JP2005277205A - Ceramic body for ferrite core, ferrite core employing the same, and common mode noise filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a conventional small-sized ferrite core, including multi-terminals and whose inter-electrode distance is small, for being employed for a common mode noise filter or the like that the insulation resistance between the electrodes of the core is reduced, resulting in causing a short circuiting, because of occurrence of migration at application of a voltage under atmosphere containing water contents, after the mount on the occurrence of drooped conductive paste and extended plating. <P>SOLUTION: The ceramic body for the ceramic core comprising a winding core part 5 on which wires are wound; guards 1 formed at both ends of the winding core 5; and a plurality of legs 2 consecutively provided to the guards 1, includes at least one step part over the entire circumference of each leg 2 and the cross-sectional area of each leg 2 at the step part 3 is selected to be the cross sectional area on a border with the guards 1 or below so as to prevent the extended electrode from taking place. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a ferrite core ceramic suitable for countermeasures against common mode noise of various electronic devices that handle high-frequency signals, a ferrite core using the same, and a conductor wire wound around the ferrite core, and used for a differential transmission circuit or the like. It relates to a common mode noise filter.

  Conventionally, a common mode noise filter has been used as a countermeasure against unnecessary radiation of power supply lines and as a countermeasure against common mode noise of high frequency signals.

  As shown in FIGS. 7A to 7C, the common mode noise filter includes a winding core portion 5 for winding a conductive wire in a case, and a flange portion 1 formed at both ends of the winding core portion 5. And an electrode 4 is formed on the bottom side end of each leg portion 2 of the ceramic body for a ferrite core, which is composed of a plurality of leg portions 2 continuously provided on the bottom side of the flange portion 1 to form a ferrite core. A plurality of conducting wires 7 are wound around the core portion 5 of the ferrite core by bifilar winding or the like, and the leading end and the end of the winding end of the conducting wire 7 are formed on the leg portion 2. Each electrode 4 is electrically connected by soldering or thermocompression bonding.

  When the electrode 4 is formed on the ferrite core ceramic body used for the common mode noise filter, baking is performed after thick film printing of a conductive metal such as Ag or AgPd using a method such as dipping, screen printing, or transfer. Next, Ni, Cu, Sn, SnPb, Au, or the like is formed on the thick film by plating several layers according to the use and requirements. This plating method involves immersing a ferrite core ceramic body that has undergone thick film printing and baking in a predetermined plating solution, and flowing current to cause the required metal on the thick film formed on the ferrite core ceramic body. A plating layer is formed and formed by washing excess plating solution adhering to the ferrite core.

  In the common mode noise filter, when an in-phase current flows through the two conductive wires 7, the magnetic flux is added and the impedance is increased. Conversely, when a reverse phase current flows through the two conducting wires 7, the magnetic flux is canceled and impedance is hardly generated. As described above, the common mode noise filter is an electronic component having a filter function that the common-mode current hardly flows and the reverse-phase current easily flows.

  In the field of information communication equipment in which this common mode noise filter is used, there is a demand for miniaturization and weight reduction of parts. In accordance with the demand, the size of the common mode noise filter is approximately 20 mm, which is the size of a substantially quadrangle, which is the mounting area, 3216 mm, 1.6 mm width, 3216 mm, 2.5 mm length, 2.0 mm width, 2520. Similarly, 2012, 1608, and 1210 have been shifted to miniaturization.

  Along with such miniaturization, when the distance between the electrodes 4 of the common mode noise filter is reduced and the conductive paste droops or the plating is elongated, the migration phenomenon occurs when a voltage is applied in an atmosphere containing moisture after mounting. This causes a problem that the insulation resistance between the electrodes 4 is lowered and short-circuited. In addition, since the adhesion strength with the ferrite core ceramic body is very low at the portion where the plating elongation occurs, there is a problem that the electrode 4 is easily peeled off from the surface. When mounting the ferrite core ceramic body with a jig or the like during mounting When the plating extension part contacts the tip of the jig, the electrode 4 is easily peeled off.

  In addition, even if the ferrite core 6 has no plating elongation, the surface of the electrode 4 is scratched by the contact of the jig with the electrode 4, and the conductive metal portion such as Ag is exposed, resulting in mounting failure. Then there was a problem to say.

  Therefore, in Patent Document 1, as shown in FIG. 7, it is proposed that all the ridge lines of each leg 2 in the ferrite core ceramic body are curved. According to this proposal, by forming a curved body having a radius of curvature of about 0.2 mm on all the ridge lines of the leg 2, it is possible to prevent problems such as disconnection and short circuit of the conductor 7 due to the ridge line.

  Patent Document 2 proposes baking a metal oxide having a high electrical resistance on the surface of a ceramic body for a ferrite core. According to this proposal, it is shown that the metal oxide is adhered to the surface of the porcelain in a barrel process which is usually performed as a burr or chamfering treatment of ceramic or the like. That is, as a method for attaching a metal oxide having a higher electrical resistance than the ferrite forming the ferrite core ceramic body to the surface, the metal oxide powder is also rotated simultaneously during the barrel treatment. Then, by printing the conductive paste and baking the metal oxide powder to the ceramic body at the same time in the next process, it becomes possible to suppress plating elongation and plating deposition on unnecessary parts in the subsequent wet plating process, This shows that a more reliable common mode noise filter can be obtained by suppressing the occurrence of a short circuit due to plating elongation.

Furthermore, Patent Document 3 proposes controlling the applied potential during wet plating within a predetermined range. According to this proposal, by controlling the variation in applied potential caused by the variation in current value control when performing electrolytic plating processing such as barrel plating within a predetermined range, the greatly displaced applied potential is reduced to the ferrite core ceramic. It has been proposed to prevent application to the body and, as a result, prevent plating elongation.
JP 2002-329618 A JP-A-8-181029 JP 2003-239095 A

  However, in the common mode noise filter using a ferrite core as shown in Patent Document 1, the ridgeline part of the leg part 2 is curved to remove the acute angle part where the charge concentrates during the plating process, thereby concentrating the charge. Although the effect of suppressing the growth of plating is expected, the electrolytic body forming method such as barrel plating always moves the ceramic body for ferrite core randomly in the plating tank, and as a result, the applied potential varies. In the ferrite core ceramic body to which a greatly deviated potential is applied, the plating metal is likely to be deposited on portions other than the thick film made of the conductive metal, and the phenomenon of plating elongation has occurred. Therefore, since the adhesion strength with the ferrite core ceramic body is very low in the portion where the plating elongation occurs, the electrode 4 is easily peeled off from the surface, and when the ferrite core 6 is sandwiched with a jig or the like during mounting, the plating elongation portion When the tip of the jig comes into contact, the electrode 4 is easily peeled off. Further, even if the ferrite core 6 has no plating elongation, when the jig comes into contact with the electrode 4, the surface of the electrode 4 is scratched, a conductive metal such as Ag is exposed, and a mounting defect occurs. There was a problem to say.

  Moreover, as shown in Patent Document 2, in the method of baking a metal oxide having a high electric resistance on the surface of the ferrite core ceramic body, the metal oxide is adhered in the barrel process, so that the surface of the ferrite core ceramic body is Plating completely because the difference in the rough state causes non-uniformity in the state of adhesion to the ceramic body for the ferrite core and the difference in the amount of metal oxide surface attached due to the difference in the cleaning state after the barrel. The problem that the elongation could not be prevented remained and had the same problem as described above.

  Furthermore, the optimum condition for the method based on the control of electrical conditions during plating as shown in Patent Document 3 has been empirically obtained from the past. However, the condition for reliably suppressing the elongation is a very low load voltage, and the plating process efficiency is greatly reduced, which is not an efficient production method.

  The present invention solves the above-mentioned problems, is to improve the elongation of the plating and secure the insulation resistance between the electrodes while using the conventional efficient plating process method. An object of the present invention is to provide a ceramic body for a ferrite core, a ferrite core, and a common mode noise filter using the same, which prevent scratches and provide stable adhesion during mounting.

  The ceramic body for a ferrite core according to the present invention includes a winding core portion for winding a conducting wire, a flange portion formed at both ends of the winding core portion, and a plurality of leg portions that are continuously provided on the flange portion. A ferrite core ceramic body comprising at least one step portion around the entire circumference of each leg portion, wherein the cross-sectional area at the step portion of each leg portion is equal to or less than the cross-sectional area at the boundary with the flange portion. And

  Moreover, the ceramic body for a ferrite core according to the present invention is characterized in that the area of the bottom surface of the leg portion is the smallest with respect to the cross-sectional area of each leg portion that is cut by a plane parallel to the bottom surface.

  Furthermore, the ceramic body for a ferrite core according to the present invention is characterized in that a ridge line portion extending from the bottom surface side to the core side of each leg portion has a curved surface.

  Furthermore, the ferrite core of the present invention is characterized in that an electrode is formed at the bottom side end of each leg of the ceramic body for a ferrite core.

  Furthermore, the ferrite core of the present invention is characterized in that each of the electrodes has substantially the same height in the axial direction of the leg portion.

  Furthermore, the common mode noise filter of the present invention is characterized in that a conductive wire is wound around the ferrite core.

  The ceramic body for a ferrite core according to the present invention includes a winding core portion for winding a conducting wire, a flange portion formed at both ends of the winding core portion, and a plurality of leg portions that are continuously provided on the flange portion. This ferrite core ceramic body has at least one step part over the entire circumference of each leg part, and the cross-sectional area at the step part of each leg part is less than or equal to the cross-sectional area at the boundary with the flange part. When the conductive paste is printed at the time of electrode formation by the step portion, it acts to dampen the dripping of the paste, and a stable electrode depth can be obtained. As a result, it is possible to suppress variations in adhesion strength during mounting. . In addition, in the plating process, it is possible to suppress the progress of elongation by having a step portion with respect to the plating elongation, and the surface distance between the electrodes increases as the surface area increases. Yes, thereby preventing the occurrence of a short circuit between the electrodes.

  In addition, the ceramic body for a ferrite core of the present invention has the smallest area at the bottom of the cross-sectional area of each of the legs, so the portion of the entire leg that forms the electrode is always from the outer periphery of the leg. Since the structure is located on the inner side, when the lead wire is wound or mounted, when the common mode noise filter around which the ferrite core and the lead wire are wound is handled with a jig or the like, the electrode forming portion is on the lower side. When placing the long side parts or short side parts with a jig after placing the jig in such a manner, the jig is in contact with the electrode during the clamping work by designing the sandwiching jig so that it is always in contact with the bottom surface. As a result, scratches on the electrode surface and electrode peeling caused by contact with the jig can be prevented.

  Furthermore, since the ridge line portion of each leg is curved, it is possible to suppress the occurrence of plating elongation because no sharp angle portion where charge tends to concentrate is formed. Occurrence can be suppressed.

  Furthermore, since the distance between the electrodes can be kept constant even when the ferrite core using the ferrite core ceramic body is downsized, the occurrence of a short circuit between the electrodes can be prevented.

  Furthermore, in the ferrite core using the ceramic body for a ferrite core, since the electrodes of each leg portion are substantially the same height in the axial direction of the leg portion, when mounting using solder, The height at which the solder crawls up to the provided electrode becomes uniform, and the force that the solder for mounting pulls on each leg portion of the ferrite core becomes uniform, so that stable mounting can be achieved.

Here, the stepped portion may be either a stepped portion with respect to the surface of the leg portion that is formed in a direction perpendicular to the bottom surface, or a plurality of stepped portions may be connected. In other words, when the projection is convex with respect to the surface of the leg, a step may be formed again so that the leg bottom area is minimized. This step portion has an effect of blocking paste dripping in conductive paste printing during electrode formation. As a result, a stable electrode depth can be obtained, and variations in adhesion strength during mounting can be kept small. Furthermore, in the plating process, having a stepped portion against the plating elongation becomes an obstacle to the progress of the elongation, and the surface distance between the electrodes increases as the surface area increases. This has the effect of reducing the size, which can prevent the occurrence of a short circuit between the electrodes.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1A is a ferrite core ceramic body of the present invention, FIG. 1B is a ferrite core formed by forming electrodes on the ferrite core ceramic body of FIG. 1A, and FIG. It is a perspective view which shows one Embodiment of a common mode noise filter formed by winding conducting wire around the ferrite core.

  The ceramic body for a ferrite core shown in FIG. 1 (a) is made of a magnetic material such as Ni—Zn ferrite and Mn—Zn ferrite, and has a core portion 5 for winding a conductive wire, and a core portion 5 1, and a plurality of leg portions 2 provided continuously on the bottom surface side of the collar portion 1, and as shown in FIG. An electrode 4 is formed at the bottom side end to obtain a ferrite core 6. For example, since the ferrite core 6 of 2520 size has a short side dimension B of 2.0 mm, the distance between the legs 2 formed on the collar 1 is a high-viscosity paste used for breaking strength and thick film printing. Considering the prevention of short circuiting, it is very small, about 0.4 mm.

  Then, as shown in FIG. 1 (c), a plurality of conducting wires 7 are wound around the core portion 5 of the ferrite core 6 by bifilar winding or the like by several to several tens of turns, A common mode noise filter is obtained by conducting conductive connection to the electrode 4 formed at the end of the winding on the leg 2 by soldering, thermocompression bonding or the like.

  Here, the ceramic body for a ferrite core of the present invention has at least one step 3 over the entire circumference of each leg 2 as shown in FIGS. 2 (a) and 2 (b). The cross-sectional area 2A in the step part 3 is set to be equal to or smaller than the cross-sectional area 2B at the boundary with the flange part 1.

  As shown in FIGS. 2A and 2B, when the legs 2 are viewed from the bottom side, the cross-sectional area 2A along the line XX ′ in the step 3 of each leg 2 is By forming the step portion 3 in the leg portion 2 so as to be equal to or smaller than the cross-sectional area 2B in the YY ′ line at the boundary, the tip of the leg portion 2 forming the electrode 4 becomes smaller than the other leg portions 2. When the electrode 4 is formed to form the ferrite core 6 as shown in FIG. 2C, the progress of plating elongation when the electrode 4 is formed by the step portion 3 can be suppressed. 2 can be formed only at the tip of the second electrode, and a short circuit between the electrodes 4 can be prevented.

  Here, when the electrode 4 is formed on the ceramic body for the ferrite core to form the ferrite core 6, a conductive metal paste such as Ag or AgPd is used after thick film printing using a method such as dipping, screen printing, or transfer. After baking, Ni, Cu, Sn, SnPb, Au, etc. are plated on the thick film according to the purpose and demands. This plating process involves forming a metal plating layer on the thick film by immersing the ceramic body for a ferrite core that has been printed and baked into a predetermined plating solution and passing an electric current. Is to wash.

  Therefore, the step 3 is formed on each leg 2 so that the paste is not printed beyond the step 3 when the conductive metal is printed on the thick film. Since it stops, it does not advance beyond the step part 3, and the short circuit which arises from the approach of the distance between the electrodes 4 by this can be prevented. Further, even when plating elongation occurs during the plating process, since the progress of the plating elongation can be suppressed by the step portion 3, a short circuit between the electrodes 4 can be prevented.

  However, since the dripping of the paste is greatly affected by the viscosity of the paste, it is more preferable to adjust the viscosity of the paste at the same time.

  Further, when the common mode noise filter is mounted on the substrate, it is sandwiched by a jig or the like. However, since the electrode 4 is formed on the inner side of the outer peripheral surface of the leg 2 on the flange 1 side, the jig and the electrode 4 are arranged. Can prevent the electrode 4 from peeling off due to the contact between the electrode 4 and the jig and the generation of scratches on the surface of the electrode 4, and can stabilize the adhesion state during mounting. it can.

  The cross section of the leg portion 2 is a cross section cut along a plane parallel to the bottom surface of the leg portion 2.

  Moreover, the step part 3 formed in each leg part 2 should just be formed so that the cross-sectional area 2A in the step part 3 may become below the cross-sectional area 2B in the boundary with the collar part 1, FIG. As shown in FIG. 3 (c), various shapes may be used, and as shown in FIG. 3 (a), a plurality of step portions 3 may be formed, and as shown in FIG. The feeding portion may be formed so that the paste enters, and as shown in (c), the step portion 3 does not have to be parallel to the bottom surface, and as shown in FIG. 3 is provided so as to be inclined closer to the core 5 side from the inside of the ferrite core ceramic body, so that the depth of the electrode 4 on the outer peripheral side of the ferrite core ceramic body is deeper than the inner side. There is an advantage that the frit can be increased and the mounting strength is increased, and the inner electrode 4 has a high height. It is also possible to prevent a short circuit when turned wire 7 wound for possible low.

  In particular, as shown in FIGS. 2, 3 (b), and 3 (c), it is preferable to form the step portion 3 so that the area of the bottom surface of the cross-sectional area of each leg portion 2 is minimized.

  Thereby, since the part which forms the electrode 4 in the whole leg part 2 becomes a structure always located inside the outer periphery of the leg part 2 by the side of the collar part 1, the ferrite core 6 and the conducting wire 7 were wound. When handling the common mode noise filter with a jig or the like, after placing the electrode 4 so that the formation part of the electrode 4 is on the lower side, when sandwiching the long side parts or the short side parts with the jig, By design so that it always touches vertically, a jig | tool does not contact the electrode 4 at the time of pinching operation | work, and the damage | wound of the surface of the electrode 4 and peeling of the electrode 4 which arise by contact with a jig | tool can be prevented. .

  Further, when the ferrite core 6 is formed, it is preferable that the electrodes 4 of each leg 2 have substantially the same height in the axial direction of the leg 2.

  This is because the height at which the solder crawls up to the electrodes 4 provided on each leg 2 at the time of mounting becomes uniform, and the force that the solder for mounting pulls on each leg 2 of the ferrite core 6 becomes uniform and stable. Can be implemented.

  Furthermore, when the electrode 4 is formed on the ferrite core ceramic body, it is necessary to manage the length 8 and thickness 9 of the electrode 4 as shown in FIG. That is, since the depth 10 of the stepped portion 3 is set to a thickness 9 or more of the electrode 4 to be formed, it is possible to prevent the jig 4 and the electrode 4 from contacting with each other when the ferrite core 6 or the common mode noise filter is sandwiched. The peeling of the electrode 4 and the unevenness of the surface of the electrode 4 can be prevented. However, the depth 10 of the stepped portion 3 is preferably not deeper than necessary, and the ratio of the cross-sectional area 2A to the cross-sectional area 2B is preferably 40% or more. This is because if the cross-sectional area 2A is too small, the mounting strength is lowered.

  Further, by setting the depth 11 of the step portion 3 that is the length from the step portion 3 to the bottom surface to be larger than the desired electrode length 8, the paste is printed beyond the step portion 3 when the conductive paste is printed. In addition, even if paste dripping occurs, it is dammed by the stepped portion 3.

  Moreover, as shown to Fig.4 (a), (b), it is preferable that the ridgeline part of each leg part 2 is a curved surface form.

  FIG. 4A shows a ridge line portion of the prismatic leg portion 2 having a curved surface, and FIG. 4B shows a shape of the leg portion 2 made cylindrical.

  Thereby, when the electrode 4 is formed on the ferrite core ceramic body, the concentration of electric charges on the ridge line portion during plating is alleviated, and the elongation of the plating can be effectively suppressed. The insulation resistance between the electrodes 4 can be ensured. In this case, the effect of alleviating the concentration of charges is maximized, and the shape is most effective for plating elongation.

  In particular, the one having the columnar leg 2 as shown in FIG. 4B has a curved ridgeline, so that even if the conductor 7 and the leg 2 are in contact with each other, the coating of the conductor 7 is damaged. There is an advantage that the pressure-resistant deterioration due to is less likely to occur.

  The curved surface means that the radius of curvature is 0.02 mm or more, and if the radius of curvature is less than 0.02 mm, it is difficult to obtain the effect of relaxing the charge concentration when forming the plating layer.

  Next, the ceramic body for a ferrite core and the method for producing the ferrite core of the present invention will be described.

  For example, when a ferrite core as shown in FIG. 2 is produced, first, a predetermined binder is added to powders such as Ni—Zn ferrite and Mn—Zn ferrite used as raw materials for the ferrite core ceramic body, and spray drying is performed. The raw material powder is obtained by granulating into granules suitable for powder molding. In particular, it is preferably made of Ni—Zn-based ferrite from the problem of operating frequency and surface resistance.

  Next, this raw material powder is set in a powder press molding machine, filled in a mold formed by dividing the core portion 5 and the leg portion 2, and pressed at a predetermined pressure to form a ferrite core ceramic body. Get.

  Thereafter, the obtained compact is fired at a predetermined firing temperature in a firing furnace such as an electric furnace or a gas furnace to obtain a sintered body.

  Next, in order to perform surface treatment and burr removal of the obtained sintered body, barrel processing is performed to obtain the ferrite core ceramic body of the present invention.

  In addition, the step part 3 formed in the leg part 2 is a method of forming a concave and convex part on the mold of the part for molding the leg part 2 at the same time or dividing the mold for molding the leg part 2 into two or more. By doing so, the step 3 can be obtained by a method of simultaneously molding. Alternatively, the stepped portion 3 can be formed by processing using a diamond tool after the ferrite core ceramic body is molded or fired.

  Thereafter, the electrode 4 is formed on the bottom side end of the leg 2. As this method, a conductive metal paste such as Ag or AgPd is baked after thick film printing by using a method such as dipping, screen printing, or transfer as described above, and then Ni, Cu, Sn is deposited on the thick film. , SnPb, Au, etc. are produced by plating several layers according to the application and requirements. This plating process was formed on the legs 2 of the ferrite core ceramic body by immersing the ferrite core ceramic body on which thick film printing was performed in a plating solution in which the components of the layer to be prepared were dissolved, and allowing current to flow. A predetermined plating layer is formed on the thick film, and then the plating core adhered to the ferrite core ceramic body is washed to obtain the ferrite core 6 on which the electrode 4 is formed.

  The ferrite core 6 obtained in this manner is obtained by winding a plurality of conducting wires 7 around the winding core portion 5 by bifilar winding or the like from several turns to several tens of turns. Are electrically connected to the electrodes 4 formed on the legs 2 by soldering, thermocompression bonding, or the like, thereby acting as a common mode noise filter.

  The ferrite core of the present invention as shown in FIG. 2 is produced.

  First, after a Ni—Zn ferrite material and a binder were kneaded as a magnetic material, a raw material powder was prepared with a spray dryer. Next, using this raw material powder, a mold formed by dividing the core portion 5 and the leg portion 2 was manufactured, set in a powder press molding machine, filled with the raw material and molded. At that time, each leg 2 was formed with a step 3 having dimensions as shown in Table 1 after firing.

  Then, 20 sintered bodies each having four legs 2 were produced by firing at 900 to 1300 ° C. The ridgeline of each leg 2 was processed into a shape as shown in Table 1.

  And this sintered compact was put into the barrel apparatus which has the pot-shaped container which consists of porcelain, and the barrel process was given, and the ceramic body for ferrite cores which performed the surface treatment and the burr | flash removal was produced.

  Next, an Ag thick film is printed by dipping on all the ceramic bodies for ferrite cores and fired. On the thick film, Ni and Sn are plated by electrolytic plating to form electrodes 4. Twenty ferrite core samples were obtained.

  The thickness of each electrode was 20 μm for Ag, 2 μm for Ni, and 7 μm for Sn, and the length of the electrode from the bottom surface side of the leg portion 2 of the Ag thick film toward the core portion 5 was set to 0.3 mm.

  The ferrite core sample had a long side called a 2520 size of 2.5 mm and a short side of 2.0 mm. The thickness was 1.2 mm, the outer shape of the leg 2 was 0.8 mm square, and the length of the leg was 0.45 mm.

  As a comparative example, a ferrite core sample having a leg portion 2 having no stepped portion 3 as shown in FIG.

  And each obtained ferrite core sample was evaluated by the following method.

(1) While confirming the presence or absence of elongation of each plating layer, the length 8 of the electrode was measured. As shown in FIG. 6 (a), the confirmation of the elongation has a sample in which the step portion 3 is formed, with the plating extending beyond the step portion 3 to the core portion 5 side. As shown in FIG. 5), the sample having no stepped portion 3 has a thickness exceeding 0.3 mm. Moreover, after measuring the elongation of plating from the bottom surface of the leg portion 2 of the Ag thick film using a measuring microscope, the average of the four leg portions 2 was calculated.

(2) The insulation resistance between adjacent electrodes 4 when each probe was applied to the electrodes 4 of each ferrite core sample and DC 50 V was applied was evaluated. The measuring instrument used here is a high resistance measuring instrument manufactured by HP, and the measurement voltage is a voltage value generally used for evaluating the insulation resistance between conductors and between the conductors and the ferrite core with an inductor. As a method, it is confirmed whether adjacent electrodes 4 are not conducting.

(3) Solder onto the mounting board using the electrode 4 of each ferrite core sample, fix the mounting board to a test stand manufactured by AIKOH, and abbreviated when mounting the ferrite core sample using CPU GAGE manufactured by AIKOH Of the square size, the core 5 is pressed with a depressor at a speed of 5 mm / min in a direction parallel to the mounting substrate. When the pressure was applied in this manner, the strength when the legs 2 were all destroyed and the ferrite core sample was detached from the mounting substrate was evaluated, and the adhesion strength was evaluated.

The results are shown in Table 1.

As can be seen from Table 1, the samples (4 to 12) having the step portions which are examples of the present invention have a slight elongation of plating, but the electrode length can be 0.41 mm or less, The insulation resistance between the electrodes could be maintained at 10 ¹⁰ Ω · cm, and the adhesion strength could be 16 N or more.

In particular, in the samples (No. 6, 7, 10, 11) in which the depth of the step portion is 0.1 mm and the ridge line portion has a curvature radius of 0.02 mm or more, the length of the electrode is constant at 0.3 mm depending on the step portion. In addition, the insulation resistance between the electrodes could be maintained at 10 ¹⁰ Ω · cm, and the adhesion strength could be 22 N or more.

On the other hand, the sample (No. 1 to 3) having no step portion has an electrode length of 0.46 to 0.52 mm, and the insulation resistance between the electrodes is 10 ⁵ Ω · cm. In some cases, the distance between the electrodes was close and a short circuit occurred.

  From the above, it was found that the problem of short circuit due to electrode elongation can be solved by forming a stepped portion on the leg as shown in FIG.

(A) is a perspective view which shows one Embodiment of the ceramic body for ferrite cores of this invention, (b) is a perspective view which shows the ceramic core formed by forming an electrode in the ceramic body for ferrite cores of the same figure (a). It is a figure and (c) is a perspective view which shows the common mode noise filter formed by winding conducting wire around the ferrite core of the figure (b). (A) is a plan view seen from the bottom showing one embodiment of the ferrite core of the present invention, (b) is a partial front view showing the legs of the ferrite core ceramic body of FIG. (C) is a partial front view showing a leg portion of a ferrite core formed by forming an electrode on the ferrite core ceramic body of FIG. (A)-(c) is a partial front view which shows the leg part in various embodiment of the ceramic body for ferrite cores of this invention. (A), (b) is a fragmentary perspective view which shows the leg part in various embodiment of the ceramic body for ferrite cores of this invention. It is a perspective view which shows the leg part of the conventional ceramic body for ferrite cores. (A) is a front view for measuring plating elongation in the leg part of the ferrite core of this invention, (b) is a front view for measuring plating elongation in the leg part of the conventional ferrite core. (A)-(c) shows the common mode noise filter using the conventional ferrite core, (a) is a front view, (b) is the top view seen from the bottom face, (c) is a side view.

Explanation of symbols

1: collar part 2: leg part 2A: sectional area 2B at step part: sectional area at boundary with collar part 3: step part 4: electrode 5: winding core part 6: ferrite core 7: conductor 8: length of electrode 9: Electrode thickness 10: Step length 11: Step depth B: Core width

Claims (6)

A ferrite core ceramic body comprising a core part for winding a conducting wire, a flange part formed at both ends of the core part, and a plurality of leg parts provided continuously to the flange part, A ferrite core ceramic body characterized by having at least one step portion over the entire circumference of each leg portion and having a cross-sectional area at a step portion of each leg portion equal to or less than a cross-sectional area at the boundary with the flange portion. 2. The ceramic body for a ferrite core according to claim 1, wherein an area of a bottom surface of each leg portion is minimum. The ferrite body ceramic body according to claim 1 or 2, wherein a ridge line portion of each leg portion is curved. The ferrite core characterized by forming the electrode in the edge part by the side of the bottom face of each leg part in the ceramic body for ferrite cores in any one of Claims 1-3. 5. The ferrite core according to claim 4, wherein the electrodes of the respective leg portions have substantially the same height in the axial direction of the leg portion. A common mode noise filter comprising a ferrite core according to claim 4 or 5 wound with a conducting wire.

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