Surface-mounted fuse and its fuse element member

Abstract

To solve the conventional problem that in a surface mount type fuse using a lead-free fuse element flux cannot uniformly be applied in sufficient quantity and to provide a surface mount type fuse and a fuse element member thereof.SOLUTION: A fuse element member 20a includes a lead-free fuse element 21, a first flux layer 24 and a first porous metal layer 25a. The first porous metal layer 25 is fixed to the surface of the lead-free fuse element 21 by the first flux layer 24. Since part of the first flux layer 24 permeates into the first porous metal layer 25 by capillarity, the pores of the first porous metal layer 25 are filled with flux, which then is uniformly distributed on the surface of the lead-free fuse element 21.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to fuses, and particularly to surface mount fuses and fuse element members thereof.

Background Art

[0002] A surface mount fuse is a component soldered to a circuit board. When an abnormality such as an overcurrent occurs in the current loop on the circuit board, the surface mount fuse cuts off the current loop on the circuit board, thereby protecting the circuit board.

[0003] Conventional surface mount fuses employ a flake fuse element made of a tin-lead alloy having a melting point of about 290°C. By the way, since the use of lead (Pb) is regulated by RoHS (Restriction of the Use of Certain Hazardous Substances Directive), instead of the flake fuse element made of a tin-lead alloy, it has been proposed to employ a flake lead-free fuse element made of a lead-free alloy, for example, a tin-bismuth alloy having a melting point of 245°C to 250°C. However, the melting point of the tin-bismuth alloy is lower than not only the melting point of the tin-lead alloy but also the temperature of the reflow soldering process (for example, 260°C). Therefore, the flake lead-free fuse element made of a tin-bismuth alloy melts during the reflow soldering process and fails to function as a fuse. Thus, as shown in FIG. 8, in a conventional surface mount fuse, a fuse element member having a structure in which a first metal layer 52b and a second metal layer 52a having a melting point higher than the temperature of reflow soldering are respectively disposed on the opposing upper and lower surfaces of a lead-free fuse element 51 is employed. Further, in a conventional surface mount fuse, in order to effectively prevent oxidation of the first metal layer 52b and accelerate its melting, a flux 53 may be applied to the surface of the first metal layer 52b.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above-described conventional surface-mounted fuse, it is difficult to uniformly apply a sufficient amount of flux onto the first metal layer, and there are cases where the lead-free fuse element and the first metal layer cannot be effectively blown to cut off the current loop under high temperatures caused by overcurrent. Therefore, further improvements are required for the conventional surface-mounted fuse.

[0005] The main object of the present invention is to provide a surface-mounted fuse and a fuse element member thereof that solve the conventional problem of being unable to uniformly apply a sufficient amount of flux in a surface-mounted fuse employing a lead-free fuse element.

Means for Solving the Problem

[0006] The surface-mounted fuse according to the present invention provided to achieve the above object of the invention includes a base having a first surface, two electrodes formed on the first surface, and a heater formed on the first surface so as to be positioned between the two electrodes, a fuse element member electrically connected to the two electrodes and the heater of the base, and a hollow lid disposed on the first surface of the base so as to cover the fuse element member therein. The fuse element member includes a lead-free fuse element having a second surface straddling the two electrodes of the base and in contact with the heater, and a third surface located on the opposite side of the second surface, a first flux layer formed on the third surface of the lead-free fuse element, and a first porous metal layer laminated on the first flux layer, the outer peripheral portion of which does not extend beyond the outer peripheral portion of the lead-free fuse element. A part of the first flux layer penetrates into the pores of the first porous metal layer, and the first porous metal layer is adhered to the third surface of the lead-free fuse element by the first flux layer, which is a characteristic point.

[0007] As can be understood from the above description, the main feature of the surface-mounted fuse according to the present invention is that a first flux layer is formed on the lead-free fuse element in the fuse element member, and a first porous metal layer is laminated on the first flux layer. Since a part of the first flux layer penetrates into the first porous metal layer due to capillary action, the flux is filled in the pores of the first porous metal layer, and thereby, it is uniformly distributed on the lead-free fuse element. Therefore, the fuse element member of the surface-mounted fuse according to the present invention has the flux uniformly distributed in a sufficient amount. When an overcurrent occurs in the current loop and the temperature becomes high, the first flux layer effectively promotes the fusing of the first porous metal layer and the lead-free fuse element, so that the current loop can be timely interrupted.

[0008] The fuse element member of the surface-mounted fuse according to the present invention provided to achieve the object of the above invention is a lead-free fuse element having a first surface and a second surface located on opposite sides of each other, a first flux layer formed on the first surface of the lead-free fuse element, a first porous metal layer laminated on the first flux layer, wherein an outer peripheral portion of the first porous metal layer does not extend beyond the outer peripheral portion of the lead-free fuse element, and a part of the first flux layer penetrates into pores of the first porous metal layer, and the first porous metal layer is adhered to the first surface of the lead-free fuse element by the first flux layer, which is characterized.

[0009] As can be understood from the above description, the main feature of the fuse element member of the surface-mounted fuse according to the present invention is that a first flux layer is formed on the first surface of the lead-free fuse element, and a first porous metal layer is laminated on the first flux layer. Since a part of the first flux layer penetrates into the first porous metal layer due to capillary action, the flux is filled in the pores of the first porous metal layer, and thereby, it is uniformly distributed on the first surface of the lead-free fuse element. Therefore, the fuse element member of the surface-mounted fuse according to the present invention has the flux uniformly distributed in a sufficient amount. When an overcurrent occurs in the current loop and the temperature becomes high, the first flux layer effectively promotes the fusing of the first porous metal layer and the lead-free fuse element, so that the current loop can be timely interrupted.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0011] Regarding the improved surface mount fuse and its fuse element member according to the present invention, a plurality of embodiments will be described in detail below with reference to the drawings.

[0012] Figure 1(A) shows a first embodiment of a surface mount fuse according to the present invention. The surface mount fuse includes a base 10, a fuse element member 20a, and a hollow lid 30.

[0013] The base 10 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 so as to be located between the two electrodes 14 and spaced apart from each electrode 14 by a distance D. In an embodiment, as shown in Figure 4, the heater 15 may have a lead-out electrode 16, a first good conductor layer 17, a heat-generating layer 18, and a second good conductor layer 19. The lead-out electrode 16 is located between the two electrodes 14. The first good conductor layer 17 covers the lead-out electrode 16. The heat-generating layer 18 covers the first good conductor layer 17. The second good conductor layer 19 is formed on the heat-generating layer 18. The first good conductor layer 17 and the second good conductor layer 19 are good conductors of electricity and heat.

[0014] The fuse element member 20a has a lead-free fuse element 21, a first flux layer 24, and a first porous metal layer 25a, and is electrically connected to the two electrodes 14 and the heater 15 of the base 10.

[0015] The lead-free fuse element 21 of the fuse element member 20a has a second surface 22 and a third surface 23. The second surface 22 faces the first surface 12 of the base 10 and straddles the two electrodes 14 of the base 10. As shown in FIG. 4, the second surface 22 is in contact with the heater 15. Specifically, the second surface 22 of the lead-free fuse element 21 is in contact with the two electrodes 14 and the second conductive layer 19 of the heater 15. Thereby, the lead-free fuse element 21 is electrically connected to the two electrodes 14 and the heater 15. The third surface 23 of the lead-free fuse element 21 is on the opposite side of the second surface 22 and is spaced apart from the first surface 12 of the base 10. In order to comply with the regulations regarding the use of lead (Pb) in RoHS, in this embodiment, the material of the lead-free fuse element 21 is a lead-free material such as tin (Sn), bismuth (Bi), or a tin-bismuth alloy, but the material of the lead-free fuse element 21 is not limited to these. When a large current flows through the lead-free fuse element 21 due to the occurrence of an overcurrent, a large current also flows through the second conductive layer 19, the heating layer 18, the first conductive layer 17, and the lead-out electrode 16 of the heater 15. Thereby, the heating layer 18 of the heater 15 generates heat. At this time, since the second conductive layer 19 uniformly heats the lead-free fuse element 21, the lead-free fuse element 21 is quickly heated to its melting point and melts.

[0016] As shown in FIG. 3A, the first flux layer 24 is formed on the third surface 23 of the lead-free fuse element 21. In certain embodiments, the material of the first flux layer 24 is rosin, but the material of the first flux layer 24 is not limited thereto. The outer peripheral portion of the first porous metal layer 25a does not extend outward beyond the outer peripheral portion of the lead-free fuse element 21. The first porous metal layer 25a is laminated on the first flux layer 24 and is adhered to the third surface 23 of the lead-free fuse element 21 by the first flux layer 24. A part of the first flux layer 24 penetrates into the first porous metal layer 25a by capillary action, that is, as shown in FIG. 1(B), the flux of the first flux layer 24 is filled in the pores 251 of the first porous metal layer 25a. Thereby, the first flux layer 24 will be uniformly distributed on the third surface 23 of the lead-free fuse element 21. Preferably, the melting point of the first porous metal layer 25a is higher than the melting point of the lead-free fuse element 21. Also, in order to further increase the amount of the flux, a third flux layer 26 may be further formed on the first porous metal layer 25. In certain embodiments, the material of the first porous metal layer 25a is a porous alloy of gold (Au), silver (Ag), copper (Cu), zinc (Zn), or at least two of gold, silver, copper, and zinc, but the material of the first porous metal layer 25a is not limited to these.

[0017] In the second embodiment shown in FIGS. 2 and 3B, the first porous metal layer 25 of the fuse element member 20 is in a frame shape. Therefore, in the present embodiment, the first flux layer 24 of the fuse element member 20 may be formed only on the outer peripheral portion 231 of the third surface 23 of the lead-free fuse element 21. Even in this case, the first porous metal layer 25 is adhered to the outer peripheral portion 231 of the third surface 23 of the lead-free fuse element 21 by the first flux layer 24. In the present embodiment, the accommodation space 230 is defined by the third surface 23 of the lead-free fuse element 21, the first flux layer 24, and the first porous metal layer 25. The third flux layer 26 is filled in the accommodation space 230 so that its position is regulated. In an embodiment, the third flux layer 26 may further cover the upper surface of the first porous metal layer 25. In the present embodiment, the frame-shaped first porous metal layer 25 has two first frame side portions 27 facing each other and two second frame side portions 28 facing each other. As shown in FIG. 2, the two first frame side portions 27 respectively correspond to the two electrodes 14 of the base 10, and the two second frame side portions 28 are respectively connected to the two first frame side portions 27. In the present embodiment, the width of each first frame side portion 27 and the width of each second frame side portion 28 may be the same. Or, like the first porous metal layer 25 having other shapes in the third embodiment shown in FIG. 4, the widths of the two opposing first frame side portions 27 and the widths of the two opposing second frame side portions 28a may not be the same. For example, each first frame side portion 27 has a first width W1, while each second frame side portion 28a has a second width W2 smaller than the first width W1 so that the fusing speed is increased when an overcurrent occurs. In the present embodiment, the fusing of each second frame side portion 28 is likely to occur between the heater 15 and each electrode 14, that is, within the range of the two intervals D shown in FIG. 2. Therefore, in the first porous metal layer 25 having other shapes in the fourth embodiment shown in FIG. 5, at least one notch 29 is formed at a location where fusing is likely to occur in each second frame side portion 28b to narrow the width of the location and increase the fusing speed when an overcurrent occurs. Preferably, two notches 29 are formed at locations where fusing is likely to occur in each second frame side portion 28b.

[0018] As shown in FIG. 1(A) and FIG. 2, the hollow lid 30 is disposed on the first surface 12 of the base 10 so as to cover the fuse element members 20a and 20 therein. The material of the hollow lid 30 is an electrical insulating material. Specifically, the hollow lid 30 is disposed on the first surface 12 of the base 10 outside the two electrodes 14.

[0019] FIGS. 6 and 7 show a fifth embodiment of the surface mount fuse according to the present invention. The surface mount fuse of this embodiment has substantially the same structure as the surface mount fuse of the second embodiment according to the present invention shown in FIG. 2, except for the points described below. In the surface mount fuse of this embodiment, the fuse element member 20' further has a second flux layer 24' and a second porous metal layer 25'. The second flux layer 24' is formed on the outer peripheral portion of the second surface 22 of the lead-free fuse element 21. The second porous metal layer 25' is laminated on the second flux layer 24'. The second porous metal layer 25' is adhered to the outer peripheral portion of the second surface 22 of the lead-free fuse element 21 by the second flux layer 24' by a part of the second flux layer 24' penetrating into the second porous metal layer 25'. As shown in FIG. 6, the second porous metal layer 25' straddles the two electrodes 14 of the base 10 and abuts on the second good conductor layer 19 of the heater 15. Thereby, the second porous metal layer 25' is electrically connected to the two electrodes 14 and the heater 15. In an embodiment, the second porous metal layer 25' may have the same structure as the first porous metal layer 25 shown in FIG. 2. That is, the second porous metal layer 25' may have two third frame side portions 27' facing each other and two fourth frame side portions 28' facing each other, and each fourth frame side portion 28' may be the same as the second frame side portions 28a and 28b shown in FIGS. 4 and 5. Note that, similarly for the fuse element member 20a shown in FIG. 3A, a second porous metal layer (not shown) corresponding to the first porous metal layer may be adhered to the second surface of the lead-free fuse element 21 by a second flux layer (not shown).

[0020] As can be understood from the above description, the main features of the surface-mounted fuse and its fuse element member according to the present invention are that a first flux layer is formed on the third surface of the lead-free fuse element in the fuse element member, and a first porous metal layer is laminated on the first flux layer. Since a part of the first flux layer penetrates into the first porous metal layer due to capillary action, the flux fills the pores of the first porous metal layer, and thereby, it is uniformly distributed on the third surface of the lead-free fuse element. Further, the amount of the flux can be increased and the adhesive strength between the first porous metal layer and the lead-free fuse element can be improved. Therefore, the fuse element member of the surface-mounted fuse according to the present invention has a sufficient amount of flux uniformly distributed. When an overcurrent occurs in the current loop and the temperature becomes high, the first flux layer effectively promotes the fusing of the first porous metal layer and the lead-free fuse element, so that the current loop can be timely interrupted.

[0021] Although the present invention has been described with reference to the above embodiments, the present invention is not limited to these disclosed embodiments, and those skilled in the art can make various changes and modifications without departing from the technical idea of the present invention and make equivalents thereof. Therefore, the content obtained by making changes, modifications and improvements to the above embodiments is also included in the technical idea of the present invention.

Description of Reference Numerals

[0022] 10 Base 12 First Surface 14 Electrode 15 Heater 16 Lead-out Electrode 17 First Good Conductor Layer 18 Heat Generation Layer 19 Second Good Conductor Layer 20, 20a, 20’ Fuse Element Member 21 Lead-free Fuse Element 22 Second Surface 23 Third Surface 230 Accommodation Space 231 Outer Peripheral Portion 24 First Flux Layer 24’ Second Flux Layer 25, 25a First porous metal layer 251 Pores 25’ Second porous metal layer 26 Third flux layer 27 First frame side portion 27’ Third frame side portion 28, 28a, 28b Second frame side portion 28’ Fourth frame side portion 29 Notch 30 Hollow cover 51 Lead-free fuse element 52a Second metal layer 52b First metal layer 53 Flux

Claims

1. A lead-free fuse element having a first surface and a second surface located on opposite sides of each other; A first flux layer formed on the first surface of the lead-free fuse element; A first porous metal layer laminated on the first flux layer, wherein an outer peripheral portion of the first porous metal layer does not extend beyond an outer peripheral portion of the lead-free fuse element; and A melting point of the first porous metal layer is higher than a melting point of the lead-free fuse element, A part of the first flux layer penetrates into pores of the first porous metal layer, and the first porous metal layer is adhered to the first surface of the lead-free fuse element by the first flux layer. A fuse element member of a surface mount fuse.

2. The first flux layer is formed on an outer peripheral portion of the first surface of the lead-free fuse element, The first porous metal layer has a frame shape having two first frame side portions facing each other and two second frame side portions facing each other and respectively connected to the two first frame side portions, Each of the first frame side portions has a first width, Each of the second frame side portions has a second width that is the same as or smaller than the first width. A fuse element member of the surface mount fuse according to claim 1.

3. The first flux layer is formed on an outer peripheral portion of the first surface of the lead-free fuse element, The first porous metal layer has a frame shape having two first frame side portions facing each other and two second frame side portions facing each other and respectively connected to the two first frame side portions, At least one notch is formed in each of the portions of each of the second frame side portions adjacent to the two first frame side portions. A fuse element member of the surface mount fuse according to claim 1.

4. The fuse element member of the surface mount fuse according to claim 1, further comprising a third flux layer formed on the upper surface of the first porous metal layer.

5. The fuse element member of the surface mount fuse according to claim 2 or 3, further comprising a third flux layer filled in the accommodation space defined by the first surface of the lead-free fuse element, the first flux layer, and the first porous metal layer.

6. A second flux layer formed on the second surface of the lead-free fuse element, and a second porous metal layer laminated on the second flux layer, a part of the second flux layer penetrates into the pores of the second porous metal layer, and the second porous metal layer is adhered to the second surface of the lead-free fuse element by the second flux layer, The fuse element member of the surface mount fuse according to any one of claims 1 to 4, wherein the melting point of the second porous metal layer is higher than the melting point of the lead-free fuse element.

7. The second flux layer is formed on the outer peripheral portion of the second surface of the lead-free fuse element, the second porous metal layer has a frame shape having two third frame side portions facing each other and two fourth frame side portions facing each other and respectively connected to the two third frame side portions, each of the third frame side portions has a first width, each of the fourth frame side portions has a second width that is the same as or smaller than the first width of the third frame side portion. The fuse element member of the surface mount fuse according to claim 6.

8. The second flux layer is formed on the outer peripheral portion of the second surface of the lead-free fuse element, the second porous metal layer has a frame shape having two third frame side portions facing each other and two fourth frame side portions facing each other and respectively connected to the two third frame side portions, The fuse element member of the surface mount fuse according to claim 6, wherein at least one notch is formed in each of the portions of each of the fourth frame side portions adjacent to the two third frame side portions.

9. The material of the lead-free fuse element is tin (Sn), bismuth (Bi), or a tin-bismuth alloy, The materials of the first flux layer and the third flux layer are rosin, The material of the first porous metal layer is gold (Au), silver (Ag), copper (Cu), zinc (Zn), or a porous alloy of at least two of gold, silver, copper, and zinc. The fuse element member of the surface mount fuse according to claim 4.

10. A base having a first surface, two electrodes formed on the first surface, and a heater formed on the first surface so as to be located between the two electrodes, The fuse element member according to any one of claims 1 to 4 and 9, wherein the second surface of the lead-free fuse element straddles the two electrodes of the base and abuts against the heater, A surface mount fuse including a hollow lid disposed on the first surface of the base so as to cover the fuse element member therein.

11. The heater is, A lead-out electrode formed on the first surface of the base so as to be located between the two electrodes, A first good conductor layer formed on the first surface of the base so as to cover the lead-out electrode, A heat-generating layer formed on the first surface of the base so as to cover the first good conductor layer, The surface mount fuse according to claim 10, having a second good conductor layer formed on the heat-generating layer and abutting against the second surface of the lead-free fuse element in the fuse element member.

Images