Flat fuse and method for its manufacture

Abstract: Separating walls (23) are formed between adjacent grooves (22) on the surface of a base (20). Circuits including fusible strips (30) are mounted in the grooves (22). Thereafter, the separating walls (23) are crushed so that they overlie the strips (30), retain them in the grooves (22), and protect them against foreign particles. Thus, if such a particle manages to impact a strip (22), no short-circuit will result, even if the strip should begin to peel.

Description: The present Invention relates to a a planar fuse in which a fusing path having a prescribed conductive capacity is disposed on the surface of an insulative base. The present Invention also relates to a method for making the fuse. BACKGROUND OF THE INVENTION Referring to Figure 11 and Figure 12, a similar type of planar fuse has been proposed in Japanese Utility Model Laid-Open Publication 56-38959. In the fuse disclosed in this Publication, the fusing path is circuit 2 formed of a thin metallic film adhered to the surface of insulative base 1 by etching and vaporization. In this configuration, electricity passes through circuit 2 on the surface of insulating base 1; when the prescribed electrical capacity is exceeded, the thin film heats up and melts, thereby breaking the circuit. In Figure 13, a blade-shaped fuse is shown. While not planar, it is similar to the foregoing fuse. A shape is molded to form two thick plates 3,3 serving as terminals, and string-shaped fusing path 4 connects the two thick plates. Resin 5 covers the outside. The prior art fuses described above have a number of problems. When a plurality of such fuses is arranged to provide circuits, foreign particles can impact on the fuse causing it to peel away, thus creating the possibility of a short-circuit with a neighboring fuse. Also, since the circuit is formed by etching and vaporization, wet production is necessary, thus requiring a difficult operating environment. With the blade-shaped fuses, it is necessary to keep the plates thick since they must also serve as terminals. Extra cutting or stamping is required in order to leave a thin, wire-shaped fusing path, and this increases production costs. Also, because of the thickness of the base, the large cross-section makes it difficult to provide a fuse for low capacities; similarly, using the fuse for multiple electrodes is also difficult. A planar fuse having the features of the preamble of claim 1 has been known from FR-A-2 397 058. This prior art planar fuse does not address and solve the above mentioned problems. SUMMARY OF THE INVENTION The object of the present invention is to overcome the problems of the prior art described above. A further object of the present invention is to provide a planar fuse which prevents short circuits between adjacent conductors and is easy to manufacture without requiring wet processes. For solving the object the invention provides a planar fuse as defined in claim 1. The dependent claims relate to further advantageous features of the invention and to a method for manufacturing the fuse. In a fuse according to the Invention, fusing paths are arranged in parallel rows on the insulative base, with a separation between each path. Thus, if a foreign particle impacts a path, it may peel off, but it will not go past the separation to come into contact with an adjacent fusing path. The paths have a predetermined capacity and are mounted between projections formed on the surface of the insulative base. In a method according to the Invention, pressure is exerted on the projections so that they spread and bear against the edges of the fusing paths, thereby retaining them on the base. In a modification of the Invention, only parts of the fusing path are overlain by the spread portions. Thus, the portion that is to come into contact with external electrodes and the like has a large exposed area, and the portion that will not come into contact has little or no exposed area. The large exposure area at the uncovered portion enhances the ability to act as contact surfaces for electrodes and the like, while the little or no exposure areas protect the fuse from foreign particles. Preferably, the surfaces of the projections slope upward toward the edges of the fusing paths. When the projections are pressed flat, they bear against the fusing paths and the under surfaces of the projections cover at least the edges thereof. In another modification of the Invention, the fusing path passes over a cavity in the base and is suspended in mid-air. This prevents heat generated in the fusing path from being dissipated into the insulative base. Thus, the heat from the portion of the fusing path that is suspended in mid-air is not absorbed, allowing heat build-up and fusing as desired. In a further embodiment of the Invention, the base is folded so that the fusing path on its surface forms a circuit from one side of the base to the other. The fusing paths can be placed in prescribed circuits by inserting the edge of the base at the fold line into a socket comprising terminals that come into contact therewith on both sides of the base. The present Invention, as described above, provides a planar fuse that prevents fusing paths from short-circuiting since adjacent paths are isolated from each other by separating walls. Thus, the need for wet processes such as etching, vaporizing, and gluing, is eliminated, and significant improvements in efficiency of production are achieved. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, constituting a part hereof, and in which like reference characters indicate like parts, Figure 1 is a perspective view of the fuse according to the present Invention; Figure 2 is an exploded view of the fuse of Figure 1 before folding and insertion of the fusible strips; Figure 3 is a partial cross-section of one form of the fuse before pressing; Figure 4 is a perspective of the fuse of Figure 3 3 before pressing; Figure 5 is a partial cross-section of the fuse of Figure 3 after pressing; Figure 6 is a perspective of the fuse of Figure 3 after pressing; Figure 7 is a plan view of the fuse with an alternative form of the projection before pressing; Figure 8 is a plan view of the fuse of Figure 7 7 after pressing; Figure 9 is a partial cross-section of the fuse showing an alternative form of the projections; Figure 10 is a partial cross section in perspective showing the mounting of the fuse in a socket; Figure 11 is a perspective of a prior art fuse before folding; Figure 12 is a perspective of the prior art fuse of Figure 11 after folding; and Figure 13 is a perspective of a prior art blade-shaped fuse. DETAILED DESCRIPTION OF THE INVENTION Referring to Figures 1 and 2, five circuits are arranged in parallel on the surface of insulative base 20 to form planar fuse 10. Fusible strips 30 are in grooves. 22 and are folded back at a point midway between their ends. Windows 21 are formed toward the center of base 20 where it intersects the circuits. Each strip 30 is suspended in mid-air at window 21, has a predetermined electrical capacity depending on its cross-section, and is designed so that it fuses when the electric current flow exceeds this capacity. Thus, the circuits serve as fusing paths. Insulative base 20 is bent in two at fold line 11 in a manner resembling two hands held together in prayer. However, base 20 does not need to be bent over, and can be flat as long as the circuits can be arranged on the surface. Also, it is not absolutely necessary to have windows 21. However, by arranging the circuits to intersect windows 21, fusible strips 30 can be suspended mid-air. This prevents the heat generated in strips 30 from being absorbed by base 20, thereby allowing the suspended portion to melt more easily and more accurately. For this reason, windows 21 are cavities. Of course, windows 21 do not need to be continuous; it is sufficient if they are cavities which allow strips 30 to be out of contact with base 20 at one point. Furthermore, strips 30 need not have a planar cross-section; the shape can be e.g. circular or trapezoidal in cross-section, as long as they can be affixed to the base. On base 20, grooves 22 correspond to the location of strips 30. Separating walls 23 arc on either side of each groove 22. Referring to Figures 3 and 4, the surface of separating wall 23 is sloped so that the ends adjacent groove 22 project upward. Strips 30 are mounted in grooves 22 and projecting portions 6 arc pressed downward. As can be seen in Figures 5 and 6, the pressed portions bear against and retain the edges of strips 30. In this embodiment, the entire surface of separating wall 23 is pressed. However, separating walls 23 need only cover and apply pressure to the edges of adjacent strips 30. Therefore, it is possible to form projections 24a at various points on separating wall 24, as shown in Figure 7. Projections 24a are then pressed to provide localized pressure on - and retention of - strips 30. Of course, the cross-section of the projection does not need to have the particular sloped form described above. In Figure 9, the surface of separating wall 23 is flat throughout and still prevents the edges of strips 30 from rising out of groove 22. In terms of strength, the embodiment of Figure 5 is stronger, but the flat structure shown in Figure 9 can be used as well, depending on the amount of strength required. Separating wall 23 need not be formed uniformly on base 20. At the portions near the ends of the base, separating walls 23 are spaced apart from groove 22. As shown in Figure 6, when pressure is exerted on the base, thereby crushing separating walls 23, the walls in this region are not pushed into groove 22 and do not overlie the edges of strips 30. Referring to figure 10, the fuse is inserted into socket 50 through slit 51. Metal terminals 52, 52 are supported by slit 51 so that they face each other and are adapted to contact the surfaces of strips 30 at windows 7. This provides a wide area of contact, insuring that good electrical connection will result; at the same time, for protection, the other portions are exposed only slightly. After wall 23 is crushed, base 20 is bent in two at fold line 11 to complete fuse 10. To produce the fuse of the present Invention, fusible strip 30 is mounted in groove 22 in base 20. Retaining projections 6 on wall 23 adjacent grooves 22 are crushed as by high-frequency welding, heating, or high-frequency heating, and the edges of strips 30 are held and retained thereby. Thus, it is not necessary to perform any wet production processes such as etching, vaporization, or gluing, thereby making production very efficient. It is also possible to form a bend beforehand, and fix the parts through heating. Fixing can be performed without heating by forming interlocking cavities and projections to facilitate engagement, and then joining the parts. If a foreign particle impacts on the surface of assembled fuse 10, it is difficult for it to affect strips 30. At the most, only a very small area of the strips is exposed; separating wall 23 seals and protects them. However, even if a particle does get through and cause strip 30 to begin to peel off, short-circuiting is prevented by the presence of separating wall 23 between adjacent circuits. In introducing fuse 10 into an electric circuit, if socket 50 is mounted as shown in Figure 10, strips 30 are substantially exposed only where separating wall 23 is not crushed downward, i.e. at windows 7, thus allowing terminals 52, 52 to form good electrical contacts with strips 30. In summary, wall 23 is formed between adjacent grooves 22 on the surface of base 20 and circuits comprising fusible strips 30 are mounted therein. By crushing separating wall 23, strips 30 are pressed down and retained. If a foreign particle impacts fuse 10, it will not short-circuit with an adjacent strip 30 even if it starts to peel off. Although only a specific number of embodiments of the present Invention have been expressly disclosed, it is, nonetheless, to be broadly construed and not to be limited except by the character of the claims appended hereto.

Claims: A planar fuse comprising an insulative base (23) having a plurality of parallel grooves (22) spaced apart laterally from each other, said grooves (22) extending from a front edge (8) to a rear edge (9), a fusible strip (30) in each said groove (22), characterized by a retaining projection (6) on said insulative base (23) adjacent one of said grooves (22), said retaining projection overlying at least a part of said fusible strip (30), thereby securing said strip (30) in said groove (22). A planar fuse according to claim 1 comprising a plurality of separating walls (23) at certain points along said fuse strips (30) and not at other points along said fuse strips (30), thereby forming windows in said paths to facilitate contact between said fusible strips and another electrical device. A planar fuse according to Claim 1 wherein said insulative base (23) comprises a cavity beneath a portion of said fusible strip (30). A planar fuse according to Claim 1 or 3 wherein said insulative base (20) comprises a fold line between said front edge (8) and said rear edge (9), said fuse being folded along said fold line so that said front edge (8) is adjacent said rear edge (9). A planar fuse according to Claims 1, 3, or 4 wherein certain portions of said grooves (22) are wider than remaining portions of said grooves, thereby creating windows (7) which facilitate contact between said fusible strips and another electrical device. A method for the manufacture of a planar fuse comprising an insulative base (23) having a plurality of parallel grooves (22) spaced apart laterally from each other, said grooves (22) extending from a front edge (8) to a rear edge (9), a retaining projection (6) adjacent one of said grooves (22), said method comprising placing a fusible strip (30) in one of said grooves, exerting pressure on said retaining projection, thereby causing it to overlie at least a portion of said strip and secure said strip in said groove. The method of Claim 6 wherein said retaining projection (6) prior to pressure being exerted thereon, has a surface which slopes upwardly toward said groove (22).

Inventors: FURUO YUTAKA, TANIGAWA HIDEMI, YASUKUNI JUN, FURUO, YUTAKA, TANIGAWA, HIDEMI, YASUKUNI, JUN
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1996
Main classification: H01H85
IPC codes: H01H85, H01H69