Thick film resistor and its manufacturing method

Abstract

To provide a thick resistor which can be miniaturized with almost no deterioration in withstand voltage characteristics and surge resistance characteristics, and which has a desired value of resistance and temperature coefficient of resistance and hardly causes the disconnection by sulfurization of an electrode.SOLUTION: A thick film resistor suitably having the form of a square chip resistive body includes: an insulation substrate 21; a thick film resistive body 22 formed on at least one surface of the insulation substrate 21; an electrically insulating first coat layer 23 coating the surface of the thick film resistive body 22 excluding electrode connection surfaces 22a on both ends of the thick film resistive body; and a pair of surface electrodes 24 connected to the electrode connection surfaces 22a on both ends of the thick film resistive body 22 not coated with the first coat layer 23, respectively. The pair of surface electrodes 24 preferably coat surfaces partially on respective both ends of the first coat layer 23.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a thick film resistor formed by printing and firing a paste, and a method for manufacturing the same. [Background technology]

[0002] Chip resistors are widely used as surface-mounted fixed resistors in various electronic devices. The chip resistor generally consists of a rectangular insulating substrate in plan view, a pair of surface electrodes spaced apart from each other on both ends of the surface of the insulating substrate, a resistor element spanning these surface electrodes, and a coating layer covering the resistor element. The resistor element has a trimming groove for adjusting its resistance value. Furthermore, chip resistors can be broadly divided into thin-film resistors with a resistor element approximately 0.001 to 1 μm thick formed by a thin-film formation method such as sputtering, and thick-film resistors with a resistor element approximately 1 to 20 μm thick formed by a printing method.

[0003] In the manufacture of the latter type of thick-film resistors, a method of simultaneously manufacturing multiple thick-film resistors from a single large insulating substrate is adopted to increase productivity. For example, Patent Document 1 discloses a method of simultaneously manufacturing multiple rectangular chip resistors by printing, drying, and firing an electrode paste on the front and back surfaces of a ceramic substrate, which has dividing slits extending vertically and horizontally. Then, a resistor paste is printed, dried, and fired across the pairs of surface electrodes to form a thick-film resistor group. A glass paste is then printed, dried, and fired on the surface of the resulting thick-film resistor group to form an undercoat layer group. A trimming groove is formed on each thick-film resistor using a laser beam, along with an undercoat layer. A resin paste is then printed and heat-cured to form an overcoat layer group. The method then divides the substrate into individual chips along the dividing slits, and side electrodes connecting the front and back electrodes and a plating layer covering these electrodes are formed to produce multiple rectangular chip resistors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-023095 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, electronic devices have become increasingly smaller and lighter, and their performance has improved. Accordingly, thick-film resistors, which are key electronic components, are also required to be smaller and more powerful. However, thick-film resistors generally have superior electrical characteristics, such as withstand voltage and surge resistance, when they have a long effective length. Therefore, a longer distance between the opposing surface electrodes is advantageous. Therefore, miniaturizing thick-film resistors adversely affects their withstand voltage and surge resistance.

[0006] Therefore, in order to minimize the degradation of voltage resistance and surge resistance characteristics when minimizing the size of a thick-film resistor, it is conceivable to reduce the size of a pair of surface electrodes to maximize the distance between them and ensure the above-mentioned effective length of the resistor. However, the manufacturing of thick-film resistors involves a trimming process in which trimming grooves are formed using a laser beam to adjust the resistor's resistance value, and during this process, a probe is brought into contact with the surface electrode to measure the resistance value. Therefore, if the size of the surface electrode is reduced as described above, the area for the probe to contact becomes smaller, making it difficult to measure the resistance value.

[0007] Furthermore, in the baking process of the electrodes and resistors that precedes the trimming process, the electrode and resistor components are prone to diffusion, which causes the electrode and resistor components to migrate across their boundaries, resulting in regions where the resistor's original composition changes. When thick-film resistors are miniaturized, the proportion of regions where the resistor's original composition changes increases relative to the entire resistor, potentially resulting in the resistor's resistance value and temperature coefficient of resistance (TCR) deviating from their target values. Furthermore, in chip resistors that use Ag or Pd-Ag alloys for the surface electrodes, external atmospheric gases containing sulfur (S) can penetrate through the gap between the coating layer and the plating layer, resulting in sulfur corrosion of the surface electrodes and potentially leading to disconnections.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a thick film resistor that can be miniaturized without substantially degrading the withstand voltage characteristics and surge resistance characteristics, has a desired resistance value and temperature coefficient of resistance, and is less likely to cause disconnection due to sulfuration of the electrodes. [Means for solving the problem]

[0009] In order to achieve the above object, the thick film resistor according to the present invention comprises an insulating substrate, a thick film resistor formed on at least one surface of the insulating substrate, an electrically insulating first coating layer covering the surface of the thick film resistor except for the electrode connection surfaces at both ends, and the first coating layer being connected to the electrode connection surfaces at both ends, and a probe for measuring the resistance value is brought into contact with the surface during trimming. The thick film resistor is mainly composed of Au, Ag, Pd, Cu or an alloy thereof, and is fired at a temperature lower than that of the thick film resistor. and a pair of electrodes, and the thick film resistor and the first coating layer have a trimming groove formed between the pair of electrodes.

[0010] The method for manufacturing a thick film resistor according to the present invention includes a thick film resistor forming step of printing a resistor paste on the surface of an insulating substrate and firing the paste at a predetermined firing temperature to form a thick film resistor; a first coating layer forming step of printing a glass paste on the surface of the thick film resistor except for the electrode connection surfaces at both ends and firing the glass paste at a temperature lower than the firing temperature in the thick film resistor forming step to form a first coating layer; and a second coating layer forming step of printing an electrode paste so as to overlap the electrode connection surfaces at both ends and firing the glass paste at a temperature lower than the firing temperature in the thick film resistor forming step. Main components are Au, Ag, Pd, Cu or their alloys The method is characterized by comprising a surface electrode forming step of forming a pair of surface electrodes, and a resistance value adjusting step of measuring the resistance value by contacting a probe with the pair of surface electrodes and trimming the thick film resistor with a laser. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a thick film resistor that can be miniaturized without substantially degrading the withstand voltage characteristics and surge resistance characteristics, has a desired resistance value and temperature coefficient of resistance, and is less likely to break due to sulfide corrosion. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic vertical cross-sectional view of a conventional chip resistor. [Figure 2] 1 is a schematic longitudinal sectional view of a chip resistor according to one embodiment of the present invention; [Figure 3] FIG. 3 is a partially cutaway perspective view of the chip resistor of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] A specific example of the thick-film resistor of the present invention will be described below, taking a rectangular chip resistor as an example. The thick-film resistor of this specific example of the present invention includes an insulating substrate made of an insulating material such as ceramic and rectangular in plan view, a thick-film resistor formed on at least one surface of the insulating substrate, an electrically insulating first coating layer covering the surface of the thick-film resistor except for the electrode connection surfaces at both ends in the voltage application direction (direction of current flow), and paired electrodes connected to the electrode connection surfaces at both ends of the thick-film resistor. Unlike conventional thick-film resistors, this configuration prevents deterioration of the withstand voltage characteristics and surge resistance characteristics even when miniaturized, and also makes it less likely to break due to sulfide corrosion.

[0014] That is, a conventional thick film resistor, as shown in the rectangular chip resistor of FIG. 1, is composed of a pair of surface electrodes 14 spaced apart from each other at both ends of the surface side of an insulating substrate 11 made of ceramic or the like, and a thick film resistor 12 that is arranged to straddle (bridge) the pair of surface electrodes 14, and both ends of the thick film resistor 12 in the voltage application direction partially overlap the surfaces of the pair of surface electrodes 14 that face each other.

[0015] The entire surface of the thick film resistor 12 is covered with a first coating layer 13 made of glass, and groove-like notches (trimming portions 15) formed by laser light are provided in the thick film resistor 12 and the first coating layer 13 to adjust (trimming) the resistance value of the thick film resistor 12. The entire surface of the first coating layer 13 is covered with a second coating layer 16 made of glass or resin.

[0016] A pair of spaced apart back electrodes 17 are provided at both ends of the back surface side of the chip resistor where the thick film resistor 12 is not provided, and a pair of terminal electrodes 18 are provided at both ends of the chip resistor so as to connect the pair of back surface electrodes 17 to the pair of front surface electrodes 14. A plating layer 19 made of nickel plating or the like is formed at each end of the chip resistor so as to cover the front surface electrodes 14, back surface electrodes 17, and terminal electrodes 18.

[0017] As described above, conventional chip resistors are formed so that both ends of the thick-film resistor overlap the surfaces of a pair of surface electrodes. As a result, the portions of the thick-film resistor that overlap the surface electrodes cannot fully function as a resistor, and as a result, the effective length of the thick-film resistor is shorter than the length from end to end of the thick-film resistor in the direction of voltage application.

[0018] As mentioned above, a longer effective length of the thick-film resistive element is advantageous for the surge resistance and voltage resistance characteristics of a resistor, so it was difficult to improve the surge resistance and voltage resistance characteristics of a conventional chip resistor with the structure shown in Figure 1. Furthermore, in conventional chip resistors with the structure shown in Figure 1, the thick-film resistor is formed by forming the surface electrode and then firing the resistor paste at high temperature, so the resistance value and temperature coefficient of resistance (TCR) of the thick-film resistor can deviate from the target values ​​due to the migration (diffusion) of the components that make up the surface electrode into the resistor, or conversely, the migration (diffusion) of the components that make up the resistor into the surface electrode.

[0019] In contrast, a thick-film resistor according to one specific example of the present invention, as shown in the rectangular chip resistor of Figures 2 and 3, is provided on the surface side of an insulating substrate 21 such as a ceramic substrate 21, typically made of alumina, so that a thick-film resistor 22 is in contact with the insulating substrate 21 from end to end in the voltage application direction, and the surface of this thick-film resistor 22, excluding electrode connection surfaces 22a at both ends in the voltage application direction, is covered with an electrically insulating first coating layer 23, and a pair of surface electrodes 24 are electrically connected to the electrode connection surfaces 22a that are not covered with this first coating layer 23.

[0020] The resistance values ​​of the thick film resistor 22 and the first coating layer 23 are adjusted (trimmed) by making cuts with a laser beam, thereby providing a trimmed portion 25 consisting of a groove that is approximately L-shaped in plan view. A second coating layer 26 made of resin or glass is provided to cover the surface of the first coating layer 23 and to bridge over (bridge) the pair of surface electrodes 24.

[0021] A pair of back electrodes 27 are provided at both ends in the voltage application direction on the back side of the chip resistor where the thick film resistor 22 is not provided, and a pair of terminal electrodes 28 are provided at both ends of the chip resistor so as to connect the pair of back electrodes 27 to the pair of surface electrodes 24. A plating layer 29 made of nickel plating or the like is formed at each end of the chip resistor so as to cover the surface electrodes 24, back electrode 27, and terminal electrodes 28.

[0022] As described above, in the thick-film resistor of one specific example of the present invention, the stacking order at both ends in the voltage application direction is different from that of the structure in Fig. 1, with the thick-film resistor 22 and the pair of surface electrodes 24 stacked in this order from the insulating substrate 21 side, and therefore the effective length of the thick-film resistor 22 can be made longer than in the structure in Fig. 1, making it possible to provide a chip resistor with better electrical properties such as surge resistance and voltage resistance characteristics, even if it is the same size as a conventional chip resistor. In other words, the resistor can be made smaller without significantly reducing electrical properties such as surge resistance and voltage resistance, making it possible to achieve both a smaller thick-film resistor and high electrical properties.

[0023] Furthermore, in a thick-film resistor according to a specific example of the present invention, a pair of surface electrodes 24 are formed on the surface of the thick-film resistor element 22 at both ends in the voltage application direction. Therefore, the surface area of ​​the pair of surface electrodes 24 exposed before the second coating layer 26 is formed can be made larger than that of the conventional chip resistor shown in FIG. 1 . This ensures a sufficient electrode area for contacting a resistance measurement probe during laser trimming. The pair of surface electrodes 24 may also partially cover not only the electrode connection surfaces 22a at both ends in the voltage application direction of the thick-film resistor element 22, but also both ends in the voltage application direction of the surface of the first coating layer 23, thereby further increasing the surface area of ​​the pair of surface electrodes 24.

[0024] Furthermore, in the thick-film resistor according to one embodiment of the present invention, as will be described later, in the step of forming a pair of surface electrodes 24 after forming the thick-film resistor 22, the firing temperature of the electrode paste is set lower than the firing temperature of the resistor paste, thereby suppressing the migration (diffusion) of components constituting the pair of surface electrodes 24 to the thick-film resistor 22, and conversely, the migration (diffusion) of components constituting the thick-film resistor 22 to the pair of surface electrodes 24. This makes it possible to manufacture a chip resistor consisting of a pair of surface electrodes 24 and thick-film resistor 22, each having a desired component composition.

[0025] Furthermore, in the chip resistor according to one specific example of the present invention, the thickness of the portion of the second coating layer 26 that partially covers the surface of each of the pair of surface electrodes 24, which coats the thick film resistor 22 and the first coating layer 23, can be made thinner than in the conventional chip resistor having the structure shown in Fig. 1, and as a result, it is possible to make the difference in thickness between the second coating layer 26 and the plating layer 29 that are in contact on the surface of each surface electrode 24 smaller than in the conventional chip resistor. This makes it less likely that gaps will occur between the second coating layer 26 and the plating layer 29.

[0026] 1, the second coating layer 16 and plating layer 19 that contact each other on the surfaces of a pair of surface electrodes 14 have a large difference in thickness, which makes it easy for gaps to form between them, allowing sulfur-containing gas to penetrate through them and causing sulfide corrosion of the surface electrodes 14, which can lead to disconnection. In contrast, the chip resistor of one specific example of the present invention is less susceptible to this sulfide corrosion problem, and therefore the surface electrodes 24 are less likely to disconnect, thereby improving the reliability of the chip resistor.

[0027] The thick-film resistor 22 constituting the chip resistor can be formed by screen-printing a resistor paste made by mixing a solvent and a binder resin with a main component consisting of ruthenium oxide, conductive powders such as Ag, Pd, and Cu, and inorganic additives such as glass powder, followed by drying and firing as necessary. The firing temperature for this resistor paste is preferably 820 to 880°C. The glass powder, which is the main component of the resistor paste, preferably has a softening point of 620°C or higher, more preferably 620°C or higher and 820°C or lower. The thickness of the thick-film resistor 22 is preferably about 1 to 20 μm.

[0028] The first coating layer 23 covers the entire surface of the thick-film resistor 22, except for the electrode connection surfaces 22a at both ends, thereby insulating the thick-film resistor 22 from the surface electrodes 24. It can be formed by screen-printing a glass paste made by mixing glass powder as the main component, additives such as pigments, a solvent, and a binder resin, followed by drying and firing as necessary. The firing temperature for this glass paste is preferably 580 to 620°C. By setting the firing temperature for forming the first coating layer 23 lower than the firing temperature for the resistor paste, the inherent characteristics of the thick-film resistor can be prevented from being impaired. The thickness of the first coating layer 23 is preferably about 3 to 10 μm.

[0029] The pair of surface electrodes 24 can be formed by screen-printing and then firing an electrode paste made by mixing a powdered metal material with low resistivity as the main component, such as Au, Ag, Pd, Cu, or an alloy thereof, glass powder for bonding with the ceramic substrate, an inorganic compound additive, a solvent, and a binder resin.The metal material for the pair of surface electrodes 24 is generally a Pd-Ag alloy containing 0.5 to 20 mass% Pd and the remainder Ag.

[0030] The firing temperature of the electrode paste is preferably 580 to 620°C. In this way, by setting the firing temperature for forming the pair of surface electrodes 24 lower than the firing temperature for the resistor paste, it is possible to suppress the migration (diffusion) of the components constituting the pair of surface electrodes 24 to the thick-film resistor 22, and conversely, the migration (diffusion) of the components constituting the thick-film resistor 22 to the surface electrode 24. As mentioned above, by setting the softening point of the glass powder, which is the main component of the resistor paste, to 620°C or higher, it is possible to suppress the components constituting the pair of surface electrodes 24 from softening to the extent that they diffuse into the thick-film resistor 22 at the firing temperature for forming the first coating layer 23 and the pair of surface electrodes 24.

[0031] In a chip resistor according to one embodiment of the present invention, a pair of back electrodes 27 are formed on the underside of an insulating substrate 21, and this shape is commonly used. The pair of back electrodes 27 can be formed by screen-printing an electrode paste containing a powdered metal material with low resistivity as the main component, a solvent, and a binder resin, followed by firing. Ag is an optimal metal material for the back electrodes 27. By forming the pair of back electrodes 27 before the step of forming the thick-film resistor 22, the firing temperature of the electrode paste for forming the pair of back electrodes 27 can be set to 820 to 880°C.

[0032] The second coating layer 26, which covers almost the entire thick-film resistor 22 covered with the first coating layer 23 and the pair of surface electrodes 24, serves as an insulating protective layer and can be formed by screen-printing a resin paste followed by a heat-curing treatment, or by screen-printing a glass paste followed by a firing treatment. When the former is used, the heat-curing treatment is preferably carried out at a temperature of 150 to 200°C. On the other hand, when the latter is used, the firing treatment is preferably carried out at a firing temperature of 580 to 620°C. The second coating layer 26 also serves to protect the thick-film resistor 22 and the trimming portion 25 of the first coating layer 23.

[0033] A pair of terminal electrodes 28 formed with a generally U-shaped cross section on both ends of insulating substrate 21 in the voltage application direction serve as a base for a pair of plating layers 29. The pair of terminal electrodes 28 can be formed by a thick-film deposition method in which an electrode paste is screen-printed and then subjected to a thermal curing treatment, or an electrode paste is screen-printed and then subjected to a firing treatment, or by a thin-film deposition method in which Ni-Cr or the like is sputtered. The pair of plating layers 29 covering the pair of terminal electrodes 28, the pair of front electrodes 24, and the pair of back electrodes 27 can be formed by electrolytic plating.

[0034] Next, an embodiment of the method for manufacturing a thick-film resistor of the present invention will be described, taking as an example a case where the thick-film resistor is a rectangular chip resistor as shown in Fig. 2. In manufacturing a rectangular chip resistor as shown in Fig. 2, a method is generally adopted in which a large insulating substrate made of ceramic is formed with a plurality of thick-film resistors and a plurality of pairs of electrodes, etc., to produce a large insulating substrate on which a plurality of resistor elements are arranged in a matrix, and then this large insulating substrate is divided lengthwise and widthwise for each resistor element, and terminal electrodes and plating layers are formed on each of the resistor elements.

[0035] That is, the method for manufacturing a thick film resistor according to an embodiment of the present invention includes an insulating substrate preparation step of printing an electrode paste on the back surface of an insulating substrate and firing the electrode paste at a firing temperature of 820 to 880°C to form a pair of back electrodes; a thick film resistor formation step of printing a resistor paste on the front surface of the insulating substrate and firing the resistor paste at a predetermined firing temperature to form a thick film resistor; a first coating layer formation step of printing a glass paste on the surface of the thick film resistor except for the electrode connection surfaces at both ends and firing the glass paste at a temperature lower than the firing temperature in the thick film resistor formation step to form a first coating layer; The method includes a surface electrode forming step of forming a pair of surface electrodes by printing an electrode paste onto the first and second thick film resistors and firing the printed electrode paste at a temperature lower than the firing temperature in the thick film resistor forming step, a resistance value adjusting step of trimming the thick film resistor with a laser, a second coating layer forming step of forming a second coating layer that covers the first coating layer, a terminal electrode forming step of forming a pair of terminal electrodes that connect the pair of surface electrodes and the pair of back electrodes, and a plating step of forming a pair of plating layers that cover the pair of surface electrodes, the pair of back electrodes, and the pair of terminal electrodes, respectively. Each of these steps will be described below.

[0036] In the insulating substrate preparation process, a paste made of Ag, Cu or an alloy of these is screen-printed on the back side of a large rectangular ceramic insulating substrate at positions corresponding to the multiple thick-film resistors that will be formed on the front side in a subsequent process, and then fired at a firing temperature of 820 to 880°C to form multiple pairs of back electrodes.

[0037] In the thick film resistor forming process, a resistor paste containing conductive powders such as ruthenium oxide, Ag, Pd, Cu, etc., and glass powder as its main components is screen-printed on the front surface of a large insulating substrate having the above-mentioned multiple pairs of rear surface electrodes formed on the rear surface side, and is dried as necessary to volatilize the solvent components contained in the resistor paste.Then, the resistor paste is fired at a firing temperature of 820 to 880°C to form multiple thick film resistors.

[0038] In the first coating layer forming step, a glass paste containing glass particles as a main component is screen-printed on the surface of each of the plurality of thick-film resistors, excluding the electrode connection surfaces located at both ends in the voltage application direction, and then the first coating layer is formed by drying the screen-printed paste as necessary and then firing at a firing temperature of 580 to 620° C. The glass paste for forming the first coating layer or the dried glass paste film obtained by drying the glass paste may be fired before printing the electrode paste in the next surface electrode forming step, or, as will be described later, may be fired simultaneously with the firing of the electrode paste printed in the surface electrode forming step or the dried electrode paste film obtained by drying the printed glass paste.

[0039] In the surface electrode forming step, an electrode paste containing Au, Ag, Cu or an alloy powder thereof as a main component is screen-printed to cover both electrode connection surfaces located at both ends in the voltage application direction of each of the plurality of thick-film resistors, and preferably both ends in the voltage application direction of the first coating layer or its dried film before firing, and then dried as necessary, and fired at a firing temperature of 580 to 620° C. to form multiple pairs of surface electrodes. As described above, the firing of this electrode paste or the electrode paste dried film obtained by drying it may be performed separately from the firing of the glass paste or its dried film, or may be performed simultaneously with the firing of the glass paste or its dried film.

[0040] In the resistance value adjustment process, in order to adjust the resistance value of each thick-film resistor to a desired value, a laser beam is applied from above the first coating layer to perform trimming, preferably forming a trimmed portion consisting of a groove that is approximately L-shaped in plan view. During this trimming, the resistance value is measured by contacting a probe with a pair of corresponding surface electrodes. Note that if resistance value adjustment is not required, this resistance value adjustment process is omitted.

[0041] In the second coating layer formation process, a thermosetting resin paste or glass paste is screen-printed to cover the first coating layer and straddle (bridge) the paired surface electrodes, and the second coating layer is formed by heat-curing the thermosetting resin paste at 150 to 200° C., or by drying the glass paste as necessary and then baking it at a baking temperature of 580 to 620° C. As shown in Figure 2, this second coating layer does not cover both end sides of the paired surface electrodes in the voltage application direction of the chip resistor.

[0042] In the terminal electrode forming process, a large insulating substrate is divided into individual thick film resistor elements, and then electrode paste is screen-printed on both ends of the divided insulating substrate in the voltage application direction so that the above-mentioned paired front surface electrodes and paired back surface electrodes are connected to each of the individual thick film resistor elements.Paired terminal electrodes are then formed by a thick film formation method in which heat curing is performed at 150 to 200°C or a baking process is performed at a baking temperature of 580 to 620°C, or by a thin film formation method in which Ni-Cr or the like is sputtered.

[0043] In the plating process, a plating layer is formed by electrolytic plating on the terminal electrodes, exposed portions of the surface electrodes not covered by the second coating layer, and the back electrode at both ends of each divided resistor element. In forming this plating layer, it is preferable to first apply nickel plating as a base to protect the three types of electrodes of the thick-film resistor, and then apply tin plating, which is compatible with solder during mounting, to the surface of the nickel plating. Through this series of processes, multiple thick-film resistors with little variation in quality can be produced with high productivity. [Example]

[0044] [Example 1] Using the three types of paste shown below, a thick film resistor, a first coating layer, and a surface electrode were formed on the surface of an insulating substrate in the order shown below to produce multiple thick film resistors for evaluation, and their characteristics were evaluated.

[0045] (1) Resistor paste A The resistor paste used to form the thick-film resistor was a mixed resistor paste A with an area resistance of approximately 3300 Ω, prepared by mixing R-13U (manufactured by Sumitomo Metal Mining Co., Ltd.), a resistor paste with a nominal area resistance of 1000 Ω, and R-14U (manufactured by Sumitomo Metal Mining Co., Ltd.), a resistor paste with a nominal area resistance of 10,000 Ω. The reason for mixing them in this manner was to ensure that the resistance between the electrodes was 6700 Ω when a thick-film resistor with an inter-electrode distance of 0.6 mm and a resistor width of 0.3 mm was fabricated, as will be described later. Note that R-13U, R-14U, and mixed resistor paste A are all resistor pastes suitable for firing in an air atmosphere at a peak temperature of 850°C for 9 minutes.

[0046] (2) Glass paste for the first coating layer The glass paste used for forming the first coating layer was I-9760 manufactured by Sumitomo Metal Mining Co., Ltd., which is suitable for firing treatment at a firing temperature of 600° C. for 5 minutes in an air atmosphere.

[0047] (3) Ag-Pd paste for surface electrodes The electrode paste used to form the mating surface electrodes was C-4420 manufactured by Sumitomo Metal Mining Co., Ltd., an Ag-Pd paste suitable for firing at 600°C for 5 minutes in an air atmosphere.

[0048] The evaluation items of the thick film resistors used for evaluation were film thickness, sheet resistance, and surge characteristics shown below.

[0049] (1) Film Thickness The film thickness of each of five thick film resistors fabricated under similar conditions was measured using a stylus thickness roughness meter (Tokyo Seimitsu Co., Ltd., model number: Surfcom 480B), and the film thickness was calculated by arithmetically averaging the measured values.

[0050] (2) Sheet resistance The resistance value of each of 25 thick film resistors fabricated under the same conditions was measured using a digital multimeter (KEITHLEY, No. 2001), and the sheet resistance value was calculated by arithmetically averaging the measured values.

[0051] (3) Surge characteristics The surge characteristics were evaluated by ESD (electrostatic discharge). Specifically, ten thick film resistors were fabricated under the same conditions, and after laser trimming, a 200pF capacitor was charged with 2kV of static electricity and discharged five times. The rate of change in resistance before and after discharge was calculated, and the average value was calculated as the arithmetic mean.

[0052] Thick-film resistors for evaluation were fabricated as follows. First, mixed resistor paste A was screen-printed onto the surface of a square alumina substrate, 1 inch (25.4 mm) on a plan view, with a thickness of 1 mm, to form a matrix pattern of 10 thick-film resistors, 0.8 mm long, 0.3 mm wide, and approximately 7 μm thick after firing. Next, the mixed resistor paste A was dried at an ambient temperature of 120°C for 10 minutes to remove the solvent, and then fired in air at a peak temperature of 850°C for 9 minutes. Five of the 30 thick-film resistors thus formed were randomly selected, and their film thicknesses were measured.

[0053] Next, a glass paste for a first coating layer was screen-printed to cover the area of ​​each of the 30 thick-film resistors formed above, excluding a range of 0.1 mm from each end in the longitudinal direction (voltage application direction). The thickness of the printed glass paste for the first coating layer was adjusted so that the film thickness after firing would be 5 μm. After printing the glass paste for the first coating layer as described above, the resistors were dried at an ambient temperature of 120° C. for 10 minutes.

[0054] The Ag-Pd paste for the surface electrodes was screen-printed onto each thick-film resistor in a pattern of two 2.5 mm squares, each with a side length of 2.5 mm, so as to cover both longitudinal ends of each thick-film resistor that were not covered with the dried film of the glass paste for the first coating layer formed above and to cover areas 0.1 mm from both ends of the first coating layer, and then dried at an ambient temperature of 120°C for 10 minutes.

[0055] The dried Ag-Pd paste film thus formed was then fired together with the dried first coating layer glass paste film in an air atmosphere at a peak temperature of 600°C for 5 minutes. This resulted in 30 thick-film resistors, each of which had a thick-film resistor element electrically connected to a pair of surface electrodes on the electrode connection surface not covered by the first coating layer within 0.1 mm of each longitudinal end. Each thick-film resistor element was covered with the first coating layer over a 0.6 mm long, 0.3 mm wide area, excluding both longitudinal ends, and had a pair of surface electrodes connected to both ends in the voltage application direction with a 0.6 mm interelectrode distance, resulting in an effective length of 0.6 mm.

[0056] The resistance values ​​of 25 randomly selected resistors were measured from the 30 thick-film resistors fabricated as described above. After measuring these resistance values, in order to adjust the resistance value to 10,000 Ω, laser trimming was performed by irradiating the resistor with a YAG laser having a wavelength of 1.06 μm, forming a trimming portion consisting of a groove that is approximately L-shaped in plan view together with the first coating layer in the thick-film resistor. After this laser trimming, the surge characteristics were evaluated by ESD.

[0057] [Comparative Example 1] Thirty pairs of surface electrodes were formed on the surface of an alumina substrate similar to that of Example 1 by screen printing C-4605, an Ag-Pd paste manufactured by Sumitomo Metal Mining Co., Ltd., in a pattern of 10 squares with 2.5 mm sides arranged in six rows, with each pair spaced 0.3 mm apart. The resulting film was then dried at an ambient temperature of 120°C for 10 minutes. The dried Ag-Pd paste film thus formed was then fired in an air atmosphere at a peak temperature of 850°C for 9 minutes to form 30 pairs of surface electrodes. C-4605 is an Ag-Pd paste suitable for firing in an air atmosphere at a peak temperature of 850°C for 9 minutes.

[0058] Next, mixed resistor paste B was prepared by mixing R-13U and R-14U so that the sheet resistance was approximately 6600 Ω, and this was screen-printed onto the opposing ends of each pair of surface electrodes, overlapping them by 0.1 mm, to form a pattern of 10 strips of paste arranged in 3 rows, each 0.3 mm wide, so as to bridge (bridge) these ends.Then, the thick-film resistor was formed by drying and firing under the same conditions as in Example 1. Note that during the above screen printing, the film thickness after firing was set to approximately 7 μm.

[0059] A glass paste for the first coating layer was screen-printed to cover the entire surface of each thick-film resistor, followed by drying and firing under the same conditions as in Example 1. Thirty thick-film resistors of Comparative Example 1 were thus produced. Each thick-film resistor had a pair of surface electrodes connected to both ends of the resistor in the voltage application direction with an interelectrode distance of 0.3 mm, resulting in an effective length of 0.3 mm and a width of 0.3 mm. The resistance was then measured in the same manner as in Example 1. To adjust the resistance to 10,000 Ω, a trimming section consisting of an approximately L-shaped groove in plan view was formed in the thick-film resistor and the first coating layer using a YAG laser with a wavelength of 1.06 μm. The surge characteristics were then evaluated by ESD. The evaluation results, along with those of Example 1, are shown in Table 1 below.

[0060] [Table 1]

[0061] As can be seen from Table 1 above, the average resistance values ​​after the formation of the first coating layer were almost the same in Example 1 and Comparative Example 1. However, the EDS evaluation results after laser trimming showed that the rate of change in Example 1 was significantly smaller than that in Comparative Example 1. This shows that the thick film resistors of the examples that satisfy the requirements of the present invention have superior electrical properties to those of Comparative Example 1. [Explanation of symbols]

[0062] 11, 21 Insulating substrate 12, 22 Thick film resistor 13, 23 First coating layer 14, 24 surface electrode 15, 25 trimming section 16, 26 Second coating layer 17, 27 Back electrode 18, 28 terminal electrode 19, 29 plating layer 22a Electrode connection surface

Claims

1. a thick-film resistor comprising an insulating substrate, a thick-film resistor formed on at least one surface of the insulating substrate, an electrically insulating first coating layer covering the surface of the thick-film resistor except for electrode connection surfaces at both ends, and a pair of electrodes connected to the electrode connection surfaces at both ends, the electrodes being adapted to be contacted with a probe for measuring resistance during trimming, the electrodes being composed primarily of Au, Ag, Pd, Cu or an alloy thereof and fired at a temperature lower than that of the thick-film resistor, wherein a trimming groove is formed between the pair of electrodes in the thick-film resistor and the first coating layer.

2. 2. The thick film resistor according to claim 1, wherein the pair of electrodes partially cover the surfaces of both ends of the first coating layer.

3. 3. The thick film resistor according to claim 1, wherein the first coating layer is made of glass.

4. 4. The thick film resistor according to claim 1, wherein a second coating layer covering the surface of the first coating layer is provided so as to straddle the pair of electrodes.

5. 5. The thick film resistor according to claim 4, wherein the second coating layer is made of glass.

6. 6. The thick film resistor according to claim 4, wherein a pair of terminal electrodes is provided at both ends of the insulating substrate, covering the portions of the pair of electrodes that are not covered with the second coating layer and the end faces of the insulating substrate.

7. 7. A chip resistor, wherein the thick film resistor according to claim 1 is a chip type.

8. a thick-film resistor forming step of printing a resistor paste on the surface of an insulating substrate and firing the paste at a predetermined firing temperature to form a thick-film resistor; a first coating layer forming step of printing a glass paste on a surface of the thick film resistor excluding electrode connection surfaces at both ends, and firing the printed surface at a temperature lower than the firing temperature in the thick film resistor forming step to form a first coating layer; a surface electrode forming step of printing an electrode paste onto the electrode connection surfaces at both ends so as to overlap each other, and firing the paste at a temperature lower than the firing temperature in the thick film resistor forming step to form a pair of surface electrodes whose main component is Au, Ag, Pd, Cu, or an alloy thereof; A method for manufacturing a thick film resistor, comprising: a resistance value measurement step in which a probe is brought into contact with the pair of surface electrodes to measure the resistance value; and a resistance value adjustment step in which laser trimming is performed on the thick film resistor.

9. 9. The method for manufacturing a thick film resistor according to claim 8, wherein the firing temperature of the resistor paste is 820 to 880°C, the firing temperature of the glass paste is 580 to 620°C, and the firing temperature of the electrode paste is 580 to 620°C.

10. 10. The method for manufacturing a thick film resistor according to claim 8, wherein the glass paste and the electrode paste are fired simultaneously.

11. The method for manufacturing a thick film resistor according to any one of claims 8 to 10, further comprising, before the thick film resistor forming step, an insulating substrate preparing step of printing an electrode paste on the back surface of the insulating substrate and firing the printed electrode paste at a firing temperature of 820 to 880°C to form a pair of back surface electrodes.

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