Method for preparing integrated chip inductor without material sheet terminal

Abstract

The invention provides a preparation method of a tablet-free terminal integrated chip inductor and the inductor. The preparation method mainly comprises the following steps of metal magnetic powder preparation, coil winding, continuous homogeneous mold forming, continuous low-temperature program curing, metallization, detection and packaging. According to the preparation method, a traditional mold pressing inductor technology is iterated, roll-to-roll continuous manufacturing is achieved, the preparation quality of the thin film outer electrode is optimized and the preparation cost of the outer electrode is reduced through continuous electroplating, and through the thickness appearance difference of left and right electrode plating layers of a product after plating, the production efficiency is improved. The broken copper wire coil product in the forming process is automatically recognized, the product is reliable, the integrated automation degree is high, and large-scale production is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated inductors, and in particular to a method for preparing a chip-type inductor without a sheet terminal. Background Art

[0002] To support the automotive industry's advancements in hybrid and battery powertrain technologies, an increasing number of electronic control units (ECUs) are required to better control various aspects of vehicle operation. As the number of ECUs increases, the average size of these ECUs must shrink to accommodate the limited available space. This means that the number and / or size of power inductors used in these ECUs must also decrease. At the same time, hybrid and battery powertrains are shifting the operating voltage requirements of power inductors from the traditional 12V to 48V, requiring them to operate over a wider temperature range and withstand higher temperatures.

[0003] The lead copper sheet of traditional wound metal powder core power inductors is bent from the side of the product to the bottom. The bending range and copper sheet thickness will increase the product size and limit the coil design, resulting in limited product characteristics, wasting circuit board space and reducing the density of integrated circuits. During the forming process, the wound coil is easily squeezed and slipped, resulting in large stress between the copper coil and the copper sheet, which poses a risk of disconnection between the electrode and the coil. The product has low reliability, is not conducive to use in harsh environments, and cannot meet market demand. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a sheet-free terminal integrated chip inductor which has a reasonable structure and can be prepared continuously and automatically.

[0005] To achieve the above method, the present invention provides a technical solution: a method for preparing a sheet-free terminal integrated chip inductor, which includes the following steps: metal magnetic powder preparation, coil winding, continuous homogeneous mold forming, continuous low-temperature process curing, metallization, testing and packaging; The metallization can be continuous inner electrode and continuous outer electrode, the inner electrode can be ion sputtering, and the outer electrode can be barrel plating or roll-to-roll continuous immersion plating; The integrated chip inductor has a structural design without sheet terminals. The end of the inductor coil is used as a material strip for homogeneous mold forming and low-temperature program curing. The inductor coil can be cut during the inspection and packaging process, or at the front end of the metallization process.

[0006] Preferably, the continuous low-temperature process curing further includes continuous coating, specifically atomized spraying, and continuously spraying the surface of the product on the material strip.

[0007] The metal magnetic powder is prepared by adding additives during the ball milling process to improve powder fluidity and filling uniformity, thereby providing guarantees for low-pressure molding, low-temperature process curing and product performance.

[0008] Preferably, the ratio of the raw materials of the metal magnetic powder is: carbonyl iron powder / alloy material: epoxy resin: acetone are mixed evenly in a weight ratio of 100:≤7:≤20, then kept warm at a temperature of ≤80°C for 1-3 hours, and then ground and granulated; additives are added during the granulation process, and the additives include a binder and a demolding lubricant; the binder is a two-component epoxy resin glue; the demolding lubricant is one or a mixture of zinc stearate and barium stearate.

[0009] Preferably, the coil is wound continuously on a jig by an automatic winding machine. At the same time, the insulating film of the wire end used to connect the material strip is removed by laser. After winding, the wire end is fixed on the stamped material strip by stamping or welding, and the coil is continuously sent to the next process through the material strip. The material strip is made of conductive material, such as copper strip, and can be continuously sent to the next process. It can also be wound by a winder or unwound by an unwinder to balance the production rate.

[0010] The thin wire coil winding is carried out on an automatic winding machine, whereby a precisely arranged hollow coil is continuously wound on multiple axes on a jig. At the end of the winding process, the inner electrode lead is biased and the metal coil is tempered by continuous heat treatment to improve its rigidity. At the same time, after the copper strip is stamped into the designed structure, the coil is fixed to the formed strip by stamping or welding and continuously sent to the next process.

[0011] Preferably, the homogeneous mold forming is carried out by unwinding a coil by a uncoiler, and the coil is continuously fed into the mold cavity of the forming machine by the positioning hole of the material strip. The hollow coil is accurately positioned through the positioning hole on the material strip, and metal powder is programmed to be injected into the mold cavity by an external automatic control powder feeder to form a product. At the same time, a notch is formed at the surface of the copper wire of the product by molding. After homogeneous hot pressing, it can be continuously sent to the next process, or a winder can be used for winding or an unwinder can be used for unwinding to balance the production rate.

[0012] Preferably, the low-temperature program curing is unwinding by an unwinder, and the product is accurately cured and formed by the low-temperature program in the cavity of the curing equipment by relying on the positioning holes of the material belt. It can be continuously sent to the next process, and the production rate can also be balanced by using a winder for winding or an unwinder for unwinding.

[0013] The atomized spraying adopts high atomized spraying to carry out continuous organic nano sealing treatment on the surface of the product on the material belt, and automatically sends and reels the roll.

[0014] Preferably, the inner electrode is unwound continuously or by an unwinder, and the product is accurately removed by laser or ground using a wear-resistant and long-lasting CBN (Cubic Boron Nitride) grinding tool near the positioning hole on the material belt, and the product is subjected to micro-fine grinding to remove the insulating layer on the surface of the enameled copper wire at the end of the product. The enameled copper wire at the end of the product is exposed by micro-grinding and the removal of the insulating layer on the surface of the copper wire is precisely controlled to form the inner electrode, or the electrode seed layer is prepared on the surface of the inner electrode by ion sputtering equipment or conductive adhesive coating equipment in a beat-based manner; it can be continuously sent to the next process, or a winder can be used for winding or an unwinder can be used for unwinding to balance the production rate.

[0015] Preferably, the external electrode includes a positioning hole through the material strip, and then the product is immersed in the solution through roll-to-roll continuous electroplating. The material strip is located above the solution and plays a conductive role. One or more thin film electrode thickening processes selected from copper electroplating, nickel electroplating, tin electroplating, silver electroplating, and gold electroplating are used at a high deposition rate. Finally, a high-brightness and easily wettable electroplated layer is formed; and the appearance and thickness of the coating are detected by an online CCD (Charge-coupled Device).

[0016] The outer electrode is unwound continuously or through an unwinder, and is located near the positioning hole of the material strip. By pulling the material strip, the material strip continuously passes through the air above the electroplating solution to play a conductive positioning role. The product part is continuously immersed in the solution and continuously electroplated through the solution to form an external electrode on the surface of the product. The solution is one or more of electroplated copper, electroplated nickel, electroplated tin, electroplated silver, and electroplated gold. It can be continuously sent to the next process, or a winder can be used for winding or an unwinder can be used for unwinding to balance the production rate.

[0017] Preferably, the inspection and packaging: after inspecting the products to eliminate defective products in terms of size, appearance and characteristics, qualified products are cut from the material strip using the notches formed during molding, and then packaged.

[0018] The present invention also provides an inductor prepared by the method for preparing a sheet-free terminal integrated chip inductor, wherein the inductor is a bottom electrode inductor or an L-shaped electrode inductor.

[0019] The fabrication method of this invention improves upon existing technologies for slurry-terminated barrel-plated, one-piece inductors, copper-terminated, and T-core, internally wound-on-wire electrodes. The thin-film electrodes produced by this method offer high reliability, reduce the product's mounting footprint on circuit boards, and increase the mounting space for integrated circuit (PCB) boards, creating favorable conditions for the development of highly integrated circuits. While maintaining the same dimensions, the overall performance of the product is significantly improved. This method is particularly suitable for the manufacture of inductors with bottom-shaped or L-shaped thin-film electrodes, enabling automated, continuous, and efficient production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a process flow chart of a preferred embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of a bottom electrode product according to a preferred embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of an "L"-shaped electrode product according to a preferred embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the integrated chip inductor continuous plating principle of the present invention.

[0024] Figure 5 This is a cross-sectional view of the product structure of a preferred embodiment of the present invention.

[0025] Figure 6 This is a schematic diagram of a bottom electrode product according to a preferred embodiment of the present invention.

[0026] Figure 7 This is a cross-sectional view of the product structure of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with all the accompanying drawings. Figure 1 To the attached Figure 7 The process flow chart of the preferred embodiment of the present invention is as follows Figure 1 As shown, specifically: Example 1: This example prepares the bottom electrode. Figure 1 Path 1.

[0028] Figure 2 Schematic diagram of the bottom electrode product of the embodiment. Figure 5 This is a cross-sectional view of the product structure of this embodiment.

[0029] The method for preparing a chip-type inductor with a terminal-free integrated chip according to the present embodiment comprises the following steps: coil winding, continuous homogenization mold forming, continuous low-temperature hot pressing and curing, continuous atomization spraying, continuous inner electrode formation, continuous outer electrode formation (copper, nickel, tin plating), and testing and packaging. Figure 4 The conductive strip can be used as both a material strip and a conductive strip during electroplating, and only as a material strip in other processes.

[0030] in, Step 1: Coil Winding: Hollow coils are produced according to the product specifications. This winding method utilizes multi-axis winding on a winding jig and must meet the corresponding technical standards. The selection and winding of the enameled copper wire were carefully tested and refined, resulting in winding equipment parameters and wire specifications suitable for mass production. The winding method involves continuously winding precisely aligned hollow coils on a jig using an automatic winding machine. At the end of the winding process, the inner electrode leads are offset, and the metal coils are tempered through continuous heat treatment to increase their rigidity. Simultaneously, the copper strip is stamped into the designed structure, and the coils are secured to the formed strip by stamping or welding before being continuously fed to the next process.

[0031] Step 2: Continuous homogeneous mold forming: Use carbonyl iron powder or alloy materials (iron silicon, iron silicon chromium, iron nickel, iron silicon aluminum and amorphous nanomaterial systems) for molding. The optimal carbonyl powder composition formula is as follows: The carbonyl iron powder / alloy material: epoxy resin: acetone are uniformly mixed in a weight ratio of 100: ≤7: ≤20, and then kept warm at a temperature of ≤80°C for 1-3 hours, and then continuous internal electrode granulation is carried out. The prepared powder needs to meet the sphericity ≥60%, and the powder particle size meets the following requirements: D50≤30μm, D90≤90μm, D10≤20μm; (D10 is the particle size at which the cumulative distribution of particles is 10%, that is, the volume content of particles smaller than this particle size accounts for 10% of all particles, and D50 is the particle size at which the cumulative distribution of particles is 50%. It is also called the median diameter or median particle size, which is a typical value indicating the particle size. D90 is the particle size at which the cumulative distribution of particles is 90%. That is, the volume content of particles smaller than this particle size accounts for 90% of all particles). Two-component epoxy resin glue is used as a binder. After the powder is granulated, zinc stearate, barium stearate or other demoulding lubricants are added. By adding additives, the powder fluidity and filling uniformity are improved, providing guarantees for low-pressure molding, low-temperature process curing and product performance.

[0032] The material strip containing the hollow coil is fed into the mold through the molding machine. When feeding, the hollow coil is accurately positioned into the mold cavity through the positioning hole on the material strip. The metal powder is programmed into the mold cavity through an external automatic control powder feeder. The mold cavity is filled with metal powder and stamped to form a product. After homogeneous hot pressing, it is automatically rolled up. The density of the molded product is not less than 3g / cm3 .

[0033] Selection of specific pressure for the molding machine: Too high a pressure will scratch or crush the paint on the coil; too low a pressure will result in insufficient density of the product, which will lead to defects such as missing corners and low inductance. After a large number of tests and statistical data, the best parameters that can meet product quality, production efficiency and yield rate are selected.

[0034] The third step: continuous low-temperature hot pressing and curing: the product is accurately passed through the cavity of the curing equipment through the positioning hole of the material strip. The temperature of the cavity of the hot pressing equipment is controlled to be not less than 100 ° C. The pressure of not less than 0.5 MPa is maintained for not less than 5 minutes to complete the continuous low-temperature hot pressing and curing operation. During the hot pressing and curing process, automatic coiling and rewinding are achieved through external equipment.

[0035] Step 4: Continuous atomization spraying: Use high atomization spraying (polyimide-based material) to perform continuous atomization spraying and sealing treatment on the surface of the product. The spraying thickness is not less than 3um. After the product is coated, bake it at above 100℃ for more than 0.5 hours to solidify the insulation layer.

[0036] Step 5: Continuous inner electrode: Through the positioning holes on the material strip, the product is accurately micro-ground by wear-resistant and long-lasting CBN grinding tools to expose the enameled copper wire at the end of the product and accurately control the removal of the insulating layer on the surface of the copper wire to form the inner electrode, or the electrode seed layer is prepared on the surface of the inner electrode by ion sputtering equipment or conductive adhesive coating equipment in a continuous manner according to the beat; automatic coiling and reeling.

[0037] Step 6: Continuous external electrode (copper, nickel, tin plating) ① Electroplate the product after the continuous inner electrode with a copper layer of not less than 0.3um.

[0038] ② Electroplate a nickel layer of no less than 1um on the copper-plated product.

[0039] ③ Electroplate the nickel-plated product with a tin layer of not less than 1um.

[0040] Step 6: Inspection and packaging: The finished products are inspected to eliminate defective products in terms of size, appearance and characteristics. Qualified products are then cut from the material strip and packaged.

[0041] Example 2: This example prepares an "L-shaped" electrode; according to the process flow Figure 1 Path 2.

[0042] like Figure 3 This is a schematic diagram of the "L"-shaped electrode product of this embodiment.

[0043] The method for preparing a chip-type inductor with a terminal-free integrated chip according to the present embodiment comprises the following steps: coil winding, continuous homogeneous mold forming, continuous low-temperature hot pressing and curing, continuous atomization spraying, continuous inner electrode forming, continuous outer electrode forming, and testing and packaging. in, Step 1: Coil Winding: Hollow coils are produced according to the product specifications. This winding method utilizes multi-axis winding on a winding jig and must meet the corresponding technical standards. The selection and winding of the enameled copper wire were carefully tested and refined, resulting in winding equipment parameters and wire specifications suitable for mass production. The winding method involves continuously winding precisely aligned hollow coils on a jig using an automatic winding machine. At the end of the winding process, the inner electrode leads are offset, and the metal coils are tempered through continuous heat treatment to increase their rigidity. Simultaneously, the copper strip is stamped into the designed structure, and the coils are secured to the formed strip by stamping or welding before being continuously fed to the next process.

[0044] Step 2: Continuous homogeneous mold forming: Use carbonyl iron powder or alloy materials (iron silicon, iron silicon chromium, iron nickel, iron silicon aluminum and amorphous nanomaterial systems) for molding. The optimal carbonyl powder composition formula is as follows: The carbonyl iron powder / alloy material: epoxy resin: acetone are uniformly mixed in a weight ratio of 100: ≤7: ≤20, and then kept warm at a temperature of ≤80°C for 1-3 hours, and then continuous internal electrode granulation is carried out. The prepared powder needs to meet the sphericity ≥60%, and the powder particle size meets the following requirements: D50≤30μm, D90≤90μm, D10≤20μm; (D10 is the particle size at which the cumulative distribution of particles is 10%, that is, the volume content of particles smaller than this particle size accounts for 10% of all particles, and D50 is the particle size at which the cumulative distribution of particles is 50%. It is also called the median diameter or median particle size, which is a typical value indicating the particle size. D90 is the particle size at which the cumulative distribution of particles is 90%. That is, the volume content of particles smaller than this particle size accounts for 90% of all particles). Two-component epoxy resin glue is used as a binder. After the powder is granulated, zinc stearate, barium stearate or other demoulding lubricants are added. By adding additives, the powder fluidity and filling uniformity are improved, providing guarantees for low-pressure molding, low-temperature process curing and product performance.

[0045] The material strip containing the hollow coil is fed into the mold through the molding machine. When feeding, the hollow coil is accurately positioned into the mold cavity through the positioning hole on the material strip. The metal powder is programmed into the mold cavity through an external automatic control powder feeder. The mold cavity is filled with metal powder and stamped to form a product. After homogeneous hot pressing, it is automatically rolled up. The density of the molded product is not less than 3g / cm 3 .

[0046] Selection of specific pressure for the molding machine: Too high a pressure will scratch or crush the paint on the coil; too low a pressure will result in insufficient density of the product, which will lead to defects such as missing corners and low inductance. After a large number of tests and statistical data, the best parameters that can meet product quality, production efficiency and yield rate are selected.

[0047] The third step: continuous low-temperature hot pressing and curing: the product is accurately passed through the cavity of the curing equipment through the positioning hole of the material strip. The temperature of the cavity of the hot pressing equipment is controlled to be not less than 100 ° C. The pressure of not less than 0.5 MPa is maintained for not less than 5 minutes to complete the continuous low-temperature hot pressing and curing operation. During the hot pressing and curing process, automatic coiling and rewinding are achieved through external equipment.

[0048] Step 4: Continuous atomization spraying: Use high atomization spraying (polyimide-based material) to perform continuous atomization spraying and sealing treatment on the surface of the product. The spraying thickness is not less than 3um. After the product is coated, bake it at above 100℃ for more than 0.5 hours to solidify the insulation layer.

[0049] Step 5: Continuous inner electrode: Through the positioning holes on the material strip, the product is accurately laser-de-filmed to expose the enameled copper wire at the end of the product and remove the insulation layer on the surface of the copper wire to form an L-shaped inner electrode; automatic rolling and rewinding.

[0050] Step 6: Continuous external electrode (copper, nickel, tin plating) ① Electroplate the product after the continuous inner electrode with a copper layer of not less than 0.3um.

[0051] ② Electroplate a nickel layer of no less than 1um on the copper-plated product.

[0052] ③ Electroplate the nickel-plated product with a tin layer of not less than 1um.

[0053] Step 7: Inspection and packaging: The finished products are inspected to eliminate defective products in terms of size, appearance and characteristics. Qualified products are cut from the material strip and then packaged.

[0054] Step 8: Inspection and packaging: The products are inspected to eliminate defective products in terms of size, appearance and characteristics, and then packaged.

[0055] The internal electrode process of this embodiment may also adopt one or a combination of two conventional processes such as laser ablation, metal paste printing or vacuum coating (ion sputtering technology) as needed.

[0056] The technical advantages of the present invention are: 1) The preparation method of this invention iterates the traditional molded inductor technology, realizes roll-to-roll continuous manufacturing, and optimizes the preparation quality of the thin film external electrode and reduces the preparation cost of the external electrode through continuous electroplating. After plating, the difference in the thickness of the left and right electrode plating of the product can be used to automatically identify products with broken copper wire coils during the molding process. The product is reliable and has a high degree of integrated automation. The use of continuous production can significantly reduce production costs, create favorable conditions for the highly integrated development of the integrated circuit industry, and facilitate large-scale production.

[0057] 2) Roll-to-roll continuous immersion electroplating process saves manufacturing costs; in particular, it eliminates the traditional roller plating method for preparing thin film electrodes, eliminates the use of conductive media (conductive balls), greatly reduces the use of electroplating anode materials, greatly reduces electroplating time, and improves manufacturing speed. The yield rate of finished electrodes is nearly 100%.

[0058] 3) The inductor device prepared by this scheme has the advantages of high frequency, low loss, chipization, miniaturization, high voltage resistance and high reliability. It is fully in line with the development trend of high-end electronic components and has a wide range of applications. Such sensor devices can meet the needs of smart terminals, 5G, industrial Internet, data centers, new energy vehicles, smart grids, aerospace, high-speed rail and other industries.

[0059] 4) The structural design without sheet terminals is adopted, and the end of the inductor coil is used as a strip, which can save the sheet implantation process, avoid the connection and contact between the sheet and the inductor coil, reduce the welding problem between the inductor coil enameled wire and the sheet, and solve the industry pain point.

[0060] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any changes made based on the shape and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a chip-less terminal integrated inductor, characterized by: The method includes the following steps: metal magnetic powder preparation, coil winding, continuous homogeneous mold forming, continuous low-temperature process curing, metallization, testing and packaging; The metallization is a continuous inner electrode or a continuous outer electrode, the inner electrode is ion sputtered, and the outer electrode is barrel-plated or roll-to-roll continuous immersion electroplating; The integrated chip inductor has a structural design without sheet terminals. The end of the inductor coil is used as a material strip for homogeneous mold forming and low-temperature program curing operations. The inductor coil is cut during the inspection and packaging process, or is cut at the front end of the metallization process.

2. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: After the continuous low-temperature process curing, the method further includes continuous coating, specifically atomized spraying, in which the surface of the product on the material strip is continuously sprayed.

3. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The raw materials of the metal magnetic powder are uniformly mixed in a weight ratio of carbonyl iron powder / alloy material: epoxy resin: acetone in a ratio of 100:≤7:≤20, then kept at a temperature of ≤80°C for 1-3 hours, and then ground and granulated. Additives are added during the granulation process, and the additives include a binder and a demoulding lubricant; the binder is a two-component epoxy resin glue; the demoulding lubricant is one or a mixture of zinc stearate and barium stearate.

4. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The coil is wound continuously on a jig by an automatic winding machine. At the same time, the insulating film of the wire end used for connecting the material strip is removed by laser, and the wire end is fixed to the stamped material strip by stamping or welding. The coil is continuously sent to the next process through the material strip. The material strip is made of conductive material and is continuously sent to the next process, or a winder is used for winding or an unwinder is used for unwinding to balance the production rate.

5. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The homogeneous mold forming is carried out by unwinding the coil through the unwinding machine, and the coil is continuously fed into the mold cavity of the forming machine by the positioning hole of the material belt. Metal powder is injected into the mold cavity by an external powder feeder to form a product. At the same time, a notch is formed at the surface of the copper wire of the product by molding. After homogeneous hot pressing, it is continuously sent to the next process, or a winder is used for winding or an unwinder is used for unwinding to balance the production rate.

6. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The low temperature program curing is unwinding by an unwinder, and the product is continuously passed through the curing equipment by the positioning hole of the material belt for low temperature program curing and molding, and continuously sent to the next process, or the production rate is balanced by using a winder for winding or an unwinder for unwinding.

7. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The inner electrode is removed by laser film removal, unwound continuously or by an unwinder, and ground by a wear-resistant and long-lasting CBN grinding tool against a positioning hole of the material strip. The insulating layer on the surface of the enameled copper wire at the end of the product is removed, and then the electrode seed layer is prepared by continuous ion sputtering or coating with a conductive adhesive layer, or roller plating; it is continuously sent to the next process, or wound by a winder or unwound by an unwinder to balance the production rate.

8. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The external electrode is unwound continuously or through an unwinder, and is located near the positioning hole of the material strip. By pulling the material strip, the material strip continuously passes through the air above the electroplating solution to play a conductive positioning role. The product part is continuously immersed in the solution and continuously electroplated by the solution to form an external electrode on the surface of the product. The solution is one or more of electroplating copper, electroplating nickel, electroplating tin, electroplating silver, and electroplating gold, and is continuously sent to the next process, or a winder is used for winding or an unwinder is used for unwinding to balance the production rate.

9. The method for preparing a chip-less terminal integrated inductor according to claim 1, characterized in that: The inspection packaging is to inspect the products, and after the inspection, the qualified products are cut from the material strip using the notches formed during the molding, and then packaged.

10. The method for preparing a chip-less terminal integrated inductor according to claims 1 to 9, characterized in that: The inductor is a bottom electrode inductor or an L-shaped electrode inductor.

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