JP4428992B2 - Glass ceramic substrate with built-in coil - Google Patents

Description

  According to the present invention, a ferrite layer for increasing an inductance value is provided in which an insulating base made of a sintered glass ceramic body is formed by simultaneous firing with a glass ceramic insulating layer and a coil conductor is embedded therein. The present invention relates to a glass ceramic substrate with a built-in coil.

  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 by incorporating the coil of the conventional chip component inside the glass ceramic substrate.

  However, in the glass ceramic substrate with a built-in coil, it is difficult to incorporate a coil exceeding 100 nH due to size restrictions. Therefore, in recent years, it is possible to incorporate a coil exceeding 100 nH by incorporating a ferrite layer in the glass ceramic substrate, thereby simplifying the surface mounting process of the chip coil and reducing the size of the glass ceramic substrate with a built-in coil. It has been.

  For example, a glass-ceramic substrate with a built-in coil used in a cellular phone generally has a coil-use substrate inside an insulating substrate 1 composed of a plurality of glass-ceramic insulating layers, as shown in a sectional view in FIG. A conductor 3, a ferrite layer 2 covering the upper and lower surfaces of the coil conductor 3 and having the same size as the glass ceramic insulating layer, and a ground conductor formed on the upper and lower surfaces of the ferrite layer 2 so as to face the coil conductor 3. Formed by layer 4.

  In such a glass-ceramic substrate with a built-in coil, in order to further reduce the size, the thickness, and the functionality, a semiconductor chip is formed on the upper and lower surfaces of the glass-ceramic substrate with a built-in coil provided with a ferrite layer 2 therein. And chip parts need to be surface mounted. And by the ground conductor layers 4 above and below the coil conductor 3, the electric lines of force generated in the coil conductor 3 have an electrical influence on the semiconductor chips and chip components mounted on the upper and lower surfaces of the coil-embedded glass ceramic substrate. As a result, malfunction of the circuit formed on the glass ceramic substrate with a built-in coil can be prevented.

In addition, in a glass-ceramic substrate with a built-in coil having a ferrite layer, the electric lines of force generated in the coil conductor are confined between the upper and lower ground conductor layers of the coil conductor and the electric lines of force are stabilized. Since the magnetic saturation of the ferrite layer caused by disturbance is less likely to occur, it is possible to prevent a decrease in inductance when a large current is passed.
JP-A-6-20839 JP-A-6-21264

  However, depending on the thickness of each layer between the coil conductors, the coil conductor is strongly electromagnetically coupled to the upper and lower ground conductor layers of the coil conductor, and electrical characteristics such as high inductance values and superposition characteristics are deteriorated.

  If the coupling between the coil conductor and the ground conductor layer is further strengthened, a resonance phenomenon occurs due to the stray capacitance generated between the coil conductor and the ground conductor layer and the inductance of the coil conductor. Will not appear.

  The present invention has been completed in view of the above-described problems in the prior art, and its purpose is that the coil conductor inside the glass-ceramic substrate with a built-in coil is not easily affected by the ground conductor layer and is high as a coil. An object of the present invention is to provide a glass-ceramic substrate with a built-in coil that can obtain inductance characteristics and superposition characteristics.

The glass-ceramic substrate with a built-in coil according to the present invention is formed in the insulating substrate formed by laminating a plurality of glass ceramic insulating layers, and is fired simultaneously with the glass ceramic insulating layer, and a plurality of layers of coil conductors are formed therein. buried, the glass ceramic insulating layer and the same size as the ferrite layer, and a ground conductor layer formed respectively are provided so as to face the coil conductors on the upper and lower surfaces of the ferrite layer, the coil when the distance between the use conductors T1, the distance between the conductor and the ground conductor layer coil was T2, Ri T1 <T2 der, permeability of the ferrite layer between the coil conductor, said It is smaller than the magnetic permeability of the ferrite layer between the coil conductor and the ground conductor layer .

According to the glass-ceramic substrate with a built-in coil of the present invention, a plurality of layers of coil conductors are formed inside an insulating substrate formed by laminating a plurality of glass ceramic insulating layers and simultaneously fired with the glass ceramic insulating layer. There are embedded, and the same size as the ferrite layers between the glass-ceramic insulating layer, and a ground conductor layer formed respectively provided so as to face the coil conductors on the upper and lower surfaces of the ferrite layer, between the conductive coil Is T1, and the distance between the coil conductor and the ground conductor layer is T2, since T1 <T2, the electromagnetic coupling between the coil conductor and the upper and lower ground conductor layers is weakened. The stray capacitance generated between the coil conductor and the ground conductor layer is suppressed, and electrical characteristics such as a high inductance value and superposition characteristics can be obtained. Further, it is possible to prevent a resonance phenomenon at the operating frequency due to stray capacitance generated between the coil conductor and the ground conductor layer and the inductance of the coil conductor. In addition, since the direction of magnetic flux differs between the coil conductors and cancels out, the magnetic flux canceling force can be weakened by lowering the permeability of the ferrite layer, and the superposition characteristics can be improved.

  The coil-embedded glass ceramic substrate (hereinafter also referred to as a substrate) of the present invention will be described in detail with reference to the 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 base composed of a plurality of glass ceramic insulating layers, 2 is a ferrite layer, 3 is a coil conductor, and 4 is a coil conductor 3. Ground conductor layers 5 are provided above and below, 5 is a mounting electrode for mounting a semiconductor chip and chip components, and 6 is an electrode pad for electrically connecting the substrate to an external electric circuit.

  The insulating substrate 1 formed by laminating a plurality of glass ceramic insulating layers is first obtained by mixing a glass powder and a filler powder (ceramic powder), and further mixing an organic binder, a plasticizer, an organic solvent and the like to obtain a slurry. A glass ceramic green sheet (hereinafter also referred to as a green sheet) is manufactured by a doctor blade method, a rolling method, a calender roll method, and the like, and after stacking a plurality of the green sheets, 800 to 1100 in the air or in a humidified nitrogen atmosphere. It is produced by firing at a temperature of ° C.

Examples of the glass powder 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 (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 system (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 glass, Bi glass, etc. can be used.

Examples of the filler powder include Al ₂ O ₃ , SiO ₂ , a composite oxide of ZrO ₂ and an alkaline earth metal oxide, a composite oxide of TiO ₂ and an alkaline earth metal oxide, and Al ₂ O. A composite oxide (for example, spinel, mullite, cordierite) containing at least one selected from ₃ and SiO ₂ can be used.

  In the present invention, when the distance between the coil conductors 3 is T1, and the distance between the coil conductor 3 and the ground conductor layer 4 is T2, T1 <T2.

  Specifically, T1 is preferably less than 0.1 mm from the viewpoint of stability of inductance between the coil conductors 3, and T2 is preferably 0.1 mm or more in relation to electric lines of force absorbed by the ground conductor layer 4. When T1 exceeds 0.1 mm, a leakage magnetic flux is generated between the coil conductors 3 and the inductance is not stabilized. When T2 is less than 0.1 mm, electric lines of force are absorbed by the ground conductor layer 4 to increase electromagnetic coupling, and a resonance phenomenon occurs between the coil conductor 3 and the ground conductor layer 4.

The ferrite layer 2 is formed inside the insulating substrate 1 with the coil conductor 3 embedded therein, and is made of 99 wt% or more of ferrite and 1 wt% or less of glass. The ferrite of the ferrite layer 2 includes ZnFe ₂ O ₄ , MnFe ₂ O ₄ , FeFe ₂ O ₄ , CoFe ₂ O ₄ , NiFe ₂ O ₄ , BaFe ₁₂ O ₄ , SrFe ₁₂ O _4, and CuFe ₂ O ₄ . It is preferable to use at least one type of ferrite because a higher magnetic permeability can be obtained.

In addition, the magnetic permeability of the ferrite layer 2 between coils conductor 3 is designed to be smaller than the magnetic permeability of the ferrite layer 2 between the coil conductor 3 and the ground conductor layer 4. In this case, the direction of the magnetic flux differs between the coil conductors 3 and cancels out. Therefore, there is an advantage that the magnetic flux canceling force can be weakened by reducing the magnetic permeability of the ferrite layer 2 and the superposition characteristics can be improved.

  The ferrite layer 2 is formed by first mixing a ferrite powder with a suitable organic binder, plasticizer, organic solvent, etc. to obtain a slurry, and using this slurry, a ferrite green by a doctor blade method, a rolling method, a calendar roll method, etc. Make a sheet. Next, the ferrite green sheet is cut into the same shape as the glass ceramic green sheet so as to cover the coil conductor 3, and the coil conductor 3 and the ferrite green sheet are placed between the ferrite green sheets inside the glass ceramic green sheet laminate. A pattern is formed and laminated so as to cover the upper and lower surfaces of the coil conductor 3.

  The ferrite powder used to form the ferrite green sheet to be the ferrite layer 2 is preferably a calcined ferrite powder having a uniform particle size and a nearly spherical shape. This is because a uniform sintered state can be obtained. For example, when a ferrite powder having a small particle size is present, the growth of crystal grains is reduced only in that portion, and after sintering, The magnetic permeability of the obtained ferrite layer 2 tends to be difficult to stabilize.

  The ferrite layer 2 comprises 1% by weight or less of glass. However, this 1% by weight or less of glass is diffused and mixed from the glass ceramic insulating layer during firing, and is not included in the ferrite green sheet before firing.

  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 glass 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, and Ag alloy with an appropriate organic binder and a solvent by a screen printing method or a gravure printing method. By applying on the surface of the ceramic green sheet, it is formed on the upper and lower surfaces of the insulating substrate 1.

  The mounting electrode 5 has a nickel layer and a gold layer sequentially deposited on the surface thereof by a plating method in order to strengthen the bonding with a semiconductor chip or chip component by solder or the like and a wiring conductor of an external electric circuit. Good.

  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 glass ceramic green sheet by a printing method, a gravure printing method or the like.

  The electrode pad 6 made of a metallized wiring layer is plated with a nickel layer and a gold layer on its surface in order to strengthen the bonding with a semiconductor chip or chip component by solder or the like, or a wiring conductor of an external electric circuit. It is good to deposit sequentially.

  In the substrate of the present invention, the ground conductor layer 4 is formed on the upper and lower surfaces of the ferrite layer 2 so as to face at least the coil conductor 3. The grounding conductor layer 4 made of a metallized layer is made of a glass ceramic using a conductive paste prepared by kneading a suitable organic binder and solvent with a metal powder such as Cu, Ag, Au, or Ag alloy by screen printing or gravure printing. It is formed by coating the surface of a green sheet or a ferrite green sheet and simultaneously firing the glass ceramic green sheet and the ferrite green sheet.

  The superposition characteristics of the coil conductor (built-in coil) 3 on the substrate of the present invention are shown in the graph of FIG. In FIG. 2, the horizontal axis represents current (unit: mA), the vertical axis represents inductance (unit: μH), the solid line represents the inductance standard value of 2 μH, and the dashed characteristic curve represents the superposition characteristics of the built-in coil on the conventional substrate. The solid characteristic curve indicates the superposition characteristic of the built-in coil in the substrate of the present invention.

  In FIG. 2, the conventional substrate is T1 (0.2 mm)> T2 (0.1 mm), and the substrate of the present invention is T1 (0.1 mm) <T2 (0.2 mm). In general, the inductance value at 300 mA, which is the maximum current used in the power supply circuit of a mobile phone, can sufficiently satisfy the standard value of 2 μH or more. That is, in the substrate of the present invention, the electric lines of force generated in the coil conductor 3 are absorbed by the ground conductor layer 4 so as to prevent electromagnetic coupling between the coil conductor 3 and the ground conductor layer 4. Therefore, the magnetic saturation of the ferrite layer 2 is less likely to occur when a current is passed through the coil conductor 3, and deterioration of the superposition characteristics can be prevented.

In FIG. 3 , the horizontal axis represents the frequency (unit: MHz), the vertical axis represents the inductance (unit: μH), and the solid line is generally 5 MHz, which is the highest frequency used in the power supply circuit of a mobile phone. The broken line characteristic curve represents the frequency characteristic of the built-in coil in the conventional substrate, and the solid line characteristic curve represents the frequency characteristic of the built-in coil in the substrate of the present invention.

  In FIG. 3, the conventional substrate is T1 (0.2 mm)> T2 (0.1 mm), and the substrate of the present invention is T1 (0.1 mm) <T2 (0.2 mm). In general, a stable inductance value is obtained at 5 MHz, which is the highest frequency used in a power supply circuit of a mobile phone. This is because, in the substrate of the present invention, the stray capacitance generated by electromagnetic coupling is reduced by the electric lines of force generated in the coil conductor 3 being absorbed in the ground conductor layer 4, so that the resonance frequency generated by the stray capacitance and the inductance value is reduced. (10 MHz) becomes higher, a sufficient distance from the stray capacitance in the ferrite layer is secured, and it can be used at 5 MHz.

  Further, since the superposition characteristics are improved because the radiation of the electric force lines generated in the coil conductor 3 is confined by the ground conductor layer 4, the electric field lines are suppressed from being emitted. Electromagnetic effects on semiconductor chips and chip components mounted on the upper and lower surfaces are also suppressed.

It is sectional drawing which shows an example of embodiment of the glass ceramic substrate with a built-in coil of this invention. It is a graph which shows the superimposition characteristic of the built-in coil in the glass ceramic substrate with a built-in coil of this invention. It is a graph which shows the frequency characteristic of the built-in coil in the glass ceramic substrate with a built-in coil of this invention.

Explanation of symbols

1: Insulating substrate 2: Ferrite layer 3: Coil conductor 4: Ground conductor layer 5: Mounting electrode 6: Electrode pad

Claims (1)

In an insulating substrate in which a plurality of glass-ceramic insulating layers are laminated, the coil conductors of the plurality of layers therein while being formed by co-firing the glass ceramic insulating layer is embedded, and the glass ceramic insulating layer A ferrite layer having the same size and ground conductor layers formed on the upper and lower surfaces of the ferrite layer so as to face the coil conductor are provided, and the distance between the coil conductors is T1, and the coil when the distance between the use conductor and the ground conductor layer and T2, T1 <T2 der is, permeability of the ferrite layer between the coil conductor, and the ground conductor layer and the coil conductors A glass-ceramic substrate with a built-in coil, which is smaller than the magnetic permeability of the ferrite layer in between .

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