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 a low-melting-point metal layer 151 and a high-melting-point coating layer 152 formed on the low-melting-point metal layer 151. When the low-melting-point metal layer 151 melts, thermal expansion and convection of the molten liquid from the molten low-melting-point metal layer 151 cause the high-melting-point coating layer 152 to split. The split high-melting-point coating layers 152 then flow together with the molten liquid, separating from each other, thereby splitting the fuse element 150 and blocking the connection between the first electrode and the second electrode.

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, the second electrode, and the heating element lead-out electrode and not directly adhere to the insulating member, and by heating, it fuses the current path between the first electrode and the second electrode. 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 where the wettability of the low melting point metal layer is high and is fused.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For protection elements, it is required to increase the fusing speed of the fuse element and shorten the interruption time during abnormal times.

[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, and a lead electrode. The first electrode and the second electrode are provided on the insulating substrate. The heating element is provided on the insulating substrate. The fuse element is provided so as to extend from the first electrode to the second electrode 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 led out from the first heating element electrode and is electrically connected to the fuse element between the first electrode and the second electrode. The fuse element includes a low melting point metal layer and a high melting point coating layer formed on the low melting point metal layer. The thermal expansion when the low-melting-point metal layer melts and the convection of the molten liquid from the molten low-melting-point metal layer cause the high-melting-point coating layer to split. The split high-melting-point coating layers then flow together with the molten liquid, separating from each other, thus severing the fuse element and 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 side view of the fuse element provided in the protective element according to Embodiment 1 of the present invention. [Figure 5] This is a schematic diagram showing how the high-melting-point coating layer is separated due to thermal expansion when the low-melting-point metal layer melts and convection of the molten metal. [Figure 6] This schematic diagram illustrates a state in which the fuse element is divided as the high-melting-point coating layers, separated along with the molten low-melting-point metal layer, flow apart from each other. [Figure 7] This is a cross-sectional view showing the configuration of a fuse element provided in a protective element according to a modified example of Embodiment 1 of the present invention. [Figure 8] This is a plan view showing a protective element according to Embodiment 2 of the present invention. [Figure 9] Figure 8 is a cross-sectional view of the protective element as seen from the direction of the arrow along the line IX-IX. [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, and a lead electrode 160.

[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 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 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 (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 electrode 162 is formed on the first main surface 111.

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

[0019] The fuse element 150 is provided so as to extend in the X-axis direction (first direction) from above the first electrode 120 to above the second electrode 130, facing 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] 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.

[0022] The soldering material primarily consists of one or more metals selected from the group consisting of Sn, Pb, In, Ag, Bi, Sb, Zn, and Cu. The soldering material may also contain one or more metals selected from the group consisting of Al, P, Ge, B, and W as minor components in a total amount of 1% by mass or less.

[0023] 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.

[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 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.

[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, 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. Figure 4 is an enlarged side view of the fuse element provided in the protective element according to Embodiment 1 of the present invention. In Figure 4, the same cross-sectional view as in Figure 2 is shown.

[0029] As shown in Figure 4, the fuse element 150 includes a low-melting-point metal layer 151 and a high-melting-point coating layer 152 formed on the low-melting-point metal layer 151. The high-melting-point coating layer 152 has a melting point, softening point, decomposition temperature, or volatilization temperature higher than the melting point of the low-melting-point metal layer 151. In this specification, the melting point refers not to the temperature at which the material is completely melted, but to the 90% liquid phase temperature at which 90% by mass is in the liquid phase. That is, it refers to the temperature at which 10% by mass of the solid phase remains unmelted. In this embodiment, the fuse element 150 has a two-layer structure. Alternatively, the high-melting-point coating layer 152 may be formed on both sides of the low-melting-point metal layer 151, giving the fuse element 150 a three-layer structure. The Pb content in the fuse element 150 is 0.1% by mass or less.

[0030] The low-melting-point metal layer 151 mainly consists of one or more metals selected from the group consisting of Sn, Bi, Sb, In, 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. The low-melting-point metal layer 151 is composed of, for example, a Sn-based alloy. Examples of Sn-based alloys include Sn-Bi alloys, Sn-Zn alloys, Sn-Sb alloys, Sn-Ag alloys, Sn-Cu alloys, Sn-Ag-Cu alloys, Sn-Cu-Ni alloys, Sn-Zn-Bi alloys, Sn-Bi-Cu alloys, or Sn-In-Bi alloys. The low-melting-point metal layer 151 may be composed of multiple layers with different compositions stacked together. For example, the low-melting-point metal layer 151 may consist of a two-layer structure: an Ag-90atom%Sn layer and an Ag3Sn layer laminated on the Ag-90atom%Sn layer. The melting point of the low-melting-point metal layer 151, which is composed of multiple layers, refers to the 90% by mass liquid phase temperature, where 90% by mass of the low-melting-point metal layer 151, including all layers combined, is in the liquid phase.

[0031] The high-melting-point coating layer 152 is composed of, for example, a metal oxide or metal sulfide. In this case, the thickness of the high-melting-point coating layer 152 is, for example, 0.5 nm or more and 1 μm or less. The thickness of the high-melting-point coating layer 152 composed of a metal oxide or metal sulfide may be 2 nm or more and 0.5 μm or less, or 5 nm or more and 0.1 μm or less. The metal oxide is, for example, an oxide of one or more metals selected from the group consisting of Ag, Cr, In, Zr, Zn, Sb, Ni, Mn, Mg, Ge, Mo, and Al. The metal oxide may also be, for example, a discoloration inhibitor composition made of an inorganic material such as Cr2O3 or ZnO. The metal sulfide is, for example, a sulfide of one or more metals selected from the group consisting of Ag, Zn, Sb, Ni, Mn, and Mo. The high-melting-point coating layer 152 may be composed of multiple layers with different compositions laminated together. For example, the high-melting-point coating layer 152 may consist of a two-layer structure: an Ag layer and an Ag2O layer laminated on the Ag layer. The melting point of the high-melting-point coating layer 152, which is composed of multiple layers, refers to the 90% by mass liquid phase temperature, where 90% by mass of the high-melting-point coating layer 152, including all layers combined, is in the liquid phase.

[0032] The high-melting-point coating layer 152, composed of a metal oxide or metal sulfide, can be formed by plating, vapor deposition, or sputtering. The high-melting-point coating layer 152 may also be composed of rolled foil laminated on the low-melting-point metal layer 151. When the high-melting-point coating layer 152 is formed by plating, additives containing Se or Sb may be added to the plating solution. The high-melting-point coating layer 152 may also be formed by pre-adding a metal to the low-melting-point metal layer 151, depositing it on the surface of the fuse element 150 by heat treatment, and then oxidizing or sulfiding the deposited metal.

[0033] The high-melting-point coating layer 152 may be composed of, for example, an organic polymer. In this case, the thickness of the high-melting-point coating layer 152 is, for example, 1 nm to 100 nm. The thickness of the high-melting-point coating layer 152 composed of an organic polymer may be 2 nm to 20 nm, or 5 nm to 10 nm. The organic polymer is, for example, a discoloration inhibitor composition for the metal contained in the low-melting-point metal layer 151.

[0034] The discoloration inhibitor composition contains, for example, one or more acidic components selected from phosphonic acid, aminoalkylenephosphonic acid, hydroxyalkylphosphonic acid, alkanesulfonic acid, alkanolsulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or salts thereof, and one or more thiourea derivatives selected from thiourea, alkylthiourea, phenylthiourea, and allylthiourea.

[0035] The high-melting-point coating layer 152, which is composed of an organic polymer, can be formed by immersing an element made of a low-melting-point metal layer 151 in a solution in which the organic polymer is dissolved, followed by washing with water and drying.

[0036] Alternatively, the high-melting-point coating layer 152 may be formed by immersing the insulating substrate 110, in which elements made of the low-melting-point metal layer 151 are connected to the first electrode 120, the second electrode 130, and the lead electrode 160, in a solution, washing with water, and drying. Or, the high-melting-point coating layer 152 may be formed by electroplating the insulating substrate 110, in which elements made of the low-melting-point metal layer 151 are connected to the first electrode 120, the second electrode 130, and the lead electrode 160, and then immersing the insulating substrate 110 in a solution, washing with water, and drying. For example, in the process of forming the high-melting-point coating layer 152, an Ag plating film may be formed by electroplating, and a film of a discoloration-preventing agent composition may be formed on the Ag plating film.

[0037] As shown in Figures 2 and 4, the surface 150f of the fuse element 150, opposite to 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 4, the portion 150h of the surface 150f of the fuse element 150, located above the central part of the heating element 140, protrudes by a 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 thickness of the high-melting-point coating layer 152. Furthermore, dimension H1 may be greater than or equal to dimension T2, which will be described later.

[0038] As shown in Figure 4, when the heating element 140 is not energized and no overcurrent is flowing through the fuse element 150, the thickness of the fuse element 150 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. 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 central part of the heating element 140 satisfy the relationship T1 > T2. T2 ≤ (T1) × 1 / 2, T2 ≤ (T1) × 1 / 3, or T2 ≤ (T1) × 1 / 5. The dimension T2 is, for example, 1 / 2 or less of the thickness of the first electrode 120 and the second electrode 130 on the first main surface 111, and preferably 1 / 3 or less.

[0039] Furthermore, as shown in Figure 4, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150, the thickness of the fuse element 150 is smaller in the portion 150h located above the central part of the heating element 140 compared to the portion 150m located between the first electrode 120 and the second electrode 130 and the lead electrode 160. In other words, the thickness T3 of the portion 150m located between the first electrode 120 and 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.

[0040] Furthermore, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150, the thickness of the fuse element 150 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.

[0041] As shown in Figure 4, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150, the ratio of the thickness of the low-melting-point metal layer 151 to the thickness of the fuse element 150 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.

[0042] Furthermore, as shown in Figure 4, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150, the ratio of the thickness of the low-melting-point metal layer 151 to the thickness of the fuse element 150 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.

[0043] In other words, the thickness of the high-melting-point coating layer 152 is maintained at approximately constant along its 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 between the first electrode 120 and the second electrode 130 and the extraction electrode 160.

[0044] Furthermore, when the heating element 140 is not energized and generating heat, and no overcurrent is flowing through the fuse element 150, 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.

[0045] 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 thickness of the high-melting-point coating layer 152.

[0046] 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, 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 151, causing the low-melting-point metal layer 151 to melt. At this set temperature, which is lower than the melting point, softening point, decomposition temperature, or volatilization temperature of the high-melting-point coating layer 152, the high-melting-point coating layer 152 does not melt, soften, decompose, or volatilize. The above set temperature is, for example, 300°C to 600°C. Note that at the above set temperature, the high-melting-point coating layer 152 may be partially or completely reduced by the flux 10.

[0047] Figure 5 is a schematic diagram showing the state in which the high-melting-point coating layer is separated by thermal expansion when the low-melting-point metal layer melts and by convection of the molten liquid. As shown in Figure 5, the linear expansion 151c when the low-melting-point metal layer 151 melts is greater than the linear expansion 152c of the high-melting-point coating layer 152, so the high-melting-point coating layer 152 is separated by thermal expansion when the low-melting-point metal layer 151 melts and by convection of the molten liquid. Note that when the low-melting-point metal layer 151 melts, it means when 90% by mass of the low-melting-point metal layer 151 is in the liquid phase. For example, at the 90% by mass liquid phase temperature of the low-melting-point metal layer 151, the linear expansion coefficient of the low-melting-point metal layer 151 is more than three times that of the high-melting-point coating layer 152. Furthermore, at the 90 mass% liquidus temperature of the low-melting-point metal layer 151, the coefficient of linear expansion of the low-melting-point metal layer 151 may be 5 times or more, 10 times or more, or 20 times or more, the coefficient of linear expansion of the high-melting-point coating layer 152. The convection of the molten metal is generated by the density difference in the low-melting-point metal layer 151 at the above-mentioned set temperature. Specifically, convection of the molten metal is generated by at least one of the density difference in the liquid phase of the low-melting-point metal layer 151 and the density difference between the liquid phase and the solid phase of the low-melting-point metal layer 151.

[0048] Figure 6 is a schematic diagram showing the state in which the fuse element is divided as the divided high-melting-point coating layers flow apart from each other along with the molten low-melting-point metal layer. As shown in Figure 6, the divided high-melting-point coating layers 152 flow apart from each other along with the molten low-melting-point metal layer 151, thereby dividing the fuse element 150. As a result, the connection between the first electrode 120 and the second electrode 130 is severed. Specifically, at the position between the first electrode 120 and the second electrode 130 and the lead electrode 160, one of the divided high-melting-point coating layers 152 flows toward the first electrode 120 or the second electrode 130 along with the molten low-melting-point metal layer 151, while the other divided high-melting-point coating layer 152 flows toward the lead electrode 160, causing the fuse element 150 to melt and the connection between the first electrode 120 and the second electrode 130 to be severed. The convection of the molten liquid promotes the flow that separates the divided high-melting-point coating layers 152 from each other.

[0049] In the protective element 100 according to Embodiment 1 of the present invention, the fuse element 150 can be blown open by dividing the high-melting-point coating layer 152 and allowing it to flow apart from each other before the high-melting-point coating layer 152 melts, softens, decomposes, or volatilizes. This increases the blowing speed of the fuse element 150 and shortens the interruption time in the event of an abnormality. Furthermore, since the high-melting-point coating layer 152 does not melt, soften, decompose, or volatilize at the above-mentioned set temperature, it is possible to suppress accidental disconnection of the fuse element 150 during the manufacturing and reflow process of the protective element 100.

[0050] In this embodiment, the high-melting-point coating layer 152 is composed of a metal oxide, metal sulfide, or organic polymer, thereby suppressing changes in the properties of the fuse element 150 due to oxidation during storage or use of the protective element 100.

[0051] In 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, a sufficient amount of molten low-melting-point metal layer 151 can divide and flow the high-melting-point coating layer 152 between the first electrode 120 and the second electrode 130 and the extraction electrode 160, enabling stable shutoff operation.

[0052] 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 molten low-melting-point metal layer 151 to be increased to, for example, 30°C or more, thereby additionally generating thermal convection in the molten liquid. The temperature difference between the upper and lower parts of the molten low-melting-point metal layer 151 may be increased to 50°C or more. This effectively promotes the generation of convection in the molten low-melting-point metal layer 151. For example, by making the fuse element 150 thicker in the portion located above the heating element 140, the temperature difference between the upper and lower parts of the molten low-melting-point metal layer 151 can be increased. Alternatively, by making the flux 10 from a material with a large heat capacity, 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 molten low-melting-point metal layer 151. 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 in the molten liquid in which the low-melting-point metal layer 151 is melted. By generating convection in the molten liquid due to the temperature difference in addition to convection due to the density difference, the fuse element 150 can be efficiently melted even when the heating temperature of the heating element 140 is set low.

[0053] Figure 7 is a cross-sectional view showing the configuration of a fuse element provided in a protective element according to a modified example of Embodiment 1 of the present invention. In Figure 7, the cross-sectional view is the same as in Figure 4. As shown in Figure 7, in the fuse element 150x provided in the protective element according to a modified example of Embodiment 1 of the present invention, high-melting-point coating layers 152 are formed on both sides of the low-melting-point metal layer 151. The fuse element 150x has a three-layer structure. Note that if the high-melting-point coating layer 152 is formed by immersing the insulating substrate 110, in which the element consisting of the low-melting-point metal layer 151 is connected to the first electrode 120, the second electrode 130, and the lead electrode 160, in a solution, washing with water, and drying, then the high-melting-point coating layer 152 is not formed in the portions where the low-melting-point metal layer 151 is connected to each of the first electrode 120, the second electrode 130, and the lead electrode 160.

[0054] In the fuse element 150x provided in the protective element according to a modified embodiment 1 of the present invention, a high melting point coating layer 152 is 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.

[0055] In the fuse element 150x provided in the protective element according to a modified 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 manufacturing or mounting of the protective element, or due to repeated exposure to thermal loads during use, thereby enabling stable interruption operation.

[0056] (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.

[0057] Figure 8 is a plan view showing a protective element according to Embodiment 2 of the present invention. Figure 9 is a cross-sectional view of the protective element of Figure 8 as seen from the direction of the IX-IX arrow. As shown in Figures 8 and 9, 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.

[0058] 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.

[0059] The lead electrode 160 is formed on the first main surface 111. In this embodiment, the first heating element electrode 170 is formed on 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.

[0060] 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. However, the surface 250f of the fuse element 250 does not have to be flat.

[0061] 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. This heat transfer causes the low-melting-point metal layer to melt, and the thermal expansion and convection of the molten liquid from the molten low-melting-point metal layer divide the high-melting-point coating layer. The divided high-melting-point coating layers then flow together with the molten liquid from the molten low-melting-point metal layer, causing them to separate from each other and thus dividing the fuse element 250, thereby blocking the connection between the first electrode 120 and the second electrode 130. This increases the melting speed of the fuse element 250, shortening the interruption time in the event of an abnormality.

[0062] (Note) Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0063] (1) Insulating substrate and The insulating substrate is provided with a first electrode and a second electrode, A heating element provided on the insulating substrate, A fuse element is provided that extends from the first electrode to the second electrode 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. The device comprises a lead electrode drawn from the first heating element electrode and electrically connected to the fuse element between the first electrode and the second electrode, The fuse element includes a low-melting-point metal layer and a high-melting-point coating layer formed on the low-melting-point metal layer. A protective element in which the high-melting-point coating layer is divided by thermal expansion when the low-melting-point metal layer melts and by convection of the molten liquid from the molten low-melting-point metal layer, and the divided high-melting-point coating layers flow apart from each other along with the molten liquid, thereby dividing the fuse element and blocking the connection between the first electrode and the second electrode.

[0064] (2) The aforementioned high-melting-point coating layer is composed of a metal oxide or metal sulfide. The protective element according to (1), wherein the thickness of the high-melting-point coating layer is 0.5 nm or more and 1 μm or less.

[0065] (3) The protective element according to (2), wherein the metal oxide is an oxide of one or more metals selected from the group consisting of Ag, Cr, In, Zr, Zn, Sb, Ni, Mn, Mg, Ge, Mo, and Al.

[0066] (4) The protective element according to (2), wherein the metal sulfide is a sulfide of one or more metals selected from the group consisting of Ag, Zn, Sb, Ni, Mn, and Mo.

[0067] (5) The aforementioned high-melting-point coating layer is composed of an organic polymer. The protective element according to (1), wherein the thickness of the high-melting-point coating layer is 1 nm or more and 100 nm or less.

[0068] (6) The protective element according to (5), wherein the organic polymer is a discoloration inhibitor composition for the metal contained in the low-melting-point metal layer.

[0069] (7) The protective element according to any one of (1) to (6), wherein the low-melting-point metal layer is composed of multiple layers with different compositions stacked together.

[0070] (8) The protective element according to any one of (1) to (7), wherein the high melting point coating layer is composed of multiple layers with different compositions stacked together.

[0071] (9) The protective element according to any one of (1) to (8), wherein the Pb content in the fuse element is 0.1% by mass or less.

[0072] In the description of the embodiments described above, the combinable configurations may be combined with each other.

[0073] 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 to be included. [Explanation of Symbols]

[0074] 10 Flux, 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, 150x, 250 Fuse element, 150b, 250b Back surface, 150f, 250f Front surface, 151 Low melting point metal layer, 152 High melting point coating 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. Insulating substrate and The insulating substrate is provided with a first electrode and a second electrode, A heating element provided on the insulating substrate, A fuse element is provided that extends from the first electrode to the second electrode 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. The device comprises a lead electrode drawn out from the first heating element electrode and electrically connected to the fuse element between the first electrode and the second electrode, The fuse element includes a low-melting-point metal layer and a high-melting-point coating layer formed on the low-melting-point metal layer. A protective element in which the high-melting-point coating layer is divided by thermal expansion when the low-melting-point metal layer melts and by convection of the molten liquid from the molten low-melting-point metal layer, and the divided high-melting-point coating layers flow apart from each other along with the molten liquid, thereby dividing the fuse element and blocking the connection between the first electrode and the second electrode.

2. The aforementioned high-melting-point coating layer is composed of a metal oxide or metal sulfide. The protective element according to claim 1, wherein the thickness of the high-melting-point coating layer is 0.5 nm or more and 1 μm or less.

3. The protective element according to claim 2, wherein the metal oxide is an oxide of one or more metals selected from the group consisting of Ag, Cr, In, Zr, Zn, Sb, Ni, Mn, Mg, Ge, Mo, and Al.

4. The protective element according to claim 2, wherein the metal sulfide is a sulfide of one or more metals selected from the group consisting of Ag, Zn, Sb, Ni, Mn, and Mo.

5. The aforementioned high-melting-point coating layer is composed of an organic polymer. The protective element according to claim 1, wherein the thickness of the high-melting-point coating layer is 1 nm or more and 100 nm or less.

6. The protective element according to claim 5, wherein the organic polymer is a discoloration inhibitor composition for the metal contained in the low-melting-point metal layer.

7. The protective element according to claim 1, wherein the low-melting-point metal layer is composed of multiple layers with different compositions stacked together.

8. The protective element according to claim 1, wherein the high melting point coating layer is composed of multiple layers with different compositions stacked together.

9. The protective element according to any one of claims 1 to 8, wherein the Pb content in the fuse element is 0.1% by mass or less.

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