JP2009170447A - Conductive pattern formation material, conductive pattern formation method, and wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material for forming a low-resistance extra-fine conductive pattern having a dense film condition and small surface roughness; a conductive pattern formation method; and a wiring board. <P>SOLUTION: This conductive pattern formation material comprises a combination of a first material 1 prepared by dispersing and mixing first conductive particles in a mixture of a thermally-degradable polymer material and a solvent, and a second material 2 prepared by dispersing second conductive particles with particle sizes smaller than those of the first conductive particles in a dispersion medium, and in the first material 1, the ratio of the weight of the first conductive particles to that of the thermally-degradable polymer material is 10:1 to 100:1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive pattern forming material, a conductive pattern forming method, and a wiring board. Specifically, the present invention relates to a conductive pattern forming material, a conductive pattern forming method, and a wiring board that reduce the porosity of the inside and the surface of the conductive pattern and improve the conductivity.

In recent years, along with the downsizing of electronic equipment and electronic devices, there has been a demand for further miniaturization of circuit wiring patterns formed on a substrate, and a conductive paste is applied to a substrate to form a wiring pattern. The method of doing is actively researched.
As a method of refining the conductive pattern, a paste liquid containing conductive nanoparticles having an average particle diameter of 1 to 100 nm is applied in a pattern having lines and spaces of several μm on the substrate surface, and the nanoparticles are baked and hardened. A method for forming a low-resistance conductive pattern is known.
Examples of the method for applying the paste liquid containing conductive nanoparticles include an inkjet method, a screen printing method, a reversal imprint method, and an offset printing method.

The ink jet method is a method of applying ink, which is a pL order conductive pattern material, ejected from an ink head to a substrate (see, for example, Patent Document 1).
The screen printing method is a method in which ink is oozed out on a substrate through a pattern mesh.

  In the reversal imprint method, a paste material in which conductive nanoparticles are mixed in a heat extinguishing material is applied to a mold in which a predetermined fine pattern is formed, and a transfer pattern is formed. In this method, a transfer pattern is transferred onto a substrate, and then the transfer pattern on the substrate is heated to extinguish the heat extinguishing material to form a conductive pattern (see, for example, Patent Document 2). In Patent Document 2, a polyoxyalkylene resin is used as a heat extinguishing material.

  In the reversal imprint method, the heat extinguishing material is a binder component for allowing the paste material to adhere to the mold and the substrate. Usually, the surface of the conductive particles is coated with a dispersant, thereby ensuring uniform dispersibility of the conductive particles in the dispersion medium and preventing aggregation of the conductive particles. Since this conductive agent has low adhesion to the mold and the substrate of the conductive particles themselves, a binder component is necessary to transfer the paste material in a predetermined pattern shape from the mold onto the substrate to be transferred.

  In the offset printing method, a paste-like transfer material layer is formed on the entire surface of a blanket having a peelable surface, and this blanket is brought into intimate contact with the relief printing plate so that the portion of the transfer material that contacts the relief of the relief printing plate is blanketed. The transfer pattern is transferred from the blanket to the transfer object by bringing the transfer object into close contact with the transfer object of the predetermined pattern, and then transferring the transfer object from the blanket to the transfer object.

  As another method, after applying a conductive material precursor to a porous film formed of conductive particles and infiltrating the conductive material precursor into the pores of the porous film, the porous film is A method has been proposed in which the conductive material precursor is changed to a conductive material by heating to fill the pores of the porous film and to relieve the irregularities on the surface (for example, Patent Document 3).

JP 2006-279038 A JP 2006-173277 A JP 2005-1000094 A1

However, the ink jet method described in Patent Document 1 has a problem that the position accuracy of the ink arrival position is lowered by the air resistance until the ink reaches the substrate.
Further, in the screen printing method, only the accuracy up to about 30 μm is obtained at present due to the problem of mesh pattern accuracy.

  In the reversal imprint method described in Patent Document 2, the transfer pattern made of the paste material on the substrate is heated to extinguish the heat extinguishing material (polyoxyalkylene resin) to form a conductive pattern. The portion occupied by the heat extinguishing material becomes aerodynamic. Therefore, the formed conductive pattern becomes a porous film and has a high surface roughness, and therefore has a high resistance.

In addition, when the conductive pattern is used as a gate, source, and drain electrode in a transistor, the manner in which the electric field is applied to them becomes non-uniform, resulting in large variations in transistor elements. Furthermore, when a coating material made of, for example, a resist or polyimide is applied on the porous conductive pattern, the surface uniformity of the coating material is affected by the unevenness of the surface of the conductive pattern.
When a resin material (such as cellulose) that does not disappear at the heating temperature of the transfer pattern is used as the binder component, the resin material remains in the formed conductive pattern, and this resin material is insulative. Therefore, there arises a problem that the resistance of the conductive pattern is increased.

  In the case of the method of Patent Document 3, the precursor is a material that changes to a conductive substance by heating, but the changed conductive substance may change its characteristics depending on the heating state. In particular, when the conductive pattern is composed of an inorganic oxide, the conductivity and transmittance of the inorganic oxide change depending on the oxidation state. In other words, the amount of oxygen around the precursor existing on the surface side of the porous conductive film is larger than the amount of oxygen around the precursor existing inside the porous conductive film. The oxidation state of the surface precursor and the internal precursor will be different. As a result, the entire porous conductive film is distributed in conductivity and transmittance, and a transparent conductive film having low resistance and high transmittance cannot be obtained.

  The present invention has been made in view of the above problems, and a forming material, a conductive pattern forming method, and a wiring for forming a conductive pattern in which pores inside and on the surface of the conductive pattern are reduced and resistance is reduced. An object is to provide a substrate.

  Thus, according to the present invention, the first material in which the first conductive particles are dispersed and mixed in the mixture of the thermally decomposable polymer material and the solvent, and the first conductive particles having a particle size smaller than that of the first conductive particles. It consists of a combination of a second material in which two conductive particles are dispersed in a dispersion medium, and in the first material, the ratio of the weight of the first conductive particles to the weight of the thermally decomposable polymer material is 10: A conductive patterning material is provided that is 1 to 100: 1.

  According to another aspect of the present invention, the first conductive particles, the thermally decomposable polymer material, and a solvent are included, and the weight of the first conductive particles, the weight of the thermally decomposable polymer material, Applying a first material obtained by dispersing and mixing the first conductive particles at a ratio of 10: 1 to 100: 1 to a transfer pattern region on the surface of the plate to form a transfer pattern (1); (2) transferring the transfer pattern on the plate to the surface of the substrate, and heating the pattern of the first material transferred onto the surface of the substrate, thereby And (2) forming a porous conductive film in which the first conductive particles are grown, and second conductive particles having a particle size smaller than that of the first conductive particles are dispersed. The porous material formed on the surface of the substrate is coated with the second material dispersed in the medium. A step (4) of applying on the film and allowing the second material to permeate into the surface and internal pores of the porous conductive film; and heating the second material applied on the porous conductive film There is provided a conductive pattern forming method comprising the step (5) of growing the second conductive particles in the pores of the porous conductive film.

  According to still another aspect of the present invention, there is provided a wiring board comprising a substrate and the conductive pattern formed on the surface of the substrate by the conductive pattern forming method, wherein the conductive pattern A wiring substrate having a surface arithmetic average roughness of 100 nm or less is provided.

  According to the present invention, since a conductive pattern can be produced by a printing method using transferability, a fine conductive pattern can be formed. In addition, since the conductive pattern has very few porous pores inside, the volume resistivity is small. Also, there is no surface roughness on the surface of the conductive pattern, and when a voltage is applied, the electric field can be applied uniformly in all directions. The influence of unevenness on the pattern surface can be reduced. Furthermore, since the conductive pattern uses conductive particles that are not of the precursor type, the distribution of conductivity and transmittance within the film is small.

(Description of conductive pattern forming material)
The conductive pattern forming material of the present invention has a first material obtained by dispersing and mixing first conductive particles in a mixture of a thermally decomposable polymer material and a solvent, and a particle size larger than that of the first conductive particles. A combination of a second material in which small second conductive particles are dispersed in a dispersion medium, and in the first material, the ratio of the weight of the first conductive particles to the weight of the thermally decomposable polymer material is It is characterized by being 10: 1 to 100: 1.

This conductive pattern forming material is a material for forming a low resistance conductive pattern by a conductive pattern forming method described later.
The first material is a material for allowing the first conductive particles contained therein to grow into a porous conductive film by firing, and the pores in the porous conductive film are smaller than the size of the first conductive particles. small.
Since the second material is a material for allowing the second conductive particles contained therein to flow into the pores of the porous conductive film to form a dense conductive film, the size of the second conductive particles is It must be smaller than the size of one conductive particle, and is desirably smaller than the size of the pores.

<First material>
In the first material, the first conductive particles are not particularly limited as long as they are particles made of a conductive material. For example, gold (Au), silver (Ag), copper (Cu), iron (Fe), platinum ( Pt), chromium (Cr), nickel (Ni), tantalum (Ta), indium (In), iridium (Ir), tin (Sn), zinc (Zn), gallium (Ga), yttrium (Y) and these It is preferably composed of one or more kinds of particles selected from metal oxides. That is, it is preferable that particles made of these materials are contained as a single component or as a plurality of components.
When the conductive pattern requires transparency, the first conductive particles include particles made of indium tin oxide (ITO), particles made of tin oxide (SnO ₂ ), and particles made of zinc oxide (ZnO). Used with a single component.

  In order to form a fine pattern, the average primary particle size is preferably 10 to 500 nm, more preferably 30 to 300 nm, and particularly preferably 30 to 100 nm as the size of the first conductive particles. When the average primary particle size of the first conductive particles is larger than 500 nm, it becomes difficult to form a fine pattern of several μm. In addition, it is difficult to stably synthesize fine particles having the average primary particle size of the second conductive particles having a particle size smaller than 1 nm.

In order for the first conductive particles to be present in a uniformly dispersed state in the first material, the surface of the first conductive particles is coated with a dispersant that prevents the particles from aggregating and increases the affinity with the solvent. It is desirable that
As the dispersant, a low molecular weight having a first functional group that adsorbs to the first conductive particles by interaction with the first conductive particles and a second functional group that maintains dispersibility in the dispersion medium. These surfactants are preferred. Specifically, examples of the first functional group include a silyl group, a thiol group, an amino group, a carboxyl group, and a carbonyl group, and examples of the second functional group include an alkyl group and a fluoroalkyl group. The combination of these first and second functional groups is not particularly limited.

  The thermally decomposable polymer material in the first material is particularly limited as long as it is a polymer material that gasifies (decomposes) and disappears at least at the firing temperature when firing the porous conductive film with the first material. For example, a polymer material that disappears (heat decomposition) by 95% by weight or more by heating at a temperature of 150 ° C. or higher and 300 ° C. or lower is preferable. A polymer material containing a group that causes a reaction is preferable. This thermally decomposable polymer material is a binder component necessary for the first material to be in close contact with the plate and substrate described later, and preferably does not affect the dispersibility of the first conductive particles.

Specific examples of such a thermally decomposable polymer material include methyl cellulose, ethyl cellulose, nitrocellulose, polymethyl methacrylate, polymethacrylic acid ester, polyoxymethylene, polyoxyethylene, etc., and these are single components. It may be contained in a plurality of components, or a material capable of obtaining appropriate adhesion can be selected according to the material of the plate and the substrate.
Further, the weight average molecular weight of the thermally decomposable polymer material is preferably 1000 to 100,000, more preferably 1000 to 50000, and particularly preferably 1000 to 10,000. In addition, when it is 1000 or less, it is difficult to express the effect as a binder for improving transferability, and when it exceeds 100,000, it takes a long time for thermal decomposition, which is not preferable.

  As the solvent used for the first material, the thermally decomposable polymer material is dissolved, the first conductive particles are uniformly dispersed, exhibit wettability to the plate and the substrate, and further, A high-boiling solvent that does not affect drying when transferring one material is preferable. For example, hydrocarbons such as decane, dodecane, toluene, xylene and cyclohexane, alcohols such as decanol, dodecanol and terpineol, tetrahydrofuran, diethylene glycol dimethyl ether Ether-based solvents such as ether solvents, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as diethylene glycol monoacetate and stearates, and amine solvents such as isobutylamine, aniline and pyrrole can be used.

The weight ratio of the first conductive particles to the thermally decomposable polymer material in the first material is preferably less (smaller) than the first conductive particles. More preferably, the ratio of the weight of the heat-decomposable polymer material is 10: 1 to 100: 1.
When the thermally decomposable polymer material is larger than 1 part by weight with respect to 10 parts by weight of the first conductive particles, the shape of the porous conductive film pattern after the thermally decomposable polymer material is heated and scattered can be maintained. It tends to be difficult. Further, when the thermally decomposable polymer material becomes smaller than 1 part by weight with respect to 100 parts by weight of the first conductive particles, the pattern of the first material is transferred from the plate to the substrate in the conductive pattern forming process described later. The transferability at the time tends to decrease.
The weight ratio between the weight of the first conductive particles and the weight of the thermally decomposable polymer material takes into consideration the specific gravity of the material of the first conductive particles to be used and the specific gravity of the thermally decomposable polymer material, This will be described in detail later.

  In addition, when the first material is applied to the transfer pattern region on the plate and the pattern is transferred to the substrate with high accuracy, the viscosity of the first material is preferably low to some extent, and is less than 53 mPa · s. It is preferably 50 mPa · s or less. When the viscosity of the first material is 53 mPa · s or more, the film thickness tends to be thick, so it tends to be difficult to apply the first material with a predetermined film thickness on the plate, and the viscosity becomes too high. When transferring to the substrate, the film of the first material may be torn in the film thickness direction (becomes disconnected). The lower limit of the viscosity of the first material is not particularly limited, but for example, 1 Pa · s or more is appropriate.

Here, the viscosity of the first material means at least the viscosity when the first material is used, and includes the viscosity immediately after the first material is prepared. That is, the first material may have a desired viscosity at the time of use, even if it is not a desired viscosity at the time of preparation.
The viscosity of the first material can be adjusted by the mixing ratio (weight ratio) of the first conductive particles, the thermally decomposable polymer material, and the solvent. Since the weight ratio between the first conductive particles and the thermally decomposable polymer material is preferably 10: 1 to 100: 1, the weight ratio between the first conductive particles and the thermally decomposable polymer material is determined in advance. It is preferable to adjust the viscosity of the first material by adjusting the weight ratio of the solvent. Note that the first material adjusted to a desired viscosity may be heated to further reduce the viscosity.
In the present invention, the viscosity of the first material is measured using a capillary viscometer, a falling ball viscometer, and a rotational viscometer described in “JISZ8803: Viscosity of liquid—Measurement method”.

<Second material>
In the second material, the second conductive particles are not particularly limited as long as they are particles made of a conductive material. For example, particles made of the same material as the first conductive particles can be used alone or in combination. . In addition, when transparency is required for the conductive pattern, similarly to the first conductive particles, the second conductive particles can be made of particles made of indium tin oxide (ITO), tin oxide (SnO ₂ ). And particles made of zinc oxide (ZnO) are used as a single component.
The size of the second conductive particles is not particularly limited as long as it is smaller than the size of the first conductive particles. For example, the average primary particle size is preferably 1 to 100 nm, more preferably 1 to 50 nm, and 1 to 30 nm. Is particularly preferred.

  In order for the second conductive particles to be present in a uniformly dispersed state in the second material, the surface of the second conductive particles is coated with a dispersant that prevents the particles from aggregating and increases the affinity with the dispersion medium. It is desirable that As the dispersant for the second conductive particles, a dispersant for the first conductive particles can be used.

  The dispersion medium used for the second material is not particularly limited as long as it can disperse the second conductive particles, but a solvent used for the first material is preferably used. Furthermore, since it is necessary for the second material to penetrate into the pores of the porous conductive film formed by firing the first material, a solvent having low surface free energy and high wettability is preferable. For example, decane, dodecane, Preferred are hydrocarbon solvents such as toluene, xylene and cyclohexane, and ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone.

The viscosity of the second material is not particularly limited as long as the second material penetrates into the pores of the porous conductive film obtained by firing the first material, but the viscosity is preferably low to some extent. It is preferable to set it as 1-50 mPa * s similarly to the viscosity of material.
Here, the viscosity of the second material means at least the viscosity at the time of use of the second material, and includes the viscosity immediately after the second material is prepared. That is, the second material may have a desired viscosity at the time of use, even if it is not a desired viscosity at the time of preparation.
The weight of the dispersion medium in the second material may be a weight adjusted so that the second material has a desired viscosity. For example, when the viscosity of the second material is 1 to 50 mPa · s, The weight of the dispersion medium in the material can be 10 to 60% by weight. In addition, you may heat and use the 2nd material adjusted to desired viscosity, and also reduce a viscosity.

(Description of conductive pattern formation method)
Formation of the conductive pattern using the above-described conductive pattern forming material is performed according to the following conductive pattern forming method.
That is, with reference to FIG. 1, this conductive pattern forming method includes first conductive particles, a thermally decomposable polymer material, and a solvent, and the weight of the first conductive particles and the high thermal decomposability. The first material 1 formed by dispersing and mixing the first conductive particles at a ratio of 10: 1 to 100: 1 with respect to the weight of the molecular material is applied to the transfer pattern region e on the surface of the plate P, thereby transferring the pattern for transfer. (1) (FIG. 1 (b)), forming the transfer pattern on the plate P onto the surface of the substrate S (2) (FIG. 1 (c)), and on the surface of the substrate S. Step (3) of heating the transferred pattern of the first material 1 to thermally decompose the thermally decomposable polymer material and forming a porous conductive film 1a in which the first conductive particles are grown. (FIG. 1 (d)) and second conductive particles having a smaller particle size than the first conductive particles are dispersed. The second material 2 dispersed therein is applied onto the porous conductive film 1a formed on the surface of the substrate S, and the second material 2 is permeated into the surface of the porous conductive film 1a and the internal pores. Step (4) (FIG. 1 (e)) and the second material 2 applied on the porous conductive film 1a are heated to form second conductive particles in the pores of the porous conductive film 1a. Step (5) (FIG. 1 (f)) of growing is provided, whereby the conductive pattern 3 having a predetermined pattern can be formed.
In FIG. 1D, a curved arrow represents a state in which the thermally decomposable polymer material is gasified and scattered into the air.

  The method for applying the first material 1 to the transfer pattern region e on the surface of the plate P is not particularly limited. For example, a layer that adheres (adheres to) the first material 1 to the surface of the plate P; There is a method in which a layer that repels the first material 1 is formed in a predetermined pattern, and the first material is applied to the entire surface of the plate P. In this way, in the step (1), the first material 1 is not placed on the layer that repels the first material 1, and the first material 1 can be easily placed only on the layer that is compatible with the first material 1. it can.

  Specifically, the plate P repels the base plate Pa made of a material that is in close contact with the first material 1 and the first material 1 formed in a region excluding the transfer pattern region e on the surface of the base plate Pa. If it has a layer Pb, the first material 1 can be easily applied only to the transfer pattern region e of the plate P. At this time, the method for applying the first material 1 to the plate P is not particularly limited, and for example, a spin coating method, a slit coating method, a die coating method, a casting method, a dip coating method, or the like can be used. In addition, when apply | coating the 1st material 1 to the plate | version | printing P, as above-mentioned, the 1st material 1 may be heated about 1-5 degreeC from room temperature, and a viscosity may be lowered | hung further.

In such a plate P, as shown in FIG. 1A, first, a first coating film is formed by applying a coating solution in which a photosensitive resin material is dissolved in a solvent over the entire surface of the base plate pa. Then, a resin material having a property of repelling the first material 1 is applied onto the first coating film to form a second coating film, and pattern exposure is performed on these coating films through a mask, and development is performed. It can be produced by exposing the transfer pattern region e on the surface of the base plate Pa. That is, the layer Pb that repels only the non-transfer pattern area on the surface of the base plate Pa is formed.
Examples of the material of the base plate Pa that is in close contact with the first material 1 include aluminum, copper, nickel, tantalum, and the like. Among these, aluminum is preferable because it has easy processability and good moldability.
Examples of the resin material that repels the first material 1 include silicone resins and fluorine resins.

  The substrate S, which is a transfer material, may be made of a heat-resistant material having a uniform thickness and a smooth surface shape. For example, glass, silicon, silicon oxide, quartz, polyethylene A substrate made of tarate, polyethylene naphthalate, polyethersulfone, polyimide film, or the like can be used.

As described above, in the step (2), the first material 1 having a predetermined pattern on the plate P is transferred to the substrate S. As described above, in the first material 1, the first conductive particles are uniformly dispersed in the mixture of the thermally decomposable polymer material and the solvent.
Since the first conductive particles are dispersed and stably present in the first material as nanometer-sized fine particles as described above, the surface of the first conductive particles is preferably coated with a dispersant. . In this case, the first conductive particles are weakened in attracting each other, and when the first material 1 is transferred from the plate P to the substrate S, the transfer between the plate P and the substrate S is sufficiently performed. It is conceivable that the transferred material (the first material layer) is divided inside without being performed, but the thermally decomposable polymer material improves the cohesive force inside the layer of the first material 1 and is divided inside. Such a problem does not occur because it has a role of eliminating. When the inside of the layer of the first material 1 is divided, not only the film thickness variation and surface irregularity of the first material 1 after transfer become large, but the formed conductive pattern 3 is broken. Cause.

In the step (3), by firing the first material 1 pattern transferred to the substrate S, the first conductive particles are fused, and the thermally decomposable polymer material is thermally decomposed, gasified and scattered. . Under the present circumstances, it is preferable that the heating temperature (baking temperature) which heats the 1st material 1 is higher than the heating temperature (baking temperature) which heats the 2nd material 2 in a subsequent process (5), and is 200-300 degreeC. More preferably it is. Note that when the heating temperature of the first material 1 is higher than 300 ° C., the process temperature is too high, which tends to affect other constituent materials such as the substrate S. At temperatures lower than 200 ° C., the first conductivity Since the firing of the conductive particles does not proceed sufficiently, and the thermally decomposable polymer material may not be completely thermally decomposed and remain in the film, it is difficult to obtain the conductive pattern 3 having a low resistance. On the other hand, when the firing temperature is lower than 200 ° C., sufficient grain growth does not proceed, so that the adhesion between the first conductive particles and the substrate S is not sufficient, and the film is easily peeled off.
In the step (3), since the dispersing agent for coating the first conductive particles is burnt down or gasified and evaporated by the baking treatment, the porous conductive material is not hindered from fusing between the first conductive particles. It does not remain in the film and become a resistance.

  The conductive particles have a melting point lower than the melting point in the bulk state due to the size effect. For example, in the case of Ag, the melting point of the bulk is 900 ° C. or higher, but the melting point starts to drop from about 100 nm, and decreases to around 200 ° C. when the particle size is 10 nm or less. In the step (3), using this size effect, grain growth is performed by fusion of nanoparticles by heating at a temperature of 300 ° C. or less. The conductive particles grow as the fine particles are fused to each other by firing, and grow to be about 10 to 500 times larger than the particle size before firing. Since the first conductive particles in the first material 1 transferred onto the substrate S do not inhibit the growth in the periphery, the first conductive particles can grow in a substantially isotropic manner in the in-plane direction of the film. . Hereinafter, the grown grains in which the first conductive particles are grown may be referred to as first grown grains.

  Through the above steps, the conductive film 1a having a predetermined pattern made of the first grown grains is formed on the substrate S. In the conductive film 1a, the region from which the thermally decomposable polymer material has been removed becomes pores as it is. Therefore, the conductive film 1a is in a porous state inside and on the surface. That is, since the solvent continues to evaporate from the pattern of the first material on the plate P in the step (1), the solvent is almost eliminated when the transfer pattern of the first material on the substrate S is baked. . Therefore, the volume fraction of the pores of the porous conductive film generally corresponds to the volume fraction of the thermally decomposable polymer material.

For example, a relatively specific gravity as the first conductive particles (density) are a class is larger platinum (specific gravity: 21.41 g / cm ³⁾ using, as the thermally decomposable polymer material using those specific gravity than 2, When the weight ratio of platinum and the thermally decomposable polymer material is 10: 1, the volume ratio occupied by the solid portion in the porous conductive film 1a made of the first grown grains is about 50%, and the remaining about 50 % Is the pore portion. That is, the porosity of the porous conductive film 1a in this case is about 50%.
In addition, silver (specific gravity: 10.49 g / cm ³ ), which has a relatively low specific gravity, is used as the first conductive particles, and those having a specific gravity of 2 or less are used as the thermally decomposable polymer material. When the weight ratio of the degradable polymer material is set to 100: 1, the volume ratio occupied by the solid portion in the porous conductive film 1a made of the first grown grains is about 95%, and the remaining about 5% is fine. It becomes a hole part. That is, the porosity of the porous conductive film 1a in this case is about 5%.
In addition, the porosity of the porous conductive film 1a can be confirmed by observing the film surface and film cross section of the porous conductive film 1a with a scanning electron microscope (SEM) and performing image analysis.

In the present invention, in order to obtain a dense and low-resistance conductive pattern 3, it is necessary to keep the porosity of the conductive pattern 3 low. The porosity of the conductive pattern 3 is greatly influenced by the porosity of the porous conductive film 1a obtained by firing the first conductive particles in the first material transferred to the substrate, and the porosity of the conductive pattern 3 is reduced. In order to suppress it, it is advantageous to keep the porosity of the porous conductive film 1a low. Therefore, the porosity of the porous conductive film 1a is preferably 50% or less.
The porosity of the porous conductive film 1a is generally determined by the ratio of the first conductive particles and the thermally decomposable polymer material in the first material and their specific gravity. As described above, when platinum having a large specific gravity is used as the first conductive particles, the first conductive particles should be set to 10 parts by weight or more with respect to 1 part by weight of the pyrolytic polymer material having a specific gravity of 2 or less. Thus, a porous conductive film 1a having a porosity of about 50% or less can be formed.

  In the step (4), as described above, the second material 2 is applied onto the porous conductive film 1a, adhered to the surface thereof, and penetrated into the internal pores. As described above, a solvent having a low surface free energy is used as the dispersion medium in the second material 2 and the second conductive particles are smaller in size than the first conductive particles. As a result of the penetration of the dispersion medium together with the second conductive particles using capillary force into the pores of 1a, the second conductive particles are taken into the pores of the porous conductive film 1a and the inside is dense and the surface is flat It becomes possible to form a conductive pattern 3. In addition, when apply | coating the 2nd material 2 on the porous electrically conductive film 1a, as above-mentioned, the 2nd material 2 may be heated about 1-5 degreeC rather than room temperature, and a viscosity may be lowered | hung further.

In this step (4), the second material 2 is selectively applied to the porous conductive film 1a and the second material 2 is applied to the entire surface of the substrate S including the porous conductive film 1a. Any of the full coating methods can be used.
In the selective coating method, the second material 2 can be selectively coated only on the porous conductive film 1a having a predetermined pattern by using an inkjet method, a dispenser method, or the like. In this case, it is preferable to appropriately adjust the droplet amount of the second material 2 penetrating into the porous conductive film 1a by capillary action. In FIG. 1E, the symbol N represents a discharge nozzle that discharges droplets of the second material.

  On the other hand, in the overall coating method, the second material 2 can be applied to the entire surface of the substrate S including the porous conductive film 1a by using a spin coating method, a slit coating method, a dip coating method, a casting method, or the like. In this case, the second material 2 applied on the porous conductive film 1a penetrates into the inside, but the second material 2 is also applied on the surface of the substrate S other than the transfer pattern region e. Therefore, when the second material 2 is baked in the subsequent step (5), the grown grains of the second conductive particles on the surface of the substrate S other than the transfer pattern region e (hereinafter sometimes referred to as second grown grains). Therefore, the step of removing the second growth grains attached to the region other than the transfer pattern region e is performed. This will be described in detail later.

  In the step (5), as described above, the second material 2 applied onto the porous conductive film 1a is heated to evaporate the dispersion medium, and the surface and inner pores of the porous conductive film 1a are evaporated. 2 Conductive grains are grown. In this case, the second conductive particles grow anisotropically because the growth direction is suppressed in order to grow so as to fill the pores in the porous conductive film 1a made of the first grown grains. Therefore, the conductive pattern 3 after firing is composed of first and second growth grains that have grown substantially isotropically and second growth grains that have grown anisotropically.

The heating temperature of the second material 2 is preferably lower than the heating temperature of the first material 1. Specifically, it is 150-200 degreeC. By making the heating temperature of the second material 2 lower than the heating temperature of the first material 1, the adhesion of the porous conductive film 1a formed by firing the first conductive particles to the substrate S, and the second conductivity Contrast can be given to the adhesion between the grown grains obtained by firing the particles and the substrate S.
Generally, the conductive particles before sintering do not have adhesion to a substrate such as glass or PET. The adhesive force between the fired conductive particles and the substrate is manifested by an anchor effect with the substrate (entanglement between the substrate and the film). This anchor effect is stronger at higher firing temperatures, and at a firing temperature of 200 ° C. or lower. It has been obtained from experiments that it has no adhesion to the substrate. In addition, the anchor effect does not appear when the size of the grown grain is small.

As described above, when the second material 2 is applied to the entire surface of the substrate S in the step (4), the second growth grains adhere to the surface of the substrate S in the region other than the porous conductive film 1a. By making the firing temperature of the second material 2 lower than the firing temperature of 1, the adhesion force of the second growth grain to the substrate S is made weaker than the adhesion force of the porous conductive film 1a to the substrate S. After the step (5), the second grown grains can be washed and separated from the surface of the substrate S. Even in the case of the selective coating method, the second material 2 spills from the porous conductive film 1a or oozes out from the porous conductive film 1a, or the droplets of the second material 2 scatter and the surface of the substrate S. Therefore, the second growth grains may be washed and separated from the surface of the substrate S.
Examples of the cleaning and peeling method include pure water, rinsing with an organic solvent, and ultrasonic cleaning.

  By the above method, the inside and the surface of the porous conductive film 1a can be densely filled with the second grown grains, and the conductive pattern 3 with high surface uniformity can be obtained. A wiring board F formed on the substrate S can be obtained.

(Description of wiring board)
In the wiring board F in which the conductive pattern 3 is formed on the substrate S, the conductive pattern 3 is filled with the second growth grains in the pores of the porous conductive film 1a having a porosity of 50% or less as described above. It has been done. Therefore, the porosity of the conductive pattern 3 is less than 50%, and is actually a low porosity of about 30 to 50%.
In addition, the porosity of the electroconductive pattern 3 can be measured by observing the film | membrane surface and film | membrane cross section of the electroconductive pattern 3 with a scanning electron microscope (SEM), and analyzing an image.

  Further, as described above, the conductive pattern 3 is filled with the inner growth pores with the second growth grains, and the surface irregularities are also flattened with the second growth grains. Specifically, the arithmetic average roughness (JIS B 0601-1994) of the surface of the conductive pattern 3 is flattened to 100 nm or less, and is hardly affected by disconnection or grain boundaries. In addition, when the arithmetic average roughness of the surface of the conductive pattern 3 exceeds 100 nm, it tends to be easily affected by disconnection or grain boundaries.

The grain size of the conductive particles in the conductive pattern 3 is at least 2 depending on the size of the first conductive particles in the first material 1 and the second conductive particles in the second material 2 and the firing temperature at which each material is fired. Have more than one distribution. In particular, the firing temperature is an important factor that gives a reaction energy for the fusion reaction of fine particles.
In general, firing at a higher temperature grows into larger size grains. For example, when conductive particles having a particle size of 40 nm are baked at 150 ° C., 200 ° C., and 250 ° C., the grain size is 100 nm, 350 nm, and 1200 nm. Since the firing temperature of the first material 1 is 200 to 300 ° C. and the firing temperature of the second material 2 is 150 to 200 ° C., the conductive pattern 3 is a film having at least two or more grain size distributions. It has become.

Here, the volume fraction of the first grown grains and the second grown grains in the conductive pattern 3 is considered as follows.
As the first conductive particles, iridium having a specific gravity (density) larger than that of platinum (specific gravity: 22.61 g / cm ³ ) is used, and a thermally decomposable polymer material having a specific gravity of 2 or less is used. When the weight ratio of the degradable polymer material is 10: 1, the volume ratio occupied by the solid portion in the porous conductive film 1a made of the first grown grains is about 47%, and the remaining about 53% is fine. It becomes a hole part. That is, the porosity of the porous conductive film 1a in this case is about 53%. When the second growth grains are filled in the pores of the porous conductive film 1a without any gap, the volume fraction of the first growth grains and the second growth grains in the conductive pattern 3 is 47: 53≈1: 1. .1.
Further, yttrium having a specific gravity (density) smaller than silver (specific gravity: 4.5 g / cm ³ ) is used as the first conductive particles, and a pyrolytic polymer material having a specific gravity of 2 or less is used. When the weight ratio of the thermally decomposable polymer material is 100: 1, the volume ratio occupied by the solid portion in the porous conductive film 1a made of the first grown grains is about 98%, and the remaining about 2% Becomes the pore portion. That is, the porosity of the porous conductive film 1a in this case is about 2%. When the second growth grains are filled in the pores of the porous conductive film 1a without any gap, the volume fraction of the first growth grains and the second growth grains in the conductive pattern 3 is 98: 2≈49: 1. It is.
Therefore, in the conductive pattern 3 of the present invention, it can be considered that the volume fraction of the first grown grains and the second grown grains is in the range of 1: 1.1 to 49: 1.

(Experimental example 1)
Ten types of first materials having different viscosities prepared using the following materials are prepared, and a pattern of the first material is formed on the plate P by the method described in FIGS. A pattern of one material was transferred from the plate P to the substrate S, the transferability at that time was evaluated, and the results are shown in Table 1. The determination of transferability is made based on whether or not the pattern shape of the plate P has been transferred onto the substrate S in accordance with the pattern shape. If the transferability is good, ○, and if the transferability is poor, ×. I wrote.
<First material>
First conductive particles: silver particles (average primary particle size 100 nm), 10 parts by weight Thermally decomposable polymer material: ethyl cellulose, 0.5 parts by weight Solvent: toluene, 10-100 parts by weight (10 parts by weight in 10 steps) increase)

In this experiment, as shown in Table 1, a threshold value indicating whether or not pattern transfer was possible was observed near a viscosity of 50 mPa · s. From this result, it was confirmed that the viscosity of the first material is preferably 50 mPa · s or less in the present invention.
However, in the present invention, the viscosity of the first material is not limited to 50 mPa · s, and even the first material having a viscosity exceeding 50 mPa · s is heated to be lowered to 50 mPa · s or less. can do.

Example 1
A conductive pattern having a line width W ₁ of 10 μm and a space width W ₂ of 30 μm was formed on a glass substrate as follows (see FIG. 1F).
The first material is silver fine particles having an average primary particle diameter of 100 nm (manufactured by ULVAC Material) as the first conductive particles whose surface is coated with a dispersant, and ethyl cellulose (manufactured by Nihon Kasei Co., Ltd.) as the thermally decomposable polymer material. Were mixed and dispersed at a weight ratio of 20: 1: 100 with respect to the terpineol solvent. The viscosity of the first material was measured and found to be 3.4 mPa · s.
The second material is prepared by dispersing and mixing silver fine particles (manufactured by ULVAC MATERIAL) with an average primary particle size of 30 nm coated with a dispersant as second conductive particles at a weight ratio of 30: 1 with respect to dodecane as a solvent. did. The viscosity of the second material was measured and found to be 2.7 mPa · s.
Further, the first material and the second material were subjected to ultrasonic treatment to improve the dispersibility of the silver fine particles.

For the plate, a positive photosensitive resin (manufactured by Tokyo Ohka Co., Ltd.) is applied on an aluminum base plate, and then a silicone resin (manufactured by Toshiba GE) is applied thereon, and a plurality of lines (width W ₁ = 10 μm). ) And a space (width W ₂ = 30 μm), and was developed by exposure to ultraviolet rays through a photomask (see FIG. 1A). In addition, the thickness of the obtained silicone layer was 500 nm.

Next, the first material is applied on the plate using a slit coater, so that there is no first material on the silicone layer, and the wet first material has a film thickness of 8 μm on the exposed base plate surface. A formed coating film was obtained (see FIG. 1B).
Subsequently, the glass substrate was brought into close contact with the first material pattern on the plate, and the glass substrate was peeled off to transfer the first material pattern on the plate onto the glass substrate (see FIG. 1C).
Then, the glass substrate which has a 1st material pattern was put in the furnace, and the porous electrically conductive film which consists of a 1st growth grain was formed by baking for 10 minutes at 250 degreeC (refer FIG.1 (d)).

Next, the second material was applied onto the porous conductive film at a droplet amount of 0.3 ml / mm by a selective application method using a dispenser, and the second material was infiltrated into the porous conductive film (FIG. 1). (See (e)). At this time, the second material partially overflowed from the porous conductive film and adhered to the glass substrate surface.
Subsequently, a glass substrate in which the second material is infiltrated into the porous conductive film is placed in a furnace and baked at 150 ° C. for 10 minutes to grow second conductive particles inside and on the surface of the porous conductive film. (See FIG. 1 (f)).
Thereafter, the glass substrate is immersed in ethanol and subjected to ultrasonic cleaning to peel off the second growth grains adhering to the substrate surface, and the line width W ₁ is 10 μm and the space width W ₂ is 30 μm on the glass substrate. A conductive substrate having a conductive pattern was formed to obtain a wiring board.

When the volume resistivity of the formed conductive pattern was measured, it was found to be 5 μΩcm, which is a low resistance pattern in the same order as bulk silver.
Moreover, in order to evaluate the structure of the film | membrane of an electroconductive pattern, the film | membrane surface and cross-sectional shape were observed with SEM. From the SEM observation of the film surface, the grain growth of the silver particles grew anisotropically so as to fill the space between the first growth grains and the first growth grains having a size of 1000 to 12000 nm which were grown in an approximately isotropic spherical shape. Second grown grains having a size of around 100 nm were present. Further, SEM observation of the cross section of the film revealed that the film was a dense film with few pores even inside the film, and the space filling rate was 85% or more.
Moreover, when the surface of the conductive pattern was observed with an atomic force microscope (AFM) and the arithmetic average roughness was calculated, it was 60 nm, which was found to be a very flat film.

(Comparative Example 1)
As in Example 1, the steps of FIGS. 1A to 1D are performed, and the steps of FIGS. 1E and 1F using the second material are not performed, and only the first grown grains are formed. A conductive pattern of a porous conductive film was prepared. When the volume resistivity of this conductive pattern was measured, it was 27 μΩcm, and the resistance value was larger than that of Example 1.
Moreover, when the film | membrane shape was observed by SEM, the grain size of the electroconductive pattern was 1000-12000 nm similarly to Example 1, and the space filling rate was about 40%. The calculated average roughness calculated by observing the surface of this conductive pattern with AFM was 540 nm, which was found to be significantly rougher than Example 1.

(Comparative Example 2)
1A to 1C in the same manner as in Example 1 except that the first conductive particles in the first material in Example 1 and ethyl cellulose and terpineol are changed to a weight ratio of 110: 1: 550. As a result, the first material pattern could not be transferred from the plate to the substrate, and a conductive pattern could not be formed.

(Comparative Example 3)
1A to 1C in the same manner as in Example 1 except that the first conductive particles in the first material in Example 1 and ethyl cellulose and terpineol are changed in weight ratio to 150: 1: 750. As a result, the first material pattern could not be transferred from the plate to the substrate at all, and a conductive pattern could not be formed.

(Comparative Example 4)
1 (a) to (d) in the same manner as in Example 1, except that the first conductive particles, ethylcellulose, and terpineol in the first material in Example 1 are changed to a weight ratio of 9: 1: 220. As a result, a disconnection occurred in the pattern of the porous conductive film obtained by firing the first material, and the subsequent steps could not be performed.

(Comparative Example 5)
1A to 1D in the same manner as in Example 1 except that the first conductive particles, ethylcellulose, and terpineol in the first material in Example 1 are changed to a weight ratio of 1: 1: 2000. As a result, disconnection further occurred in the pattern of the porous conductive film formed by firing the first material than in Comparative Example 4, and therefore the subsequent steps could not be performed.

Since Comparative Example 1 is a porous conductive pattern in which the second conductive material is not filled in the porous conductive film using the second material as in Example 1, the surface is also rough and the volume low efficiency is high. It became a thing. In Comparative Examples 2 and 3, it seems that the pattern transfer from the plate to the substrate could not be performed because the weight ratio of the thermally decomposable polymer material in the first material was too small. Conversely, in Comparative Example 4 and Comparative Example 5, the weight ratio of the thermally decomposable polymer material in the first material is too large, so it is considered that the porosity of the porous conductive film was too large and the disconnection occurred.
On the other hand, in Example 1 having the conditions of the present invention, a dense film having a flat surface and low resistance could be formed without causing the problems as in Comparative Examples 1 to 5.

  The present invention can be used for forming a wiring board, an integrated circuit, and the like having a fine wiring pattern of μm order incorporated in various electronic devices.

1A to 1F are process diagrams showing a conductive pattern forming method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st material 1a Porous conductive film 2 2nd material 3 Conductive pattern e Transfer pattern area F Wiring board N Discharge nozzle P Plate Pa Base plate Pb Layer which repels 1st material

Claims (16)

A first material in which first conductive particles are dispersed and mixed in a mixture of a thermally decomposable polymer material and a solvent, and second conductive particles having a particle size smaller than that of the first conductive particles are in a dispersion medium. A combination with a second material dispersed in
In the first material, the ratio of the weight of the first conductive particles to the weight of the thermally decomposable polymer material is 10: 1 to 100: 1.   The conductive pattern forming material according to claim 1, wherein the first material and the second material have a viscosity of 1 to 50 mPa · s.   3. The conductive pattern forming material according to claim 1, wherein an average primary particle size of the first conductive particles is 10 to 500 nm, and an average primary particle size of the second conductive particles is 1 to 100 nm. .   The conductive pattern forming material according to claim 1, wherein the thermally decomposable polymer material is made of a polymer material that is thermally decomposed at a temperature of 150 ° C. or higher and 300 ° C. or lower.   The conductive pattern forming material according to claim 1, wherein the thermally decomposable polymer material includes a thermally decomposable polymer material having a weight average molecular weight of 1000 to 100,000.   The conductive pattern forming material according to claim 1, wherein surfaces of the first conductive particles and the second conductive particles are covered with a dispersant.   The first conductive particles and the second conductive particles are selected from gold, silver, copper, iron, platinum, chromium, nickel, tantalum, indium, iridium, tin, zinc, gallium, yttrium, and oxides of these metals. The conductive pattern forming material according to claim 1, comprising one or more kinds of particles. First conductive particles, a thermally decomposable polymer material, and a solvent, and the ratio of the weight of the first conductive particles to the weight of the thermally decomposable polymer material is 10: 1 to 100: 1. (1) forming a transfer pattern by applying a first material obtained by dispersing and mixing 1 conductive particles to a transfer pattern region on the surface of the plate;
Transferring the transfer pattern on the plate to the surface of the substrate (2);
A porous conductive film obtained by thermally decomposing the thermally decomposable polymer material by heating the pattern of the first material transferred onto the surface of the substrate and growing the first conductive particles. Forming a step (3);
A second material in which second conductive particles having a particle size smaller than that of the first conductive particles are dispersed in a dispersion medium is applied onto the porous conductive film formed on the surface of the substrate, and the first A step (4) of infiltrating the two materials into the surface and the internal pores of the porous conductive film;
And (5) a step of growing the second conductive particles in the pores of the porous conductive film by heating the second material applied on the porous conductive film. A conductive pattern forming method.   The conductive pattern forming method according to claim 8, wherein the first material and the second material are prepared with a viscosity of 1 to 50 mPa · s.   The conductive pattern forming method according to claim 8 or 9, wherein, in the step (3), a heating temperature for heating the first material is higher than a heating temperature for heating the second material.   The plate includes a base plate made of a material that is in close contact with the first material, and a layer that repels the first material formed in a region excluding a transfer pattern region on the surface of the base plate. The conductive pattern formation method as described in any one of 10-10.   The conductive pattern forming method according to any one of claims 8 to 11, wherein in the step (4), the second material is selectively applied onto the porous conductive film. In the step (4), the second material is applied to the entire surface of the substrate including the porous conductive film,
Furthermore, the conductive pattern formation method as described in any one of Claims 8-11 including the process of removing the growth grain of the 2nd electroconductive particle which carried out the grain growth on the substrate surface after the said process (5).   The method for forming a conductive pattern according to claim 8, wherein the porosity of the porous conductive film formed in the step (3) is 53% or less. A wiring board comprising a substrate and the conductive pattern formed on the surface of the substrate by the conductive pattern forming method according to any one of claims 8 to 14,
The wiring board whose arithmetic mean roughness of the surface of the said conductive pattern is 100 nm or less.   The conductive pattern is composed of first grown grains in which the first conductive particles are grown isotropically and second grown grains in which the second conductive particles are grown anisotropically, The wiring board according to claim 15, wherein the volume fraction of the first grown grains and the second grown grains is in the range of 1: 1.1 to 49: 1.

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