FUSE ELEMENT, FUSE DEVICE, AND PROTECTION DEVICE

Abstract

A fuse element is a fuse element (1) including a flat plate-shaped blowout section (1e) with no through-hole disposed between a first terminal (20a) and a second terminal (20b), in which a width (1d) of the blowout section (1e) has a length equal to or greater than 80% of a width (2d) of each of joining portions joining the first terminal (20a) and the second terminal (20b) to the blowout section (1e). The width (1d) of the blowout section (1e) is preferably a length equal to or greater than 95% of the width (2d) of each of the joining portions.

Claims

1. A fuse element comprising: a flat plate-shaped blowout section with no through-hole disposed between a first terminal and a second terminal, wherein a width of the blowout section has a length equal to or greater than 100% of a width of each of joining portions joining the first terminal and the second terminal to the blowout section.

2. (canceled)

3. The fuse element according to claim 1, wherein a blowout temperature of the blowout section is 140° C. to 400° C.

4. The fuse element according to claim 1, wherein the blowout section is formed by laminating a low melting-point metal layer and a high melting-point metal layer having a melting point higher than the low melting metal layer in a thickness direction.

5. The fuse element according to claim 4, wherein the low melting-point metal layer is composed of Sn or an alloy containing Sn as a primary constituent, and the high melting-point metal layer is composed of any one selected from Ag, Cu, an alloy containing Ag as a primary constituent, and an alloy containing Cu as a primary constituent.

6. The fuse element according to claim 4, wherein the blowout section is composed of the low melting-point metal layer and the high melting-point metal layers laminated on both surfaces of the low melting-point metal layer.

7. The fuse element according to claim 1, wherein the width of the blowout section is a length equal to or less than 200% of the width of each of the joining portions.

8. The fuse element according to claim 1, wherein the blowout section is joined to the first terminal and the second terminal by a conductive connection member.

9. A fuse device comprising: the fuse element according to claim 1.

10. The fuse device according to claim 9, wherein the first terminal and the second terminal are disposed on a front surface of an insulating substrate.

11. A protection device comprising: the element according to claim 1; and a heat-generating element configured to heat the fuse element to be blown out, wherein the first terminal and the second terminal are disposed on an insulating substrate, and the fuse element is disposed across the first terminal and the second terminal.

12. The fuse element according to claim 6, wherein side surfaces of the blowout section on each side joining to the first terminal and the second terminal are coated with high melting-point metal layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1(a) is a plan view showing a fuse device of a first embodiment, and FIG. 1(b) is a sectional view along the line A-A′ of the fuse device shown in FIG. 1(a).

[0036] FIG. 2(a) is a plan view showing a fuse device of a second embodiment. FIG. 2(b) is a side view of the fuse device shown in FIG. 2(a) from a lower side of FIG. 2(a). FIG. 2(c) is a side view of the fuse device shown in FIG. 2(a) from a right side of FIG. 2(a).

[0037] FIG. 3(a) is a plan view of a fuse device of a third embodiment. FIG. 3(b) is a side view of the fuse device shown in FIG. 3(a) from a lower side of FIG. 3(a). FIG. 3(c) is a side view of the fuse device shown in FIG. 3(a) from a right side of FIG. 3(a). FIG. 3(d) is a perspective view showing a fuse element provided in the fuse device shown in FIG. 3(a).

[0038] FIG. 4(a) is a plan view showing a fuse device of a fourth embodiment. FIG. 4(b) is a side view of the fuse device shown in FIG. 4(a) from a lower side of FIG. 4(a). FIG. 4(c) is a side view of the fuse device shown in FIG. 4(a) from a right side of FIG. 4(a).

[0039] FIG. 5(a) is a plan view showing a protection device of a fifth embodiment. FIG. 5(b) is a sectional view along the line B-B′ of the protection device shown in FIG. 5(a). FIG. 5(c) is a side view of the protection device shown in FIG. 5(a) from a right side of FIG. 5(a).

[0040] FIG. 6(a) is a plan view showing a protection device of a sixth embodiment. FIG. 6(b) is a side view of the protection device shown in FIG. 6(a) from a lower side of FIG. 6(a). FIG. 6(c) is a side view of the protection device shown in FIG. 6(a) from a right side of FIG. 6(a).

DESCRIPTION OF EMBODIMENTS

[0041] Hereinafter, a fuse element, a fuse device, and a protection device according to the invention will be described in detail appropriately referring to the drawings. The drawings used in the following descriptions may be drawn with feature portions enlarged for convenience to facilitate understanding of the features of the invention, and dimensional ratios and the like between the constituent elements may differ from the actual values. Materials, dimensions, and the like exemplified in the following description are merely examples, which are not intended to limit the invention, and can be appropriately changed within a range in which effects of the invention are obtained.

First Embodiment (Fuse Device)

[0042] FIG. 1(a) is a plan view showing a fuse device of a first embodiment, and FIG. 1(b) is a sectional view along the line A-A′ of the fuse device shown in FIG. 1(a).

[0043] As shown in FIG. 1(a), a fuse device 10 of the embodiment has a first terminal 20a, a second terminal 20b, and a fuse element 1 of the embodiment composed of a blowout section 1e disposed between the first terminal 20a and the second terminal 20b.

(Fuse Element)

[0044] The fuse element 1 provided in the fuse device 10 of the embodiment is composed of the blowout section 1e. The fuse element 1 electrically connects the first terminal 20a and the second terminal 20b. The blowout section 1e (fuse element 1) is joined to the first terminal 20a and the second terminal 20b by a conductive connection member, such as solder, to be electrically connected.

[0045] As shown in FIG. 1(a), the blowout section 1e is a flat plate-shaped section with no through-hole, and the thickness of which is substantially constant. As shown in FIG. 1(a), the blowout section 1e has a substantially rectangular shape in a plan view having a direction connecting the first terminal 20a and the second terminal 20b as a long side and a direction substantially perpendicular to the direction connecting the first terminal 20a and the second terminal 20b (hereinafter, also referred to as a “width direction”) as a short side.

[0046] In the fuse device 10 shown in FIG. 1(a), although a case where the blowout section 1e includes the fuse element 1 having a substantially rectangular shape in a plan view has been described as an example, the shape of the blowout section of the fuse element is not limited to the substantially rectangular shape in a plan view. For example, a width and a thickness of the blowout section 1e may not be constant.

[0047] A blowout temperature of the blowout section 1e is preferably 140° C. to 400° C. In a case where the blowout temperature of the blowout section 1e is equal to or higher than 140° C., preferably, the fuse device 10 is not blown out at a normally used temperature. In a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., the first terminal 20a and the second terminal 20b can be prevented from reaching a high temperature at the time of blowout and negatively affecting members connected to the first terminal 20a and the second terminal 20b.

[0048] In the fuse device 10 of the embodiment, as shown in FIG. 1(b), the blowout section 1e (fuse element 1) is preferably formed of a flat plate-shaped low-melting-point metal layer 1a having a rectangular shape in sectional view and a high melting metal layer 1b laminated in such a manner that the entire surface of the low-melting-point metal layer 1a is coated at a substantially constant thickness. In this case, as shown in FIG. 1(b), the blowout section 1e has a three-layered structure composed of the low-melting-point metal layer 1a and high-melting-point metal layers 1b laminated on both surfaces of the low-melting-point metal layer 1a in a thickness direction, and all side surfaces of the low-melting-point metal layer 1a are coated with the high-melting-point metal layers 1b. For this reason, leakage of the low-melting-point metal layer 1a from the blowout section 1e or inflow of the conductive connection member, such as solder, into the blowout section 1e due to heating at the time of reflow in a manufacturing process of the fuse device 10 is suppressed. As a result, fluctuation of a resistance value of the blowout section 1e due to deformation of the blowout section 1e (fuse element 1) at the time of the reflow in the manufacturing process of the fuse device 10 is suppressed, and the fuse device 10 having a stable blowout characteristic can be easily manufactured.

[0049] The low-melting-point metal layer 1a is preferably composed of Sn or an alloy containing Sn as a primary constituent. The content of Sn in the alloy containing Sn as a primary constituent is preferably equal to or greater than 50 mass %, and more preferably, equal to or greater than 60% by mass. Examples of the alloy containing Sn as a primary constituent include a Sn—Bi alloy, an In—Sn alloy, and a Sn—Ag—Cu alloy.

[0050] The high-melting-point metal layer 1b is preferably a layer having a higher melting point than the low-melting-point metal layer 1a and is a layer composed of a metal material that is dissolved by a molten material of the low-melting-point metal layer 1b.

[0051] The melting point of the high-melting-point metal layer 1b is preferably within a range of a temperature at least 100° C. higher than the melting point of the low-melting-point metal layer 1a and equal to or lower than a temperature 900° C. higher than the melting point of the low-melting-point metal layer 1a.

[0052] The high-melting-point metal layer 1b is preferably composed of any one selected from Ag, Cu, an alloy containing Ag as a primary constituent, and an alloy containing Cu as a primary constituent, and more preferably, composed of Ag or an alloy containing Ag as a primary constituent. The content of Ag in the alloy containing Ag as a primary constituent is preferably equal to or greater than 50% by mass, and more preferably, equal to or greater than 60% by mass. Examples of the alloy containing Ag as a primary constituent include a silver-palladium alloy. Ag is a noble metal, has a low ionization tendency, is not easily oxidized in the atmosphere, and is easily dissolved by the molten material of the low-melting-point metal layer 1a. For this reason, Ag or the alloy containing Ag as a primary constituent is suitably used as the material of the high-melting-point metal layer 1b.

[0053] The blowout section 1e (fuse element 1) can be made, for example, in such a manner that the low-melting-point metal layer 1a is composed of an alloy containing Sn as a primary constituent, the high-melting-point metal layer 1b is composed of Ag, and a ratio of the thickness of the low-melting-point metal layer 1a to the total thickness of the high-melting-point metal layers 1b (low-melting-point metal layer 1a:high-melting-point metal layers 1b) is 1:1 to 50:1. The blowout section 1e has the blowout temperature of 140° C. to 400° C.

[0054] The blowout section 1e (fuse element 1) has volume resistivity (specific resistance) of about 7.4 μΩ.Math.cm in a case where the low-melting-point metal layer 1a is composed of the alloy containing Sn as a primary constituent, the high-melting-point metal layer 1b is composed of Ag, and the ratio (low-melting-point metal layer 1a:high-melting-point metal layer 1b) of the thickness of the low-melting-point metal layer 1a to the total thickness of the high-melting-point metal layers 1b is 10:1.

[0055] The fuse element 1 can be manufactured, for example, using a plating method. Specifically, a metal foil having a shape corresponding to the low-melting-point metal layer 1a of the fuse element 1 is prepared, and the high-melting-point metal layer 1b is formed on the entire surface of the metal foil using a plating method. With this, the flat plate-shaped fuse element 1 in which the entire surface of the low-melting-point metal layer 1a is coated with the high-melting-point metal layer 1b having a substantially constant thickness is obtained.

(First Terminal, Second Terminal)

[0056] In using the fuse device 10, the first terminal 20a and the second terminal 20b are joined to terminal sections of an electric circuit (not shown) to be electrically connected to the electric circuit. As shown in FIG. 1(a), an attachment hole 3a composed of a circular through-hole is provided in a center portion of the first terminal 20a. Similarly to the first terminal 20a, an attachment hole 3b composed of a circular through-hole is provided in a center portion of the second terminal 20b. The fuse device 10 of the embodiment is attachably and detachably attached at a predetermined position using joining members, such as bolts, and the attachment holes 3a and 3b.

[0057] As shown in FIG. 1(a), widths 2d of joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e are identical. Planar shapes of the first terminal 20a and the second terminal 20b are substantially symmetric with the blowout section 1e sandwiched therebetween and are substantially symmetric with respect to a center of the blowout section 1e in a width 1d direction.

[0058] The planar shapes of the first terminal 20a and the second terminal 20b are not limited to the example shown in FIG. 1(a). For example, planar shapes of the attachment holes 3a and 3b are not limited to circular shapes, and may be elliptical shapes, polygonal shapes, and the like. Instead of the attachment holes 3a and 3b, notches may be provided such that the first terminal 20a and the second terminal 20b have a C-shape in a plan view. In a case where the widths 2d of the joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e are identical, the planar shapes of the first terminal 20a and the second terminal 20b may not be substantially symmetric with the blowout section 1e sandwiched therebetween or may not be substantially symmetric with respect to the center of the blowout section 1e in the width 1d direction.

[0059] The first terminal 20a and the second terminal 20b are formed of a material having conductivity. For example, the first terminal 20a and the second terminal 20b can be composed of Cu or an alloy containing Cu as a primary constituent. Examples of the alloy containing Cu as a primary constituent include a Cu—Ni alloy.

[0060] In the fuse device 10 of the embodiment, as shown in FIG. 1(a), the width 1d of the blowout section 1e in a plan view has a length ({1d/2d}×100≥80 (%)) equal to or greater than 80% of the width 2d of each of the joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e, is preferably a length equal to or greater than 95% of the width 2d of each of the joining portions, and more preferably exceeds 100% of the width 2d of each of the joining portions.

[0061] In the specification, the width 1d of the blowout section 1e in a case where the length of the blowout section in the width direction is not constant is a length of a portion having a shortest length in the width direction. The width 2d of each of the joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e is a length parallel to the width 1d of the blowout section 1e in each of portions of the first terminal 20a and the second terminal 20b closest to the blowout section 1e.

[0062] In a case where the width 1d of the blowout section 1e is the length equal to or greater than 80% described above, an effect of decreasing the resistance of the blowout section 1e due to the large the width 1d of the blowout section 1e is sufficiently obtained. The width 1d of the blowout section 1e is preferably equal to or less than 200% of the width 2d of each of the joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e, and more preferably, equal to or less than 150%. In a case where the width 1d of the blowout section 1e is the length equal to or less than 200% described above, an influence on a reduction in size of the fuse device 10 can be suppressed due to the excessive width 1d of the blowout section 1e.

[0063] The fuse device 10 shown in FIGS. 1(a) and 1(b) can be manufactured by a known method. For example, the fuse device 10 can be manufactured by a method in which the fuse element 1 (blowout section 1e) is joined to the first terminal 20a and the second terminal 20b by a conductive connection member, such as solder, to be electrically connected.

[0064] The blowout section 1e of the fuse device 10 of the embodiment is not blown out while a rated current flows through an electric circuit joined thereto through the first terminal 20a and the second terminal 20b. In a case where an overcurrent exceeding the rated current flows through the above-described electric circuit, the blowout section 1e is blown out, the first terminal 20a and the second terminal 20b are disconnected, and a current path of the electric circuit is cut off

[0065] In a case where the blowout section 1e is formed in such a manner that the low-melting-point metal layer 1a and the high-melting-point metal layer 1b are laminated in the thickness direction, and in a case where an overcurrent exceeding the rated current flows through the electric circuit, the low-melting-point metal layer 1a of the blowout section 1e generates heat and is melted, the high-melting-point metal layer 1b is dissolved by a generated molten material of the low-melting-point metal layer 1a, and the blowout section 1 is quickly blown out.

[0066] The fuse device 10 of the embodiment in which the width 1d of the blowout section 1e is the length equal to or greater than 80% of the width 2d of each of the joining portions joining the first terminal 20a and the second terminal 20b to the blowout section 1e has the blowout section 1e that has the large width 1d and low resistance, and can thus contribute to an increase in rated current.

[0067] In a case where the blowout temperature of the blowout section 1e in the fuse device 10 of the embodiment is equal to or lower than 400° C., the first terminal 20a and the second terminal 20b can be prevented from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first terminal 20a and the second terminal 20b, and an electronic apparatus to which the fuse device 10 is attached can be restrained from exceeding a heat resistance temperature. Accordingly, in a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., there is no need to provide a plurality of small holes in the blowout section or to thin the width of the blowout section to form a local heat-generating point such that the first terminal 20a and the second terminal 20b are not excessively heated.

[0068] In a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., there is no need to form a heat-generating point in the blowout section 1e and increase the length of the blowout section 1e to increase a distance between the heat-generating point and each of the first terminal 20a and the second terminal 20b such that the first terminal 20a and the second terminal 20b are not excessively heated. Accordingly, in a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., the length of the blowout section 1e (the distance between the first terminal 20a and the second terminal 20b) can be reduced, compared to a case where the blowout temperature of the blowout section 1e exceeds 400° C.

[0069] The length and the resistance value of the blowout section 1e (fuse element 1) have a proportional relationship. Accordingly, as the length of the fuse element 1 is reduced, the resistance value of the fuse element 1 decreases. As described above, in a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., it is possible to reduce the length of the blowout section 1e, compared to a case where the blowout temperature of the blowout section 1e exceeds 400° C. Thus, it is possible to make the blowout section 1e that is small in size and has lower resistance. As a result, the size of the fuse device 10 can be reduced and the rated current can be further increased.

[0070] In a case where the blowout temperature of the blowout section 1e is equal to or lower than 400° C., the length of the blowout section 1e can be reduced. For this reason, the resistance value of the blowout section 1e can be decreased and the rated current can be increased even though the blowout section 1e is formed of a material having high volume resistivity, for example, compared to a fuse element (volume resistivity 1.62 μΩ.Math.m) that is composed of copper since the melting point (1085° C.) is high and the blowout temperature of the blowout section exceeds 400° C.

Second Embodiment (Fuse Device)

[0071] FIG. 2(a) is a plan view showing a fuse device of a second embodiment. FIG. 2(b) is a side view of the fuse device shown in FIG. 2(a) from a lower side of FIG. 2(a). FIG. 2(c) is a side view of the fuse device shown in FIG. 2(a) from a right side of FIG. 2(a). FIGS. 2(a) and 2(c) show a state in which a cover member 5 of a fuse device 20 shown in FIG. 2(b) is removed.

[0072] As shown in FIGS. 2(a) to 2(c), the fuse device 20 includes a fuse element 11, an insulating substrate 4, and a first electrode 2a and a second electrode 2b disposed on a front surface 4a of the insulating substrate 4. Each of the first electrode 2a and the second electrode 2b functions as a terminal that is conductively connected to the fuse element 11.

[0073] A difference between the fuse element 11 provided in the fuse device 20 of the second embodiment shown in FIGS. 2(a) to 2(c) and the fuse element 1 provided in the first embodiment is only that, in the fuse element 11 shown in FIGS. 2(a) to 2(c), side surfaces in a direction connecting the first electrode 2a and the second electrode 2b are not coated with the high-melting-point metal layer 1b, and the low-melting-point metal layer 1a is exposed on the side surfaces. Accordingly, the fuse element 11 provided in the fuse device 20 of the second embodiment has the same materials and layer structure as the fuse element 1 provided in the first embodiment. For this reason, the fuse element 11 provided in the second embodiment will be described focusing on only a difference from the fuse element 1 provided in the first embodiment.

[0074] In the fuse device 20 of the embodiment, as shown in FIGS. 2(a) and 2(b), the fuse element 11 has a blowout section 11e disposed between the first electrode 2a and the second electrode 2b, a first joint portion 11f joined onto the first electrode 2a by a conductive connection member (not shown), such as solder, and a second joint portion 11g joined onto the second electrode 2a by a conductive connection member (not shown), such as solder. As shown in FIG. 2(b), a space is formed between the blowout section 11e and the front surface 4a of the insulating substrate 4.

[0075] In the fuse element 11 provided in the fuse device 20 of the second embodiment, as shown in FIG. 2(b), a side surface that is joined to the first electrode 2a or the second electrode 2b is coated with the high-melting-point metal layer 1b. For this reason, leakage of the low-melting-point metal layer 1a from the blowout section 11e or inflow of the conductive connection member, such as solder, into the blowout section 11e due to heating at the time of reflow in a manufacturing process of the fuse device 20 is suppressed. As a result, fluctuation of the resistance value of the blowout section 11e due to deformation of the blowout section 11e (fuse element 11) at the time of the reflow in the manufacturing process of the fuse device 20 is suppressed, and the fuse device 20 having stable blowout characteristics can be easily manufactured.

[0076] The fuse element 11 can be manufactured, for example, using an electroless plating method. Specifically, a band-shaped (ribbon-shaped) metal foil that will become the low-melting-point metal layer 1a is prepared. As the metal foil, a metal foil having a width corresponding to the length of the low-melting-point metal layer 1a of the fuse element 11 in the direction connecting the first electrode 2a and the second electrode 2b is used. Next, the high-melting-point metal layer 1b is formed on the surface of the metal foil using an electroless plating method, and a band-shaped laminate is obtained. Thereafter, the length of the band-shaped laminate is cut at a predetermined dimension to be made into a flat plate shape. With this, the fuse element 11 that has a predetermined rectangular shape and in which the low-melting-point metal layer 1a is exposed on cut sections is obtained. This manufacturing method is particularly suitable for a case of manufacturing a small-sized fuse element.

[0077] Even in the fuse device 20 of the embodiment, as in the first embodiment, as shown in FIG. 2(c), a width 1d of the blowout section 11e in the plan view has a length ({1d/2d}×100≥80 (%)) equal to or greater than 80% of a width 2d of each of joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e, is preferably a length equal to or greater than 95% of the width 2d of each of the joining portions, and is more preferably a length exceeding 100% of the width 2d of each of the joining portions.

[0078] In the fuse element 11 provided in the fuse device 20 of the embodiment, the low-melting-point metal layer 1a is exposed on the side surfaces in the direction connecting the first electrode 2a and the second electrode 2b. That is, the low-melting-point metal layer 1a is exposed on the surfaces of the fuse element 11 in a direction substantially perpendicular to the direction connecting the first electrode 2a and the second electrode 2b. For this reason, the width 1d of the blowout section 11e in a plan view is more preferably a length exceeding 100% of the width 2d of the joining portion joining the first electrode 2a or the second electrode 2b to the blowout section 11e (the width 1d is greater than the width 2d) for the following reason. It is possible to more effectively suppress the contact of the conductive connection member, such as solder, and the low-melting-point metal layer 1a of the fuse element 11 at the time of the reflow in the manufacturing process of the fuse device 20 with the high-melting-point metal layer 1b with which the side surfaces of the fuse element 11 joined to the first electrode 2a and the second electrode 2b are coated. As a result, fluctuation of the resistance value of the blowout section 11e due to deformation of the blowout section 11e (fuse element 11) at the time of the reflow is suppressed, and the fuse device 20 having stable blowout characteristics can be easily manufactured.

[0079] The insulating substrate 4 is not particularly limited as long as the insulating substrate has electrical insulation, and, for example, a known insulating substrate that is used as a circuit board, such as a resin substrate, a ceramic substrate, or a composite substrate of a resin and a ceramic can be used. Specific examples of the resin substrate include an epoxy resin substrate, a phenol resin substrate, and a polyimide substrate. Specific examples of the ceramic substrate include an alumina substrate, a glass ceramic substrate, a mullite substrate, and a zirconia substrate. Specific examples of the composite substrate include a glass epoxy substrate.

[0080] The first electrode 2a and the second electrode 2b are disposed at a pair of facing end portions of the insulating substrate 4. Each of the first electrode 2a and the second electrode 2b is formed of a conductive pattern, such as Ag wiring or Cu wiring.

[0081] Each of the surfaces of the first electrode 2a and the second electrode 2b may be coated with an electrode protection layer to suppress changes in electrode characteristics due to oxidation or the like. As a material of the electrode protection layer, a Sn-plated film, a Ni/Au-plated film, a Ni/Pd-plated film, a Ni/Pd/Au-plated film, or the like can be used.

[0082] The first electrode 2a and the second electrode 2b are electrically connected to a first external connection electrode 42a and a second external connection electrode 42b formed on a rear surface 4b of the insulating substrate 4 through castellations 21a and 21b, respectively. The connection of the first electrode 2a and the first external connection electrode 42a and the connection of the second electrode 2b and the second external connection electrode 42b may be performed through through-holes.

[0083] In the fuse device 20 of the embodiment, as shown in FIG. 2(b), the cover member 5 is preferably attached through an adhesive. With the attachment of the cover member 5, the inside of the fuse device 20 is protected, and scattering of a molten material generated in a case where the fuse element 11 is blown out can be prevented. As a material of the cover member 5, various engineering plastics and/or ceramics can be used.

[0084] The fuse device 20 of the embodiment is mounted on a current path of the circuit board (not shown) through the first external connection electrode 42a and the second external connection electrode 42b for use. While a rated current is flowing to the current path of the circuit board, the blowout section 11e of the fuse element 11 provided in the fuse device 20 is not blown out. In a case where an overcurrent exceeding the rated current flows through the current path of the circuit board, the blowout section 11e is blown out, whereby the first electrode 2a and the second electrode 2b are disconnected and the current path of the circuit board is cut off

[0085] In a case where the blowout section 11e is formed in such a manner that the low-melting-point metal layer 1a and the high-melting-point metal layer 1b are laminated in the thickness direction, and in a case where the overcurrent exceeding the rated current flows through the current path of the circuit board, the low-melting-point metal layer 1a of the blowout section 11e generates heat to be melted, the high-melting-point metal layer 1b is dissolved by a generated molten material of the low-melting-point metal layer 1a, and the blowout section 11e is quickly blown out.

[0086] Similarly to the fuse device 10 of the first embodiment, the fuse device 20 of the embodiment in which the width 1d of the blowout section 11e is the length equal to or greater than 80% of the width 2d of each of the joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e has the blowout section 11e that has the large width 1d and low resistance, and can thus contribute to an increase in rated current.

[0087] In a case where the blowout temperature of the blowout section 11e in the fuse device 20 of the embodiment is equal to or lower than 400° C., first electrode 2a and the second electrode 2b can be restrained from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first electrode 2a and the second electrode 2b, and the circuit board to which the first external connection electrode 42a and the second external connection electrode 42b are connected. Accordingly, the length of the blowout section 11e (the distance between the first electrode 2a and the second electrode 2b) can be reduced, the size of the fuse device 20 can be reduced, and the rated current can be further increased, compared to a case where the blowout temperature of the blowout section 11e exceeds 400° C.

Third Embodiment (Fuse Device)

[0088] FIG. 3(a) is a plan view showing a fuse device of a third embodiment. FIG. 3(b) is a side view of the fuse device shown in FIG. 3(a) from a lower side of FIG. 3(a). FIG. 3(c) is a side view of the fuse device shown in FIG. 3(a) from a right side of FIG. 3(a).

[0089] FIGS. 3(a) and 3(c) show a state in which a cover member 5 of a fuse device 25 shown in FIG. 3(b) is removed. FIG. 3(d) is a perspective view showing a fuse element provided in the fuse device shown in FIG. 3(a).

[0090] As shown in FIGS. 3(a) to 3(c), the fuse device 25 includes a fuse element 15 shown in FIG. 3(d), an insulating substrate 4, and a first electrode 2a and a second electrode 2b disposed on a front surface 4a of the insulating substrate 4. As in the second embodiment, each of the first electrode 2a and the second electrode 2b functions as a terminal that is conductively connected to the fuse element 15.

[0091] A difference between the fuse device 25 of the third embodiment shown in FIGS. 3(a) to 3(c) and the fuse device 20 shown in the second embodiment is only a thickness (shape) of high-melting-point metal layer 1b in a first joint portion 15f and a second joint portion 15g of the fuse element 15 provided in the fuse device 25 shown in FIGS. 3(a) to FIG. 3(c). Accordingly, in the third embodiment, description will be provided focusing on only a difference from the second embodiment, and the same members as those in the second embodiment are represented by the same reference numerals and description thereof will not be repeated.

[0092] In the fuse element 15 provided in the fuse device 25 of the third embodiment, as shown in FIGS. 3(b) and 3(d), the thickness of the high-melting-point metal layer 1b in the first joint portion 15f and the second joint portion 15g is greater than that in the blowout section 15e. This gives a cut section of the fuse element 15 shown in FIGS. 3(b) and 3(d) a dog-bone shape. The first joint portion 15f is a portion that is joined to the first electrode 2a by a conductive connection member (not shown), such as solder. The second joint portion 15g is a portion that is joined to the second electrode 2b by a conductive connection member (not shown), such as solder. For this reason, in the fuse device 25 of the third embodiment, it is possible to effectively suppress the contact of the conductive connection member, such as solder, and the low-melting-point metal layer 1a of the fuse element 15 at the time of reflow in a manufacturing process of the fuse device 25, with the high-melting-point metal layer 1b that forms the first joint portion 15f and the second joint portion 15g. As a result, fluctuation of a resistance value of the blowout section 15e due to deformation of the blowout section 15e (fuse element 15) at the time of the reflow is more effectively suppressed, and the fuse device 25 having stable blowout characteristics can be easily manufactured.

[0093] The fuse element 15 can be manufactured, for example, using an electroplating method. Specifically, a band-shaped (ribbon-shaped) metal foil that will become the low-melting-point metal layer 1a is prepared. As the metal foil, a metal foil having a width corresponding to a length of the low-melting-point metal layer 1a of the fuse element 15 in a direction connecting the first electrode 2a and the second electrode 2b is used. Next, the high-melting-point metal layer 1b is formed on the surface of the metal foil using the electroplating method, and a band-shaped laminate is obtained. Thereafter, the length of the band-shaped laminate is cut at a predetermined dimension to be made into a flat plate shape. With this, the fuse element 15 that has a predetermined rectangular shape and in which the low-melting-point metal layer 1a is exposed on the cut sections is obtained.

[0094] In the embodiment, the high-melting-point metal layer 1b is formed to be thicker in end portions in a width direction than in a center portion in the width direction of the band-shaped metal foil due to current concentration at the time of electroplating processing. For this reason, as shown in FIG. 3(d), the fuse element 15 has a cut section in a dog-bone shape in which the thickness of the high-melting-point metal layer 1b of each of the first joint portion 15f and the second joint portion 15g is greater than that in the blowout section 15e. This manufacturing method is particularly suitable for a case of manufacturing a small-sized fuse element.

[0095] In the fuse device 25 of the embodiment, as in the first embodiment and the second embodiment, as shown in FIG. 3(c), a width 1d of the blowout section 15e in a plan view is preferably a length ({1d/2d}×100≥80 (%)) equal to or greater than 80% of a width 2d of each of joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 15e, is preferably is a length equal to or greater than 95% of the width 2d of each of the joining portions, and more preferably exceeds 100% of the width 2d of each of the joining portions.

[0096] In the fuse element 15 provided in the fuse device 25 of the embodiment, the low-melting-point metal layer 1a is exposed on the side surfaces in the direction connecting the first electrode 2a and the second electrode 2b. For this reason, as in the second embodiment, the width 1d of the blowout section 15e in a plan view is more preferably a length exceeding 100% of the width 2d of each of the joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 15e.

[0097] Similarly to the fuse devices of the first embodiment and the second embodiment, the fuse device 25 of the embodiment in which the width 1d of the blowout section 15e is the length equal to or greater than 80% of the width 2d of each of the joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 15e has the blowout section 15e that has the large width 1d and low resistance, and can thus contribute to an increase in rated current.

[0098] In a case where a blowout temperature of the blowout section 11e in the fuse device 25 of the embodiment is equal to or lower than 400° C., the first electrode 2a and the second electrode 2b can be prevented from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first electrode 2a and the second electrode 2b, and the circuit board to which the first external connection electrode 42a and the second external connection electrode 42b are connected. Accordingly, the length of the blowout section 11e (the distance between the first electrode 2a and the second electrode 2b) can be reduced, the size of the fuse device 25 can be reduced, and the rated current can be increased, compared to a case where the blowout temperature of the blowout section 11e exceeds 400° C.

Fourth Embodiment (Fuse Device)

[0099] FIG. 4(a) is a plan view showing a fuse device of a fourth embodiment. FIG. 4(b) is a side view of the fuse device shown in FIG. 4(a) from a lower side of FIG. 4(a). FIG. 4(c) is a side view of the fuse device shown in FIG. 4(a) from a right side of FIG. 4(a). FIGS. 4(a) and 4(c) show a state in which a cover member 5 of a fuse device 40 shown in FIG. 4(b) is removed.

[0100] As shown in FIGS. 4(a) to 4(c), the fuse device 40 includes a fuse element 50, an insulating substrate 4, and a first electrode 2a and a second electrode 2b disposed on a front surface 4a of the insulating substrate 4.

[0101] In the fourth embodiment, as the fuse element 50, the same fuse element as the fuse element 11 provided in the second embodiment is provided. In other words, the configuration of a cross section of the fuse element 50 perpendicular to an in-plane direction of the insulating substrate 4 of the fuse device 40 shown in FIG. 4(a) is the same as the configuration of a cross section of the fuse element 20 perpendicular to an in-plane direction of the insulating substrate 4 of the fuse device 20 shown in FIG. 2(a). For this reason, in the fourth embodiment, description of the blowout temperature, the materials, and the layer structure of the fuse element 50 will not be repeated.

[0102] As shown in FIGS. 4(a) and 4(b), the fuse element 50 provided in the fuse device 40 of the embodiment has a blowout section 51 disposed between the first electrode 2a and the second electrode 2b, a first joint portion 52a joined onto the first electrode 2a by a conductive connection member (not shown), such as solder, and a second joint portion 52b joined onto the second electrode 2b by a conductive connection member (not shown), such as solder. As shown in FIG. 4(b), a space is formed between the blowout section 51 and the front surface 4a of the insulating substrate 4.

[0103] In the embodiment, as shown in FIG. 4(b), the fuse element 50 is continuously covered from the top of the first electrode 2a and the second electrode 2b over the side surfaces of the insulating substrate 4. With this, the first electrode 2a and the second electrode 2b are electrically connected to a first external connection electrode 42a and a second external connection electrode 42b disposed on a rear surface 4b of the insulating substrate 4 through the fuse element 50.

[0104] In the embodiment, the first joint portion 52a is electrically connected to the first external connection electrode 42a, and functions as a terminal that is conductively connected to the blowout section 51 of the fuse element 50. The second joint portion 52b is electrically connected to the second external connection electrode 42b, and functions as a terminal that is conductively connected to the blowout section 51 of the fuse element 50.

[0105] In the fuse device 40 of the embodiment, since the first joint portion 52a and the second joint portion 52b composed of a part of the band-shaped fuse element 50 function as terminals, a width of the blowout section 51 in a plan view is identical to a width of each of the first joint portion 52a and the second joint portion 52b. Therefore, the width of the blowout section 51 in a plan view has a length of 100% of a width of each of joining portions joining the first joint portion 52a and the second joint portion 52b to the blowout section 51.

[0106] In the fuse device 40 of the embodiment, the insulating substrate 4, the first electrode 2a, the second electrode 2b, the first external connection electrode 42a, and the second external connection electrode 42b that are the same as those in the fuse device 20 of the second embodiment can be used.

[0107] Similarly to the fuse device 20 of the second embodiment, as shown in FIG. 4(b), the cover member 5 is preferably attached to the fuse device 40 of the embodiment through an adhesive. As a material of the cover member 5, the same material as in the fuse device 20 of the second embodiment can be used.

[0108] The fuse device 40 of the embodiment is mounted on a current path of a circuit board (not shown) through the first external connection electrode 42a and the second external connection electrode 42b for use. In a case where an overcurrent exceeding a rated current flows through the current path of the circuit board, the blowout section 51 is blown out, whereby the first electrode 2a and the second electrode 2b are disconnected and the current path of the circuit board is cut off

[0109] In a case where the blowout section 51 is formed in such a manner that a low-melting-point metal layer 1a and high-melting-point metal layer 1b are laminated in a thickness direction, and in a case where the overcurrent exceeding the rated current flows through the current path of the circuit board, the low-melting-point metal layer 1a of the blowout section 51 generates heat and is melted, the high-melting-point metal layer 1b is dissolved by a generated molten material of the low-melting-point metal layer 1a, and the blowout section 51 is quickly blown out.

[0110] The fuse device 40 of the embodiment in which the width of the blowout section 51 is the length of 100% of the width of each of the joining portions joining the first joint portion 52a and the second joint portion 52b to the blowout section 51 has the blowout section 51 that has a large width and low resistance, and can thus contribute to an increase in rated current.

[0111] In a case where a blowout temperature of the blowout section 51 in the fuse device 40 of the embodiment is equal to or lower than 400° C., the first electrode 2a and the second electrode 2b can be restrained from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first electrode 2a and the second electrode 2b, and the circuit board to which the first external connection electrode 42a and the second external connection electrode 42b are connected. Accordingly, the length of the blowout section 51 (the distance between the first joint portion 52a and the second joint portion 52b) can be reduced, the size of the fuse device 40 can be reduced, and the rated current can be further increased, compared to a case where the blowout temperature of the blowout section 51 exceeds 400° C.

Fifth Embodiment (Protection Device)

[0112] FIG. 5(a) is a plan view of a protection device of a fifth embodiment. FIG. 5(b) is a sectional view along the line B-B′ of the protection device shown in FIG. 5(a). FIG. 5(c) is a side view of the protection device shown in FIG. 5(a) from a right side of FIG. 5(a). FIGS. 5(a) and 5(c) show a state in which a cover member 5 of a protection device 30 shown in FIG. 5(b) is removed.

[0113] As shown in FIGS. 5(a) to 5(c), the protection device 30 includes a fuse element 11, a heat-generating element 7 that heats the fuse element 11 to be blown out, an insulating substrate 4, and a first electrode 2a and a second electrode 2b disposed on a front surface 4a of the insulating substrate 4. In the protection device 30 of the embodiment, as shown in FIG. 5(b), the fuse element 11 is disposed across the first electrode 2a and the second electrode 2b. That is, the fuse element 11 spans from the first electrode 2a to the second electrode 2b. Each of the first electrode 2a and the second electrode 2b functions as a terminal that is conductively connected to the fuse element 11. The protection device 30 of the embodiment has a first heat-generating element electrode 9a and a second heat-generating element electrode 9b that are connected to the heat-generating element 7, and a heat-generating element lead-out electrode 9 that is connected to the second heat-generating element electrode 9b.

[0114] The protection device 30 of the fifth embodiment includes, as the fuse element 11, the insulating substrate 4, the first electrode 2a, and the second electrode 2b, the same ones provided in the fuse device 20 of the second embodiment. For this reason, in the fifth embodiment, description of the blowout temperature, the materials, and the layer structure of the fuse element 11 will not be repeated. In the fifth embodiment, description of the insulating substrate 4, the first electrode 2a, and the second electrode 2b will not be repeated.

[0115] In the protection device 30 of the embodiment, as shown in FIGS. 5(a) and 5(b), the fuse element 11 has a blowout section 11e disposed between the first electrode 2a and the second electrode 2b, a first joint portion 11f joined onto the first electrode 2a by a conductive connection member (not shown), such as solder, and a second joint portion 11g joined onto the second electrode 2b by a conductive connection member (not shown), such as solder.

[0116] In the protection device 30 of the embodiment, as shown in FIG. 5(b), a surface of the blowout section 11e on the insulating substrate 4 side and the heat-generating element lead-out electrode 9 are electrically connected. The blowout section 11e and the heat-generating element lead-out electrode 9 are electrically connected by a conductive connection member (not shown), such as solder.

[0117] In the protection device 30 of the embodiment, as shown in FIG. 5(b), the blowout section 11e is in a protruding shape on an opposite side to the front surface 4a of the insulating substrate 4 in sectional view. Further, the heat-generating element 7 disposed on the front surface 4a of the insulating substrate 4, an insulating member 8 with which the heat-generating element 7 is coated, and the heat-generating element lead-out electrode 9 formed on the heat-generating element 7 through the insulating member 8 are disposed between the blowout section 11e and the front surface 4a of the insulating substrate 4.

[0118] The heat-generating element 7 is formed of a high-resistance conductive material that has comparatively high resistance and generates heat with electrical conduction provided thereto. Examples of the high-resistance conductive material include materials containing nichrome, W, Mo, and Ru. The heat-generating element 7 can be formed by, for example, a method of forming a pattern with a substance in a paste obtained by mixing the above-described high-resistance conductive material, a resin binder, and the like, on the front surface 4a of the insulating substrate 4 using a screen printing technique and baking the pattern.

[0119] The insulating member 8 is formed of an insulating material, such as glass. The heat-generating element lead-out electrode 9 is disposed to face the heat-generating element 7 through the insulating member 8. With this, the heat-generating element 7 is superimposed on the blowout section 11e of the fuse element 11 through the insulating member 8 and the heat-generating element lead-out electrode 9. With such a superimposed structure, it is possible to allow heat generated by the heat-generating element 7 to be efficiently transmitted to the blowout section 11e.

[0120] Even in the protection device 30 of the embodiment, similarly to the fuse device 20 of the second embodiment, as shown in FIG. 5(c), a width 1d of the blowout section 11e in a plan view has a length ({1d/2d}×100≥80 (%)) equal to or greater than 80% of a width 2d of each of joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e, is preferably a length equal to or greater than 95% of the width 2d of each of the joining portions, and more preferably exceeds 100% of the width 2d of each of the joining portions.

[0121] Similarly to the fuse device 20 of the second embodiment, as shown in FIG. 5(b), a cover member 5 is preferably attached to the protection device 30 of the embodiment through an adhesive. As a material of the cover member 5, the same material as in the fuse device 20 of the second embodiment can be used.

[0122] As shown in FIG. 5(a), the first electrode 2a and the second electrode 2b are disposed in a pair of facing end portions on the front surface 4a of the insulating substrate 4. The first heat-generating element electrode 9a and the second heat-generating element electrode 9b are disposed in another pair of facing end portions on the front surface 4a of the insulating substrate 4.

[0123] Each of the first electrode 2a, the second electrode 2b, the first heat-generating element electrode 9a, the second heat-generating element electrode 9b, and the heat-generating element lead-out electrode 9 is formed with a conductive pattern of Ag wiring, Cu wiring, or the like.

[0124] Each of the first electrode 2a, the second electrode 2b, the first heat-generating element electrode 9a, the second heat-generating element electrode 9b, and the heat-generating element lead-out electrode 9 may be coated with an electrode protection layer to suppress changes in electrode characteristics due to oxidation or the like. As a material of the electrode protection layer, a Sn-plated film, a Ni/Au-plated film, a Ni/Pd-plated film, a Ni/Pd/Au-plated film, or the like can be used.

[0125] In the protection device 30 of the embodiment, the first electrode 2a, the second electrode 2b, and the first heat-generating element electrode 9a are electrically connected to the first external connection electrode 42a, the second external connection electrode 42b, and the heat-generating element power feed electrode 6 formed on a rear surface 4b of the insulating substrate 4 through castellations, respectively. The connection of the first electrode 2a and the first external connection electrode 42a, the connection of the second electrode 2b and the second external connection electrode 42b, and the connection of the first heat-generating element electrode 9a and the heat-generating element power feed electrode 6 may be performed through through-holes. The connection of the second heat-generating element electrode 9b and the heat-generating element lead-out electrode 9 can be performed by a known method, such as one using a through-hole (not shown).

[0126] In the protection device 30 of the embodiment, an electrical conduction path to the heat-generating element power feed electrode 6, the first heat-generating element electrode 9a, the heat-generating element 7, the second heat-generating element electrode 9b, the heat-generating element lead-out electrode 9, and the blowout section 11e of the fuse element 11, and an electrical conduction path to the first external connection electrode 42a, the first electrode 2a, the blowout section 11e, the second electrode 2b, and the second external connection electrode 42b are formed.

[0127] The protection device 30 of the embodiment is mounted on a current path of a circuit board (not shown) through the first external connection electrode 42a, the second external connection electrode 42b, and the heat-generating element power feed electrode 6 for use. With this, for example, the blowout section 11e of the protection device 30 is connected to the current path of the circuit board through the first external connection electrode 42a and the second external connection electrode 42b, and the heat-generating element 7 is connected to a current control device provided on the circuit board through the heat-generating element power feed electrode 6.

[0128] In the protection device 30 of the embodiment, in a case where an abnormality occurs in the circuit board, electrical conduction is provided to the heat-generating element 7 through the heat-generating element power feed electrode 6 by the current control device provided on the circuit board. With this, the heat-generating element 7 generates heat, the blowout section 11e is heated through the insulating member 8 and the heat-generating element lead-out electrode 9, and the blowout section 11e is blown out. With this, the first electrode 2a and the second electrode 2b are disconnected, and the current path of the circuit board is cut off.

[0129] In a case where the blowout section 11e is formed in such a manner that a low-melting-point metal layer 1a and high-melting-point metal layer 1b are laminated in a thickness direction, and in a case where electrical conduction is provided to the heat-generating element 7 by the current control device provided on the circuit board, the low-melting-point metal layer 1a of the blowout section 11e is heated and melted, the high-melting-point metal layer 1b is dissolved by a generated molten material of the low-melting-point metal layer 1a, and the blowout section 11e is quickly blown out.

[0130] Similarly to the fuse device 20 of the second embodiment, the protection device 30 of the embodiment in which the width 1d of the blowout section 11e is the length equal to or greater than 80% of the width 2d of each of the joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e has the blowout section 11e that has the large width 1d and low resistance, and can thus contribute to an increase in rated current.

[0131] In a case where a blowout temperature of the blowout section 11e in the protection device 30 of the embodiment is equal to or lower than 400° C., the first electrode 2a and the second electrode 2b can be restrained from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first electrode 2a and the second electrode 2b, and the circuit board to which the first external connection electrode 42a and the second external connection electrode 42b are connected. Accordingly, the length of the blowout section 11e (the distance between the first electrode 2a and the second electrode 2b) can be reduced, the size of the protection device 30, and a rated current can be further increased, compared to a case where the blowout temperature of the blowout section 11e exceeds 400° C.

Sixth Embodiment (Protection Device)

[0132] FIG. 6(a) is a plan view showing a protection device of a sixth embodiment. FIG. 6(b) is a side view of the protection device shown in FIG. 6(a) from a lower side of FIG. 6(a). FIG. 6(c) is a side view of the protection device shown in FIG. 6(a) from a right side of FIG. 6(a). FIGS. 6(a) and 6(c) show a state in which a cover member 5 of a protection device 60 shown in FIG. 6(b) is removed.

[0133] As shown in FIGS. 6(a) to 6(c), the protection device 60 includes a fuse element 11, a heat-generating element 17 that heats the fuse element 11 to be blown out, an insulating substrate 4, and a first electrode 2a and a second electrode 2b disposed on a front surface 4a of the insulating substrate 4. In the protection device 60 of the embodiment, as shown in FIG. 6(b), the fuse element 11 is disposed across the first electrode 2a and the second electrode 2b. That is, the fuse element 11 spans from the first electrode 2a to the second electrode 2b. Each of the first electrode 2a and the second electrode 2b functions as a terminal that is conductively connected to the fuse element 11. The protection device 60 of the embodiment has a heat-generating element lead-out electrode 19 that is connected to the heat-generating element 17.

[0134] A difference between the protection device 60 of the sixth embodiment and the protection device 30 of the fifth embodiment is only the shape of the blowout section 11e, the disposition of the heat-generating element 17 and an insulating member 18, and the disposition of wiring connected to the heat-generating element 17. Accordingly, in the sixth embodiment, only the difference from the fifth embodiment will be described, and the same members as those in the fifth embodiment are represented by the same reference numerals and description thereof will not be repeated.

[0135] In the protection device 60 of the embodiment, unlike the protection device 30 of the fifth embodiment, as shown in FIG. 6(b), side surfaces of the blowout section 11e in a direction connecting the first electrode 2a and the second electrode 2b are in rectangular shapes in sectional view. That is, the shapes of surfaces in a direction substantially perpendicular to the direction connecting the first electrode 2a and the second electrode 2b among surfaces of the blowout section 11e are rectangular shapes. Then, a heat-generating element lead-out electrode 19 is disposed between the blowout section 11e and the front surface 4a of the insulating substrate 4. The heat-generating element 17 and the insulating member 18 with which the heat-generating element 17 is coated are disposed on a rear surface 4b of the insulating substrate 4.

[0136] The heat-generating element lead-out electrode 19 is disposed to face the heat-generating element 17 through the insulating substrate 4. With this, the heat-generating element 17 is superimposed on the blowout section 11 e of the fuse element 11 through the insulating substrate 4 and the heat-generating element lead-out electrode 19. With such a superimposed structure, it is possible to allow heat generated by the heat-generating element 17 to be efficiently transmitted to the blowout section 11e.

[0137] In the protection device 60 of the embodiment, similarly to the protection device 30 of the fifth embodiment, as shown in FIG. 6(c), a width 1d of the blowout section 11e in a plan view has a length ({1d/2d}×100≥80 (%)) equal to or greater than 80% of a width 2d of each of joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e, is preferably is a length equal to or greater than 95% of the width 2d of each of the joining portions, and more preferably exceeds 100% of the width 2d of each of the joining portions.

[0138] In the protection device 60 of the embodiment, in a case where an abnormality occurs in the circuit board, electrical conduction is provided to the heat-generating element 17 by a current control device provided on the circuit board. With this, the heat-generating element 17 generates heat, the blowout section 11e is heated through the insulating substrate 4 and the heat-generating element lead-out electrode 19, and the blowout section 11e is blown out. With this, the first electrode 2a and the second electrode 2b are disconnected, and the current path of the circuit board is cut off.

[0139] In a case where the blowout section 1e is formed in such a manner that a low-melting-point metal layer 1a and high-melting-point metal layer 1b are laminated in a thickness direction, and in a case where electrical conduction is provided to the heat-generating element 17 by the current control device provided on the circuit board, the low-melting-point metal layer 1a of the blowout section 11e is heated and melted, the high-melting-point metal layer 1b is dissolved by a generated molten material of the low-melting-point metal layer 1a, and the blowout section 11e is quickly blown out.

[0140] Similarly to the protection device 30 of the fifth embodiment, the protection device 60 of the embodiment in which the width 1d of the blowout section 11e is the length equal to or greater than 80% of the width 2d of each of the joining portions joining the first electrode 2a and the second electrode 2b to the blowout section 11e has the blowout section 11e that has the large width 1d and low resistance, and can thus contribute to an increase in rated current.

[0141] In a case where a blowout temperature of the blowout section 11e in the protection device 60 of the embodiment is equal to or lower than 400° C., the first electrode 2a and the second electrode 2b can be restrained from reaching a high temperature at the time of blowout and adversely influencing a member connected to the first electrode 2a and the second electrode 2b, and the circuit board to which the first external connection electrode 42a and the second external connection electrode 42b are connected. Accordingly, the length of the blowout section 11e (the distance between the first electrode 2a and the second electrode 2b) can be reduced, to reduce the size of the protection device 60, and the rated current can be further increased, compared to a case where the blowout temperature of the blowout section 11e exceeds 400° C.

REFERENCE SIGNS LIST

[0142] 1, 11, 15, 50: Fuse element [0143] 1a: Low melting-point metal layer [0144] 1b: High melting-point metal layer [0145] 1e, 11e, 15e, 51: Blowout section [0146] 1f, 11f, 15f, 52a: First joint portion [0147] 1g, 11g, 15g, 52b: Second joint portion [0148] 2a: First electrode [0149] 2b: Second electrode [0150] 3a, 3b: Attachment hole [0151] 4: Insulating substrate [0152] 4a: Front surface [0153] 4b: Rear surface [0154] 5: Cover member [0155] 6: Heat-generating element power feed electrode [0156] 7, 17: Heat-generating element [0157] 8, 18: Insulating member [0158] 9, 19: Heat-generating element lead-out electrode [0159] 9a: First heat-generating element electrode [0160] 9b: Second heat-generating element electrode [0161] 10, 20, 25, 40: Fuse device [0162] 20a: First terminal [0163] 20b: Second terminal [0164] 21a, 21b: Castellation [0165] 30, 60: Protection device [0166] 42a: First external connection electrode [0167] 42b: Second external connection electrode