CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority under 35 U.S.C. 119 from Taiwan Patent Application No. 112138350 filed on Oct. 5, 2023, which is hereby specifically incorporated herein by this reference thereto.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a fuse, and more particularly to a surface mount fuse and fuse element thereof.
2. Description of the Prior Arts
A surface mount fuse is soldered to a circuit board. When an abnormality such as overcurrent occurs in the current loop on the circuit board, the surface mount fuse immediately interrupts the current loop to protect the circuit board.
A conventional surface mount fuse uses a flat fuse made of tin-lead alloy with a melting point of 290 degrees Celsius. To meet Restriction of Hazardous Substance (RoHS), a material of lead (Pb) is prohibited in the flat fuse. A lead-free flat fuse made of a lead-free alloy is raised accordingly. Tin-bismuth alloy is an example of a lead-free alloy, with a melting point ranging from 245° C. to 250° C. However, the melting point of the tin-bismuth alloy is lower than that of the tin-lead alloy and even lower than the reflow temperature of about 260° C. Therefore, the lead-free flat fuse made of Tin-bismuth alloy melted in the reflow procedure. With reference to FIG. 7, a conventional surface mount fuse has a lead-free flat fuse 51 and two metal layers 52a and 52b, respectively, mounted on two opposite surfaces of the lead-free flat fuse 51. In addition, a flux 53 is further coated on the first metal layer 52a to avoid the first metal layer 52a being oxidized and to increase fuse efficiency.
To overcome the shortcomings, the present invention provides a surface mount fuse and fuse element thereof to mitigate or to obviate the aforementioned problems.
SUMMARY
An objective of the present invention is to provide a surface mount fuse and fuse element thereof.
To achieve the objective as mentioned above, the surface mount fuse has:
- a base having a first surface, two electrodes and a heater, wherein the two electrodes and the heater are formed on the first surface and the heater is located between the two electrodes;
- a fuse element electrically connected to the two electrodes and the heater and having:
- a lead-free flat fuse having a second surface and a third surface opposite to the second surface, wherein the second surface lies across the two electrodes and contacts the heater;
- a first flux layer formed on the third surface of the lead-free flat fuse; and
- a first porous metal layer stacked on the first flux layer, wherein a periphery of the first porous metal layer does not extend beyond that of the lead-free flat fuse, wherein a part of the first flux layer penetrates into a plurality of pores of the first porous metal layer and the first porous metal layer is bonded to the third surface of the lead-free flat fuse through the first flux layer; and
- a hollow cover mounted on the first surface of the base to cover the fuse element therein.
Based on the foregoing description, the surface mount fuse of the present invention mainly forms the first flux layer on the lead-free flat fuse and then stacks the first porous metal layer on the first flux layer. Therefore, a part of the first flux layer penetrates into the first porous metal layer through capillary action. Since the flux fills the pores of the first porous metal layer to distribute on the lead-free flat fuse evenly, the flux in the surface mount fuse of the present invention is evenly distributed and is sufficient. When overcurrent occurs in the current loop and high temperature occurs, the first flux layer helps the first porous metal layer and the lead-free flat fuse to melt effectively, thereby interrupting the current loop in time.
To achieve the objective as mentioned above, the fuse element of the surface mount fuse has:
- a lead-free flat fuse having a first surface and a second surface opposite to the first surface;
- a first flux layer formed on the first surface of the lead-free flat fuse; and
- a first porous metal layer stacked on the first flux layer, wherein a periphery of the first porous metal layer does not extend beyond that of the lead-free flat fuse, wherein a part of the first flux layer penetrates into a plurality of pores of the first porous metal layer, and the first porous metal layer is bonded to the first surface of the lead-free flat fuse through the first flux layer.
Based on the foregoing description, the fuse element of the surface mount fuse of the present invention mainly forms the first flux layer on the lead-free flat fuse and then stacks the first porous metal layer on the first flux layer. Therefore, a part of the first flux layer penetrates into the first porous metal layer through capillary action. Since the flux fills the pores of the first porous metal layer to distribute on the lead-free flat fuse evenly, the flux in the surface mount fuse of the present invention is evenly distributed and is sufficient. When overcurrent occurs in the current loop and high temperature occurs, the first flux layer helps the first porous metal layer and the lead-free flat fuse to melt effectively, thereby interrupting the current loop in time.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a cross-sectional view of a first embodiment of a surface mount fuse in accordance with the present invention;
FIG. 1B is an enlarge view in part of FIG. 1A;
FIG. 1C is a cross-sectional view of a second embodiment of a surface mount fuse in accordance with the present invention;
FIG. 2A is a perspective exploded view of a first embodiment of a fuse element of a surface mount fuse in accordance with the present invention;
FIG. 2B is a perspective exploded view of a second embodiment of a fuse element of a surface mount fuse in accordance with the present invention;
FIG. 3 is a top view of a third embodiment of a fuse element mounted 22 on a base in accordance with the present invention;
FIG. 4 is a top view of a fourth embodiment of a fuse element mounted on a base in accordance with the present invention;
FIG. 5 is a cross-sectional view of a third embodiment of a surface mount fuse in accordance with the present invention;
FIG. 6 is a perspective exploded view of the fuse element in FIG. 5; and
FIG. 7 is a cross-sectional view of a conventional surface mount fuse in accordance with the prior art.
DETAILED DESCRIPTION OF THE EMBODIMENTS
With reference to FIG. 1A, a first embodiment of a surface mount fuse in accordance with the present invention is shown. The surface mount fuse has a base 10, a first element 20a, and a hollow cover 30.
The base is made of an electrical insulating material and has a first surface 12, two electrodes 14 and a heater 15. The two electrodes 14 are formed on the first surface 12. The heater 15 is formed on the first surface 12 and located between the two electrodes 14. A gap D is between each electrode 14 and the heater 15. In one embodiment, with further reference to FIG. 3, the heater 15 has a leading electrode 16, a first conductive layer 17, a heating layer 18, and a second conductive layer 19. The leading electrode 16 is located between the two electrodes 14. The first conductive layer 17 encapsulates the leading electrode 16, and the heating layer 18 encapsulates the first conductive layer 17. The second conductive layer 19 is formed on the heating layer 18. The first and second conductive layers 17, 19 are good conductors of electricity and heat.
The fuse element 20a is electrically connected to the two electrodes 14 and the heater 15 on the base 10 and has a lead-free flat fuse 21, a first flux layer 24 and a first porous metal layer 25a.
The lead-free flat fuse 21 of the fuse element 20a has a second surface 22 and a third surface 23. The second surface 22 faces to the first surface 12 of the base 10 and lies across the two electrodes 14 of the base 10. With further reference to FIG. 3, the second surface 22 contacts the heater 15. In particular, the second surface 22 of the lead-free flat fuse 21 contacts the two electrodes 14 and the second conductive layer 19 of the heater 15. Therefore, the lead-free flat fuse 21 is electrically connected to the two electrodes 14 and the heater 15. The third surface 23 of the lead-free flat fuse 21 is opposite to the second surface 22 and away from the first surface 12 of the base 10. To meet RoHS, in the present embodiment, the lead-free flat fuse 21 is made of Sn or Bi or tin-bismuth alloy, but not limited to. When a large current flows through the lead-free flat fuse 21 due to overcurrent, the large current also passes through the second conductive layer 19, the heating layer 18, the first conductive layer 17, and the leading electrode 16. The heating layer 18 of the heater 15 generates heat thereby. At the time, the second conductive layer 19 heats the lead-free flat fuse 21 evenly so the lead-free flat fuse 21 is rapidly heated to its melting point and then melted.
With further reference to FIG. 2A, the first flux layer 24 is formed on the third surface 23 of the lead-free flat fuse 21. In one embodiment, the first flux layer is made of rosin but is not limited thereto. A periphery of the first porous metal layer 25a does not extend beyond that of the lead-free flat fuse 21. The first porous metal layer 25a stacks on the first flux layer 24, so the first porous metal layer 25a is bonded on the third surface 23 of the lead-free flat fuse 21 through the first flux layer 24. At the time, a part of the first flux layer 24 penetrates into the first porous metal layer 25a through capillary action. As shown in FIG. 1B, since the flus of the first flux layer 24 fills a plurality of pores 251 of the first porous metal layer 25a, the first flux layer 24 is evenly distributed on the third surface 23 of the lead-free flat fuse 21. In one embodiment, a melting point of the first porous metal layer 25a is greater than that of the lead-free flat fuse 21. In addition, to add more flux, a third flux layer 26 may be further formed on the first porous metal layer 25a. In another embodiment, the first porous metal layer 25a is made of Au, Ag, Cu, Zn or a porous alloy formed by at least two components of Au, Ag, Cu and Zn but is not limited thereto.
With reference to FIGS. 1C and 2B, a second embodiment of a surface mount fuse is shown. In the second embodiment, a first porous metal layer 25 of a fuse element 20 is formed as a frame and a first flux layer 24 is be formed on a peripheral area of the third surface 23 of the lead-free flat fuse 21. The first porous metal layer 25 is bonded on the peripheral area of the third surface 23 of the lead-free flat fuse 21 through the first flux layer 24. A chamber 230 is defined among the third surface 23, the first flux layer 24, and the first porous metal layer 25. The third flux layer 26 may fill in the chamber 230 to limit a position of the third flux layer 26. In one embodiment, the third flux layer 26 may further cover a top surface of the first porous metal layer 25. In the present embodiment, the frame-shaped first porous metal layer 25 has two opposite first frame strips 27 and two opposite second frame strips 28. As shown in FIG. 1C, the two first frame strips 27 respectively correspond to the two electrodes 14 of the base 10 and the second frame strips 28 are respectively connected between the two first frame strips 27. In the present embodiment, a width of each first frame strip 27 may be equal to that of each second frame strip 28 or may be different from that of each second frame strip 28, as shown in FIG. 3. For example, in FIG. 3, the first frame strip 27 has a first width W1 and the second frame strip 28a has a second width W2. The second width is less than the first width W1 to shorten a melting time when overcurrent occurs. In the present embodiment, a fracture by melting of each second frame strip 28 is usually formed between each electrode 14 and the heater 15 or in the gap D, as shown in FIG. 1C. Therefore, as shown in FIG. 4, at least one notch 29 may be further formed on a fracture by melting each second frame strip 28b of another frame-shaped first porous metal layer 25 and a width of the fracture by melting is narrower, thereby to shorten a melting time when overcurrent occurs. In one embodiment, two notches 29 are formed on the fracture by melting of each second frame strip 28b.
With reference to FIGS. 1A and 1C, the hollow cover 30 is mounted on the first surface 12 of the base 10 and is made of an electrical insulating material. The hollow cover 30 covers the fuse element 20a, 20. In particular, the hollow cover 30 is mounted on the first surface 12 of the base and located outside the two electrodes.
With reference to FIGS. 5 and 6, a third embodiment of a surface mount fuse is shown and similar to the second embodiment of FIG. 1C. The difference in the third embodiment is that a fuse element 20′ further has a second flux layer 24′ and a second porous metal layer 25′. The second flux layer 24′ is formed on a peripheral area of the second 22 of the lead-free flat fuse 21. The second porous metal layer 25′ stacks on the second flux layer 24′ and a part of the flux layer 24′ penetrates into the second porous metal layer 25′. The second porous metal layer 25′ is bonded on the peripheral area of the second surface 22 of the lead-free flat fuse 21 through the second flux layer 24′. As shown in FIG. 5, the second porous metal layer 25′ lies across the two electrodes 14 and contacts the second conductive layer 19. The second porous metal layer 25′ is electrically connected to the two electrodes 14 and the heater 15. In one embodiment, the second porous metal layer 25′ may be the same as the second porous metal layer 25 of FIG. 1C and has two opposite third frame strip 27′ and two opposite fourth frame strip 28′. Each fourth frame strip 28′ may be the same as the second frame strip 28a of FIG. 3 and the second frame strip 28b of FIG. 4. In addition, the second surface of the lead-free flat fuse 21 of the fuse element 20a may be bonded to a second porous metal layer matching the first porous metal layer 25a through a second flux layer.
Based on the foregoing description, the surface mount fuse as described mainly forms the first flux layer on the lead-free flat fuse and then stacks the first porous metal layer on the first flux layer. Therefore, a part of the first flux layer penetrates into the first porous metal layer through capillary action. Since the flux fills the pores of the first porous metal layer to distribute on the lead-free flat fuse evenly, the flux in the surface mount fuse as described is evenly distributed and is sufficient. A bonding strength therebetween is also enhanced. When overcurrent occurs in the current loop and high temperature occurs, the first flux layer helps the first porous metal layer and the lead-free flat fuse to melt effectively, thereby interrupting the current loop in time.
Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Patent Application
20250118519
