Inductor and method for producing the same

<u>BACKGROUND OF THE INVENTION</u>

1. Field of the Invention:

0001The present invention relates to a ceramic chip inductor and a method for producing the same, and in particular, a lamination ceramic chip inductor used in a high density circuit and a method for producing the same.

2. Description of the Related Art:

0002Recently, lamination ceramic chip inductors are widely used in high density mounting circuits, which have been demanded by size reduction of digital devices such as devices for reducing noise.

0003As an example of the conventional art, a method for producing a conventional lamination ceramic chip inductor described in Japanese Laid-Open utility Model Publication No. 59-145009 will be described.

0004On each of a plurality of magnetic gareensheets, a conductive pattern formed of a conductive paste of less than one turn is printed. The plurality of magnetic greensheets are laminated and attached by pressure to form a lamination body. The conductive lines on the magnetic greensheets are electrically connected with each other sequentially via a through-hole formed in the magnetic sheets to form a conductive coil. The lamination body is sintered entirely to produce a lamination ceramic chip inductor.

0005Such a lamination ceramic chip inductor requires a larger number of turns of the conductive coil and thus a larger number of greensheets in order to have a higher impedance or inductance.

0006An increase in the number of greensheets requires a larger number of lamination steps and thus raises production cost. In addition, such an increase raises the number of the points of connection between the conductive patterns on the greensheets, thus reducing the reliability of connection.

0007A solution to these problems is proposed in Japanese Laid-Open Patent Publication No. 4-93006. A lamination ceramic chip inductor disclosed in this publication is produced in the following manner.

0008On each of a plurality of magnetic sheets, a conductive pattern of more than one turn is formed using a thick film printing technology, and the plurality of magnetic sheets are laminated. The conductive patterns on the magnetic sheets are electrically connected to each other sequentially via a through-hole formed in advance in the magnetic sheets. A lamination ceramic chip inductor produced in this manner has a relatively large impedance even if the number of the magnetic sheets is relatively small.

0009Such a lamination ceramic chip inductor produced using a thick film technology has the following two disadvantages. <ul id="ul0001" list-style="none"><li>(1) In the production of a lamination ceramic chip inductor having an outer profile as small as, for example, 2.0 mm × 1.25 mm or 1.6 mm × 0.8 mm using a thick film printing technology, the number of turns of each conductive pattern is approximately 1.5 at the maximum for practical use with the production yield and the like considered. In order to produce an inductor having a larger impedance, the number of the magnetic sheets needs to be increased.</li><li>(2) In order to increase the number of turns in one magnetic sheet, the width of each conductive pattern needs to be reduced. Since a reduced width of the conductive pattern increases the resistance thereof, the thickness of the conductive pattern needs to be increased. However, in order to maintain the printing resolution, the thickness of the conductive pattern needs to be reduced as the width thereof is decreased. For example, when the width is 75 µm, an appropriate thickness of the conductive pattern when being dry is approximately 15 µm at the maximum.</li></ul>

0010From the above description, it is appreciated that increasing the number of turns of each conductive pattern is not practical although effective to some extent in reducing the number of the magnetic sheets.

0011In order to reduce the resistance of the conductive pattern, Japanese Laid-Open Patent Publication No. 3-219605 discloses a method by which a greensheet is grooved, and the groove is filled with a conductive paste to increase the thickness of the conductive pattern. However, it is difficult to mass-produce a grooved greensheet in a complicated pattern.

0012Japanese Laid-Open Patent Publication No. 60-176208 also discloses a method for reducing the resistance of the conductive pattern of a lamination body having magnetic layers and conductive patterns each of approximately a half turn alternately laminated. In this method, the conductive patterns to be formed into a conductive coil are formed by punching a metal foil. However, it is difficult to punch out a pattern with sufficient precision to fit into a microscopic planar area as demanded by the recent size reduction of various devices. In fact, it is impossible to obtain a complicated coil pattern having one or more turns by punching. Further, it is difficult to arrange a plurality of metal foils obtained by punching on a magnetic sheet at a constant pitch with high precision. Moreover, when the metal foils adjacent to each other are connected with a magnetic sheet interposed therebetween, defective connection can undesirably occur unless the connection technology is sufficiently high.

0013A solution to the above-described problems from a different point view is disclosed in Japanese Patent Publication No. 64-42809 and Japanese Laid-Open Patent Publication 4-314876. In these publications, a metal thin layer formed on a film is transferred onto a ceramic greensheet to produce a lamination ceramic capacitor.

0014In detail, on a releasable metal thin layer formed on a film by evaporation, a desired metal layer is formed by wet plating. When necessary, an extra portion of the metal layer is removed by etching. The resultent pattern is transferred onto a ceramic greensheet.

0015Such a transfer method can be applied to transfer a conductive coil onto a magnetic greensheet in the following manner to produce a lamination ceramic chip inductor.

0016A relatively thin metal layer (having a thickness of, for example, 10 µm or less) formed on a film is etched using a photoresist to form a fine conductive coil pattern (having a width of, for example, 40 µm and a space between lines of, for example, 40 µm). The resultant coil is then transferred onto a magnetic greensheet. In this manner, a lamination ceramic chip inductor for having a large impedance can be produced.

0017By the above-described transfer method, it is difficult to produce a relatively thick conductive coil having a pattern to be transferred (having a thickness of, for example, 10 µm or more) for the following reason.

0018By the transfer method using wet plating, the metal layer which is once formed on the entire surface of a film is patterned by removing an unnecessary portion. Accordingly, production of a complicated coil pattern becomes more difficult as the thickness of the metal film increases.

0019Further, since the desired pattern is obtained under the photoresist, the photoresist needs to be removed before the transfer. When the photoresist is removed, the conductive coil pattern may also be undesirably removed. Such a phenomenon becomes easier to occur ae the thickness of the metal layer increases. The reason is that: as the thickness of the metal layer increases, etching takes a longer period of time and thus the thin metal film is exposed to the etchant to a higher degree.

0020For the above-described reasons, the transfer method cannot provide a lamination ceramic chip inductor having a low resistance.

0021Reference is also made to JP-A-6089811, which describes a method for forming a thin film type inductor/transformer, to obtain a device in which a soft magnetic oxide film is not peeled and cracks are not generated at the time of baking. After spiral type coils are screen-printed on a green sheet for a ceramic substrate, ceramic soft magnetic oxide composite layers are screen printed by using solution composed of ceramic particles and soft magnetic particles. Green sheets of soft magnetic oxide films are laminated on the layers and baked. Since the percentage of contraction of the ceramic soft magnetic oxide composite layers is in the range between that of the ceramic substrate and that of the soft magnetic oxide films, peeling and cracking due to the difference in percentage of contraction at the time of baking is said to be prevented.

0022Reference is also made to US-A-3798059 which describes a thick film inductor suitable for hybrid integrated circuits. The inductor comprises successive layers of powdered sintered ferromagnetic material in a cured catalyst-hardenable resin binder and a pattern of conductors comprising powdered metal in a cured catalyst hardenable resin.

SUMMARY OF THE INVENTION

0023In one aspect, the invention provides a method of producing a lamination ceramic chip inductor, comprising the steps of: <ul id="ul0002" list-style="none" compact="compact"><li>forming a conductive pattern on a conductive base plate by electroforming, said base plate having a surface roughness so that said conducive pattern has a releasable capability;</li><li>forming a first and a second insulating layer having a surface with a desired surface tackiness by providing a film , coating said film with a ferrite paste, drying said paste so as to obtain said desired tackiness,</li><li>transferring the electroformed conductive pattern onto said surface of said first insulation layer by first pressing said base plate to said first insulating layer and by then peeling off said insulating layer and said conductive pattern from said base plate; and</li><li>laminating said second insulation layer onto the surface of the first insulation layer comprising the electroformed conductive pattern.</li></ul>

0024In a second related aspect, the invention provides a method of producing a lamination ceramic chip inductor, comprising the steps of: <ul id="ul0003" list-style="none" compact="compact"><li>forming a conductive pattern on a conductive base plate by electroforming, said base plate having a surface roughness of 0.05 to 1 µm so that said conducive pattern has a releasable capability;</li><li>forming a first and a second insulating layer having a surface with a desired surface tackiness by providing a film, coating said film with a ferrite paste, drying said paste so as to obtain said desired tackiness,</li><li>adhering a thermally releasable foam sheet on the surface of the conducive base plate having the electroformed conductive pattern by heating and foaming;</li><li>peeling off the thermally releasable foam sheet and the electroformed conductive pattern from the conducive base plate;</li><li>applying said surface of said first insulating layer to said thermally releasable foam,</li><li>peeling off the thermally releasable foam sheet by heating thus transferring said electroformed conductive pattern to said surface of said first insulating layer,</li><li>laminating said second insulation layer onto the surface of the first insulation layer comprising the electroformed conductive pattern.</li></ul>

0025A lamination ceramic chip inductor formed using the method of the present invention includes a conductive pattern formed by electroforming. Accordingly, the thickness of the conductive pattern can be sufficient to obtain a sufficiently low resistance, and the width of the conductive pattern can be adjusted with high precision.

0026In contrast to a thick film conductive pattern formed by printing or the like, the conductive pattern formed according to the method of the present invention is shrunk in the thickness direction only slightly by sintering. Thus, the magnetic sheet and the conductive patterns are scarcely delaminated from each other.

0027Thus, the invention described herein makes possible the advantages of providing a lamination ceramic chip inductor including a relatively small number of sheets, a sufficiently high impedance, and a low resistance of the conductive coil; and a method for producing the same.

0028These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

0029<ul id="ul0004" list-style="none"><li>Figure <b>1</b> is an exploded isometric view of a lamination ceramic chip inductor in a first example according to the present invention;</li><li>Figures <b>2</b> through <b>5</b> are cross sectional views illustrating a method for producing the lamination ceramic chip inductor shown in Figure 1;</li><li>Figure <b>6</b> is an isometric view of the lamination ceramic chip inductor produced in a method shown in Figures <b>2</b> through <b>5.</b></li><li>Figure <b>7</b> is an exploded isometric view of a lamination ceramic chip inductor in second, fifth and sixth examples according to the present invention;</li><li>Figure <b>8</b> is an exploded isometric view of a lamination ceramic chip inductor in a third example according to the present invention;</li><li>Figure <b>9</b> is an exploded isometric view of a lamination ceramic chip inductor in a fourth example according to the present invention;</li><li>Figure <b>10</b> is a cross sectional view illustrating a step for producing the lamination ceramic chip inductor in the fifth example;</li><li>Figure <b>11A</b> through <b>11E</b> are cross sectional views illustrating a method for producing the lamination ceramic chip inductor in the sixth example;</li><li>Figure <b>12</b> is an exploded isometric view of a lamination ceramic chip inductor in a seventh example according to the present invention;</li><li>Figure <b>13</b> is an isometric view illustrating a modification of the lamination ceramic chip inductor in the first example;</li><li>Figure <b>14</b> is a schematic illustration of a method for producing a lamination ceramic chip inductor in a comparative example;</li><li>Figure <b>15</b> is an exploded isometric view of a lamination ceramic chip inductor in an eighth example according to the present invention; and</li><li>Figures <b>16A</b>, <b>16B</b>, <b>17A</b> and <b>17B</b> are cross sectional views illustrating a method for producing the lamination ceramic chip inductor in the eighth example.</li></ul>

<u>DESCRIPTION OF THE PREFERRED EMBODIMENTS</u>

0030Hereinafter, the present invention will be described by way of illustrative examples with reference to the accompanying drawings.

Example 1

0031A lamination ceramic chip inductor <b>100</b> in a first example according to the present invention will be described with reference to Figures <b>1</b> through <b>6</b>. Figure <b>1</b> is an exploded isometric view of the lamination ceramic chip inductor (hereinafter, referred to simply as an "inductor") <b>100.</b>

0032In all the accompanying figures, only one lamination body to be formed into one inductor is illustrated for simplicity. In actual production, a plurality of lamination bodies are formed on one plate and separated after the lamination bodies are completed.

0033The inductor <b>100</b> shown in Figure <b>1</b> includes a plurality of magnetic sheets <b>1</b>, <b>3</b> and <b>6,</b> and a plurality of coil-Shaped plated conductive pattern (hereinafter, referred to simply as "conductive patterns") <b>2</b> and <b>5.</b>

0034The conductive patterns <b>2</b> and <b>5</b> are each formed by electroforming; namely, a resist film is formed on a base plate to expose a desired pattern and immersing the base plate in a plating bath. The magnetic sheets <b>1</b> and <b>6</b> respectively have the conductive patterns <b>2</b> and <b>5</b> transferred thereon. The conductive patterns <b>2</b> and <b>5</b> are connected to each other via a through-hole <b>4</b> formed in the magnetic sheet <b>3.</b>

0035A method for producing the inductor <b>100</b> will be described.

[Formation of the conductive patterns]

0036First, how to form the conductive patterns <b>2</b> and <b>5</b> will be described with reference to Figure <b>2.</b>

0037A stainless steel base plate <b>8</b> is entirely treated by strike plating (plating at a high speed) with Ag to form a conductive release layer <b>9</b> having a thickness of approximately 0.1 µm or less. The strike plating is performed by immersing the base plate <b>8</b> in an alkaline AgCN bath, which is generally used. An exemplary composition of an alkaline AgCN bath is shown in Table 1. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">AgCN</entry><entry namest="col2" nameend="col2" align="left">3.8 to 4.6 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">KCN</entry><entry namest="col2" nameend="col2" align="left">75 to 90 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">Liquid temperature</entry><entry namest="col2" nameend="col2" align="left">20 to 30°C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Current density</entry><entry namest="col2" nameend="col2" align="left">1.6 to 3.0 A/dm²</entry></row></tbody></tgroup></table></tables>

0038When the bath shown in Table 1 is used, a release layer having a thickness of approximately 0.1 µm is formed after approximately 5 to 20 seconds.

0039One probable reason that the release layer <b>9</b> has releasability is: since an Ag layer is formed by highspeed plating (strike plating) on the stainless steel base plate <b>8</b> having a low level of adherence with Ag, the resultant Ag layer (the release layer <b>9</b>) becomes highly strained and thus cannot be sufficiently adhered with the base plate <b>8</b>.

0040In order to obtain an optimum level of releasability between the release layer <b>9</b> and the base plate <b>8</b>, the surface of the base plate <b>8</b> is preferably roughened to have a surface roughness (Ra) of approximately 0.05 µm to approximately 1 µm. The surface roughness (Ra) is measured by a surface texture analysis system using, for example, Dektak 3030ST (produced by Sloan Technology Corp). The surface is roughened by acid treatment, blasting or the like.

0041In the case where the surface roughness (Ra) is less than approximately 0.05 µm, the adherence between the release layer <b>9</b> and the base plate <b>8</b> is insufficient, and thus the release layer <b>9</b> is possibly delaminated during the later process. In the case where the surface roughness (Ra) is more than approximately 1 µm, the adherence between the release layer <b>9</b> and the base plate <b>8</b> is excessive. Thus, the release layer <b>9</b> cannot be satisfactorily transferred onto the magnetic sheet, or the resolution of a plating reaiat pattern <b>11</b> formed in the following step (described below) is lowered.

0042Appropriate roughening the surface of the base plate <b>8</b> has such side effects that the adherence of the plating resist pattern <b>11</b> on the release layer <b>9</b> is improved and that the release layer <b>9</b> is prevented from being released from the base plate <b>8</b> during removal of the plating resist pattern <b>11</b>.

0043The release layer <b>9</b> can also be formed by silver mirror reaction.

0044The base plate <b>8</b> can be formed of an electrically conductive material other than stainless steel and processed to have releasability. Exemplary materials which can be used for the base plate <b>8</b> and the respective methods for providing the base plate <b>8</b> with releasability are shown in Table 2. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Usable metal</entry><entry namest="col2" nameend="col2" align="left">Method for providing releasability</entry></row><row><entry namest="col1" nameend="col1" align="left">Iron-nickel-type metal</entry><entry namest="col2" nameend="col2" align="left">Anodizing with NaOH(10%) to form an excessively thin oxide film.</entry></row><row><entry namest="col1" nameend="col1" align="left">Copper-nickel-type metal</entry><entry namest="col2" nameend="col2" align="left">Immersing in potassium bichromate to form a chromate film.</entry></row><row><entry namest="col1" nameend="col1" align="left">Aluminum</entry><entry namest="col2" nameend="col2" align="left">Immersing in a zinc substitution liquid to form a zincate.</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Copper, brass</entry><entry namest="col2" nameend="col2" align="left">Immersing a 0.5% solution of selenium dioxide</entry></row></tbody></tgroup></table></tables>

0045Instead of metal, the base plate <b>8</b> can be formed of a printed circuit board having a copper foil laminated thereon, or a polyethyleneterephthalate (hereinafter, referred to as "PET") film or the like provided with conductivity. The same effects are obtained as by metal, but a metal plate is more efficient since it is not necessary to provide a metal plate with conductivity.

0046Especially, stainless steel is chemically stable and has satisfactory releasability due to a chrome oxide film existent on a surface thereof. Thus, stainless steel is the easiest to use from among the usable materials.

0047After the release layer <b>9</b> is formed, a photoresist film is formed on the release layer <b>9</b> and pre-dried. Then, a photomask having a width of approximately 70 µm and approximately 2.5 turns is formed on each of unit areas of the photoresist film. Each unit area has a size of 2.0 mm × 1.25 mm. The photomask has such a pattern as to form a desirable conductive pattern depending on the type of photoresist (i.e., positive-type or negative-type). The photoresist film having a photomask thereon is exposed to light and developed to form the plating resist pattern <b>11</b> having a thickness T = 55 µm.

0048As the photoresist, various kinds (liquid, paste, dry film) or the like can be used. A dry film has a uniform thickness and thus controls the thickness of the conductive patterns with relatively high precision, but is preferably used for forming a conductive pattern having a width of approximately 50 µm or more with the sensitivity thereof being considered. With a liquid photoresist, a plating resist pattern having a width as small as several microns can be obtained. With a paste photoresist, which is the photoresist most generally used, a plating resist pattern having a width of approximately 40 µm and a thickness of approximately 30 to 40 µm can be obtained. In detail, for example, a plating resist pattern having approximately five turns can be easily formed on a unit area of approximately 2.0 mm × 1.25 mm, and a plating resist pattern having approximately three turns can be easily formed on a unit area of approximately 1.6 mm × 0.8 mm. The photoresist can be formed by printing, spin-coating, roll-coating, dipping, laminating or the like, depending on the kind of the photoresist.

0049The exposure is performed by an exposure device emitting collimated ultraviolet light rays, and conditions such as exposure time and the light intensity are determined in accordance with the photoresist used.

0050Development is performed using a developer suitable for the photoresist used. When necessary, exposure to ultraviolet or post-curing is performed after the development to improve the resistance against chemicals.

0051After the plating resist pattern <b>11</b> is formed, the lamination body is immersed in the Ag electroplating bath to form an Ag conductive pattern <b>10</b> having a necessary thickness t, which will be transferred on the magnetic sheet. In this example, the Ag conductive pattern <b>10</b> has a thickness t of approximately 50 µm. An alkaline Ag bath, which is the type generally used as the Ag electroplating bath, cannot be used because the Ag bath removes the plating resist pattern <b>11</b>. Accordingly, a weak alkaline, neutral, or acid Ag plating bath is required as the Ag electroplating bath. An exemplary composition of a weak alkaline or neutral Ag plating bath is shown in Table 3. <tables id="tabl0003" num="0003"><table frame="all"><title>Table 3</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">KAg(CN)₂</entry><entry namest="col2" nameend="col2" align="center">30 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">KSCN</entry><entry namest="col2" nameend="col2" align="center">330 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">Potassium citrate</entry><entry namest="col2" nameend="col2" align="center">5 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">pH</entry><entry namest="col2" nameend="col2" align="center">7.0 to 7.5</entry></row><row><entry namest="col1" nameend="col1" align="left">Liquid temperature</entry><entry namest="col2" nameend="col2" align="center">Room temperature</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Current density</entry><entry namest="col2" nameend="col2" align="center">2.0 A/dm² or less</entry></row></tbody></tgroup></table></tables>

0052The pH value of the Ag plating bath is adjusted by ammonia and a citrate. As a result of various experiments, it has been found that plating resist pattern <b>11</b> formed of most kinds of photoresist is removed by a plating bath having a pH value of more than 8.5. Accordingly, the pH value of the plating bath is preferably set to be 8.5 or less.

0053An exemplary composition of an acid Ag plating bath is shown in Table 4. <tables id="tabl0004" num="0004"><table frame="all"><title>Table 4</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">AgCl</entry><entry namest="col2" nameend="col2" align="left">12 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">Na₂S₂O₃</entry><entry namest="col2" nameend="col2" align="left">36 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">NaHSO₃</entry><entry namest="col2" nameend="col2" align="left">4.5 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">NaSO₄</entry><entry namest="col2" nameend="col2" align="left">11 g/ℓ</entry></row><row><entry namest="col1" nameend="col1" align="left">pH</entry><entry namest="col2" nameend="col2" align="left">5.0 to 6.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Liquid temperature</entry><entry namest="col2" nameend="col2" align="left">20 to 30°C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Current density</entry><entry namest="col2" nameend="col2" align="left">1.5 A/dm² or less</entry></row></tbody></tgroup></table></tables>

0054The plating bath shown in Table 4 does not remove the plating resist pattern <b>11</b> because of being acid. When an acid Ag plating bath containing a surfactant (methylimidazolethiol, furfural, turkey-red oil, or the like) is used, the brilliance and the smoothness of the surface of the Ag conductive pattern <b>10</b> are improved.

0055In this example, the weak alkaline or neutral Ag plating bath shown in Table 3 is used. The pH value is 7.3, and the current density for plating is approximately 1 A/dm². The current density is set to be such a value because an excessively high current density required for accelerating a plating speed causes strain of the Ag conductive pattern <b>10</b>, thus possibly removing the Ag conductive pattern <b>10</b> before being transferred.

0056The Ag conductive pattern <b>10</b> having a thickness of approximately 50 µm is obtained after immersing the base plate <b>8</b> in the plating bath for approximately 260 minutes.

0057In this example, the release layer <b>9</b> is formed by strike-plating the base plate <b>8</b> in an alkali Ag bath. Alternatively, the base plate <b>8</b> can be immersed in a weak alkaline, neutral, or acid bath. In this case, a sufficiently high current density is used for the first several minutes in order to strain the Ag conductive pattern <b>10</b> sufficiently to provide an area of the Ag conductive pattern <b>10</b> in the vicinity of the surface of the stainless steel base plate <b>8</b> with releasability. Accordingly, it is not necessary to form the release layer <b>9</b>. Figure <b>3</b> shows a cross section of the lamination body formed in this manner.

0058After the Ag conductive pattern <b>10</b> is formed, the plating resist pattern <b>11</b> is removed as is shown in Figure 4, using a removing liquid suitable for the photoresist used. Usually, the removal is performed by immersing the lamination body in an approximately 5% solution of NaOH having a temperature of approximately 40°C for approximately 1 minute.

0059After the plating resist pattern <b>11</b> is removed, the release layer <b>9</b> is treated by soft etching for a short period of time (several seconds) with a 5% solution of nitric acid to leave the Ag conductive pattern <b>10</b> on the base plate <b>8</b> as is shown in Figure <b>5</b>. The lamination of the release layer <b>9</b> and the Ag conductive pattern <b>10</b> corresponds to the conductive patterns <b>2</b> and <b>5.</b> As the soft etchant, a sulfuric acid bath of chromic anhydride, a hydrochloric acid bath of an iron chloride (FeCl₂), or the like can be also used. Since soft etching is performed only for several seconds, the release layer beneath the Ag conductive pattern <b>10</b> is not removed. Thus, the Ag conductive pattern <b>10</b> is not removed.

[Formation of the magnetic sheets]

0060Hereinafter, a method for forming the magnetic sheets <b>1</b>, <b>3</b> and <b>6</b> will be described.

0061A resin such as a butyral resin, an acrylic resin or ethylcellulose, and a plasticizer such as dibutylphthalate are dissolved in an alcohol having a low boiling point such as isopropylalcohol or butanol, or in a solvent such as toluene or xylene to obtain a vehicle. The vehicle and a Ni·Zn·Cu type ferrite powder having an average diameter of approximately 0.5 to 2.0 µm are kneaded together to form a ferrite paste (slurry). A PET film is coated with the ferrite paste using a doctor blade and then dried at 80 to 100°C until slight tackiness is left.

0062The magnetic sheets <b>1</b> and <b>6</b> are each formed to have a thickness of 0.3 to 0.5 mm, and the magnetic sheet <b>3</b> is formed to have a thickness of 20 to 100 µm. Then, the magnetic sheet <b>3</b> is punched to form the through-hole <b>4</b> having a side which is approximately 0.15 to 0.3 mm long.

[Transfer of the conductive patterns]

0063Next, a method for transferring the conductive patterns <b>2</b> and <b>5</b> on the magnetic sheets <b>1</b> and <b>6</b> and laminating the magnetic sheets <b>1</b>, <b>3</b> and <b>6</b> will be described.

0064The base plate <b>8</b> having the conductive pattern <b>2</b> is pressed on the magnetic sheet <b>1</b> formed on the PET film. When necessary, pressure and heat are provided. In an alternative manner, the magnetic sheet <b>1</b> is released from the PET film and the base plate <b>8</b> having the conductive pattern <b>2</b> is pressed on a surface of the magnetic sheet <b>1</b> having tackiness (the surface which has been in contact with the PET film).

0065The conductive pattern <b>2</b> has appropriate releasability from the base plate <b>8</b> and also has appropriate adhesion (tackiness) with the magnetic sheet <b>1</b>. Thus, the conductive pattern <b>2</b> can be transferred on the magnetic sheet <b>1</b> easily by peeling off the magnetic sheet <b>1</b> from the base plate <b>8</b>.

0066In the case where the mechanical strength of the magnetic sheet <b>1</b> is insufficient, an additional strength can be provided by forming a viscous sheet on the magnetic sheet <b>1.</b>

0067In the same manner, the conductive pattern <b>5</b> is transferred on the magnetic sheet <b>6</b>.

0068The magnetic sheet <b>3</b> is located between the magnetic sheet <b>1</b> having the conductive pattern <b>2</b> and the magnetic sheet <b>6</b> having the conductive pattern <b>5.</b> The magnetic sheets <b>1</b>, <b>3</b> and <b>6</b> are laminated so that the conductive patterns <b>2</b> and <b>5</b> are connected to each other via the through-hole <b>4</b> to form a conductor coil. The adherence between the magnetic sheets <b>1</b>, <b>3</b> and <b>6</b> of the resultant lamination body are strengthened by heat (60 to 120°C) and pressure (20 to 500 kg/cm²), and thus the lamination body is formed into an integral body.

0069Connecting the two conductive patterns <b>2</b> and <b>5</b> through a thick film conductor provides better ohmic electric connection. Accordingly, a printed thick film conductor <b>7</b> is preferably provided in the through-hole <b>4</b> of the magnetic sheet <b>3</b> as is shown in Figure <b>13.</b>

0070Usually in the above-described process, a plurality of conductive patterns are formed on one magnetic sheet, and the magnetic sheets are laminated in the state of having the plurality of conductive patterns, in order to mass-produce inductors with higher efficiency. After the integral bodies are formed, the resultant greensheet is cut into a plurality of integral bodies, and each integral body is sintered at a temperature of 850 to 950°C for approximately 1 to 2 hours. The cutting can be performed after sintering.

0071An electrode of a silver alloy (for example, AgPd) is formed on each of two opposed side surfaces of each integral body and connected to the conductor coil. Then, the integral body is sintered at approximately 600 to 850°C to form outer electrodes <b>12</b> shown in Figure <b>6.</b> When necessary, the outer electrodes <b>12</b> are plated with nickel, solder or the like.

0072In this manner, the inductor <b>100</b> having an outer size of 2.0 mm × 1.25 mm and a thickness of approximately 0.8 mm is obtained. The conductor coil, which includes the two conductive patterns <b>2</b> and <b>5</b> each having 2.5 turns, has 5 turns in total. Accordingly, an impedance of approximately 700 Ω is obtained at a frequency of 100 MHz. The DC resistance can be as small as approximately 0.12 Ω because the thickness of the conductor coil is as much as approximately 50 µm.

0073The inductor <b>100</b> was cut for examination. No specific gap was found at the interfaces between the conductor coil and the magnetic sheets. The probable reason is that: in contrast to a conductor coil formed of thick film conductive patterns, the conductor coil produced by electroforming according to the present invention scarcely shrinks from sintering and thus is surrounded by the sintered magnetic body with a high density.

0074The material for the magnetic sheets used in the present invention is not limited to the one used in this example. Although a magnetic sheet is preferably used in order to obtain a high impedance, an insulation sheet having dielectricity can also be used.

Example 2

0075A lamination ceramic chip inductor <b>200</b> in a second example according to the present invention will be described with reference to Figure <b>7</b>. Figure <b>7</b> is an exploded isometric view of the inductor <b>200</b>.

0076The inductor <b>200</b> includes a plurality of magnetic sheets <b>13</b>, <b>15</b> and <b>18</b>, a coil-shaped plated conductive pattern <b>14</b> formed by electroforming and transferred onto the magnetic sheet <b>13</b>, and a thick film conductive pattern <b>17</b> printed on the magnetic sheet <b>15</b> having a through-hole <b>16.</b>

0077The conductive patterns <b>14</b> and <b>17</b> are connected to each other via the through-hole <b>16.</b>

0078A method for producing the inductor <b>200</b> will be described.

0079First, the plated conductive pattern <b>14</b> is produced by electroforming in the same manner as in the first example. In this example, the plated conductive pattern <b>14</b> having a width of approximately 40 µm, a thickness of approximately 35 µm, and approximately 3.5 turns is formed on an area of approximately 1.6 mm × 0.8 mm. The photoresist used for forming the plated conductive pattern <b>14</b> is of a paste type, is printable, and has high sensitivity.

0080Hereinafter, a method for forming the magnetic sheets <b>13, 15</b> and <b>18</b> will be described.

0081A resin such as a butyral resin, an acrylic resin or ethylcellulose, and a plasticizer such as dibutylphthalate are dissolved in a solvent having a high boiling point such as terpineol to obtain a vehicle. The vehicle and a Ni·Zn·Cu type ferrite powder having an average diameter of approximately 0.5 to 2.0 µm are kneaded together to form a ferrite paste. The ferrite paste is printed on a PET film using a metal mask and then dried at approximately 80 to 100°C until the thickness of the ferrite paste becomes approximately 0.3 to 0.5 mm. Thus, the magnetic sheets <b>13 and 18</b> are obtained. When necessary, printing and drying are repeated a plurality of times.

0082Alternatively, the magnetic sheets <b>13</b> and <b>18</b> can be obtained by laminating a plurality of magnetic sheets, each of which has a ferrite paste having a thickness of approximately 50 to 100 µm printed thereon and dried.

0083The magnetic sheet <b>15</b> is produced by forming a pattern having the through-hole <b>16</b> on a PET film by screen printing. The thickness of the magnetic sheet <b>15</b> is adjusted to be approximately 40 to 100 µm.

0084Next, a method for transferring the plated conductive pattern <b>14</b> on the magnetic sheet <b>13</b> will be described.

0085The base plate <b>8</b> having the plated conductive pattern <b>14</b> is pressed on the magnetic sheet 13 formed on the PET film. The pressure is preferably in the range of 20 to 500 kg/cm², and the heating temperature is preferably in the range of 60 to 120°C.

0086The plated conductive pattern <b>14</b> has appropriate releasability from the base plate <b>8</b> and also has appropriate adhesion with the magnetic sheet <b>13</b>. Further, the plated conductive pattern <b>14</b> has a relatively small width of 40 µm and thus is slightly buried in the magnetic sheet <b>13.</b> For these reasons, the plated conductive pattern <b>14</b> can be transferred on the magnetic sheet <b>13</b> easily by peeling off the magnetic sheet <b>13</b> from the base plate 8.

0087Alternatively, the plated conductive pattern <b>14</b> can be transferred by releasing the magnetic sheet <b>13</b> from the PET film and pressing the base plate <b>8</b> having the plated conductive pattern <b>14</b> on a surface of the magnetic sheet <b>13</b> film which has been in contact with the PET film as in the first example.

0088Then, the thick film conductive pattern <b>17</b> is printed on the magnetic sheet <b>15</b> having the through-hole <b>16</b>.

0089The magnetic sheet <b>13</b> having the plated conductive pattern <b>14</b> and the magnetic sheet <b>15</b> having the thick film conductive pattern <b>17</b> are laminated so that the conductive patterns <b>14</b> and <b>17</b> are connected to each other via the through-hole <b>16</b> to form a conductor coil. The magnetic sheet <b>18</b> is laminated on the magnetic sheet <b>15</b> having the thick film conductive pattern <b>17</b>, and the resultant lamination body is heated (60 to 120°C) and pressurized (20 to 500 kg/cm²) to be formed into an integral body.

0090Usually in the above-described process, a plurality of conductive patterns are formed on one magnetic sheet, and the magnetic sheets are laminated in the state of having the plurality of conductive patterns, in order to mass-produce inductors with higher efficiency. After the integral bodies are formed, the resultant greensheet is cut into a plurality of integral bodies, and each integral body is sintered at a temperature of 850 to 950°C for approximately 1 to 2 hours.

0091An electrode of a silver alloy (for example, AgPd) is formed on each of two opposed side surfaces of each integral body and connected to the conductor coil. Then, the integral body is sintered at approximately 600 to 850°C to form outer electrodes <b>12</b> shown in Figure 6. When necessary, the outer electrodes <b>12</b> are plated with nickel, solder or the like.

0092In this manner, the inductor <b>200</b> having an outer size of approximately 1.6 mm × 0.8 mm and a thickness of approximately 0.8 mm is obtained. The conductor coil, having a total number of turns of 3.5, includes the plated conductive pattern <b>14</b> having approximately 3.5 turns and the thick film conductive pattern <b>17.</b> Accordingly, an impedance of approximately 300 Ω is obtained at a frequency of 100 MHz. The DC resistance can be as small as approximately 0.19 Ω because the thickness of the conductor coil is as much as approximately 35 µm.

0093In the second example, the conductive coil includes only two conductive patterns <b>14</b> and <b>17</b>. When necessary, a plurality of coil-shaped conductive patterns <b>14</b> and a plurality of thick film conductive patterns <b>17</b> can be connected alternately.

0094Connection between the coil-shaped conductive pattern <b>14</b> and the thick film conductive pattern <b>17</b> is more reliable than the direct connection between coil-shaped conductive patterns. The probable reason is that: since the thick film conductive pattern is easily strained during the lamination, the lamination body is sintered in the state where the adherence between the coil-shaped conductive pattern and the thick film conductive pattern is strengthened.

Example 3

0095A lamination ceramic chip inductor <b>300</b> in a third example according to the present invention will be described with reference to Figure <b>8.</b> Figure <b>8</b> is an exploded isometric view of the inductor <b>300.</b>

0096The inductor <b>300</b> includes a plurality of magnetic sheets <b>19</b>, <b>21</b> and <b>24</b> and coil-shaped plated conductive patterns <b>20</b> and <b>23</b> formed by electroforming and respectively transferred on the magnetic sheets <b>19</b> and <b>24.</b>

0097The conductive patterns <b>20</b> and <b>23</b> are connected to each other via a through-hole <b>22</b> formed in the magnetic sheet <b>21.</b> The through-hole <b>22</b> is filled with a thick film conductor <b>25.</b>

0098A method for producing the inductor <b>300</b> will be described.

0099First, the conductive patterns <b>20</b> and <b>23</b> are produced by electroforming in the same manner as in the first example. In this example, the conductive patterns <b>20</b> and <b>23</b> each having a width of approximately 40 µm and a thickness of 35 µm are formed on an area of approximately 1.6 mm × 0.8 mm. The conductive pattern <b>20</b> has approximately 3.5 turns, and the conductive pattern <b>23</b> has approximately 2.5 turns. The photoresist used for forming the conductive patterns <b>20</b> and <b>23</b> is of a paste type, is printable, and has high sensitivity.

0100Hereinafter, a method for forming the magnetic sheets <b>19</b>, <b>21</b> and <b>24</b> will be described.

0101A resin such as a butyral resin, an acrylic resin or ethylcellulose, and a plasticizer such as dibutylphthalate are dissolved in a solvent having a high boiling point such as terpineol to obtain a vehicle. The vehicle and a Ni·Zn·Cu type ferrite powder having an average diameter of approximately 0.5 to 2.0 µm are kneaded together to form a ferrite paste. The ferrite paste is printed on a PET film using a metal mask and then dried at approximately 80 to 100°C until slight tackiness is left. Thus, the magnetic sheets <b>19</b> and <b>24</b> each having a thickness of approximately 0.3 to 0.5 mm are obtained. The magnetic sheet <b>21</b> is produced by forming a pattern having the through-hole <b>22</b> on the PET film by screen printing, and the thickness thereof is adjusted to be approximately 40 to 100 µm.

0102Then, the thick film conductor <b>25</b> is formed in the through-hole <b>22</b> by printing.

0103Next, a method for transferring the conductive patterns <b>20</b> and <b>23</b> on the magnetic sheets <b>19</b> and <b>24</b> and laminating the magnetic sheets <b>19</b>, <b>21</b> and <b>24</b> will be described.

0104The base plate <b>8</b> having the conductive pattern <b>20</b> is pressed to transfer the conductive pattern <b>20</b> onto the magnetic sheet <b>19</b> formed on the PET film. When necessary, pressure and heat are provided. The conductive pattern <b>23</b> is transferred on the magnetic sheet <b>24</b> in the same manner. The conductive pattern <b>23</b> can be transferred on the magnetic sheet <b>21</b>.

0105The magnetic sheet <b>21</b> is located between the magnetic sheet <b>19</b> having the conductive pattern <b>20</b> and the magnetic sheet <b>24</b> having the conductive pattern <b>23.</b> The magnetic sheets <b>19, 21</b> and <b>24</b> are laminated so that the conductive patterns <b>20</b> and <b>23</b> are connected to each other via the through-hole <b>22</b> to form a conductor coil. Then, the resultant lamination body is heated (60 to 120°C) and pressurized (20 to 500 kg/cm²) to be formed into an integral body.

0106Usually in the above-described process, a plurality of conductive patterns are formed on one magnetic sheet, and the magnetic sheets are laminated in the state of having the plurality of conductive patterns, in order to mass-produce inductors with higher efficiency. After the integral bodies are formed, the resultant greensheet is cut into a plurality of integral bodies, and each integral body is sintered at a temperature of 850 to 1,000°C for approximately 1 to 2 hours.

0107An electrode formed of a silver alloy (for example, AgPd) is formed on each of two opposed side surfaces of each integral body and connected to the conductor coil. Then, the integral body is sintered at approximately 600 to 850°C to form outer electrodes <b>12</b> shown in Figure <b>6</b>. When necessary, the outer electrodes <b>12</b> are plated with nickel, solder or the like.

0108In this manner, the inductor <b>300</b> having an outer size of approximately 1.6 mm × 0.8 mm and a thickness of approximately 0.8 mm is obtained. The conductor coil includes the conductive patterns <b>20</b> and <b>23</b> each having a width of approximately 40 µm. The conductive pattern <b>20</b> has approximately 3.5 turns, and the conductive pattern <b>23</b> has approximately 2.5 turns. The total number of turns is 6. Accordingly, an impedance of approximately 1,000 Ω is obtained at a frequency of 100 MHz. The DC resistance can be as small as approximately 0.32 Ω because the thickness of the conductor coil is as much as approximately 35 µm.

Example 4

0109A lamination ceramic chip inductor <b>400</b> in a fourth example according to the present invention will be described with reference to Figure <b>9</b>. Figure <b>9</b> is an exploded isometric view of the inductor <b>400</b>.

0110The inductor <b>400</b> includes a plurality of magnetic sheets <b>26</b>, <b>28</b> and <b>31</b> and coil-shaped plated conductive patterns <b>27</b> and <b>30</b> formed by electroforming and respectively transferred onto the magnetic sheets <b>26</b> and <b>31</b>.

0111The conductive patterns <b>27</b> and <b>30</b> are connected to each other via a through-hole <b>29</b> formed in the magnetic sheet <b>28</b>.

0112The inductor <b>400</b> has the same structure as the inductor <b>100</b> in the first example except that the width of the conductive pattern <b>27</b> is 40 µm.

0113In this example, the inductor <b>400</b> having an outer size of approximately 2.0 mm × 1.25 mm and a thickness of approximately 0.8 mm is obtained. The conductor coil includes the conductive pattern <b>27</b> having a width of approximately 40 µm and approximately 5.5 turns and the conductive pattern <b>30</b> having a width of approximately 70 µm and approximately 2.5 turns. The total number of turns is a. Accordingly, an impedance of approximately 1,400 Ω is obtained at a frequency of 100 MHz. The DC resistance can be as small as approximately 0.47 Ω because the thickness of the conductor coil is approximately 35 µm.

Example 5

0114A lamination ceramic chip inductor in a fifth example according to the present invention, which has the same structure as that of the inductor <b>200</b> in the second example, will be described with reference to Figure <b>7</b>. The inductor <b>200</b> includes a plurality of magnetic sheets <b>13, 15</b> and <b>18</b>, a coil-shaped conductive pattern <b>14</b> formed by electroforming and transferred onto the magnetic sheet <b>13</b>, and a thick film conductive pattern <b>17</b> printed on the magnetic sheet <b>15</b> having a through-hole <b>16</b>. The conductive patterns <b>14</b> and <b>17</b> are connected to each other via the through-hole <b>16.</b>

0115A method for producing the inductor in the fifth example will be described.

0116First, the plated conductive pattern <b>14</b> is produced by electroforming in the same manner as in the second example. The conductive pattern <b>14</b> having a width of approximately 40 µm, a thickness of approximately 35 µm, and approximately 3.5 turns is formed on an area of approximately 1.6 mm × 0.8 mm. The photoresist used for forming the plated conductive pattern <b>14</b> is of a paste type, is printable, and has high sensitivity.

0117Hereinafter, a method for forming the magnetic heet <b>13</b> will be described with reference to Figure <b>10.</b>

0118A resin such as a butyral resin, an acrylic resin or ethylcellulose, and a plasticizer such as dibutylphthalate are dissolved in a solvent having a high boiling point such as terpineol to obtain a vehicle. The vehicle and a Ni·Zn·Cu type ferrite powder having an average diameter of approximately 0.5 to 2.0 µm are kneaded together to form a ferrite paste. The ferrite paste is printed on a stainless steel base plate <b>32</b> having an Ag conductive pattern <b>34</b> (corresponding to the plated conductive pattern <b>14</b>) thereon using a metal mask and then dried at 80 to 100°C until the thickness of the ferrite paste becomes approximately 0.3 to 0.5 mm. Thus, a magnetic sheet <b>33</b> is formed. When necessary, printing and drying are repeated a plurality of times.

0119Next, a thermally releasable sheet <b>35</b> is pasted on the magnetic sheet <b>33</b>, with pressure and heat when necessary. The lamination of the Ag conductive pattern <b>34</b>, the magnetic sheet <b>33</b>, and the thermally releasable sheet <b>35</b> is peeled off from the base plate <b>32</b>. In this manner, a greensheet having the Ag conductive pattern <b>34</b> buried in the magnetic sheet <b>33</b> is obtained. The thermally releasable sheet <b>35</b> is peeled off by heating (for example, 120°C).

0120When necessary, before the formation of the Ag conductive pattern <b>34</b>, a release layer can be formed on the base plate <b>32</b> as in the first example. By providing the release layer, the releasability between the magnetic sheet <b>33</b> and the base plate <b>32</b> is improved. The release layer is formed by dip-coating the base plate <b>32</b> with a liquid fluorine coupling agent (for example, perfluorodecyltriethoxysilane) and drying the resultant lamination body at a temperature 200°C. The thickness of the release layer is preferably approximately 0.1 µm.

0121The magnetic sheet <b>15</b> is formed on the PET film by screen printing so as to have the through-hole <b>16</b>. The thickness of the magnetic sheet <b>15</b> is adjusted to be approximately 40 to 100 µm, and the magnetic sheet <b>15</b> is formed on the magnetic sheet <b>13</b> having the plated conductive pattern <b>14</b>.

0122For the lamination, the pressure is preferably in the range of 20 to 500 kg/cm²; and the heating temperature is preferably in the range of 80 to 120°C.

0123In this example, the plated conductive pattern <b>14</b> is buried in the magnetic sheet <b>13</b> and has very little ruggedness. Accordingly, the magnetic sheet <b>15</b> can be easily formed on the magnetic sheet <b>13.</b>

0124After the plated conductive pattern <b>14</b> is transferred on the magnetic sheet <b>13</b>, the thick film conductive pattern <b>17</b> is printed on the magnetic sheet 15 so as to be connected to the conductive pattern <b>14</b> via the through-hole <b>16.</b> Then, The magnetic sheet <b>18</b> is laminated on the magnetic sheet 15 having the thick film conductive pattern <b>17</b>. The resultant lamination body is heated (80 to 120°C) and pressurized (20 to 500 kg/cm²) to be formed into an integral body. The magnetic sheet <b>18</b> can be directly printed on the magnetic sheet <b>15</b> having the thick film conductive pattern <b>17</b>.

0125The resultant greensheet is cut into a plurality of integral bodies, sintered, and provided with two electrodes for each integral body in the same manner as in the second example.

0126The electric characteristics of the inductor produced in the fifth example are the same as those of the inductor <b>200</b> in the second example.

<u>Example 6</u>

0127A lamination ceramic chip inductor in a sixth example according to the present invention, which has the same structure as those of the inductors <b>200</b> in the second and the fifth examples, will be described with reference to Figure <b>7</b>. The inductor <b>200</b> includes a plurality of magnetic sheets <b>13, 15</b> and <b>18,</b> a coil-shaped plated conductive pattern <b>14</b> formed by electroforming and transferred on the magnetic sheet <b>13</b>, and a thick film conductive pattern <b>17</b> printed on the magnetic sheet <b>15</b> having a through-hole <b>16</b>. The conductive patterns <b>14</b> and <b>17</b> are connected to each other via the through-hole <b>16</b>.

0128Hereinafter, a method for transferring the plated conductive pattern <b>14</b> on the magnetic sheet <b>13</b> in the sixth example will be described with reference to Figures <b>11A</b> through <b>11E.</b>

0129First, as is shown in Figure <b>11A</b>, an Ag conductive pattern <b>38</b> is formed on a stainless steel base plate <b>36</b>. In this example, the Ag conductive pattern <b>38</b> having a width of approximately 40 µm, a thickness of approximately 35 µm, and approximately 3.5 turns is formed on an area of approximately 1.6 mm × 0.8 mm of the base plate <b>36</b> in the state of interposing a release layer <b>37</b> therebetween. The release layer <b>37</b> is formed by strike-plating the base plate <b>36</b> with Ag. The lamination of the release layer <b>37</b> and the Ag conductive pattern <b>38</b> corresponds to the plated conductive pattern <b>14.</b>

0130Then, as is shown in Figure <b>11B</b>, a foam sheet <b>39</b> is attached to the Ag conductive pattern <b>38</b> by performing heating and foaming from above. The foam sheet <b>39</b> is thermally releasable from the base plate <b>36</b>. When necessary, additional heat and pressure are provided.

0131Since the foam sheet <b>39</b> has high adhesion. Thus, when the foam sheet <b>39</b> is pealed off from the base plate <b>36</b>, the Ag conductive pattern <b>38</b> and the release layer <b>37</b> are also peeled off and thus transferred onto the foam sheet <b>39</b> as is shown in Figure <b>11C.</b>

0132Then, as is shown in Figure <b>11D</b>, a magnetic sheet <b>40</b> (corresponding to the magnetic sheet <b>13</b>) formed on a PET film or the like by printing or the like having a thickness of approximately 50 to 500 µm is laminated on the release layer <b>37</b> so that a surface of the magnetic sheet <b>40</b> having plasticity is in contact with the release layer <b>37</b>. Then, more magnetic sheets <b>40</b> are laminated thereon until the total thickness of the magnetic sheets 40 becomes approximately 0.3 to 0.5 mm. When necessary, appropriate heat and pressure are provided for lamination.

0133The resultant lamination body is heated at a temperature of approximately 120°C for approximately 10 minutes, and the foam sheet 39 is foamed to be released. In this manner, the Ag conductive pattern <b>38</b> (corresponding to the plated conductive pattern <b>14</b>) is transferred on the magnetic sheet <b>40</b> (corresponding to the magnetic sheet <b>13</b>) as is shown in Figure <b>11E.</b>

0134Returning to Figure <b>7,</b> the magnetic sheet <b>15</b> having the through-hole <b>16</b> is laminated or printed on the magnetic sheet <b>13</b> having the plated conductive pattern <b>14.</b> Then, the thick film conductive pattern <b>17</b> is laminated or printed on the magnetic sheet <b>15</b> to be connected with the plated conductive pattern <b>14</b> via the through-hole 16.

0135The magnetic sheet <b>18</b> is laminated on the magnetic sheet <b>15</b> having the thick film conductive pattern <b>17</b> thereon, and the resultant lamination body is supplied with heat (for example, 60 to 120°C) and pressure (for example, 20 to 500 kg/cm²) to be formed into an integral body. The magnetic sheet <b>18</b> can be printed directly onto the magnetic sheet <b>15</b>.

0136The greensheet produced in this manner is cut into a plurality of integral bodies, sintered, and provided with two electrodes for each integral body in the same manner as in the second example.

0137The electric characteristics of the inductor produced in the sixth example are equal to those of the inductor <b>200</b> in the second example.

0138In the first through sixth examples, coil-shaped conductive patterns are formed by electroforming. Alternatively, a plurality of straight conductive patterns can be connected to form a conducive coil.

Example 7

0139A lamination ceramic chip inductor <b>700</b> in a seventh example according to the present invention will be described with reference to Figure <b>12.</b>

0140Figure <b>12</b> is an exploded isometric view of the inductor <b>700.</b> The inductor <b>700</b> includes a plurality of magnetic sheets <b>41</b> and <b>43</b> and a wave-shaped plated conductive pattern <b>42</b> formed by electroforming. The wave-shaped conductive pattern <b>42</b> is drawn to edge surfaces of the chip.

0141The inductor <b>700</b> having the above-described structure is formed in the same manner as in the first example.

0142The inductor <b>700</b> has an outer size of approximately 2.0 mm × 1.25 mm and a thickness of approximately 0.8 mm. The wave-shaped conductive pattern <b>42</b> has a width of approximately 50 µm and runs along a longitudinal direction of the magnetic sheets <b>41</b> and <b>43</b>. The impedance of approximately 120 Ω is obtained at a frequency of 100 MHz.

0143The DC resistance can be as small as approximately 0.08 Ω because the thickness of the conductive pattern <b>42</b> is as much as approximately 35 µm.

0144In the above seven examples, the conductive patterns are formed of Ag. If price, specific resistance or resistance against acid need not be considered, Au, Pt, Pd, Cu, Ni or the like and alloys thereof can be used.

0145In the above seven examples, the sheets to be laminated are formed of a magnetic material containing Ni·Zn·Cu. Needless to say, a lamination ceramic chip inductor having an air-core coil characteristic can be produced using a Ni·Zn or Mn·Zn material, an insulation material having a low dielectric constant, or the like.

Example 8

0146A lamination ceramic chip inductor <b>800</b> in an eighth example according to the present invention will be described with reference to Figures <b>15</b>, <b>16A, 16B</b>, <b>17A</b> and <b>17B</b>. Figure <b>15</b> is an exploded isometric view of the lamination ceramic chip inductor <b>800.</b>

0147The inductor <b>800</b> shown in Figure <b>15</b> includes a plurality of magnetic sheets <b>201, 203</b> and <b>206,</b> and a plurality of coil-shaped plated conductive patterns <b>202</b> and <b>205</b> formed by electroforming. The magnetic sheet <b>203</b> has a conductive bump <b>204</b> formed by electroforming in a through-hole <b>207</b> thereof.

0148The magnetic sheets <b>201</b> and <b>206</b> respectively have the conductive patterns <b>202</b> and <b>205</b> transferred thereon. The conductive patterns <b>202</b> and <b>205</b> are connected to each other via the Conductive bump <b>204.</b>

0149A method for producing the inductor <b>800</b> will be described.

[Formation of the conductive patterns]

0150First, how to form the conductive patterns <b>202</b> and <b>205</b> will be described with reference to Figures <b>16A</b> and <b>16B.</b>

0151On a stainless steel base plate <b>210,</b> a liquid photoresist is screen-printed and dried at a temperature of approximately 100°C to form a photoresist film <b>211</b> having a thickness of approximately 25 µm. The resultant lamination is exposed to collimated light using the photoresist film <b>211</b> as a mask and immediately developed. In this example, the development is performed using an aqueous solution of sodium carbonate. After the development, the resultant lamination is sufficiently rinsed and activated with an acid by, for example, immersing the lamination in a 5% solution of H₂SO₄ for 0.5 to 1 minute. Then, the resultant lamination is treated with strike plating using a neutral Ag plating material containing no cyanide (for example, Dain Silver Bright AG-PL 30 produced by Daiwa Kasei Kabushiki Kaisha) for approximately 1 minute at a current density of 0.3 A/dm² to form a release layer <b>212</b> having a thickness of approximately 0.1 µm. Immediately thereafter, the resultant lamination is further immersed in an Ag plating bath containing no cyanide (using, for example, Dain Silver Bright AG-PL 30 produced by Daiwa Kasei Kabushiki Kaisha) at a pH value of 1.0 (acid) for approximately 20 minutes at a current density of approximately 1 A/dm². The pH value of the Ag bath is adjustable in the range of approximately 1.0 to 8.0. In this manner, an Ag layer <b>213</b> having a thickness of 20 µm is obtained as is shown in Figure <b>16A.</b> The lamination of the release layer <b>212</b> and the Ag layer <b>213</b> corresponds to the conductive patterns <b>202</b> and <b>205</b> and the conductive bump <b>204</b>. The Ag plating bath containing no cyanide used in this example has no toxicity, and thus provides safety and simplifies the disposal process of the waste fluid. As a result, improvement in the operation efficiency and reduction in production cost are achieved.

0152After the formation of the Ag layer <b>213</b>, the photoresist film <b>211</b> is removed by immersion in a 5% solution of NaOH. The conductive patterns <b>202</b> and <b>205</b> thus obtained each have a thickness of approximately 20 µm, a width of approximately 35 µm, a space between lines of approximately 25 µm, and approximately 2.5 turns. Such conductive patterns <b>202</b> and <b>205</b> are suitable for a magnetic sheet having a size of 16 mm × 0.8 mm. The conductive bump <b>204</b> thus obtained has a thickness of approximately of 20 µm and a planar size suitable for a through-hole having a diameter of 0.1 mm.

[Formation of the magnetic sheets]

0153Hereinafter, a method for forming the magnetic sheets <b>201</b>, <b>203</b> and <b>206</b> will be described with reference to Figures <b>17A</b> and <b>17B.</b>

0154A resin such as a butyral resin, an acrylic resin or ethylcellulose, and a plasticizer such as dibutylphthalate are dissolved in a solvent having a low boiling point such as toluene or xylene together with a small amount of additive to obtain a vehicle. The vehicle and a Ni·Zn·Cu type ferrite powder having an average diameter of approximately 1.2 to 2.7 µm are mixed together in a pot to form a ferrite paste (slurry). The ferrite powder is obtained as a result of pre-sintering at a high temperature (800 to 1,100°C). A PET film is coated with the ferrite paste using a doctor blade to obtain greensheets having thicknesses of approximately 100 µm and approximately 40 µm.

0155Four such greensheets having a thickness of 100 µm are laminated to obtain a greensheet having a thickness of approximately 400 µm (corresponding to the magnetic sheets <b>201</b> and <b>206</b>). The greensheet having a thickness of 40 µm is punched by a puncher (a device for mechanically forming a hole using a pin-type mold) to form the through-hole <b>207</b> having a diameter of approximately 0.1 mm. Thus, the magnetic sheet <b>203</b> is obtained.

[Transfer of the conductive patterns]

0156The magnetic sheets <b>201</b> and <b>206</b> are pressed on the base plate <b>210</b> having the conductive patterns <b>202</b> and <b>205</b> at a temperature of approximately 100°C and a pressure of 70 kg/cm² for 5 seconds, and then the magnetic sheets <b>201</b> and <b>206</b> having the conductive patterns <b>202</b> and <b>205</b> buried therein are peeled off from the base plate <b>210</b>. In this manner, the conductive patterns <b>202</b> and <b>205</b> are transferred onto the magnetic sheets <b>201</b> and <b>206</b> as is shown in Figure <b>17A</b>. The magnetic sheet <b>203</b> is pressed on the base plate <b>210</b> having the conductive bump <b>204</b> after positioning, and the magnetic sheet <b>203</b> having the conductive bump <b>204</b> is peeled off from the base plate <b>210</b>. In this manner, the conductive bump <b>204</b> is transferred to the through-hole <b>207</b> in the magnetic sheet <b>203</b> as is shown in Figure <b>17B.</b>

0157The magnetic sheets <b>201, 203</b> and <b>206</b> are laminated so that the conductive patterns <b>202</b> and <b>205</b> are electrically connected to each other via the conductive bump <b>204</b>.

0158Usually in the above-described process, a plurality of conductive patterns are formed on one magnetic sheet, and the magnetic sheets are laminated in the state of having the plurality of conductive patterns, in order to mass-produce inductors with higher efficiency. After the integral bodies are formed in the same manner as in the first example, the resultant greensheet is cut into a plurality of integral bodies, and each integral body is sintered at a temperature of 900 to 920°C for approximately 1 to 2 hours.

0159Then, outer electrodes <b>12</b> shown in Figure <b>6</b> are formed in the same manner as in the first example. When necessary, burrs are removed, and the outer electrodes <b>12</b> are plated with nickel, solder or the like.

0160In this manner, the inductor <b>800</b> having an outer size of 1.6 mm × 0.8 mm and a thickness of approximately 0.8 mm is obtained.

0161In general, in order to increase the density of the sintered magnetic body, a fine ferrite powder having a diameter of 0.2 to 1.0 µm and pre-sintered at 700 to 800°C is used. Such a powder shrinks from sintering by 15 to 20%. The low-ratio shrinkage powder used in this example has grains having a diameter of 1 to 3 µm and pre-sintered at a high temperature (800 to 1,100°C). Thus, the shrinkage ratio from sintering is restricted to 2 to 10%. Exemplary compositions of such a ferrite powder are shown in Table 6 together with the characteristics thereof. The shrinkage ratio is restricted in order to match, to a maximum possible extent, the shrinkage ratio of the magnetic greensheets and that of the Ag conductive patterns and bump, which shrink from sintering only slightly. By matching the shrinkage ratios, the internal strain in the sintered magnetic body is reduced.

0162As the pre-sintering temperature of the powder increases, the shrinkage ratio is reduced but the magnetic characteristic of the powder is deteriorated. It is important that an additive for restricting such deterioration should be used. The inventors of the present invention have found that it is effective to add an organolead compound such as lead octylate in a small amount (0.1 to 1.0% with respect to ferrite) in order to restrict the deterioration of the magnetic characteristics while maintaining the shrinkage ratio low. One probable reason that such a compound is effective is: since an organolead compound is well dispersed in the ferrite slurry, Pb metal or PbO at an atomic level obtained by thermal decomposition of the organolead composition is dissolved into the grain boundary in the sintered magnetic body, thus to improve the sintering efficiency. By contrast, a PbO powder has a high specific gravity and thus easily separates from the ferrite in the slurry; namely, is poorly dispersed. Further, the PbO powder has inferior reactivity with the ferrite powder to Pb metal or PbO resulting from the thermal decomposition of the organolead compound. Accordingly, an oxide powder such as PbO is not effective as the additive.

0163Instead of the powder which is pre-sintered at a high temperature, non-shrinkage ferrite is also effective to reduce the shrinkage ratio. In this case, a Ni·Zn·Cu type ferrite powder, the amount of Fe₂O₃ of which is reduced, is pre-sintered, and then mixed with a mixture containing an Fe powder and unreacted NiO, ZnO and CuO. The compositions of the ferrite powder and the mixture, and also the mixture ratio are adjusted so that the expansion ratio of the Fe powder caused by oxidation into Fe₂O₃ and the shrinkage ratio of the ferrite powder as a result of the sintering will be equal to each other, as is shown in Table 5. Thus, the shrinkage ratio is reduced. <tables id="tabl0005" num="0005"><img file="EP0701262B1_D0001.tif" /></tables><tables id="tabl0006" num="0006"><img file="EP0701262B1_D0002.tif" /></tables>

0164The characteristics of the non-shrinkage ferrite are also shown in Table 6. The data in Table 6 are obtained under the conditions of the temperature of 910°C and the sintering time of one hour.

Comparative Example

0165A lamination ceramic chip inductor 900 in a comparative example will be described. Figure <b>14</b> is a schematic illustration of a method for producing the inductor <b>900.</b>

0166As is shown in (a), a ferrite paste is printed in a rectangle to form an insulation sheet <b>101</b>. Next, as is shown in (b), an Ag conductive paste of approximately half turn is printed on the sheet <b>101</b> to form a thick film conducive pattern <b>102</b>. As is shown in (c), a ferrite paste is printed on the insulation sheet <b>101</b> so as to expose an end part of the conductive pattern <b>102,</b> thereby forming an insulation sheet <b>103</b>. As is shown in (d), an Ag conductive paste of approximately half turn is printed on the sheet <b>103</b> to be connected to the conductive pattern <b>102</b>, thereby forming a thick film conductive pattern <b>104</b>.

0167As is shown in (e) through (k), insulation sheets <b>105</b>, <b>107</b>, <b>109</b> and <b>111</b> and thick film conductive patterns <b>106, 108</b> and <b>110</b> are printed alternatively in the same manner. The resultant lamination body is sintered at a high temperature to produce the inductor <b>900</b> including a conductive coil having approximately 2.5 turns.

0168By this method, each conductive pattern has a width of approximately 150 µm and a thickness after being dried of approximately 12 µm is formed on an area of approximately 1.6 mm × 0.8 mm.

0169Because the conductive coil has approximately 2.5 turns, the impedance of the inductor <b>900</b> is approximately 150 Ω at a frequency of 100 MHz. The DC resistance is approximately 0.16 Ω because the thickness of the conductive coil after being sintered is approximately 8 µm.

0170The conductive coil in the conventional inductor <b>900</b> has only 2.5 turns despite that the inductor <b>900</b> includes eleven layers. The impedance is excessively small in consideration of the number of the layers, and DC resistance is large for the impedance.

0171Further, the production method is complicated, and the connection between the conductive patterns is not sufficiently reliable.

0172Although the DC resistance can be reduced by forming the thick film conductive patterns using strike-plating as in the present invention, effects such as reduction in the number of the layers and increase in impedance are not achieved.

0173As has been described so far, according to the present invention, a conductor coil of the inductor is formed by electroforming. Since the photoresist, which is used in electroforming, has relatively high resolution, the width of the conductive patterns can be adjusted with high precision, for example, to the extent of several microns. The width of the conductive patterns can be adjusted in accordance with the resolution of the photoresist. Accordingly, a conductive coil having a larger number of turns can be formed in a smaller area than a conductor formed by printing.

0174Due to such a larger number of turns, a higher impedance is obtained despite the smaller number of layers.

0175The thickness of the conductive patterns can be controlled to be in the range from submicrons to several tens of microns by using an appropriate photoresist or appropriate plating conditions. The thickness of the conductive patterns can be even several millimeters by using appropriate conditions. Accordingly, the DC resistance can be easily controlled and thus can be reduced by increasing the thickness of the conductive patterns despite the fine patterns thereof.

0176Moreover, magnetic or insulation films having a high density can be obtained even before sintering by electroforming in contrast to formation of a coil pattern only by thick film conductive patterns. Thus, reduction of the thickness of the conductive patterns after sintering is insignificant, and the magnetic sheets and the conductive patterns are scarcely delaminated from each other.

0177The precise pattern and the high density of the conductor improve the reliability of the resultant inductor.

0178In the case where a low-ratio shrinkage powder or a non-shrinkage powder is used for the magnetic sheets, the shrinkage ratio by sintering is reduced. Thus, the sintered magnetic body having a higher and more uniform density is obtained.

0179According to the present invention, an inductor and a method for producing the same for providing a higher impedance at a lower resistance with a smaller number of layers are obtained.

0180Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope of this invention.