Preparation method of multi-layer chip inductor magnetic core

Abstract

The invention relates to a preparation method of a multi-layer chip inductor magnetic core, and belongs to the technical field of multi-layer chip inductor elements. The preparation method of the magnetic core of the multi-layer chip inductor comprises the following steps: (1) carrying out glue removal on a green body of the multi-layer chip inductor; (2) carrying out first-stage sintering and second-stage sintering on the multi-layer chip inductor after glue removal, wherein the first-stage sintering is as follows: heating to 820-880 DEG C at a heating rate of 0.5-2 DEG C / min; in the second-stage sintering, the temperature is raised to 900-920 DEG C at the temperature raising rate of 0.8-1.2 DEG C / min, and heat preservation is conducted for 3-5 h; and (3) cooling to obtain the multi-layer chip inductor magnetic core. The multi-layer chip inductor core with uniform grain size and few air holes is obtained by adjusting the sintering process during preparation of the multi-layer chip inductor core, and hysteresis loss can be effectively reduced, so that the reliability of the multi-layer chip inductor is improved, and the application field of the product is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of multilayer chip inductor components, and in particular relates to a method for preparing a multilayer chip inductor magnetic core. Background Art

[0002] Ferrite material is one of the main magnetic powders used in multilayer chip inductors. The electrical properties, magnetic properties, and mechanical properties of ferrite products depend not only on the chemical composition, but also on the basic physical properties and internal structural characteristics of the sintered body, such as the composition of the reaction products, the phase structure, the condition of impurities, the crystal structure (the shape, size, uniformity, and defects of the grains), the pore structure, and the density, etc. The sintering process will affect the internal structural characteristics of the ferrite. From the heating and temperature rise of the sample to the insulation of the final ferrite product, there are many process links. Therefore, determining the role of each process link in the sintering process and optimizing it is a key issue to improve the performance of ferrite materials.

[0003] Sintering refers to sintering the formed ferrite green body at a certain temperature to form a ferrite material with certain performance, appearance and geometric dimensions. After the raw material formulation, molding and other processes are completed, sintering is the key process to make the material obtain the expected microstructure so that the material performance can be fully exerted. The reliability of the product is mainly related to the material, design and internal structure characteristics of the product. When the material and design of the product are the same, the reliability of the product is mainly affected by the internal structure characteristics of the product. Therefore, adjusting the sintering process of the product can improve the reliability of the product.

[0004] The current sintering methods include: traditional sintering, pulse sintering, vacuum sintering and hot isostatic pressing. The products sintered by pulse sintering, vacuum sintering and hot isostatic pressing have higher densification and controllable grain size, but these sintering methods are more expensive than traditional sintering. Therefore, current industrial production is still dominated by traditional sintering, which has the advantages of being more economical and easier to operate.

[0005] However, the currently common traditional sintering process cannot significantly improve the reliability of multilayer chip inductors. It is of great significance to develop a new sintering process that can effectively improve the reliability. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a method for preparing a multi-layer chip inductor magnetic core.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for preparing a multilayer chip inductor magnetic core, comprising the following steps:

[0009] (1) Debinding the multi-layer chip inductor green body;

[0010] (2) performing the first stage sintering and the second stage sintering on the multilayer chip inductor after debinding, wherein the first stage sintering is: heating to 820°C-880°C at a heating rate of 0.5-2°C / min; the second stage sintering is: heating to 900°C-920°C at a heating rate of 0.8-1.2°C / min, and keeping the temperature for 3h-5h;

[0011] (3) Cooling to obtain the multi-layer chip inductor core.

[0012] In the preparation method of the present invention, step (1) is the initial stage of sintering, which mainly involves debinding the green body, removing organic matter such as solvent and binder, and the grains in the particles do not change at this stage, and the shape of the particles remains basically unchanged. The first stage sintering in step (2) is the mid-stage of sintering, in which the product begins to sinter slowly, and the grains also grow rapidly as the temperature rises. If the heating rate is too fast at this stage, the grains will grow abnormally, resulting in uneven grain size, so it is necessary to adopt slow heating to sinter in the mid-stage of sintering. Ferrite materials decompose and release oxygen when sintered at high temperatures. Slow heating sintering can make the gas slowly discharged, reduce the internal porosity of the product, and in the mid-stage of sintering, the energy is relatively low, mainly based on grain boundary diffusion, and the slow heating rate can make the internal grains of the product more uniform. The second stage sintering is the final stage of sintering, in which the product continues to densify, the material on the grain boundary diffuses and fills the pores, and the grains grow further. By adjusting the heating rate and temperature during sintering, the size and internal structure of the grains can be effectively controlled to improve the reliability of the multilayer chip inductor.

[0013] Preferably, in step (1), the multilayer chip inductor green body comprises NiZn ferrite material, and the particle size D50 of the NiZn ferrite material is 0.6 μm-1.6 μm.

[0014] Preferably, the NiZn ferrite material is doped with copper oxide, and the content of the copper oxide is 3.5wt%-8wt%; in a certain embodiment, the content of the copper oxide in the NiZn ferrite material is 3.5wt%-4.5wt%.

[0015] Ferrite materials will produce energy loss under the action of alternating magnetic fields, causing the core to heat up and thus causing large fluctuations in product performance, which in turn affects product reliability. Therefore, the key to improving product reliability is to reduce product energy loss. The energy loss of ferrite products is divided into three types: eddy current loss, hysteresis loss and residual loss, and hysteresis loss is greatly affected by the microstructure of the material. The present invention adjusts the sintering rate in the preparation method to obtain a material with complete grain shape, uniform grain size, fewer pores and smaller size. It has lower high-frequency loss, higher current impact resistance stability and temperature stability, and can prevent the performance change rate of multilayer chip inductors from being too large when used.

[0016] The present invention does not limit the source of the NiZn ferrite material, which can be commercially available or homemade, as long as it meets the above-mentioned particle size range.

[0017] Preferably, in the step (1), the temperature during the debinding is 470°C-510°C, and the heating rate is 0.3-0.6°C / min.

[0018] Preferably, in the step (1), air is introduced during the debinding, and the gas pressure difference during the debinding is 50-60 Pa.

[0019] Specifically, the gas pressure difference in the present invention = inlet pressure - outlet pressure.

[0020] In the debinding stage, the above-mentioned temperature, heating rate and gas pressure difference can ensure sufficient air content and effectively decompose and discharge the organic matter inside the green body.

[0021] Preferably, in the step (2), air is introduced during the first stage sintering, and the gas pressure difference during the first stage sintering is 20-30 Pa.

[0022] Preferably, in the step (2), the heating rate during the first stage sintering is 0.5-1.5°C / min.

[0023] The first stage sintering in step (2) of the present invention is in the middle stage of sintering, and the amount of oxygen required is reduced. It is preferred to maintain the above pressure difference in this stage.

[0024] Preferably, in the step (2), no air is introduced during the second stage sintering.

[0025] The second stage of sintering is the final stage of sintering. It does not use air for smoldering, which can ensure the temperature in the furnace is stable and the product is sintered more evenly.

[0026] Preferably, in step (3), the cooling includes a first stage cooling and a second stage cooling, and the first stage cooling is: cooling to 700°C-800°C at a cooling rate of 0.5-3°C / min.

[0027] Slowly cooling down according to the first stage cooling process can slowly release the stress of the product, reduce internal defects, and make it more compact, thereby producing a high-reliability multilayer chip inductor with uniform grain size and small pores.

[0028] Preferably, the second stage of cooling is natural cooling.

[0029] Specifically, the natural cooling described in the present invention is natural cooling along with the furnace.

[0030] The present invention has the following beneficial effects: the present invention obtains a multilayer chip inductor core with uniform grain size and few pores by adjusting the sintering process during the preparation of the multilayer chip inductor core, which can effectively reduce hysteresis loss, thereby improving the reliability of the multilayer chip inductor and achieving the expansion of the application field of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a scanning electron microscope image of the multilayer chip inductor core of Example 3;

[0032] Figure 2 This is a scanning electron microscope image of the multilayer chip inductor core of comparative example 1. DETAILED DESCRIPTION

[0033] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0035] The multilayer chip inductor green body described in the following embodiments and comparative examples includes NiZn ferrite material, which is NiZn ferrite material doped with 3.5wt%-4.5wt% copper oxide, and has a particle size D50 of 0.6μm-1.6μm, purchased from Feiyue Technology Co., Ltd.;

[0036] The preparation method of the multi-layer chip inductor green body is as follows: adding a solvent and an adhesive to NiZn ferrite material magnetic powder to prepare a slurry, casting the slurry into a dielectric layer as a bottom, then casting a conductive layer on the dielectric layer, alternately casting the dielectric layer and the conductive layer to form a block, and drying, pressing and cutting the block to obtain the multi-layer chip inductor green body.

[0037] Example 1

[0038] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0039] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0040] (2) The furnace is heated to 850°C, the heating rate is controlled at 2°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 910°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0041] (3) The furnace is cooled down to 750° C. at a cooling rate of 2° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0042] Example 2

[0043] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0044] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0045] (2) The furnace is heated to 850°C, the heating rate is controlled at 1.5°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 900°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0046] (3) The furnace is cooled down to 750° C. at a cooling rate of 1° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0047] Example 3

[0048] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0049] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0050] (2) The furnace is heated to 850°C, the heating rate is controlled at 1°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 900°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0051] (3) The furnace is cooled down to 750° C. at a cooling rate of 0.5° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0052] Example 4

[0053] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0054] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0055] (2) The furnace is heated to 850°C, the heating rate is controlled at 0.5°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 900°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0056] (3) The furnace is cooled down to 750° C. at a cooling rate of 1° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0057] Comparative Example 1

[0058] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0059] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0060] (2) The furnace is heated to 850°C, the heating rate is controlled at 4.5°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 910°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0061] (3) The furnace is cooled down to 750° C. at a cooling rate of 2° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0062] Comparative Example 2

[0063] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0064] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0065] (2) The furnace is heated to 850°C, the heating rate is controlled at 3°C / min, air is introduced, the gas pressure difference in the furnace is 20Pa, and the first stage sintering of the multilayer chip inductor after debinding is performed; then the temperature is increased to 910°C at a heating rate of 0.8°C / min, and the temperature is kept for 4 hours. The ventilation window is closed to allow the product to smolder;

[0066] (3) The furnace is cooled down to 750° C. at a cooling rate of 1° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0067] Comparative Example 3

[0068] A method for preparing a multilayer chip inductor magnetic core comprises the following steps:

[0069] (1) Place 60g of multilayer chip inductor green embryos evenly into a 10-bowl support plate, shake well, open the furnace door, neatly stack the products in the furnace, open the ventilation window, let in air, close the furnace door, heat up the products for debinding, heat to 500°C, control the heating rate at 0.4°C / min, and the gas pressure difference in the furnace is 50Pa;

[0070] (2) The furnace is heated to 910°C and kept at this temperature for 4 hours. The heating rate is controlled at 2°C / min. Air is introduced. The gas pressure difference in the furnace is 20Pa. The multilayer chip inductor after debinding is sintered.

[0071] (3) The furnace is cooled down to 750° C. at a cooling rate of 2° C. / min, and then cooled down along with the furnace to obtain the multilayer chip inductor core.

[0072] The multilayer chip inductor cores prepared in the examples and comparative examples were subjected to scanning electron microscopy testing to analyze the crystal structure. The scanning electron microscopy image of the multilayer chip inductor core of Example 3 is as follows: Figure 1As shown, the scanning electron microscope image of the multilayer chip inductor core of Comparative Example 1 is as follows Figure 2 shown.

[0073] The scanning electron microscope results show that the ferrite grains of the multilayer chip inductor core obtained by the preparation method of the embodiment of the present invention are complete in shape, uniform in size, and have fewer pores. Figure 1 The grain size of Example 3 is uniform and the pores are small. However, the ferrite grain size uniformity obtained by the comparative preparation method is poor and the pores are large. Figure 2 The grain size difference of comparative example 1 is large, and the pores are large. Therefore, it can be seen that the preparation method of the present invention can improve the internal crystal phase and microstructure of the inductor core to achieve the effect of improving reliability.

[0074] The multilayer chip inductor cores prepared in the embodiments and comparative examples were made into finished multilayer chip inductors and subjected to reliability tests. The reliability test method was to place the product in an environment of 85°C, apply a certain current to the product, and operate it for 1000 hours in this state; the working life qualification criterion was: -10% ≤ product inductance change rate before and after the working life test ≤ 10%; the test results are shown in Table 1.

[0075] Table 1 Preparation method parameters and reliability test results of the embodiments and comparative examples

[0076]

[0077] The test results in Table 1 show that the reliability results of the multilayer chip inductor obtained by the preparation method provided in the embodiment of the present invention are qualified, and the reliability result judgment standard is that the change in inductance before and after the product's working life is within ±10%. Combined with the results of scanning electron microscopy, it can be seen that the preparation method of the present invention can obtain a ferrite grain structure with complete grain shape, uniform grain size, and fewer pores, which makes the multilayer chip inductor have lower hysteresis loss. The low loss leads to lower heating of the magnetic core, thereby having higher current impact resistance stability and temperature stability, which can prevent excessive performance change rate during use.

[0078] In Comparative Examples 1 and 2, the heating rate during the first stage of sintering was too fast, resulting in uneven growth of the internal grains, affecting the reliability of the multilayer chip inductor. In Comparative Example 3, the temperature was directly raised to the insulation temperature at 2°C / min, resulting in a too fast heating rate in the second stage, affecting the internal size and densification of the grains, resulting in unqualified service life. From the comparison of the results of Comparative Examples 1-3, it can be seen that the present invention divides the sintering into the first stage and the second stage, while ensuring the sintering efficiency, it can also effectively adjust the size and internal structure of the grains, so that the multilayer chip inductor finally obtained has excellent reliability.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a multilayer chip inductor core, characterized in that: The following steps are involved: (1) Debinding the multi-layer chip inductor green body; (2) performing the first stage sintering and the second stage sintering on the multilayer chip inductor after debinding, wherein the first stage sintering is: heating to 820°C-880°C at a heating rate of 0.5-2°C / min; the second stage sintering is: heating to 900°C-920°C at a heating rate of 0.8-1.2°C / min, and keeping the temperature for 3h-5h; (3) Cooling to obtain the multi-layer chip inductor core.

2. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (1), the multi-layer chip inductor green body comprises NiZn ferrite material, and the particle size D50 of the NiZn ferrite material is 0.6 μm-1.6 μm.

3. The method for preparing a multi-layer chip inductor core according to claim 2, characterized in that: The NiZn ferrite material is doped with copper oxide, and the content of the copper oxide is 3.5wt%-8wt%.

4. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (1), the temperature during the debinding is 470°C-510°C, and the heating rate is 0.3-0.6°C / min.

5. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (1), air is introduced during the debinding process, and the gas pressure difference during the debinding process is 50-60 Pa.

6. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (2), the heating rate during the first stage sintering is 0.5-1.5°C / min.

7. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (2), air is introduced during the first stage sintering, and the gas pressure difference during the first stage sintering is 20-30Pa.

8. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (2), no air is introduced during the second stage sintering.

9. The method for preparing a multi-layer chip inductor core according to claim 1, characterized in that: In the step (3), the cooling includes a first stage cooling and a second stage cooling, and the first stage cooling is: cooling to 700°C-800°C at a cooling rate of 0.5-3°C / min.

10. The method for preparing a multi-layer chip inductor magnetic core according to claim 9, characterized in that: The second stage of cooling is natural cooling.

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