Powder composition for coating thick film resistors and glass paste for coating thick film resistors

Abstract

To provide a powder composition for thick-film resistor coating that can be calcined at 650°C or lower, or even at lower temperatures, has chemical resistance, and is substantially free of lead, and a glass paste for thick-film resistor coating.SOLUTION: A powder composition for thick-film resistor coating contains lead-free glass powder, and inorganic oxide powder. There is also provided a glass paste for thick-film resistor coating that contains lead-free glass powder, inorganic oxide powder, resin, and solvent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a powder composition for coating a thick film resistor and a glass paste for coating a thick film resistor. In particular, the present invention relates to a powder composition for coating a thick film resistor and a glass paste for coating a thick film resistor that can be used as a material for a protective glass layer for protecting a thick film resistor or the like in the manufacture of electronic components such as chip resistors, hybrid ICs, or resistor networks.

Background Art

[0002] In the manufacturing process of general chip resistors, hybrid ICs, resistor networks, etc., a thick film conductor paste mainly composed of Ag or Au is printed on an alumina substrate and fired to form a pair of electrodes by providing an electrode interval, and a resistor paste is printed between the obtained pair of electrodes so as to connect the pair of electrodes and fired to form a thick film resistor. The thick film resistor in the state of being printed and fired in this way has a problem that the yield is poor in order to obtain a resistance value within a target range because the resistance value distribution is large.

[0003] In order to solve such a yield problem, generally, the resistance value of the thick film resistor is increased by laser trimming and adjusted to a resistance value within a target range. Further, for the purpose of improving the accuracy of laser trimming and the reliability of an electronic component, which is a product using the obtained thick film resistor, a protective glass paste may be printed and fired on the thick film resistor before laser trimming. Thereby, a protective glass layer (precoat) is formed, and then laser trimming is performed through the obtained protective glass layer.

[0004] For example, Patent Document 1 discloses a method for manufacturing a resistor. The precoat glass paste or the like fired at 590 ° C. disclosed in Patent Document 1 was generally composed of a glass powder containing lead. However, in recent years, the lead component is undesirable from the viewpoints of influence on the human body and environmental pollution, and the development of a lead-free composition for coating a thick film resistor has been strongly demanded.

[0005] As an example of a chip resistor, FIG. 1 shows a schematic cross-sectional side view of a chip resistor 100. The chip resistor 100 includes an electrode 20 mainly made of silver formed by providing an interelectrode distance on the surface of an alumina substrate 10, a thick film resistor 30 provided so as to straddle the electrode 20, and a protective glass layer 41 covering the thick film resistor 30. The electrode 20 is covered with a plating layer 60 such as nickel.

[0006] The protective glass layer 41 prevents the scattered matter generated by laser trimming from adhering onto the thick film resistor 30, and also prevents the laser light used for laser trimming from directly hitting the thick film resistor 30 due to the protective glass layer 41. Thus, the protective glass layer 41 has the function of reducing the damage that the thick film resistor 30 receives from the laser light during laser trimming.

[0007] After laser trimming, as an overcoat, a protective glass paste identical to the protective glass layer 41 or a protective glass paste different from the protective glass layer 41 is printed and baked so as to cover the surfaces of the thick film resistor 30 and the protective glass layer 41, thereby forming a surface protective glass layer 42 for protecting the thick film resistor 30 from the external environment. Alternatively, instead of the surface protective glass layer 42, after laser trimming, a thermosetting protective resin paste is printed and thermoset to form a surface protective resin layer 42 for protecting the thick film resistor 30 from the external environment.

[0008] After forming the surface protective glass layer 42 or the surface protective resin layer 42, the surface of the electrode 20 is coated with nickel plating or tin plating by, for example, a wet plating method. The surface protective glass layer 42 and the surface protective resin layer 42 have chemical resistance that is not eroded by the plating solution. However, even when the thick film resistor 30 can be protected from the external environment by the surface protective glass layer 42 or the surface protective resin layer 42, the protective glass layer 41 between the surface protective glass layer 42 or the surface protective resin layer 42 and the thick film resistor 30 is also required to have the same chemical resistance so as not to be eroded by the plating solution.

[0009] In addition, Patent Document 2 discloses a glass paste technology for a precoat layer that can be fired at 700°C or lower and has chemical durability, and substantially contains no lead. And Patent Document 2 discloses the result of forming a precoat layer by firing at 650°C. Note that the firing temperature when forming a precoat layer in Patent Document 2 is higher than the firing temperature disclosed in Patent Document 1.

[0010] When the protective glass layer 41 is formed by firing, if the firing temperature is high, the variation in the resistance value of the thick film resistor 30 becomes large. In particular, when the firing temperature exceeds 650°C, the resistance value of the thick film resistor 30 may vary significantly. Therefore, it is important to form the protective glass layer 41 at a firing temperature of 650°C or lower in order not to reduce the product yield.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] In view of such circumstances, an object of the present invention is to provide a powder composition for coating a thick film resistor and a glass paste for coating a thick film resistor that can be fired at 650°C or lower, and further at a lower temperature, have chemical resistance, and substantially contain no lead.

Means for Solving the Problems

[0013] In order to solve the above problems, the powder composition for coating a thick film resistor of the present invention contains a lead-free glass powder and an inorganic oxide powder. See, the lead-free glass powder contains 5 mass% to 25 mass% of SiO 2 and 1 mass% to 5 mass% of B 2 O 3 and 2 mass% to 5 mass% of Al2 O 3 and 40 mass% to 80 mass% of Bi 2 O 3 and the inorganic oxide powder is chromium sesquioxide powder 。

[0016] In addition, in order to solve the above problems, the glass paste for coating a thick film resistor of the present invention contains lead-free glass powder, inorganic oxide powder, resin, and solvent.

Effect of the Invention

[0017] According to the present invention, it is possible to provide a powder composition for coating a thick film resistor and a glass paste for coating a thick film resistor that can be fired at 650°C or lower, further at a lower temperature, have chemical resistance, and are substantially free of lead.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0019] Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments.

[0020] [Powder Composition for Coating a Thick Film Resistor] The powder composition for coating a thick film resistor of the present embodiment is characterized by containing lead-free glass powder and inorganic oxide powder.

[0021] 〈Lead-free glass powder〉 For the powder composition for coating thick film resistors, it is necessary that the glass powder melts sufficiently during firing so that each particle of the glass powder fuses. If each particle of the glass powder does not fuse in this way, the strength as a protective glass layer will be insufficient, and the chemical resistance against nickel plating, tin plating, etc. will not be satisfied. Also, when defects occur in the surface protective glass layer or the surface protective resin layer, if there are also defects in the protective glass layer, there is a problem that the thick film resistor itself is directly exposed to the external environment.

[0022] Also, when printing and firing a glass paste for coating thick film resistors on a thick film resistor to form a protective glass layer, if the firing temperature TC (°C) is high, the variation in the resistance value of the thick film resistor will increase. In a normal thick film resistor, when firing the glass paste for coating thick film resistors at a firing temperature TC (°C) exceeding 650 °C, the variation in the resistance value of the thick film resistor becomes too large. Therefore, the firing temperature TC (°C) of the thick film protective glass paste is preferably 650 °C or lower, more preferably 640 °C or lower, and even more preferably 620 °C or lower. Note that the lower limit of the firing temperature (°C) needs to be higher than the decomposition temperature of the organic binder contained in the glass paste for coating thick film resistors, so it is 400 °C.

[0023] To correspond to such a firing temperature and to achieve a state where each particle of the glass powder fuses, it is desirable that the softening point of the lead-free glass powder is 10 °C to 50 °C lower than the firing temperature when forming the protective glass layer. Here, the softening point can be measured for the lead-free glass by differential thermal analysis (TG-DTA). In the atmosphere, the temperature is raised and heated at 10 °C / min, and the temperature of the peak where the next differential thermal curve on the high-temperature side of the temperature at which the decrease in the differential thermal curve on the lowest-temperature side of the obtained differential thermal curve appears is the softening point temperature.

[0024] If the softening point deviates from a temperature 10°C to 50°C lower than the firing temperature, even after firing, each particle of the glass powder will not fuse sufficiently, resulting in defects in the protective glass layer. As a result, the thick film resistor itself may be directly exposed to the external environment. In addition, the glass powder may melt and flow out into areas other than between the electrodes of the chip resistor, possibly causing defects in the shape of the protective glass layer.

[0025] In this embodiment, as the composition of the lead-free glass powder, 5% by mass to 25% by mass of SiO 2 1% by mass to 5% by mass of B 2 O 3 , 2% by mass to 5% by mass of Al 2 O 3 , 40% by mass to 80% by mass of Bi 2 O 3 can be mentioned. Glass containing Bi is widely known as a lead-free glass with a low softening point, and Bi 2 O 3 has been attracting attention as a low softening point glass as a component to replace PbO.

[0026] Here, "lead-free" means that it contains substantially no lead, including the case where it does not contain lead and the case where, for example, due to lead being mixed into raw material powders such as conductive powders and oxide powders containing lead during the manufacturing process, it is allowed to include the case where lead is contained as an unavoidable impurity at 100 ppm by mass or less.

[0027] The lead-free glass powder preferably contains 5% by mass to 25% by mass of SiO 2 and more preferably contains 5% by mass to 23% by mass of SiO 2 . If the content of SiO 2 is less than 5.0% by mass, the water resistance and acid resistance of the resulting protective glass layer may decrease. Also, if the content of SiO 2 exceeds 25.0% by mass, there is a risk that the softening point SPa (°C) will become too high.

[0028] Next, the lead-free glass powder contains 1% by mass to 5% by mass of B 2 O3 Preferably contains B 2 O 3 If the content of B 2 O 3 is less than 1.0% by mass, the softening point (°C) becomes high, and the mechanical strength of the obtained thick-film protective glass layer may decrease. Also, when the content of B

[0029] And the lead-free glass powder preferably contains 2% to 5% by mass of Al 2 O 3 If the content of Al 2 O 3 is less than 2.0% by mass, the obtained thick-film protective glass layer is likely to crystallize, and the water resistance and acid resistance of the obtained thick-film protective glass layer may decrease. If the content of Al 2 O 3 exceeds 5.0% by mass, there is a risk that the softening point (°C) becomes too high.

[0030] Also, the lead-free glass powder preferably contains 40% to 80% by mass of Bi 2 O 3 If the content of Bi 2 O 3 is less than 40.0% by mass, there is a risk that the softening point (°C) becomes too high. If the content of Bi 2 O 3 exceeds 80.0% by mass, the water resistance and acid resistance of the obtained thick-film protective glass layer may decrease.

[0031] (Other components) Also, the lead-free glass powder may contain components other than SiO 2 , B 2 O 3 , Al 2 O 3 , and Bi 2 O 3 Examples of other components include BaO, CaO, SrO, TiO 2 , ZrO 2 , ZnO, SnO 2or MgO or the like and Li 2 O, Na 2 O, or K 2 O or other alkali metal oxides can be mentioned. Although the alkali metal oxide has a great effect of lowering the softening point SPa (°C), if it is contained in a large amount, there is a possibility of increasing the resistance value variation due to the voltage load of the thick film resistor. Therefore, the content of these as other components is preferably 1.0% by mass or less in total.

[0032] The particle size of the lead-free glass powder is desirably such that the 50% volume cumulative particle size (median diameter) is 10 μm or less. If the median diameter is larger than 10 μm, it may be difficult to form a dense protective glass layer. Furthermore, due to the miniaturization of electronic components in recent years, the thickness of the protective glass layer also tends to become thinner. Considering this trend, it is desirable to further reduce the 50% volume cumulative particle size of the lead-free glass powder, which is the raw material of the protective glass layer, so that the median diameter is 5 μm or less. The 50% volume cumulative particle size can be measured by a particle size distribution meter using laser diffraction.

[0033] 〈Inorganic oxide powder〉 When the protective glass layer obtained by firing the powder composition for coating a thick film resistor of this embodiment, which contains lead-free glass powder and inorganic oxide powder, is immersed in sulfuric acid having the same pH as nickel plating solution, tin plating solution, etc., although cracks may occur on its surface, the portion surrounded by the cracks does not peel off. That is, this protective glass layer can satisfy the chemical resistance in that it prevents the occurrence of defects by suppressing the peeling of cracks and can prevent the thick film resistor itself from being directly exposed to the external environment.

[0034] The inorganic oxide powder used in combination with the lead-free glass powder coexists with the protective glass layer during the firing process, thereby satisfying the chemical resistance and suppressing the peeling of cracks during acid immersion.

[0035] The inorganic oxide powder needs not to melt during the firing of the powder composition for coating the thick film resistor. Such inorganic oxide powders can use silicates such as aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, zircon, white pigments such as titanium oxide, red pigments such as red lead, green pigments such as chromium sesquioxide, and black pigments such as Co-Cr-Fe oxide and Co-Mn-Fe oxide.

[0036] In the powder composition for coating the thick film resistor, it is desirable that the inorganic oxide powder is contained in an amount of 0.5 parts by mass or more and 5.6 parts by mass or less, more preferably 0.8 parts by mass or more and 3 parts by mass or less, based on 100 parts by mass of the lead-free glass powder. If the inorganic oxide powder is contained in an amount exceeding 5.6 parts by mass based on 100 parts by mass of the lead-free glass powder, it may be difficult to ensure the transparency of the protective glass layer to such an extent that laser trimming is not hindered.

[0037] The particle size of the inorganic oxide powder is preferably 0.5 μm to 2.5 μm in terms of 50% volume cumulative particle size (median diameter). Note that the 50% volume cumulative particle size can be measured by a particle size distribution meter using laser diffraction.

[0038] (Other components) In addition to the lead-free glass powder and chromium sesquioxide powder, the powder composition for coating the thick film resistor of the present invention can contain components such as additives as needed. Examples of the additives include inorganic powders for adjusting the thermal expansion coefficient, such as mullite powder.

[0039] [Glass paste for coating thick film resistor] The powder composition for coating the thick film resistor of the present invention can be made into a glass paste for coating the thick film resistor by mixing and dispersing it together with an organic vehicle or a solvent to form a paste. Also, instead of or in combination with the powder composition for coating the thick film resistor, the aforementioned lead-free glass powder and inorganic oxide powder may be used.

[0040] For the reasons described above, the inorganic oxide powder is contained in an amount of 0.5 parts by mass or more and 5.6 parts by mass or less with respect to 100 parts by mass of the lead-free glass powder.

[0041] Also, for the reasons described above, the lead-free glass powder preferably contains 5% to 25% by mass of SiO 2 and 1% to 5% by mass of B 2 O 3 and 2% to 5% by mass of Al 2 O 3 and 40% to 80% by mass of Bi 2 O 3

[0042] 〈Resin〉 Examples of the resin that can be used include resins generally used in pastes such as glass pastes for coating thick film resistors. For example, ethyl cellulose, alkyd resin, acrylic resin, etc. can be used.

[0043] 〈Solvent〉 Examples of the solvent that can be used include solvents generally used in pastes such as glass pastes for coating thick film resistors. For example, terpineol, butyl carbitol, etc. can be mentioned.

[0044] The resin and the solvent can be premixed to form an organic vehicle state, and a paste for forming a thick film conductor can be manufactured using this. For example, from the viewpoints of cost and ease of handling, a solution of ethyl cellulose dissolved in terpineol can be used as the organic vehicle. In the organic vehicle, the ratio of the resin to the solvent is appropriately selected according to the printability and coating method in the final glass paste composition for coating thick film resistors. For example, the resin content in the organic vehicle can be 2 to 50% by mass.

[0045] ​The content in the glass paste for coating thick film resistors as an organic vehicle can be appropriately selected in consideration of the viscosity of the paste, the oil supply amount of the powder, the coating workability, etc. If the viscosity of the glass paste for coating thick film resistors is too high, it may be substantially impossible to coat the paste. Also, if the content of the organic vehicle becomes too large, there is a risk of sedimentation and separation of lead-free glass particles and inorganic oxide powder particles, and there is a risk that the density of the protective glass layer after firing will be greatly reduced and the chemical resistance will not be satisfied.

[0046] For example, with respect to 100 parts by mass in total of the lead-free glass powder and the inorganic oxide powder, the content of the organic vehicle can be 15 parts by mass to 100 parts by mass. Considering printability, ease of coating, sedimentation and separation of particles as a paste, chemical resistance, raw material cost, etc., such content is preferably 20 parts by mass to 80 parts by mass.

[0047] The glass paste for coating thick film resistors of the present invention can be manufactured by mixing and dispersing a powder composition for coating thick film resistors and an organic vehicle. This mixing method and dispersion method are not particularly limited, but for example, it is common to use a three-roll mill, a ball mill, etc. Even when using lead-free glass powder and inorganic oxide powder instead of or in combination with the powder composition for coating thick film resistors, the glass paste for coating thick film resistors can be manufactured in the same manner as above. Also, the viscosity of the obtained glass paste for coating thick film resistors is appropriately selected according to the film thickness of the target protective glass layer, the type of the thick film resistor to be coated with the paste, etc.

[0048] (Other components) In the glass paste for coating thick film resistors of the present invention, in addition to the lead-free glass powder and the chromic oxide powder, components such as additives can be contained as necessary.

[0049] [Method for forming protective glass layer] The protective glass layer can be formed by printing the glass paste for coating the thick-film resistor of the present invention so as to cover the thick-film resistor, drying it, and then firing it. Considering chemical resistance and processability such as laser trimming, it is desirable to form the protective glass layer to have a film thickness of 3 μm to 10 μm after firing.

[0050] The method for forming the protective glass layer can include, for example, a coating step of applying the glass paste for coating the thick-film resistor of the present invention to the surface of the thick-film resistor of the chip resistor, a drying step of drying the chip resistor coated with the paste, and a firing step of firing it at a temperature of 650 °C or lower thereafter.

[0051] (Coating step) The coating method is not particularly limited, and known techniques such as screen printing, printing methods such as letterpress printing and gravure printing, and other drawing methods using a dispenser can be used. However, from the viewpoint of mass production with an appropriate film thickness, it is preferable to apply by screen printing.

[0052] (Drying step) After applying the glass paste for coating the thick-film resistor to the thick-film resistor, it is preferable to dry the coated film together with the chip resistor under temperature conditions of 80 °C or higher and 200 °C or lower for 2 minutes or more and 15 minutes or less. In this way, by providing a drying step between the coating step and the firing step, it is possible to prevent the volatilization and combustion of volatile components such as solvents due to the remaining of volatile components such as solvents even during firing. Therefore, when using a firing furnace in the firing step, the effect of preventing the contamination of the firing furnace can be obtained. In this step, the drying method is not particularly limited, and known means such as an oven or a belt-type drying furnace can be used. However, from the viewpoint of mass productivity, it is preferable to dry by a belt-type drying furnace. Note that if the drying temperature is less than 80 °C, the time required for drying becomes long, which may deteriorate productivity, so it may not be preferable. Also, if the drying temperature exceeds 200 °C, the resin may oxidize and the film after drying may become brittle.

[0053] (Firing step) In the firing process after the drying process, the dried film is heated together with each chip resistor to fire the film. As the firing method, it is preferable to use a belt furnace. In this case, the peak temperature in firing is carried out at 650°C or lower so that the resistance value of the thick film resistor does not significantly fluctuate. Also, considering that the particles of the lead-free glass fuse together, it is preferable to fire under a temperature condition of 400°C or higher.

[0054] It is necessary to hold at the above peak temperature for 2 to 20 minutes, preferably 5 to 13 minutes. If the holding time of the peak temperature exceeds 20 minutes, the protective glass layer may be over-sintered, and if such a holding time is less than 2 minutes, there is a risk that the sintering will be insufficient. Also, the total time of the firing process, including the temperature rise to the peak temperature, the holding of the peak temperature, and the cooling from the peak temperature, needs to be 20 to 90 minutes, preferably 30 to 60 minutes. If the total time is less than 20 minutes, the temperature rise rate and the cooling rate become too large, and there is a risk that cracks will occur in the protective glass layer due to rapid temperature changes. Also, if the total time exceeds 90 minutes, there may be a problem that productivity deteriorates.

[0055] In order to fire at the above-mentioned peak temperature and firing time, the temperature rise rate to the peak temperature is preferably 20°C / min or more and 150°C / min or less, and the cooling rate from the peak temperature is preferably 20°C / min or more and 200°C / min or less. If the temperature rise rate is less than 20°C / min or the cooling rate is less than 20°C / min, the productivity may deteriorate, which is not preferable. Also, if the temperature rise rate exceeds 150°C / min or the cooling rate exceeds 200°C / min, there is a possibility that cracks will occur in the protective glass layer due to rapid temperature changes, which is not preferable.

[0056] Also, the atmosphere during firing is not particularly limited, but from the viewpoint of the softening of the lead-free glass, it is preferable to fire in an air atmosphere.

[0057] With the protective glass layer formed as described above, chemical resistance can be satisfied. Specifically, when the protective glass layer is immersed in sulfuric acid with a pH corresponding to a nickel plating solution, the glass layer will not dissolve in the sulfuric acid. Although cracks may occur on its surface, the areas surrounded by the cracks will not peel off. However, the cracks that occur will not erode to the inside of the protective glass layer, and the thick film resistor can be protected from the external environment by the protective glass layer.

[0058] Note that if the film thickness of the protective glass layer is extremely thin, for example, less than 2 μm, when cracks with a width of 2 μm or more occur, the thick film resistor may not be protected. Therefore, the film thickness of the protective glass layer is important, and it is desirable to form it so that the film thickness of the protective glass layer after firing is 3 μm to 10 μm as described above.

Example

[0059] Hereinafter, the present invention will be further described with reference to examples, but the scope of the present invention is not limited by these examples.

[0060] [Manufacture of Powder Composition for Coating Thick Film Resistor] As shown in Table 1, 100 parts by mass of a lead-free glass powder with a softening point (°C) of 595°C and a 50% volume cumulative particle size of 2.0 μm, having a composition of SiO 2 : 21.6% by mass, B 2 O 3 : 1.4% by mass, Al 2 O 3 : 3.3% by mass, and Bi 2 O 3 : 72.8% by mass, and 1.4 parts by mass of chromic oxide powder with a 50% volume cumulative particle size (median diameter) of 1.0 μm were blended at the blending ratios shown in Table 2 to obtain a powder composition for coating a thick film resistor.

[0061]

Table 1

[0062] [Manufacture of Glass Paste for Coating Thick Film Resistors] To 100 parts by mass of the obtained powder composition for coating thick film resistors, 30 parts by mass of a 4% ethyl cellulose solution in terpineol as an organic vehicle was added, and the mixture was mixed and dispersed with a three-roll mill to obtain the glass paste for coating thick film resistors of the example.

[0063] Also, without mixing chromium sesquioxide powder, to 100 parts by mass of a lead-free glass powder having the composition shown in Table 1, 30 parts by mass of a 4% ethyl cellulose solution in terpineol as an organic vehicle was added, and the mixture was mixed and dispersed with a three-roll mill in the same manner as in the example to obtain the glass paste for coating thick film resistors of the comparative example.

[0064] The obtained glass paste for coating thick film resistors was screen-printed on a 96% alumina substrate (25.4 mm × 25.4 mm × 1 mm) in a square pattern of 20 mm in length and 20 mm in width. After drying, it was fired in a firing furnace under the conditions of a peak temperature (°C) of 600°C and a peak time of 5 minutes to obtain the protective glass layers according to Example 1 and Comparative Example 1 having the film thicknesses shown in Table 2.

[0065] The protective glass layers according to Example 1 and Comparative Example 1 were immersed in 5% sulfuric acid at 25°C for 240 minutes together with the alumina substrate to evaluate the chemical resistance and crack peeling of the protective glass layer. The evaluation of the chemical resistance was performed by visually observing the change in the surface of the protective glass layer before and after immersion in sulfuric acid. Also, the evaluation of crack growth inhibition was performed by scanning electron microscope (SEM) observation after sulfuric acid immersion. The evaluation results are shown in Table 2.

[0066] The SEM image taken before sulfuric acid immersion of the surface of the protective glass layer according to Example 1 is shown in Figure 2, and the SEM image taken after sulfuric acid immersion of the surface of the protective glass layer according to Example 1 is shown in Figure 3. Also, the SEM image taken before sulfuric acid immersion of the surface of the protective glass layer according to Comparative Example 1 is shown in Figure 4, and the SEM image taken after sulfuric acid immersion of the surface of the protective glass layer according to Comparative Example 1 is shown in Figure 5.

[0067] Although cracks have occurred on the surface of the protective glass layer according to Example 1 after sulfuric acid immersion as shown in Figure 3, no peeling of the surface has occurred. On the other hand, as shown in Figure 5, it can be seen that cracks have occurred on the surface of the protective glass layer according to Comparative Example 1 after sulfuric acid immersion and the surface has peeled off. According to Figures 3 and 5, it can be seen that the protective glass layer of Example 1 has chemical resistance.

[0068]

Table 2

[0069] The protective glass layer obtained using the powder composition for coating a thick film resistor of the example containing lead-free glass powder and chromic oxide powder did not change in surface appearance upon visual observation even when immersed in sulfuric acid. Also, even when looking at the SEM image, although cracks sometimes occurred on the surface, peeling of the areas surrounded by the cracks was suppressed, confirming that there is no problem with chemical resistance. Also, the fact that the appearance such as gloss did not change visually even when the protective glass layer was immersed in sulfuric acid means that the protective glass layer has chemical resistance. Since the visual appearance did not change in the protective glass layer in the example, it was confirmed that there is no problem with chemical resistance even in visual observation.

[0070] On the other hand, the protective glass layer obtained using the powder composition for coating a thick film resistor of the comparative example that uses the same lead-free glass powder as in the example and does not contain chromic oxide powder did not change in appearance such as gloss in visual observation due to immersion in sulfuric acid, but it was confirmed from the SEM image that peeling of cracks has occurred, indicating that there may be a possibility that it does not satisfy chemical resistance.

[0071] [Summary] From the above results, according to this embodiment, it was confirmed that the lead-free protective glass layer formed at a firing temperature of 600 °C also has chemical resistance. Therefore, the thick-film resistor coating glass paste of the present invention, which is a molding material for the protective glass layer having chemical resistance, does not contain lead and is a desirable material from the viewpoint of environmental protection, and can replace the thick-film resistor glass paste and the like disclosed in Patent Document 1 and the like.

Explanation of Signs

[0072] 10 Alumina substrate 20 Electrode 30 Thick-film resistor 41 Protective glass layer 42 Surface protective glass layer (surface protective resin layer) 60 Plating layer 100 Chip resistor

Claims

1. A powder composition for coating a thick film resistor, comprising lead-free glass powder and inorganic oxide powder, wherein the lead-free glass powder contains 5% to 25% by mass of SiO₂, 1% to 5% by mass of B₂O₃, 2% to 5% by mass of Al₂O₃, and 40% to 80% by mass of Bi₂O₃, and the inorganic oxide powder is chromium sesquioxide powder.

2. The powder composition for coating a thick film resistor according to Claim 1, wherein the inorganic oxide powder is contained in an amount of 0.5 part by mass or more and 5.6 parts by mass or less with respect to 100 parts by mass of the lead-free glass powder.

3. A glass paste for coating a thick film resistor, containing the powder composition for coating a thick film resistor according to Claim 1 or 2.

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