JPH023524B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to compositions useful in the manufacture of thick film resistors, and particularly to such compositions in which the conductive phase is based on hexaboride. Thick film materials are mixtures of metal, glass, and/or ceramic powders dispersed in an organic medium. These materials are applied to non-conductive substrates to produce conductive, resistive or insulating films.
Thick film materials are used in a wide variety of electronic and optoelectronic components. The properties of a particular composition will depend on the particular components that make up the composition. All compositions contain three main ingredients. The conductive phase determines the electrical properties and influences the mechanical properties of the final film. In conductor compositions, the conductive phase is generally a noble metal or a mixture of noble metals. In resistor compositions, the conductive phase is generally a metal oxide.
In derivative compositions, the functional phase is generally a glass or ceramic material. The binder is usually a glass that holds the film together and bonds it to the substrate. Binders also affect the mechanical properties of the final film. The organic medium or vehicle is a solution of the polymer in an organic solvent. The vehicle determines the application properties of the composition. In the composition, the functional phase and binder are generally in powder form and completely dispersed in the vehicle. A thick film material is applied to the substrate. The substrate serves as a support for the final film and may also have electrical functionality, such as capacitor dielectric properties. The substrate material is generally non-conductive. The most common base material is ceramic. High purity (typically 96%) aluminum oxide is the most widely used. Various titanate ceramics, mica, beryllium oxide and other substrates have been used for specific applications. These are commonly used because of the special electrical or mechanical properties required for the application. Glass is used in applications where the substrate must be transparent, such as in displays. Thick film technology is more focused on the process than on the material or application. The basic steps of thick film process are screen printing, drying and baking. Thick film compositions are generally applied to substrates by screen printing. Dipping, bending, brushing or spraying are sometimes used with irregularly shaped substrates. The screen printing process consists of extruding the thick film composition with a squeegee through a stencil screen onto a substrate. The open pattern of the stencil screen forms the pattern to be printed on the substrate. After printing, the film is dried and fired, typically in air at a peak temperature of 500° to 1000°C.
This process produces a hard adhesive film with desired electrical and mechanical properties. Thick film compositions of that value can be applied onto the same substrate by repeating the screen printing, drying and baking steps. In this way complex interconnected conductive, resistive and insulating films can be produced. Thick film resistor compositions are typically manufactured in resistance values of 10 and have a wide range of sheet resistances (0.5Ω/□ to 1×
Materials are available that give 10 ⁹ Ω/□. The aspect ratio of the resistor, that is, the change in length:width, is
Give a resistance value of 0.5Ω/□ or less and 1×10 ⁹ Ω/□ or more, and any intermediate resistance value. Composition blending is a widely used technique to obtain resistance values between standard decimal values. Adjacent decimal elements are mixed in all proportions to obtain intermediate values of sheet resistance. Although the mixing operation is simple, it requires care and appropriate equipment. Typically blends have minimal effect on temperature coefficient of resistance (TCR). High electrical stability and low process and refire sensitivity are critical requirements for thick film resistor compositions for microcircuit applications. In particular, it is necessary that the film resistance (R) be stable over a wide range of temperature conditions. That is, TCR is a critical variable in all thick film resistor compositions. Because thick film resistor compositions include a functional or conductive phase and a permanent binder phase, the nature of the conductor phase and binder phase and their interactions with each other and with the substrate affect the resistivity and Affects both TCR. Since copper is an economical electrode material, there is a need for a thick film resistor system that is compatible with copper and can be fired in a non-oxidizing atmosphere, and that has properties comparable to air fired resistors. Among the resistor materials suggested for this purpose are lanthanum 6
There are borides, yttrium hexaborides, rare earth hexaborides, and alkaline earth hexaborides. In this regard, French Patent No. 2 397 704 covers a mixture of finely divided particles of a metal hexaboride and a glass frit of an alkaline earth metal boroaluminate.
We are proposing a resistor material that is stable in a non-oxidizing firing atmosphere. This patent discloses that glasses that do not react with metal hexaborides do not contain more than about 1% by volume of metal oxides that are reduced by metal hexaborides. Furthermore, the applicant's EPO Patent No. 0008437 discloses a resistive material comprising a finely divided particle mixture of a metal hexaboride and a glass that is not cyclized with the metal hexaboride. This patent discloses that the glass contains no more than 2 mole percent reducible metal oxides. Additionally, U.S. Patent No.
No. 4,225,468 discloses a similar hexaboride resistor material that includes a finely divided particle mixture of a metal hexaboride, a non-reducible glass, and various TCR modifiers including TiO and NbO dispersed therein in particulate form. It is related to. "Izvestia Vysshikl Uchebnykl Zavendenii
16 (6) 99-102 (1973), thick film resistors based on relatively coarse LaB ₆ and borosilicate glasses were initiated. These resistors are said to be resistant to hydrogen gas, but the films are moisture sensitive. GB 1282023 discloses an electrical resistor dispersion containing a rare earth or alkaline earth hexaboride conductor pigment and a glass phase dispersed in an ethylcellulose medium. The glasses used are lead shelf silicates and lead aluminoborosilicates, the latter of which contain only 16 mol% of hexaboride reducing oxides of low melting point metals such as Pb, Na, Co and Ni. It has been shown to contain only small amounts. Although such metal hexaboride-based resistors have been found to be very useful, they are nonetheless difficult to manufacture, especially when they are formulated for resistor material production in the 1K-100K ohm range. have also been shown to have some limitations in their power handling capabilities. Recently, U.S. Pat. No. 4,420,338 discloses a metal hexaboride resistor containing an alkaline earth silicate glass modified with small amounts (up to 5 mole %) of reducing oxides of V, Nb and Ta. are doing. It is believed that the purpose of reducing oxides is to improve TCR. However, it has been found that such oxides react with the hexaboride to form metal diboride particles that progressively reduce resistance. This process instability is manifested by an excessive drop in resistance upon refiring. Although the disadvantages of prior art hexaboride resistive materials with respect to power handling performance and electrical stability process sensitivity and refire characteristics are substantially overcome by the present invention, the present invention primarily focuses on A rare earth hexaboride materials. conductive metal 6 selected from the group consisting of CaB ₆ , SrB ₆ and mixtures thereof;
2 to 70% by weight (on a total solids basis) of boride; A thick film resistor containing a mixture of finely divided particles of 98-30% by weight (on a total solids basis) of crystalline glass dissolved in _Ta2O5 which is reduced with _oxides to form _TaB2 and crystalline tantalate. The present invention relates to a composition for manufacturing. In a second form, the present invention comprises (1) the production of a dispersion of the hexaboride-containing composition in an organic medium; (2) the formation of a patterned thin layer of the dispersion of step (1); (3) ) drying of the layer of step (2) and (4) step (3) for reducing the reducing metal oxide, evaporating the organic medium and liquid phase sintering of the glass in a non-oxidizing atmosphere. sintering of a layer dried in a process for producing a resistor element. The invention also relates to a resistor manufactured by the method described above. A Metal Hexaboride The first conductor phase component of the present invention is the applicant's EPO patent no.
Same as taught in US Pat. No. 0008437. That is, a suitable conductor phase material is
Rare earth hexaborides including LaB ₆ and YB ₆ ,
CaB ₆ , BaB ₆ , SrB ₆ or a mixture thereof. Although the above empirical formula is used herein, the stoichiometry of these compounds may vary somewhat and this is, for example, La _0.7-1 B ₆ for lanthanum hexaboride. it is conceivable that. Among the metal hexaborides listed above, LaB ₆ is preferred. As pointed out in EPO Patent No. 0008437, the size of the hexaboride particles is preferably 1 micron (μm) or less. More preferably the average particle size is from 0.055 μm
0.32 μm, and even more preferably the average particle size is about 0.2 μm. The particle size cited above can be measured by a Coulter counter or, assuming spherical particles, using the following equation particle diameter (μm) = 6/surface area (m ² /g) x density (dl/ cm ³ ). Surface area can be determined by conventional methods, for example by measuring the weight gain after equilibrium gas adsorption by the particles. For LaB ₆ the density is 4.72 g/cm ³ . Substituting into the above equation, the surface area for LaB ₆ is approximately 1 m ² /
g, but a preferred surface area range is about 4 to 23 m ² /g, with a more preferred value of about 6 m ² /g. To obtain the fine particle size 6 borides of the present invention from commercially available coarser materials, eg 5.8 μm for LaB ₆ , they are usually vibratory milled. Vibratory milling involves placing the inorganic powder and alumina balls in a container in an aqueous medium and then vibrating it for a length of time, as described above, which is included herein by reference.
This is carried out by achieving the desired particle size as described in EPO Patent No. 0008437. The compositions of the present invention typically have a total solids content of 2 to
It contains 70% by weight of metal hexaboride, and preferably 5-50% by weight. B Glass The glass component of the present invention must be crystalline and substantially non-reducible. Suitable crystalline glasses are alkali metal and alkali metal aluminosilicates and especially boroaluminosilicates. Examples include: Li ₂ O・Al ₂ O ₃・SiO ₂ MgO・Al ₂ O ₃・SiO ₂ Ca・MgO・Al ₂ O ₃・SiO ₂ BaO・Al ₂ O ₃・2SiO ₂ 2MgO・2Al ₂ O ₃・5SiO ₂ SiO ₂・LiAlO ₂・Mg (AlO ₂ ) K ₂ O・MgO・Al ₂ O ₃・SiO ₂・B ₂ O ₃・F Many are suitable for use in the present invention. These glasses have the following composition. SiO ₂ 40-70% Al ₂ O ₃ 10-31% Li ₂ O 3-20% B ₂ O ₃ 2-15% These glasses may contain small amounts of As ₂ O ₃ ,
It has been shown to contain Na ₂ O, K ₂ O and Bi ₂ O ₃ . However, for use in the present invention, the amount of such oxides should be limited to less than 2% if they are reducible to hexaboride. Other types of crystalline glasses suitable for the present invention have the following compositions. SiO ₂ 35-55% Al ₂ O ₃ 5-15% CaO, SrO or BaO 10-30% B ₂ O ₃ 10-35% These glasses may also contain
ZrO ₂ (≦4%), TiO ₂ (≦1%) and Li ₂ O (≦
2%). In addition to the basic glass components cited above, the glasses for use in the present invention contain at least 50% Ta ₂ O ₅ , which is believed to act as a nucleating agent.
% must be dissolved therein. Furthermore, within certain narrow limits, the glass must be substantially non-reducible, excluding Ta ₂ O ₅ . Preferably, the glass contains at least 5.5%, but not more than 10%, Ta ₂ O ₅ . As used herein, "reducible"
and the term "non-reducible" is used to refer to the ability, or lack thereof, of the metal oxide to react with the metal hexaboride under the non-oxidizing calcination conditions to which the composition is subjected in normal use. There is. More specifically, the non-reducible glass component is considered to have a Gibbs free energy of formation (ΔF°) of -78 kcal/mole or greater of negativity with respect to O in the unit. Conversely, the reducing glass component is considered to have a Gibbs free energy of formation (△F°) less negative for O in the unit of the formula than -78 kcal/mole, e.g. -73.2 kcal/mole. . Measurement of the Gibbs free energy of formation is described in the above-mentioned EPO patent specifications. Suitable component oxides for the non-reducing glass of the present invention include the following (inside the box: △kcal/mole per oxygen moiety at -1200〓).
F°(M-O) values are shown). CaO(−121),
ThO ₂ (−119), BeO (−115), La ₂ O ₃ (−115),
SrO (−113), MgO (−112), Y ₂ O ₃ (−111), rare earth oxide Sc ₂ O ₃ (−107), BaO (−106),
HfO ₂ (−105), ZrO ₂ (−103), Al ₂ O ₃ (−103),
Li ₂ O (−103), TiO (−97), CeO ₂ (−92),
_TiO2 (−87), _SiO2 (−80), _B2O3 ( ₋₇₈ ). _SiO2
and B ₂ O ₃ appear to be borderline in their reducibility, but they are thought to be further stabilized during glass formation and are therefore included in the non-reducing category as a practical matter. . The non-reducing component of glass is 95 mol% of the total glass.
The above is not configured. This amount is usually the solderability number of the reducing oxide contained therein. However, at least 70 mole % and preferably at least 85 mole % non-reducing component is preferred. 90-95 mol% is considered optimal. Unlike the metal hexaboride resistors of our EPO Patent No. 0004823, the resistor compositions of the present invention contain at least 5 mol % dissolved in an otherwise non-reducible glass; Preferably it should contain at least 5.5 mol% Ta ₂ O ₅ . Gibbs free energy of Ta ₂ O ₅ (△
F゜) is -73.2kcal/mol at 900℃. ie it can be reduced by _LaB6 . Due to its high melting point, reduced Ta metal does not sinter. It remains very finely divided and itself contributes to the conduction of the resistor. Fine particle size and high dispersion produce resistors with reduced resistance. The reduced metal is further converted into a reacted boride e.g.
TaB ₂ is formed, but this is due to the
It is highly dispersed and finely divided as evidenced by line diffraction. This in-situ formed boride also contributes to the conductivity and stability of the resistor. However, they produce sensitivity in the form of progressively lower resistance. By using a sufficiently high amount of Ta ₂ O ₅ in combination with crystalline glass, CaTa ₄ O ₁₁ is formed that does not reduce the resistance. It appears that this CaTa ₄ O ₁₁ is not formed when the Ta ₂ O ₅ concentration is below about 5 mol %. at least 5 mol% (preferably at least 5.5
In addition to the aforementioned metal hexaboride-reducing metal oxides, which must be present in solution in the glass to the extent of may contain substances whose melting point is 2000°C or less. However, the amount of these other substances must remain within very narrow limits and in all cases should be less than 2 mol % and preferably less than 1 mol % of the glass.
Such other acceptable reducing oxides include _Cr2O3 , _MnO , NiO, FeO, _{V2O5 ,
Na2O} , ZnO, _K2O , CdO, MnO, NiO,
_Mention may be made of FeO, _{V2O5 ,} PbO, _Bi2O3 , _Nb2O5 , _{WO3 and MoO3} . Glass surface area is not critical. However, it preferably lies in the range from 2 to 4 m ² /g. Assuming a density of approximately 3 g/ ^cm3 , this range is 0.5
This corresponds to an approximate particle size range of ~1 μm.
A surface area of 1.5 m ² /g (approximately 1.3 μm) may also be used. The manufacture of such glass frits is well known and consists of melting together the glass components, for example in the form of their oxides, and pouring such molten composition into water to form a frit. The patch component can, of course, be any compound that will form the desired oxide under normal frit manufacturing conditions. For example, boron oxide is obtained from boric acid, silicon dioxide is produced from frit, barium oxide is produced from barium carbonate, and so on. The glass is preferably milled in a ball mill with water to reduce the particle size of the frit and obtain a substantially uniform sized frit. Glass is manufactured by conventional glass manufacturing techniques by mixing the desired components in the desired proportions and heating the mixture to form a melt. As is well known in the art, heating is carried out to a peak temperature and for a time such that the melt becomes completely liquid and homogeneous. In this study, the components are premixed by shaking in a polyethylene jar with plastic balls and then melted in a platinum crucible at the desired temperature. The melt is heated at peak temperature for 1-11/2 hours. This melt is then poured into cold water. The maximum temperature of the water during quenching is kept as low as possible by increasing the volume ratio of water to melt. After separation from the water, the crude frit is free of residual water by air drying or washing with methanol to displace the water. The crude frit is then ball milled in an alumina container using an alumina ball for 3 to 5 hours. Alumina contamination by this material, if any, is not within the observation limits as determined by X-ray diffraction analysis. After discharging the milled frit slurry from the mill, excess solvent is removed by decanting and the frit powder is air-dried at room temperature.
The dry powder is then screened through a 325 mesh screen to remove any large particles. The compositions of the present invention typically have a total solids content of 95 to 30
% by weight, and preferably 80-50% inorganic glass binder. C Organic Medium Mixing inorganic particles with an essentially inert liquid organic medium (vehicle) by mechanical mixing (e.g. on a roll mill) to produce a paste-like composition with a consistency and rheology suitable for screen printing. let This composition is printed as a "thick film" in a conventional manner onto a conventional dielectric substrate. Various organic liquids can be used as vehicles, with or without the addition of thickening and/or stabilizing agents and/or other common additives. Examples of organic liquids that can be used are aliphatic alcohols, esters of such alcohols such as acetate and propionate, terpenes such as pine oil, terpineol, etc., resins such as solutions of polymethacrylates in lower alcohols and in solvents such as pine oil. solution of ethyl cellulose and monobutyl ether of ethylene glycol monoacetate. The vehicle can contain a volatile liquid to promote rapid solidification after application to the substrate. One particularly preferred vehicle for forming a resistor composition paste is at least 53% by weight
It is based on an ethylene-vinyl acetate copolymer with vinyl acetate. Preferred ethylene-vinyl acetate polymers used in the vehicles of this invention are from 0.1 to 2
It is a solid high molecular weight polymer with a melt flow rate of g/10 min. The vinyl acetate content limit is imposed by the room temperature dissolution requirements of the polymer in a solvent suitable for thick film printing. Such vehicles are described in US patent application Ser. No. 934,271, filed concurrently with the present application. This application is incorporated herein by reference. The vehicle to solids ratio in a dispersion can vary considerably and this depends on the method of applying the dispersion and the type of vehicle used. Typically, to achieve good coverage the dispersion should be supplemented with 60-90% solids and 40-10% solids.
Contains vehicle. The compositions of the invention can, of course, be modified by the addition of other substances which do not adversely affect its advantageous properties.
Such formulation is within the skill of the art. The paste is conveniently made on a three roll mill. The viscosity of the paste is typically within the following ranges as measured on a Bruckfield HBT viscometer at low, medium, and high shear rates:

Table: The amount of vehicle used is determined by the final desired formulation viscosity. Formulation and Application In the preparation of the compositions of the invention, particulate inorganic solids are mixed with an organic medium and prepared in a suitable apparatus, e.g.
Dispersion using a roll mill to produce a suspension of approximately 100-150 Pa at a shear rate of 4 ^s
A composition with a viscosity in the range of seconds (Pa.s) is produced. In the examples below, formulations were carried out in the following manner. The paste ingredients, reduced by about 5% of the organic components corresponding to about 5% by weight, are weighed together into a container. The ingredients are then mixed vigorously to produce a homogeneous blend. This blend is then adapted to a dispersing device such as a three roll mill to achieve a good particle dispersion. Measure the state of particle dispersion in the paste using a Hegman gauge. The device consists of a channel in a steel block that is 25 μm deep (1 mil) at one end and slopes to zero depth at the other end. Use a blade to pull the paste along the length of this channel. Scratches appear in the channel where the agglomerate diameter is greater than the channel depth. Satisfactory dispersions typically provide a fourth scratch point of 10-1 .mu.m. The point at which half of the channel is not covered by a well-dispersed paste is typically between 3 and 8 μm. §20μm 4th scratch measurement and §10μm “half channel”
The measured values indicate a deterioration in the dispersion of the suspension. The remaining 5% of the organic component of the paste is then added and the resin content is adjusted to the appropriate screen printing rheology. The composition is then applied to a substrate such as alumina, ceramic, usually by screen printing techniques, to a wet thickness of about 30 to 80 microns, preferably 35 to 70 microns, and most preferably 40 to 50 microns. The electrode compositions of the present invention can be printed onto a substrate in a conventional manner using conventional automatic or manual printing machines. Automatic screen stenciling techniques are preferably used using 200-325 mesh screens. The printed pattern is then dried at less than 200° C., such as about 150° C., for about 5 to 15 minutes, and then fired. Calcining to effect sintering of the inorganic binder is carried out in an inert atmosphere, for example nitrogen, using a belt conveyor furnace. The temperature profile of the furnace is adjusted to about 300-600℃, about 5-15℃ of about 800-950℃
Combustion of organic material with maximum temperature periods lasting for minutes and controlled cooling to prevent oversintering, unwanted chemical reactions at intermediate temperatures, or substrate destruction as may result from too rapid cooling is possible. Adjusted to tighten. The entire fired mass preferably lasts about 1 hour, including 20-25 minutes to reach the firing temperature, about 10 minutes at the firing temperature, and about 20-25 minutes at the firing temperature.
Includes minutes of cooling. In some cases full cycle times as short as 30 minutes can be used. Sample Preparation The sample to be tested is prepared as follows. The pattern of the resistor formulation to be tested was screen printed onto a 1 x 1" 96% alumina ceramic substrate with 10 coded, each pre-sintered copper conductor patterns, equilibrated at room temperature and then at 125°C. The semi-uniform thickness of each set of dried films before firing should be 22-28 microns as measured with a brush surf analyzer.
The drying and printing substrate was then heated under nitrogen to 900°C at 35°C/min for about 60 minutes, a 9-10 minute dwell at 900°C, and cooled to ambient temperature at a rate of 30°C/min. and bake it. Test Method A Resistance Measurement and Calculation The test substrate is mounted on the end post in a controlled temperature chamber and electrically connected to a digital ohmmeter. The temperature in the chamber is adjusted to 25° C. and allowed to equilibrate, after which the resistance of the test resistor on each substrate is measured and recorded. The temperature in the chamber is then raised to 125°C and allowed to equilibrate before testing the on-substrate resistor again. The temperature of the chamber is then allowed to cool to -55°C and equilibrate, and the cold resistance is measured and recorded. Hot and cold temperature coefficient (TCR) of this resistor
is calculated as follows. Hot TCR= R125℃−R25℃/R25℃×(10000) ppm/℃ Cold TCR= R−55℃−R25℃/R25℃×(−12500) ppm/℃ R25℃ and hot and cold TCR (Each
HTCR and CTCR) and normalize the R25°C value to a dry print thickness of 25μ and record the resistivity as ohms per square of the dry print thickness of 25μ. Normalization of multiple test values is calculated using the following relationship: Normalized Resistance = Average Measured Resistance x Average Dry Print Thickness (μ)/25 (μ). B. Coefficient of Variation The coefficient of variation (CV) is the function of the average and individual resistance for the resistor being tested and is expressed by the relation, σ/R _av , where: R _i = measured resistance of an individual specimen R _av = calculated average value of all specimens (Σ _i
R _i /n) n = number of samples CV = σ / R _av × 100 (%) C Laser trimming stability Laser trimming of thick film resistors is an important technology for manufacturing hybrid microelectronic circuits [Thick Film Hybrid
Microcircuit Technology” DWHamer &
JV Biggers, p. 173 ff Wiley (1972)]. Its use can be understood by considering that the resistance of a particular resistor printed with the same resistance ink on a group of substrates has a Gaussian-like distribution. In order to ensure that all resistors have the same design values for proper circuit performance, a laser is used to trim the resistors by removing (vaporizing) a small portion of the resistor material. The stability of a trimmed resistor is then a measure of the small change in resistance (drift) that occurs after laser trimming. Low resistance drift - high stability is necessary for the resistance to remain close to its design value for adequate circuit performance. D Solder dip drift After measuring the initial resistance, remove the resistor from Alpha 611.
Deepen the solder flux and 60/
Dip in 40Pb/Sn molten solder for 10 seconds,
Remove and then dip in a second 10 second interval. It is calculated by measuring the resistance of a twice-dipped resistor and comparing its change (drift) with the first resistance measurement. E 150°C Aging Drift After first measuring the resistance at room temperature, the resistor
Place in a heating cabinet with dry air at 150°C and hold at that temperature for a specified period of time (usually 100 or 1000 hours). At the end of this prescribed time, the resistor is removed and allowed to cool to room temperature.
The resistance is measured again and the change in resistance is calculated by comparing it to the initial resistance measurement. F. Sealing This test is conducted in the same manner as the aging test described above, except that the air in the heating cabinet is maintained at 40° C. (90% RH/40° C.) at 90% relative humidity (RH). G Standard Overvoltage (STOL) Using a 1 mm x 1 mm resistor with copper metal terminals, solder the wire leads to the copper terminals and connect the resistor to a DC power source. The resistor is exposed to a series of 5 second pulses of increasing voltage. After each pulse, equilibrate the resistor and measure the resistance. Maintain this sequence until a 0.1% resistance change occurs. This voltage is expressed in terms of STOL (0.1%). The power input for overvoltage generation is calculated as follows. Power (Watts/inch square) = [STOL (0.1%) x 0.4] ² /Ω x 645 H Process Sensitivity Refire Stability The resistance is measured and the resistor is refired according to the method described above. Measure resistance and calculate % drift. Peak Temperature Stability The above cycle fires the resistor at peak temperatures of 875°C, 900°C and 925°C.
Measure resistance and calculate peak temperature drift. △%／゜(875−900)＝
(R ₉₀₀ −R ₈₇₅ )×100/(R ₉₀₀ +R ₈₇₅ )/2)×25 Examples In the following examples, test samples were prepared and tested in the manner described above. All ratios are on a molar basis unless otherwise specified. Examples 1-3 Using the method outlined above, the amount of 6-boride can be reduced to 60-10% and the amount of crystalline glass can be reduced to 40%.
A series of three compositions were prepared varying from ~90%. _This glass contained 11.1% _Ta2O5 . The electrical properties of resistors made from them show that a wide range of resistivities can be obtained by varying the hexaboride/glass ratio. These data are given in Table 1 below.

Table: Examples 4-7 A series of four resistor compositions were prepared using 5.9% Ta ₂ O ₅ in glass, which is considered the optimum concentration. Electrical data of resistors made from them show excellent process stability, especially at high resistivities. According to the X-ray diffraction study of this resistor
It showed the presence of LaB ₆ , TaB ₂ and CaTa ₄ O ₁₁ , the latter two of which were formed during calcination. These data are shown in Table 2 below.

【table】

TABLE Examples 8-16 Three additional series of resistor compositions were made by adding Ta ₂ O ₅ to the crystalline glass at 2%, about 4% and 7.6% levels. Resistors containing only 2% Ta ₂ O ₅ (Examples 8-10) showed no glass crystallization and were significantly inferior in terms of process stability. Approximately 4
% Ta ₂ O ₅ (Examples 11-13) also did not exhibit glass crystallization and the resistors had poor refire stability. However, 5% of glass
The resistors containing the above Ta ₂ O ₅ exhibited glass crystallization and the resistor refire stability was thereby greatly improved. Those data are given in Table 3 below.

【table】

【table】

【table】

【table】

【table】

Claims (1)

[Scope of Claims] 1 A 2 to 70% by weight (on a total solid basis) of a conductive metal hexaboride selected from the group consisting of rare earth hexaborides, CaB ₆ , SrB ₆ and mixtures thereof; B the conductive material; It contains 70 to 95 mol% of components that cannot be reduced by the metal hexaboride, and contains 30
Crystalline glass with ~5 mol% _Ta2O5 dissolved _in it
A composition for making thick film resistors comprising a mixture of finely divided particles with 98-30% by weight (on a total solids basis). 2. The composition according to claim 1, wherein the crystalline glass is an alkaline earth metal aluminosilicate. 3. The composition according to claim 2, wherein the crystalline glass is an alkaline earth metal boroaluminosilicate. 4. A composition according to claim 1, wherein the glass contains ₅ to 10% _Ta2O5 . 5. The composition of claim 1, wherein the conductive metal hexaboride is _LaB6 . 6. The composition of claim 1, wherein the conductive metal hexaboride is _YB6 . 7. The composition according to claim 1, wherein the conductive metal hexaboride has a particle size of 1 micron or less. 8 A conductive metal selected from the group consisting of A rare earth hexaborides, CaB ₆ , SrB ₆ and mixtures thereof, dispersed in an organic medium 6
B contains 2 to 70% by weight (on a total solid basis) of a boride, and 70 to 95 mol% of a component that is not reduced by the conductive metal hexaboride;
Crystalline glass with ~5 mol% _Ta2O5 dissolved _in it
A screen printable composition comprising a composition for making thick film resistors comprising a mixture of finely divided particles with 98 to 30% by weight (on a total solids basis).