JP2008084917A - Method of forming conductive pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a conductive pattern with high conductivity which uses an etching liquid with less environmental load, the reduced number of steps and low-temperature processing that is applicable even for a plastic substrate. <P>SOLUTION: The method includes at least a step to apply conductive ink composition containing at least metallic particles with an average particle size of 1 nm or more and 50 nm or less and an aqueous solvent to a substrate; a step to dry the ink composition; a step to form an etching resist pattern on the dried ink composition by printing method; a step to immerse the substrate processed in the above steps in water and to remove he dried ink composition in an area without the etching resist ink; a step to remove the etching resist; and a step to heat the substrate processed in the above steps and to produce conductivity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for forming a conductive pattern by forming an ink pattern containing metal particles and heat-treating it, and is used for forming a wiring pattern of a printed circuit board, a multilayer circuit board, an LCD, and the like. The

  In recent years, various improvements and new methods have been proposed for forming fine conductive patterns in response to demands for downsizing, cost reduction, and area increase of electronic devices. One is an improvement of a conventional method of forming a metal film on a substrate and performing pattern etching. Improvements in the method of forming a metal film, the composition of an etching resist, and the patterning method are being promoted. For example, Patent Document 1 discloses an etching resist particularly suitable for screen printing. The advantage of this method is that the number of steps can be reduced by forming the resist pattern by the screen printing method, compared with the case of forming the resist pattern by the conventional photolithography method. The problem with this method is that iodine / potassium iodide (Au), phosphoric acid / acetic acid / nitric acid (Ag), cupric chloride, ferric chloride (Cu), etc. are required as the etching solution for the metal layer. These uses are not preferable in terms of environmental load and cost.

  Second, there is a method using an ink (paste) containing a metal powder. A so-called thermosetting conductive ink (paste) is a type that develops conductivity when it is simply applied, dried, and cured, but has a low electrical conductivity because of its resin content. Therefore, the use is limited. On the other hand, what is called fired conductive ink (paste) removes the resin content in the ink in the firing process and sinters the metal powder, so it has high conductivity and high reliability. Is used. For example, it is described that the method disclosed in Patent Document 2 can be used for wiring of printed circuit boards, multilayer circuit boards, LCDs, plasma displays, and the like. The problem with this method is that the temperature required for firing is high and a plastic substrate cannot be used. The firing temperature described in the examples in Patent Document 2 is 800 ° C. Various ideas have been made, but at present, about 400 ° C. is the lower limit of the firing temperature.

  Third, there is a method using an ink in which nanometer-sized metal particles are dispersed in a dispersion medium. Heat to sinter the metal particles to develop conductivity. As the particle size of the metal particles is reduced, the temperature required for sintering decreases. As a patterning method, development of a method using an ink jet is in progress. However, it is difficult to form a high-definition pattern by the inkjet method.

Prior art documents are shown below.
JP 2004-260143 A Japanese Patent Laid-Open No. 11-307907

  The present invention has been made in view of this problem, and forms an electrically conductive pattern with high conductivity by low temperature treatment that can be applied to a plastic substrate with an etching solution with a small environmental load, with a small number of steps. It is an object to provide a method that can be used.

The present invention has been made in view of the above problems, and the invention according to claim 1 is a conductive ink composition comprising at least metal particles having an average particle diameter of 1 nm to 50 nm and an aqueous solvent at least on a substrate. A step of applying (ink application step), followed by a step of drying the ink composition (ink drying step), and a step of forming an etching resist pattern on the dried ink composition by a printing method (etching resist) Pattern forming step), then, immersing the substrate that has undergone each of the above steps in water to remove the dried ink composition present in the region where the etching resist ink is not formed (etching step), A step of removing the etching resist (resist removing step), and subsequently a step of heat-treating the base material that has undergone each of the above steps to develop conductivity (heat treatment) A method for forming a conductive pattern characterized in that it comprises a degree).

  Note that the term “etching” used here means that the conductive ink is removed rather than dissolving the metal particles. That is, it is the same as “etching” used in Patent Document 2.

  The invention according to claim 2 is the method for forming a conductive pattern according to claim 1, wherein a step of curing the etching resist is performed following the step of forming the etching resist pattern.

  The invention according to claim 3 is the method for forming a conductive pattern according to claim 1 or 2, wherein the conductive ink composition contains a water-soluble resin.

  The invention according to claim 4 is the method for forming a conductive pattern according to claim 3, wherein the water-soluble resin is polyethylene oxide having an average molecular weight of 200 or more and 20,000 or less.

  According to a fifth aspect of the present invention, at least a part of the metal particles in the conductive ink composition is silver particles or / and silver alloy particles. This is a method for forming a conductive pattern.

  A sixth aspect of the present invention is the conductive pattern forming method according to any one of the first to fifth aspects, wherein the ink drying step is performed in an unheated atmosphere.

  7. The conductive pattern forming method according to claim 2, wherein the resist ink is a UV curable ink, and the resist curing step is performed by UV curing. It is.

  The invention according to claim 8 is the method for forming a conductive pattern according to any one of claims 1 to 7, wherein a heat treatment temperature in the heat treatment step is 120 ° C. or more and 250 ° C. or less.

  In the method for forming a conductive pattern of the present invention, at least a step of applying a conductive ink composition containing at least metal particles having an average particle diameter of 1 nm to 50 nm and an aqueous solvent to a substrate (ink application step) is followed. A step of drying the ink composition (ink drying step), a step of forming an etching resist pattern on the dried ink composition by a printing method (etching resist pattern forming step), and then the steps described above. The step of immersing the base material in water and removing the dried ink composition present in the region where the etching resist ink is not formed (etching step), followed by the step of removing the etching resist (resist removing step) ), And then a step (heat treatment step) of heat-treating the base material that has undergone each of the steps to develop conductivity. It has become possible to form a conductive pattern by heating at a low temperature without performing an etching process using a metal salt or mixed acid, which was necessary in the conventional method for forming a conductive pattern at a low temperature. The above effect could be obtained by using nanometer-sized metal particles, forming an ink using an aqueous solvent, and using the above process.

  Subsequent to the etching resist pattern forming step, the etching resist is cured, so that the etching resist is less likely to be peeled off in the etching step, so that the etching step can be performed more stably.

  In addition, if the metal particles are fused before the etching step, the etching is hindered. However, by adding a water-soluble resin to the conductive ink composition, the metal particles can be prevented from being fused. .

  In order to develop conductivity, it is necessary to remove the water-soluble resin in the heat treatment step. By making the water-soluble resin into polyethylene oxide having an average molecular weight of 200 or more and 20,000 or less, it is more than 250 ° C. It can be removed by heating at a low temperature, and sufficient conductivity is exhibited even at a low temperature of 250 ° C. or lower, so that the heat treatment temperature can be lowered. Furthermore, polyethylene oxide can use not only alkaline water and acidic water but also neutral water as an etching solution. This point is also an effect of the present invention.

  In addition, by making at least a part of the metal particles in the conductive ink composition silver particles or / and silver alloy particles, the heat treatment temperature for developing the conductivity can be lowered. It becomes easy.

  In addition, by performing the ink drying step in an unheated atmosphere, fusion of metal particles that can be caused by heating is suppressed.

  Further, by using a UV curable type instead of a thermosetting type as the etching resist, fusion of metal particles that can be caused by heating is suppressed.

  Moreover, it is possible to form a conductive pattern on a plastic substrate by using silver as the metal fine particles and setting the heat treatment temperature in the heat treatment step to 120 ° C. to 250 ° C.

As an example of forming the conductive pattern of the present invention, the steps in the case of using a curable resist for the etching resist are shown below in the order of steps based on FIG.
(A) Ink application step: First, the conductive ink composition 2 containing at least metal particles having an average particle diameter of 1 nm to 50 nm and an aqueous solvent is applied to the substrate 1.
(B) Ink drying step: The ink composition 2 is dried.
(C) Etching resist pattern forming step: A pattern of the etching resist 4 is formed on the dried ink composition 3 by printing.
(D) Resist curing step: The resist ink 4 is cured.
(E) Etching step: The base material that has undergone the above step is immersed in water to remove the dried ink composition present in the region where the resist ink is not formed.
(F) Resist peeling process: The cured resist ink 5 is peeled off.
(G) Heat treatment process: The base material which passed through the said process is heat-processed.
The conductive pattern 6 is formed by the above process.

Details of various materials and each process will be described below.
(material)
Any substrate can be used as long as the conductive ink composition can be applied and it can withstand heat treatment. In particular, the conductive pattern of the present invention exhibits good conductivity even at a temperature of 250 ° C. or lower. It is possible to use some plastic substrates together with materials such as soda lime glass, quartz, and silicon wafers. For example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), cycloolefin polymer, polyimide (PI), polyethersulfone (PES), polymethyl methacrylate (PMMA), polycarbonate (PC), polyarylate, etc. are used. can do.

  The conductive ink composition used in the present invention contains an aqueous solvent and metal particles having an average particle size of 1 nm to 50 nm as a conductive component. As the metal particles, particles having an average particle size of 1 nm or more and 50 nm or less are used, and particles having an average particle size of 1 nm or more and 20 nm or less are preferable. Metal particles having an average particle size of 1 nm or less are difficult to produce and store.

  On the other hand, the reason why the upper limit of the average particle diameter is 50 nm is that it is a necessary condition for the conductivity to be manifested by heat treatment at 250 ° C. or lower. That is, it is generally known that in nanometer-sized metal particles, when the particle size is reduced, the temperature at which the particles are fused decreases. When the particles are fused, bulk conductivity is exhibited. Therefore, the particle size is important in ensuring the conductivity especially during the low-temperature heat treatment. When the average particle size is 50 nm or more, sufficient conductivity cannot be obtained during low-temperature heat treatment. In the present invention, the upper limit of the average particle diameter is 50 nm in order for conductivity to be exhibited by a heat treatment at 250 ° C. or lower.

  The metal particles include gold, silver, copper, nickel, platinum, palladium, rhodium and the like as the metal species, but it is preferable that silver is mainly used from the viewpoint of conductivity. The form of the particles may be alloy particles or core-shell particles of the metal in addition to the single component particles of the metal. Gold, silver, and copper are metal species that are particularly likely to exhibit electrical conductivity by low-temperature heat treatment. The minimum heating temperature at which conductivity is exhibited is about 150 ° C. for silver and 200 ° C. or less for gold or copper, and any of the methods of the present invention can be suitably applied. In particular, the heat treatment temperature can be lowered by the presence of silver particles or silver alloy particles as metal particles. In order to stabilize dispersion in the ink, a surfactant or the like may be adsorbed on the surface of the metal particles.

  When the water-soluble resin is contained in the ink, the metal particle dispersion medium needs to be capable of dissolving the water-soluble resin. The aqueous dispersion medium for that purpose is not particularly limited, and examples thereof include water, ethanol, and isopropanol. In the case where the water-soluble resin is not contained, it is only necessary that the metal particles can be stably dispersed.

  The conductive ink composition is generally available as a metal particle dispersion in which metal particles are dispersed in an aqueous dispersion medium. For example, there is MGI-21 manufactured by Ishihara Sangyo Co., Ltd. The particle concentration in the conductive ink composition is not particularly limited, but is usually 50 wt% or less. As the aqueous dispersion medium, water, a mixture of water and ethanol, a mixture of water and 2-propanol, or the like is used.

  The conductive ink composition preferably contains a water-soluble resin. The reason is that when a material that needs to be heated is used in the ink drying step or the resist curing step, fusion of metal particles may occur due to heating. When the metal particles are fused, it becomes difficult to remove the dried conductive ink composition in the etching step, but the fusion of the metal particles can be suppressed by adding a water-soluble resin.

As the water-soluble resin, those soluble in the metal particle dispersion are used. For example, polyethylene oxide, polypropylene oxide, polyacrylate, polyvinyl pyrrolidone, carboxyvinyl polymer, cellulose, natural polysaccharide, polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose and the like can be mentioned. Therefore, polyethylene oxide is preferable, and the average molecular weight is preferably 200 or more and 20,000 or less. When the average molecular weight is 200 or less, it is liquid at room temperature and a film cannot be formed. On the other hand, when the average molecular weight is 20,000 or more, a high temperature of 250 ° C. or more and a long time of 2 hours or more are required in order to remove polyethylene oxide which is a water-soluble resin in the heat treatment step. That is, when polyethylene oxide having an average molecular weight of 200 or more and 20,000 or less is used, practically sufficient conductivity can be obtained by heat treatment at 250 ° C. or less.

  Moreover, in order to apply | coat uniformly to a base material, a conductive ink composition may contain surfactant and a leveling agent as needed.

  The ink for the etching resist is not particularly limited, and various commercially available products can be used, but it is particularly preferable to use a UV curable type. In UV curing, since the dried conductive ink composition is not heated at the time of curing, it is possible to suppress fusion of metal particles that hinder the etching process. For example, there is ER-225N-35 from Toyobo.

(Each process)
The ink application step is a step of applying the conductive ink composition to the substrate. The coating method is not particularly limited, and examples thereof include bar coating, die coating, and spin coating.

  The ink drying process is a process for evaporating and removing the dispersion medium of the conductive ink composition applied to the substrate. Drying is preferably performed in an unheated atmosphere. When heated and dried, the metal particles may be fused to each other, which may hinder the subsequent etching process. Vacuum drying is effective in avoiding fusion and is performed as necessary.

  The etching resist forming step is a step of forming an etching resist ink pattern on the base material that has undergone the ink drying step. The pattern forming method is not particularly limited, and examples thereof include printing methods such as screen printing and flexographic printing. Screen printing that can obtain high resolution by using a high-viscosity paste is preferable. The thickness of the resist ink is not particularly limited, but may be thick enough to prevent peeling in the etching process.

  The resist curing step is a step of curing the resist ink. Curing is performed by heating or UV irradiation depending on the resist ink used. In order to suppress metal particle fusion, it is important to avoid excessive heating and UV irradiation during curing. For example, in the case of UV irradiation, a heat ray absorbing glass is placed between the light source and air cooling is performed.

  In the etching step, the base material that has undergone each of the above steps is immersed in a solvent that can dissolve or swell water and other conductive inks and that does not dissolve or swell the etching resist. This is a step of removing the conductive ink composition in the non-formation region by dissolving or swelling it. In this step, application of ultrasonic waves may be effective for promoting etching, and is applied as necessary.

  The resist stripping step is a step of removing the resist. The resist is removed by immersing in an appropriate processing solution (disclosed by the resist manufacturer) that dissolves or swells the resist. In this step, application of ultrasonic waves may be effective in promoting resist removal, and is applied as necessary.

The heat treatment step is a step of heating the base material that has undergone the resist stripping step, evaporating and removing the water-soluble resin, and sufficiently fusing metal particles together to develop conductivity. The necessary heat treatment temperature differs depending on the metal particles used and the water-soluble resin, but if an appropriate material is selected, it is possible to develop practically sufficient conductivity at a heat treatment temperature of 250 ° C. or less. Application to a plastic film substrate is possible.

(material)
-Polyethylene oxide (average molecular weight 1,000, manufactured by Aldrich) in a conductive ink composition silver particle aqueous dispersion (average particle size 20 nm, manufactured by Ishihara Sangyo), (polyethylene oxide / silver particles / water) = (1/8) The conductive ink composition was prepared by dissolving to a weight ratio of / 31).
-Resist UV curing etching resist for screen printing (ER-225N-35, manufactured by Toyobo) was used.
-Base material Soda lime glass (100 mm x 100 mm, 0.7 mm thickness) was used.
(process)
The conductive ink composition was spin coated on a glass substrate at 500 rpm for 20 seconds. Next, it was allowed to stand in the air at room temperature for several minutes and dried until a metallic luster was generated. The dry film thickness was 400 nm. Subsequently, an etching resist is screen-printed on the dried conductive ink composition to form a stripe-like pattern having a thickness of about 10 μm and a line space of about 50 μm, and then UV irradiation is performed using a high-pressure mercury lamp to cure the resist. (Irradiation amount: 400 mJ). Subsequently, this base material was immersed in water, and an ultrasonic wave was applied for 2 minutes using an ultrasonic cleaner to dissolve and remove the portion of the conductive ink composition having no etching resist pattern. Next, it was immersed in acetone, and ultrasonic waves were applied for 2 minutes using an ultrasonic cleaner to dissolve and remove the resist. Finally, the substrate was heat-treated at 200 ° C. for 30 minutes in the air to obtain a conductive pattern.
(result)
When the conductive pattern was observed with an optical microscope, a line-space pattern was confirmed (line / space = 70 μm / 30 μm). Moreover, the film thickness of the conductive pattern was 200 nm. When the resistivity was measured from the film thickness and the resistance value, it was 5 × 10 ⁻⁶ Ωcm, and it was found that the conductivity was practically sufficient, about 35% of bulk silver.

As the substrate, a polyethylene naphthalate (PEN) film having a thickness of 100 μm was used. The other materials were the same as in Example 1. The process was the same as that of Example 1 except that the heat treatment was performed at 150 ° C. for 120 minutes.
(result)
When the conductive pattern was observed with an optical microscope, a line-space pattern was confirmed (line / space = 70 μm / 30 μm). Moreover, the film thickness of the conductive pattern was 200 nm. When the resistivity was measured from the film thickness and the resistance value, it was found to be 11 × 10 ⁻⁶ Ωcm, and it was found to show practically sufficient conductivity.

It is sectional drawing for demonstrating the formation example of the electroconductive pattern concerning embodiment to this invention to process order.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Conductive ink composition 3 Dry conductive ink composition 4 Resist ink 5 Hardened resist ink 6 Conductive pattern

Claims (8)

  At least a step of applying a conductive ink composition containing at least metal particles having an average particle diameter of 1 nm to 50 nm and an aqueous solvent (ink application step) to a substrate (ink application step), and subsequently a step of drying the ink composition (ink) Drying step), subsequently, a step of forming an etching resist pattern on the dried ink composition by a printing method (etching resist pattern forming step), and then immersing the substrate after each of the above steps in water to perform the etching. A step of removing the dried ink composition existing in a region where the resist ink is not formed (etching step), a step of removing the etching resist (resist removing step), and then a base material that has undergone each of the above steps A method for forming a conductive pattern, comprising a step (heat treatment step) of heat-treating the substrate to develop conductivity.   The method for forming a conductive pattern according to claim 1, wherein a step of curing the etching resist is performed subsequent to the step of forming the etching resist pattern.   The method for forming a conductive pattern according to claim 1, wherein the conductive ink composition contains a water-soluble resin.   The method for forming a conductive pattern according to claim 3, wherein the water-soluble resin is polyethylene oxide having an average molecular weight of 200 or more and 20,000 or less.   The method for forming a conductive pattern according to claim 1, wherein at least a part of the metal particles in the conductive ink composition is silver particles or / and silver alloy particles.   The method for forming a conductive pattern according to claim 1, wherein the ink drying step is performed in an unheated atmosphere.   The method for forming a conductive pattern according to claim 2, wherein the resist ink is a UV curable ink, and the resist curing step is performed by UV curing.   The method for forming a conductive pattern according to claim 1, wherein a heat treatment temperature in the heat treatment step is 120 ° C. or more and 250 ° C. or less.

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