JPH0438801A - Thermistor - Google Patents

Abstract

PURPOSE:To obtain an insulating layer in which no reaction takes place even at a high temperature and which is excellent in mechanical strength and insulating property by covering an element and connecting sections between the element and metallic lead wires with a ceramic layer which is composed mainly of silicon nitride and coated with a coating material composed mainly of a polysiloxane, fined and formed. CONSTITUTION:Various kinds of polysilazines can be used for the coating material for forming an insulating layer on a thermistor element and connecting sections between the thermistor element and metallic lead wires. The insulating layer (ceramic layer) having an Si-N joint is formed by firing the coating material after the material is applied on the surface of the thermistor element connected with the metallic lead wires. When the polysiloxane used is in a liquid state, it can be used as the coating material as it is and, when the polysiloxane is in a solid state, it is dissolved in an organic solvent. The ceramic layer formed on the surface of the thermistor and composed mainly of silicon nitride is a compact layer and excellent in insulating property, thermal shock resistance, mechanical strength, especially, in high-temperature strength and shows no reaction upon the thermistor element.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermistor with excellent heat resistance.

(Prior Art and its Problems) Thermistors of various structures have been known in the past and have been applied as temperature sensors in various fields. Among such thermistors, one having excellent heat resistance is known to have an insulating layer made of glass formed on the element surface.

By the way, in a thermistor having such a glass insulating layer, if it is placed in a high temperature condition of 300°C or higher,
In addition to reducing the insulating properties and mechanical strength of the glass, problems such as the formation of fine racks on the glass or a reaction between the glass and the thermistor element resulting in a change in the resistance value of the element occur.

Conventionally, in order to solve this problem, borosilicate glass was used as the glass (JP-A-60-57903, JP-A-60-57903), or a mixture of glass particles and alumina particles was fired. Insulating layer (Unexamined Japanese Patent Publication No. 62-
No. 287601) etc. have been proposed. However, since all of these still use glass as the insulating material, they do not provide an essential solution to the above-mentioned problem.

In JP-A-63-187602, a coating material containing an organosilicon polymer (silicone resin or polysiloxane resin), glass frit, and an 8-metal oxide filler (alumina, magnesia, etc.) is applied to the surface of the element. It discloses a thermistor in which an insulating layer is formed by coating and baking at 350° C. for 1 hour and 650° C. for 1 hour.

However, such an insulating layer is still unsatisfactory because it contains a glass frit and therefore tends to cause a reaction between the glass frit and the thermistor element at high temperatures and is susceptible to cracking.

(Problems to be solved by the invention) The present invention solves the above-mentioned problems found in conventional thermistors, does not cause any reaction with the thermistor element even at high temperatures, and has excellent mechanical strength and precision at high temperatures. The object is to provide a thermistor having an insulating layer.

(Means for Solving the Problems) The present inventors have conducted extensive research to solve the above problems, and as a result, have completed the present invention.

That is, according to the present invention, a thermistor element is connected to a metal lead wire, and the element and the connection portion between the element and the metal lead wire are coated with a ceramic layer containing silicon nitride as a main component. provides a thermistor characterized in that it is formed by applying a coating material containing polysilazane as a main component and firing it.

In the present invention, various conventionally known polysilazane can be used as a coating material for forming an insulating layer on the thermistor element and the connection portion between the thermistor element and the metal lead wire (hereinafter also simply referred to as the surface of the thermistor element). However, preferred are the following polysilazane.

(1) Number average molecular weight having a repeating unit of the general formula is 100 to 50,
000 cyclic inorganic polysilazane, linear inorganic polysilazane or a mixture thereof.

(2) Silazane high polymer, that is, polysilazane as mentioned above or A, 5tock, Ber, 54. p7
40 (1921), V.M., 5cantlin, Ino
rrganic Chemistry, 11 (1972
), A.5eyFerth, U.S. Pat. No. 4,397,3
The silazane polymer disclosed in Specification No. 28 etc. is used as a solvent with tertiary amines such as trialkylamine, 21I & amines having a sterically hindered group, basic compounds such as phosphine, or the like. A non-basic solvent.

For example, a number average molecular weight of 200 to soo, ooo, preferably 5oo-1 can be obtained by adding it to hydrocarbons and heating it at 8°C to 300'C to carry out a dehydration condensation reaction.
00,000 high polymer.

(3) A polymer obtained by a modification reaction of inorganic polysilazane has a crosslink bond -+NH←n (n=1 or 2), and the atomic ratio of nitrogen bonded to a silicon atom and silicon is C~/Si
) is 0.8 or more and the number average molecular weight is 200-500, 0
00, preferably 500 to 100,000. This modified polysilazane can be produced by carrying out a dehydrogenation condensation reaction of polysilazane using ammonia or hydrazine (Japanese Patent Application No. 1982-202757) ).

(4) Repeating unit 1+SiH, NH) and -+si
o, o←, and the degree of polymerization is 5 to 300. Preferably 5~
100 polysiloxane (Japanese Unexamined Patent Publication No. 195024/1983).

(5) Composition formula (R5iHNH) x [(R5iH)□,,
N), 1 (However, in formula 1, R is an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, or a group other than these groups in which the atom directly connected to Si is carbon.

It represents an alkylsilyl group, an alkylamino group, or an alkoxy group, and 0, 4<x<1. ) polyorganohydrosilazane (patent application 1986-
293472).

In the present invention, various polysilazane as described above can be arbitrarily applied, but in order to maintain oxidation stability and prevent deterioration of physical properties such as strength, the free cut content is preferably 10% by weight or less, preferably 5% by weight. It is desirable to keep it below %.

Furthermore, in the present invention, polymetallosilazanes made by reacting metal alkoxides etc. (Japanese Patent Application No. 1982-223790), polyborosilazane etc. made by reacting compounds (Japanese Patent Application No. 1982-223790), etc.
69169) may also be used. Depending on the type, these polysilazane exhibits a liquid to solid state at room temperature.

To form an insulating layer on the thermistor surface according to the present invention,
After applying the polysilazane as a forming material to the surface of the thermistor element connected to the metal lead wire,
If the polysilazane used, which is heated and fired to form an insulating layer (ceramic layer), is liquid, it can be used as it is as a coating material. Further, if polysilazane is in a solid state, it can be dissolved in an organic solvent and used as a coating material.

Polymeric binders can be added to coating materials containing polysilazane, as well as organic amines, carboxylic acid anhydrides, incyanates, thiols, carboxyimides, and metal alkoxides.

A hardening agent such as a metal halide can be added, and an appropriate amount of ceramic powder, such as a metal nitride, oxide, or carbide, can also be added. In particular, in order to obtain an insulating layer with excellent thermal conductivity, it is preferable to add aluminum nitride to the coating material.The amount of aluminum nitride added is 20-90% by weight, preferably 50-90% by weight in the insulating layer. %.

The firing of the coating material applied to the surface of the thermistor is -
For boat fishing, use vacuum or inert gas (NZ, argon, etc.)
or reducing gases (e.g. ammonia).

hydrazine, etc.) and an oxidizing gas (0□, air, ozone, water vapor, etc.) by heating to a temperature of 200° C. or higher, preferably 400° C. or higher. By this baking, the coating layer made of polysilazane has a
This results in a ceramic (silicon nitride) layer having i-N bonds.

In the present invention, the coating material is fired under vacuum or in an atmosphere of inert gas or reducing gas.

This can be preferably carried out by preheating at a temperature of 200°C or higher, preferably 400°C or higher, and then heating at a temperature of 100°C or higher, preferably 300°C or higher in an oxidizing gas atmosphere. In this case, in the ceramic layer formed on the thermistor surface, an oxide layer having 5i-0 bonds is formed as a surface layer.The thickness of the surface oxide layer depends on the type of oxidizing gas.

It can be controlled by firing temperature, firing time, etc.
It is usually 0.01 to 54, preferably 0.1 to 3. Further, the ceramic layer having the oxide layer on the surface can also be formed by directly firing the coated layer in an oxidizing gas atmosphere. In the above-described ceramic layer having an oxide layer on its surface, the ratio of oxygen atoms bonded to silicon atoms (0/Si) is usually 0.1-1.
5, preferably 0.2 to 1.0.

The ceramic layer mainly composed of silicon nitride formed on the surface of the thermistor as described above is dense and has excellent insulation, thermal shock resistance, and mechanical strength.

In particular, it has excellent high-temperature strength and does not cause any reaction with the thermistor element even at high temperatures. Furthermore, those with an oxide layer formed on the surface have excellent oxidation resistance and have further improved high-temperature usage characteristics. Furthermore, the polysilazane used as a coating material in the present invention is as follows.

It has excellent coating properties, excellent ceramic yield, and high productivity.

The thermistor of the present invention includes various types having an insulating layer on the surface, such as bead type, disc type,
Thermistors include rond type, thick film type, thin film type, and chip type thermistors.

(Effects of the Invention) The thermistor of the present invention uses a ceramic layer containing silicon nitride as the main component for its insulating layer, so it has significantly superior high-temperature usage characteristics, compared to conventional glass used as an insulating layer. This method does not cause any problems such as a decrease in mechanical strength at high temperatures, reaction with the thermistor element, and generation of cracks, which were observed in the above. Furthermore, since the ceramic layer is formed by a simple method of applying a coating material containing borasilazane to the thermistor surface and firing it, it is possible to manufacture the desired heat-resistant thermistor with high productivity. can.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

Reference Example 1 A four-loaf flask with an internal volume of 500 d was equipped with a gas blowing pipe, a mechanical stirrer, and a dewar condenser. After replacing the inside of the reactor with deoxygenated dry nitrogen, 280 m of degassed dry pyridine was placed in the four-loaf flask. Then, 51.6 g of dichlorodisilane was added to the water-cooled 7-duct C3xHzCQ・2C,H,
The 0 reaction mixture in which N) was produced was cooled on ice, and while stirring,
30.0 g of purified ammonia was blown through a sodium hydroxide tube and an activated carbon tube.

After the reaction was completed, the reaction mixture was centrifuged, washed with dry pyridine, and further filtered under a nitrogen atmosphere to obtain a filtrate 520-. When the solvent was distilled off from the filtrate 572 under reduced pressure, 0.98 g of resinous solid polysilazane was obtained.

The number average molecular weight of the obtained polymer was measured by GPC and was found to be 1020. Also, the I of this polymer
R (infrared absorption) spectrum (solvent: dry 0-xylene:
Considering the concentration of polysilazane (9.8 g/R), absorption based on NH at wave number (cm-1) 3350 and 1175; absorption based on 5i)1 of 2170; 1020-82
It was confirmed that absorption based on 0 SiH and 5iNSi was exhibited. In addition, this polymer's HNMR (proton nuclear magnetic resonance) spectrum (60MHz, solvent CDCQ□
/Reference material TMS), it was confirmed that all of them exhibited a wide range of absorption.

That is, 64.8 and 4.4 (br, 5iH); 1.5
Absorption of (br, NH) was confirmed.

Example 1 The polysilazane obtained above was dissolved in ortho-xylene to obtain a solution having a polysilazane concentration of 70% by weight.

Next, this solution is used as a coating material, and it is uniformly applied to the surface of a chip-type thermistor (a structure in which an electrode layer is provided on the surface of the chip of the thermistor element, and a Dumet wire is connected to this electrode layer as a lead wire). After coating and drying, the coating was placed in a heating furnace, and the temperature was raised from room temperature to 600°C, and maintained at this temperature for 1 hour to obtain a thermistor having a dense ceramic layer made of silicon nitride on the surface.

This thermistor has excellent high-temperature usage characteristics, and even in a heating test in which it was held at a temperature of 500°C for 1000 hours, no cracks appeared on the ceramic surface.
Furthermore, the change in resistance before and after the test was as low as 0.3% or less.

Example 2 The coating material made of polysilazane shown in Example I was applied to a thin film thermistor (an electrode film was formed on both ends of an alumina substrate, and a silicon carbide film was formed as a thermistor element on the surface of the substrate including the electrode film). ) was applied and dried, placed in a heating furnace, heated from room temperature to 400°C, and held at this temperature for 1 hour to obtain a thermistor having a ceramic layer made of silicon nitride on the surface.

As a result of subjecting this thermistor to the heating test shown in Example 1, it was confirmed that no cracks were generated on the surface of the ceramic layer and that it had good high-temperature usage characteristics.

Patent applicant Tonen Corporation Representative Patent Attorney Toshiaki Ikeura (1 other person)

Claims (1)

[Claims] (1) A thermistor element is connected to a metal lead wire, and the element and the connection part between the element and the metal lead wire are coated with a ceramic layer containing silicon nitride as the main component, and the ceramic layer contains polysilazane as the main component. A thermistor characterized in that it is formed by applying a coating material and firing the coating material.