Productive element and method for manufacturing productive element

Abstract

The objective of this invention is to achieve rapid and reliable melting even when the cross-sectional area of ​​the meltable is large by properly applying flux. The protective element of the present invention comprises: an insulating substrate 2, a heating element 4, an insulating layer 5 covering the heating element 4, an intermediate electrode 6, a fusible body 3, a cover member 30, and a flux 7. The protrusion 31 of the cover member 30 is erected facing the intermediate electrode 6. The intermediate electrode 6 has a length longer than the width of the fusible body 3 in a direction orthogonal to the energizing direction of the fusible body 3, and at least one of its ends 6a and 6b protrudes beyond the fusible body 3. The protrusion 31 is disposed at a position opposite to the position of the intermediate electrode 6 on which the fusible body 3 is mounted, and at a position opposite to the ends 6a and 6b on which the fusible body 3 is not mounted.

Description

Protection element and method for manufacturing the same The present technology relates to a protection element installed on a current path, which utilizes heating by a heating element to melt a fusible element and cut off the current path. Lithium-ion secondary batteries offer high output and energy density, and are used in small mobile devices such as laptops, mobile phones, and smartphones. In recent years, their adoption has been steadily increasing in power tools, electric bicycles, electric motorcycles, electric vehicles, and household batteries, which require high capacitance, high current, and high voltage. However, these batteries use organic solvents, which can cause fire and smoke hazards when the battery's temperature, input / output current, and charging voltage exceed their operating ranges. Therefore, they typically incorporate electronic protection circuits and components. These components include FETs that electrically turn on and off, thermistors that sense temperature, and fuses that physically cut off the circuit. Fuses with heating elements are often used. In addition to the typical overcurrent-induced tripping function of conventional current fuses, fuses with attached heating elements can also heat the heating element, melting the fusible element and tripping the circuit when the electronic circuit senses an anomaly. Compared to conventional current fuses that only trip due to overcurrent, these protection elements offer the following advantages: they can trip quickly in the event of an anomaly, and safety margins can be easily configured within the circuit to account for battery characteristics, usage conditions, and other factors, allowing the fusible element to melt and trip at the desired timing. Figure 21 shows an example of the structure of a front-mounted protection element. (A) is a top view with the cover omitted, (B) is a cross-sectional view, and (C) is a bottom view. The protection element 100 shown in Figure 21 comprises: an insulating substrate 101; first and second electrodes 102 and 103 formed on the front surface of the insulating substrate 101; a heating element 104 formed on the front surface of the insulating substrate 101; an insulating layer 105 covering the heating element 104; an intermediate electrode 106 laminated on the insulating layer 105 and connected to the heating element 104; a fusible conductor 107, which is a fusible conductor mounted across the first electrode 102, the intermediate electrode 106, and the second electrode 103 via a connecting material 110 composed of a tin-based solder paste; and a flux 111 applied to the fusible element 107. The first and second electrodes 102 and 103 are terminals connected to a current path connected to an external circuit of the protection element 100. They are connected via a crenellated portion to first and second external connection electrodes 102a and 103a formed on the back surface of the insulating substrate 101. By connecting the first and second external connection electrodes 102a and 103a to connection electrodes provided on the external circuit substrate on which the protection element 100 is mounted, the fusible element 107 is incorporated into a portion of the current path formed on the external circuit substrate. The heating element 104 is a conductive component with a relatively high resistance value that generates heat when electricity is applied, and is made of materials such as nickel, W, Mo, Ru, or materials containing the same. In addition, the heating element 104 is connected to the heating element electrode 108 formed on the front surface of the insulating substrate 101. The heating element electrode 108 is connected to the third external connection electrode 108a formed on the back surface of the insulating substrate 101 via a battlement-shaped portion. The protection element 100 connects the heating element 104 to an external power supply provided in an external circuit by connecting the third external connection electrode 108a to a connection electrode provided on an external circuit substrate on which the protection element 100 is mounted. Moreover, the heating element 104 is always controlled to be energized by a switching element not shown in the figure. The heating element 104 is covered with an insulating layer 105 made of a glass layer or the like, and an intermediate electrode 106 is formed on the insulating layer 105, thereby overlapping the intermediate electrode 106 via the insulating layer 105. Furthermore, a fusible element 107 is connected to the intermediate electrode 106 via a connecting material 110, spanning the connection between the first and second electrodes 102 and 103. In this way, the protection element 100 is thermally connected by overlapping the heating element 104 and the fusible element 107 . When the heating element 104 is heated by electricity, the fusible element 107 can be melted. The fusible element 107 is connected from the first electrode 102 through the intermediate electrode 106 to the second electrode 103, thereby forming a part of the current path of the external circuit in which the protection element 100 is incorporated. Furthermore, the fusible element 107 melts due to self-heating (Joule heat) caused by the flow of current exceeding the rated value. Alternatively, the fusible element 107 melts due to the heat generated by the heating element 104, and the molten conductor condenses on the first and second electrodes 102, 103 and the intermediate electrode 106, thereby melting. In this way, the first and second electrodes 102, 103 are cut off. [Prior Art Literature] [Patent Literature] [Patent Document 1] Japanese Patent No. 5072796 [Patent Document 2] Japanese Patent No. 5876346 [Problems to be solved by the invention] In recent years, the expansion of lithium-ion secondary battery applications has led to their adoption in devices with high capacitance, high current, and high voltage. Consequently, protection components are also being required to have higher ratings and higher voltages. To increase the rated current and reduce the resistance of the fuse itself, a common method is to increase the cross-sectional area of ​​the fuse. However, reducing the resistance of the fuse by increasing the cross-sectional area of ​​the fusible element will affect the melting action of the fusible element caused by the heating element. Specifically, during the melting action of the fusible element caused by the heating element, the fusible element melts by wetting, spreading, and agglomerating on the intermediate electrode, causing the fusible element to melt. However, if the cross-sectional area of ​​the fusible element is increased, the fusible element melted by the heating element will not be completely contained on the electrode and will overflow, resulting in a situation where the current path cannot be cut off. Therefore, the purpose of this technology is to provide a protective element that can quickly and reliably melt even if the cross-sectional area of ​​the fusible element is large by appropriately applying flux. [Technical means to solve the problem] Observation of samples of protection elements that failed to interrupt the current path revealed areas of the intermediate electrode where the molten fusible material had not wetted and expanded. This area was not loaded with fusible material and was not coated with flux. The reasons for this non-wetting and expansion of the fusible material include: the lack of flux retention, which allowed the molten fusible material to continue oxidizing, degrading its fluidity and wettability. Furthermore, since this area of ​​the intermediate electrode was not covered by flux, it became non-wettable due to electrode degradation (oxidation, sulfidation, etc.). The inventors of this case have previously discovered that by retaining the flux in the unwetted and unextended portion of the fusible body, the wetted and unextended area of ​​the molten fusible body is increased, and even a fusible body with an enlarged cross-sectional area can be reliably cut off. That is, in order to solve the above-mentioned problems, the protection element of the present technology has: an insulating substrate; a heating element, which is arranged on the front side of the above-mentioned insulating substrate; an insulating layer, which covers the above-mentioned heating element; an intermediate electrode, which is arranged on the above-mentioned insulating layer; a fusible element, which is mounted on the above-mentioned intermediate electrode; a cover member, which covers the front side of the above-mentioned insulating substrate; and a flux; and the protrusion of the above-mentioned cover member that holds the above-mentioned flux at a specified position is uprightly arranged opposite to the above-mentioned intermediate electrode; the above-mentioned intermediate electrode has a length longer than the width of the above-mentioned fusible element in a direction perpendicular to the current-carrying direction of the above-mentioned fusible element, and at least one of the end portions protrudes more than the above-mentioned fusible element; the above-mentioned protrusion is arranged at a position opposite to the position of the above-mentioned intermediate electrode where the above-mentioned fusible element is mounted and at a position opposite to the above-mentioned end portion where the above-mentioned fusible element is not mounted, so as to hold the above-mentioned flux on the above-mentioned fusible element and the above-mentioned end portion. In addition, the protection element of the present technology comprises: an insulating substrate; an intermediate electrode, which is arranged on the front side of the above-mentioned insulating substrate; a fusible element, which is mounted on the above-mentioned intermediate electrode; a cover member, which covers the front side of the above-mentioned insulating substrate; a flux; a heating element, which is arranged on the back side of the above-mentioned insulating substrate opposite to the front side; and an insulating layer, which covers the above-mentioned heating element; and the protrusion of the above-mentioned cover member that holds the above-mentioned flux at a specified position is erected opposite to the above-mentioned intermediate electrode; the above-mentioned intermediate electrode has a length longer than the width of the above-mentioned fusible element in a direction perpendicular to the direction of conduction of electricity to the above-mentioned fusible element, and at least one of the end portions protrudes more than the above-mentioned fusible element; the above-mentioned protrusion is arranged at a position opposite to the position of the above-mentioned intermediate electrode where the above-mentioned fusible element is mounted and at a position opposite to the above-mentioned end portion where the above-mentioned fusible element is not mounted, so as to hold the above-mentioned flux on the above-mentioned fusible element and the above-mentioned end portion. Furthermore, the manufacturing method of the protection element of the present technology includes the following steps: forming a connector, and the connector has: an insulating substrate, a heating element arranged on the front side of the above-mentioned insulating substrate, an insulating layer covering the above-mentioned heating element, and an intermediate electrode arranged on the above-mentioned insulating layer, and a fusible element is mounted on the above-mentioned intermediate electrode; a flux is coated on the above-mentioned fusible element and the above-mentioned intermediate electrode through a mask having an opening portion corresponding to the coating area; and a cover member is connected to the front side of the above-mentioned insulating substrate on which the fusible element is mounted and the substrate is covered. front side; and the protrusion of the cover member that holds the flux in a specified position is erected opposite to the intermediate electrode; the intermediate electrode has a length that is longer than the width of the fusible body in a direction perpendicular to the direction of conduction of electricity to the fusible body, and at least one of the end portions protrudes beyond the fusible body; the protrusion is arranged at a position opposite to the position of the intermediate electrode on which the fusible body is mounted and at a position opposite to the end portion on which the fusible body is not mounted, so as to hold the flux on the fusible body and the end portion. Furthermore, the manufacturing method of the protection element of the present technology includes the following steps: forming a connector, the connector having: an insulating substrate, an intermediate electrode arranged on the front side of the above-mentioned insulating substrate, a heating element arranged on the back side of the above-mentioned insulating substrate opposite to the front side, and an insulating layer covering the above-mentioned heating element, and a fusible element is mounted on the above-mentioned intermediate electrode; a flux is coated on the above-mentioned fusible element and the above-mentioned intermediate electrode through a mask having an opening corresponding to the coating area; and a front connection cover member on the above-mentioned insulating substrate on which the fusible element is mounted The front side of the substrate is covered; the protrusion of the cover member that holds the flux in a predetermined position is erected opposite the intermediate electrode; the intermediate electrode has a length that is longer than the width of the fusible element in a direction perpendicular to the direction of current flow through the fusible element, and at least one of its ends protrudes beyond the fusible element; the protrusion is disposed at a position opposite to the position of the intermediate electrode where the fusible element is mounted and at a position opposite to the end where the fusible element is not mounted, thereby holding the flux on the fusible element and the end. [Effects of the Invention] According to the present technology, a protection element can be provided that can be quickly and reliably melted even if the cross-sectional area of ​​the fusible element is enlarged. The following describes in detail the protection element to which this technology is applied, with reference to the accompanying drawings. Furthermore, this technology is not limited to the following embodiments; various modifications may be made without departing from the spirit of the invention. Furthermore, the drawings are schematic, and the proportions of various dimensions may differ from actual dimensions. Specific dimensions should be determined in light of the following description. Furthermore, the drawings may contain portions with different dimensional relationships or proportions. [First embodiment] The protection element 1 to which the present technology is applied comprises, as shown in Figures 1(A) to (C), an insulating substrate 2; a heating element 4, which is arranged on the front surface 2a side of the insulating substrate 2; an insulating layer 5, which covers the heating element 4; an intermediate electrode 6, which is arranged on the insulating layer 5; a fusible element 3, which is mounted on the intermediate electrode 6; a cover member 30, which covers the front surface 2a of the insulating substrate 2; and a flux 7. The protrusion 31 of the cover member 30, which holds the flux 7 in a predetermined position, is erected opposite the intermediate electrode 6. The intermediate electrode 6 has a length that is longer than the width of the fusible element 3 in a direction perpendicular to the direction of current flow through the fusible element 3, and at least one of the end portions 6a, 6b, and preferably both end portions 6a, 6b, protrudes beyond the fusible element 3. The protrusion 31 is arranged at a position opposite to the position of the intermediate electrode 6 where the fusible element 3 is mounted and at a position opposite to the end 6a and end 6b where the fusible element 3 is not mounted, so as to hold the flux 7 on the fusible element 3 and the end 6a and end 6b. In this way, the protection element 1 can also keep the flux 6 in the portion of the intermediate electrode 6 that is not equipped with the fusible element 3, and the area where the melted fusible element 3 is wetted and spread is increased, so even if the cross-sectional area of ​​the fusible element 3 is enlarged, it can be quickly and reliably melted. This protection element 1 is incorporated into an external circuit, such as a lithium-ion secondary battery protection circuit, and the fusible element 3 forms part of the current path of the external circuit. The fusible element 3 melts due to heat generated by the heating element 4 or an overcurrent exceeding the rated value, thereby interrupting the current path (see Figure 2). The following describes the various components of the protection element 1 in detail. [Insulating Substrate] The insulating substrate 2 is formed from an insulating material such as alumina, glass ceramic, mullite, or zirconia. Alternatively, the insulating substrate 2 may be made of materials used for printed wiring boards, such as glass epoxy substrates and phenolic substrates. In this specification, the surface of the insulating substrate 2 on which the fusible material 3 is mounted is referred to as the front surface 2a, and the surface opposite the surface on which the fusible material 3 is mounted is referred to as the back surface 2b. [First and Second Electrodes] A first electrode 11 and a second electrode 12 are formed at opposite ends of the front surface 2a of the insulating substrate 2. The first electrode 11 and the second electrode 12 are each formed from a conductive pattern of Ag, Cu, or an alloy thereof. The first electrode 11 and the second electrode 12 can be formed by, for example, screen-printing an Ag paste in a predetermined pattern and then firing the paste at a predetermined temperature. The first electrode 11 is connected to the first external connection electrode 15 formed on the back surface 2b of the insulating substrate 2 via the crenellated portion. Furthermore, the second electrode 12 is connected to the second external connection electrode 16 formed on the back surface 2b of the insulating substrate 2 via the crenellated portion. In a front-mount type protection element 1, when the protection element 1 is mounted on an external circuit board, the first and second external connection electrodes 15 and 16 are connected to connection electrodes provided on the external circuit board, thereby integrating the fusible element 3 into a portion of the current path formed on the external circuit board. The first and second electrodes 11 and 12 are electrically connected via the fusible element 3 by carrying the fusible element 3 through various solder pastes or other conductive connecting materials with a tin base. Furthermore, as shown in FIG2 , the first and second electrodes 11 and 12 are disconnected by the heating element 4 heating up as power is applied, thereby melting the fusible element 3, or by the self-heating (Joule heat) of the fusible element 3 melting due to a current exceeding the rated value flowing through the protection element 1. [Heating element] The heating element 4 is a conductive component having a high resistance value and generating heat when electricity is applied, and includes, for example, nickel-chromium alloy, W, Mo, Ru, etc., or materials containing the same. The heating element 4 can be formed by mixing a powder of such alloys or compositions or compounds with a resin binder, etc. to form a paste, forming a pattern of the paste on the insulating substrate 2 using a screen printing technique, and calcining the paste. As an example, the heating element 4 can be formed by adjusting a mixed paste of a ruthenium oxide paste and a silver and glass paste according to a specified voltage, forming a film with a specified area at a specified position on the front surface 2a of the insulating substrate 2, and then calcining the film under appropriate conditions. In addition, the shape of the heating element 4 can be appropriately designed, but as shown in FIG1 , it is better to set it to a roughly rectangular shape according to the shape of the insulating substrate 2 in order to maximize the heating area. Furthermore, one end 4a of the heating element 4 is connected to the first lead-out electrode 17, and the other end 4b is connected to the second lead-out electrode 18. The first lead-out electrode 17 is led out from the first heating element electrode 8 formed on one side edge of the front surface 2a of the insulating substrate 2. The second lead-out electrode 18 is led out from the second heating element electrode 9 formed on the other side edge of the front surface 2a of the insulating substrate 2. The first lead-out electrode 17 is led out from the first heating element electrode 8 along one end 4a of the heating element 4, and in the protection element 1 shown in FIG1 , extends along one side edge of the heating element 4 formed in a roughly rectangular shape, and overlaps one side edge of the heating element 4. Similarly, the second lead-out electrode 18 is led out from the second heating element electrode 9 along the other end 4b of the heating element 4, and in the protection element 1 shown in FIG1 , extends along the other side edge of the heating element 4 formed in a roughly rectangular shape, and overlaps the other side edge of the heating element 4. [Insulating Layer] The heating element 4, the first extraction electrode 17, and the second extraction electrode 18 are covered with an insulating layer 5. On the insulating layer 5, an intermediate electrode 6 is formed. The insulating layer 5 protects and insulates the heating element 4. To efficiently transfer heat from the heating element 4 to the intermediate electrode 6 and the fusible element 3, the insulating layer 5 is formed to a thickness of, for example, 10 to 40 μm. The insulating layer 5 can be formed by applying and firing a glass-based paste, for example. The first heating element electrode 8 and the second heating element electrode 9 are formed on the side edge of the insulating substrate 2 that faces a different direction from the side edge where the first and second electrodes 11 and 12 are provided. The first heating element electrode 8 serves as a power supply terminal for the heating element 4 and is connected to one end 4a of the heating element 4 via the first lead electrode 17. Furthermore, it is connected to the third external connection electrode 10 formed on the back surface 2b of the insulating substrate 2 via the battlement-shaped portion. The second heating element electrode 9 is connected to the other end 4b of the heating element 4 via the second lead electrode 18 and is also connected to the intermediate electrode 6. The first and second heating element electrodes 8, 9, the first and second extraction electrodes 17, 18, and the intermediate electrode 6 can be formed by printing and firing a conductive paste such as Ag or Cu, similar to the first and second electrodes 11, 12. Furthermore, by using the same material as the electrodes formed on the front surface 2a of the insulating substrate 2, these electrodes can be formed in one or more printing and firing steps. In addition, the first heating element electrode 8 may be provided with a regulating wall (not shown), which prevents the connection solder provided on the electrode of the external circuit substrate connected to the third external connection electrode 10 from melting during reflow installation, climbing onto the first heating element electrode 8 through the battlement-shaped portion, and wetting and spreading on the first heating element electrode 8. The first and second electrodes 11 and 12 may also be provided with regulating walls. The regulating wall may be formed using an insulating material that does not have wettability for solder, such as glass, solder resist, or insulating adhesive, and may be formed on the first heating element electrode 8 and the first and second electrodes 11 and 12 by printing, etc. By providing the regulating wall, the molten connection solder can be prevented from wetting and spreading to the first heating element electrode 8 and the first and second electrodes 11 and 12, thereby maintaining the connectivity between the protection element 1 and the external circuit substrate. The intermediate electrode 6 is an electrode extending from the second heating element electrode 9 to the insulating layer 5. One end of the intermediate electrode 6 is connected to the other end 4b of the heating element 4 via the second heating element electrode 9 and the second lead-out electrode 18. Furthermore, the other end of the intermediate electrode 6 extends on the insulating layer 5 in the region between the first electrode 11 and the second electrode 12, overlapping the heating element 4 via the insulating layer 5. Furthermore, the intermediate electrode 6 is connected to the fusible element 3 via a bonding material such as solder. The fusible element 3 is installed across the first and second electrodes 11 and 12. The heating element 4 generates heat due to current flow, or generates self-heating (Joule heat) due to current flow exceeding the rated value, causing it to melt, thereby interrupting the current path between the first electrode 11 and the second electrode 12. A flux 7 is applied to the fusible element 3 to prevent oxidation, improve wettability, and ensure rapid melting. The structure of the fusible element 3 will be described in detail later. Furthermore, it is preferred that the front surfaces of the first and second electrodes 11, 12, and the intermediate electrode 6 be coated with a coating such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by a known method such as plating. This prevents oxidation of the first and second electrodes 11, 12, and the intermediate electrode 6, thereby preventing a rating fluctuation associated with an increase in on-resistance. Furthermore, when the protection element 1 is reflow mounted, the solder connecting the fusible element 3 melts, thereby preventing corrosion (solder erosion) of the first and second electrodes 11, 12, and the intermediate electrode 6. [Flux] Here, the intermediate electrode 6 of the present technology has a length greater than the width of the fusible element 3 in a direction perpendicular to the direction of current flow through the fusible element 3 in a plan view, and at least one of the end portions 6a and 6b protrudes from the fusible element 3. Furthermore, the flux 7 is retained on the fusible element 3 and on the end portions 6a and / or 6b protruding from the fusible element 3 by a protrusion 31 of the cover member 30 described later. The direction perpendicular to the direction of current flow through the fusible element 3 is the direction in which the fusible element 3 melts. By melting across this direction, the fusible element 3 can cut off the current path between the first and second electrodes 11 and 12. Furthermore, at least one of the ends 6a and 6b of the intermediate electrode 6 protrudes in this direction, holding the flux 7 on the fusible element 3 and the ends 6a and / or 6b. Thus, the protective element 1 can also retain the flux 6 at the end 6a and / or end 6b of the intermediate electrode 6 where the fusible element 3 is not mounted, thereby preventing oxidation of the intermediate electrode 6. Consequently, the area of ​​the intermediate electrode 6 wetted and spread by the molten fusible element 3 is increased, allowing for rapid and reliable melting even when the cross-sectional area of ​​the fusible element 3 increases and the amount of melting increases. Furthermore, the rapid melting of the fusible element 3 prevents damage to the intermediate electrode 6 and the heating element 4 itself, stabilizing the heat shutoff operation. Furthermore, in order to increase the amount of the molten fusible material 3 held by the intermediate electrode 6 , it is preferable that both end portions 6 a and 6 b of the intermediate electrode 6 protrude from the fusible material 3 to hold the flux 7 , as shown in FIG. 1 . By applying flux 7 through a mask 36 having openings 37 corresponding to the coating area, a predetermined amount of flux 7 can be applied within a predetermined range (see Figure 7). In this coating method, a mask such as a metal mask or a silk screen mask with openings corresponding to the flux 7 coating area is prepared. This mask is placed around the flux 7 coating area and pressed with a squeegee. This allows flux 7 to be printed in the mask's openings to the thickness of the mask. [Cover Member] Cover member 30 is attached to front surface 2a of insulating substrate 2, where fusible element 3 is mounted, using an adhesive. Cover member 30 protects the interior of protective element 1 and prevents the molten material generated when fusible element 3 melts from scattering. Cover member 30 can be made of insulating materials such as various engineering plastics and ceramics. The cover member 30 has protrusions 31 disposed upright on the inner side of the top surface, which hold the flux 7 in a predetermined position. The protrusions 31 are disposed opposite the position of the intermediate electrode 6 where the fusible element 3 is mounted, and opposite the end 6a and / or end 6b where no fusible element 3 is mounted. By contacting the flux 7 and exerting tension, the flux 7 is held on the fusible element 3 and the end 6a and / or end 6b. Furthermore, the protrusions 31 may be disposed upright at positions opposite the position of the intermediate electrode 6 where the fusible element 3 is mounted, and opposite the end 6a and / or end 6b where no fusible element 3 is mounted, as shown in FIG1 , or may be disposed upright so as to straddle these two positions, as shown in FIG3 . In addition, in this specification, the protrusions 31 of the plurality of upright protrusions 31 that are opposite to the end portions 6a, 6b of the intermediate electrode 6 that are not equipped with the fusible element 3 are referred to as end protrusions 31a, and the protrusions that are opposite to the position of the intermediate electrode 6 that is equipped with the fusible element 3 are referred to as intermediate protrusions 31b. The length of the protrusion 31 is determined by the distance from the intermediate electrode 6 or the fusible element 3. The distance between the end protrusion 31a, located opposite the ends 6a, 6b of the intermediate electrode 6 where the fusible element 3 is not carried, and the end protrusion 31a and the end 6a, 6b of the intermediate electrode 6 is set to a distance that allows the end protrusion 31a to contact and retain the flux 7, and is set to, for example, 350 μm or less. Similarly, the distance between the intermediate protrusion 31b, located opposite the position of the intermediate electrode 6 where the fusible element 3 is carried, and the fusible element 3 is also set to a distance that allows the intermediate protrusion 31b to contact and retain the flux 7, and is set to, for example, 350 μm or less. Furthermore, the end protrusions 31a and the intermediate protrusions 31b must avoid contact with the molten conductor 3a of the fusible element 3 that has accumulated on the intermediate electrode 6. Specifically, as the cross-sectional area of ​​the fusible element 3 increases, the amount of the molten conductor 3a of the fusible element 3 held by the intermediate electrode 6 also increases. Consequently, the molten conductor 3a that has accumulated on the intermediate electrode 6 may come into contact with the protrusions 31. Consequently, heat from the heating element 4 is dissipated to the protrusions 31 and the cover member 30 via the molten conductor 3a, potentially hindering the heating of the fusible element 3 and causing it to melt. Therefore, the distances between the end protrusions 31a and the end portions 6a and 6b of the intermediate electrode 6, and the distance between the intermediate protrusions 31b and the fusible element 3, are set to correspond to the volume of the molten conductor 3a and are each set to, for example, 100 μm or greater. The end protrusions 31a and the middle protrusions 31b have a length that does not contact the fusible conductor 3a, thereby preventing the heat of the heating element 4 from being dissipated due to contact with the fusible conductor 3a, and quickly and reliably melting the fusible element 3. The shape of the protrusion 31 is not particularly limited, and for example, it may be formed into a cylindrical shape, a columnar shape, or a columnar shape. Furthermore, the protrusion 31 may be provided in one or more forms. The front surface of the protrusion 31 that contacts the flux 7 may be smooth or may be rough like a pear skin. The protrusions 31 may all be formed in the same shape and size, or the shapes and sizes may be partially different. For example, as shown in FIG4 , the end protrusion 31a may be formed to have a smaller diameter than the middle protrusion 31b. Furthermore, as shown in FIG5 , the end protrusion 31a may be provided in a shape and size that is opposite to the ends 6a, 6b of the intermediate electrode 6 and partially protrudes from the ends 6a, 6b. In this way, the flux 7 can be maintained at a position that exceeds the ends 6a, 6b of the intermediate electrode 6. In the configuration shown in FIG. 5 , the end protrusion 31 a is formed into an elliptical column having a major axis in the width direction (melting direction) perpendicular to the current-carrying direction of the fusible element 3 , but the shape of the end protrusion 31 a is not limited thereto. The protrusions 31 are arranged above the intermediate electrode 6 along its length. This maintains the flux 7 along the area of ​​the intermediate electrode 6 heated by the heating element 4. The pattern of the protrusions 31 is not particularly limited and can be arranged in a single row or multiple rows. Furthermore, even in the case of multiple rows, the protrusions 31 can be arranged side by side or staggered. Furthermore, the protrusions 31 are preferably arranged at regular intervals to prevent uneven distribution of the flux, but the spacing of the protrusions 31 may not be regular. For the same reason, the protrusions 31 are preferably arranged symmetrically in a direction perpendicular to the direction of current flow through the fusible element in a cross-sectional view, but they may not be symmetrical. In addition, in order to increase the amount of molten fusible material 3 that the intermediate electrode 6 can hold, it is preferred that the two end portions 6a and 6b of the intermediate electrode 6 protrude from the fusible material 3, and the flux 7 is held to the front ends of the two end portions 6a and 6b by the end protrusions 31a to prevent oxidation in the entire area of ​​the intermediate electrode 6. [Fuse Component] Next, the fusible element 3 will be described. The fusible element 3 is installed across the first and second electrodes 11 and 12. It is melted by heat generated by the heating element 4 due to current flow, or by self-heating (Joule heat) due to current flow exceeding the rated value, thereby shutting off the current path between the first electrode 11 and the second electrode 12. The fusible element 3 can be any conductive material that melts due to the heat generated by the heating element 4 or due to an overcurrent condition. For example, a Pb-free solder of the SnAgCu series, or a BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc. can be used. Alternatively, the fusible body 3 may be a structure containing a high-melting-point metal and a low-melting-point metal. For example, as shown in FIG6 , the fusible body 3 is a laminated structure consisting of an inner layer and an outer layer, with a low-melting-point metal layer 13 as the inner layer and a high-melting-point metal layer 14 as the outer layer laminated on the low-melting-point metal layer 13. The fusible body 3 is connected to the first and second electrodes 11 and 12 and the intermediate electrode 6 via a conductive connecting material such as solder. The low-melting-point metal layer 13 is preferably solder or a metal primarily composed of Sn, a material generally referred to as "Pb-free solder." The melting point of the low-melting-point metal layer 13 does not necessarily need to be higher than the reflow oven temperature and can melt at approximately 200°C. The high-melting-point metal layer 14 is a metal layer laminated on the front surface of the low-melting-point metal layer 13. For example, it can be Ag, Cu, or a metal primarily composed of any of these. It has a relatively high melting point that prevents melting even during reflow, allowing for connection of the first and second electrodes 11, 12, and the intermediate electrode 6 to the fusible element 3 and for mounting the protection element 1 on an external circuit board. This fusible body 3 can be formed by forming a high melting point metal layer on a low melting point metal foil using a plating technique, or can also be formed using other well-known lamination techniques or film formation techniques. In this case, the fusible body 3 can adopt a structure in which the low melting point metal layer 13 is completely covered by the high melting point metal layer 14, or can adopt a structure in which the low melting point metal layer 13 is covered except for a pair of opposing side surfaces. In addition, the fusible body 3 can be formed by providing the high melting point metal layer 14 as the inner layer and the low melting point metal layer 13 as the outer layer, or can be formed by providing a multilayer structure of three or more layers in which the low melting point metal layer 13 and the high melting point metal layer 14 are alternately laminated, and an opening is provided in a part of the outer layer to expose a part of the inner layer, etc. The fusible element 3 is formed by laminating the high melting point metal layer 14 as an outer layer on the low melting point metal layer 13 serving as the inner layer. Therefore, even when the reflow temperature exceeds the melting temperature of the low melting point metal layer 13, the fusible element 3 can maintain its shape and not melt. Therefore, the first and second electrodes 11, 12, and the intermediate electrode 6 can be efficiently connected to the fusible element 3 and the protective element 1 can be mounted on an external circuit board by reflow. Furthermore, reflow can prevent variations in the fusing characteristics, such as failure to melt at a specific temperature or melting at a temperature lower than the specific temperature, caused by deformation of the fusible element 3 and localized increases or decreases in resistance. Furthermore, the fusible element 3 does not melt due to self-heating even when the specified rated current is flowing. Furthermore, when a current exceeding the rated value is flowing, it melts due to self-heating, interrupting the current path between the first and second electrodes 11 and 12. Furthermore, the heating element 4 is heated by the passage of current, causing it to melt and interrupt the current path between the first and second electrodes 11 and 12. At this point, the fusible element 3 erodes the high-melting-point metal layer 14 (solder erosion) through the molten low-melting-point metal layer 13, causing the high-melting-point metal layer 14 to melt at a temperature lower than its melting point. Therefore, the fusible element 3 can be quickly melted by the erosion of the high-melting-point metal layer 14 by the low-melting-point metal layer 13. Furthermore, the molten conductor 3a of the fusible element 3 is physically pulled in by the intermediate electrode 6 and the first and second electrodes 11 and 12, quickly and reliably interrupting the current path between the first and second electrodes 11 and 12 (Figure 2). Furthermore, the fusible element 3 is preferably formed so that the volume of the low-melting-point metal layer 13 is larger than that of the high-melting-point metal layer 14. The fusible element 3 is heated by self-heating due to overcurrent or by the heating element 4. The low-melting-point metal melts and erodes the high-melting-point metal, thereby rapidly melting and fusing. Therefore, by forming the volume of the low-melting-point metal layer 13 larger than that of the high-melting-point metal layer 14, the fusible element 3 promotes this erosion and rapidly cuts off the first and second electrodes 11 and 12. Furthermore, because the fusible element 3 is constructed by laminating a high-melting-point metal layer 14 on a low-melting-point metal layer 13, which serves as an inner layer, the fuse element 3 can achieve a significantly lower fusing temperature than conventional chip fuses containing high-melting-point metals. Consequently, the fusible element 3 can have a larger cross-sectional area and a significantly higher current rating than conventional chip fuses of the same size. Furthermore, this allows for a more compact and thinner design than conventional chip fuses with the same current rating, while also providing superior fast-acting performance. Furthermore, the fusible element 3 can improve its resistance to surges (pulse resistance) caused by the instantaneous application of abnormally high voltages to the electrical system in which the protective element 1 is assembled. That is, the fusible element 3 will not melt even when a current of, for example, 100 A flows for a few milliseconds. In this regard, since a large current flowing for a very short time flows through the surface layer of the conductor (skin effect), the fusible element 3 is provided with a high-melting-point metal layer 14 such as Ag plating with a low resistance value as an outer layer, so that the current applied by the surge can be easily passed, thereby preventing melting due to self-heating. Therefore, the fusible element 3 can significantly improve its resistance to surges compared to previous fuses containing solder alloys. [Manufacturing process of the protection element] Next, the manufacturing process of the protection element 1 will be described. FIG7 is a cross-sectional view showing the manufacturing process of the protection element 1, FIG7(A) shows the process of applying the flux, FIG7(B) shows the connector 35 coated with the flux, and FIG7(C) shows the protection element 1. The manufacturing process of the protection element 1 includes the following steps: forming a connector 35, the connector 35 having: an insulating substrate 2, a heating element 4 arranged on the front surface 2a side of the insulating substrate 2, an insulating layer 5 covering the heating element 4, and an intermediate electrode 6 arranged on the insulating layer 5, and a fusible element 3 connected to the intermediate electrode 6; applying a flux 7 on the fusible element 3 via a mask 36 having an opening corresponding to the coating area; and connecting a cover member 30 to the front surface 2a of the insulating substrate 2 on which the fusible element 3 is mounted to cover the front surface of the substrate. As described above, on the front surface 2a of the insulating substrate 2, the first and second electrodes 11, 12, the first and second heating body electrodes 8, 9, and the first and second lead electrodes 17, 18 are formed by printing and calcining a conductive paste such as Ag or Cu using screen printing technology. The heating element 4 is made of nickel, W, Mo, Ru, or a material containing such materials. This can be formed by mixing powders of these alloys, compositions, or compounds with a resin binder to form a paste, patterning the paste on the insulating substrate 2 using screen printing techniques, and then firing the paste. The insulating layer 5 is formed by applying a glass-based paste onto the heating element 4 and the first and second extraction electrodes 17 and 18 using screen printing techniques, followed by firing. Furthermore, by printing and calcining a conductive paste such as Ag or Cu using screen printing technology, the intermediate electrode 6 is formed over the entire surface from the second heating element electrode 9 to the insulating layer 5. The first and second electrodes 11, 12, and the intermediate electrode 6 are printed with a conductive connecting material such as solder, and after being loaded with the fusible element 3, they are submitted to the reflow process. This results in a connected body 35 connected to the fusible element 3. Next, flux 7 is applied to the fusible material 3 via a mask 36 (e.g., a metal mask or a screen mask) having openings 37 corresponding to the coating area. In this coating process, as shown in FIG7(A), in the screen printing method, a mask 36 having openings 37 corresponding to the printed area is arranged around the printed area of ​​the flux 7. By sliding a scraper 38 on the front of the mask 36, flux 7 is applied to the position and area corresponding to the openings 37 by the thickness of the mask 36 (FIG7(B)). Next, a cover member 30 is attached to the front surface 2a of the insulating substrate 2, where the fusible element 3 is mounted, to cover the front surface of the substrate, thereby obtaining the protective element 1 ( FIG. 7(C) ). At this time, by providing the protrusion 31 on the cover member 30, the surface tension of the flux 7 contacting the front end of the protrusion 31 can pull the flux 7 closer, thereby maintaining the flux 7 in a predetermined position. [Circuit Configuration Example] This protection element 1 is used by being incorporated into a circuit within a lithium-ion secondary battery pack 20. As shown in FIG8 , the battery pack 20 includes, for example, a battery stack 25 containing a total of four lithium-ion secondary battery cells 21a to 21d. The battery pack 20 includes: a battery stack 25; a charge and discharge control circuit 26, which controls the charge and discharge of the battery stack 25; a protection element 1 applying the present invention, which cuts off the charge and discharge path when the battery stack 25 is abnormal; a detection circuit 27, which detects the voltage of each battery cell 21a~21d; and a current control element 28, which becomes a switching element that controls the action of the protection element 1 according to the detection result of the detection circuit 27. The battery stack 25 is composed of battery cells 21a to 21d connected in series to protect against overcharge and overdischarge. The battery pack 20 is detachably connected to a charging device 22 via its positive and negative terminals 20a and 20b, and a charging voltage is applied thereto. By connecting the positive and negative terminals 20a and 20b of the battery pack 20, after being charged by the charging device 22, to an electronic device that utilizes the battery, the electronic device can be operated. The charge-discharge control circuit 26 includes two current control elements 23a and 23b connected in series in the current path between the battery stack 25 and the charging device 22, and a control unit 24 that controls the operation of these current control elements 23a and 23b. The current control elements 23a and 23b are composed of, for example, field-effect transistors (FETs). The control unit 24 controls the gate voltage to control the conduction and interruption of the current path to the battery stack 25 in the charging and / or discharging directions. The control unit 24 operates by receiving power from the charging device 22. In response to the detection results of the detection circuit 27, the control unit 24 controls the operation of the current control elements 23a and 23b by interrupting the current path when the battery stack 25 is over-discharged or over-charged. The protection element 1 is connected to the charge and discharge current path between the battery stack 25 and the charge and discharge control circuit 26 , for example, and its operation is controlled by the current control element 28 . The detection circuit 27 is connected to each of the battery cells 21a-21d, detects the voltage value of each battery cell 21a-21d, and supplies each voltage value to the control unit 24 of the charge and discharge control circuit 26. Furthermore, when any of the battery cells 21a-21d reaches an overcharge voltage or an overdischarge voltage, the detection circuit 27 outputs a control signal to control the current control element 28. The current control element 28 is composed of, for example, a FET. Based on the detection signal output by the self-detection circuit 27, when the voltage value of the battery cells 21a~21d exceeds the voltage of a specific over-discharge or over-charge state, the protection element 1 is activated, and the control is performed by cutting off the charge and discharge current path of the battery stack 25 without relying on the switching action of the current control elements 23a and 23b. The protection element 1 of the present invention used in the battery pack 20 having the above structure has a circuit structure as shown in FIG9 . That is, the protection element 1 connects the first external connection electrode 15 to the battery stack 25 side, and connects the second external connection electrode 16 to the positive terminal 20a side, thereby connecting the fusible element 3 in series to the charge and discharge path of the battery stack 25. In addition, the protection element 1 connects the heating element 4 to the current control element 28 via the first heating element electrode 8 and the third external connection electrode 10, and connects the heating element 4 to the battery stack 25. In this way, the heating element 4 connects one end to the side connected to the fusible element 3 and the battery stack 25 via the intermediate electrode 6, and connects the other end to the current control element 28 and the other end of the battery stack 25 via the third external connection electrode 10. In this way, a power supply path is formed to the heating element 4 whose power supply can be controlled by the current control element 28. [Action of the protection element] When the detection circuit 27 detects an abnormal voltage in any of the battery cells 21a to 21d, it outputs a cutoff signal to the current control element 28. In this way, the current control element 28 controls the current by energizing the heating element 4. The protection element 1 flows current from the battery stack 25 to the heating element 4, whereby the heating element 4 begins to generate heat. The fusible element 3 of the protection element 1 is melted by the heat generated by the heating element 4, thereby cutting off the charge and discharge path of the battery stack 25. In addition, the protection element 1 is formed by making the fusible element 3 contain a high melting point metal and a low melting point metal, and before the high melting point metal is melted, the low melting point metal melts, and the fusible element 3 can be melted in a short time by utilizing the corrosion effect of the molten low melting point metal on the high melting point metal. Since the fusible element 3 is melted, the protection element 1 also cuts off the power supply path to the heating element 4, thereby stopping the heating of the heating element 4. In addition, when an overcurrent exceeding the rated value flows through the protection element 1 in the battery pack 20 , the fusible element 3 also melts due to self-heating, thereby cutting off the charge and discharge path of the battery pack 20 . In this manner, the fusible element 3 of the protection element 1 melts due to heat generated by the passage of current to the heating element 4 or due to self-heating of the fusible conductor 3 caused by overcurrent. In this case, even during reflow mounting of the protection element 1 on a circuit board, or when the circuit board with the protection element 1 mounted is further exposed to high-temperature environments such as reflow heating, the structure of the low-melting-point metal covered by the high-melting-point metal suppresses deformation of the fusible element 3. This prevents changes in the fusing characteristics caused by changes in resistance value due to deformation of the fusible element 3, and allows for rapid melting by a specified overcurrent or heating of the heating element 4. The protection element 1 of the present invention is not limited to being used in a lithium-ion secondary battery pack, but can be applied to various applications requiring the interruption of a current path by an electrical signal. [Second Embodiment] Next, a second embodiment of a protection element to which the present technology is applied will be described. In the following description, components identical to those of the aforementioned protection element 1 are sometimes denoted by the same reference numerals, and details are omitted. As shown in FIG. 10 , the length of the end protrusion 31 a of the protection element 50 of the second embodiment is longer than the length of the middle protrusion 31 b. When multiple protrusions 31 are provided, the thickness of the fusible element 3 is varied, or the viscosity of the flux is low, the protrusions 31 may not be able to retain the flux 7 sufficiently due to the spacing between the protrusions 31, causing the flux 7 to shift to one side (see Figure 11). Consequently, the end 6a or end 6b of the intermediate electrode 6, where the flux 7 is not retained, may oxidize due to the heating element 4, preventing the molten conductor 3a from being wetted. This may cause the molten conductor 3a of the enlarged fusible element 3 to overflow, hindering melting. To this end, the protective element 50 makes the length of the end protrusion 31a opposite to the end 6a and / or end 6b of the intermediate electrode 6 where the flux 7 may be insufficient due to uneven distribution of the flux 7 longer than the length of the intermediate protrusion 31b. This prevents excessive clearance between the end protrusion 31a of the protection element 50 and the ends 6a, 6b of the intermediate electrode 6, maintaining the retention force of the end protrusion 31a on the flux 7 and preventing uneven distribution. Consequently, the flux 7 is retained between the ends 6a, 6b of the intermediate electrode 6, preventing a decrease in wettability due to insufficient flux 7, allowing the fusible element 3 to be quickly and reliably melted. Here, similar to the protection element 1, the protection element 50 preferably has a length such that the protrusions 31 (i.e., the end protrusions 31a and the intermediate protrusions 31b) do not contact the molten fusible element 3. If the protrusions 31 are shortened to avoid contact with the molten conductor 3a of the fusible element 3, the distance between the protrusions 31 and the fusible element 3 and the end portions 6a and 6b of the intermediate electrode 6 increases, thereby reducing the retention force of the flux 7. In particular, as shown in FIG11 , the increased distance between the end portions 6a and 6b of the intermediate electrode 6, which do not carry the fusible element 3, and the end protrusions 31a may cause uneven distribution of the flux 7 within the protection element. As shown in Figure 12, the molten conductor 3a of the fusible material 3 aggregated on the intermediate electrode 6 is highest in the center of the intermediate electrode 6 and gradually decreases toward the end portions 6a and 6b of the intermediate electrode 6. The intermediate protrusion 31b of the protective element 50, which faces the aggregated molten conductor 3a in the center of the intermediate electrode 6, is shorter, preventing contact with the aggregated molten conductor 3a. Furthermore, the end protrusions 31a facing the ends 6a and 6b of the intermediate electrode 6 are longer, but the positions of the end protrusions 31a correspond to the lower portions of the aggregated molten conductor 3a. Therefore, by making the end protrusions 31a longer than the intermediate protrusions 31b, the protective element 50 maintains the retention force of the flux 7, preventing uneven distribution. It also prevents the heat from the heating element 4 from being dissipated due to contact between the end protrusions 31a and the intermediate protrusions 31b and the fusible material 3, thereby quickly and reliably melting the fusible material 3. In the configuration where the end protrusion 31a is longer than the middle protrusion 31b, the end protrusion 31a may be formed to have a smaller diameter than the middle protrusion 31b, as shown in FIG13 . Furthermore, the end protrusion 31a may be erected at a position opposite the position of the intermediate electrode 6 where the fusible element 3 is mounted and at a position opposite the ends 6a and 6b where no fusible element 3 is mounted. Alternatively, as shown in FIG14 , the end protrusion 31a may be erected so as to straddle both positions. In this case, the end protrusion 31a may be formed in a stepped shape, with the portion opposite the position of the intermediate electrode 6 where the fusible element 3 is mounted being shorter, similar to the middle protrusion 31b, and the portion opposite the ends 6a and 6b of the intermediate electrode 6 being longer than the middle protrusion 31b. Alternatively, as shown in FIG15 , the end protrusion 31a may be longer than the middle protrusion 31b, facing the ends 6a and 6b of the middle electrode 6 and partially protruding from the ends 6a and 6b. This allows the flux 7 to be held at a position extending beyond the ends 6a and 6b of the middle electrode 6. The end protrusion 31a shown in FIG15 is formed in the shape of an elliptical cylinder with its major axis being in the width direction (melting direction) perpendicular to the direction of current flow of the fusible element 3, but the shape of the end protrusion 31a is not limited to this. [Variation 1] Next, a variation of the protection element to which the present invention is applied will be described. In addition, in the following description, the same symbols are sometimes given to the same structures as those of the above-mentioned protection elements 1 and 50, and their details are omitted. As shown in Figure 16 (A) (B), the protection element 60 can independently form a power supply path to the heating element 4 and a current path to the fusible element 3. The protection element 60 shown in Figure 16 sets the intermediate electrode 6 and the second heating element electrode 9 to be non-connected. In addition, the second heating element electrode 9 is connected to the fourth external connection electrode 61 formed on the back side 2b of the insulating substrate 2 via a battlement-shaped portion, similarly to the first heating element electrode 8. By connecting the third external connection electrode 10 and the fourth external connection electrode 61 to the connection electrode provided on the external circuit substrate on which the protection element 60 is installed, the heating element 4 is connected to the external power supply provided in the external circuit. The other structures are the same as those of the protection element 1. FIG17 is a diagram showing the circuit structure of the protection element 60. The protection element 60 is installed in an external circuit to connect the first external connection electrode 15 to the battery stack 25 side and the second external connection electrode 16 to the positive terminal 20a side, thereby connecting the fusible element 3 in series to the charge and discharge path of the battery stack 25. The heating element 4 is connected to the current control element 28 via the first heating element electrode 8 and the third external connection electrode 10, and is connected to the battery stack 25. In addition, the heating element 4 is connected to the ground (not shown) via the second heating element electrode 9 and the fourth external connection electrode 61. In this way, a power supply path is formed for the heating element 4, the power supply of which can be controlled by the current control element 28. When the fusible element 3 is blown, the protection element 60 stops the power supply to the heating element 4 by detecting this situation through the detection circuit 27 and the current control element 28. The protection element 60 has the protrusions 31 formed thereon similarly to the protection elements 1 and 50 . The protrusions 31 hold the flux 7 at a predetermined position, thereby achieving the same functions and effects as the protection elements 1 and 50 . [Variation 2] Next, a second variation of a protective element employing the present technology will be described. In the following description, components identical to those of the aforementioned protective elements 1, 50, and 60 are sometimes designated with the same reference numerals, and details thereof are omitted. FIG18 shows a variation of a protective element 70, (A) being a top view with the cover omitted, (B) being a cross-sectional view taken along line AA of (A), (C) being a cross-sectional view taken along line BB of (A), and (D) being a bottom view. As shown in Figures 18(A) to 18(D), the protective element 70 of the second variation has a heating element 4, first and second extraction electrodes 17 and 18, and an insulating layer 5 covering them formed on the back surface 2b opposite the front surface 2a of the insulating substrate 2. Furthermore, first and second heating element electrodes 8 and 9, and first and second external connection electrodes 15 and 16 are formed on the back surface 2b of the insulating substrate 2. Furthermore, first and second electrodes 11 and 12 and an intermediate electrode 6 are formed on the front surface 2 a of the insulating substrate 2 , and a fusible body 3 is mounted on each of the electrodes 11 , 12 , and 6 . The first and second electrodes 11, 12, and the intermediate electrode 6 arranged on the front surface 2a of the insulating substrate 2, and the heating element 4, the first and second lead-out electrodes 17, 18, the first and second heating element electrodes 8, 9, and the first and second external connection electrodes 15, 16 arranged on the back surface 2b of the insulating substrate 2 can be formed by the same process as the above-mentioned protection element 1. The second heating element electrode 9 and the intermediate electrode 6 are electrically connected via a battlement-shaped portion formed on the side of the insulating substrate 2 and a conductive through-hole penetrating the insulating substrate 2. That is, the intermediate electrode 6 is electrically and thermally connected to the heating element 4 via the second heating element electrode 9. In this way, the heating element 4 of the protective element 70 heats the intermediate electrode 6 via the insulating substrate 2, and the heat of the heating element 4 is transferred to the intermediate electrode 6 via the second heating element electrode 9 and the battlement-shaped portion, which have excellent thermal conductivity, thereby heating the fusible element 3 and causing it to melt (Figure 19). In addition, in the protection element 70, since the first and second heating body electrodes 8 and 9 also become external connection electrodes connected to the electrodes of the external circuit substrate, the third external connection electrode 10 provided on the protection element 1 and the fourth external connection electrode 61 provided on the protection element 60 are not provided. The protection element 70 has the protrusion 31 formed thereon similarly to the protection elements 1 , 50 , and 60 . The protrusion 31 holds the flux 7 at a predetermined position, thereby achieving the same function and effect as the protection elements 1 , 50 , and 60 . Furthermore, in the protection element 70, similarly to the protection element 60, by disconnecting the intermediate electrode 6 and the second heating element electrode 9, a power supply path to the heating element 4 and a current path to the fusible element 3 can be independently formed. [Example] [First embodiment] Next, an embodiment of the present invention will be described. In the first embodiment, samples of protection elements with varying numbers of protrusions were fabricated, and a 33W power was applied to the heating element to conduct a melting test of the fusible element. The protective element samples of the Example and Comparative Examples had the same structure as the protective element 1 described above, except for the number of protrusions provided on the cover member. Furthermore, each sample used a 100 μm thick fusible material. Furthermore, a mask having openings corresponding to the flux application area of ​​the protective elements of the Example and Comparative Examples was used to apply a predetermined amount of flux within a predetermined range. For the protection elements of the Examples and Comparative Examples, the average melting time (seconds), minimum and maximum melting times (seconds), and the failure rate (%) were calculated. The number of samples, n, for both the Examples and Comparative Examples was 192. The failure rate (%) refers to the percentage of samples in which the fusible element did not melt even after the specified time. This is caused by oxidation of the fusible element and the intermediate electrode hindering melting, resulting in failure to melt. [Example 1] In Example 1, four cylindrical protrusions of the same size are formed in a row along the intermediate electrode on the top surface of the cover member. The end protrusions are erected so as to span two locations: one opposite the location of the intermediate electrode where the fusible element is mounted, and one opposite the end where the fusible element is not mounted (see Figure 3). Flux is applied and maintained over the fusible element and on both ends of the intermediate electrode protruding from the fusible element, depending on the location of the protrusions. [Example 2] In Example 2, five cylindrical protrusions of the same size are formed in a row along the intermediate electrode on the top surface of the cover member. These protrusions are positioned vertically opposite the portion of the intermediate electrode where the fusible element is mounted and opposite the end portion where the fusible element is not mounted (see Figure 1). Flux is applied to the entire area of ​​the fusible element and both ends of the intermediate electrode protruding from the fusible element, depending on the position of the protrusions. Flux is maintained throughout the entire area from the fusible element to the front end of the intermediate electrode. Comparative Example 1: The protective element of Comparative Example 1, as shown in Figure 20, has three cylindrical protrusions of the same size formed in a row along the intermediate electrode on the top surface of the cover member. These protrusions are erected only at locations opposite the intermediate electrode where the fusible element is mounted. Flux is applied and retained only on the fusible element 3, depending on the location of the protrusions. [Table 1] As shown in Table 1, the protection elements of Example 1 and Example 2 also have protrusions at positions opposite to the ends of the intermediate electrodes that protrude more than the fusible body, so that the flux can be applied and maintained to both end sides of the intermediate electrodes, and the melting time and the occurrence rate of uncut parts are both good results. Comparative Example 1 only erects the protrusions opposite the fusible element, without retaining flux at either end of the intermediate electrode. Consequently, the amount of flux applied is relatively small, and oxidation of the fusible element and the ends of the intermediate electrode continues due to heating by the heating element, resulting in a longer melting time and an increased incidence of uncut connections. In addition, comparing Example 1 with Example 2, Example 2, in which the number of protrusions and the amount of flux applied are greater, and the flux is applied and maintained to the front end of the intermediate electrode, has relatively favorable results in terms of melting time and non-cutting incidence rate. [Second embodiment] Next, the second embodiment will be described. In the second embodiment, samples of protective elements with varying protrusion lengths were fabricated, and a 33 W power was applied to the heating element to conduct a melting test of the fusible element. The protective element samples of the Example and Comparative Examples had the same structure as the protective element 1 described above, except for the length of the protrusion provided on the cover member. Furthermore, each sample used a 125 μm thick fusible material. Furthermore, a mask having an opening corresponding to the flux application area of ​​the protective elements of the Example and Comparative Examples was used to apply a predetermined amount of flux within a predetermined range. [Example 3] In Example 3, five cylindrical protrusions are formed in a row along the intermediate electrode on the top surface of the cover member. The intermediate protrusions formed opposite the position where the fusible element is mounted are shorter than the end protrusions formed opposite the end of the intermediate electrode where the fusible element is not mounted (see Figure 10). The distance between the end protrusions and the end of the intermediate electrode is set to maintain the flux in the center (approximately 350 μm or less), and the distance between the intermediate protrusions and the fusible element is set to prevent contact with the fusible element's molten conductor (approximately 100 μm or more). Comparative Example 2: Comparative Example 2 was constructed similarly to Example 3 (see Figure 1), except that five cylindrical protrusions of the same size were formed in a row along the intermediate electrode on the top surface of the cover member. The distance between the end of each protrusion and the end of the intermediate electrode was set to maintain flux in the center (approximately 350 μm or less). Comparative Example 3: Comparative Example 3 was constructed similarly to Example 3 (see FIG11 ), except that five cylindrical protrusions of the same size were formed in a row along the intermediate electrode on the top surface of the cover member. Each protrusion was set at a distance (approximately 100 μm or greater) that would not contact the molten conductor of the fusible material. [Table 2] As shown in Table 2, Example 3 provides a sufficient length for retaining flux between the end of the intermediate electrode and the protruding end of the intermediate electrode. This allows flux to be applied to the fusible element and both ends of the intermediate electrode protruding from the fusible element, preventing oxidation of the intermediate electrode and effectively maintaining the molten conductor at both ends. Furthermore, since the intermediate protrusion does not contact the molten fusible element 3, heat absorption by the protrusion and the cover member is prevented, resulting in excellent melting times and a low rate of unsevered conductors. In Comparative Example 2, all protrusions are formed by using the end protrusions to maintain the length of the flux between the end of the intermediate electrode, and the distance between the intermediate protrusion and the fusible element is shortened (approximately less than 100 μm). Therefore, the melted fusible element contacts the intermediate protrusion, dissipating the heat of the heating element to the cover member, reducing the temperature of the fusible element, lengthening the melting time, and increasing the incidence of uncut parts. Therefore, it can be seen that if the distance between the protrusion and the fusible element is shortened due to the thickness of the fusible element, there is a risk of contact between the molten conductor of the fusible element and the intermediate protrusion. Therefore, it is necessary to ensure a distance corresponding to the volume (melting amount) of the fusible element (at least 100 μm). In Comparative Example 3, by shortening the length of all protrusions, the flux retention capacity was reduced, resulting in uneven flux distribution. Consequently, one end of the intermediate electrode oxidized due to heating by the heating element, reducing the molten conductor's retention capacity, increasing the melting time and the incidence of unsevered conductors. 1, 50, 60, 70, 100: Protective element 2, 101: Insulating substrate 2a: Front surface 2b: Back surface 3, 107: Fusible element 3a: Fusible conductor 4, 104: Heating element 4a: One end portion 4b: Other end portion 5, 105: Insulating layer 6, 106: Intermediate electrode 6a: One end portion / end portion 6b: Other end portion / end portion 7, 111: Flux 8: First heating element electrode 9: Second heating element electrode 10, 108a: Third external connection electrode 11, 102: First electrode 12, 103: Second electrode 13: Low melting point metal 14: High melting point metal 15, 102a: First external connection electrode 16, 103a: Second external connection electrode 17: First lead electrode 18: Second lead electrode 20: Battery pack 20a: Positive terminal 20b: Negative terminal 21: Battery cell 21a, 21b, 21c, 21d: Battery cell 22: Charging device 23: Current control element 23a, 23b: Current control element 24: Control unit 25: Battery stack 26: Charge and discharge control circuit 27: Detection circuit 28: Current control element 30: Cover member 31: Protrusion 31a: End protrusion 31b: Middle protrusion 35: Connector 36: Shield 37: Opening 38: Scraper 61: Fourth external connection electrode 108: Heating element electrode 110: Connecting material Figure 1 is a diagram showing an example of a configuration of a protection element having a heating element provided on the front surface of an insulating substrate, (A) is a top view showing the configuration with the cover member omitted, (B) is an AA cross-sectional view, and (C) is a BB cross-sectional view. Figure 2 is a diagram showing a state in which the fusible element in the protection element shown in Figure 1 has blown, (A) is a top view showing the configuration with the cover member omitted, and (B) is a BB cross-sectional view. Figure 3 is a diagram showing a protection element in which the end protrusion is erected so as to span both a position opposite to the position of the intermediate electrode where the fusible element is mounted and an end portion where the fusible element is not mounted, (A) is a top view showing the configuration with the cover member omitted, and (B) is an AA cross-sectional view. Figure 4 is a diagram showing a configuration in which the end protrusion is formed to have a smaller diameter than the intermediate protrusion, (A) is a top view showing the configuration with the cover member omitted, and (B) is an AA cross-sectional view. Figure 5 shows a configuration in which the end protrusion faces the end of the intermediate electrode and partially protrudes from the end of the intermediate electrode. (A) is a top view showing the cover member omitted, and (B) is an AA cross-sectional view. Figure 6 is a cross-sectional view of a fusible conductor. Figure 7 is a cross-sectional view showing the manufacturing process of a protective element. (A) shows the process of applying flux, (B) shows the connector coated with flux, and (C) shows the protective element. Figure 8 is a circuit diagram showing an example of a battery pack configuration. Figure 9 is a circuit diagram of a protective element. Figure 10 is a cross-sectional view showing a configuration in which the length of the end protrusion is longer than the length of the intermediate protrusion. Figure 11 shows a state in which uneven distribution of flux occurs within the protective element. (A) is a top view showing the cover member omitted, and (B) is an AA cross-sectional view. Figure 12 is a cross-sectional view showing a state in which the fusible molten conductor is aggregated on the intermediate electrode. Figure 13 shows a configuration in which the end protrusion is longer than the middle protrusion and has a smaller diameter than the middle protrusion. (A) is a top view with the cover omitted, and (B) is a cross-sectional view taken along line AA. Figure 14 shows a configuration in which the end protrusion is longer than the middle protrusion and is erected to span both a position opposite the position of the intermediate electrode carrying the fusible element and an end portion thereof not carrying the fusible element. (A) is a top view with the cover omitted, and (B) is a cross-sectional view taken along line AA. Figure 15 shows a configuration in which the end protrusion is longer than the middle protrusion and partially protrudes from the end portion of the intermediate electrode. (A) is a top view with the cover omitted, and (B) is a cross-sectional view taken along line AA. Figure 16 shows a modified example of a protective element. (A) is a top view with the cover omitted, and (B) is a cross-sectional view taken along line AA. Figure 17 is a circuit diagram of the modified example of the protective element. Figure 18 is a diagram showing an example of the structure of a protective element in which a heating element is provided on the back side of an insulating substrate, (A) is a top view with the cover member omitted, (B) is an AA cross-sectional view, (C) is a BB cross-sectional view, and (D) is a bottom view.Figure 19 is a top view showing the state in which the fusible element in the protection element shown in Figure 18 has melted, with the cover omitted. Figure 20 shows a protection element of Comparative Example 1, (A) a top view showing the protection element with the cover omitted, and (B) a cross-sectional view taken along line AA. Figure 21 shows an example of the configuration of a front-mounted protection element, (A) a top view showing the protection element with the cover omitted, (B) a cross-sectional view, and (C) a bottom view. 1: Protective components 2: Insulating substrate 2a: Front 2b: Back 3: Meltable 4: Heating element 4a: one end 4b: The other end 5: Insulation layer 6: Middle electrode 6a: one end / end 6b: other end / end 7: Flux 8: 1st heating element electrode 9: Second heating element electrode 10: 3rd external connection electrode 11: 1st electrode 12: Second electrode 15: 1st external connection electrode 16: Second external connection electrode 17: 1st lead electrode 18: Second lead electrode 30: Cover member 31: protrusion 31a: end protrusion 31b: Middle protrusion

Claims

1. A protective element comprising: an insulating substrate; a heating element disposed on the front side of the insulating substrate; an insulating layer covering the heating element; an intermediate electrode disposed on the insulating layer; a fusible element mounted on the intermediate electrode; a cover member covering the front side of the insulating substrate; and a flux; wherein a protrusion of the cover member holding the flux at a predetermined position is vertically disposed opposite to the intermediate electrode; the intermediate electrode has a length longer than the width of the fusible element in a direction orthogonal to the energizing direction of the fusible element, and at least one end protrudes beyond the fusible element; the protrusion is disposed at a position opposite to the position of the intermediate electrode where the fusible element is mounted, and at a position opposite to the end of the intermediate electrode where the fusible element is not mounted, holding the flux on the fusible element and at the end of the electrode.

2. The protective element of claim 1, wherein the protrusion has a length that does not contact the molten fusible material.

3. The protective element of claim 1 or 2, wherein the length of the protrusion disposed at the position opposite to the end of which the fusible material is not mounted is longer than the length of the protrusion formed at the position opposite to the position on which the fusible material is mounted.

4. The protective element as claimed in claim 1 or 2, wherein the intermediate electrode protrudes beyond the fusible body at both ends in a direction orthogonal to the energizing direction of the fusible body; and the protrusion is positioned opposite to the two ends.

5. The protective element as claimed in claim 1 or 2, wherein the protrusions are symmetrically arranged in a direction orthogonal to the energizing direction of the fusible element.

6. A protective element comprising: an insulating substrate; an intermediate electrode disposed on the front side of the insulating substrate; a fusible element mounted on the intermediate electrode; a cover member covering the front side of the insulating substrate; a flux; a heating element disposed on the back side of the insulating substrate opposite to the front side; and an insulating layer covering the heating element; wherein a protrusion of the cover member holding the flux at a predetermined position is vertically disposed opposite to the intermediate electrode; the intermediate electrode has a length longer than the width of the fusible element in a direction orthogonal to the energizing direction of the fusible element, and at least one end protrudes beyond the fusible element; the protrusion is disposed at a position opposite to the position of the intermediate electrode where the fusible element is mounted, and at a position opposite to the end of the intermediate electrode where the fusible element is not mounted, holding the flux on the fusible element and at the end of the electrode.

7. A method for manufacturing a protective element, comprising the following steps: forming a connector having: an insulating substrate, a heating element disposed on the front side of the insulating substrate, an insulating layer covering the heating element, and an intermediate electrode disposed on the insulating layer, wherein a fusible element is mounted on the intermediate electrode; applying flux to the fusible element and the intermediate electrode via a mask having an opening corresponding to a coating area; and connecting a cover member to the front side of the insulating substrate on which the fusible element is mounted to cover the front side of the substrate; wherein a protrusion of the cover member holding the flux at a predetermined position is vertically disposed opposite to the intermediate electrode; wherein the intermediate electrode has a length longer than the width of the fusible element in a direction orthogonal to the energizing direction of the fusible element, and at least one of its ends protrudes beyond the fusible element; The protrusions are positioned opposite the location on the intermediate electrode where the fusible element is mounted, and opposite the end portion where the fusible element is not mounted, thereby retaining the flux on the fusible element and the end portion.

8. A method for manufacturing a protective element, comprising the following steps: forming a connector having: an insulating substrate, an intermediate electrode disposed on a front side of the insulating substrate, a heating element disposed on a back side of the insulating substrate opposite to the front side, and an insulating layer covering the heating element, and a fusible element mounted on the intermediate electrode; applying flux to the fusible element and the intermediate electrode via a mask having an opening corresponding to a coating area; and connecting a cover member to the front side of the insulating substrate on which the fusible element is mounted to cover the front side of the substrate; wherein a protrusion of the cover member holding the flux at a predetermined position is vertically disposed opposite to the intermediate electrode; the intermediate electrode having a length longer than the width of the fusible element in a direction orthogonal to the energizing direction of the fusible element, and at least one end protruding beyond the fusible element; The protrusions are positioned opposite the location on the intermediate electrode where the fusible element is mounted, and opposite the end portion where the fusible element is not mounted, thereby retaining the flux on the fusible element and the end portion.

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