Method for manufacturing a resistor

Abstract

To provide a resistive element that does not contain a lead component and is capable of suppressing a temperature coefficient.SOLUTION: The resistive element has a pair of electrodes and a resistive film arranged between the pair of electrodes. The resistive film has an insulating material, conducting particles, and coated particles having an iridium oxide film arranged on the surface of insulating particles. The conducting particles and the coated particles are arranged inside the insulating material. The total volume fraction of the conductive particles and the coated particles in the resistive film is 15% or more and 60% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resistor and a method for manufacturing the resistor.

Background Art

[0002] Conventionally, as methods for forming a resistor of an electronic component, a thick film method using a resistor paste and a thin film method of forming a film by sputtering or the like using a film forming material are well known.

[0003] The thick film method forms a resistor by printing and firing a resistor paste on a ceramic substrate. Since the equipment is inexpensive and the productivity is high, it is widely used in the manufacture of resistors such as chip resistors and hybrid ICs.

[0004] The resistor paste used in the thick film method is substantially composed of conductive particles, glass frit, and an organic vehicle for making them into a paste suitable for printing. As the conductive particles, ruthenium dioxide (RuO2) and pyrochlore-type ruthenium-based oxides (Pb2Ru2O 7-x , Bi2Ru2O7) are generally used. According to Patent Document 1, by using an Ru-based oxide as the conductive particles, a ceramic resistor element having a TCR of about 0.01% or less per 1 ° C can be provided for a resistance region ranging from a value lower than 100 ohms per square to a value exceeding 180,000 ohms per square.

[0005] Further, Patent Document 2 discloses adding a glass corresponding to glass frit as an inorganic binder, and discloses using a glass containing a large amount of lead such as lead silicate glass or lead borosilicate glass as the glass.

[0006] The reason why lead borosilicate-based glass is used for the glass frit is that it has good wettability with the Ru-based oxide, the values of the thermal expansion coefficient are close to those of the substrate, and the viscosity during firing is suitable. (Non-Patent Document 1) However, in recent years, due to the requirement to eliminate the use of toxic lead from electronic devices, lead-free conductive powders that replace lead oxide powder as the conductive powder for thick film resistors in the high-resistance region are desired. Further, in order to completely eliminate lead from the thick film resistor, it is necessary to also eliminate lead from the glass frit used simultaneously. However, even in a state where all lead has been eliminated from the resist paste, it is required to obtain a good resistor with respect to electrical characteristics such as the temperature coefficient of resistance.

[0007] In Patent Document 3, it has been proposed to use iridium oxide (IrO2) as the conductive material. A paste for forming a thick film resistor using iridium oxide powder as the conductive powder is particularly useful as a paste for forming a thick film resistor in the high-resistance region that does not contain lead and replaces lead oxide powder. However, iridium is a precious metal and its price is more than ten times higher than that of ruthenium. In particular, when applied to general-purpose resistance components, there is a problem in terms of cost for replacement from conventional conductive materials.

[0008] Manufacturing a lead-free resistor using thin film resistors instead of thick film resistors has also been considered. Although single layer films of Ni or Cr and alloy films of Ni-Cr have been put into practical use, since the metal films have low resistance, high-resistance resistors cannot be fabricated.

[0009] Patent Document 4 describes a thin film resistor characterized by being composed of two or more thin films of metals having different magnitudes of temperature coefficients of resistance in a bulk form, each thin film having positive and negative temperature coefficients of resistance, and having a predetermined resistance value and a small temperature coefficient of resistance by controlling the film thickness of each thin film and the ratio of each film thickness.

[0010] However, a resistor using a metal thin film as described above has a problem that a paste material cannot be used because the metal thin film is formed on a substrate.

[0011] As shown in Non-Patent Document 2 and Patent Document 5, the development of conductive adhesives and resin resistors using resins and conductive fillers has also been advanced, but it has been difficult to obtain resistors with low temperature coefficients of resistance.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0014] In view of the problems of the above prior art, one aspect of the present invention aims to provide a resistor that does not contain a lead component and can suppress the temperature coefficient of resistance.

Means for Solving the Problems

[0015] To solve the above problems, the present invention provides a pair of electrodes, and a resistor film disposed between the pair of electrodes. The resistance film has an insulating material, conductive particles, and coated particles in which an iridium oxide film is disposed on the surface of insulating particles, and the conductive particles and the coated particles are disposed in the insulating material. Provided is a resistor in which the total volume ratio of the conductive particles and the coated particles in the resistance film is 15% or more and 60% or less.

Effects of the Invention

[0016] According to one aspect of the present invention, it is possible to provide a resistor that does not contain a lead component and can suppress the resistance temperature coefficient.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] Hereinafter, the resistor and the method for manufacturing the resistor of the present invention will be described. [Resistor] FIG. 1 shows an explanatory diagram of the resistor of the present embodiment. FIG. 1 schematically shows a cross-sectional view of the resistor 10 in a plane parallel to the direction in which a pair of electrodes 111 and a resistance film 112 described below are arranged. In FIG. 1, for convenience of explanation, the conductive particles and the coated particles are shown larger than actual.

[0019] As shown in FIG. 1, the resistor 10 of the present embodiment can have a pair of electrodes 111 and a resistance film 112 disposed between the pair of electrodes 111.

[0020] The resistance film 112 can have an insulating material 12, conductive particles 13, and coated particles 14 in which an iridium oxide film 142 is disposed on the surface of insulating particles 141.

[0021] The conductive particles 13 and the coated particles 14 are arranged in the insulating material 12 as shown in FIG. 1.

[0022] And the total volume ratio of the conductive particles 13 and the coated particles 14 in the resistance film 112 can be 15% or more and 60% or less.

[0023] The inventor of the present invention studied a resistor that does not contain a lead component and can suppress the temperature coefficient of resistance. Then, paying attention to the fact that the conductive particles have a positive temperature coefficient of resistance and the thin film has a negative temperature coefficient of resistance, it was found that a resistor with a suppressed temperature coefficient of resistance can be formed by using the conductive particles and the coated particles that form the thin film, and the present invention was completed.

[0024] Each member of the resistor of the present invention will be described. (1) Conductive particles As will be described later, the resistor of this embodiment can be formed, for example, by applying a paste containing an insulating material 12, conductive particles 13, and coated particles 14 between electrodes 111 and drying and firing. Therefore, the conductive particles 13 are preferably made of a material whose resistance does not change due to annealing when the paste is heat-cured, and are preferably one or more materials selected from noble metals such as Au (gold) and Ag (silver), and RuO2 (ruthenium oxide), IrO2 (iridium oxide), etc.

[0025] The shape of the conductive particles 13 is not particularly limited, and can have, for example, one or more shapes selected from spherical, flake-like, etc. Also, the average particle size of the conductive particles 13 is not particularly limited, but is preferably, for example, 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 2 μm or less. In this specification, the average particle size means the particle size at 50% of the integrated value in the particle size distribution obtained by the laser diffraction / scattering method.

[0026] The manufacturing method of the conductive particles 13 is not particularly limited, and depending on the type of material used and the like, they can be manufactured by various manufacturing methods. When manufacturing ruthenium oxide particles as the conductive particles 13, for example, by neutralizing, washing, and drying an aqueous solution of ruthenium chloride with KOH (potassium hydroxide), hydrated ruthenium oxide particles can be obtained. Further, for example, by performing heat treatment at a temperature exceeding 400°C, for example, 600°C or higher and 850°C or lower, in an oxidizing atmosphere, the crystal water can be removed to obtain ruthenium oxide powder. Note that the oxidizing atmosphere is an atmosphere containing 10% by volume or more of oxygen, and for example, air or the like can be preferably used. (2) Coated particles (2-1) Insulating particles The insulating particles 141 are not particularly limited, but for example, particles containing oxides of one or more elements selected from Si (silicon), Ta (tantalum), Zr (zirconium), Nb (niobium), and Al (aluminum) can be preferably used. As the insulating particles, particles containing one or more selected from SiO2, Ta2O5, ZrO2, Nb2O5, Al2O3, etc. can be more preferably used.

[0027] Among them, SiO2 is a high resistor and can easily manufacture particles with suppressed variations in shape and particle size, so it can be particularly preferably used as the material of the insulating particles.

[0028] The average particle size of the insulating particles 141 is not particularly limited, but for example, 2 μm or more and 5 μm or less is preferable, and 2.5 μm or more and 3 μm or less is more preferable. (2-2) Iridium oxide film The coated particles 14 can have an iridium oxide (IrO2) film on the surface of the above insulating particles. The film thickness of the iridium oxide film is not particularly limited, but for example, it is preferably 1 nm or more and 100 nm or less, and more preferably 4 nm or more and 80 nm or less.

[0029] When measuring the film thickness of the iridium oxide film, first embed the coated particles in a resin or the like so that the cross-section of the particles can be observed by cross-section polisher processing or the like. Then, in the coated particles in the resin, measure the distance between two points where the distance between the outer circumference and the inner circumference of the iridium oxide film is the shortest at three or more arbitrary positions, and obtain the average thickness of the iridium oxide film for each particle.

[0030] Similarly, by averaging the average thickness of the iridium oxide film for each particle obtained for 10 or more coated particles, the thickness of the iridium oxide film in the coated particles of the resistor can be obtained. (2-3) Regarding the content of the coated particles The mixing ratio of the conductive particles 13 and the coated particles 14 contained in the resistive film 112 is not particularly limited, and can be arbitrarily selected according to, for example, the resistance value required for the resistor 10, the degree of the resistance temperature coefficient, etc. Further, it can be selected according to the particle size of the conductive particles 13 used, the film thickness of the iridium oxide film of the coated particles 14, and the like.

[0031] In the resistor 10 of the present embodiment, it is preferable that the resistance temperature coefficient is suppressed. For this reason, it is preferable to select the mixing ratio of the conductive particles 13 and the coated particles 14 so that their resistance values are about the same. As described above, the conductive particles 13 have a positive resistance temperature coefficient, and the iridium oxide film of the coated particles 14 has a negative resistance temperature coefficient. Therefore, by mixing the conductive particles 13 and the coated particles 14 so that their resistance values are about the same, the resistance temperature coefficient of the entire resistor 10 can be made close to 0. Note that the resistance values of the conductive particles 13 and the coated particles 14 being about the same does not mean that they have exactly the same value, but means adjusting the resistance values of both particles to such an extent that the resistance temperature coefficient allowed for the resistor is obtained.

[0032] As the conductive particles 13 in the resistive film 112, ruthenium oxide particles with an average particle size of 0.5 μm or more and 2 μm or less are used. When the average particle size of the insulating particles is 2 μm or more and 5 μm or less, and the film thickness of the iridium oxide film is 4 nm or more and 80 nm or less, it is preferable that the volume ratio of the conductive particles to the coated particles is 70:30 or more and 50:50 or less. That is, when the total of the conductive particles 13 and the coated particles 14 is 100% by volume, in the case of the above conditions, the ratio of the conductive particles 13 by volume is preferably 50% by volume or more and 70% by volume or less. (2-4) Mixing ratio of conductive particles and coated particles in the resistive film In the resistor of this embodiment, in the resistive film 112 disposed between the pair of electrodes 111, current is generated through the conductive particles 13 and the coated particles 14, and electricity can flow between the pair of electrodes 111.

[0033] Specifically, for example, as shown in FIG. 1, by arranging the conductive particles 13 and the coated particles 14 in series between the electrodes 111, current can flow along the dotted line A through the conductive particles 13 and the coated particles 14. Therefore, in order to allow current to flow between the electrodes 111 of the resistor 10, it is preferable to contain a certain amount or more of the conductive particles 13 and the coated particles 14 in the insulating material 12. Such a content varies depending on the size of the conductive particles 13 and the coated particles 14, etc. For example, the total volume ratio of the conductive particles 13 and the coated particles 14 in the resistive film 112 is preferably 15% or more, and more preferably 20% or more.

[0034] However, if the ratio of the conductive particles 13 and the coated particles 14 in the resistive film 112 becomes excessively high, there is a risk that the resistive film 112 may not be able to maintain its film shape, or the strength may decrease. Also, the fluidity of the resistive film paste used to form the resistive film 112 may decrease, and there is a risk that a uniform resistive film 112 cannot be formed during coating and drying.

[0035] Therefore, the total volume ratio of the conductive particles 13 and the coated particles 14 in the resistive film 112 is preferably 60% or less, and more preferably 50% or less. (3) Insulating material The insulating material 12 may be any insulating material that contains the aforementioned conductive particles 13 and coating particles 14 and can form the resistive film 112, and is not particularly limited.

[0036] The insulating material 12 can contain a resin, and examples of the resin include one or more selected from thermosetting resins and thermoplastic resins. Further, the insulating material 12 can contain a curing agent as needed.

[0037] As the thermosetting resin, one or more selected from epoxy resins, polyimide resins, phenol resins, bismaleimide resins, etc. can be preferably used.

[0038] Also, as the thermoplastic resin, one or more selected from polyester resins, polyurethane resins, acrylic resins, etc. can be preferably used.

[0039] As the resin of the insulating material 12, an epoxy resin can be more preferably used because it is particularly well-balanced in terms of heat resistance, moisture resistance, electrical properties, curability, etc. As the epoxy resin, those having a number of epoxy groups greater than 1 in one molecule can be preferably used. Examples of the epoxy resin include polyglycidyl ethers obtained by reacting polyhydric phenols such as bisphenol A, bisphenol AD, bisphenol F, catechol, resorcin, or polyhydric alcohols such as glycerin and polyethylene glycol with epichlorohydrin, glycidyl ether esters obtained by reacting hydroxycarboxylic acids such as P-hydroxybenzoic acid and β-hydroxynaphthoic acid with epichlorohydrin, polyglycidyl esters obtained from polycarboxylic acids such as phthalic acid and terephthalic acid, and further novolac-type epoxies and epoxidized polyolefins.

[0040] In addition, the resistance film 112 is formed by adding a diluent or the like in addition to the material constituting the resistance film 112 to make a paste for forming the resistance film, and then applying, drying, and firing the paste between a pair of electrodes 111. Therefore, the resistance film 112 may contain inevitable components due to a diluent or the like in addition to the above-described insulating material 12, conductive particles 13, and coating particles 14. (4) Electrode The material of the pair of electrodes 111 is not particularly limited, and various electrodes used for resistors can be used. Note that the resistor 10 of the present embodiment can be formed on various insulating substrates.

[0041] It is preferable that each member of the resistor of the present embodiment described above does not contain lead. Not containing lead here means that it is not intentionally added, and cases where it is included as an inevitable component are not excluded.

[0042] According to the resistor of the present embodiment described above, the resistance film 112 includes conductive particles 13 having a positive temperature coefficient of resistance and coating particles 14 having a negative temperature coefficient of resistance. Therefore, by adjusting the mixing ratio and the addition amount of the conductive particles 13 and the coating particles 14, the resistance value of the resistor 10 can be easily controlled, and the temperature coefficient of resistance can be suppressed. Therefore, even without using a material containing a lead component, a resistor having a desired resistance value and a suppressed temperature coefficient of resistance can be obtained. [Manufacturing Method of Resistor] The manufacturing method of the resistor of the present embodiment will be described. According to the manufacturing method of the resistor of the present embodiment, the above-described resistor can be manufactured. Therefore, descriptions of matters already described will be omitted.

[0043] The manufacturing method of the resistor of the present embodiment can include the following coating particle forming step, paste preparing step, and resistance film forming step.

[0044] Hereinafter, each step will be described. (1) Coating Particle Forming Step The coated particle forming step can form an iridium oxide film on the surface of insulating particles to form coated particles. That is, in the coated particle forming step, the aforementioned coated particles can be formed.

[0045] In the coated particle forming step, the method for forming an iridium oxide film on the surface of insulating particles is not particularly limited.

[0046] Examples of the method for forming an iridium oxide film on the insulating particles 141 include one or more selected from vapor phase methods such as sputtering method, vapor deposition method, and CVD method, and wet methods such as sol-gel method. Since the insulating particles 141 have a three-dimensional shape, as the method for forming the iridium oxide film, one or more selected from barrel sputtering method, CVD method, and sol-gel method are preferable, and the polygonal barrel sputtering method is more preferable. That is, in the coated particle forming step, it is more preferable to form an iridium oxide film on the surface of insulating particles by the polygonal barrel sputtering method.

[0047] The polygonal barrel sputtering method can be carried out, for example, using the sputtering apparatus 20 shown in FIG. 2. Note that FIG. 2 is a side view of the sputtering apparatus capable of carrying out the polygonal barrel sputtering method, seen along the rotation axis of the polygonal container 21. The sputtering apparatus 20 can include a polygonal container (barrel) 21, a cathode 22, and a target 23. Further, in order to control the atmosphere during sputtering, a chamber 24 can be included. The inside of the chamber 24 can be evacuated, for example, and a gas such as argon can be introduced.

[0048] The polygonal container 21 is configured to be rotatable and swingable along the double-arrow B about the rotation axis C in the figure. Note that the cathode 22 and the target 23 are configured not to rotate. For this reason, insulating particles (not shown) accommodated in the polygonal container 21 move as the polygonal container 21 rotates and swings. However, when the rotation angle of the polygonal container 21 exceeds a certain angle, the insulating particles come off the inner peripheral surface of the polygonal container 21 and fall. At that time, the insulating particles rotate, and the surface facing the target 23 changes.

[0049] Thus, according to the multi-sided barrel sputtering method, insulating particles are accommodated in the polygonal container 21, and the polygonal container 21 is rotated and swung, so that sputtering film formation can be performed while changing the surface of the insulating particles facing the target 23. Therefore, a uniform film can be formed on the surface of the insulating particles.

[0050] For substances such as iridium oxide that undergo volume expansion when oxidized from the metallic state, when a metal film is formed and then oxidized, the film is likely to peel off from the insulating particles. For this reason, when forming an iridium oxide film by the multi-sided barrel sputtering method or the like as described above, it is preferable to use a Ru metal target as the target and mix oxygen into the sputtering gas to perform film formation. By mixing oxygen into the sputtering gas, an iridium oxide film can be directly formed on the surface of the insulating particles. The content ratio of oxygen in the sputtering gas is not particularly limited, but is preferably, for example, 5 vol% or more and 20 vol% or less.

[0051] Although it is also conceivable to use an iridium oxide target as the target, iridium oxide has sublimability, so it is difficult to sinter and difficult to manufacture the target. On the other hand, a target of iridium, which is a metal, can be manufactured by, for example, a melting method by plasma melting. In addition, a target of metallic iridium can also be manufactured by a hot press method, hot isostatic pressing (HIP), or the like using metallic iridium powder as a raw material. (2) Paste preparation step The paste preparation process can prepare a paste for a resist film by mixing an insulating material, conductive particles, and coating particles.

[0052] Since the insulating material, conductive particles, and coating particles have already been described, the description is omitted here.

[0053] When preparing the paste for the resist film in the paste preparation process, a curing agent and / or a diluent can be added as necessary to make it into a paste state.

[0054] The curing agent and diluent can be selected according to the type of resin of the insulating material used, etc.

[0055] For example, when an epoxy resin is selected as the resin of the insulating material, a curing agent that can cause a rapid curing reaction with the epoxy resin during heating (for example, 60°C or higher and 300°C or lower) and has long-term storage stability at room temperature or lower can be preferably used.

[0056] When the resin of the insulating material is an epoxy resin, examples of the curing agent include polyhydric phenols such as resorcin, catechol, hydroquinone, and pyrogallol; imidazoles such as 2-ethyl-4-methylimidazole, 2-phenol-4,5-dihydroxymethylimidazole, and 2-heptadecylimidazole; acid anhydrides such as dicyandiamide, tetrahydrophthalic anhydride, and tetrahydromethylphthalic anhydride; complexes of Lewis acids; and urea salts such as DCMU. These compounds can be used alone or in combination of two or more. And the addition amount of the curing agent only needs to be an amount that can cause a curing reaction with the epoxy resin without excess or deficiency when the insulating material is an epoxy resin.

[0057] The diluent is a component for adjusting the viscosity etc. of the paste for the resist film, and after the resist film is formed, it will evaporate and be removed. Therefore, the diluent is not particularly limited, and examples thereof include monoepoxy compounds such as dimethylhexyl glycidyl ether, diethylhexyl glycidyl ether, and dipropylhexyl glycidyl ether, high-boiling paraffin, aromatic hydrocarbons, cellosolve acetate, carbonyl acetate (diethylene glycol monoethyl ether), alcohols such as diethylene glycol, 1,3-propanediol, etc. It is desirable that it has compatibility with the epoxy resin and has an epoxy equivalent of 100 to 250. This value of the epoxy equivalent is a preferable value in order to react with the curing agent without excess or deficiency in a short time and maintain the strength of the obtained cured product. If the epoxy equivalent is less than 100, the reactivity is poor and the heat resistance of the cured product may not be expected. On the other hand, if it exceeds 250, the viscosity due to the increase in molecular weight becomes high, and there is a risk of a decrease in dilution efficiency and an increase in curing time.

[0058] The method of mixing the materials in the paste preparation process is not particularly limited, and for example, various mixers can be used. However, when mixing and dispersing with a device having a large grinding force such as a three-roll mill, the iridium oxide film of the coating particles may crack, so it is preferable not to use a device with a strong grinding force. (2-1) Regarding the mixing ratio of each component The ratio of each component in the paste for the resist film is not particularly limited and can be selected according to the materials used, the required properties, etc.

[0059] Here, let the volume ratio of the conductive particles in the paste for the resist film be A1, the volume ratio of the coating particles be A2, the volume ratio of the resin among the insulating materials be B, the volume ratio of the diluent be C, and the curing agent be D.

[0060] Here, the case where an epoxy resin is used as the resin among the insulating materials will be described as an example.

[0061] In this case, it is preferable that (A1 + A2) / (B + D) satisfies 60 / 40 or more and 15 / 85 or less.

[0062] That is, among the insulating material, conductive particles, and coating particles contained in the paste for resistive film, the total volume ratio of the conductive particles and the coating particles is preferably 15% or more and 60% or less, and more preferably 20% or more and 50% or less. Note that the above-mentioned insulating material means the resin and curing agent contained in the insulating material.

[0063] By setting the above ratio to 15% or more, the amounts of the conductive particles and the coating particles in the resistive film are sufficient, and the conductive particles and the coating particles are continuously connected, that is, percolated, and the electrodes can be electrically connected.

[0064] Also, by setting the above ratio to 60% or less, the fluidity of the paste for resistive film is increased, and a particularly uniform resistive film can be formed during coating and drying.

[0065] Moreover, (A1 + A2 + B + D) / C is preferably 90 / 10 or more and 50 / 50 or less. That is, the volume ratio of the diluent in the paste for resistive film is preferably 10% or more and 50% or less, and more preferably 15% or more and 35% or less.

[0066] By setting the volume ratio of the diluent in the paste for resistive film to 10% or more, the viscosity of the paste for resistive film can be suppressed and the coatability can be improved. Also, by setting the volume ratio of the diluent in the paste for resistive film to 50% or less, the shrinkage of the paste for resistive film after coating can be suppressed, and a particularly uniform resistive film can be formed.

[0067] The paste for resistive film may contain inevitable impurities, but among the impurity ion concentrations, the hydrolyzable chlorine ions are preferably 100 ppm or less, and the metal ions such as alkali are preferably 50 ppm or less. By setting the impurity ion concentration within the above range, bleeding of the paste during bonding of electronic components can be prevented, and characteristics such as adhesive strength, heat resistance, moisture resistance, heat cycle resistance, conductivity, and workability can be particularly enhanced.

[0068] In addition to the above-described components, the paste for the resistive film may contain a curing accelerator such as blocked isocyanate, a silane coupling agent or a titanate coupling agent for improving the bonding strength, and a colorant such as a pigment or a dye, if necessary. (3) Resistive film forming step In the resistive film forming step, a resistive film can be formed by applying a paste for the resistive film between a pair of electrodes.

[0069] Specifically, a resistor can be formed by applying a paste for the resistive film between a pair of electrodes previously formed on an insulating substrate, followed by drying and heat treatment.

[0070] The coating conditions at this time are not particularly limited and can be selected according to the composition of the paste for the resistive film and the characteristics required for the resistor.

[0071] Also, the conditions for drying and heat treatment are not particularly limited, and the drying and heat treatment conditions can be selected according to each component contained in the paste for the resistive film. The drying and curing temperature is preferably not less than the boiling point of the diluent, for example, preferably not less than 80°C and not more than 200°C. For example, the temperature can be raised from room temperature to the curing temperature (120°C to 250°C) at a rate of 12°C / min, held at a constant temperature for 20 minutes or more and 2 hours or less at the curing temperature for curing, and then taken out of the furnace and allowed to cool naturally.

Examples

[0072] Specific examples, comparative examples, etc. will be given below for explanation, but the present invention is not limited to these examples. (Evaluation method) The evaluation method of the resistors produced in the following examples and comparative examples will be described. (1) Resistance value measurement For the film thickness, the film thickness was measured for 5 resistors produced under the same conditions in each example and comparative example using a stylus thickness roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., model number: Surfcom 480B), and the calculated value was averaged.

[0073] For the five manufactured resistors, the resistance values were measured using a digital multimeter (manufactured by KEITHLEY, model number 2001), and the obtained resistance values were converted to the case where the thickness of the resistor was 50 μm. Then, the average of the resistance values of the five converted thick-film resistors was taken as the resistance value of the thick-film resistor. (2) Temperature Coefficient of Resistance The temperature coefficient of resistance was calculated by the following procedure.

[0074] In the following examples and comparative examples, five resistors with a width of 1 mm and a length of 10 mm were fabricated under the same conditions. Each resistor was held at -55 °C, 25 °C, and 125 °C for 15 minutes each, and then the resistance value was measured. The resistance values of each thick-film resistor at each temperature are R -55 , R 25 , R 125 . For example, R -55 means the resistance value at -55 °C.

[0075] Next, for each thick-film resistor, the low-temperature side temperature coefficient of resistance COLD-TCR and the high-temperature side temperature coefficient of resistance HOT-TCR were calculated by the following formulas (A) and (B), and the average of the five resistors was taken as the temperature coefficient of resistance (COLD-TCR, HOT-TCR) of the thick-film resistor in each example and comparative example. COLD-TCR (ppm / °C) = (R -55 - R 25 ) / R 25 / (-80) × 10 6 ···(A) HOT-TCR (ppm / °C) = (R 125 - R 25 ) / R 25 / (100) × 10 6 ···(B) Note that it is desirable that the temperature coefficient of resistance be close to 0, and a resistance temperature coefficient of -100 ppm / °C ≤ resistance temperature coefficient ≤ 100 ppm / °C is regarded as a standard for an excellent resistor. (Manufacturing Conditions) [Example 1] (Coated Particle Formation Step) As insulating particles, spherical silica with an average particle diameter of 3 μm (manufactured by AGC Si-Tech Co., Ltd., model number: NP-30) was prepared.

[0076] The spherical silica was placed in a sputtering apparatus 20 using the polygonal barrel sputtering method shown in FIG. 2, and the barrel rotation speed was set to 0.1 rpm. That is, the rotation axis C was rotated 120 degrees around the center of rotation in 200 seconds. The degree of vacuum in the chamber 24 before sputtering was 2×10 -4 Pa. As the sputtering gas, an Ar:O2 mixed gas was used, and the flow rate ratio was Ar:O2 = 9:1.

[0077] Then, an iridium oxide film was formed on the surface of the insulating particles to an average thickness of 4 nm. When evaluated, it was confirmed that the thickness of the iridium oxide film of the obtained coated particles was 4 nm.

[0078] When measuring the thickness of the iridium oxide film, first, the coated particles were embedded in resin, and the cross-section of the particles was made observable by cross-section polisher processing. Then, in the coated particles in the resin, at three arbitrary positions, the distance between two points where the distance between the outer circumference and the inner circumference of the iridium oxide film is the shortest was measured, and the average thickness of the iridium oxide film for each particle was obtained.

[0079] The average thickness of the iridium oxide film for each particle obtained for 10 coated particles in the same manner was averaged to obtain the thickness of the iridium oxide film in the coated particles. (Paste preparation process) Ruthenium oxide particles with an average particle size of 0.8 μm, which are conductive particles, and the above-mentioned coated particles were mixed so that the volume ratio was 70:30 and placed in a container.

[0080] In addition, an insulating material was prepared by adding 40 parts by mass of a phenol novolac curing agent and 1 part by mass of imidazole IBMZ-OK (trade name; manufactured by Shikoku Kasei Co., Ltd.) as a latent curing accelerator to 100 parts by mass of an epoxy resin (bisphenol A).

[0081] The insulating material was placed in the container such that the volume ratio of the ruthenium oxide particles and the coated particles to the insulating material was 1:1. Further, 2-ethylhexyl glycidyl ether was placed in the container at a ratio of 20 parts by mass with respect to 100 parts by mass of the insulating material as a diluent.

[0082] The materials placed in the container were degassed under vacuum using a rotary-revolution mixer (Shinke Vacuum LED type ARV-310LED), and then stirred and mixed at 1200 rpm for 10 minutes to form a paste. (Resistance film formation step) The paste for the resistance film obtained in the paste preparation step was applied onto an alumina substrate on which a pair of electrodes had been previously formed through a mask, left standing at room temperature for 30 minutes, and then heated and cured in an electric oven at 150 °C for 30 minutes.

[0083] As a result, a resistance film having a width of 1 mm, a length of 10 mm, and an average film thickness of 50 μm was formed between the pair of electrodes. The electrodes were formed using an Ag paste.

[0084] The obtained resistor was evaluated for its resistance value and temperature coefficient of resistance. The evaluation results are shown in Table 1. [Example 2] In the paste preparation step, a resistor paste and a resistor were produced and evaluated in the same manner as in Example 1, except that the mixing ratio of the ruthenium oxide particles and the coated particles was changed to a volume ratio of 80:20.

[0085] The evaluation results are shown in Table 1. [Comparative Example 1] A resistor paste and a resistor were produced and evaluated in the same manner as in Example 1, except that the volume ratio of the ruthenium oxide particles and the coated particles to the insulating material was changed to 1:9.

[0086] The resistance value of the film could not be measured.

[0087] [Comparative Example 2] A resistor paste and a resistor were prepared and evaluated in the same manner as in Example 1, except that the volume ratio of ruthenium oxide particles and coated particles to the insulating material was changed to 7:3.

[0088] The film after curing was porous and did not form a continuous film, and the resistance value could not be measured.

[0089] In addition, cracks occurred in the obtained resistor, and the surface of the alumina substrate was exposed.

[0090]

Table 1

Explanation of Symbols

[0091] 10 Resistor 111 Electrode 112 Resistance film 12 Insulating material 13 Conductive particles 14 Coated particles 141 Insulating particles 142 Iridium oxide film

Claims

Claim 1: A coating particle forming step of forming an iridium oxide film having a film thickness of 4 nm or more on the surface of insulating particles having an average particle diameter of 2.5 μm or more and 3 μm or less and being SiO₂ by a polygonal barrel sputtering method to form coating particles; A paste preparation step of mixing an insulating material, conductive particles which are ruthenium oxide particles, and the coating particles to prepare a paste for a resistive film; A resistive film forming step of applying the paste for a resistive film between a pair of electrodes to form a resistive film, the method having: A method for manufacturing a resistor, wherein, among the insulating material, the conductive particles, and the coating particles contained in the paste for a resistive film, the total volume ratio of the conductive particles and the coating particles is 15% or more and 60% or less.

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