A patch type magnetostrictive micro-speaker and a preparation method thereof

Abstract

The application discloses a patch type magnetostrictive micro loudspeaker and a preparation method thereof, and belongs to the technical field of electroacoustic transducers. The magnetostrictive micro loudspeaker comprises a PCB substrate, a printed driving coil, an insulating isolation layer and a soft magnetic alloy thin strip. The printed driving coil is arranged on the upper surface of the PCB substrate, the insulating isolation layer covers the outer surface of the printed driving coil, and the soft magnetic alloy thin strip is directly attached to the printed driving coil with the insulating layer and completely coincides with the projection of the printed driving coil. A stress release slit is formed in the lower surface of the PCB substrate, the main direction of the driving magnetic field of the printed driving coil is consistent with the length direction of the soft magnetic alloy thin strip, and the overall thickness of the device is less than 0.3 mm. The patch type magnetostrictive micro loudspeaker and the preparation method thereof have the advantages of greatly improving the magnetic conversion efficiency, realizing extreme thinning, abandoning the rare earth permanent magnet and the independent diaphragm, high sound radiation efficiency, high reliability, low cost and wide application scenarios.

Description

Technical Field

[0001] This invention relates to the field of electroacoustic transducer technology, and in particular to a patch-type magnetostrictive micro loudspeaker and its fabrication method. Background Technology

[0002] Currently, with the rapid development of consumer electronics and wearable devices, the ultra-thinness, miniaturization, high reliability, and low cost of micro-speakers have become the core development direction of the industry. The current mainstream micro-speaker technologies face the following insurmountable technical bottlenecks: Dynamic miniature loudspeakers rely on the combined structure of magnetic circuit components, voice coils and independent diaphragms, making it difficult to compress their thickness to below 0.5mm, which cannot meet the design requirements of ultra-thin terminals. Furthermore, the assembly process is complex and the vibration resistance is poor. MEMS diaphragm miniature loudspeakers: They are fabricated using semiconductor microfabrication technology, which can achieve miniaturization, but the process steps are complicated, the manufacturing cost is high, the yield is low, and the output sound pressure is limited, making it difficult to use on a large scale for commercial applications. Piezoelectric ceramic miniature loudspeakers: They rely on the inverse piezoelectric effect of piezoelectric materials to produce sound. However, piezoelectric ceramic materials are brittle and have poor bending resistance. They cannot withstand the peak temperature of 260°C during reflow soldering, are incompatible with mainstream SMT surface mount technology, and have poor low-frequency response performance. Traditional magnetostrictive transducers, while having advantages such as large driving force, fast response speed and simple structure, generally adopt a structure that combines a wound frame, an independent diaphragm and a permanent magnet. They are large in size and thickness, with a large gap between the magnetostrictive material and the driving coil, resulting in serious magnetic field leakage and low conversion efficiency. They cannot achieve ultra-thinness and patch integration, and they rely on rare earth permanent magnet materials, resulting in poor supply chain stability and high cost.

[0003] In summary, existing micro-speaker technology cannot simultaneously meet the industry's core requirements of "ultra-thin (<0.3mm), SMT surface mount compatibility, rare earth-free, high magnetic conversion efficiency, high reliability, and low cost," becoming a key technological barrier restricting the upgrade of ultra-thin terminal electroacoustic solutions. Summary of the Invention

[0004] The purpose of this invention is to provide a patch-type magnetostrictive micro loudspeaker and its fabrication method, which eliminates the need for rare-earth permanent magnets and independent diaphragms, and solves the problems of thickness bottleneck, low magnetic efficiency, poor process compatibility, high cost, and insufficient reliability in existing technologies.

[0005] To achieve the above objectives, the present invention provides a patch-type magnetostrictive micro loudspeaker, wherein the overall thickness of the patch-type magnetostrictive micro loudspeaker is less than 0.3 mm, and includes a PCB substrate, a printed drive coil, an insulating layer, and a soft magnetic alloy strip. The printed drive coil is disposed on the upper surface of the PCB substrate, and the insulating layer fully covers the outer surface of the printed drive coil. The soft magnetic alloy strip is directly attached to the printed drive coil covered with an insulating layer, and completely overlaps with the projection area of ​​the printed drive coil in the thickness direction of the PCB substrate; the two ends of the soft magnetic alloy strip are electrically connected and fixed to the electrode pads on the PCB substrate through conductive connection layers, forming a vibration boundary with fixed ends and the main body area in the middle tightly attached to the insulating layer. The printed drive coil adopts an 8-shaped winding structure or a concentric double-winding structure. The main direction of the driving magnetic field generated by the printed drive coil after being energized is consistent with the length direction of the soft magnetic alloy strip. The lower surface of the PCB substrate is provided with a stress relief slit, and the projection of the stress relief slit in the thickness direction of the PCB substrate at least partially overlaps with the projection area of ​​the soft magnetic alloy strip.

[0006] Preferably, the soft magnetic alloy strip is an amorphous soft magnetic alloy strip or a nanocrystalline soft magnetic alloy strip, with a saturation magnetostriction coefficient λs ≥ 20ppm, a Curie temperature Tc ≥ 180℃, and a strip thickness of 10μm-30μm.

[0007] Preferably, the nanocrystalline soft magnetic alloy strip is an Fe-Cu-Nb-Si-B nanocrystalline alloy.

[0008] Preferably, the length L of the stress relief slit and the length R of the soft magnetic alloy strip satisfy: 0.2R≤L≤0.8R; the stress relief slit is any one of a single straight slit, multiple parallel slits, or an array-type mesh slit, and the slit width is 0.1mm-0.5mm.

[0009] Preferably, the insulating layer is a high-temperature resistant insulating resin layer with a thickness of 5μm-15μm, a temperature resistance peak of ≥280℃, and is made of any one of polyimide (PI), modified epoxy resin, or BT resin.

[0010] Preferably, the conductive connection layer is a high-temperature resistant conductive adhesive or solder paste with a temperature resistance peak of ≥260℃; the overlap width between the two ends of the soft magnetic alloy strip and the electrode pad is ≥0.5mm, forming a rigidly supported vibration boundary.

[0011] Preferably, the PCB substrate is any one of FR-4 substrate, BT resin substrate or high-frequency PTFE substrate, and the substrate body thickness is 0.1mm-0.2mm.

[0012] Preferably, when the copper wire width and wire spacing of the printed drive coil are both 150μm, the number of turns of the coil is 8-12 turns, and the width of the soft magnetic alloy strip is 6.5mm-7mm.

[0013] This invention also provides a method for fabricating a patch-type magnetostrictive micro loudspeaker, comprising the following steps: S1. Substrate circuit preparation: Printed drive coils and electrode pads are fabricated on the upper surface of the PCB substrate by photolithography etching process. The printed drive coils adopt an 8-shaped winding structure or a concentric double winding structure. S2. Insulation layer preparation: On the upper surface of the PCB substrate after circuit fabrication, an insulating layer with a thickness of 5μm-15μm is prepared by coating process, and then cured. S3. Stress relief structure preparation: On the lower surface of the PCB substrate, stress relief slits are made in the preset mounting area corresponding to the printed drive coil and soft magnetic alloy strip by laser etching or chemical etching process. S4. Transducer unit assembly: The soft magnetic alloy strip is precisely attached to the surface of the insulating layer so that the strip coincides with the projection area of ​​the printed drive coil. The two ends of the soft magnetic alloy strip are fixed and electrically connected to the electrode pads through the conductive connection layer to form a vibration boundary with fixed ends. S5. Performance Laser Tuning: The length and width of the stress relief slit are adjusted by laser etching to calibrate the resonant frequency and output sound pressure performance of the micro-speaker, thus completing the device fabrication.

[0014] Preferably, the steps further include: S6. Surface Mount Compatibility Processing: The prepared devices undergo solderability processing to enable them to be reflow soldered at a peak temperature of 260°C via SMT surface mount technology, thus achieving integration with downstream circuits.

[0015] Therefore, the beneficial effects of the above-mentioned patch-type magnetostrictive micro loudspeaker and its fabrication method are as follows: (1) This invention uses pure PCB integration process to compress the overall thickness of the device to less than 0.3mm, which is far below the thickness limit of existing moving coil micro loudspeakers. The entire structure can withstand the reflow soldering process with a peak temperature of 260℃. It can achieve SMT automated mounting like surface mount LEDs, which completely solves the industry pain point that traditional electroacoustic devices cannot be integrated with the circuit board.

[0016] (2) This invention completely eliminates the permanent magnet, T-iron, voice coil skeleton and other structures required by traditional magnetostrictive transducers. It also does not require an independent diaphragm. It only relies on the Joule magnetostriction effect of the magnetostrictive soft magnetic alloy strip to achieve electro-mechanical-acoustic conversion. The PCB substrate itself is used as the resonant radiator. The structure is extremely simple, the manufacturing cost is greatly reduced, and there is no reliance on rare earth materials, which significantly improves the security of the supply chain.

[0017] (3) The present invention uses a figure-eight or concentric double-ring printed coil design to make the main direction of the driving magnetic field completely consistent with the length direction of the soft magnetic alloy strip, thereby maximizing the excitation of the axial magnetostrictive deformation of the strip; combined with the stress relief slit design on the back of the PCB substrate, the micro-stretching deformation of the strip is transformed into large bending vibration in the local area of ​​the PCB substrate, which greatly improves the sound radiation efficiency and solves the technical problem of small deformation and low output sound pressure of the magnetostrictive strip. (4) High reliability and wide operating conditions: The soft magnetic alloy strip used in this invention has a Curie temperature of ≥180℃, which can withstand the high temperature impact of reflow soldering without magnetic performance decay. It does not have the brittle fracture problem of piezoelectric ceramics and has excellent vibration and impact resistance. At the same time, by adjusting the slit parameters with laser, the acoustic performance of the device can be calibrated in batches, greatly improving the yield. It can be adapted to the harsh operating conditions of multiple scenarios such as consumer electronics, automotive, and industrial IoT.

[0018] (5) The entire process of this invention adopts mature PCB technology and SMT assembly technology, without the need for semiconductor-grade MEMS processing equipment, resulting in low production line transformation costs and enabling large-scale, low-cost mass production, which has strong commercialization value.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of an embodiment of a patch-type magnetostrictive micro loudspeaker according to the present invention; Figure 2 This is a step diagram illustrating the fabrication method of a patch-type magnetostrictive micro loudspeaker according to the present invention.

[0021] Figure Labels 1. PCB substrate; 2. Printed drive coil; 3. Insulating layer; 4. Soft magnetic alloy strip; 5. Stress relief slit; 6. Conductive connection layer; 7. Electrode pad. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] Example 1: like Figure 1 As shown, the present invention provides a patch magnetostrictive micro loudspeaker with an overall thickness of 0.23 mm, including a PCB substrate 1, a printed drive coil 2, an insulating layer 3, and a soft magnetic alloy strip 4.

[0025] The PCB substrate is any one of FR-4 substrate, BT resin substrate, or high-frequency PTFE substrate, and the substrate thickness is 0.1mm-0.2mm. In this embodiment, the PCB substrate 1 is a BT resin substrate with a thickness of 0.2mm, a dielectric constant of 4.2, and a peak temperature resistance of ≥280℃.

[0026] The printed drive coil 2 is arranged on the upper surface of the PCB substrate 1. In this embodiment, the printed drive coil 2 adopts an 8-shaped winding structure. The copper wire width and wire spacing of the printed drive coil 2 are both 150μm, and the number of turns of the coil is 10 turns, so that the main direction of the driving magnetic field generated after the printed drive coil 2 is energized is consistent with the length direction of the soft magnetic alloy strip 4.

[0027] The insulating layer 3 completely covers the outer surface of the printed drive coil 2. The insulating layer 3 is a high-temperature resistant insulating resin layer made of modified epoxy resin, with a thickness of 10μm. After curing, the breakdown voltage is ≥1.5kV and the peak temperature resistance is ≥280℃. Notably, the non-coil area on the upper surface of the PCB substrate 1 does not have an insulating layer, which can appropriately save manufacturing costs.

[0028] The soft magnetic alloy strip 4 is directly attached to the printed drive coil 2 covered with the insulating isolation layer 3. In this embodiment, the soft magnetic alloy strip 4 is a Fe-Cu-Nb-Si-B nanocrystalline alloy strip with the following composition by atomic percentage: Fe 73.5%, Cu 1%, Nb 3%, Si 13.5%, B 9%. The strip thickness is 20μm, the saturation magnetostriction coefficient λs=25ppm, and the Curie temperature Tc=210℃. The strip has a length of 8mm and a width of 6.8mm and is directly attached to the printed drive coil 2 covered with the insulating isolation layer 3, completely overlapping with the projected area of ​​the printed drive coil 2.

[0029] The two ends of the soft magnetic alloy strip 4 are electrically connected and fixed to the electrode pads 7 on the PCB substrate 1 through the conductive connection layer 6. The conductive connection layer 6 uses high-temperature resistant solder paste with a temperature resistance peak of ≥260℃. The overlap width between the two ends of the strip and the electrode pads is 0.8mm, forming a vibration boundary with rigid support at both ends and the main body area in the middle closely attached to the coil.

[0030] A stress-relief slit 5 is formed on the lower surface of the PCB substrate 1. The projection of the stress-relief slit 5 in the thickness direction of the PCB substrate 1 at least partially overlaps with the projection area of ​​the soft magnetic alloy strip 4. In this embodiment, the stress-relief slit 5 consists of multiple parallel slits. Since the length L of the stress-relief slit 5 and the length R of the soft magnetic alloy strip 4 must satisfy: 0.2R≤L≤0.8R, the slit width of the stress-relief slit 5 is 0.3mm.

[0031] like Figure 2 As shown, the above-mentioned method for fabricating a patch-type magnetostrictive microspeaker includes the following steps: S1. Substrate circuit preparation: A 0.2mm thick BT resin substrate is selected. The figure-eight printed drive coil and electrode pads are fabricated on the upper surface of the substrate by photolithography-etching process. The copper wire thickness is 35μm, the line width is 150μm, the line spacing is 150μm, and the number of turns is 10. After completion, the circuit is cleaned and deburred. S2. Insulation layer preparation: On the outer surface of the printed drive coil 2 after completion, a modified epoxy resin insulation layer is precisely coated by high-precision screen printing process, covering only the area of ​​the printed drive coil, with a coating thickness of 10μm. A stepped curing process is adopted: 80℃ for 30min, 120℃ for 30min, and 180℃ for 60min. After curing, the surface roughness of the insulation layer Ra≤0.3μm and the breakdown voltage≥1.5kV. S3. Stress relief structure preparation: Stress relief slits are made on the lower surface of PCB substrate 1 by ultraviolet laser etching process. The slits are 4.8mm long, 0.3mm wide, and the etching depth is 1 / 2 of the thickness of PCB substrate 1. After completion, the slits are cleaned to remove residue. S4. Transducer Unit Assembly: The bonding surface of the Fe-Cu-Nb-Si-B nanocrystalline soft magnetic alloy strip 4 is cleaned with argon plasma at a power of 100W for 60s. After cleaning, the strip is precisely attached to the printed drive coil covered with an insulating layer using a high-precision pick-and-place machine, ensuring that the projection areas of the strip and the coil completely overlap. The bonding pressure is 0.3MPa and the bonding temperature is 80℃. The two ends of the strip are connected to the electrode pads with solder paste. After completion, reflow curing is performed to form a vibration boundary that is fixed at both ends and tightly bonded to the coil in the middle. S5. Performance Laser Tuning: The resonant frequency of the device is tested by an impedance analyzer, and the length of the stress relief slit is finely adjusted by laser etching. The resonant frequency of the device is calibrated to the range of 1kHz±50Hz. At the same time, the output sound pressure performance is calibrated to complete the device fabrication. S6, Surface Mount Compatibility Processing: The electrode pads 7 of the device are treated with immersion gold solderability processing, enabling the device to be automatically mounted by a standard SMT placement machine and compatible with lead-free reflow soldering processes with a peak temperature of 260°C.

[0032] Ultimately, the micro-speaker prepared in this embodiment has an overall thickness of only 0.23mm. At 1kHz and 1W driving power, the output sound pressure level at a distance of 10cm can reach 90dB. After three 260℃ peak reflow soldering impacts, the magnetic performance attenuation rate is ≤2%, and the acoustic performance has no significant change, fully meeting the requirements of SMT surface mount technology.

[0033] Therefore, the present invention adopts the above-mentioned patch magnetostrictive micro loudspeaker and its preparation method, which achieves ultra-thin design through pure PCB process, is fully compatible with SMT reflow soldering, eliminates rare earth permanent magnets and independent diaphragms, has high sound radiation efficiency, strong reliability and low cost, and can be widely used in ultra-thin electroacoustic scenarios such as consumer electronics and wearable devices.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A patch-type magnetostrictive micro loudspeaker, characterized in that: The overall thickness of the patch-type magnetostrictive micro loudspeaker is less than 0.3 mm, including a PCB substrate, a printed drive coil, an insulating layer, and a soft magnetic alloy strip; The printed drive coil is disposed on the upper surface of the PCB substrate, and the insulating layer fully covers the outer surface of the printed drive coil. The soft magnetic alloy strip is directly attached to the printed drive coil covered with an insulating layer, and completely overlaps with the projection area of ​​the printed drive coil in the thickness direction of the PCB substrate; the two ends of the soft magnetic alloy strip are electrically connected and fixed to the electrode pads on the PCB substrate through conductive connection layers, forming a vibration boundary with fixed ends and the main body area in the middle tightly attached to the insulating layer. The printed drive coil adopts an 8-shaped winding structure or a concentric double-winding structure. The main direction of the driving magnetic field generated by the printed drive coil after being energized is consistent with the length direction of the soft magnetic alloy strip. The lower surface of the PCB substrate is provided with a stress relief slit, and the projection of the stress relief slit in the thickness direction of the PCB substrate at least partially overlaps with the projection area of ​​the soft magnetic alloy strip.

2. The patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: The soft magnetic alloy strip is an amorphous soft magnetic alloy strip or a nanocrystalline soft magnetic alloy strip, with a saturation magnetostriction coefficient λs≥20ppm, a Curie temperature Tc≥180℃, and a strip thickness of 10μm-30μm.

3. A patch-type magnetostrictive micro loudspeaker according to claim 2, characterized in that: The nanocrystalline soft magnetic alloy strip is a Fe-Cu-Nb-Si-B series nanocrystalline alloy.

4. A patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: The length L of the stress relief slit and the length R of the soft magnetic alloy strip satisfy the following condition: 0.2R≤L≤0.8R; the stress relief slit is any one of a single straight slit, multiple parallel slits, or an array-type mesh slit, and the slit width is 0.1mm-0.5mm.

5. A patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: The insulating layer is a high-temperature resistant insulating resin layer with a thickness of 5μm-15μm and a peak temperature resistance of ≥280℃. The material is any one of polyimide (PI), modified epoxy resin, or BT resin.

6. A patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: The conductive connection layer is a high-temperature resistant conductive adhesive or solder paste with a temperature resistance peak of ≥260℃; the overlap width between the two ends of the soft magnetic alloy strip and the electrode pad is ≥0.5mm, forming a rigidly supported vibration boundary.

7. A patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: The PCB substrate is any one of FR-4 substrate, BT resin substrate or high-frequency PTFE substrate, and the substrate body thickness is 0.1mm-0.2mm.

8. A patch-type magnetostrictive micro loudspeaker according to claim 1, characterized in that: When the copper wire width and wire spacing of the printed drive coil are both 150μm, the number of turns of the coil is 8-12 turns, and the width of the soft magnetic alloy strip is 6.5mm-7mm.

9. A method for fabricating a patch-type magnetostrictive micro loudspeaker as described in any one of claims 1-8, characterized in that: Includes the following steps: S1. Substrate circuit preparation: Printed drive coils and electrode pads are fabricated on the upper surface of the PCB substrate by photolithography etching process. The printed drive coils adopt an 8-shaped winding structure or a concentric double winding structure. S2. Insulation layer preparation: On the upper surface of the PCB substrate after circuit fabrication, an insulating layer with a thickness of 5μm-15μm is prepared by coating process, and then cured. S3. Stress relief structure preparation: On the lower surface of the PCB substrate, stress relief slits are made in the preset mounting area corresponding to the printed drive coil and soft magnetic alloy strip by laser etching or chemical etching process. S4. Transducer unit assembly: The soft magnetic alloy strip is precisely attached to the surface of the insulating layer so that the strip coincides with the projection area of ​​the printed drive coil. The two ends of the soft magnetic alloy strip are fixed and electrically connected to the electrode pads through the conductive connection layer to form a vibration boundary with fixed ends. S5. Performance Laser Tuning: The length and width of the stress relief slit are adjusted by laser etching to calibrate the resonant frequency and output sound pressure performance of the micro-speaker, thus completing the device fabrication.

10. A method for fabricating a patch-type magnetostrictive microspeaker according to claim 9, characterized in that, The steps also include: S6. Surface Mount Compatibility Processing: The prepared devices undergo solderability processing to enable them to be reflow soldered at a peak temperature of 260°C via SMT surface mount technology, thus achieving integration with downstream circuits.

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