Flexible circuit board magnetic field coil for chip atomic clock

Abstract

The utility model provides a flexible circuit board magnetic field coil for a chip atomic clock. The flexible circuit board magnetic field coil comprises a flexible circuit board and a tubular structure, wherein one short edge of the flexible circuit board is curled around the outer surface of an atomic gas chamber in the direction of the long edge of the flexible circuit board and is connected with the other short edge of the flexible circuit board to form the tubular structure; the flexible circuit board sequentially comprises an outer wire layer, an insulating layer and an inner wire layer from outside to inside, the outer wire layer comprises a spiral wire, the inner wire layer comprises a switching wire, the spiral wire and the switching wire are connected through a welding hole in the insulating layer to form a complete wire, and a plurality of wires are sequentially connected to form a magnetic field coil; the head and tail ends of the magnetic field coil are electrified to form a uniform magnetic field in the atomic gas chamber. The device can meet the requirement of atomic clock transition spectral lines on the stability of a magnetic field.

Description

Technical Field

[0001] This utility model relates to the field of laser technology, specifically to a flexible circuit board magnetic field coil for a chip atomic clock. Background Technology

[0002] Currently, atomic clocks on chips generate magnetic fields using solenoid coils and Helmholtz coils. The conditions for a Helmholtz coil to generate a magnetic field are quite stringent: a pair of parallel and coaxial current-carrying coils; identical currents; and the distance between the two coils equal to the coil radius. Only when these three conditions are met can a large-scale uniform magnetic field be generated near the axial center. Traditional copper wire-wound solenoid coils, using multidimensional orthogonal coils or a mixture with other types of magnetic field coils, produce relatively high magnetic field uniformity, but the winding process is complex and unsuitable for large-scale mass production. Furthermore, existing solutions have the following drawbacks: First, the composite layout of multidimensional orthogonal coils results in excessive space occupation, failing to meet the millimeter-level packaging requirements of atomic clocks on chips; second, the interlayer coupling between the bottom-layer cyclotron magnetic field coil and the top-layer static magnetic field coil introduces additional magnetic field interference, disrupting the axial uniformity of the magnetic field; third, the helical coil configuration formed by welding the short side of a flexible board carries the risk of misalignment at the joint, making it difficult to guarantee an axial magnetic field uniformity better than 10. -4 Technical requirements at the scale. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a flexible circuit board magnetic field coil for a chip atomic clock. This coil meets the stability requirements of the magnetic field for atomic clock transition lines, and solves the problem that traditional flexible coils, formed by short-side welding to create a helical configuration, suffer from limitations in axial magnetic field uniformity due to circuit board extension tolerances and joint misalignment. -4 The magnitude of the problem is insufficient to meet the stability requirements of atomic clock transition lines.

[0004] The technical solution provided by this utility model is as follows:

[0005] A flexible circuit board magnetic field coil for a chip atomic clock, surrounding the atomic gas chamber within the chip atomic clock and tightly attached to its outer surface, includes a flexible circuit board. The flexible circuit board is a rectangular thin plate, with one short side rolled around the outer surface of the atomic gas chamber along its long side and connected to the other short side to form a tubular structure. The flexible circuit board, from the outside in, includes an outer conductor layer, an insulating layer, and an inner conductor layer. The outer conductor layer includes multiple vertically parallel spiral conductors surrounding the insulating layer. The inner conductor layer includes multiple vertically parallel connecting conductors. The spiral conductors and connecting conductors are connected through solder holes in the insulating layer to form a complete conductor. Multiple vertically evenly distributed conductors are sequentially connected to form a spirally wound magnetic field coil surrounding the tubular structure. When energized at both ends of the magnetic field coil, a uniform magnetic field is generated inside the atomic gas chamber. This invention establishes a model of a wound magnetic field coil, with an effective area of ​​the atomic gas chamber greater than or equal to 3 × 10⁻⁶. -5 With magnetic field uniformity as the objective, the conductor inclination angle, conductor spacing, and weld hole distribution of the inner and outer conductor layers are iteratively optimized.

[0006] The flexible circuit board magnetic field coil is a solenoid coil wound and welded from a single layer of FPC board, with the coil tightly attached to the outer surface of the polyimide film. The outer conductor layer includes a spiral conductor made of multiple resistance wires and positive and negative leads; there are 50-70 of these leads, arranged in parallel and equally spaced rows on the insulating layer made of polyimide film. By using spiral conductors made of copper-nickel alloy and transition conductors made of nickel-chromium alloy, the difference in material resistivity compensates for the non-uniformity of current distribution, further improving the uniformity of the magnetic field.

[0007] Furthermore, the central axis of the flexible circuit board magnetic field coil is on the same straight line as the central axis of the atomic gas cell, and the distance between the center point of the atomic gas cell and the center point of the flexible circuit board magnetic field coil is less than or equal to 1 / 4 of the axial length of the flexible circuit board magnetic field coil.

[0008] Furthermore, the weld holes are radially opened along the tubular structure, with 60-70 holes and a diameter of 0.05mm. Multiple weld holes are arranged axially, with the outer end of each hole connected to the beginning of the helical wire and its inner end connected to the beginning of the adapter wire. The tail end of the helical wire connects to the adapter wire of the next row, and the tail end of the adapter wire connects to the helical wire of the previous row. The adapter resistance wire is provided with 60-70 resistance wire adapter solder points, arranged in a parallel and equally spaced magnetic field coil manner on an insulating layer made of polyamide film. The long axis of the resistance wire adapter solder points is parallel to the long axis of the insulating layer. This invention achieves vertical conduction between the outer helical wire and the inner adapter wire by laser processing axially equidistant weld holes on the insulating layer and sputtering coating, thus eliminating interlayer magnetic field coupling.

[0009] Furthermore, the angle between the conductor on the outer conductor layer and the radial surface of the tubular structure is an acute angle, such that the starting position of the Nth resistance wire and the ending position of the (N-1)th resistance wire are at the same height; the cross-sectional diameter of the spiral conductor of the outer conductor layer is 20um to 30um; the spacing between the upper and lower conductors ranges from 42um to 60um; and the thickness of the insulation layer ranges from 0.7 to 1.5mm.

[0010] Furthermore, the conductors on the outer and inner conductor layers are resistance wires, and the insulating layer is a polyimide film with a thickness of 1-1.5 mm; the main material of the resistance wire is copper, and nickel metal is deposited at the solder joints.

[0011] This invention constructs an equivalent infinitely long solenoid current loop by using inclined spiral wires in the outer conductor layer and transition wires in the inner conductor layer of a flexible circuit board. The inclination angle and spacing of the wires are optimized through finite element simulation to ensure that the tubular structure formed after winding generates a uniform axial magnetic field in the axial region and eliminates the radial magnetic field component.

[0012] This invention uses a single-layer polyimide film to form the insulating layer and constructs a double-sided wiring scheme. The planar circuit is converted into a three-dimensional coil structure through a precision winding process. A rectangular flexible plate is designed to be rolled into a tubular structure with an inner diameter of 4mm along the short side. Laser positioning and low-temperature welding technology are used to achieve high-precision docking of the short side, ensuring that the coil axis is strictly coaxial with the atomic gas cell with a deviation of ≤0.05mm. From a physical structure perspective, this avoids the redundant space occupation of traditional three-dimensional coils.

[0013] The technical effects of this utility model are as follows:

[0014] This invention employs a parallel interconnection design between an outer spiral conductor and an inner transition conductor to eliminate parasitic magnetic field components in the orthogonal direction, achieving an axial magnetic field purity of 99.7%, avoiding magnetic field distortion caused by interlayer coupling, and suppressing interfering magnetic fields.

[0015] This invention achieves a magnetic field uniformity of 3×10⁻⁶ in the effective area of ​​the atomic gas chamber by setting the tilt angle of the outer spiral wire and the inner transition wire, as well as setting the spacing and number of turns of the outer spiral wire and the inner transition wire, and by limiting the center axis of the magnetic field coil of the flexible circuit board and the center axis of the atomic gas chamber. -5 This represents an improvement of nearly one order of magnitude over existing technologies, ensuring the stability of the transition frequency of the 87Rb atomic clock. It also solves the problem that traditional flexible coils, formed by short-side welding to create a spiral configuration, are affected by circuit board extension tolerances and joint misalignment, making it difficult to achieve axial magnetic field uniformity exceeding 10. -4 The magnitude is insufficient to meet the stability requirements of atomic clock transition lines.

[0016] This invention uses a flexible circuit board to form a quasi-long solenoid equivalent structure, compressing the coil packaging size to Φ5mm×10mm. Compared with the traditional multi-dimensional coil solution, the volume is reduced by nearly 80%, which is suitable for the micro cavity of the chip atomic clock. It solves the problem that the existing flexible circuit board magnetic field coil adopts a three-dimensional orthogonal coil layout, resulting in an excessively large overall structure size, which cannot meet the millimeter-level packaging requirements of the chip atomic clock, and the interlayer magnetic field coupling will introduce interference components.

[0017] The flexible circuit board magnetic field coil provided by this utility model is formed by winding and welding a flexible circuit board into a multi-turn solenoid. On the one hand, it reduces the process and cost of manufacturing the magnetic field coil support, making the manufacturing of atomic clocks simpler and more integrated. On the other hand, compared with the two traditional magnetic field coil manufacturing processes, the magnetic field uniformity and quality control are further improved. Compared with traditional copper wire wound coils, the magnetic field coil is lighter and thinner, making it suitable for space-sensitive scenarios, such as chip atomic clocks, and can be integrated with other components, such as with cantilever beam polyimide film structures, simplifying the assembly process. At the same time, the resistance wire pattern is made using photolithography, which results in high manufacturing precision and improves magnetic field uniformity and efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a flexible circuit board magnetic field coil for a chip atomic clock, as described in an embodiment of this utility model.

[0019] Figure 2 This is a front view of the unfolded magnetic field coil of a flexible circuit board for a chip atomic clock, as described in this embodiment of the present invention.

[0020] Figure 3 yes Figure 2 Rear view;

[0021] Figure 4 yes Figure 2 Enlarged view of region A in the middle;

[0022] Figure 5 yes Figure 3 Enlarged schematic diagram of region B in the middle. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0024] As attached Figure 1 To be continued Figure 5 As shown, this embodiment of the invention provides a flexible circuit board magnetic field coil for a chip atomic clock. The coil surrounds the atomic gas chamber 1 within the chip atomic clock and is tightly fitted to the outer surface of the atomic gas chamber 1. The central axis of the flexible circuit board magnetic field coil is on the same straight line as the central axis of the atomic gas chamber 1, and the distance between the center point of the atomic gas chamber 1 and the center point of the flexible circuit board magnetic field coil is less than or equal to 1 / 4 of the axial length of the flexible circuit board magnetic field coil. This embodiment of the invention optimizes the wire arrangement parameters through finite element simulation to ensure that the axial offset between the center point of the atomic gas chamber 1 and the center point of the coil is ≤2.5mm, i.e., 1 / 4 of the coil's axial length.

[0025] The flexible circuit board magnetic field coil includes a flexible circuit board 2, which is a rectangular thin plate. It is a tubular structure formed by curling one of its short sides around the outer surface of the atomic gas chamber 1 along its long side and connecting it with the other short side.

[0026] The flexible circuit board 2 comprises, from the outside in, an outer conductive layer 2-1, an insulating layer 2-2, and an inner conductive layer 2-3. The conductors on the outer conductive layer 2-1 and the inner conductive layer 2-3 are resistance wires, and the insulating layer 2-2 is a polyimide film. The polyimide film serves as the supporting structure for the inner and outer conductive layers 2-1, i.e., the supporting structure for the magnetic field coil. The polyimide film is shaped like a large rectangle supporting the coil combined with small rectangles for the positive and negative leads.

[0027] The outer conductor layer 2-1 includes multiple segments of spiral conductors 3 that are parallel to each other in the vertical direction and surround the insulating layer 2-2. The inner conductor layer 2-3 includes multiple segments of adapter conductors 4 that are parallel to each other in the vertical direction. The spiral conductors 3 and adapter conductors 4 are connected through solder holes on the insulating layer 2-2 to form a complete conductor. The angle between the conductors on the outer conductor layer 2-1 and the radial surface of the tubular structure is an acute angle of 15 degrees. The cross-sectional diameter of the spiral conductors 3 in the outer conductor layer 2-1 is 20µm to 30µm. The spacing between the upper and lower conductors ranges from 42µm to 60µm. The thickness of the insulating layer 2-2 ranges from 0.7 to 1.5mm. Multiple conductors that are evenly distributed vertically are connected in sequence to form a spiral magnetic field coil that surrounds the tubular structure. The spiral conductors 3 in the outer conductor layer 2-1 are arranged on the polyamide film in a parallel and equally spaced manner. The starting position of the Nth resistance wire and the ending position of the (N-1)th resistance wire are at the short axis position. The short rectangular line on the left connects to the positive pole of the magnetic field coil, and the long rectangular line on the left connects to the negative pole of the magnetic field coil.

[0028] The outer conductor layer 2-1 is fabricated using photolithography to create a 50-turn parallel helical conductor 3. The conductor material has a resistivity of 4.8 × 10⁻⁶. -7Ω·m copper-nickel alloy resistance wire. The inner conductor layer 2-3 achieves interlayer conductivity via a connecting conductor 4. The cross-sectional diameter (i.e., wire width) of the connecting conductor 4 is 30µm, and it connects to the outer spiral conductor 3 through axially equidistantly distributed solder holes on the insulating layer 2-2. All conductors are inclined at a 15° angle to the radial plane on the radial cross-section of the tubular structure, simulating the axial magnetic field distribution characteristics of an infinitely long solenoid.

[0029] When the magnetic field coil is energized at both ends, a uniform magnetic field is formed inside atomic gas chamber 1. The energization test shows that when a 200mA current is applied to the coil, the magnetic field strength in the axial central region of atomic gas chamber 1 is 1.2mT, with a uniformity of 3×10⁻⁶ m / s². -5 This satisfies the stability requirements of the C field for the transition spectral lines of the 87Rb atomic clock.

[0030] Preferably, the weld holes are radially opened along the tubular structure, and multiple weld holes are arranged axially. The outer end of each weld hole is connected to the beginning of the spiral wire 3 and its inner end is connected to the beginning of the adapter wire 4. The tail end of the spiral wire 3 is connected to the adapter wire 4 of the next row, and the tail end of the adapter wire 4 is connected to the spiral wire 3 of the previous row. In this embodiment, the tail end of the nth turn of the spiral wire 3 is connected downward to the beginning of the (n+1)th turn of the adapter wire 4 through the (n+1)th weld hole, and the beginning of the nth turn of the spiral wire 3 is connected upward to the tail end of the (n-1)th turn of the adapter wire 4, forming a continuous spiral path.

[0031] Multiple connecting wires 4 and connecting solder joints are arranged on the inner surface of the flexible circuit board 2. The solder holes on the inner and outer surfaces are consistent, and the connecting solder joints are distributed on the left side of the solder holes. The line width spacing is consistent with the spiral wires 3 on the outer conductor layer 2-1.

[0032] After the flexible circuit board 2 is wound and soldered, the current flows through the positive lead, then through the solder hole a1 to the first transition solder point b1 on the inner surface. This solder point is connected to the rightmost position c1 of the first spiral wire 3 on the outer layer. The current then flows through the spiral wire 3 of the outer conductor layer 2-1 of the first magnetic field coil and returns to the second solder hole a2, where position b1 is soldered to position c1. The current then reaches the second transition solder point b2 on the inner layer through the second solder hole a2. This transition solder point is connected to the rightmost position c2 of the second spiral wire 3 on the outer layer. The current then flows through the second spiral wire 3, and so on, in a cycle. The direction of the current is: positive terminal point → a1 → b1 → c1 → a2 → b2 → c2 → a3 → b3 → c3 → a4 → b4 → c4 → … → an → bn → cn → negative terminal point.

[0033] In this embodiment of the utility model, a tubular structure is formed by rolling up a flexible circuit board 2. A spiral wire 3 is arranged in the outer conductor layer 2-1, and a transition wire 4 is arranged in the inner conductor layer 2-3. The tail end of the nth turn of the spiral wire 3 is connected downward to the head end of the n+1th turn of the transition wire 4 through the (n+1)th solder hole, forming a continuous spiral path.

[0034] This embodiment of the invention provides a flexible circuit board magnetic field coil for a chip atomic clock. The coil surrounds the atomic gas chamber 1 within the chip atomic clock and is tightly fitted to the outer surface of the atomic gas chamber 1. The flexible circuit board 2, from the outside in, includes an outer conductor layer 2-1, an insulating layer 2-2, and an inner conductor layer 2-3. The outer conductor layer 2-1 includes a spiral conductor 3. The tail end of the nth turn of the spiral conductor 3 is connected downwards through the (n+1)th solder hole to the head end of the (n+1)th turn of the adapter conductor 4, forming a spiral-shaped, tubular magnetic field coil. When a current of 0.4mA is applied to the coil, a uniform magnetic field with a magnetic field strength of 1.2mT is generated in the axial central region of the atomic gas chamber 1, with a uniformity of 3×10⁻⁶. -5 This technology meets the magnetic field stability requirements of the 87Rb atomic clock transition lines, and solves the problem that traditional flexible coils, formed by short-side welding to create a helical configuration, are affected by circuit board extension tolerances and joint misalignment, making it difficult to achieve axial magnetic field uniformity exceeding 10. -4 The magnitude of the problem is insufficient to meet the stability requirements of atomic clock transition lines.

Claims

1. A flexible circuit board magnetic field coil for a chip atomic clock, which is wrapped around the outside of an atomic cell (1) in the chip atomic clock and closely adheres to the outer surface of the atomic cell (1), and comprises a flexible circuit board (2), characterized in that the flexible circuit board (2) is in the shape of a rectangular thin plate, and is wound around the outer surface of the atomic cell (1) along the long direction of one short side and connected to the other short side to form a tubular structure; the flexible circuit board (2) comprises, from the outside to the inside, an outer conductor layer (2-1), an insulating layer (2-2), and an inner conductor layer (2-3), the outer conductor layer (2-1) comprises a plurality of helical conductors (3), and the inner conductor layer (2-3) comprises a plurality of adapter conductors (4), the helical conductors (3) and the adapter conductors (4) are connected through the solder holes in the insulating layer (2-2) to form a complete conductor, and a plurality of conductors are connected in sequence to form a helical magnetic field coil wrapped around the tubular structure, the central axis of the magnetic field coil is in the same straight line as the central axis of the atomic cell (1), and a uniform axial magnetic field is formed in the effective area inside the atomic cell (1) after the first and last ends of the magnetic field coil are energized.

2. The flexible circuit board magnetic field coil for a chip atomic clock according to claim 1, characterized in that the distance between the center point of the atomic cell (1) and the center point of the flexible circuit board magnetic field coil is less than or equal to 1 / 4 of the axial length of the flexible circuit board magnetic field coil.

3. The flexible circuit board magnetic field coil for a chip atomic clock according to claim 1 or 2, characterized in that the solder holes are radially opened along the tubular structure, a plurality of solder holes are arranged in the axial direction, and the outer end of each solder hole is connected to the first end of the helical conductor (3) and the inner end is connected to the first end of the adapter conductor (4), the tail end of the helical conductor (3) is connected to the adapter conductor (4) in the next row, and the tail end of the adapter conductor (4) is connected to the helical conductor (3) in the previous row.

4. The flexible circuit board magnetic field coil for a chip atomic clock according to claim 3, characterized in that the included angle between the conductor on the outer conductor layer (2-1) and the radial surface of the tubular structure is an acute angle, the cross-sectional diameter of the helical conductor (3) of the outer conductor layer (2-1) is 20-30 um, the spacing between the upper and lower rows of conductors is 42-60 um, and the thickness of the insulating layer (2-2) is 0.7-1.5 mm. ​ ​ ​ ​

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