Powder-pressed inductor and method of manufacture

Abstract

The application belongs to the technical field of inductors, and provides a powder-pressing inductor and a manufacturing method. In the manufacturing method of the powder-pressing inductor, the outgoing wire of the winding coil is first bonded to the terminal tab welding lug, and then the bonding position of the outgoing wire of the winding coil and the terminal tab welding lug is fusion welded, so that a spherical welding structure is formed at the fusion welding position, the air gap between the outgoing wire and the terminal tab welding lug is eliminated, the spherical welding structure formed by fusion completely wraps the bonding position, the tensile strength of the welding point is high, and there is no outgoing wire rebound or cracking phenomenon after reflow soldering, and the open-circuit failure hidden danger caused by virtual welding and brittle fracture in the conventional welding process is solved.

Description

Technical Field

[0001] This application belongs to the field of inductor technology, and more specifically, relates to a powder-pressed inductor and its manufacturing method. Background Technology

[0002] As electromagnetic compatibility (EMC) components in electronic devices, chip common-mode inductors are widely used in communications, medical, and automotive electronics. Their welding reliability and structural stability directly affect the overall performance of the device. Regarding welding processes, conventional methods typically use single thermocompression welding or resistance welding to connect the coil leads to the terminal plates. Air gaps or incomplete connections are easily left at the solder joints. Under the high-temperature impact of subsequent reflow soldering or long-term thermal cycling, the solder joints are prone to lead bounce or even detachment, leading to open-circuit failure. In terms of the magnet structure, the thermal stress generated by the temperature difference between the inside and outside of the magnetic powder during the curing and cooling process is difficult to release. Combined with the difference in thermal expansion coefficients between the magnetic powder and the coil / terminal plates, microcracks are easily induced inside the magnet. These cracks can further propagate under mechanical vibration or temperature shock, leading to permeability decay and inductance drift. In addition, the coils and magnets of existing inductors are mostly physically pressed together, resulting in a weak bonding force. Under high-frequency vibration or high-acceleration impact environments, the coils are prone to displacement or deformation, leading to deterioration of electrical parameters. This makes it difficult to meet the stringent requirements for vibration and shock resistance of components in fields such as automotive electronics and aerospace. Summary of the Invention

[0003] This application provides a powder-pressed inductor and a manufacturing method thereof, in order to solve the technical problem of insufficient structural strength of inductors in the prior art.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: A method for manufacturing a powder-pressed inductor is provided, comprising the following steps: Preparation of the magnetic core base: The magnetic core base is prepared by cold pressing magnetic powder. Winding coils: Two winding coils are wound using enameled wire; Assemble the winding coils: Fit the two winding coils onto the magnetic core base; Welding the end plates: After stripping the enamel from the lead wires of the winding coil, the lead wires of the winding coil are first bonded to the end plate welding lugs. Then, the joint between the lead wires of the winding coil and the end plate welding lugs is fused and welded to form a spherical welding structure at the fused and welded part. Hot pressing integral molding: Magnetic powder is filled into the mold to form the magnetic core base and the outer periphery of the coil. The magnetic core base, the winding coil and the outer magnetic powder are then hot-pressed to form an integral structure. Forming electrodes: Lead out the terminal plates and bend and flatten them to form the four external electrodes of the powder-pressed inductor.

[0005] As a further improvement to the above technical solution: Optionally, when stripping the enamel from the leads of the winding coil, the stripping length of the leads shall not be less than 5 mm.

[0006] Compared with existing technologies, the beneficial effects of the powder-pressed inductor manufacturing method provided in this application are as follows: The manufacturing method of the powder-pressed inductor provided in this application eliminates the air gap between the lead end and the terminal plate solder lug by introducing a composite welding process. The spherical welding structure formed by melting completely wraps the joint, resulting in high tensile strength of the solder joint. Moreover, there is no lead rebound or cracking after reflow soldering, which solves the open circuit failure risk caused by poor soldering and brittle fracture in conventional welding processes.

[0007] This application also provides a powder-pressed inductor, including a magnetic core base, a winding coil, terminal plates, and an integrally formed magnet; the winding coil is disposed on the magnetic core base, and the terminal plates are connected to the leads of the winding coil; the integrally formed magnet covers the magnetic core base and the outer periphery of the winding coil, and the terminal plates form the four external electrodes of the powder-pressed inductor.

[0008] As a further improvement to the above technical solution: Optionally, the magnetic core base is a T-shaped magnetic core base, and the winding coil is wound around the outer periphery of the protrusion of the T-shaped magnetic core base.

[0009] Optionally, the connection between the end electrode and the lead wire of the winding coil is a spherical welded structure formed by fusion welding.

[0010] Optionally, the four external electrodes are formed by bending and flattening after being led out from the end electrode plate, and the four external electrodes are arranged on the same plane.

[0011] Optionally, the powder-pressed inductor is a common-mode inductor, and the winding coil consists of two coupled windings wound in parallel with two wires.

[0012] Optionally, both the magnetic core base and the integrally molded magnet are made of magnetic powder, and the two are hot-pressed together to form an integrally molded magnet structure, with the winding coil sealed inside the integrally molded magnet. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 A schematic diagram of the main structure of the powder-pressed inductor provided in this application; Figure 2 A top view of the powder-pressed inductor provided in this application; Figure 3 A bottom view of the powder-pressed inductor provided in this application; Figure 4 A schematic diagram of the connection structure between the blank of the terminal plate and the winding coil provided in this application.

[0015] The following are the labeling elements in the figure: 1. Magnetic core base; 2. Winding coil; 3. End poles; 4. One-piece molded magnet. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0017] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of the present invention.

[0022] In the following description, suffixes such as "circuit," "component," "assembly," or "unit" are used only for the purpose of illustrative purposes and do not have any specific meaning in themselves. Therefore, they can be used interchangeably.

[0023] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0024] This application provides a method for manufacturing a powder-pressed inductor, which is applicable to the fabrication of chip common-mode inductors, power inductors, and other wire-wound electronic components, and specifically includes the following steps: To prepare the magnetic core base 1, soft magnetic alloy powder with a particle size distribution of 5μm to 50μm is selected as the magnetic powder. The magnetic powder can be one or more combinations of iron-silicon-aluminum, iron-nickel-molybdenum, or carbonyl iron powder. 0.5% to 3% by weight of epoxy resin is mixed into the powder as a binder. The mixed powder is placed into the cavity of a cold-pressing mold and cold-pressed at a pressing pressure of 800MPa to 1200MPa and room temperature for a holding time of 3s to 8s. After demolding, a magnetic core base 1 with a T-shaped cross-section structure is obtained. The magnetic core base 1 includes a base plate for support and positioning and a column for passing through the coil. The relative density of the magnetic core base 1 after cold pressing is controlled between 75% and 85% to ensure that it has sufficient mechanical strength to support the subsequent assembly and positioning of the winding. For winding coil 2, round copper enameled wire with a diameter of 0.1mm to 0.8mm is selected as the winding material. The surface of the enameled wire is coated with polyurethane or polyamide-imide insulating varnish. Two winding coils 2 are symmetrically wound on the same magnetic core column using a double-wire parallel winding process. The number of turns of each winding coil 2 is set according to the target inductance. During the winding process, the inner diameter of the coil is controlled to match the outer diameter of the column part of the magnetic core base 1. After the winding is completed, the coil lead wire ends are pre-shaped to meet the spatial position requirements of subsequent assembly and welding. Assemble the winding coil 2 by coaxially mounting the two wound winding coils 2 onto the cylindrical part of the magnetic core base 1. During the assembly process, control the axial position of the two winding coils 2 on the cylindrical part of the magnetic core base 1 so that the lead wires of the two coils face the same side, and maintain a preset insulation distance between the coil body and the bottom plate of the magnetic core base 1 to ensure that the coil does not shift during the subsequent powder pressing process. To weld the terminal plate 3, the lead wires of the winding coil 2 are first stripped of their enamel. This stripping process involves mechanical scraping or chemical etching to remove a 5mm to 10mm layer of insulating enamel from the lead wire surface, exposing the internal copper conductor. After stripping, the lead wire surface is free of residual enamel and oxide layer. Then, a spot welding process is used to connect the lead wires of the winding coil 2 to the welding lugs of the terminal plate 3. The spot welding process parameters are set as follows: welding current 200A to 500A and welding time 5ms to 15ms. The spot welding establishes the connection between the lead wires and the welding lugs of the terminal plate 3. To achieve a tight fit and initial adhesion without gaps, after spot welding, laser welding is used to melt weld the joint position of the lead wire and the terminal plate 3 welding lug. The laser welding uses a fiber laser with a wavelength of 1064nm, an output power of 20W to 50W, and a welding speed of 5mm / s to 15mm / s. The laser beam is focused on the joint position to locally melt the metal. After cooling, the molten metal forms a spherical welding structure. This spherical welding structure completely wraps the lead wire and the terminal plate 3 welding lug. The tensile strength of the weld point is not less than 50N. The hot-pressing integral molding process involves placing the welded magnetic core base 1, winding coil 2, and end plate 3 into the hot-pressing mold cavity. Magnetic powder with the same composition as the cold-pressed powder is evenly filled around the magnetic core base 1 and winding coil 2. After mold closing, a hot-pressing pressure of 300MPa to 600MPa is applied, while controlling the mold temperature between 150℃ and 200℃. The holding time is 30s to 90s. Under high temperature and high pressure, the epoxy resin in the filled magnetic powder undergoes a cross-linking and curing reaction. At the same time, the newly filled powder and the pre-formed magnetic core base 1 undergo interfacial diffusion and mechanical interlocking, so that the magnetic core base 1, winding coil 2, and surrounding magnetic powder are combined into an integral molding structure. After hot pressing, the structure is cooled to below 60℃ in the furnace and demolded. The resulting integral molding structure has a relative density of over 95% and no internal cracks or pore defects. The electrodes are formed by taking out the lead-out portion of the terminal plate 3 from the body of the integrally formed structure, bending and flattening the lead-out portion by 90 degrees using a bending die to form the four external electrodes of the powder-pressed inductor. The four electrodes are located on the same bottom surface of the inductor and are symmetrically distributed. The electrode surface is tin-plated or nickel-plated to improve solderability. The coplanarity of the electrodes is controlled within 0.05mm to meet the requirements of surface mount technology.

[0025] In some specific embodiments of this application, when stripping the varnish from the leads of the winding coil 2, the stripping length is not less than 5 mm. This length is set based on the heat-affected zone range of spot welding and laser welding, as well as the solder joint strength requirements. Insufficient stripping length will lead to residual insulating varnish causing poor soldering, while excessive stripping length will affect the miniaturization design of the inductor. Experiments have verified that when the stripping length is 5 mm to 8 mm, the tensile strength and electrical performance stability of the solder joint achieve the optimal balance. In the hot-pressing integral molding step, the matching relationship between the hot-pressing temperature and pressure parameters is controlled. When the hot-pressing temperature is set to 180°C, the hot-pressing pressure is preferably 450 MPa, and the holding time is preferably 60 s. Under this parameter combination, the fluidity of the magnetic powder and the curing reaction rate are balanced, which can effectively avoid microcracks caused by stress concentration inside the magnet, while ensuring the bonding strength between the magnetic core base 1 and the outer powder. In the third step of welding the terminal electrode, the spot welding process enables a close physical contact between the lead wire and the welding lug of the terminal electrode 3, eliminating the air gap between them and providing a good energy conduction basis for subsequent laser welding. The spherical welding structure formed by laser welding not only increases the welding contact area, but also significantly improves the shear and tensile resistance of the weld joint through the metallurgical bonding characteristics of the molten metal. After high-temperature impact testing during reflow soldering, the weld joint showed no cracking or lead wire rebound after 10 cycles at 260℃, completely solving the hidden danger of incomplete welding in conventional welding processes.

[0026] In the process of preparing the magnetic core base 1, the design of the T-shaped cross-section structure enables the bottom plate of the magnetic core base 1 to play a positioning and support role during the hot pressing process, preventing the winding coil 2 from axially moving during the powder filling and pressing process. The column part provides radial positioning for the winding coil 2, ensuring the coaxiality of the two winding coils 2, thereby ensuring the common mode rejection ratio and impedance characteristics of the inductor.

[0027] In the electrode forming process, the bending and leveling process of the end electrode 3 adopts a progressive forming method. First, it is pre-bent to 45 degrees, and then it is bent to 90 degrees and held under pressure for leveling. This process can effectively release the internal stress during the bending process, prevent the electrode from deforming due to stress release during subsequent use, and ensure the flatness of the electrode and the reliability of welding.

[0028] The powder-pressed inductor prepared by the above method has vibration resistance performance that meets the vibration test requirements of 20g acceleration in the frequency range of 10Hz to 2000Hz, and shock resistance performance that meets the shock test requirements of half sine wave, peak acceleration of 1000g, and pulse width of 6ms. The magnet has no cracks or defects after X-ray flaw detection, and the average value of the solder joint tensile test reaches more than 65N. All performance indicators are superior to those of conventional wire-wound chip inductors.

[0029] like Figures 1 to 3 As shown, this application also provides a powder-pressed inductor, which is manufactured using an integral molding process and has an overall flat chip structure, suitable for surface mount technology. Specifically, it includes a magnetic core base 1, a winding coil 2, an end plate 3, and an integrally molded magnet 4.

[0030] The magnetic core base 1 serves as the internal support frame of the inductor. It is pre-formed from magnetic powder through a cold pressing process and has a T-shaped structure. The T-shaped structure includes a base plate for bearing and axial positioning and a protruding column for passing through the winding. The cross-sectional area of ​​the base plate is larger than that of the protruding column. This structural feature allows the magnetic core base 1 to be stably positioned in the mold cavity during the subsequent hot-pressing encapsulation process, preventing axial displacement during the pressing process.

[0031] Two winding coils 2 are provided. Both winding coils 2 are made of enameled wire with a circular cross section. The wire diameter of the enameled wire is selected according to the rated current and DC resistance requirements of the inductor. The two winding coils 2 are coaxially sleeved on the outer periphery of the protruding part of the magnetic core base 1 in a double-wire parallel winding manner. The winding directions of the two winding coils 2 are opposite to form the differential mode impedance characteristics required for the common mode inductor. The leads of the two winding coils 2 are led out from the winding body in the same direction, and the insulating varnish layer at the end of the leads is removed in advance to expose the metal conductor.

[0032] like Figure 4As shown, the end electrode 3 is formed by stamping a thin strip of copper alloy or iron-nickel alloy with excellent conductivity. The number of end electrode 3 matches the number of leads of the winding coil 2. The end electrode 3 includes a lug for connecting with the leads and a lead for forming an external electrode. The lug of the end electrode 3 and the leads of the winding coil 2 are electrically connected and mechanically fixed through a composite welding process. The specific structure of this connection part is a spherical welding structure formed by spot welding pre-fixation and then laser melting welding. The spherical welding structure is formed by the metal of the leads of the winding coil 2 and the metal of the lug of the end electrode 3 being melted and solidified together. The surface tension of the spherical structure allows the molten metal to completely wrap the interface between the leads and the lug, thereby forming a high-strength metallurgical bonding layer. The welding structure was subjected to a destructive tensile test, and its fracture location was located in the enameled wire body rather than the solder joint, indicating that the bonding strength of the solder joint is higher than the tensile strength of the enameled wire itself.

[0033] An integrally molded magnet 4 is wrapped around the core base 1 and the winding coil 2, completely sealing the core base 1, the winding coil 2 and the welding parts inside. The integrally molded magnet 4 is also made of magnetic powder, and its material system is consistent with or has a similar coefficient of thermal expansion to the core base 1. During the manufacturing process, the powder of the integrally molded magnet 4 and the core base 1 undergo interfacial diffusion and mechanical interlocking under hot pressing conditions, so that there is no obvious physical interface between the core base 1 and the outer integrally molded magnet 4. The two are hot-pressed together into a dense, macro-crack-free integral structure. The relative density of the integrally molded magnet 4 is usually controlled above 95%, and the internal porosity is less than 1%. This high-density encapsulation structure not only provides excellent physical protection for the winding coil 2, but also forms a complete closed magnetic circuit, effectively improving the magnetic permeability and electromagnetic shielding performance of the inductor.

[0034] The lead-out portion of the terminal plate 3 extends from the same side surface of the integrally formed magnet 4. After bending and leveling processes, it forms the four external electrodes of the powder-pressed inductor. The four external electrodes are located on the mounting bottom surface of the inductor and are arranged in a matrix of two rows and two columns. The end faces of the four external electrodes are ground or stamped and leveled to control the coplanarity error of the four electrodes within 0.05 mm, which meets the picking accuracy requirements of automated placement equipment. The electrode surface is usually also electroplated with a nickel layer and a tin layer. The nickel layer acts as a barrier layer to prevent copper ion migration, and the tin layer acts as a solderable layer to ensure good wetting with solder paste.

[0035] In some specific embodiments of this application, the powder-pressed inductor is specifically implemented as a chip common-mode inductor, which is used for electromagnetic interference suppression of high-speed differential signal lines. At this time, the double-wire parallel winding structure of the winding coil 2 makes the two coupled windings have extremely high symmetry and mutual inductance coefficient. The common-mode impedance can reach more than 60 ohms at a frequency of 100MHz, and the differential-mode impedance is less than 0.5 ohms at the same frequency, showing excellent common-mode noise filtering capability and differential-mode signal transmission characteristics.

[0036] In some specific embodiments of this application, the height of the protruding part of the magnetic core base 1 matches the axial height of the wound coil 2 after winding, so that after the integrally molded magnet 4 is covered, a powder protective layer of 0.1 mm to 0.3 mm is retained between the top of the wound coil 2 and the upper surface of the integrally molded magnet 4. This protective layer can prevent the coil from directly contacting the mold wall during the pressing process, which would cause the paint to break, and at the same time can balance the stress distribution inside the magnet.

[0037] In some specific embodiments of this application, the diameter of the spherical welding structure is controlled between 0.3 mm and 0.8 mm. This size range ensures sufficient welding strength while preventing the weld molten ball from being too large and penetrating the coating layer of the integrally formed magnet 4, thus ensuring the appearance yield and insulation reliability of the inductor.

[0038] In some specific embodiments of this application, the integrally molded magnet 4 has a regular cuboid or cube outline. Its length, width and height dimensions are designed according to the inductance and rated current. Typical dimensions range from 3.2 mm in length, 2.5 mm in width and 2.0 mm in height to 12.7 mm in length, 12.7 mm in width and 5.0 mm in height, covering a variety of chip component package specifications from 0201 to 5050. Actual testing has verified that the powder-pressed inductor with the above-mentioned structural design exhibits an inductance change rate of less than ±5% and a DC resistance change rate of less than ±10% under temperature cycling conditions ranging from -55°C to +125°C. After random vibration testing with an acceleration of 20g in the frequency range of 10Hz to 2000Hz, the inductance drift is less than ±2%. After mechanical shock testing with a peak acceleration of 1000g and a pulse width of 6ms, the inductor shows no external damage, no solder joint detachment, and no cracks detected by internal X-ray inspection. All reliability indicators meet or exceed the requirements of relevant standards GJB244A and IEC60191.

[0039] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for manufacturing a powder-pressed inductor, characterized in that, Includes the following steps: Preparation of magnetic core base (1): Magnetic core base (1) is prepared by cold pressing magnetic powder. Winding coil (2): Two winding coils (2) are wound using enameled wire; Assemble the winding coils (2): Place the two winding coils (2) onto the magnetic core base (1); Welding end plate (3): After stripping the paint from the lead wire of the winding coil (2), first bond the lead wire of the winding coil (2) to the welding lug of the end plate (3), and then perform fusion welding on the joint position of the lead wire of the winding coil (2) and the welding lug of the end plate (3) to form a spherical welding structure at the fusion welding part. Hot pressing integral molding: Magnetic powder is filled into the core base (1) and the outer periphery of the coil in the mold, and then hot pressing is performed to combine the core base (1), the winding coil (2) and the outer periphery magnetic powder into an integral molding structure. Forming electrodes: Lead out the terminal plate (3) and bend and flatten it to form the four external electrodes of the powder-pressed inductor.

2. The manufacturing method of the powder-pressed inductor as described in claim 1, characterized in that, When stripping the varnish from the lead wire of the winding coil (2), the stripping length of the lead wire shall not be less than 5 mm.

3. A powder-pressed inductor, characterized in that, It includes a magnetic core base (1), a winding coil (2), end plates (3), and an integrally formed magnet (4); the winding coil (2) is disposed on the magnetic core base (1), and the end plates (3) are connected to the lead wires of the winding coil (2); the integrally formed magnet (4) covers the magnetic core base (1) and the winding coil (2), and the end plates (3) form the four external electrodes of the powder-pressed inductor.

4. The powder-pressed inductor as described in claim 3, characterized in that, The magnetic core base (1) is a T-shaped magnetic core base (1), and the winding coil (2) is wound around the outer periphery of the protrusion of the T-shaped magnetic core base (1).

5. The powder-pressed inductor as described in claim 3, characterized in that, The connection between the end electrode (3) and the lead wire of the winding coil (2) is a spherical welded structure formed by fusion welding.

6. The powder-pressed inductor as described in claim 3, characterized in that, The four external electrodes are formed by bending and flattening after being led out from the end electrode plate (3), and the four external electrodes are arranged on the same plane.

7. The powder-pressed inductor as described in claim 3, characterized in that, The powder-pressed inductor is a common-mode inductor, and the winding coil (2) consists of two coupled windings wound in parallel with two wires.

8. The powder-pressed inductor as described in claim 3, characterized in that, The magnetic core base (1) and the integrally formed magnet (4) are both made of magnetic powder. They are hot-pressed together to form an integrally formed magnet (4) structure. The winding coil (2) is sealed inside the integrally formed magnet (4).

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