US2438250A - Film-type resistor and method of manufacturing the same - Google Patents

Description

March 23, 1948. 2,438,250

FILM-TYPE REsIsToR AND METHOD oF MANUFACTURING THE SAME D. W. MOOREJ JR Filed Dec. 8, 1944 v ATTORNEYS Patented Mar. 23, 1948 y y 2.43am FILM-ms nssrs'ron AND Ms'rnon or MANUFAc'rUmNafme Davia W. Moore, Jr., New Yrx, N. Y., mimo:

to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application December I, 1944, Serial No. 567,220

(Cl. 20L-75l 16 Claims. l

This invention relates to film-type resistors and the method of manufacturing the same and particularly to such resistors of the high-resistance type having an accurately predetermined displacement-resistance characteristic and suitable for use as a variable resistor. y

In' electrical control systems, there are frequently required adjustable resistors of extremely high-resistance value and having accurately predetermined displacement-resistance characteristics. It is well known that the ordinary wirewound resistor does not have a high enough resistance value for many of such applications and even where it is adequate the wire becomes so fine that it is quickly worn by the adjustable contact. Therefore, resort is frequently had to a variable-pressure granular-type resistor but the displacement-resistance characteristic of such resistors cannot be accurately predetermined and tends to be unstable and erratic in operation.

While certain nlm-type adjustable resistors have heretofore been proposed, it is necessary in such resistors to provide a structure in which the y adjustable contact does not bear on the film, which would be quickly worn away. Certain of the prior art resistors of this general type have proposed to use a plurality of collecting conductors extending into a body .or layer 0f highresistance material, the portions of the conductors extending beyond the resistance body being adapted to be contacted directly or indirectly by a wiping contact. However, this latter type of resistor structure, in general, has been complicated and not 'suitable for mass production and has been diilicult to construct with various accurately predetermined displacement-resistance characteristics, that is withvarious tapers.

It is an object of the invention, therefore, to provide a new and improved film-type resistor which avoids one or more of the above mentioned disadvantages and limitations of the structures of the prior art.

It is another object of the invention to provide` a new and improved film-type resistor having one or more of the following advantages: an accurately predetermined displacement-resistance characteristic of any desired form; estable and reproducible operating characteristic; long-service life; and a construction which is simple and suitable for mass production.

It is a further object of the invention to provide a new and improved method of manufacturing a resistor of the type described.

In accordance with the invention, a resistor SAME RElSSUED APR 11195@ characteristic comprises an elongated form, a plurality of open-circuit parallel conductors secured to a surface of the form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited highresistance film formed directly on,'bonded to, and bridging the conductors and having a tapered conguration correlated to the predetermined characteristic.

Further in accordance with the invention, the method of manufacturing a resistor of the type described comprises securing a plurality of opencircuit parallel conductors to a surface of a form with aligned portions exposed and adapted to be wiped by adjustable contacts, and depositing and bonding a thin high-resistance film directly on the conductors with a tapered conguration correlated to the predetermined characteristic.

By the term deposited film as used herein and in the appended claims is meant a lm formed by painting or spraying a resistance-material-containing solution or by sputtering, plating or precipitating a metallic illm on the co1- lector conductors to form a non-self-supporting film bonded to the conductors, in contradlstinction to a self-supporting mass of resistance material in which collecting conductors are embedded. By the term open-circuit conductors as used herein and in the appended claims is meant a series of conductors in which the circuits between adjacent conductors are opened, as by removing portions of a continuous winding, or in which the conductors comprise elongated, insulated, conductive bars or segments.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings while its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig, 1 is a view l in elevation and Fig. 2 is an enlarged cross-sectional view of a resistor embodying the invention; Fig. 3 is a view in elevation of a modiiled form of the invention including two overlapping high-resistance films; while Fig. 4 is a view in elevation of the resistor of Fig. l in an intermediate phase of manufacture.

Referring now to Figs. 1 and 2 of the drawings. there is represented a resistor embodying the invention and having a predetermined resistancedisplacement characteristic. prises an elongated rectangular form I0, preferably of Bakelite or similar thermosetting plastic having a predetermined resistance-displacement insulation material. Disposed on the form Il The resistor comare a plurality or series of open-circuit parallel conductors il extending completely across the front surface and the top and bottom edge surfaces of the form I 0. as shown in Fig. 2. The conductors il are cemented or otherwise secured to the surfaces of the form lll and are insulated from each other, as by utilizing an insulating cement for securing them to the form i6. The portions Haof the conductors Il extending over the upper edge of the form comprise aligned exposed portions of the conductors which are to be adapted to be wiped by an adjustable contact. While the conductors il are illustrated as substantially spaced for clarity, in practice they may be closed spaced, providing a more nearly continuous resistance-displacement characteristic.

The resistor of Figs. l and 2 also comprises a thin deposited high-resistance film l2 formed directly on, bonded to, and bridging the conductors il and having a tapered configuration lila correlated to the desired predetermined resistancedisplacement characteristic. The :dim lil may be of colloidal graphite, such as 'that commercially available under the trade name Aouadag or an extremely thin film, such as monatomic film, of a metal, the noble metals being particularly sultable for this purpose because or their resistance to corrosion. il the desired resistance-dispiacement characteristic of the resistor is expressed by the relation R=;f(ml, the condguration ci the :dim is expressed by the relation In case a resistance-displacement characteristic is desired which is complicated in conlguration or involves extreme rates ci change, the single nlm of Fig. l may be replaced by two or `y more overlapping thin deposited high-resistance iilms, represented by the films lil and lil of Fig. 3. In this instance, the films is and i'l preferably have dillerent speciilc resistauces and different congurations ida and idc, respectively, which are jointly correlated to the desired predetermined resistance-displacement characteristic.

While the resistor described maybe manufactured by any of a number of methods, in a preerred method the form l@ is an elongated platelilse iorm and a single continuous conductor l5 is wound op. the form as shown in Fig. d. The portions of the conductor on onaprincipal surface of 'the form, for example the'iroiit surface as represented in Fig. d, and on at least one edge surface thereof, preferably on both edge surfaces, are cemented or otherwise secured to the form. The portions of the conductor l5 on another surface of the form, preferably the baci: surface as represented in Fig. 4, are then removed by shearing, grinding or the like to form the plurality of parallel open-circuit conductors, while the portions of the continuous conductor l5 on one of thel edge surfaces, for example the upper edge surface, are cleaned on their upper faces to constitute aligned exposed portions of the parallel conductors adapted to be wiped by an adjustable contact.

After the formation of the parallel open-circuit conductors on the form lo as shown in Fig. 4 and described above7 the front surfaces of the conductors are cleaned of any insulating cement and there is deposited directly on the conductors a thin high-resistance lm or a plurality of overlapping lmsof different specic resistances, the conguration of the lm or lms being correlated to the desired predetermined resistance-displaceobtained by ment characteristic, as described above. Such fllm or lms as represented in Figs. 1 and 3 may be deposited directly on the conductors by spraying or precipitating the lm, in case of the use of colloidal graphite or the like. In case-of the use of a metallic film, it may be deposited by sputtering, plating, or by photographic sensitization of a normally non-conductive composition In any case, the desired configuration may be rst plotting the relationship Flc/date] on a sti paper or like template, cutting the tenplate along the curve and utilizing it as a mask to cover the portion of the resistor conductors which are not to be coated. The resistor with a template in place is then subjected to any of the various processes described for depositing the high-resistance nlm thereon.

it will be apparent that the resistor constructed as described above .may be used in any conventional electrical control system, either as an adjustable resistor or as a voltage divider, by suitably mounting a resistor in such position that 'the upper edge portions ci the conductors il may be wiped by an adjustable electrical contact.

The resistor oi the invention manufactured as described has the advantages that it is extremely simple in construction and readily adapted to mass production; that its resistance-displacement characteristic is stableand accurately reproducible in operation; and that the adjustable contact is made on the collector conductors which may. be of suitable rigidity and dimensions to withstand wear and provide a llong-service liie. At the same time, any desired resistance-displacement characteristic within extremely wide limits and including extremely high rates-oichange ci resistance may be readily provided, particularly by the use or" multiple films as represented in Fig. 3. Further, vention is particularly effective in dissipating heat in that it has a, maximum ratio of heatdissipating surface to heat-generating volume.

While there have been described what are at present considered to be the preferred .embodiments oi' the invention, it will be apparent to those skilled in the art that various changes and modications may be made therein without departing from the spirit or scope of the invention.

What is claimed as new is:

l. A resistor having a predetermined resistance-displacement characteristic comprising,` an elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited high-resistance nlm formed directly on, bonded to, and bridging said conductors and having a tapered conguration correlated to said predetermined characteristic.

2. A resistor having a predetermined resistance-displacement characteristic comprising, an elongated rectangular .form, a plurality of open circuit parallelconductors extending completely across and secured to .a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable'contact, and a thin deposited high-resistance lm formed directly on, bonded to, and bridging said conductors and having a tapered conguration correlated to said predetermined characteristic.

.3. A resistor having a'predetermined resistthe resistor oi the in.

ance-displacement characteristic comprising, an elongated form, a plurality of opencircuit parallel conductors cemented to a surface of said form and insulated from each other and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited high-resistance film formed directly on, bonded to. and bridging said conductors and having a tapered configuration correlated to said predetermined characteristic. y

4. A resistor having a predetermined resistance-displacement characteristic comprising, an elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and extending over an edge thereof, the extended portions of said conductors being exposed and being adapted to be wiped by an adjustable contact, and a thin deposited high-resistance film formed directly on, bonded to, and bridging said conductors and having a tapered configuration correlated to said predetermined characteristic.

5. A resistor having a predetermined resistance-displacement characteristic comprising, an

elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited high-resistance film of colloidal graphite formed directly on, bonded to, and bridging said conductors and having a tapered configuration correlated to said predetermined characteristic.

6. A resistor having a predetermined resistance displacement characteristic comprising, an elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited high-resistance lm of metal formed' directly on, bonded to, and bridging said conductors and having a tapered coniiguration correlated to said predetermined characteristic.

7. A resistor having a predetermined resistance-displacement characteristic comprising, an elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited high-resistance film of noble metal formed directly on, bonded to, and bridging said conductors and having a tapered configuration correlated to said predetermined characteristic.

8. A resistor having a predetermined resistance-displacement characteristic expressed by the relation R=J'(:r) comprising, an elongated form, a plurality of open circuit parallel conductors secured to a surface of said form and including aligned exposed portions adapted to be wiped by an adjustable contact, and a thin deposited highresistance film formed directly on, bonded to, and bridging said conductors and having a tapered configuration expressed by the relation 9. A resistor having a predetermined resistance-displacement characteristic comprising, anl

` said conductors, said films having different specific resistances and different tapered configurations correlated to said predetermined characteristic.

l0. The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, securing a plurality of open circuit parallel conductors to a surface of said form with aligned portions exposed and adapted to be wiped by an adjustable contact, and depositing and bonding a thin high-resistance film directly on and bridging said conductors in a tapered configuration correlated to said predetermined characteristic.

11. The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated platelike form which comprises, winding a conductor on said form, securing to said form the portions of said conductor on a principal surface of said form and on at least one edge surface thereof, removing the portions of said conductor on another surface of said form, the portions of said conductor on said edge surface being exposed and adapted to be wiped by an adjustable contact, and depositing and bonding a thin high-resistance film directly on and bridging said conductors in a tapered configuration correlated to said prel determined characteristic.

12. The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, cementing a plurality of open circuit parallel conductors to a surface of said form insulated from each other and with aligned portions exposed and adapted to be wiped by van adjustable contact, and depositing and bonding a thin high-resistance lm directly on and bridging said conductors in a tapered configuration correlated to said predetermined characteristic.

13. .The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, securing a plurality of open circuit parallel conductors to a surface of said form with aligned portions exposed and adapted to be wiped by an adjustable contact, and spraying a thin high-resistance film directly on and bridging said conductors in a tapered configuratioin correlated to said predetermined characterist c.

14. 'I'he method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, securing a plurality of open circuit parallel conductors to a surface of said form with aligned portions exposed and adapted to be wiped by an adjustable contact, and precipitating a thin high-resistance lm directly on and bridging said conductors in a tapered coniiguration correlated to said predetermined characteristic.

15. The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, securing a plurality of open circuit paraliei conductors to a surface of said form with aligned portions exposed and adapted to be wiped by an adjustable contact, and sputtering a thin high-resistance metallic film directly on and bridging said conductors in a tapered configuration correlated to said predetermined characteristic.

16. The method of manufacturing a resistor having a predetermined resistance-displacement characteristic and formed on an elongated form which comprises, securing a plurality of open circuit parallel conductors to a surface of said 1 form with aligned portions exposed and adapted to be wiped by an adjustable contact, and depositing and bonding directly on and bridging said conductors a plurality of overlapping thin high-resistance lms of different specific resistance; and of different, tapered configurations correlated to said predetermined characteristic.

Davm w. MOORE. JR;

The following referen es are of record in the me of this patent:l

Number Number 'UNITED STATES PATENTS Name l Date Smith Nov. 22, 1927 Lodge I Jan. 8, 1935 Lodge II Dec. 10, 1935 Takanashi Oct. 27, 1936 Bagno May 25. 1937 Richter June 28. 1938 Gaut et' al. Apr. 2, 1940 FOREIGN PATENTS Country Date Great Britain Feb. 11. 1937

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