TWI700305B - Heat-curing conductive paste for laser etching - Google Patents

Abstract

The present invention provides a heat-curable conductive paste with excellent laser processability. According to the present invention, there is provided a heat-curable conductive paste for laser etching containing conductive powder, thermosetting resin, and curing agent. For the conductive powder, the average particle size based on the laser diffraction and light scattering method is 0.5 μm to 3 μm, and the average aspect ratio is 1.0 to 1.5. When the conductive powder is 100 parts by mass, the content of the thermosetting resin is 35 parts by mass or less.

Description

Heat-curing conductive paste for laser etching

The present invention relates to a heat-curing conductive paste for laser etching.

For electronic devices, performance improvements such as miniaturization, higher density, and higher operating speeds are progressing. Along with this, for electronic parts for electronic devices, further high-density and thinning of electrode wiring is required. However, it is difficult to accurately form thin line-shaped electrodes with the conventional printing method used to form electrode wiring. For example, it is difficult to accurately form the line width and the space between them (line and space: L/S) of 80 μm/ An electrode of 80 μm or less, and further 50 μm/50 μm or less.

Therefore, in recent years, the use of a laser etching method that uses laser light has been studied.

In this method, first, a conductive paste is prepared in the same manner as before. Then, the prepared conductive paste is printed on a desired substrate to form a conductive film (conductive film). Then, the formed conductive film is masked so that the electrode wiring of the desired shape (thin line shape) is formed, and laser light is irradiated to the other (unnecessary) parts. Thereby, the conductive film located in the part irradiated with the laser light is thermally decomposed and removed, and the part not irradiated with the laser light remains as the electrode wiring.

Patent Document 1 and Patent Document 2 disclose conductive pastes for laser etching that can be used for such applications. For example, Patent Document 1 discloses a kind of scaly (thin Flakes) conductive paste of conductive powder. In addition, Patent Document 2 discloses a conductive paste containing a thermoplastic binder resin.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2014-2992

[Patent Document 2] International Publication No. 2014/013899

[Patent Document 3] Japanese Patent Application Publication No. 2003-147316

[Patent Document 4] Japanese Patent Application Publication No. 2009-105361

[Patent Document 5] Japanese Patent Application Publication No. 11-134935

[Patent Document 6] Japanese Patent Application Publication No. Hei 5-36307

As described in Patent Document 1, when forming electrode wiring, generally flat conductive particles are used in order to achieve good conductivity. That is, the flat-shaped conductive particles have good stacking properties, and the interface of the particles can be reduced compared to the case of using spherical conductive particles. Therefore, there is an effect of improving the conductivity or integrity of the electrode. However, according to studies by the inventors, when such flat-shaped conductive particles are used, defects such as thinning of the electrode or disconnection may occur during laser processing.

The situation will be described while referring to the schematic diagrams of FIG. 1(C) and FIG. 1(D). As shown in FIG. 1(C), as a whole, the planar surface area of one particle of flat conductive particles is large. Therefore, the flat conductive particles (scale-like particles 2) sometimes straddle the remaining part as electrode wiring and are removed by laser processing. Exists in the state of the part (laser irradiation part 3). If laser light is irradiated in this state, as shown in FIG. 1(D), heat is also transmitted to the conductive particles remaining as the electrode, and the conductive film may be shaved off more than necessary. As a result, the electrode may become thinner than a predetermined width, or the wire may be broken, or the electrode surface may become rough. The more the electrode is made thinner, the deeper the problem.

In addition, as described in Patent Document 2, the thermoplastic resin has good thermal decomposition properties and is suitable for laser processing. On the other hand, however, thermoplastic resins tend to have low heat resistance. Therefore, if laser light is irradiated in the state shown in FIG. 1(C), heat may be transferred to the resin at the portion remaining as the electrode, and the resin may be deteriorated. As a result, durability sometimes decreases.

The present invention is made in view of the above-mentioned aspects, and its object is to provide a conductive paste that is excellent in laser processing suitability and can form electrode wiring with high durability.

The inventors of the present invention studied the use of thermosetting resin in order to realize highly durable electrode wiring. Furthermore, in order to improve the laser processing suitability or durability of a conductive paste using a thermosetting resin (thermosetting type conductive paste), intensive research has been conducted and the present invention has been completed.

According to the present invention, there is provided a heat-curable conductive paste for laser etching containing conductive powder, thermosetting resin, and curing agent. For the conductive powder, based on laser diffraction. The average particle size of the light scattering method is 0.5μm~3μm, and the average aspect ratio is 1.0~1.5. When the conductive powder is 100 parts by mass, the content of the thermosetting resin is 35 parts by mass or less.

According to the above configuration, as shown in Fig. 1(A), the straddle serves as the electrode and The number of conductive particles (spherical particles 1) existing in the state of the remaining part and the part removed by laser processing decreases. Therefore, the suitability of laser processing is improved, and as shown in Fig. 1(B), an electrode with stable processing line width can be formed. Therefore, it is possible to reduce the occurrence rate of defects such as thinning or disconnection of the electrode wiring. In addition, the smoothness of the electrode surface can be improved. Moreover, for example, it is also possible to preferably form a thin line-shaped electrode wiring with L/S=30 μm/30 μm. Furthermore, by using a thermosetting resin, compared with the case of using a thermoplastic resin, the resin component is relatively less likely to be changed or deteriorated, and the durability of the electrode wiring can be improved.

In addition, other prior art documents related to the conductive paste include Patent Document 3 to Patent Document 6.

In addition, the "average particle size" in this specification refers to laser diffraction. In the volume-based particle size distribution of the light scattering method, the particle size D ₅₀ value (median diameter) corresponding to 50% of the cumulative particle size from the smaller particle size.

In addition, the "average aspect ratio" in this specification refers to the average value of the long diameter/short diameter ratio of a plurality of conductive particles. For example, at least 30 (for example, 30 to 100) conductive particles are observed using an electron microscope. Next, the smallest rectangle that circumscribes each particle image is drawn, and the ratio (A/B) of the length A of the long side of the rectangle to the length (for example, thickness) B of the short side is calculated as the aspect ratio. The arithmetic average of the obtained aspect ratios can be used to obtain the average aspect ratio.

In a preferred aspect disclosed herein, the average aspect ratio of the conductive powder is 1.1 to 1.4. Thereby, compared with the case of using (spherical) conductive powder having an average aspect ratio of 1.0, for example, the suitability for laser processing is further improved. therefore, The effect of the invention in this application can be exerted at a higher level.

In a preferred aspect disclosed here, the conductive powder does not contain conductive particles with an aspect ratio exceeding 5. Thereby, the thin wire-shaped electrode wiring can be formed more accurately. Therefore, the effect of the invention of this application can be exerted at a higher level.

In a preferred aspect disclosed herein, the number average molecular weight of the thermosetting resin is 2000 or less. Thereby, the thermal decomposability of the conductive film is improved, and the suitability for laser processing is improved. In addition, the releasability (releasability) of the self-made plate when printing paste becomes better, and the printing accuracy can also be improved.

Furthermore, the "number average molecular weight" in this specification refers to the value measured by gel chromatography (Gel Permeation Chromatography (GPC)) and converted using a standard polystyrene calibration curve. Average molecular weight based on number.

In a preferred aspect disclosed here, the thermosetting resin contains epoxy resin. By using epoxy resin, at least one of laser processing suitability, adhesiveness, durability, heat resistance, and chemical resistance can be improved.

The epoxy resin preferably includes a multifunctional epoxy resin having two or more epoxy groups and a monofunctional epoxy resin having one epoxy group.

In a preferred embodiment, the mass ratio of the multifunctional epoxy resin to the monofunctional epoxy resin is 20:80 to 45:55. With this, the conductivity can be improved at a higher level.

1: spherical particles

2: scaly particles

3: Laser irradiation part

Figures 1(A) to 1(D) are schematic cross-sectional views showing the state of the conductive film before and after laser etching. Figures 1(A) and 1(B) illustrate the present invention, and Figures 1(C), Figure 1(D) illustrates the prior art.

Fig. 2 is a laser microscope image of the electrode wiring of Example 2.

Fig. 3 is a laser microscope image of the electrode wiring of the reference example whose laser processability is evaluated as "×".

Hereinafter, a preferred embodiment of the present invention will be described. In addition, items other than the items specifically mentioned in this specification (for example, the composition of the heat-curable conductive paste for laser etching) and items necessary for the implementation of the present invention (for example, the preparation method of the paste or the method of laser etching, etc.) It can be grasped as a design matter of a person skilled in the art based on the prior art in this field. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

In addition, the "A to B (where A and B are arbitrary values)" in this specification are considered to include the values (upper limit and lower limit) of A and B unless otherwise specified.

<Heat-curing conductive paste for laser etching>

The heat-curable conductive paste disclosed here (hereinafter sometimes referred to as "paste") contains (a) conductive powder, (b) thermosetting resin, and (c) curing agent as essential components. In addition, no thermoplastic resin is typically contained. It is also characterized in that the conductive powder satisfies predetermined properties, and the blending amount of the thermosetting resin is not more than a predetermined value. Therefore, there is no particular limitation other than this, and it can be arbitrarily determined based on various criteria. Hereinafter, the constituent components of the paste and the like will be described.

<(a) Conductive powder>

The conductive powder is a component for imparting conductivity to the electrode wiring. The conductive powder is not particularly limited, and various metals, alloys, etc. having required conductivity or other physical properties can be appropriately used according to the application and the like. A preferred example can include: gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os) ), nickel (Ni), aluminum (Al) and other metals and coating mixtures or alloys of these metals. Among them, the simple substance of precious metals such as silver (Ag), platinum (Pt), palladium (Pd) and the mixture of these precious metals (silver-coated copper, silver-coated copper-zinc alloy, silver-nickel) or alloys (silver- Palladium (Ag-Pd), silver-platinum (Ag-Pt), silver-copper (Ag-Cu), etc.). Especially in terms of relatively low cost and excellent conductivity, silver, silver-coated products, and silver alloys are preferred.

The conductive powder of the paste disclosed here has an average aspect ratio of 1.0 to 1.5, for example, 1.0 to 1.4. Thereby, the planar surface area of the electroconductive particle which comprises electroconductive powder becomes small. As a result, it is possible to effectively reduce conductive particles in a state that straddles the part remaining as the electrode wiring and the part thermally decomposed and removed by laser processing. Therefore, the thinning or disconnection of the electrode can be significantly improved. That is, the suitability of laser processing is greatly improved, and it is possible to form thin wire electrodes with a stable processing line width.

In addition, in the case of using spherical or substantially spherical (including spherical, elliptical, polygonal, etc.) conductive particles, for example, conductive particles with a larger aspect ratio such as scales are used. Compared with the case of sexual particles, the contact area between particles becomes smaller. Therefore, there is usually a concern that the resistance of the electrode wiring will increase. However, according to the technology disclosed here, it is possible to accurately form the effect of thin wire-shaped electrodes and to achieve a high degree of The effects of achieving a balance of the constituent components of the paste interact with each other to suppress the increase in the resistance of the entire electrode wiring. As a result, compared to the conventional paste using scaly-like conductive particles with a large aspect ratio, it is possible to achieve a high volume resistivity not inferior to that.

In a preferred aspect, the aspect ratio of the conductive powder is 1.1 to 1.4. According to the above configuration, the laser processability can be further improved. That is, spherical conductive particles with an aspect ratio closer to 1.00 have less friction, and have high sliding properties or mobility. Therefore, during laser processing, the conductive particles may not be irradiated with the laser efficiently. If the conductive particles have a slightly flat shape compared to a sphere, the shape can exhibit the function of "anti-slip". That is, friction increases, and sliding properties or mobility are reduced. As a result, compared with the case of using spherical conductive particles, the conductive powder is accurately irradiated with laser light. Therefore, the energy or processing time during laser processing can be reduced.

In another preferred aspect, the conductive powder does not contain scaly or dendritic conductive particles. That is, it is desirable that the conductive powder does not contain conductive particles having an aspect ratio of more than 10 (preferably more than 5, more preferably more than 3, for example, more than 2). In other words, the conductive powder may include spherical or substantially spherical (for example, an aspect ratio of 1.0 to 2.0, preferably an aspect ratio of 1.1 to 1.4) conductive particles. Thereby, the effect of the present invention can be stably obtained at a higher level.

The conductive powder of the paste disclosed here has an average particle size of 3 μm or less, for example, 2.5 μm or less. Thereby, the area of the conductive particles in plan view is reduced, and the conductive particles in a state of straddling the remaining part as an electrode and the part decomposed by laser heat can be effectively reduced. Therefore, the suitability for laser processing is further improved, and thin wire-shaped electrodes can be formed stably.

The conductive powder of the paste disclosed here has an average particle size of 0.5 μm or more, for example, 1.0 μm or more. Thereby, the contact points of the particles in the electrode wiring are reduced, and the internal resistance is reduced. Therefore, higher conductivity can be achieved. In addition, the paste can have better fluidity (viscosity), and the workability of the paste can also be improved, or the workability when applying the paste on the substrate.

Furthermore, when generally spherical or substantially spherical conductive particles are used, the contact area between the conductive particles tends to change compared to the case of using conductive particles with a larger aspect ratio such as scales. small. As a result, the volume resistance of the electrode wiring tends to increase. Therefore, in order to form an electrode wiring with excellent conductivity, it is extremely important to reduce the contact between particles by setting the average particle size of the conductive powder to a predetermined value or more.

In a preferred aspect, the conductive particles constituting the conductive powder are provided with a film containing fatty acid on the surface in order to prevent aggregation. The fatty acid may be, for example, saturated higher fatty acids having 10 or more carbon atoms such as capric acid, palmitic acid, and stearic acid; unsaturated fatty acids such as oleic acid and linoleic acid. When the conductive particles are provided with a fatty acid-containing film, the hydroxyl groups on the surface of the particles increase and the hydrophilicity can be effectively improved. Thermosetting resins are typically hydrophobic. Therefore, according to this aspect, the wettability between the conductive particles and the thermosetting resin decreases. As a result, there is an effect that conductive particles can easily form contact points.

More preferably, the fatty acid is a polyunsaturated fatty acid having a valence of two or more. Examples of the polyunsaturated fatty acids having two or more valences include alkyl succinic acid or alkenyl succinic acid.

The total mass of the necessary constituents of the conductive powder in the paste (i.e. (a) + (b) The proportion of +(c)) is not particularly limited, and it can usually be 50% by mass or more, typically 60% to 95% by mass, preferably 70% to 95% by mass, for example 80% by mass ~90% by mass. By satisfying the above-mentioned range, it is possible to achieve both the formation of highly conductive electrode wiring and the excellent workability and operability at a higher level.

<(b) Thermosetting resin>

The thermosetting resin is a component for imparting adhesiveness or durability to the electrode wiring. When a thermosetting resin is added with a curing agent and heated, a network-like cross-linked structure is formed between molecules to be cured. Once hardened, it is difficult to dissolve in the solvent, and does not show plasticization (no deformation) even if heated. Therefore, by using a thermosetting resin, it is possible to realize electrode wiring with excellent heat resistance, chemical resistance, mechanical strength, and durability compared to conventional products using thermoplastic resin.

The thermosetting resin is not particularly limited, and conventionally known thermosetting resins can be suitably used according to the application and the like. A preferred example includes epoxy resin, novolak resin, phenol resin such as resol phenol resin, alkylphenol resin, urea resin, melamine resin, alkyd resin, silicone resin, and urethane resin. These thermosetting resins may be used individually by 1 type, and may use 2 or more types together. Among them, from the viewpoint of laser processability (thermal decomposition property) or adhesiveness, epoxy resin or phenol resin is preferred. In addition, from the viewpoint of heat resistance or durability, the thermal decomposition temperature (the temperature at which the weight is reduced by 5% when the temperature is increased by the thermogravimetric analysis (TGA) method in an air environment at a temperature increase rate of 10°C/min) ) May be approximately 200°C or higher, for example 240°C or higher, especially 300°C or higher.

In a preferred aspect, the thermosetting resin contains epoxy resin. Here The so-called epoxy resin refers to all compounds having one or more epoxy groups in the molecule as three-membered cyclic ethers. Among thermosetting resins, epoxy resins are excellent in adhesiveness, heat resistance, chemical resistance, and durability. Therefore, by using epoxy resin, electrode wiring with more excellent shape retention and stability can be obtained. The epoxy resin can account for approximately 95% by mass or more of the entire thermosetting resin.

The epoxy equivalent of the epoxy resin is not particularly limited. In order to exhibit the characteristics (especially adhesiveness) at a high level, it can be roughly 100g/eq~1000g/eq, typically 100g/eq~500g/eq, For example, around 150g/eq~450g/eq. In addition, the epoxy equivalent can be calculated based on Japanese Industrial Standards (JIS) K7236 (2009).

In a preferred aspect, the epoxy resin is a mixture of a multifunctional epoxy resin having two or more epoxy groups in the molecule and a monofunctional epoxy resin having one epoxy group in the molecule. Thereby, the effect of the invention of this application can be exerted at a higher level.

That is, by using a multifunctional epoxy resin, the mechanical strength or shape stability of the electrode wiring is improved, and more excellent durability can be achieved. On the other hand, multifunctional epoxy resins are hard due to their rigid skeleton structure and have low fluidity or mobility. Therefore, it is difficult to remove by laser, and the laser processability tends to decrease. In addition, even after heating and curing, a large amount of resin remains at the contact points between the conductive particles, and the volume resistance tends to increase. According to the research conducted by the inventors of the present invention, when the spherical or substantially spherical conductive powder as disclosed herein is used, such a tendency to increase the volume resistance may be particularly noticeable.

Therefore, it is preferable to mix a monofunctional epoxy resin with a multifunctional epoxy resin. Thereby, moderate flexibility can be imparted to the resin, and the laser processability can be improved. In addition, according to the research of the inventors, by reducing the crosslinking point of epoxy resin to improve flexibility or softness, the following effect can be obtained: the resin existing at the contact point of conductive particles is cured by heating. Repel (to be excluded). Therefore, the contact area of conductive particles increases, and the volume resistance can be suppressed lower.

Examples of multifunctional epoxy resins include: bisphenol A epoxy resin, bisphenol F epoxy resin, phenol novolac epoxy resin, cresol novolac epoxy resin, naphthalene epoxy resin, and dicyclopentane Diene epoxy resins, multifunctional phenol epoxy resins, biphenyl epoxy resins, glycidyl ester epoxy resins, glycidylamine epoxy resins, and modified types of these resins. These resins may be used individually by 1 type, and may use 2 or more types together. Among them, from the viewpoints of adhesiveness, hydrophobicity, and ease of availability, etc., bisphenol-type epoxy resins and novolak-type epoxy resins are preferred. In particular, from the viewpoint of lowering volume resistance at a higher level, etc., a bisphenol-type epoxy resin is preferable.

Examples of monofunctional epoxy resins include alkyl glycidyl ethers, alkylphenyl glycidyl ethers, alkenyl glycidyl ethers, carbon numbers of 6 to 36 (typically 6 to 26, such as 6 to 18). Glycidyl ether epoxy resins such as alkynyl glycidyl ether and phenyl glycidyl ether; alkyl glycidyl esters and alkenyl glycidyl esters with carbon numbers of 6 to 36 (typically 6 to 26, such as 6 to 18) Glycidyl ester-based epoxy resins such as glycerides and phenyl glycidyl esters. These resins may be used individually by 1 type, and may use 2 or more types together. Among them, alkyl glycidyl ether, phenyl glycidyl ether, alkyl glycidyl ester, and phenyl glycidyl ester are preferred. Especially preferred is phenyl glycidyl ether.

The mass ratio of the multifunctional epoxy resin and the monofunctional epoxy resin is not particularly limited. As a rough guideline, it is preferable that the monofunctional epoxy resin accounts for more than half of the total epoxy resin. In a preferred example, the mass ratio of the multifunctional epoxy resin to the monofunctional epoxy resin is approximately 20:80~45:55, for example 20:80~30:70. Thereby, a relatively thin (for example, 10 μm or less) conductive film suitable for laser processing can be obtained. In addition, it is possible to obtain electrode wiring that has both conductivity and durability at a higher level.

The properties of the thermosetting resin are not particularly limited, and the number average molecular weight Mc may be approximately 5000 or less, preferably 2000 or less, for example, 100 to 1000. If the number average molecular weight Mc is equal to or less than a predetermined value, the thermal decomposition property of the thermosetting resin is improved, and the laser processability can be further improved. In addition, the releasability (releasability) of the self-made plate when printing paste becomes better, and the printing accuracy can be improved. Furthermore, if the number average molecular weight Mc is more than a predetermined value, the adhesiveness with a base material and the shape integration of a wiring electrode can improve.

When the conductive powder is 100 parts by mass, the content of the thermosetting resin in the paste is 35 parts by mass or less. In a preferred example, the content ratio of the thermosetting resin is 25 parts by mass or less, more preferably 20 parts by mass or less. Thereby, electrode wiring with excellent conductivity can be realized.

The lower limit of the content of the thermosetting resin is not particularly limited, and it may be approximately 2 parts by mass or more, preferably 5 parts by mass or more, for example, 8 parts by mass or more. As a result, electrode wiring with more excellent adhesiveness, durability, and reliability can be realized.

The total mass of the necessary components of the thermosetting resin in the paste (i.e. (a) + (b)+(c)) can be approximately 3% by mass or more, preferably 5% by mass or more, for example, 8% by mass or more, and typically can be 30% by mass or less, preferably 25 Mass% or less, for example, 20 mass% or less. If the ratio of the thermosetting resin is more than a predetermined value, the viscosity of the paste can be appropriately increased, and good printability can be obtained. In addition, if the ratio of the thermosetting resin is equal to or less than a predetermined value, the self-made plate will be better released when printing paste, and defects such as wire drawing can be suppressed. Therefore, it is possible to obtain fine wire-shaped electrode wiring with high accuracy, and the effect of the present invention can be exhibited at a higher level.

<(c) Hardener>

The curing agent is a component for forming a cross-linked structure between molecules of the thermosetting resin and curing it. The curing agent is not particularly limited, and can be appropriately used according to the type of thermosetting resin and the like. For example, when an epoxy resin is used as the thermosetting resin, a compound that can react with the epoxy group of the epoxy resin to form a crosslinked structure can be used. A preferred example includes imidazole-based curing agents, acid anhydride-based curing agents, phenol-based curing agents, amine-based curing agents, amide-based curing agents, isocyanate-based curing agents, organic phosphines, and derivatives of these compounds. These compounds may be used alone or in combination of two or more.

The content ratio of the curing agent in the paste is not particularly limited. When the conductive powder is 100 parts by mass, it can usually be 0.5 parts by mass or more, preferably 1 part by mass or more, for example, 2 parts by mass or more, and typically It may be 7 parts by mass or less, for example, 5 parts by mass or less. Thereby, it is possible to prevent the occurrence of poor curing and allow the curing reaction to proceed smoothly. In addition, the unreacted hardener can be prevented from remaining and the volume resistance can be suppressed lower.

The total mass of the necessary components of the hardener in the paste (i.e. (a) + (b) + The proportion in (c)) is not particularly limited, and it can be generally 0.1% by mass or more, preferably 0.5% by mass or more, for example, 1% by mass or more, and typically can be 5% by mass or less, preferably 3% by mass or less, for example, 2.5% by mass or less. By satisfying the above range, it is possible to stably form electrode wiring with reduced volume resistance.

<(d) Other ingredients>

The paste disclosed here may contain various additional components as needed in addition to the above-mentioned (a) component to (c) component (that is, conductive powder, thermosetting resin, and curing agent). Examples of such additives include: reaction accelerators (catalysts), laser light absorbers, inorganic fillers, surfactants, dispersants, tackifiers, defoamers, plasticizers, stabilizers, and antioxidants , Pigments, dilution solvents, etc. As these additional components, those known to be used in general conductive pastes can be suitably used.

Examples of reaction accelerators (co-catalysts) include alkoxides, chelate (complex), and acyl compounds containing metal elements such as zirconium (Zr), titanium (Ti), aluminum (Al), and tin (Sn) . These compounds may be used alone or in combination of two or more. Among them, it is preferable to contain an organic zirconium compound.

In addition, examples of the dilution solvent include organic solvents such as glycol solvents, glycol ether solvents, ester solvents, alcohol solvents, and hydrocarbon solvents.

The content ratio of the additive component is not particularly limited, and when the conductive powder is 100 parts by mass, for example, it may be 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

<Preparation of Paste>

This paste can be prepared by the following method: to become a predetermined content rate (mass ratio Weigh the materials by means of rate), stir and mix homogeneously. Stirring and mixing of materials can be performed using various known stirring and mixing devices, such as roller mills, magnetic stirrers, planetary mixers, and dispersers.

<How to use paste>

In an example of use of the paste, a substrate is first prepared. The substrate is not particularly limited. For example, a plastic substrate, a glass substrate, an amorphous silicon substrate, etc. can be considered. Especially when a substrate containing a material with low heat resistance is used, the present invention can be preferably adopted.

Then, the paste is applied (typically, printed) on the substrate so as to have a desired thickness (for example, 1 μm to 50 μm, preferably 1 μm to 10 μm). At this time, the paste is applied slightly larger (wider) than the size of the required electrode wiring. The application of the paste can be performed using screen printing, bar coater, slit coater, gravure coater, dip coater, spray coater, etc., for example.

Then, the paste applied on the substrate is heated and dried. The heating temperature can be set to a temperature higher than the glass transition point of (b) thermosetting resin, for example. Thereby, the applied paste is cured, and a film-like conductor (conductive film) is formed on the substrate.

Then, masking is performed so that the conductive film becomes an electrode of a desired shape (for example, a thin line shape), and laser light is irradiated to other parts.

The type of laser is not particularly limited, and known lasers that can be used for such applications can be appropriately used. A preferred example includes infrared (IR) lasers, fiber lasers, CO ₂ lasers, excimer lasers, Yttrium Aluminum Garnet (YAG) lasers, semiconductor lasers, and the like. For example, a laser that generates near-infrared laser light in a wavelength range of 750 nm to 1500 nm, and further a wavelength range of 900 nm to 1100 nm can be used.

In a preferred embodiment, the type of laser is selected in such a way that the basic wavelength of the laser light is inconsistent with the absorption wavelength range of the substrate. For example, the type of laser is selected so that the basic wavelength of the laser light becomes a double (double wave, triple wave, etc.) in the absorption wavelength range of the substrate. This can minimize damage to the substrate.

In another preferred embodiment, the type of laser is selected in such a way that the fundamental wavelength of the laser light coincides with the absorption wavelength range of the components constituting the conductive film. Thereby, the conductive film has an absorption band with respect to the wavelength of the laser light, thereby improving the workability and productivity during laser processing. For example, the absorption wavelength range of the cured film (specifically, the cured product formed by curing the (b) thermosetting resin with the (c) curing agent) of the conductive film is approximately 9000 cm ^-1 to 10000 cm ^-1 , for example When it is in the range of 9300 cm ^-1 to 9900 cm ^-1 , an IR laser with a fundamental wavelength of 1064 nm can be preferably used.

The irradiation conditions of the laser light are not particularly limited. For example, the laser output also depends on the thickness of the conductive film, etc. From the viewpoint of avoiding damage to the base material and appropriately removing unnecessary parts of the conductive film, it can be approximately 0.5W-100W. For example, when using an IR laser to process a conductive film with a thickness of about 1 μm to 10 μm, the laser output can be set to about 1W to 10W.

In addition, from the viewpoint of maintaining high productivity and appropriately removing unnecessary parts of the conductive film, the scanning speed of the laser may be approximately 1000 mm/s to 10000 mm/s, for example, 1500 mm/s to 5000 mm/s.

In addition, the laser light irradiation environment can be an atmospheric environment, an inert environment, a reducing environment, etc.

The light energy of the laser is converted into heat energy and reaches the conductive film. Thereby, the conductive film is thermally decomposed, melted, and removed in the area irradiated by the laser light. In addition, the conductive film remains only in the portion not irradiated with the laser light, and the electrode wiring is formed.

As described above, a structure (wiring board) provided with electrode wiring of a predetermined pattern on the substrate can be obtained.

<Use of Paste>

The heat-curable conductive paste for laser etching disclosed here can form highly durable electrodes. In addition, the heat-curing conductive paste for laser etching disclosed here is excellent in laser processability, so it can be particularly preferably used for forming L/S=80μm/80μm or less, and further L/S=50μm/50μm or less The thin wire-shaped electrode wiring.

A representative application can include the formation of electrodes of various electronic parts, or the formation of conductor circuits of flexible elements such as touch panels with flexible substrates, liquid crystal displays, and electronic paper. Examples of flexible substrates include polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polycarbonate (polycarbonate, PC), polyamide and other resin film-like plastic substrates, or glass substrates. Furthermore, it may be a state in which a conductive film containing an oxide, such as an indium tin oxide (ITO) film, is formed on the flexible substrate.

Hereinafter, some embodiments related to the present invention will be described, but the intention is not to limit the present invention to the content shown in the embodiments.

First, the following materials are prepared as constituent components of the heat-curable conductive paste for laser etching.

<Conductive powder>

. Conductive powder 1: spherical silver powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =0.5μm, average aspect ratio is 1.0)

. Conductive powder 2: spherical silver powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =1.0μm, average aspect ratio is 1.1)

. Conductive powder 3: spherical silver powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =3.0μm, average aspect ratio is 1.1)

. Conductive powder 4: spherical silver-coated copper powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =2.2μm, average aspect ratio is 1.1)

. Conductive powder 5: silver-coated copper-zinc alloy powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =2.2μm, average aspect ratio is 1.1)

. Conductive powder 6: spherical silver powder

(Manufactured by Futian Metal Foil Co., Ltd., D ₅₀ =2.5μm, average aspect ratio is 1.4)

. Conductive powder 7: scaly silver powder

(Manufactured by DOWA ELECTRONICS Co., Ltd., D ₅₀ =15μm, average aspect ratio is 16.7)

<Multifunctional epoxy resin>

. Multifunctional epoxy resin A: Novolac type epoxy resin

(Manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent is 193g/eq, number average molecular weight Mc is 1100)

. Multifunctional epoxy resin B: Bisphenol modified epoxy resin

(Manufactured by DIC Co., Ltd., epoxy equivalent is 403g/eq, number average molecular weight Mc is 800)

<Monofunctional epoxy resin>

. Phenyl glycidyl ether type epoxy resin

(Manufactured by ADEKA Co., Ltd., epoxy equivalent is 206g/eq, number average molecular weight Mc is 210)

<hardener>

. Imidazole hardener

(Manufactured by Ajinomoto Fine-techno Co., Ltd., epoxy imidazole adduct)

<Additive (catalyst)>

. Organic Zirconium Compound

(Manufactured by Matsumoto Fine Chemical Co., Ltd., zirconium tetraacetone)

[Formation of conductive film]

The prepared materials were weighed and mixed so as to become the mass ratio shown in Table 1 to prepare heat-curing conductive pastes (Example 1 to Example 9, Reference Example 1 to Reference Example 3).

The prepared paste was screen-printed on the surface of the glass substrate in a square shape of □10cm×10cm with a thickness of about 5 μm (overall coating), and heated and dried at 150°C for 30 minutes. Thereby, a conductive film (cured film) is formed on the glass substrate.

[Evaluation of Laser Processability]

The conductive film formed as described above was irradiated with a laser under the following conditions, and an attempt was made to form a thin line of L/S=30 μm/30 μm.

<Laser processing conditions>

. Laser type: IR laser (basic wavelength: 1064nm)

. Laser output: 5W

. Scanning speed: 2000mm/s

The thin lines formed by the laser processing were observed with a laser microscope to evaluate the laser processing properties. During microscope observation, three fields of view are confirmed at a magnification of 10. The results are shown in the "laser processability" column of Table 1. In Table 1, "◎" means that there is no wire breakage or cutting residue, and the residual line width is 20μm or more and 30μm or less, "○" means that there is no wire breakage or cutting residue, and the residual line width is 10μm or more and less than 20μm, "△" means that there is no broken wire or cutting residue, but the residual line width is less than 10μm, "×" means that there is broken wire or cutting residue in the laser irradiation part. The observation image of Example 2 is shown in FIG. 2. In addition, the observation image of the reference example evaluated as "×" is shown in FIG. 3.

[Measurement of absorption wavelength]

The absorption wavelength of the prepared paste was measured using an ultraviolet-visible-near infrared spectrophotometer. The results are shown in the column of "absorption wavelength" in Table 1.

[Subsequent evaluation]

A cellophane tape was attached to the thin thread formed, and the rubber was pressed from it to fully adhere the cellophane tape, and then the cellophane tape was peeled off at an angle of 45° to evaluate the adhesion. The results are shown in the column of "Adhesion" in Table 1. In Table 1, "○" indicates that the peeling of the thin line (adhesion of the conductive film to the Cyrofan tape) was not confirmed, and "×" indicates that the peeling of the thin line was confirmed.

[Measurement of volume resistance]

A resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., model: Loresta GP MCP-T610) was used to measure the volume resistivity of the thin wire formed. Specifically, the terminal is brought into contact with one end and the other end of the thin wire, and the resistance is measured by the two-terminal method. In addition, a laser microscope was used to observe the cross section of the thin line to measure the cross-sectional area of the thin line. Calculate the volume resistivity from the obtained resistance and cross-sectional area. The results are shown in the column of "Volume Resistivity" in Table 1.

As shown in Table 1 and Figure 2, the laser processability of Examples 1 to 9 is excellent. In addition, the adhesion of Examples 1 to 9 to the substrate is high, and the volume resistivity can be suppressed to 200μΩ. cm or less (preferably 150 μΩ·cm or less, especially 100 μΩ·cm or less).

In contrast, in Reference Example 1 and Reference Example 2 in which conductive powder having an average particle diameter of more than 3 μm and/or an aspect ratio of more than 1.5 was used, the laser processability was reduced. In addition, in Reference Example 3 in which the resin content ratio exceeded 40 parts by mass, the laser processability was reduced, and the volume resistivity was also greatly deteriorated.

Among Examples 1 to 9, the laser processability of Examples 1 to 3 and 7 is particularly excellent. Although the reason is not certain, it can be presumed that the conductive powder contains silver or the aspect ratio is less than 1.4, so the suitability for laser processing is improved (that is, the electrode wiring is less likely to be scraped off).

In addition, among Examples 1 to 6, Examples 1, 2, 3, and 6 can suppress the volume resistivity to 100μΩ. cm below. As for the reason, it can be presumed that the material of the conductive powder is different, that is, the conductivity of the silver powder is better than that of the silver-coated copper powder. Especially in Example 2 where conductive powder 2 is used, the volume resistivity is suppressed to the lowest level, 55μΩ. cm below. Although the reason is uncertain, it is conceivable that the average particle size and the resin amount are balanced. That is, regarding Examples 3 to 6, the average particle size is larger (in other words, the specific surface area is smaller) than that of Example 2, and the amount of resin per specific surface area increases. Therefore, it can be presumed that the amount of resin present at the interface between the conductive particles increases, and the volume resistivity is increased compared to Example 2. In addition, regarding Example 1, it can be estimated that since the average particle diameter is smaller than that of Example 2, the contact points between the conductive particles increase, the interface resistance increases, and the volume resistivity increases compared to Example 2.

These results show the technical significance of the invention of the present application that defines the properties of the conductive powder and the blending ratio of the conductive powder and the thermosetting resin.

The present invention has been described in detail above, but these descriptions are only examples, and various changes can be made to the present invention within a range that does not deviate from the gist.

Claims (7)

A heat-curing conductive paste for laser etching, comprising conductive powder, thermosetting resin, and curing agent, and the conductive powder has an average particle size of 0.5 based on the laser diffraction and light scattering method μm to 3 μm, an average aspect ratio of 1.0 to 1.5, and when the conductive powder is 100 parts by mass, the content of the thermosetting resin is 35 parts by mass or less. The heat-curable conductive paste for laser etching described in the first item of the scope of patent application, wherein the conductive powder has an average aspect ratio of 1.1 to 1.4. The heat-curable conductive paste for laser etching described in the first or second patent application, wherein the conductive powder does not contain conductive particles with an aspect ratio exceeding 5. In the heat-curable conductive paste for laser etching described in item 1 or item 2 of the scope of patent application, the number average molecular weight of the thermosetting resin is 2000 or less. The heat-curable conductive paste for laser etching described in the first or second patent application, wherein the heat-curable resin contains an epoxy resin. The heat-curable conductive paste for laser etching as described in the 5th item of the patent application, wherein the epoxy resin includes a multifunctional epoxy resin having two or more epoxy groups, and a polyfunctional epoxy resin having one epoxy group Monofunctional epoxy resin. The heat-curable conductive paste for laser etching as described in item 6 of the scope of patent application, wherein the mass ratio of the multifunctional epoxy resin to the monofunctional epoxy resin is 20:80 to 45:55.

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