Composite fuse element and method of making

Abstract

An improved fuse element for use in a circuit protection fuse. The fuse element may include an insulating substrate portion and a conductive metallic portion disposed on at least one surface of the insulating substrate portion, wherein the metallic portion extends along, and is in continuous, intimate contact with the substrate portion. When the metallic portion melts and separates upon the occurrence of an overcurrent condition, the substrate portion bridges the resulting gap that is formed in the metallic portion and provides electrical arc suppression therein.

Claims

1. A fuse comprising: a hollow fuse body defining a central cavity; a fuse element disposed within the cavity and comprising: an insulating substrate portion having a planar top surface, an opposing, planar bottom surface, and opposing side surfaces extending between the top surface and the bottom surface, the side surfaces having respective series of slots formed therein; a plurality of electrically conductive metallic portions disposed on the top surface and the bottom surface of the insulating substrate portion, the slots at least partially filled with an electrically conductive material connecting the metallic portions on the top surface to the metallic portions on the bottom surface, wherein the metallic portions and the electrically conductive material in the slots define a single, continuous, electrically conductive, helical pathway that extends 720 degrees about an axis of the substrate portion from a first end of the substrate portion to a second end of the substrate portion; and a first end cap connected to a first end of the fuse element and a second end cap connected to a second end of the fuse element.

2. The fuse of claim 1, further comprising at least one cutout formed in the metallic portions.

3. The fuse of claim 2, wherein the at least one cutout is semicircular in shape.

4. The fuse of claim 2, wherein the at least one cutout is rectangular in shape.

5. The fuse of claim 1, further comprising at least one aperture formed in the metallic portions.

6. The fuse element of claim 1, wherein the metallic portions have at least one weak point that separates more quickly upon the occurrence of an overcurrent condition than other portions of the metallic portions.

7. The fuse of claim 1, wherein the cavity is at least partially filled with an insulative filler material.

8. A fuse element comprising: an insulating substrate portion having a planar top surface an opposing, planar bottom surface, and opposing side surfaces extending between the top surface and the bottom surface, the side surfaces having respective series of slots formed therein; and a plurality of conductive metallic portions disposed on the top surface and bottom surface of the insulating substrate portion, the slots at least partially filled with an electrically conductive material connecting the metallic portions on the top surface to the metallic portions on the bottom surface to define a single, continuous, electrically conductive, helical pathway that extends 720 degrees about an axis of the substrate portion from a first end of the substrate portion to a second end of the substrate portion.

9. The fuse of claim 8, further comprising at least one aperture formed in the metallic portions.

10. The fuse element of claim 8, wherein the metallic portions have at least one weak point that separates more quickly upon the occurrence of an overcurrent condition than other portions of the metallic portions.

11. The fuse of claim 8, wherein the substrate portion has a rectangular cross sectional shape.

12. A method of making a fuse element comprising: providing an insulating substrate portion having a planar top surface, an opposing, planar bottom surface, and opposing side surfaces extending between the top surface and the bottom surface, the side surfaces having respective series of slots formed therein; applying a plurality of metallic portions to the top surface and bottom surface of the substrate portion; and at least partially filling the slots with an electrically conductive material connecting the metallic portions on the top surface to the metallic portions on the bottom surface; wherein the metallic portions and the electrically conductive material in the slots define a single, continuous, electrically conductive, helical pathway that extends 720 degrees about an axis of the substrate portion from a first end of the substrate portion to a second end of the substrate portion.

13. The method of claim 12, further comprising forming at least one cutout in the metallic portions.

14. The method of claim 12, further comprising forming at least one aperture in the metallic portions.

15. The method of claim 12, further comprising forming at least one weak point in the metallic portions that separates more quickly upon the occurrence of an overcurrent condition than other portions of the metallic portions.

16. The method of claim 12, further comprising applying electrically conductive termination portions to opposite ends of a surface of the substrate portion, wherein the termination portions are in contact with the metallic portions.

17. A method of making a fuse element comprising: providing an insulating substrate having a planar top surface and an opposing, planar bottom surface; forming rows of perforations in the substrate, wherein the rows extend along parallel, laterally spaced lines; forming patterned, parallelogram-shaped electrically conductive metallic portions on opposing, major surfaces of the substrate, wherein each metallic portion extends to at least one of the perforations; depositing electrically conductive paste in each of the perforations, wherein the paste is in contact with at least one of the metallic portions; and dicing the substrate along lines that laterally bisect each row of perforations; wherein the metallic portions and paste depositions define continuous, helical, electrically conductive pathways that extend 720 degrees about axes of respective diced substrate portions, and wherein the pathways are in continuous, intimate contact with, and extend from a first end to a second end of, the respective diced substrate portions.

18. The method of claim 17, further comprising applying electrically conductive termination portions to opposite ends of a surface of the substrate, wherein the termination portions are in contact with the metallic portions.

19. The method of claim 17, further comprising forming at least one cutout in the metallic portions.

20. The method of claim 17, further comprising forming at least one aperture in the metallic portions.

21. The method of claim 17, further comprising forming at least one weak point in the metallic portions that separates more quickly upon the occurrence of an overcurrent condition than other portions of the metallic portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) By way of example, specific embodiments of the disclosed device will now be described, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a side cross sectional view illustrating a prior art fuse.

(3) FIG. 2a is a side cross sectional view illustrating a fuse in accordance with an embodiment of the present disclosure.

(4) FIG. 2b is graph that presents arc time data for a fuse according to the fuse embodiment shown in FIG. 2, as well as arc time data for two conventional fuses.

(5) FIGS. 3a-3d illustrate an exemplary method of making the fuse shown in FIG. 2a.

(6) FIGS. 3e-3f are perspective views illustrating alternative composite fuse elements in accordance with the present disclosure.

(7) FIGS. 4a-4d are top perspective and bottom perspective views illustrating an alternative composite fuse element in accordance with the present disclosure.

(8) FIGS. 5a-5f illustrate an exemplary method of making the composite fuse element shown in FIGS. 4a-4d.

(9) FIG. 6 illustrates an exemplary fuse that employs the fuse element shown in FIGS. 4a-4d.

DETAILED DESCRIPTION

(10) Various embodiments of a fuse having a composite fuse element including a ceramic substrate and a method for making the same in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

(11) For the sake of convenience and clarity, terms such as front, rear, top, bottom, up, down, vertical, horizontal, lateral, and longitudinal may be used herein to describe the relative placement and orientation of various structures and components described below. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

(12) FIG. 2a illustrates a side cross-sectional view of an exemplary fuse 270 that is consistent with certain embodiments of the present disclosure. The fuse 270 includes conductive end caps 272 that fit over opposing longitudinal ends of a tubular fuse body 274, such as by press-fitting or other means of secure engagement, to define an enclosed cavity 276 therein. The end caps 272 may be formed wholly or partially of any suitable electrically conductive material, including, but not limited to, copper or brass, and may be coated with additional materials such as tin or silver. The fuse body 274 can be formed of any suitable insulative material, including, but not limited to, glass, ceramic, plastic, and various composites, and may have any suitable cross sectional shape, such as round, rectangular, triangular, or irregular. The cross sectional size and shape of the end caps 272 may substantially match the cross sectional size and shape of the fuse body 274 to facilitate mating engagement therebetween. The cavity 276 of the fuse 270 may be filled with air, inert gas, various powdered or granular insulative materials, or may be vacuum sealed.

(13) A composite fuse element 278 may extend between the end caps 272 and includes an insulative substrate portion 280 and a conductive metallic portion 282. The substrate portion 280 of the fuse element 278 may be formed of any suitable insulative material, including, but not limited to, ceramic, glass, plastic, and various composites. The metallic portion 282 may be formed of any known metallic material that is suitable for use as a conductive fuse element, including, but not limited to, tin, lead, and zinc. The substrate portion 280 and the metallic portion 282 are disposed in a parallel, flatly abutting relationship within the cavity 276 and are in intimate contact with one another. The longitudinal ends of the fuse element 278 may be connected to the end caps 272 with any suitable, electrically conductive means of affixation, such as with solder fillets or with various conductive adhesives, for example.

(14) It has been found through experimentation that the composite fuse element 278 provides improved resistance to electrical arc formation upon the occurrence of an overcurrent condition as compared to a fuse having a conventional fuse element defined only by a conductive metallic member that may or may not be surrounded an insulative filler material. For example, the graph shown in FIG. 2b presents exemplary arcing time data for several fuses having uniform sizes and current ratings. In particular, arcing time data for a fuse having a composite fuse element in accordance with the present disclosure is represented by curve 290 in FIG. 2b, while curves 292 and 294 in FIG. 2b represent arcing time data for two fuses having conventional, non-composite fuse elements. Of course, it will be appreciated by those of ordinary skill in the art that variations in fuse ratings and fuse size will result in corresponding variations in arcing time. As shown in FIG. 2b, the arcing time for the fuse in accordance with the present disclosure was about 100 microseconds or less, while the arcing time for the fuses having conventional fuse elements was on the order of one millisecond (as shown by curve 292) or many milliseconds (as shown by curve 294). It has therefore been demonstrated that the arc quenching capability of a composite fuse element in accordance with the present disclosure is significantly better than that of conventional fuse elements.

(15) The improved arc suppression of the fuse 270 relative to conventional fuses is a direct result of the metallic portion 282 of the fuse element 278 being in continuous, intimate contact with the insulating portion 280 of the fuse element 278. Particularly, the insulating portion 280, which does not melt or break apart upon the occurrence of an overcurrent condition, extends across a gap in the metallic portion 282 that is formed when the metallic portion 282 melts or breaks apart (i.e., when longitudinally-opposing, unmelted portions of the metallic portion 282 melt and recede longitudinally away from each other). The insulating portion 280 thus acts as an arc suppressor within the longitudinally expanding gap, with the area of contact between the insulating portion 280 and the metallic portion 282 being greater than the area of contact between filler materials and metallic fuse elements in conventional fuses (as shown in FIG. 1).

(16) FIGS. 3a-3d depict an exemplary method of making a fuse 270 that is consistent with the present disclosure. Referring first to FIG. 3a, an insulating substrate 300, such as may be formed of ceramic or other insulative materials as discussed above, is provided with overlaying metallic portions 302. The metallic portions 302 may be formed as strips, and in various embodiments may be produced and applied to the insulating substrate 300 using screen printing, plating, vapor deposition, or other known techniques for forming and depositing coatings or layers upon a substrate. The width and thickness of the metallic portions 302 may be varied according to the desired characteristics of the composite fuse element to be formed. For example, the metallic portion of a fuse element that is designed to have a relatively higher current limit may be made wider and/or thicker than the metallic portion of a fuse element that is designed to have a relatively lower current limit.

(17) In FIG. 3b, the substrate 300 is prepared for dicing to form several individual composite fuse elements 278 (as shown in FIG. 2a and FIGS. 3c-d). For example, scribing lines 304 may be made in the substrate 300, laterally-intermediate the metallic portions 302 as shown. Although not shown, it is contemplated that the metallic portions 302 may be similarly prepared for being cut to a desired width.

(18) Referring to FIGS. 3e and 3f, alternative embodiments of a fuse element are contemplated in which various weak points are formed in the metallic portion thereof to split electrical arcing that may occur upon melting of the metallic portions of the fuse elements during an overcurrent condition. In particular, FIG. 3e illustrates a fuse element 380a that includes a metallic portion 385a having a series of semicircle cutouts 390a formed along each of its lateral edges, such as by cutting or etching. The resulting narrow portions 395a of the metallic portion 385a, located laterally intermediate the semicircle cut-outs 390a, serve as weak points that accommodate splitting of electrical arcing when the narrow portions 395a melt upon the occurrence of an overcurrent condition.

(19) Similarly, FIG. 3f illustrates a fuse element 380b that includes a metallic portion 385b having a series of rectangular cutouts 390b formed along each of its lateral edges. The resulting narrow portions 395b of the metallic portion 385b, located laterally intermediate the rectangular cut-outs 390b, serve as weak points that facilitate splitting of electrical arcing when the narrow portions 395b melt upon the occurrence of an overcurrent condition as described above. It will be appreciated by those of ordinary skill in the art that thinned or narrowed weak points similar to those described above may be formed in a fuse element using various techniques, and that such weak points may be formed with many different shapes, sizes, and configurations. All such variations are contemplated and may be implemented without departing from the present disclosure.

(20) In FIG. 3c, the metallic portion 282 of a single diced composite fuse element 278 (cut from the substrate 300 and metallic portion 302 shown in FIG. 3b) is connected to end caps 272, such as with solder, conductive epoxy, or other electrically conductive means of affixation (not shown). The metallic portion 282 thus forms a continuous, electrically conductive pathway between the end caps 272. The insulating substrate portion 280 may or may not be affixed to the end caps 272. While the substrate portion 280 is shown as having longitudinal ends that extend completely to the end caps 272, it is contemplated that the substrate portion 280 may alternatively be shorter than the metallic portion 282, and that one or both of the longitudinal ends of the metallic portion 282 may be spaced apart from their respective end caps 272. In FIG. 3d, a fuse body 274 is installed intermediate the end caps 272 to house the composite fuse element 278 and to define a cavity 276. As described above, the cavity 276 may optionally be filled with an insulative material or gas (not shown) to further enhance the arc-quenching capability of the fuse 270.

(21) FIGS. 4a-4d depict top perspective and bottom perspective views of an alternative composite fuse element 400 in accordance with further embodiments of the present disclosure. The composite fuse element 400 includes a metallic portion 402 having a three dimensional, substantially helical shape that is wrapped around, and that is in continuous, intimate contact with an insulating substrate portion 404. The metallic portion 402 of the fuse element 400 may be formed of any known metallic material that is suitable for use as a conductive fuse element, including, but not limited to, tin, lead, and zinc. The substrate portion 404 may be formed of any suitable insulative material, including, but not limited to, ceramic, glass, plastic, and various composites.

(22) The substrate portion 404 is shown as having a rectangular cross sectional shape with opposing top and bottom surfaces 412 and 416, but it is contemplated that the shape of the substrate portion 404 can be varied without departing from the present disclosure. For example, the substrate portion 404 may alternatively have a circular, triangular, or irregular cross sectional shape. It is further contemplated that the substrate portion 404 may be tubular with a hollow cavity extending longitudinally therethrough. Regardless of the particular shape or size of the substrate portion 404, the metallic portion 402 of the fuse element 400 should be helically wrapped about the substrate portion 404 in a closely conforming, flatly abutting relationship therewith.

(23) Referring to FIG. 4a, the top surface portions 408 of the metallic portion 402 of the composite fuse element 400 may be arranged as evenly spaced, diagonally oriented strips on the top surface 412 of the substrate portion 404. Referring to FIG. 4b, the bottom surface portions 414 of the metallic portion 402 may be arranged on the bottom surface 416 of the substrate portion 404 in a manner similar to the top side portions 408. The bottom surface portions 414 are electrically conductively connected to the top surface portions 408 by side metallic portions 418 that extend perpendicularly between the lateral edges of the top surface portions 408 and the bottom surface portions 414. The metallic portion 402 thus forms a continuous, electrically conductive path having a shape that is substantially similar to that of a flat, helical ribbon that has been creased along lines corresponding to the lateral edges of the substrate portion 404. Thus, while the shape of the metallic portion 402 does not conform to the strict definition of the term helix as it is conventionally used, the terms helix and helical shall be defined herein to encompass the shape of the metallic portion 402 as it shown in the FIGS. 4a and 4b, as well as all conventional helices and variations thereon.

(24) Referring to FIGS. 4a and 4b, apertures or holes 410 may be formed in the top surface portions 408 and bottom surface portions 414 of the metallic portion 402. The holes 410 are shown as being circular and extending across the majority of the longitudinal width of the top and bottom surface portions 408 and 414, but it is contemplated that the shape and size of the holes 410 can be varied without departing from the present disclosure. Referring to FIGS. 4c and 4d, the formation of the holes 410 creates weak points 420 in the metallic portion 402 that are significantly narrower than the imperforate areas of the top and bottom surface portions 408 and 414. Particularly, each hole 410 creates two adjacent weak points 420, as illustrated.

(25) Since the weak points 420 in the metallic portion 402 are relatively narrow, they melt or break apart faster than the relatively wider, imperforate portions of the metallic portion 402 upon the occurrence of an overcurrent condition. The fuse element 400 therefore exhibits a faster circuit interrupt response than would be provided by an entirely imperforate metallic portion. The generally helical shape of the metallic portion 402 of the exemplary fuse element 400 provides a total of five top and bottom surface portions 408 and 412, and therefore a total of 10 weak points 420. Of course, a greater number of windings and corresponding holes 410 in the metallic portion 402 will provide a greater number of weak points 420. Accordingly, the helical metallic portion 402 facilitates a fuse element configuration in which a plurality of weak points can be compactly arranged within a fuse element of a given longitudinal length as compared to conventional, straight fuse elements. The fuse element 400 may thereby add to the breaking capacity of a fuse relative to conventional fuse elements of similar size. Breaking capacity is defined herein to mean the maximum current that can safely be interrupted by a fuse. At the same time, and as described above with respect to the fuse element 278, the fuse element 400 is resistant to electrical arcing because the metallic portion 402 is in continuous, intimate contact with the insulating substrate portion 404. Particularly, the substrate portion 404 bridges any gaps that may form in the metallic portion 402 upon metaling or breaking and thus acts as an arc suppressor.

(26) FIGS. 5a-5d depict an exemplary method of making a fuse 400 that is consistent with the present disclosure. In FIG. 5a, an insulating substrate 500 is provided which may be formed of, for example, a flat sheet of ceramic material, insulative organic material, flexible substrate material, or any other suitable insulative substrate material as discussed above. In FIG. 5b, a series of perforations or slots 502 are formed in the insulating substrate 500, such by using any of a variety of known techniques that will be familiar to those of ordinary skill in the art. The slots 502 may be formed along parallel, longitudinally extending, laterally spaced lines as shown.

(27) FIG. 5c illustrates a top surface 500a of the substrate 500 having exemplary patterned, parallelogram-shaped metallic portions 504a formed thereon, wherein each metallic portion 504a has a hole formed therethrough. Similarly, FIG. 5d illustrates a bottom surface 500b of the substrate 500 having exemplary patterned, parallelogram-shaped metallic portions 504b formed thereon, wherein each metallic portion 504b has a hole formed therethrough. The patterned metallic portions 504a and 504b may be produced and applied to the substrate 500 using screen printing, plating, vapor deposition, or other known techniques for forming and depositing coatings or layers upon a substrate. The lateral edges of the metallic portions 504a may be vertically aligned with the lateral edges of the metallic portions 504b.

(28) A metallic paste 506 may be deposited in, and may substantially fill, each of the slots 502. The paste 506 may be formed of any suitable, electrically conductive material, and may be deposited in the slots 502 using any suitable deposition technique. The paste 506 provides an electrically conductive connection between the metallic portions 504a on the top surface 500a of the substrate 500 and the metallic portions 504b on the bottom surface 500b of the substrate 500 as further described below.

(29) Optionally, metallic termination portions 507a and 507b may be deposited on the longitudinal ends of the bottom surface 500b of substrate 500. The termination portions 507a and 507b may be formed of any suitable, electrically conductive material and may be produced and applied to the substrate 500 using any of the layering and/or deposition techniques discussed above. The termination portions 507a and 507b may be disposed in direct or indirect electrically conductive contact with the metallic portions 504a and 504b, such as via the paste 506, for providing electrical connections between the metallic portions 504a and 504b and the end caps of a fuse as further described below.

(30) Finally, the substrate 500 may be diced, such as by breaking or cutting the substrate 500 along longitudinally extending lines that laterally bisect each row of paste-filled slots 502, to produce individual fuse elements 400 as shown in FIGS. 4a-4d and 5e-5f. Although not shown, scribe lines may first be made in the substrate 500 and used as guides during dicing.

(31) FIG. 5e and FIG. 5f illustrate perspective views of the top and bottom of the fuse element 400 after the substrate 500 is diced. As discussed above, the metallic paste 506 that was deposited in the slots 502 provides an electrical connection between the metallic portions 504a and 504b on the top and bottom sides of the fuse element 400, thereby creating a continuous, generally helical electrical pathway that wraps around, and that is in intimate contact with, the insulative substrate of the fuse element 400. The size and/or shape of the slots 502 and the amount of metallic paste 506 deposited therein may be adjusted in order to shrink or expand the electrical pathways created by the paste 506 and/or to provide wider or narrower lateral margins between individual fuse elements 400 for the dicing process. As discussed above, the metallic termination portions 507a and 507b are located on the longitudinal ends of the bottom fuse element 400 for providing electrical connections to the end caps of a fuse.

(32) FIG. 6 illustrates a side cross-sectional view of an exemplary fuse that employs the fuse element 400 described above, wherein the fuse element 400 is disposed within a tubular fuse body 574. The fuse 270 includes conductive end caps 572a and 572b that fit over opposing longitudinal ends of the fuse body 574, such as by press-fitting or other means of secure engagement. The end caps 572a and 572b may be formed wholly or partially of any suitable electrically conductive material, including, but not limited to, copper or brass that may or may not be coated with tin or silver. The fuse body 574 can be formed of any suitable insulative material, including, but not limited to, glass, ceramic, plastic, and various composites, and may have any suitable cross sectional shape, such as round, rectangular, triangular, or irregular. The cross sectional size and shape of the end caps 572a and 572b may substantially match the cross sectional size and shape of the fuse body 574 to facilitate mating engagement therebetween. The fuse body 574 may optionally be filled with air, inert gas, various powdered or granular insulative materials, or may be vacuum sealed.

(33) The composite fuse element 400 may extend between the end caps 572a and 572b, and a solder fillet 555a may electrically connect the termination portion 507a of the fuse element 400 to the end cap 572a. Similarly, a solder fillet 555b may electrically connect the termination portion 507b of the fuse element 400 to the end cap 572b.

(34) As used herein, an element or step recited in the singular and proceeded with the word a or an should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to one embodiment of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

(35) While certain embodiments of the disclosure have been described herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.