A low temperature co-fired ferrite powder with magnetic permeability rising with superimposed current rising and a preparation method thereof

Abstract

A low-temperature co-fired ferrite powder with increasing magnetic permeability as the superimposed current increases, and its preparation method, are disclosed. The powder comprises a base material and additives. The base material formula, by mass ratio, is: Fe₂O₃ 60.0%–75.0%, NiO 15.0%–30.0%, CuO 5.0%–10.0%. The additive is a composite frit, comprising 2.0%–6.0% of the total base material mass. The composite frit formula, by mass ratio, is: Bi₂O₃ 50.0%–65.0%, CoO 8.0%–15.0%, Sm₂O₃ 0.5%–1.5%, MnO₂ 1.0%–3.0%, Al₂O₃ 20.0%–30.0%, Mo₂O₃ 1.0%–3.0%. The base material is pretreated, mixed, spun dry, dried, pre-fired, and pulverized. Then, the composite frit is added, and the mixture is mixed, spun dry, dried, and pulverized again. By adjusting and optimizing the base material and additive formulation, a low-temperature co-fired ferrite powder was obtained, in which the magnetic permeability initially increases and then decreases with increasing superimposed current. Inductors made using this material as the sandwich layer exhibit a significantly smaller decrease in inductance when energized compared to inductors using conventional non-magnetic materials as the sandwich layer; simultaneously, the saturation current of the inductor is improved.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials and their preparation technology, specifically relating to a low-temperature co-fired ferrite powder whose magnetic permeability increases with increasing superimposed current and its preparation method. Background Technology

[0002] With the development of information technology, circuit design is moving towards low voltage and high current, which places higher demands on the miniaturization and current withstand characteristics of components. This necessitates improvements in design and materials to enhance the current withstand characteristics of components. As a product of the miniaturization and surface-mount technology of inductors, multilayer chip power inductors are required to have low power consumption and high rated current.

[0003] Current multilayer chip power inductors use magnetic ferrite materials as the base powder and non-magnetic materials as the interlayer to improve the device's saturation current. There are currently two main technical approaches for selecting non-magnetic interlayer materials. The first approach uses non-magnetic ferrite materials as the interlayer, leveraging the non-magnetic nature of the interlayer to increase the device's saturation current. This approach is chosen because both the base and interlayer materials are ferrite, allowing for good co-firing and reducing manufacturing defects such as cracking, open circuits, and delamination. However, the inductance of the device tends to decrease continuously after energization. The second approach uses ceramic materials with a dielectric constant less than 6 as the interlayer. Ceramic materials have excellent current superposition characteristics, resulting in better current withstand characteristics for the inductor. However, ceramic materials and the ferrite materials used in the base powder are completely different material systems, and the co-firing effect has been difficult to achieve. This leads to cracking and delamination during device fabrication, causing fatal defects in device reliability.

[0004] Moreover, regardless of which sandwich material is used, it is equivalent to creating an air gap in the matrix ferrite material of the power inductor, which leads to a sharp decrease in the permeability of the matrix powder material and a sharp decrease in the inductance of the device. Therefore, the above two technical routes can only produce inductors with an inductance of less than or equal to 4.7 microhenries. Inductors with an inductance higher than 4.7 microhenries can only increase the inductance by increasing the number of turns. However, at a certain frequency, although the inductance increases with the increase of the number of coil turns, the inductive reactance also increases. The inductive reactance has a greater resistance to AC current, which inevitably leads to a decrease in current. Ultimately, this will result in the disadvantages of reduced saturation current and increased DC resistance of the inductor.

[0005] In addition, although the above two technical routes can solve the current withstand requirement of inductors with an inductance of less than or equal to 4.7 microhenries, in order to increase the inductance of the inductor after being energized, the number of printed turns must be increased, which leads to a decrease in production efficiency; moreover, since the conventional material for printed coils is silver, the material cost is also very high.

[0006] Therefore, developing a manufacturing material that can effectively reduce the decrease in inductance after the inductor is powered on, make the inductance significantly higher than that of inductors made with non-magnetic materials as the interlayer, and ensure good co-firing properties between the inductor's base powder and the interlayer material has become an urgent technical problem to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a low-temperature co-fired ferrite powder whose permeability increases with increasing superimposed current and its preparation method, thereby effectively solving the problems of reduced inductance after the device is powered on due to the sandwich material of the current multilayer chip power inductor, which makes it impossible to improve the current saturation value, and the poor co-firing properties of the two materials inside the multilayer chip power inductor.

[0008] To achieve the above objectives, the present invention provides a low-temperature co-fired ferrite powder whose permeability increases with increasing superimposed current. The powder comprises a base material and additives. The base material, by mass ratio, is: Fe₂O₃ 60.0%–75.0%, NiO 15.0%–30.0%, CuO 5.0%–10.0%. The additive is a composite frit, comprising 2.0%–6.0% of the total base material mass. The composite frit, by mass ratio, is: Bi₂O₃ 50.0%–65.0%, CoO 8.0%–15.0%, Sm₂O₃ 0.5%–1.5%, MnO₂ 1.0%–3.0%, Al₂O₃ 20%–30%, Mo₂O₃ 1.0%–3.0%.

[0009] This invention also provides a method for preparing low-temperature co-fired ferrite powder with increasing magnetic permeability as the superimposed current increases. The method includes the following steps: 1) pre-treating the raw materials of each component of the base material; 2) accurately weighing the pre-treated raw material dry powder according to the proportions of each component of the base material; 3) mixing the powder with grinding balls at a weight ratio of 3:1:1.3 to form a base material slurry, with a particle size requirement of D50 = 0.4–0.5 micrometers and D90 < 1.5 micrometers; 4) drying the base material slurry and filtering out more than 90% of the water to form a base material plate; 5) drying the base material plate, reducing the moisture content after drying. 6) Powder and sieve the dried base material; 7) Pre-fire the pulverized and sieved base material at a sintering temperature of 800±10℃ for 2-3 hours; 8) Powder and sieve the pre-fired base material to obtain dry base powder; 9) Accurately weigh each dry base powder and composite frit dry powder according to the finished product formula; 10) Mix the dry base powder and composite frit dry powder, and stir and grind them according to the weight ratio of grinding balls:dry powder:deionized water = 3:1:2 to obtain the finished slurry. The particle size requirements are D50 = 0.6-1.0 micrometers, D90 < 2.0 micrometers, and BET = 3.0-4.0 g / m³.2 11) Spin dry the finished slurry and filter out more than 90% of the water to form a finished material plate; 12) Dry the finished material plate until the moisture content is ≤0.6%; 13) Crush and sieve the dried finished material to obtain the finished product.

[0010] In step 1), the specific steps of the pretreatment are as follows: i) calcining each component raw material at a temperature of 800±10℃ and holding for 2 to 3 hours; ii) ball milling the calcined raw material, with a slurry particle size requirement of D50 = 0.1 to 0.3 micrometers; iii) passing the slurry through a 300-mesh sieve; iv) spin-drying and filtering the sieved slurry; v) drying the spin-dryed raw material, with a moisture content of <0.5% after drying; vi) pulverizing and sieving the dried raw material to form fine powder, thus completing the pretreatment.

[0011] In step 9), the preparation steps of the composite frit dry powder are as follows: I) Accurately weigh the components according to the distribution ratio of each component of the composite frit; II) Mix the components according to the weight ratio of grinding balls:dry powder:deionized water = 3.0:1.0:2.0 to form a frit slurry, with a particle size requirement of D50 = 0.4~0.5 micrometers and D90 < 1.2 micrometers; III) Spin-dry the frit slurry, filter out more than 90% of the water, and form a frit plate; IV) Dry the frit plate, and the moisture content after drying is ≤0%. 0.5%; V) Powder and sieve the dried frit material; VI) Melt the pulverized and sieved frit material at a sintering temperature of 1200-1250℃ and hold for 3-4 hours; VII) Pour the molten frit material into deionized water for water quenching; VIII) Extrude and crush the water-quenched frit material until the particle size is <0.1mm; IX) Perform air jet milling on the crushed frit material until the particle size D50 is 1.5-3.5 micrometers, to obtain composite frit dry powder.

[0012] In step 5), the drying temperature is 200-250 degrees Celsius, and the drying time is 15-20 hours.

[0013] In step 8), the sieve mesh size for crushing is 80 mesh.

[0014] In step 13), the sieve mesh size for crushing is 60 mesh.

[0015] This invention optimizes the formulation of the base material and additives in ferrite powder to obtain a low-temperature co-fired ferrite powder whose permeability increases with increasing superimposed current. The powder has a permeability μ′ = 10–20 (20MHz, 500mV), a quality factor Q > 60 (20MHz, 500mV), and a sintering temperature of 900±10℃. Under a 5A current surge, the permeability increases by more than 0.5%. Under DC bias: tested at a 5A current, the permeability increases by 5%–15%. This powder exhibits a continuous increase in permeability with increasing superimposed current. Once the current reaches a certain value, further increases in current cause the permeability to begin to decrease, thus significantly improving the saturation current value of the device. Using this powder as a sandwich layer in inductors results in a significant decrease in inductance when the inductor is energized, as its permeability is significantly higher than that of non-magnetic materials. Furthermore, the characteristic of this powder's permeability initially increasing and then decreasing with current flow enhances the inductor's saturation current. Additionally, the powder and the ferrite material used in the inductor's matrix are from the same material system, resulting in excellent co-firing performance. This prevents cracking and delamination during device fabrication, ensuring device reliability. Attached Figure Description

[0016] Figure 1 Permeability-quality factor-frequency curves of HQ24-1, HQ24-2, and HQ24-3;

[0017] Figure 2 Permeability-quality factor-frequency curves of HQ24-4, HQ24-5, and HQ24-6;

[0018] Figure 3 Permeability-quality factor-frequency curves of HQ24-7, HQ24-8, and HQ24-9;

[0019] Figure 4 Permeability-quality factor-frequency curves of HQ24-10, HQ24-11, and HQ24-12;

[0020] Figure 5 Impedance-frequency curves for HQ24-1, HQ24-2, and HQ24-3;

[0021] Figure 6 Impedance-frequency curves for HQ24-4, HQ24-5, and HQ24-6;

[0022] Figure 7 Impedance-frequency curves for HQ24-7, HQ24-8, and HQ24-9;

[0023] Figure 8Impedance-frequency curves for HQ24-10, HQ24-11, and HQ24-12;

[0024] Figure 9 Permeability-current impact curves of HQ24-1, HQ24-2, HQ24-3, and HQ24-4;

[0025] Figure 10 Permeability-current impact curves of HQ24-5, HQ24-6, HQ24-7, and HQ24-8;

[0026] Figure 11 Permeability-current impact curves for HQ24-9, HQ24-10, HQ24-11, and HQ24-12;

[0027] Figure 12 Permeability-DC bias curves for HQ24-1, HQ24-2, HQ24-3, and HQ24-4;

[0028] Figure 13 Permeability-DC bias curves for HQ24-5, HQ24-6, HQ24-7, and HQ24-8;

[0029] Figure 14 Permeability-DC bias curves for HQ24-9, HQ24-10, HQ24-11, and HQ24-12;

[0030] Figure 15 Permeability-DC bias curves of conventional ferrite materials;

[0031] Figure 16 Electron microscope image of HQ24-1;

[0032] Figure 17 Electron microscope image of HQ24-2;

[0033] Figure 18 HQ24-3 electron microscope image;

[0034] Figure 19 HQ24-4 electron microscope image;

[0035] Figure 20 HQ24-5 electron microscope image;

[0036] Figure 21 HQ24-6 electron microscope image;

[0037] Figure 22 HQ24-7 electron microscope image;

[0038] Figure 23 HQ24-8 electron microscope image;

[0039] Figure 24 HQ24-9 electron microscope image;

[0040] Figure 25 HQ24-10 electron microscope image;

[0041] Figure 26 HQ24-11 electron microscope image;

[0042] Figure 27 Electron microscope image of HQ24-12. Detailed Implementation

[0043] The purity requirements for the chemical materials involved in this invention are as follows: ferric oxide ≥ 99.3%, nickel oxide ≥ 76.5%, copper oxide ≥ 70%, bismuth oxide ≥ 99.95%, cobalt oxide ≥ 76.5%, samarium oxide ≥ 99.5%, manganese dioxide ≥ 99%, aluminum oxide ≥ 99.5%, and molybdenum oxide ≥ 99%.

[0044] The low-temperature co-fired ferrite powder of the present invention comprises a base material and additives. The base material, by mass ratio, comprises: Fe₂O₃ 60.0%–75.0%, NiO 15.0%–30.0%, and CuO 5.0%–10.0%. The additive is a composite frit, comprising 2.0%–6.0% of the total mass of the base material. The composite frit, by mass ratio, comprises: Bi₂O₃ 50%–65%, CoO 8%–15%, Sm₂O₃ 0.5%–1.5%, MnO₂ 1.0%–3.0%, Al₂O₃ 20%–30%, and Mo₂O₃ 1.0%–3.0%.

[0045] The method for preparing low-temperature co-fired ferrite powder of the present invention includes the following steps: 1) pre-treating the raw materials of each component of the base material; 2) accurately weighing the pre-treated raw material dry powder according to the distribution ratio of each component of the base material; 3) mixing the powder with grinding balls at a weight ratio of 3:1:1.3 to form a base material slurry, with a particle size requirement of D50 = 0.4-0.5 micrometers and D90 < 1.5 micrometers; 4) drying the prepared base material slurry and filtering out more than 90% of the water to form a relatively dry base material plate; 5) drying the base material plate until the moisture content after drying is ≤0.5%; 6) ... 7) Pulverize and sieve the dried base material; 8) Pre-fire the pulverized and sieved base material at a sintering temperature of 800±10℃ for 2-3 hours; 9) Pulverize and sieve the pre-fired base material to obtain dry base powder; 10) Accurately weigh each dry base powder and composite frit dry powder according to the finished product formula; 11) Mix the pre-fired dry base powder and composite frit dry powder, and stir and grind them according to the weight ratio of grinding balls:dry powder:deionized water = 3:1:2 to obtain the finished slurry. The particle size requirements are D50 = 0.6-1.0 micrometers, D90 < 2.0 micrometers, and BET = 3.0-4.0 g / m³. 2 11) Spin dry the finished slurry and filter out more than 90% of the water to form a relatively dry finished material plate; 12) Dry the finished material plate until the moisture content is ≤0.6%; 13) Crush and sieve the dried finished material to obtain the finished product.

[0046] The preparation of this powder includes four main steps: raw material pretreatment, base material preparation, additive preparation, and finished product preparation. Specifically: 1) Raw material pretreatment involves calcining the components of the base material at high temperatures to remove volatiles; 2) Base material preparation involves calcining the base material at high temperatures to form a uniform and stable spinel phase through a solid-state reaction. The uniformity of this composite phase directly affects the stability of the ferrite powder material's performance; 3) Additive preparation involves preparing a BCS-MMA composite frit, which is based on Bi-Co-Sm-Mo-Mn-Al (bismuth, cobalt, samarium, molybdenum, manganese, ... The oxides of aluminum are used as the raw material for the composite. Through the preparation of the composite frit, the trace components that can be directly added to the base material, such as oxides of bismuth, cobalt, samarium, molybdenum, manganese and aluminum, are added to the composite frit in a larger amount, which reduces the weighing error and makes the addition more accurate. In addition, the preparation of the composite frit in advance saves the tedious batching process in the preparation of ferrite powder. 4) The preparation of the finished material is the process of mixing and refining the base material after high-temperature solid-phase reaction with the BCS-MMA composite frit.

[0047] The technical solution of the present invention will be described in detail below through specific embodiments.

[0048] Through orthogonal experimental verification, we determined the following base material formula, and then prepared powder that meets the performance requirements by adding various modifying components, such as bismuth trioxide, cobalt oxide, and samarium trioxide.

[0049] Table 1 shows the specific formulations of each component of the base material and each component of the finished product in Examples 1 to 12.

[0050] Table 1. Component formulations for Examples 1 to 12

[0051]

[0052]

[0053] The specific preparation method is as follows:

[0054] 1. Preprocessing:

[0055] The raw materials that need to be pretreated are the components of the base material. The base material of this invention is selected from high-purity acid-treated ferric oxide, high-purity black nickel oxide, and acid-treated copper oxide.

[0056] 1.1 Raw material calcination: Ferric oxide, nickel oxide, and copper oxide powders are loaded into a corundum-mullite crucible and calcined at 800±10℃ for 2–3 hours in a box furnace, followed by natural cooling. The purpose of calcining the raw materials is to remove volatiles such as chloride ions and moisture.

[0057] 1.2 Raw material refinement: The calcined ferric oxide, nickel oxide, and copper oxide dry powders were refined separately using a horizontal high-speed sand mill. The weight ratio of grinding balls:dry powder:deionized water was 1:1:1. Zirconia balls with a diameter of 0.6 mm were selected for grinding. The sand mill speed was 2400-2500 rpm, and the ball milling time was 4-6 hours. The particle size of the slurry after ball milling was D50 = 0.1-0.3 micrometers.

[0058] 1.3 Slurry sieving: Sieve the slurry through a 300-mesh sieve to remove any remaining large particles.

[0059] 1.4 Slurry drying: The sieved slurry is dried and filtered using a centrifugal dryer to remove water-soluble ions such as chloride ions, sodium ions, and potassium ions.

[0060] 1.5 Drying: The spin-dried raw materials are dried at 200-250℃ for 20 hours to obtain refined raw materials with a moisture content of <0.5%;

[0061] 1.6 Crushing and Sieving: The dried raw materials are crushed using a 20B universal crusher, then sieved through a 200-mesh sieve, and placed in plastic bags and sealed to prevent moisture absorption and impurities from entering. This completes the raw material pretreatment.

[0062] 2. Base material preparation:

[0063] 2.1 Base Material Preparation: Using an electronic balance with an accuracy of 0.01 grams, accurately weigh the pretreated dry powder of each component raw material according to the base material formula of each embodiment in Table 1.

[0064] 2.2 Base Material Grinding: The weighed dry powder components are added to the mixing tank of a high-speed sand mill at a weight ratio of grinding balls:dry powder:deionized water of 3.0:1.0:1.3. The mixture is thoroughly stirred and ground using a dual-tank (A / B) mixing system. The sand mill speed is 800–850 rpm. The particle size requirement after grinding is D50 = 0.4–0.5 micrometers, D90 < 1.5 micrometers. Refining the slurry particle size to the nanometer level ensures maximum uniform mixing of the base material components, guaranteeing the full progress of the subsequent high-temperature solid-phase reaction.

[0065] The working principle of the A / B dual-drum mixing and circulation system is as follows: The slurry is drawn from drum A, passes through a sand mill, and then enters drum B. After drum A is completely emptied, its walls are rinsed with deionized water to ensure all powder has been ground in the sand mill. Then, the slurry is drawn from drum B, passes through the sand mill, and then enters drum A again. This cycle continues until the particle size meets the requirements. This dual-drum mixing and circulation system ensures all materials are ground in the sand mill, eliminating the problem of uneven mixing caused by grinding dead zones in traditional grinding methods.

[0066] The mixing tank of the sand mill is lined with polyurethane, ensuring that all parts in contact with the material are completely encased in polyurethane. This utilizes the excellent wear resistance and toughness of polyurethane to improve grinding efficiency and reduce the introduction of impurities during the grinding process. If the grinding tank lining is made of metal, impurities, especially free iron ions, will be introduced into the base material during grinding, significantly deteriorating the material properties.

[0067] The grinding balls are yttrium-stabilized zirconia balls with a diameter of 3mm; taking advantage of the high hardness and strength and low wear of zirconia balls, the introduction of impurities during the grinding process is reduced.

[0068] 2.3 Base Material Spin Drying: The ground base material slurry is filtered using a centrifugal spin dryer at a speed of 2500-3000 rpm. 3927 high-density filter cloth is used. Spin drying forms a relatively dry base material plate, further removing residual water-soluble impurities such as chloride ions. Moreover, the evenly mixed slurry, after spin drying, has more than 90% of its water removed, reducing the electricity cost of subsequent drying.

[0069] 2.4 Base Material Drying: Place the material plate in a tray and then put it in an electric heating drying oven to dry the moisture. The drying temperature is 200-250 degrees Celsius, and the time is 15-20 hours, with a moisture content ≤0.5%. The electric heating drying oven and tray are made of 304 stainless steel, which reduces the introduction of rust and has a long service life, making it cost-effective.

[0070] 2.5 Base material crushing: Use a 20B universal crusher to crush the dried powder, then pass it through a 200-mesh sieve, pack the powder into plastic bags and seal them to prevent moisture absorption and the entry of impurities.

[0071] 2.6 Pre-firing of the base material: The powder is loaded into a corundum-mullite sagger (length*width*height = 320*320*75mm), stacked in double layers, and placed in a box furnace for solid-phase reaction under a specific temperature curve to form a spinel phase with uniform composition. The high-temperature zone temperature is 800±10℃, and the holding time is 2-3 hours. The specific temperature curve is: room temperature -- 5h -- 600℃ -- 2h -- 600℃ -- 3h -- 750℃ -- 2h -- 750℃ -- 2h -- 800℃ -- 2h -- 800℃ -- Natural cooling. The holding temperatures of 600℃ and 750℃ are to allow the furnace temperature to gradually rise to the maximum temperature, enabling the base material to slowly heat up to the maximum temperature and achieve the best solid-phase reaction effect.

[0072] 2.7 Pre-calcined Powdering: The pre-calcined powder is finely pulverized using a high-speed pulverizer at 4000 rpm, and then passed through an 80-mesh sieve. This pulverization and sieving process breaks down and removes large particles that agglomerated during the pre-calcination process, ensuring uniformity and consistency of particle size during subsequent grinding of the finished product, reducing the difference between D50 and D90. It also reduces grinding time during finished product processing, improving production efficiency. Furthermore, high-speed pulverization effectively performs a secondary mixing of the pre-calcined powder, increasing the uniformity of the spinel phase in the matrix.

[0073] 3. Additive preparation:

[0074] Before preparing the finished product, the composite frit needs to be prepared first. The additive in the powder of this invention is BCS-MMA composite frit, which is a synthetic material made of Bi-Co-Sm-Mo-Mn-Al (bismuth, cobalt, samarium, molybdenum, manganese, aluminum) oxides.

[0075] 3.1 Fused Ingredients: Using an electronic balance with an accuracy of 0.01 g, accurately weigh each component according to the composite fused ingot formula. The composite fused ingot formula, by mass ratio, is: Bi₂O₃ 50%–65%, CoO 8%–15%, Sm₂O₃ 0.5%–1.5%, MnO₂ 1.0%–3.0%, Al₂O₃ 20%–30%, Mo₂O₃ 1.0%–3.0%. For example, based on this formula: for a total weight of 500 g, weigh according to the mass ratio of Bi₂O₃ 60%, CoO 10%, Sm₂O₃ 0.8%, MnO₂ 2.0%, Al₂O₃ 25%, and Mo₂O₃ 2.2%.

[0076] 3.2 Fused Crust Grinding: The weighed dry powder components are added to the mixing tank of a high-speed sand mill at a weight ratio of grinding balls:dry powder:deionized water of 3.0:1.0:2.0. The mixture is thoroughly stirred and ground using a dual-tank (A / B) mixing system. The sand mill speed is 800–850 rpm. The particle size requirement after grinding is D50 = 0.4–0.5 micrometers, D90 < 1.2 micrometers. Refining the slurry particle size to the nanometer level ensures maximum uniform mixing of the composite frit components, guaranteeing the full progress of the subsequent high-temperature solid-phase reaction.

[0077] The working principle of the A / B dual-barrel stirring cycle, the selection of the mixing tank and grinding balls of the sand mill, and their corresponding benefits are all related to the content of "base material grinding" in section 2.2 of "base material preparation".

[0078] 3.3 Melt drying: Same as item 2.3 "Base material drying" in "Base material preparation".

[0079] 3.4 Fused material drying: Place the fused material plate in a tray and then place it in an electric heating drying oven to dry the moisture. The drying temperature is 200-250 degrees Celsius, and the time is 10-20 hours. The moisture content is ≤0.5%. The electric heating drying oven and the tray are made of 304 stainless steel.

[0080] 3.5 Fused Ingot Crushing: Same as item 2.5 "Base Material Crushing" in "Base Material Preparation".

[0081] 3.6 Fused Ingot Synthesis: The pulverized fused ingot powder is packed into a 95% ceramic corundum crucible and compacted. It is then placed in a box furnace and held at 1200–1250℃ for 3–4 hours for melting and synthesis. The synthesis temperature curve is as follows: room temperature – 5h – 800℃ – 2h – 800℃ – 2h – 1000℃ – 2h – 1000℃ – 1h – 1150℃ – 2h – 1150℃ – 4h – 1230℃ – 3h – 1230℃ – natural cooling. This temperature curve incorporates multiple isothermal sections during the heating process. During these isothermal sections, the temperature uniformity within the furnace is ensured before further heating, thus reducing the temperature difference within the furnace. Using this process, the temperature difference within the furnace can be maintained within ±5℃ (using an ETH-type temperature sensing ring).

[0082] 3.7 Water quenching of fused material: After the constant temperature is completed, the molten fused material is poured into deionized water for water quenching. The quenched fused material becomes glass-like fragments.

[0083] 3.8 Fused material crushing: The water-quenched fused material is crushed by extrusion using a ceramic double roller mill until the crushed particle size is <0.1mm.

[0084] 3.9 Airflow milling: The fused material crushed by the ceramic roller mill is fed into a ceramic airflow mill for further pulverization until the particle size D50 = 1.5–3.5 micrometers. The pulverized fused material is then bagged and sealed for storage. At this point, the additive preparation is complete.

[0085] 4. Preparation of finished materials:

[0086] 4.1 Finished Material Batching: Using an electronic balance with an accuracy of 0.01 g, accurately weigh each component according to the finished material formulas of each embodiment in Table 1;

[0087] 4.2 Finished Material Grinding: Add the weighed components to a mixing tank, add deionized water, and thoroughly mix and grind to achieve the required particle size: D50 = 0.6–1.0 micrometers, D90 < 2.0 micrometers; BET = 3.0–4.0 g / m². Zirconia balls are used for grinding, taking advantage of their excellent wear resistance to reduce the introduction of other impurities into the formulation.

[0088] 4.3 Finished material drying: Same as item 2.3 "Base material drying" in "Base material preparation".

[0089] 4.4 Finished Material Drying: Place the finished material plates in trays and then put them in an electric heating drying oven to dry the moisture. The drying temperature is 200-250 degrees Celsius, and the time is 15-20 hours. The moisture content is ≤0.6%. The electric heating drying oven and trays are made of 304 stainless steel.

[0090] 4.5 Finished Material Crushing: Using a ceramic-lined vibrating pellet mill, the dried powder is crushed and passed through a 60-mesh sieve to obtain the finished powder. The finished powder is then packed into plastic bags and sealed. The preparation of the finished material is now complete.

[0091] Performance tests were conducted on the ferrite powders prepared by the 12 schemes in the above embodiments, and performance tests were also conducted on conventional ferrite powders with magnetic permeability of 1 and 20 for comparison.

[0092] First, prepare the inspection magnetic ring: Take 10g of the finished dry powder of the above powder, add a binder with 3% PVA solid content to granulate, and use a molding die with specifications of Φ20mm×Φ10mm; use an automatic tablet molding machine to form the ring, with a molding pressure of 10MPa; the magnetic ring blank size is: outer diameter × inner diameter × thickness = Φ20mm × Φ10mm × 3mm; the blank density is 4.0mm±0.1g / cm3; the sintering temperature of the inspection magnetic ring is 900±10℃ (tested by an imported ETH temperature measuring ring), and the temperature is maintained for 5 hours.

[0093] Table 2. Test methods and conditions

[0094]

[0095]

[0096] The fabricated magnetic ring was subjected to performance testing according to the inspection methods and test conditions in Table 2. The test data are shown in Table 3.

[0097] Table 3 Test Data for Magnetic Rings

[0098]

[0099] From Table 3 and Appendix Figures 1-27 It is known that the permeability of conventional ferrite materials shows a continuous decreasing trend when an electric current is applied, while the permeability of the ferrite powder of this invention first increases and then decreases when an electric current is applied. This invention, by adding a BCS-MMA composite frit, differs significantly from the single bismuth oxide sintering aid in conventional ferrite powder formulations. This composite frit, containing multiple elements, not only acts as a sintering aid but is also key to ensuring the powder exhibits the characteristic of increasing permeability when an electric current is applied. This results in an increase in bias characteristics; the permeability first increases and then decreases when an electric current is applied, changing the characteristic of conventional ferrites where the permeability continuously decreases after being energized.

[0100] Meanwhile, the powder of the present invention has the following characteristics:

[0101] 1. Compared with non-magnetic materials, the powder of this invention has a permeability of 10 to 20. Using this powder as a sandwich layer, because of its certain permeability, can effectively reduce the decrease in inductance after the inductor is used. Under the same design number of turns, the inductance will be significantly higher than that of devices made with non-magnetic materials as sandwich layers. This solves the problem that the high inductance of the original process route cannot increase the saturation current value of the inductor. At the same time, this material is a ferrite material, which belongs to the same system as the ferrite material used in conventional inductor matrix materials. The co-firing effect of the two is good, and there will be no cracking or delamination problems during device manufacturing, thus ensuring the reliability of the device.

[0102] Since the permeability of the powder of this invention is between 10 and 20, it can be used directly to make high-current inductors. By utilizing the characteristic that the permeability of the powder rises first and then falls when current is applied, the saturation current value of the inductor can be significantly improved (the saturation current value of a high-current inductor is determined by the current value when the inductance decreases by 30%).

[0103] 2. The quality factor Q is above 60 (20MHz, 500mV), indicating excellent performance.

[0104] 3. The internal coil of the multilayer chip power inductor uses silver as the internal electrode. Silver's temperature resistance is only 930℃, so the temperature for dense sintering of the material must be lower than 910℃ to meet the manufacturing requirements of the inductor. Ordinary sintering aids can achieve dense sintering, but they cannot improve the saturation current. We have specially developed and designed the Bi-Co-Sm-Mo-Mn-Al (bismuth, cobalt, samarium, molybdenum, manganese, aluminum) composite frit in this application. This composite frit can achieve a sintering temperature of 900℃±10℃, a holding time of 5 hours, and a magnet density greater than 5.2g / cm3, which fully meets the above sintering requirements.

[0105] 4. Current surge: When the current is 5A, the permeability increases by more than 0.5%. This data ensures that the inductance of the manufactured inductor will decrease after electroplating.

[0106] 5. DC bias: Tested at 5A current, the permeability increased by 5% to 15%. This data is a key parameter for improving the saturation current of the inductor. The saturation current of the inductor is defined as the current value when the inductance decreases by 30%. After using this material as the sandwich layer, although the overall inductance of the inductor shows a decreasing trend due to the inductance reduction characteristics of the base powder itself, the decrease is significantly reduced, thereby effectively improving the saturation current of the inductor.

Claims

1. A low-temperature co-fired ferrite powder whose magnetic permeability increases with increasing superimposed current, characterized in that, Its components are base material and additives; wherein, the base material formula, by mass ratio, is: Fe2O3 60.0%~75.0%, NiO 15.0%~30.0%, CuO 5.0%~10.0%; the additive is composite frit, by mass ratio, composite frit is 2.0%~6.0%; the composite frit formula, by mass ratio, is: Bi2O3 50.0%~65.0%, CoO 8.0%~15.0%, Sm2O3 0.5%~1.5%, MnO2 1.0%~3.0%, Al2O3 20.0%~30.0%, Mo2O3 1.0%~3.0%; the permeability of the low-temperature co-fired ferrite powder increases by more than 0.5% under a 5A current impact, and increases by 5%~15% under a 5A DC bias.

2. The method for preparing low-temperature co-fired ferrite powder according to claim 1, characterized in that, The steps include: 1) Pre-treating the raw materials of each component of the base material; 2) Accurately weighing the pre-treated raw material dry powder according to the distribution ratio of each component of the base material; 3) Mixing the base material slurry according to the weight ratio of grinding balls: raw material dry powder: deionized water = 3:1:1.3, with a particle size requirement of D50 = 0.4~0.5 micrometers and D90 < 1.5 micrometers; 4) Spinning the base material slurry to remove more than 90% of the water, forming a base material plate; 5) Drying the base material plate, with a moisture content ≤ 0.5% after drying; 6) Crushing and sieving the dried base material powder. 7) Pre-fire the pulverized and sieved base material at a sintering temperature of 800±10℃ for 2-3 hours; 8) Pulverize and sieve the pre-fired base material to obtain dry base powder; 9) Accurately weigh each dry base powder and composite frit dry powder according to the finished product formula; 10) Mix the dry base powder and composite frit dry powder, and stir and grind them according to the weight ratio of grinding balls:dry powder:deionized water = 3:1:2 to obtain the finished slurry. The particle size requirements are D50 = 0.6-1.0 micrometers, D90 < 2.0 micrometers, and BET = 3.0-4.0 g / m³. 2 11) Spin dry the finished slurry and filter out more than 90% of the water to form a finished material plate; 12) Dry the finished material plate until the moisture content is ≤0.6%; 13) Crush and sieve the dried finished material to obtain the finished product.

3. The method for preparing low-temperature co-fired ferrite powder according to claim 2, characterized in that, In step 1), the specific pretreatment steps are as follows: i) calcining each component raw material at a temperature of 800±10℃ and holding for 2-3 hours; ii) ball milling the calcined raw material to achieve a slurry particle size of D50 = 0.1-0.3 micrometers; iii) passing the slurry through a 300-mesh sieve; iv) spin-drying and filtering the sieved slurry; v) drying the spin-dryed raw material to achieve a moisture content of <0.5%. vi) The dried raw materials are crushed and sieved to form fine powder, and the pretreatment is completed.

4. The method for preparing low-temperature co-fired ferrite powder according to claim 2, characterized in that, In step 9), the preparation steps of the composite frit dry powder are as follows: I) Accurately weigh the components according to the distribution ratio of each component of the composite frit; II) Mix the components according to the weight ratio of grinding balls:dry powder:deionized water = 3.0:1.0:2.0 to form a frit slurry, with a particle size requirement of D50 = 0.4~0.5 micrometers and D90 < 1.2 micrometers; III) Spin-dry the frit slurry, filter out more than 90% of the water, and form a frit plate; IV) Dry the frit plate, and the moisture content after drying is ≤0%. 0.5%; V) Powder and sieve the dried frit material; VI) Melt the pulverized and sieved frit material at a melting temperature of 1200-1250℃ and hold for 3-4 hours; VII) Pour the molten frit material into deionized water for water quenching; VIII) Extrude and crush the water-quenched frit material until the particle size is <0.1mm; IX) Perform air jet milling on the crushed frit material until the particle size D50 is 1.5-3.5 micrometers, to obtain composite frit dry powder.

5. The method for preparing low-temperature co-fired ferrite powder according to claim 2, characterized in that, In step 5), the drying temperature is 200-250 degrees Celsius and the drying time is 15-20 hours.

6. The method for preparing low-temperature co-fired ferrite powder according to claim 2, characterized in that, In step 8), the sieve mesh size for crushing and sieving is 80 mesh.

7. The method for preparing low-temperature co-fired ferrite powder according to claim 2, characterized in that, In step 13), the sieve mesh size for crushing and sieving is 60 mesh.

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