JP2010109069A - Wiring board and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board which can be used even in an environment that the board is exposed to a corrosive fluid. <P>SOLUTION: The wiring board (1) includes: a substrate (2) including alumina; a via conductor (3) which is formed in the substrate (2), also exposes the end to a surface of the substrate (2), and includes molybdenum or tungsten; a thin film (4) including an active metal formed on the surface of the substrate (2) so as to cover the end; and a conductor layer (5) formed on the thin film (4) and including platinum. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wiring board used for, for example, a sensor used in a corrosive fluid and a manufacturing method thereof.

Conventionally, a conductor material made of a refractory metal such as molybdenum or tungsten has been used to form a via conductor in a ceramic substrate containing alumina. These metals have good adhesion to a ceramic substrate containing alumina.
Osamu Nakashige and Shigeru Hayakawa “Electronic Materials Ceramics”, Ohmsha, 1986, P186-188

  However, when the ceramic substrate is used in an environment exposed to a corrosive fluid, there is a problem that the conductor material corrodes.

  The objective of this invention is providing the wiring board which can be used also in the environment exposed to corrosive fluid, and the manufacturing method of the wiring board.

  A wiring board according to the present invention includes a substrate containing alumina, a via conductor containing molybdenum or tungsten, one end of which is exposed on the surface of the substrate, and the surface of the substrate. A thin film containing an active metal provided so as to cover the one end and a conductor layer containing platinum provided on the thin film.

  Preferably, in the wiring board, the via conductor includes particles made of the alumina.

  The method for manufacturing a wiring board according to the present invention includes a step of preparing a plurality of ceramic green sheets containing alumina, a step of forming a hole in at least one of the plurality of ceramic green sheets, A step of injecting a first conductive paste containing molybdenum or tungsten, and laminating the plurality of ceramic green sheets so that the green sheet in which the hole is formed is disposed on at least one surface layer. Forming the body, firing the green sheet laminate in a reducing atmosphere to form a ceramic substrate having via conductors, and covering the end portions of the via conductors on the ceramic substrate. And forming a thin film containing an active metal and applying a second conductive paste containing platinum on the thin film. A step, the ceramic substrate in which said second conductive paste is applied and a step of firing in a vacuum atmosphere.

  Preferably, in the method for manufacturing a wiring board, the first conductor paste includes particles made of the alumina.

  According to the wiring board of the present invention, the corrosion of the via conductor can be suppressed even when used in an environment exposed to a corrosive fluid.

  According to the method for manufacturing a wiring board of the present invention, it is possible to manufacture a wiring board capable of suppressing the corrosion of the via conductor even when used in an environment exposed to a corrosive fluid.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration example of a wiring board according to an embodiment of the present invention. The wiring substrate 1 according to the present embodiment includes a substrate 2. A via conductor 3 is provided inside the substrate 2. The via conductor 3 includes a via portion 3a at an end portion and a via portion 3b disposed in the center so as to be sandwiched between them. The end portion of the via conductor 3 is exposed on the surface 6 of the substrate 2, and the thin film 4 is formed so as to cover the end portion of the via conductor 3. Further, a conductor layer 5 is formed so as to cover the thin film 4. The thin film 4 and the conductor layer 5 are formed so as to cover one end or both ends of the via conductor 3 depending on an application in which the wiring board is used. Here, the thin film 4 and the conductor layer 5 are formed so as to cover both ends of the via conductor 3.

  Further, in the wiring substrate 1, the via conductor 3 is a through-hole penetrating the substrate 2, but it may be a groove. Furthermore, the via conductor 3 may be one in which a hole provided in the substrate 2 is filled with a conductor, or one in which a conductor layer is formed on the inner wall of the hole.

The substrate 2 is made of an electrically insulating material and includes alumina (Al ₂ O ₃ ). Hereinafter, the case where this board | substrate 2 consists of ceramics containing alumina (henceforth "alumina ceramics") is demonstrated, for example. Alumina ceramics include silica (SiO ₂ ), calcia (CaO), magnesia (MgO), and the like in addition to alumina (Al ₂ O ₃ ) as a main component. Since alumina ceramics are excellent in corrosion resistance, they are effective when a wiring board is used in an environment exposed to a corrosive fluid.

  The via conductors 3a and 3b are mainly made of a refractory metal such as molybdenum or tungsten. Molybdenum has a melting point of 2323 ° C. and tungsten has a melting point of 3422 ° C., which is sufficiently higher than the firing temperature of alumina ceramics (1200 to 1800 ° C.). As a result, the wiring board is less likely to be deformed, and cracks and voids between the via conductors 3a and 3b and the alumina ceramics are hardly formed. In addition, since the components such as silica added to the alumina ceramic are melted and the gap between the particles of the alumina ceramic and molybdenum or tungsten is filled, the adhesion with the ceramic becomes very good.

  However, when molybdenum or tungsten is exposed to a corrosive fluid, it is easily corroded, for example, by oxidation. According to the wiring board 1 according to the present embodiment, the via conductor 3 is covered with the thin film 4 and the conductor layer 5, so that corrosion is suppressed.

  The thin film 4 contains an active metal such as titanium and is firmly bonded to the alumina ceramic. This is because the active metal oxidizes and binds strongly to the alumina in the alumina ceramic. In addition, the thin film 4 causes a chemical reaction between the via conductor 3 and the conductor layer 5, the metal component contained in the via conductor 3 diffuses into the conductor layer 5, and is exposed on the surface of the conductor layer 5, resulting in a conductor. It also serves as a barrier layer that suppresses corrosion of the surface of the layer 5.

  Further, in order to improve the bonding strength between the via conductor 3 and the thin film 4 by utilizing the feature that the active metal and the alumina ceramic are firmly bonded, the via conductor 3 may contain particles made of alumina. Good. Thereby, the alumina particles contained in the via conductor 3 and the active metal contained in the thin film 4 are bonded more firmly. However, since the alumina particles are non-conductors, if they are added to the via conductor 3, the conductor resistance is remarkably increased, so that the amount of alumina added to the via portion 3a is increased and the amount of alumina added to the via portion 3b is decreased. desirable. For example, 4 to 8% by weight of alumina is added to the via part 3a, and 0 to 4% of alumina is added to the via part 3b. The upper limit value of the amount of alumina added to the via conductor 3 is determined by the limit value at which the via conductor 3 can maintain conduction.

  The conductor layer 5 contains platinum. Platinum has resistance to a corrosive fluid, and can prevent the via conductor 3 disposed inside the wiring board 1 from being corroded by the corrosive fluid.

  Below, the manufacturing method of the wiring board 1 by this Embodiment is demonstrated. FIG. 2 is a diagram for explaining a method of manufacturing a wiring board according to an embodiment of the present invention. 2A is a step of preparing a ceramic green sheet, FIG. 2B is a step of forming a hole in the ceramic green sheet, FIG. 2C is a step of injecting a conductive paste into the ceramic green sheet, FIG. (D) is a step of forming a laminate of ceramic green sheets, FIG. 2 (e) is a step of firing the ceramic green sheets, FIG. 2 (f) is a step of forming the thin film 4, and FIG. 2 (g) is a conductor layer. 5 shows a step of forming 5.

(Process for preparing ceramic green sheets)
In FIG. 2A, a plurality of ceramic green sheets 7 are prepared. The ceramic green sheet 7 is made into a slurry by adding and mixing an appropriate organic solvent and solvent to raw material powders such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), calcia (CaO), and magnesia (MgO). In addition, this can be obtained by employing a conventionally known doctor blade method, calendar roll method, or the like, and forming it into a sheet shape.

(Process for forming holes)
In FIG. 2B, the hole 8 is formed in at least one of the plurality of ceramic green sheets 7. The hole 8 is formed at an appropriate position of the ceramic green sheet formed into a sheet shape by punching or laser processing.

(Process for injecting via conductor paste)
In FIG. 2C, the first conductor paste 9 is injected into the hole 8 formed in the ceramic green sheet 7 using a screen printing method or the like. The first conductor paste 9 is mixed and mixed by kneading means such as a ball mill, a three-roll mill, or a planetary mixer, with an organic binder and an organic solvent and, if necessary, a dispersant added to the main component molybdenum or tungsten powder. Manufactured by kneading. An appropriate amount of ceramic powder may be added to the first conductor paste 9 in order to increase the bonding strength with the thin film 4. This ceramic powder may be the same as or different from the material contained in the ceramic green sheet. Thus, by adding ceramic powder to the first conductor paste 9, it is possible to match the shrinkage behavior of the ceramic green sheet 7 or the thermal expansion coefficient with the alumina ceramics. The peeling between the substrate and the via conductor can be suppressed.

  Further, the composition of the first conductor paste 9 injected into the hole 8 of the ceramic green sheet 7 may be the same or different in each ceramic green sheet 7, but here, as an example, the ceramic powder Two types of conductor pastes 9a and 9b having different amounts of addition were prepared and injected into the corresponding holes 8 of the ceramic green sheet 7.

(Process for forming a laminate)
In FIG. 2D, the ceramic green sheets 7 are laminated to obtain a green sheet laminate 10. In FIG. 2D, only the ceramic green sheets 7 in which the holes 8 are formed are stacked, but the ceramic green sheets 7 in which the holes 8 are not formed may be stacked together. In order to form the green sheet laminate 10, the ceramic green sheets 7 are stacked and then subjected to pressure bonding. The pressure bonding is performed by applying a pressure of about 3.0 to 8.0 MPa, and heating is performed at 35 to 80 ° C. as necessary. Moreover, in order to obtain sufficient adhesiveness between the ceramic green sheets 7, an adhesive produced by mixing a solvent and a resin binder may be used. Also, in different ceramic green sheets 7, when the addition amount of ceramic powder (here, alumina particles) contained in the first conductor paste is different, the adhesion to the thin film 4 to be described later and the conductivity of the via conductor 3 are different. In consideration of the property, as shown in FIG. 2D, the ceramic green sheet 7 in which the first conductor paste 9a having a large amount of added alumina particles is injected into the hole 8 is provided on the surface layer side of the green sheet laminate 10. It is preferable to dispose the ceramic green sheet 7 in which the first conductor paste 9b having a small amount of added alumina particles is injected into the hole 8 at the center.

  A more desirable structure is shown in FIG. FIG. 3 is an enlarged cross-sectional view of a portion of an unfired via conductor of the ceramic green sheet after lamination. Reference numerals 9a-1, 9a-2, and 9b are first conductor pastes having different amounts of added alumina particles. The first conductor paste 9a-1 is in contact with the thin film 4 in the subsequent steps. If the first conductor paste 9a-1> the first conductor paste 9a-2> the first conductor paste 9b in the descending order of the amount of alumina particles added to the first conductor paste 9a-1, 9a-2, 9b, The adhesion between the via conductor 3 and the thin film 4 after firing is improved, and the difference in thermal expansion coefficient between the via portions in contact with each other can be reduced.

(Step of firing)
In FIG.2 (e), the unfired green sheet laminated body 10 is baked. Firing is performed at a high temperature of 1200 to 1800 ° C. in a reducing atmosphere. The reducing atmosphere is, for example, one in which 10 to 20% by volume of hydrogen is added to nitrogen. The reason for using the reducing atmosphere is to suppress the oxidation of molybdenum and tungsten contained in the via conductors 3a and 3b. It is desirable to add an appropriate amount of water vapor to the atmosphere in order to decompose the organic solvent added to the ceramic green sheet and to control the particle growth of the via conductor.

(Process for manufacturing the thin film 4)
FIG. 2F shows a process of manufacturing the thin film 4 on the surface of the substrate 2 obtained by firing the green sheet laminate 10. Before forming the thin film 4 on the surface 6 of the baked substrate 2, the surface 6 is polished using a polishing grindstone, barrel polishing or the like in order to improve the adhesion of the thin film 4. In order to form the thin film 4 with a uniform thickness and improve the adhesion between the thin film 4 and the surface 6, the surface roughness Ra of the surface 6 is desirably 0.1 microns or less. The thin film 4 includes an active metal such as titanium, and is formed at a predetermined position by sputtering. In order to make good adhesion with the conductor layer 5 covering the thin film 4, the thin film 4b containing platinum may be formed after the thin film 4a containing active metal is formed as shown in FIG. The thin film 4b containing platinum is more closely adhered to platinum contained in the conductor layer 5.

(Process for producing conductor layer 5)
FIG. 2G is a step of forming a conductor layer 5 that covers the thin film 4. Specifically, first, a second conductor paste containing platinum is applied by screen printing so as to cover the thin film 4. The second conductor paste is mixed and kneaded by a kneading means such as a ball mill, a three-roll mill, or a planetary mixer, with an organic binder and an organic solvent and, if necessary, a dispersant added to the main component platinum powder. Manufactured by. You may add noble metal powders, such as gold | metal | money and palladium, to the 2nd conductor paste according to required electroconductivity and mechanical characteristics. The board | substrate 2 which apply | coated the 2nd conductor paste is heat-processed at 800-1200 degreeC in a vacuum atmosphere. By performing this heat treatment, a part of the active metal contained in the thin film 4 is oxidized, and the platinum powder contained in the conductor layer 5 exhibits high bonding strength with the alumina ceramics and the alumina particles contained in the via conductor 3a. Sintering to form a dense film, and at the same time, the thin film 4 and the conductor layer 5 are joined.

  By using the wiring board and the manufacturing method thereof according to the embodiment of the present invention described above, the wiring board 1 that can be used in a corrosive fluid can be manufactured.

It is sectional drawing of the wiring board by embodiment of this invention. It is sectional drawing of the manufacturing process of the wiring board by embodiment of this invention. It is sectional drawing of the wiring board by embodiment of this invention, and is an enlarged view of a via conductor. It is an enlarged view of the cross section of the wiring board by embodiment of this invention.

Explanation of symbols

1... Wiring board 2... Boards 3 a and 3 b .. Via portion 4... Thin film 5. Surface 7 ··· Ceramic green sheet 8 ··· Hole 9 ··· First conductor paste 10 ··· Green sheet laminate

Claims (4)

A substrate comprising alumina;
A via conductor including molybdenum or tungsten, provided inside the substrate and having an end exposed on the surface of the substrate;
A thin film containing an active metal provided on the surface of the substrate so as to cover the end; and
A wiring board having a conductor layer containing platinum provided on the thin film.   The wiring board according to claim 1, wherein the via conductor includes particles made of the alumina. Preparing a plurality of ceramic green sheets containing alumina;
Forming a hole in at least one of the plurality of ceramic green sheets;
Injecting a first conductor paste containing molybdenum or tungsten into the hole;
Laminating the plurality of ceramic green sheets so that the green sheet in which the hole is formed is disposed on at least one surface layer, and forming a green sheet laminate,
Firing the green sheet laminate in a reducing atmosphere to form a ceramic substrate having via conductors;
On the ceramic substrate, forming a thin film containing an active metal so as to cover an end of the via conductor;
Applying a second conductive paste containing platinum on the thin film;
And firing the ceramic substrate coated with the second conductive paste in a vacuum atmosphere.   The method for manufacturing a wiring board according to claim 3, wherein the first conductor paste includes particles made of the alumina.

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