth layer of conductors is “×·×·”.

[0033] Configuration B: The arrangement of the first layer of conductors is “·××·”, the arrangement of the second layer of conductors is “×··×”, the arrangement of the third layer of conductors is “·××·”, and the arrangement of the fourth layer of conductors is “×··×”.

[0034] C configuration: The arrangement of the first layer of conductors is “·××·”, the arrangement of the second layer of conductors is “×··×”, the arrangement of the third layer of conductors is “×··×”, and the arrangement of the fourth layer of conductors is “·××·”.

[0035] Using an infinitely long straight conductor model, the magnetic field generated by each conductor at point P is calculated using the conductor spacing d1 (horizontal conductor spacing), d2 (vertical conductor spacing), the distance D between the points to be measured, and the number of conductors per layer K. This magnetic field is then decomposed, summed, and used to represent the magnetic field at point P.

[0036]

[0037] The distance from each wire to point P i represents the i-th conductor in the transverse (layer width) direction, j represents the j-th conductor in the longitudinal (layer thickness) direction, μ0 represents the free permeability, and I represents the current in each conductor.

[0038] Based on the typical manufacturing capabilities of flexible PCBs, 2, 4, and 8 layers are suitable choices. The trace spacing d1 is set as the layer width direction, typically 10 mil; the spacing d2 is set as the layer thickness direction, typically 3 mil. Numerical calculations were used to obtain the magnetic field magnitude M generated at point P when the distance D between the test points varies from 1 to 10 mm, assuming a 100 mA current is transmitted. sum As shown in Table 1.

[0039] Table 1

[0040]

[0041] All of the above configurations can cancel the magnetic field to 1nT at a distance of 1cm from the point to be measured. Among them, the C scheme of the 4×4 configuration has the best symmetry and therefore the strongest magnetic field cancellation effect.

[0042] In the design of flexible PCBs, based on the requirements of the testing environment and factors such as cost and size, the appropriate number of layers, trace width, layer width spacing (i.e., conductor spacing d1 in the layer width direction) and layer thickness spacing (i.e., conductor spacing d2 in the layer thickness direction) are selected. The electrical connections are then designed according to the transmission target to complete the design of the magnetic compatibility current transmission scheme. Here, layer width spacing refers to the distance between adjacent conductors on the same layer, and layer thickness spacing refers to the distance between adjacent layers.

[0043] According to an embodiment of the present invention, the method for realizing high current transmission on a flexible PCB in a weak magnetic environment mainly includes three steps:

[0044] First, the wiring topology is designed based on actual needs: Figure 1 The paper presents one 2×2 and three 4×4 cancellation configurations. According to theoretical calculations, structure C exhibits the strongest symmetry and provides the best cancellation effect. In the detection of extremely weak magnetic fields, such as biomagnetic measurements like magnetocardiography and magnetoencephalography, where the signal magnitude is in the range of pT to fT, configuration C with more layers is more advantageous. Configurations with even higher layer counts offer better cancellation effects, but current flexible PCB technologies mostly support only 2 to 12 layers. Therefore, while meeting the magnetic compatibility requirements of the signal under test, choosing fewer layers can better control costs and reduce design and manufacturing complexity.

[0045] Secondly, plan the PCB lamination structure: for example, after selecting a 4-layer flexible PCB, determine the trace width and spacing, plan the lamination structure, and determine the PCB geometry based on the measurement environment. Figure 2 As shown, a 4-layer flexible PCB configuration C is selected, with four conductors laid on each layer. The conductors on the top and bottom layers are defined sequentially as "+", "-", "-", "+", and the conductors on the middle two layers are defined as "-", "+", "+", "-". The "+" and "-" are connected at the beginning and end respectively to complete the conductor definition. Here, "+" indicates the positive direction of current propagation, and "-" indicates the return path of current, in the opposite direction of propagation. Multiple vias are used to connect the conductors of different layers without interference. Each layer is bonded together using an insulating material such as polyimide, and a protective layer is then laid on the surface to form a laminated structure, determining the total thickness of the flexible PCB.

[0046] Finally, the electrical connection method is designed specifically according to the structure or function of the object being transmitted: the connection method is designed according to the actual object to be connected. For example, for unpackaged bare chips that meet magnetic compatibility requirements, wire bonding is required for connection. Figure 2 As shown, after the "+" and "-" wires are connected to each other through vias, mounting pads are set on the flexible PCB to form an electrical connection with the wires, and then connected to the chip through wire bonding and other methods to complete the electrical connection design.

[0047] In summary, this invention discloses a method for high-current transmission on flexible printed circuit boards in weak magnetic environments. This method includes designing a trace structure, decomposing the current loop into an array and arranging it with high symmetry; planning the flexible PCB lamination structure, designing the trace width, trace spacing, and geometric dimensions according to the determined trace structure, and connecting the current conductors of different layers using vias; completing the electrical connection according to the structure and function of the object being transmitted, connecting the designed current traces to pads, connectors, and other structures to form an electrical connection and complete the current transmission. This invention enables the application of high current in weak magnetic environments, reducing the magnetic field of a hundred-milliampere current to the nanotesla level, while also possessing the functionality of complex structural design and electrical connection.

[0048] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can make modifications and changes to the above embodiments without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be as set forth in the claims.

Claims

1. A method for high current transmission on a flexible printed circuit board in a weak magnetic environment, characterized in that, The method transmits hundreds of milliamperes of current in a weak magnetic environment, while reducing the magnetic field generated at close range to the nanotesla level. The method includes the following steps: The back-and-forth conductors in the multilayer flexible PCB are divided into an even number of equal parts, namely conductors in the first current direction and conductors in the second current direction, wherein the first current direction is the opposite of the second current direction. The conductors in the first current direction and the conductors in the second current direction are arranged in an N×N distribution pattern to cancel out the magnetic field, wherein the conductors in the first current direction and the conductors in the second current direction are arranged alternately in both the layer width direction and the layer thickness direction of the multilayer flexible PCB. High current transmission and reduced magnetic field are achieved by using N×N distributed conductors in multilayer flexible PCBs; The magnetic field at the point P to be measured is calculated using the following formula: in, Let P be the distance from each wire to point P. ; This represents the i-th horizontal wire. This represents the j-th longitudinal wire. Represents the permeability of free space. This indicates the current in each wire; Indicates the horizontal spacing between conductors. The longitudinal conductor spacing is represented by D, the distance between the points to be measured is represented by K, and the number of conductors per layer is represented by K. The N×N distribution is a 4×4 distribution, representing a 4-layer flexible PCB with 4 conductors laid in each layer; The 4×4 distribution has the following configuration, where "·" and "×" represent the first current direction and the second current direction, respectively: The first layer of conductors is arranged in the pattern "·××·", the second layer of conductors is arranged in the pattern "×··×", the third layer of conductors is arranged in the pattern "×··×", and the fourth layer of conductors is arranged in the pattern "·××·".

2. The method according to claim 1, characterized in that, Based on the requirements of the testing environment and factors such as cost and size, the line width, layer width spacing, and layer thickness spacing of the flexible PCB are selected, and the electrical connection is designed according to the transmission object, thereby forming a magnetically compatible current transmission scheme.

3. The method according to claim 2, characterized in that, By setting multiple vias, the conductors of different layers of the flexible PCB are connected without interference. Each layer is bonded with insulating material, and a protective layer is laid on the surface to form a laminated structure, thereby determining the total thickness of the flexible PCB.

4. The method according to claim 3, characterized in that, After the wires are interconnected through vias, mounting pads are placed on the flexible PCB to form an electrical connection with the wires, and then connected to the chip by wire bonding to complete the electrical connection.

5. A flexible printed circuit board in a weak magnetic environment implementing the method of any one of claims 1 to 4, characterized in that, The invention includes a multilayer flexible PCB; the back-and-forth conductors in the multilayer flexible PCB are divided into an even number of equal parts, namely conductors in a first current direction and conductors in a second current direction, wherein the first current direction is the opposite of the second current direction. The conductors in the first current direction and the conductors in the second current direction are arranged in an N×N distribution pattern to cancel out the magnetic field. The conductors in the first current direction and the conductors in the second current direction are arranged alternately in both the layer width direction and the layer thickness direction of the multilayer flexible PCB. The N×N distribution is a 4×4 distribution, which means that there are 4 layers of flexible PCB and 4 conductors are laid in each layer.

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