METHOD FOR MANUFACTURING COMPOSITE POWER INDUCTOR

Abstract

 A plurality of cylindrical upper core pellets that are molded in advance are inserted upright respectively into insertion holes in an inductor core insertion support plate having perforated therein the plurality of insertion holes and then a coil is wound on the outer circumferential surfaces of the core pellets by an automatic winding device, and thus the core pellets are used as inductor cores. As such, the peeling-off damage of a coating on the winding coil and the unwinding of the winding coil in inductors being manufactured are prevented, enabling stable maintenance and thus making it possible to manufacture a composite power inductor that is uniform in quality such as an inductance value.

Description

TECHNICAL FIELD

[0001] The present invention relates to a new manufacturing method capable of mass-producing a composite power inductor at a time.

BACKGROUND ART

[0002] As is well known in the art, power inductors are generally used in power supply devices and circuits, for example, power circuits (e.g., an integrated circuit (IC)) for changing a particular voltage to a required voltage, and is designed to exhibit low resistance characteristics while maintaining a constant inductance. Such power inductors may be generally classified into three types of a winding type, a thin film type, and a stacked type, according to a manufacturing method. In addition, a power inductor body (referred to as a magnetic core) may be selected from a magnetic metal powder, for example, Fe-Si-Cr powder, Ni-Zn-based ferrite, Mn-Zn-based ferrite, Fe-based alloy powder, carbonyl iron powder, or a combination thereof, such that the power inductor body is suitable for electrical properties according to a purpose of use.

[0003] In particular, the present invention relates to an improved method for manufacturing a "winding-type" composite power inductor (hereinafter simply referred to as a "power inductor" or more simply referred to as an "inductor").

[0004] Prior to the completion of the present invention, for example, as disclosed in Korean Patent No. 10-790777 (Patent Document 1), methods for manufacturing a power inductor have been used in which an air core coil wound with a predetermined number of turns is placed in a predetermined position inside a press-molding machine, a certain amount of selected magnetic metal powder is injected into and filled in the press-molding machine, and press-molding is performed under a pressure designed in the press-molding machine.

[0005] In addition, Korean Patent No. 10-1430427 (Patent Document 2) discloses a method for obtaining a secondary molded body, that is, a final power inductor, by transferring an air core coil, which is obtained by continuously winding a coil on an outer circumferential surface of each of a plurality of winding pins integrally protruding from a surface of a metal coil winding plate, to a primary molding machine while maintaining the air core coil on the winding plate, injecting magnetic metal powder into the primary molding machine and performing press-molding to obtain a primary molded body, placing the air core coil, which is obtained by removing the coil winding plate from the primary molded body, in a final molding machine, and injecting the same magnetic metal powder from an upper portion thereof and performing press-molding to obtain a secondary molded body, that is, a final power inductor.

[0006] In addition, Korean Patent No. 10-2178709 (Patent Document 3) discloses a method for manufacturing a power inductor in which a groove for accommodating an air core coil is provided, the air core coil is accommodated in each air core coil accommodation groove of a predetermined molded body obtained by performing pressure-molding with magnetic metal powder, and the same magnetic metal powder is filled in the air core of the air core coil to perform secondary pressure-molding.

[0007] These prior patent documents have a common feature in that the air core coil prepared by separately winding is placed inside the press-molding machine, and a predetermined metal magnetic powder is injected into and filled in the press-molding machine to perform pressure-molding under a designed pressure.

[0008] In addition, in Korean Patent No. 10-1044607 (Patent Document 4) and Korean Patent No. 10-1044608 (Patent Document 5), a preliminary core molded body is prepared by press-molding a metal magnetic powder in a preliminary core molding machine, in which an outer diameter of the preliminary core molded body is designed to generally correspond to an inner diameter of an air core coil so as to be equal to or slightly higher than a height of the air core coil. Thereafter, the preliminary core molded body is inserted into an air core of the air core coil aligned in a separate press-molding machine, and then the molding machine is filled with metal magnetic powder to press-mold the metal magnetic powder under a predetermined molding pressure, thereby obtaining a desired magnetic core. Next, external electrical terminals are deposited on left and right lead wires exposed to a predetermined position outside the magnetic core to complete a power inductor product.

[0009] Korean Patent No. 10-1275168 (Patent Document 6) discloses an example of a method for depositing an external terminal of an inductor.

[0010] However, in the method disclosed in each of these prior patent documents, unbalance is likely to occur due to a molding pressure transmitted to the periphery of the coil during the press-molding, and accordingly, there is a partial difference in filling density of the magnetic metal powder. This causes fine fissures (cracks) in the magnetic core around the coil of the finished inductor product, and thus it is pointed out that that results in significant deterioration in the quality of the product.

[0011] Moreover, in the inside of the inductor manufactured by the methods described in each of the prior Patent Documents 1 to 5, while the magnetic metal powder is injected into inner and outer peripheries of the air core coil and is press-molded in the molding machine, a portion of the air core coil is crushed, and thus the height of the coil winding is changed or a partial unwinding phenomenon occurs in the winding part of the coil, and thus an unstable winding state of the air core coil embedded in the magnetic metal is often caused. In addition, when a core preliminary molded body is inserted into the air core coil, damage such as peeling of the insulating coating of the coil is likely to occur due to a frictional force generated when the core preliminary molded body is inserted into the air core coil. Therefore, in electric/electronic circuits using such power inductors, an electric short circuit may occur due to an electrical short circuit phenomenon, which may cause damage to the circuit itself.

[0012] In these conventional inductor products, the distribution of electrical characteristics such as inductance (and/or resistance) is increased, which significantly reduces the quality and production yield of the finished inductor products. Furthermore, in the inductor in which the unwinding phenomenon of the coil occurs, for example, an inductance value thereof is increased, which is not preferable as the inductor is classified as a defective product. In particular, in the case of composite power inductors used in components and accessories of various precision machines or devices such as medical machines, aircraft, automobiles, rocket weapons, autonomous vehicles, and drones today, there is a risk that instability or non-uniformity of such inductance values, resistance values, and the like may cause inoperability or malfunction of the above-described precision machines, and thus it is necessary to find and improve the cause of quality defects in the process of manufacturing the composite power inductor.

DISCLOSURE

TECHNICAL PROBLEM

[0013] An object of the present invention is to provide an improved method for manufacturing a high-quality inductor in which all relevant electrical properties, such as inductance values, are uniform throughout the entire produced product by maintaining an initial winding state almost as it is without causing an unwinding phenomenon in an air core coil during the molding of a power inductor.

TECHNICAL SOLUTION

[0014] Accordingly, the present applicants have made the present invention as a result of intensive examination to solve the problems of the conventional technology described above. That is, the problems and objects of the present invention are achieved by the following.

(1) A method for manufacturing a composite power inductor, the method including: - a first step of molding upper core pellets and lower core pellets formed of magnetic metal powder;

• a second step of providing an upper core pellet insertion support plate having an appropriate number of insertion holes formed therethrough transversely and longitudinally such that lower edge parts of the upper core pellets are inserted thereinto while being accommodated in the upper core pellet insertion support plate;
• a third step of vertically inserting the lower edge parts of the upper core pellets into the insertion holes of the upper core pellet insertion support plate, and transferring the lower edge parts of the upper core pellets into a coil automatic winding machine to wind a coil on an outer circumferential surface of each of the upper core pellets;
• a fourth step of obtaining a first preliminary molded body by placing the upper core pellet insertion support plate wound with the coil in a molding machine by transferring the upper core pellet insertion support plate, filling the metal magnetic powder in the molding machine, and performing press-molding;
• a fifth step of obtaining a second preliminary molded body by pushing the lower core pellets into a lower end part of an upper core of the first preliminary molded body and performing press-molding; and
• a sixth step of obtaining a third preliminary molded body by allowing the second preliminary molded body to be subjected to a conventional underwater isotropic press-molding process.

(2) In the method of (1), one tape selected from a silicone tape, a synthetic resin film tape, and a paper tape may be adhered to a rear surface of the upper core pellet insertion support plate as an auxiliary support unit for assisting a support force of the support plate, before the third step is initiated.

(3) In the method of (1), a sequence of the first and second steps may be reversible.

(4) In the method of (1) or (3), the upper core pellet insertion support plate may be formed of a metal or synthetic resin thin plate.

(5) In the method of (1), an inner diameter of each core insertion hole of the upper core pellet insertion support plate may correspond to an outer diameter of the upper core pellet.

(6) In the method of (1), a thickness of the upper core pellet insertion support plate may be 0.5 mm to 1 mm.

(7) In the method of (1), the fourth step may be performed after removing the upper core pellet insertion support plate.

ADVANTAGEOUS EFFECTS

[0015] According to the present invention, damage to the coating of the air core coil and the unwinding phenomenon of the air core coil, which may occur during the molding of the inductor, may be actively prevented, thereby obtaining a high-quality inductance product having uniform main electrical properties such as inductance values.

DESCRIPTION OF DRAWINGS

[0016] 

FIG. 1(A) is a view showing a portion of FIG. 5 described in Patent Document 4 as it is, and FIG. 1(B) is a perspective image (photograph) showing an inside of a conventional inductor product in which a coil unwinding phenomenon has occurred.

FIGS. 2(A) to 2(C) are views depicting molding examples of an inductor core according to the present invention, in which upper core pellets and lower core pellets to be used in the present invention may be molded by the method, respectively.

FIG. 3(A) is a plan view depicting an upper core pellet insertion support plate having a plurality of insertion holes formed therethrough transversely and longitudinally in order to vertically insert the upper core pellet thereinto, which is obtained by the method of FIG. 2, and FIG. 3(B) is a cross-sectional view taken along line a-a of FIG. 3(A).

FIG. 4(A) is a perspective view depicting a state where the upper core pellet is inserted into each insertion hole of the upper core pellet insertion support plate of FIG. 3(A), and FIG. 4(B) is a cross-sectional view taken along line b-b of FIG. 4(A).

FIG. 5(A) is a perspective view depicting a state where a coil is wound on an outer circumferential surface of each upper core pellet, and FIG. 5(B) is a cross-sectional view taken along line c-c of FIG. 5(A).

FIG. 6a(A) is a cross-sectional view depicting a process of placing the upper core pellet insertion support plate, into which the upper core pellets are inserted, in a molding machine, the upper core pellet having the coil wound on the outer circumferential surface, and filling a predetermined amount of magnetic powder in the molding machine to perform compression molding, thereby obtaining a first preliminary molded block, FIG. 6a(B) is a cross-sectional view showing a state where the upper core pellet insertion support plate is removed from the first preliminary molded block obtained in the step of FIG. 6a(A), FIG. 6a(C) is a plan view showing a state of a surface of FIG. 6a(B), and FIG. 6a(D) is a plan view showing a state of a bottom surface of FIG. 6a(B).

FIG. 6b(A) a view depicting a process of molding a second preliminary molded body from the first preliminary molded body of FIG. 6a(B), and FIG. 6b(B) is a cross-sectional view of the resulting second preliminary molded body, wherein an enlarged portion shows a shape of a lead wire L exposed to the bottom surface.

FIG. 7 is a view showing a flowchart of a series of main process steps performed in the present invention.

FIG. 8(A) is a view showing an assembled state of a second preliminary molded body/transfer jig/back plate according to the present invention, FIG. 8(B) is a view depicting a cross-section of the second preliminary molded body obtained from FIG. 8(A), and FIG. 8(C) is a view depicting a state of the bottom surface of the molded body.

FIGS. 9(A) and 9(B) are schematic views showing states before and after external terminals T and T are deposited on lead wires L and L of individual inductors, respectively.

FIG. 10 is a cross-sectional image of comparing states of coils in inventive product samples and control product samples.

FIGS. 11(A) and 11(B) are diagrams for comparing and explaining electrical properties of the inventive samples and the control samples.

MODE FOR INVENTION

[0017] As described above, FIG. 1(A) shows an example of the related art described in FIG. 5 of Patent Document 4, which is the prior patent document described above, and briefly illustrates a method for molding a final inductor product by inserting a preliminary core molded body B molded using metal magnetic powder into a hollow part, that is, an air core, of a coil element 15 so that the preliminary core molded body B is integrally assembled with a separate upper part and a preliminary peripheral molded body (reference numerals thereof are omitted) and press-molded. FIG. 1(B) is a perspective image obtained by a cone beam computed tomography (CBCT; model name XSCAN-H130-OCT, applied voltage 130 kV, XAVIS Co., Ltd., Seongnam City, Korea) of an inside of a conventional inductor product in which a coil unwinding phenomenon has occurred.

[0018] However, as shown in the image of FIG. 1(B), the inductor according to the conventional methods has a disadvantage in that a defective processing rate is high because there are many cases in which unwinding occurs in the wound air core coil. The coil unwinding phenomenon is considered to be caused by the fact that, even if the specification (particularly, the diameter) of the preliminary core molded body B is designed in consideration of the specification of the coil element 15, the coating of the air core coil is peeled off and damaged due to a frictional force caused by the contact with the coil during insertion into the air core, so that a short circuit occurs at the damaged portion when power is supplied or a winding state of the coil is changed due to a pressing force during the press-molding due to a clearance caused by the generation of a space between the core molded body B and the coil.

[0019] Therefore, as described above, the present invention has been made to complete the present invention as a result of exemplifying a method capable of minimizing the damage to the coating of the air core coil and the unwinding of the coil.

[0020] In other words, the method of the present invention is significantly different from the method of Patent Document 4 in particular in that an air core coil formed by winding a coil around a winding pin of a winding machine is not used, but the coil that is directly and firmly wound around a pre-molded core pellet is in an inductor molding process, so that a rate of occurrence of defects such as damage to coating of the coil and coil unwinding in an inductor product during molding may be significantly reduced.

[0021] As described above, the present invention is for improving the conventional method, and hereinafter, the method of the present invention will be described in detail by dividing the method into stages according to the accompanying drawings.

First Step: Molding of Upper and Lower Core Pellets

[0022] In order to perform the present invention, as shown in FIG. 2(A), a predetermined amount of magnetic metal powder 10 was injected into and filled in a press-molding machine M1 in which a press PR1 is provided with a pressing pin P, and pressed using the press PR1 to mold an upper preliminary core pellet 11 of FIG. 2(B) (hereinafter simply referred to as an "upper core pellet 11").

[0023] According to the present invention, Fe-Si-Cr powder having an average particle size of about 10 µm was used as the magnetic metal powder.

[0024] In one embodiment of the present invention, 0.12 g of Fe-Si-Cr powder was injected into and filled in a single core pellet molding machine M1 (Mold Standard 40 mm × 40 mm × 60 mm) shown in FIG. 2(A), and the press PR1 was molded at a set molding pressure, for example, a molding pressure of about 5 ton/cm² to obtain the upper core pellet 11. The upper core pellet 11 had a cylindrical shape with a diameter R₁ of 3 mm and a height H₁ of 3 mm. In a similar manner, a thin cylindrical (or disc-shaped) lower preliminary core pellet 12 (R₂ = 3 mm and H₂ = 1.5 mm; hereinafter simply referred to as a "lower core pellet 12") was separately molded as shown in FIG. 2(C) under the same molding conditions. Referring to FIG. 2(A), if necessary, a lower press PR1' may be installed on the molding machine M1 so that molded bodies (upper core pellets 11 and lower core pellets 12) may be easily removed from a lower part of the molding machine M1 by opening the lower press PR1' after the molding operation. However, for the sake of simplicity, the lower press PR1' will be omitted hereinafter.

[0025] In implementing the present invention, as the magnetic metal powder for molding the upper core pellets 11 and the lower core pellets 12, a material obtained by mixing Fe-Si-Cr powder with a thermosetting resin-based (e.g., epoxy-based) binder in an appropriate ratio (in an amount of about 1 to 5 wt% based on the magnetic metal powder) was used. Various magnetic metal powder materials corresponding thereto are commercially available. In this case, the magnetic metal powder for molding the lower core pellets 12 may be the same component as the Fe-Si-Cr powder described above, or may be a combination of different components or two or more magnetic metal powders.

[0026] In this case, an example in which the upper core pellets 11 and the lower core pellets 12 are molded using the single molding machine M1 shown in FIG. 2(A) has been described, but when a molding device having a plurality of single core pellet molding machines M1 arranged in parallel is used, a plurality of upper and lower core pellets may be separately molded in a large amount at a time. In this case, as the press PR1, a press including a plurality of pressing pins P corresponding to the number of the molding machines M1 may be used.

Second Step: Preparation of Core Pellet Insertion Support Plate

[0027] As shown in FIG. 3(A), an upper core pellet insertion support plate 20 was prepared in order to insert and maintain the upper core pellets 11. To this end, according to the embodiment of the present invention, the support plate 20 was prepared from a stainless steel thin plate material having a width of 45 mm, a length of 45 mm, and a thickness of 1 mm. The thickness of the support plate 20 is preferably 0.5 to 1 mm or less, for example, 0.5 mm, which is intended to allow the coil to be wound as close as possible to a lower edge part of an upper core during winding of the coil to be described below. In general, the smaller the thickness of the support plate 20, the lower the height of the upper core pellet 11 may be selected. Next, a plurality of circular insertion holes 21, for example, 6 columns and 6 rows (6 × 6 = 36) circular insertion holes 21 having a diameter of about 3 mm were formed through the support plate transversely and longitudinally. The front, rear, left, and right intervals between each upper core pellet insertion hole 21 and the neighboring insertion hole were set to 2.0 mm. A state where the plurality of upper core pellet insertion holes 21 are provided is well depicted in FIG. 3(A), which is a plan view of the core pellet insertion support plate 20, and FIG. 3(B), which is a cross-sectional view taken along line a-a of FIG. 3(A).

[0028] In implementing the present invention, the support plate 20, a support plate formed of a stainless steel thin plate was used, but the present invention is not limited to this material. Any material may be used, as long as it may be processed to be thin, does not easily deform at a working temperature, and has an insertion hole 21 through which the upper core pellet 11 may be sufficiently inserted and supported. For example, a hard synthetic resin plate may be used. The inner diameter of the upper core pellet insertion hole 21 was designed to correspond to the outer diameter of the upper core pellet 11 to be inserted, and in this case, the size of the coil to be wound on the outer circumferential surface of the upper core pellet 11 was also considered.

[0029] The molding step of the upper core pellets 11 and the preparation step of the upper core pellet insertion support plate 20 are not performed in a fixed order, and may be performed in a different order if necessary, which does not affect the result.

Third Step: Insertion of Upper Core Pellets and Coil Winding

[0030] The lower edge part of each of the upper core pellets 11 was inserted into each of the insertion holes 21 formed in the above-described support plate 20, and maintained vertically. In this case, the upper core pellet 11 is inserted so that an outer circumferential surface of the lower edge part is tightly fitted into an inner circumferential surface of the insertion hole 21. A state where the upper core pellets 11 are inserted into the support plate 20 will be fully understood from FIG. 4(A) and FIG. 4(B) that is a cross-sectional view of FIG. 4(A). Preferably, any auxiliary support unit 30 selected from a thin synthetic resin film tape, a silicone tape, and a paper tape is adhered to a bottom surface (rear surface) of the support plate 20 immediately before and after the upper core pellets 11 are inserted, thereby making it convenient to prevent the upper core pellets 11 from falling off, tilting and/or shaking during the handling of the support plate 20, such as during transferring of the support plate 20 to a subsequent coil winding machine. However, the auxiliary support unit 30 is not essential.

[0031] Subsequently, the support plate 20, which is in a state where each upper core pellet 11 inserted and supported in the insertion hole 21, was transferred to an automatic coil winding machine (not shown), and the winding machine was operated so that the coil 31 is firmly wound a plurality of times (for example, 5 to 10 times) on the outer circumferential surface of each upper core pellet 11. The coil 31 was supplied directly from a coil feeder (not shown) provided in the coil automatic winding machine.

[0032] Thus, FIG. 5(A) depicts a final state where the coil 31 is continuously wound on the outer circumferential surface of each upper core pellet 11. In addition, FIG. 5(B) is a cross-sectional view taken along line c-c, which depicts a final state of the coil 31 wound on each upper core pellet 11. In this case, the coil 31 is a commercially available general-purpose enamel-coated copper coil having a diameter of 0.2 mm (200 µm).

Fourth Step: Molding of First Preliminary Molded Body after Coil Winding

[0033] As shown in FIG. 6a(A), the upper core pellet insertion support plate 20 (having the auxiliary support plate 30 adhered to a rear surface thereof), into which the upper core pellets 11 having the coil 31 wound thereon were inserted and maintained, was placed in a molding machine M2, and a predetermined amount (about 35 g) of selected magnetic metal (Fe-Si-Cr) powder 10 was injected in to the molding machine M2, and a pressure of 1 ton/cm² was applied by a press PR2 to mold a first preliminary molded body 42 as shown in FIG. 6a(B). Subsequently, the support plate 20 to which the auxiliary support unit 30 was adhered was removed from a bottom surface of the first preliminary molded body 42. In this case, the states of the surface and the bottom surface of the first preliminary molded body 42 were as depicted in FIGS. 6a(C) and 6a(D), respectively.

Fifth Step: Adjustment of Position of Winding Coil

[0034] As described above, since the upper core pellets 11 are inserted into the surface of the support plate 20, the coil 31 wound thereon is located near the bottom surface of the first preliminary molded body 42. However, in order to secure the desired electrical properties of the inductor, it is necessary to dispose the coil 31 so as to be located at the central part of the inside of the first preliminary molded body 42.

[0035] To this end, the first preliminary molded body 42 of FIG. 6a(B) was placed inside a molding machine M3 (the PR2 is provided with a pressing pin P) in an inverted state (that is, a state where the surface and the bottom surface were turned upside down), as shown in FIG. 6b(A). Thereafter, the lower core pellets 12 (having a diameter of about 3 mm and a height of about 1.5 mm) were placed between the lower edge parts of the upper core pellets 11 and the lead wires L and L on both sides thereof, the magnetic metal (Fe-Si-Cr) powder 10 (about 0.05 g per each upper core pellet 11) was added thereonto, and the press PR2 was operated at a pressure of 1 ton/cm² or more to push the lower core pellets 12 by means of the pressing pin P. As a result, the upper core pellet 11 having the coil 31 wound thereon was located while being slightly pushed to the central part from the initial position shown in FIG. 6a(B). The reason why the coil is located at the center of the inductor is to implement inductance characteristics with minimum magnetic loss. The obtained molded body is a second preliminary molded body 43. Accordingly, both lead wires L and L inside the second preliminary molded body 43 are also spaced slightly upward from an inner bottom surface of the preliminary molded body 43 toward the central part. That is, in this step, each coil lead wire L is located on a bottom part of the second preliminary molded body 43, as shown in the enlarged portion of FIG. 6b(B).

[0036] Since the processes of FIGS. 6a(A) and 6a(B) are partially similar to the description contents (paragraphs [0031] to [0036]) related to FIG. 2 of Patent Document 3 described above, the corresponding description contents are included as a portion of the present specification for reference. In this case, as described above, the Fe-Si-Cr powder 10 may be replaced with a component that is the same as or different from the component of each of the upper core pellets 11 or the lower core pellets 12 depending on the desired properties of the final inductor product.

[0037] It can be seen that the fifth step of the method of the present invention described above is performed in a state where the core pellet insertion support plate 20 is removed.

[0038] FIG. 7 is a flowchart briefly summarizing the processes from the first step to the fifth step of the method of the present invention described above for easy understanding.

[0039] Sixth Step: Underwater Isotropic Press-Molding and Separation of Individual Inductor Products (Conventional Process)

[0040] The second preliminary molded body 43 obtained in the fifth step was transferred to an inside of a metal transfer jig 44 having a predetermined standard as shown in FIG. 8(A), and a back plate 45 was brought into close contact with the bottom surface, so that the second preliminary molded body 43, the metal transfer jig 44, and the back plate 45 are integrally assembled. An assembly FA including the second preliminary molded body 43/the transfer jig 44/the back plate 45 was subjected to a known underwater isotropic press-molding process. To this end, the assembly FA was put into a commercially available vacuum wrap (not shown), and molding was performed at 80°C for 0.5 hours under a molding pressure of 5 ton/cm² using an isotropic press-molding machine (not shown) (See descriptions of paragraphs [0033] to [0035] of Patent Document 3). As a result, a third preliminary molded body 46 as depicted in FIG. 8(B) was obtained.

[0041] In this case, since the upper core pellets 11 and the lower core pellets 12 were integrally mixed with the Fe-Si-Cr powder 10 during the press-molding process, it was observed that a mutual boundary in the third preliminary molded body 46 between the magnetic metal powder, that is, the Fe-Si-Cr powder 10, the upper core pellet 11, and the lower core pellet 12 disappeared.

[0042] Subsequently, a bottom surface of the third preliminary molded body 46 was polished using appropriate polishing equipment. Therefore, as the bottom surface of the third preliminary molded body 46 was polished, the enamel coating was also removed, and as shown in the enlarged portion of FIG. 8(B), a set of left and right coil lead wires L and L was clearly exposed to the bottom surface of the third preliminary molded body, and thus a pattern as shown in FIG. 8(C) was entirely shown on the bottom surface.

[0043] Next, after cleaning the polished surface, a sputtering process widely known in the art was applied to deposit a thin film of a set of left and right external electric terminals T and T corresponding to the surface to which the set of lead wires L and L was exposed. In implementing the present invention, silver (Ag) is used as a sputtering target metal, but the present invention is not limited thereto, and an electrode terminal thin film may be deposited by using gold (Au), copper (Cu), nickel (Ni), or the like. Since the terminal deposition process by the sputtering method described above is known, and is described in relatively detail throughout the specification of Patent Document 6 (paragraphs [0023] to [0032] and FIGS. 6(A), (B), and 7), which are included as part of the present specification, further descriptions thereof will be omitted. Subsequently, a plurality of (6 × 6 = 36) individual inductors I were cut and separated from the third preliminary molded body 46. The set dimension of the cut and separated individual inductor I was 5 mm in width, 5 mm in length, and 2 mm in height. Since the example of the method for cutting and separating the individual inductor I is described in detail in Patent Document 5 (see paragraph [0042] and FIG. 6(D)), further descriptions thereof will be omitted.

[0044] FIGS. 9(A) and 9(B) depict models before and after the electric terminals T and T are deposited on front ends of the coil lead wires L and L, respectively.

Seventh Step: Quality Inspection and Comparative Test

[0045] A quality inspection was performed on a sample (an "inventive sample") of a product of the inductor obtained in the sixth step and pursued by the present invention. For the comparative test for the quality inspection, a composite power inductor product (model name 50204R7C, SST Inc., Anyang City, Korea) manufactured by the conventional method and commercially available was used as a control product (a "control sample"). Both the inventive sample and the control sample were randomly selected. The standard of each of the samples was the same as 5 mm × 5 mm × 2 mm, and a magnetic metal component of a main body (magnetic core) was common as 8 turns of Fe-Si-Cr (including 3% of thermosetting resin binder) and copper coil (having a diameter of 200 µm).

(1) Comparison of Shapes of Inner Winding Coils

[0046] In order to confirm a longitudinal sectional shape of each coil in the randomly selected inventive samples A and B and control samples a and b, cross section processing was performed using a metal specimen processor (EcoMet^™ 30, Buehler). After the cross section processing, a cross-sectional shape of each sample was observed using an optical microscope (BX53MRF, Olympus/image capture Mosaic V2.2 Software). In this case, a measurement magnification was set to ×50. The results thereof are shown in FIG. 10. Accordingly, it was observed that the inner winding coils of the control samples A and B deviated from an initial winding state and were all pushed outward to be unwound on average, but the inner winding coils of the inventive samples A and B exhibited a very stable shape maintaining the initial winding state as it is on average.

(2) Comparison of Inductance Values

[0047] Likewise, inductance values of the control samples a and b randomly selected and the inventive samples A and B were measured and compared. For the measurement, 20 groups of samples were used, in which each group consisting of control samples a+b and inventive samples A+B. Accordingly, the inductance values of the sample items 1 to 20 in a table are 1/2 of the sum of the inductance values of the control samples a and b, and the same applies to the inventive samples. The inductance was measured using an LCR instrument (Model: IM3536 LCR meter, Hioki). In this case, a L2001 probe of Hioki was used as a test fixture, and measurement conditions were a frequency of 100 kHz and 1 V. The results are shown in the following Table 1.

Table 1

Inductance Values (µH) of Control Sample and Inventive Sample
Sample group	Control sample	Inventive sample
1	4.45	4.50
2	4.51	4.58
3	4.20	4.62
4	4.25	4.50
5	4.50	4.59
6	4.40	4.80
7	4.00	4.66
8	4.03	4.69
9	3.90	4.53
10	4.12	4.89
11	4.42	4.63
12	4.09	4.78
13	4.54	4.64
14	4.36	4.69
15	4.29	4.53
16	4.51	4.63
17	4.08	4.64
18	4.56	4.63
19	4.43	4.49
20	4.26	4.64
Minimum value	3.90	4.49
Maximum value	4.56	4.89
Average value	4.30	4.63
Standard deviation	0.20	0.10

[0048] In Table 1, when comparing the standard deviation experimentally obtained for the inductance values of the control sample and the inventive sample, the standard deviation of the inductance value of the control sample is 0.20, whereas the standard deviation of the inductance value of the inventive sample is 0.10. From a statistical point of view, the larger the standard deviation, the larger the measured value deviates from the average value, which means that the distribution of the measured value is wide, and on the contrary, the smaller the standard deviation (that is, closer to 0), the closer the measured value is to the average value, that is, the distribution of the measured value is narrow.

[0049] For more detailed comparison, the results of Table 1 are shown in the distribution diagrams of FIGS. 11(A) and 11(B).

[0050] As shown in Table 1, the inductance values of the control samples of FIG. 11(A) are scattered over a very wide range (that is, a level far from the average value) from 3.90 µH to about 4.75 µH. On the other hand, it can be seen that the inductance values of the inventive samples in FIG. 11(B) are intensively and narrowly distributed in a very narrow range (that is, a range close to the average value) of about 4.5 µH to 5.0 µH.

[0051] These results clearly show that the inventive sample has a very stable and good quality indicating an average inductance value compared to the control sample. That is, according to the present invention, it is possible to provide a high-quality product having uniform electrical properties such as inductance values throughout the entire product of the manufactured composite power inductor by maintaining the initial winding state almost as it is without causing a coating peeling phenomenon and/or an unwinding phenomenon in the inner coil of the inductor during the molding of the composite power inductor. Therefore, it can be said that the method of the present invention has great significance in the manufacturing industry of components and accessories of various precision machines or devices such as medical machines, aircraft, automobiles, rocket weapons, autonomous vehicles, and drones.

[0052] Hereinabove, although the present invention has been described with respect to the best embodiment for improving the conventional technology related to the method for manufacturing a power inductor, it should be recognized by those skilled in the art that modification, correction, and addition/deletion of the components of the present invention are within the scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

[0053] 

10: Magnetic metal powder

11: Upper core pellet

12: Lower core pellet

20: Upper core pellet insertion support plate

21: Upper core pellet insertion hole

30: Auxiliary support unit

31: Coil

42: First preliminary molded body

43: Second preliminary molded body

44: Jig

45: Back plate

46: Third preliminary molded body

M1, M2, M3: Molding machine

PR1, PR2: Press

P: Pressing pin

I: Inductor

L: Lead wire

T: External electric terminal

Claims

1. A method for manufacturing a composite power inductor, the method comprising:

- a first step of molding upper core pellets and lower core pellets formed of magnetic metal powder;

- a second step of providing an upper core pellet insertion support plate having an appropriate number of insertion holes formed therethrough transversely and longitudinally such that lower edge parts of the upper core pellets are inserted thereinto while being accommodated in the upper core pellet insertion support plate;

- a third step of vertically inserting the lower edge parts of the upper core pellets into the insertion holes of the upper core pellet insertion support plate, and transferring the upper core pellet insertion support plate into a coil automatic winding machine to wind a coil on an outer circumferential surface of each of the upper core pellets;

- a fourth step of obtaining a first preliminary molded body by placing the upper core pellet insertion support plate wound with the coil in a molding machine, filling the metal magnetic powder in the molding machine, and performing press-molding;

- a fifth step of obtaining a second preliminary molded body by pushing the lower core pellets into a lower end part of an upper core of the first preliminary molded body and performing press-molding; and

- a sixth step of obtaining a third preliminary molded body by allowing the second preliminary molded body to be subjected to a conventional underwater isotropic press-molding process.

2. The method according to claim 1, wherein one tape selected from a silicone tape, a synthetic resin film tape, and a paper tape is adhered to a rear surface of the upper core pellet insertion support plate as an auxiliary support unit for assisting a support force of the support plate, before the third step is initiated.

3. The method of claim 1, wherein a sequence of the first and second steps are reversible.

4. The method of claim 1 or 3, wherein the upper core pellet insertion support plate is formed of a metal or synthetic resin thin plate.

5. The method of claim 1, wherein an inner diameter of each core insertion hole of the upper core pellet insertion support plate corresponds to an outer diameter of the upper core pellet.

6. The method of claim 1, wherein a thickness of the upper core pellet insertion support plate is 0.5 mm to 1 mm.

7. The method of claim 1, wherein the fourth step is performed after removing the upper core pellet insertion support plate.

Drawing