JP2013138162A - Wiring board with built-in coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce diffusion of silver into a ferrite substrate from a wiring conductor, and suppress deterioration of a magnetic permeability of the ferrite substrate.SOLUTION: A wiring board 1 with a built-in coil comprises: a ferrite layer containing iron oxide, nickel oxide, copper oxide, zinc oxide and a glass component; a wiring conductor 12 which contains silver and is provided on the surface and the inner part of the ferrite layer; and a coil conductor 13 which is electrically connected to the wiring conductor 12 and is provided in the inner part of the ferrite layer. The glass component is contained by 0.25-5 mass% with respect to the mass of the ferrite layer, and contains 3-12 mass% of silicon oxide, 5-12 mass% of boron oxide, 1-9 mass% of aluminum oxide, 1-12 mass% of barium oxide and 60-80 mass% of bismuth oxide, with respect to the mass of the glass component. Silver components are reduced to be diffused in the ferrite layer, because the burning temperature of the wiring board 1 with the built-in coil is lower than a melting point of the silver.

Description

  The present invention relates to a wiring board with a built-in coil.

  In recent years, development of a wiring board with a built-in coil in which a coil is provided inside the wiring board has been promoted. The coil-embedded wiring board is used in, for example, a DC-DC converter having a function of converting a direct current voltage. An exemplary coil-embedded wiring board is a ferrite board with a built-in coil in which ferrite is used as a material of a base constituting the wiring board, and silver is used as a material of the coil conductor and the wiring conductor (for example, Patent Documents). 1). A ferrite substrate with a built-in coil in which silver is used as a material for the coil conductor and the wiring conductor is produced by firing at a temperature lower than the melting point of silver.

JP-A-6-21264

However, when a molded body that is a coil-embedded wiring board in which silver is used as the material of the coil conductor and wiring conductor is fired at a temperature close to the melting point of silver (962 ° C.), even if the temperature is lower than the melting point of silver There is a possibility that silver diffuses from the wiring conductor into the wiring board and the magnetic permeability of the wiring board is lowered. When the magnetic permeability is lowered, there is a problem that an inductance value generated when a current is passed through the coil built-in wiring board is lowered.

  A wiring board with a built-in coil according to one aspect of the present invention includes a ferrite layer containing iron oxide, nickel oxide, copper oxide, zinc oxide and a glass component, and silver and is provided on the surface and inside of the ferrite layer. A wiring conductor and a coil conductor electrically connected to the wiring conductor and provided inside the ferrite layer are provided. The glass component is contained in an amount of 0.25 to 5% by mass with respect to the mass of the ferrite layer, 3 to 12% by mass of silicon oxide, 5 to 12% by mass of boron oxide, and aluminum oxide with respect to the mass of the glass component. 1 to 9% by mass, 1 to 12% by mass of barium oxide, and 60 to 80% by mass of bismuth oxide.

  In the coil-embedded wiring board according to one embodiment of the present invention, the glass component contained in the ferrite layer includes 3 to 12% by mass of silicon oxide, 5 to 12% by mass of boron oxide, and 1 to 9% by mass of aluminum oxide. By containing 1 to 12% by mass of barium oxide and 60 to 80% by mass of bismuth oxide, the firing temperature during production can be reduced, the diffusion of silver is reduced, and the inductance value is improved. ing.

1 is an exploded perspective view of an electronic device according to a first embodiment of the present invention. FIG. 2 is a longitudinal sectional view taken along line AA of the electronic device shown in FIG. 1. The longitudinal cross-sectional view of the electronic device in the 2nd Embodiment of this invention is shown.

Hereinafter, some exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
As shown in FIGS. 1 and 2, the electronic device according to the first embodiment of the present invention includes a coil built-in wiring board 1 and an IC element 2 provided on the upper surface of the coil built-in wiring board 1. It is out. The electronic device is mounted on a circuit board that constitutes an electronic component module, for example.

  The wiring board 1 with a built-in coil includes a plate-like base portion 11 including a ferrite layer, a coil conductor 13 and a wiring conductor 12 embedded in the base portion 11, and a connection electrode 14 provided on the upper surface of the base portion 11. And a terminal electrode 15 provided on the lower surface of the base portion 11. In FIG. 1, the electronic device is mounted on an xy plane in a virtual xyz space. 1 and 2, the upward direction refers to the positive direction of the virtual z axis.

  The base portion 11 includes a magnetic material and is integrally formed by firing. The exemplary base portion 11 has a ferrite layer containing iron oxide, nickel oxide, copper oxide, zinc oxide, and a glass component.

The ferrite layer contains 98.5% or more of a ferrite material, and in order to obtain high magnetic permeability, ZnFe ₂ O ₄ , MnFe ₂ O ₄ , FeFe ₂ O ₄ , CoFe ₂ O ₄ , and NiFe _{2 are used.}
It is preferable that at least one type of ferrite among O ₄ , BaFe ₂ O ₄ , SrFe ₂ O ₄ and CuFe ₂ O ₄ is included.

The glass component contained in the ferrite layer is contained in an amount of 0.25 to 5% by mass with respect to the total mass of the ferrite layer. The glass component is 3 to 12% by mass of silicon oxide (SiO ₂ ), 5 to 12% by mass of boron oxide (B ₂ O ₃ ), and 1 aluminum oxide (Al ₂ O ₃ ) with respect to the total mass of the glass component. to 9% by weight, 1 to 12 wt% barium oxide (BaO), contains bismuth oxide _(Bi 2 _{O 3)} 60~80% by weight.

When the glass component contains Bi ₂ O ₃ in an amount of 60 to 80% by mass, it has an action of reducing the viscosity in the vicinity of the sintering temperature of the glass, and is uniformly dispersed in the ferrite layer as a liquid phase during firing. Since the liquid phase sintering between the ferrite crystals is promoted, the ferrite layer can be sintered at a low temperature.

When BaO is contained in an amount of 1 to 12% by mass, it is difficult to form a compound with Bi ₂ O ₃ and it can be used together with Bi ₂ O ₃ to further reduce the viscosity in the vicinity of the sintering temperature of the glass. Therefore, the ferrite layer can be further sintered at a low temperature.

As the glass component, it is conceivable to add other metal oxides, for example CaO or the like instead of BaO, CaO since become chemically reacted with _Bi 2 _{O 3,} it is less CaO and _Bi 2 _{O 3} There is a possibility that low-temperature sintering may be hindered.

SiO ₂ and Al ₂ O ₃ have the effect of improving the chemical resistance of the ceramic substrate, and it is difficult to lower the insulation reliability of the ceramic substrate even after the plating process.

SiO ₂ and B ₂ O ₃ reinforce the glass network structure and are effective for retaining other glass components in the glass structure.

The base portion 11 has a plate shape, and includes a first layer 111 to a fourth layer 114 stacked on each other. In FIG. 2, the interface between the first layer 111 and the fourth layer 114 is indicated by a virtual two-dot chain line. The second layer 112 is stacked on the first layer 111, and the third layer 113 is the second layer 112.
The fourth layer 114 is stacked on the third layer 113.

  The wiring conductor 12 is embedded in and between the first layer 111 to the fourth layer 114. The wiring conductor 12 electrically connects the coil conductor 13, the connection electrode 14, and the terminal electrode 15 to each other. As the material of the wiring conductor 12, for example, a material containing Ag such as Ag, Ag—Pd alloy or Ag—Pt alloy can be used.

The coil conductor 13 has a shape surrounding the central portion of the base portion 11 in a plan view, and is embedded in the base portion 11. The coil conductor 13 includes a first coil pattern 131 formed on the upper surface of the first layer 111 and a second coil pattern 132 formed on the upper surface of the second layer 112. The first coil pattern 131 and the second coil pattern 132 are electrically connected by a via conductor provided in the second layer 112 of the base portion 11. In FIG. 1, the electrical connection relationship between the first coil pattern 131 and the second coil pattern 132 is indicated by a dotted line. As the material of the coil conductor 13, the same material as that of the wiring conductor 12 can be used.

  The connection electrode 14 is electrically connected to the IC element 2, and the terminal electrode 15 is electrically connected to an external circuit board. As the material of the connection electrode and the wiring conductor, for example, a material such as Ag, Au, Pt, Ag—Pd alloy or Ag—Pt alloy can be used.

  The IC element 2 is provided on the upper surface of the base portion 11 of the coil built-in wiring board 1. The IC element 2 is a control IC element in a DC-DC converter, for example. The IC element 2 and the toroidal coil conductor 13 of the coil built-in wiring board 1 are electrically connected.

  Hereinafter, a method for manufacturing the coil-embedded wiring substrate 1 containing ferrite as a magnetic material will be described. The manufacturing method of the coil-embedded wiring substrate 1 includes a step of obtaining a slurry containing ferrite, a step of obtaining a ferrite green sheet using the slurry, a step of obtaining a laminate including a coil pattern and a wiring pattern, and firing the laminate. Process.

  The slurry is obtained by mixing ferrite powder and glass material with an appropriate organic binder, plasticizer, organic solvent and the like. The ferrite powder is calcined in order to make it uniform in the sintered state of the ferrite green sheet, has a uniform particle size, and preferably has a shape close to a spherical shape. When the ferrite powder contains particles with a small particle size, the growth of crystal grains is reduced only at the small particle size, and the permeability of the ferrite layer obtained after sintering tends to be difficult to stabilize. There is.

  The ferrite green sheet is manufactured by using a slurry by a doctor blade method, a rolling method, a calendar roll method, or the like. The laminate includes a plurality of ferrite green sheets in which a coil pattern or a wiring pattern is formed on some ferrite green sheets. For the coil pattern and wiring pattern, a conductive paste in which a suitable organic binder and solvent are kneaded with metal powder such as silver (Ag) or silver alloy is applied to the surface of the ferrite green sheet by screen printing or gravure printing. Formed by.

  The laminated body thus obtained is fired at 850 ° C. to 900 ° C., whereby the coil-embedded wiring substrate 1 is produced.

  In the coil-embedded wiring substrate 1 in this embodiment, the glass component is contained in an amount of 0.25 to 5% by mass with respect to the total mass of the ferrite layer, and 3 to 12% by mass of silicon oxide with respect to the total mass of the glass component. It contains 5-12 mass% boron oxide, 1-9 mass% aluminum oxide, 1-12 mass% barium oxide, and 60-80 mass% bismuth oxide to reduce the firing temperature of the wiring board with a built-in coil. it can.

  The firing temperature of the coil-embedded wiring board 1 is reduced by containing bismuth oxide, and further reduced by containing barium oxide. This is because bismuth oxide and barium oxide do not chemically react and each can reduce the firing temperature. Since the firing temperature of the coil-embedded wiring substrate 1 can be lower than the melting point of silver, it is possible to reduce the diffusion of the silver component into the ferrite layer.

(Second Embodiment)
Next, a wiring board with a built-in coil according to a second embodiment of the present invention will be described with reference to FIG.

The wiring board with a built-in coil according to the second embodiment of the present invention differs from the wiring board with a built-in coil 1 of the first embodiment described above in that the glass component contains 7.1% of silicon oxide with respect to the total mass of the glass component. 3 to 11.9 mass%, boron oxide 5.1 to 6.9 mass%, aluminum oxide 1.1 to 3.9 mass%, barium oxide 1.3 to 5.9 mass%, bismuth oxide 74.2 to 79.9 mass%, and as shown in FIG. As in the example described above, the glass layer 16 containing the glass component is further provided between the surface of the base portion 11 containing the ferrite layer and the wiring conductor 12.

  In the glass component, since it is difficult for bismuth oxide and barium oxide to form a compound, the glass component can have a higher proportion of bismuth oxide having a relatively low melting point. Since the melting point of such a glass component is close to the firing temperature of the coil-embedded wiring substrate 1, the glass component has high fluidity when firing the coil-embedded wiring substrate 1. The glass component easily oozes out on the surface of the base portion 11 during firing, spreads between the surface of the base portion 11 and the glass layer 16, and contacts the base portion 11 and the wiring conductor 12 over a wide area. The glass component spread between the surface of the base portion 11 and the wiring conductor 12 is solidified to form the glass layer 16. Since the glass layer 16 and the surface of the base portion 11 and the wiring conductor 12 are joined in a wide area, the base portion 11 and the wiring conductor 12 can be firmly joined by the glass layer 16.

  An example of the coil built-in wiring board 1 in the above embodiment will be described in detail below.

(First embodiment)
A first example of the coil-embedded wiring board 1 in the first embodiment will be described in detail below.

First, as ferrite powder, FeFe ₂ O ₄ powder 700 g, CuO powder 60 g, NiO powder 60 g, ZnO powder 180 g and pure water 4000 cm ³ together with zirconia balls have a capacity of 7000.
After putting in a cm ³ pot and mixing in a ball mill by rotating the pot for 24 hours, the dried mixed powder is put in a zirconia crucible and heated at 730 ° C. in the atmosphere for 1 hour, thereby forming ferromagnetic ferrite. A powder was prepared. To 100 parts by mass of the ferrite powder, 0.75 to 1.5 parts by mass of glass powder, 10 parts by mass of butyral resin as an organic binder, and 45 parts by mass of IPA as an organic solvent are added and mixed by the same ball mill method as above. A slurry was obtained. Using this slurry, a ferrite green sheet having a thickness of 200 μm was formed by a doctor blade method. Glass powder, 60 a SiO ₂ 3 to 12 _wt%, the B 2 _{O 3} 5 to 12 wt%, the _Al 2 _{O 3} 1 to 9 wt%, 1 to 12 wt% of BaO, and _Bi 2 _{O 3} Contains 80% by mass.

Through holes with a diameter of 150 μm for through conductors were formed in this ferrite green sheet by punching with a mold. This through hole was filled with a through conductor paste by screen printing, and dried at 70 ° C. for 30 minutes to form a through conductor composition to be a through conductor. As a penetrating conductor paste, 100 parts by mass of Ag powder, 10 parts by mass of glass powder as a sintering aid, 12 parts by mass of acrylic resin and 2 parts by mass of α-terpineol as an organic solvent are added, and a stirring deaerator Then, the mixture was sufficiently kneaded with three rolls after being sufficiently mixed.

Subsequently, a conductor paste was applied to each ferrite green sheet to a thickness of 30 μm by screen printing and dried at 70 ° C. for 30 minutes to form a coil conductor pattern, a wiring conductor pattern, a connection electrode pattern, or an external terminal pattern. . As the conductive paste, 10 parts by mass of an acrylic resin and 1 part by mass of α-terpineol as an organic solvent were added to 100 parts by mass of Ag powder, and the mixture was sufficiently mixed by a stirring deaerator.

  Next, two ferrite green sheets on which coil conductor patterns are formed are stacked, and one ferrite sheet on each of the upper and lower sides is stacked, and ferrite green sheets on which connection electrode patterns or terminal electrode patterns and wiring conductor patterns are formed are stacked to 20 MPa. A laminate was produced by thermocompression bonding at a pressure of 55 ° C. and a temperature of 55 ° C.

Next, this laminate was heated in air at 500 ° C. for 3 hours to remove organic components, and then fired in air at 900 ° C. for 1 hour to produce a coil built-in wiring board. .

  On the connection electrode and the terminal electrode formed on the surface of the wiring board with a built-in coil, an Ni plating film and an Au plating film were sequentially formed by using an electroless plating method.

As a comparative example for comparison with the first example, the glass powder contains less than 3% by mass or more than 12% by mass of SiO ₂ , less than 5% by mass or 12% by mass of B ₂ O ₃ More than 1% by weight or less than 9% by weight Al ₂ O ₃ , less than 1% by weight or more than 12% by weight BaO, 60% Bi ₂ O ₃ Each containing less than 80% by mass or more than 80% by mass was prepared.

  The samples of the first examples 1 to 15 and the samples of the second comparative examples 1 to 13 shown in Table 1 obtained in this way were each prepared in five to measure the relative permeability and insulation reliability. A test was conducted.

  The relative permeability was measured using an impedance measuring instrument (model “4294A Precision Impedance Analyzer”, measurement accuracy ± 0.08%, manufactured by Agilent Technologies) under the conditions of a measurement frequency of 3 MHz and a measurement temperature of 25 ° C. Then, it calculated from the measured inductance value.

The insulation reliability test is a test in which 5V is applied to two insulated wires in the wiring board with a built-in coil and left for 96 hours in a humidity of 130 ° C and 85% to check for a decrease in insulation resistance. is there. A product having an insulation resistance value of less than 1 megohm was judged as a defective product, and a product having an insulation resistance value of 1 megohm or more was judged as a good product.

  Table 1 shows the results of relative permeability measurement and insulation reliability test. The numerical values shown in the insulation reliability test in the test results shown in Table 1 indicate how many of the five samples are non-defective, OK indicates non-defective, and NG indicates defective.

As shown in Table 1, the coil-embedded wiring substrate 1 of the first to first embodiments has a relative permeability of 150 or more required as a coil-embedded wiring substrate as a result of measuring the relative permeability. In the insulation reliability test, the insulation resistance of all the samples was 1 megohm or more. The first comparative examples 2, 4, 5 and 12 have a relative permeability of less than 150, and the first comparative examples 1, 3, 6 to 11 have an insulation resistance of less than 1 megohm in all samples in the insulation reliability test. Therefore, it cannot be used as a wiring board with a built-in coil.

  From the above results, it was found that the coil-embedded wiring boards of the first to first examples had high relative magnetic permeability and high insulation reliability.

  From the above, the glass component described in the above embodiment is contained in an amount of 0.25 to 5% by mass with respect to the mass of the ferrite layer, and 3 to 12% by mass of silicon oxide with respect to the mass of the glass component. The coil-embedded wiring board 1 containing 5 to 12% by mass of boron oxide, 1 to 9% by mass of aluminum oxide, 1 to 12% by mass of barium oxide, and 60 to 80% by mass of bismuth oxide has a high relative magnetic permeability. It was confirmed that the insulation reliability was high.

(Second embodiment)
The second example of the wiring board 1 with a built-in coil according to the second embodiment will be described in detail below. In addition, about the wiring board 1 with a built-in coil in a present Example, it describes below about a different point from the wiring board 1 with a built-in coil of the above-mentioned 1st Example.

The glass powder contained in the ferrite green sheet contains 7.1 to 11.9% by mass of SiO ₂
, B ₂ O ₃ , 5.1 to 6.9 mass%, Al ₂ O ₃ 1.1 to 3.9 mass%, BaO 1.3 to 5.9 mass%, and Bi ₂ O ₃ 74.2 to 79.9 mass%.

As a second comparative example for comparison with the second example, the glass powder contains less than 7.1 mass% or more than 11.9 mass% of SiO ₂ , less than 5.1 mass% of B ₂ O ₃ or One containing more than 6.9% by mass, one containing Al ₂ O ₃ less than 1.1% by mass or more than 3.9% by mass, one containing BaO less than 1.3% by mass or more than 5.9% by mass, Bi ₂ O ₃ containing less than 74.2% by mass or more than 79.9% by mass were prepared.

  Five samples each of the second examples 1 to 9 and the second comparative examples 1 to 29 shown in Table 2 obtained in this way were prepared to confirm the presence or absence of vitrification and the bonding strength. Measurement and chemical resistance test were conducted.

The bonding strength was measured by conducting a tensile test in a state where the coil-embedded wiring board was bonded to an external printed wiring board with solder. The tensile test was measured using a load tester MODEL-1310DW (manufactured by Aiko Engineering Co., Ltd.) under a tensile speed of 10 mm / min. In general, the tensile strength is 1.0 kg / mm from the required value required for portable devices.
^A product of ² or more was judged as a good product.

The chemical resistance test is a test for measuring a mass difference before and after the plating process in the process of producing the coil built-in wiring board. In the plating process, when the plating solution enters the base part 11, the glass component constituting the base part 11 is melted, so that the mass of the base part 11 is reduced. From this, compared with before the plating process, the mass reduction after the plating process was determined to be a non-defective product within 0.3% by mass.

  Table 2 shows the results of confirmation of vitrification, measurement of bonding strength, and chemical resistance test. The numerical values shown in the chemical resistance test in the test results shown in Table 2 indicate how many of the five samples are non-defective, OK indicates non-defective, and NG indicates defective.

As shown in Table 2, the coil-embedded wiring boards 1 of the second examples 1 to 9 had a bonding strength of all samples of 1.0 kg / mm ² or more as a result of measuring the bonding strength. All samples had a mass loss within 0.3% by weight. The joint strengths of the second comparative examples 1, 2, 4, and 6 to 29 were less than 1.0 kg / mm ^{2 in} all the samples. In addition, although the bonding strengths of the second comparative examples 3 and 5 were 1.0 kg / mm ² or more, the mass reduction was 0.3% by mass or more in all the samples in the chemical resistance test. Therefore, the second comparative examples 1 to 29 cannot be used as a coil built-in wiring board.

  From the above results, it was found that the coil-embedded wiring boards 1 of the first examples 1 to 10 had high bonding strength and reduced penetration of a chemical solution such as a plating solution.

From the above, the glass component described in the second embodiment is 7.1 to 11.9% by mass of silicon oxide, 5.1 to 6.9% by mass of boron oxide, and 1.1 to 3.9% of aluminum oxide with respect to the mass of the glass component. It was confirmed that the wiring board 1 with a built-in coil containing mass%, barium oxide 1.3 to 5.9 mass%, and bismuth oxide 74.2 to 79.9 mass% has high bonding strength between the base portion 11 and the wiring conductor 12. .

1 ... Wiring board with built-in coil
11 ... Base part
111-114 ... 1st-4th layer
12 ... Wiring conductor
13 ... Coil conductor
14 ... Connection electrode
15 ... Terminal electrode
16 ... Glass layer
131, 132 ... 1st and 2nd coil pattern 2 ... IC element

Claims (2)

A ferrite layer containing iron oxide, nickel oxide, copper oxide, zinc oxide and a glass component; a wiring conductor containing silver and provided on the surface and inside of the ferrite layer;
A coil conductor that is electrically connected to the wiring conductor and provided inside the ferrite layer;
The glass component is contained in an amount of 0.25 to 5% by mass with respect to the total mass of the ferrite layer, and 3 to 12% by mass of silicon oxide, 5 to 12% by mass of boron oxide, and oxidized with respect to the total mass of the glass component. A wiring board with a built-in coil comprising 1 to 9% by mass of aluminum, 1 to 12% by mass of barium oxide, and 60 to 80% by mass of bismuth oxide. The glass component contains 7.1 to 11.9% by mass of silicon oxide with respect to the total mass of the glass component.
, Containing boron oxide 5.1-6.9% by mass, aluminum oxide 1.1-3.9% by mass, barium oxide 1.3-5.9% by mass, bismuth oxide 74.2-79.9% by mass,
The wiring board with a built-in coil according to claim 1, wherein a glass layer containing the glass component is further provided between the surface of the ferrite layer and the wiring conductor.

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