Magnetic core material, preparation method therefor, and coated inductor

Abstract

The present invention relates to the technical field of electronic components, and specifically discloses a magnetic core material, a preparation method therefor, and a coated inductor. The magnetic core material, which is used in a coated inductor, has a cracking resistance coefficient Z, wherein the cracking resistance coefficient Z = 0.1 x - 0.5 y, x is a Vickers hardness of the magnetic core material, expressed in N / mm2, y is a fracture toughness of the magnetic core material, expressed in N / mm, and 2 ≤ Z ≤ 8.25. The magnetic core material of the present invention exhibits excellent crack resistance when used in coated inductors, improves reliability of coated inductors using said magnetic core material, and effectively reduces magnetic core material cracking risks during coated inductor use.

Description

Magnetic core materials and their preparation methods, coated inductors

[0001] Related cross-references

[0002] This application claims priority to Chinese Patent Application No. 2024119543431, filed on December 27, 2024, entitled “Magnetic Core Material and Preparation Method Thereof, Coated Inductor”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the technical field of electronic components, and more particularly to a magnetic core material and its preparation method, and a coated inductor. Background Technology

[0004] The magnetic core material, as the core component of coated inductors, is mainly composed of sintered magnetic metal oxides. The performance of the magnetic core material directly affects the operating efficiency of coated inductors. During the use of coated inductors, under long-term operation or extreme environments, the magnetic core material often cracks, leading to a decrease in the inductance performance or even failure of the coated inductor. Summary of the Invention

[0005] To quickly identify magnetic core materials with better crack resistance and improve the inductance performance of coated inductors, embodiments of the present invention disclose a magnetic core material, its preparation method, and a coated inductor.

[0006] In a first aspect, embodiments of the present invention provide a magnetic core material for coating inductors. The magnetic core material has a crack resistance coefficient Z, wherein Z = 0.1x - 0.5y, and x is the Vickers hardness of the magnetic core material, in N / mm². 2 y represents the fracture toughness of the magnetic core material, expressed in N / mm, where 2 ≤ Z ≤ 8.25.

[0007] As an optional implementation, in an embodiment of the present invention, the crack resistance coefficient is 3≤Z≤8.

[0008] As an optional implementation, in an embodiment of the present invention, x is 60 N / mm. 2 ~100N / mm 2 The value of y is between 2 N / mm and 10 N / mm.

[0009] As an optional implementation, in an embodiment of the present invention, x is at 65 N / mm. 2 ~85N / mm 2 The value of y is between 3 N / mm and 8.5 N / mm.

[0010] As an optional implementation, in an embodiment of the present invention, the Vickers hardness of the magnetic core material is obtained by testing according to GB / T 4340.1-2009, and the fracture toughness is obtained by testing according to GB / T 21143-2014.

[0011] As an optional implementation, in an embodiment of the present invention, the magnetic core material is a nickel-zinc ferrite core, which comprises Fe2O3, ZnO, and NiO. The mass percentages of Fe2O3, ZnO, and NiO, taken as 100% of their total mass, are as follows:

[0012] Fe2O3 60%–70%

[0013] ZnO 10%–15%

[0014] NiO 20%–25%.

[0015] As an optional implementation, in an embodiment of the present invention, the permeability of the nickel-zinc ferrite core is μ, wherein μ is greater than or equal to 1000, and the loss of the nickel-zinc ferrite core is P, wherein P is less than or equal to 0.5 W / kg.

[0016] Secondly, the present invention provides a method for preparing a magnetic core material.

[0017] A method for preparing a magnetic core material, as mentioned in the first aspect, includes the following steps:

[0018] The raw materials for preparing the magnetic core material are mixed, pressed into shape, and sintered to obtain the magnetic core material.

[0019] As an optional implementation, in an embodiment of the present invention, the sintering treatment is carried out at 1100℃~1250℃ for 1.5h~4h.

[0020] Thirdly, embodiments of the present invention provide a coated inductor.

[0021] A coated inductor includes a core material as mentioned in the first aspect or a core material prepared by the preparation method mentioned in the second aspect.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention provides a magnetic core material for coated inductors. The crack resistance coefficient Z of this magnetic core material is 2–8.25, indicating excellent crack resistance when used in coated inductors. This improves the reliability of coated inductors using this material and effectively reduces the risk of core material cracking during use. The crack resistance coefficient Z is reflected by the Vickers hardness and fracture toughness of the magnetic core material, which are related by Z = 0.1x - 0.5y, with Z ranging from 2 to 8.25. In other words, by selecting magnetic core materials whose Vickers hardness and fracture toughness satisfy the above-mentioned relationship, a magnetic core material with excellent crack resistance can be obtained, meeting the application requirements of coated inductors.

[0024] Unlike existing technologies that require first winding a coil around the magnetic core material and coating it to form a coated inductor before conducting reliability tests to determine its crack resistance, this application's embodiment obtains a magnetic core material with excellent crack resistance simply by ensuring that the Vickers hardness and fracture toughness of the magnetic core material themselves satisfy the aforementioned relationship range. This eliminates the need to fabricate the magnetic core material into a coated inductor and allows for early confirmation of its reliability within such inductors. This facilitates timely identification of potential cracking problems, improves the manufacturing efficiency and yield of coated inductors, and reduces their production costs.

[0025] Furthermore, unlike existing technologies that require lengthy cyclic testing to reflect the reliability of magnetic core materials in coated inductors, the Vickers hardness and fracture toughness tests in this application are simple, rapid, and low-cost. Thus, this invention can accurately assess the crack resistance of magnetic core materials based on whether their Vickers hardness and fracture toughness satisfy the aforementioned specific relationship, replacing traditional high-cost reliability testing. Therefore, this invention is of great significance for judging and improving the crack resistance of magnetic core materials used in coated inductors. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0027] Coated inductors mainly consist of a magnetic core material, a wire coil wound around the outer periphery of the magnetic core material, and a coating material encapsulating the wire coil and the surface of the magnetic core material. However, the relatively easy cracking of the magnetic core material often leads to a decrease in the performance of coated inductors, affecting the overall stability of the device. To ensure the reliability of coated inductors and guarantee the good crack resistance of the magnetic core material during use, various reliability tests are required, such as high and low temperature reliability tests and mechanical shock reliability tests. However, these testing methods are generally time-consuming and costly.

[0028] Taking high and low temperature reliability testing as an example, this test simulates the extreme temperature environments that coated inductors might encounter in real-world applications. During the test, the coated inductor needs to be cycled between high and low temperatures multiple times, and its performance must be observed and evaluated after each cycle. Since the number of temperature cycles and the performance evaluation after each cycle both require time, the entire testing process is time-consuming. Furthermore, maintaining the high and low temperature environments and conducting performance evaluations require significant resources, thus increasing testing costs. Other reliability tests also face similar problems, either requiring numerous repeated tests of the same indicator, conducting cyclic experiments with long testing cycles, or purchasing expensive test setups and building simulated test environments, etc.

[0029] Furthermore, if the reliability test results of coated inductors are unsatisfactory, not only will the magnetic core material need to be scrapped or reprocessed, but the wire coil and coating material will also be wasted. Therefore, ensuring good reliability for coated inductors involves significant time-consuming and costly processes, from raw material selection and manufacturing to testing.

[0030] Through in-depth analysis and research on the above problems, this application provides a magnetic core material and its preparation method, as well as a coated inductor, to solve the above problems by obtaining a magnetic core material with excellent crack resistance.

[0031] The technical solution of the present invention will be further described below with reference to the embodiments.

[0032] In a first aspect, embodiments of the present invention provide a magnetic core material.

[0033] A magnetic core material is disclosed for use in coated inductors. The core material has a crack resistance coefficient Z, which is defined as Z = 0.1x - 0.5y, where x is the Vickers hardness of the core material in N / mm². 2 y represents the fracture toughness of the magnetic core material, in N / mm, where 2≤Z≤8.25.

[0034] The inventors discovered that the crack resistance coefficient Z of this magnetic core material ranges from 2 to 8.25, indicating excellent crack resistance when used in coated inductors. This improves the reliability of coated inductors using this core material and effectively reduces the risk of core material cracking during use. The crack resistance coefficient Z is reflected by the Vickers hardness and fracture toughness of the core material, which are related by Z = 0.1x - 0.5y, with Z ranging from 2 to 8.25. In other words, in this application, by selecting core materials whose Vickers hardness and fracture toughness satisfy the above-mentioned relationship, a core material with excellent crack resistance can be obtained, meeting the application requirements of coated inductors.

[0035] Unlike existing technologies that require first winding a coil around the magnetic core material and coating it to form a coated inductor before conducting reliability tests to determine its crack resistance, this application's embodiment obtains a magnetic core material with excellent crack resistance simply by ensuring that the Vickers hardness and fracture toughness of the magnetic core material themselves satisfy the aforementioned relationship range. This eliminates the need to fabricate the magnetic core material into a coated inductor and allows for early confirmation of its reliability within such inductors. This facilitates timely identification of potential cracking problems, improves the manufacturing efficiency and yield of coated inductors, and reduces their production costs.

[0036] Furthermore, unlike existing technologies that require lengthy cyclic testing to reflect the reliability of magnetic core materials in coated inductors, the Vickers hardness and fracture toughness tests in this application are simple, rapid, and low-cost. Thus, this invention can accurately assess the crack resistance of magnetic core materials based on whether their Vickers hardness and fracture toughness satisfy the aforementioned specific relationship, replacing traditional high-cost reliability testing. Therefore, this invention is of great significance for judging and improving the crack resistance of magnetic core materials used in coated inductors.

[0037] It should be noted that Vickers hardness is a standard for expressing the hardness of a material. This test is conducted by pressing a square pyramidal diamond indenter with an angle of 136° between its two faces into the material surface under a certain load. After holding the indentation for a specified time, the diagonal length of the indentation is measured, and the hardness value is obtained by dividing the load value by the surface area of ​​the indentation.

[0038] Fracture toughness is the resistance value exhibited by a material when it undergoes unstable fracture, used to represent its ability to resist the unstable propagation of macroscopic cracks. The fracture toughness of this invention is the fracture toughness value (KIC). This fracture toughness is determined by indentation method.

[0039] The crack resistance coefficient is used to represent the crack resistance of the magnetic core material used in coated inductors. When the crack resistance coefficient satisfies 2 ≤ Z ≤ 8.25, it indicates that the magnetic core material has excellent crack resistance, and the coated inductor is less prone to core material cracking during use, resulting in high reliability. When the Vickers hardness and fracture toughness of the magnetic core material are less than 2 or greater than 8.25, it indicates that the crack resistance of the magnetic core material is relatively poor, and the coated inductor is prone to core material cracking during use, resulting in reduced reliability.

[0040] In some embodiments, the crack resistance coefficient is 3≤Z≤8.

[0041] When the value of z is between 3 and 8, it indicates that the crack resistance of the magnetic core material is further improved. This helps to better reduce the risk of core material cracking during use in coated inductors, and further improves the reliability of coated inductors.

[0042] In some embodiments, x is 60 N / mm 2 ~100N / mm 2 Between 2N / mm and 10N / mm.

[0043] When the value of z is between 2 and 8.25, and the given values ​​of x and y fall within specific ranges, it reveals that the core material has superior crack resistance. Compared to the traditional method of evaluating crack resistance after the coated inductor is manufactured, establishing the Vickers hardness and fracture toughness ranges of the core material allows for a faster assessment of its crack resistance, thereby quickly identifying the risk of core material cracking during the use of coated inductors.

[0044] Furthermore, this also means that by adjusting the hardness and fracture toughness of the magnetic core material to a specific range, the crack resistance of the magnetic core material can be significantly optimized.

[0045] In some embodiments, x is at 65 N / mm 2 ~85N / mm 2 Between 3 N / mm and 8.5 N / mm.

[0046] By further limiting the ranges of x and y, the value of z can fall into an even more optimal range. This indicates that by restricting the hardness and fracture toughness of the core material within this range, the crack resistance of the core material in coated inductors is further improved.

[0047] In some embodiments, the core material is a nickel-zinc ferrite core, which comprises Fe2O3, ZnO, and NiO. The mass percentages of Fe2O3, ZnO, and NiO are as follows:

[0048] Fe2O3 60%–70%

[0049] ZnO 10%–15%

[0050] NiO 20%–25%.

[0051] Nickel-zinc ferrite cores are magnetic core materials primarily composed of nickel-zinc ferrite. By adjusting the composition of Fe2O3, ZnO, and NiO in the nickel-zinc ferrite core material, the microstructure can be optimized. This improves the hardness of the nickel-zinc ferrite core material while reducing its brittleness, thereby further optimizing its crack resistance and reducing the risk of cracking in coated inductors.

[0052] In some embodiments, the permeability of the nickel-zinc ferrite core is μ, where μ is greater than or equal to 1000, and the loss of the nickel-zinc ferrite core is P, where P is less than or equal to 0.5 W / kg.

[0053] When Fe2O3, ZnO, and NiO are combined in the above proportions in a nickel-zinc ferrite core, it not only helps to balance the hardness and brittleness of the nickel-zinc ferrite core, but also helps to further improve the permeability of the nickel-zinc ferrite core, reduce the loss of the nickel-zinc ferrite core, and improve the overall performance of the nickel-zinc ferrite core, so as to better improve the overall operation of coated inductors.

[0054] Secondly, the present invention provides a method for preparing a magnetic core material.

[0055] A method for preparing a magnetic core material, as mentioned in the first aspect, includes the following steps:

[0056] The raw materials for preparing magnetic core materials are mixed, pressed into shape, and sintered to obtain magnetic core materials.

[0057] The magnetic core material with the Vickers hardness and fracture toughness satisfying the specific relationship can be obtained by the relatively simple preparation method described above.

[0058] In some embodiments, the sintering process is carried out at 1100℃ to 1250℃ for 1.5h to 4h.

[0059] By controlling the sintering temperature and time, the magnetic core material can be sintered under specific conditions, which helps to further improve the control of the hardness and brittleness of the magnetic core material. This allows for the improvement of the material's fracture toughness while increasing Vickers hardness, which in turn helps to further improve the crack resistance of the magnetic core material and enhance the reliability of coated inductors.

[0060] In some embodiments, the preparation of the magnetic core material includes the following steps:

[0061] Powdered Fe2O3, ZnO and NiO are mixed evenly to obtain magnetic powder;

[0062] The magnetic core powder, polyvinyl alcohol and silica sol are mixed and pressed, then pre-fired in air and pulverized to obtain pre-fired powder.

[0063] The pre-calcined powder and glass powder are mixed and ball-milled. Then, coupling agent, polyvinyl alcohol and lithium carbonate are added and mixed and granulated. The mixture is then pressed and molded to obtain a magnetic core blank. The magnetic core blank is placed in an air atmosphere for secondary sintering to obtain the magnetic core material.

[0064] Thirdly, embodiments of the present invention provide a coated inductor.

[0065] A coated inductor includes a core material as mentioned in the first aspect or a core material prepared by the preparation method mentioned in the second aspect.

[0066] The technical solution of the present invention will be further described below with reference to more specific embodiments.

[0067] Example 1

[0068] This invention provides a method for preparing a magnetic core material, comprising the following steps:

[0069] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. The total mass of Fe2O3, ZnO, and NiO was 100%, with Fe2O3 accounting for 60%, ZnO accounting for 15%, and NiO accounting for 25%.

[0070] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1100°C for 3 hours, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0071] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0072] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0073] Example 2

[0074] This invention provides a method for preparing a magnetic core material, comprising the following steps:

[0075] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. Based on the total mass of Fe2O3, ZnO, and NiO, the proportion of Fe2O3 was 65%, the proportion of ZnO was 12%, and the proportion of NiO was 23%.

[0076] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1150°C for 2.5 h, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0077] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0078] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0079] Example 3

[0080] This invention provides a method for preparing a magnetic core material, comprising the following steps:

[0081] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. The total mass of Fe2O3, ZnO, and NiO was 100%, with Fe2O3 accounting for 70%, ZnO accounting for 10%, and NiO accounting for 20%.

[0082] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1200°C for 4 hours, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0083] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0084] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0085] Comparative Example 1

[0086] This invention provides a comparative example of a method for preparing a magnetic core material, comprising the following steps:

[0087] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. Based on the total mass of Fe2O3, ZnO, and NiO, the proportion of Fe2O3 was 72%, the proportion of ZnO was 10%, and the proportion of NiO was 18%.

[0088] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1100°C for 3 hours, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0089] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0090] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0091] Comparative Example 2

[0092] This invention provides a comparative example of a method for preparing a magnetic core material, comprising the following steps:

[0093] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. Based on the total mass of Fe2O3, ZnO, and NiO, the proportion of Fe2O3 was 58%, the proportion of ZnO was 12%, and the proportion of NiO was 30%.

[0094] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1100°C for 3 hours, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0095] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0096] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0097] Comparative Example 3

[0098] This invention provides a comparative example of a method for preparing a magnetic core material, comprising the following steps:

[0099] Fe2O3 with an average particle size of 1.8 μm, ZnO with an average particle size of 5 μm, and NiO with an average particle size of 26 μm were mixed to prepare magnetic powder. The total mass of Fe2O3, ZnO, and NiO was 100%, with Fe2O3 accounting for 60%, ZnO accounting for 15%, and NiO accounting for 25%.

[0100] The magnetic powder, silica particles with an average particle size of 0.5 μm and silica sol were mixed evenly, wherein the mass ratio of magnetic powder, silica particles and silica sol was 1:0.035:1.2. The mixed material was placed in an air atmosphere and pre-calcined at 1100°C for 3 hours, and then pulverized to obtain pre-calcined powder with an average particle size of 12 μm.

[0101] The pre-calcined powder was mixed with glass powder with an average particle size of 4.5 μm and ball-milled to form a mixed powder. The glass powder was composed of SiO2, B2O3 and Al2O3 mixed in a mass ratio of 55:15:30, and the mass ratio of the pre-calcined powder to the glass powder was 1:0.0015.

[0102] Mixed powder, trimethoxysilane, silica particles with an average particle size of 0.5 μm, and lithium carbonate with an average particle size of 0.4 μm were mixed and granulated. The mass ratio of the mixed powder, trimethoxysilane, silica particles, and lithium carbonate was 1:0.0015:0.035:0.003. The mixture was then pressed into a core blank, which was then sintered in air at 1250 °C for 1.5 h to obtain the core material.

[0103] Experiment 1

[0104] Vickers hardness and fracture toughness testing of magnetic core materials

[0105] Magnetic core material samples were prepared according to the preparation methods provided in the above embodiments and comparative examples. The Vickers hardness of the magnetic core material samples was tested using the Vickers hardness method. The Vickers hardness of the magnetic core material was obtained according to GB / T4340.1-2009, and the fracture toughness of the magnetic core material was obtained according to GB / T 21143-2014. The formula for calculating the fracture toughness is as follows:

[0106] Fracture toughness (KIC) = (Load P × Young's modulus E) / (Crack length C). Where E is the Young's modulus of the material, typically 300 GPa for Si3N4 systems. P is in kg, C is in mm, and HV (microhardness) is in GPa.

[0107] The crack resistance coefficient was calculated based on the Vickers hardness and fracture toughness test results above. The test results of Experiment 1 are detailed in Table 1.

[0108] Experiment 2

[0109] 2.1 Magnetic Core Mechanical Strength Test

[0110] The tests include:

[0111] 2.1.1 Pendulum bending strength: The pendulum bending strength of the magnetic core material samples prepared in the above examples and comparative examples was tested using a material testing machine. The pendulum bending strength test indenter was a square indenter with a diameter of 0.5mm × 0.4mm, and the downward pressing speed of the indenter was less than or equal to 10mm / min. The pendulum bending strength was recorded in N.

[0112] 2.1.2 Core bending strength: The core bending strength of the magnetic core material samples prepared in the above examples and comparative examples was tested using a material testing machine. The core bending strength test indenter was a square indenter with a diameter of 0.2mm × 2mm, and the downward pressing speed of the indenter was less than or equal to 10mm / min. The core bending strength was recorded in N.

[0113] 2.2 Reliability Testing of Coated Inductors

[0114] First, fabricate a coated inductor:

[0115] 1. Winding: Wind a copper wire with a conductor diameter of 0.09mm around the I-shaped magnetic core 10.75 times;

[0116] 2. Soldering: Place the wound product into a 400℃ solder bath for soldering, ensuring that the solder evenly covers the ends of the coil and the contact area with the magnetic core to form a good electrical connection.

[0117] 3. Magnetic adhesive coating: Apply magnetic adhesive evenly to the gap between the coil and the magnetic core. After coating, perform a curing process to allow the magnetic adhesive to solidify and form a magnetic shielding layer.

[0118] Magnetic core material samples were prepared using the methods provided in the above embodiments and comparative examples, respectively, as raw materials for preparing coated inductors. Coated inductor samples were then prepared and tested.

[0119] Then perform the following reliability tests:

[0120] 2.2.1 High and low temperature shock reliability test:

[0121] Seventy-seven parallel-coated inductor samples were selected and subjected to three reflow soldering pretreatments to ensure they reached a stable state before testing.

[0122] The samples were subjected to cyclic testing within a temperature range of -40℃ (holding temperature for 30 min) to +85℃ (holding temperature for 30 min), with the temperature zone transition time not exceeding 20 seconds, for a total of 100 cycles. If the samples still meet the test standards after 100 cycles, the number of cycles can be increased as needed.

[0123] After testing, the samples are inspected. Samples that meet the following requirements are considered to have met the inspection standards:

[0124] 1. No visible physical damage;

[0125] 2. The rate of change in inductance before and after the test is within 10%.

[0126] For specific testing methods and standards, refer to Method 107 in MIL-STD-202.

[0127] 2.2.2 Low-frequency vibration reliability test:

[0128] Select coated inductor samples and perform three reflow soldering pretreatments to ensure they reach a stable state before testing;

[0129] The sample was soldered onto the PCB board and placed in the vibration testing equipment. The test frequency was set to 10–55–10 Hz, with each frequency band lasting 1 minute and the amplitude (PP) being 1.524 mm. The test covered vibration in the X, Y, and Z directions, with each direction vibrating for 2 hours, for a total of 6 hours. After the 6-hour vibration test, if the sample still met the inspection standards, the vibration time could be extended as needed.

[0130] After testing, the samples are inspected. Samples that meet the following requirements are considered to have met the inspection standards:

[0131] 1. No visible physical damage;

[0132] 2. The rate of change in inductance before and after the test is within 10%.

[0133] For specific testing methods and standards, refer to Method 201 in MIL-STD-202.

[0134] The test results for Experiment 2 are shown in Table 2.

[0135] Table 1

[0136] Table 2

[0137] From the comparison of the test results of Examples 1-3 and Comparative Examples 1-3 in Table 2, it can be clearly observed that Examples 1-3 significantly outperform Comparative Examples 1-3 in terms of sway strength, core fold strength, high and low temperature shock reliability, and low-frequency vibration reliability. This result proves that the magnetic core material used in Examples 1-3 has excellent crack resistance, and can effectively resist cracking in the actual application of coated inductors, thereby significantly improving the overall reliability of coated inductors. Specifically, this high crack resistance means that the inductance of coated inductors is less likely to change significantly due to cracking of the magnetic core material during use, ensuring the stability of the performance of coated inductors.

[0138] Further analysis of the test results in Table 1 shows that the crack resistance coefficients of the core materials in Examples 1-3 are strictly controlled within the range of 2 to 8.25, while the crack resistance coefficients of the core materials in Comparative Examples 1-3 all exceed this range. This data comparison not only verifies the importance of the crack resistance coefficient within a specific range (i.e., 2 to 8.25) for improving the crack resistance of the core material, but also directly demonstrates that only when the crack resistance coefficient of the core material meets this condition can the coated inductor using this core material exhibit higher reliability. In other words, by optimizing the crack resistance coefficient of the core material to fall within the range of 2 to 8.25, we can effectively reduce the risk of failure caused by core material cracking during the use of coated inductors, which is of great significance for improving the long-term stability and service life of inductors.

[0139] The magnetic core materials and their preparation methods, as well as coated inductors disclosed in the embodiments of the present invention, have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the magnetic core materials and their preparation methods, coated inductors, and their core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A magnetic core material, characterized in that, The magnetic core material is used to coat inductors. The magnetic core material has a crack resistance coefficient Z, which is defined as Z = 0.1x - 0.5y, where x is the Vickers hardness of the magnetic core material, in N / mm². 2 y represents the fracture toughness of the magnetic core material, expressed in N / mm, where 2 ≤ Z ≤ 8.

25.

2. The magnetic core material according to claim 1, characterized in that, The crack resistance coefficient is 3≤Z≤8.

3. The magnetic core material according to claim 1, characterized in that, said x is between 60 N / mm 2 ~ 100 N / mm 2 and said y is between 2 N / mm and 10 N / mm.

4. The magnetic core material according to claim 3, characterized in that, The x is at 65 N / mm 2 ~85N / mm 2 The value of y is between 3 N / mm and 8.5 N / mm.

5. The magnetic core material according to any one of claims 1-4, characterized in that, The Vickers hardness of the magnetic core material was tested according to GB / T 4340.1-2009, and the fracture toughness was tested according to GB / T 21143-2014.

6. The magnetic core material according to any one of claims 1-4, characterized in that, The magnetic core material is a nickel-zinc ferrite core, which comprises Fe2O3, ZnO, and NiO. The mass percentages of Fe2O3, ZnO, and NiO are as follows, taking the total mass of Fe2O3, ZnO, and NiO as 100%: Fe2O3 60%–70% ZnO 10%–15% NiO 20%–25%.

7. The magnetic core material according to claim 6, characterized in that, The magnetic permeability of the core material is μ, where μ is greater than or equal to 1000, and the loss of the core material is P, where P is less than or equal to 0.5 W / kg.

8. A method for preparing a magnetic core material, characterized in that, The method for preparing the magnetic core material according to any one of claims 1-7 includes the following steps: The raw materials for preparing the magnetic core material are mixed, pressed into shape, and sintered to obtain the magnetic core material.

9. The method for preparing the magnetic core material according to claim 8, characterized in that, The sintering process involves sintering at 1100℃~1250℃ for 1.5h~4h.

10. A coated inductor, characterized in that, It includes the magnetic core material as described in any one of claims 1-7 or the magnetic core material prepared by the preparation method as described in any one of claims 8-9.

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