JP2995829B2 - Circuit board with built-in magnetic material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board having a magnetic layer formed inside a substrate, and in particular, the constituents of the magnetic substance and the substrate at the time of firing are mutually diffused. The present invention relates to a structure capable of preventing the characteristics from deteriorating and reducing the product cost.

[Conventional technology]

A circuit board with a built-in magnetic material, in which a magnetic layer is embedded inside an insulating substrate, is designed because the entire substrate can be reduced in height and thickness, and the magnetic layer can be formed at an arbitrary position inside the substrate. Is attracting attention as a circuit board for high-density mounting that can improve the degree of freedom. As such a circuit board with a built-in magnetic body, there is a circuit board proposed in, for example, JP-A-63-300593. This circuit board is mainly constructed by printing an internal conductor connected to an external circuit on a magnetic sheet made of ferrite, superimposing an insulating sheet made of ceramic so as to sandwich the magnetic sheet, and sintering this integrally. Have been. Conventionally, Ag or Ag / Pd is generally used for the inner conductor.

[Problems to be solved by the invention]

However, since the above-described conventional circuit board with a built-in magnetic material is integrally fired in a state where the magnetic material sheet and the ceramic sheet are in direct contact with each other, the elements constituting the magnetic material and the ceramic are liable to diffuse at the time of this firing. As a result, there is a problem that characteristics are deteriorated. That is, the Fe element of the ferrite employed as the magnetic material diffuses into the ceramic sheet, and the glass component from the ceramic diffuses into the ferrite, and in some cases, loses the function as the ferrite.

In addition, noble metal
Since Ag and Ag / Pd are used, there is a problem that the product cost rises accordingly.In addition, when Ag / Pd is used, the conductor resistance increases, which limits its use as a circuit board. There is also a problem.

The present invention has been made in view of the above conventional situation,
An object of the present invention is to provide a circuit board with a built-in magnetic material that can prevent the deterioration of characteristics by preventing diffusion of a magnetic material and a ceramic element at the time of sintering, can reduce product cost, and can be used for a wider range of applications.

[Means for solving the problem]

Therefore, the invention of claim (1) of the present application is to form a thick film layer between a substrate and a ferrite-based magnetic layer formed inside the substrate to suppress diffusion of Fe element in ferrite into the substrate. This is a circuit board with a built-in magnetic material, characterized in that:
The invention according to claim (2) is characterized in that copper is used for an internal conductor formed inside the substrate and connected to an external circuit.

The invention according to claim (3) is characterized in that the thick film layer is a TiO ₂ -based ceramic layer or a ceramic layer containing TiO ₂ as a main component. This can be realized by forming the TiO ₂ -based ceramic into a paste and printing it, or forming it into a green sheet and overlapping it.

[Action]

According to the circuit board with a built-in magnetic material according to the invention of claim (1), since the thick film layer that suppresses the diffusion of both components is formed between the substrate and the ferrite magnetic layer, Fe in ferrite of magnetic layer during firing by film layer
The element can be prevented from diffusing to the substrate side, and the glass component in the substrate can be prevented from diffusing into the magnetic material layer. As a result, special degradation can be avoided.

According to the invention of claim (2), since copper is used for the internal electrode, the cost is lower than that of a noble metal such as Ag, and the product cost can be reduced accordingly. Moreover, since the specific resistance is about Ag, the conductor resistance can be reduced as compared with the case where Ag / Pd is used, and the application as a circuit board can be expanded. Since the melting point of the copper is higher than the firing temperature, the copper does not melt.

In the invention of claim (3), the TiO ₂ -based ceramic layer or the ceramic layer containing TiO ₂ as a main component is employed for the thick film layer, so that the diffusion of the Fe element to the substrate can be prevented.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 3 are views for explaining a circuit board with a built-in magnetic material according to an embodiment of the present invention, FIG. 1 is an exploded perspective view thereof, and FIG. 2 is a sectional view thereof.

In FIG. 1, reference numeral 1 denotes a circuit board with a built-in magnetic material according to the present embodiment, which is provided inside a rectangular plate-shaped insulator substrate 2 made of ceramic first and second substrates 2a and 2b as a magnetic material. The ferrite layer 3 and the internal conductor 4 are buried and sintered integrally. The internal conductor 4 is a copper band, and electrode pads 4a are integrally formed at both ends thereof. The both pads 4a are located at both ends of the insulating substrate 2 in the longitudinal direction. The ferrite layer 3 includes a pair of upper and lower ferrite layers 3a and 3b, and is opposed to each other with a central portion of the inner conductor 4 interposed therebetween. The upper and lower ferrite layers 3a and 3b are formed by printing a paste made of Ni-Zn ferrite. Further, an external conductor 6 is formed on a portion of the upper surface of the second substrate 2b opposite to the pad portions 4a, and the external conductor 6 and the pad portion 4a are connected by a through-hole electrode 5.

Then, between the first substrate 2a and the lower ferrite layer 3a,
The thick film layer 7 of the present embodiment is formed between the second substrate 2b and the upper ferrite layer 3b. The thick film layer 7 is formed by printing a ceramic paste containing TiO ₂ as a main component, and the components are diffused between the insulator substrate 2 and the ferrite layer 3 by the thick film layer 7. Has been prevented.

Next, a method of manufacturing the circuit board 1 with a built-in magnetic material of the present embodiment will be described.

First, an outline of a manufacturing process of the circuit board 1 of the present embodiment will be described. This includes a process of manufacturing a ceramic sheet forming the insulator substrate 2, a process of manufacturing a ferrite paste forming the ferrite layer 3, a process of manufacturing a copper paste forming the internal conductor 4, and forming the thick film layer 7.
The method comprises the steps of manufacturing a TiO ₂ paste. The ceramic sheet and the respective pastes prepared in the above steps are printed in a predetermined order and method, and then pressed and fired.

Manufacturing process of the ceramic sheet to be the insulator substrate: SiO ₂ : 55 parts by weight, BaO: 30 parts by weight, B ₂ O ₃ : 5 parts by weight, and Ca
O: 5 parts by weight of ceramic raw material powder having an average particle diameter of 2 μm and 100 parts by weight, 12 parts by weight of an acrylic binder and 3 parts by weight of a plasticizer / octyl phthalate were added and mixed. A green sheet having a thickness of 300 μm is formed, and the green sheet is cut into a predetermined size to produce a rectangular ceramic sheet corresponding to the first and second substrates 2a and 2b.

Manufacturing Process of Ferrite Paste to be Ferrite Layer The Ni—Zn ferrite composed of 48.5 mol% of Fe ₂ O _3, 22.5 mol% of NiO, and 29 mol% of ZnO was added with 1.7 parts by weight of PbO as an auxiliary component and B ₂ 30 parts by weight of an acrylic varnish was added to 100 parts by weight of a mixed powder having an average particle size of 1 μm obtained by mixing O ₃ : 0.2 part by weight and SiO ₂ : 0.1 part by weight, and the mixture was kneaded with a three-roll mill. To produce a ferrite paste.

Manufacturing Process of Copper Paste as Internal Conductor To 100 parts by weight of copper powder having an average particle diameter of 1 μm or less, 25 parts by weight of an ethylcellulose varnish is added and kneaded with a three-roll mill to produce a copper paste.

Production process of TiO ₂ paste for forming the above thick film layer 100 parts by weight of ceramic powder composed of 95 mol of TiO ₂ , 4 mol% of NiO, and 1 mol% of MnO, 3.2 parts by weight of PbO as auxiliary components, B ₂ O ₃ : 30 parts by weight of an acrylic varnish was added to 100 parts by weight of a mixed powder having an average particle diameter of 1 μm obtained by mixing 0.6 parts by weight and SiO ₂ : 0.2 parts by weight, and the mixture was kneaded with a three-roll mill to obtain TiO ₂ Make a paste.

Next, a process of manufacturing the magnetic substance built-in type circuit board 1 of this embodiment using the green sheets and the pastes manufactured as described above will be described with reference to FIG.

I. The TiO ₂ paste prepared above is screen-printed on the upper surface of the ceramic sheet having the predetermined dimensions prepared above, that is, the sheet to be the first substrate 2a, to form the thick film layer 7. In this case, the thick film layer 7 is formed such that the peripheral edge is located inside the peripheral edge of the first substrate 2a (see FIG. 3A).

II. Next, the ferrite paste prepared above was printed on the center of the upper surface of the thick film layer 7 to form a lower ferrite layer 3a.
To form The lower ferrite layer 3a is formed so that the area is smaller than the area of the thick film layer 7 and the periphery of the ferrite layer 3a is located inside the periphery of the thick film layer 7 (see FIG. 3B).

III. The copper paste produced as described above is printed on the upper surface of the lower ferrite layer 3a of the first substrate 2a to form the internal conductor 4. The internal conductor 4 extends in the longitudinal direction of the first substrate 2a, and each pad portion 4a of the internal conductor 4 is connected to the first substrate 2a.
(See FIG. 3 (c)).

IV. Next, the inner conductor 4
A ferrite paste is printed so as to face the ferrite layer 3a with the interposition therebetween, thereby forming an upper ferrite layer 3b. Subsequently, a TiO ₂ paste is printed on the upper surface of the upper ferrite layer 3b so as to face the thick film layer 7. To form a thick film layer 7 (see FIGS. 3 (d) and 3 (e)).

V. Then, a second substrate 2b is laminated on the upper surface of the first substrate 2a, and this is subjected to a pressure of 0.1 torr, a temperature of 80 ° C., and a pressure of
thermocompression bonding in kg / cm ^2. Thus, the insulator substrate 2 in which the internal conductor 4, the ferrite layer 3, and the thick film layer 7 are embedded is formed (see FIG. 3 (f)).

VI. Next, through holes are formed at both ends of the insulator substrate 2 so as to penetrate both pad portions 4a of the internal conductor 4, and a copper paste is printed in the through holes to form through hole electrodes 5. At the same time, an external conductor 6 is formed by printing copper paste on the periphery of the through-hole electrode 5 of the substrate 2. As a result, the inner conductor 4 is connected to the outer conductor 6 via the through-hole electrode 5 (third conductor).
FIG. (G)).

VII. Finally, the insulator substrate 2 is heated and fired at 950 ° C. in a nitrogen-water vapor atmosphere to be integrally sintered. As a result, the circuit board 1 with a built-in magnetic body of this embodiment is manufactured.

 Next, the operation and effect of this embodiment will be described.

According to the circuit board 1 with a built-in magnetic material of this embodiment, the thick film layer 7 containing TiO ₂ as a main component is provided between the first substrate 2a and the lower ferrite layer 3a and between the second substrate 2b and the upper ferrite layer 3b. Is formed, the two substrates 2a and 2b do not come into direct contact with the ferrite layers 3a and 3b, and the diffusion of the Fe element and the glass component at the time of heating and firing can be prevented, and as a result, deterioration of characteristics can be avoided.

Further, in this embodiment, since the copper paste is used for the internal conductor 4, the cost can be reduced as compared with a noble metal such as Ag, and the conductor resistance can be reduced as compared with the case where Ag / Pd is used. Applications can be expanded. Further, since copper has a melting point of 1083 ° C., it does not melt or oxidize even when fired in the non-oxidizing atmosphere.

Here, the inductance of the circuit board with a built-in magnetic material manufactured by the above manufacturing method was measured, and the initial permeability was measured from the size and shape of the ferrite layer, and a value of 150 was obtained. A toroidal core having the same composition as that of the ferrite layer was prepared, and its initial magnetic permeability was measured to be equal to 150. This shows that the application of the structure of the present embodiment makes it possible to express the inherent characteristics of ferrite. Further, for comparison, in the conventional circuit board without the thick film layer, the ferrite component and the ceramic component diffused, and a predetermined magnetic permeability was not obtained.

〔The invention's effect〕

As described above, according to the circuit board with a built-in magnetic material according to the invention of claim (1), a thick film layer is formed between the substrate and the magnetic material layer to suppress the diffusion of Fe element in ferrite into the substrate. Therefore, there is an effect that diffusion of both the substrate and the magnetic layer can be suppressed, and deterioration of characteristics can be avoided. Claim (2)
According to the invention, since copper is used for the internal conductor, in this case, the product cost can be reduced, the specific resistance can be reduced, and the application can be expanded.

In the invention of claim (3), the TiO ₂ -based ceramic layer or the ceramic layer containing TiO ₂ as a main component is employed for the thick film layer, so that the diffusion of the Fe element to the substrate can be prevented.

[Brief description of the drawings]

1 to 3 are views for explaining a circuit board with a built-in magnetic material according to an embodiment of the present invention. FIG. 1 is an exploded perspective view, FIG. 2 is a sectional front view, and FIG. 3 (a) to 3 (g) are process diagrams for explaining the manufacturing method. In the figure, 1 is a circuit board with a built-in magnetic material, 2 is an insulating substrate, 3 is a ferrite layer (magnetic material layer), 4 is an internal conductor, 7
Is a thick film layer.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H05K 1/16 H05K 3/46

Claims (3)

(57) [Claims] A thick film layer formed between a substrate and a ferrite magnetic layer formed inside the substrate to suppress diffusion of Fe element in ferrite into the substrate. Built-in circuit board. 2. A circuit board with a built-in magnetic material according to claim 1, wherein an internal conductor connected to an external circuit is formed inside said substrate, and copper is used for said internal conductor. 3. The circuit according to claim 1, wherein the thick film layer is a TiO ₂ -based ceramic layer or a ceramic layer containing TiO ₂ as a main component. substrate.