JP6418487B2 - Bismuth glass composition, powder material and powder material paste - Google Patents

Description

  The present invention relates to a bismuth-based glass composition, a powder material, and a powder material paste. Specifically, the present invention relates to a bismuth-based glass composition, a powder material, and a powder material paste suitable for coating a varistor element body.

  In recent years, miniaturization and integration are rapidly progressing in the field of electronic devices employed in communication devices and the like. Furthermore, there is a demand for a reduction in the withstand voltage by increasing the density of the IC, and accordingly, a protection element and circuit design for preventing destruction and malfunction of the IC circuit due to the invasion of high voltage noise are required. ing. As such a protective element, a multilayer chip varistor having voltage nonlinearity is employed.

  This chip varistor is formed by alternately laminating semiconductor ceramic layers and internal electrodes and integrally sintering them, exposing one end face of the internal electrode to both end faces of the sintered body (varistor element body), and An external electrode connected to one end surface of the internal electrode is formed.

  The varistor having the above configuration is often fixed and connected to a printed circuit board or the like by soldering the external electrode. However, a normal external electrode is easily melted and dispersed in the solder, thereby causing poor connection. For this reason, the external electrode is configured to have a base electrode and a plated layer of Ni or the like formed on the surface thereof. Then, the plating layer is formed by electroplating from the viewpoint of manufacturing cost and the like.

  However, when electroplating is performed, the formation area of the base electrode protrudes and a plating layer is formed, or the plating layer adheres to an area other than the base electrode, leading to a short circuit between the external electrodes. was there. This phenomenon becomes more apparent as the chip varistor becomes smaller.

  In order to avoid this problem, it is effective to insulate by forming a coating layer on the outer surface of the varistor element body excluding the external electrodes.

JP 05-301739 A JP 2009-2221027 A JP 2007-63105 A Japanese Patent No. 4598008

  The coating layer is formed by firing a powder material (glass powder), but the firing temperature is limited to 800 ° C. or lower in order to prevent a situation in which the characteristics of the internal electrodes and the like are deteriorated. For this reason, the powder material is required to be able to be fired at a temperature of 800 ° C. or lower.

  In addition, the powder material is required not to cause warping of the varistor element body after firing and not to easily peel from the varistor element body. Furthermore, since the plating solution is an acidic solution, the powder material is also required to have acid resistance.

Conventionally, PbO—B ₂ O ₃ —SiO ₂ -based glass has been used as a powder material that satisfies these required characteristics (see Patent Document 1).

In recent years, from the viewpoint of environmental protection, reduction of environmentally hazardous substances, for example, reduction of PbO has been promoted, and various lead-free glasses have been proposed in place of PbO—B ₂ O ₃ —SiO ₂ based glass. Yes. For example, Patent Documents 2 to 4 describe Bi ₂ O ₃ —B ₂ O ₃ —ZnO-based glass.

However, the Bi ₂ O ₃ —B ₂ O ₃ —ZnO-based glass described in Patent Documents 2 to 4 has a low acid resistance, so that it is easily eroded by the plating solution, and it is difficult to maintain characteristics such as insulation. Have.

  Therefore, the present invention has been made in view of the above circumstances, and its technical problem is that it can be fired at a temperature of 800 ° C. or less without containing PbO, and warps of the varistor element body and varistor element body. It is to create a bismuth-based glass composition, a powder material, and a powder material paste that are unlikely to be peeled off from the metal and that are not easily eroded by the plating solution.

As a result of various experiments, the present inventor adopted bismuth-based glass as a glass system that hardly causes warping and peeling, and strictly determines the content ratio of SiO ₂ , ZrO ₂ , and Al ₂ O _{3 in} the glass composition. It is found that the above technical problem can be solved by restricting to the above, and is proposed as the present invention. That is, the bismuth-based glass composition of the present invention is, as a glass composition, in mass%, Bi ₂ O ₃ 35 to 67%, SiO ₂ 22 to 40%, ZrO _{2 0 to} 12%, Al ₂ O ₃ 0.1. 10 to 10%, and the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is smaller than 50, and is used for coating the varistor element body.

Bismuth-based glass generally has low acid resistance. However, in the bismuth-based glass composition of the present invention, acid resistance is enhanced by regulating the SiO ₂ content to 22% by mass or more. On the other hand, if the content of ZrO ₂ increases when the content of SiO ₂ is large, zircon (ZrSiO ₄ ) crystals that lower the acid resistance during molding may precipitate, making it difficult to ensure the desired acid resistance. is there. Further, the glass may be phase-divided during molding, and it may be difficult to ensure desired acid resistance. Therefore, in the bismuth-based glass composition of the present invention, the content of Al ₂ O ₃ in the glass composition is 0.1 mass% or more, and the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is regulated to less than 50. By doing this, the precipitation of the zircon crystal at the time of shaping | molding and the phase separation of glass are suppressed.

Secondly, the bismuth-based glass composition of the present invention has a glass composition of mass%, Bi ₂ O ₃ 40 to 55%, SiO ₂ 28 to 40%, ZrO _{2 over} 5 to 9%, Al ₂ O _3. 2 to 10%, B ₂ O ₃ 0 to 5% are contained, and the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is preferably smaller than 15.

  Third, the bismuth-based glass composition of the present invention preferably further contains 0.1 to 9% by mass of BaO.

  Fourth, the bismuth-based glass composition of the present invention has an MgO content of 5 mass% or less, a CaO content of 5 mass% or less, an SrO content of 5 mass% or less, and a ZnO content. It is preferable that it is 5 mass% or less.

  Fifth, it is preferable that the bismuth-based glass composition of the present invention does not substantially contain PbO. Here, “substantially free of PbO” means that PbO is allowed to be mixed in at an impurity level, but avoids aggressive introduction. Specifically, the content of PbO in the glass composition Is less than 1000 ppm.

  Sixth, the powder material of the present invention is a powder material containing a glass powder made of the bismuth-based glass composition and a ceramic powder, wherein the content of the glass powder is 50 to 100% by mass, Content is 0-50 mass%, It is characterized by the above-mentioned.

  Seventh, the powder material of the present invention preferably has a softening point of 600 to 800 ° C. Here, the “softening point” refers to the temperature at the fourth inflection point measured with a macro-type differential thermal analyzer (DTA).

  Eighth, the powder material of the present invention is a powder material paste containing a powder material and a vehicle, wherein the powder material is the powder material described above.

The bismuth-based glass composition of the present invention has, as a glass composition, mass%, Bi ₂ O ₃ 35-67%, SiO ₂ 22-40%, ZrO ₂ 0-12%, Al ₂ O ₃ 0.1-10. %, And the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is less than 50. The reason why the content range of each component is regulated as described above will be described below. In addition, in description of the containing range of each component,% display means the mass%.

Bi ₂ O ₃ is a component that lowers the softening point, and is a component that ensures adhesion with semiconductor ceramics mainly composed of ZnO, but is a component that lowers acid resistance. The content of Bi ₂ O ₃ is 35 to 67%, preferably 38 to 60%, 40 to 55%, 41 to 54%, 42 to 53%, particularly 43 to 52%. When the content of Bi ₂ O ₃ is reduced, the softening point is unduly raised and it becomes difficult to fire at a temperature of 800 ° C. or lower. On the other hand, when the content of Bi ₂ O ₃ is increased, the acid resistance is likely to be lowered, and the coating layer is easily eroded by the plating solution. As a result, it is difficult to insulate and protect the varistor element body. Furthermore, when the content of Bi ₂ O ₃ is increased, the raw material cost is likely to increase.

SiO ₂ is a component that forms a glass skeleton and a component that increases acid resistance. The content of SiO ₂ is 22 to 40%, preferably 26 to 40%, 28 to 40%, 29 to 38%, particularly 30 to 36%. When the content of SiO ₂ is reduced, the acid resistance is likely to be lowered, and the coating layer is easily eroded by the plating solution. As a result, it is difficult to insulate and protect the varistor element body. On the other hand, when the content of SiO ₂ is increased, the softening point is unreasonably raised and it becomes difficult to fire at a temperature of 800 ° C. or lower.

ZrO ₂ is a component that increases acid resistance. The content of ZrO ₂ is 0 to 12%, preferably 0.1 to 11%, 3 to 10%, more than 5 to 9%, 5.5 to 8.5%, particularly 6 to 8%. When the content of ZrO ₂ is reduced, the acid resistance is likely to be lowered, and the coating layer is easily eroded by the plating solution. As a result, it is difficult to insulate and protect the varistor element body. On the other hand, when the content of ZrO ₂ is increased, zircon crystals are likely to precipitate during molding, and the softening point is unduly raised, making it difficult to fire at a temperature of 800 ° C. or lower.

Al ₂ O ₃ is a component that enhances acid resistance and is a component that stabilizes glass, particularly a component that suppresses the precipitation of zircon crystals. The content of Al ₂ O ₃ is 0.1 to 10%, preferably 2 to 10%, 2.5 to 9%, particularly 3 to 8%. When the content of Al ₂ O ₃ is reduced, the glass becomes unstable and zircon crystals are likely to precipitate during molding. On the other hand, when the content of Al ₂ O ₃ is increased, the softening point is unreasonably raised and it becomes difficult to fire at a temperature of 800 ° C. or lower.

The mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is 50 or less, preferably 25 or less, 15 or less, 13 or less, 11 or less, particularly 9 or less. When the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is excessive, zircon crystals are likely to precipitate or glass is likely to be phase-separated.

  In addition to the above components, for example, the following components may be introduced.

B ₂ O ₃ is a component that forms a glass skeleton and widens the vitrification range, but when its content increases, the acid resistance may be significantly reduced. Therefore, the content of B ₂ O ₃ is 0 to 5%, preferably 0 to 4%, 0 to 3%, particularly 0.5 to 2%.

  MgO is a component that lowers the softening point and is a component that stabilizes the glass. The content of MgO is preferably 0 to 5%, 0 to 4%, particularly 0 to 3%. When the content of MgO increases, the acid resistance tends to decrease, the coating layer is easily eroded by the plating solution, and as a result, it becomes difficult to insulate and protect the varistor element body.

  CaO is a component that lowers the softening point and is a component that stabilizes the glass. The content of CaO is preferably 0 to 5%, 0 to 4%, particularly 0 to 3%. When the content of CaO is increased, the acid resistance is likely to be lowered, and the coating layer is easily eroded by the plating solution. As a result, it is difficult to insulate and protect the varistor element body.

  SrO is a component that lowers the softening point and is a component that stabilizes the glass. The content of SrO is preferably 0 to 5%, 0 to 4%, particularly 0 to 3%. When the SrO content is increased, the acid resistance is likely to be lowered, and the coating layer is easily eroded by the plating solution. As a result, it is difficult to insulate and protect the varistor element body.

  BaO is a component that lowers the softening point and is a component that stabilizes the glass, particularly a component that suppresses phase separation. The content of BaO is preferably 0-9%, 0.1-9%, 1-9%, 2-8%, especially 3-7%. When the content of BaO decreases, the glass tends to become unstable. On the other hand, when the content of BaO increases, the acid resistance tends to decrease, and the coating layer is easily eroded by the plating solution. As a result, it becomes difficult to insulate and protect the varistor element body.

  ZnO is a component that lowers the softening point, but is a component that reduces acid resistance. The content of ZnO is 0 to 5%, preferably 0 to 4%, particularly 0 to 3%. When the ZnO content is increased, the acid resistance is significantly reduced, and the coating layer is easily eroded by the plating solution, and as a result, it is difficult to protect the varistor element from insulation.

In addition to the above components, various components may be introduced as long as the characteristics of the chip varistor are not significantly impaired. For example, in order to lower the softening point, Cs ₂ O, Rb ₂ O, or the like may be introduced up to 5%, particularly up to 1%, alone or in total. Moreover, in order to stabilize glass and to improve water resistance and acid resistance, Y ₂ O ₃ , La ₂ O ₃ , Ta ₂ O ₅ , SnO ₂ , TiO ₂ , Nb ₂ O ₅ , P ₂ O ₅ , CuO , CeO ₂ , V ₂ O _5, etc. may be introduced in a total amount or independently up to 10%, particularly up to 1%.

  PbO is a component that lowers the softening point, but is also an environmentally hazardous substance, so it is preferable to avoid substantial introduction.

  The powder material of the present invention is a powder material containing a glass powder made of the bismuth-based glass composition and a ceramic powder, wherein the glass powder content is 50 to 100% by mass, and the ceramic powder content is 0. It is -50 mass%, It is characterized by the above-mentioned.

  The glass powder can be produced, for example, by forming molten glass into a film and then crushing and classifying the obtained glass film.

The average particle diameter D ₅₀ of the glass powder is preferably 3.0 μm or less, and the maximum particle diameter D _max is preferably 20 μm or less. If the particle size of the glass powder is too large, it is difficult to reduce the thickness of the coating layer, and large bubbles tend to remain in the coating layer. Here, the “average particle diameter D ₅₀ ” refers to a value measured with a laser diffractometer, and in an accumulated particle size distribution curve based on volume when measured by a laser diffraction method, the accumulated amount is accumulated from the smaller particle. The particle diameter is 50%. “Maximum particle size D _max ” refers to a value measured by a laser diffractometer, and in the volume-based cumulative particle size distribution curve measured by the laser diffraction method, the accumulated amount is accumulated from the smaller particle. The particle size is 99%.

  The content of the ceramic powder is preferably 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, and particularly less than 1% by mass. If the ceramic powder is too much, the proportion of the glass powder becomes relatively small and it becomes difficult to form a dense coating layer, so that the coating layer is easily eroded by the plating solution. It becomes difficult to protect the insulation. If ceramic powder is added, the thermal expansion coefficient, mechanical strength, and acid resistance of the powder material can be adjusted.

  Various materials can be used as the ceramic powder. For example, one or more of alumina, zirconia, mullite, silica, cordierite, titania, tin oxide, and the like can be added.

  In the powder material of the present invention, the softening point is preferably 600 to 800 ° C, 650 to 790 ° C, particularly 700 to 780 ° C. If the softening point is too high, it becomes difficult to form a coating layer having good surface accuracy at a baking temperature of 800 ° C. or lower. On the other hand, if the softening point is too low, it is difficult to adjust the glass composition, and it becomes difficult to ensure acid resistance.

In the powder material of the present invention, the thermal expansion coefficient is preferably 45 to 65 × 10 ⁻⁷ / ° C., particularly preferably 50 to 60 × 10 ⁻⁷ / ° C. This makes it easy to prevent warping of the varistor element body and peeling of the coating layer after the coating layer is formed. Here, the “thermal expansion coefficient” is a value measured in a temperature range of 30 to 300 ° C. by a thermomechanical analyzer (TMA).

  The powder material paste of the present invention is a powder material paste containing a powder material and a vehicle, wherein the powder material is the above powder material. Here, the vehicle is a material for dispersing glass powder into a paste, and is usually composed of a thermoplastic resin, a plasticizer, a solvent, and the like.

  The powder material paste can be prepared by preparing a powder material and a vehicle, and mixing and kneading them at a predetermined ratio.

  The thermoplastic resin is a component that increases the film strength after drying, and is a component that imparts flexibility. The content of the thermoplastic resin in the powder material paste is preferably 0.1 to 20% by mass. As the thermoplastic resin, polybutyl methacrylate, polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, ethyl cellulose and the like are preferable, and it is preferable to use one or more of these.

  The solvent is a component for dissolving the thermoplastic resin. The content of the solvent in the powder material paste is preferably 10 to 30% by mass. As the solvent, terpineol, diethylene glycol monobutyl ether acetate, 2,2,4-trimethyl-1,3-pentadiol monoisobutyrate and the like are preferable, and it is preferable to use one or more of these.

  In order to form a coating layer on the varistor element body using the powder material paste, first, the powder material paste is applied to a region excluding the external electrode of the varistor element body, and after forming a coating layer having a predetermined film thickness, Dry to obtain a dry film. Then, a predetermined coating layer (baked film) can be formed by baking the dried film at a temperature of 700 to 800 ° C. for 5 to 20 minutes. If the firing temperature is too low or the firing time (holding time) is too short, the dried film will not sinter sufficiently, making it difficult to form a dense and smooth fired film. On the other hand, if the firing temperature is too high or the holding time is too long, the internal electrode or the like reacts with the powder material, and the characteristics of the internal electrode or the like easily deteriorate.

  In addition to the above method, after charging the varistor element body and the powder material into the heat resistant container, it is fired at a temperature of 750 to 850 ° C. for 0.5 to 2 hours while rotating the heat resistant container. A coating layer (fired film) can also be formed.

  Hereinafter, based on an Example, this invention is demonstrated in detail. The present invention is not limited to the following examples. The following examples are merely illustrative.

  Table 1 shows Examples (Sample Nos. 1 to 5) and Comparative Examples (Sample No. 6) of the present invention.

  Each sample was prepared as follows. First, raw materials were prepared and mixed uniformly so as to have the glass composition shown in the table. Then, after putting in a platinum crucible and melting at 1350 to 1450 ° C. for 2 hours, it was formed into a film.

  The obtained glass film was attached and the moldability was evaluated. “O” indicates that no devitrification crystals (bumps) are observed on the surface of the glass film and no phase separation is observed, and “△” indicates that devitrification crystals and / or phase separation is slightly observed. A sample in which a permeable crystal and / or phase separation was remarkably recognized was evaluated as “x”.

Subsequently, the above glass film was pulverized with a ball mill and then classified into an air stream to obtain a glass powder having an average particle size D _{50 of} 3.0 μm or less and a maximum particle size D _{max of} 20 μm or less. The softening point and thermal expansion coefficient were evaluated using the obtained glass powder.

  The softening point is the temperature at the fourth inflection point measured with a macro-type differential thermal analyzer (DTA).

  The coefficient of thermal expansion was determined by pressing each glass powder and firing it at (softening point +10) ° C., then processing to a diameter of 5 mm and a length of 20 mm to obtain a measurement sample, and then a thermomechanical analyzer (TMA) ) In the temperature range of 30 to 300 ° C.

  Next, the glass powder and vehicle (terpineol containing 5% by mass of ethyl cellulose and 3% by mass of tributyl acetylcitrate) were mixed and kneaded by a three-roll mill to obtain a powder material paste. Furthermore, after applying a powder material paste on a substrate with a semiconductor ceramic layer (based on ZnO) by a screen printing method so that a fired film (coating layer) of about 10 μm is obtained, the coating film is dried, Firing was carried out for 10 minutes at a temperature of (softening point + 10) ° C. in an electric furnace. Acid resistance was evaluated using the obtained substrate with a fired film. Specifically, the substrate with the fired film was immersed in 5% by mass sulfuric acid at 40 ° C. for 5 hours, washed with water, dried, then measured for mass decrease, and evaluated the rate of mass decrease before and after immersion. In addition, it means that acid resistance is so low that the ratio of mass reduction is large.

  As is clear from Table 1, sample No. Nos. 1 to 5 had a low softening point and could be fired at a temperature of 800 ° C. or lower, and had good moldability and acid resistance. Sample No. No. 6 had a low softening point, but was poor in moldability and acid resistance.

Claims (8)

As a glass composition, in _{mass%, Bi 2 O 3 35~ 60} %, and containing _{SiO 2 22~40%, ZrO 2 3} ~12%, the Al 2 O 3 0.1~10%, the weight ratio (SiO ₂ A bismuth-based glass composition having + ZrO ₂ ) / Al ₂ O ₃ of 25 or less and used for coating a varistor element body. As a glass composition, in _{mass%, Bi 2 O 3 40~55%} , SiO 2 28~40%, ZrO 2 5 super _{~9%, Al 2 O 3 2~10} %, the 2 O 3 0~5% _{B 2.} The bismuth-based glass composition according to claim 1, wherein the bismuth-based glass composition is contained and the mass ratio (SiO ₂ + ZrO ₂ ) / Al ₂ O ₃ is smaller than 15. 5.   Furthermore, 0.1-9 mass% of BaO is included, The bismuth-type glass composition of Claim 1 or 2 characterized by the above-mentioned.   The MgO content is 5% by mass or less, the CaO content is 5% by mass or less, the SrO content is 5% by mass or less, and the ZnO content is 5% by mass or less. The bismuth-type glass composition in any one of -3.   The bismuth-based glass composition according to any one of claims 1 to 4, which is substantially free of PbO. A powder material comprising a glass powder and a ceramic powder comprising the bismuth-based glass composition according to any one of claims 1 to 5,
Content of glass powder is 50-100 mass%, Content of ceramic powder is 0-50 mass%, The powder material characterized by the above-mentioned.   The powder material according to claim 6, wherein the softening point is 600 to 800 ° C. In a powder material paste containing a powder material and a vehicle,
A powder material paste, wherein the powder material is the powder material according to claim 6 or 7.