US3252831A

US3252831A - Electrical resistor and method of producing the same

Info

Publication number: US3252831A
Application number: US365399A
Authority: US
Inventors: Randall C Ragan
Original assignee: Electra Manufacturing Co
Current assignee: Electra Manufacturing Co
Priority date: 1964-05-06
Filing date: 1964-05-06
Publication date: 1966-05-24
Anticipated expiration: 1983-05-24

Description

R. C. RAGAN May 24, 1966 ELECTRICAL RESISTOR AND METHOD OF PRODUCING THE SAME Filed May 6, 1964 PI G. 2

Fl G. 1

FIG. 4

FIG. 3

I IIIIIII I Tern perafure Temperature FIG. 6

FIG. 5

INVENTOR.

RANDALL C. RAGAN BY M54 United States Patent i 3,252,831 ELECTRICAL RESISTOR AND METHOD OF PRODUCING THE SAME Randall C. Ragan, Tarzana, Califi, asslgnor to Electra Manufacturing Company, Independence, Kans., a corporation of Missouri Filed May 6, 1964, Ser. No. 365,399 17 Claims. (Cl. 117217) This application is a continuation-in-part of my copending application Serial No. 779,605, Precision Electrical Circuit Elements, filed December 11, 1958, which in turn is a continuation-in-part of application Serial No. 618,728, Precision Electrical Circuit Elements, filed October 29, 1956, now abandoned.

The present invention relates generally to electrical resistors and, more particularly, to an improved film type resistor and a method of producing the same.

Heretofore, a great variety of different film-type resistors have been proposed. In general, these resistors are formed by depositing thin metal films on electrically insulating base materials, such as by cathode sputtering, vacuum evaporation, or electrodeposition processes. More recently, it has been proposed to form such resistors of various metal-glass films, withthe glass serving as a binder for the electrically conductive metal particles. However, the metal-glass films developed thus far have exhibited a number of serious shortcomings. For example, the rnetal-glass films previously proposed are gen erally of non-uniform composition through the film thickness so that abrading of the film surface, either during manufacture or during wear, changes the characteristics of the film. Moreover, it has been found that heating of the metal-glass film to the temperature required to fuse the glass increases the resistance of the film considerably, so that the film must either be made relatively thick or made with a relatively high percentage of metal. Also, perhaps more important than any of the other shortcomings is the fact that .difliculties have been encountered in producing films with properties which are predictable and stable.

It is a primary object of the present invention to provide an improved metal-glass film resistor which is capable of being reproduced with accurately predictable electrical resistance, temperature coefiicient of thermal expansion, and other characteristics. A related object of the invention is to provide a resistor of the foregoing type which is stable electrically, chemically and physically. Thus, it is an object to provide such a resistor which is characterized by high load life stability and good voltage coeflicient of-electrical resistivity, i.e., the resistance remains constant regardless of the magnitude of the voltage applied, assuming no self heating.

It is another object of the present invention to provide an improved metal-glass film resistor which is of substantially uniform composition through its thickness. In this connection, it is a particular object of the invention to provide a metal-glass film resistor which can be abraded without changing its characteristics,' other than the change in resistance due to the decrease in cross sectional area.

. A- further object of the invention is to provide an improved method of producing a metal-glass film resistor of the foregoing type whereby the glass component of the film may be fused without increasing the resistance of the film. A related object is to provide such a method which permits the attainment of any given resistance with a thinner film and/ or a lower percentage of metal than the methods of the prior art.

It is still another object of the invention to provide an improved metal-glass film resistor which can be manu 3,252,831 Patented May 24, 1966 factured in a wide range of electrical resistance values, and at a low cost. Yet another object of the invention is to provide such a resistor which is characterized by very low noise, and which is ideally suited for use as the resistor element in a potentiometer.

Other objects and advantages of the invention Will become apparentupon reading the following description and appended claims and upon reference to the drawings, in which:

FIGURE 1 is a plan view of a film-type electrical resistor embodying the present invention;

FIG. 2 is a section taken along line 22 in FIG. 1;

FIG. 3 is a temperature-resistivity curve showing the variations in electrical resistivity with changes in temperature during the manufacture of a metal-glass film resistor according to the methods of the prior art;

FIG. 4 is a temperature-resistivity curve showing the variations in electrical resistivity with changes in temperature during the manufacture of a metal-glass film resistor according to the method of this invention;

FIG. 5 is a plan view of a linear potentiometer made in accordance with this invention; and

FIG. 6 is a plan view of a nonlinear potentiometer made in accordance with the invention.

While the invention will be decribed in connection with a preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, it is intended to cover the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Turning now to the drawings, in FIGURE 1 there is shown a film-type electrical resistor including a substrate 10 formed of an electrically insulating material which is resistant to high temperatures, and a thin film 11 of an electrical resistance material comprising at least one noble metal and a low melting glass bonded to the surface of the substrate 10. As used herein, the term noble metal includes gold, silver, palladium, platinum, rhodium, and iridium. The substrate 10 may be made of any suitable thermally stable substrate material such as, for example, alumina, steatite, fosterite, glass, porcelain, mica and other ceramic materials having the necessary physical, chemical, and electrical properties forthe particular use intended. The substrate must, of course, be capable of withstanding the action of any chemicals used in the deposition of the film 11, as well as any changes in temperature encountered both'during the manufacturing process and during use of the final product. For the purpose of connecting the resistor element into the desired circuit, a pair of highly conductive metal terminals 13 are deposited on the substrate 10 in electrical'contact with opposite ends of the film 11'. The terminals 13 may be made of any suitable metal, such as silver for example,

In forming the metal-glass film 11.1, a finely divided metal-glass mixture of the desired composition is deposited on the surface of the substrate and then fired to a temperature sufficiently high to fuse the glass component of the mixture, but below the melting point 'of the metal component. The metal-glass system is then held at that temperature for a period sufiicient to form a continuous glassy film which is bonded. firmly to the substrate. As the metal-glass system is fired, its electrical resistance has been found to follow a general pattern. Thus, atypical "metal-glass system hasi'a temperature-resistance curve as illustrated in FIG. 3. The electrical resistance of the metal-glass system as initially deposited on the insulating substrate, i.e., at. temperature T is essentially infinite, especially where a relatively 'high percentage of glass is employed. As the temperature of the metal-glass system is increased, its electrical resistance decreases rather rapidly until the curve becomes-asymptotic to the temperature axis, as at temperature T This represents the minimum resistance value of the metal-glass system, and further increases in temperature cause the resistance to increase at a rather rapid rate.

In order .to form a continuous glassy film from the metal-glass system, it must be heated at least to the fusion point of the glass component of the system, which is temperature T in FIG, 3. However, as can be seen from the curve, if the temperature is increased from T to T at the same rate as from T to T the resistance increases to a level considerably above the minimum value attained at T The resistance dips somewhat at the glass fusion point, but it is still well above the resistance value at T Consequently, the thickness of the final film must be considerably greater than the thickness which would be required with the resistance value attained at T Since one of the main objects of film-type resistors is to minimize the size of the resistor, it would naturally be desirable to produce a film in which the glass component has been fused at temperature T but which still hasthe relatively low resistance value attained at T Moreover, it has been found that the results of such a heating treatment are unpredictable in that the characteristics of the final resistor are largely indeterminate.

In accordance with the present invention, it has been unexpectedly discovered that the objectionable increase in resistance of the metal-glass film. between T and T can be substantially avoided by initially increasing the temperature of the system at a relatively slow rate from T to T increasing the temperature from T to T at a relatively rapid rate, and then maintaining the system at T for a period just sufficient to complete the fusion of the glass component without degrading the system. Thus, it has been surprisingly found that by carrying out the firing process in two stages, with a relatively rapid heating rate being used in the second stage, the glass component of the system can be completely fused without increasing the electrical resistance of the system. Indeed, if the heating rate in the second stage is properly controlled, the resistance of the film may actually be decreased below the resistance value attained at T Furthermore, the characteristics ofresistors produced by this two-stage process are accurately predictable so that any given resistor can. be faithfully reproduced time. after time.

Referring to FIG. 4, which illustrates a temperatureresistance curve for a typical metal-glass film produced by the method of this invention, it canv be seenv that the first stage of the firing process, i.e., from T to. T is similar to the corresponding portion of the curve of FIG.

3. From T to T however, the tempera-tureis increased at such a r-apid rate that the resistance remains the same as, or even drops: below, the resistance. value at T It will be understood that theexact temperatures represented by T and T and. also the, exact heating rates employed in the two stages, will vary with the composition of the metal-glass film. Forexample, in the case of a metalglass system comprising a. glass component of lead-borosilicate glass and, a ternary metal component of silver,

gold, and platinum resinates, a suitable, procedure for the first stage of the process is to. place. a. substrate coated with the metal-glass mixture in an ovenv at 250 F. and then increase the temperature: to about 720 'F. in about fifteen minnes. This decomposes the. metal resinates, depositing the three noble metals on. the substrate and driving offthe volatile decomposition products, and produces a metal-glass film. having the minimum electrical resistance for this particular system. 1

For the second stage of the process, the resistor element: is removed from the first oven and transferredto a second oven which has been. preheated to ab;out:1020 R, which is slightly above the, fusing point-0f the lead-borosilicate glass but below, thev melting, points of the three noble metals. Since the mass of the resistor element is small, the temperature ofthe metal-glass film is, increased to the temperature of the second furnace in amatter of aasasai seconds, thereby fusing the glass component with practically no increase in the electrical resistance ofthe system. The resist-or element is allowed to remain in'the second furnace for about 4 to 6 minutes, which is sufficient to insure complete fusion of the glass 'Without changing the resistance or other electrical properties of the film. Below four minutes, the' film does not mature, i.e., there may be inadequate fusion. Above six minutes, there is an increase in the noise level of the resistor element, probably because the conductive metal phase of the film begins to become discontinuous.

In order to achieve the desired glassy coating, the metal-glass system must be fired at least to its fusing point. However, overfiring may cause bubbling or blistering of the glass component of the system and, therefore, is to be avoided. The fusion temperature must also be below the melting point of the metal component of the system. The firing temperature employed in any given case depends on the particular composition used, and it will be understood that different firing procedures may be devised according to the teachings of this invention.

In accordance with one aspect of this invention, the metal component of the metal-glass system comprises a ternary systemof silver, platinum, and gold, either alone or in combination with one or more metal oxides such as the oxides of iridium, ruthenium, palladium, rhodium, nickel, cobalt, iron, manganese, chromium, vanadium,

and titanium. The preferred ternary systems are those containing about 25 to 65% by weight silver, 20 to-45% by weight platinum,-and 5 to 35% by weight gold. The silver-platinum-gold ternary system has been found to produce a highly conductive film with accurately predictable and reproducible characteristics. By contrast, it has. been found that silver and gold, when used alone, are practically non-conductors, and platinum when used alone is a poor conductor. Similarly, most binary systems are also unsuitable for use in this invention; thus, a silver-gold system is not sutficiently conductive and a platinum-silver system is diffi-cult to reproduce with uniform properties. One binary system which may be used is a platinum-gold system, with the major portion gold, but this is still inferior to the ternary system.

In addition to the high degree of predictability, the metal-glass resistors made from the preferred silverplatinum-gold system according to this invention have been found to be extremely stable electrically, chemically, and physically. Thus, these films have high loadlife stability and good voltage coefficient of electrical resistivity, i.e., the resistance remains constant regardless of the magnitude of the voltage applied (assuming no self heating). Moreover, the temperature coeficient of electrical resistivity is always positive and predictable, being 200 parts per million positive, plus or minus only about 20 parts per million. These preferred films also, exhibit .low noise (too low to measure in the low resistance values), are. physically strong, and chemically inert.

Although the explanation of the vastly superior performance of the silver-platinum-gold system is not completely understood, it is believed. that one or two metals existing alone in the metal-glass matrix tend -to' coalesce or cohere so that instead of having a large number of tiny metal particles evenly spaced, there are produced large irregularly shaped' masses of conductive material surrounded by the insulating glass. In the preferred ternary system, however, each metal seems to prevent the others from coalescing so that the metalparticles tend to remain separated andeve nly distributed, thereby forming a continuous phase metal-glass alloy. Thus, the resulting metal-glass film, isuniformly'conductive throughout and may be faithfully duplicated in mass production with exactly the desired characteristics. Moreover, it

has been surprisingly found that silver, platinum, and gold are the only noble metals which are nonoxidizable in the method of this invention.

- lead oxide (PbO).

borate glasses have been found to produce non-uniform As mentioned above, the preferred silver-platinurn-gold ternary system may be modified with certain additives.

Especially valuable additives are the oxides of nickel, cobalt, and copper. Although these oxides are highly soluble in the glass matrix, they have unexpectedly been found to reduce the temperature coeflicient of electrical resistivity of the metal-glass film, to increase the electrical,

resistance of the film, and to improve its abrasion resistance.

for the glass component is a low melting lead-boro-silicate glass, such as a glass composed of 75% PhD, B 0 and 10% SiO This glass melts at 900 E, which is below the melting points of the noble metals, and remains stable over extended periods of operation at elevated temperatures. In general, the preferred lead-bor-o-silicate glasses are those containing at least about 75% by weight Both the lead-silicate and the leadof the resistor either in the process of manufacture or in use, the coefiicient of thermal expansion of the glass component should be adjusted to correspond with the coetficient of thermal expansion of the substrate to which the film is bonded. For example, in the case of the preferred lead-boro-silicate glass, the coefficient of thermal expansion may be adjusted by the addition of zirconium oxide (ZrO). the coefficient of thermal expansion, but also produces a mechanical matrix for the glass so that the glass becomes less fluid and thus less likely to flow. The glass may also be modified to improve its acid and alkali resistance, such as by the addition of zirconium oxide or titanium oxide (TiO to lead-boro-silicate glass. The addition of these modifying agents is usually accomplished by the addition of active fiuxes, such as alkali metal oxides or fluorides,

to the boric glass composition.

The electrical resistivity of the metal-glass film of this invention depends not only on the firing procedure, but also on the particular proportions of metal and glass employed, the dimensions of the film, and the composition of the particular metal and glass components employed. It is generally preferred to use less than about 80% by weight glass, suitably about 50% by weight, but higher percentages may be used for certain applications. The exact thickness of the metal-glass film will, of course, vary with different resistors, but the thickness will generally be less than five mils, preferably within the range of 0.0001 to 0.005 inch.

Although the metal-glass films are resistant to moisture, nevertheless it is often desirable to provide a protective coating over the resistor film. In this connection, the metal-glass films of this invention because of their inertness are capable of tolerating a wider range of protective coatings than other types of resistors. Typical coating materials include glass of the same composition as the matrix and certain lacquers. The coating material should not include any catalysts, such as epoxy resins and silicones with a drier or polymerizing agent.

In order to deposit a uniform and accurately reproducible metal-glass film, it is preferred to intimately mix the metal and glass components in a liquid vehicle which is then applied to the substrate. One particularly preferred method is to mix the finely ground glass component with the appropriate metals in the forms of soluble metal resinates which are thermally decomposable. The metal resinates'are dissolved in a suitable solvent and intimately The zirconium oxide not only corrects mixed with the finely ground glass to form a uniform mixture which can be easily applied to the desired substrate by a suitable stencilling technique, such as silk screening for example, or by the application of ordinary printing, engraving, and lithographing techniques and the like. The metal resinates and the glass flux shouldbe thoroughly mixed, such as in a conventional three-roll paint mill for example. In order to provide proper screenprinting consistency and to improve the ignition properties of the resinates, a plasticizer such as hydroabietyl alcohol or the like may be added to the mixture.

After. the mixture has been deposited on the substrate, the coated substrate is then placed in an oven and fired to the decomposition temperature of the metal resinates. In this particular method, the firing procedure should be carried out in an oxygen-containing atmosphere so that the carbonaceous decomposition products are oxidized to form carbon oxides which may pass off in gaseous form rather than being left on the resistor element. This also eliminates any possibility of the carbon reducing a portion of the glass component to a metallic phase, such as lead oxide to the metal lead for example.

It will be understood that the thermal decomposition of the metal resinates represents only the first stage of the two-stage method of this invention, andthe resist-or must still be heated to the fusing temperature of the glass component of the film at a relatively high heating rate as de scribed above. In order to determine the actual termination temperature of the first stage of the process, it has been found convenient to monitor a resistor element consisting of a mixture of resinates of the same noble metals and in the same proportions as in the resistors under treatment, but without the glass component. This glass-free mixture provides the lowest possible resistance for a given system and thus gives a more sensitive indication of changes in the monitoredresistance value. The resistance starts out at a high level and then drops rapidly as the resinates are decomposed and the organic material driven off. When the monitored resistance levels'otf at the bottom of the curve, the first stage of the heat treatment is terminated and the resistor is ready for the second stage treatment.

It will be appreciated that other thermally decomposable organo-metallic compounds may be used as sources of the noble metals. such compound decompose completely at a temperature below the fusion point of the particular glass employed, and that it produce decomposition products which are easily volatilized or otherwise disposed of without leaving any deleterious residue. Also, to facilitate liquid application, the compound should be readily soluble in a solvent which can be evaporated to leave a stable mechanical configuration. Typical compounds which meet these requirements include not only the resinates, but also octoates, palmatates, oleates, and many other salts of organic acids. It will be understood that the commercial forms of the resinates and other compounds normally include various fluxes, such as a small amount of bismuth, to render them more adherent. However, the bismuth or other flux forms no part of the present reaction and is promptly absorbed by the glass component.

For the purpose of avoiding unpredictable variations in the resistivity, noise level, and other characteristics of the resistor element, the metal-glass system should be fired in a purified atmosphere and under controlled humidity conditions. Thus, when the films are fired in an'oven, for example, the air which is fed to the oven is preferably fed through a bed of charcoal to remove various organic gaseous impurities. Moreover, the relative humidity is preferably controlled to stay within the range of about 40 to 60% at 75 F., or the preferred moisture content is between about 5 and 6 grains per cubic foot, regardless of temperature. I 1 In aseries of examples of the present invention, a number of different metal-glass films were deposited from It is important that any 7 various mixtures of lead-boro-silicate glass (75% PbO, 15% B SiO and silver platinum, and gold resinates. Each mixture contained about 50% by weight glass and the followingvpercentages by weight of the various metal resinates:

In each example, the mixture was deposited on an alumina substrate, placed in a first oven at 250 F., and heated to 720 F. in about minutes. The resistor was then removed from the first oven and placed in a second oven which had been preheated to 1020 F. After about 4 to 6 minutes, the resistor was removed from the second oven, allowed to cool to room temperature, and tested for electrical resistance temperature coefficient of electrical resistivity, and other properties.

The compositions of Examples 1 and 2 produced films which were practically non-conductive and therefore useless as resistors. Examples 3 through 9 produced films with the desired combination of properties and were distinguished from each other only by small differences in resistance and temperature coeflicient of electrical resistivity. All these films had low noise levels and were not subject to change with variations in the firing conditions. Moreover, the temperature coeflicient of electrical resistivity of all these films was stable. The film of Example 10 exhibited relatively large changes in both resistance and temperature'coefficient of electrical resistivity, while Example 11 was stable and reproducible but too high in temperature coefiicient for most practical applications. Examples 12 and 13 produced films with extremely high resistance values and high and variable temperature ooeificients of electrical resistivity, and were not stable under electrical load. The last two Examples, 14 and 15, were lower in resistance than 12 and 13 and were relatively stable with a comparatively good combination of properties.

The metal-glass films of this invention have smooth glassy surfaces which are especially useful in potentiometer. Thus, in FIG. 5, a linear potentiometer is formed by depositing a circular metal-glass film of uniform width and cross section on an insulating substrate 21. For the purpose of connecting the film 20 into the desired circuit, a pair of highly conductive metal. tab-s 22 are deposited on the substrate 21 at the ends of the film 20. The usual potentiometer slide (not shown) may be supported rotatably to contact the resistance film 20 at any desired point along ts length. To improve the wear and noise qualities of the potentiometer, the slide preferably has its contact surface made of a conductive metalglass film.

The potentiometer of FIG. 6 is similar to that of FIG. 5- except that the metal-glass resistance film 20a gradually increases in width around its circumference so as to form a nonlinear potentiometer. The substrate 21, the terminals 22, and the slide arrangement may be the same as described about for FIG. 5'.

; In accordance with one aspect of this invention, a metal-glass film which is especially useful in potentiometer application is produced by coating the substrate with the glass to be used in the metal-glass film, fusing the glass coating to form a smooth continuous glass composite film which is ideal 8 film bonded to the substrate, and then-depositing th metal-glass film in the manner described above. During firing of the metal-glass film, it sinks into the previously deposited glass coating so as to form an extremely smooth for use as a miniaturized potentiometer.

While various specific forms of the present invention have been illustrated and describe-d herein in some detail, it will be apparent that the same are susceptible of numerous modifications within the spirit and scope of the invention. For example, instead of proceeding directly from the first stage of the firing process to the second stage, the metal-glass film may be allowed to cool to room temperature or some other intermediate temperature between the two stages without any appreciable effect on the final result. Also, more than one layer of the metalglass film may be deposited on a single substrate, and in any desired configuration;

I claim as my invention:

1. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which is resistant to high temperatures, depositing a mixture of finely divided glass and thermally decomposable organic compounds of the metals silver, platinum, and gold as a thin coating on the surface of said substrate, said glass having a fusing point below the melting points of said metals, increasim the temperature of said coating at a relatively slow rate until the electrical resistance of the metal-glass system is reduced to substantially its minimum value, increasing the temperature of said coating at least to the fusing point of said glass, but below the melting point of said metals, at a relatively rapid rate sufficient to avoid any substantial increase in the electrical resistance of the metal-glass system, maintaining the coating at the fusing temperature for a period sufficient to completely fuse the glass without substantially increasing the electrical resistance of the metal-glass system, and cooling the resulting glassy coating to solidify the glass and form a continuous impervious metal-glass film bonded to the surface of the substrate.

2. The method of claim 1 Whereinthe glass component of said metal-glass film has a coefiicient of thermal expansion compatible with. the coefficient of thermal expansion of said electrically insulating substrate.

3. The method of claim 1 wherein the glass component of said metal-glass film is a lead-boro-silicate glass.

4. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which has a. smooth surface and is resistant to high temperatures, depositing a. mixture of finely divided glass and a thermally decomposable organic compound of a noble metal in a liquid vehicle as a thin coating on the smooth surface of the substrate, said glass having a fusing point below the melting point of the noble metal, heating the coating at a relatively slow rate in an oxidizing atmosphere so as to decompose said organic com- I pound and reduce the electrical resistance of the metalglass system to substantially its minimum vlaue, heating the metal-glass system at least to the fusing point of the glass component, but below the melting point of the noble metal, at a relatively rapid rate sutficient to avoid any substantial increase in the electrical resistance of the metal-glass system, maintaining the coating at the fusing temperature fora period suflicient to completely fuse the glass without substantially increasing the .electrical resistance of the metal-glass system, and cooling the resulting iglassy coating to solidify the glass and form a continuous impervious metai-glass film bonded to the surface of the substrate.

5.' The method of claim 4 wherein said heating steps are carried out in a purified atmosphere having a relative humidity of about 40 to at F. v

-6. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which has a smooth surface and is resistant to high temperatures, depositing a mixture of finely divided glass and a ternary noble metal resinate system consisting essentially of silver resinate, platinum substantial increase in the electrical resistance of the metal-glass system, maintaining the coating at the fusing temperature for a period sufficient to completely fuse the glass without substantially increasing the electrical resistance of the metal-glass system, and cooling the resulting glassy coating to solidify the glass and form a continuous impervious metal-glass film bonded to the surface of the substrate.

7. A method of producing a film-type electrical resistorcomprising the steps of providing an electrically insulating substrate which has a smooth surface that is resistant to high temperatures, depositing a mixture of about equal parts by weight of a finely divided leadboro-silicate glass and a ternary noble metal resinate system consisting essentially of the resinates of silver, platinum, and gold as a thin coating on the surface of said substrate, heating said coating to about 720 F. in about 15 minutes so as to decompose the metal resinates and reduce the electrical resistance of the metal-glass system to substantially its minimum value, the heating being carried out in an oxidizing atmosphere so as to oxidize the volatile decomposition products from the resinates, heating the resulting metal-glass coating to about 1020 F. substantially instantaneously so asto fuse the lead-boro-silicate glass without increasing the electrical resistance of the metal-glass system, maintaining the metal-glass coating at about 1020 F. for about 4 to 6 minutes to completely fuse the glass Without increasing the electrical resistance of the metalglass system, and cooling the resulting glass coating to solidify the glass and form a continuous impervious metalglass film bonded to the surface of the substrate.

8. Afilm-type electrical resistor comprising the combination of an electrically insulating substrate which is resistant to high temperat ires, and a metal-glass film deposited on the surface of aid substrate and having a glass component with a fusing ;oint below the melting point of the metal component, sa d glass component having been fused to form a contim ous impervious metal-glass film bonded to the surface of the substrate, and a metal component consisting essentially of silver, platinum, and gold.

9. A film-type electrical resistor comprising the combination of an electrically insulating substrate which is resistant to high temperatures, and a metal-glass film deposited on the surface of said substrate and having a glass component with a fusing point below the melting point of the metal component, said glass component having been fused to form a continuous impervious metal- -glass film bonded to the surface of the substrate, and a metal component consisting essentially of about 25 to 65% by Weight silver, about 20 to 45% by weight platinum, and about to 35% by Weight gold.

10. The film-type electrical resistor of claim 9 wherein the glass component of said metal-glass film is lead-borosilicate glass.

11. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which is resistant to high temperatures, depositing a thin glass coating on the surface of said substrate and fusing the glass coating so as to form a smooth continuous glass film bonded to the substrate, solidifying the glass coating, depositing a mixture of finely divided glass and thermally decomposable organic compounds of the metals silver, platinum, and gold as a thin coating on the surface of the solidified glass coating, said finely divided glass having substantially the same composition as the initial glass coating and also having a fusing point below the melting point of said metals, increasing the temperature of said metal-glass mixture to at least the fusing point of theglass, but below the melting point of said metals, so that the metal-glass mixture penetrates into the initial glass coating forming a smooth surfaced composite metal-glass film, and cooling said composite film to solidify the glass and form a continuous impervious metal-glass film.

12. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which is resistant to high temperatures, depositing an initial glass coating on the surface of the substrate and fusing said glass to form a continuous glass film, solidifying the fused glass, depositing a mixture of finely divided glass and thermally decomposable organic compounds of the metals silver, platinum, and gold as a thin coating of the surface of the initial glass film, said finely divided glass having a composition substantially the same as that of the initial glass film and also having a fusing point below the melting point of said metals, increasing the temperature of said coating at a relatively slow rate until the electrical resistance of the metal-glass system is reduced to substantially its minimum value, increasing the temperature of the metal-glass coating to at least the fusing point of the glass, but below the melting point of said metals, at a relatively rapid rate sufficient to avoid any substantial increase in the electrical resistance of the metal-glass system, whereby said metal-glass system penetrates into the initial glass film, maintaining the metal-glass coating at the fusing temperature for a period sutficient to completely fuse the glass without substantially increasing the electrical resistance of the metal-glass system, and cooling the resulting glassy coating to solidify :the glass and form a continuous impervious composite metal-glass film bonded to the substrate.

13. A film-type electrical resistor comprising the combination of an electrically insulating substrate which is resistant to high temperatures, a glass coating deposited on the surface of said substrate and bonded thereto, and a metal-glass film integral with the upper portion of said glass coating and having a glass component of substantially the same composition as said glass coating and with a fusing point below the melting point of the metal component, said glass component having been fused to form a continuous impervious metal-glass film integral with said glass coating, said metal component consisting essentially of silver, platinum, and gold.

14. A method of producing a film-type electrical resistor comprising the steps of providing an electrically insulating substrate which is resistant to high temperatures, depositing a mixture of :finely divided glass and thermally decomposable organic compounds of the metals gold and platinum as a thin coating on the surface of said substrate, said glass having a fusing point below the melting point of said metal, increasing the temperature of said coating at a relatively slow rate until the electrical resistance of the metal-glass system is reduced to substantially its minimum value, increasing the temperature of said coating at least to the fusing point of said glass, but below the melting point of said metals, at a relatively rapid rate sufiicient to avoid any substantial increase in the electrical resistance of the metal-glass system, maintaining the coating at the fusing temperature for a period sufiicient to completely fuse the glass without substantially increasing the electrical resistance of the metal-glass system, and cooling the resulting glassy coating to solidify the glass and form a continuous impervious metal-glass film bonded to the surface of the substrate.

15. A film-type electrical resistor comprising the combination of an electrically insulating substrate which is resistant to high temperatures, and a metal-glass film decomponent with a fusing point below the melting point of the metal component, said glas component having been fused to form a continuous impervious metal-glass film bonded to the surface of the substrate, and a metal component consisting essentially of gold and platinum 16. A film-type electrical resistor comprising the combination of an electrically insulating substrate which is resistant to high temperatures, a glass coating deposited on the surface of said substrate and bonded thereto, and a metal-glass film integral with the upper portion of said glass coating and having a glass component of substantially the same composition as said glass coating and with a fusing point below the melting point of the metal component, said glass component having been fused to form a continuous impervious metal-glass film integral with said glass coating, said metal component consisting essentially of gold and platinum.

17. A method .of producing a film-type electrical resistor' comprising the steps of providing an electrically insulating substrate which is resistant to high temperatures, depositing a thin glass coating on the surface of said substrate and fusing .the glass coating 50 as to form a smooth continuous glass film bonded to the substrate,

solidifying the glass coating, depositing a mixture of finely divided glass and thermally decomposable organic compounds of the metals gold and platinum as a thin coating on the surface of the solidified glass coating, said finely divided glass having substantially the same composition as the inital glass coating and also having a fusing point below the melting point of said metals, increasing the temperature of said metal-glass mixture to at least the fusing point of the glass, but below the melting point of said metals, so that the metal-glass mixture penetrates into the initial glass coating forming a smooth surfaced composite metal-glass film, and cooling said composite film to solidify the glass and form a continuous impervious metalglass film.

References Cited by the Examiner UNITED STATES PATENTS 2,357,473 4/1944 Jira 33826 2 2,457,678 12/ 1948 Iira l172l7 2,461,878 2/1949 Christensen et al. 338-30 8 2,882,187 4/1959 Kwate 1172i 17 2,939,807 6/ 1960 Needham 1172:1 7

RICHARD D. NEVIUS, Primary Examiner.

Claims

1. A METHOD OF PRODUCING A FILM-TYPE ELECTRICAL RESISTOR COMPRISING THE STEPS OF PROVIDING AN ELECTRICALLY INSULATING SUBSTRATE WHICH IS RESISTANT TO HIGH TEMPERATURES, DEPOSITING A MIXTURE OF FINELY DIVIDED GLASS AND THERMALLY DECOMPOSABLE ORGANIC COMPOUNDS OF THE METALS SILVER, PLATINUM, AND GOLD AS A THIN COATING ON THE SURFACE OF SAID SUBSTRATE, SAID GLASS HAVING A FUSING POINT BELWO THE MELTING POINTS OF SAID METALS, INCREASING THE TEMPERATURE OF SAID COATING AT A RELATIVELY SLOW RATE UNTIL THE ELECTRICAL RESISTANCE OF THE METAL-GLASS SYSTEM IS REDUCED TO SUBSTANTIALLY ITS MINIMUM VALUE, INCREASING THE TEMPERATURE OF SAID COATING AT LEAST TO THE FUSING POINT OF SAID GLASS, BUT BELOW THE MELTING POINT OF SAID METALS, AT A RELATIVELY RAPID RATE SUFFICIENT TO AVOID ANY SUBSTANTIALLY INCREASE IN THE ELECTRICAL RESISTANCE OF THE METAL-GLASS SYSTEM, MAINTAINING THE COATING AT THE FUSING TEMPERATURE FOR A PERIOD SUFFICIENT TO COMPLETELY FUSE THE GLASS WITHOUT SUBSTANTIALLY INCREASING THE ELECTRICAL RESISTANCE OF THE METAL-GLASS SYSTEM, AND COOLING THE RESULTING GLASSY COATING TO SOLIDIFY THE GLASS AND FORM A CONTINUOUS IMPERVIOUS METAL-GLASS FILM BONDED TO THE SURFACE OF THE SUBSTRATE.