JP4557690B2 - Coil built-in board - Google Patents

Description

  The present invention relates to a coil-embedded substrate in which an insulating base made of a nonmagnetic ferrite sintered body is provided with a ferrite layer in which a coil conductor is embedded.

  2. Description of the Related Art Conventionally, many electronic devices are incorporated in electronic devices such as mobile communication devices such as mobile phones. Such communication devices such as mobile phones have been rapidly reduced in size in recent years, and various electronic devices mounted thereon are required to be reduced in size and thickness. For example, an LC filter having a configuration in which a coil is built in a glass ceramic substrate is known. In the case of this LC filter, there is an advantage that it is possible to reduce the size and thickness of the LC filter, which has conventionally been externally attached using a coil of a chip component, in an insulating substrate such as a ceramic substrate. Among them, a coil having a large inductance exceeding 100 nH is relatively large as a chip component, and incorporating this in an insulating substrate has an advantage that the effect of miniaturization and thinning is great.

  However, in an insulating substrate such as a ceramic having a built-in coil, the coil is formed in a substrate that does not have magnetism. Therefore, in order to incorporate a coil capable of obtaining a relatively large inductance of about 100 nH, the number of turns of the coil is large. There is a problem that it is impossible to effectively reduce the size and thickness.

  Therefore, in recent years, by using a ferromagnetic ferrite for the insulating substrate and embedding the coil inside the ferrite, an inductance exceeding 100 nH can be realized without increasing the number of turns of the coil, and the size and thickness can be effectively reduced. In addition, it is possible to simplify the mounting process by omitting the process of mounting the chip component on the surface.

  However, in a substrate using ferrite as an insulating substrate, when a wiring is formed together with a coil, a high inductance is generated in the wiring that does not want to have magnetism, and the circuit may malfunction due to noise generated in the wiring. Therefore, a ferrite layer is built inside non-magnetic ferrite that does not have magnetism, a coil is formed in the ferrite layer, and wiring is formed in the non-magnetic ferrite to reduce wiring inductance and prevent malfunction of the circuit. I was trying to do it.

  For example, as shown in FIG. 3, a substrate with a built-in coil used in a cellular phone includes an insulating base 11 in which a plurality of nonmagnetic ferrite layers are laminated, and a laminated structure sandwiched between insulating bases 11 and a coil inside. It is comprised by the ferrite layer 12 with which the conductor 13 was embed | buried.

And even in such a coil-embedded substrate in which a ferrite layer and a coil conductor are provided inside the non-magnetic ferrite substrate, it is necessary to further reduce the size, thickness, and functionality in the future. In addition, it has become necessary to further surface-mount semiconductor chips and chip components on the bottom surface.
Japanese Patent Laid-Open No. 2-101714 JP-A-6-20839 JP-A-6-21264 JP-A-6-333743

  However, in the conventional coil-embedded substrate in which the ferrite layer and the coil conductor are provided inside the non-magnetic ferrite substrate, the magnetic force lines generated in the coil conductor are radiated toward the outside of the coil-embedded substrate, and the magnetic force lines are unstable. Therefore, the magnetic saturation of the ferrite layer caused by the disturbance of the magnetic field lines is likely to occur, and the so-called superposition characteristic is lowered, that is, the inductance is lowered when a large current is passed. Furthermore, the lines of magnetic force radiated toward the outside of the coil-embedded substrate electrically affect, for example, semiconductor chips, chip components, and wiring mounted on the upper and lower surfaces of the coil-embedded substrate, causing malfunction of the circuit. It was.

  Therefore, in order to prevent the magnetic field lines generated in the coil conductor from electrically affecting the semiconductor chip, chip components, and wiring mounted on the upper and lower surfaces of the coil-embedded substrate, the coil conductor and the semiconductor It is necessary to ensure a sufficient distance between the chip, the chip component, and the wiring. As a result, the entire coil-embedded substrate becomes thick and is not suitable for thinning.

  The present invention has been devised in order to solve the above-mentioned problems, and its purpose is to suppress the magnetic field lines generated in the coil conductor, thereby improving the superimposition characteristics and improving the superposition characteristics on the upper and lower surfaces of the coil-embedded substrate. An object of the present invention is to provide a small coil-embedded substrate with improved electrical influence on a mounted semiconductor chip and chip parts.

In the coil-embedded substrate of the present invention, a ferrite layer in which a coil conductor is embedded is sandwiched between a pair of insulating bases each formed of a laminate of a plurality of nonmagnetic ferrite layers, and a semiconductor chip or chip to form the electrode pads for connecting to the mounting electrodes or external electrical circuit equipped with components electrically in upper and lower surfaces of the insulating substrate between the insulating base material and the ferrite layer, for the coil It is characterized in that a grounding conductor layer facing the conductor is interposed.

  The coil-embedded substrate according to the present invention is characterized in that the coil conductor is arranged so that the entire surface thereof overlaps the ground conductor layer in plan view.

In the coil-embedded substrate of the present invention, the ferrite layer contains Fe ₂ O ₃ , CuO, NiO and ZnO, the Fe ₂ O ₃ content is a mass%, and the CuO content is b mass. %, The content of NiO is c mass%, and the content of ZnO is d mass%, the a, b, c, d are “63 ≦ a ≦ 73, 5 ≦ b ≦ 10, 5 ≦ c ≦ 12. 10 ≦ d ≦ 23 and a + b + c + d ≦ 100 ″ are satisfied.

According to the coil-embedded substrate of the present invention, the ferrite layer in which the coil conductor is embedded is sandwiched between a pair of insulating bases each formed of a laminate of a plurality of nonmagnetic ferrite layers, and a semiconductor chip or an electrode pad for electrically connecting and forming the upper and lower surfaces of the insulating substrate to the mounting electrodes or external electrical circuit mounting chip components, between the insulating base material and the ferrite layer, and a coil conductor Since the opposing ground conductor layers are interposed, the magnetic lines of force generated in the coil conductor are confined between the upper and lower ground conductor layers of the coil conductor to stabilize the magnetic lines of force, and the magnetic saturation of the ferrite layer caused by the disturbance of the magnetic field lines is prevented. Since it is difficult to occur, it is possible to effectively prevent the deterioration of the superposition characteristics.

  In addition, the lines of magnetic force generated in the coil conductors have less electrical effects on the semiconductor chips and chip components mounted on the upper and lower surfaces of the coil-embedded substrate, resulting in malfunction of the circuit formed on the coil-embedded substrate. The coil-embedded substrate can be made small and thin.

  Further, according to the coil-embedded substrate of the present invention, the ground conductor layer completely covers the upper and lower surfaces of the coil conductor by arranging the coil conductor so that the entire surface thereof overlaps the ground conductor layer in plan view. Since the magnetic field lines generated in the coil conductor are more stable and magnetic saturation is less likely to occur, the superposition characteristics can be prevented more effectively, and the magnetic field lines generated in the coil conductor are reduced. The semiconductor chip and chip components mounted on the upper surface and surface of the coil built-in substrate are less likely to be electrically affected, and as a result, malfunction of the circuit formed on the coil built-in substrate can be more effectively prevented.

Still further, according to the coil-embedded substrate of the present invention, in the above configuration, the ferrite layer is formed to contain Fe ₂ O ₃ , CuO, NiO and ZnO, and the content of Fe ₂ O ₃ is a mass%, CuO. When the content of is b mass%, the content of NiO is c mass%, and the content of ZnO is d mass%, a, b, c, d are “63 ≦ a ≦ 73, 5 ≦ b ≦ 10, When 5 ≦ c ≦ 12, 10 ≦ d ≦ 23, and a + b + c + d ≦ 100 ”are satisfied at the same time, NiCuZn ferrite obtained by combining CuZn ferrite, which can be sintered at a low temperature, with NiZn ferrite having excellent high frequency band characteristics is used. It is possible to form a ferrite layer having the same size as the nonmagnetic ferrite layer and having a coil embedded therein. As a result, the ferrite layer can be fired at the same time as the insulating substrate without adding glass powder or sintering aids such as SiO ₂ and Al ₂ O _3, so delamination and cracks due to differences in shrinkage behavior In addition, it is possible to obtain a high magnetic permeability in a high frequency band and to obtain a coil-embedded substrate having a high inductance.

In addition, since the ferrite layer can be fired at a low temperature, a low-resistance metal such as Cu, Ag, Au, or an Ag alloy that can handle high frequencies can be used for the wiring conductor, and a highly functional coil-embedded substrate can be obtained. .
With the above configuration, according to the present invention, the lines of magnetic force generated in the coil conductor can be suppressed, the superimposition characteristics can be improved, and the electricity to the semiconductor chips and chip components mounted on the upper and lower surfaces of the coil-embedded substrate can be improved. It is possible to provide a small coil-embedded substrate in which the influence is improved.

  A coil built-in substrate (hereinafter also referred to as a substrate) according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing an example of an embodiment of a substrate of the present invention, wherein 1 is an insulating substrate composed of a plurality of nonmagnetic ferrite layers, 2 is a ferrite layer, 3 is a coil conductor, and 4 is a coil conductor 3. contact Chishirube layer provided on the upper and lower, 5 mounted electrode for mounting the semiconductor chip and the chip component, 6 is an electrode pad for electrically connecting the board to an external electrical circuit.

  The insulating substrate 1 composed of a plurality of nonmagnetic ferrite layers is first composed of a main component and a first oxide component of a nonmagnetic ferrite composition, or a main component and a first oxide component and a second oxide component of a nonmagnetic ferrite composition. Furthermore, an organic binder, plasticizer, organic solvent, etc. are mixed to obtain a slurry, from which a non-magnetic ferrite green sheet is produced by a doctor blade method, a rolling method, a calender roll method, etc. After the lamination, it is produced by firing at a temperature of 800 to 1100 ° C. in the air or in a humidified nitrogen atmosphere.

As the main component of the nonmagnetic ferrite composition, powder of Fe ₂ O ₃ and at least one of CuO and ZnO can be used. For example, these are wet-mixed, then calcined, and pulverized as granules After that, the raw material powder can be obtained. In this case, it is preferable to set the content of Fe ₂ O ₃ to 46 to 50% by mass, the content of CuO to 2 to 20% by mass, and the content of ZnO to 33 to 52% by mass.

The ferrite layer 2 is formed together with the coil conductor 3 on the inner layer of the insulating base 1 so as to cover the upper and lower surfaces of the coil conductor 3. When the composition of the main component of the ferrite layer 2 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 23% by mass of ZnO, firing at a low temperature is possible. This is preferable because it is possible and a sufficiently high magnetic permeability can be obtained in a high frequency band.

Fe ₂ O ₃ is a basic component of ferrite. If the main component of the ferrite is a solid solution having an inverted spinel structure represented as X—Fe ₂ O ₄ (X is Cu, Ni, Zn, etc.), the ferrite layer 2 _Fe 2 _{O 3} of the must constitute the 63-73 wt%. When Fe ₂ O ₃ is less than 63% by mass, it is difficult to obtain sufficient magnetic permeability. On the other hand, if the Fe ₂ O ₃ exceeds 73 wt%, the mechanical strength is lowered due to a decrease in sintering density.

CuO must constitute 5 to 10% by mass of the main component of the ferrite layer 2. This is because CuO greatly contributes to lowering the sintering temperature, and the effect of CuO to promote sintering by forming a liquid layer at a low temperature makes it possible to sinter nonmagnetic ferrite without impairing magnetic properties. It is for baking at 800-1000 degreeC which is temperature. When the content is less than 5% by mass, the sintering density becomes insufficient and the mechanical strength is insufficient when firing is performed in the low temperature range targeted by the present invention. 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 is increased, so that the magnetic property is impaired.

NiO is contained in order to ensure the magnetic permeability of the ferrite in the high frequency range. 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 at a relatively high value in the high frequency range. If it is less than%, the magnetic permeability in a high frequency region of 10 MHz or more is lowered. Also, if more than 12 wt%, the initial permeability is decreased due to the proportion of NiFe ₂ O ₄ is increased. Therefore, it is important to set the content of the main component of ferrite to 5 to 12% by mass.

  ZnO is an important element for improving the magnetic permeability of ferrite, and if it is less than 10% by mass of the main component of ferrite, it causes a problem of insufficient magnetic properties. Deteriorate.

  The ferrite layer 2 is formed by first mixing a ferrite powder with an appropriate organic binder, plasticizer, organic solvent, etc. to obtain a slurry, from which a ferrite green sheet is produced by a doctor blade method, a rolling method, a calender roll method, or the like. . Next, the ferrite green sheet is cut into the same shape as the glass ceramic green sheet in plan view so as to cover the predetermined coil conductor 3, and the coil green sheet is interposed between the glass ceramic green sheet laminate and the coil. A conductor pattern to be the conductor 3 is arranged and laminated so as to cover the upper and lower surfaces of the coil conductor 3.

  At this time, in order to effectively increase the inductance of the coil conductor 3, it is necessary to completely cover the upper and lower surfaces of the coil conductor 3 with the ferrite layer 2. Therefore, in order to form such a coil conductor 3 and a ferrite layer 2, a ferrite green sheet that becomes the lower ferrite layer 2 and a conductor paste that becomes the coil conductor 3 are formed on the surface of a predetermined glass ceramic green sheet. Each layer may be arranged and laminated in the order of the pattern and the ferrite green sheet to be the upper ferrite layer 2.

  The ferrite powder used to form the ferrite green sheet used as the ferrite layer 2 is a calcined ferrite powder, an average particle diameter in the range of 0.1 μm to 0.9 μm, and a particle having a nearly spherical shape Is desirable. This is because 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 green sheet. If the average particle size is larger than 0.9 μm, the sintering temperature of the ferrite is increased. It is. In addition, since a uniform sintered state can be obtained when the particle size is uniform and nearly spherical, for example, when a small particle size is present in ferrite powder, the crystal grains grow only in that portion. It tends to decrease and the magnetic permeability of the ferrite layer 2 obtained after sintering tends to be less stable.

  The coil conductor 3 made of a metallized wiring layer is embedded in the ferrite layer 2 with the upper and lower surfaces covered with the ferrite layer 2, and an appropriate organic binder, solvent and the like in a metal powder such as Cu, Ag, Au, and Ag alloy. The conductive paste prepared by kneading the above is applied to the surface of the ferrite green sheet by a screen printing method, a gravure printing method, or the like, and is fired simultaneously with the ceramic green sheet and the ferrite green sheet.

  The mounting electrode 5 made of a metallized layer is made of a conductive paste prepared by kneading a metal powder such as Cu, Ag, Au, or Ag alloy with an appropriate organic binder and solvent, by a screen printing method or a gravure printing method. By applying on the surface of the green sheet, the insulating substrate 1 is formed on the upper surface and the lower surface.

Incidentally, mounting electrode 5, or the like bonding between the semiconductor chip and the chip unit products in order to make firm by the solder, it is preferable to successively deposited by plating a nickel layer and a gold layer on its surface.

  An electrode pad 6 made of a metallized wiring layer electrically connected to an external electric circuit is obtained by applying a conductive paste prepared by kneading a suitable organic binder and solvent to a metal powder such as Cu, Ag, Au, or Ag alloy. It is formed on at least one of the upper surface and the lower surface of the insulating substrate 1 by being applied to the surface of the ceramic green sheet by a printing method, a gravure printing method, or the like.

The electrode pad 6 made of metallized wiring layer, the bonding between the wiring conductor of the external electric circuit that by the solder in order to make firm, sequentially be by plating a nickel layer and a gold layer on the surface You should wear it.

In the coil-embedded substrate of the present embodiment, contact Chishirube layer 4 are respectively formed so as to face at least a coil conductor 3 on the upper and lower surfaces of the ferrite layer 2.

The contact Chishirube layer 4, it is more desirable to the entire upper and lower surfaces of the ferrite layer 2 is formed so as to overlap with the coil conductor 3 when viewed. This is because the lines of magnetic force generated in the coil conductors 3 are blocked by the ground conductor layer 4, it becomes difficult to leak outside, it is possible to further stabilize, thereby sufficiently improving the bias characteristic, further coil This is because the electrical influence on semiconductor chips and chip components mounted on the upper and lower surfaces of the built-in substrate is improved.

  The grounding conductor layer 4 made of a metallized wiring layer is formed by using a screen paste method, a gravure print method, or the like using a conductive paste prepared by kneading a suitable organic binder and solvent in a metal powder such as Cu, Ag, Au, or Ag alloy. The ceramic green sheet or the ferrite green sheet is applied to the surface, and is fired simultaneously with the ceramic green sheet and the ferrite green sheet.

  In Example 1, a coil-embedded substrate having the configuration shown in FIG. 1 in which the ground conductor layer was formed on the upper and lower surfaces of the ferrite layer so as to face the coil conductor, and the superposition characteristics and the magnetic permeability were measured.

  The insulating base is formed by laminating two nonmagnetic ferrite layers each having a thickness of 50 μm. A magnetic permeability of 500 (H) is formed in the insulating substrate by being simultaneously fired with the nonmagnetic ferrite layer, and a 30 μm thick coil conductor made of Ag is embedded in the insulating substrate and sandwiched between the insulating substrates. / M) ferrite layer is incorporated.

  Further, on the upper and lower surfaces of the ferrite layer, an inner ground conductor layer having a thickness of 10 μm made of Ag, which is formed so as to face the coil conductor, is provided.

  The measurement of the superimposition characteristic was performed by the current-voltage method using an impedance analyzer (HP-4194A: manufactured by Hewlett Packard).

  Moreover, the measurement of the magnetic permeability produced and measured the test piece for evaluation of a ring shape with an outer diameter of 16 mm and an inner diameter of 8 mm as shown in FIG. The permeability was measured using an impedance analyzer (HP-4291A: manufactured by Hewlett Packard) by the high frequency current voltage method.

  In Example 2, a coil-embedded substrate in which the ground conductor layer completely covered the coil conductor in the coil-embedded substrate of Example 1 was produced, and the same evaluation as in Example 1 was performed.

In Example 3, in the coil-embedded substrate of Example 2, the composition of the ferrite layer is 65% by mass of Fe ₂ O ₃ , 6% by mass of CuO, 6% by mass of NiO, ZnO A coil-embedded substrate having a content of 23% by mass was prepared and evaluated in the same manner as in Examples 1 and 2.

Comparative example

  In order to compare with the above-described Examples 1 to 3, conventional coil-embedded substrates in which the ground conductor layer is not provided in Examples 1 and 3 as conventional configurations were created as Comparative Examples 1 and 2, and Examples 1 to 3 were prepared. The same evaluation was performed.

Table 1 shows the results of evaluating the superposition characteristics and the magnetic permeability of Examples 1 to 3 and Comparative Examples 1 and 2 described above.

  In the superimposition characteristic evaluation column of Table 1, ◎ indicates that the inductance value at 500 mA satisfies the standard 2 μH, ○ indicates that the inductance value at 300 mA satisfies the standard 2 μH, and Δ indicates that the inductance value at 100 mA satisfies the standard 2 μH. The thing x represents something that does not meet the standard at all. In general, a coil used for a mobile phone functions satisfactorily if it is 300 mA or more and 2 μH or more.

  From Table 1, it was confirmed that Example 1 in which the ground conductor layer was formed on the upper and lower surfaces of the ferrite layer so as to face the coil conductor was superior to the superposition characteristics of Comparative Example 1.

  Further, in Example 2 in which the ground conductor layer completely covers the coil conductor, the superposition characteristics are higher than in Example 1, and the magnetic lines of force are less likely to leak to the outside, so that the magnetic lines of force can be stabilized and the superposition characteristics are excellent. It was confirmed.

  In addition, it was confirmed that Example 3 using the ferrite layer having the composition according to claim 3 had superior characteristics as compared with the magnetic permeability of Example 2.

  On the other hand, Comparative Example 2 using the same ferrite layer as in Example 3 is inferior in superposition characteristics because no ground conductor layer is provided.

  250 g each of the raw materials set to various preparation composition ratios were weighed and mixed in a 2 L ball mill using zirconia grinding balls together with 1 L of pure water for 24 hours, then the raw material powder was separated and dried, and then 730 in a zirconia crucible. C. calcination was performed. After calcination, it is confirmed that the required compound is obtained by X-ray diffraction, pulverized with a ball mill, separated by a mesh sieve after drying, and the particle size of the calcined powder is 0.5 to 0.7 μm. The size was adjusted so that A 10% by weight PVA solution was added to this, granulated with a reiki machine, the granulated powder was press-molded with a mold, and then fired in the atmosphere at 900 ° C. for 2 hours to obtain an outer diameter. A toroid-shaped sintered test piece having a diameter of 16 mm, an inner diameter of 8 mm, and a thickness of 2 mm was prepared. The density of the test piece was measured by a submerged weighing method, and the permeability was measured by using an impedance analyzer (HP-4291A: manufactured by Hewlett-Packard Company) at 1.0 MHz and 10 MHz.

In addition, the composition ratio of the raw materials used for the preparation of the firing test pieces is as shown in Table 2, and the measurement results of the sintered density and permeability of each firing test piece are also shown in the same table.

  According to Table 2, it is confirmed that any of the main component compositions within the range defined by the present invention is excellent in sintered density and magnetic permeability.

Is a sectional view showing an example of an embodiment of a coil in Zomoto plate of the present invention. It is sectional drawing which shows the test piece for evaluation used for the magnetic permeability measurement of an Example. Is a sectional view showing an example of the conventional coil Zomoto plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Ferrite layer 3 ... Conductor for coils 4 ... Grounding conductor layer 5 ... Electrode for mounting 6 ... Electrode pad

Claims (3)

A ferrite layer in which a coil conductor is embedded is sandwiched between a pair of insulating bases each formed of a laminate of a plurality of nonmagnetic ferrite layers, and mounting electrodes or semiconductor chips or chip components are mounted thereon. electrode pads for electrical connection to an external electric circuit and forming the upper and lower surfaces of the insulating substrate between the insulating base material and the ferrite layer, the grounding conductor layer to the conductor facing for the coil A coil-embedded substrate characterized by being interposed.   2. The coil-embedded substrate according to claim 1, wherein the coil conductor is disposed so that the entire surface thereof overlaps the ground conductor layer in a plan view. The ferrite layer contains Fe ₂ O ₃ , CuO, NiO and ZnO, the Fe ₂ O ₃ content is a mass%, the CuO content is b mass%, and the NiO content is c mass%. 3. The coil-embedded substrate according to claim 1, wherein when a ZnO content is d mass%, the a, b, c, and d satisfy the following formula.
63 ≦ a ≦ 73
5 ≦ b ≦ 10
5 ≦ c ≦ 12
10 ≦ d ≦ 23
a + b + c + d ≦ 100

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