CHIP INDUCTOR AND METHOD FOR MANUFACTURING THE SAME

Abstract: The electrical characteristic of the chip inductor is improved by preventing the occurrence of short circuits among the linear conductor sections of the coil section of the inductor by appropriately insulating the conductor sections from each other and, at the same time, the mounting surface of the exterior section of the inductor is flattened so that the inductor can be mounted accurately on an object. The chip inductor is provided with a prism-like main body (1) made of an insulating material, electrode sections (6) positioned to both end sections of the main body (1), the coil section (5) which is connected to the electrode sections (6) and, at the same time, positioned on the outer periphery of the main body (1) between the electrode sections (6), and the exterior section (9) coating the coil section (5) with an insulating resin (8). The coil section (5) has the linear conductor sections (3) and groove sections (4) formed by grooving a conductor layer (2) formed on the surface of the main body (1). The internal spaces of the groove sections (4) are also filled up with the insulating resin (8).

Description: TECHNICAL FIELD The present invention relates to a manufacturing method of a chip inductor used in electronic appliances, communication appliances, and others. BACKGROUND ART In Fig. 6 to Fig. 9, a conventional chip inductor comprises a square columnar main body 21 made of an insulating material, a coil unit 25 having a linear conductor 23 and a groove 24 formed by spirally grooving a conductor layer 22 on the surface of the main body 21, an exterior unit 29 made of an insulating resin 28 applied on the surface of the coil unit 25, and an electrode unit 26 provided at the end portion of the main body 21. Its manufacturing method comprises a first step of forming a conductor layer 22 on a square columnar main body 21 made of an insulating material, a second step of forming a coil unit 25 having a linear conductor 23 and a groove 24 by grooving the conductor layer 22 by laser 27, a third step of forming electrode units 26 at both ends of the coil unit 25, and a fourth step of forming an exterior unit 29 by coating the coil unit 25 with an insulating resin 28 and drying. Herein, at the fourth step, while rotating the main body 21 forming the coil unit 25 in the direction of arrow A in Fig. 9 (c), on the tape to which the insulating resin 28 is adhered, the insulating resin 28 is applied on the coil unit 25, and the entire circumference of the coil unit 25 is coated with the insulating resin 28. By drying this insulating resin 28, the exterior unit 29 is formed. In such conventional constitution, the insulating resin 28 is applied on the surface of the coil unit 25, but the insulating resin 28 was not applied in the inner part of the groove 24 of the coil unit 25. Generally, in a very small part such as chip inductor (overall dimension being about 1 mm), the interval of adjacent linear conductors 23 in the coil unit 25 is as narrow as scores of microns, and it is hard to coat the insulating resin 28 due to effects of surface tension and others of the insulating resin 28, and coated portions and uncoated portions of the insulating resin 28 coexisted inside the groove 24. As a result, gaps 40 were formed inside the groove 24 as shown in Fig. 7, and due to air or moisture in the gaps 40, appropriate insulation is not provided between the adjacent linear conductors 23 of the coil unit 25, and short-circuit is caused. Also in the conventional method, since the insulating region 28 is applied on the coil unit 25 while rotating the main body 21 forming the coil unit 25 on the tape to which the insulating resin 28 is adhered, as shown in Fig. 8, the insulating resin 28 applied on the coil unit 25 forms a circular profile, while surrounding the square columnar main body 21 due to the surface tension. As a result, the mounting surface by the exterior unit 29 is round, and when mounting a packed substrate or the like, accurate mounting is difficult, and gaps 40 are likely to be formed in the groove 24. JP 09 055321 A discloses a chip coil having a square pole-like main body formed by providing a conductor layer on an insulating surface. A coil part is formed by grooving the conductor layer of the outer circumferential surface of the main body spirally, and electrode parts are formed at both end parts of the main body. A recessed part is provided on the upper and lower surfaces of the outer circumferential surface of the main body, and insulation resin is applied to the outer circumferential surface of the coil part, in the inside of the recessed part. This allows good flatness between a surface of the electrode part and a surface of the resin layer, and mounting defects on a printed board can be reduced. DISCLOSURE OF THE INVENTION It is hence an advantage of the invention to provide a manufacturing method for a chip inductor capable of preventing short-circuit and enhancing the electric characteristics by applying an appropriate insulation between adjacent linear conductors of the coil unit, and mounting appropriately by forming a flat mounting surface in the exterior unit. The present invention provides a manufacturing method which comprises a first step of forming a conductor layer on a square columnar main body made of an insulating material, a second step of forming a coil unit having linear conductors and grooves by grooving the conductor layer, a third step of forming electrode units at both ends of the coil unit, and a fourth step of forming an exterior unit by coating the coil unit with an insulating resin drying, characterised in that, in said fourth step, the insulating resin applied to each side (10) of the main body (1) is dried before an adjacent side (11) of the main body is coated. In this constitution, since the insulating resin is provided also in the entire inside of the groove, there is no gap in the groove, and air or moisture is forced out, and appropriate insulation can be applied between linear conductors, so that short-circuit can be prevented. Also, in this method, in the coil unit formed on the surface to which the main body is adjacent, the insulating resin is applied and dried on the coil unit formed at one side, and then the insulating resin is applied and dried on the coil formed at another side, thereby forming the exterior unit. In this case, the insulating resins applied on the coil units at the adjacent sides are not formed in a circular external shape due to mutual effects of surface tension because one side is already cured. Moreover, since the area of applying and drying the insulating resin in one step is small, the surface tension is smaller, and the insulating resin is easily applied in the entire inside of the groove. As a result, in the square columnar main body, the insulating resin is also applied in a square columnar form, and an exterior unit of square columnar form is fabricated, and the mounting surface on the exterior unit is flat, and mounting on packed substrate or the like is improved, and the insulating resin may be easily applied to the entire inside of the groove of the coil unit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a chip inductor manufactured in accordance with an embodiment of the invention, Fig. 2 is a magnified sectional view near the coil unit (part A in Fig. 1) of the same chip inductor, Fig. 3 is a perspective view of the same chip inductor, Fig. 4 (a) to (e) are perspective views showing a series of forming steps of the chip inductor, and Fig. 5 (a) to (c) are sectional views showing the formed state of the exterior unit of the same chip inductor. Fig. 6 is a perspective view of a conventional chip inductor, Fig. 7 is a sectional view of the same chip inductor, Fig. 8 is a sectional view showing the formed sate of the exterior unit of the same chip inductor, and Fig. 9 (a) to (d) are perspective views showing a series of forming steps of the same chip inductor. BEST MODE FOR CARRYING OUT THE INVENTION A chip inductor manufactured in accordance with an embodiment of the invention is described in detail below by referring to the accompanying drawings. In Fig. 1 to Fig. 5, the chip inductor comprises a square columnar main body 1 made of an insulating material, electrode units 6 disposed at both ends of this main body 1, a coil unit 5 connected to the electrode units 6 and disposed on the outer circumference of the main body 1 between the electrode units 6, and an exterior unit 9 having the coil unit 5 coated with an insulating resin 8. The coil unit 5 includes linear conductors 3 and grooves 4 formed by grooving a conductor layer 2 covering the surface of the main body 1, and the insulating resin 8 is also formed in the entire inside of the grooves 4. Further, recesses 12 are formed in all side surfaces except for the end surface of the main body 1, and the coil unit 5 is formed in the recesses 12, and the insulating resin 8 is formed inside the recesses 12. The insulating resin 8 is a thixotropic epoxy resin. Its manufacturing method comprises a first step of forming a conductor layer 2 on a square columnar main body 1 made of an insulating material, a second step of forming a coil unit 5 having linear conductors 3 and grooves 4 by grooving the conductor layer 2 by laser 7, a third step of forming electrode units 6 at both ends of the coil unit 5, and a fourth step of forming an exterior unit 9 by coating the coil unit 5 with an insulating resin 8 and drying. The second step also includes a step of removing conductor chips formed when grooving the conductor layer 2, in which etching removal method, sand blasting removal method, or the like is employed. At the fourth step, moreover, in the coil unit 5 formed at adjacent sides of the main body 1, after coating the coil unit 5 formed at one side 10 in direction A in Fig. 4 (c) with the insulating resin and drying, the coil unit 5 formed at other side in direction B in Fig. 4 (c) is coated with the insulating resin 8 and dried, thereby forming the exterior unit 9. At this time, the main body 1 has a square columnar shape, and recesses 12 are formed in all sides of the main body 1, and the coil unit 5 is provided in the recesses 12, and, at the fourth step, after coating the coil unit 5 formed at one confronting side 10 of the main body 1 with the insulating resin 8 and drying, the coil unit 5 formed in other confronting side 11 is coated with the insulating resin 8 and dried to form the exterior unit 9, and the insulating resin 8 is formed within the recess 12 so as not to ooze outside of the recess 12. When coating with the insulating resin 8, the entire inside of the groove 4 is also coated, and a transfer coating process by a roller is employed. The insulating resin 8 used herein is a thixotropic epoxy resin. The operation of the chip inductor having such constitution is described below. Since the insulating resin 8 is provided also in the entire inside of the grooves 4, there is no gap in the grooves 4, and air or moisture is forced out, and an appropriate insulation is guaranteed between the adjacent linear conductors 3, and short-circuit can be prevented. In the recess 12 having the coil unit 5, at least the insulating resin 8 is provided, and therefore the level of the insulating resin 8 is not higher than the level of the electrode units 6 at both sides of the recess 12, and the square columnar plane of the main body 1 can be used as the mounting surface, and the mounting performance on packed substrate or the like is improved. In particular, since the recess 12 is formed in all sides except for the end face of the main body 1 to cover the insulating resin 8, it is possible to mount on any side, and the productivity is enhanced. Moreover, since the insulating resin 8 is a thixotropic epoxy resin, shape change does not occur when curing the insulating resin 8, and the surface shape of the exterior unit 9 can be accurately defined in a plane, and the mounting performance may be enhanced. Also according to this manufacturing method, in the coil units 5 formed at adjacent sides of the main body 1, after coating the coil unit 5 formed at one side 10 with the insulating resin 8 and drying, the coil unit 5 formed in other side 11 is coated with the insulating resin 8 and dried to form the exterior unit 9. In this case, of the insulating resins 8 applied on the coil units 5 at the adjacent sides, since one side has been already cured, the external shape does not become circular due to mutual effects of surface tension. Still more, the area of coating with the insulating resin 8 and drying in one step is smaller, and the surface tension is smaller, and therefore it is easy to coat the entire inside of the groove 4 with the insulating resin 8. As a result, in the square columnar main body 1, the insulating resin 8 is also applied in a square columnar shape, and the square columnar exterior unit 9 is formed, and the mounting surface by the exterior unit 9 is a flat shape, and the mounting performance on a packed substrate or the like may be enhanced. Since the coil units 5 formed at the confronting one side 10 and other side 11 of the main body 1 are coated with the insulating resin 8 and dried, the process of forming the exterior unit 9 on the main body 1 is finished in two steps, and the manufacture may be simplified. Since the entire inside of the groove 4 is coated with the insulating resin 8, gap is not formed in the groove 4, and corrosion or short-circuit between the adjacent linear conductors 3 due to air or moisture in the gap may be prevented, and it is also effective to prevent short-circuit between the adjacent linear conductors 3 by conductor chips or other dust formed at the time of grooving the conductor layer 2. Since the insulating resin 8 is formed in the recess 12 provided in the sides of the main body 1, the level of the insulating resin is not higher than the level of the electrode units 6 at both ends of the recess 12, and the mounting performance on a packed substrate or the like may be enhanced. Since conductor chips formed when grooving the conductor layer 2 are removed, it is effective to prevent short-circuiting between the adjacent linear conductors 3 due to the conductor layer of a conductive matter, or prevent change of inductance value due to deposit on the linear conductors 3, thereby enhancing the electric characteristics. Since the insulating resin 8 is a thixotropic epoxy resin, when coated with the insulating resin 8, the exterior unit 9 can be formed by drying and curing while maintaining the shape of coating. As a result, shape changes when curing the insulating resin 8 are smaller, the shape of the surface of the exterior unit 9 can be defined, and the mounting performance is enhanced. Moreover, since the insulating resin 8 is applied by transfer coating process, the insulating resin 8 can be applied very sparingly and uniformly. Therefore, the sectional area of the main body 1 may be extended to the maximum limit, and the size can be reduced while maximizing the inductance value attributable to the sectional area of the main body 1. Thus, according to the invention, there is no gap in the grooves 4, and air or moisture is forced out, and an appropriate insulation is guaranteed between the linear conductors 3, and short-circuit can be prevented, and therefore the electric characteristics may be enhanced. The level of the insulating resin 8 is not higher than the level of the electrode units 6 at both sides of the recess 12, and the square columnar plane of the main body 1 can be used as the mounting surface, and the mounting performance on packed substrate or the like is improved, and moreover, since the recess 12 is formed in all sides except for the end face of the main body 1 to cover the insulating resin 8, it is possible to mount on any side, and the productivity is enhanced. Moreover, since the insulating resin 8 is a thixotropic epoxy resin, shape change does not occur when curing the insulating resin 8, and the surface shape of the exterior unit 9 can be accurately defined in a plane, and the mounting performance may be enhanced. Also according to this manufacturing method, in the square columnar main body 1, the insulating resin 8 is also applied in a square columnar shape, and the square columnar exterior unit 9 is formed, and the mounting surface by the exterior unit 9 is a flat shape, and the insulating resin 8 is provided in the recess 12 formed at the side of the main body 1, and therefore the level of the insulating resin is not higher than the level of the electrode units 6 at both ends of the recess 12, and the mounting performance on packed substrate or the like is enhanced. In particular, since the insulating resin 8 is a thixotropic epoxy resin, the shape of the surface the exterior unit 9 can be defined, and the mounting performance may be further improved. Since the insulating resin 8 is also applied in the gap, corrosion or short-circuit between adjacent linear conductors 3 can be prevented, and deterioration in use in high frequency current region can be suppressed, and further by transfer coating process, the insulating resin 8 can be applied very sparingly and uniformly, and the size may be reduced while maximizing the inductance value. Conductor chips formed when grooving the conductor layer 2 are removed, which prevents occurrence of short-circuit between the adjacent linear conductors 3 due to the conductive matter formed by conductor chips or change of inductance value due to deposit on the linear conductor 3, thereby enhancing the electric characteristics. Since the coil unit 5 formed at the confronting one side 10 of the main body 1 and the coil unit 5 formed at the confronting other side 11 are coated with the insulating resin 8 and dried, the process of forming the exterior unit 9 on the main body 1 is finished in two steps, and the manufacture may be simplified. Meanwhile, in the embodiment of the invention, the exterior unit 9 is formed on the main body 1 in two steps, but the exterior unit may be also formed in several steps, by applying and drying the insulating resin 8 sequentially in each side of the side surfaces of the main body 1. Incidentally, the method of removing conductor chips may be also other method than the etching removal method or sand blasting removal method. INDUSTRIAL APPLICABILITY Thus, the invention gives rise to a chip inductor obtainable by the claimed method comprising a square columnar main body made of an insulating material, electrode units disposed at both sides of the main body, a coil unit connected to the electrode units, and disposed on the outer circumference of the main body between the electrode units, and an exterior unit having the coil unit coated with an insulating resin, in which the coil unit has linear conductors and grooves formed by grooving the conductor layer applied on the surface of the main body, and the insulating resin is provided also in the entire inside of the grooves. In this constitution, since the insulating resin is provided also in the entire inside of the groove, there is no gap in the groove, and air or moisture is forced out, and appropriate insulation can be applied between linear conductors, so that short-circuit can be prevented, and therefore the chip inductor enhanced in the electric characteristics can be presented. The manufacturing method of the invention comprises a first step of forming a conductor layer on a square columnar main body made of an insulating material, a second step of forming a coil unit having linear conductors and grooves by grooving the conductor layer, a third step of forming electrode units at both ends of the coil unit, and a fourth step of forming an exterior unit by coating the coil unit with an insulating resin and drying, in which the fourth step is intended to form the exterior unit by first coating the coil unit formed on one side of the main body with an insulating resin and drying, then coating the coil unit formed on other side with an insulating resin and drying. Also, in this method, in the coil unit formed on the surface to which the main body is adjacent, the insulating resin is applied and dried on the coil unit formed at one side, and then the insulating resin is applied and dried on the coil formed at other side, thereby forming the exterior unit. Therefore, the insulating resins applied on the coil units at the adjacent sides are not formed in a circular external shape due to mutual effects of surface tension because one side is already cured. As a result, in the square columnar main body, the insulating resin is also applied in a square columnar form, and an exterior unit of square columnar form is fabricated, and the mounting surface on the exterior unit is flat, so that a chip inductor enhanced in mounting on packed substrate or the like is presented. List of Reference Numerals in the Drawings 1 Main body 2 Conductor layer 3 Linear conductor 4 Groove 5 Coil unit 6 Electrode unit 7 Laser 8 Insulating resin 9 Exterior unit 10 One side 11 Other side 12 Recess 21 Main body 22 Conductor layer 23 Linear conductor 24 Groove 25 Coil unit 26 Electrode unit 28 Insulating resin 29 Exterior unit 40 Gap

Claims: A manufacturing method of a chip inductor comprising: a first step of forming a conductor layer (2) on a square columnar main body (1) made of an insulating material, a second step of forming a coil unit(5) having linear conductors (3) and grooves (4) by grooving said conductor layer, a third step of forming electrode units (6) at both ends of said coil unit, and a fourth step of forming an exterior unit (9) by coating said coil unit (5) with an insulating resin (8) and drying, characterised in that , in said fourth step, the insulating resin applied to each side (10) of the main body (1) is dried before an adjacent side (11) of the main body is coated. A manufacturing method of a chip inductor as claimed in claim 1 wherein, in the fourth step, the insulating resin (8) is first coated onto two opposite sides of the main body (1) and dried, and is then coated onto the remaining two opposite sides and dried. A manufacturing method of a chip inductor as claimed in claim 1 wherein, in the fourth step, the insulating resin (8) is coated onto each side of the main body (1) sequentially, by applying and drying the insulating resin on each side in turn. A manufacturing method of a chip inductor as claimed in claim 1, 2 or 3, further comprising a step of forming recesses (12) in side surfaces of the main body (1), forming the coil unit (5) at least in said recesses, and forming the insulating resin (8) inside said recesses. A manufacturing method of a chip inductor as claimed in any preceding claim, further comprising a step of removing conductor chips formed when grooving the conductor layer (2). A manufacturing method of a chip inductor as claimed in any preceding claim, wherein the insulating resin (8) is a thixotropic epoxy resin. A manufacturing method of a chip inductor as claimed in any preceding claim, wherein coating is applied by transfer coating process.

Inventors: FUJIMORI AKIRA, KANETAKA TOYONORI, NAKAYAMA HIDEAKI, TAOKA MIKIO, YOSHIZAWA TOSHIHIRO, FUJIMORI, AKIRA, KANETAKA, TOYONORI, NAKAYAMA, HIDEAKI, TAOKA, MIKIO, YOSHIZAWA, TOSHIHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: H01F41
IPC codes: H01F27, H01F17, H01F41