Protection components, battery packs

Abstract

The present invention provides a protection element, which prevents the element from being destroyed by discharging the pressure inside the box through an opening provided in the box, and can ensure proper insulation. The protection element comprises: a fusible conductor (3); first and second external connection terminals (7, 8) connected to both ends of the fusible conductor (3); and a box (6) having a lower shell (4) and an upper shell (5), one end of each of the first external connection terminal (7) and the second external connection terminal (8) being led out from the box (6), and a first opening (24) being formed on the surface of the box (6) facing the first external connection terminal (7), and a second opening (25) being formed on the surface of the box (6) facing the second external connection terminal (8).

Description

Technical Field

[0001] The present technology relates to a protection element that cuts off a current path, and a battery pack using the protection element. This application claims priority based on Japanese patent application No. 2019-157432 filed in Japan on August 29, 2019, and the application is incorporated into this application by reference. Background Art

[0002] Secondary batteries that can be recharged and reused are mostly processed into battery packs and provided to users. In particular, in order to ensure the safety of users and electronic devices, lithium-ion secondary batteries with high weight energy density usually have built-in protection circuits such as overcharge protection and over-discharge protection in the battery pack, which have the function of cutting off the output of the battery pack under predetermined circumstances.

[0003] In electronic devices using lithium-ion secondary batteries, the output is turned on / off by using a FET switch built into the battery pack, thereby performing overcharge protection or over-discharge protection actions on the battery pack. However, in the case where the FET switch is short-circuited and damaged due to some reasons, in the case where a surge or other instantaneous large current flows, or in the case where the output voltage is abnormally reduced due to the life of the battery cell, or conversely, an excessive abnormal voltage is output, it is necessary to protect the battery pack and electronic equipment from accidents such as fire. Therefore, in order to safely cut off the output of the battery cell even in any abnormal state that can be assumed, a protection element composed of a fuse element having the function of cutting off the current path according to a signal from the outside is used.

[0004] As such a protection element for a protection circuit of a lithium ion secondary battery or the like, a structure is used in which a heating element is provided inside the protection element and a fusible conductor on a current path is melted by the heat generated by the heating element.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-53260 Summary of the invention

[0008] Problems to be solved by the invention

[0009] In recent years, the use of lithium-ion secondary batteries has become more and more widespread. Research has been conducted on the use of larger currents, such as electric tools such as electric screwdrivers, hybrid vehicles, electric vehicles, electric power-assisted bicycles and other transportation equipment, and some applications have begun. In these uses, especially during startup, sometimes a large current of more than 10A to 100A flows. It is expected to realize a protection element corresponding to this large current capacity.

[0010] In order to realize a protection element that can cope with such a large current, a protection element has been proposed that uses a fusible conductor having an increased cross-sectional area and connects an insulating substrate forming a heating element to the surface of the fusible conductor.

[0011] Fig.17 , Fig.18 , Fig.19 FIG. 1 is a diagram showing a configuration example of a protection element assumed to be used for large current. Fig.17 It is a three-dimensional picture of the appearance. Fig.18 is a cross-sectional view, Fig.19 It is a top view showing the upper casing omitted. Fig.17 The protection element 100 shown constitutes a part of the external circuit by connecting a fusible conductor 103 between the first and second external connection terminals 101 and 102 connected to an external circuit such as a battery charging and discharging circuit. When an abnormality such as overvoltage occurs, the fusible conductor 103 melts, thereby cutting off the current path between the first external connection terminal 101 and the second external connection terminal 102.

[0012] The protection element 100 includes an insulating substrate 105, first and second external connection terminals 101 and 102 connected to an external circuit, two heating elements 106 arranged in parallel on the surface of the insulating substrate 105, an insulating layer 107 covering the heating elements 106, a surface electrode 108 stacked on the insulating layer 107 and connected to the heating elements 106, and a soluble conductor 103 mounted via solder paste throughout the first external connection terminal 101, the surface electrode 108, and the second external connection terminal 102.

[0013] In the protection element 100, the first and second external connection terminals 101 and 102 are provided throughout the inside and outside of the element case, and are connected to connection electrodes provided on an external circuit substrate on which the protection element 100 is mounted by screw fixing or the like, thereby integrating the soluble conductor 103 into a part of the current path formed on the external circuit substrate.

[0014] The heating element 106 is a component having a high resistance value and being conductive and generating heat when energized, and is made of, for example, nickel-chromium alloy, W, Mo, Ru, or a material containing them. In addition. The heating element 106 is connected to a heating element power supply electrode 109 formed on the surface of the insulating substrate 105. The heating element power supply electrode 109 is connected to a third external connection terminal 110 via solder paste. In the protection element 100, the third external connection terminal 110 is connected to a connection electrode provided on an external circuit substrate on which the protection element 100 is mounted, thereby connecting the heating element 106 to an external power supply provided in an external circuit. Moreover, the energization and heating of the heating element 106 are always controlled by a switching element, etc., not shown in the figure.

[0015] The heating element 106 is covered with an insulating layer 107 made of a glass layer or the like, and a surface electrode 108 is formed on the insulating layer 107, thereby overlapping the surface electrode 108 via the insulating layer 107. In addition, the soluble conductor 103 connected between the first and second external connection terminals 101 and 102 is connected to the surface electrode 108 via solder paste.

[0016] Thus, the heating element 106 and the soluble conductor 103 of the protection element 100 are thermally connected by overlapping each other, and when the heating element 106 generates heat by being energized, the soluble conductor 103 can be melted.

[0017] The soluble conductor 103 is formed of a low melting point metal such as a Pb-free solder, a high melting point metal such as an alloy mainly composed of Ag, Cu, or these metals, or has a laminated structure of a low melting point metal and a high melting point metal. Moreover, the soluble conductor 103 is connected from the first external connection terminal 101 to the second external connection terminal 102 across the surface electrode 108, thereby forming a part of the current path of the external circuit in which the protection element 100 is installed. Moreover, the soluble conductor 103 is cut off between the first and second external connection terminals 101 and 102 by flowing a current exceeding the rated value, and melting by self-heating (Joule heat) or melting by heating of the heating element 106.

[0018] Furthermore, when the protection element 100 needs to cut off the current path of the external circuit, the switching element is used to energize the heating element 106. As a result, the heating element 106 of the protection element 100 is heated to a high temperature, and the fusible conductor 103 installed on the current path of the external circuit is melted. The molten conductor of the fusible conductor 103 is attracted by the surface electrode 108 with high wettability and the first and second external connection terminals 101 and 102, thereby the fusible conductor 103 is melted. Therefore, the protection element 100 can melt between the first external connection terminal 101, the surface electrode 108 and the second external connection terminal 102, and cut off the current path of the external circuit.

[0019] The protection element 100 includes a lower housing 111 and an upper housing 112, which are joined to form a housing 113 of the protection element 100. The lower housing 111 supports the insulating substrate 105, the first and second external connection terminals 101, 102, and the third external connection terminal 110. The upper housing 112 has a space for accommodating the internal structure of the above-mentioned element. An adhesive is supplied to the outer edge of the lower housing 111, and the lower housing 111 is joined to the upper housing 112 by abutting against it.

[0020] Here, in order to cope with high current applications, the protection element 100 requires a larger size of the fusible conductor 103 and an increase in the amount of heat generated by the heating element 106 as described above. However, the thermal shock when the fusible conductor 103 melts also increases, and the air inside the housing expands rapidly. Fig. 20 As shown, there is a possibility that the upper housing 112 may fall off. In order to solve this problem, a method of providing the box body 113 with a bonding strength that can withstand the pressure or providing an opening to release the pressure has been proposed.

[0021] However, in order to improve the strength of the box, it is necessary to form a cylindrical or box-shaped structure with ceramics, etc., which has the problem of high cost. In addition, even if the opening is provided, if the opening is not in an appropriate position, the vaporized material when the fuse element is blown will spray around the element, causing the risk of contamination inside the electronic device and accidental short circuit, and the problem of not being able to ensure proper insulation.

[0022] Therefore, an object of the present technology is to provide a protection element and a battery pack using the protection element that can release the pressure inside the case through an opening provided in the case to prevent damage to the element and ensure appropriate insulation.

[0023] Solutions to Solve Problems

[0024] In order to solve the above-mentioned problems, the protection element of the present technology comprises: a fusible conductor; a first external connection terminal and a second external connection terminal, which are connected to the two ends of the above-mentioned fusible conductor; and a box body, which has a lower shell and an upper shell body, and one end of each of the above-mentioned first external connection terminal and the above-mentioned second external connection terminal is led out from the above-mentioned box body, and the surface of the above-mentioned box body facing the above-mentioned first external connection terminal is formed with a first opening portion, and the surface of the above-mentioned box body facing the above-mentioned second external connection terminal is formed with a second opening portion.

[0025] In addition, the battery pack of the present technology comprises: one or more battery cells; and a protection element, which is connected to the charge and discharge path of the above-mentioned battery cells to cut off the charge and discharge path, and the above-mentioned protection element comprises: a fusible conductor; a first external connection terminal and a second external connection terminal, which are connected to the two end portions of the above-mentioned fusible conductor; and a box body, which has a lower shell and an upper shell, and one end of the above-mentioned first external connection terminal and the above-mentioned second external connection terminal are each led out from the above-mentioned box body, and the above-mentioned box body has a first opening portion formed on the surface facing the above-mentioned first external connection terminal, and a second opening portion is formed on the surface facing the above-mentioned second external connection terminal.

[0026] Effects of the Invention

[0027] According to the present technology, a first opening is formed on the surface facing the first external connection terminal, and a second opening is formed on the surface facing the second external connection terminal, so that the air that expands rapidly inside the box when the fusible conductor is melted can be discharged, thereby preventing the box from being damaged due to a sudden increase in internal pressure. In addition, according to the present technology, even if the molten conductor and its vaporized material of the fusible conductor are scattered from the first and second openings to the outside of the box, they can be captured by the first and second external connection terminals. As a result, the protection element can discharge the pressure inside the box, preventing the element from being damaged, and the molten conductor and its vaporized material ejected from the first and second openings will not adhere to the periphery of the element, thereby preventing the risk of contamination inside the electronic device and accidental short circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a perspective view of the appearance of a protection element to which this technology is applied.

[0029] Figure 2 This is a cross-sectional view of a protection element to which this technology is applied.

[0030] Figure 3 This is a plan view showing the protection element of the present technology with the upper case omitted.

[0031] Figure 4 This is a cross-sectional view showing a state in which a fusible conductor is melted in a protection element to which the present technique is applied.

[0032] Figure 5 This is a side view of a protection element to which this technology is applied.

[0033] Figure 6 This is a side view of a protection element to which this technology is applied.

[0034] Figure 7 This is a side view of a protection element to which this technology is applied.

[0035] Figure 8 This is a side view of a protection element to which this technology is applied.

[0036] Fig. 9 This is a side view of a protection element to which this technology is applied.

[0037] Fig.10 This is a top view of a protection element to which this technology is applied.

[0038] Fig.11 This is a three-dimensional diagram of the appearance of a fusible conductor.

[0039] Fig.12 This is a circuit diagram showing a structural example of a battery pack.

[0040] Fig.13This is a circuit diagram of a protection element to which this technology is applied.

[0041] Fig.14 It is a cross-sectional view showing a modified example of the protection element to which the present technology is applied.

[0042] Fig.15 is a circuit diagram of a protection element according to a modified example.

[0043] Fig.16 It is a cross-sectional view showing a state in which the fusible conductor is melted in the protection element according to the modification.

[0044] Fig.17 This is a perspective view showing the appearance of a protection element that supports large currents.

[0045] Fig.18 yes Fig.17 A cross-sectional view of the protection element is shown.

[0046] Fig.19 The upper shell is omitted. Fig.17 A top view of the protection element is shown.

[0047] Fig. 20 It means in Fig.17 A perspective view showing a state in which the upper case of the protection element is removed due to the internal pressure when the fusible conductor melts. DETAILED DESCRIPTION

[0048] Hereinafter, the protection element and battery pack to which the present technology is applied are described in detail with reference to the accompanying drawings. In addition, the present technology is not limited to the following embodiments, and various changes can obviously be made without departing from the purpose of the present technology. In addition, the accompanying drawings are schematic diagrams, and the ratios of various dimensions are sometimes different from the actual ones. The specific dimensions should be determined by referring to the following description. In addition, of course, the drawings also contain parts with different dimensional relationships and ratios.

[0049] [First embodiment]

[0050] Figure 1 , Figure 2 , Figure 3The figure shows a protection element 1 to which the present technology is applied. The protection element 1 includes: an insulating substrate 2; a fusible conductor 3 mounted on the surface of the insulating substrate 2; and a housing 6 including a lower housing 4 supporting the back of the insulating substrate 2 and an upper housing 5 covering the surface of the insulating substrate 2, and the insulating substrate 2 is accommodated by joining the lower housing 4 and the upper housing 5. In addition, the protection element 1 includes first and second external connection terminals 7 and 8. The first and second external connection terminals 7 and 8 are provided throughout the inside and outside of the housing 6, and are connected to connection electrodes provided in an external circuit on which the protection element 1 is mounted by screw fixing or the like. The first and second external connection terminals 7 and 8 are supported by the lower housing 4, and one end of each is connected by the fusible conductor 3. Furthermore, the protection element 1 is installed in the external circuit via the first and second external connection terminals 7 and 8, whereby the fusible conductor 3 constitutes a part of the current path of the external circuit, and the current path can be cut off by utilizing the heat generated by the heating element 10 described later or by melting due to an overcurrent exceeding the rated value.

[0051] [Insulating substrate]

[0052] The insulating substrate 2 is formed of a material having insulating properties, such as alumina, glass ceramics, mullite, zirconia, etc. Alternatively, the insulating substrate 2 may be made of a material used for a printed wiring substrate such as a glass epoxy substrate or a phenolic substrate. Figure 3 In the insulating substrate 2 shown, both side edges in the extending direction of the soluble conductor 3 connected via the surface electrode 11 described later are the first side edges 2c, and both side edges formed with the heating element electrode 15 and the heating element power supply electrode 16 described later are the second side edges 2d.

[0053] [Heat generating element]

[0054] The heating element 10 that melts the fusible conductor 3 is a component with a high resistance value and conductivity that generates heat when electricity is applied, and is composed of, for example, nickel-chromium alloy, W, Mo, Ru, Cu, Ag, or an alloy containing them as a main component. The heating element 10 is formed by mixing a powder of these alloys or compositions or compounds with a resin binder or the like to form a paste, patterning the paste on the surface 2a of the insulating substrate 2 using a screen printing technique, and sintering the paste.

[0055] The heating element 10 is covered by an insulating layer 9 on the surface 2a of the insulating substrate 2. A surface electrode 11 described later is stacked on the insulating layer 9. The insulating layer 9 protects and insulates the heating element 10, and is provided to efficiently transfer the heat of the heating element 10 to the surface electrode 11 and the soluble conductor 3, and is composed of, for example, a glass layer.

[0056] One end of the heating element 10 is connected to a heating element electrode 15 formed on the surface 2a of the insulating substrate 2. In addition, the heating element electrode 15 is connected to a surface electrode 11 formed on the insulating layer 9. Thus, the heating element 10 is electrically connected to the soluble conductor 3 mounted on the surface electrode 11. In addition, the other end of the heating element 10 is connected to a heating element power supply electrode 16. The heating element power supply electrode 16 is formed on the surface 2a of the insulating substrate 2, and is connected to a third external connection terminal 17 via a connection material 20 such as solder paste, and is connected to an external circuit via the third external connection terminal 17. Moreover, the heating element 10 is connected to the external circuit through the protection element 1, and is installed in a power supply path for the heating element 10 formed in the external circuit via the third external connection terminal 17.

[0057] In addition, if Figure 3 As shown, the heating element 10 is formed so that the current-carrying direction intersects with the current-carrying direction of the soluble conductor 3, and the heating element electrode 15 and the heating element power supply electrode 16 are formed on the second side edge portion 2d. This is preferable in terms of effectively using the area of ​​the insulating substrate 2.

[0058] In addition, a plurality of heating elements 10 may be formed on the surface of the insulating substrate 2. Figure 3 In the example of the protection element 1 shown, two heat generating elements 10 are formed. One end of each heat generating element 10 is connected to a heat generating element electrode 15, and the other end is connected to a heat generating element power supply electrode 16, and they are electrically connected in parallel.

[0059] In addition, the protection element 1 may form the heating element 10 inside the insulating layer 9 stacked on the surface 2a of the insulating substrate 2. In addition, the protection element 1 may form the heating element 10 inside the insulating substrate 2. In addition, the protection element 1 may form the heating element 10 on the back surface 2b of the insulating substrate 2. In addition, when the heating element 10 is formed on the back surface 2b of the insulating substrate 2, one end of the heating element 10 is connected to the back electrode formed on the back surface 2b of the insulating substrate 2, and is electrically connected to the fusible conductor 2 mounted on the surface electrode 11 via a conductive through hole penetrating between the back electrode and the surface electrode 11. In addition, the other end of the heating element 10 is connected to the third external connection terminal 17 via the heating element power supply electrode formed on the back surface 2b of the insulating substrate 2.

[0060] [Surface electrode]

[0061] A surface electrode 11 is formed on the insulating layer 9 and is connected to the heating element 10 via the heating element electrode 15 and is connected to the soluble conductor 3. The surface electrode 11 is connected to the soluble conductor 3 via a bonding material 20 such as solder paste. In addition, when the soluble conductor 3 melts, the surface electrode 11 causes the molten conductor 3a to aggregate, thereby being able to melt the soluble conductor 3.

[0062] The surface electrode 11 may also be formed with a suction hole 12. When the fusible conductor 3 melts, the suction hole 12 sucks the molten conductor 3a by capillary action, thereby reducing the volume of the molten conductor 3a held on the surface electrode 11 (see Figure 4 ). The protective element 1 increases the cross-sectional area of ​​the fusible conductor 3 in order to cope with high current applications. Thus, even when the amount of melting increases, the volume of the fusible conductor 3a can be reduced by allowing the suction hole 12 to suck. The insulating substrate 2 having such a structure constitutes the following fuse component 18: when the heating element 10 is energized and generates heat, the fusible conductor 3 is melted by the heat, and the fusible conductor 3a is sucked into the suction hole 12 and cut off.

[0063] As a result, the protection element 1 reduces the volume of the molten conductor 3a maintained on the surface electrode 11, and more reliably realizes the insulation between the first and second external connection terminals 7 and 8. In addition, it reduces the scattering of the molten conductor 3a caused by the arc discharge generated when the soluble conductor 3 is melted, prevents the reduction of insulation resistance, and further, can prevent the soluble conductor 3 from adhering to the peripheral circuit of the mounting position and causing a short-circuit fault.

[0064] A conductive layer 13 is formed on the inner surface of the suction hole 12. By forming the conductive layer 13, the suction hole 12 can easily suck the molten conductor 3a. The conductive layer 13 is formed of, for example, any one of copper, silver, gold, iron, nickel, palladium, lead, and tin, or an alloy containing any one of them as a main component, and can be formed on the inner surface of the suction hole 12 by a known method such as electroplating or printing of a conductive paste. Alternatively, the conductive layer 13 may be formed by inserting a plurality of metal wires or an aggregate of conductive tapes into the suction hole 12.

[0065] In addition, the suction hole 12 is preferably formed as a through hole that penetrates in the thickness direction of the insulating substrate 2. Thus, the suction hole 12 can suck the molten conductor 3a to the back surface 2b side of the insulating substrate 2, and can suck more molten conductor 3a, thereby reducing the volume of the molten conductor 3a at the fused portion. In addition, the suction hole 12 may be formed as a non-through hole.

[0066] The conductive layer 13 of the suction hole 12 is continuous with the surface electrode 11 formed on the surface 2a of the insulating substrate 2. The surface electrode 11 supports the fusible conductor 3 and aggregates the molten conductor 3a. Therefore, by making the surface electrode 11 and the conductive layer 13 continuous, the molten conductor 3a can be easily introduced into the suction hole 12.

[0067] Furthermore, the conductive layer 13 and the surface electrode 11 are heated by the heating element 10, so that the molten conductor 3a of the soluble conductor 3 can be easily attracted into the attraction hole 12, and can be easily aggregated on the surface electrode 11. Therefore, the protection element 1 can promote the action of attracting the molten conductor 3a from the surface electrode 11 to the attraction hole 12 via the conductive layer 13, and can reliably melt the soluble conductor 3.

[0068] In addition, a back electrode 14 connected to the conductive layer 13 of the suction hole 12 may be formed on the back surface 2b of the insulating substrate 2. The back electrode 14 is continuous with the conductive layer 13, so that when the soluble conductor 3 is melted, the molten conductor 3a moving through the suction hole 12 is condensed (see Figure 4 ). As a result, the protection element 1 can attract more molten conductors 3a, thereby reducing the volume of the molten conductors 3a at the fused portion.

[0069] In addition, the protective element 1 may also form a plurality of attraction holes 12 to increase the paths for attracting the molten conductor 3a of the soluble conductor 3, thereby attracting more molten conductor 3a and reducing the volume of the molten conductor 3a at the fused portion. In this case, the plurality of attraction holes 12 may be formed over the width direction of the soluble conductor 3 where the surface electrode 11 and the soluble conductor 3 overlap. In addition, the attraction holes 12 may be formed in the region where the surface electrode 11 and the soluble conductor 3 do not overlap where the molten conductor 3a wets and spreads.

[0070] In addition, when two heating elements 10 are arranged in parallel, when they are formed on any one of the surface 2a, the back surface 2b and the inside of the insulating substrate 2, they are preferably formed on both sides of the suction hole 12 in order to heat the surface electrode 11 and the back surface electrode 14 and attract and condense more molten conductors 3a.

[0071] [Box]

[0072] Next, the case 6 of the protection element 1 is described. The case 6 is formed by bonding the lower case 4 and the upper case 5 with an adhesive. The case 6 can be formed using, for example, various engineering plastics, thermoplastics, ceramics, or other insulating members. In addition, the case 6 has a sufficient internal space so that the fusible conductor 3 expands into a spherical shape when it melts on the surface 2a of the insulating substrate 2 and the fusible conductor 3a condenses on the surface electrode 11 and the first and second external connection terminals 7 and 8.

[0073] [Lower side case]

[0074] like Figure 2As shown, the lower shell 4 is provided with a concave portion 23 in the approximate center portion thereof for hollowly holding the center portion of the insulating substrate 2. The lower shell 4 supports the outer edge of the insulating substrate 2 along the side edge of the concave portion 23. By providing the concave portion 23, the contact area between the lower shell 4 and the insulating substrate 2 is reduced, and the heat of the heating element 10 can be suppressed from being absorbed by the lower shell 4. Therefore, the protection element 1 can efficiently transfer the heat of the heating element 10 to the fusible conductor 3, and can be melted more quickly. In particular, by providing the concave portion 23 in the approximate center portion of the lower shell 4, the area directly below the heating element 10 is hollow, and the heat dissipation of the heat of the heating element 10 to the lower shell 4 can be suppressed.

[0075] [Upper side case]

[0076] The upper case 5 covers the soluble conductor 3 and the first and second external connection terminals 7 and 8 formed on the surface 2 a of the insulating substrate 2 , and has an internal space that allows the fused soluble conductor 3 a to condense on the surface electrode 11 and the first and second external connection terminals 7 and 8 .

[0077] In addition, the upper housing 5 has a recessed portion formed on the lower end surface of the side wall that is butted against the lower housing 4, for arranging the first and second external connection terminals 7, 8 and the third external connection terminal 17 supported on the lower housing 4 throughout the inside and outside of the housing 6. The recessed portion is formed at a position corresponding to the arrangement position of the first and second external connection terminals 7, 8 and the third external connection terminal 17, and has a shape corresponding to the shape of the first and second external connection terminals 7, 8 and the third external connection terminal 17. Therefore, the housing 6 can butt-join the lower housing 4 and the upper housing 5 without a gap, and can lead the first and second external connection terminals 7, 8 and the third external connection terminal 17 out of the housing.

[0078] [First to third openings]

[0079] The protection element 1 to which the present technology is applied has a first opening 24 formed on the surface facing the first external connection terminal 7 and a second opening 25 formed on the surface facing the second external connection terminal 8. The protection element 1 has a third opening 26 formed on the surface facing the third external connection terminal 17.

[0080] When the protective element 1 has a larger fusible conductor 3 for high current use or the heat generated by the heating element 10 increases, the load on the housing 6 due to the increase in internal pressure when the fusible conductor 3 melts becomes larger. The protective element 1 is provided with the first to third openings 24 to 26, so that the air that rapidly expands inside the housing 6 when the fusible conductor 3 melts can be discharged, thereby preventing the housing 6 from being damaged due to the rapid increase in internal pressure.

[0081] The first opening 24 is formed facing the surface of the first external connection terminal 7, the second opening 25 is formed facing the surface of the second external connection terminal 8, and the third opening 26 is formed facing the surface of the third external connection terminal 17. The first to third openings 24 to 26 are formed at the lower edge of the upper case 5, so when the lower case 4 and the upper case 5 are molded from plastic such as LCP (Liquid Crystal Polymer), the moldability is excellent, and the processability is also excellent in other materials and manufacturing processes.

[0082] The first to third external connection terminals 7, 8, 17 are led out of the housing 6 and connected to the electrode terminals of the external circuit, so the temperature is significantly lower than that of the molten conductor 3a and its vaporized material of the fusible conductor 3 that is melted by the heat of the heating element 10 or the self-heating caused by the overcurrent. In addition, the first to third external connection terminals 7, 8, 17 having conductivity have excellent wettability with respect to the molten conductor 3a. Therefore, the molten conductor 3a and its vaporized material that have passed through the first to third openings 24 to 26 are easily in contact with the first to third external connection terminals 7, 8, 17 facing the first to third openings 24 to 26, and are rapidly cooled by the contact.

[0083] Therefore, in the protection element 1, even when the molten conductor 3a of the fusible conductor 3 and its vaporized substances are scattered from the first to third openings 24 to 26 to the outside of the housing 6, they can be attached to and captured by the first and second metal external connection terminals 7, 8 and the third external connection terminal 17. Thus, the protection element 1 can release the pressure inside the housing to prevent the destruction of the element, and the molten conductor 3a and its vaporized substances ejected from the first to third openings 24 to 26 will not adhere to the periphery of the element, thereby preventing the risk of contamination inside the electronic device and accidental short circuit.

[0084] The first to third openings 24 to 26 are formed at the lower edge of the side surface of the upper case 5 and face the first to third external connection terminals 7, 8, 17 arranged inside and outside the box 6 from between the lower case 4 and the upper case 5 when the lower case 4 and the upper case 5 are joined.

[0085] In addition, the first to third external connection terminals 7, 8, and 17 are supported on the lower shell 4 in the same manner as the insulating substrate 2 on which the soluble conductor 3 is mounted, so that the first to third openings 24 to 26 are opened on a plane substantially the same as the soluble conductor 3 through the lower edge formed on the side of the upper shell 5, and the flow of expanded air is discharged smoothly.

[0086] The shapes of the first to third openings 24 to 26 are not particularly limited, and may be rectangular ( Figure 5 ), round( Figure 6 ),triangle( Figure 7 ), semi-cylindrical ( Figure 8 ), elliptical, trapezoidal, etc. Among them, preferably a triangle, trapezoidal, etc., in which the width of the lower side is wider than the width of the upper side in side view. By increasing the width of the lower side, the melting conductor 3a and its vaporized material passing through the first to third openings 24 to 26 can be easily captured by contacting the first to third external connection terminals 7, 8, 17 facing the lower side of the first to third openings 24 to 26. In addition, the first to third openings 24 to 26 with circular or elliptical shapes can easily capture the spherical melting conductor 3a.

[0087] In addition, it is preferable that a plurality of the first to third openings 24 to 26 are formed. This is because more molten conductors 3a and their vaporized substances can be captured. The plurality of first to third openings 24 to 26 can be of the same size and shape, or of different shapes. For example, the first to third openings 24 to 26 formed near the center of the first to third external connection terminals 7, 8, 17 in the width direction are formed larger than the first to third openings 24 to 26 formed on the side edges of the first to third external connection terminals 7, 8, 17 in the width direction, thereby capturing more molten conductors 3a and their vaporized substances near the center of the terminals.

[0088] In addition, since the first and second openings 24 and 25 are opened on the side of the first and second external connection terminals 7 and 8 that cut off conduction, the molten conductor 3a can be discharged to the outside of the box, so that the molten conductor 3a in the box can be prevented from being retained, which is advantageous in improving insulation. Therefore, the number of the first and second openings 24 and 25 may be greater than the number of the third opening 26. Alternatively, the total area of ​​the opening diameters of the first and second openings 24 and 25 may be larger than the total area of ​​the opening diameters of the third opening 26.

[0089] Furthermore, in the protection element 1, in addition to the first to third openings 24 to 26, an auxiliary opening 27 may be formed at a location other than the location facing the first to third external connection terminals 7, 8, 17. The auxiliary opening 27 is mainly an opening for releasing the internal pressure in the box 6, and its location is not limited. For example, Fig. 9 As shown, the auxiliary opening 27 is formed near the upper edge of the side wall of the upper housing 5. Fig.10 As shown, it is formed on the top surface of the upper housing 5 .

[0090] [Fusible conductor]

[0091] Next, the soluble conductor 3 is described. The soluble conductor 3 is installed between the first and second external connection terminals 7 and 8, and is melted by self-heating (Joule heat) due to the heat generated by the energization of the heating element 10 or the flow of a current exceeding the rated value, thereby cutting off the current path between the first external connection terminal 7 and the second external connection terminal 8.

[0092] The fusible conductor 3 can be any conductive material as long as it is heated by the heating element 10 or melted by an overcurrent condition. For example, in addition to SnAgCu-based Pb-free solder, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc. can also be used.

[0093] In addition, the fusible conductor 3 may also be a structure containing a high melting point metal and a low melting point metal. Fig.11 As shown, the soluble conductor 3 is a laminated structure composed of an inner layer and an outer layer, and has a low melting point metal layer 31 as an inner layer and a high melting point metal layer 32 as an outer layer laminated on the low melting point metal layer 31. The soluble conductor 3 is connected to the first and second external connection terminals 7 and 8 and the surface electrode 11 via a bonding material 20 such as solder paste.

[0094] The low melting point metal layer 31 is preferably solder or a metal with Sn as the main component, which is generally called "Pb-free solder". The melting point of the low melting point metal layer 31 does not necessarily have to be higher than the temperature of the reflow furnace, and it can also melt at about 200°C. The high melting point metal layer 32 is a metal layer stacked on the surface of the low melting point metal layer 31, for example, Ag or Cu or a metal with any of them as the main component, and has a high melting point that does not melt even when the first and second external connection terminals 7, 8 and the surface electrode 11 are connected to the soluble conductor 3 by reflow soldering.

[0095] Such a soluble conductor 3 can be formed by forming a high melting point metal layer on a low melting point metal foil using an electroplating technique, or by using other known lamination techniques or film formation techniques. In this case, the soluble conductor 3 may be a structure in which the entire surface of the low melting point metal layer 31 is covered by the high melting point metal layer 32, or a structure in which only a pair of opposing side surfaces are covered. In addition, the soluble conductor 3 may be configured such that the high melting point metal layer 32 is provided as an inner layer and the low melting point metal layer 31 is provided as an outer layer, or a multilayer structure in which three or more layers of low melting point metal layers and high melting point metal layers are alternately stacked is formed, or an opening is provided in a part of the outer layer to expose a part of the inner layer, and various structures can be used.

[0096] The soluble conductor 3 is formed by laminating the high melting point metal layer 32 as an outer layer on the low melting point metal layer 31 as an inner layer, so that even when the reflow temperature exceeds the melting temperature of the low melting point metal layer 31, the soluble conductor 3 can maintain its shape and not be melted. Therefore, the protection element 1 can efficiently connect the first and second external connection terminals 7 and 8 and the surface electrode 11 to the soluble conductor 3 by reflow. In addition, the protection element 1 can prevent the melting characteristics from changing, such as not melting at a predetermined temperature or melting at a temperature lower than a predetermined temperature, due to the resistance value being locally increased or decreased due to deformation of the soluble conductor 3, even by reflow.

[0097] In addition, the fusible conductor 3 does not melt due to self-heating while a predetermined rated current is flowing. Moreover, when a current higher than the rated value is flowing, the fusible conductor 3 melts due to self-heating, thereby cutting off the current path between the first and second external connection terminals 7 and 8. In addition, the fusible conductor 3 is heated by the heating element 10 and melts, thereby cutting off the current path between the first and second external connection terminals 7 and 8.

[0098] At this time, the soluble conductor 3 causes the molten low melting point metal layer 31 to corrode (solder corrode) the high melting point metal layer 32, and the high melting point metal layer 32 melts at a temperature lower than the melting temperature. Therefore, the soluble conductor 3 can be melted in a short time by the corrosive action of the low melting point metal layer 31 on the high melting point metal layer 32. In addition, the molten conductor 3a of the soluble conductor 3 is separated by the physical attraction of the surface electrode 11 and the first and second external connection terminals 7 and 8, so that the current path between the first and second external connection terminals 7 and 8 can be quickly and reliably cut off ( Figure 5 ).

[0099] In addition, the soluble conductor 3 is preferably formed such that the volume of the low melting point metal layer 31 is larger than the volume of the high melting point metal layer 32. The soluble conductor 3 is heated by the self-heating caused by the overcurrent or the heat of the heating element 10, and the low melting point metal is melted to corrode the high melting point metal, thereby being able to melt and fuse quickly. Therefore, the soluble conductor 3 is formed such that the volume of the low melting point metal layer 31 is larger than the volume of the high melting point metal layer 32, so that the corrosion action can be promoted and the first and second external connection terminals 7 and 8 can be quickly cut off.

[0100] In addition, the soluble conductor 3 is formed by laminating a high melting point metal layer 32 on a low melting point metal layer 31 as an inner layer, so the melting temperature can be significantly lowered compared to conventional sheet-shaped fuses made of high melting point metals. Therefore, compared to sheet-shaped fuses of the same size, the soluble conductor 3 can have a larger cross-sectional area and a significantly higher current rating. In addition, compared to conventional sheet-shaped fuses having the same current rating, it is possible to achieve miniaturization, thinness, and excellent rapid melting performance.

[0101] In addition, the fusible conductor 3 can improve the resistance (pulse resistance) to surges in which abnormally high voltages are applied instantaneously to the electrical system in which the protection element 1 is installed. That is, the fusible conductor 3 will not melt even when a current of, for example, 100A flows for a few milliseconds. This is because a large current that flows for a very short time flows through the surface layer of the conductor (skin effect), and the fusible conductor 3 is provided with a high melting point metal layer 32 such as Ag plating with a low resistance value as an outer layer, so that the current applied by the surge can easily flow through, and it can prevent melting due to self-heating. Therefore, compared with the existing fuse composed of solder alloy, the fusible conductor 3 can greatly improve the resistance to surges.

[0102] Furthermore, the soluble conductor 3 may be coated with a flux (not shown) for the purpose of preventing oxidation and improving wettability during melting.

[0103] [Circuit Configuration Example]

[0104] like Fig.12 As shown, such a protection element 1 is used by being incorporated into a circuit in a lithium ion secondary battery pack 33. The battery pack 33 has a battery stack 35 composed of, for example, four lithium ion secondary battery cells 34a to 34d in total.

[0105] The battery pack 33 includes: a battery stack 35; a charge and discharge control circuit 36, which controls the charge and discharge of the battery stack 35; a protection element 1, which cuts off the charge and discharge path when the battery stack 35 is abnormal and applies the present invention; a detection circuit 37, which detects the voltage of each battery cell 34a~34d; and a current control element 38 as a switching element, which controls the operation of the protection element 1 according to the detection result of the detection circuit 37.

[0106] The battery stack 35 is connected in series with battery cells 34a to 34d that are required to be controlled to avoid overcharge and overdischarge, and is detachably connected to the charging device 29 via the positive terminal 33a and the negative terminal 33b of the battery pack 33, and is applied with a charging voltage from the charging device 29. The battery pack 33 charged by the charging device 29 connects the positive terminal 33a and the negative terminal 33b to an electronic device operated by the battery, thereby enabling the electronic device to be operated.

[0107] The charge and discharge control circuit 36 ​​includes two current control elements 39a and 39b connected in series to the current path between the battery stack 35 and the charging device 29, and a control unit 40 that controls the operation of these current control elements 39a and 39b. The current control elements 39a and 39b are composed of, for example, field effect transistors (hereinafter referred to as FETs), and the control unit 40 controls the gate voltage to control the conduction and disconnection of the battery stack 35 in the charging direction and / or the discharging direction of the current path. The control unit 40 operates by receiving power supply from the charging device 29, and controls the operation of the current control elements 39a and 39b to disconnect the current path when the battery stack 35 is over-discharged or over-charged based on the detection result of the detection circuit 37.

[0108] The protection element 1 is connected to, for example, a charge and discharge current path between the battery stack 35 and the charge and discharge control circuit 36 ​​, and its operation is controlled by a current control element 38 .

[0109] The detection circuit 37 is connected to each battery cell 34a to 34d, detects the voltage value of each battery cell 34a to 34d, and supplies each voltage value to the control unit 40 of the charge and discharge control circuit 36. In addition, the detection circuit 37 outputs a control signal for controlling the current control element 38 when any of the battery cells 34a to 34d reaches an overcharge voltage or an overdischarge voltage.

[0110] The current control element 38 is composed of, for example, a FET, and is controlled according to the detection signal output from the detection circuit 37 so that when the voltage value of the battery cells 34a~34d exceeds the voltage of a predetermined over-discharge or over-charge state, the protection element 1 is activated, and the charge and discharge current path of the battery stack 35 is cut off regardless of the switching action of the current control elements 39a and 39b.

[0111] The protection element 1 to which the present invention is applied and used for the battery pack 33 having the above structure has Fig.13 The circuit structure shown. That is, in the protection element 1, the first external connection terminal 7 is connected to the battery stack 35 side, and the second external connection terminal 8 is connected to the positive terminal 33a side, thereby, the fusible conductor 3 is connected in series to the charge and discharge path of the battery stack 35. In addition, in the protection element 1, the heating element 10 is connected to the current control element 38 via the heating element power supply electrode 16 and the third external connection terminal 17, and the heating element 10 is connected to the open end of the battery stack 35. Thus, the heating element 10 connects one end to the fusible conductor 3 and the open end of one side of the battery stack 35 via the surface electrode 11, and connects the other end to the current control element 38 and the open end of the other side of the battery stack 35 via the third external connection terminal 17. Thus, a power supply path to the heating element 10 is formed, in which the current control element 38 controls the power supply.

[0112] [Operation of protection element]

[0113] When the detection circuit 37 detects an abnormal voltage in any of the battery cells 34a to 34d, a cutoff signal is output to the current control element 38. Then, the current control element 38 controls the current to energize the heating element 10. In the protection element 1, the current flows from the battery stack 35 to the heating element 10, whereby the heating element 10 starts to generate heat. The protection element 1 causes the fusible conductor 3 to melt due to the heat generated by the heating element 10, thereby cutting off the charge and discharge path of the battery stack 35. In addition, the protection element 1 forms the fusible conductor 3 to contain a high melting point metal and a low melting point metal, so that the low melting point metal can be melted before the high melting point metal melts, and the fusible conductor 3 can be melted in a short time by utilizing the corrosive effect of the molten low melting point metal on the high melting point metal.

[0114] When the soluble conductor 3 of the protection element 1 is melted, the power supply path to the heating element 10 is also cut off, so that the heating element 10 stops generating heat.

[0115] Furthermore, when an overcurrent exceeding the rating flows through the battery pack 33 , the protection element 1 can melt the soluble conductor 3 by self-heating, thereby interrupting the charge and discharge path of the battery pack 33 .

[0116] Here, the surface of the protection element 1 facing the first external connection terminal 7 is formed with a first opening 24, and the surface facing the second external connection terminal 8 is formed with a second opening 25. In addition, the surface of the protection element 1 facing the third external connection terminal 17 is formed with a third opening 26. Therefore, the protection element 1 can discharge the pressure inside the box to prevent the damage of the element.

[0117] Furthermore, even when the molten conductor 3a of the fusible conductor 3 and its vaporized substances are scattered from the first to third openings 24 to 26 to the outside of the housing 6, the protection element 1 can capture the first and second external connection terminals 7 and 8 and the third external connection terminal 17. Thus, in the protection element 1, the molten conductor 3a and its vaporized substances ejected from the first to third openings 24 to 26 do not adhere to the periphery of the element, and the risk of contamination inside the electronic device and an unexpected short circuit can be prevented.

[0118] In this way, the protection element 1 melts the soluble conductor 3 by the heat generated by the energization of the heating element 10 or the self-heating of the soluble conductor 3 caused by the overcurrent. At this time, even when the protection element 1 is exposed to a high temperature environment in which the soluble conductor 3 is reflow-mounted on the first and second external connection terminals 7 and 8, the surface electrode 11, etc., the deformation of the soluble conductor 3 is suppressed because the low-melting-point metal is covered with the high-melting-point metal. Therefore, the change in the fusing characteristics caused by the change in the resistance value due to the deformation of the soluble conductor 3 can be prevented, and the soluble conductor 3 can be quickly melted by the predetermined overcurrent and the heat generated by the heating element 10.

[0119] The protection element 1 of the present invention is not limited to being used in a battery pack of a lithium ion secondary battery, but can be applied to various uses that require interruption of a current path using an electric signal.

[0120] [Modifications]

[0121] Next, a modified example of a protection element to which the present technology is applied is described. In the following description, the same reference numerals are sometimes used to indicate the same structure as the above-mentioned protection element 1, and the details thereof are omitted. Fig.14 As shown, in a protection element 50 according to a modified example, the soluble conductor 3 may be sandwiched between a plurality of fuse members 18 . Fig.14 In the protection element 50 shown, the fuse members 18 are disposed on one surface and the other surface of the soluble conductor 3 . Fig.15 This is a circuit diagram of the protection element 50. Each of the fuse components 18 disposed on the surface and the back surface of the soluble conductor 3 has one end of the heating element 10 connected to the soluble conductor 3 via the heating element electrode 15 and the surface electrode 11 formed on each insulating substrate 2, and the other end of the heating element 10 is connected to a power source for generating heat for the heating element 10 via the heating element power supply electrode 16 and the third external connection terminal 17 formed on each insulating substrate 2.

[0122] In addition, if Fig.16 As shown, when the protective element 50 melts the fusible conductor 3 by the heat generated by the heating element 10, the heating elements 10 of the fuse components 18, 18 connected to both sides of the fusible conductor 3 generate heat, thereby heating the fusible conductor 3 from both sides. Therefore, the protective element 50 can quickly heat and melt the fusible conductor 3 even when the cross-sectional area of ​​the fusible conductor 3 is increased to cope with high current applications.

[0123] The protection element 50 also has the same housing 6 as the protection element 1, and has a first opening 24 formed on the surface facing the first external connection terminal 7, and a second opening 25 formed on the surface facing the second external connection terminal 8. In addition, the protection element 50 has a third opening 26 formed on the surface facing the third external connection terminal 17.

[0124] In addition, the protection element 50 draws the molten conductor 3a from both sides of the molten conductor 3 into each of the draw holes 12 of the insulating substrate 2 formed in each of the fuse parts 18. Therefore, even when the cross-sectional area of ​​the molten conductor 3 is increased to cope with a large current application and a large amount of the molten conductor 3a is produced, the protection element 50 can draw the molten conductor 3 through the plurality of fuse parts 18 and reliably blow the molten conductor 3. In addition, the protection element 50 draws the molten conductor 3a through the plurality of fuse parts 18, thereby making it possible to blow the molten conductor 3 more quickly.

[0125] The protection element 50 can also quickly blow the soluble conductor 3 when using a coating structure in which a low-melting-point metal constituting an inner layer is coated with a high-melting-point metal as the soluble conductor 3. That is, when the soluble conductor 3 coated with the high-melting-point metal is heated by the heating element 10, it takes time to heat the high-melting-point metal of the outer layer to a temperature at which the high-melting-point metal melts. Here, the protection element 50 has a plurality of fuse components 18, and by causing each heating element 10 to heat at the same time, the high-melting-point metal of the outer layer can be quickly heated to a melting temperature. Therefore, according to the protection element 50, the thickness of the high-melting-point metal layer constituting the outer layer can be thickened, and a higher rating can be achieved while maintaining the rapid blowout characteristics.

[0126] In addition, if Fig.14 As shown, the protection element 50 is preferably connected to the soluble conductor 3 by a pair of fuse parts 18, 18 facing each other. Thus, the protection element 50 can heat the same part of the soluble conductor 3 from both sides at the same time by using the pair of fuse parts 18, 18, and attract the molten conductor 3a, so that the soluble conductor 3 can be heated and melted more quickly.

[0127] In the protection element 50, the surface electrodes 11 of the insulating substrates 2 formed on the pair of fuse components 18, 18 are preferably opposed to each other via the soluble conductor 3. Thus, by symmetrically connecting the pair of fuse components 18, 18, the load applied to the soluble conductor 3 during reflow mounting or the like can be prevented from being unbalanced, and the resistance to deformation can be improved.

[0128] Furthermore, when the heating element 10 is formed on either the surface 2a or the back surface 2b of the insulating substrate 2, it is preferably formed on both sides of the suction hole 12 in order to heat the surface electrode 11 and the back surface electrode 14 and to condense and suction more molten conductors 3a.

[0129] Explanation of symbols

[0130] 1—protection element, 2—insulating substrate, 2a—surface, 2b—back surface, 2c—first side edge, 2d—second side edge, 3—fusible conductor, 3a—melting conductor, 4—lower shell, 5—upper shell, 6—box, 7—first external connection terminal, 8—second external connection terminal, 9—insulating layer, 10—heating element, 11—surface electrode, 12—attraction hole, 13—conductive layer, 14—back electrode, 15—heating element electrode, 16—heating element power supply electrode, 17—third external connection terminal, 18—fuse component, 20—joining material, 24—first opening portion, 25—second opening portion, 26—third opening portion, 29—charging device, 31—low melting point metal layer, 32—high melting point metal layer, 33—battery pack, 33a—positive terminal, 33b—negative terminal, 34—battery cell, 35—battery stack, 36—charge and discharge control circuit, 37—detection circuit, 38—current control element, 39—current control element, 40—control unit, 50—protection element, 100—protection element.

Claims

1. A protection element, characterized in that: have: Fusible conductors; A first external connection terminal and a second external connection terminal connected to both ends of the fusible conductor; and A box body, comprising a lower shell and an upper shell, One end of each of the first external connection terminal and the second external connection terminal is led out from the box body. The box body has a first opening formed on a surface facing the first external connection terminal, and a second opening formed on a surface facing the second external connection terminal. The first external connection terminal and the second external connection terminal are led out from between the lower housing and the upper housing. The first opening and the second opening are formed at the lower edge of the side surface of the upper housing. At least one of the first opening and the second opening has a lower width wider than an upper width in a side view. The protection element further comprises an insulating substrate having the fusible conductor mounted on the surface thereof. The insulating substrate supports the back side of the lower shell. The insulating substrate includes a heating element and a third external connection terminal connected to the heating element and serving as a power supply terminal for the heating element. One end of each of the third external connection terminals is led out from the box body. A third opening is formed on a surface of the box body facing the third external connection terminal. The heating element is covered with an insulating layer on the surface of the insulating substrate. A surface electrode is stacked on the insulating layer. The surface electrode is connected to the fusible conductor. The surface electrode forms a suction hole. When the soluble conductor melts, the suction hole sucks the molten conductor to reduce the volume of the molten conductor held on the surface electrode.

2. The protection element according to claim 1, characterized in that: The third external connection terminal is led out from between the lower housing and the upper housing. The third opening is formed at a lower edge of a side surface of the upper housing.

3. The protection element according to claim 1, characterized in that: The third opening has a width at a lower side wider than a width at an upper side in a side view.

4. The protection element according to claim 1, characterized in that: A plurality of the first openings and the second openings are formed.

5. The protection element according to claim 1, characterized in that: A plurality of the third openings are formed.

6. The protection element according to claim 1, characterized in that: Auxiliary openings are also formed at locations other than the locations from which the first external connection terminal and the second external connection terminal are led out.

7. A battery pack, characterized in that: have: More than one battery cell; and A protection element is connected to the charge and discharge path of the battery cell to cut off the charge and discharge path. The above protection element has: Fusible conductors; A first external connection terminal and a second external connection terminal connected to both ends of the fusible conductor; and A box body having a lower shell and an upper shell, One end of each of the first external connection terminal and the second external connection terminal is led out from the box body. The box body has a first opening formed on a surface facing the first external connection terminal, and a second opening formed on a surface facing the second external connection terminal. The first external connection terminal and the second external connection terminal are led out from between the lower housing and the upper housing. The first opening and the second opening are formed at the lower edge of the side surface of the upper housing. At least one of the first opening and the second opening has a lower width wider than an upper width in a side view. The protection element further comprises an insulating substrate having the fusible conductor mounted on the surface thereof. The insulating substrate supports the back side of the lower shell. The insulating substrate includes a heating element and a third external connection terminal connected to the heating element and serving as a power supply terminal for the heating element. One end of each of the third external connection terminals is led out from the box body. A third opening is formed on a surface of the box body facing the third external connection terminal. The heating element is covered with an insulating layer on the surface of the insulating substrate. A surface electrode is stacked on the insulating layer. The surface electrode is connected to the fusible conductor. The surface electrode forms a suction hole. When the soluble conductor melts, the suction hole sucks the molten conductor to reduce the volume of the molten conductor held on the surface electrode.

Images