Copper ink, electronic circuit board, and method for producing electronic circuit board

Abstract

Provided are a copper ink that suppresses bleeding when printing copper ink on a substrate and makes it possible to manufacture a highly reliable circuit pattern with few short circuits, and an electronic circuit board using the same and a method for producing an electronic circuit board. The present invention is a copper ink containing copper particles, wherein the thixotropy index TI, defined by the ratio (η1 / η10) of the viscosity η10 at a shear rate of 10 sec-1 to the viscosity η1 at a shear rate of 1 sec-1, is 7.5 or less and the hysteresis area of shear stress by dynamic viscoelasticity measurement, when the shear rate is raised from 0.01 sec-1 to 300 sec-1 over 50 seconds, held at 300 sec-1 for 50 seconds, and lowered from 300 sec-1 to 0.01 sec-1 over 50 seconds, is 3000 Pa∙sec-1 or more.

Description

Copper ink, electronic circuit board, and method for manufacturing electronic circuit board

[0001] The present invention relates to a copper ink, an electronic circuit board, and a method for manufacturing an electronic circuit board, and more particularly to a copper ink that can be used in a screen printing method, an electronic circuit board using the same, and a method for manufacturing an electronic circuit board.

[0002] As electronic devices and information terminals become smaller and lighter, the electronic components used inside the devices are becoming smaller and smaller. This has led to a gradual decrease in the size of the wiring patterns inside the electronic components, as well as narrower widths of the wiring patterns and spacing between the wires.

[0003] Optical patterning, which involves exposure and etching processes, is a common method for forming high-resolution wiring patterns on electronic components. However, optical patterning has the drawback of excessive waste of materials such as photoresist, developer, and etching solution. Optical patterning also has the drawback of being difficult to improve process efficiency due to its complex process. Optical patterning also has the drawback of requiring the use of large-area masks, making it difficult to apply new designs to the production line within the shortest possible time.

[0004] In order to overcome the various drawbacks of optical patterning, a method for forming metal wiring by printing using ink has been developed as a method for directly applying a pattern to a substrate without a mask. One known printing method using ink is screen offset printing. This screen offset printing method involves printing a predetermined pattern by screen printing on the surface of a silicone blanket (a blanket made of silicone rubber), and then transferring the printed pattern to the substrate or film that is the intended printing target, thereby forming a pattern. Various inks that can be used for screen offset printing have been developed in the past (see, for example, Patent Documents 1 to 3).

[0005] JP 2017-069198 A JP 2020-009554 A JP 2014-507510 A

[0006] In response to the recent demand for finer circuit patterns, there is a demand for copper ink to be printed on substrates with higher resolution than ever before. For example, if the copper ink bleeds on the substrate when it is applied, short circuits may occur in the resulting circuit pattern. In particular, in the manufacture of electronic circuit boards having ultrafine wiring with a wiring line width of 20 μm or less, the characteristics of the copper ink used to print the wiring may affect the reliability of the electronic circuit board.

[0007] In view of the above problems, the present invention provides a copper ink that can suppress bleeding when printing copper ink onto a substrate and can produce a highly reliable circuit pattern with few short circuits, as well as an electronic circuit board and a method for manufacturing an electronic circuit board using the same.

[0008] In order to solve the above problems, according to one embodiment of the present invention, there is provided a copper ink containing copper particles, the copper ink having a shear rate of 1 sec -1 Viscosity η1 at shear rate of 10 sec -1 The thixotropy index TI (1 / 10) defined as the ratio of viscosity η10 at η1 / η10 is 7.5 or less, and the shear rate is 0.01 sec -1 From 300 seconds -1 It was raised to 300 sec in 50 sec, held for 50 sec, and then -1 From 0.01 seconds -1 The hysteresis area of ​​the shear stress measured by dynamic viscoelasticity measurement when the shear stress was lowered to 3000 Pa·sec in 50 seconds -1 That's it, copper ink.

[0009] According to another embodiment of the present invention, there is provided an electronic circuit board comprising a wiring layer using the above-mentioned copper ink.

[0010] According to yet another embodiment of the present invention, there is provided a method for manufacturing an electronic circuit board, comprising: forming a copper ink film on a blanket by screen printing using a copper ink; transferring the copper ink film from the blanket onto a substrate; and firing the copper ink film transferred onto the substrate to form a circuit on the substrate.

[0011] According to the present invention, it is possible to provide a copper ink that can suppress bleeding when printing copper ink onto a substrate and can produce a highly reliable circuit pattern with few short circuits, as well as an electronic circuit board and a method for manufacturing an electronic circuit board using the same.

[0012] FIG. 1 is an explanatory diagram illustrating the hysteresis area of ​​copper inks according to an embodiment of the present invention, and is a graph showing the hysteresis area of ​​copper ink No. 1 of an example. FIG. 2 is a graph showing the flow curve of copper ink No. 1. FIG. 3 is a photograph of a linear pattern with a wiring line width of 20 μm printed on a PDMS blanket by screen offset printing using copper ink No. 1. FIG. 4 is a photograph of a linear pattern with a wiring line width of 20 μm printed on a PI substrate by screen offset printing using copper ink No. 1. FIG. 5 is a photograph of a linear pattern with a wiring line width of 15 μm printed on a PDMS blanket by screen offset printing using copper ink No. 7. FIG. 6 is a photograph of a linear pattern with a wiring line width of 20 μm printed on a PI substrate by screen offset printing using copper ink No. 6. FIG. 7 is a graph showing the relationship between the thixotropy index TI (1 / 10) and the hysteresis area. Shear rate 156 sec -1 10 is a graph showing the relationship between the viscosity η156 of the copper ink and the hysteresis area in the case of

[0013] (Copper Ink) One embodiment of the copper ink according to the present invention will be described in detail below. The copper ink according to the present invention is suitable for use in printing on a substrate. The copper ink is used in printing in which the copper ink is directly printed onto a substrate, such as screen printing through a mesh. Alternatively, as is known as screen offset printing, for example, the copper ink according to the present invention is particularly suitable as a copper ink for use in screen offset printing in which the copper ink is first printed onto the surface of a blanket in the form of a roll, plate, or block to form a copper ink film, and then the copper ink film is transferred from the blanket to a substrate.

[0014] <Thixotropy Index> Thixotropy describes the property of a substance where the viscosity changes over time, and can be expressed by the thixotropy index (TI). TI is expressed as the ratio of viscosities at different shear rates. A substance with a TI close to 1 is called a Newtonian fluid. A TI of 1 or greater is considered to be more thixotropic, with a high viscosity in the low shear region (static state) and a low viscosity in the high shear region (flowing state). The copper ink according to this embodiment preferably has a TI that allows it to be fluid with low viscosity during printing (high shear region), making printing possible.

[0015] Specifically, the copper ink according to this embodiment has a shear rate of 1 sec -1 Viscosity η1 at shear rate of 10 sec -1 When the TI (1 / 10) is higher than 7.5, bleeding occurs when a circuit pattern with a line and space (L / S) of 20 μm or less is printed by screen offset printing, and the rate at which short circuits occur (defect rate) may increase.

[0016] The lower limit of TI(1 / 10) is not particularly limited. However, a small TI(1 / 10) indicates that there is little difference between the low shear region (e.g., in a stationary state) and the high shear region (e.g., in a printed state). In order to provide a copper ink capable of accurately forming fine wiring with high connection reliability, it is preferable to have a TI(1 / 10) that has a certain degree of fluidity in a printed state and a certain degree of viscosity in a stationary state. Therefore, TI(1 / 10) is more preferably 1.5 or more, and even more preferably 2.5 or more.

[0017] The TI (1 / 10) can be measured using a dynamic viscoelasticity measuring device (rheometer). In this embodiment, a rheometer (model number: MCR102) manufactured by Anton Paar was used as the dynamic viscoelasticity measuring device, with the measurement section temperature set to 25°C, the measuring jig set to PP (parallel plate) 25, and the gap set to 0.5 mm. Using the dedicated software (RheoCompass ver. 1.20.471) provided with the dynamic viscoelasticity measuring device, the measurement mode was set to "flow curve measurement," and the shear rate was set to 0.01 to 1000 sec. -1 The viscosity was measured in the range of 1 s. -1 Viscosity at shear rate of 10 sec -1 The TI (1 / 10) was calculated based on the viscosity at the time of measurement. The amount of copper ink used for measurement was an amount that could fill the gap between the measurement jig and the device. Any copper ink that spilled out from the measurement jig was wiped off before measurement.

[0018] <Hysteresis Area> Copper ink exhibits a slightly different stress-strain relationship when loaded and unloaded, resulting in a so-called hysteresis loop. Figure 1 shows an example of a hysteresis loop obtained when the shear rate is changed using a copper ink viscoelasticity measuring device according to this embodiment. Under conditions in which the shear rate is increased, the increase in shear stress accompanying the increase in shear rate follows the curve for loading (the upper curve in Figure 1). Under conditions in which the shear rate is decreased from an increased state, the decrease in shear stress accompanying the decrease in shear rate follows the curve for unloading (the lower curve in Figure 1). The hysteresis area, which represents the area of ​​this hysteresis loop, indicates how long it takes for the shear stress to change in response to a change in shear rate. Therefore, the hysteresis area is one indicator of the time dependence of the viscosity of copper ink when the shear rate of the copper ink is increased and then decreased.

[0019] A large hysteresis area indicates that the viscosity recovers slowly when the shear rate is increased and then decreased, i.e., when the viscosity of the copper ink is changed from a high state to a low state and then changed from a low state to a high state. In screen offset printing, a delay time is required after the circuit pattern is printed on the blanket before the transfer to the substrate begins. If the hysteresis area of ​​the copper ink is large, the viscosity of the circuit pattern gradually recovers during the time until the transfer begins. In other words, if the hysteresis area of ​​the copper ink is large, unevenness (mesh marks) on the circuit pattern surface caused by the screen mesh are gradually alleviated and smoothed before the transfer begins. As a result, pressure is applied uniformly to the circuit pattern during transfer, reducing bleeding of the circuit pattern after transfer, improving linearity, and suppressing contact (short circuit) between adjacent circuit patterns. Considering these characteristics, the copper ink according to this embodiment has a hysteresis area of ​​3000 Pa·sec. -1 or more, 5000 Pa·sec -1 It is preferable that the viscosity is 10,000 Pa·sec or more. -1 It is even more preferable that the above is true.

[0020] On the other hand, if the hysteresis area is too large, the recovery of the viscosity of the copper ink until it is transferred to the substrate during screen offset printing is delayed, and the transfer may occur while the viscosity is still low. As a result, the copper ink wiring may overlap with each other, making it difficult to form fine wiring. Therefore, the hysteresis area of ​​the copper ink is, for example, 500,000 Pa·sec. -1 Preferably it is less than 450,000 Pa·sec, more preferably 450,000 Pa·sec -1 Below 350,000 Pa·sec, more preferably -1 The following is the result.

[0021] The hysteresis area is measured using a dynamic viscoelasticity measuring device (rheometer). In this embodiment, a rheometer (model number: MCR102) manufactured by Anton Paar is used as the dynamic viscoelasticity measuring device, with the measurement section temperature set to 25°C, the measuring jig set to PP (parallel plate) 25, and the gap set to 0.5 mm. Using dedicated software (RheoCompass ver. 1.20.471) provided with the dynamic viscoelasticity measuring device, the measurement mode was set to "flow curve measurement (rise-hold-fall)," and a shear rate profile for calculating the hysteresis area of ​​the copper ink was set. The profile was set to a shear rate of 0.01 sec. -1 From 300 seconds -1 It takes 50 seconds to rise to 300 seconds. -1 After holding for 50 seconds, -1 From 0.01 seconds -1 The temperature was set to drop to 0°C in 50 seconds. The hysteresis area was determined by the value automatically output by the above-mentioned software (RheoCompass ver. 1.20.471). The amount of copper ink used for the measurement was set to an amount that could fill the gap between the measurement jig and the device, similar to the above-mentioned TI, and any copper ink that spilled out of the measurement jig was wiped off before the measurement.

[0022] <Viscosity η156> Shear rate 156 sec -1 This roughly corresponds to the printing speed (squeegee speed) on the blanket using a screen mask in the Examples described later. If the viscosity of the copper ink during printing is low, for example, when a blanket made of polydimethylsiloxane (PDMS) is used as the blanket, the copper ink may sag during screen printing, making it difficult to form fine wiring.

[0023] Considering the above characteristics of the copper ink during printing, the viscosity η156 of the copper ink according to this embodiment is preferably 2.0 Pa·sec or more, more preferably 3.0 Pa·sec or more, and even more preferably 3.5 Pa·sec or more. On the other hand, if the viscosity of the copper ink during printing is high, it may be difficult to eject the ink cleanly from the screen, making it difficult to realize a fine wiring shape. In addition, the shear rate of 156 sec-1 There is also a problem that it is difficult to produce a copper ink having a viscosity η156 exceeding 15.0 at 15.0 Pa·sec. The viscosity η156 is preferably 15.0 Pa·sec or less, more preferably 13.0 Pa·sec or less, and even more preferably 12.0 Pa·sec or less.

[0024] In particular, copper inks that have little bleeding during printing and can improve the linearity of fine wiring patterns with an L / S of 20 μm / 20 μm or less require a viscosity η of 156 [Pa sec] and a hysteresis area [Pa sec -1 ] and Y satisfy the following relational expression (1): Y<43000X-85000 ... (1). -1 The viscosity η156 was measured using a rheometer (model: MCR102) manufactured by Anton Paar as a dynamic viscoelasticity measuring device, with the measuring section temperature set to 25°C, the measuring jig set to PP25, and the gap set to 0.5 mm. Using the dedicated software (RheoCompass ver. 1.20.471) attached to the dynamic viscoelasticity measuring device, the measurement mode was set to "flow curve measurement," and the shear rate was set to 156 sec. -1 The viscosity of the copper ink was measured in the same manner as in the above-mentioned TI, with the amount of copper ink used being an amount that could fill the gap between the measurement jig and the device, and the copper ink that spilled out of the measurement jig was wiped off before the measurement.

[0025] <Viscosity η1> Shear rate 1 sec -1 The viscosity η1 at shear rate 1 sec can be likened to the viscosity of copper ink in a stationary state. In particular, as a copper ink that can suppress bleeding when printing copper ink onto a substrate during circuit pattern creation and can create a highly reliable circuit pattern with few short circuits, it is preferable that the ink has a certain degree of viscosity in a stationary state. -1 The viscosity η1 at, for example, 10 sec -1 ~1000sec -1 It is preferable that the time is 20 seconds. -1 ~150 seconds -1 It is more preferable that:

[0026] (Copper Ink Composition) The copper ink according to this embodiment contains (a) copper particles, (b) a binder resin, (c) a solvent, and (d) an additive.

[0027] (a) Copper particles Copper particles contain copper (Cu) and are often composed mostly of copper. The copper content of the copper particles, excluding copper oxide, is, for example, 98% by mass or more, and typically 99.5% by mass or more. The copper content of the copper particles can be confirmed and measured by X-ray diffraction (XRD).

[0028] The average particle size D50 of the copper particles can be, for example, 0.01 μm to 5.00 μm, preferably 0.05 μm to 1.00 μm, and more preferably 0.10 μm to 0.80 μm. The copper particles may be composed of a mixture of two or three types of copper particles with different average particle sizes D50. For example, copper particles having an average particle size D50 of 0.01 μm to 5.00 μm, copper particles having an average particle size D50 of 0.05 μm to 1.00 μm, and copper particles having an average particle size D50 of 0.10 μm to 0.80 μm may be mixed to produce copper particles. The method for measuring the particle size D50 of copper particles will be described below.

[0029] The content of copper particles in the copper ink can be, for example, 60.0% by mass to 90.0% by mass, preferably 65.0% by mass to 85.0% by mass, and more preferably 70.0% by mass to 80.0% by mass.

[0030] (b) Binder Resin The binder resin is not particularly limited, but may include, for example, one or a mixture of two or more resins selected from the group consisting of copolymer polyester, polyester, ethyl cellulose, acrylic resin, and epoxy resin. In particular, the copper ink according to this embodiment preferably includes an acrylic resin.

[0031] Examples of acrylic resins include resins containing (meth)acrylate units, such as polymers or copolymers of acrylic monomers such as alkyl (meth)acrylic esters, (meth)acrylic acid, and (meth)acrylamide, as well as copolymers of the above acrylic monomers with monomers such as styrene and maleic anhydride.

[0032] Considering the various properties required for a copper ink capable of printing fine wiring with an L / S ratio of 20 μm / 20 μm or less on a substrate with high precision, the weight-average molecular weight Mw of the resin is preferably 5,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. Specifically, the weight-average molecular weight Mw of the resin is preferably 5,000 or more and 500,000 or less, more preferably 30,000 or more and 400,000 or less, and even more preferably 50,000 or more and 300,000 or less.

[0033] The content of the binder resin in the copper ink can be, for example, 1.0% by mass to 25.0% by mass, preferably 2.0% by mass to 22.0% by mass, and more preferably 5.0% by mass to 20.0% by mass.

[0034] When preparing the copper ink, the binder resin may be used in the form of a solution by mixing it with a solvent, which will be described later. Considering the properties required for a copper ink that can print fine wiring on a substrate with high precision and little bleeding, the solids ratio of the binder resin in the binder solution can be adjusted to between 20.0% by mass and 80.0% by mass, more preferably between 25.0% by mass and 75.0% by mass, and even more preferably between 30.0% by mass and 70.0% by mass.

[0035] Furthermore, the resin solids ratio of the binder resin to the copper particles in the copper ink [mass % vs Cu] is preferably 1.0 mass % to 15.0 mass %, more preferably 2.0 mass % to 10.0 mass %, and even more preferably 3.0 mass % to 8.0 mass %.

[0036] (c) Solvent The solvent mainly serves as a viscosity adjuster or diluent (solvent) to dissolve the binder resin and allow it to blend with the copper particles. The solvent is not particularly limited, but examples include terpenes such as terpineol and dihydroterpineol, ethers such as ethylene glycol butyl ether, diethylene glycol methyl ether, and diethylene glycol ethyl ether, and esters such as diethylene glycol monobutyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, ethyl lactate, butyl lactate, γ-butyrolactone, and propylene carbonate. These solvents can be used alone or in combination of two or more.

[0037] As described above, the solvent is contained in the binder resin so that the solids content of the binder resin is 20.0% by mass to 80.0% by mass. In addition, in the preparation of the copper ink, a solvent may be further added to the mixture of copper particles, binder resin, and additives as a solvent for dissolving and blending the copper particles, binder resin, and additives. The amount of solvent added together with the copper particles, binder resin, and additives when preparing the copper ink can be adjusted to, for example, a range of 0.5% by mass to 20.0% by mass depending on the desired properties of the copper ink.

[0038] (d) Additives Additives are substances added to improve the dispersibility or thixotropy of copper particles in the copper ink. Additives for improving dispersibility include, for example, polyether phosphate esters or mixtures of higher fatty acids and amines. Additives for improving thixotropy include, for example, polyolefins. The additives are diluted with the above-mentioned solvents as needed.

[0039] Considering the properties required of a copper ink that can print fine wiring on a substrate with high precision and little bleeding, the additive ratio to copper particles in the copper ink [mass % vs Cu] is preferably 10.0 mass % or less, more preferably 5.0 mass % or less, and even more preferably 3.0 mass % or less.

[0040] In addition to the materials described above, various additives may be added to improve the stability and printability of the ink. For example, a leveling agent, a viscosity modifier, a rheology control agent, an antifoaming agent, an anti-sagging agent, etc. Rheology control agents are used to control the rheology of the copper ink to prevent settling during storage of the copper ink, prevent sagging of printed matter, and improve ease of application.

[0041] (Method of Producing Copper Ink) Copper particles, a binder resin, a solvent, and an additive are prepared, mixed together, and then kneaded to produce copper ink.

[0042] The order in which the copper particles, binder resin, solvent, and additives are mixed together is not limited. For example, the additives may be mixed with the solvent, or in some cases, the additives may be mixed with the solvent beforehand, and then mixed with the copper particles and binder resin. The binder resin may be mixed with the solvent beforehand, and then mixed with the copper particles and additives. The copper particles used in the production of copper ink may be purchased or otherwise obtained. Alternatively, copper particles having predetermined properties may be prepared in advance by a liquid phase method such as a known chemical reduction method or disproportionation method.

[0043] According to this embodiment, by preparing appropriate copper particles, binder resin, solvent, and additives in appropriate ratios, bleeding when printing copper ink onto a substrate can be suppressed, thereby obtaining a copper ink that can produce highly reliable circuit patterns with few short circuits.

[0044] (Electronic Circuit Board and Method for Manufacturing Electronic Circuit Board) An electronic circuit board having a wiring layer formed using the copper ink according to this embodiment can be manufactured by a screen printing method, more preferably a screen offset printing method, using the copper ink. The method for manufacturing the electronic circuit board is not particularly limited. For example, when using screen offset printing as the method for manufacturing the electronic circuit board, a copper ink film is formed on a blanket using the copper ink. The copper ink film is then transferred from the blanket to a substrate. Furthermore, the copper ink film transferred to the substrate is fired to form a circuit on the substrate, thereby obtaining an electronic circuit board having a wiring layer using the copper ink according to this embodiment.

[0045] A polyimide substrate is preferred as the substrate. A blanket made of polydimethylsiloxane (PDMS) is preferred as the blanket. In a method for manufacturing an electronic circuit board using screen offset printing, for example, a screen mask is used in which a pattern plate made of Ni or the like on which a predetermined wiring pattern is formed is attached to a screen mesh. The number of meshes per inch of the screen mesh can be, for example, 400 to 900. The thickness of the screen mesh can be, for example, 15 μm to 42 μm.

[0046] Copper ink is placed on a screen mask, coated with a doctor blade, and then squeegeeed onto a blanket to form a copper ink film on the blanket. Urethane squeegee rubber or the like can be used as the squeegee. The squeegee speed is not limited to the following. To accurately print fine wiring with an L / S ratio of 20 μm / 20 μm or less, the speed is set to, for example, 5 mm / s to 50 mm / s. The squeegee pressure can be set to, for example, 0.5 mm to 3.0 mm, and the clearance can be set to, for example, 0.1 mm to 1.0 mm.

[0047] The copper ink film printed on the blanket is then transferred onto a substrate. The transfer conditions can be, for example, a transfer speed of 5 mm / s to 50 mm / s, a push-in amount of 50 μm to 400 μm, and a delay time of 0 sec to 60 sec. The copper ink film transferred onto the substrate is baked in an inert gas atmosphere at 200°C to 400°C for 10 to 60 minutes, thereby forming a circuit on the substrate. The delay time refers to the time from when a predetermined amount of copper ink (one cycle of copper ink) has been printed on the blanket until the transfer of the copper ink to the substrate begins.

[0048] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the present invention.

[0049] (Preparation of Copper Inks) Copper particles A to D, binder resins E to K, additives L to N, and solvents O to S were weighed into a 100 mL container so as to obtain the mixing ratios shown in Tables 1 and 2. This was stirred at 2000 rpm for 1 minute using a rotation / revolution mixer (Awatori Taro, ARE-310, manufactured by Thinky Corporation), and then degassed at 2000 rpm for 1 minute. The degassed mixture was passed through a three-roll mill (80E, manufactured by EXAT Co., Ltd.) for 10 passes at a roll gap of 5 μm and a roll rotation speed of 130 rpm, to obtain copper inks Nos. 1 to 19, 22 to 24, 26 to 27, 29, and 30.

[0050] (Copper particles) Average particle size D 50 Copper particles A and B having an average particle size of 0.18 μm and average particle size D 50 Copper particles C having an average particle size of 0.15 μm and copper particles D 50 Copper particles D having a particle size of 0.77 μm were prepared. The average particle size D50 of copper particles A to D was determined by measuring the particle size of each copper particle using a laser diffraction / scattering particle size distribution analyzer. The average particle size D50 refers to the particle size at which the cumulative volume-based frequency of each copper particle reaches 50% in the particle size histogram (particle size distribution graph) obtained, and was measured in accordance with JIS Z8825 (2013). Specifically, 1 g of copper slurry was added to 10 mL of 2-propanol and subjected to ultrasonic irradiation for 10 minutes (ultrasonic cleaner US-3KS, 120 W, 38 kHz, manufactured by SND Corporation). 5 mL of the resulting dispersion was mixed with 15 mL of an aqueous solution of hexasodium metaphosphate, and the mixture was subjected to ultrasonic irradiation for 20 minutes to obtain a dispersion for measurement. The aqueous solution of hexasodium metaphosphate was prepared by dissolving 10 g of hexasodium metaphosphate manufactured by Junsei Chemical Co., Ltd. in 5 L of water. The laser diffraction / scattering particle size distribution measuring device used for the measurement was a MASTERSIZER 3000 manufactured by Malvern, and the measurement was carried out at a temperature of 40° C., with a stirrer speed of 2000 rpm and while irradiating 12 W of 40 kHz ultrasonic waves.

[0051] (Binder Resin) The following binder resins were used as binder resins E to K. Binder resin E: ER2300 manufactured by Kusumoto Chemical Co., Ltd. (30.0 mass% acrylic resin, 70.0 mass% terpineol, weight average molecular weight 200,000) Binder resin F: ER2602 manufactured by Kusumoto Chemical Co., Ltd. (70.0 mass% acrylic resin, 30.0 mass% butyl carbitol acetate (BCA), weight average molecular weight 5,000) Binder resin G: KFA2000 manufactured by GOO Chemical Co., Ltd. (35.0 mass% acrylic resin, 65.0 mass% terpineol, weight average molecular weight 250,000) Binder resin H: S-LEC ASM-3010 manufactured by Sekisui Chemical Co., Ltd. (35.0 mass% acrylic resin, 65.0 mass% terpineol, weight average molecular weight 50,000) Binder resin I: S-LEC manufactured by Sekisui Chemical Co., Ltd. ASM-3010 (acrylic resin 48.0 mass%, terpineol 52.0 mass%, weight average molecular weight 50,000) Binder resin J: M4200 (acrylic resin 35.0 mass%, terpineol 65.0 mass%, weight average molecular weight 200,000) manufactured by Soken Chemical Co., Ltd. Binder resin K: M4210 (acrylic resin 30.0 mass%, dihydroterpineol 70.0 mass%, weight average molecular weight 20,000) manufactured by Soken Chemical Co., Ltd.

[0052] (Additives) The following dispersants or thixotropic agents were used as additives L to N. Dispersant L: ED-152 (polyether phosphate ester) manufactured by Kusumoto Chemicals Co., Ltd. Dispersant M: ED-120 (mixture of higher fatty acid and amine) manufactured by Kusumoto Chemicals Co., Ltd. Thixotropic agent N: ET4010 (polyolefin) manufactured by Kusumoto Chemicals Co., Ltd.

[0053] (Solvents) The following solvents were used as solvents O to S. Solvent O: terpineol (specific gravity 0.934, boiling point 213°C) Solvent P: γ-butyrolactone (specific gravity 1.13, boiling point 204°C) Solvent Q: ethylene glycol (specific gravity 1.11, boiling point 197°C) Solvent R: ethylene glycol monobutyl ether (specific gravity 0.902, boiling point 171°C) Solvent S: propylene carbonate (specific gravity 1.2, boiling point 240°C)

[0054] Tables 1 and 2 show the mixing ratios of copper particles A to D, binder resins E to K, additives L to N, and solvents O to S for copper inks No. 1 to 19, 22 to 24, 26 to 27, 29, and 30 used in the preparation of the copper inks. While the total of copper particles, binder resin, additives, and solvents equals 100%, some inks in Tables 1 and 2 do not total 100% due to rounding to the nearest tenth. In Tables 1 and 2, "Copper Particle Content" refers to the content (mass %) of copper particles in the prepared copper ink. "Resin Solids Ratio" refers to the ratio of the resin solids of the binder resin to the mass of copper particles in the copper ink (mass % vs. Cu). "Additive Ratio" refers to the ratio of additives to copper particles in the copper ink (mass % vs. Cu).

[0055]

[0056]

[0057] The evaluation results of the obtained copper inks Nos. 1 to 19, 22 to 24, 26 to 27, 29, and 30 are shown in Tables 3 and 4.

[0058]

[0059]

[0060] The measurement equipment and conditions for evaluating the copper ink were as follows. Conditions not specified were the same as those described above. Dynamic viscoelasticity measuring equipment: Rheometer (model: MCR102) manufactured by Anton Paar. Temperature of the measuring part of the equipment: 25°C. Measuring jig: PP25 (parallel plate). Gap: 0.5 mm.

[0061] <Measurement of Viscosity and Thixotropy Index> Using the dynamic viscoelasticity measuring device, the measurement mode was set to "flow curve measurement," and the viscosity and thixotropy index were measured at each shear rate [sec -1 In the flow curve measurement, the shear rate of the copper ink was 0.01 sec. -1 From 1000 seconds -1 The change in viscosity η was measured when the viscosity was changed to 1. An example of the flow curve for copper ink No. 1 is shown in Figure 2.

[0062] <Measurement of hysteresis area> Measurement is performed using a dynamic viscoelasticity measuring device (rheometer). In this embodiment, a rheometer (model number: MCR102) manufactured by Anton Paar is used as the dynamic viscoelasticity measuring device, with the measurement section temperature set to 25°C, the measuring jig set to PP (parallel plate) 25, and the gap set to 0.5 mm. Using dedicated software (RheoCompass ver. 1.20.471) provided with the dynamic viscoelasticity measuring device, the measurement mode was set to "flow curve measurement," and a shear rate profile for calculating the hysteresis area of ​​the copper ink was set. The profile was set to a shear rate of 0.01 sec. -1 From 300 seconds -1 It takes 50 seconds to rise to 300 seconds. -1 After holding for 50 seconds, -1 From 0.01 seconds -1 The temperature was set to decrease over 50 seconds to 100°C. Figure 1 shows an example of the hysteresis area of ​​copper ink No. 1.

[0063] <Evaluation of Defect Rates When Printing on PDMS Blankets or PI Substrates> Screen offset printing was performed using copper inks Nos. 1 to 19, 22 to 24, 26 to 27, 29, and 30, and the printability was confirmed. A commercially available printing device (manufactured by Mino Group Co., Ltd., model number SO-1010) was used.

[0064] The substrate used for printing was a PI substrate (Apical, polyimide substrate, manufactured by Kaneka Corporation), and the blanket was the aforementioned polydimethylsiloxane (PDMS) blanket roll (Fujikura Composites, Type: #700-STD). A 32 cm x 32 cm screen mask with a linear pattern formed on a 2 cm x 2 cm area with L / S of 20 μm / 20 μm, 15 μm / 15 μm, and 10 μm / 10 μm was used. A Ni pattern plate was used as the mask, and this was attached to a screen mesh by electroplating. The mesh count per inch was 500, the mesh material was stainless steel, the mesh wire diameter was 13 μm, and the total thickness was 31 μm. For screen offset printing, copper ink was placed on the screen, coated (filled) with a doctor blade, and then squeegeeed onto the blanket. The printing conditions were as described above.

[0065] The copper ink circuit patterns printed on the substrate were observed with an optical microscope, and images were obtained. Examples of the obtained images are shown in Figures 3 to 6. Five prints were performed using each copper ink, and images of arbitrary regions of each resulting wiring pattern were obtained. The percentage of straight lines in which adjacent straight lines were connected horizontally among the total number of straight lines present in the five obtained images was defined as the "defect rate," and the average defect rate was calculated. When printing onto the PDMS blanket, a defect rate of 5% or less was rated "Good," a defect rate of more than 5% was rated "Fair," and a defect rate of unprintable was rated "Poor." When printing onto the PI substrate, a defect rate of 7% or less was rated "Good," a defect rate of more than 7% was rated "Fair," and a defect rate of untransferable was rated "Poor." In this evaluation, "unprintable" refers to cases where printing onto the PDMS blanket using copper ink was not possible. "Untransferable" refers to both cases where printing onto the PDMS blanket was possible but printing from the PDMS blanket to the polyimide substrate was not possible, and cases where printing onto the PDMS blanket was not possible.

[0066] Figure 3 shows an image after printing on a blanket using copper ink No. 1 (Example) with a line / space ratio of 20 μm / 20 μm. Figure 4 shows an image after transferring from the blanket to a PI substrate using copper ink No. 1 (Example) with a line / space ratio of 20 μm / 20 μm. In both of the examples shown in Figures 3 and 4, there are no connections between adjacent straight lines. Therefore, the defect rate for both is 0%. Note that Figure 3 does not show short circuits between adjacent lines in the horizontal direction, but rather several breaks within the same line. However, these breaks are largely dependent on the ink printing conditions and are therefore excluded from the defect rate evaluation. Figure 5 shows a photograph after transferring to a blanket using copper ink No. 7 (Example) with a line / space ratio of 15 μm / 15 μm. In this example, it was confirmed that adjacent straight line patterns were connected horizontally in 20 of the 160 straight lines, resulting in a defect rate of (20 / 160) x 100 = 12.5%, and the evaluation was Fair. Figure 6 shows a photograph after printing on a PI substrate using copper ink No. 6 (comparative example) with an L / S ratio of 20 μm / 20 μm. In this example, printing was successful, so the evaluation was Fair, but because all lines were connected horizontally, the defect rate was 100%.

[0067] (Evaluation) <Relationship between TI (1 / 10) and hysteresis area> In Table 3, TI (1 / 10) is 7.5 or less, and the hysteresis area is 3000 Pa·sec. -1It can be seen that for the above-mentioned copper inks Nos. 1, 2, 3, 11, 14, 18, 5, 13, 16, 27, 10, 23, 24, 15, 26, 7, and 12 according to the examples, when creating a linear pattern with an L / S of 20 μm / 20 μm, the defect rate was kept below 5% for both the PDMS blanket and the PI substrate. For copper inks Nos. 29 and 30 according to the examples, the linear pattern transferred from the PDMS blanket to the PI substrate was evaluated when the L / S was 15 μm / 15 μm, without forming a linear pattern with an L / S of 20 μm / 20 μm. It can be seen that for copper inks Nos. 29 and 30, the defect rate for printing on the PI substrate was kept below 5% even when the L / S was 15 μm / 15 μm. From these results, it can be seen that copper ink Nos. When a wiring pattern with an L / S of 15 μm / 15 μm is printed on a PDMS blanket using copper inks Nos. 29 and 30, the defect rate is likely to be 5% or less. Figure 7 is a graph showing the relationship between TI and hysteresis area for copper inks Nos. 1 to 7, 9 to 19, 22 to 24, 26 to 27, 29, and 30. Note that copper ink No. 8 has a hysteresis area of ​​0 Pa·sec. -1 Therefore, they are not shown in Fig. 7. When the TI (1 / 10) and hysteresis area of ​​any of the copper inks satisfy the ranges of the copper ink according to this embodiment, a highly reliable circuit pattern with a low defect rate and few short circuits can be produced in the production of a linear pattern with an L / S of 20 µm / 20 µm.

[0068] <Relationship between viscosity η156 (X) and hysteresis area (Y)> Figure 8 shows the relationship between viscosity η156 (X) and hysteresis area (Y) at a shear rate of 156 sec. -18 is a graph showing the relationship between the viscosity η156 of copper ink and the hysteresis area in the copper ink of Example 1. The copper inks located to the left of the line Y=43000X-85000 shown in FIG. 8 do not satisfy the above-mentioned relational expression (1). As can be seen from FIG. 8, copper ink No. 27 is an example copper ink, but does not satisfy relational expression (1). Copper inks No. 14 and No. 26 have TI (1 / 10) values ​​relatively close to the TI (1 / 10) of copper ink No. 27. Of these, copper ink No. 14 has the hysteresis area closest to that of copper ink No. 27. Therefore, when viewed from the perspectives of TI (1 / 10) and hysteresis area, copper ink No. 27 and copper ink No. 14 can be said to be somewhat similar. However, copper ink No. 27 does not satisfy relational expression (1). Copper ink No. 14 had superior transferability to the PI substrate compared to copper ink No. 27, which did not satisfy relational expression (1).

Claims

1. A copper ink containing copper particles, -1 Viscosity η1 at shear rate of 10 sec -1 The thixotropy index TI (1 / 10) defined as the ratio of viscosity η10 at η10 (η1 / η10) is 7.5 or less, and the shear rate is 0.01 sec -1 From 300 seconds -1 It takes 50 seconds to rise to 300 seconds. -1 After holding for 50 seconds, -1 From 0.01 seconds -1 The hysteresis area of ​​the shear stress measured by dynamic viscoelasticity measurement when the shear stress was lowered to 3000 Pa·sec in 50 seconds -1 That's it, copper ink.

2. Shear rate 156 sec -1 The viscosity η156 [Pa·sec] is 2.0 Pa·sec or more, and X represented by the viscosity η156 and the hysteresis area [Pa·sec -1 2. The copper ink according to claim 1, wherein X represents a number of atoms and Y represents a number of atoms, and Y represents a number of atoms and Y represents a number of atoms, and Y represents a number of atoms and Y represents a number of atoms, and Y represents a number of atoms and Y represents a number of atoms, and 3. The copper ink according to claim 1, wherein the thixotropy index TI(1 / 10) is 1.5 or more.

4. The copper ink according to claim 2, wherein the viscosity η156 is 15.0 Pa·sec or less.

5. The hysteresis area is 500,000 Pa·sec -1 2. The copper ink of claim 1, wherein:

6. The copper ink according to claim 1, which is a copper ink used in screen offset printing.

7. The copper ink according to claim 6, which is a copper ink for printing using a blanket made of polydimethylsiloxane.

8. The copper ink according to claim 7, which is a copper ink for printing on a polyimide substrate.

9. The copper ink according to any one of claims 1 to 8, comprising the copper particles, a binder resin, a solvent, and an additive.

10. The copper ink according to claim 9, wherein the copper particles have an average particle size (D50) of 0.01 μm to 5.00 μm.

11. The copper ink according to claim 9, wherein the binder resin comprises at least one selected from the group consisting of copolymer polyester, polyester, ethyl cellulose, acrylic resin, and epoxy resin.

12. The copper ink of claim 9, wherein the solvent comprises at least one selected from the group consisting of terpenes, ethers, and esters.

13. The copper ink according to claim 9, wherein the resin solids ratio of the binder resin to the copper particles is 1.0% by mass to 15.0% by mass.

14. An electronic circuit board comprising a wiring layer using the copper ink according to any one of claims 1 to 8.

15. A method for manufacturing an electronic circuit board, comprising: forming a copper ink film on a blanket by screen printing using the copper ink according to any one of claims 1 to 8; transferring the copper ink film from the blanket onto a substrate; and firing the copper ink film transferred onto the substrate to form a circuit on the substrate.

Images