protective element

Abstract

The fuse element's melting speed is increased to shorten the interruption time in case of an abnormality. [Solution] The fuse element 150 includes at least one layer. The at least one layer is made of a eutectic alloy having a composition other than a eutectic composition, with a solid-liquid coexistence temperature range of 30°C or more. The at least one layer is in a state of coexistence of solid and liquid phases, and as the solid phase melts with convection of the liquid phase, the fuse element 150 is melted and cut, thereby blocking the connection between the first electrode 120 and the second electrode 130.

Description

Technical Field

[0001] The present invention relates to a protection element.

Background Art

[0002] As a prior art document that discloses a protection element, there is Patent No. 6249602 (Patent Document 1). The protection element described in Patent Document 1 includes an insulating substrate, a heating element, an insulating member, a first electrode and a second electrode, a heating element lead-out electrode, and a soluble conductor. The heating element is laminated on the insulating substrate. The insulating member is laminated on the insulating substrate so as to cover at least the heating element. The first electrode and the second electrode are laminated on the insulating substrate on which the insulating member is laminated. The heating element lead-out electrode is electrically connected to the heating element on the current path between the first electrode and the second electrode. The soluble conductor is laminated so as to span between the first electrode and the second electrode and the heating element lead-out electrode and not directly adhere to the insulating member, and by heating, the current path between the first electrode and the second electrode is blown. The soluble conductor is composed of a laminate including at least a high melting point metal layer and a low melting point metal layer. The low melting point metal layer is melted by the heat generated by the heating element, and while eroding the high melting point metal layer, it is attracted to the side of the first electrode, the second electrode, and the heating element lead-out electrode having high wettability of the low melting point metal layer and is blown.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a protection element, it is required to increase the fusing speed of the fuse element and shorten the interruption time in case of abnormality.

[0005] The present invention has been made in view of the above problems, and aims to provide a protective element that can shorten the interruption time in the event of an abnormality by increasing the melting speed of the fuse element. [Means for solving the problem]

[0006] The protective element according to the present invention comprises an insulating substrate, a first electrode and a second electrode, a heating element, a fuse element, a first heating element electrode and a second heating element electrode, a lead electrode, and flux. The insulating substrate has a first main surface and a second main surface. The first electrode and the second electrode are provided on the insulating substrate. The heating element is provided on the insulating substrate and is located between the first electrode and the second electrode when viewed from a direction perpendicular to the first main surface. The fuse element is provided extending from the first electrode to the second electrode so as to face the first main surface and is connected to the first electrode and the second electrode. The first heating element electrode and the second heating element electrode are provided on the insulating substrate and are electrically connected to the heating element. The lead electrode is electrically connected to the fuse element between the first electrode and the second electrode and is led out from the first heating element electrode so as to be interposed between the first main surface and the fuse element. The flux covers the surface of the fuse element opposite to the back surface facing the first main surface. The fuse element includes at least one layer. The at least one layer is made of a eutectic alloy having a composition other than a eutectic composition, with a solid-liquid coexistence temperature range of 30°C or more. When the at least one layer is in a state of coexistence of solid and liquid phases, the solid phase melts with convection of the liquid phase, and the fuse element is melted, thereby blocking the connection between the first electrode and the second electrode. [Effects of the Invention]

[0007] According to the present invention, the fuse element's melting speed can be increased, thereby shortening the interruption time in the event of an abnormality. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view showing a protective element according to Embodiment 1 of the present invention. [Figure 2] Figure 1 is a cross-sectional view of the protective element as seen from the direction of the arrow along line II-II. [Figure 3] This is an equivalent circuit diagram of a protective element according to Embodiment 1 of the present invention. [Figure 4] This is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a first modified example of Embodiment 1 of the present invention. [Figure 5] This is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a second modified example of Embodiment 1 of the present invention. [Figure 6] This is an enlarged cross-sectional view schematically showing a crack in the fuse element of a protective element according to a second modified example of Embodiment 1 of the present invention. [Figure 7] This is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a third modified example of Embodiment 1 of the present invention. [Figure 8] This is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a fourth modified example of Embodiment 1 of the present invention. [Figure 9] This is a plan view showing a protective element according to Embodiment 2 of the present invention. [Figure 10] Figure 9 is a cross-sectional view of the protective element as seen from the direction of the arrow XX. [Figure 11] This is a plan view showing a protective element according to Embodiment 3 of the present invention. [Figure 12] Figure 11 is a cross-sectional view of the protective element as seen from the direction of the arrow XII-XII. [Modes for carrying out the invention]

[0009] Hereinafter, protective elements according to each embodiment of the present invention will be described with reference to the drawings. In the following description of embodiments, the same or corresponding parts in the figures will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0010] (Embodiment 1) FIG. 1 is a plan view showing a protection element according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the protection element of FIG. 1 as viewed from the direction of the arrow II-II. As shown in FIGS. 1 and 2, the protection element 100 according to Embodiment 1 of the present invention includes an insulating substrate 110, a first electrode 120 and a second electrode 130, a heating element 140, a fuse element 150, a first heating element electrode 170 and a second heating element electrode 180, a lead-out electrode 160, and a flux 10.

[0011] The insulating substrate 110 has a first main surface 111 and a second main surface 112. The insulating substrate 110 has a rectangular plate shape. The insulating substrate 110 is formed of a material having insulating properties such as, for example, alumina, glass ceramics, mullite, or zirconia. The insulating substrate 110 may be formed of a material used for a printed wiring board such as a glass epoxy substrate or a phenolic substrate. Half-through holes are formed in each of three side surfaces of the insulating substrate 110.

[0012] The first electrode 120 and the second electrode 130 are provided on the insulating substrate 110. The first electrode 120 is located on one side in the X-axis direction. The second electrode 130 is located on the other side in the X-axis direction. Each of the first electrode 120 and the second electrode 130 is formed over the first main surface 111, the second main surface 112, and the side surface of the half-through hole.

[0013] The heating element 140 is provided on the insulating substrate 110 and is located between the first electrode 120 and the second electrode 130 when viewed from the direction orthogonal to the first main surface 111 (Z-axis direction). In the present embodiment, the heating element 140 is formed on the first main surface 111. The heating element 140 has a rectangular plate shape.

[0014] The heating element 140 is a conductive member with a relatively high resistance value that generates heat when energized, and is formed, for example, from W, Mo, or Ru. A paste made by mixing powders of these alloys, compositions, or compounds with a resin binder or the like is screen printed or the like onto the insulating substrate 110 to form a pattern, and the heating element 140 is formed by firing the pattern.

[0015] The first heating element electrode 170 and the second heating element electrode 180 are provided on the insulating substrate 110 and are electrically connected to the heating element 140. The first heating element electrode 170 and the second heating element electrode 180 are located at the center in the X-axis direction. The second heating element electrode 180 is located on one side in the Y-axis direction and is spaced apart from the end of the heating element 140 on one side in the Y-axis direction. The first heating element electrode 170 is located on the other side in the Y-axis direction and is spaced apart from the end of the heating element 140 on the other side in the Y-axis direction.

[0016] The first heating element electrode 170 is formed on the first main surface 111. The first heating element electrode 170 is connected to the heating element 140 via a first lead electrode 161 that extends in the Y-axis direction along the edge on the other side in the X-axis direction of the heating element 140. The first lead electrode 161 is formed on the first main surface 111.

[0017] The second heating element electrode 180 is formed across the first main surface 111, the second main surface 112, and the side surface of the half-through hole. The second heating element electrode 180 is connected to the heating element 140 via a second lead electrode 162 that extends in the Y-axis direction along the edge on one side in the X-axis direction of the heating element 140. The second lead electrode 162 is formed on the first main surface 111.

[0018] The upper surfaces of the heating element 140, the first extraction electrode 161, and the second extraction electrode 162 are substantially flush. An insulating film 190 is formed to cover the heating element 140, the first extraction electrode 161, and the second extraction electrode 162. The insulating film 190 also covers a portion of the first main surface 111. The extraction electrodes 160 are formed to face the heating element 140 via the insulating film 190. The insulating film 190 insulates the heating element 140 from the extraction electrodes 160.

[0019] The fuse element 150 is provided extending from the first electrode 120 to the second electrode 130 so as to face the first main surface 111, and is connected to the first electrode 120 and the second electrode 130. In this embodiment, the fuse element 150 is connected to the lead electrode 160 by a solder joint 11, to the first electrode 120 by a solder joint 12, and to the second electrode 130 by a solder joint 13.

[0020] The area of ​​the fuse element 150 connected to the lead electrode 160 is larger than the area of ​​the fuse element 150 connected to the first electrode 120 and the second electrode 130.

[0021] Voids may be formed inside the solder joint 11 where gases volatilized from the flux have accumulated. Due to the voids inside the solder joint 11, as shown in the modified example described later, the portion 150h located above the central part of the heating element 140 may protrude more than the portions 150e located on the first electrode 120 and the second electrode 130. In addition to increasing the coating area of ​​the solder joint 11, the volume of the solder joint 11 may also be increased by increasing the coating thickness of the solder joint 11. In this case, the volume of the solder joint 11 on the lead electrode 160 is greater than the volume of the solder joint 12 on the first electrode 120 and the volume of the solder joint 13 on the second electrode 130.

[0022] Each of the bonding solders 11, 12, and 13 is, for example, a solder paste containing a flux and a solvent that are volatile at or below the solidus temperature of the metal they contain. Alternatively, each of the bonding solders 11, 12, and 13 may be solder foils bonded to the fuse element 150. Cladding may be used as a method for bonding the solder foils to the fuse element 150.

[0023] The solder used for joining is composed of a tin-based alloy. Examples of tin-based alloys include tin-ag alloys, tin-cuu alloys, tin-ni alloys, tin-sb alloys, tin-Zn alloys, tin-bi alloys, tin-ag-cuu alloys, tin-cuu-ni alloys, tin-Zn-bi alloys, tin-bi-cuu alloys, or tin-in-bi alloys. The solder used for joining may contain 30 atom% or less of intermetallic compounds. Furthermore, the content of intermetallic compounds in the solder used for joining may be 10 atom% or less.

[0024] The solder joint may be formed by eutectic melting with at least one element from among the constituent elements of the fuse element 150. The solder joint may also be formed by eutectic melting with at least one element from among the constituent elements of the first electrode 120, the second electrode 130, and the lead electrode 160.

[0025] Since some of the constituent elements of the solder joint move into the fuse element 150 by diffusion, the solid-liquid coexistence temperature range of the fuse element 150, as described later, can also be adjusted by the composition of the solder joint.

[0026] The solder joints 11, 12, and 13 do not necessarily have to be provided, and the lead electrode 160, the first electrode 120, and the second electrode 130 may be directly joined to the fuse element 150.

[0027] The entire surface 150f of the fuse element 150, opposite to the back surface 150b facing the first main surface 111, is covered with flux 10. The flux 10 may contain a filler such as SiO2. Details of the structure of the fuse element 150 will be described later.

[0028] The lead electrode 160 is electrically connected to the fuse element 150 between the first electrode 120 and the second electrode 130, and is led out from the first heating element electrode 170 so as to be interposed between the first main surface 111 and the fuse element 150. In other words, the lead electrode 160 is connected to the first heating element electrode 170.

[0029] Each of the first electrode 120, the second electrode 130, and the drawing electrode 160 includes, for example, one or more layers of a sintered layer mainly composed of Ag or an Ag alloy, and one of the following platings is applied to the sintered layer: Ag plating, Sn plating, Au plating, Pt plating, or Rh plating. These platings may be alloy platings. For example, in the case of Ag plating, it may be an alloy plating such as Ag-Sn, Ag-Pt, or Ag-Pd. In addition, if necessary, Ni plating or Ni-P plating may be applied as an underlayer located on top of the sintered layer.

[0030] Figure 3 is an equivalent circuit diagram of a protective element according to Embodiment 1 of the present invention. As shown in Figure 3, the protective element 100 has a circuit configuration comprising a fuse element 150 connected in series between a first electrode 120 and a second electrode 130 via a lead electrode 160 and a first heating element electrode 170, and a heating element 140 connected between the first heating element electrode 170 and a second heating element electrode 180, which melts the fuse element 150 by generating heat when energized.

[0031] Here, the detailed configuration of the fuse element 150 provided in the protective element 100 according to Embodiment 1 of the present invention will be described. The fuse element 150 includes at least one layer. The at least one layer is made of a eutectic alloy having a composition other than a eutectic composition, with a solid-liquid coexistence temperature range of 30°C or more. The solid-liquid coexistence temperature range may be 50°C or more. Alternatively, the solid-liquid coexistence temperature range may be 100°C or more. Furthermore, the solid-liquid coexistence temperature range may be 200°C or more. In this embodiment, the fuse element 150 is made of a single layer, but is not limited to this, and the fuse element 150 may be made of multiple layers.

[0032] At least one of the layers of the fuse element 150 is composed of, for example, a sn-based alloy. Examples of sn-based alloys include sn-bi alloys, sn-Zn alloys, sn-ag alloys, sn-cu alloys, or sn-pb alloys. The fuse element 150 may also contain at least one intermetallic compound. That is, at least one of the layers of the fuse element 150 may contain at least one intermetallic compound.

[0033] In the case of Sn-Ag alloys, the eutectic temperature is 221°C. For example, in Ag-49.6atom%Sn, the liquidus temperature is 480°C, and the solid-liquid coexistence temperature range is between 200°C and 300°C. In Ag-90atom%Sn, the liquidus temperature is 300°C, and the solid-liquid coexistence temperature range is between 50°C and 100°C. In the intermetallic compound Ag3Sn, the liquidus temperature is 480°C, and the solid-liquid coexistence temperature range is between 200°C and 300°C.

[0034] In the case of Sn-Pb alloys, the eutectic temperature is 183°C. For example, in 70 mass%Pb-Sn, the liquidus temperature is 260°C and the solid-liquid coexistence temperature range is 50°C or more and less than 100°C; in 86 mass%Pb-Sn, the liquidus temperature is 292°C and the solid-liquid coexistence temperature range is 100°C or more and less than 200°C; and in 92 mass%Pb-Sn, the liquidus temperature is 306°C and the solid-liquid coexistence temperature range is 100°C or more and less than 200°C.

[0035] In the case of Sn-Cu alloys, the eutectic temperature is 227°C. For example, in Cu-86.7atom%Sn, the liquidus temperature is 415°C, and the solid-liquid coexistence temperature range is between 100°C and 200°C. In the intermetallic compound Cu6Sn5, the liquidus temperature is 435°C, and the solid-liquid coexistence temperature range is between 200°C and 300°C.

[0036] The composition of at least one layer of the fuse element 150 is not limited to a composition that satisfies the above-mentioned solid-liquid coexistence temperature range in the state before the protective element 100 is mounted on the printed circuit board by reflow, but is sufficient if the composition satisfies the above-mentioned solid-liquid coexistence temperature range in the state after the protective element 100 is mounted on the printed circuit board by reflow.

[0037] The operation of the protective element 100 according to Embodiment 1 of the present invention will be described below. When the heating element 140 is energized and generates heat, or when an overcurrent flows through the fuse element 150, and the fuse element 150 reaches a set temperature above the reflow temperature and above the solid phase temperature but below the liquid phase temperature of the alloy constituting at least one layer of the fuse element 150, the at least one layer enters a state of coexistence between solid and liquid phases. Convection of the liquid phase occurs due to the difference in density between the solid phase and the liquid phase. For example, the difference in density between the solid phase and the liquid phase is 3% or more of the density of the solid phase. The difference in density between the solid phase and the liquid phase may be 5% or more of the density of the solid phase, or 10% or more of the density of the solid phase. The larger the difference in density between the solid phase and the liquid phase, the more the generation of convection of the liquid phase can be promoted.

[0038] Due to the convection of the liquid phase, at least one of the buoyancy and sedimentation of the solid phase in the liquid phase may occur. When at least one of the buoyancy and sedimentation of the solid phase in the liquid phase occurs, the melting of the solid phase can be promoted. As the solid phase melts with the convection of the liquid phase and the fuse element 150 melts, the connection between the first electrode 120 and the second electrode 130 is interrupted.

[0039] Specifically, the convection of the liquid phase in the fuse element 150 melts the solid phase while eliminating segregation in the solid phase. Furthermore, the convection of the liquid phase causes cracks in the metal oxide film on the surface of the fuse element 150, making it spheroidal and thus easier to melt. In addition, the convection of the liquid phase moves the fillers of the flux 10 attached to the surface 150f of the fuse element 150, allowing the active ingredients of the flux 10 to reach the surface 150f of the fuse element 150 and remove the metal oxide film on the surface of the fuse element 150. Finally, the fuse element 150 located between the first electrode 120 and the second electrode 130 and the lead electrode 160 melts and the fuse element 150 is cut, thereby blocking the connection between the first electrode 120 and the second electrode 130.

[0040] Thus, in the protective element 100 according to Embodiment 1 of the present invention, at least one layer of the fuse element 150 is in a state of coexistence of solid phase and liquid phase, and as the solid phase melts with the convection of the liquid phase, the fuse element 150 is blown, thereby blocking the connection between the first electrode 120 and the second electrode 130. By promoting the melting of the solid phase and the removal of the metal oxide film on the surface of the fuse element 150 through the convection of the liquid phase, the blowing speed of the fuse element 150 can be increased, and the interruption time in the event of an abnormality can be shortened.

[0041] Furthermore, when the heating element 140 is energized and generates heat, heating the fuse element 150, the heating element 140 is positioned below the fuse element 150, which allows the temperature difference between the upper and lower parts of the fuse element 150 in the liquid phase to be, for example, 30°C or more, thereby additionally generating thermal convection in the liquid phase. The temperature difference between the upper and lower parts of the fuse element 150 in the liquid phase may be increased to 50°C or more. This effectively promotes the generation of convection in a solid-liquid coexistence state. For example, the temperature difference between the upper and lower parts of the fuse element 150 in the liquid phase can be increased by making the portion of the fuse element 150 located above the heating element 140 thicker. Alternatively, the flux 10 may be made of a material with a large heat capacity, thereby lowering the temperature of the surface 150f of the fuse element 150 in contact with the flux 10 and increasing the temperature difference between the upper and lower parts of the fuse element 150 in the liquid phase. Alternatively, by configuring the flux 10 to contain a solvent with a high heat of vaporization, the temperature of the surface 150f of the fuse element 150 in contact with the flux 10 can be lowered, thereby increasing the temperature difference between the upper and lower parts of the fuse element 150 in the liquid phase. By generating convection in the liquid phase due to the temperature difference in addition to convection in the solid phase due to the density difference between the solid and liquid phases, the fuse element 150 can be efficiently melted even when the heating temperature of the heating element 140 is set low.

[0042] The following describes a protective element relating to a modified example in which the fuse element is composed of multiple layers. Figure 4 is an enlarged cross-sectional view showing the configuration of the fuse element provided in the protective element relating to the first modified example of Embodiment 1 of the present invention.

[0043] As shown in Figure 4, the fuse element 150v of the protective element according to the first modified embodiment of the present invention includes a low-melting-point metal layer 151 and a high-melting-point metal layer 153 formed on the low-melting-point metal layer 151. In the first modified embodiment, the fuse element 150v has a two-layer structure.

[0044] The low-melting-point metal layer 151 is composed of a eutectic alloy having a solid-liquid coexistence temperature range of 30°C or more, other than the eutectic composition. The above solid-liquid coexistence temperature range may be 50°C or more. Alternatively, the above solid-liquid coexistence temperature range may be 100°C or more. Furthermore, the above solid-liquid coexistence temperature range may be 200°C or more.

[0045] The low-melting-point metal layer 151 is, for example, an alloy mainly composed of one or more metals selected from the group consisting of Sn, Bi, Sb, In, Pb, Zn, and Cu. The low-melting-point metal layer 151 is, for example, composed of a Sn-based alloy. The low-melting-point metal layer 151 may also contain, for example, one or more metals selected from the group consisting of Al, Ag, Cu, Ni, Ti, Y, Zr, P, Ge, B, and W as minor components.

[0046] Furthermore, in order to suppress the melting of the low-melting-point metal layer 151 due to reflow during the manufacturing and mounting of the protective element, it is preferable that at least 50% or more of the low-melting-point metal layer 151 be in the solid phase at the reflow temperature. For this reason, it is preferable to include the above-mentioned auxiliary components in the low-melting-point metal layer 151 to broaden the temperature range in which the solid-liquid state coexists in the eutectic composition, thereby increasing the solid phase ratio at the reflow temperature.

[0047] Furthermore, in order to suppress the dissolution of the high-melting-point metal layer 153 into the low-melting-point metal layer 151 due to reflow during the manufacturing and mounting of the protective element, it is preferable that the low-melting-point metal layer 151 contains the same metal as the high-melting-point metal layer 153. For example, if the high-melting-point metal layer 153 contains Ag, it is preferable that the low-melting-point metal layer 151 is composed of an alloy of Sn, Sb, and Ag.

[0048] The high-melting-point metal layer 153 is composed of a metal having a higher liquidus temperature than the metal constituting the low-melting-point metal layer 151. For example, the high-melting-point metal layer 153 mainly consists of one or more metals selected from the group consisting of Sn, Bi, Sb, In, Pb, Zn, Cu, Ag, Cu, Ni, Au, Pd, Pt, Rh, and Sb. The high-melting-point metal layer 153 can be formed by plating, vapor deposition, or sputtering. The high-melting-point metal layer 153 may also consist of rolled foil laminated on the low-melting-point metal layer 151.

[0049] When forming the high-melting-point metal layer 153 by plating, additives containing Se or Sb may be added to the plating solution.

[0050] To suppress the dissolution of the high-melting-point metal layer 153 into the low-melting-point metal layer 151 due to reflow during the manufacturing and mounting of the protective element, it is preferable that the high-melting-point metal layer 153 contains the same metals as the low-melting-point metal layer 151. For example, if the low-melting-point metal layer 151 contains Sn and Pb, it is preferable that the high-melting-point metal layer 153 is composed of an alloy of Sn and Ag, or an alloy of Pb and Ag.

[0051] In other words, in the fuse element 150v according to the first modified example, multiple layers made of metals with different densities are laminated together. Specifically, in the fuse element 150v, two layers made of metals with different densities are laminated together. Note that in the state before reflow during the manufacturing and mounting of the protective element, the fuse element 150v only needs to consist of multiple layers made of metals with different densities laminated together, and in the state after reflow, it may be a single alloy layer.

[0052] The multiple layers constituting the fuse element 150v may each contain the same first element with the highest content and the second element with the second highest content, and the density difference between the multiple layers may be 3% or more of the density of the layer with the highest density.

[0053] For example, if the low-melting-point metal layer 151 is composed of 70 mass% Pb-Sn and the high-melting-point metal layer 153 is composed of 92 mass% Pb-Sn, then in both the low-melting-point metal layer 151 and the high-melting-point metal layer 153, the first element with the highest content is Pb, and the second element with the second highest content is Sn. The density difference between the 70 mass% Pb-Sn of the low-melting-point metal layer 151 and the 92 mass% Pb-Sn of the high-melting-point metal layer 153 is 3% or more of the density of the 92 mass% Pb-Sn of the high-melting-point metal layer 153, which is the densest layer of the two layers. The density difference between the low-melting-point metal layer 151 and the high-melting-point metal layer 153 may be 5% or more, 10% or more, or 30% or more of the density of the densest layer of the two layers. The greater the density difference between the low-melting-point metal layer 151 and the high-melting-point metal layer 153, the more the generation of convection in the liquid phase of the low-melting-point metal layer 151 can be promoted.

[0054] The shape of the fuse element 150v is the same as that of the fuse element 150w in the second modification, and will be explained in the second modification described below.

[0055] The operation of the protective element according to the first modified embodiment of the present invention will be described below. When the heating element 140 is energized and generates heat, or when an overcurrent flows through the fuse element 150v, and the fuse element 150v reaches a set temperature higher than the set temperature which is above the reflow temperature and above the solid phase temperature but below the liquid phase temperature of the alloy constituting the low-melting-point metal layer 151, the low-melting-point metal layer 151 enters a state where solid and liquid phases coexist. Due to the difference in density between the solid phase and the liquid phase, convection occurs in the liquid phase. The above set temperature is, for example, 250°C to 450°C. As the solid phase of the low-melting-point metal layer 151 melts along with the convection of the liquid phase of the low-melting-point metal layer 151, the solid phase of the high-melting-point metal layer 153 also melts, causing the fuse element 150v to melt and thus interrupting the connection between the first electrode 120 and the second electrode 130.

[0056] In the protective element according to the first modified embodiment of the present invention, the low-melting-point metal layer 151 of the fuse element 150v is in a state of coexistence of solid and liquid phases, and the convection of the liquid phase promotes the melting of the solid phase and the removal of the metal oxide film on the surface of the fuse element 150v, thereby increasing the blowing speed of the fuse element 150v and shortening the interruption time in the event of an abnormality. At the above set temperature, the high-melting-point metal layer 153 may also be in a state of coexistence of solid and liquid phases. In this case, the density difference between the liquid phase of the low-melting-point metal layer 151 and the liquid phase of the high-melting-point metal layer 153 promotes the generation of convection of the liquid phase, further increasing the blowing speed of the fuse element 150v and shortening the interruption time in the event of an abnormality.

[0057] Figure 5 is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a second modification of Embodiment 1 of the present invention. As shown in Figure 5, the fuse element 150w provided in the protective element according to the second modification of Embodiment 1 of the present invention includes a low-melting-point metal layer 151, an intermetallic compound layer 152 formed on the low-melting-point metal layer 151, and a high-melting-point metal layer 153 formed on the intermetallic compound layer 152. In the second modification of this embodiment, the fuse element 150w has a three-layer structure.

[0058] The intermetallic compound layer 152 contains 80% by mass or more of the intermetallic compound. The intermetallic compound layer 152 may also contain less than 20% by mass of an alloy consisting of two or more metals from among the metals constituting the intermetallic compound. Furthermore, the intermetallic compound layer 152 may contain 90% by mass or more of the intermetallic compound, or 95% by mass or more of the intermetallic compound. In addition, the intermetallic compound does not need to be continuously present throughout the entire plane of the intermetallic compound layer 152, but may be present intermittently.

[0059] The intermetallic compound described above has a melting point higher than that of the low-melting-point metal layer 151 and lower than that of the high-melting-point metal layer 153. The melting point of the intermetallic compound described above is higher than the reflow temperature during the manufacturing and mounting of the protective element.

[0060] The above intermetallic compound consists of one or more metals selected from the group consisting of Sn, Ag, Cu, Ni, Au, Pd, Pt, Rh, and Sb. Specifically, for example, at least one of the following intermetallic compounds can be used.

[0061] Examples of AgSn intermetallic compounds include Ag6Sn, Ag3Sn, and Ag4Sn. Examples of AgAl intermetallic compounds include Ag3Al and Ag2Al. Examples of AgPt intermetallic compounds include AgPt3, Ag3Pt, and AgPt. Examples of AgZn intermetallic compounds include AgZn, AgZn3, and Ag5Zn8. Examples of AgIn intermetallic compounds include AgIn2, Ag2In, and AgIn. Examples of AgSb intermetallic compounds include Ag3Sb and Ag 13 There are Sb3, Ag7Sb, and AgSb.

[0062] CuSn-based intermetallic compounds include Cu3Sn, Cu6Sn5, and Cu5Sn. CuIn-based intermetallic compounds include Cu9In4, CuIn2, Cu4In3, Cu3In, and Cu2In. CuSb-based intermetallic compounds include Cu2Sb and Cu3Sb.

[0063] NiSn-based intermetallic compounds include Ni3Sn, Ni3Sn2, and Ni3Sn4. NiIn-based intermetallic compounds include Ni3In, NiIn, NiIn3, and Ni2In. NiBi-based intermetallic compounds include NiBi and NiBi3. NiSb-based intermetallic compounds include Ni3Sb, NiSb, and NiSb2. NiAl-based intermetallic compounds include Ni3Al.

[0064] As an AuSn intermetallic compound, Au 10 There are Sn, Au5Sn, AuSn, AuSn2, and AuSn4. AuIn-based intermetallic compounds include AuIn, Au4In, AuIn2, and Au9In4. AuPb-based intermetallic compounds include Au2Pb and AuPb2. AuBi-based intermetallic compound is Au2Bi. AuSb-based intermetallic compound is AuSb2.

[0065] Pd3Bi is an example of a PdBi-based intermetallic compound. PdSn-based intermetallic compounds include PdSn4, PdSn3, PdSn2, and PdSn.

[0066] PtSn-based intermetallic compounds include Pt3Sn, PtSn, Pt2Sn3, PtSn2, and PtSn4. PtPb-based intermetallic compounds include Pt3Pb, PtPb, and PtPb4. PtSb-based intermetallic compounds include Pt4Sb, PtSb, and PtSb2. PtNi-based intermetallic compounds include PtNi3 and PtNi. PtCu-based intermetallic compounds include PtCu.

[0067] RhSb is an example of an RhSb intermetallic compound. Examples of SbSn intermetallic compounds include Sb2Sn3 and SbSn. Examples of SbZn intermetallic compounds include Sb2Zn3, Sb3Zn4, and SbZn.

[0068] The intermetallic compound layer 152 is joined to the low-melting-point metal layer 151 by cladding by placing a foil of the intermetallic compound on at least one surface of the low-melting-point metal layer 151.

[0069] However, the method for forming the intermetallic compound layer 152 is not limited to the above. An intermetallic compound layer 152 may also be formed at the interface between the low-melting-point metal layer 151 and the high-melting-point metal layer 153 by laminating a high-melting-point metal layer 153 on a low-melting-point metal layer 151 and then applying heat treatment. When forming the intermetallic compound layer 152 by heat treatment, if the surface layer of the high-melting-point metal layer 153 is completely converted into an intermetallic compound, it may become brittle and the subsequent workability may deteriorate. Therefore, as in this modified example, by leaving the surface layer of the high-melting-point metal layer 153 without converting it into an intermetallic compound, a decrease in the windability and workability of the fuse element 150w can be suppressed. For example, an intermetallic compound layer 152 made of Ag3Sn can be formed by heat treatment of a laminate in which a high-melting-point metal layer 153 is formed by Ag plating on a low-melting-point metal layer 151 made of Sn or an Sn-based alloy, while leaving the surface layer of the high-melting-point metal layer 153 made of Ag.

[0070] When the intermetallic compound layer 152 is formed by heat treatment, the intermetallic compound is composed of at least one metal from among the metals contained in the low-melting-point metal layer 151 and at least one metal from among the metals contained in the high-melting-point metal layer 153.

[0071] For example, if the low-melting-point metal layer 151 is mainly composed of Sn and the high-melting-point metal layer 153 is mainly composed of Ag, the intermetallic compound layer 152 contains at least one intermetallic compound from among Ag6Sn, Ag3Sn, and Ag4Sn.

[0072] Furthermore, when performing the above heat treatment, the fuse element 150w may be pressed with a jig from the high-melting-point metal layer 153 side toward the low-melting-point metal layer 151 side. In this case, a portion of the low-melting-point metal layer 151 that has been liquefied by the heat treatment can be made to flow from the portion 150h located above the central part of the heating element 140 toward the portion 150e located above the first electrode 120 and the second electrode 130. This makes it possible to make the thickness of the low-melting-point metal layer 151 thicker in the portion 150e located above the first electrode 120 and the second electrode 130 compared to the portion 150h located above the central part of the heating element 140. In this case, the electrical resistance value of the portion between the first electrode 120 and the second electrode 130 and the lead electrode 160, which is the thickest part of the fuse element 150w where the low-melting-point metal layer 151 is located, can be reduced. When an overcurrent flows through the fuse element 150w, the current value flowing through that portion can be increased, causing it to heat up and preferentially break the circuit in that portion.

[0073] Furthermore, the high-melting-point metal layer 153 may contain 1% by mass or less of one or more metals selected from the group consisting of P, Ge, Al, Sb, and Cr, and these metals may diffuse into the interface between the high-melting-point metal layer 153 and the low-melting-point metal layer 151 by the heat treatment described above to form an intermetallic compound or metal oxide contained in the intermetallic compound layer 152.

[0074] Furthermore, as a method for forming the intermetallic compound layer 152, an alloy plating may be applied to the low-melting-point metal layer 151, and the intermetallic compound may be formed from the alloy by heat treatment. For example, when forming an intermetallic compound from an AgSn alloy plating, the molar ratio is Ag:Sn = 1 or more:1, preferably Ag:Sn = 2 or more:1, and more preferably Ag:Sn = 3 or more:1. The formed intermetallic compound may be mixed in the low-melting-point metal layer 151.

[0075] As shown in Figures 2 and 5, the surface 150f of the fuse element 150w opposite the back surface 150b facing the first main surface 111 has a portion 150h located above the central part of the heating element 140 that is further away from the first main surface 111 than the portion 150e located above the first electrode 120 and the second electrode 130. As shown in Figure 5, the portion 150h located above the central part of the heating element 140 has a protrusion of dimension H1 in the Z-axis direction compared to the portion 150e located above the first electrode 120 and the second electrode 130. Dimension H1 may be greater than or equal to the sum of the thickness of the intermetallic compound layer 152 and the thickness of the high-melting-point metal layer 153. Furthermore, dimension H1 may be greater than or equal to dimension T2, which will be described later.

[0076] As shown in Figure 5, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the thickness of the fuse element 150w is smaller in the portion 150h located above the center of the heating element 140 compared to the portion 150e located on the first electrode 120 and the second electrode 130. That is, the thickness T1 of the portion 150e located on the first electrode 120 and the second electrode 130 and the thickness T2 of the portion 150h located above the center of the heating element 140 satisfy the relationship T1 > T2. T2 ≤ (T1) × 1 / 2, T2 ≤ (T1) × 1 / 3, or T2 ≤ (T1) × 1 / 5. Dimension T2 is, for example, 1 / 2 or less of the thickness dimension of the first electrode 120 and the second electrode 130 on the first main surface 111, and preferably 1 / 3 or less.

[0077] Furthermore, as shown in Figure 5, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the thickness of the fuse element 150w is smaller in the portion 150h located above the central part of the heating element 140 compared to the portion 150m located on the first electrode 120 and between the second electrode 130 and the lead electrode 160. In other words, the thickness T3 of the portion 150m located on the first electrode 120 and between the second electrode 130 and the lead electrode 160, and the thickness T2 of the portion 150h located above the central part of the heating element 140 satisfy the relationship T3 > T2.

[0078] Furthermore, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the thickness of the fuse element 150w may decrease from the portion 150e located on the first electrode 120 and the second electrode 130 towards the portion 150h located above the central part of the heating element 140.

[0079] As shown in Figure 5, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the ratio of the thickness of the low-melting-point metal layer 151 to the thickness of the fuse element 150w is smaller in the portion 150h located above the central part of the heating element 140 compared to the portion 150e located on the first electrode 120 and the second electrode 130.

[0080] Furthermore, as shown in Figure 5, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the ratio of the thickness of the low-melting-point metal layer 151 to the thickness of the fuse element 150w is smaller in the portion 150h located above the central part of the heating element 140 compared to the portion 150m located on the first electrode 120 and between the second electrode 130 and the lead electrode 160.

[0081] In other words, the thickness of the intermetallic compound layer 152 and the high-melting-point metal layer 153 are maintained at approximately constant levels along the entire length in the X-axis direction, whereas the thickness of the low-melting-point metal layer 151 is thinner in the portion 150h located above the central part of the heating element 140 compared to the portion 150e located on the first electrode 120 and the second electrode 130. Furthermore, the thickness of the low-melting-point metal layer 151 is thinner in the portion 150h located above the central part of the heating element 140 compared to the portion 150m located on the first electrode 120 and between the second electrode 130 and the extraction electrode 160.

[0082] Furthermore, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the thickness of the low-melting-point metal layer 151 may decrease from the portion 150e located on the first electrode 120 and the second electrode 130 towards the portion 150h located above the central part of the heating element 140.

[0083] The thickness of the high-melting-point metal layer 153 is, for example, 0.5 μm or more and 2 μm or less. The sum of the thickness of the intermetallic compound layer 152 and the thickness of the high-melting-point metal layer 153 is, for example, 2 μm or more and 8 μm or less. The thickness of the low-melting-point metal layer 151 in the portion 150m located between the first electrode 120 and the second electrode 130 and the extraction electrode 160 is, for example, 35 μm or more and 95 μm or less. In the portion 150m located between the first electrode 120 and the second electrode 130 and the extraction electrode 160, the thickness of the low-melting-point metal layer 151 is, for example, 2 times or more, preferably 5 times or more, the sum of the thickness of the intermetallic compound layer 152 and the thickness of the high-melting-point metal layer 153.

[0084] As shown in Figure 5, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the ratio of the thickness of the intermetallic compound layer 152 to the sum of the thickness of the high-melting-point metal layer 153 and the thickness of the intermetallic compound layer 152 on any imaginary line perpendicular to the first main surface 111 is 30% or more.

[0085] Furthermore, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150w, the ratio of the thickness of the intermetallic compound layer 152 to the sum of the thickness of the high-melting-point metal layer 153 and the thickness of the intermetallic compound layer 152 on any imaginary line perpendicular to the first main surface 111 may be 50% or more, or 80% or more.

[0086] For the intermetallic compound in the intermetallic compound layer 152, the crystallite size determined by Scherrer's method from at least one of the top two peaks with strong diffraction intensity obtained using an X-ray diffractometer is 400 Å or larger, preferably 600 Å or larger.

[0087] When the above heat treatment is performed at a temperature below the solid phase temperature of the low-melting-point metal layer 151 made of a Sn-based metal, the heat treatment time is adjusted so that the crystallite size of the intermetallic compound is 400 Å or more, more preferably 600 Å or more.

[0088] The above heat treatment conditions may be set such that the temperature is maintained at or above the solid phase temperature of the low melting point metal layer 151 for 10 seconds or more, preferably at 230°C or above for 10 seconds or more, and more preferably at 245°C for 10 seconds or more, and the total heat treatment time at any of these temperatures is 60 seconds or less.

[0089] Since the reflow temperature during the manufacturing and mounting of the protective element is lower than the melting point of the intermetallic compound layer 152, the intermetallic compound layer 152 and the high-melting-point metal layer 153 do not melt at the reflow temperature. Even if the low-melting-point metal layer 151 melts at the reflow temperature, the intermetallic compound layer 152 and the high-melting-point metal layer 153 are not melted.

[0090] Furthermore, because the intermetallic compound layer 152 is pre-formed, intermetallic compounds between the metal contained in the low-melting-point metal layer 151 and the metal contained in the high-melting-point metal layer 153 are not formed at the interface between the low-melting-point metal layer 151 and the high-melting-point metal layer 153 due to heating by reflow during the manufacturing and mounting of the protective element, or repeated exposure to thermal loads during use, and the characteristics of the fuse element 150w hardly change. Specifically, changes in characteristics such as the shape change of the fuse element 150w, the electrical resistance value of the fuse element 150w, the breaking speed of the fuse element 150w, and the breaking current value of the fuse element 150w are suppressed.

[0091] The operation of the protective element according to a second modified example of Embodiment 1 of the present invention will be described below. When the heating element 140 is energized and generates heat, or when an overcurrent flows through the fuse element 150w, and the fuse element 150w reaches a set temperature above the reflow temperature and above the solid phase temperature but below the liquid phase temperature of the alloy constituting the low-melting-point metal layer 151, the low-melting-point metal layer 151 enters a state where solid and liquid phases coexist. Convection of the liquid phase occurs due to the difference in density between the solid phase and the liquid phase. The set temperature is, for example, 250°C to 450°C. The solid phase of the low-melting-point metal layer 151 melts and the intermetallic compound layer 152 melts, accompanied by convection of the liquid phase of the low-melting-point metal layer 151.

[0092] Furthermore, after the solid phase of the low-melting-point metal layer 151 and the intermetallic compound layer 152 melt, the solid phase of the high-melting-point metal layer 153 melts, causing the fuse element 150w to melt and thus blocking the connection between the first electrode 120 and the second electrode 130. Specifically, after the solid phase of the low-melting-point metal layer 151 and the intermetallic compound layer 152 melt, the solid phase of the high-melting-point metal layer 153 located between the first electrode 120 and the second electrode 130 and the extraction electrode 160 melts, causing the fuse element 150w to melt and thus blocking the connection between the first electrode 120 and the second electrode 130.

[0093] In the second modified example of this embodiment, the thickness of the low-melting-point metal layer 151 located between the first electrode 120 and the second electrode 130 and the extraction electrode 160 is greater than the thickness of the low-melting-point metal layer 151 located above the central part of the heating element 140. Therefore, the solid phase of the high-melting-point metal layer 153 can be melted between the first electrode 120 and the second electrode 130 and the extraction electrode 160 with sufficient convection of the liquid phase of the low-melting-point metal layer 151, enabling stable shutoff operation.

[0094] Furthermore, since the intermetallic compound layer 152 is formed in advance, the fuse element 150w can be blown open by melting the solid phase of the low-melting-point metal layer 151 and the intermetallic compound layer 152 after the solid phase of the high-melting-point metal layer 153 has melted, without undergoing a phase change in which an intermetallic compound is formed at the interface between the low-melting-point metal layer 151 and the high-melting-point metal layer 153. This allows the fuse element 150w to be blown open by increasing the blowing speed of the fuse element 150w and shortening the interruption time in case of an abnormality.

[0095] Figure 6 is a schematic enlarged cross-sectional view showing a crack in a fuse element of a protective element according to a second modification of Embodiment 1 of the present invention. As shown in Figure 6, a crack 152c may be formed in the intermetallic compound layer 152, connecting the low-melting-point metal layer 151 and the high-melting-point metal layer 153. The crack 152c may be formed by convection of the liquid phase of the low-melting-point metal layer 151. Alternatively, the crack 152c may be formed by lattice defects in the intermetallic compound. Or, the crack 152c may be a grain boundary of a coarsened intermetallic compound.

[0096] Due to the formation of a crack 152c in the intermetallic compound layer 152, in the fuse element 150w, the solid phase of the high-melting-point metal layer 153 begins to melt with convection of the liquid phase of the low-melting-point metal layer 151 passing through the crack 152c, before the intermetallic compound layer 152 completely melts. Subsequently, after the solid phase of the low-melting-point metal layer 151 and the intermetallic compound layer 152 have melted, the solid phase of the high-melting-point metal layer 153 can melt, causing the fuse element 150w to blow open. This allows the melting start time of the high-melting-point metal layer 153 to be accelerated, thereby increasing the blowing speed of the fuse element 150w and shortening the interruption time in case of abnormality.

[0097] Figure 7 is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a third modification of Embodiment 1 of the present invention. As shown in Figure 7, in the fuse element 150x provided in the protective element according to the third modification of Embodiment 1 of the present invention, high-melting-point metal layers 153 are formed on both sides of a low-melting-point metal layer 151, and an intermetallic compound layer 152 is formed between each of the two high-melting-point metal layers 153 and the low-melting-point metal layer 151. In the third modification, the fuse element 150x has a five-layer structure.

[0098] The sum of the thicknesses of the two intermetallic compound layers 152 and the two high-melting-point metal layers 153 is, for example, 4 μm to 16 μm. The thickness of the low-melting-point metal layer 151 located between the first electrode 120 and the second electrode 130 and the extraction electrode 160 is, for example, 40 μm to 100 μm. At the position between the first electrode 120 and the second electrode 130 and the extraction electrode 160, the thickness of the low-melting-point metal layer 151 is, for example, 6 times or more, preferably 10 times or more, the sum of the thicknesses of the two intermetallic compound layers 152 and the two high-melting-point metal layers 153.

[0099] The thickness dimension T2 of the portion 150h located above the central part of the heating element 140 is, for example, 1 / 3 or less of the thickness dimension of the first electrode 120 and the second electrode 130 on the first main surface 111, and preferably 1 / 5 or less. Dimension T2 is, for example, 6 μm or more and 20 μm or less. Dimension T1 is, for example, 50 μm or more and 100 μm or less.

[0100] In the fuse element 150x provided in the protective element according to the third modification of Embodiment 1 of the present invention, high-melting-point metal layers 153 are formed on both sides of the low-melting-point metal layer 151, which effectively suppresses changes in the shape of the fuse element 150x due to heating by reflow during the manufacturing and mounting of the protective element 100, or repeated exposure to thermal loads during use.

[0101] In the fuse element 150x provided in the protective element according to the third modification of Embodiment 1 of the present invention, the melting speed of the fuse element 150x is increased to shorten the interruption time in the event of an abnormality, while the characteristics of the fuse element 150x are less likely to change due to heating by reflow during the manufacture or mounting of the protective element, or due to repeated exposure to thermal loads during use, thereby enabling stable interruption operation.

[0102] Figure 8 is an enlarged cross-sectional view showing the configuration of a fuse element provided in a protective element according to a fourth modification of Embodiment 1 of the present invention. As shown in Figure 8, the fuse element 150y provided in the protective element according to the fourth modification of Embodiment 1 of the present invention includes only a low-melting-point metal layer 151 and an intermetallic compound layer 152 formed on the low-melting-point metal layer 151. In the fourth modification, the fuse element 150y has a two-layer structure.

[0103] The intermetallic compound contained in the intermetallic compound layer 152 has a melting point higher than the liquidus temperature of the low-melting-point metal layer 151 and lower than the melting points of each metal constituting the intermetallic compound. The thickness of the intermetallic compound layer 152 is, for example, 2 μm to 8 μm. The thickness of the low-melting-point metal layer 151 located between the first electrode 120 and the second electrode 130 and the extraction electrode 160 is, for example, 40 μm to 100 μm. At the position between the first electrode 120 and the second electrode 130 and the extraction electrode 160, the thickness of the low-melting-point metal layer 151 is, for example, 2 times or more, preferably 5 times or more, the thickness of the intermetallic compound layer 152. The heating element 140 is configured to generate heat to a temperature higher than the melting point of the intermetallic compound layer 152.

[0104] In the protective element according to the fourth modified example, when the heating element 140 is energized and generates heat, or when an overcurrent flows through the fuse element 150, the fuse element 150y reaches a set temperature higher than the set temperature which is above the reflow temperature and above the solid phase temperature but below the liquid phase temperature of the alloy constituting the low-melting-point metal layer 151. At this point, the low-melting-point metal layer 151 enters a state where solid and liquid phases coexist. Convection of the liquid phase occurs due to the difference in density between the solid phase and the liquid phase. The set temperature is, for example, 250°C to 450°C. As the solid phase of the low-melting-point metal layer 151 melts and the intermetallic compound layer 152 melts, accompanied by convection of the liquid phase of the low-melting-point metal layer 151, the fuse element 150v is blown open, thereby interrupting the connection between the first electrode 120 and the second electrode 130.

[0105] In the fuse element 150y provided in the protective element according to the fourth modification of Embodiment 1 of the present invention, the melting point of the intermetallic compound layer 152 is set lower, thereby increasing the melting speed of the fuse element 150y and shortening the interruption time in the event of an abnormality. Furthermore, since the intermetallic compound layer 152 is formed in advance in the fuse element 150y, the properties of the fuse element 150y are less likely to change due to heating by reflow during the manufacturing or mounting of the protective element, or due to repeated exposure to thermal loads during use, enabling stable interruption operation.

[0106] (Embodiment 2) The protective element according to Embodiment 2 of the present invention will now be described with reference to the figures. The protective element 200 according to Embodiment 2 of the present invention differs from the protective element 100 according to Embodiment 1 in that the surface of the fuse element is flat; therefore, the same configuration as the protective element 100 according to Embodiment 1 will not be repeated in the description.

[0107] Figure 9 is a plan view showing a protective element according to Embodiment 2 of the present invention. Figure 10 is a cross-sectional view of the protective element of Figure 9 as seen from the direction of the arrow XX. As shown in Figures 9 and 10, the protective element 200 according to Embodiment 2 of the present invention comprises an insulating substrate 110, a first electrode 120 and a second electrode 130, a heating element 140, a fuse element 250, a first heating element electrode 170 and a second heating element electrode 180, a lead electrode 160, and a flux 10. The protective element 200 further comprises a first lead electrode 161, a second lead electrode 162, and an insulating film 190.

[0108] The surface 250f of the fuse element 250, opposite to the back surface 250b facing the first main surface 111, is flat. For example, the surface 250f of the fuse element 250 can be made flat by appropriately adjusting the thickness of the first electrode 120, the second electrode 130, and the lead electrode 160, as well as the thickness of the solder joints 11, 12, and 13.

[0109] The thickness of the fuse element 250 is thinner in the portion 250h located above the central part of the heating element 140 compared to the portion 250m located on the first electrode 120 and between the second electrode 130 and the lead electrode 160.

[0110] In the protective element 200 according to Embodiment 2 of the present invention, since the surface 250f of the fuse element 250 is flat, the surface 250f of the fuse element 250 is easily held by the mounter, and the fuse element 250 can be accurately mounted on the first electrode 120, the second electrode 130, and the lead electrode 160.

[0111] (Embodiment 3) The protective element according to Embodiment 3 of the present invention will now be described with reference to the figures. The protective element 300 according to Embodiment 3 of the present invention differs from the protective element 200 according to Embodiment 2 in that the heating element is provided on the second main surface; therefore, the same configuration as the protective element 200 according to Embodiment 2 will not be repeated in the description.

[0112] Figure 11 is a plan view showing a protective element according to Embodiment 3 of the present invention. Figure 12 is a cross-sectional view of the protective element of Figure 11 as seen from the direction of the arrow XII-XII. As shown in Figures 11 and 12, the protective element 300 according to Embodiment 3 of the present invention comprises an insulating substrate 110, a first electrode 120 and a second electrode 130, a heating element 140, a fuse element 250, a first heating element electrode 170 and a second heating element electrode 180, a lead electrode 160, and flux 10.

[0113] The heating element 140 is provided on the second main surface 112. The portion of each of the first electrode 120 and the second electrode 130 located on the second main surface 112 may be thicker than or equal to the combined thickness of the heating element 140 and the insulating film 190, or it may be thinner than the combined thickness of the heating element 140 and the insulating film 190. Even if the portion of each of the first electrode 120 and the second electrode 130 located on the second main surface 112 is thinner than the combined thickness of the heating element 140 and the insulating film 190, the protective element 300 can be mounted by adjusting the thickness of the solder paste placed on the portion of each of the first electrode 120 and the second electrode 130 located on the second main surface 112. The heating element 140 is connected to the portion of each of the first heating element electrode 170 and the second heating element electrode 180 located on the second main surface 112.

[0114] The lead electrode 160 is formed on the first main surface 111. In this embodiment, the first heating element electrode 170 is formed across the first main surface 111, the second main surface 112, and the side surface of the half-through hole. The lead electrode 160 is electrically connected to the heating element 140 via the first heating element electrode 170.

[0115] In the protective element 300 according to Embodiment 3 of the present invention, since the heating element 140 is provided on the second main surface 112, the heat generated by the energization of the heating element 140 is transmitted to the fuse element 250 via the insulating substrate 110. Due to this heat transfer, at least one layer of the fuse element 250 becomes a state of coexistence of solid and liquid phases, and the solid phase melts with the convection of the liquid phase, causing the fuse element 250 to blow open. This increases the blowing speed of the fuse element 250 and shortens the interruption time in the event of an abnormality.

[0116] (Note) Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0117] (1) An insulating substrate having a first main surface and a second main surface, The insulating substrate is provided with a first electrode and a second electrode, A heating element provided on the insulating substrate and located between the first electrode and the second electrode when viewed from a direction perpendicular to the first main surface, A fuse element is provided extending from the first electrode to the second electrode so as to face the first main surface, and is connected to the first electrode and the second electrode, The insulating substrate is provided with a first heating element electrode and a second heating element electrode, which are electrically connected to the heating element. A lead electrode is electrically connected to the fuse element between the first electrode and the second electrode, and is drawn out from the first heating element electrode so as to be interposed between the first main surface and the fuse element, The fuse element comprises a flux covering the surface opposite to the back surface facing the first main surface, The fuse element includes at least one layer, The aforementioned at least one layer is composed of a eutectic alloy having a composition other than the eutectic composition, with a solid-liquid coexistence temperature range of 30°C or more. A protective element in which at least one layer is in a state of coexistence of a solid phase and a liquid phase, and the solid phase is melted with convection of the liquid phase, causing the fuse element to melt and thus blocking the connection between the first electrode and the second electrode.

[0118] (2) The protective element according to (1), wherein the solid-liquid coexistence temperature range is 50°C or more.

[0119] (3) The protective element according to (1), wherein the solid-liquid coexistence temperature range is 100°C or more.

[0120] (4) The protective element according to (1), wherein the solid-liquid coexistence temperature range is 200°C or more.

[0121] (5) The protective element according to any one of (1) to (4), wherein the difference between the density of the solid phase and the density of the liquid phase is 3% or more of the density of the solid phase.

[0122] (6) The protective element according to any one of (1) to (5), wherein the fuse element comprises multiple layers made of metals with different densities stacked on top of each other.

[0123] (7) The aforementioned multiple layers are such that the first element with the highest content and the second element with the second highest content are identical in each layer. The protective element according to (6), wherein the density difference between the layers in the plurality of layers is 3% or more of the density of the layer with the highest density in the plurality of layers.

[0124] (8) The fuse element is a protective element according to any one of (1) to (7), comprising at least one intermetallic compound.

[0125] (9) The protective element according to (8), wherein the fuse element includes a low-melting-point metal layer, an intermetallic compound layer formed on the low-melting-point metal layer, and a high-melting-point metal layer formed on the intermetallic compound layer.

[0126] (10) The protective element according to any one of (1) to (9), wherein the fuse element is connected to each of the first electrode, the second electrode, and the lead electrode by solder joints.

[0127] In the description of the embodiments described above, the combinable configurations may be combined with each other.

[0128] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0129] 10 Flux, 100, 200, 300 Protective element, 110 Insulating substrate, 111 First main surface, 112 Second main surface, 120 First electrode, 130 Second electrode, 140 Heating element, 150, 150v, 150w, 150x, 150y, 250 Fuse element, 150b, 250b Back surface, 150f, 250f Front surface, 151 Low melting point metal layer, 152 Intermetallic compound layer, 152c Crack, 153 High melting point metal layer, 160 Extraction electrode, 161 First extraction electrode, 162 Second extraction electrode, 170 First heating element electrode, 180 Second heating element electrode, 190 Insulating film.

Claims

1. An insulating substrate having a first main surface and a second main surface, The insulating substrate is provided with a first electrode and a second electrode, A heating element provided on the insulating substrate and located between the first electrode and the second electrode when viewed from a direction perpendicular to the first main surface, A fuse element is provided extending from the first electrode to the second electrode so as to face the first main surface, and is connected to the first electrode and the second electrode, A first heating element electrode and a second heating element electrode are provided on the insulating substrate and electrically connected to the heating element, A lead electrode is electrically connected to the fuse element between the first electrode and the second electrode, and is drawn out from the first heating element electrode so as to be interposed between the first main surface and the fuse element, The fuse element comprises a flux covering the surface opposite to the back surface facing the first main surface, The fuse element includes at least one layer, The aforementioned at least one layer is composed of a eutectic alloy having a composition other than the eutectic composition, with a solid-liquid coexistence temperature range of 30°C or more. A protective element in which at least one layer is in a state of coexistence of a solid phase and a liquid phase, and the solid phase is melted with convection of the liquid phase, causing the fuse element to melt and thus blocking the connection between the first electrode and the second electrode.

2. The protective element according to claim 1, wherein the solid-liquid coexistence temperature range is 50°C or more.

3. The protective element according to claim 1, wherein the temperature range of coexistence of solid and liquid is 100°C or more.

4. The protective element according to claim 1, wherein the temperature range of coexistence of solid and liquid is 200°C or more.

5. The protective element according to claim 1, wherein the difference between the density of the solid phase and the density of the liquid phase is 3% or more of the density of the solid phase.

6. The protective element according to claim 1, wherein the fuse element has multiple layers made of metals with different densities stacked on top of each other.

7. In each of the aforementioned layers, the first element with the highest content and the second element with the second highest content are identical. The protective element according to claim 6, wherein the density difference between the layers in the plurality of layers is 3% or more of the density of the layer with the highest density among the plurality of layers.

8. The protective element according to claim 1, wherein the fuse element comprises at least one intermetallic compound.

9. The protective element according to claim 8, wherein the fuse element includes a low-melting-point metal layer, an intermetallic compound layer formed on the low-melting-point metal layer, and a high-melting-point metal layer formed on the intermetallic compound layer.

10. The protective element according to claim 1, wherein the fuse element is connected to each of the first electrode, the second electrode, and the lead electrode by soldering.

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