JP5003250B2 - Thick film resistor paste, thick film resistor and method for forming the same - Google Patents

Description

  The present invention relates to a thick film resistor paste, specifically, a copper-nickel thick film resistor paste that can form a thick film resistor having high adhesive strength with an insulating substrate and does not contain harmful lead or cadmium, and the same. The present invention relates to a method for forming a thick film resistor using a thick film resistor, and a thick film resistor obtained by this method.

Conventionally, in order to obtain a ceramic thick film substrate having a thick film resistor, a paste containing a noble metal powder such as Ag or Pd and glass frit in an organic vehicle is printed on the ceramic substrate and fired to obtain a conductor. After the (electrode) is formed, a resistor paste containing conductive powder such as RuO ₂ or Ag—Pd and lead oxide glass is printed thereon and then fired.

  In recent years, as electronic components have become lighter, thinner and shorter, reduction in manufacturing cost is strongly demanded, and when using a noble metal composition containing silver, there is a concern about an increase in insulation failure due to silver electromigration. Yes. From such a viewpoint, instead of a paste containing an expensive noble metal powder such as Ag or Pd, a paste using a copper powder has been studied, and a thick film substrate on which a copper electrode is formed has been put to practical use.

Thus, when using copper as an electrode, in order to prevent copper being oxidized at the time of baking, it is necessary to perform baking of a paste in nitrogen atmosphere. However, in the firing in a nitrogen atmosphere, when a resistor paste containing a conductive powder such as RuO ₂ or Ag—Pd and lead oxide glass is used for resistor formation, the oxide in the resistor paste is used. Has undergone a reduction, which makes it difficult to obtain a desired resistance value.

  In addition, firing in a nitrogen atmosphere has a problem that organic components in the paste react with oxygen and volatilize, so-called burnout tends to be insufficient. In particular, when baking a large number of substrates patterned with paste at once, or when the pattern area of a resistor formed with paste on the substrate is large, the unburned residue of organic components in the paste increases, The sintered compactness of the resulting resistor was deteriorated, and the adhesive strength with the ceramic substrate was likely to be lowered.

  In addition, since lead, cadmium, and the like have an adverse effect on the environment, in recent years, there has been a demand for a hazardous substance-free material with measures such as deleading and cadmium removal. The same applies to thick film substrates, and there is a strong demand for thick film resistor pastes that use toxic substance-free materials, particularly glass powder that does not contain lead or cadmium.

  In response to this demand, Japanese Patent Application Laid-Open No. 11-233302 discloses a conductive powder made of copper and nickel, a glass powder not containing cadmium having a softening point in the range of 400 to 500 ° C., vanadium oxide, or vanadium oxide. Film resistor paste (composition), and at least one metal oxide selected from the group consisting of bismuth oxide, manganese oxide, silicon oxide, titanium oxide, antimony oxide, tin oxide and cobalt oxide, and an organic vehicle Has been proposed.

  In this thick film resistor paste, the conductive powder is copper-nickel based and glass powder that does not contain cadmium harmful to the environment is used. The thick film resistor paste is fired in a nitrogen atmosphere and has excellent adhesion strength to the ceramic substrate. A film resistor can be formed. However, since this thick film resistor paste needs to use lead oxide glass in order to obtain a desired softening point, it does not sufficiently satisfy the demand for harmful substances.

  Japanese Patent Laid-Open No. 2006-066475 discloses a thick film resistor paste (composition) containing conductive powder made of copper and nickel, NiO powder, glass powder not containing lead and cadmium, and an organic vehicle. ) Has been proposed. This thick film resistor paste satisfies the requirement of no harmful substances. However, there is a problem that it is easily influenced by the atmosphere such as oxygen concentration, and does not adhere to the substrate unless the firing atmosphere is strictly controlled, and peels off when the substrate size increases.

  Specifically, the thick film resistor paste described in Japanese Patent Application Laid-Open No. 2006-066475 has no problem when the substrate size is about 1 inch square, but is currently widely used in the manufacture of chip resistors. When the ceramic substrate has a size of 5 cm × 6 cm or more, the substrate size is large, and therefore, the thick film resistor formed on the ceramic substrate is partially peeled off due to the influence of variations in the furnace atmosphere. For this reason, as a thick film resistor paste applied to a large substrate, it could not withstand practical use.

JP 11-233302 A JP 2006-066475 A

  In view of the above-described conventional problems, the present invention uses a copper-nickel-based conductive powder, is free of harmful substances containing no harmful lead or cadmium, and is fired in a nitrogen atmosphere. Film resistor paste having a high adhesive strength, little variation in resistance value, and having an excellent resistance temperature coefficient (TCR) regardless of the size of the film, and a thick film resistor using the same And a method of forming the same.

  The inventors of the present invention use conventional copper-nickel-based conductive powder and have a problem with thick film resistor paste that does not contain harmful lead and cadmium, that is, when the substrate size is increased, it is formed on the ceramic substrate. As a result of intensive research on the cause of partial peeling of thick film resistors, the content of iron mixed during kneading with a conventional three-roll mill made of iron has been affected. I found out. Based on this finding, by suppressing the iron content of the paste, a thick film resistor with high adhesive strength can be obtained even when fired in a non-oxidizing atmosphere such as nitrogen, even with a large ceramic substrate. This has been proved and the present invention has been completed.

That is, the thick film resistor paste provided by the present invention includes a conductive powder composed of copper and nickel, a glass powder not containing lead and cadmium, a NiO powder, and an organic vehicle, and has an iron content of 50. It is the mass ppm or less.

In thick-film resistor paste of the present invention, the glass _powder, SiO 2: 5 to 20 _{wt%, B} 2 O 3: _{30~50 wt%, Al} 2 O 3: _1~5 wt%, ZnO: 30-40 _wt%, Na 2 O: preferably consists of 5 to 10 wt%.

  In the above thick film resistor paste of the present invention, the mass ratio of copper and nickel in the conductive powder is preferably Cu: Ni = 40: 60 to 80:20. Moreover, it is preferable that content of the said electroconductive powder is 50-90 mass% with respect to the whole paste.

  In the thick film resistor paste of the present invention, the content of the glass powder is preferably 3 to 40 parts by mass with respect to 100 parts by mass of the conductive powder. Furthermore, it is preferable that content of the said NiO powder is 1-40 mass parts with respect to 100 weight part of electroconductive powder.

  In the thick film resistor paste of the present invention, the organic vehicle is preferably composed of a methacrylic ester resin or a poly-α-methylstyrene resin and a solvent terpineol or dihydroterpineol.

  The present invention also provides a method for forming a thick film resistor, characterized in that the thick film resistor paste described above is applied to a ceramic substrate and then fired at a temperature of 1000 ° C. or lower in a non-oxidizing atmosphere. To do. Furthermore, the present invention provides a thick film resistor which is formed by this method of forming a thick film resistor and does not contain lead and cadmium.

  According to the present invention, there is provided a thick film resistor paste which is free of harmful substances containing no harmful lead and cadmium and can be obtained by firing in a non-oxidizing atmosphere to obtain a thick film resistor having high adhesive strength. be able to. Also, by using this thick film resistor paste, the resistance value variation and the resistance temperature coefficient (TCR) are excellent, the adhesive strength with the ceramic substrate is high, and the harmful substance-free thick film resistor and its simple formation A method can be provided.

  In particular, the conventional copper-nickel-based conductive powder and harmful substance-free thick film resistor paste is formed on the substrate when the substrate size is about 5 cm × 6 cm, which is currently widely used in the manufacture of chip resistors. The thick film resistor was partially peeled, whereas the thick film resistor paste of the present invention did not cause partial peeling even when the substrate size was about 5 cm × 6 cm or more. A highly reliable thick film resistor can be formed stably.

  The thick film resistor paste of the present invention comprises conductive powder (A) made of copper and nickel, glass powder (B) containing no lead or cadmium, NiO powder (C), and organic vehicle (D). Contains. Particularly when a thick film resistor is formed on a ceramic substrate having a large substrate size, the iron content in the thick film resistor paste is 100 mass ppm or less in order to prevent peeling of the thick film resistor during firing. It is important to.

  For example, for a thick film resistor paste having an iron content of 120 mass ppm, a belt-type firing furnace is printed on an alumina substrate of 5 cm × 6 cm and dried, and has a peak temperature of 900 ° C. and a holding time of 10 minutes in a non-oxidizing atmosphere. When fired, partial peeling occurs in a portion of the thick film resistor obtained. On the other hand, in the thick film resistor paste having an iron content of 40 mass ppm, the resulting thick film resistor may be partially or wholly peeled even when fired in the same manner using the same substrate as above. There is no.

  The cause of the peeling of a part of the thick film resistor is considered to be the influence of iron in the paste as described above. That is, the iron in the paste inhibits the melting of the glass powder during firing, and further, the melting of the glass powder is locally inhibited by the variation in the non-oxidizing atmosphere. However, when the iron content is reduced to 100 ppm by mass or less, even if there is a variation in the non-oxidizing atmosphere, since there is no obstacle due to iron, melting of the glass powder is ensured, and the thick film resistor No peeling occurs.

  In general, each raw material of the paste described above is purified in order to improve the purity of the raw material for manufacturing these materials, or is washed in order to remove impurities when manufacturing each raw material. However, as a result, it may contain several tens of mass ppm of iron as an impurity. Therefore, the thick film resistor paste using these raw materials contains iron as an impurity. Furthermore, a large amount of iron is mixed in the paste from an iron manufacturing apparatus, a spatula, a medicine spoon, and the like that are conventionally used when manufacturing a paste, particularly from an iron three-roll mill in the paste kneading process.

  Therefore, in the present invention, in addition to refining and washing the raw materials, the production apparatus such as a three-roll mill uses a ceramic product that does not contain iron. The iron contained in the resistor paste is controlled to 100 mass ppm or less. The lower the iron content in the paste, the more desirable, preferably 80 ppm by mass or less, and more preferably 50 ppm by mass or less.

  The iron content in the paste can be obtained by chemical analysis. For example, the paste can be dissolved in an acid such as aqua regia, sulfuric acid, nitric acid, etc. and measured by an ICP (inductively coupled plasma) emission spectrometer.

  In the main component constituting the thick film resistor paste of the present invention, the conductive powder (A) may be made of copper (Cu) and nickel (Ni), specifically, copper powder and nickel powder. A mixed powder, an alloy powder of copper and nickel, or a mixture powder obtained by mixing copper powder and / or nickel powder with copper-nickel alloy powder can be used.

  In the conductive powder (A), the copper powder and the nickel powder can be obtained by reducing each sulfate aqueous solution with hydrazine, and can be obtained by atomizing a metal melt. Moreover, if hydrazine is added to the mixed solution of the copper and nickel sulfate aqueous solution, a coprecipitation mixture of copper and nickel is generated, and dried to obtain a mixed powder of copper powder and nickel powder. On the other hand, the copper-nickel alloy powder can be manufactured by atomizing a mixed melt of copper and nickel.

The particle size of the conductive powder (A) made of copper and nickel is preferably 10 μm or less at D ₅₀ and more preferably 7 μm or less at D ₅₀ . A particle size D ₅₀ exceeding 10 μm is not preferable from the viewpoint of mixing with NiO powder or glass powder and dispersibility in an organic vehicle. For confirmation of the particle size, a known particle size analyzer (for example, “Microtrack” registered trademark) can be used. D ₅₀ is the cumulative particle size distribution and the median value of the particle size.

  The weight ratio of copper (Cu) and nickel (Ni) in the conductive powder (A), that is, the Cu: Ni mass ratio is preferably in the range of 40:60 to 80:20. This is because when the Cu: Ni mass ratio is outside the above range, the temperature coefficient of resistance (TCR) exceeds 200 ppm / ° C. and cannot be used as a thick film resistor. In order to obtain a thick film resistor having a good resistance value and resistance temperature coefficient characteristics, a Cu: Ni mass ratio of 50:50 to 70:30 is particularly preferable.

  The content of the conductive powder (A) in the thick film resistor paste is desirably 50 to 90% by mass with respect to the entire paste. This is because if the content of the conductive powder (A) is less than 50% by mass, the conductivity is insufficient, and if it exceeds 90% by weight, the screen printability deteriorates.

The glass powder (B) is an essential component for bonding the thick film resistor to a ceramic substrate such as alumina, and also functions as a binder for the conductive powder. The particle size of the glass powder (B) _is desirably 10μm or less at _{D 50,} 7 [mu] m or less is more preferable in _{D 50.} A particle size D ₅₀ exceeding 10 μm is not preferable from the viewpoints of mixing with copper powder, nickel powder and NiO powder, and dispersibility in an organic vehicle.

The lead (Pb) and glass powder that does not contain cadmium _{(Cd) (B), SiO} 2: 5~20 _{wt%, B} 2 O 3: _{30~50 wt%, Al} 2 O 3: _1~5 wt% , ZnO: 30 to 40% by mass, Na ₂ O: 5 to 10% by mass are preferable. ZnO has an action of promoting debinding, and B ₂ O ₃ and Na ₂ O reduce the glass softening point to about 400 to 500 ° C. A thick film resistor paste that does not contain lead is now possible.

  Further, the content of the glass powder (B) in the thick film resistor paste is preferably in the range of 3 to 40 parts by mass with respect to 100 parts by mass of the conductive powder (A), and further in the range of 4 to 20 parts by mass. preferable. If the content of the glass powder (B) is less than 3 parts by mass, the adhesion to the substrate becomes insufficient. Conversely, if it exceeds 40 parts by mass, the glass tends to exude or the rate of change in resistance value due to heat cycle is high. It is not preferable because it becomes large.

  The nickel oxide (NiO) powder (C) prevents sintering of the metal at a low temperature during the baking process of the paste, improves the volatilization (burnout) of the binder component, and dissolves in the glass. Crystallization, high softening point, and high viscosity, and prevents the molten glass from passing through the sintered grain boundary to the resistor surface, thereby strengthening the interface between the resistor and the substrate. There exists an effect | action which accelerates | stimulates formation of a glass contact bonding layer. By using the NiO powder having such a specific action and effect, combined with the suppression of the iron content described above, the glass substrate (B) containing no lead or cadmium is used, and the adhesive strength to the ceramic substrate is excellent. A copper-nickel thick film resistor can be formed.

  Further, the effect of the NiO powder (C) will be explained. When a thick film resistor is formed by baking a thick film resistor paste to which the NiO powder (C) is not added, heat such as mechanical impact or soldering is formed. When an impact is applied, the thick film resistor may be peeled off from a ceramic substrate such as alumina. By adding the NiO powder (C), it is possible to prevent the thick film resistor from being peeled off from the ceramic substrate even when a mechanical impact or the like is applied due to the above-described effects.

The particle size of the NiO powder (C) _is desirably 10μm or less at _{D 50,} 7 [mu] m or less is more preferable in _{D 50.} A particle size D ₅₀ exceeding 10 μm is not preferable in terms of mixing with copper powder, nickel powder and glass powder, and dispersibility in an organic vehicle.

  The content of the NiO powder (C) in the thick film resistor paste is preferably in the range of 1 to 40 parts by weight, more preferably in the range of 1 to 30 parts by weight with respect to 100 parts by weight of the conductive powder (A). When the content of the NiO powder (C) is less than 1 part by weight with respect to 100 parts by weight of the conductive powder (A), the above-described specific effects cannot be sufficiently exhibited. On the other hand, if it exceeds 40 parts by mass, the variation in sheet resistance value increases and the rate of change in heat cycle also increases, which is not preferable.

  The organic vehicle (D) is a medium composed of a solvent component that uniformly dissolves and disperses the conductive powder (A), the glass powder (B), and the NiO powder (C), and a resin component as a binder. Any organic vehicle having such a function is not particularly limited, and a conventionally used thick film resistor paste can be used.

  The solvent component of the organic vehicle (D) functions to dissolve the resin component and to stably disperse the conductive powder (A), the glass powder (B), and the NiO powder (C) in the paste. When the paste is applied to the substrate, the powder must be spread uniformly and vaporized by firing. Therefore, the boiling point of the solvent component is desirably about 200 to 300 ° C. If a solvent having a boiling point lower than 200 ° C. is used, the viscosity changes due to the volatilization of the solvent during the printing operation, and the boiling point is higher than 300 ° C. With the solvent, efficient drying is difficult to be performed in the drying process, and the solvent remains in the dry film. The remaining solvent component volatilizes during firing and changes the non-oxidizing atmosphere, so that the thick film resistor is altered and desired characteristics cannot be obtained.

  Specific examples of solvents that satisfy such requirements include terpineol, dihydroterpineol, butyl carbitol, butyl carbitol acetate, octanol, and diethyl phthalate. Of these solvents, terpineol, dihydroterpineol, and octanol are preferred in view of the fact that there is no fear of oxidizing copper in the conductive powder (A), availability, and handling.

  Examples of the resin component of the organic vehicle (D) include methacrylic acid ester resin, poly-α-methylstyrene resin, ethyl cellulose, maleic acid resin, vinyl acetate resin, polyvinyl alcohol, rosin, polyethylene, polyester resin, and vinylidene chloride resin. It has been known.

  Among these resins, methacrylic ester resins and poly-α-methylstyrene resins are excellent in decomposability in a non-oxidizing atmosphere such as nitrogen. The molecular weight of the methacrylic acid ester resin or poly-α-methylstyrene is not particularly limited as long as it dissolves in the solvent component. Further, there is no problem even if a copolymer obtained by copolymerizing these resins is used. On the other hand, ethyl cellulose or the like hardly decomposes in a non-oxidizing atmosphere, and therefore remains as carbon in the fired film of the thick film resistor. Residual carbon is not preferable because it impedes the meltability of the glass powder (B) and tends to cause problems such as peeling of the thick film resistor.

  Various additives conventionally used in pastes, for example, stabilizers, lubricants, antioxidants, viscosity modifiers, antifoaming agents, and the like can be blended with the organic vehicle (D). For example, when applied by screen printing, unevenness due to screen mesh marks is likely to occur in the applied paste, but glycols can be added to the organic vehicle to prevent this. This is because glycols such as ethylhexanediol, methylpentadiol, and ethylheptanediol are generally solid at room temperature, but have the effect of suppressing the generation of cracks and pinholes when used in combination with other solvents. .

  In order to adjust the thick film resistor paste of the present invention, the conductive powder (A), glass powder (B) and NiO powder (C) described above are kneaded with the organic vehicle (D) to form a paste. Good. In this case, attention should be paid to the mixing of iron from the production equipment in the so-called kneaded meat process, particularly the mixing of iron from the three-roll mill. Therefore, when the paste is kneaded, it is desirable to use a ceramic three-roll mill, pots and balls that are made of ceramic, and rotors and beads that are made of ceramic.

  In preparing the paste, the raw materials such as conductive powder and organic vehicle are agitated for coarse dispersion before kneading with three rolls, or the kneaded paste is agitated with a mixer for defoaming. However, the mixing of iron in these stirring steps is very small compared to mixing from the kneading process using an iron roll or the like, and does not affect the resistor film during firing.

  Further, the above-mentioned paste meat is a term widely known in the technical field relating to pastes, and means finish kneading in which a powder such as a pigment is dispersed in a vehicle by a bead mill or the like. In the present invention, it is a finish kneading for further dispersing a coarsely dispersed conductive powder or the like and an organic vehicle using a roll mill, a ball mill, a bead mill or the like.

  The thick film resistor paste of the present invention is applied to a ceramic substrate such as alumina by a method such as screen printing, dried at a temperature of 100 ° C. to 200 ° C., and then fired at a temperature of 1000 ° C. or less in a non-oxidizing atmosphere. By doing so, a thick film resistor can be formed.

  The thick film resistor of the present invention thus obtained does not contain harmful substances such as lead and cadmium, and has good variation in sheet resistance value and resistance temperature coefficient (TCR). Moreover, even if the adhesive strength with the ceramic substrate is high and the substrate size is large, specifically, a substrate of 5 cm × 6 cm or more, which is frequently used in the manufacture of chip resistors, partially or entirely. Also, peeling of the thick film resistor can be eliminated.

[Preparation of thick film resistor paste]
30 parts by mass of Ni powder (particle size D ₅₀ = 1 μm) and 70 parts by mass of Cu powder (particle size D ₅₀ = 3 μm) are mixed. Glass powder (particle size D ₅₀ = 4 μm) 4 with respect to 100 parts by weight of the conductive powder. Part by mass and 1 part by weight of NiO powder (particle size D ₅₀ = 1.5 μm) were blended. The glass powder used was SiO ₂ : 10% by mass, B ₂ O ₃ : 45% by mass, Al ₂ O ₃ : 2% by mass, ZnO: 36% by mass, Na ₂ O: 7% by mass. The raw material is prepared, melted at 1300 ° C., rapidly cooled, and pulverized with a jet mill.

  Next, an organic vehicle is added to the inorganic powder (conducting powder + glass powder + NiO powder) having the above composition, and blended so that the organic vehicle becomes 20% by mass with respect to 80% by mass of the inorganic powder. The thick film resistor paste of Sample 1 was prepared by kneading. The organic vehicle is obtained by dissolving 20% by mass of a methacrylic ester resin (molecular weight 60000) and 80% by mass of terpineol by heating to 60 ° C.

  Next, a thick film resistor paste of Sample 2 was prepared in the same manner as Sample 1 above, with 30 parts by weight of NiO powder per 100 parts by weight of conductive powder. As comparative examples, pastes of Sample 3 having the same composition as Sample 1 and Sample 4 having the same composition as Sample 2 were prepared in the same manner as Sample 1 except that an iron three-roll mill was used. Further, the paste of the sample 5 of the comparative example was prepared in the same manner as the sample 1 except that the NiO powder was not included.

  For each thick film resistor paste of Samples 1 to 5, the blending amount of NiO powder, the material of the three-roll mill used, and the iron content contained in the paste are summarized in Table 1 below. The iron content of the paste is obtained by dissolving the paste in aqua regia and measuring with ICP.

[Formation of thick film resistor]
The thick film resistor paste of each sample shown in Table 1 above is patterned on a alumina substrate having a length of 5 cm, a width of 6 cm, and a thickness of 0.6 mm on which a thick film copper electrode has been previously baked to form a pattern of 1.0 mm × 1.0 mm. Screen printed and dried. Thereafter, using a belt-type firing furnace, firing was performed in a nitrogen atmosphere at a peak temperature of 900 ° C. for a holding time of 10 minutes to form thick film resistors each having a fired film thickness of 15 μm. The thick film resistors of these samples were formed on five substrates, and 120 were formed on each substrate.

[Evaluation of thick film resistors]
About each obtained thick film resistor, the state of peeling with an alumina substrate was confirmed visually, and the result was shown in following Table 2. That is, for the peeling mode, “no peeling” was evaluated as “◯”, “partial peeling” as “Δ”, and “total peeling” as “×”. Regarding the peeling rate, the ratio of the total number of “partial peeling” and “total peeling” to 600 total thick film resistors was expressed in%. Here, “partial peeling” means a state where a part of the resistor is peeled off, and “total peeling” means a state where the whole resistor is peeled off. A thick film resistor in which “total peeling” or “partial peeling” has occurred is not suitable for practical use.

  Moreover, about the thick film resistor paste of each sample, sheet resistance value, its dispersion | variation, and resistance temperature coefficient (TCR) were measured, and the result was combined with following Table 2, and was shown. A digital multimeter was used for measuring the resistance value, and a TCR measuring device including a digital multimeter and a thermostat was used for measuring the TCR. In addition, the thick film resistor which measured resistance value and TCR selected one sheet | seat arbitrarily from five board | substrates for every sample, and selected 25 pieces from the board | substrate.

The variation of the sheet resistance value of the thick film resistor was calculated as a coefficient of variation (CVR) shown in the following formula 1. It is a practical level that CVR is less than 5%.
[Formula 1]
Coefficient of variation (CVR) = population standard deviation × 100 / average value of sheet resistance

  As for the temperature coefficient of resistance (TCR), there are a low temperature side TCR (CTCR) at −55 ° C. to + 25 ° C. and a high temperature side TCR (HTCR) at 25 ° C. to 125 ° C. In both cases, −200 ppm to +200 ppm is a practical range. CTCR and HTCR are calculated from Equation 2 and Equation 3 below.

[Formula 2]
CTCR = (resistance value at −55 ° C.−resistance value at −25 ° C.) × 10 ⁶ / resistance value at 25 ° C./(−55−25)
[Formula 3]
HTCR = (resistance value at 125 ° C.−resistance value at 25 ° C.) × 10 ⁶ / resistance value at 25 ° C./(125-25)

  Furthermore, the change rate of the sheet resistance value by the heat cycle test was measured for the thick film resistor paste of each sample, and the results are also shown in Table 2 below. Heat cycle test: low temperature (−55 ° C. × retention time 30 minutes) → room temperature (25 ° C. × retention time 3 minutes) → high temperature (125 ° C. × retention time 30 minutes) → room temperature (25 ° C. × retention time 3 minutes) One cycle was performed, and this heat cycle was performed continuously for 5 cycles. The sheet resistance value at room temperature before and after the test was measured, and the change rate of the resistance value was calculated by the following mathematical formula 4. If the rate of change in resistance value by this heat cycle test exceeds 4%, it cannot be said to be a practical thick film resistor.

[Formula 4]
Resistance value change rate = (resistance value after heat cycle test−resistance value before heat cycle test) × 100 / resistance value before heat cycle test

  Comparing sample 1 of the present invention with sample 3 of the comparative example, and sample 2 of the present invention and sample 4 of the comparative example, an alumina substrate having a substrate size of 5 cm × 6 cm despite the same paste composition. The state of peeling of the thick film resistor formed above is different. That is, no peeling occurred in Samples 1 and 2 of the present invention, whereas partial peeling occurred in Samples 3 and 4 of the comparative example, which is not practical as a thick film resistor. The evaluation such as was canceled. Moreover, although the sample 5 of the comparative example did not peel off the thick film resistor, since it does not contain NiO powder, the resistance change rate due to heat cycle greatly exceeds 4%, which is considered practical. .

[Reference example]
Using a thick film resistor paste of each of samples 1 to 5 shown in Table 1 above, a screen in a pattern of 1.0 mm × 1.0 mm is formed on a 1 inch square alumina substrate on which a thick film copper electrode is previously baked. Printing and drying were performed, and firing was performed at a peak temperature of 900 ° C. in a nitrogen atmosphere using a belt-type firing furnace for 10 minutes to form a thick film resistor having a fired film thickness of 15 μm. The thick film resistors of each sample were formed on five substrates, and ten were formed per substrate.

  About each obtained thick film resistor, it carried out similarly to the said Example, and confirmed the state of peeling with an alumina substrate by visual observation. As a result, peeling of the thick film resistor was not observed for the samples 1 to 2 of the present invention and the samples 3 to 5 as comparative examples. This is because the substrate size is smaller than in the above example, so the variation in the nitrogen atmosphere in the firing furnace is also reduced, and as a result, no decrease in adhesion to the substrate occurs regardless of the iron content in the paste. It is a thing.

Claims (9)

A thick film resistor comprising a conductive powder composed of copper and nickel, a glass powder not containing lead and cadmium, a NiO powder, and an organic vehicle, and having an iron content of 50 mass ppm or less paste. The glass powder is SiO ₂ : 5 to 20% by mass, B ₂ O ₃ : 30 to 50% by mass, Al ₂ O ₃ : 1 to 5% by mass, ZnO: 30 to 40% by mass, Na ₂ O: 5 to 5%. The thick film resistor paste according to claim 1, comprising 10% by mass.   The thick film resistor paste according to claim 1 or 2, wherein a mass ratio of copper and nickel in the conductive powder is Cu: Ni = 40: 60 to 80:20.   The thick film resistor paste according to any one of claims 1 to 3, wherein the content of the conductive powder is 50 to 90 mass% with respect to the entire paste.   The thick film resistor paste according to any one of claims 1 to 4, wherein a content of the glass powder is 3 to 40 parts by mass with respect to 100 parts by mass of the conductive powder.   The thick film resistor paste according to any one of claims 1 to 5, wherein the content of the NiO powder is 1 to 40 parts by mass with respect to 100 parts by weight of the conductive powder.   The thick film resistor paste according to any one of claims 1 to 6, wherein the organic vehicle comprises a methacrylic ester resin or poly-α-methylstyrene resin and a solvent terpineol or dihydroterpineol. .   After the thick film resistor paste according to any one of claims 1 to 7 is applied to a ceramic substrate, the thick film resistor is fired at a temperature of 1000 ° C or less in a non-oxidizing atmosphere. Method.   A thick film resistor formed by the method of claim 8 and containing no lead or cadmium.