JP2016110939A - Conductive paste, and wiring board and solid electrolytic capacitor prepared with the conductive paste - Google Patents

Abstract

An object of the present invention is to provide a conductive paste containing a silver-coated copper powder and capable of forming a conductor that is hard to be disconnected or cut off, a wiring board using the conductive paste, and a solid electrolytic capacitor. A conductive paste includes silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent. The wiring board has a wiring pattern formed by the conductive paste having the above configuration. The solid electrolytic capacitor has an electrode formed of the conductive paste having the above configuration. [Selection diagram] Fig. 1

Description

  The present invention relates to a conductive paste used for forming a wiring pattern or forming an electrode of a solid electrolytic capacitor, or both, a wiring substrate using the conductive paste, and a solid electrolytic capacitor.

  As a conductive material used as a conductive paste used for forming a wiring pattern, silver powder and copper powder have been widely used conventionally. However, as described in Patent Document 1, a copper powder having a surface coated with silver instead of silver powder, A technique using so-called silver-coated copper powder is known.

  Such a conductive paste can reduce the silver content in the conductive paste compared to a conductive paste containing silver powder, and has a cost advantage, and copper powder is used as a conductive material. There is a merit that the decrease in conductivity due to the oxidation of copper, which is a problem with the conductive paste, hardly occurs.

  On the other hand, with the miniaturization and high density of electronic devices, there is a high need for reducing the thickness of wiring patterns, and the need for thinning has become apparent. Similarly, there is an increasing need for thinning the electrodes of solid electrolytic capacitors.

JP-A-5-347106

  However, when a wiring pattern is formed using a conductive paste containing silver-coated copper powder, which is cheaper than silver powder, there is a problem in that disconnection is likely to occur when the thickness is reduced as described above. Moreover, when forming the electrode of a solid electrolytic capacitor using the electrically conductive paste containing silver coat copper powder, there exists a problem that a film | membrane cut | disconnection tends to produce in an edge part, if an electrode film thickness is made thin.

  Then, it aims at providing the conductive paste which can form the conductor which contains silver coat copper powder, and is hard to be disconnected or film | membrane cut | disconnected, the wiring board using the conductive paste, and a solid electrolytic capacitor.

  The conductive paste according to the present invention includes silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent.

  According to the said conductive paste, compared with the conductive paste which contains only silver powder and silver coat copper powder as conductive particles, the conductor which is hard to produce a disconnection and a film breakage can be formed.

It is the graph which plotted the characteristic of each sample shown by Table 3. FIG.

[Description of Embodiment of Present Invention]
First, embodiments of the present invention will be listed and described.
(1) The conductive paste according to the embodiment includes silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent.

  According to the conductive paste having the above configuration, a stable conductor (wiring pattern or electrode of a solid electrolytic capacitor) can be formed depending on the specific surface area of the carbon powder, the surface structure of the carbon powder, and the like. For example, in the formation of a wiring pattern, even if the film thickness is reduced, the pattern becomes less blurred at the time of formation, so that disconnection of the wiring pattern is suppressed. Further, in the formation of the electrode of the solid electrolytic capacitor, even if the film thickness is reduced, it is difficult for the edge of the capacitor element to be blurred, so that the film is not easily broken at the edge.

(2) In the said electrically conductive paste, it is preferable that the content rate of the said carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 1 mass% or more.
When the carbon powder content is less than 1% by mass, the thixotropy is poorly improved. According to the above configuration, since thixotropy is sufficiently improved, disconnection of the wiring pattern is suppressed.

(3) In the said electrically conductive paste, it is preferable that the content rate of the said carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 2 mass% or less.
When the content of the carbon powder is larger than 2% by mass, the specific resistance of the wiring pattern formed by the conductive paste is greatly increased. The reason why the specific resistance is greatly increased is not clear, but when the ratio of carbon powder is high, the carbon powder aggregates and coarsens, and the carbon powder that aggregates the formation of the conductive path between the silver powder and the silver-coated copper powder It is thought to interfere. In this regard, according to the conductive paste having the above-described configuration, the carbon powder content is 2% by mass or less, and therefore, compared with the specific resistance of the wiring pattern formed by the conductive paste having a carbon powder content greater than 2% by mass. Thus, a wiring pattern having a small specific resistance can be formed.

(4) In the said electrically conductive paste, it is preferable that the compounding ratio of the said silver powder and the said silver coat copper powder is 70: 30-20: 80 by mass ratio.
When the compounding ratio of the silver-coated copper powder is reduced, silver ion migration is likely to occur. On the other hand, when the compounding ratio of the silver-coated copper powder is increased, the specific resistance is increased. In this regard, according to the conductive paste having the above configuration, the occurrence of ion migration can be suppressed, and the specific resistance of the wiring pattern can be set to a value within a predetermined range.

  (5) In the conductive paste, the average particle diameter of the silver powder is preferably 0.01 μm or more and 15 μm or less, and the average particle diameter of the silver-coated copper powder is preferably 5 μm or more and 15 μm or less.

  When the average particle size of the silver powder is larger than 15 μm, the leveling property is lowered. When the average particle diameter of the silver powder is smaller than 0.01 μm, it is difficult to produce the silver powder. When the average particle size of the silver-coated copper powder is larger than 15 μm, the leveling property is lowered and the wiring pattern is likely to be disconnected, so that it is difficult to form a narrow wiring pattern. When the average particle size of the silver-coated copper powder is smaller than 5 μm, copper is exposed and copper oxide is easily formed, so that the specific resistance of the wiring pattern formed by the conductive paste may increase with time. is there.

  In this respect, the conductive paste having the above configuration has leveling properties because the average particle size of the silver powder is 0.01 μm or more and 15 μm or less, and the average particle size of the silver-coated copper powder is 5 μm or more and 15 μm or less. Is easy, the disconnection of the wiring pattern at the time of formation is suppressed, and the change over time in the specific resistance of the wiring pattern formed by this conductive paste is small.

  (6) In the conductive paste, it is preferable that the silver powder further includes a spherical silver powder having an average particle diameter of 10 nm to 1000 nm. According to this configuration, the spherical silver powder is filled between the powders and the silver density is not increased, so that the specific resistance of the wiring pattern is lowered.

  (7) In the said electrically conductive paste, the content rate of the said carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 1 mass% or more and 2 mass% or less, and the said silver powder and the said silver coat copper powder The compounding ratio is preferably 70:30 to 20:80 in terms of mass ratio, and the silver content relative to the conductive paste is preferably 20% by mass or less.

  According to this structure, since silver content is 20 mass% or less, it contributes to resource saving. Further, according to this conductive paste, an electrode of a solid electrolytic capacitor that suppresses disconnection during formation and forms a wiring pattern that satisfies the required characteristics, or suppresses edge film breakage during formation and satisfies the required characteristics. Can be formed.

  (8) In the conductive paste, the thixo index is preferably 6 or more. According to this configuration, the shape of the wiring pattern immediately after printing is more stable. For this reason, printing workability is improved.

(9) In the conductive paste, the carbon powder is preferably at least one selected from ketjen black and acetylene black.
According to this structure, compared with the case where other carbon black is contained, the conductivity of the wiring pattern formed by the conductive paste can be increased.

(10) The wiring board has a wiring pattern formed of the conductive paste.
Since the wiring pattern formed by the conductive paste has no blurring or blurring or the frequency thereof is low, a wiring board having such a wiring pattern has high reliability (for example, heat shock resistance). Have.

(11) The solid electrolytic capacitor has an electrode formed of the conductive paste.
Since the electrode formed of the conductive paste has a film thickness at the edge (the film thickness at the edge is larger than that of the conventional conductive paste), a solid electrolytic capacitor having such an electrode. Has high reliability (for example, heat shock resistance).

[Details of the embodiment of the present invention]
Specific examples of the conductive paste according to the embodiment will be described below with reference to the drawings. It should be noted that the present invention is not limited to these exemplifications, is shown by the scope of claims, and includes meanings equivalent to the scope of claims and all modifications within the scope of claims. Intended.

The average particle diameter shown below is defined as the median diameter (D50) calculated based on the particle diameter measured by the particle size distribution measuring apparatus applying the laser Doppler method.
A BET specific surface area shows the value measured with the automatic specific surface area measuring apparatus using nitrogen as adsorption gas. The thixotropy indicates a property represented by a thixo index. The thixo index is a viscosity at a rotation speed of 1 rpm (V1 rpm) measured at 25 ° C. using an E-type rotational viscometer (for example, TVE viscometer manufactured by Toki Sangyo Co., Ltd.) and a viscosity at a rotation speed of 10 rpm (V10 rpm). )) (V1 rpm / V10 rpm). The above-mentioned “improvement of thixotropy” means that the thixotropy index is higher than the conventional one.

The conductive paste according to the embodiment will be described.
The conductive paste includes silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent.

As the silver powder, at least one of scale-like silver powder, spherical silver powder, and dendritic silver powder is used.
These silver powders are appropriately selected depending on the wiring width formed by the conductive paste. When a wiring pattern having a line width of about 30 μm is formed, spherical silver powder, scaly silver powder, or a mixed powder of spherical silver powder and scaly silver powder is preferably used. Moreover, it is preferable that the average particle diameter of silver powder is 0.01 micrometer or more and 15 micrometers. As the spherical silver powder, those having an average particle diameter of 15 μm or less are preferably used. This is because when the average particle size is larger than 15 μm, the leveling property is lowered.

  Scaly silver powder is used from the viewpoint of reducing contact resistance. For example, as a scaly silver powder, the thickness is 1/2 or less of the maximum value of the width (length perpendicular to the thickness direction), particularly 1/50 to 1/5, and the average particle size is 0.00. The thing of 5 micrometers or more and 15 micrometers or less is used suitably. This is because when the average particle size is smaller than 0.5 μm, the effect of reducing the contact resistance by the scaly silver powder cannot be obtained. Further, when the average particle diameter exceeds 15 μm, the contact resistance increases, clogging of the screen plate, etc. occurs, and printing abnormality such as blurring or wiring breakage occurs. As the scaly silver powder, those produced by various conventionally known methods such as a liquid phase reduction method and a vapor phase growth method can be used.

The BET specific surface area of the scaly silver powder is preferably 0.5 m ² / g or more and 3.0 m ² / g or less. This is because when the BET specific surface area of the flaky silver powder is larger than 3.0 m ² / g, the viscosity of the conductive paste becomes too high, and the BET specific surface area of the flaky silver powder is more than 0.5 m ² / g. This is because when it is small, the scaly silver powder is large and is not suitable for forming a narrow wiring pattern.

Furthermore, from the viewpoint of improving conductivity, it is preferable to add spherical silver powder having an average particle size of nano-order (hereinafter referred to as “nanosilver”).
For example, as the silver, silver particles having a spherical or elliptical shape in which the ratio of the minor axis to the major axis is 1/1 or more and 1/2 or less and the average particle diameter is 10 nm or more and 1000 nm or less are used. This is because the production becomes difficult when the average particle size is smaller than 10 nm, and when the average particle size exceeds 1000 nm, the effect of increasing the packing density by the spherical silver powder may not be obtained. In addition, Preferably, the average particle diameter of nano silver is 50 nm or less, More preferably, it is 20 nm or less. Thereby, printing abnormalities such as fading, cutting, and bleeding during printing can be reduced, and the packing density of the silver powder is increased, and the conductivity of the wiring pattern is further improved.

  In addition, when nano silver is included in the conductive paste, the content of nano silver is 0.1% by mass or more and 10% by mass or less in terms of mass ratio with respect to the entire metal powder (silver powder, silver-coated copper powder). preferable. When the amount of nanosilver is less than 0.1% by mass, the effect of the addition hardly occurs. When the content of nanosilver is greater than 10% by mass, nanosilver is added to 10% by mass or more. It is because the effect by this is not acquired.

When scaly silver powder and nano silver are mixed and used, the blending ratio of both is set, for example, in the range of 99: 1 to 80:20 by mass ratio.
Thereby, the effect of electrical conductivity improvement by nano silver and the reduction effect of contact resistance by scaly silver powder can be exhibited. The contact resistance reduction effect refers to an effect of reducing the contact resistance between another component brought into contact with the wiring pattern and the wiring pattern (for example, land) by improving the surface roughness of the wiring pattern.

  The silver-coated copper powder includes scaly, spherical, and dendritic ones, and any of them can be used. For example, spherical silver-coated copper powder is preferably used from the viewpoints of filling properties and conductivity. There is no limitation in particular in the manufacturing method of silver coat copper powder. For example, any silver-coated copper powder such as silver-coated copper powder by silver plating or silver-coated copper powder by a substitution reaction of copper and silver can be used.

The average particle size of the silver-coated copper powder is preferably 5 μm or more and 15 μm or less.
If the average particle diameter of the silver-coated copper powder is larger than 15 μm, the leveling property of the conductive paste is lowered, or the wiring pattern is likely to be disconnected, and it becomes difficult to form a narrow wiring pattern. It is. Moreover, if the average particle diameter of the silver-coated copper powder is smaller than 5 μm, the copper of the core is exposed and the copper is oxidized from this portion, and the specific resistance of the wiring pattern may increase with time.

The BET specific surface area of the silver-coated copper powder is preferably 0.5 m ² / g or more and 3.0 m ² / g or less. This is because when the BET specific surface area of the silver-coated copper powder is larger than 3.0 m ² / g, the viscosity of the conductive paste becomes too high, and the BET specific surface area of the silver-coated copper powder is 0.5 m ² / g. This is because the silver-coated copper powder is too large to be suitable for forming a narrow wiring pattern.

  The silver content in the silver-coated copper powder is preferably 5% by mass or more and 30% by mass or less. This is because when the silver content is less than 5% by mass, the copper of the core may be exposed, and the specific resistance of the wiring pattern may increase over time. Moreover, it is because possibility that ion migration will arise when the content rate of silver is larger than 30 mass%.

  Moreover, it is preferable that the compounding ratio of silver powder and silver coat copper powder is 70: 30-20: 80. This is because if the compounding ratio of the silver-coated copper powder is too small, silver ion migration tends to occur. Moreover, it is because the specific resistance of a wiring pattern will become large when the compounding ratio of silver coat copper powder is made too high. In addition, it is preferable that the compounding ratio of silver powder and silver coat copper powder is 50: 50-30: 70 from a viewpoint of resource saving.

  As the carbon powder, acetylene black, graphite powder, ketjen black and the like can be used. From the viewpoint of improving the conductivity of the wiring pattern, it is particularly preferable to use ketjen black.

  When ketjen black is used as the carbon powder, the average particle size of the primary particles is preferably 50 nm or less, and more preferably 10 nm or more and 40 nm or less.

The BET specific surface area of ketjen black is preferably 50 m ² / g or more for the purpose of improving thixotropy.
Furthermore, the BET specific surface area of ketjen black is preferably 1300 m ² / g or less. If the BET specific surface area exceeds this upper limit, the average particle diameter of the ketjen black becomes too small and the ketjen black is likely to aggregate, thereby forming a wiring formed by the conductive paste containing the ketjen black. This is because the specific resistance of the pattern may increase.

As the carbon powder, a mixed powder of ketjen black and other carbon powder can be used.
For example, a mixed powder of ketjen black and graphite powder can be used.

  It is preferable that the content rate of carbon powder is 1 mass% or more and 2 mass% or less by mass ratio with respect to the whole metal powder (silver powder, silver coat copper powder). This is because if the content of the carbon powder exceeds 2% by mass, the specific resistance of the wiring pattern formed using the conductive paste increases. This is because if the carbon powder content is less than 1% by mass, the thixo index decreases and the printability decreases. In addition, More preferably, the content rate of the said carbon powder is 1.5 to 1.8 mass%.

  The content rate of electroconductive particle (silver powder, silver coat copper, and carbon powder) is a mass ratio with respect to an electroconductive paste, and it is preferable that they are 30 mass% or more and 80 mass% or less. This is because if the content of the conductive particles exceeds 80% by mass, fading of the wiring pattern is likely to occur during printing formation. Further, if the content of the conductive particles is less than 30% by mass, the wiring pattern is likely to bleed during printing formation. More preferably, the content rate of the said electroconductive particle is 50 to 75 mass%.

An organic insulating resin is used as the binder resin.
The organic insulating resin is preferably a heat resistant resin considering that the resin remains in the wiring pattern after the heat treatment. Examples of the heat resistant resin include fluorine resin, polyimide resin, polyamideimide resin, polyesterimide resin, polyester resin, polyethersulfone resin, polyetherketone resin, polyetheretherketone resin, polybenzimidazole resin, and polybenzoxazole resin. , Polyphenylene sulfide resin, bismaleimide resin, epoxy resin, phenol resin, phenoxy resin and the like. These heat resistant resins can be used alone or in combination of two or more.

  In addition, a binder resin suitable for the purpose of use, the environment of use, the curing temperature, etc., while maintaining good printability, is appropriately selected from these resins. For example, an epoxy resin, a polyester resin, a polyimide resin, a polyamideimide resin, a polyesterimide resin, a phenol resin, or a mixture thereof is suitably used as a binder resin for forming a wiring pattern.

  Among these, an epoxy resin is suitably used for forming the wiring pattern. For example, polyphenol type epoxy resin (bisphenol A type, F type, AD type, etc.), phenol and cresol type epoxy resin (novolac type, etc.), polyol glycidyl ether type epoxy resin, polyacid glycidyl ester type epoxy resin, polyamine type Any of various types of thermosetting epoxy resins such as glycidylamine type epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins can be used.

In addition, the conductive paste includes a curing agent for curing the binder resin, other additives, and the like.
Examples of the curing agent for the epoxy resin include conventionally known various curing agents such as amine curing agents, polyaminoamide curing agents, acid anhydride curing agents, basic active hydrogenation compounds, tertiary amines, and imidazoles. A curing agent that is suitable for the epoxy resin to be combined is appropriately selected. Moreover, as a curing agent for polyester, for example, an isocyanate compound such as a hexamethylene diisocyanate curing agent, a polyisocyanate curing agent, and the like, which are suitable for a polyester to be combined, among various conventionally known curing agents, are appropriately used. Selected.

  However, the conductive paste is preferably cured in a temperature range of 200 ° C. or lower in consideration of using a combination of a base material or a chip made of a versatile material having a low heat resistant temperature. It is preferable that a curing agent capable of causing the binder resin to undergo a curing reaction at the following predetermined temperature is appropriately selected. In addition, a hardening | curing agent is mix | blended for the theoretical equivalent of binder resin.

As the solvent, a solvent in which the binder resin is soluble, does not corrode the substrate on which the paste is applied, and has low volatility from the viewpoint of improving printing workability.
For example, organic solvents such as butyl carbitol, butyl carbitol acetate, terpineol, diethyl phthalate, and butyl cellosolve are preferably used as the solvent. In the formation of a wiring pattern by screen printing, a material having a boiling point of 200 ° C. or higher and less volatile such as butyl carbitol acetate and terpineol is preferably used. By using such a solvent having a high boiling point, for example, when forming a fine pattern by screen printing, the drying resistance of the conductive paste is improved and clogging of the screen plate is less likely to occur. Even when performing, it is possible to improve the formation accuracy of the wiring pattern.

Next, the flow characteristics of the conductive paste will be described.
The viscosity of the conductive paste is 5 Pa · s or more and 1200 Pa · s or less at a temperature of 25 ° C. and a rotation speed of 1 rpm from the viewpoint of dimensional accuracy of the wiring pattern and printing workability. More preferably, the viscosity is 200 Pa · s or more and 900 or less at a temperature of 25 ° C. and a rotation speed of 1 rpm.

The thixo index of the conductive paste is preferably 6 or more. More preferably, the thixo index is 4 or more and 11 or less, and further preferably 6 or more and 9 or less.
This is because if the thixo index of the conductive paste is too high, fading of the wiring pattern is likely to occur at the time of print formation, and if the thixo index of the conductive paste is too low, bleeding occurs at the time of print formation. In addition, the suitable range of the thixo index of the electrically conductive paste which concerns on this embodiment is high compared with the electrically conductive paste which contains only silver powder as electroconductive particle.

The above conductive paste can be used for forming a wiring pattern or for forming an electrode by a dipping method in a solid electrolytic capacitor (for example, a tantalum capacitor).
As described above, when the conductive paste having the above-described configuration is used for forming a wiring pattern, the wiring pattern is prevented from being blurred, so that the wiring pattern is prevented from being disconnected during the formation. Moreover, since the wiring pattern formed of the conductive paste having the above configuration has high dimensional accuracy, the reliability of the wiring board is increased. For example, according to the conductive paste having the above configuration, the frequency of occurrence of disconnection is suppressed in the formation of a wiring pattern having a line width of 30 μm.

  When the conductive paste having the above structure is used for forming the electrode of the tantalum capacitor, the film thickness at the edge portion of the chip is maintained to some extent, so that the film at the edge portion of the chip (hereinafter referred to as “edge”). "Slice breakage") is suppressed. For example, according to the conductive paste having the above configuration, the occurrence frequency of edge film breakage is suppressed in the formation of electrodes having a film thickness of 10 μm or more and 30 μm or less.

An example of a conductive paste applicable to both the formation of a wiring pattern and the formation of a solid electrolytic capacitor will be given.
For example, the content of carbon powder with respect to the entire metal powder (silver powder, silver-coated copper powder) is set to 1% by mass or more and 2% by mass or less, and the mixing ratio of silver powder and silver-coated copper powder is 70:30 in mass ratio. It is set to the range of -20: 80, and the silver content with respect to the conductive paste is 20% by mass or less. The thixo index of the conductive paste is preferably 6 or more and 9 or less, and the viscosity at 25 ° C. and 1 rpm is preferably 10 Pa · s. An epoxy resin or the like is suitably used as the binder resin, and a phenol resin or the like is suitably used as the curing agent.

  Such a conductive paste is advantageous in its production. Conventionally, since the composition of the conductive paste is different for each application, it has been necessary to produce it individually. However, since the conductive paste having the above configuration has at least two applications, it is possible to increase the production amount per time. it can. For this reason, there is an advantage that productivity of the conductive paste is improved.

Example 1 shows an example in which a wiring pattern is formed on a substrate using a conductive paste.
Sample S11 and sample S12 shown in Table 1 are reference examples, and sample S13 is an example. The specific resistance was measured by the four probe method. The disconnection was determined by whether or not the specific resistance was larger than a reference value (10 times the specific resistance at a line width of 3 mm).

[Sample S11 (reference example)]
The conductive paste of sample S11 includes scale-like silver powder having an average particle diameter of 12 μm and nanosilver having an average particle diameter of 28 nm.
-Binder resin is an epoxy resin.
-A hardening | curing agent is a phenol resin.
The solvent is butyl carbitol acetate.
-The compounding ratio of binder resin and a hardening | curing agent is 1.0: 2.3 by mass ratio.
-The blending amount of the binder resin, the curing agent, and the solvent is adjusted so that the content of the conductive particles is within a predetermined range, and the viscosity of the conductive paste is within a predetermined range. .
-The content rate of the electroconductive particle (scale-like silver powder and nano silver) in an electroconductive paste is 70 mass%.
-The compounding ratio of scaly silver powder and nano silver is 90: 1 by mass ratio.

The conductive particles of sample S11 are composed of silver particles and nanosilver, and do not contain silver-coated copper powder.
As shown in Table 1, the conductive paste of sample S11 has a low specific resistance and a disconnection rate of the wiring pattern of 0%. For this reason, this conductive paste can be suitably used in forming a narrow wiring pattern. However, since the silver content is high, this conductive paste does not satisfy the demand for resource saving.

[Sample S12 (reference example)]
-The electroconductive paste of sample S12 contains the scale-like silver powder whose average particle diameter is 12 micrometers, and the silver coat copper powder whose average particle diameter is 12 micrometers.
-The content rate of the electroconductive particle (scaly silver powder and silver coat copper powder) in an electroconductive paste is 60 mass%.
-The compounding ratio of scaly silver powder and silver coat copper powder is 25:75 by mass ratio.
-About binder resin, a hardening | curing agent, and a solvent, it is the same as that of sample S11.

The feature of this conductive paste is that it contains silver-coated copper powder in addition to silver powder and has a low silver content.
As shown in Table 1, the conductive paste of sample S12 has a low silver content and a specific resistance of 300 μΩ · cm or less, and the occurrence of ion migration is suppressed. The thixo index is equal to the conductive paste of sample S11. However, the disconnection rate of the wiring pattern is significantly increased. This result shows that when silver-coated copper powder is contained in the conductive paste, a reliable wiring pattern can be formed simply by setting the thixo index within the same range as the conductive paste containing silver powder and nanosilver. Indicates that you cannot do it.

[Sample S13 (Example)]
The conductive paste of sample S13 is made of flaky silver powder having an average particle diameter of 12 μm, silver-coated copper powder having an average particle diameter of 12 μm, and carbon powder (Ketjen black) having an average primary particle radius of 34 nm. Including.
-The content rate of the electroconductive particle (scale-like silver powder, silver coat copper powder, and carbon powder) in an electroconductive paste is 45 mass%.
-The content rate of the carbon powder with respect to the whole metal powder (scaly silver powder, silver coat copper powder) is 2 mass%.
-The compounding ratio of scaly silver powder and silver coat copper powder is 25:75 by mass ratio.
-About binder resin, a hardening | curing agent, and a solvent, it is the same as that of sample S11.

The feature of this conductive paste is that it contains silver-coated copper powder and carbon in addition to silver powder, and has a low silver content relative to the conductive paste.
As shown in Table 1, the conductive paste of sample S13 has a low silver content, a specific resistance of 300 μΩ · cm or less, the occurrence of ion migration is suppressed, and the disconnection rate of the wiring pattern is 0%. . That is, the conductive paste of sample S13 contains silver-coated copper powder, but can be suitably used for forming a narrow wiring pattern. The thixo index is higher than that of the conductive pastes of sample S11 and sample S12. This is an effect of carbon powder.

Example 2 shows an example in which an electrode of a solid electrolytic capacitor is formed using a conductive paste.
Sample S21 and sample S22 shown in Table 2 are reference examples, and sample S23 is an example.

The “silver content” in Table 2 indicates the silver content in the conductive paste.
Samples S21, S22, and S23 shown in Table 2 have the same compositions as the samples S11, S12, and S13 shown in Table 1, respectively. The film thickness of the electrode of the tantalum capacitor formed by each sample is 20 μm. In addition, in each sample, the edge film is not cut during the formation of the electrode of the solid electrolytic capacitor. In Sample S22 (Sample S12), disconnection occurred in the formation of the wiring pattern, but no edge film breakage occurred in the formation of the electrode of the solid electrolytic capacitor.

  The silver content of the conductive paste of sample S21 is 50% by mass, the silver content of the conductive paste of sample S22 is 20% by mass, and the silver content of the conductive paste of sample S23 is 15% by mass. . Thus, the silver content rate of the electrically conductive paste of an Example (sample S23) is the lowest. This is due to the addition of silver-coated copper powder and carbon powder in addition to silver powder as conductive particles.

  The thixo index of the conductive paste of sample S23 is 8.7, which is higher than the other samples. Although not shown in Table 2, the viscosity of the conductive paste of sample S23 (viscosity at 1 rpm) is higher than that of other samples. For this reason, cutting of the edge film at the time of forming the electrode of the tantalum capacitor is suppressed.

From the results shown in Example 1 and Example 2, the following can be understood.
The conductive pastes of the examples (sample S13 and sample S23) can be suitably used for forming wiring patterns and electrodes for tantalum capacitors, and contribute to resource saving because of low silver content. To do.

Table 3 describes the characteristics of the conductive paste when the content of the carbon powder is changed in the conductive paste containing silver powder and silver-coated powder.
Sample S31 does not contain carbon powder, and sample S32-sample S34 contain carbon powder.
-The electrically conductive paste of sample S31 contains the flaky silver powder whose average particle diameter is 12 micrometers, and the silver coat copper powder whose average particle diameter is 12 micrometers.
-Binder resin is an epoxy resin.
-A hardening | curing agent is a phenol resin.
The solvent is butyl acetate cellosolve.
-The compounding ratio of binder resin and a hardening | curing agent is 1.0: 2.3 by mass ratio.
-The blending amount of the binder resin, the curing agent, and the solvent is adjusted so that the content of the conductive particles is within a predetermined range, and the viscosity of the conductive paste is within a predetermined range. .
-The content rate of the electroconductive particle (scaly silver powder and silver coat copper powder) in an electroconductive paste is 45 mass%.
-The compounding ratio of scaly silver powder and silver coat copper powder is 25:75 by mass ratio.

The conductive paste of samples S32 to S34 has the following configuration.
The conductive paste of sample S31 is a flaky silver powder having an average particle diameter of 12 μm, a silver-coated copper powder having an average particle diameter of 12 μm, and a carbon powder (Ketjen black) having an average particle diameter of 34 nm. including.
-The content rate of the carbon powder of the electrically conductive paste of sample S32-S34 is 1 mass%, 2 mass%, and 3 mass%, respectively.
-Content rate of the electroconductive particle (scaly silver powder, silver coat copper powder, and carbon black) in the electroconductive paste of sample S32-S34 is 45 mass%.
-The compounding ratio of scaly silver powder and silver coat copper powder is 25:75 by mass ratio.
-About binder resin, a hardening | curing agent, and a solvent, it is the same as sample S31.

  FIG. 1 is a graph showing the values in Table 3 in relation to the carbon powder content. The horizontal axis in FIG. 1 indicates the mass ratio of the carbon powder. The left vertical axis in FIG. 1 indicates the specific resistance of the formed wiring pattern. The right vertical axis in FIG. 1 indicates the thixo index of the conductive paste.

  As shown in FIG. 1, the sample S31 has a lower thixotropy than other conductive pastes. This is because the conductive paste does not contain carbon powder. For this reason, in the sample S31, the wiring pattern may be disconnected.

  Further, as shown in FIG. 1, the specific resistance of the wiring pattern formed by the samples S31 to S33 is substantially constant. 1 is an approximate line obtained from the specific resistance values of the samples S31 to S33. This approximate line is substantially horizontal (parallel to the horizontal axis). The specific resistance of the wiring pattern formed by the sample S34 is significantly larger than the specific resistances of the samples S31 to S33. The reason why the specific resistance is greatly increased when the carbon powder content is excessively high is not necessarily clear, but the carbon powder aggregated by the increase in density causes the formation of a conductive path between the silver powder and the silver-coated silver. It is thought to act to prevent.

  From this, it is preferable that the content rate of the carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 2 mass% or less. Moreover, it is preferable that the content rate of the carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 1 mass% or more from a viewpoint which makes a thixo index an appropriate value.

The effect of the conductive paste of this embodiment will be described.
(1) The conductive paste according to the embodiment includes silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent. Thereby, a stable conductor (wiring pattern or electrode) can be formed. For example, in the formation of a wiring pattern, even if the film thickness is reduced, the pattern becomes less blurred at the time of formation, so that disconnection of the wiring pattern is suppressed. Further, in forming electrodes of a solid electrolytic capacitor, even if the film thickness is reduced, blurring at the edge portion of the capacitor element is difficult to occur, so that film breakage is unlikely to occur. In addition, the low silver content contributes to resource saving.

  (2) In the said electrically conductive paste, it is preferable that the content rate of the carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 1 mass% or more. According to this configuration, the thixotropy of the conductive paste is sufficiently improved (because the thixo index becomes a value large enough to produce the effect), so that the disconnection of the wiring pattern is suppressed.

  (3) In the said electrically conductive paste, it is preferable that the content rate of the carbon powder with respect to the whole metal powder (silver powder, silver coat copper powder) is 2 mass% or less. According to this conductive paste, it is possible to form a wiring pattern having a specific resistance lower than that of the wiring pattern formed by the conductive paste having a carbon powder content greater than 2% by mass.

  (4) In the said electrically conductive paste, it is preferable that the compounding ratio of silver powder and silver coat copper powder is 70: 30-20: 80 by mass ratio. According to this configuration, the occurrence of ion migration is suppressed, and the specific resistance of the wiring pattern can be set to a value within a predetermined range.

(5) In the said electrically conductive paste, it is preferable that the average particle diameter of silver powder is 0.01 micrometer or more and 15 micrometers or less, and the average particle diameter of silver coat copper powder is 5 micrometers or more and 15 micrometers or less.
According to this configuration, the conductive paste has leveling properties, is easy to produce silver powder, suppresses disconnection of the wiring pattern during formation, and has a specific resistance of the wiring pattern formed by this conductive paste. The change with time is also small.

  (6) In the said electrically conductive paste, it is preferable to contain spherical silver powder whose average particle diameter is 10 to 1000 nm further as silver powder. According to this configuration, the specific resistance of the wiring pattern is reduced.

  (7) In the conductive paste, the content of carbon powder with respect to the entire metal powder (silver powder, silver-coated copper powder) is 1% by mass or more and 2% by mass or less, and the blending ratio of silver powder and silver-coated copper powder is The mass ratio is preferably 70:30 to 20:80, and the silver content relative to the conductive paste is preferably 20% by mass or less.

  According to this structure, since silver content is 20 mass% or less, it contributes to resource saving. In addition, according to this conductive paste, it is possible to form a wiring pattern that satisfies the required characteristics by suppressing disconnection at the time of formation, or an electrode of a solid electrolytic capacitor that satisfies the required characteristics by suppressing film breakage at the time of formation. Or can be formed. In other words, this conductive paste contributes to resource saving and has the duality that it can be used for forming wiring patterns and electrodes for solid electrolytic capacitors. Since it increases, it contributes to the productivity improvement of an electrically conductive paste.

  (8) In the conductive paste, the thixo index is preferably 6 or more. According to this configuration, the shape of the wiring pattern immediately after printing is more stable. For this reason, printing workability is improved.

  (9) In the conductive paste, the carbon powder is preferably ketjen black. According to this structure, compared with the case where other carbon black is contained, the conductivity of the wiring pattern formed by the conductive paste can be increased.

(10) The wiring board has a wiring pattern formed of the conductive paste. This wiring board has high reliability (for example, heat shock resistance).
(11) The solid electrolytic capacitor has an electrode formed of the conductive paste.

This solid electrolytic capacitor has high reliability (for example, heat shock resistance).
[Other Embodiments]
The present technology is not limited to the above embodiment. Hereinafter, other embodiments will be described.

  In the present embodiment, the description has been made on the assumption that the wiring pattern is formed by the printing method. However, the conductive paste is not applied only when the wiring pattern is formed by the printing method. The conductive paste is used as a wiring pattern forming material regardless of the type of wiring pattern forming method. This conductive paste is also suitably used when forming a wiring pattern with a dispenser.

  In the present embodiment, the conductive paste is described as being suitable for forming a narrow wiring pattern or a solid electrolytic capacitor electrode, but the application is not limited thereto. For example, the conductive paste according to the present technology is used for forming a wiring pattern that is not narrow (a wiring pattern having a line width of 30 μm or more), lands, and terminals on the substrate. In the solid electrolytic capacitor, the conductive paste according to the present technology can be used for forming an electrode that is not a thin film (forming an electrode having a thickness of 30 μm or more).

  The conductive paste shown in the embodiment is useful when used for forming a wiring pattern (including wiring, terminals, lands) of a substrate, forming an electrode of a solid electrolytic capacitor, and the like.

Claims (11)

  A conductive paste containing silver powder, silver-coated copper powder, carbon powder, a binder resin, a curing agent, and a solvent. The conductive paste according to claim 1, wherein a content of the carbon powder with respect to the entire metal powder is 1% by mass or more. The conductive paste according to claim 1 or 2, wherein a content of the carbon powder with respect to the entire metal powder is 2% by mass or less. The conductive paste according to any one of claims 1 to 3, wherein a mixing ratio of the silver powder and the silver-coated copper powder is 70:30 to 20:80 by mass ratio. The conductive paste according to any one of claims 1 to 4, wherein an average particle diameter of the silver powder is 0.01 µm or more and 15 µm or less, and an average particle diameter of the silver-coated copper powder is 5 µm or more and 15 µm or less. . The conductive paste according to any one of claims 1 to 5, further comprising a spherical silver powder having an average particle diameter of 10 nm to 1000 nm as the silver powder. The content of the carbon powder with respect to the whole metal powder is 1% by mass or more and 2% by mass or less, and the compounding ratio of the silver powder and the silver-coated copper powder is 70:30 to 20:80 by mass ratio. And the silver content rate with respect to the said electrically conductive paste is 20 mass% or less, The electrically conductive paste of Claim 1. The thixo index is 6 or more. The conductive paste according to any one of claims 1 to 7. The conductive paste according to any one of claims 1 to 8, wherein the carbon powder is at least one selected from ketjen black and acetylene black.   The wiring board which has a wiring pattern formed with the electrically conductive paste of any one of Claims 1-9.   The solid electrolytic capacitor which has an electrode formed with the electrically conductive paste of any one of Claims 1-9.