protective element

Abstract

This prevents the cap from expanding, deforming, and detaching from the insulating substrate due to the increase in internal pressure when the flux is heated. [Solution] The flux 10 covers the surface 150f of the fuse element 150 opposite to the back surface 150b that faces the first main surface 111. The cap 20 is provided on the first main surface 111 so as to cover the fuse element 150 and the flux 10. The internal space 40 surrounded by the cap 20 and the first main surface 111 is sealed. The fuse element 150 is made of an Sn-based alloy with a Pb content of 0.1 mass% or less. The flux 10 is formulated such that the weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute is 5% or less. This suppresses expansion deformation of the cap 20 and detachment from the insulating substrate 110 due to the pressure increase in the internal space 40 when the flux 10 is heated.

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 Japanese Patent Application Laid-Open No. 2021-18983 (Patent Document 1). In the protection element described in Patent Document 1, a heating element, at least a pair of main electrodes, and an energization electrode of the heating element are provided on an insulating substrate. The protection element has a fuse element and a lid body. The fuse element is made of a fusible metal material and is provided so as to conduct the main electrode and the energization electrode. The lid body covers at least the upper portion of the fuse element and is fixed to the insulating substrate. The fuse element has an alloy material containing a reducing element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the flux is soldered and mounted on the protection circuit board and when the protection element performs a fusing operation, the flux is heated, and a part of the flux vaporizes during the heating. When the vaporization rate of the flux during heating is high, the cap may expand and deform or detach from the insulating substrate due to an increase in pressure inside the cap.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a protection element in which expansion deformation of the cap and detachment from the insulating substrate are suppressed due to an increase in internal pressure when the flux is heated.

Means for Solving the Problems

[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, flux, and a cap. The insulating substrate has a first main surface and a second main surface. The first electrode and the second electrode are provided on the insulating substrate. The heating element is provided on the insulating substrate and is located between the first electrode and the second electrode when viewed from a direction perpendicular to the first main surface. The fuse element is provided extending from the first electrode to the second electrode so as to face the first main surface and is connected to the first electrode and the second electrode. The first heating element electrode and the second heating element electrode are provided on the insulating substrate and are electrically connected to the heating element. The lead electrode is electrically connected to the fuse element between the first electrode and the second electrode and is led out from the first heating element electrode so as to be interposed between the first main surface and the fuse element. The flux covers the surface of the fuse element opposite to the back surface facing the first main surface. The cap is provided on the first main surface so as to cover the fuse element and the flux. The internal space enclosed by the cap and the first main surface is sealed. The fuse element is made of a sn-based alloy with a Pb content of 0.1 mass% or less. The flux is formulated such that the weight loss rate during the heating time, from when it is heated from room temperature to 190°C at a rate of 10°C / min and held at 190°C for 1 minute, is 5% or less. This suppresses expansion deformation of the cap and detachment from the insulating substrate due to the pressure increase in the internal space when the flux is heated. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the expansion and deformation of the cap and its detachment from the insulating substrate due to the increase in internal pressure when the flux is heated. [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 a plan view showing the protective element according to Embodiment 1 of the present invention with the cap removed. [Figure 4] Figure 3 is a cross-sectional view of the protective element as seen from the direction of the arrow along line IV-IV. [Figure 5] This is an equivalent circuit diagram of a protective element according to Embodiment 1 of the present invention. [Figure 6] This is a plan view showing a protective element according to Embodiment 2 of the present invention. [Figure 7] Figure 6 is a cross-sectional view of the protective element as seen from the direction of the VII-VII arrow. [Figure 8] This is a plan view showing the protective element according to Embodiment 2 of the present invention with the cap removed. [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 taken from the direction of the arrow II-II. Figure 3 is a plan view showing the protective element according to Embodiment 1 of the present invention with the cap removed. Figure 4 is a cross-sectional view of the protective element of Figure 3 taken from the direction of the arrow IV-IV.

[0011] As shown in Figures 1 to 4, 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, a flux 10, and a cap 20.

[0012] 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.

[0013] The first electrode 120 and the second electrode 130 are provided on the insulating substrate 110. The first electrode 120 is located on one side in the X-axis direction. The second electrode 130 is located on the other side in the X-axis direction. Each of the first electrode 120 and the second electrode 130 is formed across the first main surface 111, the second main surface 112, and the side surface of the half-through hole.

[0014] 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.

[0015] The heating element 140 is a conductive material with 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.

[0016] The first heating element electrode 170 and the second heating element electrode 180 are provided on the insulating substrate 110 and are electrically connected to the heating element 140. The first heating element electrode 170 and the second heating element electrode 180 are located at the center in the X-axis direction. The second heating element electrode 180 is located on one side in the Y-axis direction and is separated from the end of the heating element 140 on one side in the Y-axis direction. The first heating element electrode 170 is located on the other side in the Y-axis direction and is separated from the end of the heating element 140 on the other side in the Y-axis direction.

[0017] 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 along the edge of the heating element 140 on the other side in the X-axis direction. The first lead-out electrode 161 is formed on the first main surface 111.

[0018] 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 along the edge of the heating element 140 on one side in the X-axis direction. The second lead-out electrode 162 is formed on the first main surface 111.

[0019] 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 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.

[0020] The fuse element 150 is provided extending from the first electrode 120 to the second electrode 130 so as to face the first main surface 111, and is connected to the first electrode 120 and the second electrode 130. In this embodiment, the fuse element 150 is connected to the lead electrode 160 by a solder joint 11, to the first electrode 120 by a solder joint 12, and to the second electrode 130 by a solder joint 13.

[0021] 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.

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

[0023] The 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.

[0024] 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.

[0025] The entire surface 150f of the fuse element 150, opposite to the back surface 150b facing the first main surface 111, is covered with flux 10. The fuse element 150 is made of a sn-based alloy. Examples of sn-based alloys include sn-bi alloys, sn-Zn alloys, sn-ag alloys, sn-cu alloys, or sn-sb alloys. For example, the sn-based alloy may be SAC305 or sn-0.7Cu. The Pb content in the fuse element 150 is 0.1% by mass or less.

[0026] 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.

[0027] 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.

[0028] The cap 20 is provided on the first main surface 111 so as to cover the fuse element 150 and the flux 10. The internal space 40 enclosed by the cap 20 and the first main surface 111 is sealed. Specifically, a bonding agent 30 is applied to seal the space between each of the first electrode 120, the second electrode 130, the first heating element electrode 170, the second heating element electrode 180, and the first main surface 111 and the cap 20. The bonding agent 30 is made of a sealant such as epoxy resin.

[0029] The cap 20 is made of ceramics or a thermoplastic resin. In this embodiment, the cap 20 is made of a liquid crystal polymer. The liquid crystal polymer may be filled with fillers such as glass fibers. The filler filling rate is, for example, 5 mass% to 50 mass%. The thickness of the cap 20 is, for example, 0.1 mm to 0.2 mm.

[0030] The shortest distance between the surface 10s of flux 10 and the inner surface of cap 20 in the direction perpendicular to the first main surface 111 (Z-axis direction) is 0 mm or more and 0.2 mm or less.

[0031] The flux 10 is formulated such that the weight loss rate during the heating time, from when it is heated from room temperature to 190°C at a rate of 10°C / min and held at 190°C for 1 minute, is 5% or less. The flux 10's composition only needs to be adjusted so that the cap 20 is placed on the first main surface 111, and the internal space 40 surrounded by the cap 20 and the first main surface 111 is sealed.

[0032] For example, flux 10 contains EO-based glycol ethers such as triethylene glycol monobutyl ether, diethylene glycol monohexyl ether, 2-{2-(2-ethylhexyloxy)ethoxy}ethanol, 2-(benzyloxy)ethanol, diethylene glycol monobenzyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, or 2-(2-ethoxyethoxy)ethanol as organic solvents. By adjusting the type and content of the organic solvent, the weight loss rate of flux 10 during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute is 5% or less.

[0033] Alternatively, flux 10 contains amine halogen salts, organic acids, or amine organic acid salts as activators. By adjusting the type and concentration of the activator, the weight loss rate of flux 10 during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute is 5% or less.

[0034] Furthermore, by adjusting both the type and content of the organic solvent and the type and content of the activator, the weight loss rate of the flux 10 during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute may be 5% or less. The flux 10 may contain a wax component. The wax component is, for example, a polyolefin wax. In this case, the surface 10s of the flux 10 may be covered with a wax film. This can effectively reduce the weight loss rate of the flux 10 by preventing a portion of the flux 10 from vaporizing due to the wax film. The wax film may be formed when the wax in the flux 10 melts and moves to the surface during heating when the fuse element 150 is connected to the lead electrode 160, the first electrode 120, and the second electrode 130, or it may be formed by coating the surface of the flux 10.

[0035] Figure 5 is an equivalent circuit diagram of a protective element according to Embodiment 1 of the present invention. As shown in Figure 5, 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 the second heating element electrode 180, which melts the fuse element 150 by generating heat when energized.

[0036] The operation of the protective element 100 according to Embodiment 1 of the present invention will now be described. 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 above the melting point, and the fuse element 150 melts. The set temperature is, for example, 400°C or more and 800°C or less. When the fuse element 150 melts, the connection between the first electrode 120 and the second electrode 130 is interrupted.

[0037] Here, we will describe experimental examples that confirmed the effect of the protective element 100 according to Embodiment 1 of the present invention. In this experiment, five protective elements were formed for Comparative Example 1, Comparative Example 2, and Examples 1 to 4, each with different flux components and filler content of the liquid crystal polymer constituting the cap. The thickness of the cap was 0.1 mm. For the flux components, the type and content of the organic solvent contained in the flux were varied. The weight loss rate of the flux when heated from room temperature to the heating temperature at a rate of 10°C / min was measured by differential thermogravimetric analysis (DTG). The state of the cap was checked at reflow maximum temperatures of 190°C, 230°C, and 260°C during mounting of the protective element. The reflow maximum temperature was adjusted by changing the type of solder used for mounting the protective element. When the reflow maximum temperature was 190°C, a Sn-Bi alloy was used for mounting. When the reflow maximum temperature was 230°C, SAC305 was used for mounting. When the maximum reflow temperature reached was 260°C, a Sn-Sb alloy was used for the solder used for mounting.

[0038] The table below summarizes the experimental results. If detachment of the cap from the insulating substrate was observed in even one of the five samples due to increased internal pressure, it is indicated as "detachment." If no detachment was observed in any of the five samples, but expansion deformation of the cap was observed in even one of the five samples due to increased internal pressure, it is indicated as "expansion deformation." If neither detachment nor expansion deformation of the cap was observed in any of the five samples, it is indicated as "good."

[0039] [Table 1]

[0040] As shown in Table 1, in the protective elements of Examples 1 to 4, where the flux weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute was 5% or less, the cap was in good condition when the maximum reflow temperature reached during mounting of the protective element was 190°C. In the protective elements of Comparative Examples 1 to 2, where the flux weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute exceeded 5%, expansion deformation was observed in the cap when the maximum reflow temperature reached during mounting of the protective element was 190°C.

[0041] In the protective elements of Examples 1 to 3, where the flux weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and holding at 190°C for 1 minute was 2% or less, and the flux weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and holding at 230°C for 1 minute was 5% or less, the cap was in good condition when the maximum reflow temperature reached during mounting of the protective element was 230°C. In the protective elements of Comparative Examples 1 to 2 and Example 4, where the flux weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and holding at 230°C for 1 minute exceeded 5%, detachment of the cap from the insulating substrate was observed when the maximum reflow temperature reached during mounting of the protective element was 230°C.

[0042] In the protective element of Example 3, where the flux weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and held at 230°C for 1 minute was 3% or less, the cap was in good condition when the maximum reflow temperature reached during mounting of the protective element was 230°C, even when the filler content of the liquid crystal polymer constituting the cap was 0 mass%.

[0043] In the protective elements of Examples 1 and 2, where the flux weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and holding at 230°C for 1 minute was 5% or less, the cap was in good condition when the maximum reflow temperature reached during mounting of the protective element was 230°C, even if the filler content of the liquid crystal polymer constituting the cap was 15 mass% or more and 30 mass% or less.

[0044] In the protective element of Example 1, where the flux weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and held at 230°C for 1 minute was 5%, and the filler content of the liquid crystal polymer constituting the cap was 30 mass%, the cap was also in good condition when the maximum reflow temperature reached during mounting of the protective element was 260°C.

[0045] From the experimental results described above, it was confirmed that the composition of flux 10 is adjusted so that the weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and held at 190°C for 1 minute is 5% or less, thereby suppressing the expansion deformation of the cap 20 and its detachment from the insulating substrate 110 due to the pressure increase in the internal space of the cap 20 when the flux 10 is heated.

[0046] (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.

[0047] 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. Figure 8 is a plan view showing the protective element according to Embodiment 2 of the present invention with the cap removed. Figure 9 is a cross-sectional view of the protective element of Figure 8 as seen from the direction of the IX-IX arrow.

[0048] As shown in Figures 6 to 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, a lead electrode 160, a flux 10, and a cap 20.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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. Therefore, a portion of the flux 10 formed on the surface 250f of the fuse element 250 is vaporized by heating from the heating element 140. However, in this embodiment as well, the components of the flux 10 are adjusted so that the weight loss rate during the heating time from when the flux 10 is heated from room temperature to 190°C at a rate of 10°C / min and held at a temperature of 190°C for 1 minute is 5% or less. This suppresses expansion deformation of the cap 20 and detachment from the insulating substrate 110 due to the pressure increase in the internal space of the cap 20 when the flux 10 is heated.

[0053] (Note) Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0054] (1) An insulating substrate having a first main surface and a second main surface, The insulating substrate is provided with a first electrode and a second electrode, A heating element provided on the insulating substrate and located between the first electrode and the second electrode when viewed from a direction perpendicular to the first main surface, A fuse element is provided extending from the first electrode to the second electrode so as to face the first main surface, and is connected to the first electrode and the second electrode, The insulating substrate is provided with a first heating element electrode and a second heating element electrode, which are electrically connected to the heating element. A lead electrode is electrically connected to the fuse element between the first electrode and the second electrode, and is drawn out from the first heating element electrode so as to be interposed between the first main surface and the fuse element, A flux covering the surface of the fuse element opposite to the back surface facing the first main surface, The fuse element and the cap provided on the first main surface so as to cover the flux are provided. The internal space enclosed by the cap and the first main surface is sealed. The fuse element is made of a Sn-based alloy having a Pb content of 0.1% by mass or less. The flux is heated at a rate of 10°C / min from room temperature to 190°C and held at 190°C for 1 minute. The composition of the flux is adjusted so that the weight loss rate during the heating time is 5% or less, thereby suppressing the expansion deformation of the cap and detachment from the insulating substrate due to the pressure increase in the internal space when the flux is heated.

[0055] (2) The protective element according to (1), wherein the flux is adjusted such that the weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and held at a temperature of 190°C for 1 minute is 2% or less.

[0056] (3) The protective element according to (2), wherein the flux is adjusted such that the weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and held at a temperature of 230°C for 1 minute is 5% or less.

[0057] (4) The aforementioned cap is made of liquid crystal polymer, The protective element according to any one of (1) to (3), wherein the liquid crystal polymer has a filler filling rate of 15 mass% or more and 30 mass% or less.

[0058] (5) The protective element according to any one of (1) to (4), wherein the surface of the flux is covered with a wax film.

[0059] In the above-described embodiments and examples, the combinatable configurations may be combined with each other.

[0060] The embodiments and examples 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]

[0061] 10 Flux, 10s, 150f, 250f Surface, 20 Cap, 30 Bonding agent, 40 Internal space, 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, 250b Back surface, 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 extending from the first electrode to the second electrode so as to face the first main surface, and is connected to the first electrode and the second electrode, The insulating substrate is provided with a first heating element electrode and a second heating element electrode, which are electrically connected to the heating element. A lead electrode is electrically connected to the fuse element between the first electrode and the second electrode, and is drawn out from the first heating element electrode so as to be interposed between the first main surface and the fuse element, A flux covering the surface of the fuse element opposite to the back surface facing the first main surface, The fuse element and the cap provided on the first main surface so as to cover the flux are provided. The internal space enclosed by the cap and the first main surface is sealed. The fuse element is made of a Sn-based alloy having a Pb content of 0.1% by mass or less. The flux is heated at a rate of 10°C / min from room temperature to 190°C and held at 190°C for 1 minute. The composition of the flux is adjusted so that the weight loss rate during the heating time is 5% or less, thereby suppressing the expansion deformation of the cap and detachment from the insulating substrate due to the pressure increase in the internal space when the flux is heated.

2. The protective element according to claim 1, wherein the flux is adjusted such that the weight loss rate during the heating time from room temperature to 190°C at a rate of 10°C / min and held at a temperature of 190°C for 1 minute is 2% or less.

3. The protective element according to claim 2, wherein the flux is adjusted such that the weight loss rate during the heating time from room temperature to 230°C at a rate of 10°C / min and held at a temperature of 230°C for 1 minute is 5% or less.

4. The aforementioned cap is made of liquid crystal polymer, The protective element according to claim 3, wherein the liquid crystal polymer has a filler filling rate of 15 mass% or more and 30 mass% or less.

5. The protective element according to any one of claims 1 to 4, wherein the surface of the flux is covered with a wax film.

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