Method for manufacturing a resistor

Abstract

To provide a resistive element that does not contain a lead component and is capable of suppressing the resistance temperature coefficient.SOLUTION: The resistive element has a pair of electrodes and a resistive film arranged between the electrodes. The resistive film has an insulating material and coated particles with a conducting film arranged on the surface of insulating particles. The coated particles are arranged within the insulating material. The conductive film has a thin film portion and a thick film portion having a thickness thicker than the thin film portion. The volume fraction of the coated particles in the resistive film is 20% or more or 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 resistors of electronic components, a thick film method using a resist 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 resist 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 resist 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 °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] Also, 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 coefficients with the substrate are close, 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 high-resistance regions are desired. Also, in order to completely eliminate lead from the thick film resistor, it is necessary to eliminate lead from the glass frit used at the same time. However, even when all lead is eliminated from the resistance 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 is proposed to use iridium oxide (IrO2) as a 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 a high-resistance region that does not contain lead and replaces lead oxide powder.

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

[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 and the film thickness ratio of each thin film.

[0010] However, a resistor using the above-described metal thin film 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 promoted, but it has been difficult to obtain a resistor with a low temperature coefficient of resistance.

Prior Art Documents

Patent Documents

[0012] [Patent Document 1] Japanese Patent Publication No. 54-1917 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 6-45102 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2007-277040 [Patent Document 4] Japanese Patent Publication No. 50-25149 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2001-2892 [Non-Patent Document]

[0013] [Non-Patent Document 1] M. Prudenziati, J. Hormadaly, "Printed films", 2012, Woodhead Publishing limited, Oxford [Non-Patent Document 2] Shigeaki Kohinata, Journal of the Institute of Electronics Packaging, Vol.9 No.6 (2006), pp495 [Summary of the Invention] [Problems to be Solved by the Invention]

[0014] In view of the problems of the above prior art, an 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, and has the resistor film includes an insulating material and coated particles having a conductive film disposed on the surface of insulating particles, and the coated particles are disposed within the insulating material, the conductive film has a thin film portion and a thick film portion having a thicker film thickness than the thin film portion, Provide a resistor in which the volume ratio of the coating particles in the resistance film is 20% or more and 60% or less.

Advantages 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 temperature coefficient of resistance.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Embodiments 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 coating particles are shown larger than the actual size.

[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 and coating particles 13 in which a conductive film 132 is disposed on the surface of insulating particles 131.

[0021] The coating particles 13 are disposed in the insulating material 12 as shown in FIG. 1.

[0022] And the conductive film 132 can have a thin film portion 1321 and a thick film portion 1322 that is thicker than the thin film portion 1321. Also, the volume ratio of the coating particles 13 in the resistance film 112 can be 20% 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 thick film has a positive temperature coefficient of resistance and the thin film has a negative temperature coefficient of resistance, by using coating particles in which a conductive film including a thin film portion and a thick film portion is formed on the surface of insulating particles, it was found that a resistor with a suppressed temperature coefficient of resistance can be obtained, and the present invention was completed.

[0024] Each member included in the resistor of the present invention will be described. (1) Coating particles (1-1) Insulating particles The insulating particles 131 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.

[0025] Among them, SiO2 is a high-resistance material, and particles with suppressed variations in shape and particle size can be easily manufactured, so it can be particularly preferably used as the material of the insulating particles.

[0026] The average particle size of the insulating particles 131 is not particularly limited, but for example, it is preferably 2 μm or more and 50 μm or less, and more preferably 2.5 μm or more and 30 μm or less. In this specification, the average particle size means the particle size at the integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. (1-2) Conductive film The coating particles 13 can have a conductive film 132 on the surface of the insulating particles 131.

[0027] As shown in FIGS. 1 and 2, the conductive film 132 can have a thin film portion 1321 and a thick film portion 1322 having a thickness greater than that of the thin film portion 1321 on the surface of the insulating particles 131. That is, the conductive film 132 can have a thin film portion 1321 with a different thickness and a thick film portion 1322 on the insulating particles 131 at the same time. For example, in the conductive film 132, a region where the film thickness is equal to or less than a predetermined threshold value can be defined as the thin film portion 1321, and a region where the film thickness is greater than the threshold value can be defined as the thick film portion 1322. The threshold value is not particularly limited, but can be, for example, 100 nm.

[0028] As described above, since the thick film has a positive temperature coefficient of resistance and the thin film has a negative temperature coefficient of resistance, the temperature coefficient of resistance of the resistor 10 can be suppressed by using the coated particles 13 having the thin film portion 1321 and the thick film portion 1322.

[0029] The material of the conductive film 132 is not particularly limited. However, since it has excellent followability to the shape of the insulating particles 131 to be coated and is easy to form a conductive film 132 with a desired shape, the conductive film 132 preferably contains iridium oxide or ruthenium oxide. Particularly from the viewpoint of cost and the like, the conductive film 132 is preferably a ruthenium oxide film.

[0030] The thicknesses of the thin film portion 1321 and the thick film portion 1322 are not particularly limited. For example, the thickness of the thin film portion 1321 is preferably 1 nm or more and 100 nm or less, and the thickness of the thick film portion 1322 is preferably more than 100 nm and 2 μm or less.

[0031] When measuring the thickness of the conductive film 132, first, the coated particles 13 are processed by FIB (focused ion beam) or the like so that the cross-section of the particles can be observed, for example, in the state shown in FIG. 2. The coated particles 13 may be embedded in a resin or the like in advance before FIB processing, and cross-section polisher processing or the like may be performed as necessary. Then, using a TEM (transmission electron microscope) or FE-SEM (field emission scanning electron microscope), the thickness T132 of the conductive film 132 can be measured in the coated particles 13. The thickness T132 of the conductive film 132 can be measured along a straight line L connecting the center O of the insulating particle 131 and the outer surface of the conductive film 132 at the location where the thickness T132 is measured. When the insulating particle 131 is not circular, the thickness of the conductive film 132 can be measured along a straight line connecting the center of the circumscribed circle of the insulating particle 131 and the outer surface of the conductive film 132.

[0032] The average value of the difference between the maximum value and the minimum value of the thickness of the conductive film 132 is preferably 50 nm or more and 2000 nm or less. By setting the average value of the difference between the maximum value and the minimum value of the thickness of the conductive film 132 within the above range, the ratio between the thin film portion 1321 and the thick film portion 1322 can be controlled particularly appropriately, and the resistance temperature coefficient can be particularly suppressed.

[0033] When measuring the average value of the difference between the maximum value and the minimum value of the thickness of the conductive film 132, first, the coated particles are processed by FIB or the like so that the cross-section of the particles can be observed. The coated particles 13 may be embedded in a resin or the like in advance before FIB processing, and cross-section polisher processing or the like may be performed as necessary. Then, using a TEM or FE-SEM, in the above coated particles, the thickness T132 of the conductive film 132 is measured at the location where it is maximum and at the location where it is minimum, and the difference between the maximum value and the minimum value of the thickness of the conductive film 132 in the particles is calculated. The method for measuring the thickness T132 of the conductive film 132 has already been described.

[0034] Similarly, by averaging the differences between the maximum value and the minimum value of the conductive film for each of 10 or more coated particles, the difference between the maximum value and the minimum value of the thickness of the conductive film in the coated particles of the resistor can be obtained.

[0035] (1 - 3) Content of coated particles in the resistance film In the resistor of the present embodiment, in the resistance film 112 disposed between the pair of electrodes 111, current is generated through the coated particles 13, and electricity can flow between the pair of electrodes 111.

[0036] Specifically, for example, as shown in FIG. 1, by arranging the coated particles 13 continuously between the electrodes 111, current can flow through the coated particles 13 along the dotted line A. 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 coated particles 13 in the insulating material 12. Such content varies depending on the size of the coated particles 13 and the like. For example, the volume ratio of the coated particles 13 in the resistance film 112 is preferably 20% or more, and more preferably 25% or more.

[0037] However, if the ratio of the coated particles 13 in the resistance film 112 becomes excessively high, there is a risk that the resistance film 112 may not be able to maintain its film shape, or the strength may decrease. Also, the fluidity of the paste for the resistance film used when forming the resistance film 112 may decrease, and there is a risk that a uniform resistance film 112 cannot be formed during coating and drying.

[0038] Therefore, the volume ratio of the coated particles 13 in the resistance film 112 is preferably 60% or less, and more preferably 55% or less. (2) Conductive particles The resistor of the present embodiment may further contain conductive particles for the purpose of adjusting the resistance value. As will be described later, the resistor of the present embodiment can be formed, for example, by applying a paste containing the insulating material 12 and the coated particles 13 between the electrodes 111 and drying and firing. Therefore, the conductive particles are preferably materials whose resistance does not change due to annealing when the paste is heat - cured. For example, it is preferably one or more materials selected from noble metals such as Au (gold), Ag (silver), and RuO2 (ruthenium oxide), IrO2 (iridium oxide), etc.

[0039] The shape of the conductive particles is not particularly limited, and they can have one or more shapes selected, for example, from spherical, flaky, etc. Also, the average particle size of the conductive particles is not particularly limited, but for example, it is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 2 μm or less.

[0040] The manufacturing method of the conductive particles is not particularly limited, and depending on the type of material used, etc., they can be manufactured by various manufacturing methods. When manufacturing ruthenium oxide particles as the conductive particles, for example, by neutralizing, washing, and drying an aqueous ruthenium chloride solution with KOH (potassium hydroxide), hydrated ruthenium oxide particles can be obtained. Further, for example, by heat-treating at a temperature exceeding 400 °C, for example, 600 °C or more and 850 °C or less, in an oxidizing atmosphere, the crystal water can be removed and ruthenium oxide powder can be obtained. Note that the oxidizing atmosphere is an atmosphere containing 10% by volume or more of oxygen, and for example, air, etc. can be preferably used. (3) Insulating material The insulating material 12 may be any insulating material that contains the above-described coated particles 13 and can form the resistive film 112, and is not particularly limited.

[0041] The insulating material 12 can contain a resin, and examples of the resin include one or more selected from thermosetting resins and thermoplastic resins. Also, the insulating material 12 can contain a curing agent as needed.

[0042] As the thermosetting resin, one or more selected from epoxy resins, polyimide resins, phenol resins, bismaleimide resins, etc. can be preferably used.

[0043] Also, as the thermoplastic resin, one or more selected from polyester resins, polyurethane resins, acrylic resins, etc. can be preferably used.

[0044] 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 polyhydric phenols such as bisphenol A, bisphenol AD, bisphenol F, catechol, and resorcinol, or polyglycidyl ethers obtained by reacting polyhydric alcohols such as glycerin and polyethylene glycol with epichlorohydrin, or glycidyl ether esters obtained by reacting hydroxycarboxylic acids such as P - hydroxybenzoic acid and β - oxynaphthoic acid with epichlorohydrin, or polyglycidyl esters obtained from polycarboxylic acids such as phthalic acid and terephthalic acid, and further novolac type epoxy, epoxidized polyolefin, and the like.

[0045] In addition, the resistance film 112 is formed by adding a diluent or the like 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 unavoidable components due to a diluent or the like in addition to the above-described insulating material 12 and coating particles 13. (4) Electrodes 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.

[0046] 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 contained as an unavoidable component are not excluded.

[0047] According to the resistor of the present embodiment described above, it has a resistor film 112 including coated particles 13 having a thin film portion and a thick film portion. Therefore, by adjusting the ratio of the thin film portion to the thick film portion, the addition amount of the coated particles 13, etc., the resistance value of the resistor 10 can be easily controlled, and the resistance temperature coefficient can be suppressed. Therefore, even without using a material containing a lead component, a resistor having a desired resistance value and suppressing the resistance temperature coefficient can be obtained. [Method for manufacturing a resistor] The method for manufacturing the resistor of the present embodiment will be described. According to the method for manufacturing the resistor of the present embodiment, the resistor described above can be manufactured. Therefore, the description of the matters already described will be omitted.

[0048] The method for manufacturing the resistor of the present embodiment can include the following coated particle forming step, paste preparing step, and resistor film forming step.

[0049] Hereinafter, each step will be described. (1) Coated particle forming step In the coated particle forming step, a conductive film can be formed on the surface of the insulating particles to form coated particles. That is, in the coated particle forming step, the coated particles described above can be formed, and a conductive film can be formed on the surface of the insulating particles so as to include a thin film portion and a thick film portion having a film thickness thicker than that of the thin film portion.

[0050] In the coated particle forming step, the method for forming a conductive film on the surface of the insulating particles is not particularly limited.

[0051] Examples of the method for forming a conductive film on the insulating particles 131 include one or more selected from vapor phase methods such as sputtering, vapor deposition, and CVD methods, and wet methods such as sol-gel methods. Since the insulating particles 131 have a three-dimensional shape, as the method for forming a conductive film, one or more selected from barrel sputtering, CVD, and sol-gel methods are preferable, and a multi-angle barrel sputtering method is more preferable. That is, in the coated particle forming step, it is more preferable to form a conductive film on the surface of the insulating particles by the multi-angle barrel sputtering method.

[0052] The multi-sided barrel sputtering method can be implemented using, for example, the sputtering apparatus 30 shown in FIG. 3. Note that FIG. 3 is a side view of a sputtering apparatus capable of implementing the multi-sided barrel sputtering method, viewed along the rotation axis of the polygonal container 31. The sputtering apparatus 30 can include a polygonal container (barrel) 31, a cathode 32, and a target 33. Further, in order to control the atmosphere during sputtering, a chamber 34 can be included. The inside of the chamber 34 can be evacuated, for example, and a gas such as argon can be introduced.

[0053] The polygonal container 31 is configured to be rotatable and swingable along the double arrow B about the rotation axis C in the figure. Note that the cathode 32 and the target 33 are configured not to rotate. For this reason, the insulating particles 131 accommodated in the polygonal container 31 move with the rotation and swing of the polygonal container 31. However, when the rotation angle of the polygonal container 31 exceeds a certain angle, the insulating particles come off the inner peripheral surface of the polygonal container 31 and fall. At that time, the insulating particles rotate, and the surface facing the target 33 changes.

[0054] As described above, according to the multi-sided barrel sputtering method, by accommodating the insulating particles 131 in the polygonal container 31 and rotating or swinging the polygonal container 31, sputtering film formation can be performed while changing the surface of the insulating particles facing the target 33.

[0055] The conductive film 132 of the coating particles 13 to be manufactured can have a thin film portion 1321 and a thick film portion 1322 as described above.

[0056] Therefore, for example, at the start of sputtering, a film is formed on a part of the surface of the insulating particles 131 without rotating or rocking the polygonal container 31, so that a part of the thick film portion 1322 can be formed (first film forming step). At this time, depending on the amount of the insulating particles 131 in the polygonal container 31, the insulating particles 131 may be stacked, and there is a possibility that the insulating particles 131A on the bottom side disposed on the polygonal container 31 side may not be formed with a film. In this case, after sputtering for a certain period of time, the polygonal container 31 may be rotated or rocked for a short time to perform an operation of exchanging positions with the upper insulating particles 131B, and then sputtering may be performed again for a certain period of time.

[0057] Thereafter, by performing sputtering film formation while rotating or rocking the polygonal container 31, a film with a uniform thickness can be further formed on the surface of the insulating particles 131 (second film forming step).

[0058] The portion formed in the first film forming step becomes thicker in the second film forming step and can be made into a thick film portion. For the portion not formed in the first film forming step, a conductive film is formed in the second film forming step to become a thin film portion.

[0059] Here, an example of film formation by the multi-barrel sputtering method has been used for explanation. However, as described above, a conductive film may be formed by a method other than the multi-barrel sputtering method. Further, for example, the first film forming step may be formed by the multi-barrel sputtering method, and the second film forming step may be formed by another method. As the above-mentioned other method, for example, a chemical vapor deposition method (CVD method) or the like can be used.

[0060] As described above, the material of the conductive film is not particularly limited, and it is preferably contained with iridium oxide or ruthenium oxide. In particular, as the conductive film, a ruthenium oxide film can be preferably used.

[0061] Substances such as ruthenium oxide that undergo volume expansion when oxidized from the metallic state are likely to have the film peeled off from the insulating particles when a metal film is formed and then oxidized. Therefore, when forming a ruthenium 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 form the film. By mixing oxygen into the sputtering gas, a ruthenium oxide film can be formed directly on the surface of the insulating particles. The content ratio of oxygen in the sputtering gas is not particularly limited, but for example, it is preferably 5% by volume or more and 20% by volume or less.

[0062] In addition, although it is conceivable to use a ruthenium oxide target as the target, ruthenium oxide has sublimability, so it is difficult to sinter and difficult to manufacture the target. On the other hand, a ruthenium target, which is a metal, can be manufactured by, for example, a melting method by plasma melting. Also, a ruthenium metal target can be manufactured by a hot pressing method, hot isostatic pressing (HIP), or the like using ruthenium metal powder as a raw material. (2) Paste preparation process In the paste preparation process, an insulating material and coating particles can be mixed to prepare a paste for a resistance film.

[0063] Since the insulating material and the coating particles have already been described, the description is omitted here.

[0064] When preparing a paste for a resistance film in the paste preparation process, a curing agent and a diluent can be added as necessary to make it into a paste form.

[0065] The curing agent and the diluent can be selected according to the type of resin of the insulating material used.

[0066] For example, when an epoxy resin is selected as the resin of the insulating material, a curing agent that can preferably be used is one that rapidly undergoes a curing reaction with the epoxy resin when heated (for example, 60°C or more and 300°C or less) and has long-term storage stability at room temperature or lower.

[0067] When the resin of the insulating material is an epoxy resin, examples of the curing agent include polyhydric phenols such as resorcinol, 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 may be used alone or in combination of two or more. 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.

[0068] The diluent is a component for adjusting the viscosity of the paste for the resist film and will evaporate and be removed after the resist film is formed. 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, and 1,3-propanediol. It is desirable that it is compatible 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 may be 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 will increase, which may lead to a decrease in dilution efficiency and an increase in curing time.

[0069] 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 an apparatus having a strong grinding force such as a three-roll mill, the conductive film of the coated particles may be cracked, so it is preferable not to use an apparatus with a strong grinding force. (2-1) Regarding the mixing ratio of each component The ratio of each component in the paste for the resistive film is not particularly limited and can be selected according to the materials used, the required characteristics, etc.

[0070] Here, let the volume ratio of the coating particles in the paste for the resistive film be A, 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.

[0071] Here, the case of using an epoxy resin as the resin among the insulating materials will be described as an example.

[0072] In this case, it is preferable that A / (B + D) satisfies 20 / 80 or more and 60 / 40 or less.

[0073] That is, among the insulating material and the coating particles contained in the paste for the resistive film, the volume ratio of the coating particles is preferably 20% or more and 60% or less, and more preferably 25% or more and 55% or less. Here, the above-mentioned insulating material means the resin contained in the insulating material and the curing agent.

[0074] By setting the above ratio to 20% or more, the amount of the coating particles in the resistive film can be made sufficient, and the coating particles are continuously connected, that is, percolated, and the electrodes can be electrically connected.

[0075] Also, by setting the above ratio to 60% or less, the fluidity of the paste for the resistive film can be increased, and a particularly uniform resistive film can be formed during coating and drying.

[0076] Also, it is preferable that (A + B + D) / C is 90 / 10 or more and 50 / 50 or less. That is, the volume ratio of the diluent in the paste for the resistive film is preferably 10% or more and 50% or less, and more preferably 15% or more and 35% or less.

[0077] By setting the volume ratio of the diluent in the paste for the resistive film to 10% or more, the viscosity of the paste for the resistive film can be suppressed, and the coatability can be enhanced. Also, by setting the volume ratio of the diluent in the paste for the resistive film to 50% or less, the shrinkage of the paste for the resistive film after coating can be suppressed, and a particularly uniform resistive film can be formed.

[0078] The paste for the resistive film can also 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 the 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.

[0079] In addition to the above-described components, the paste for the resistive film can also contain a curing accelerator such as blocked isocyanate, a silane-based coupling agent, a titanate-based coupling agent for improving the bonding strength, and a colorant such as a pigment or a dye, as required. (3) Resistive film formation step In the resistive film formation step, a resistive film can be formed by applying the paste for the resistive film between a pair of electrodes.

[0080] Specifically, a resistor can be formed by applying the paste for the resistive film between a pair of electrodes previously formed on an insulating substrate, followed by drying and heat treatment.

[0081] 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.

[0082] 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 resistor film paste. The drying and curing temperature is preferably equal to or higher than the boiling point of the diluent, for example, preferably 80°C or higher and 200°C or lower. 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 isothermally at the curing temperature for 20 minutes or more and 2 hours or less for curing, and then taken out of the furnace and allowed to cool naturally.

Examples

[0083] 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, for the five resistors produced under the same conditions in each example and comparative example, the film thickness was measured with a stylus thickness roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., model number: Surfcom 480B), and the calculated value was obtained by averaging the measured values.

[0084] For the five manufactured resistors, the resistance value was measured at room temperature (300K) with a digital multimeter (manufactured by KEITHLEY, model number: 2001), and the obtained resistance value was converted to the case where the thickness of the resistor was 50μm. Then, the average of the resistance values of the five thick film resistors after conversion 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.

[0085] Five resistors with a width of 1 mm and a length of 10 mm were produced under the same conditions in each of the following examples and comparative examples. 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 value of each thick film resistor at each temperature is R -55 , R 25 , R 125 . For example, R -55 means the resistance value at -55°C.

[0086] Next, for each thick-film resistor, the temperature coefficient of resistance COLD-TCR on the low-temperature side and the temperature coefficient of resistance HOT-TCR on the high-temperature side 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 -100 ppm / °C ≤ temperature coefficient of resistance ≤ 100 ppm / °C is regarded as a standard for an excellent resistor. (Manufacturing conditions) [Example 1] (Coated particle formation process) As insulating particles, spherical silica with an average particle diameter of 20 μm (manufactured by AGC Si-Tech Co., Ltd., model number: NP-200) was prepared.

[0087] (First film formation process) Such spherical silica was put into a sputtering apparatus 30 by the polygonal barrel sputtering method shown in FIG. 3, and film formation was performed without barrel rotation. Note that a Ru target was used as the target. The degree of vacuum in the chamber 34 before sputtering was 2 × 10 -4 Pa, and an Ar:O2 mixed gas was used as the sputtering gas, and the flow rate ratio was Ar:O2 = 9:1. A ruthenium oxide film was formed on the surface of the spherical silica to a maximum thickness of 500 nm.

[0088] In addition, in order to swap the positions of the spherical silica in the polygonal container 31, sputtering was once stopped, the polygonal container 31 was swung twice, and the operation of performing sputtering again was carried out 20 times. As a result, the positions of the insulating particles 131A on the bottom side and the insulating particles 131B on the upper side placed in the polygonal container 31 were swapped, and a ruthenium oxide film was formed on a part of the surface of each insulating particle 131 placed in the polygonal container 31 to a maximum of 500 nm. (Second film formation step) Next, with the barrel rotation speed set to 0.1 rpm, that is, at a rotation speed at which the rotation axis C rotates 120 degrees around the center of rotation in 200 seconds, a ruthenium oxide film was formed on the entire surface of the insulating particles to an average thickness of 5 nm.

[0089] When the obtained coated particles were evaluated, it was confirmed that the ruthenium oxide film possessed by the obtained coated particles had a thin film portion with a thickness of 100 nm or less and a thick film portion with a thickness exceeding 100 nm, and the average of the difference between the maximum value and the minimum value was 280 nm.

[0090] When measuring the film thickness of the ruthenium oxide film, first, the coated particles were processed by FIB so that the cross-section of the particles could be observed. Then, using TEM, in the above-mentioned coated particles 13, the thickness T132 of the conductive film 132 was measured. The thickness T132 of the conductive film 132 was measured along a straight line L connecting the center O of the insulating particle and the outer surface of the conductive film 132 at the location where the thickness T132 was measured.

[0091] When measuring the average value of the difference between the maximum value and the minimum value of the thickness of the conductive film 132, first, the coated particles were processed by FIB so that the cross-section of the particles could be observed. Then, using TEM, in the above-mentioned coated particles, the thickness T132 of the conductive film 132 was measured at the location where it was maximum and the location where it was minimum, and the difference between the maximum value and the minimum value of the thickness of the conductive film 132 in the particles was calculated.

[0092] By averaging the differences between the maximum and minimum values of the conductive films for each of the 10 coated particles obtained in the same manner, the difference between the maximum and minimum values of the thickness of the conductive film in the coated particles of the resistor was determined. (Paste Preparation Step) An insulating material was prepared by adding 40 parts by mass of a phenol novolak 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).

[0093] The insulating material was placed in the container so that the volume ratio of the coated particles to the insulating material was 1:1. Also, 2-ethylhexyl glycidyl ether was placed in the container as a diluent at a ratio of 20 parts by mass per 100 parts by mass of the insulating material.

[0094] The materials placed in the container were defoamed under vacuum using a rotary-revolution mixer (manufactured by Shinchi, vacuum LED type ARV-310LED) and then stirred and mixed at 1200 rpm for 10 minutes to form a paste. (Resistive Film Formation Step) The resistive film paste 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.

[0095] As a result, a resistive film with 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.

[0096] The obtained resistor was evaluated for its resistance value and temperature coefficient of resistance. The evaluation results are shown in Table 1.

[0097] [Comparative Example 1] A resistive film paste and a resistor were produced and evaluated in the same manner as in Example 1, except that the volume ratio of the coated particles to the insulating material was changed to 2:1.

[0098] In this comparative example, since the content ratio of the coated particles was high, the strength of the resistance film of the obtained resistor was low. In addition, the contact between the coated particles increased, and the contact between the thick film portions also increased. As a result, electrons did not pass through the thin film portion, the resistance decreased, and metallic conduction became dominant, so it is considered that the temperature coefficient of resistance increased.

[0099] [Comparative Example 2] 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 coated particles to the insulating material was changed to 1:5.

[0100] In this comparative example, since the content ratio of the coated particles was low, the resistance value was 50 MΩ, which was the upper limit value of the measuring device, and it was confirmed that there was no conduction between the electrodes 111. Note that the temperature coefficient of resistance is considered to be the value for the substrate.

[0101]

Table 1

Explanation of Symbols

[0102] 10 Resistor 111 Electrode 112 Resistance film 12 Insulating material 13 Coated particle 131, 131A, 131B Insulating particle 132 Conductive film 1321 Thin film portion 1322 Thick film portion T132 Film thickness

Claims

Claim 1: A coating particle forming step of forming a conductive film, which is a ruthenium oxide film, on the surface of insulating particles having an average particle diameter of 2.5 μm or more and 30 μm or less and being SiO₂ to form coated particles; A paste preparation step of mixing an insulating material and the coated 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; and the method for manufacturing a resistor has: In the coating particle forming step, the insulating particles are put into a sputtering apparatus by a multi-angle barrel sputtering method, the conductive film is formed without barrel rotation, and then the conductive film is formed while rotating the barrel, so that the conductive film is formed on the surface of the insulating particles to include a thin film portion and a thick film portion having a film thickness thicker than that of the thin film portion; A method for manufacturing a resistor, wherein the volume ratio of the coated particles among the insulating material and the coated particles contained in the paste for a resistive film is 20% or more and 60% or less.

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