protective element

Abstract

The fuse element's melting speed is increased to shorten the interruption time in case of an abnormality. [Solution] When viewed from a direction perpendicular to the first main surface 111, the fuse element 150 has recesses 151 formed on its edge in the second direction (Y-axis direction) perpendicular to the first direction (X-axis direction) at the position between the first electrode 120 and the lead electrode 160, and at the position between the second electrode 130 and the lead electrode 160. A portion 10p of the flux 10 accumulates inside the recesses 151.

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 first electrode, the second electrode, and the heating element lead-out electrode side having high wettability of the low melting point metal layer and is blown.

Prior Art Documents

Patent Documents

[0003] [[ID=2,3]]

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 so as to extend in a first direction 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 has recesses formed on its edges in a second direction perpendicular to the first direction, at the positions between the first electrode and the lead electrode, and between the second electrode and the lead electrode, when viewed from a direction perpendicular to the first main surface. A portion of the flux covers at least a portion of the inner surface of the recess. [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 side view of the fuse element and flux of the protective element according to Embodiment 1 of the present invention, viewed from the direction of arrow IV in Figure 1. [Figure 5] This is a cross-sectional view showing the configuration of the fuse element and solder joint of a protective element according to a modified example of Embodiment 1. [Figure 6] This is a plan view showing a protective element according to Embodiment 2 of the present invention. [Figure 7] Figure 5 is a cross-sectional view of the protective element as seen from the direction of the VII-VII arrow. [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) Figure 1 is a plan view showing a protective element according to Embodiment 1 of the present invention. Figure 2 is a cross-sectional view of the protective element of Figure 1 as seen from the direction of the arrow line II-II. As shown in Figures 1 and 2, the protective element 100 according to Embodiment 1 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 150, a first heating element electrode 170 and a second heating element electrode 180, a lead electrode 160, and 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 from an insulating material such as alumina, glass ceramics, mullite, or zirconia. The insulating substrate 110 may also be formed from a material used for printed circuit boards, such as a glass epoxy substrate or a phenolic substrate. Half-through holes are formed on each of the three sides 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 (first direction). The second electrode 130 is located on the other side in the X-axis direction (first direction). Each of the first electrode 120 and the second electrode 130 is formed across 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 a direction perpendicular to the first main surface 111 (Z-axis direction). In this 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 material with a relatively high resistance that generates heat when current is passed through it, and is formed from, for example, W, Mo, or Ru. A paste made by mixing powdered versions of these alloys, compositions, or compounds with a resin binder is formed on an insulating substrate 110 by screen printing or the like to create 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 first direction). The second heating element electrode 180 is located on one side in the Y-axis direction (the second direction) and is spaced apart from the end of the heating element 140 on one side in the Y-axis direction (the second direction). The first heating element electrode 170 is located on the other side in the Y-axis direction (the second direction) and is spaced apart from the end of the heating element 140 on the other side in the Y-axis direction (the second 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-out electrode 161 that extends in the Y-axis direction (the second direction) along the edge on the other side of the heating element 140 in the X-axis direction (the first direction). The first lead-out 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-out electrode 162 that extends in the Y-axis direction (the second direction) along the edge on one side of the heating element 140 in the X-axis direction (the first direction). The second lead-out electrode 162 is formed on the first main surface 111.

[0018] The upper surfaces of the heating element 140, the first lead-out electrode 161, and the second lead-out electrode 162 are substantially flush. An insulating film 190 is formed to cover the heating element 140, the first lead-out electrode 161, and the second lead-out electrode 162. The insulating film 190 also covers a part of the first main surface 111. A lead-out electrode 160 is formed so as to face the heating element 140 through the insulating film 190. The insulating film 190 insulates between the heating element 140 and the lead-out electrode 160.

[0019] The fuse element 150 is provided so as to extend in the X-axis direction (the first direction) from above the first electrode 120 to above 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 the present embodiment, the fuse element 150 is connected to the lead-out electrode 160 by the bonding solder 11, is connected to the first electrode 120 by the bonding solder 12, and is connected to the second electrode 130 by the bonding solder 13.

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

[0021] Each of the bonding solder 11, the bonding solder 12, and the bonding solder 13 is, for example, a cream solder containing a flux and a solvent that are volatile below the solid phase temperature of the contained metal. Note that each of the bonding solder 11, the bonding solder 12, and the bonding solder 13 may be a solder foil bonded to the fuse element 150. As a method of bonding the solder foil to the fuse element 150, clad processing may be used. Note that the bonding solder 11, the bonding solder 12, and the bonding solder 13 may be composed of one solder foil. That is, bonding solder may also be disposed at the position between the first electrode 120 and the lead-out electrode 160 and at the position between the second electrode 130 and the lead-out electrode 160.

[0022] The bonding solder has, for example, one or more metals selected from the group consisting of Sn, Pb, In, Ag, Bi, Sb, Zn, and Cu as a main component. The bonding solder may contain, for example, one or more metals selected from the group consisting of Al, P, Ge, B, and W as sub-components in a range of 1 mass% or less in total.

[0023] Note that the bonding solder 11, the bonding solder, 12, and the bonding solder 13 do not necessarily have to be provided, and each of the lead-out electrode 160, the first electrode 120, and the second electrode 130 and the fuse element 150 may be directly bonded.

[0024] The entire surface 150f of the fuse element 150, opposite to the back surface 150b which faces the first main surface 111, is covered with flux 10. Details of the configuration of the fuse element 150 will be described later.

[0025] 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.

[0026] Each of the first electrode 120, the second electrode 130, and the extraction 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 beneath the sintered layer. Note that each of the first electrode 120, the second electrode 130, and the extraction electrode 160 does not necessarily have to be plated.

[0027] 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.

[0028] Here, a detailed configuration of the fuse element 150 included in the protection element 100 according to Embodiment 1 of the present invention will be described. FIG. 4 is an enlarged side view showing the fuse element and the flux included in the protection element according to Embodiment 1 of the present invention as viewed from the direction of arrow IV in FIG. 1.

[0029] As shown in FIGS. 1 and 4, when viewed from the direction (Z-axis direction) orthogonal to the first main surface 111, at each of the positions between the first electrode 120 and the lead-out electrode 160 and between the second electrode 130 and the lead-out electrode 160, recesses 151 recessed in the Y-axis direction (second direction) are formed at the edges in the Y-axis direction (second direction) orthogonal to the X-axis direction (first direction).

[0030] In the present embodiment, when viewed from the direction (Z-axis direction) orthogonal to the first main surface 111, at each of the positions between the first electrode 120 and the lead-out electrode 160 and between the second electrode 130 and the lead-out electrode 160, the recesses 151 are formed at both edges in the Y-axis direction (second direction) of the fuse element 150. However, the recess 151 may be formed only at either one of the both edges in the Y-axis direction (second direction) of the fuse element 150.

[0031] Alternatively, at the position between the first electrode 120 and the lead-out electrode 160, the recess 151 may be formed at one of the both edges in the Y-axis direction (second direction) of the fuse element 150, and at the position between the second electrode 130 and the lead-out electrode 160, the recess 151 may be formed at the other of the both edges in the Y-axis direction (second direction) of the fuse element 150.

[0032] As shown in FIGS. 1 and 4, when viewed from the direction (Z-axis direction) orthogonal to the first main surface, the dimension of the maximum length Lmax in the Y-axis direction (second direction) of the recess 151 is equal to or greater than the dimension of the maximum thickness Tmax of the fuse element 150. That is, the relationship of Tmax≤Lmax is satisfied. Note that the relationship of Tmax / 2≤Lmax<Tmax may be satisfied, or the relationship of 2Tmax≤Lmax may be satisfied.

[0033] In this case, the electrical resistance value of the portion 150n in the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed can be increased, and when an overcurrent flows through the fuse element 150, the current flows and heats up in that portion intensively, causing that portion to be preferentially disconnected.

[0034] In this embodiment, the portion 150n of the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed is the portion sandwiched between two recesses 151 that face each other in the Y-axis direction (second direction).

[0035] As shown in Figures 1, 2, and 4, the minimum thickness Tmin of the portion 150n in the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed is less than or equal to half of the maximum thickness Tmax of the portions located on the first electrode 120, the second electrode 130, and the lead electrode 160 in the fuse element 150. That is, the relationship Tmin ≤ Tmax / 2 is satisfied. However, the relationship Tmin ≤ Tmax / 3 or Tmin ≤ Tmax / 4 may also be satisfied. However, the portion 150n in the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed may have a thickness equivalent to that of other portions of the fuse element 150.

[0036] As a method for thinning the portion 150n of the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed, known methods such as press working can be employed.

[0037] In this embodiment, the recess 151, when viewed from a direction perpendicular to the first main surface (Z-axis direction), has a semicircular shape, but is not limited to this; it may also be V-shaped or U-shaped.

[0038] In the recess 151 located between the first electrode 120 and the extraction electrode 160, it is preferable that the most recessed portion of the recess 151, when viewed from a direction perpendicular to the first main surface (Z-axis direction), is located midway between the first electrode 120 and the extraction electrode 160 in the X-axis direction (first direction). The recess 151 may also be formed to be in contact with the first electrode 120 and the extraction electrode 160, respectively, when viewed from a direction perpendicular to the first main surface (Z-axis direction).

[0039] In the recess 151 located between the second electrode 130 and the extraction electrode 160, it is preferable that the most recessed portion of the recess 151, when viewed from a direction perpendicular to the first main surface (Z-axis direction), is located midway between the second electrode 130 and the extraction electrode 160 in the X-axis direction (first direction). The recess 151 may also be formed to be in contact with the second electrode 130 and the extraction electrode 160, respectively, when viewed from a direction perpendicular to the first main surface (Z-axis direction).

[0040] The fuse element 150 includes a low-melting-point metal layer and a high-melting-point metal layer formed on the low-melting-point metal layer. The solid-state temperature of the low-melting-point metal layer is, for example, 210°C to 240°C. The Pb content in the fuse element 150 is 0.1% by mass or less.

[0041] The low-melting-point metal layer mainly consists 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 may also contain 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 in a total range of 4% by mass or less. The low-melting-point metal layer may be composed of, for example, Sn-3.5Ag or Sn-3Ag-0.5Cu.

[0042] The high-melting-point metal layer mainly consists of one or more metals selected from the group consisting of Ag, Cu, Ni, Au, Pd, Pt, Rh, Sn, Pb, and Sb. The high-melting-point metal layer can be formed by plating, vapor deposition, or sputtering. The high-melting-point metal layer may also consist of rolled foil laminated on a low-melting-point metal layer. When the high-melting-point metal layer is formed by plating, additives containing Se or Sb may be added to the plating solution as a brightener.

[0043] The thickness of the high-melting-point metal layer is maintained at approximately a constant length along the entire length in the Y-axis direction (second direction), whereas the thickness of the low-melting-point metal layer is thinner in the portion 150n where the recess 151 is located and the width in the Y-axis direction (second direction) is narrower, compared to the portions located on the first electrode 120, the second electrode 130, and the extraction electrode 160.

[0044] The maximum thickness of the high-melting-point metal layer is, for example, 0.5 μm to 2 μm. In the fuse element 150, the maximum thickness of the low-melting-point metal layer is, for example, 35 μm to 95 μm. The maximum thickness of the low-melting-point metal layer is, for example, 2 times or more, preferably 5 times or more, than the maximum thickness of the high-melting-point metal layer.

[0045] The maximum thickness of the low-melting-point metal layer in the portion 150n of the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed is, for example, 5 μm or more and 30 μm or less.

[0046] In this case, the electrical resistance value of the portion 150n in the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed, which is the part of the fuse element 150 where the low-melting-point metal layer is thin, can be further increased. When an overcurrent flows through the fuse element 150, this portion will be energized and heated intensively, causing that portion to be preferentially disconnected.

[0047] In this embodiment, the recess 151 is formed by laser processing. However, the method of forming the recess 151 is not limited to the above, and it may also be formed by the partial melting and flow of the fuse element 150 during reflow during the manufacturing and mounting of the protective element 100. Alternatively, the recess 151 may be formed by the partial melting and flow of the fuse element 150 by aging at a temperature lower than the reflow temperature. Furthermore, the recess 151 may be formed by the partial melting and flow of a thin portion of the low-melting-point metal layer in the fuse element 150 during reflow during the manufacturing and mounting of the protective element 100, or by aging.

[0048] As shown in Figures 1 and 4, a portion 10p of the flux 10 accumulates inside the recess 151. Specifically, a portion 10p of the flux 10 covers at least a portion of the inner surface of the recess 151. A portion 10p of the flux 10 may cover the entire inner surface of the recess 151.

[0049] 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 that is above the reflow temperature and higher than the melting point of the low-melting-point metal layer, the low-melting-point metal layer in the portion 150n where the recess 151 is located and whose width in the Y-axis direction (second direction) is narrowed, starts from the recess 151 due to the action of a portion 10p of the flux 10 accumulated inside the recess 151. At this set temperature, the high-melting-point metal layer does not melt because it is lower than the melting point of the high-melting-point metal layer. The set temperature is, for example, 400°C to 800°C.

[0050] Next, the high-melting-point metal layer melts into the molten mixture containing the molten low-melting-point metal layer, causing the fuse element 150 to melt and thus blocking the connection between the first electrode 120 and the second electrode 130. Specifically, the high-melting-point metal layer located between the first electrode 120 and the second electrode 130 and the lead electrode 160 melts into the molten mixture containing the molten low-melting-point metal layer, causing the fuse element 150 to melt and thus blocking the connection between the first electrode 120 and the second electrode 130. For example, if the low-melting-point metal layer is composed of Sn-5Sb and the high-melting-point metal layer is composed of Ag, the solid-state temperature of the low-melting-point metal layer is 235°C to 238°C, the liquid-state temperature of the low-melting-point metal layer is 240°C to 241°C, and the melting point of the high-melting-point metal layer is 962°C, resulting in the above-described blocking behavior.

[0051] In this embodiment, the fuse element 150 has recesses 151 formed on its edge in the Y-axis direction (second direction) perpendicular to the X-axis direction (first direction) at positions between the first electrode 120 and the lead electrode 160, and between the second electrode 130 and the lead electrode 160, when viewed from a direction perpendicular to the first main surface 111 (Z-axis direction). A portion 10p of the flux 10 accumulates inside the recesses 151. As a result, starting from the recesses 151, the portion 150n where the recesses 151 are located and the width in the Y-axis direction (second direction) is narrowed can be preferentially disconnected, thereby increasing the blowing speed of the fuse element and shortening the interruption time in case of abnormality.

[0052] In this embodiment, the minimum thickness Tmin of the portion 150n of the fuse element 150 where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed is less than or equal to half of the maximum thickness Tmax of the portions of the fuse element 150 located on the first electrode 120, the second electrode 130, and the lead electrode 160. This allows the portion 150n where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed to be disconnected early, increasing the fuse element's blowing speed and shortening the interruption time in case of abnormality.

[0053] In this embodiment, the solid phase temperature of the low-melting-point metal layer is, for example, 210°C to 240°C. This makes it possible to form the recess 151 by partially melting and flowing the fuse element 150 during the reflow process when manufacturing and mounting the protective element 100.

[0054] Here, we will describe a modified protective element in which the first electrode 120, the lead electrode 160, and the second electrode 130 are connected to a single solder joint.

[0055] Figure 5 is a cross-sectional view showing the configuration of the fuse element and solder joint of a protective element according to a modified example of Embodiment 1. As shown in Figure 5, in the protective element according to a modified example of Embodiment 1, the fuse element 150 is connected to each of the first electrode 120, the second electrode 130, and the lead electrode 160 by a single solder joint 14.

[0056] The thickness of the solder joint 14 is smallest at the center C1 in the first direction (X-axis direction) in section R1 between the first electrode 120 and the lead electrode 160, and smallest at the center C2 in the first direction (X-axis direction) in section R2 between the second electrode 130 and the lead electrode 160. Specifically, the thickness of the solder joint 14 is smallest at the thickness T1 at the center C1 of section R1, or at the thickness T2 at the center C2 of section R2.

[0057] The sum of the thickness of the fuse element 150 and the thickness of the solder joint 14 is greater at both ends than at the central part C1 in the first direction (X-axis direction) in section R1 between the first electrode 120 and the lead electrode 160, and also greater at both ends than at the central part C2 in the first direction (X-axis direction) in section C2 between the second electrode 130 and the lead electrode 160. Specifically, regarding the sum of the thickness of the fuse element 150 and the thickness of the solder joint 14, in section R1, the thickness T4 at the outer end and the thickness T5 at the inner end are greater than the thickness T3 at the central part C1, and in section R2, the thickness T7 at the outer end and the thickness T8 at the inner end are greater than the thickness T6 at the central part C2. This makes it easier to attract the fuse element 150 and solder joint 14 in section R1, which have been melted by the heat generated by the heating element 140, to the first electrode 120 and the lead electrode 160, thereby shortening the tripping speed. Similarly, this makes it easier to attract the fuse element 150 and solder joint 14 in section R2, which have been melted by the heat generated by the heating element 140, to the second electrode 130 and the lead electrode 160, thereby shortening the tripping speed.

[0058] The fuse element 150 includes a low-melting-point metal layer 152 and a high-melting-point metal layer 153 formed on the low-melting-point metal layer 152. The low-melting-point metal layer 152 has a vertex 152p above the center of the lead electrode 160 in the first direction (X-axis direction), and its thickness increases as it moves away from the center of the lead electrode 160 in the first direction (X-axis direction). The high-melting-point metal layer 153 is formed with substantially the same thickness throughout. Specifically, the sum of the thickness of the fuse element 150 and the thickness of the solder joint 14 is such that the thickness T10 at the vertex 152p is greater than the thickness T11 at one end in the first direction (X-axis direction) and the thickness T12 at the other end in the first direction (X-axis direction).

[0059] Regarding the thickness dimensions of the low-melting-point metal layer 152, the thickness T13 is smallest at the apex 152p and increases as you move away from the apex 152p in one direction (X-axis direction). Therefore, regarding the thickness dimensions of the low-melting-point metal layer 152, in section R1, the thickness T14 at the inner end is larger than the thickness T15 at the outer end. Similarly, regarding the thickness dimensions of the low-melting-point metal layer 152, the thickness T13 is smallest at the apex 152p and increases as you move away from the apex 152p in the other direction (X-axis direction). Therefore, regarding the thickness dimensions of the low-melting-point metal layer 152, in section R2, the thickness T16 at the inner end is larger than the thickness T17 at the outer end. As a result, the low-melting-point metal layer 152, which is melted by the heat generated by the heating element 140, efficiently erodes the high-melting-point metal layer 153 in each of sections R1 and R2, thereby shortening the breakage rate.

[0060] (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 heating element is provided on the second main surface; therefore, the same configuration as the protective element 100 according to Embodiment 1 will not be described again.

[0061] Figure 6 is a plan view showing a protective element according to Embodiment 2 of the present invention. Figure 7 is a cross-sectional view of the protective element of Figure 6 as seen from the direction of the VII-VII arrow. As shown in Figures 6 and 7, 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, and a lead electrode 160.

[0062] 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 200 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.

[0063] 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.

[0064] In the protective element 200 according to Embodiment 2 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. When viewed from a direction perpendicular to the first main surface 111 (Z-axis direction), the fuse element 250 has recesses 251 formed on its edge in the Y-axis direction (second direction) perpendicular to the X-axis direction (first direction) at positions between the first electrode 120 and the lead electrode 160, and between the second electrode 130 and the lead electrode 160, with a portion 10p of the flux 10 accumulating inside the recesses 251. As a result, starting from the recess 151, the portion 250n where the recess 151 is located and the width in the Y-axis direction (second direction) is narrowed can be preferentially disconnected, thereby increasing the melting speed of the fuse element and shortening the interruption time in case of abnormality.

[0065] (Note) Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0066] (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 so as to extend in a first direction 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, when viewed from a direction perpendicular to the first main surface, has recesses formed on its edge in a second direction perpendicular to the first direction at the position between the first electrode and the lead electrode, and at the position between the second electrode and the lead electrode, respectively. A portion of the flux is a protective element that accumulates inside the recess.

[0067] (2) The protective element according to (1), wherein, when viewed from a direction perpendicular to the first main surface, the maximum length dimension of the recess in the second direction is greater than or equal to the maximum thickness dimension of the fuse element.

[0068] (3) The protective element according to (1) or (2), wherein, when viewed from a direction perpendicular to the first main surface, the recess is formed at both end edges of the fuse element in the second direction at the position between the first electrode and the lead electrode, and at the position between the second electrode and the lead electrode.

[0069] (4) The protective element according to any one of (1) to (3), wherein the minimum thickness of the portion of the fuse element in which the recess is located and the width in the second direction is narrowed is less than or equal to half the maximum thickness of each portion of the fuse element located on the first electrode, the second electrode, and the lead electrode.

[0070] (5) The fuse element includes a low-melting-point metal layer and a high-melting-point metal layer formed on the low-melting-point metal layer. The protective element according to any one of (1) to (4), wherein the solid phase temperature of the low-melting-point metal layer is 210°C or higher and 240°C or lower.

[0071] (6) The protective element according to any one of (1) to (5), wherein the Pb content in the fuse element is 0.1% by mass or less.

[0072] (7) The fuse element is connected to each of the first electrode, the second electrode, and the lead electrode by a single solder joint. The thickness of the solder joint is smallest at the center in the first direction in the section between the first electrode and the lead electrode, and smallest at the center in the first direction in the section between the second electrode and the lead electrode. The sum of the thickness of the fuse element and the thickness of the solder joint is such that, in the section between the first electrode and the lead electrode, the ends are larger than the center in the first direction, and in the section between the second electrode and the lead electrode, the ends are larger than the center in the first direction. The protective element according to (5), wherein the low-melting-point metal layer has a peak portion on the central portion of the extraction electrode in the first direction and becomes thicker as it moves away from the central portion of the extraction electrode in the first direction.

[0073] In the description of the embodiments described above, the combinable configurations may be combined with each other.

[0074] 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]

[0075] 10 Flux, 10p Part of flux, 11,12,13,14 Joint solder, 100,200 Protective element, 110 Insulating substrate, 111 First main surface, 112 Second main surface, 120 First electrode, 130 Second electrode, 140 Heating element, 150,250 Fuse element, 150b Back surface, 150f Front surface, 150n,250n Narrowed portion of fuse element, 151,251 Recess, 152 Low melting point metal layer, 153 High melting point metal layer, 152p Apex, 160 Lead-out electrode, 161 First lead-out electrode, 162 Second lead-out 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 so as to extend in a first direction 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, when viewed from a direction perpendicular to the first main surface, has recesses formed in the second direction at its edge in a second direction perpendicular to the first direction, at the position between the first electrode and the lead electrode, and at the position between the second electrode and the lead electrode. A protective element wherein a portion of the flux covers at least a portion of the inner surface of the recess.

2. The protective element according to claim 1, wherein, when viewed from a direction perpendicular to the first main surface, the maximum length dimension of the recess in the second direction is greater than or equal to the maximum thickness dimension of the fuse element.

3. The protective element according to claim 1, wherein, when viewed from a direction perpendicular to the first main surface, the recess is formed at both end edges of the fuse element in the second direction at the position between the first electrode and the lead electrode, and at the position between the second electrode and the lead electrode.

4. The protective element according to claim 1, wherein the minimum thickness of the portion of the fuse element in which the recess is located and the width in the second direction is narrowed is less than or equal to half the maximum thickness of each portion of the fuse element located on the first electrode, the second electrode, and the lead electrode.

5. The fuse element includes a low-melting-point metal layer and a high-melting-point metal layer formed on the low-melting-point metal layer. The protective element according to any one of claims 1 to 4, wherein the solid phase temperature of the low-melting-point metal layer is 210°C or higher and 240°C or lower.

6. The protective element according to claim 5, wherein the Pb content in the fuse element is 0.1% by mass or less.

7. The fuse element is connected to each of the first electrode, the second electrode, and the lead electrode by a single solder joint. The thickness of the solder joint is smallest at the center in the first direction in the section between the first electrode and the lead electrode, and smallest at the center in the first direction in the section between the second electrode and the lead electrode. The sum of the thickness of the fuse element and the thickness of the solder joint is such that, in the section between the first electrode and the lead electrode, the ends are larger than the center in the first direction, and in the section between the second electrode and the lead electrode, the ends are larger than the center in the first direction. The protective element according to claim 5, wherein the low-melting-point metal layer has a peak portion on the central portion of the extraction electrode in the first direction, and becomes thicker as it moves away from the central portion of the extraction electrode in the first direction.

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