JP2008084921A - Substrate with built-in coil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate with a built-in coil wherein the degradation of superposition property due to lamination displacement of a plane coil conductor thereof can be suppressed and which is compact and has high inductance. <P>SOLUTION: The substrate with a built-in coil is provided with a pair of insulation layers 1 wherein a wiring conductor 4 is formed, a ferrite magnetic layer 2 that is pinched with the insulation layers 1, and a coil layer 3 that is formed in the ferrite magnetic layer 2. The coil layer 3 is made from a plurality of plurally wound plane coil conductors that are arranged opposite to each other in the direction of thickness, and the plane coil conductors are comprised of a first plane coil conductor 3a and a second plane coil conductor 3b that is smaller in width than the first plane coil conductor. Thus, displacement is absorbed by a difference in width between the first plane coil conductor 3a and the second plane coil conductor 3b, making the substrate with a built-in coil in which the degradation of superposition characteristic is suppressed and which is compact and has high inductance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coil-embedded substrate in which a ferrite magnetic layer in which a coil conductor is embedded is provided inside an insulating layer.

  2. Description of the Related Art Conventionally, many electronic devices are incorporated in electronic devices such as mobile communication devices such as mobile phones. These electronic devices have been rapidly reduced in size, and accordingly, various electronic devices are also required to be reduced in size and thickness. As an example of downsizing and thinning of electronic devices, LC filters that were conventionally formed by mounting a relatively large chip coil or chip capacitor on a substrate are made of glass ceramics instead of mounting the chip coil. Thinning is achieved by using a coil-embedded substrate in which a coil conductor is formed inside a ceramic substrate on which an insulating layer is laminated.

  However, in an electronic device that requires a relatively high inductance such as a DC-DC converter used in a cellular phone, the coil-embedded substrate is formed with a coil in a ceramic substrate that does not have magnetism. In order to obtain a relatively large inductance, the number of turns of the coil conductor has to be increased, and there has been a problem that it is impossible to effectively reduce the size and thickness.

  Therefore, in recent years, a ferrite magnetic layer having a high magnetic permeability is formed inside the ceramic substrate, and a coil conductor is embedded in the ferrite magnetic layer, so that a coil exceeding 100 nH can be built in without increasing the number of turns of the coil. In other words, a high-inductance coil-embedded substrate is used (see, for example, Patent Documents 1 and 2).

Such a coil-embedded substrate is, for example, a pair of insulating layers 11 on which wiring conductors 14 are formed and laminated between the insulating layers 11 as shown in the cross-sectional view of FIG. The layer 13 is formed of the ferrite magnetic layer 12 embedded therein, the planar coil conductor 13a of the coil layer 13 is formed in a plurality of winding shapes, and the plurality of planar coil conductors 13a are arranged so as to face each other in the thickness direction. A large inductance is obtained. Such a coil-embedded substrate is manufactured by a so-called green sheet lamination method in which a green sheet of ferrite or ceramics on which a wiring conductor or a planar coil conductor is formed is laminated and fired with a conductor paste or the like.
JP-A-6-20839 JP-A-6-21264

  However, in the case of a coil-embedded substrate in which a plurality of planar coil conductors of a plurality of windings are arranged so as to face each other in the thickness direction, they are positioned up and down when the green sheets on which the planar coil conductors are formed are laminated in the manufacturing process. The positional deviation of the plurality of planar coil conductors is likely to occur. In addition, the coil-embedded substrate in which the positional deviation has occurred has a problem that the superimposition characteristics are deteriorated. This is because part of the magnetic flux generated around each planar coil conductor passes through the gap between the inner and outer conductors of each planar coil conductor, and each gap located above and below the coil layer Although it passes consistently in the thickness direction, the gap between the upper and lower gaps is reduced when the position shift occurs, so the path of the magnetic flux is reduced and the magnetic flux is easily saturated. It was.

  Even when misalignment occurs, it is conceivable to increase the gap between the conductors of the planar coil conductor in order to ensure the width of the magnetic flux in the thickness direction of the coil layer as designed, but the substrate becomes large. There was a problem.

  The present invention has been devised to solve the above-mentioned problems, and its purpose is to achieve a small and high-inductance characteristic that suppresses the deterioration of the superposition characteristic due to the stacking deviation of the planar coil conductor of the coil-embedded substrate. It is providing the coil built-in board | substrate which has this.

  The coil-embedded substrate of the present invention includes a pair of insulating layers on which wiring conductors are formed, a ferrite magnetic layer sandwiched between the pair of insulating layers, and a coil layer formed in the ferrite magnetic layer. The coil-embedded substrate, wherein the coil layer is composed of a plurality of turns of a plurality of planar coil conductors arranged to face each other in the thickness direction, and the plurality of planar coil conductors are one first width having a maximum width. It consists of a planar coil conductor and a second planar coil conductor having a smaller width than the first planar coil conductor.

  The coil-embedded substrate according to the present invention is characterized in that, in the above-described configuration, there are a plurality of the second planar coil conductors, and the width thereof is gradually reduced as the distance from the first planar coil conductor is increased. is there.

  The coil-embedded substrate according to the present invention is characterized in that, in the above configuration, there are a plurality of the second planar coil conductors, and the widths thereof are the same.

  According to the coil-embedded substrate of the present invention, the coil layer is composed of a plurality of turns of a plurality of planar coil conductors arranged so as to face each other in the thickness direction, and the plurality of planar coil conductors are one first having the maximum width. Of the first planar coil conductor and the second planar coil conductor having a smaller width than the first planar coil conductor, the first planar coil conductor having one maximum width in the manufacturing process is Even when the position of the second planar coil conductor whose width is smaller than that of the planar coil conductor is shifted, the positional shift is absorbed by the difference between the width of the first planar coil conductor and the width of the second planar coil conductor, The overlap of the gaps between the inner and outer conductors of the coil conductor is suppressed, and the width is secured as the magnetic flux passes through the gaps located above and below in the thickness direction of the coil layer. , Magnetism Saturation is suppressed, it is possible to obtain a coil embedded substrate reduced is suppressed in superimposition characteristics.

  In addition, according to the coil-embedded substrate of the present invention, in the above configuration, when there are a plurality of second planar coil conductors and the width is gradually reduced as the distance from the first planar coil conductor increases, When sequential lamination is performed using the coil conductor pattern laminated on the layer as the alignment reference for lamination, the positional deviation at each lamination is absorbed by the difference in the width of the planar coil conductors located above and below. In the thickness direction of the coil layer, a width is ensured so that the magnetic flux consistently passes through the gaps positioned above and below, so that the coil built-in substrate is obtained in which the saturation of the magnetic flux is suppressed and the deterioration of the superposition characteristics is suppressed. be able to.

  Further, according to the coil-embedded substrate of the present invention, in the above configuration, when there are a plurality of the second planar coil conductors and the widths thereof are the same, a fixed layer is used as the alignment reference for the lamination in the manufacturing process. In this case, since the displacement is absorbed by the difference between the width of the first planar coil conductor having the maximum width and the width of the other second planar coil conductor, each of the upper and lower positions in the thickness direction of the coil layer is absorbed. A width is ensured as the magnetic flux passes through the gap consistently, the saturation of the magnetic flux is suppressed, and the coil-embedded substrate in which the deterioration of the superposition characteristics is suppressed can be obtained.

  The coil-embedded substrate of the present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 are cross-sectional views showing an example of an embodiment of a coil-embedded substrate of the present invention, wherein 1 is an insulating layer, 2 is a ferrite magnetic layer, 3 is a coil layer, and 3a is a first planar coil conductor. 3b is a 2nd planar coil conductor, 4 is a wiring conductor.

  In the example shown in FIG. 1, as the wiring conductor 4, a mounting electrode 4 b on which a semiconductor chip such as an IC or a chip component is mounted on the outer surface of the insulating layer 1 and an electrode pad electrically connected to an external electric circuit. 4 d is formed, an internal wiring conductor 4 a is formed in the insulating layer 1, and a ground conductor 4 e is formed between the insulating layer 1 and the ferrite magnetic layer 2. Inside the ferrite magnetic layer 2, a first planar coil conductor 3 a and two second planar coil conductors 3 b are formed as a coil layer 3 so as to overlap each other, and one end of the first planar coil conductor 3 a is formed. One end portion of the upper planar coil conductor 3b and the other end portion of the upper second planar coil conductor 3b and one end portion of the lower second planar coil conductor 3b are through conductors (not shown). Are connected in series from the first planar coil conductor 3a to the lower second planar coil conductor 3b. The other ends of the first planar coil conductor 3a and the lower second planar coil conductor 3b are connected to the wiring conductor 4 by a through conductor (not shown). The internal wiring conductor 4a, the mounting electrode 4b, the electrode pad 4d, and the planar coil conductor 3 are connected to each other through the through conductor 4c.

  The coil-embedded substrate of the present invention is formed in a pair of insulating layers 1 on which wiring conductors 4 are formed, a ferrite magnetic layer 2 sandwiched between the pair of insulating layers 1, and the ferrite magnetic layer 2. A coil-embedded substrate having a coil layer 3, wherein the coil layer 3 is composed of a plurality of planar coil conductors of a plurality of turns arranged to face each other in the thickness direction, and the plurality of planar coil conductors have a maximum width. The first planar coil conductor 3a includes a first planar coil conductor 3a having a width smaller than that of the first planar coil conductor 3a.

  According to the coil-embedded substrate of the present invention, the second planar coil conductor 3b having a smaller width than the first planar coil conductor 3a is positioned with respect to one first planar coil conductor 3a having the maximum width in the manufacturing process. Even when a deviation occurs, the positional deviation is absorbed by the difference between the width of the first planar coil conductor 3a and the width of the second planar coil conductor 3b, and the gap between the inner and outer conductors of the planar coil conductor is overlapped. The width is ensured so that the magnetic flux passes through the gaps positioned above and below in the thickness direction of the coil layer in the thickness direction of the coil layer, so that the saturation of the magnetic flux is suppressed, and the superposition characteristics are reduced. A suppressed coil-embedded substrate can be obtained.

  Further, as shown in FIG. 1, the coil-embedded substrate of the present invention has a plurality of second planar coil conductors 3b in the above-described configuration, and the width gradually decreases as the distance from the first planar coil conductor 3a increases. It is preferable. As a result, when sequential lamination is performed using the coil conductor pattern laminated immediately before in the manufacturing process as the alignment reference of the lamination, the positional deviation at each time of the lamination is a planar coil conductor located above and below. Is absorbed by the difference in the width of the coil layer, so that the magnetic flux is consistently passed through the gaps positioned above and below in the thickness direction of the coil layer, the saturation of the magnetic flux is suppressed, and the superposition characteristics are reduced. It is possible to obtain a coil-embedded substrate in which the above is suppressed.

  As shown in FIG. 2, the coil-embedded substrate of the present invention preferably has a plurality of second planar coil conductors 3b and the same width in the above-described configuration. Thus, in the manufacturing process, the difference between the width of the first planar coil conductor 3a having the maximum width and the width of the other second planar coil conductor 3b is obtained when the alignment reference for the stack is a fixed layer. Therefore, the width is ensured as the magnetic flux passes through the gaps positioned in the upper and lower directions in the thickness direction of the coil layer, the saturation of the magnetic flux is suppressed, and the superposition characteristic is lowered. A suppressed coil-embedded substrate can be obtained.

  The insulating layer 1 is an insulator that is co-fired at a temperature of 800 to 1000 ° C. together with the wiring conductor 4 formed on the surface or inside thereof, the ferrite magnetic layer 2 formed between the insulating layer 1 and the coil layer 3. A non-magnetic insulator such as non-magnetic ferrite or glass ceramic is preferable from the viewpoint of suppressing the increase in inductance of the wiring conductor 4 because it is made of a powdered sintered body. For the insulating layer 1, a green sheet for the insulating layer 1 mainly composed of an insulating powder and an organic binder is manufactured, and the green sheets for the insulating layer 1 are laminated as many as necessary to expand the wiring, and then 800 to 1000 are stacked. It is produced by firing at a temperature of ° C.

When the insulating layer 1 is made of nonmagnetic ferrite, Zn-based ferrite or Cu-based ferrite may be used. Among them, a Cu—Zn-based ferrite which is a solid solution having a positive spinel structure shown as X—Fe ₂ O ₄ (X is Cu, Zn) is preferable.

In the case of Cu—Zn ferrite, the composition ratio is 1000 ° C. when the sintered body is 50 to 70 mass% Fe ₂ O ₃ , 5 to 20 mass% CuO and 20 to 35 mass% ZnO. High density firing with a sintered density of 5.0 g / cm ³ or more is possible at the following low temperature, and the nonmagnetic ferrite layer after firing is preferable because it is nonmagnetic even in a low temperature range. Fe ₂ O ₃ is the main component of ferrite, and if its proportion is less than 50% by mass, magnetism tends to occur, and if it exceeds 70% by mass, mechanical strength tends to decrease due to a decrease in sintered density. is there. CuO is an important factor for lowering the sintering temperature, and CuO promotes sintering by forming a liquid phase at a low temperature, and the low temperature of 800 to 1000 ° C. without damaging the magnetic properties. Can be fired. For this reason, if the ratio is less than 5% by mass, sintering at 800 to 1000 ° C. simultaneously with the wiring conductor 4 tends to result in insufficient sintering density and insufficient mechanical strength. On the other hand, if it exceeds 20% by mass, the Curie temperature rises and magnetism tends to occur in a low temperature region. ZnO is an important element for making nonmagnetic ferrite nonmagnetic. If the ratio is less than 20% by mass, the mechanical strength tends to decrease due to a decrease in sintered density, and if it exceeds 35% by mass. There is a tendency to generate magnetism.

Further, when the insulating layer 1 is made of nonmagnetic ferrite, it may be a nonmagnetic ferrite powder added with a glass having a low softening point and fired at a low temperature. Examples of the glass at this time include SiO ₂ —B ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —MO system (however, M Represents Ca, Sr, Mg, Ba or Zn), SiO ₂ —Al ₂ O ₃ —M ¹ O—M ² O system (where M ¹ and M ² are the same or different, and Ca, Sr, Mg, Ba) Or Zn), SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —M ¹ O—M ² O (where M ¹ and M ² are the same as above), SiO ₂ —B ₂ O ₃ -M ³ ₂ O system (where M ³ represents Li, Na or K), SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -M ³ ₂ O system (where M ³ is the same as above) ), Pb-based glass, Bi-based glass, and the like, and the softening point of the glass is 600 ° C. or lower. This is desirable from the viewpoint of not inhibiting the sintering of ferrite.

When the insulating layer 1 is made of glass ceramics, the insulator powder is made of a sintered body of a mixture of glass powder and filler powder as described above. Examples of filler powder include Al ₂ O ₃ , SiO ₂ , ZrO. ₂ and an alkaline earth metal oxide, a composite oxide of TiO ₂ and an alkaline earth metal oxide, a composite oxide containing at least one selected from Al ₂ O ₃ and SiO ₂ (for example, spinel) , Mullite, cordierite) and the like.

  The wiring conductor 4 is made of a metallized metal that is a sintered body of a low resistance metal powder such as Cu, Ag, Au, Pt, Ag—Pd alloy, and Ag—Pt alloy, and is used as a green sheet for the insulating layer 1. A wiring conductor pattern is formed by printing a conductor paste for the wiring conductor 4, and is formed by simultaneous firing with the green sheet for the insulating layer 1.

  In addition, as the wiring conductor 4, a ground conductor 4 e is preferably formed on at least one of the surfaces of the insulating layer 1 in contact with the ferrite magnetic layer 2. Since this grounding conductor 4e functions as a shield, the influence of the noise radiated from the coil layer 3 on the wiring conductor 4 is suppressed, and a built-in coil capable of operating the mounted IC more stably. A substrate can be obtained. In order to completely suppress the influence of the radiated noise on the wiring conductor 4, it is desirable that the ground conductor 4 e be formed so as to completely cover the coil layer 3 in plan view.

The ferrite magnetic layer 2 is a sintered body of magnetic ferrite powder such as Ni—Zn ferrite, Mn—Zn ferrite, Mg—Zn ferrite, Ni—Co ferrite, etc., which are ferromagnetic ferrites. Ni—Zn ferrite, which is a solid solution having an inverse spinel structure represented as Fe ₂ O ₄ (X is Cu, Ni, Zn), is preferable for obtaining a sufficiently high magnetic permeability in a high frequency band.

In the case of Ni-Zn ferrite, the composition ratio of the sintered body is 63 to 73% by mass of Fe ₂ O ₃ , 5 to 10% by mass of CuO, 5 to 12% by mass of NiO, and 10 to 10% of ZnO. A mass ratio of 23% by mass is preferable because high-density firing at a sintering density of 5.0 g / cm ³ or higher is possible at a low temperature of 1000 ° C. or lower, and a sufficiently high magnetic permeability can be obtained in a high-frequency band. Fe ₂ O ₃ is the main component of ferrite, and if its proportion is less than 63% by mass, there is a tendency that sufficient magnetic permeability cannot be obtained, and if it exceeds 73% by mass, mechanical strength is reduced due to a decrease in sintered density. There is a tendency to decrease. CuO is an important factor for lowering the sintering temperature, and CuO promotes sintering by forming a liquid layer at a low temperature, and the low temperature of 800 to 1000 ° C. without damaging the magnetic properties. Can be fired. Therefore, if the ratio is less than 5% by mass, the sintering density tends to be inadequate and the mechanical strength tends to be insufficient when the wiring conductor 4 and the planar coil conductor 3 are simultaneously fired at 800 to 1000 ° C. is there. On the other hand, when the amount is more than 10% by mass, the ratio of CuFe ₂ O ₄ having a low magnetic property increases, so that the magnetic property tends to be easily lost. NiO is contained in order to ensure the magnetic permeability in the high frequency region of the ferrite magnetic layer 2. NiFe ₂ O ₄ does not cause the attenuation of the magnetic permeability due to resonance up to the high frequency range, and can maintain the magnetic permeability in the high frequency range at a relatively high value. However, since NiFe ₂ O ₄ has a characteristic that the initial permeability is low, 5 mass If it is less than%, the magnetic permeability in a high frequency region of 10 MHz or more tends to decrease. On the other hand, when the content is more than 12% by mass, the initial permeability tends to decrease. ZnO is an important factor for improving the magnetic permeability of the ferrite magnetic layer 2, and if the ferrite composition is less than 10% by mass, the magnetic permeability is lowered, and conversely if it is more than 23% by mass, the magnetic properties are poor. Tend to be.

  The ferrite magnetic layer 2 is produced by using a ferrite magnetic layer 2 green sheet formed by the same method as the insulating layer green sheet used for the insulating layer 1.

  The coil layer 3 is made of a metallized metal layer, which is a sintered body of metal powder, similarly to the wiring conductor 4, and the first is obtained by printing the conductor paste for the coil layer 3 on the ferrite magnetic substance layer 2 green sheet. The first planar coil conductor pattern to be the planar coil conductor 3a and the through conductor pattern to be the through conductor are formed, and the second planar coil conductor 3b is similarly formed on the other green sheet for the ferrite magnetic layer 2. A second planar coil conductor pattern and a through conductor pattern to be a through conductor are formed, and these are laminated and fired simultaneously to be embedded in the ferrite magnetic layer 2.

  The conductor width of the first planar coil conductor 3a and the second planar coil conductor 3b depends on the required inductance value and size, but when formed by printing as described above, the conductor width and the adjacent outer periphery and inner It can be easily formed if the distance between the peripheral conductors is about 0.1 mm or more. In order to increase the number of coil turns in an area as small as possible, the line width may be about 0.1 to 1 mm, and the distance between conductors may be about 0.1 to 0.2 mm.

  Due to the difference in conductor width between the first planar coil conductor 3a and the second planar coil conductor 3b, the first planar coil conductor pattern and the second planar coil conductor 3b, which become the first planar coil conductor 3a when stacked, Therefore, the difference in the conductor width is preferably 10 μm to 50 μm, although it depends on the position accuracy of the lamination. If the difference in the conductor width is 10 μm or less, it will not be a difference in the conductor width that can sufficiently absorb the deformation and misalignment of each ferrite magnetic layer that occurs in the lamination process. The width of the street is narrowed, and the effect of suppressing the deterioration of the superimposition characteristics is reduced. Further, in order to completely absorb the stacking position shift, the conductor width difference may be made larger than the stacking position shift. However, when the conductor width difference is 50 μm or more, the number of second planar coil conductors 3b is large. In particular, since it is necessary to reduce the width of the second planar coil conductor 3b or increase the width of the first planar coil conductor 3a, the conductor resistance of the coil becomes high, and a higher current cannot flow. In some cases, it may be impossible to mount an IC with a high output current on the coil-embedded substrate. Or since the magnitude | size of the planar view of the coil layer 3 will become large, a coil built-in board | substrate may enlarge.

  In the case where the width of the second planar coil conductor 3b gradually decreases as the distance from the first planar coil conductor 3a increases, the sequentially decreasing amounts between the plurality of second planar coil conductors 3b are as described above. You can do it.

  As the metal powder used for the production of the coil layer 3, a low resistance metal powder such as Cu, Ag, Au, Pt, Ag—Pd alloy and Ag—Pt alloy similar to the wiring conductor 4 is used. For example, if the semiconductor chip mounted on the coil-embedded substrate is for a power source for a DC-DC converter, it is preferable that a high current can flow through the planar coil conductors 3a and 3b. The conductors of the planar coil conductors 3a and 3b If the resistance is high, the planar coil conductors 3a and 3b may generate heat, thereby affecting the operation of the semiconductor chip. Therefore, the low resistance metal as described above is preferable.

  The green sheet for the insulating layer 1 or the green sheet for the ferrite magnetic layer 2 is obtained by mixing the insulating powder or the magnetic ferrite powder with an organic binder, an organic solvent, and a dispersant or a plasticizer as necessary, to obtain a slurry. From this, it is produced by applying in a sheet form by a doctor blade method, a rolling method, a calendar roll method, an extrusion molding method, and the like, and drying and molding.

When the insulating layer 1 is made of nonmagnetic ferrite, the insulator powder used for the green sheet for the insulating layer 1 is obtained by mixing and calcining Fe ₂ O ₃ and CuO or ZnO powder at a predetermined ratio. It can be pulverized into raw powder.

The ferromagnetic ferrite powder used for the ferrite magnetic layer 2 green sheet is a ferrite powder prepared by pre-calcining Fe ₂ O ₃ and CuO, ZnO, or NiO, and has an average particle size of 0.1 μm. It is uniform in a range of ˜0.9 μm, and the grain shape is preferably close to a spherical shape. If the average particle size is smaller than 0.1 μm, it is difficult to uniformly disperse the ferrite powder in the production of the ferrite magnetic layer 2 green sheet. If the average particle size is larger than 0.9 μm, the ferrite magnetic layer 2 is used. This is because the sintering temperature of the green sheet tends to increase. Moreover, a uniform sintered state can be obtained because the particle diameter is uniform and nearly spherical. For example, when a small particle size is present in the ferrite powder, the crystal grain growth is reduced only in that portion, and the magnetic permeability of the ferrite magnetic layer 2 obtained after sintering tends to be difficult to stabilize.

  As the organic binder, those conventionally used for ceramic green sheets can be used. For example, acrylic (acrylic acid, methacrylic acid or a homopolymer or copolymer thereof, specifically an acrylic ester. Copolymer, methacrylic acid ester copolymer, acrylic acid ester-methacrylic acid ester copolymer, etc.), polyvinyl butyral, polyvinyl alcohol, acrylic-styrene, polypropylene carbonate, cellulose, etc. Examples thereof include a polymer or a copolymer. In view of decomposability and volatility in the firing step, an acrylic binder is more preferable.

  The organic solvent for the green sheet is not particularly limited as long as the insulator powder or ferrite powder and the organic binder can be well dispersed and mixed, and examples thereof include organic solvents such as toluene, ketones, alcohols, water, and the like. Among these, solvents having a high evaporation coefficient such as toluene, methyl ethyl ketone, and isopropyl alcohol are preferable because the drying step after slurry application can be performed in a short time.

  The slurry for preparing the green sheet is, for example, added 5 to 20 parts by mass of an organic binder and 15 to 50 parts by mass of an organic solvent with respect to 100 parts by mass of the insulator powder or ferrite powder, and mixed by a mixing means such as a ball mill. To prepare a viscosity of 3 to 100 cps.

  The wiring pattern to be the internal wiring conductor 4a, the mounting electrode 4b, the electrode pad 4d, and the ground conductor 4e is obtained by printing a conductive paste for the wiring conductor 4 on the surface of the green sheet for the insulating layer 1 by a screen printing method or a gravure printing method. Is formed by printing in a predetermined pattern. The wiring pattern to be the through conductor 4c penetrates the green sheet for the insulating layer 1 by punching, laser processing or the like prior to the formation of the wiring pattern to be the internal wiring conductor 4a, the mounting electrode 4b, the electrode pad 4d, and the ground conductor 4e. A hole is formed, and the through-hole is filled with a conductor paste for the wiring conductor 4 by embedding means such as printing or press filling.

  Similarly, the coil pattern to be the coil layer 3 is formed by applying a conductor paste for the coil layer 3 on the surface of the green sheet for the ferrite magnetic layer 2 by a printing method such as a screen printing method or a gravure printing method. The through conductor pattern which is formed by printing on the pattern to be the second planar coil conductor 3b and which is the through conductor in the ferrite magnetic layer 2 is also formed in the same manner as the wiring pattern to be the through conductor 4c. The conductor paste for the coil layer 3 may be the same as the conductor paste for the wiring conductor 4.

  The conductor paste for the wiring conductor 4 and the conductor paste for the coil layer 3 are kneading means such as a ball mill, a three-roll mill, a planetary mixer, etc. by adding an organic binder, an organic solvent, and a dispersant as required to the main component metal powder. By mixing and kneading.

  As the organic binder for the conductive paste, those conventionally used for the conductive paste can be used. For example, acrylic (a homopolymer or copolymer of acrylic acid, methacrylic acid or esters thereof, specifically acrylic Acid ester copolymer, methacrylate ester copolymer, acrylic ester-methacrylic ester copolymer, etc.), polyvinyl butyral, polyvinyl alcohol, acrylic-styrene, polypropylene carbonate, cellulose, etc. A homopolymer or a copolymer is mentioned. In view of decomposition and volatility in the firing step, acrylic and alkyd organic binders are more preferable.

  The organic solvent for the conductor paste is not particularly limited as long as the above-described metal powder and organic binder can be well dispersed and mixed, and terpineol, butyl carbitol acetate, phthalic acid, and the like can be used.

  Conductive paste for wiring conductor 4 for forming wiring patterns to be the internal wiring conductor 4a, mounting electrode 4b and electrode pad 4d, and the first planar coil conductor pattern and the second plane to be the first planar coil conductor 3a The conductor paste for planar coil conductor for forming the second planar coil conductor pattern to be the coil conductor 3b is 3 to 15 parts by mass of organic binder and 10 to 30 parts by mass of organic solvent with respect to 100 parts by mass of the metal conductor powder. It is desirable that the viscosity be such that a pattern having a predetermined shape can be satisfactorily formed by printing without causing problems such as bleeding and fading of the conductor paste by printing.

  The conductor paste for forming the through conductor pattern to be the through conductor of the through conductor 4c and the coil layer 3 has a wiring pattern to be the internal wiring conductor 4a, the mounting electrode 4b, and the electrode pad 4d depending on the amount of solvent and the amount of organic binder. The conductor paste for wiring conductor 4 and the conductor paste for planar coil conductor to be formed should be adjusted to a paste with relatively low fluidity to facilitate filling into the through-hole and to be heated and cured. . Moreover, it is good also as an inorganic component which added the powder of glass or ceramics to the metal conductor powder for adjustment of sintering behavior.

  When the insulating layer 1 is formed of nonmagnetic ferrite, the conductor paste for the wiring conductor 4 for forming the wiring conductor 4 formed on the outer surface of the insulating layer 1 such as the mounting electrode 4b and the electrode pad 4d is used. It is desirable to add a powder of a divalent metal oxide such as ZnO, CuO, MgO, CoO, NiO, MnO, or FeO. By adding a divalent metal oxide, the wiring conductor 4 on the outer surface can be firmly bonded to the insulating layer 1 mainly composed of nonmagnetic ferrite.

  A laminate is prepared by placing a predetermined number of green sheets for insulating layer 1 each having a wiring conductor pattern on top and bottom of a predetermined number of green sheets for ferrite magnetic layer 2 including a coil conductor pattern. The coil-embedded substrate is manufactured by firing this laminate.

  The method for producing the laminated body includes a method in which heat and pressure are applied to the stacked green sheet for the insulating layer 1 and the green sheet for the ferrite magnetic layer 2 by thermocompression bonding, an organic binder, a plasticizer, a solvent, and the like. A method of applying an adhesive between sheets and thermocompression bonding can be employed. The conditions for heating and pressing during lamination vary depending on the type and amount of the organic binder used, but are generally 30 to 100 ° C. and 2 to 20 MPa.

  The laminate is fired by debinding at a temperature of 300 to 600 ° C. and then firing at a temperature of 800 to 1000 ° C. As the firing atmosphere, when the planar coil conductor 7 and other wirings are made of a material that is difficult to oxidize such as Ag, the firing atmosphere is performed in the air, and when made of a material that is easily oxidized such as Cu, a nitrogen atmosphere is used. Use a humidified product to facilitate debinding.

  In addition, the mounting electrode 4b and the electrode pad 4d formed on the surface of the coil-embedded substrate after firing are bonded to a semiconductor chip, a chip component, and an external electric circuit by soldering or the like. A nickel layer and a gold layer may be sequentially deposited on the surface by a plating method.

  In addition, this invention is not limited to the example of the above embodiment, and the Example shown below, A various change may be performed in the range which does not deviate from the summary of this invention.

It is sectional drawing which shows an example of embodiment of the board | substrate with a built-in coil of this invention. It is sectional drawing which shows an example of embodiment of the board | substrate with a built-in coil of this invention. It is sectional drawing which shows an example of the conventional board | substrate with a built-in coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulating layer 2 ... Ferrite magnetic material layer 3 ... Coil layer 3a ... 1st plane coil conductor 3b ... 2nd plane coil conductor 4 ... Wiring conductor

Claims (3)

A coil-embedded substrate comprising a pair of insulating layers formed with wiring conductors, a ferrite magnetic layer sandwiched between the pair of insulating layers, and a coil layer formed in the ferrite magnetic layer, The coil layer includes a plurality of turns of a plurality of planar coil conductors arranged so as to face each other in the thickness direction, and the plurality of planar coil conductors includes a first planar coil conductor having a maximum width, and the first And a second planar coil conductor having a width smaller than that of the planar coil conductor. 2. The coil-embedded substrate according to claim 1, wherein there are a plurality of the second planar coil conductors, and the width of the second planar coil conductors gradually decreases as the distance from the first planar coil conductor increases. 2. The coil built-in substrate according to claim 1, wherein there are a plurality of the second planar coil conductors, and the widths thereof are the same.

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