CN112602158B - conductive paste - Google Patents

Abstract

The conductive paste of the present invention is a conductive paste containing a metal powder containing copper, a glass composition, and an organic vehicle, wherein the glass composition contains sulfur (S), and the content of the sulfur (S) is 10ppm to 370ppm relative to the metal powder. According to the present invention, there can be provided: the firing behavior of the metal powder monomer containing copper is suitably controlled, and as a result, the firing window is wide, and problems such as voids and glass floating after firing are less likely to occur.

Description

Conductive paste

Technical Field

The present invention relates to a conductive paste using metal powder containing copper as a main component as a conductive component.

Background Art

As an example, when forming external electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors and multilayer ceramic inductors, a conductive paste containing conductive powder, a glass composition, and an organic vehicle is used.

As conductive powder, metal powders such as silver (Ag) and palladium (Pd) have been used in the past. In recent years, conductive pastes containing metal powders including copper (Cu) (hereinafter referred to as copper pastes) have been widely used from the viewpoints of excellent conductivity and production costs.

In order to form the external electrodes of multilayer ceramic electronic components using copper paste, generally speaking, first, a chip-shaped laminated body formed by alternating dielectric layers and internal electrode layers is prepared, and the copper paste is applied to its end surface by a suitable technique (such as dip coating printing method, screen printing method). Then, the copper-containing metal powder is heated and fired in an atmosphere that is not easily oxidized, so that the organic components in the paste are scattered and decomposed, and the glass is fluidized, and the metal particles containing copper are sintered to each other, thereby forming an external electrode. At this time, the range of heating temperature suitable for firing is determined according to the type and combination of the metal powder, glass composition, organic carrier, other additives, etc. contained in the paste.

Furthermore, a plating layer of tin, nickel or the like is formed on the surface of the formed external electrode to improve the reliability as the electrode and facilitate soldering.

However, in the case of conventional copper paste, when the end surface of the chip-shaped laminate is coated and then fired, if the temperature range suitable for the firing (hereinafter referred to as the "firing window") is narrow, there is a problem that over-sintering is easily caused by uneven temperature and slight temperature changes in the firing furnace. During over-sintering, the metal powder containing copper shrinks rapidly, causing the glass component to float, and the glass component is unevenly distributed on the surface of the pattern after firing, resulting in so-called "glass floating". Such glass floating reduces the adhesion of the fired pattern to various metals such as tin and nickel, making it difficult to form a plating layer.

In order to suppress the occurrence of such glass floating, it is possible to consider lowering the firing temperature in a way that does not cause over-sintering. However, the firing window is narrow, so in this case, the density of the fired film (electrode) becomes low, and voids (voids) occur in the film. As a result, in addition to the deterioration of the conductivity of the electrode and the bonding strength with the ceramic element, the plating solution penetrates into the film when the fired film is plated in the subsequent process, resulting in a decrease in insulation resistance and the occurrence of cracks in the element. In addition, the immersed plating solution is heated and vaporized during solder reflow, which becomes the cause of "solder explosion" in which the molten solder is scattered.

However, in order to control the sintering behavior of metal powders, attempts have been made to perform specific surface treatments on the surfaces of metal powders. For example, in Patent Document 1, in order to control the sintering start temperature, an attempt was made to attach any one of Al, Si, Ti, Zr, Ce, and Sn to the surface of copper powder. In addition, Patent Document 2 states that coating the surface of any one of metal powders of nickel, silver, copper, and palladium with a metal compound containing sulfur can effectively suppress the catalytic effect of the metal powder.

However, according to the research of the present inventors, when these surface treatments are applied to metal powder containing copper, there are cases where the influence on the firing behavior of the metal powder containing copper alone is too great, and even if the sintering start temperature can be controlled, the firing window is narrow; and the firing temperature and firing atmosphere of the copper paste when the surface treatment is not performed must be greatly changed. In this case, not only does the paste need to be redesigned, but also the overall cost of the paste increases due to the characteristics and restrictions of the raw materials and materials that can be used for the paste, or in some cases, the manufacturing line such as the firing furnace needs to be inspected.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2016-033850

Patent Document 2: Japanese Patent Application Publication No. 2014-005491

Summary of the invention

Technical problem solved by the invention

An object of the present invention is to provide a conductive paste that appropriately controls the firing behavior of a metal powder alone containing copper, thereby widening the firing window and making it less likely to cause problems such as voids and glass floating after firing.

Technical means of solving problems

Such an object is achieved by the present invention described in the following (1) to (6).

(1) A conductive paste comprising a metal powder containing copper, a glass composition, and an organic vehicle, wherein:

The glass composition contains sulfur (S), and the content of the sulfur (S) is 10 ppm to 370 ppm based on the metal powder.

(2) A conductive paste comprising a metal powder containing copper, a glass composition, an organic vehicle, and an inorganic additive, wherein:

The inorganic additive includes sulfur (S), and the content of the sulfur (S) is 10 ppm to 370 ppm based on the metal powder.

(3) The conductive paste described in (2), wherein the inorganic additive is a sulfate.

(4) A conductive paste comprising a metal powder containing copper, a glass composition, an organic vehicle, and an organic additive, wherein:

The organic additive has a thiol group, and a content of sulfur (S) in the organic additive is 10 ppm or more and 370 ppm or less relative to the metal powder.

(5) The conductive paste according to any one of (1) to (4), wherein the metal powder is copper powder.

(6) The conductive paste according to any one of (1) to (5), wherein the content of sulfur (S) contained in the metal powder is less than 10 ppm.

Effects of the Invention

According to the present invention, it is possible to provide a conductive paste in which voids are less likely to occur in a fired film during firing and in which adverse effects due to over-sintering are less likely to occur.

Specific embodiments of the present invention

Hereinafter, preferred embodiments of the present invention will be described in detail.

[Conductive paste]

1. First Implementation Method

A conductive paste according to a preferred embodiment of the present invention is a conductive paste comprising metal powder containing copper, a glass composition, and an organic vehicle, wherein the glass composition contains sulfur (S) in an amount of 10 ppm to 370 ppm inclusive relative to the metal powder.

By such a structure, it is possible to provide a conductive paste containing copper, in which the variation in firing behavior is smaller than in the case where the surface of the metal powder containing copper itself is subjected to surface treatment, and the firing behavior of the copper paste as a whole can be appropriately controlled, and a conductive paste having a wider firing window is less likely to cause problems such as voids and glass floating after firing.

Such excellent effects are believed to be obtained for the following reasons. Specifically, the present inventors speculate that, compared with the case where sulfur (S) is mixed with metal powder or the surface of the metal powder is coated with a sulfur compound as in the conventional example, the sulfur contained in the glass composition acts on the copper constituting the metal powder from the flow of the glass composition in the conductive paste during firing, and as a result, the sintering behavior of the metal powder is slowly controlled.

2. Second Implementation Method

In addition, the conductive paste according to another suitable embodiment of the present invention is a conductive paste containing metal powder including copper, a glass composition, an organic vehicle and an inorganic additive, wherein the inorganic additive contains sulfur, and the content of the sulfur is 10 ppm to 370 ppm relative to the metal powder.

By such a structure, it is possible to provide a conductive paste containing copper, in which the variation in firing behavior is smaller than in the case where the surface of the metal powder containing copper itself is subjected to surface treatment, and the firing behavior of the copper paste as a whole can be appropriately controlled, and a conductive paste having a wider firing window is less likely to cause problems such as voids and glass floating after firing.

Such excellent effects are believed to be obtained for the following reasons. Specifically, the present inventors presume that, compared with the case where sulfur (S) is mixed with metal powder or the surface of metal powder is coated with a sulfur compound as in the conventional example, sulfur constituting the inorganic additive is temporarily dissolved in the glass composition from the time when the glass composition in the conductive paste flows during firing, and then the sulfur dissolved in the glass composition acts on copper constituting the metal powder, resulting in the sintering behavior of the metal powder being slowly controlled.

3. Third Implementation Method

In addition, the conductive paste of another suitable embodiment of the present invention is a conductive paste containing a metal powder including copper, a glass composition, an organic vehicle and an organic additive, wherein the organic additive has a thiol group and the sulfur content in the organic additive is greater than 10 ppm and less than 370 ppm relative to the metal powder.

By such a structure, it is possible to provide a conductive paste containing copper, in which the variation in firing behavior is smaller than in the case where the surface of the metal powder containing copper itself is subjected to surface treatment, and the firing behavior of the copper paste as a whole can be appropriately controlled, and a conductive paste having a wider firing window is less likely to cause problems such as voids and glass floating after firing.

Such excellent effects are believed to be obtained for the following reasons. Specifically, the present inventors presume that, compared with the case where sulfur (S) is mixed with metal powder or the surface of metal powder is coated with a sulfur compound as in the conventional example, the sulfur constituting the organic additive is temporarily dissolved in the glass composition when the glass composition in the conductive paste flows during firing, and then the sulfur dissolved in the glass composition acts on the copper constituting the metal powder, resulting in that the sintering behavior of the metal powder is slowly controlled.

In each of the above-mentioned embodiments, in the case of the glass composition of the first embodiment including a given amount of sulfur and the inorganic additive of the second embodiment including a given amount of sulfur (particularly, the glass composition including a given amount of sulfur), even if fired at a relatively low temperature (e.g., 750°C), the density of the fired film can be particularly excellent, and the range of firing temperatures (firing window) suitable for forming the fired film is particularly wide, which is advantageous. In the present invention, the first embodiment is particularly preferred. It should be noted that in the case of the third embodiment, there is a situation where the organic additive is firmly bonded to the metal powder over time, and therefore environmental management including storage temperature is required.

If the above-mentioned constitution is not satisfied, satisfactory results cannot be obtained.

For example, in the first to third embodiments, when the sulfur content in the given components of the conductive paste is less than the lower limit, it is not possible to sufficiently prevent adverse effects caused by over-sintering during firing. In particular, when firing is performed at a relatively high temperature (e.g., 780° C. or higher), adverse effects caused by over-sintering are likely to occur significantly.

In the first to third embodiments, when the sulfur content in the given components of the conductive paste exceeds the upper limit, it is not possible to sufficiently prevent the formation of voids in the fired film during firing. In particular, when firing is performed at a relatively low temperature (e.g., 750° C. or less), voids are likely to be significantly formed in the fired film.

In addition, even in the case where the sulfur content of the conductive paste as a whole is a value within the above range, when the sulfur content in the above given component does not satisfy the given content condition, more specifically, when a large amount of sulfur is contained in the metal powder, the influence on the firing behavior of the metal powder, such as the sintering start temperature, is too great, thereby reducing the density of the fired film and easily generating voids in the fired film.

As described above, the sulfur content in the given components (glass composition, inorganic additives, organic additives) of the conductive paste may be 10 ppm to 370 ppm, preferably 12 ppm to 200 ppm, and particularly preferably 15 ppm to 100 ppm, relative to the metal powder.

Thereby, the above-mentioned effect is further significantly exerted.

<Metal powder>

The conductive paste in the present invention contains metal powder, and the metal powder contains copper.

As such metal powder, for example, pure copper powder containing only copper, copper alloy powder, etc. can be cited. In addition, it can be a metal powder with a core-shell structure having a copper particle as a core and a thin film containing copper oxide or an oxide thin film containing an element other than copper coated on its surface. As the thin film, glass is particularly preferred. The coating of the metal powder with a glassy thin film can be achieved, for example, by the method described in Japanese Patent No. 3206496.

The metal powder has a core-shell structure of the thin film, so it is possible to suppress oxidation of the metal powder or control the sintering start temperature of the metal powder.

Although the film containing copper oxide and the oxide film containing an element other than copper do not contain sulfur, the film may contain sulfur when the film is glassy. The glassy film not only inhibits oxidation of the metal powder, but also softens and flows during firing, and also functions as a sintering aid for the metal powder. When the glassy film contains sulfur, the total amount of sulfur contained in other glass compositions, inorganic additives or organic additives may be 10 ppm to 370 ppm relative to the metal powder.

The content of the copper element (Cu) is preferably 50 mass % to 100 mass %, and more preferably 80 mass % to 100 mass %, relative to the total amount of metal elements contained in the metal powder.

The metal powder in the present invention does not substantially contain sulfur, but does not exclude the possibility of containing sulfur as an unavoidable impurity. That is, in the present invention, "the metal powder does not substantially contain sulfur" means that the sulfur content contained in the metal powder is less than 10 ppm, more preferably less than 7 ppm, and even more preferably less than 5 ppm.

Thereby, compared with the case where the metal powder containing copper itself is subjected to the surface treatment, the fluctuation of the firing behavior is small, and the firing behavior of the copper paste as a whole can be appropriately controlled.

The average particle size (D ₅₀ ) of the metal powder is not particularly limited, but is preferably 0.2 μm to 5.0 μm, more preferably 0.5 μm to 4.5 μm, and further preferably 1.0 μm to 4.0 μm.

In the present specification, the average particle size (D ₅₀ ), unless otherwise specified, refers to the weight-based cumulative fraction 50% value of the particle size distribution measured using a laser particle size distribution analyzer, and can be obtained, for example, by measurement using a laser diffraction/scattering particle size distribution analyzer LA-960 (manufactured by HORIBA Corporation).

The BET specific surface area of the metal powder is not particularly limited, but is preferably 0.30 ^m2 /g to 1.00 ^m2 /g, more preferably 0.40 ^m2 /g to 0.90 ^m2 /g, and further preferably 0.50 ^m2 /g to 0.80 ^m2 /g. The BET specific surface area can be obtained using, for example, TRISTAR 3000 (manufactured by Shimadzu Corporation).

The content of the metal powder in the conductive paste is not particularly limited, but is preferably 50.0 mass % to 80.0 mass %, more preferably 55.0 mass % to 75.0 mass %, and further preferably 60.0 mass % to 70.0 mass %.

This makes it possible to fully exert the function of the metal powder containing copper and more reliably improve the conductivity of the fired film.

It should be noted that the various particles constituting the metal powder constituting the conductive paste of the present invention are preferably metal particles having the same or uniform metal composition, and may include metal particles having different metal compositions as long as the effects of the present invention are not impaired. For example, the metal powder may include various particles having different copper contents. In such a case, the copper content of the metal powder as a whole preferably satisfies the above conditions.

<Glass Composition>

The glass composition contained in the conductive paste of the present invention may have any composition as long as its softening point is not more than the firing temperature, but is preferably a glass composition containing substantially no Pb, Cd, and Bi. For example, in the present invention, a glass composition can be suitably used which contains SiO ₂ in a range of 2.0 mass % to 12.0 mass %, B ₂ O ₃ in a range of 15.0 mass % to 30.0 mass %, and Al ₂ O ₃ in a range of 2.0 mass % to 12.0 mass % as essential components, and contains BaO in a range of 40.0 mass % to 65.0 mass %, ZnO in a range of 5.0 mass % to 50.0 mass %, TiO 2 in a range of 0.5 mass % to 7.0 mass %, CaO in a range of 3.0 mass % to 7.5 mass %, K ₂ O in a range of 1.5 mass % to 4.0 mass %, and MnO ₂ in a range of 2.5 mass % to _12.0 mass % as other optional components.

When the glass composition having the above composition is used, even when firing is performed in a non-oxidizing atmosphere, a dense electrode film having excellent acid resistance and free from strength defects and infiltration of a plating solution can be easily formed.

In the first embodiment of the present invention, the glass composition contains sulfur. Sulfur can be mixed into the glass composition by any method. As an example, when manufacturing the glass composition, _BaSO4 can be mixed with materials constituting glass as a sulfur source, and the glass composition can be manufactured by a common method such as melting, rapid cooling, and pulverization. In this case, the sulfur source is weighed so that the amount of sulfur contained in the sulfur source is 10 ppm or more and 370 ppm or less relative to the metal powder.

The glass composition may be contained in the conductive paste in a form of, for example, coating the metal powder as the glassy thin film, and is preferably contained in a form of glass powder independent of the metal powder.

Therefore, it is particularly advantageous from a cost perspective.

The glass powder may be in the form of a powder in which particles of, for example, granular, flaky, fibrous, needle-shaped, or irregular shapes are aggregated.

In the following description, the case where the glass composition constituting the conductive paste is a glass powder will be mainly described.

The average particle size of the glass composition is not particularly limited, but is preferably 0.1 μm to 4.5 μm, more preferably 0.3 μm to 4.0 μm, and further preferably 0.8 μm to 3.5 μm.

The BET specific surface area of the glass composition is not particularly limited, but is preferably 0.90 ^{m 2} /g to 5.00 m ² /g, more preferably 1.20 m ² /g to 4.50 m ² /g, and further preferably 1.50 m ² /g to 4.00 m ² /g.

The content of the glass composition in the conductive paste is not particularly limited, but is preferably 4.0 mass % to 20.0 mass %, more preferably 5.0 mass % to 15.0 mass %, and further preferably 6.0 mass % to 10.0 mass %.

It should be noted that the various particles constituting the glass composition constituting the conductive paste of the present invention may be glass particles having the same or uniform glass composition, and may include various glass particles having different compositions, particle sizes, etc., for the purpose of improving the control of firing behavior, adhesion and tightness to the substrate, etc., by generally known techniques.

<Organic Carrier>

The organic vehicle contained in the conductive paste of the present invention is not particularly limited. For example, one or more organic binders selected from cellulose resins (such as ethyl cellulose, nitrocellulose, etc.), (meth) acrylic resins (such as polymethacrylate, polymethyl methacrylate, etc.), ester resins (such as rosin esters, etc.), polyvinyl acetals (such as polyvinyl butyral, etc.) and the like can be dissolved or dispersed in one or more organic solvents selected from alcohols (such as terpineol, α-terpineol, β-terpineol, etc.), esters (such as hydroxyl-containing esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, butyl carbitol acetate, etc.), ethers (such as glycol ethers such as dipropylene glycol-n-propyl ether, etc.), etc., and can be used. However, depending on the application and the coating method, there is a case where the organic vehicle only contains the organic solvent and does not contain the organic binder.

As the organic solvent, it is preferred that at least one of alcohols (particularly terpineol) and ethers (particularly dipropylene glycol-n-propyl ether) be contained, and it is more preferred that both be contained.

Furthermore, as the organic binder, it is preferred that a (meth)acrylic resin be contained.

The content of the organic vehicle in the conductive paste is not particularly limited, but is preferably 10.0 mass % to 40.0 mass %, more preferably 15.0 mass % to 35.0 mass %, and further preferably 20.0 mass % to 30.0 mass %.

The content of the organic solvent in the conductive paste is not particularly limited, but is preferably 7.0 mass % to 30.0 mass %, more preferably 10.0 mass % to 28.0 mass %, and further preferably 14.0 mass % to 25.0 mass %.

The content of the organic binder in the conductive paste is not particularly limited, but is preferably 1.0 mass % to 15.0 mass %, more preferably 2.0 mass % to 10.0 mass %, and further preferably 3.0 mass % to 8.0 mass %.

<Inorganic additives>

The conductive paste may contain a sulfur-containing inorganic additive as a component other than the above components. In this case, the amount of the inorganic additive added is weighed so that the amount of sulfur contained in the inorganic additive is within a range of 10 ppm to 370 ppm relative to the metal powder.

By using such an inorganic additive, for example, by adjusting the amount of the inorganic additive added, the sulfur content relative to the metal powder in the conductive paste can be appropriately adjusted without adjusting the sulfur content in the glass composition. As a result, for example, a glass composition that is easily available can be appropriately used for the production of a conductive paste.

The sulfur-containing inorganic additive may be present in a dissolved state in the conductive paste, but is preferably contained as an insoluble component.

Thereby, for example, during storage of the conductive paste, it is possible to more effectively prevent the conductive paste from unintentionally reacting with the metal powder.

Examples of the sulfur-containing inorganic additive include sulfates, sulfites, persulfates, thiosulfuric acid, and metal sulfides, and sulfates are preferred.

Sulfate is a component that is relatively easy to dissolve in glass when the glass flows during firing of the conductive paste among various inorganic additives. Therefore, when sulfate is used as an inorganic additive, the above-mentioned effect is more significantly exerted.

Examples of the sulfate include barium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, sodium sulfate, potassium sulfate, sodium potassium sulfate, and ammonium sulfate. Among them, barium sulfate is preferred.

Thus, the above effect is further significantly exerted. In addition, barium sulfate is a poorly soluble component with high chemical stability under normal conditions (for example, conditions of storing the conductive paste at 0°C or above and 40°C or below), and is a component that is not easy to react with the metal powder unavoidably. In addition, barium sulfate is a relatively low-priced substance that can be easily and stably obtained, and is preferred from the perspective of stable supply of conductive paste, reduction of production costs, etc.

When the inorganic additive in the conductive paste is a small-diameter powder, sulfur is more easily mixed into the glass composition. Although not particularly limited, the average particle size (D ₅₀ ) is preferably 0.5 μm or less, more preferably 0.1 μm or less. Considering the availability, the most preferred average particle size is 0.01 μm or more and 0.05 μm or less.

<Organic Additives>

The conductive paste may contain a sulfur-containing organic additive as a component other than the above components. In this case, the amount of the organic additive added is weighed so that the amount of sulfur contained in the organic additive is within a range of 10 ppm to 370 ppm relative to the metal powder.

By using such an organic additive, for example, by adjusting the amount of the organic additive added, the sulfur content relative to the metal powder in the conductive paste can be appropriately adjusted without adjusting the sulfur content in the glass composition. As a result, for example, a glass composition that is easily available can be appropriately used for the production of a conductive paste.

The sulfur-containing organic additive may be present in the conductive paste in a dissolved state or may be contained as an insoluble component.

Examples of the sulfur-containing organic additive include compounds having a thiol group.

Examples of the compound having a thiol group (organic additive) include thiols (mercaptoalkane compounds) such as dodecyl mercaptan and thiol compounds (compounds having both functional groups of an OH group and an SH group) such as mercaptoethanol.

<Other ingredients>

The conductive paste may contain other components in addition to the above components, for example, plasticizers, defoamers, dispersants such as higher fatty acids and fatty acid esters, leveling agents, stabilizers, adhesion promoters, surfactants, etc., which are usually added to the conductive paste, preferably without sulfur in the components.

[Application of conductive paste]

The conductive paste of the present invention can be applied and fired by a generally known method to form a conductive portion. The use thereof is not particularly limited, but it is particularly suitable for forming internal conductors (internal electrodes) and terminal electrodes of multilayer ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, and multilayer ceramic actuators.

The conductive paste is applied to a desired substrate by, for example, screen printing, transfer printing, dipping, brush coating, a method using a dispenser, etc., and then dried and fired.

The drying temperature of the conductive paste is not particularly limited, and can be, for example, 100° C. to 200° C. In addition, the firing temperature (peak temperature) is also not particularly limited, and as an example, can be 600° C. to 900° C., preferably 700° C. to 880° C., and more preferably 730° C. to 850° C.

As mentioned above, although the preferred embodiments of the present invention have been described, the present invention is not limited to these.

Example

The present invention is described in more detail below by giving specific examples, but the present invention is not limited to the following examples. It should be noted that in the following description, especially the treatment without showing the temperature condition and humidity condition, it is carried out at room temperature (25°C) and relative humidity of 50%. In addition, for various measurement conditions, especially when the temperature condition and humidity condition are not shown, the values are at room temperature (25°C) and relative humidity of 50%.

[1]Manufacturing of conductive paste

(Preparation)

First, as metal powder, flaky copper powder having an average particle size D ₅₀ of 2.7 μm and a BET specific surface area of 0.65 m ² /g was prepared. The copper powder was a single metal (pure copper) powder containing substantially no metal element other than copper and substantially no sulfur.

In addition, three basic compositions were prepared as glass compositions. Glass compositions A, B and C were obtained by mixing glass raw materials using the oxide compositions shown in Table 1 as basic compositions in terms of oxides, melting them at 1200° C. in a platinum crucible, air cooling or rapid cooling, and then pulverizing them to an average particle size D ₅₀ of 2.1 μm.

[Table 1]

SiO _{2 B2O3 ​} BaO CaO Al ₂ O _{3 TiO2} ZnO _{K2O MnO2} total Glass composition A 7.6 20.4 59.8 4.6 6.7 0.9 - - - 100.0 Glass composition B 4.5 17.5 48.0 4.0 4.0 - 22.0 - - 100.0 Glass composition C 10.9 27.1 - - 6.1 - 49.0 2.1 4.8 100.0

[quality%]

It should be noted that when sulfur is further added to the glass composition, barium sulfate (BaSO ₄ ) is added as a sulfur source as a component added in addition to the glass raw materials described in Table 1 (in other words, a component further added with the total of the glass raw materials described in Table 1 being 100 mass %) to glass composition A and glass composition B. In this case, since the Ba component increases as a glass composition, the amount of Ba raw material used relative to the basic composition can be adjusted by this amount, and only the sulfur content is changed without changing the basic composition of glass composition A and glass composition B. Furthermore, when sulfur is added to glass composition C, potassium sulfate (K ₂ SO ₄ ) is used as a sulfur source, and the amount of K raw material used is adjusted, and the sulfur content is changed in the same manner except that.

As an organic binder, a mixed resin (acrylic resin) was prepared by mixing VL-7501 (manufactured by MITSUBISHI Chemical Co., Ltd.), Dianald MB-2677 (manufactured by MITSUBISHI Chemical Co., Ltd.), and Dianald BR-105 (manufactured by MITSUBISHI Chemical Co., Ltd.) at a mass ratio of 1:5:1.

As an organic solvent, a mixed solvent was prepared in which terpineol (EK terpineol manufactured by Ogawa Fragrances Co., Ltd.) and glycol ether (DOWANOL DPnP glycol ether manufactured by DOW CHEMICAL Japan Co., Ltd.) were mixed at a mass ratio of 8:2.

Furthermore, BaSO ₄ powder having an average particle size (D ₅₀ ) of 0.5 μm was prepared as a sulfur-containing inorganic additive, and mercaptoethanol, dodecyl mercaptan, and dimethyl sulfoxide were prepared as organic additives.

(Example 1)

A conductive paste was prepared by mixing metal powder, glass composition A to which a sulfur component was added, an organic binder, and an organic solvent at a mass ratio of 65:9:5:21, and kneading the mixture by a roll mill. In this conductive paste, the glass composition was contained as glass powder.

In addition, when the sulfur content was confirmed by a carbon-sulfur analyzer EMIA-320V (manufactured by HORIBA Corporation), the sulfur content in Example 1 was 198 ppm relative to the metal powder.

(Examples 2 to 7)

A conductive paste was produced in the same manner as in Example 1 except that the amount of sulfur added to the glass composition A was changed so that the content of sulfur relative to the metal powder became the value shown in Table 2.

(Example 8)

A conductive paste was produced in the same manner as in Example 1 except that no sulfur component was added to the glass composition A and BaSO ₄ powder was added as an inorganic additive.

The addition of _BaSO4 powder resulted in a sulfur content of 115 ppm relative to the metal powder.

(Examples 9 to 11)

A conductive paste was produced in the same manner as in Example 8 except that the amount of BaSO ₄ powder added was changed so that the content of sulfur relative to the metal powder became the value shown in Table 2.

(Example 12)

A conductive paste was produced in the same manner as in Example 8 except that mercaptoethanol was added instead of BaSO ₄ powder.

The addition of mercaptoethanol resulted in a sulfur content of 115 ppm relative to the metal powder.

(Examples 13 to 15)

A conductive paste was produced in the same manner as in Example 12 except that the amount of mercaptoethanol added was changed so that the content of sulfur relative to the metal powder became the value shown in Table 2.

(Example 16)

A conductive paste was produced in the same manner as in Example 12 except that dodecyl mercaptan was used instead of mercaptoethanol.

(Examples 17 to 19)

A conductive paste was produced in the same manner as in Example 16 except that the amount of dodecyl mercaptan added was changed so that the content of sulfur relative to the metal powder became the value shown in Table 2.

(Comparative Example 1)

A conductive paste was produced in the same manner as in Example 1 except that no sulfur component was added to the glass composition A. In Comparative Example 1, no sulfur-containing inorganic additive or organic additive was added.

(Comparative Example 2)

A conductive paste was produced in the same manner as in Example 1 except that the amount of sulfur added to the glass composition A was changed so that the content of sulfur in the metal powder was 381 ppm.

(Comparative Example 3)

A conductive paste was produced in the same manner as in Example 12 except that the amount of mercaptoethanol added was changed so that the sulfur content relative to the metal powder was 9 ppm.

(Comparative Examples 4 to 5)

A conductive paste was produced in the same manner as in Example 12 except that dimethyl sulfoxide was used instead of mercaptoethanol and the amount of dimethyl sulfoxide added was adjusted so that the sulfur content relative to the metal powder became the value shown in Table 2.

(Comparative Example 6)

A conductive paste was produced in the same manner as in Example 1 except that the amount of sulfur added to the glass composition A was changed so that the content of sulfur in the metal powder was 653 ppm.

[2] Evaluation

[2-1] Firing at 750℃

First, the conductive paste of each embodiment and each comparative example is applied and printed on the end face of a ceramic chip component having a size of 3.2×2.5 mm so that the film thickness after drying is 165 μm. After drying at 150°C for 10 minutes, the product is fired in a temperature-controlled furnace for 70 minutes so that the peak temperature is 750°C, thereby obtaining a fired body.

The sintered body was then subjected to EDX analysis using Quantax75 (manufactured by Bruker) at an accelerating voltage of 5 kV, a measuring time of 100 seconds, and a magnification of 200 times to measure the amount of glass floating (amount of Si) in the center of the sintered film and evaluate the over-sintering properties based on the following criteria.

A: The glass floating amount is less than 15%.

B: The amount of glass floating is 15% or more and less than 20%.

C: The amount of glass floating is 20% or more.

Next, the fired body was ground, and a cross-sectional SEM image of the fired film approximately in the center was taken using TM-4000 (manufactured by HITACHI HIGH-TECH CO., LTD.), and the area of voids (voids) in the fired film was calculated. The density of the fired film was evaluated based on the following criteria.

A: The density is 99% or more (the void ratio is 1% or less).

B: The density is 98% or more and less than 99% (the void ratio is more than 1% and less than 2%).

C: The density is less than 98% (the void ratio exceeds 2%).

[2-2] Firing at 780℃

Sintered bodies were prepared in the same manner as in Examples 1 to 19 and Comparative Examples 1 to 6 except that the peak temperature during sintering was 780° C., and the oversintering property and the density were evaluated.

These results are summarized in Table 2.

[Table 2]

[3]Manufacturing of conductive paste

(Examples 20 to 24, Comparative Examples 7 to 8)

A conductive paste was produced in the same manner as in Example 1 except that a glass composition B to which BaSO ₄ was added so that the sulfur content relative to the metal powder was the value shown in Table 3 was used as the glass composition, and the metal powder, the glass composition B, the organic binder, and the organic solvent were mixed in a mass ratio of 66:10:6:18.

(Examples 25 to 29, Comparative Examples 9 to 10)

A conductive paste was produced in the same manner as in Example 1 except that glass composition C to which K ₂ SO ₄ was added so that the sulfur content relative to the metal powder was the value shown in Table 3 was used as the glass composition, and the metal powder, glass composition C, organic binder, and organic solvent were mixed at a mass ratio of 69:7:5:19.

[4] Evaluation

[4-1] Firing

Except for using the conductive pastes of Examples 20 to 29 and Comparative Examples 7 to 10, the fired bodies were prepared by firing at peak temperatures of 750° C. and 780° C. in the same manner as described above, and the oversintering property and the densification property were evaluated.

Furthermore, fired bodies were prepared according to Examples 1 to 7, Examples 20 to 29, Comparative Examples 2, and Comparative Examples 6 to 10 in the same manner as described above except that the peak temperature during firing was 830° C., and the oversintering property and density were evaluated.

These results are summarized in Table 3.

It should be noted that part of the evaluation results concerning Examples 1 to 7, Comparative Example 2, and Comparative Example 6 in Table 3 are repeated in Table 2 in order to compare the effects of adding sulfur to the glass composition.

[Table 3]

As can be seen from Tables 2 and 3, the conductive paste of the present invention is less likely to suffer from adverse effects caused by over-sintering, and effectively prevents glass floating in the fired film and the occurrence of voids in the fired film, thereby achieving a sufficiently wide firing window. In contrast, in the comparative example, satisfactory results were not obtained.

In addition, a conductive paste was produced in the same manner as in the above-described Examples and Comparative Examples except that a copper alloy powder containing 2 mass % of silver was used as the metal powder, and the average particle size of the metal powder was in the range of 0.2 μm to 5.0 μm, and the BET specific surface area of the metal powder was in the range of 0.30 m ² /g to 1.00 m ² /g, and the average particle size of the glass powder as the glass composition was in the range of 0.1 μm to 4.5 μm, and the BET specific surface area of the glass composition was in the range of 0.90 m ² /g to 5.00 m ^{2 /g.} /g or less, the content of the metal powder in the conductive paste is in the range of 50.0 mass % to 80.0 mass %, the content of the glass composition in the conductive paste is in the range of 4.0 mass % to 20.0 mass %, the content of the organic vehicle in the conductive paste is in the range of 10.0 mass % to 40.0 mass %, the content of the organic solvent in the conductive paste is in the range of 7.0 mass % to 30.0 mass %, and the content of the organic binder in the conductive paste is in the range of 1.0 mass % to 15.0 mass %, and other than making various changes, conductive pastes were manufactured in the same manner as in the Examples and Comparative Examples, and the same evaluations as above were performed, and the same results as above were obtained.

Industrial Applicability

The conductive paste of the present invention is a conductive paste containing a metal powder containing copper, a glass composition and an organic vehicle, wherein the glass composition contains sulfur (S), and the content of the sulfur (S) is 10 ppm or more and 370 ppm or less relative to the metal powder. In addition, the conductive paste of the present invention is a conductive paste containing a metal powder containing copper, a glass composition, an organic vehicle and an inorganic additive, wherein the inorganic additive contains sulfur (S), and the content of the sulfur (S) is 10 ppm or more and 370 ppm or less relative to the metal powder. In addition, the conductive paste of the present invention is a conductive paste containing a metal powder containing copper, a glass composition, an organic vehicle and an organic additive, wherein the organic additive has a thiol group, and the content of sulfur (S) in the organic additive is 10 ppm or more and 370 ppm or less relative to the metal powder. Therefore, it can be provided: it is suitable to control the firing behavior of the metal powder monomer containing copper, and as a result, the firing window is wide, and it is not easy to cause problems such as voids and glass floating after firing. Therefore, the conductive paste of the present invention has industrial applicability.

Claims (3)

1. A conductive paste for forming external electrodes of a laminated ceramic electronic component, which is a conductive paste for forming external electrodes of a laminated ceramic electronic component containing a metal powder containing copper, a glass composition, and an organic vehicle, wherein,

the glass composition contains sulfur (S) in an amount of 10 to 370ppm relative to the metal powder,

the metal powder contains less than 10ppm of sulfur (S),

the metal powder is copper powder,

the glass composition contains SiO in a range of 2.0 mass% to 12.0 mass% ₂ B is contained in a range of 15.0 mass% to 30.0 mass% ₂ O ₃ Al is contained in a range of 2.0 mass% to 12.0 mass% ₂ O ₃ ，

The glass composition is substantially free of Pb, cd, and Bi.

2. The conductive paste for forming external electrodes of a laminated ceramic electronic component according to claim 1, wherein,

the content of sulfur in the glass composition is 12ppm to 200ppm relative to the metal powder.

3. The conductive paste for forming external electrodes of a laminated ceramic electronic component according to claim 1, wherein,

the content of sulfur in the glass composition is 15ppm to 100ppm relative to the metal powder.