Method for manufacturing paste for thick-film thermistor

Abstract

FIELD: thermistors.SUBSTANCE: method for producing a paste for a thick-film thermistor, used to form resistive elements by thick-film technology, in particular for creating low-resistance thermistors with a high negative temperature coefficient of resistance (TCR). The method includes obtaining a thermistor composition, a resistive composition and mixing them. The thermistor composition is synthesized in the form of a paste with a specific surface resistance of at least 700 Ohm / sq and with a negative |TCR|≥5900 ppm / °C. The resistive composition is synthesized in the form of a paste with a specific surface resistance of no more than 100 mOhm / sq and with |TCR|≤50 ppm / °C, wherein the resistive composition contains a conductive phase based on Pd / Ag powders taken in a ratio of 55 / 45 to 60 / 40 by weight, respectively. Then, the thermistor composition with a particle size of no more than 5 μm is mixed with a resistive composition with a particle size of no more than 10 μm in a ratio of 70 / 30 to 65 / 35 by weight, respectively.EFFECT: paste for the production of low-resistance thick-film thermistors with a high negative TCR, compatible with an LTCC substrate.1 cl, 1 ex

Description

[0001] The invention relates to electrical engineering technologies and products used to form resistive elements using thick-film technology, in particular for creating low-resistance thermistors with a high negative temperature coefficient of resistance (hereinafter referred to as TCR) on low-temperature co-sintered ceramics (hereinafter referred to as LTCC). More specifically, the invention relates to pastes for thick-film thermistors and methods for their manufacture.

[0002] There are many known methods for producing pastes for thick-film thermistors, including paste formulations. The pastes consist of a functional component, a special glass powder, and an organic binder. The resulting paste is applied to a ceramic substrate using screen printing and then burned into the substrate.

[0003] Pastes with a conductive component based on ruthenium dioxide and ruthenites are the most widely used for thick-film thermistors. For example, a method has been proposed for producing a paste consisting of ruthenium oxide (RuO2) and more complex ruthenium compounds / oxides mixed with a glass binder (frit) and an organic carrier. This paste is used to form columnar resistive layers with the required specific resistance and TCR in an LTCC structure [see US Patent 6,720,859, Temperature Compensating Device with Embedded Columnar Thermistors, H01C 7 / 10].

[0004] Another group of thermoresistive pastes with an electrically conductive component based on ruthenium dioxide and ruthenites with a fairly wide range of ratings and TCR involves burning only into alumina ceramics [see, for example, patent JP 4068598 Manufacturing method of thick film thermistor composition H01C 7 / 04, patent JP 4042003 Thick-film thermistor composition H01C 7 / 04],

[0005] A significant disadvantage of such pastes is the need for long-term sintering of powders, as well as energy costs during grinding, and the incompatibility of pastes with LTCC material due to the interdiffusion of components during firing.

[0006] Thus, there are no pastes for producing low-resistance thick-film thermistors with high negative TCR on LTCC material.

[0007] The technical result is the production of a functional component of paste for LTCC substrate.

[0008] The technical result is achieved in that in a method for producing a paste for a thick-film thermistor, which includes obtaining a thermistor composition, a resistive composition, and mixing them, the thermistor composition is synthesized in the form of a paste with a specific surface resistance of at least 700 Ohm / sq and with a negative |TCR|≥5900 ppm / °C; a resistive composition is synthesized in the form of a paste with a specific surface resistance of no more than 100 mOhm / sq and with |TCR|≤50 ppm / °C; wherein the resistive composition contains a conductive phase based on Pd / Ag powders taken in a ratio of 55 / 45 to 60 / 40 by weight, respectively; The thermistor composition with a particle size of no more than 5 μm is mixed with a resistive composition with a particle size of no more than 10 μm in a ratio of 70 / 30 to 65 / 35 by weight, respectively.

[0009] The essence of the technical solution is as follows.

[0010] Synthesize a thermistor composition in the form of a paste with a specific surface resistance of at least 700 Ohm / sq and with a negative |TCR|≥5900 ppm / °C and a resistive composition in the form of a paste with a specific surface resistance of no more than 100 mOhm / sq and with |TCR|≤50 ppm / °C.

[0011] In the resistive composition, the conductive phase based on Pd / Ag powders taken in a ratio of 55 / 45 to 60 / 40 by weight, respectively, allows to reduce the TCR value.

[0012] The particle sizes of the thermistor (no more than 5 µm) and resistive composition (no more than 10 µm) allow for a highly homogeneous paste to be achieved during mixing. Larger particles result in the formation of a heterogeneous dispersed system, characterized by uneven particle distribution throughout the mixture and a variation in properties after firing.

[0013] A thermistor / resistance ratio of 70 / 30 to 65 / 35 by weight allows for the production of a thermistor with the desired specific resistance and TCR. Experiments have shown that with other thermistor / resistance ratios, the resistance and TCR do not reach the required values.

[0014] Compositions in the form of pastes allow for a more homogeneous mass to be obtained when mixed, and the resulting mixture in the form of a paste simplifies the process of application to a substrate using screen printing.

[0015] Thus, the physical and chemical characteristics of each of the pastes make it possible to form a composition that, when applied to an LTCC substrate, ensures good sintering and the desired characteristics of the thermistor.

[0016] The method is implemented as follows. The thermistor composition is manufactured by mixing powders of a semiconductor phase, ruthenium oxide, lead borosilicate glass, and an organic binder.

[0017] The percentage ratio of the components is selected based on the requirement to obtain the minimum surface resistance of a 1×1 mm planar thermistor on an LTCC substrate with a negative TCR of at least 5900 ppm / °C.

[0018] The low-ohmic resistive composite is manufactured from a mixture of Pd and Ag powders, lead-barium-borosilicate glass, and an organic binder. The Pd / Ag powder ratio is selected within the range of 55 / 45 to 60 / 40. With this ratio, the TCR of the low-ohmic resistor can be significantly reduced to 50-60 ppm / °C. The percentage of conductive phase and glass in the resistive composite is selected based on the requirement for a 1x1 mm thermistor on an LTCC substrate with a surface resistance of 50 mΩ / sq. with a TCR of less than +50 ppm / °C.

[0019] Mix a thermistor composition with a particle size of no more than 5 μm with a resistive composition with a particle size of no more than 10 μm in a ratio of 70 / 30 to 65 / 35 by weight, respectively.

[0020] An example of a specific implementation.

[0021] A thermistor composition is prepared from a mixture of sintered powder based on MnO2, NiO, Co3O4, Fe2O3, RuO2, RuO2 powder, glass powder based on Pb-Si-B-Ca-Al-O with a specific surface area of ​​6000-8000 cm 2 / g, organic binder based on ethylcellulose N22 and lecithin, a mixture of terpineol, dibutyl phthalate, dimethyl phthalate, diisononyl phthalate, butyl carbitol, butyl carbitol acetate, castor oil.

[0022] Thermistor paste is prepared by mixing 72% by weight of dry composition and 28% by weight of organic binder in a mixer, then using a paste grinder until a grinding degree of no more than 5 µm is obtained.

[0023] A low-resistance resistive composition is prepared from a mixture of silver and palladium powders in a Pd / Ag ratio of, for example, 60 / 40, glass powder based on Si-Pb-Ba-B-Ca-Sr-Zr-Al-Mg-O with a specific surface area of ​​6000-8000 cm 2 / G.

[0024] A low-resistance resistive paste is prepared by mixing 80% by weight of the dry composition and 20% by weight of the organic binder in a mixer, then using a paste grinder until a grinding degree of less than 10 μm is obtained.

[0025] Mix the thermistor composition with the resistive composition in a ratio of, for example, 65 / 35 by weight, respectively.

[0026] The resulting mixture has good homogeneity, and its physical and chemical properties allow it to be used on an LTCC substrate to produce high-quality temperature sensors with good sensitivity and thermal attenuators with a series resistance of about 15-30 Ohm / sq and a TCR of about -5000 ppm / °C.

[0027] Thus, new technological methods in the manufacture of paste for thick-film thermistor, namely mixing a high-resistance thermistor composition and a low-resistance resistive composition based on Pd / Ag powders, make it possible to obtain a low-resistance paste with a high TCR for LTCC substrates, which confirms the achievement of the stated technical result.

Claims

A method for producing a paste for a thick-film thermistor, comprising obtaining a thermistor composition, a conductive resistive composition and mixing them, characterized in that the thermistor composition is synthesized in the form of a paste with a specific surface resistance of at least 700 Ohm / sq and with a negative |TCR|≥5900 ppm / °C; a resistive composition is synthesized in the form of a paste with a specific surface resistance of no more than 100 mOhm / sq and with |TCR|≤50 ppm / °C; wherein the resistive composition contains a conductive phase based on Pd / Ag powders taken in a ratio of 55 / 45 to 60 / 40 by weight, respectively; The thermistor composition with a particle size of no more than 5 μm is mixed with a resistive composition with a particle size of no more than 10 μm in a ratio of 70 / 30 to 65 / 35 by weight, respectively.