Ferrite element as well as preparation method and application thereof

Abstract

The invention discloses a ferrite element and a preparation method thereof, and relates to the technical field of ferrite. According to the ferrite element provided by the invention, the fluorine-containing compound coating with moderate thickness is introduced on the surfaces of the ferrite magnet and the silver layer at the end part of the magnet, and the obtained coating has hydrophobicity and certain insulativity, so that the ferrite magnet can be protected in the subsequent tin layer and nickel layer electroplating process, and the overplating phenomenon is avoided; meanwhile, electroplating on the surface of the fluorine-containing compound coating with the silver layer as the substrate is not affected, high efficiency is achieved, the element characteristics are not affected, and the weldability, the soldering resistance and other test indexes of the obtained element can all reach the qualified level.

Description

Technical Field

[0001] The present invention relates to the technical field of ferrites, and in particular to a ferrite element and a preparation method and application thereof. Background Art

[0002] With the rapid development of integrated circuits and communications technology worldwide, electronic devices are becoming increasingly smaller and lighter. In electronic devices, components such as chip inductors and chip beads made from chip ferrite play important roles in filtering and energy storage. The size of these components has a significant impact on the size of electronic devices, especially inductors, which typically occupy the vast majority of the area and space in electronic devices. To produce smaller components such as chip inductors, ferrites are currently being miniaturized.

[0003] Ferrite, a composite oxide formed by sintering a mixture of metal elements such as Fe, Ni, Cu, and Zn, retains a small amount of metal ions on its surface after sintering that do not enter the crystal lattice and participate in oxide formation. To fabricate ferrite into components such as magnetic beads and inductors, a three-layer terminal electrode consisting of silver, nickel, and tin is formed at the ends of the ferrite. The silver layer is typically formed by applying a silver paste to the ends of the ferrite magnet and sintering it, while the nickel and tin layers are formed by electroplating, with the silver layer serving as a substrate for the nickel layer. However, a common side reaction during the electroplating process is the reduction of hydrogen ions to release hydrogen atoms. These hydrogen atoms easily migrate to the surface of the ferrite magnet, reacting with free metal ions on the ferrite surface, causing creep plating. This phenomenon manifests as the end electrodes extending toward the center of the ferrite magnet. Because the distance between the positive and negative electrodes is smaller in smaller ferrite magnets, this creep plating phenomenon is more severe in smaller ferrite magnets and can even cause short circuits in the product.

[0004] There are two main traditional methods to prevent creep plating. One is to add a remelting process before electroplating, and keep the product at a certain temperature for a long time. The disadvantage of this method is that it takes a long time. The second is to use strong acid to corrode and oxidize the metal ions on the surface of the magnet. The disadvantage of this method is that while corroding and oxidizing the metal ions on the surface of the ferrite magnet, it will also corrode the magnet and silver layer of the product, causing the end electrode adhesion to deteriorate, affecting the reliability of the component (including solderability, whether creep plating, welding reliability or solder resistance, among which unqualified solderability and solder resistance can easily cause poor welding and open circuit failure, and creep plating can easily cause component short circuit failure), resulting in the problem of component failure after subsequent welding. Moreover, the operation process of acidic materials is highly dangerous and has a great impact on the environment. For this reason, it is urgent to propose a chip ferrite preparation method that is more efficient and does not affect the reliability of the component. Summary of the Invention

[0005] In order to address the shortcomings of the existing technology, the present invention provides a ferrite component, in which a layer of fluorine-containing compound coating of moderate thickness is introduced on the surface of the silver layer of the ferrite magnet and the end of the magnet. The resulting coating is hydrophobic and has certain insulation properties, which can prevent the ferrite magnet from creeping during the subsequent electroplating of the tin layer and the nickel layer. At the same time, it does not affect the electroplating occurring on the surface of the fluorine-containing compound coating based on the silver layer, thereby greatly improving the reliability of the resulting component.

[0006] Another object of the present invention is to provide a method for preparing a ferrite component.

[0007] Another object of the present invention is to provide an application of a ferrite component.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0009] A ferrite element comprises an end electrode and a ferrite magnet, wherein the end electrode comprises a silver layer, a fluorine-containing compound coating, a nickel layer, and a tin layer; the ferrite magnet comprises a substrate and a fluorine-containing compound coating on the surface of the substrate; the substrate comprises a ferrite layer and a conductive coil;

[0010] The raw materials for preparing the fluorine-containing compound coating include fluorine-containing compounds, and the fluorine-containing compounds include at least one of fluorinated alkanes, fluorinated alkenes, and fluorinated alkynes, wherein the percentage of fluorine atoms in the total number of atoms is ≥50%; the thickness of the fluorine-containing compound coating is 1 to 5 μm.

[0011] During the preparation of ferrite components, a terminal electrode comprising three layers, namely, a silver layer, a nickel layer, and a tin layer, is formed at the end of the ferrite. Typically, the silver layer is formed by applying a silver paste to the end of the ferrite magnet and then sintering it, while the nickel and tin layers are formed by electroplating, with the silver layer serving as a substrate for the nickel layer. The ferrite component provided by the present invention incorporates a fluorine-containing compound coating on the silver layer at the end of the ferrite magnet and on the surface of the ferrite magnet (not covered by the silver layer). This prevents creep plating during the subsequent electroplating of the tin and nickel layers, while maintaining the electroplating effect on the surface of the fluorine-containing compound coating based on the silver layer, and thus, does not affect the bonding force between the ferrite magnet and the terminal electrode. This is because the fluorine-containing compound coating introduced in the present invention is a coating formed by using fluorine-substituted alkanes, alkenes or alkynes as raw materials for preparation, and the fluorine atom content in the compound is ≥50at%, that is, the number of fluorine atoms accounts for more than 50% of the total number of atoms. The coating thus formed has a low surface energy and strong hydrophobicity, which can reduce the probability of hydrogen atom migration formed by the hydrogen evolution side reaction during the subsequent electroplating process. At the same time, the fluorine-containing compound coating has a certain insulating property. The inventors of this application have found through a large number of experimental studies that when the thickness of the fluorine-containing compound coating is 1 to 5 μm, the resulting coating can simultaneously protect the surface of the weakly conductive ferrite magnet through hydrophobicity and insulation, avoiding the occurrence of creep plating, and will not affect the electroplating process of the fluorine-containing compound coating surface with a silver layer as the substrate, which has stronger conductivity. When the coating thickness is too high, although it can also reduce the occurrence of creep plating, the bonding ability between the end electrode and the ferrite magnet is reduced, which will affect the characteristics of the resulting ferrite component product. The inventors of this application have discovered through extensive experimental research that when the fluorine atom content of the fluorine-containing compound is less than 50 at%, the technical effects of this application cannot be achieved due to the excessively low fluorine content. It should be noted that the fluoroalkanes, fluoroalkenes, and fluoroalkynes described in this application contain only carbon, hydrogen, and fluorine. When the fluorine-containing compound also contains elements such as oxygen, the degree of surface energy reduction is reduced, and the hydrophobicity decreases.

[0012] In a specific embodiment of the present invention, the substrate comprises several ferrite layers and several layers of conductive coils, which can be manufactured using conventional methods in the art. For example, the substrate comprises the following steps: printing the conductive coils in a specified pattern on the ferrite layers to form a composite layer; and then laminating the composite layers with different patterns of conductive coils to form the substrate. The pattern of the conductive coils printed on each ferrite layer can vary, depending on the design, such as 1 turn, 3 / 4 turn, or 1 / 2 turn.

[0013] More specifically, with the stacking direction of the ferrite layers as a first direction, the end electrodes are arranged on both end surfaces of the ferrite magnet in a second direction perpendicular to the first direction.

[0014] Preferably, the fluorine-containing compound has 1 to 4 carbon atoms.

[0015] More preferably, the fluorine-containing compound includes at least one of C3F6, CF4, C4F8, and CHF3.

[0016] The coating formed by the fluorine-containing compound on the surface of the ferrite magnet and the silver layer can have more moderate hydrophobicity and insulation, and while better avoiding the occurrence of creep plating, the electroplating process on the surface of the silver layer is also less affected.

[0017] Preferably, the thickness of the silver layer is 25-40 μm.

[0018] Preferably, the nickel layer has a thickness of 2 to 6 μm.

[0019] Preferably, the thickness of the tin layer is 2-10 μm.

[0020] Preferably, the thickness of the ferrite element is 0.1-1 mm.

[0021] Ferrite components with thicknesses within the aforementioned range include 0201 (0.6mm x 0.3mm x 0.3mm) and smaller sizes. The smaller the size, the more severe the creep plating phenomenon that occurs during the electroplating process. The preparation method of the present invention can avoid this creep plating phenomenon during the preparation of small-sized ferrite components.

[0022] Preferably, the number of layers of the conductive coil is 1 to 12.

[0023] The present invention also provides a method for preparing the ferrite element, comprising the following steps:

[0024] The ends of the ferrite magnets are sealed to obtain a component to be processed, and plasma treatment is performed in a fluorine-containing compound atmosphere to form a fluorine-containing compound coating. Then, nickel layers and tin layers are electroplated in sequence on the surface of the fluorine-containing compound coating at the ends of the ferrite magnets to obtain a ferrite component.

[0025] In a specific embodiment of the present invention, since the fluorine-containing compound coating is prepared by plasma deposition using a fluorine-containing compound as a raw material, the existence form of the fluorine-containing compound in the coating may change, but subsequent characterization can confirm that the coating contains -CF- groups.

[0026] Preferably, the plasma treatment is performed at 2 to 10 kgf / cm 2 carried out under pressure.

[0027] More preferably, the plasma treatment is performed at 4 to 6 kgf / cm 2 carried out under pressure.

[0028] Preferably, the power of the plasma treatment is 80-120W.

[0029] Preferably, the plasma treatment time is 50 to 250 seconds.

[0030] Preferably, the loading amount of the component to be processed during the plasma treatment process is 20-200 g.

[0031] In a specific embodiment of the present invention, the loading amount of components to be processed during the plasma processing process refers to the amount of components to be processed placed in the plasma processing equipment.

[0032] Preferably, the end-capping includes two steps: silver dipping and silver burning.

[0033] The silver dipping process includes: coating the end of the ferrite magnet with a slurry, wherein the slurry includes glass powder, adhesive, solvent, and silver powder;

[0034] The silver burning comprises: calcining at 600-750°C.

[0035] The purpose of the silver burning in the present invention is to sinter the silver paste on the end of the ferrite magnet into a dense silver electrode through high temperature sintering.

[0036] In a specific embodiment of the present invention, the adhesive comprises a polymer resin, more specifically, the polymer resin comprises PVB (polyvinyl butyral) resin.

[0037] In a specific embodiment of the present invention, the solvent can be a high-boiling point alcohol, ester, hydrocarbon, or ether commonly used in the art. More specifically, the solvent includes at least one of polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyhydroxyethyl methacrylate, and polypropylene alcohol.

[0038] More preferably, the nickel electroplating comprises the following steps: immersing the component to be treated, having the fluorine-containing compound coating on its surface, and elemental nickel in a nickel plating electrolyte, and then electroplating. More preferably, the nickel plating electrolyte comprises nickel sulfamate. More preferably, the current applied is 25 to 30 A.

[0039] More preferably, the electroplating of the tin layer comprises the following steps: immersing the component to be treated after the nickel electroplating layer and the elemental tin in a tin plating electrolyte, and applying an electric current for electroplating. More preferably, the tin plating electrolyte comprises an acidic electrolyte containing a tin sulfonate salt, such as a tin methanesulfonate electrolyte. More preferably, the applied current is 10-15A.

[0040] The present invention also protects the application of the above ferrite element in chip inductors and chip ferrite beads.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The ferrite element provided by the present invention not only does not suffer from creep plating after a complete end electrode is formed at the end of the ferrite magnet by electroplating, but also does not affect the bonding between the end electrode and the ferrite magnet, and the welding indicators such as solder resistance and solderability can reach qualified levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the plating phenomenon on chip ferrite inductors.

[0044] Figure 2 Schematic diagram of the finished ferrite inductor without creep plating obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0046] Examples 1 to 7 and Comparative Examples 1 to 2

[0047] This embodiment provides a series of methods for preparing ferrite components with different fluorine-containing compound gases, fluorine-containing compound coating thicknesses, and plasma treatment parameters, including the following steps:

[0048] The ends of the ferrite magnet are sealed to obtain a component to be processed, and a fluorine-containing compound coating is formed by plasma treatment in a fluorine-containing compound atmosphere. Then, a nickel layer and a tin layer are electroplated on the surface of the fluorine-containing compound coating at the ends of the ferrite magnet in sequence to obtain a ferrite component;

[0049] The plasma treatment was carried out at 5 kgf / cm 2 The plasma treatment is carried out under a pressure of 100W, the time is 50 to 300s, and the loading amount of the component to be treated during the plasma treatment is 20 to 200g;

[0050] The end-capping includes two steps: silver dipping and silver burning.

[0051] The silvering step includes: applying a slurry on the end of the ferrite magnet by scraping, wherein the slurry includes glass powder, PVB resin, polyethylene glycol, and silver powder;

[0052] The silver burning comprises: calcining at 700°C;

[0053] The ferrite elements prepared in this embodiment and the comparative example include end electrodes and ferrite magnets. The end electrodes include a silver layer with a thickness of 30 μm, a fluorine-containing compound coating with a thickness of 1 to 5 μm, a nickel layer with a thickness of 2 μm, and a tin layer with a thickness of 3 μm. The ferrite magnets include a substrate and a fluorine-containing compound coating on the surface of the substrate. The substrate includes 14 staggered ferrite layers and 8 conductive coils.

[0054] The fluorine-containing compound gas, fluorine-containing compound coating thickness and plasma treatment parameters specifically used in this embodiment are shown in Table 1 below:

[0055] Table 1. Gases, coating thicknesses, and plasma treatment parameters selected in Examples 1 to 7 and Comparative Examples 1 to 2

[0056]

[0057] Comparative Example 3

[0058] A method for preparing a ferrite component, which differs from Example 1 only in that:

[0059] After the silver layer is bonded to the end of the ferrite magnet, a nickel layer and a tin layer are directly and sequentially electroplated on the surface of the silver layer without plasma treatment.

[0060] Comparative Example 4

[0061] A method for preparing a ferrite component, which differs from Example 2 only in that:

[0062] After the silver layer is bonded to the end of the ferrite magnet, a nickel layer and a tin layer are directly and sequentially electroplated on the surface of the silver layer without plasma treatment.

[0063] Comparative Example 5

[0064] A method for preparing a ferrite component, which differs from Example 1 only in that:

[0065] The plasma treatment was performed in an N2 atmosphere.

[0066] Comparative Example 6

[0067] A method for preparing a ferrite component, which differs from Example 1 only in that:

[0068] The plasma treatment was performed in an Ar atmosphere.

[0069] Comparative Example 7

[0070] A method for preparing a ferrite component, which differs from Example 1 only in that:

[0071] The plasma treatment was performed in a CH3F atmosphere.

[0072] Comparative Example 8

[0073] A method for preparing a ferrite component, which differs from Example 1 only in that:

[0074] The plasma treatment was performed in a CH2ClF atmosphere.

[0075] Performance Testing

[0076] Solderability test: Use the solder bath method and the following rules: a) Take 50 pieces of ferrite component products and pour them into the sieve plate of corresponding specifications, shake the sieve plate until the products fill each hole; b) Stick the products on the sieve plate to a double-sided tape with a width of 2.4cm and a length of about 80mm, tear it from top to bottom, and mark it on the tinning fixture; c) Use a brush to apply flux to the products on the tinning fixture. The flux composition is 25% rosin and 75% isopropyl alcohol. The terminal electrodes of the component should be completely immersed in the flux and slowly removed. The excess flux should be removed with absorbent paper; d) Hang the fixture on the tinning machine After pressing the button, the product is automatically immersed. The solder composition is Sn96.5Ag3.0Cu0.5, the solder temperature is (245±3)℃, the immersion depth is 10mm, and the immersion time is (3±0.3)s; e) After the product cools down, observe the state of the component after soldering under an appropriate light source and using a magnification of 10 times or more. If the electrodes at both ends are bright and full after tinning, and there are no defects such as pinholes, silver shedding, exposed magnetism at corners, broken magnetism, and bursting at the ends, it is evaluated as "qualified"; if defects such as poor tinning, pinholes, silver shedding, exposed magnetism at corners, broken magnetism, and bursting occur after soldering, it is evaluated as "unqualified".

[0077] Solder resistance test method: Use the solder bath method to test, and adopt the following rules: a) Take 50 pcs of ferrite component products and pour them into the sieve plate of corresponding specifications, shake the sieve plate until the product fills each hole; b) Stick the product on the sieve plate on a double-sided tape with a width of 2.4cm and a length of about 80mm, tear it from top to bottom, and mark it on the tinning fixture; c) Use a brush to apply flux to the product on the tinning fixture. The flux composition is 25% rosin and 75% isopropyl alcohol. The end electrode of the component should be completely immersed in the flux and slowly removed. The excess flux should be removed with absorbent paper; d) Hang the fixture to the tinning fixture. After the button is pressed on the machine, the product is automatically immersed in the solder with a composition of Sn96.5Ag3.0Cu0.5, a solder temperature of (260±5)°C, an immersion depth of 10mm, and an immersion time of (10±1)s; e) After the product has cooled, check the tinning quality under an appropriate light source and using a 10x or higher magnification device. If the electrodes at both ends are bright and full after tinning, and there are no defects such as pinholes, silver shedding, exposed corners, broken magnetism, or cracked pieces at the ends, it is evaluated as "qualified"; if defects such as poor tinning, pinholes, silver shedding, exposed corners, broken magnetism, or cracked pieces appear after soldering, it is evaluated as "unqualified".

[0078] Boiling aging test method: a) Take 50 pieces of ferrite component products and place them in a stainless steel bowl, affix high-temperature glue and mark them, place them on the rack of a steam aging test chamber with a water temperature of 95±10℃, and steam age them continuously for 8 hours; b) After the steam aging is completed, remove the products and observe the tinning quality according to the "Solderability Test" section. If the electrodes at both ends are bright and full after tinning, and there are no defects such as pinholes, silver shedding, exposed corners, broken magnets, and cracked chips at the ends, the evaluation is "qualified"; if defects such as poor tinning, pinholes, silver shedding, exposed corners, broken magnets, and cracked chips are found after soldering, the evaluation is "unqualified".

[0079] Detection and judgment of creep plating phenomenon: Use the naked eye to observe the appearance of the ferrite component with the assistance of measuring tools to judge whether creep plating occurs. If no creep plating is seen with the naked eye, it is evaluated as "no creep plating"; if creep plating is observed with the naked eye, and the length of the middle magnet, that is, the length of the non-creep plating area, is calculated according to the measuring tool, it is evaluated as "mild creep plating"; if creep plating is observed with the naked eye, and the length of the middle magnet, that is, the length of the non-creep plating area, is calculated according to the measuring tool, it is greater than 1 / 2 of the component length, it is evaluated as "serious creep plating".

[0080] The data of the above performance test are shown in Table 2 below:

[0081] Table 2. Performance test data of ferrite components obtained in Examples and Comparative Examples

[0082]

[0083] According to Table 2 above, the ferrite component prepared by the preparation method provided by the present invention not only does not have the creep plating phenomenon, but also does not affect the bonding between the end electrode and the ferrite magnet, and the welding indicators such as solder resistance and solderability can reach the qualified level.

[0084] According to Comparative Examples 1 and 2, the thickness of the fluorine-containing compound coating needs to be in the range of 1 to 5 μm. If the coating thickness is too thin (Comparative Example 1), creep plating is easy to occur, and if it is too thick (Comparative Example 2), the solderability and other indicators are unqualified.

[0085] According to Comparative Examples 3 and 4, if the surface of the terminated ferrite magnet is not plasma treated, creep plating will occur on the surface of the resulting ferrite component, and the creep plating phenomenon is more serious for components with smaller sizes (Comparative Example 1).

[0086] According to Comparative Examples 5 to 8, the gas used in the plasma treatment is a non-fluorine-containing compound (Comparative Examples 5 to 6), or the fluorine content in the fluorine-containing compound is less than 50at% (Comparative Examples 7 to 8), which will lead to the unavoidable occurrence of the creep plating phenomenon. This is because the content of the fluorine-containing compound and the fluorine content therein have a crucial influence on the avoidance of the creep plating phenomenon.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A ferrite component, characterized in that: The invention comprises an end electrode and a ferrite magnet, wherein the end electrode comprises a silver layer, a fluorine-containing compound coating, a nickel layer and a tin layer, the ferrite magnet comprises a substrate and a fluorine-containing compound coating on the surface of the substrate, and the substrate comprises a ferrite layer and a conductive coil; The raw materials for preparing the fluorine-containing compound coating include fluorine-containing compounds, and the fluorine-containing compounds include at least one of fluorinated alkanes, fluorinated alkenes, and fluorinated alkynes, wherein the percentage of fluorine atoms in the total number of atoms is ≥50%; the thickness of the fluorine-containing compound coating is 1 to 5 μm.

2. The ferrite component according to claim 1, wherein The fluorine-containing compound has 1 to 4 carbon atoms.

3. The ferrite component according to claim 2, wherein: The fluorine-containing compound includes at least one of C3F6, CF4, C4F8, and CHF3.

4. The ferrite component according to claim 1, wherein Include at least one of the following (a) to (c): (a) the thickness of the silver layer is 25 to 40 μm; (b) the thickness of the nickel layer is 2 to 6 μm; (c) The thickness of the tin layer is 2 to 10 μm.

5. The ferrite component according to claim 1, wherein The thickness of the ferrite element is 0.1-1 mm.

6. The ferrite component according to claim 1, wherein: The number of layers of the conductive coil is 1 to 12.

7. The method for preparing a ferrite element according to any one of claims 1 to 6, characterized in that: The steps include: The ends of the ferrite magnets are sealed to obtain a component to be processed, and plasma treatment is performed in a fluorine-containing compound atmosphere to form a fluorine-containing compound coating. Then, nickel layers and tin layers are electroplated in sequence on the surface of the fluorine-containing compound coating at the ends of the ferrite magnets to obtain a ferrite component.

8. The method for preparing a ferrite component according to claim 7, wherein: The method according to claim 1, comprising at least one of the following (d) to (g): (d) The plasma treatment is performed at 2 to 10 kgf / cm 2 Under pressure; (e) the power of the plasma treatment is 80 to 120 W; (f) The plasma treatment time is 50 to 250 seconds; (g) The loading amount of the component to be processed during the plasma treatment process is 20 to 200 g.

9. The method for preparing a ferrite component according to claim 7, wherein: The end-capping includes two steps: silver dipping and silver burning. The silver dipping process includes: coating the end of the ferrite magnet with a slurry, wherein the slurry includes glass powder, adhesive, solvent, and silver powder; The silver burning comprises: calcining at 600-750°C.

10. Use of the ferrite component according to any one of claims 1 to 6 in chip inductors and chip ferrite beads.

Images