Coupling inductor and preparation method thereof

Abstract

The invention discloses a coupling inductor and a preparation method thereof.The coupling inductor comprises a magnet and a coil assembly, the magnet comprises a first magnetic core and a second magnetic core, and a magnetic core middle column is formed on the first magnetic core; the magnet is formed by adding another magnetic core or filling magnetic powder on the first magnetic core assembled with the coil assembly in an embedded manner for hot pressing, and the second magnetic core is obtained by hot pressing the other magnetic core or the magnetic powder; the coil assembly surrounds the magnetic core middle column, the top face of the coil assembly is flush with the top face of the first magnetic core and the top face of the magnetic core middle column, and the common top face formed through flush is horizontally connected with the bottom face of the second magnetic core.

Description

Technical Field

[0001] The invention relates to a coupled inductor and a preparation method thereof, and belongs to the technical field of electronic components. Background Art

[0002] As more and more coupled inductors are used in computers and mobile phones, and their sizes are gradually shrinking, the production of coupled inductors is becoming increasingly difficult. Existing one-piece molded coupled inductors are generally formed by cold pressing with powder filling to form a first magnetic core, and then winding wires on the first magnetic core to form the first inductor coil structure; the first inductor coil structure is then implanted into a mold, and after powder filling, it is cold pressed a second time to form a secondary cold-pressed magnetic core, and then the second inductor coil is wound on the secondary cold-pressed magnetic core; finally, the structure with two inductor coils is implanted into a mold, filled with powder and hot pressed to form an one-piece molded coupled inductor. In this type of coupled inductor, the two coils are vertically distributed, and the coupling coefficient is changed by adjusting the coil spacing; the preparation scheme of this type of coupled inductor has extremely high requirements for cold pressing strength, which is extremely difficult for small-sized products, especially ultra-thin products; and the coil spacing is highly related to the accuracy of cold pressing powder filling, and is almost entirely dependent on the process control of secondary cold pressing powder filling. The process requirements are very high, and the accuracy is difficult to guarantee, so the coil spacing is difficult to accurately control. Summary of the Invention

[0003] In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes an improved coupled inductor and a preparation method thereof, which can accurately control the coil spacing while avoiding the problem of insufficient secondary cold pressing strength.

[0004] According to one aspect of the present invention, a coupled inductor is provided, comprising a magnet and a coil assembly, wherein the magnet comprises a first magnetic core and a second magnetic core, wherein the first magnetic core is formed with a magnetic core center column, and the magnet is formed by adding another magnetic core or filling magnetic powder to the first magnetic core embedded with the coil assembly and hot pressing the magnet, wherein the second magnetic core is obtained by hot pressing the another magnetic core or the magnetic powder; the coil assembly surrounds the magnetic core center column, and the top surface of the coil assembly is flush with the top surface of the first magnetic core and the top surface of the magnetic core center column, and the flush common top surface is horizontally joined to the bottom surface of the second magnetic core.

[0005] Furthermore, the coil assembly includes a first coil and a second coil stacked axially, and a spacer sandwiched between the first coil and the second coil.

[0006] Furthermore, the spacer is an annular gasket, and a thickness thereof is determined by a preset spacing requirement between the first coil and the second coil.

[0007] Furthermore, the thickness of the annular gasket is 0.04-0.08 mm.

[0008] Furthermore, the height of the magnet is below 0.8 mm.

[0009] According to another aspect of the present invention, a method for preparing a coupled inductor is also proposed, which is used to prepare the aforementioned coupled inductor, comprising the following steps: S1, cold pressing to produce the first magnetic core, wherein the first magnetic core is pressed with grooves of a predetermined pattern, and the grooves define a core center column; S2, placing the coil assembly in the grooves and sleeved on the core center column, while allowing the leads of the coil assembly to be led out from the opening of the grooves and bent to the bottom of the first magnetic core; S3, implanting the assembly obtained in step S2 into a mold, adding another magnetic core or filling powder for hot pressing, and forming it together with the first magnetic core into the magnet.

[0010] Furthermore, step S2 includes: S21, placing a first coil in the groove with its lead facing in a first direction and sleeved on the core center column, so that the lead of the first coil is led out from the opening of the groove in the first direction; S22, sleeved on the core center column, above the first coil; S23, placing a second coil in the groove with its lead facing in a second direction and sleeved on the core center column, so that the lead of the second coil is led out from the opening of the groove in the second direction;

[0011] S24. Bend the leads of the first coil and the second coil to the bottom of the first magnetic core respectively.

[0012] Furthermore, the predetermined pattern of grooves includes a first groove for accommodating a coil body and a second groove for accommodating a coil lead, wherein the first groove surrounds the core center column, and the second groove penetrates the first core from the first direction to the second direction.

[0013] Further, the first direction is opposite to the second direction.

[0014] Furthermore, the second groove includes two parallel linear grooves extending from the first direction to the second direction, and the two parallel linear grooves intersect with the two sides of the first groove respectively; the two leads of the first coil are respectively led out from the first direction openings of the two parallel linear grooves and bent along the surface of the magnet, and the two leads of the second coil are respectively led out from the second direction openings of the two parallel linear grooves and bent along the surface of the magnet.

[0015] Furthermore, the sum of the thicknesses of the first coil, the second coil and the annular gasket is equal to or approximately equal to the depth of the groove.

[0016] Furthermore, the height of the second magnetic core is 0.2 to 0.4 times the height of the magnet.

[0017] The beneficial effects of the technical solution of the present invention are embodied in:

[0018] 1. For smaller and smaller product sizes and lower and lower product heights, the existing two-time cold pressing method greatly weakens the strength of the cold-pressed magnetic core (the thickness of the cold-pressed magnetic core is shared, and it is difficult to have a high strength by preparing a secondary cold-pressed magnetic core on the first magnetic core). The solution of the present invention eliminates the secondary cold pressing, and forms a cold-pressed magnetic core by cold pressing in one go, and then assembles the coil assembly with the cold-pressed magnetic core. Finally, another magnetic core or directly fills magnetic powder to hot-press the cold-pressed magnetic core assembled with the coil assembly. In this way, the thickness of the cold-pressed magnetic core will not be shared, which is beneficial to improving the strength of the cold-pressed magnetic core and is suitable for preparing high-strength ultra-thin products;

[0019] 2. The coil spacing is no longer controlled by a secondary cold pressing process as in the prior art. Instead, it is controlled by a separate spacer (such as an annular gasket). After the coil spacing is determined according to the coupling coefficient requirements, precise spacing control can be achieved by using a gasket of corresponding thickness, thereby ensuring a stable coupling coefficient for the product.

[0020] 3. Forming the coupling coil by assembly rather than winding can also reduce the dependence on the core strength to a certain extent.

[0021] The preparation method of the present invention is more suitable for the preparation of ultra-small and ultra-thin coupled inductors, and is intended to prepare one-piece molded coupled inductors with a height of less than 0.8 mm and a length and width of less than 2.0*1.6 mm (±0.2 mm tolerance). The design of its first magnetic core is to ensure a certain degree of strength and avoid winding action (direct assembly with the wound coil). Its groove design also facilitates coil assembly in ultra-thin size. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is a schematic diagram of the assembly of a coupled inductor according to an embodiment of the present invention.

[0023] Figure 2 Schematic diagram of the assembly of the first magnetic core and coil of the coupled inductor according to an embodiment of the present invention.

[0024] Figure 3 Schematic diagram of a product obtained after hot pressing and forming according to the method for preparing a coupled inductor according to an embodiment of the present invention.

[0025] Figure 4 yes Figure 3 Cross-section of the product shown.

[0026] Figure 5 This is a cross-sectional view of the product produced by the existing secondary cold pressing process. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings, specific implementation methods, and examples, which are provided for the purpose of illustration only and are not intended to be limiting.

[0028] Furthermore, spatial terms such as "up," "down," "left," "right," "top," and "bottom" used in the description of the technical solutions of the present invention are intended to facilitate description of the relative positions of the product's components and do not necessarily imply that the product can be positioned in only the orientations shown in the figures. In actual use, as the product's orientation varies (e.g., rotated 90 degrees or in other orientations), spatial terms describing that orientation should be interpreted similarly.

[0029] In addition, terms such as "first" and "second" are only used to distinguish components. It should be understood that these components should not be limited by such terms. They themselves do not mean that these elements have the aforementioned ordinal numbers, nor do they represent the arrangement order of one component and another component or the order of manufacturing methods.

[0030] After the cold pressed core is pressed, in order to ensure the strength during winding, it will be baked and cured to a certain extent (the resin glue in the core is in a semi-cured state or low-cured state). Figure 5 In the prior art, secondary cold pressing requires filling powder on the combination of the first magnetic core 11' and the primary coil 21 to press the secondary cold-pressed magnetic core 13. This will inevitably create a certain physical interface between the first magnetic core and the secondary cold-pressed magnetic core. If the strength requirement is slightly higher when winding the second set of coils 22, the secondary cold-pressed magnetic core 13 may fall off or break directly. Even if the secondary cold pressing of the prior art is changed to hot pressing, although the strength can be guaranteed, it will cause the glue in the magnetic core to solidify, affecting subsequent processes, such as the bonding between the magnetic core 12' and the secondary cold-pressed magnetic core 13. In summary, the prior art has the following defects:

[0031] 1. It is difficult to ensure the strength of secondary cold pressed magnetic cores, and the requirements for powder materials and processes are very high;

[0032] 2. The coil spacing is completely dependent on the process control of secondary cold pressing and powder filling, and the accuracy is difficult to guarantee;

[0033] 3. With the development trend of smaller and smaller product sizes, especially when the product height is getting lower and lower, the vertical arrangement of two sets of coils is extremely difficult to design and manufacture.

[0034] In order to overcome the above-mentioned defects, the present invention proposes the following technical ideas:

[0035] 1. Cancel the secondary cold pressing to avoid the problem of insufficient secondary cold pressing strength and the exploration and verification of the secondary cold pressing process;

[0036] 2. Instead of winding the coil directly on the magnetic core, assemble the wound coil on the magnetic core, that is, use the semi-finished product assembly method;

[0037] 3. Two sets of coils are stacked axially (the existing technology is radially and vertically distributed) and separated by a component such as a gasket. In this way, the coil spacing is controlled by the thickness of the gasket;

[0038] 4. A flat-plate first magnetic core is produced by cold pressing in one step, and grooves for assembling coils and gaskets are pressed on the surface. After all coils, gaskets and the first magnetic core are assembled, they are hot-pressed in one step by filling with powder or adding another magnetic core.

[0039] Based on the above ideas, the embodiment of the present invention proposes an improved coupled inductor and a preparation method thereof. Please refer to Figure 1 、 Figure 3 and Figure 4 The coupled inductor of the embodiment of the present invention includes a magnet 10 and a coil assembly. The magnet 10 includes a first magnetic core 11 and a second magnetic core 12. The first magnetic core 11 is formed with a magnetic core center column. The magnet 10 is formed by adding another magnetic core or filling magnetic powder to the first magnetic core 11 embedded with the coil assembly and hot pressing. The second magnetic core 12 is obtained by hot pressing the other magnetic core or the magnetic powder. Preferably, the height of the first magnetic core 11 is greater than the height of the second magnetic core 12. The coil assembly is located as a whole in the first magnetic core 11. The coil assembly surrounds the magnetic core center column. The top surface of the coil assembly is flush with the top surface of the first magnetic core and its magnetic core center column. The common top surface formed by the flushing is horizontally connected to the bottom surface of the second magnetic core 12. The coil assembly includes an axially stacked first coil 21 and a second coil 22 and a spacer sandwiched between the first coil 21 and the second coil 22. The spacer is, for example, an annular gasket 3.

[0040] In an embodiment of the present invention, the coil assembly is preferably flush with the first magnetic core. On the one hand, this can prevent the risk of the coil shaking or falling off during assembly; on the other hand, if the coil assembly is much higher than the first magnetic core, after hot pressing, the deformation difference between the first coil and the second coil may be too large, that is, the deformation of the second coil is significantly larger, resulting in the two coils inside the magnet being inconsistent in size after hot pressing or the second coil being bent or tilted, etc., which will cause the actual electrical performance of the inductor to be too different from the design target.

[0041] In the embodiment of the present invention, the first magnetic core 11 is formed by cold pressing in one go, and a predetermined pattern of grooves is pressed thereon for assembling the first coil 21, the second coil 22 and the annular gasket 3; after obtaining the first magnetic core, the first coil, the annular gasket and the second coil are sequentially assembled into the grooves of the first magnetic core in an axial stacking manner, and the leads are bent to reserve the prototype of the external electrode, and the obtained assembly is implanted into a mold, and finally another magnetic core (preferably also pre-cold pressed) is added to the first magnetic core or directly filled with powder, and hot pressed together to obtain Figure 3 and Figure 4 Products shown.

[0042] Based on the above ideas, an embodiment of the present invention proposes a method for preparing the coupled inductor of the aforementioned embodiment, comprising the following steps S1 to S6:

[0043] S1. Fabricate a first magnetic core 11. A predetermined pattern of grooves is formed on the first magnetic core 11, and the grooves define a core center column 4. The first magnetic core 11 is manufactured by cold pressing and then baking for a slight curing process. This ensures winding strength and prevents premature curing of the adhesive in the core, which could result in insufficient density during subsequent hot pressing.

[0044] S2. Place the wound first coil 21 in the groove of the first magnetic core 11 with the lead wire facing the first direction and put it on the core center column 4, so that the lead wire of the first coil is led out from the opening of the groove in the first direction. Figure 2 ;

[0045] S3, put the annular gasket 3 on the core column 4 so that the annular gasket 3 is pressed on the first coil 21, as shown in FIG. Figure 2 ;

[0046] S4, place the second coil 22 in the groove of the first magnetic core with the lead wire facing the second direction and put it on the core center column 4, so that the second coil 22 is pressed on the annular gasket 3, as shown in FIG. Figure 2 ;

[0047] S5. Bend the leads of the first coil 21 and the second coil 22 to the bottom of the first magnetic core 11 respectively. Figure 2 The assembly shown;

[0048] S6. The above-obtained assembly is implanted into a mold, and another cold-pressed magnetic core is placed on the assembly obtained in step S5 and then hot-pressed. During hot-pressing, the uncured adhesive in the first magnetic core 11 and the other cold-pressed magnetic core first softens above the glass transition temperature (this allows the two magnetic cores to be "combined" into a whole) and then gradually solidifies, undergoing a "breaking and reshaping" process, and finally solidifies into the following shape. Figure 3The product shown. Step S6 employs hot pressing to achieve higher density and better electrical performance. It should also be noted that after the assembly is implanted into the mold in step S6, powder filling can also be used to replace the other cold-pressed magnetic core described above for hot pressing with the first magnetic core.

[0049] In getting Figure 3 After the product is shown, resin glue will be sprayed on the surface of the product to serve as an anti-corrosion function and an insulating function when the electrode is made in the subsequent electroplating process. It can cover the exposed leads on the side of the first magnetic core, and the bottom electrode position (the position that needs to be electroplated) will be opened by laser stripping and the lead will be exposed again, which is called the bottom electrode.

[0050] The integrally molded coupled inductor and its preparation method provided in the aforementioned embodiments of the present invention solve the difficulties of insufficient core strength and low consistency of coupling coefficient of small-sized coupled inductors by cold-pressing the first magnetic core, assembling the first magnetic core with the coil and gasket, and hot-pressing the integrally molded product.

[0051] like Figure 1 As shown, in some specific embodiments, the grooves of a predetermined pattern pressed and formed on the first magnetic core 11 include: a first groove for accommodating the coil body and a second groove for accommodating the coil lead. The shape of the first groove is consistent with the shape of the main body of the first coil and the second coil (for example, if the coil is wound into a ring shape, the first groove is also ring-shaped). The first groove defines the core center column 4, that is, the first groove surrounds the core center column 4. The second groove includes two parallel linear grooves, and the two parallel linear grooves pass through the first magnetic core 11 from the first direction to the second direction, and the two parallel linear grooves intersect with the first groove on both sides of the first groove. Preferably, the first direction and the second direction are two opposite directions, such as the front and the back of the first magnetic core 11. Based on such an orientation description, the two parallel linear grooves intersect with the first groove on the left and right sides of the first groove respectively. The first coil 21, the annular gasket 3, and the second coil 22 are sequentially sleeved on the core center column 4 and embedded in the groove. The lead of the first coil 21 faces the first direction and is led out from the opening of the groove in the first direction. The lead of the second coil 22 faces the second direction and is led out from the opening of the groove in the second direction. The annular gasket 3 is sandwiched between the first coil 21 and the second coil 22 to limit the distance between the first coil 21 and the second coil 22. By adding another magnetic core or filling powder, combining it with the first magnetic core 11 by hot pressing and curing together to form an integral magnet 10 of coupled inductance, the first coil 21, the second coil 22 and the spacer 3 are wrapped inside, and the lead wires are bent along the magnet to the bottom of the first magnetic core 11 as the prototype of the bottom electrode, thereby obtaining the following. Figure 3 Products shown.

[0052] In an embodiment of the present invention, two sets of coupled coils are placed vertically in the axial direction, and the coupling coefficient is controlled by the axial spacing between the coils. The specific value of the thickness of the annular gasket is limited by factors such as the coupling coefficient required by the customer and the size of the product itself. The embodiment of the present invention is more suitable for ultra-small and ultra-thin products with a height of less than 0.8 mm. The size of the product itself determines that the coil spacing will not be too large. The thickness of the annular gasket is usually set between 0.04-0.08 mm, and the coupling coefficient is usually above 0.5. The material of the annular gasket can be magnetic or non-magnetic, and the specific material is not limited. The sum of the thicknesses of the first coil 21, the second coil 22 and the annular gasket 3 is equal to or approximately equal to the depth of the groove. Preferably, in the axial direction of the core center column 4, the height of the first magnetic core 11 is greater than the height of the second magnetic core 12, so that the two sets of coils are located at the middle height position of the product as a whole. In some embodiments of the present invention, the thickness of the second magnetic core 12 is 0.2 to 0.4 times the thickness of the entire magnet.

[0053] It should also be noted that the first coil 21 and second coil 22 of the present invention are described using annular coils as an example. The annular hollow portion of the coil body can be circular, racetrack-shaped, elliptical, rectangular, or polygonal. The shape of the hollow portion of the gasket and the cross-sectional shape of the core column are consistent with the hollow portion of the coil to facilitate assembly. Furthermore, the coil can be made of flat enameled wire, round enameled wire, or other conductor with an insulating layer. The winding method is not specifically limited and can be wound vertically as shown in the example diagram or wound perpendicularly to the coil's central axis.

[0054] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art will recognize that several equivalent substitutions or obvious variations can be made without departing from the scope of the present invention, and that any equivalent performance or application should be considered to fall within the scope of protection of the present invention.

Claims

1. A coupled inductor, comprising a magnet and a coil assembly, characterized in that: The magnet includes a first magnetic core and a second magnetic core, the first magnetic core is formed with a magnetic core center column, and the magnet is formed by adding another magnetic core or filling magnetic powder to the first magnetic core embedded with the coil assembly and hot pressing, wherein the second magnetic core is obtained by hot pressing the other magnetic core or the magnetic powder; the coil assembly surrounds the magnetic core center column, and the top surface of the coil assembly is flush with the top surface of the first magnetic core and the magnetic core center column, and the common top surface formed by the flushing is horizontally connected to the bottom surface of the second magnetic core.

2. The coupled inductor according to claim 1, wherein: The coil assembly includes a first coil and a second coil stacked axially, and a spacer interposed between the first coil and the second coil.

3. The coupled inductor according to claim 2, wherein: The spacer is an annular gasket, and the thickness of the spacer is determined by the preset spacing requirement between the first coil and the second coil.

4. The coupled inductor according to claim 3, wherein: The thickness of the annular gasket is 0.04-0.08 mm.

5. The coupled inductor according to any one of claims 1 to 4, wherein: The height of the magnet is less than 0.8 mm.

6. A method for preparing a coupled inductor, for preparing the coupled inductor according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Cold-pressing the first magnetic core, wherein grooves of a predetermined pattern are pressed on the first magnetic core, and the grooves define a core center column; S2. placing the coil assembly in the groove and sleeved on the central column of the magnetic core, while leading the lead wire of the coil assembly out from the opening of the groove and bending it to the bottom of the primary magnetic core; S3. Implanting the assembly obtained in step S2 into a mold, adding another magnetic core or filling powder, and hot pressing to form the magnet together with the first magnetic core.

7. The preparation method according to claim 6, wherein Step S2 includes: S21, placing a first coil in the groove with its lead facing in a first direction and sleeved on the central column of the magnetic core, such that the lead of the first coil is led out from an opening of the groove in the first direction; S22, putting an annular gasket on the center column of the magnetic core, above the first coil; S23, placing a second coil in the groove with its lead facing the second direction and sleeved on the central column of the magnetic core, so that the lead of the second coil is led out from the opening of the groove in the second direction; S24. Bend the leads of the first coil and the second coil to the bottom of the first magnetic core respectively.

8. The preparation method according to claim 7, wherein The predetermined pattern of grooves includes a first groove for accommodating a coil body and a second groove for accommodating a coil lead, wherein the first groove surrounds the core center leg and the second groove penetrates the first core from the first direction to the second direction.

9. The preparation method according to claim 7, wherein The first direction is opposite to the second direction.

10. The preparation method according to claim 8, characterized in that The second groove includes two parallel linear grooves extending from the first direction to the second direction, and the two parallel linear grooves intersect with two sides of the first groove respectively; The two leads of the first coil are respectively led out from the first direction openings of the two parallel linear slots and bent close to the surface of the magnet, and the two leads of the second coil are respectively led out from the second direction openings of the two parallel linear slots and bent close to the surface of the magnet.

11. The preparation method according to claim 7, wherein The sum of the thicknesses of the first coil, the second coil and the annular gasket is equal to or substantially equal to the depth of the groove.

12. The coupled inductor according to claim 6, wherein: The height of the second magnetic core is 0.2 to 0.4 times the height of the magnet.

Images