JP4774750B2 - Conductive paste and wiring board using the same - Google Patents

Description

  The present invention relates to a conductive paste used when forming a wiring circuit on a substrate, and a wiring substrate obtained using the conductive paste.

  Conductive paste containing mainly metal powder as a solid component is used widely in electronic equipment parts because it shows good conductivity, for example, used as a conductive path when forming an electrical circuit on a wiring board. Has been. As the conductive paste, for example, a paste obtained by dispersing metal powder and glass frit in an organic vehicle is used. Then, the conductive paste is patterned and applied to a ceramic or glass substrate by a printing method such as screen printing, and then baked at a high temperature to evaporate the organic vehicle and sinter between the metal powders. To form a continuous film. Since such a conductive paste is sintered between metal powders to form a continuous film, good conductivity can be obtained.

  Here, in order to increase the density of electronic equipment components in which the conductive paste is used, it is necessary to efficiently form a fine wiring pattern (or fine pattern). Therefore, a conductive paste for improving the formation accuracy of the fine pattern to be formed is disclosed.

For example, the ratio of the median particle diameter D _{50 of} the conductive powder containing the spherical conductive powder having an average particle diameter of 0.8 μm or less and the organic vehicle to the minimum value D _min of the detectable particle diameter Conductive pastes having (D ₅₀ / D _min ) of 2 to 5 have been proposed. It is described that the use of this conductive paste can reduce the waviness of the surface of the conductor pattern and form a fine pattern with excellent shape accuracy. In the conductive paste, the ratio of the viscosity V ₁ rpm measured under the condition of _{1 rpm} and the viscosity V _{10 rpm} measured under the condition of 10 _rpm using a Brookfield rotary viscometer (V _{1 rpm} / V _{10 rpm} ). Is preferably 2 to 5. It is described that by using a conductive paste having such a viscosity characteristic, the conductive paste applied in a predetermined pattern is less likely to sag and the shape maintaining property is improved (for example, see Patent Document 1). .

Also proposed is a conductive paste containing a spherical metal powder having a particle size of 100 μm or less, a thermosetting phenol resin as a binder resin, and 0.01 to 5 wt% of a polyethylene resin with respect to 100 parts by weight of the metal powder. Has been. It is described that, by using this conductive paste, a fine pattern with good shape accuracy can be formed, and a high-quality and high-definition conductor circuit can be manufactured (for example, see Patent Document 2).
JP 2004-139838 A JP 9-310006 A

  Here, generally, when a fine pattern is formed on a wiring board by screen printing, a screen plate having a mesh having a fine opening diameter is used. Therefore, as in the above prior art, if the particle size of the metal powder is large, problems such as plate clogging and a portion where the metal powder becomes coarse at the line edge portion occur. There is a need to. However, in general, when the particle size of the metal powder is small, secondary agglomeration is liable to occur, making it difficult to paste, and poor conductivity. Therefore, it is possible to achieve both high conductivity and fine pattern printability. There was a need for a sex paste.

  In addition, in order to perform fine pattern printing, it is necessary to improve the printing properties such as the rheology of the conductive paste, the plate slipping property, and the plate release property, and therefore generally additives such as thixotropic agents are used. . However, for example, inorganic powders such as aerosil and carbon black used as the thixotropic agent are inferior in conductivity compared to metal powders, so that the use of the additive decreases the conductivity of the entire conductive paste. There was a problem that.

  Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to provide a conductive paste excellent in the formation accuracy of a fine pattern having high conductivity and a wiring board using the same.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a conductive paste mainly composed of metal powder, glass frit and organic vehicle, wherein the metal powder has an average primary particle size of 0.00. The spherical particles (A) having 1 to 3 μm are mainly composed of 50 to 99% by weight of the whole metal powder, and the spherical particles (B) having an average primary particle size of 50 nm or less are mainly 1 to 50% by weight of the whole metal powder. The ratio (V1 rpm / V10 rpm) of the viscosity (V1 rpm) at a rotation speed of 1 rpm and the viscosity at a rotation speed of 10 rpm (V1 rpm / V10 rpm) measured at 25 ° C. by an E-type rotational viscometer is 4 or more and 10 or less, and the rotation speed is 1 rpm. der viscosity (V1rpm) is 400 Pa · s or more 1200 Pa · s or less at is, the working point of the glass frit is at 450 ° C. or less, B of the spherical particles (B) Wherein the T specific surface area of less 4.0 m ² / g or more 200m ² / g.

According to the structure of Claim 1, since the spherical particle (B) with a small particle size is filled between the particles of the spherical particle (A) with a relatively large particle size, the packing density of the metal powder is increased, As a result, the conductivity can be improved. In addition, when the conductive paste is printed on the substrate and the wiring is formed with a fine pattern, the density of the metal powder in the wiring can be made more uniform, so that the metal powder has a low density at the line edge portion of the fine line. Can be avoided. Therefore, an increase in volume resistance can be suppressed, and as a result, a fine pattern having high conductivity can be formed. Further, when printing the conductive paste, it is possible to improve the detachability of the conductive paste from the screen plate, and it is possible to make the applied paste difficult to drip. Accordingly, the fine pattern formation accuracy can be improved while maintaining the optimum leveling performance, and as a result, the printability is improved. Furthermore, since the spherical particles (B) having excellent dispersibility and a large specific surface area act as a thixotropic agent, it is not necessary to use an additive that is inferior in conductivity compared to a metal powder. The disadvantage that the conductivity of the entire conductive paste is reduced can be avoided.
Further, since the BET specific surface area of the spherical particles (B) is 4.0 m ² / g or more and 200 m ² / g or less, the dispersibility of the spherical particles (B) is good, and the spherical particles (B) in the paste have a good dispersibility. Since the dispersion can be made uniform, a local increase in volume resistance can be suppressed, and the conductivity can be improved.

  Invention of Claim 2 is the electrically conductive paste of Claim 1, Comprising: The boiling point of the solvent which comprises an organic vehicle is 200 degreeC or more, It is characterized by the above-mentioned.

  According to the structure of Claim 2, since the boiling point of the solvent to be used is high, for example, when forming a fine pattern by screen printing, the drying resistance of the conductive paste is improved, and the screen plate is clogged. It is hard to wake up. Therefore, it is possible to improve the fine pattern formation accuracy even during continuous printing.

  The invention according to claim 3 is the conductive paste according to claim 1 or 2, wherein the organic vehicle is a mixture of a resin and a solvent, and ethyl cellulose is a total of the resin components as a constituent component of the resin. It contains 60% by weight or more based on the value.

  According to the configuration of claim 3, when applying the conductive paste to the substrate by screen printing or the like, it is possible to make the conductive paste homogeneous and to suppress bleeding and flow of the print pattern. As a result, it is possible to improve the plate release property and plate release property of the conductive paste from the screen plate.

Invention of Claim 4 is an electrically conductive paste as described in any one of Claim 1 thru | or 3, Comprising: While containing a phthalate plasticizer, the phthalate plasticizer with respect to the whole conductive paste of Content is 0.1 to 3 weight%, It is characterized by the above-mentioned. Here, the plasticizer means a material used for adjusting the rheology of the conductive paste, and has a characteristic different from that of the solvent constituting the organic vehicle.

  According to the structure of Claim 4, when performing continuous printing by screen printing etc., it becomes possible to improve drying resistance.

  The metal powder of the present invention may be any metal selected from simple metals, alloys, and composite metals. As in the invention according to claim 5, the metal powder is platinum, gold, silver, copper, nickel, And one or more metals or alloys selected from palladium and palladium. In particular, it is more preferable to use silver from the viewpoints of conductivity, reliability, and the like.

Invention of Claim 6 is an electrically conductive paste as described in any one of Claim 1 thru | or 5 , Comprising: Glass frit is a powder form, The average particle diameter is 2 micrometers or less. Features.

According to the configuration of the sixth aspect , the glass frit is not easily segregated, and is excellent in dispersibility in the conductive paste, so that high conductivity can be obtained. It is possible to avoid the frit from clogging the mesh.

In this case, in consideration of the environment, it is preferable to use a glass frit that does not contain lead as in the seventh aspect of the invention.

The invention according to claim 8 is a wiring board characterized in that the conductive paste according to any one of claims 1 to 7 is printed on a base material to form a wiring.

According to the structure of Claim 8 , in order to use the electrically conductive paste as described in any one of Claims 1 thru | or 7, it is highly conductive on a base material by methods, such as screen printing, for example. It is possible to obtain a wiring board on which a wiring having a property is formed.

In addition, since the conductive paste according to any one of claims 1 to 7 of the present invention has a property of being excellent in the formation accuracy of a fine pattern having high conductivity, It is suitably used for a wiring board on which a fine pattern having high conductivity and a wiring width of 100 μm or less is formed. Particularly, as in the invention according to claim 9 , the wiring board according to claim 8 , wherein the wiring width is 25 μm or more and 100 μm or less and the volume resistivity is 7 μΩ · cm or less. Preferably used.

  In this case, the width of all the wirings on the wiring board does not need to be 25 μm or more and 100 μm or less, and the wiring board of the present invention only needs to include wiring having a width of 25 μm or more and 100 μm or less.

  According to the present invention, it is possible to form a fine pattern having high conductivity, and it is possible to improve the formation accuracy of the fine pattern. As a result, it is possible to improve printability.

Hereinafter, a preferred embodiment of the present invention will be described.
In the metal powder of the present invention, two types of spherical particles (A) having an average primary particle diameter of 0.1 μm to 3 μm and spherical particles (B) having an average primary particle diameter of 50 nm or less are used. The Of these, commercially available spherical particles (A) can be used. The average primary particle size of the spherical particles (A) is preferably 0.1 μm to 3 μm, and more preferably 0.1 μm to 1 μm. The average particle size refers to a 50% particle size (D ₅₀ ), and a particle size distribution measuring device (Nikkiso Co., Ltd., Nanotrac (registered trademark) particle size distribution measuring device UPA-EX150) applying the laser Doppler method. Etc. can be measured.

  On the other hand, the spherical particles (B) can be produced by wet reduction treatment of the metal compound. More specifically, it is prepared by adding a water-soluble metal compound to water or a mixture of water and a lower alcohol to dissolve, then adding an aqueous solution in which a reducing agent and a surface treatment agent are dissolved, and stirring at 30 ° C. or lower. it can.

  For example, when silver powder is used as the metal powder, silver nitrate is dissolved in a liquid in which pure water and ethanol are mixed in equal amounts, and ammonia water is added to adjust the pH to 11.3, thereby making the solution transparent. . Subsequently, L-ascorbic acid as a reducing agent and polyacrylic acid as a dispersing agent are dissolved in a liquid obtained by mixing equal amounts of pure water and ethanol. In addition, a dispersant is used to prevent a plurality of fine particles from aggregating to a large particle size by gently controlling the progress of the precipitation reaction of the silver fine particles precipitated by the reduction reaction. is there. Next, while maintaining the solution in which the reducing agent and the dispersant are dissolved at 25 ° C. and stirring the solution, the silver nitrate solution prepared earlier is gradually dropped to precipitate silver fine particles, and then washed and recovered. By doing so, spherical silver particles (B) having an average particle diameter of 20 nm can be obtained. For other metal powders, a fine metal powder can be obtained by the same operation.

  And in this invention, it is set as the structure using the metal powder which mixed spherical particle | grains (A) and (B) from which two types differ in size by a fixed ratio. Here, when the content ratio of the spherical particles (B) in the whole metal powder is less than 1% by weight, the spherical particles (B) are not sufficiently distributed around the spherical particles (A). A conductive path is not formed. On the other hand, when the spherical particles (B) exceed 50% by weight of the entire metal powder, the spherical particles (A) are completely surrounded by the spherical particles (B), and the conductivity can be sufficiently improved. Since the amount of spherical particles (B) used increases, the cost increases. Therefore, it can be said that the spherical particles (A) should be used in the range of 50 to 99% by weight of the whole metal powder and the spherical particles (B) in the range of 1 to 50% by weight of the whole metal powder. It is more preferable to use 90 to 97% by weight of the whole metal powder and spherical particles (B) in the range of 3 to 10% by weight of the whole metal powder.

  By adopting such a configuration, the small spherical particles (B) having a particle size of 50 nm or less are filled between the spherical particles (A) having a relatively large particle size, so that the packing density of the metal powder is high. As a result, the conductivity can be improved at a low sintering temperature (for example, 450 ° C. or lower). In addition, when the conductive paste is printed on the substrate by a screen printing method or the like and the wiring is formed by the fine pattern, the density of the metal powder in the wiring can be made more uniform. It is possible to avoid the formation of a portion where the metal powder has a low density. Therefore, an increase in volume resistance can be suppressed, and as a result, a fine pattern having high conductivity can be formed. Further, when forming the fine pattern, it is possible to avoid clogging the metal powder with the mesh of the screen, so that it is possible to improve the formation accuracy of the fine pattern. Furthermore, by using the spherical particles (A) and the spherical particles (B) in the above-mentioned range, it becomes possible to suppress the cost. In addition, it is preferable that content of the metal powder with respect to the whole electrically conductive paste is 60 weight% or more from a viewpoint of ensuring electroconductivity.

In addition, the conductive paste of the present invention was measured with a rotor No. It is preferable to use one having a viscosity (V _{1 rpm} ) at a rotational speed of 1 rpm measured using No. 7 of 400 Pa · s to 1200 Pa · s (preferably 600 Pa · s to 900 Pa · s). When the conductive paste has a too high viscosity, when the conductive paste is screen-printed, the ability to remove the conductive paste from the screen plate is deteriorated, and when the conductive paste has a too low viscosity, it is applied. This is because the paste tends to sag and it is difficult to form a fine pattern in any case.

In addition, the conductive paste of the present invention was measured with a rotor No. A viscosity at rpm 1rpm measured using a 7, as the ratio of the viscosity _{(V 10 rpm)} in the rotational speed 10 rpm _{(V 1rpm / V 10 rpm)} is (preferably 6 to 8) 4 to 10 is Is used. By reducing the viscosity at a rotation speed of 10 rpm (V _{10 rpm} ) within such a viscosity ratio range, when the conductive paste is screen-printed, the plate-out property of the conductive paste from the screen plate is improved. Further, by increasing the viscosity (V ₁ rpm) at a rotation speed of 1 rpm within the above-mentioned range (400 Pa · s or more and 1200 Pa · s or less), the applied paste is less likely to sag. Accordingly, the fine pattern formation accuracy can be improved while maintaining the optimum leveling performance, and as a result, the printability is improved.

  In general, when adjusting the viscosity or the viscosity ratio, additives such as the above-mentioned thixotropic agent are used. In the present invention, the average particle size of primary particles having excellent dispersibility and a large specific surface area is used. The spherical particles (B) having a diameter of 50 nm or less are used. Accordingly, since the spherical particles (B) act as a thixotropic agent, it is not necessary to use an additive having inferior conductivity as compared with the metal powder, and as a result, without reducing the conductivity of the entire conductive paste. It is possible to adjust the viscosity or the viscosity ratio (that is, it is possible to lower the viscosity at 10 rpm and increase the viscosity at 1 rpm as described above). The viscosity or viscosity ratio may be adjusted depending on the type of solvent constituting the organic vehicle, the type of resin constituting the organic vehicle, the blending ratio thereof, and the content of the organic vehicle relative to the entire conductive paste. Can be adjusted.

Moreover, the BET specific surface area of the spherical particles (B) improves the dispersibility of the spherical particles (B) used, makes the dispersion of the spherical particles (B) in the paste uniform, and increases the local volume resistance. From the viewpoint of improving conductivity by suppressing, it is necessary to be 4.0 m ² / g or more. The BET specific surface area can be adjusted by adjusting the average particle diameter of the spherical particles (B) at 50 nm or less, which is the average particle diameter of the spherical particles (B). In addition, although it does not specifically limit about the upper limit of a BET specific surface area, It is preferable that it is 200 m < ² > / g or less. This is because if the BET specific surface area exceeds this upper limit, the average particle diameter of the spherical particles (B) becomes too small, making it difficult to handle without agglomerating.

  Glass frit is a binder used for the purpose of improving the adhesion between the formed pattern and the substrate. The kind of the glass frit can be selected from commercially available products, and it is preferable to use a glass frit containing no lead in consideration of the environment. Examples of such a lead-free glass frit that has a working point as low as 450 ° C. or lower include Bi-based glass frit.

  Further, regarding the size of the glass frit, since the particle size of the metal powder to be used is small, segregation is likely to occur when the particle size of the glass frit is large, and as a result, the conductivity may be affected. Further, when a fine pattern is formed by screen printing, a screen plate having a mesh having a fine opening diameter is used, and therefore, when the fine pattern is formed, the glass frit may be clogged in the mesh. . Accordingly, the glass frit to be used has an average particle size of 2 μm or less, and there is a variation in particle size, so it is preferable to use a glass frit having a maximum particle size of 50 μm or less. By using such a glass frit, it is difficult to segregate and is excellent in dispersibility in the conductive paste, so that high conductivity can be obtained, and the glass frit is meshed when forming a fine pattern. It is possible to avoid clogging.

  Although the blending amount of the glass frit can be used from a very small amount, if it is used in a blending amount of 0.1 wt% or more and 15 wt% or less with respect to the total value of the metal powder and the glass frit, the conductive paste and the base material are used. Can be secured, which is preferable.

  The organic vehicle used in the present invention is a mixture of a resin and a solvent, maintains a uniformly mixed state of the metal powder and the glass frit, and transfers the conductive paste to the substrate by screen printing or the like. When applying, the conductive paste is required to have a characteristic that makes the conductive paste homogeneous, suppresses bleeding and flow of the printing pattern, and improves the plate release and release properties of the conductive paste from the screen plate. Therefore, from the viewpoint of maintaining these characteristics, a cellulose resin or an acrylic resin dissolved in a solvent can be preferably used. More specifically, for example, ethyl cellulose and nitrocellulose are preferable, and ethyl cellulose is particularly preferable from the viewpoints of safety and stability. In addition, these resins can be mixed and used, but from the viewpoint of maintaining the above-mentioned characteristics, ethyl cellulose is used as a constituent component of the resin dissolved in the solvent constituting the organic vehicle with respect to the total value of the resin components. The content is preferably 60% by weight or more, particularly preferably 80% by weight or more and 98% by weight or less.

  As the solvent, if the resin is soluble, non-corrosive to the base material on which the paste is applied, and low volatility, drying resistance is improved and printing workability is improved. . Therefore, from the viewpoint of maintaining these characteristics, organic solvents such as butyl carbitol, butyl carbitol acetate, terpineol, and diethyl phthalate are preferable. Moreover, when forming a pattern by screen printing, what has a boiling point of 200 degreeC or more and does not volatilize easily, such as a butyl carbitol acetate and a terpineol, is preferable. By using such a solvent with 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. It is possible to improve the fine pattern formation accuracy even when performing.

  In addition, content of the organic vehicle with respect to the whole electroconductive paste is not restrict | limited in particular, According to printing methods, such as screen printing, it can adjust suitably. For example, when drawing a pattern in which the line width of printed wiring is 200 μm or less in screen printing, 10 to 20% by weight of ethyl cellulose having a molecular weight of 10,000 to 20,000 is dissolved in butyl carbitol acetate or the like as an organic vehicle. What was done can be used conveniently.

  Moreover, in this invention, in order to adjust the rheology of an electrically conductive paste, various additives, such as a thixotropic agent, a leveling agent, a plasticizer, etc. which are conventionally used for the electrically conductive paste can be used. For example, when continuous printing is performed by screen printing or the like, drying resistance is an important characteristic, but by adding a plasticizer, drying resistance can be improved. Examples of the plasticizer include phthalic acid derivatives, isophthalic acid derivatives, tetrahydrophthalic acid derivatives, adipic acid derivatives, maleic acid derivatives, fumaric acid derivatives, trimellitic derivatives, pyromellitic derivatives, stearic acid derivatives, oleic acid derivatives, itacones. Acid derivatives, ricinol derivatives, hydrogenated castor oil and derivatives thereof can be suitably used. Of these plasticizers, phthalate plasticizers such as phthalic acid derivatives, isophthalic acid derivatives, and tetrahydrophthalic acid derivatives are particularly preferable from the viewpoint of improving drying resistance. More specifically, examples of the phthalic acid derivative include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di- (2-ethylhexyl) phthalate, dioctyl phthalate, diisooctyl phthalate, diisobutyl phthalate, diheptyl phthalate, and diphenyl phthalate. Preferably, the isophthalic acid derivative is, for example, dimethyl isophthalate. The content of the plasticizer in the entire conductive paste is preferably 0.1% by weight or more and 3% by weight or less, and more preferably 0.3% by weight or more and 3% by weight or less.

  In addition, the conductive paste of the present invention is suitably used, for example, when an electric circuit such as a highly conductive wiring or electrode is formed on a base material (glass base material or the like). More specifically, the conductive paste of the present invention is applied by patterning on a substrate by a conventionally known printing method (particularly preferably, a screen printing method), printed, and then fired at a high temperature. Thus, it is possible to obtain a wiring substrate in which an electric circuit such as a desired wiring or electrode is formed on a base material by sintering between metal powders.

  Further, as described above, the conductive paste of the present invention has excellent characteristics of forming a fine pattern having excellent formation accuracy and high conductivity. Therefore, the conductive paste of the present invention is a case of manufacturing a wiring board in which a plurality of wirings are formed on a base material, and has a fine pattern with high conductivity and a wiring width (line width) of 100 μm or less. It is preferably used for forming, and particularly suitable for forming a fine pattern having a wiring width of 25 μm to 100 μm (preferably 25 μm to 50 μm) and a volume resistivity of the wiring of 7 μΩ · cm or less. used.

  Below, this invention is demonstrated based on an Example and a comparative example. In addition, this invention is not limited to these Examples, These Examples can be changed and changed based on the meaning of this invention, and they are excluded from the scope of the present invention. is not.

(Examples 1-4, Comparative Examples 1-2)
As an organic vehicle, ethyl cellulose having a molecular weight of 18000 was dissolved in butyl carbitol acetate by heating to prepare a solution having a content of 12% by weight based on the entire conductive paste. Furthermore, dioctyl phthalate was added to this solution so that the content with respect to the entire conductive paste was 3% by weight. In this case, the content of ethyl cellulose with respect to the total value of the resin components (ethyl cellulose and dioctyl phthalate) dissolved in butyl carbitol acetate as a solvent is 80% by weight. Next, as the metal powder, the type and amount of silver powder shown in Table 1 were added to this solution, and mixed uniformly using a rotary stirring defoamer. Further, the type and amount of glass frit shown in Table 1 were used. The mixture was continued to be mixed and judged to be uniform by observation, and then this solution was passed through a three-roll mill to produce conductive pastes shown in Examples 1 to 4 and Comparative Examples 1 and 2 in Table 1. . In addition, when the BET specific surface area of the spherical particles (B) used in the production of Examples 1 to 4 and Comparative Example 1 was measured using an automatic specific surface area measurement device (Gemini 2375, manufactured by Malvern), 5. It was 7 m ² / g. In each of the conductive pastes, no abnormalities in the normal appearance were observed in all of Examples 1 to 4 and Comparative Examples 1 and 2. Next, the viscosity (V1 rpm) at a rotation speed of 1 rpm and the viscosity at a rotation speed of 10 rpm (V10 rpm) in each conductive paste were measured, and a viscosity ratio (V1 rpm / V10 rpm) was calculated. The viscosity was measured using an E-type rotational viscometer (Toki Sangyo Co., Ltd., TV-20 viscometer complate type (TVE-20H)). 7 was measured at room temperature (25 ° C.).

  Next, the conductive pastes of Examples 1 to 4 and Comparative Examples 1 and 2 were subjected to a glass substrate (manufactured by Asahi Glass Co., Ltd., PD200) using a screen printer (Neurong Co., Ltd., LS-150TVA). A predetermined pattern was printed thereon to form a wiring. For this screen printing, a screen plate (manufactured by Tokyo Process Service Co., Ltd.) of SUS500 mesh (diameter 18 mm, opening 33 μm) was used. The screen plate pattern has wiring (line) widths of 25 μm, 30 μm, 40 μm, and 50 μm (design values of the screen plate), a wiring interval (line interval) of 100 μm, and a wiring length of 25 mm. Next, using a thermostatic bath, the solvent was volatilized by heating at 150 ° C. for 30 minutes, and then transferred to a sintering furnace having a sintering temperature of 450 ° C. for 30 minutes. After sintering, the resistance value at a line length of 25 mm was measured by a four-terminal method for a wiring with a line width of 30 μm. Furthermore, the cross-sectional area of the line was measured using a laser microscope (manufactured by KEYENCE, VK-8510), and the volume resistivity was calculated.

  Moreover, the wiring formability in each line width of each conductive paste was evaluated using an optical microscope (manufactured by LEICA, MZ12). Specifically, the presence or absence of printing defects (homogeneity of conductive paste, presence or absence of disconnection in wiring) was observed with an optical microscope. The evaluation index is: among 66 wirings formed in each line width, ◎: 0 print defects, ○: 1-6 print defects, Δ: 7-20 print defects, x: Print defects Went with 21 or more. Note that the magnification of the optical microscope was 157.5 times for wirings with line widths of 25 μm and 30 μm, and 125 times for wirings with 40 μm and 50 μm. The results are shown in Table 1.

表１から判るように、ライン幅が４０μｍ、および５０μｍの場合は、実施例１〜４、および、比較例１〜２のいずれの場合においても、優れた配線形成性を示した。また、ライン幅が３０μｍの場合は、実施例１、２において、優れた配線形成性を示し、実施例３、４においては良好な配線形成性を示したが、比較例１〜２においては、ライン幅が４０μｍ、および５０μｍの場合に比し、配線形成性が低下した。また、ライン幅が２５μｍの場合は、実施例１〜４においては良好な配線形成性を示したが、比較例１においては、ライン幅が３０μｍの場合より、配線形成性が更に低下し、比較例２においては、ライン幅が３０μｍの場合と同様に低い配線形成性が示された。これは、比較例１においては、回転数１ｒｐｍにおける粘度が１２００Ｐａ・ｓを超えており、高い値となっているためであると考えられる。また、実施例１〜４においては、ライン幅３０μｍの配線における体積抵抗率が、判断基準である７μΩ・ｃｍ以下の値が得られ、高い導電性を示しており、後述の図１（実施例１の導電性ペーストを用いて形成されたライン幅５０μｍの配線の光学顕微鏡写真）に示す様に、緻密で均質なラインが形成されている。しかし、比較例１においては、体積抵抗率が、７μΩ・ｃｍを超え、十分な導電性が得られていない。また、比較例２においては、後述の図２（ライン幅５０μｍの配線の光学顕微鏡写真）に示す様に、ラインが不均質で、特に銀が粗密になる部分が生じており、ライン幅３０μｍの配線において、ライン抵抗を測定することができず、体積抵抗値を算出することができなかった。即ち、比較例２の体積抵抗率は、実施例１〜４、比較例１よりも大きいことが示された。以上より、実施例１〜４の導電性ペーストは、ファインパターンの形成精度に優れているとともに、実施例１〜４の導電性ペーストにより形成された配線は、低温の焼結温度（４５０℃）で高い導電性を示すことが判る。

As can be seen from Table 1, when the line width was 40 μm and 50 μm, excellent wiring formability was exhibited in any of Examples 1 to 4 and Comparative Examples 1 and 2. Further, when the line width was 30 μm, excellent wiring formability was shown in Examples 1 and 2, and good wiring formability was shown in Examples 3 and 4, but in Comparative Examples 1 and 2, Compared with the line widths of 40 μm and 50 μm, the wiring formability was lowered. In addition, when the line width was 25 μm, good wiring formability was shown in Examples 1 to 4, but in Comparative Example 1, the wiring formability was further lowered as compared with the case where the line width was 30 μm. In Example 2, a low wiring formability was exhibited as in the case where the line width was 30 μm. This is presumably because, in Comparative Example 1, the viscosity at a rotational speed of 1 rpm exceeds 1200 Pa · s, which is a high value. Further, in Examples 1 to 4, the volume resistivity in the wiring having a line width of 30 μm is a value of 7 μΩ · cm or less, which is a criterion, and shows high conductivity. As shown in an optical micrograph of a wiring having a line width of 50 μm formed using the conductive paste 1, dense and homogeneous lines are formed. However, in Comparative Example 1, the volume resistivity exceeds 7 μΩ · cm, and sufficient conductivity is not obtained. Further, in Comparative Example 2, as shown in FIG. 2 (an optical micrograph of a wiring having a line width of 50 μm) described later, the line is inhomogeneous, and in particular, a portion in which silver is coarse is generated, and the line width is 30 μm. In wiring, the line resistance could not be measured, and the volume resistance value could not be calculated. That is, it was shown that the volume resistivity of Comparative Example 2 is larger than that of Examples 1 to 4 and Comparative Example 1. As mentioned above, while the conductive paste of Examples 1-4 is excellent in the formation precision of a fine pattern, the wiring formed with the conductive paste of Examples 1-4 is a low-temperature sintering temperature (450 degreeC). It can be seen that it exhibits high conductivity.

  An optical micrograph of the wiring (line width 50 μm) formed using the conductive paste of Example 1 is shown in FIG. 1, and the wiring (line width 50 μm) of the wiring formed using the conductive paste of Comparative Example 2 is shown in FIG. An optical micrograph is shown in FIG. As can be seen from the comparison between FIG. 1 and FIG. 2, the wiring formed using the conductive paste of Example 1 is denser than the wiring formed using the conductive paste of Comparative Example 2. It can be seen that the film is formed in a homogeneous state and the fine pattern formation accuracy is good.

(Example 5)
In the wiring formed using the conductive paste, the volume resistivity with respect to the line width was measured, and the conductivity was evaluated. Specifically, using the conductive paste of Example 1 and Comparative Example 2 described above, a screen printing machine (manufactured by Neurong Co., Ltd., LS-150TVA), a glass substrate (manufactured by Asahi Glass Co., Ltd.) Printed on a PD200 substrate) to form wiring. For this screen printing, a screen plate (manufactured by Tokyo Process Service Co., Ltd.) of SUS500 mesh (diameter 18 mm, opening 33 μm) was used. Further, in the printing of the conductive paste of Example 1, the width of the wiring (line) is 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, and 150 μm (design value of the screen plate), and the wiring interval A screen plate having a (line interval) of 100 μm and a wiring length of 25 mm was used. In the conductive paste printing of Comparative Example 2, the wiring (line) widths are 60 μm, 80 μm, 100 μm, and 150 μm (design values of the screen plate), and the wiring interval (line interval) is 100 μm. A screen plate having a length of 25 mm was used. Then, using a thermostatic bath, the solvent was volatilized by heating at 150 ° C. for 30 minutes, and then transferred to a sintering furnace having a sintering temperature of 450 ° C. and heated and sintered for 30 minutes. After sintering, the resistance value at a line length of 25 mm was measured by a four-terminal method for each line width wiring. Furthermore, the cross-sectional area of the line was measured using a laser microscope (manufactured by KEYENCE, VK-8510), and the volume resistivity was calculated. The results are shown in Table 2.

表２から判るように、実施例１の導電性ペーストを用いて形成された配線は、全てのライン幅の場合で体積抵抗率が７μΩ・ｃｍ以下となっている。一方、比較例２においては、ライン幅が１００μｍ、１５０μｍの場合は、体積抵抗率が７μΩ・ｃｍ以下となっているが、ライン幅が６０μｍ、８０μｍの場合は、体積抵抗率が高く、十分な導電性が得られていない。このことから、実施例１の導電性ペーストを用いて形成された配線は、比較例２の導電性ペーストを用いて形成された配線に比べて、体積抵抗率が低く、実施例１の導電性ペーストは高導電性を有するファインパターンの形成に優れており、特に、ライン幅が１００μｍ以下のファインパターンを形成する際に好適に使用できることが判る。

As can be seen from Table 2, the wiring formed using the conductive paste of Example 1 has a volume resistivity of 7 μΩ · cm or less for all line widths. On the other hand, in Comparative Example 2, when the line width is 100 μm and 150 μm, the volume resistivity is 7 μΩ · cm or less, but when the line width is 60 μm and 80 μm, the volume resistivity is high and sufficient. Conductivity is not obtained. From this, the wiring formed using the conductive paste of Example 1 has a lower volume resistivity than the wiring formed using the conductive paste of Comparative Example 2, and the conductivity of Example 1 is low. It can be seen that the paste is excellent in forming a fine pattern having high conductivity, and can be suitably used particularly when forming a fine pattern having a line width of 100 μm or less.

(Example 6)
The conductive paste was printed on the substrate continuously (repeatedly) by screen printing, and the fine pattern formation accuracy was examined by measuring the line width of the fine pattern formed. More specifically, using the conductive paste of Example 1, on a glass substrate (Asahi Glass Co., Ltd., PD200 substrate) by a screen printer (Neurong Co., Ltd., LS-150TVA). Then, continuous printing was performed to form wiring. For this screen printing, a screen plate (manufactured by Tokyo Process Service Co., Ltd.) of SUS325 mesh (diameter 28 mm, aperture 41 μm) was used. The screen plate pattern has a wiring (line) width of 60 μm (screen plate design value), a wiring interval (line interval) of 100 μm, and a wiring length of 25 mm. In addition, for the evaluation of the fine pattern formation accuracy, the wiring formed by the conductive paste with the first and 500th printing on the glass substrate was used. As for the number of times of printing in the continuous printing test, the screen plate was not filled with paste in the first time and no line was formed. Therefore, except for the first time, the second time was 1 of the continuous printing test. It was the second time. The same applies to Example 7 to be described later. Then, using a thermostatic bath, the solvent was volatilized by heating at 150 ° C. for 30 minutes, and then transferred to a sintering furnace having a sintering temperature of 450 ° C. and heated and sintered for 30 minutes. After sintering, the maximum and minimum values of the line width in the wiring formed with the first and 500th conductive pastes are measured, and the average value of these is calculated for fine pattern formation accuracy in continuous printing. Evaluated. The results are shown in Table 3.

表３から判るように、実施例１の導電性ペーストによれば、スクリーン印刷法により連続して印刷を行った場合においても、ライン幅の最大値、最小値、およびこれらの平均値が殆ど変化しておらず、形状精度に優れたファインパターンを形成することができることが判る。これは、実施例１の導電性ペーストが、表１に示す粘度、および粘度比を有するため、実施例１の導電性ペーストをスクリーン印刷する際に、スクリーン版からの導電性ペーストの版抜け性を良くすることができ、また、塗布された導電性ペーストを垂れにくくすることが可能になるためであると考えられる。また、実施例１の導電性ペーストにおいて使用される銀粉末に、一次粒子の平均粒径が５０ｎｍ以下（２０ｎｍ）の球状粒子（Ｂ）を使用しているため、ファインパターンを形成する際に、銀粉末がメッシュに目詰まりするのを回避することが可能になるためであると考えられる。

As can be seen from Table 3, according to the conductive paste of Example 1, the maximum value, the minimum value, and the average value of the line width are almost changed even when printing is continuously performed by the screen printing method. It can be seen that a fine pattern with excellent shape accuracy can be formed. This is because the conductive paste of Example 1 has the viscosities and viscosity ratios shown in Table 1, and therefore, when the conductive paste of Example 1 is screen-printed, the detachability of the conductive paste from the screen plate. This is considered to be because the applied conductive paste can be made difficult to drip. Moreover, since the silver powder used in the conductive paste of Example 1 uses spherical particles (B) having an average primary particle size of 50 nm or less (20 nm), when forming a fine pattern, This is considered to be because silver powder can be prevented from clogging the mesh.

(Example 7)
The volume resistivity with respect to the line width in the wiring formed by continuously printing the conductive paste by the screen printing method was measured, and the conductivity was evaluated. Specifically, the conductive paste of Example 1 was used on a glass substrate (Asahi Glass Co., Ltd., PD200 substrate) using a screen printing machine (Neurong Co., Ltd., LS-150TVA). Continuous printing was performed to form wiring. For this screen printing, a screen plate (manufactured by Tokyo Process Service Co., Ltd.) of SUS325 mesh (diameter 28 mm, aperture 41 μm) was used. The screen plate pattern has a wiring (line) width of 60 μm, 80 μm, 100 μm, 120 μm and 150 μm (design value of the screen plate), a wiring interval (line interval) of 100 μm, and a wiring length of 25 mm. is there. And the following evaluation was performed about the wiring board of the frequency | count of printing 1st time, 100th time, 200th time, 300th time, 400th time, and 500th time.

  After wiring formation, using a thermostatic bath, it was heated at 150 ° C. for 30 minutes to volatilize the solvent, and then transferred to a sintering furnace having a sintering temperature of 450 ° C. for 30 minutes. After the sintering, the resistance value at a line length of 25 mm was measured by a four-terminal method with respect to the wiring of each line width formed by the conductive paste of each number of printing times. Furthermore, the cross-sectional area of the line was measured using a laser microscope (manufactured by KEYENCE, VK-8510), and the volume resistivity was calculated. The average volume resistivity in each line width (for example, for the line width of 60 μm, each of the line width of 60 μm formed by the first, 100th, 200th, 300th, 400th, and 500th conductive pastes) Conductivity was evaluated by calculating the volume resistivity average value in the wiring. The above results are shown in Table 4 together with the volume resistivity of the conductive paste of Comparative Example 2 in Example 5 described above.

表４から判るように、実施例１の導電性ペーストを用いて形成された配線は、スクリーン印刷法により連続して印刷を行った場合においても、体積抵抗率が４μΩ・ｃｍ以下となっており、特に、配線の幅が１００μｍ以上１５０μｍ以下のファインパターンの場合には、体積抵抗率が３μΩ・ｃｍ以下となっている。即ち、このことから、実施例１の導電性ペーストを用いて形成された配線は、スクリーン印刷法により連続して印刷を行った場合においても、体積抵抗率が低く、実施例１の導電性ペーストは高導電性を有するファインパターンの形成に優れていることが判る。

As can be seen from Table 4, the wiring formed using the conductive paste of Example 1 has a volume resistivity of 4 μΩ · cm or less even when printed continuously by the screen printing method. In particular, in the case of a fine pattern having a wiring width of 100 μm or more and 150 μm or less, the volume resistivity is 3 μΩ · cm or less. That is, for this reason, the wiring formed using the conductive paste of Example 1 has a low volume resistivity even when continuously printed by the screen printing method, and the conductive paste of Example 1 It can be seen that is excellent in the formation of fine patterns having high conductivity.

  As an application example of the present invention, there is a conductive paste used when an electric circuit is formed on a wiring board requiring high conductivity.

2 is an optical micrograph of wiring formed using the conductive paste of Example 1. FIG. 4 is an optical micrograph of a wiring formed using the conductive paste of Comparative Example 2.

Claims (9)

A conductive paste mainly composed of metal powder, glass frit and organic vehicle,
In the metal powder, spherical particles (A) having an average primary particle size of 0.1 to 3 μm are 50 to 99% by weight of the entire metal powder, and spherical particles (B) having an average primary particle size of 50 nm or less. Is a ratio (V1rpm) of the viscosity (V1rpm) at a rotational speed of 1rpm and the viscosity at a rotational speed of 10rpm (V10rpm) measured at 25 ° C by an E-type rotational viscometer. / V10rpm) is 4 or more and 10 or less state, and are viscosity (V1rpm) is 400 Pa · s or more 1200 Pa · s or less in the rotational speed 1 rpm,
The working point of the glass frit is 450 ° C. or less,
The spherical particle (B) has a BET specific surface area of 4.0 m ² / g or more and 200 m ² / g or less.
A conductive paste characterized by that.   The conductive paste according to claim 1, wherein a boiling point of a solvent constituting the organic vehicle is 200 ° C. or more.   The organic vehicle is a mixture of a resin and a solvent, and contains ethyl cellulose as a constituent component of the resin in an amount of 60% by weight or more based on the total value of the resin components. Conductive paste. The phthalate plasticizer is contained, and the content of the phthalate plasticizer with respect to the entire conductive paste is 0.1 wt% or more and 3 wt% or less. The conductive paste according to one item . The metal powder, platinum, gold, silver, copper, conductive as claimed in any one of claims 1 to 4, characterized in that a nickel, and one or more metal or metal alloy chosen from palladium Sex paste. The conductive paste according to any one of claims 1 to 5, wherein the glass frit is in a powder form and has an average particle size of 2 µm or less. The conductive paste according to any one of claims 1 to 6, wherein the glass frit does not contain lead. A wiring board, wherein the conductive paste according to claim 1 is printed on a base material to form a wiring. The wiring board according to claim 8 , wherein the width of the wiring is 25 μm or more and 100 μm or less, and the volume resistivity is 7 μΩ · cm or less.

Images