DE2333495A1 - Carbon film resistors deposited inside glass or quartz tubes - with hermetically sealed ends and resistance values adjusted using laser beam - Google Patents

Abstract

The carbon, plus any doping elements, i deposited in the bore of the tube made from glass free of alkali-ions, and the tube is hermetically sealed, esp. by using the terminals. The resistance value is then adjusted by spiralling the carbons layer using a laser beam. Accurate, stable, close-tolerance resistance values are obtd.

Description

Method for producing an electrical sheet resistor

The invention relates to a method for producing an electrical sheet resistance, in which one of elementary Resistance layer consisting of carbon, optionally with the addition of dopant, from the gas phase on the Surface of an insulating support body forming a structural unit with the resistance layer is deposited and is provided with electrical connections at their ends.

Such electrical sheet resistors are common. Your electrical connections to the resistance layer are For example, as caps at the ends of a cylindrical carrier, in particular made of glass or insulating ceramic Body attached, the cylinder jacket of the - is covered by the - especially coiled - resistance layer.

Sheet resistors made of carbon / iron compared to resistors with metal layers have the advantage of a cheaper electrical one Behavior with impulsive loads. On the other hand, they are much more sensitive to moisture and oxidation as metal layer resistors. It is therefore advisable to install the sheet resistor hermetically in a housing. However, this has the disadvantage of complex assembly, high production costs of the housing and difficulties in relation to it on the necessary electrical balancing, as the resistance layer in the time between the balancing and the installation in the protective housing comes into contact again with the influences of the environment.

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The invention therefore proposes the resistance layer on the inner wall of an insulating layer which is free of alkali ions To deposit the existing glass tube, then its ends hermetically, especially with the electrical connections to the resistance layer, and finally, if necessary, only after closing - the adjustment through Make twisting of the resistance layer.

For the final setting of the resistance value of the carbon layer The adjustment and twisting method disclosed in the German patent application P 2.238.557-5 (VPA 72/1133) is recommended apply. This application relates to a method for manufacturing an electrical resistance element in FIG Form of a conductive layer adhering to the surface of a cylindrical or conical core made of insulating material, the first applied as the core surrounding jacket and then along a helical line with one of the electrical The resistance of the conductive layer between the two ends equipped with connection elements is provided to increase the groove will. This method is characterized in that the increases the electrical resistance of the conductive layer Furrow at the same time at two axially offset points of the conductive layer by means of a punctiform impinging and the material of the conductive layer at the respective point of impact Vaporising energy beam, in particular laser beam, is generated by the points of impact of both energy beams in parallel to the axis of the conductive layer rotating together with the insulating core around its axis, forming one each helical groove are mutually displaced.

First, when carrying out the method according to the invention, a tube made of a suitable insulating glass, for example quartz or an alkali-free glass, is heated and a reaction gas capable of separating elemental carbon in the heat flows through it. A layer of carbon is deposited in the process

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on the inner wall of the tube. It is advisable to carry out this process on an elongated tube and, after the creation of a carbon layer firmly adhering to its inner wall, to separate it into the lengths corresponding to the individual resistors to be produced and to process each of the pieces obtained into a sheet resistor. It is useful here to heat the tube by means of an annealing zone that successively traverses the tube from one end to the other. It can find use apparatus shown AEIE i ⁿ FIG. 1

That, for example, held in a vertical position in brackets 1 and 2 at its ends and possibly also supported in the middle A tube consisting of a glass free of alkali ions is attached to one. e.g. the upper end with a supply device connected for a reaction gas capable of separating elemental carbon. As a reaction gas For example, methane or ethane diluted with argon or nitrogen can be used. Is also beneficial the use of a hydrocarbon such that it is in a liquid state at room temperature, for example of hexane or heptane. In this case one can provide an evaporator vessel 4, which with the liquid hydrocarbon 11 is filled and in which a carrier gas flow supplied by a bomb 5 via a flow meter 6 is fed. There, the carrier gas stream is loaded with the vapor of the liquid carbon compound and arrives Via the supply pipe e.g. from above into the pipe 3 to be coated and leaves this e.g. at the lower end. The pipe is controlled by a heating device that can be moved axially in relation to it

jO e.g. in the form of a glow ring 7 made of conductive, heat-resistant Metal and an induction coil coupled to it. The induction coil 8 is impressed by a one Power supplying high-frequency source 9 is fed. When the high-frequency alternating current is switched on, it heats up

^ c the glow ring? and in turn generates by radiation an annealing zone 10 (shown hatched in the drawing)

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in the tube 3. The annealing zone 10 is guided, for example, from bottom to top, that is to say counter to the flow of reaction gas. In the annealing zone 10, elemental carbon is then deposited on the inner edge of the tube 3. The temperature in the annealing zone 10 is set to 900 to 1100 ⁰ C, so that a composed of lustrous carbon layer is deposited. The glow ring 7 with the induction coil 8 is displaced in the axial direction relative to the tube 3 (direction of the double arrow 14-), so that the glow zone 10 is successively passed through the tube 3 and the inner wall thereof is covered with a layer of carbon.

In production, it is expedient to coat the inner wall of the tubular carrier on elongated glass or quartz tubes by so-called "normal pressure carbonation", thus using a gaseous carbon compound flowing through the pipe under normal pressure. You can heat the entire tube at once, or as in the embodiment just described, zone by zone, while the pipe of the pyrolytically decomposed hydrocarbon compound, primarily in a mixture with protective and carrier gas, is flowed through.

This method can be used if the glass to be used is the one required for carbon deposition Temperature has such a high viscosity that no deformation occurs.

But you can also carbonize the inner wall of the pipe Carry out this during the production of the pipe string by pulling it back out of glass pods. You blow while pulling again into the resulting glass tube in the absence of air for separation of elemental carbon suitable gas diluted with an inert component against the pulling device.

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At the point of drawing, the glass tube is hot enough to allow the reaction gas to decompose with the formation of carbon to enable coating on the inner wall of the pipe. In the case of a vertically arranged redrawing system with withdrawal direction downwards, hydrocarbons which are liquid at room temperature can also flow in from above as coaling agents permit.

The electrical and mechanical properties of the dejected The carbon layer and the optimal coating speed depend on the properties and temperature the inner wall of the tube made of glass or quartz during the coaling process. To have favorable properties To achieve coating as quickly as possible, the glass surface can be sensitized. This is possible e.g. through the addition of Si (-O -) ^ -, Αΐζ-Ο -) ^ -, BC-O-), or P (-O -) ^ - groups, which are caused by thermolysis can be generated by volatile silicon, aluminum, boron or phosphorus compounds. Can be used, for example Siloxanes, aluminum halides or aluminum organyls, boric acid esters and phosphoric acid esters.

The sensitization can be carried out in practice in separate operations before the actual coaling is carried out or by adding the sensitizing substances to the reaction gas causing the coaling. In this case, the sensitizing substances will be selected in such a way that they either form the gaseous compounds which are produced in the pyrolysis of the carbon to be deposited
a) are not built into the carbon layer; This is

For example, the case when, when the feed line is from the side not yet coated, the decomposition temperature of the Sensitizer is higher than that of the carbonizer. When using the coaling process described fractional decomposition then takes place;

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b) the installation takes place without affecting the layer properties (example: installation of carbon atoms from the thermal decomposed esters) or

c) the incorporation of the sensitizing substances · Specifically influenced the shift in a favorable manner.

To improve the electrical properties, e.g. by reducing the temperature coefficient of the electrical Resistance of the carbon layer, the gaseous carbonizing agent can be selectively acting doping substances be added. Mention should be made here of the addition of boron compounds, which is known per se.

The carbon layer can be contacted, for example, by depositing a metal, e.g. from a gaseous Metal connection. (Carbonyl or metal organyls

Ί5 or volatile metal halides) - generated at the intended separation point of the tubular strand or at the ends of the tube. Here, the intended separation point can be constricted or narrowed using methods known from glass processing technology in order to facilitate the sealing process during or after separation. The solderability of the contact can be improved by, after a primary metallization (for example using nickel or copper as contacting metal), leading a solution through the pipeline which contains ions of a more noble metal, for example silver. Then, in a manner known per se, the surface of the metal that has already been deposited is covered (cemented) by the nobler metal May contain complexing agents, reducing agents, p. Buffers and wetting agents. The catalytic effect of the thermolytically produced contact layer is only

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this is further metallized, but not the metal-free carbon layer the free resistance path.

Both in the cementing process and in the case of electroless reinforcement of the deposited metal layer, one is preferred Use aqueous or non-aqueous solutions that are free from alkali ions. Alkali ions were namely through the carbon layer adsorbs and cannot be easily removed; they were later operated by the Resistance elements impair the DC strength.

The adjustment of the resistance layer to the desired final value takes place from the outside through the wall of the glass or quartz existing tubular support through with the help of focused electromagnetic rays of suitable Wavelength, for example with laser light of 1.06 / µm, v / obei advantageous in the already mentioned German patent application P 2-238,557.5 (VPA 72/1133) disclosed adjustment and Spiral process is used. The adjustment can be carried out are in the case of larger value tolerances on the pipe string that has not yet been cut after coating or after after coating and contacting, while with tight tolerances you first close the resistor and then the Makes comparison. In this case, the tube will be filled with a gas that contains the locally heated carbon converted into a gaseous compound, but not able to use the unheated part of the carbon layer to attack. Atmospheric air, for example, is suitable.

The component is closed in a manner known per se Way either

a) with the help of additional construction elements (for example with the help of bushings made of glass or oxide ceramic), whereby the contact between the centric Connection wire and the layer contact through a wire bridge and / or through metallization of the inside and the edge of the bushing is made,

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b) with the help of a metallic conductive inner cap, to which a feed wire is welded and which itself is fused with the glass by means of a suitable energy source, e.g. by means of laser light,

c) by melting and optionally squeezing the End of the tube forming the individual resistance element with the connecting wire embedded in the center.

The gas filling of the interior of the closed resistance tube can be based on different points of view. E.g. with laser beam coiling you will already completed resistance elements fill the interior with air to remove the carbon to be removed from the focal groove to convert into carbon monoxide. The oxygen content is then adjusted so that the combustion process cannot spread beyond the area of the separating furrow. Appropriate this can be a hydrogen filling, with absolutely the possibility exists that the carbon to be removed from the separating groove is converted into hydrocarbons can be. A hydrogen filling also means an increased heat dissipation capacity from the resistance layer. The use of helium as the filling gas enables a simple leak rate test with the help of a mass spectrometer, what can be of importance for the verification of the hermetically sealed installation in the case of MIL specifications. Is to be used preferably a gas filling with negative pressure to avoid an explosion if the resistance is overloaded due to excessive pressure increase to avoid.

12 claims
1 figure

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Claims (12)

Claims 1. Method for producing an electrical film resistor ¹ ^ "Stand in which a resistance layer consisting of elemental carbon, optionally with the addition of dopant, is deposited from the gas phase on the surface of an insulating support body forming a structural unit with the resistance layer and provided with electrical connections at its ends, characterized in that that the carbon layer is deposited on the inner wall -a tube consisting of an insulating glass free of alkali ions, that the ends of the tube are hermetically sealed, in particular with the electrical connections to the resistance layer, and finally - if necessary only after sealing - the adjustment by coiling the carbon layer is made. 2. The method according to claim 1, characterized in that that an elongated, made of glass or quartz tube in the heated state of a causing the deposition at high temperature, in particular let through reaction gas diluted with a carrier gas and that the tube is then divided into the pieces forming the individual resistance elements and each piece is completed to a resistance element. J. The method according to claim 1 or 2, characterized in that that the heating of the elongated glass or quartz tube is carried out by a moving annealing zone will. 4. The method according to claim 1, characterized in that that the carbonization of the inner wall simultaneously with the production of the insulating, made of glass or quartz existing tube is made. VPA 9/1 ^ 0/1077 - 10 - 409884/0671 - ίο - 5- The method according to claim 1, characterized in, that the heated inner wall of the tubular carrier with a liquid carbon compound, in particular with a liquid hydrocarbon as a coal agent. 6. The method according to claim 1 to 5j, characterized in that that the inner wall of the support before or during the carbonization with a sensitization of the glass surface causing substance, e.g. a volatile silicon, aluminum, boron or phosphorus compound is treated. 7. The method according to claim 1 to 6, characterized in that that the carbon layer with the lowering of the temperature coefficient or some other influence doping substance used for electrical conductivity, in particular at the same time as deposition, is moved. 8. The method according to claim 1 to 7 »characterized in that that the ends of the tubular carrier with conductive, the contacting of the carbon layer is used Substances, e.g. with a contacting metal, are fired, 9. The method according to claim 2 and 8, characterized in that that the intended separation points of the tubular strand with the contact are used Substances impregnated v / earth, that then after the carbonization of the inner wall of the tubular carrier, the separation points, especially after previous tapering, separated and the ends of the resulting sections at the same time be melted shut with this process. 10. The method according to claim 1 to 9 »characterized in that that the inside of the tubular carrier VPA 9/140/1077 - 11 - 409884/0671 with one which combines with carbon in the heat and forms a gaseous compound with it Reaction gas, e.g. air or hydrogen, is filled in such a way that when the carbon layer is locally heated through an energy beam, in particular a laser beam, which at the Heating point existing carbon is converted into a gaseous compound, while on the other hand the consentration of these carbon-forming elements in the treatment gas is set so low that one Broadening the response from the field of direct action of the energy beam cannot take place. 11. The method according to claim 1 to 10, characterized in that that the inside of the tube is filled with helium. 12. The method according to claim 1 to 11, characterized in that that the gas pressure inside the tubular The carrier is adjusted to a value below one atmosphere. VPA 9 / 1W1O77 Α0988Λ / 0671 Blank page