JPS6128201B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a film resistor.

The coating produced by the method according to the invention can be used as an electrical resistor. The outer layer, like many electrically conductive coatings, can also be used as a shielding coating, for example for container earthing purposes.

Particularly when using electrical resistance, there is a requirement that the temperature coefficient of the coating be as small as possible and constant over a wide temperature range. The temperature coefficient is the rate of change in resistance value with respect to temperature change, and is obtained by dividing the change in resistance value with respect to the resistance value at room temperature by the resistance value at room temperature and the temperature difference. Temperature differences are particularly important when resistance tolerances are tight. A small and constant temperature coefficient is therefore an important requirement, especially for precision resistors.

It is known to produce electrically resistive coatings by so-called organic thick film technology. In this production method, conductive particles such as carbon black, graphite, carbon fibers, silver, nickel, chromium or metal alloys, metal oxides can be made of organic materials such as polyethylene or epoxide resins or phenolic resins. After being dispersed in an electrically insulating and adhesive polymer and curing, a conductive matrix is formed, the conductivity of the coating depending, among other things, on the loading concentration, arrangement and electrical properties of the particles incorporated into the polymer. determined by.

The temperature coefficient of a coating containing carbon particles depends on the temperature. In the case of metal-metal oxide coatings, the temperature coefficient may also depend on the coating composition, in which case it is independent of the resistance value. In carbon film resistors, the achievable conductivity is limited for low ohmic values by the relatively poor conductivity of the incorporated carbon particles in the form of graphite, carbon black or carbon fibers, and the carbon film resistors are Has a high negative temperature coefficient.

In particular when mixing base metals and therefore low-cost metals, the long-term electrical stability is often impaired by oxidative ring processes at the surface. Generally, a resistor with a positive temperature coefficient is obtained.

Furthermore, it is known to produce electrically resistive coatings by inorganic thick film technology. In this case, glasses with a low melting point are used as the non-conductive and sticky component. Preferably, expensive and therefore oxidation-resistant metals such as silver, platinum, ruthenium, palladium, etc. or their oxides are used as conductive matrices. By mixing several pastes with different conductivities, the specific resistance and temperature coefficient can be changed, the conductivity of the paste depending on the conductivity of the noble metal mixed in the frit and the mixing ratio thereof.

Several disadvantages arise when using carbon black or graphite as conductive particles in electrically insulating polymers. As mentioned above, the electrical conductivity of the coating depends, among other things, on the packing density of the particles, and therefore various compounds having different packing densities must be prepared for a wide range of electrical resistance values. Thus, different packing densities result in different rheological properties of the coating. Additionally, different packing densities lead to different shrinkage behavior during curing of the coating. Variations in surface tension from coating to coating, caused by variations in the properties of carbon black and graphite, also result in batch-to-batch resistance variations, particularly when silk screen printing methods are used to produce resistive coatings.

To achieve different resistance values without changing the packing density of the particles in the polymer, the conductive particles are made of a refractory inorganic oxide material and coated with a layer of carbon-containing thermoresponsive polymer. It is known that The conductive component is relative to the final composition of the mixture.
The content is 10 to 95% by weight, and the particle size is 20 μm or less. Such differences in particle conductivity are obtained only by varying the thickness of the pyrolytic carbon film surrounding the individual refractory particles. The low conductivity range required for high ohmic resistance is obtained by significantly reducing the layering of the carbon-containing thermoresponsive polymer down to a single layer. The high resistance values achieved in this case are associated with an increasingly deteriorating behavior of the temperature coefficient. This is due to the relatively weak continuity of the "grain boundaries" of the carbon coating. This contact location becomes increasingly important as the film thickness decreases. Since the resistance at the contact point at the grain boundary is extremely sensitive to temperature, macroscopically, this condition can be said to be a rapid deterioration of the temperature coefficient of resistance as the carbon film thickness decreases. A thick material coating with a high resistivity but the same resistance per unit area therefore has a small temperature coefficient.

The invention is characterized in that the packing density of the electrically conductive component in the binder remains unchanged, making it possible to achieve different resistance values and guaranteeing the lowest possible value of the external temperature coefficient. The objective is to find a method for manufacturing various types of conductive film resistors.

This task is based on the invention, in which the electrically conductive component consists of a semiconductor material, which material is obtained by pyrolysis of carbon-containing compounds and is doped and/or layered with elements of the - group of the periodic system. It is solved by Doping and/or layering is carried out by simultaneous and/or successive thermal decomposition of carbon and of chemical compounds containing the doping elements.

In one embodiment of the invention, the semiconductor material can be obtained by pyrolysis of gaseous or liquid hydrocarbons and/or mixtures thereof, such as aliphatic, aromatic or heterocyclic hydrocarbons.

Another possibility is that the semiconductor material is obtained by pyrolysis of pulverulent, carbon-containing organic materials such as glucose, glucose, starch or coal pitch.

Thermal decomposition is carried out in both embodiments at temperatures of 600-1600°C.

The doping and/or layering of the semiconductor material is effected by temperature action from the gas phase of a compound of an element of the -group of the periodic system.

For example, boron, silicon, germanium, or phosphorus can be used as the element. Other materials such as aluminum, titanium, zirconium, vanadium, chromium, tungsten, iron, cobalt,
There is also the possibility of using metals such as nickel or molybdenum. Semiconductor materials are about 10 ^-8 to about 10
It has a conductivity of ° (Ω ^-1 cm ^-1 ).

In addition to electrically conductive components, substances with large electrical loss factors and large dielectric constants can be incorporated into the polymer. This material is ground into fine particles.

If the pyrolysis is carried out in a temperature range of 600 DEG -1600 DEG C., the carbon is precipitated as a compound in the form of a coating by the doping or layering elements. The resulting electrical conductivity of such carbon results from the ratio of hydrocarbon to doping material.
Since many elements of the -group of the periodic system are precipitated in the form of insulators, the resulting electrical conductivity can be adjusted by means of these doping substances.

The small temperature coefficients that occur when using materials of this type are probably due to several factors. The elements of the - group of the periodic system facilitate the dehydrogenation or graphitization process that takes place during hydrocarbon pyrolysis. The effect of "contact points" between carbon grain boundaries is reduced by the thick film thickness.

Short-circuit coupling between adjacent carbon atomic coatings caused by doping elements is also not excluded. All these factors contribute to the temperature stability of resistors made from this type of material.

Refractory materials with large electrical loss factors and large relative dielectric constants include barium titanate, titanium oxide, silicon oxide, aluminum oxide, iron oxide, silicon carbide, iron carbide, iron silicide, chromium silicide, or Mixtures of these are utilized.

Of course, the conductive component can include mixtures of various semiconductor materials with other conductivities.

In yet another embodiment of the invention, the semiconductor material is tempered in vacuum, in a nitrogen atmosphere or in an inert gas atmosphere at a temperature between 800-1600C.

Curing of carbon-filled resistive coatings doped with elements of the -group of the periodic system can be reasonably carried out in a microwave field. The effect of microwave-induced thermal evolution is enhanced by the dielectric position within the carbon itself or by the presence of dielectric pigments. This refers in particular to aluminum oxide, titanium oxide, aluminum phosphate, silicon dioxide, silicon carbide, aluminum nitride, etc.

Dielectric materials placed within a polymer matrix develop heat extremely rapidly in a microwave field. Even distribution of these particles within the polymer matrix results in rapid and rational curing of the polymer binder.

Reasonably microwave curing is about 2400−
It is carried out in the frequency range of 6000MHz.

The invention is illustrated in detail by the following example: EXAMPLE A gas mixture consisting of 45% propane, 5% boron trichloride and 50% hydrogen was used to
100g of titanium oxide on m ² /g surface - 1000℃
processed at a temperature of

The electrically conductive material thus produced was finely ground in a ball mill and dispersed in a pearl mill with a mixing ratio of 55% by weight electrically conductive material and 45% epoxy binder.

The resulting silk-screen printable paste is printed onto a kraft paper-substrate by silk-screen printing and in a microwave oven.
Cured with a power of 40 W/cm ² within 1.5 minutes.

The generated resistance structure has a value of 840KΩ/□ and -
It had a temperature coefficient of 200 ppm/°C.

Example with 17m ² /g surface and <5μm particle size
100 g of aluminum phosphate was treated with a gas mixture consisting of 80% nitrogen and 20% cyclohexane at a temperature of 800° C. for 25 minutes.

Subsequently, the temperature was raised to 900°C and 5
% silicon trichloride treatment continued for 5 minutes.

The electrically conductive material obtained is rolled out into a silk screen printing paste as in the example and printed on kraft paper and heated in a microwave oven.
It was cured for 2 minutes with a power of 25V/cm ² .

The obtained resistance has a value of 120KΩ/□ and -
It had a temperature coefficient of 300 ppm/°C.

Claims (1)

[Scope of Claims] 1. (a) At least one layer of pyrolytic carbon is layered on a finely divided carrier made of a refractory inorganic oxidizing material; (b) The carbon-coated carrier is non-conductive and curable. (c) the resulting paste is placed on a substrate and subsequently cured. (d) Under the action of temperature, carbon is pyrolytically deposited on the carrier, and at the same time carbon is deposited in a single layer or layers as boron, germanium, phosphorous, aluminium, titanium, zirconium, vanadium, chromium, tungsten, iron. , doped and/or layered in a reducing atmosphere consisting of a gas phase with cobalt, nickel or molybdenum; The carrier is a material with a large electrical loss coefficient and large dielectric constant, such as barium titanium, titanium oxide, zirconium oxide, iron oxide, aluminum oxide, silicon carbide, iron carbide, iron silicide, chromium silicide or mixtures thereof. A method for manufacturing a film resistor, characterized by comprising the steps of: 2. The method of manufacturing a film resistor according to claim 1, wherein the thermal decomposition process is carried out at a temperature of 600° to 1600°C. 3 After its doping or layering, the carrier is heated to 800°C in a vacuum, nitrogen atmosphere or inert gas atmosphere.
Claim 1 tempered at ~1600°C
A method for manufacturing a film resistor according to item 1 or 2.