Method of manufacturing multilayer-type chip inductors

[0002] This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 9-39153 filed in Japan on Feb. 24, 1997, the entire content of which is hereby incorporated by reference.

[0003] 1. Field of the Invention

[0004] The present invention relates to a method of manufacturing a multilayer-type chip inductor, and in particular, a multilayer-type chip inductor having a small DC resistance.

[0005] 2. Description of the Related Art

[0006] A method of reducing the DC resistance of a multilayer-type chip inductor involves increasing the cross-sectional area of an internal conductor. In order to increase the cross-sectional area of an internal conductor, the width and the thickness of the internal conductor may be increased. If the width of the internal conductor is increased, however, the inductance decreases. Increasing the cross-sectional area of the internal conductor also may cause various manufacturing problems. Therefore, it is difficult in practice to increase the cross-sectional area of the internal conductor. For this reason, a coil comprising parallel internal conductors has been conceived as a method for decreasing the DC resistance of an inductor.

[0007] First, a multilayer-type chip inductor of a first conventional example in which coils are connected in parallel will be described with reference to FIGS. 4 and 5. FIG. 5 is a cross-sectional view of the device shown in FIG. 4.

[0008] With reference to both FIGS. 4 and 5, a multilayer-type chip inductor 1 is formed in such a way that green sheets 2ato 2ehaving electrode films 3ato 3eformed thereon, respectively, are multilayered in two upper and lower stages and sintered together. Further, external electrodes (not shown) are formed on both ends of this sintered body.

[0009] The first green sheets 2ato 2eare formed into sheets from an insulating ceramic slurry, such as ferrite or a dielectric. The electrode films 3ato 3e, which become internal conductors, are formed on one surface of the sheets by printing or like technique. Furthermore, in the first green sheets 2bto 2e, via holes 4bto 4eare provided at one end of each of the electrode films 3bto 3e. The upper and lower stages of first green sheets 2ato 2eare multilayered in sequence, causing the electrode films 3ato 3eto conduct in order to form two inductors 5. In parts of the electrode films 3aand 3e, one end of each film is extended to the end of each of the green sheets 2aand 2eso that it connects to and provides conduction with the external electrode (not shown), forming extension electrodes 6aand 6e, respectively.

[0010] The multilayer-type chip inductor 1 is obtained in the following way. As shown in FIG. 4, a predetermined number of dummy green sheets 2fon which no electrode film is formed are multilayered in sequence to form a bottom portion of the device. Next, the first green sheets 2ato 2econtaining the electrode films 3ato 3eon their respective top faces are multilayered on top of the dummy green sheets 2f. Further, in the same manner, another series of green sheets 2ato 2eare multilayered, and a predetermined number of dummy green sheets 2fare applied. Then, the body is contact-bonded and sintered. Then, external electrodes are formed at both ends (the right side and the left side in FIG. 4) of this sintered body.

[0011] Since the first green sheets 2ato 2eshown in FIG. 4 are formed with the electrode films 3ato 3eof a ¾ turn, respectively, two inductors 5 of 3.5 turns are formed inside the sintered body.

[0012] The external electrode on the right side is made to conduct with the extension electrodes 6aand 6aof the inductors 5 and 5, and the external electrode on the left side is made to conduct with the extension electrodes 6eand 6eof the inductors 5 and 5. Therefore, as shown in FIG. 5, the multilayer-type chip inductor 1 is such that the two upper and lower inductors 5 and 5 are connected in parallel.

[0013] Next, a multilayer-type chip inductor of a second conventional example comprising a coil of parallel internal conductors will be described with reference to FIGS. 6 and 7. Components in FIGS. 6 and 7 which are the same as those of the above-described first conventional example are given the same reference numerals and a detailed description thereof is omitted.

[0014] A multilayer-type chip inductor 11 is formed in such a way that first green sheets 2ato 2ehave electrode films 3ato 3eformed thereon, respectively. First green sheets 12ato 12eare similar to the first green sheets 2ato 2e. The green sheets 2ato 2eare alternately arranged (e.g., interleaved) in a multilayered fashion with the green sheets 12ato 12e. These multiple layers are then sintered, and then external electrodes (not shown) are formed at both ends of this sintered body.

[0015] The first green sheets 12ato 12eare formed into sheets from an insulating ceramic slurry in the same manner as the first green sheets 2ato 2e, and electrode films 13ato 13eare formed on one surface thereof. Further, in the first green sheets 12bto 12e, via holes 14bto 14eare formed at the ends of the electrode films 13bto 13e, respectively. In the first green sheets 12ato 12d, via holes 17ato 17dare provided at the other ends of the electrode films 13ato 13d, respectively.

[0016] The multilayer-type chip inductor 11 is obtained in the following way. As shown in FIG. 6, a predetermined number of dummy green sheets 2fare multilayered in sequence to from a bottom portion. Next, the first green sheets 2a, 12a, 2b, 12b, 2c, 12c, 2d, 12d, 2e, and 12eare multilayered on top of the bottom portion, with each surface having an electrode formed on its top side. Further, a predetermined number of dummy green sheets 2fare applied on top of the body, and then the body is contact-bonded and sintered. Then, external electrodes are formed at both ends (the right side and the left side in FIG. 6) of this sintered body.

[0017] Therefore, in the multilayer-type chip inductor 11, an inductor 15 of 3.5 turns which is made to branch into two lines via the respective via holes is formed within the multilayered body. The external electrode on the right side is made to conduct with the extension electrodes 6aand 16aof the inductor 15, and the external electrode on the left side is made to conduct with extension electrodes 6eand 16eof the inductor 15.

[0018] However, in the above-described conventional first and second examples, although the DC resistance of the inductor is reduced, the following problems are present. In the first conventional example, because the decrease in inductance is large, the number of windings of the coil must be increased to maintain the inductance at a desired value. In the second conventional example, although the decrease in inductance is small, the number of via holes corresponding to via holes 17ato 17dprovided in the first green sheets 12ato 12dand the number of types of first green sheets increases, causing the manufacturing process to become more complex.

[0019] An object of the present invention is to solve at least the above-described problems. More specifically, an object of the present invention is to provide a method of manufacturing a multilayer-type chip inductor such that the DC resistance of the inductor is small without decreasing the inductance and the impedance.

[0020] To achieve the above-described object, according to the present invention, there is provided a method of manufacturing a multilayer-type chip inductor, comprising the steps of: preparing a ceramic green sheet; forming an electrode film on one surface of the green sheet; multilayering a plurality of the green sheets in such a way that the surfaces having electrode films formed thereon face each other for pairs of the green sheets; contact-bonding the green sheets; and sintering the green sheets.

[0021] More specifically, the present invention provides a method of manufacturing a multilayer-type chip inductor, comprising the steps of: preparing a ceramic green sheet; overlaying a first green sheet having a coil-like electrode film of less than one complete turn formed on one surface of the green sheet and a second green sheet having formed thereon a coil-like electrode film which is symmetrical with the first green sheet so that the electrode films face each other in order to be formed into a pair; multilayering a plurality of such pairs of the green sheets; and sintering the green sheets, wherein the respective coil-like electrode films are made to conduct by via holes provided at the ends of the coil-like electrode films, thereby forming an inductor.

[0022] Preferably, the ceramic is an insulating ceramic.

[0023] The method of manufacturing a multilayer-type chip inductor further includes a step of forming external electrodes which conduct to the ends of the inductor before or after being sintered.

[0024] As a result, as in the first and second conventional examples, it is possible to increase the cross-sectional area of the conductor and to reduce the DC resistance of the inductor. In the present invention, however, the design does not result in a decrease in the inductance and the impedance. Further, the manufacturing method of the present invention is less complex than the manufacturing method of the above-described second conventional example (e.g., because it reduces the number of via holes required).

[0025] The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which:

[0026] FIG. 1 is a perspective view illustrating a method of manufacturing a multilayer-type chip inductor before multilayering according to an exemplary embodiment of the present invention;

[0027] FIG. 2 is a perspective view of the multilayer-type chip inductor shown in FIG. 1;

[0028] FIG. 3 is a longitudinal sectional view taken along the plane A of the multilayer-type chip inductor shown in FIG. 2;

[0029] FIG. 4 is a perspective view of a multilayer-type chip inductor of a first conventional example before multilayering;

[0030] FIG. 5 is a longitudinal sectional view corresponding to FIG. 3 of the multilayer-type chip inductor of the first conventional example;

[0031] FIG. 6 is a perspective view of a multilayer-type chip inductor of a second conventional example before multilayering; and

[0032] FIG. 7 is a longitudinal sectional view corresponding to FIG. 3 of the multilayer-type chip inductor of the second conventional example.

[0033] The preferred embodiment of the present invention will be described below in detail with reference to FIGS. 1 to 3. Components which are the same as those of the above-described conventional examples are given the same reference numerals. Detailed description of these common components is omitted.

[0034] A multilayer-type chip inductor 21 is formed in such a way that each one of first green sheets 2ato 2ehas electrode films 3ato 3eformed respectively thereon, and each one of second green sheets 22ato 22ehas electrode films 23ato 23eformed respectively thereon. These green sheets are alternately multilayered and sintered. External electrodes 28 and 29 are formed at both ends of this sintered body.

[0035] In the same manner as the first green sheets 2ato 2e, the second green sheets 22ato 22eare formed into sheets from an insulating ceramic slurry, such as ferrite or a dielectric or other suitable material. These sheets have electrode films 23ato 23e, which become internal conductors, respectively formed by printing or other suitable technique on one surface thereof. The respective electrode films 23ato 23eare formed symmetrically with respect to the electrode films 3ato 3ewhen they face the electrode films 3ato 3e. Further, in the second green sheets 22ato 22d, via holes 24ato 24dare formed at one end of each of the electrode films 23ato 23e. In parts of the electrode films 23aand 23e, one end of each film is extended to the ends of the green sheets 22aand 22eso as to conduct to the external electrodes, forming extension electrodes 26aand 26e.

[0036] The multilayer-type chip inductor 21 is obtained in the following way. As shown in FIG. 1, a predetermined number of dummy green sheets 2f, on the surface of which no electrode film is formed, are multilayered in sequence to form a bottom portion of the device. Next, the first green sheet 2a, the second green sheet 22a, the first green sheet 2b, the second green sheet 22b, . . . the first green sheet 2e, and the second green sheet 22eare overlaid and multilayered in such a way that each pair of electrode films (the electrode film 3aand the electrode film 23a, . . . the electrode film 3eand the electrode film 23e) face each other. Further, a predetermined number of dummy green sheets 2fare multilayered on top of the body, and then the body is contact-bonded and sintered. Then, external electrodes 28 and 29 are formed at both ends of this sintered body. Alternatively, the external electrodes can be applied before sintering.

[0037] Since the first green sheets 2ato 2eand the second green sheets 22ato 22eshown in FIG. 1 are formed with the electrode films 3ato 3eand the electrode films 23ato 23eof a ¾ turn, respectively, in the multilayer-type chip inductor 21, an inductor 25 of 3.5 turns is formed inside the multilayered body. One external electrode 28 is made to conduct with the extension electrodes 6aand 6aof the inductor 25, and the other external electrode 29 is made to conduct to the extension electrodes 6eand 6eof the inductor 25.

[0038] Therefore, in the multilayer-type chip inductor 21, as shown in FIG. 3, an inductor 25, whose internal conductor is thicker than the thickness of the internal conductor of the multilayer-type chip inductors 1 and 11 shown in FIGS. 5 and 7, that is, having a larger cross-sectional area, is formed inside the multilayered body.

[0039] The multilayer-type chip inductor in accordance with the multilayer-type manufacturing method of the present invention is not limited to this embodiment, and various modifications are possible within the spirit and scope of the invention. For example, although an electrode film of a ¾ turn is shown, in addition to this, the electrode film may be of a ½ turn. Further, the shape of the electrode film is not limited to a coil shape, and may be a rectangular parallelepiped which connects the section between the two external electrodes by a straight line.

[0040] Further, the total number of windings of the inductor may be changed to any desired number of windings by increasing or decreasing the number of multilayers of the first and second green sheets.

[0041] As described above, in the method of manufacturing a multilayer-type chip inductor according to the present invention, since green sheets are multilayered so that surfaces on which electrode films are formed face each other in order to form an inductor, the thickness of the internal conductor is large, and the cross-sectional area increases accordingly.

[0042] Therefore, in the multilayer-type chip inductor according to the present invention, it is possible to reduce the DC resistance of the inductor without decreasing the inductance or the impedance. Further, the multilayer-type chip inductor according to the present invention becomes capable of withstanding a high-current load, and the allowable current value increases.

[0043] Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiment described in this specification. To the contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention as hereafter claimed. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications, equivalent structures and functions.