US2796504A - Electrical resistor and method of making resistors en measse - Google Patents

Description

June 18, 1.957 N, PR|T|K|N ErAL 2,796,504

ELECTRICAL RESISTOR AND METHOD OF MAKING RESISTO-RS EN MASSE Filed May 9, 1951 3 Sheets-Sheep l 1m/mmm.

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June 18, 1957 N PR|T|K|N ETAL 2,796,504

ELECTRICAL RESISTOR AND METHOD OF MAKING RESISTORS EN MASSE Filed May 9, 1951 3 Sheets-Sheet 2 fyM///MZ June 18, 1957 N. PRI'TIKIN ErAL 2,796,504

ELECTRICAL REsIsToR AN/D. 'METHOD oF MAKING REsIsToRs EN MAssE 5 Sheets-Sheet 3 Filed May 9, 195] JNVENToRs Z141 K/1M@ ELECTRICAL RESISTR AND METHD F MAKING RESISTRS EN MASSE Nathan Pritikin and Harold Weinstein, Chi ago, Ill.; said Weinstein assigner to said Pritt n Application May 9, 1951, Serial No. 225,382

19 Claims. (Cl. Mil-64) This invention relates to an electrical resistor and to a method of producing electrical resistors en masse. It is an object of the invention to provide an improved resistor and an improved method of that character.

At the present time, resistors are generally produced by mass production methods but most if not all operations are performed seriatim on individual resistors or partially formed resistors. It is another object of the invention to provide an improved method of producing electrical resistors wherein a plurality of resistors are manufactured in a single body, each resistor being complete with leads when severed from the others.

Resistors constructed in accordance with the prior art are commonly uninsulated, and where resistors have been insulated, the insulation has conventionally been applied to the resistors individually. Also, resistors constructed in accordance with the prior art have dissipated their heat either directly to the atmosphere or along a substantial length of the resistance material to the resistor leads.

It is an object of the present invention to provide an improved resistor which is completely or partially insulated. lt is another object of the invention to provide an improved method by which such resistors may be produced en masse.

It is another object of the invention to provide an improved resistor in which the resistor leads are arranged closely adjacent at least the major portion of the resistance element whereby heat generated in the resistance element may be readily dissipated along the resistor lead. It is another object of the invention to provide an improved method for producing such resistors envmasse.

This invention, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings in which like parts are designated by like reference numerals,

Fig. 1 is a perspective view of a resistor constructed in accordance with one embodiment of the invention;

Fig. 2 is a plan View of the same resistor;

Fig. 3 is a cross-sectional plan View of the same resistor taken along the line 3-3 of Fig. 1;

Fig. 4 is a cross-sectional View of the same resistor taken along the line 4-4 of Fig. 2;

Fig. 5 is an end View of the same resistor;

Fig. 6 is a cross-sectional view of the resist-or taken along the line 6-6 of Fig. 4;

Fig. 7 is a cross-sectional View of the same resistor taken along the line 7-7 of Fig. 4;

Fig. 8 is a cross-sectional view of the same resistor taken along the line 8 8 of Fig. 4;

Fig. 9 is a plan view of a plurality of resistors produced en masse, each resistor being the same as that disclosed in the preceding gures;

Fig. 10 is an exploded view of certain elements of the ysame resistor;

arent O 2,7916 ,5014 Patented June 18, 1957 Fig. l1 is a cross-sectional view of the same resistor elements shown in Fig. 10, assembled for heat and pressure treatment;

Fig. l2 is a plan view of a resistor illustrating a varia- 'iorl of the embodiment of the invention shown in Figs.

Fig. 13 is a longitudinal cross-sectional View of a Iesistor illustrating another variation of the embodiment of the invention shown in Figs. 1-11;

Fig. 14 is a partial plan view of a bank of resistors partially assembled, illustrating another embodiment of the invention;

Fig. 15 is a cross-sectional view taken along the line 'l5-15 of Fig. 14;

Fig. 16 is a cross-sectional view similar to Fig. l5 but showing the resistor bank in a later stage of assembly;

Fig. 17 is a partial bottom plan view of the same bank of resistors in a still later stage of assembly;

Fig. 18 is a cross-sectional view of the same bank of resistors taken along the line 13-18 of Fig. 17 and illustrating its condition immediately prior .to the last assembly operation;

Fig. 19 is an enlarged detail View of a variation of the embodiment of the invention shown in Figs. 14-18;

Fig. 20 is a cross-sectional View taken along the line 20-20 of Fig. 19; and

Fig. 21 is al cross-sectional view taken along the line 21-21 of Fig. 19.

The method which constitutes one feature of the invention is particularly adapted to the manufacture of a large number of resistors en masse. In the embodiments of this method disclosed in Figs. l-l3, an elongated strip of insulating material 11 is painted along its edges with a metallic or another conducting paint which, after drying or hardening, provides electrically conducting strips 12, 13 and 14 along both longitudinal edges of the sheet 11. These conducting strips serve to conduct current between the resistor leads 15 and a resistance iilm 16 which is subsequently applied to one vsurface of the sheet 11. In the drawings the thickness of the strips 12, 13 and 14, and others to be described subsequently, are greatly exaggerated in the interest of clarity.

Preferably, the insulating sheet 11 is of cured thermosetting plastic in order that it may aid in maintaining the desired shape and contour of the ultimate resistor or resistors during various steps in the manufacture of the same. The conducting paint which forms the strips 12, 13 and 14 comprises metallic or other conducting particles in a thermosetting carrier. The strips 12 are preferably applied first, one along each longitudinal edge of the sheet, after which the sheet 11, along with the strips 12, is subjected to heat to cause thermal setting of these strips. A

Subsequent to the setting of the conducting strips 12, the conducting strips 13 and 14 are applied and permitted to dry in their uncured state. At the same time an uncured sheet of thermosetting plastic 17 is painted along its longitudinal edges with the same form of conducting paint to form conducting strips 1S, which are also permitted to dry in their uncured state.

The resistor leads 15 are swaged or flattened over a substantial length at the resistor engaging ends thereof so that they form flat blades, as best seen in Figs. 3 and 4. The elements so far described are assembled with the leads 15 lying against the lower surface of the sheet 11 and contacting the conducting strips 14. The sheet 17 is then placed against the leads 15 with the conducting strips 18 contacting the leads. Additional sheets 19 and 20 of uncured thermosetting plastic and a iinal sheet 21 of a cured thermosetting plastic are next applied, all as best seen in Figs. l0 and 11. The entire assembly is ICC then subjected to heat and pressure to `cure or set the plastic members and to bond all the elements lirmly together as a unit.

If the sheets 11 and 21 are precured, as suggested above, an adhesive is preferably employed to assure a firm bond between these and adjoining sheets. The adhesive is, of course, so applied as not to interfere with the desired electrical contact between such elements as the leads 15 and the conducting strips 12 and 14. f

During the last-mentioned curing step, the she-et 17 iiows around the leads 15 to assume a shape, in the region of the leads 15, similar to that illustrated in Fig. 4. The conducting strips 18 also flow around the leads 15 and assume the shape illustrated in Figs. 5 and 6. The sheet 11 retains its original flat shape since it was cured prior ,to the assembly of the various elements of the resistor. Similarly the bottom sheet 21 having been cured prior to the final assembly serves to retain the desired contour of the lower surface of the resistor.

The conducting strips 14, which, as noted above, are not cured prior to the iinal assemblytend to flow over the upper surfaces of the leads 15, while the conducting strips 1S, following the flow of the sheet 17, flow around the respective leads and join the corresponding conducting strips 14 adjacent the leads to form single conducting elements which surround the leads 15 and make secure mechanical bond and electrical connection there Y with.

Ateach end of the resistor the single electrical conducting means formed by the conducting strips 1e and 13 is also bonded mechanically and electrically with the conducting strip 13 and hence with the conducting strip.

A iilm or strip of resistance material such as granular carbon mixed with a suitable carrier is applied to the upper surface of the insulating sheet 11 and permitted to dry or harden. The lm is arranged to make electrical contact with the conducting strip 12 at each end of the resistor. It will now be apparent that a conducting path is provided between the two resistor leads 15-15. This path may be traced from one resistor lead to the two conducting strips 14 and 13, through the strips 13 and 12, across the resistance iilrn 16 to the other end of the resistor and through the conducting strips 12, 13, 14 and 18 to the other resistor lead. The resistance of the film 16 may, of course, be made of any desired value by controlling the length, width, thickness and nature of the lm.

In accordance with one embodiment of the invention another conducting strip 22 is arranged near the center of the resistor. Where this strip is employed, it is preferably applied to the insulating sheet 11 at the same time as the conducting strips 12 and is cured at the same time as the latter strips. The resistance film 1d makes electrical contact with the conducting strip 22 as it does with the conducting strips 12. The resistance iilrn may or may not overlie the conducting strip 22, even as it may overlie the strips 12, but the eiective length of the resistance nlm is thecomoined distance from the inner edges of the strips 12 to the adjacent or facing edges of the center strip 22. Stated otherwise the conducting strip 22 short-circuits the centralmost portion of the resistance lm even though the latter may be a continuous iilm eX- i processes.

of the ends of the leads since this greatly-increases the area of each lead. By extending these leads substantially to the center of the resistor, the flattened surfaces thereof are made to lie closely adjacent all portions of the resistance lm except that portion which may lie at the center of the resistor. lf compensation for this irregularity were not provided, it is apparent that the centralmost portion of the resistor would be the hottest and would thereby be the limiting factor in the powerrating of the resistor. It is for this reason that the conducting strip 22 is preferably employed, this strip overlying the gap between the ends of the resistor leads 15 and substantially eliminating the generation of heat in that area. The power-rating of the resistor is then determined by the temperature rise of the main body of the resistance iilm rather than being limited by one local hot spot.

Over the top of the resistance film 16 and the conducting strips 12 and 22, there is preferably applied a layer of insulating material 23 to protect thc-se elements against damage and to insure that they will be electrically insulated from any electrical conductor which they may contact when in use, particularly when they are used in the crowded chassis of a radio or television set. This sheet of insulating material may be of thermosetting plastic material and, optionally, may be applied, along with the resistance film 16, prior to the nal curing operation of the lower portion of the resistor unit.

Another embodiment of the invention is shown in Fig. l2 in which the leads 15 are arranged out of alignment with each other. Each of the leads in this arrangement may extend substantially the entire length of thc resistor. The need of the conducting strip 22 in the first described embodiment is eliminated since there is no longitudinal gap between the leads. This arrangement also provides a substantialiy uniform lateral disposition of the heat conducting means, namely the resistor leads. Other than in the arrangement of the leads, the resistor shown in Fig. l2 may be identical to that shown in the other figures.'

As indicated above the resistor and lits method of manufacture are particularly adapted to the construction of a large number of resistors en masse. The various sheets of insulating material 11, 17, 19, 20, 21 and 23 may be elongated, with pairs of leads 15 for the individual resistors arranged to extend laterally thereof, all as clearly seen in Fig. 9. lt is preferable that :the various noninsulative elements, including the resistance film 16, be intenrupted between the various individual resistors. in Fig. 9, it will be noted, for example, that the resistance lm 16 is not a continuous strip but is in the form of rectangles which rare individual to the various resistors. Similarly, the conducting strip 22 can be seen in Fig. 9 as being interrupted, each segment of the strip being substantially coextensive with the rectangles of resistance material 16 in a direction lateral to the individual rcsistors. Still further, the conducting strips 12, 13, 14 and 18 all are interrupted between `tne individual rcsisters.

The resistance lm and the various conductors can readily beso arranged by any one of several weil-known Perhaps the most practical of these is the common practice known as screening, similar to stenciling. In this process, a screen is arranged over the insulating Isheet 11, for example, when it is desired to apply the conducting strips 12 and 22 to the upper surface thereof. By properly selecting the openings in the screen through which the conducting material for the strips 12 and 22 is applied to the surface of they insulating sheet 11, and by properly aligning the screen, it is possible to control accurately the width, length, and position of the individual conducting lstrips. A similar process and screens may be employed to control the size and position of the resistance films 16 and the conducting strips 13, 14 and 18.

Since eaoh of the noninsulative elements referred to above is interrupted between individual resistors in the assembly shown in Fig. 9, when the individual'resistors avesse;

are ultimately separated as by cutting with a very fine saw through the channels indicated by the letter A in Fig. 9, none of these noninsulative elements will extend to the edges of the resistor. In this manner four surfaces of the completed individual resistors will be insulated, namely the top and bottom surfaces and the two longitudinal edges. This represents a substantial improvement over the conventional resistor since it eliminates the possibility off a short-circuit which might otherwise result if the resistor were to come into contact with another conductor in a crowded electrical device such as a radio or television receiver.

The two ends of the resistors so far described are not insulated since the surface of the conducting strip 13 is exposed at each end of the resistor. In many applications, it is not to lgreat interest that these surfaces of the resistors be insulated since they are relatively small and in any event lie closely adjacent the resistor leads 15 which are normally uninsullated and hence must be spaced clear of any other conducting elements of a different potential. However, in Fig. 13 there is shown a variation of the resistors so far described which is insulated on all surfaces. In this construction, the insulating sheets 21' and 23 are wider than the remainder of the sheets making up the body of the resistor and both are of uncured plastic. The resistor is otherwise the same as that shown in the preceding figures. During the final thermal setting of the resistor assembly the ends of these sheets lap over the end-s of the resistor body as shown in Fig. 13 and insulate the ends of the resistors. By this method, resistors are obtained which are insulated on all six surfaces.

In accordance with another variation of the resistors so far described, the various conducting strips 12, 13, 14 and 18 at the ends of the resistor may be eliminated and the resistance film 16 arranged to extend down over the edges of the sheet 11 to make electrical contact with the leads 15. This is, of course, a simpler construction but has the disadvantage that local hot spots may be produced in the resistance film adjacent the leads 15, Where the current may be concentrated. Furthermore, the total resistance value of the resistor is less easily predetermined or controlled than in the resistors previously described wherein there is employed a resistance film of accurately controlled length and cross-section. 'Ilhis variation, in which the Various conducting strips at the ends of the resistors are eliminated, may be desirable, however, where low cost is the predominating requirement. In this same variation, it is possible, of course, to insulate the ends of the resistor as well as the longitudinally extending -surfaces by the means disclosed in Fig. 13 and described labove.

In accordance with still another variation, not illustrated in the drawings, a second resistance film may be applied to the lower surface off the insulating sheet 17, the ends of this resistance film being connected to the conducting strip 18 and 'hence to the two resistor lead-s 15 by conducting strips corresponding to the strips 12 and 13. In such a resistor, it Would be preferable, but not necessary, that both of the insulating sheets 11 and 17 be uncured until after the final assembly. This same construction could also be employed where the resistance films are brought over the edges of the sheets 11 and 17 thereby eliminating the necessity of fthe various conducting strips at the ends of the resistors. Similarly the ends of such resistors might be insulated in the manner disclosed in Fig. 13.

In any of the variations of -the resistors so far described, any or all of the fthermosetting portions` of the resistors may be left uncured until the nal assembly. A somewhat better bond may thereby be obtained between the various elements of the resistors. More specically, where `all of the insulating sheets are cured or thermally set after the final assembly, there is no need for the use of an adhesive and accordingly, the final yresistor construction is less vulnerable to severe condi- G tions of humidity and temperature changes. The curing of the insulating sheets 11 and 21 prior to the final assembly, as suggested above, has cert-ain compensating advantages previously explained.

The embodiment of 4the invention and variations thereof shown in Figs. 14 to 21 are characterized by the use of staples 30 for temporarily holding resistor leads 31 to a sheet of uncured thermosetting plastic 32 and for conducting current from the leads 31 Ito a resistance lm 33. It will be noted in Fig. 14 that the leads 31 are arranged in pairs extending transversely of the elongated sheet 32, similar to the arrangement shown in Fig. 9. With the leads 31 properly positioned with respect to the sheet 32, the staples 30 are driven through the sheet adjacent the edges thereof to secure the leads 31 thereto. A second sheet 34 of uncured thermosetting plastic i-s then applied to the surface of the sheet 32 to which the leads 31 are secured, as shown in Fig. 16.

The assembly shown in Fig. 16 is next subjected to heat and pressure whereby the sheets are cured and firmly bonded together. During this operation the crowns ofthe staples 30 are forced into the sheet 32 and become flush with lower surface thereof.

The resistance films 33 are then applied to the surface of the sheet 32 opposite the leads 31, and are arranged to extend between and to contact corresponding pairs of staples 30. Each staple then may conduct current from one lead 31 through the sheet 32 to one end of a resistance lm 33. With this arrangement the leads may extend for substantially the entire length of the resistance film while being electrically insulated therefrom except at the ends thereof. The leads thereby serve as thermal conductors for carrying heat from the resistance film. If desired, a conducting strip similar to the strip 22, employed in the previously described embodiment, may be used to eliminate the possibility of a local hot spot at the center of the resistance lm.

Finally, a third sheet 35 of uncured thermosetting plastic |is applied to that surface of the sheet 32 upon which the resistance films are laid, as may be seen in Fig. 18. The entire assembly is then subjected to heat and pressure to cure the sheet 35 and to bond it to the sheet 32, an adhesive preferably being employed to improve such bonding. Alternatively, the three sheets 32, 34 and 35 may all be cured in the final curing operation.

As in the case of the embodiment previously described, the conducting elements of the resistors, and the resistance films 33 are interrupted longitudinally in the mass assem-bly. Accordingly, the assembly may be cut, as by a fine saw, along the lines Idesignated A to separate the resistors, and each will be completely insulated along its longitudinal edges since none of the conducting elements extends to the lines A. The top and bottom surfaces are, of course, entirely insulated by the uninterrupted sheets 34 and 35. The ends of the individual resistors are also completely insulated since no electrically conducting elements extend to the edges of the sheets other than the resistor leads 31.

The staples 30 may be Klriven through the center sheet 32 in either direction. That is, either the legs or the crowns of the staples may be arranged to contact the lead 31. It is believed to be preferable that tlre ends of the staples engage the leads, as shown Iin the drawings, since this leaves tlhe uninterrupted head portion of each staple to carry current to the end of a resistance film 33 throughout the width thereof. It will be noted that the staples employed in this embodiment of the invention serve the same function as the conducting strips 12, 13, 14 and 18 of the embodiment disclosed in Figs. 1 to l2. Specifically, they conduct electricity from the resistor leads on one side of an insulating sheet to the resistance element on the other side of that sheet. This permits the ends of the leads to extend substantially to the center of the resistor in close proximity to the actual resistor element in order that they may serve as thermal conductors.

In Figs. 19, 20 and 21, there is disclosed a variation of posite ends of one of said resistance films, and the end portions of said pair of leads secured between said sheets extending in combination over the major portion of the distance between said opposite ends of said one resistance film.

7. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of leads having one end portion each secured between said sheets, and a resistance film adhering to at least one principal surface of at least one of said sheets, said leads being electrically connected to spaced points on said resistance film.

8. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of leads having one end portion each secured between said sheets, and a resistance film and two spaced-apart films of conducting material adhering to at least one principal surface of at least one of ysaid sheets, said resistance film extending between and being electrically connected to said two conducting films, and said leads being electrically connected one each to said conducting films.

9. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of leads having one deformed end portion each secured between said sheets, and a resistance film and two spaced-apart films of conducting material adhering to at least one principal surface of at least one of said sheets, said resistance film extending between and being electrically connected to said two conducting films, and said leads being electrically connected one each to said conducting films.

l0. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of leads having one end portion each secured between said sheets, and a resistance film and two spaced-apart films of conducting material adhering to at least one principal surface of at least one of said sheets, said films of conducting material being located closely adjacent opposed edges of said one of said sheets, said resistance lm extending between and being electrically connected to said two conducting films, and said leads being electrically connected one each to said conducting films.

ll. A resistor comprising a pair of insulated sheets, a resistance element adhering to one principal surface of one of said sheets, and a pair of conductors electrically connected respectively to spaced points on said resistor element, said conductors having portions extending outwardly of said sheets to form leads, said conductors also having heat conducting portions extending inwardly between said sheets closely adjacent but insulated from said element, said heat conducting portions extending, in combination, over the major portion of the distance between said spaced points.

12. A resistor comprising a pair of insulated sheets, a resistance element adhering to one principal surface of one of said sheets, and a pair of conductors electrically connected respectively to spaced points on said resistor element, said conductors having portions extending outwardly of said sheets to form leads, said conductors also having heat conducting portions arranged between said sheets closely adjacent but electrically insulated from said element.

13. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of .wire leads having one end portion each secured between said sheets, and la resistance film adhering to at least one principal 10 surface of at least one of said sheets, said leads being electrically connected to spaced points on said resistance film.

14. A resistor comprising a pair of insulated sheets secured in face-to-face relationship, a pair of wire leads having one end portion each secured between said sheets, and a resistance film and two spaced-apart films of conducting material adhering to at least one principal surface of at least one of said sheets, said resistance film extending between and being electrically connected to said two conducting films, and said leads being electrically connected one each to said conducting films.

l5. A resistor comprising a pair lof insulated sheets secured in face-to-face relationship, a pair of wire leads having one deformed end portion each secured between said sheets, and a resistance film and two spaced-apart films of conducting material adhering to at least one principal surface of at least one of said sheets, said resistance film extending Ibetween and being electrically connected to said two conducting films, and said leads being electrically connected one each to said conducting films.

16. A resistor construction comprising a pair of elongated insulated strips secured in facc-to-.face relationship, a plurality of pairs of leads, each lead having one end portion secured between said strips, each of said .pairs of leads extending out from between said strips on opposite elongated sides thereof, and a plurality of resistance films .adhering to at least one principal surface of one of said strips, each of said pairs of `leads being electrically connected to spaced points on one of said resistance films.

17. A resistor construction comprising a pair of elongated insulated strips secured in face-to-face relationship, a plurality of pairs of wire leads, each lead having one end :portion secured between said strips, each of vsaid pairs of leads extending out from between said strips on opposite elongated sides thereof, land a plurality of resistance films adhering to at least one principal surface of one of said strips, each of said pairs of leads being electrically connected to spaced points on one of said lresistance films.

18. A resistor comprising the elements of claim 7 in which a mass of insulating material is arranged between said sheets, firmly .adhering to said leads and said sheets and filling the space between said sheets resulting from the presence of said leads therebetween.

19. A resistor comprising the elements of claim 7 in which said sheets provide recesses for receiving said end portions of said leads.

References Cited in the file of this patent UNITED STATES PATENTS 1,702,062 `Sonkin Feb. 12, 1929 1,739,256 Pender et al Dec. 10, 1929 1,771,236 Schellenger July 22, 1930 2,051,517 Creager Aug. 18, 1936 2,143,414 Grisdale Jan. `10, 1939 2,173,186 Swartz et al Sept. 19, 1939 2,176,604- Benkelman Oct. 17, 19.39 2,440,691 lira May 4, 1948 FOREIGN PATENTS 397,296 Great Britain Aug. 24, 1933 958,010 [France Aug. 29, 1949

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