JP7664685B2 - Thick film resistor composition and thick film resistor paste containing same - Google Patents

Description

This invention relates to a thick film resistor composition used in the manufacture of chip resistors, thick film resistor substrates, thick film resistor heaters, etc.

Generally, chip resistors, thick film resistors, thick film resistor heaters, etc. use an alumina substrate as the base, thick film electrodes as the electrodes, and thick film or thin film resistors as the resistors. There are many different types of resistors depending on their applications and characteristics, and as devices become more compact, resistor-related parts are also becoming increasingly miniaturized.

Furthermore, there are various types of chip resistors with different characteristics, such as surge resistance, trimmable products, and high precision products.
The resistance value of chip resistors is generally adjusted by laser trimming, which removes part of the thick-film resistor with a laser beam. However, adjusting the resistance value by laser trimming leaves a trace on the surface of the thick-film resistor. Therefore, there are methods for adjusting the resistance value of thick-film resistors that do not leave traces, such as irradiating the thick-film resistor with a laser beam to change its characteristics and lowering its resistance value, or applying a pulse voltage to the thick-film resistor to lower its resistance value.

These methods of causing characteristic changes using laser light and of lowering the resistance value by applying a pulse voltage to a thick-film resistor are adjustment methods that utilize the fact that the resistance value can be lowered by applying laser light or a pulse voltage of an energy level that does not physically damage the appearance of the thick-film resistor.
Among these, a method of applying a high voltage pulse to a thick-film resistor to reduce its resistance value is known as a pulse trimming method. Patent Documents 1 and 2 disclose techniques relating to the pulse trimming method.
It is believed that with the further miniaturization of components in the future, such a method of adjusting resistance value without physically destroying anything will become even more necessary.

JP 2002-067366 A JP 2002-127483 A

However, depending on the composition of the thick-film resistor composition, even if an attempt is made to adjust the resistance value of the resulting thick-film resistor by pulse trimming, the adjustment of the resistance value, i.e., the change in the resistance value, may not be sufficient.
In view of the above circumstances, an object of the present embodiment is to provide a thick-film resistor composition that allows the resistance value of a thick-film resistor to be efficiently adjusted by a pulse trimming method.

A first aspect of the present invention is a thick film resistor composition comprising a glass frit and a ruthenium compound powder, the ruthenium compound powder being acicular particles having a maximum width of 100 nm or less in a cross section perpendicular to the particle length direction, and an aspect ratio expressed by the formula "particle length (L)/maximum width (φ ₁ )" calculated from the particle length and the maximum width being 1.5 to 5.0 , and the glass frit being heated in air at a temperature increase rate of 10°C/min by differential thermal analysis (TG-DTA), the softening point of the glass frit being the temperature at which the next differential thermal curve on the higher side decreases after a temperature at which a decrease in the differential thermal curve on the lowest side appears, is 600°C or more and 900°C or less .

A second aspect of the present invention is a thick-film resistor composition according to the first aspect, characterized in that the ruthenium compound powder in the first aspect is ruthenium dioxide powder.

A third aspect of the present invention is a thick-film resistor paste comprising the thick-film resistor composition according to the first or second aspect of the present invention and a vehicle in which a resin is dissolved in an organic solvent.

According to this embodiment, a resistor with a large resistance change range can be easily obtained when adjusting the resistance value with a pulse, which contributes greatly to improving the adjustment work and has a significant industrial effect.

FIG. 2 is an explanatory diagram of the form of a ruthenium compound powder according to the present embodiment.

The thick-film resistor composition according to this embodiment is characterized in that it contains glass frit and a conductive ruthenium compound powder, and the ruthenium compound powder is acicular. Furthermore, it is preferable that the ruthenium compound powder is ruthenium dioxide powder.

The thick film resistor composition can be used to obtain a thick film resistor paste by kneading the thick film resistor composition with an organic vehicle described below.
The thick film resistor paste thus obtained is printed on the surface of a ceramic substrate such as an alumina substrate to form a printed film containing the thick film resistor composition, which is then fired to obtain a thick film resistor.
Each component will be described below.

[Glass frit]
The composition and manufacturing method of the glass frit are not particularly limited.
Lead-containing lead aluminoborosilicate is often used as the glass frit for thick-film resistor compositions, but other lead-free compositions such as zinc borosilicate, calcium borosilicate, and barium borosilicate are also used. In recent years, it has become desirable to use lead-free glass from the viewpoint of environmental protection.

As described above, for example, the glass of the glass frit can be one or more selected from lead aluminoborosilicate glass, zinc borosilicate glass, calcium borosilicate glass, and barium borosilicate glass. Also, lead-free glass can be one or more selected from zinc borosilicate glass, calcium borosilicate glass, and barium borosilicate glass.

The _SiO2 component contained in the glass frit constitutes the glass skeleton, and PbO _{, B2O3} , and RO (R is an alkaline earth element) adjust the melting property of the glass. Furthermore, for the purpose of adjusting the weather resistance of the glass and the fluidity during firing, one or more types selected from _Al2O3 , _ZrO2 , _TiO2 , _SnO2 , _ZnO , _Li2O , _Na2O , _K2O , etc. can be _{mentioned. Al2O3 easily} suppresses the phase separation of the glass, _ZrO2 and _TiO2 improve the weather resistance of the glass, and _SnO2 , ZnO, _Li2O , _Na2O , _K2O , etc. have the function of increasing the fluidity of the glass.

The glasses are generally produced by mixing the desired components or their precursors in the desired formulation, melting the resulting mixture, and quenching it.
The melting temperature is not particularly limited, but is, for example, about 1400° C. Rapid cooling is often performed by placing the molten material in cold water or by passing it over a cold belt.
The glass is ground to the desired particle size using a ball mill, a vibration mill, a planetary mill, a bead mill, or the like.

The particle size of the glass frit is not limited, but the 50% volume cumulative particle size measured by a particle size distribution analyzer utilizing laser diffraction is preferably 5 μm or less, and more preferably 3 μm or less.
Thus, if the particle size of the glass frit is too large, the sheet resistance value of the fired thick film resistor is low, but the variation in the sheet resistance value increases, resulting in a decrease in yield. Furthermore, the possibility of problems such as a decrease in load characteristics increases. Therefore, from the viewpoint of sufficiently increasing the yield and improving the load characteristics, it is preferable that the 50% volume cumulative particle size of the glass particles used is 5 μm or less.
Incidentally, if the particle size of the glass frit is made too small, the productivity may decrease and the inclusion of impurities may increase, so the 50% volume cumulative particle size of the glass frit is preferably 0.5 μm or more.

The softening point of glass is a measure that affects the fluidity of glass during firing. In general, the temperature at which a composition for a thick-film resistor is fired during production of a thick-film resistor is 800° C. or higher and 900° C. or lower.
In this way, when the firing temperature of the composition for a thick film resistor when manufacturing a thick film resistor is 800° C. or higher and 900° C. or lower, the softening point of the glass used in the composition for a thick film resistor of this embodiment is preferably 600° C. or higher and 900° C. or lower.
Also, a glass frit having a softening point of 600° C. or more and 800° C. or less can be mixed with a glass frit having a higher softening point.
The softening point herein is a temperature at which a differential thermal curve next to a peak of decrease appears on the higher side of a temperature at which a decrease appears on the lowest temperature side of a differential thermal curve obtained by heating a glass in air at a temperature increase rate of 10° C./min by differential thermal analysis (TG-DTA).

The thick film resistor is obtained by firing the thick film resistor composition. The firing temperature for obtaining the thick film resistor is 800°C to 900°C as described below, and the glass frit melts during the firing process, and the individual particles of the glass frit fuse together to form a glass matrix. The individual particles of the ruthenium compound powder that constitutes the thick film resistor do not melt during the firing process like the glass frit. The thick film resistor obtained by firing the thick film resistor composition has as its component a conductive network of ruthenium compound particles that are held together by the glass matrix.

[Ruthenium compound powder]
The ruthenium compound powder in the thick film resistor composition functions as a conductive component.
As the ruthenium compound powder, a ruthenium composite oxide powder such as a ruthenium dioxide powder, a lead ruthenate powder, or a strontium ruthenate powder can be used.

In addition, the ruthenium compound powder used in this embodiment has the form of straight acicular particles as shown in FIG. 1, and the particle length L, which is the maximum length of the straight acicular particles, and the maximum width _φ1 of a cross section perpendicular to the direction of the particle length are 100 nm or less, and the aspect ratio of the straight acicular particles calculated from the particle length L and the maximum width _φ1 of the cross section by the formula "particle length L/maximum width of cross section _φ1 " is 1.5 or more, and preferably 5.0 or less.

The thick film resistor comprises a conductive network of needle-shaped particles of a ruthenium compound powder held in place by a glass matrix.
In this embodiment, since each particle constituting the ruthenium compound powder is an acicular particle, a conductive network in the major axis direction and a conductive network in the minor axis direction are formed in each ruthenium compound powder.
When a current is applied to a thick-film resistor having such a structure during pulse trimming, the glass matrix around the conductive network is heated and remelted, causing a shift in the arrangement of each particle constituting each ruthenium compound powder constituting the conductive network in the major axis direction, and the conductive network is reconstructed. This reconstruction of the conductive network changes the resistance value.

On the other hand, in a conductive network that is different from the present embodiment and is composed only of granular ruthenium compound powder, the ratio of the long axis to the short axis in the cross section (long axis in the long axis direction/short axis in the cross section) is less than 1.5, even if the conductive network is reconstructed after the current is applied during pulse trimming, the deviation in the arrangement of the particles that compose each ruthenium compound powder is small, and the change in the resistance value is small.

The ruthenium compound powder is preferably contained in the thick film resistor composition in an amount of 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 55% by mass or less, and even more preferably 15% by mass or more and 50% by mass or less.

In the thick-film resistor composition, the resistance value of the thick-film resistor obtained is adjusted by the mixing ratio of the glass frit and the ruthenium compound powder. If the content of the ruthenium compound powder in the thick-film resistor composition is less than 5 mass%, the resistance value becomes too high. On the other hand, if the content of the ruthenium compound powder in the thick-film resistor composition exceeds 60 mass%, the sintered surface of the thick-film resistor does not become dense, and the mechanical strength of the thick-film resistor cannot be ensured.

The ruthenium compound constituting the powder is preferably ruthenium dioxide.
This is because ruthenium dioxide has a lower resistivity than ruthenium composite oxides such as lead ruthenate, and is suitable for realizing a resistance value in the range of 50 Ω to 3000 Ω for thick-film resistors in the low resistance range.
When using a thick-film resistor as a heating resistor, it is desirable to set the resistance value of the thick-film resistor to 50 Ω to 100 kΩ, taking into consideration pulse trimming properties and the power consumption of the resulting thick-film resistor.

An example of synthesis of the ruthenium compound powder of this embodiment will be described.
One example of a method for producing ruthenium dioxide powder of acicular particles includes an acicular heat treatment step in which granular ruthenium dioxide powder is heat-treated in the presence of a bismuth compound to form acicular ruthenium dioxide powder, followed by a separation step in which the acicular ruthenium dioxide powder is separated into solid and liquid from a solution obtained by dissolving the bismuth compound in a solvent.

To explain the series of steps in detail, in the acicular heat treatment step, a first mixture prepared by mixing ruthenium dioxide powder with a bismuth compound is subjected to heat treatment to obtain a second mixture, which is then cooled to room temperature. The cooled second mixture is then subjected to a separation step in which the second mixture is dissolved in an acid or the like to obtain acicular ruthenium dioxide powder by solid-liquid separation.

The granular ruthenium dioxide powder is preferably spherical or nearly spherical particles with an average primary particle size of 100 nm or less as observed using an SEM and an aspect ratio of the powder of less than 1.5. When ruthenium dioxide powder having such a shape as described above is used as a raw material, needle-shaped ruthenium dioxide powder with a maximum width of 100 nm or less in a cross section perpendicular to the particle length direction can be easily obtained.

The bismuth compound is a compound containing bismuth, and any known bismuth compound can be used as long as it does not form an alloy with ruthenium dioxide during heat treatment.
The bismuth compound may be, for example, bismuth chloride, bismuth oxychloride, bismuth oxide, a mixture thereof, etc. Among them, it is preferable to use at least one of bismuth chloride and bismuth oxychloride, and it is more preferable to use bismuth oxychloride.

The first mixture is obtained by mixing the granular ruthenium dioxide powder and the bismuth compound. The mixing ratio of the granular ruthenium dioxide powder and the bismuth compound is, for example, a molar ratio of the bismuth compound to the granular ruthenium dioxide powder of 0.1 to 5, preferably 0.5 to 3, and more preferably 0.5 to 2.

The method for mixing the granular ruthenium dioxide powder and the bismuth compound is not particularly limited as long as the two can be mixed sufficiently, and they can be mixed using a known mixing device. For example, they can be mixed using a general mixing device such as a ball mill, a mortar and pestle mixer, or a shaker mixer.

The acicular heat treatment step can be carried out in an oxidizing atmosphere at a temperature of 600° C. to 900° C. By adjusting the heat treatment temperature within the above range, the particle length (L) and thickness (maximum width φ1 of a cross section perpendicular to the direction of the particle length) of the obtained acicular particles of ruthenium dioxide powder can be easily controlled.
The conditions of this heat treatment can be appropriately adjusted depending on the types and shapes of the raw material granular ruthenium dioxide powder and the bismuth compound, as well as the mixing ratio, within a range in which acicular ruthenium dioxide powder can be obtained.
For example, the heat treatment can be performed in an oxidizing atmosphere, such as an air atmosphere. The oxidizing atmosphere refers to a gas containing 10% or more by volume of oxygen, such as air. The heat treatment time is not particularly limited, and can be, for example, from 1 hour to 4 hours, preferably from 1 hour to less than 3 hours.

In the separation step, the bismuth compound contained in the second mixture (mixed powder containing the acicular ruthenium dioxide powder and the bismuth compound) is dissolved in a solvent, and then the acicular ruthenium dioxide powder is subjected to solid-liquid separation from the resulting solution.
The solvent used to dissolve the bismuth compound is not particularly limited as long as it dissolves only the bismuth compound without dissolving the ruthenium dioxide powder, and for example, an inorganic acid (mineral acid) or an organic acid can be used. The conditions for dissolving the bismuth compound in the solvent are not particularly limited as long as the bismuth compound is sufficiently dissolved in the solvent. For example, the liquid temperature during dissolution can be about 30 to 60°C.

After dissolving the bismuth compound in the solvent, the ruthenium dioxide powder in the form of acicular particles is dispersed, and a solution containing the dissolved bismuth compound is obtained. From the resulting solution, ruthenium dioxide powder in the form of acicular particles can be obtained through a solid-liquid separation process. The ruthenium dioxide powder in the form of acicular particles obtained by solid-liquid separation may be further dried, and the drying temperature and time may be any temperature at which moisture can be removed.

Acicular ruthenium composite oxide powder, such as strontium ruthenate powder ( _SrRuO3 ) having acicular particles, can be obtained by mixing a solution of a chelate compound of a metal element other than ruthenium that constitutes a ruthenate salt such as strontium with acicular ruthenium dioxide powder to prepare a mixed liquid, drying the mixed liquid to gel it, thereby obtaining a chelate complex gel, and heat-treating the chelate complex gel at a temperature of 800°C or lower.

[Thick Film Resistor Composition]
The thick film resistor composition according to the present embodiment contains glass frit and ruthenium compound powder. In addition, the thick film resistor composition may contain known _TiO2 powder or the like, which has an effect of adjusting the temperature coefficient of resistance, which is one of the electrical properties of the thick film resistor.

[Organic vehicle]
The organic vehicle used in this embodiment does not need to be a specific one, and may be one generally used for manufacturing thick-film resistor paste. It is preferable that the organic vehicle is one that volatilizes and decomposes when the binder is removed during drying and firing. The following organic solvents can be used, for example, cellulose-based resins such as ethyl cellulose and nitrocellulose, and resins such as acrylic resins.

These resins can be dissolved in organic solvents such as terpene alcohols such as terpineol, terpenes such as limonene, ethers such as butyl carbitol acetate and butyl cellosolve acetate, etc., and these organic solvents can be used as organic vehicles. To adjust the viscosity of the thick-film resistor paste, an organic solvent such as terpineol may be further added.
In order to disperse the thick film resistor composition in the vehicle, a polymer dispersant having a carboxyl group or an amino group, a fatty acid such as stearic acid, or a phospholipid such as lecithin may be added as a dispersant.

[Method of manufacturing thick film resistor paste]
It is desirable to disperse the ruthenium compound powder, glass frit, organic vehicle, and organic solvent uniformly. There is no limitation on the method, but a known dispersion method using a three-roll mill is suitable.

[Method of forming thick film resistor]
The resulting thick-film resistor paste is screen-printed onto a ceramic substrate such as an alumina substrate in the form of a thick-film resistor pattern, which is then dried and fired to form a thick-film resistor.

The firing conditions are a peak temperature of 800°C to 900°C in air, and a holding time at the peak temperature of 5 to 60 minutes. The heating time from room temperature to the peak temperature is 5 to 60 minutes, and after the peak temperature is held, the material is cooled to room temperature. When the temperature is raised during the firing process, a binder removal process is performed to remove organic solvents and resin components remaining in the printed film of the thick-film resistor paste.
The thick film resistor fired at a peak temperature of 800° C. to 900° C. has a thickness adjusted to 5 μm to 20 μm, and more preferably 8 μm to 15 μm.

Furthermore, the surface of the thick-film resistor can be covered with a glass paste that can be fired at a firing temperature of about 600° C., and the glass paste can be fired to form a protective film for the thick-film resistor, thereby forming a thick-film resistor with a protective film. By providing the surface of the thick-film resistor with a protective film made of glass paste in this way, the surface of the thick-film resistor can be made smooth.
Prior to the formation of the thick film resistor, electrodes that will become the terminals of the thick film resistor may be formed on the surface of the ceramic substrate by a known thick film technique.

[Pulse trimming of thick film resistors]
The resistance value of the thick-film resistor obtained by firing is adjusted by a pulse trimming method.
Specifically, a pulse voltage is applied to the thick-film resistor until a predetermined resistance value is reached. The applied voltage may be appropriately selected depending on the resistance value of the thick-film resistor. If the rate of change in the resistance value after application of the pulse voltage is small compared to the resistance value before application when the pulse voltage is applied successively, it becomes difficult to efficiently adjust the resistance value.

The following describes this embodiment in detail using examples.

A thick-film resistor composition consisting of 13% by mass of acicular ruthenium dioxide powder A, 50% by mass of lead aluminoborosilicate glass frit B, and the remainder being an organic vehicle was kneaded in a three-roll mill so that the various inorganic materials constituting the composition were dispersed in the organic vehicle, to produce the thick-film resistor paste of Example 1. The organic vehicle used was terpineol in which ethyl cellulose had been dissolved.

The ruthenium dioxide powder A used had needle-shaped particles with a maximum cross-sectional width φ1 perpendicular to the particle length direction of 25 nm and an aspect ratio of 2.0, calculated from the particle length L and the maximum width φ1, expressed as "particle length (L) / maximum width in cross section (φ1)". The particle length (L) and maximum cross-sectional width (φ1) of the ruthenium dioxide powder A were observed using TEM images.

Glass frit B had a 50% volume cumulative particle size of 1.3 μm and a softening point of 860° C.
The organic vehicle was prepared by mixing 85% by mass of terpineol and 15% by mass of ethyl cellulose and dissolving them at 80°C.

[Method of forming thick film resistor]
The prepared thick-film resistor paste was printed with a width of 0.3 mm between five pairs of thick-film Au electrodes with a spacing of 0.3 mm formed on an alumina substrate in advance, and dried in a belt furnace with a peak temperature of 150°C x 5 minutes to remove the solvent component terpineol. Then, the sample was fired in a belt furnace with a peak temperature of 810°C x 9 minutes. Five samples were prepared in the same manner, one per alumina substrate. The film thickness was measured by selecting one of the samples for evaluation at random from the alumina substrate using a stylus-type surface roughness meter (Tokyo Seimitsu Co., Ltd., model number: Surfcom 480B), and the film thickness of each of the five thick-film resistors was measured. The average value of the five thick-film resistors was 13 μm.

Furthermore, AGC glass paste AP5564 was applied so as to cover the thick film resistor, and dried in a belt furnace at a peak temperature of 150°C for 5 minutes. After that, it was fired in a belt furnace at a peak temperature of 810°C for 9 minutes to prepare an evaluation sample.

[Pulse trimming of thick film resistors]
The resistance value Rs of the thick film resistor of the evaluation sample before voltage application was measured. Then, using "ESS-6008 (manufactured by Noise Laboratory Co., Ltd.)", a pulse of each voltage was applied to the thick film resistor of the evaluation sample with a capacitance of 200 pF, an internal resistance of 0 Ω, and a voltage of 1500 V, and then a pulse of 1500 V was applied again after an interval of 1 second, and the resistance value Re after the voltage application was measured. The rate of change in the resistance value was calculated by the following formula (1). The applied voltage and the calculated rate of change in the resistance value at that time are shown in Table 1.
The resistance value was measured using a digital multimeter (manufactured by Keithley, No. 2001).

(Comparative Example 1)
A thick-film resistor composition consisting of 11% by mass of ruthenium dioxide powder C of roughly spherical granular particles, 2% by mass of granular lead ruthenate powder D, 45% by mass of lead alumina borosilicate glass frit E, and the remainder being the same organic vehicle as in Example 1, was kneaded by a three-roll mill so that the various inorganic materials constituting the composition were dispersed in the organic vehicle, to prepare a thick-film resistor paste of Comparative Example 1. The granular ruthenium dioxide powder C used had a maximum width (φ1) of 20 nm in a cross section perpendicular to the direction of the particle length, and an aspect ratio of 1.1. The particle length (L) and maximum width (φ1) of the ruthenium dioxide powder were observed by TEM images, as in Example 1.

Lead ruthenate powder D was observed in a TEM image and was a nearly spherical powder with a maximum width (φ1) of 50 nm in a cross section perpendicular to the particle length direction, and an aspect ratio formed by the particle length (L) and the maximum width (φ1) of 1.1.
Glass frit E had a 50% volume cumulative particle size of 1.4 μm and a softening point of 660° C.

Thick-film resistors were also prepared as evaluation samples in the same manner as in Example 1, and were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. The film thickness of each of the five thick-film resistors was measured, and the average value for the five thick-film resistors was 8.6 μm.

As shown in Table 1, the thick-film resistor of Example 1 formed from the thick-film resistor paste made with the acicular ruthenium dioxide powder of this example had a larger negative resistance change rate in the pulse trimming evaluation than the thick-film resistor of Comparative Example 1 formed from the conventional thick-film resistor paste made with granular ruthenium dioxide powder, demonstrating superior pulse trimming properties.

1 Ruthenium compound powder L Particle length φ1 Maximum width of cross section

Claims (3)

Contains glass frit and ruthenium compound powder,
the ruthenium compound powder is in the form of needle-like particles, the maximum width of a cross section perpendicular to the particle length direction is 100 nm or less, and the aspect ratio calculated from the particle length and the maximum width, expressed by the formula "particle length (L)/maximum width (φ ₁ )", is 1.5 or more and 5.0 or less ,
The thick film resistor composition is characterized in that the glass frit has a softening point of 600°C or more and 900°C or less, which is a peak temperature at which a differential thermal curve next to a temperature at which a decrease in a differential thermal curve on the higher side appears when the differential thermal curve obtained by heating the glass frit at a temperature increase rate of 10°C/ min in air by differential thermal analysis (TG-DTA). The thick-film resistor composition according to claim 1, characterized in that the ruthenium compound powder is ruthenium dioxide powder. A thick-film resistor paste comprising the thick-film resistor composition according to claim 1 or 2 and a vehicle in which a resin is dissolved in an organic solvent.

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