Protective element

Abstract

The present invention provides a protective element which can interrupt a current pathway quickly and reliably using a fusible conductor having a high-melting-point metal layer and a low-melting-point metal layer, and which can also be manufactured through a simple process.　A protective element (1) comprises an insulating substrate (2), a heating element (5), first and second electrodes (3, 4), a heating element lead electrode (6), and a fusible conductor (7) that melts, and thus interrupts a current pathway, due to self-heating and / or heating by the heating element (5) caused by application of an overcurrent exceeding the rated current, wherein the fusible conductor (7) has a laminated structure of a high-melting-point metal layer (10) and a second low-melting-point metal layer (12), the fusible conductor (7) is connected on top of the first electrode (3), on top of the second electrode (4), and on top of the heating element lead electrode (6) via the second low-melting-point metal layer (12) in an orientation such that the second low-melting-point metal layer (12) faces the insulating substrate (2), with at least part of the second low-melting-point metal layer (12) being in direct or indirect contact with the insulating substrate (2) in the space between the first electrode (3) and the heating element lead electrode (6) and in the space between the second electrode (4) and the heating element lead electrode (6).

Description

Protection Elements

[0001] This technology relates to a protection element mounted on a circuit board, which cuts off current to at least a portion of the circuit board when an abnormality occurs in the circuit board. This application claims priority based on Japanese Patent Application No. 2024-52593, filed in Japan on March 27, 2024, which is incorporated herein by reference.

[0002] Many rechargeable and reusable secondary batteries are provided to users as battery packs. For example, lithium-ion secondary batteries, which have a high weight energy density, generally have several built-in protection circuits, such as overcharge protection and overdischarge protection, to ensure the safety of users and electronic devices, and have the function of cutting off the output of the battery pack in specified cases.

[0003] For example, a battery pack protection mechanism may use a built-in FET switch to turn the output on and off to protect the battery pack from overcharging or overdischarging. However, if the FET switch is short-circuited or destroyed for some reason, if a lightning surge or other event causes a momentary large current to flow, or if the output voltage of a battery cell drops abnormally due to its lifespan or, conversely, if an excessively large voltage is output, the battery pack and electronic devices must be protected from accidents such as fire. Therefore, in order to safely shut off the output of the battery cell in any of these possible abnormal conditions, a protection element consisting of a fuse element that has the function of interrupting the current path in response to an external signal is used.

[0004] As a protective element for such a protection circuit for a lithium-ion secondary battery or the like, as described in Patent Document 1, a structure is generally used in which a heating element is provided inside the protective element and this heating element melts a soluble conductor on the current path.

[0005] In the protective element described in Patent Document 1, when reflow mounting is used, a high melting point solder containing Pb with a melting point of 300° C. or higher is generally used for the fusible conductor so that it does not melt due to the heat of reflow. However, the RoHS Directive and other regulations only permit the use of Pb-containing solder in limited cases, and it is expected that the demand for Pb-free solder will increase in the future.

[0006] JP 2010-170801 A JP 2004-185960 A JP 2012-003878 A

[0007] Here, "solder erosion" and "corrosion phenomenon" have long been known as the phenomenon in which Au or Ag plating on electronic components dissolves in molten solder. A protective element compatible with Pb-free solder material that utilizes this phenomenon is described in Patent Document 2. However, as described in Patent Document 2, in a structure in which a high-melting-point metal film is adhered to an insulating layer, the high-melting-point metal film only causes a corrosion phenomenon (also known as a dissolution phenomenon) due to the melting of the low-melting-point metal film, which can result in incomplete circuit interruption. Furthermore, to ensure the melting of the fusible conductor, it is preferable to form slits and thickness steps in the high-melting-point metal layer, but this increases the number of steps required to form the slits and thickness steps (see, for example, Patent Document 3).

[0008] Therefore, the present technology aims to provide a protective element that can quickly and reliably interrupt a current path using a fusible conductor having a high-melting point metal layer and a low-melting point metal layer, and can be manufactured using a simple process.

[0009] In order to solve the above-mentioned problems, the protective element according to the present technology includes an insulating substrate, a heating element provided on the insulating substrate, a first electrode and a second electrode provided on the insulating substrate, a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode, and a fusible conductor connected across the first electrode, the heating element lead electrode, and the second electrode, which melts between the first electrode and the second electrode due to self-heating caused by the passage of an overcurrent exceeding a rated current and / or heat generation by the heating element, thereby interrupting the current path. The fusible conductor includes a high-melting point metal layer, The soluble conductor has a laminated structure of a second low-melting point metal layer composed of an alloy of a high-melting point metal constituting the high-melting point metal layer and a first low-melting point metal having a melting point lower than that of the high-melting point metal, and the soluble conductor is connected to the first electrode, the second electrode, and the heating element extraction electrode via the second low-melting point metal layer with the second low-melting point metal layer facing the insulating substrate, and at least a portion of the second low-melting point metal layer of the soluble conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode.

[0010] Further, a protective element according to the present technology includes an insulating substrate, a heating element provided on the insulating substrate, first and second electrodes provided on the insulating substrate, a heating element lead electrode electrically connected to the heating element on a current path between the first and second electrodes, and a soluble conductor connected across the first electrode, the heating element lead electrode, and the second electrode, which melts between the first and second electrodes due to self-heating caused by the passage of an overcurrent exceeding a rated current and / or heat generated by the heating element, thereby interrupting the current path. The soluble conductor has a coated structure in which both sides of a low-melting-point metal layer are coated with a high-melting-point metal layer having a melting point higher than that of the low-melting-point metal layer, and the soluble conductor is connected to each of the first electrode, the second electrode, and the heating element lead electrode via a conductive connecting material. At least a portion of the soluble conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode.

[0011] Further, a manufacturing method of a protection element according to the present technology includes a mounting step of mounting a laminate including a heating element, a first electrode, a second electrode, and an insulating substrate provided with a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode, the laminate including a high-melting-point metal layer and a first low-melting-point metal layer made of a first low-melting-point metal having a lower melting point than the high-melting-point metal constituting the high-melting-point metal layer, over the first electrode, the heating element lead electrode, and the second electrode formed on the insulating substrate, in an orientation in which the first low-melting-point metal layer, the first electrode, the heating element lead electrode, and the second electrode are in contact with each other; The method includes a heating step of heating the insulating substrate at a mounting temperature equal to or higher than the eutectic temperature of an alloy of the high-melting point metal and the first low-melting point metal, a melting step of forming a second low-melting point metal layer composed of an alloy of the high-melting point metal and the first low-melting point metal and having a solidus temperature lower than the mounting temperature by mutual diffusion and / or melting of a part of the high-melting point metal and the first low-melting point metal, and a connection step of connecting the soluble conductor to the first electrode, the heating element lead electrode, and the second electrode via the second low-melting point metal layer of the soluble conductor in which the second low-melting point metal layer solidified with the high-melting point metal layer is laminated by cooling the molten second low-melting point metal layer.

[0012] Further, a manufacturing method of a protection element according to the present technology includes a heating element, a first electrode, a second electrode, and an insulating substrate provided with a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode, and includes a conductive connecting material forming step of providing a conductive connecting material on the first electrode, the heating element lead electrode, and the second electrode formed on the insulating substrate, and between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode; and a low-melting point insulating material forming step of providing a conductive connecting material on the first electrode, the heating element lead electrode, and the second electrode via the conductive connecting material. The method includes a mounting process for mounting a soluble conductor having a coated structure in which both sides of a low-melting-point metal layer are coated with a high-melting-point metal layer having a melting point higher than that of the low-melting-point metal layer; a heating and melting process for heating and melting the conductive connecting material at a temperature higher than the solidus temperature of the conductive connecting material; and a connecting process for connecting the soluble conductor with the first electrode, the heating element extraction electrode, and the second electrode by cooling the molten conductive connecting material, wherein at least a portion of the soluble conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode.

[0013] According to this technology, a protective element can be realized that can quickly and reliably interrupt a current path using a fusible conductor having a high-melting point metal layer and a low-melting point metal layer, and can be manufactured using a simple process.

[0014] In a protective element according to one aspect of the present technology, by adhering the low-melting-point metal layer of the soluble conductor to the insulating substrate, the problem of the circuit not being able to be completely shut off due to residual corrosion of the high-melting-point metal layer in a structure in which a high-melting-point metal layer is closely arranged to an insulating layer as described in Patent Document 2 can be avoided.

[0015] In a protective element according to one aspect of the present technology, the heat generated by the heating element heats the low-melting point metal layer through the heating element extraction electrode, and also directly heats the low-melting point metal layer that is at least partially in close contact with or in contact with the insulating substrate through the insulating substrate, causing a wide range of the low-melting point metal layer to melt in a short period of time, thereby efficiently melting the high-melting point metal layer and improving the fusing characteristics of the fusible conductor.

[0016] In a protective element according to one aspect of the present technology, in an overcurrent state, the low-melting-point metal layer of the fusible conductor between the electrodes is in close contact with or in contact with the insulating substrate, so that the heat generated by the fusible conductor is dissipated directly to the insulating substrate, thereby improving the current rating of the protective element.

[0017] In a protective element according to one aspect of the present technology, a protective element that does not require precise control of the solder paste can be realized by connecting a first electrode, a second electrode, and a heating element lead electrode on an insulating substrate to a soluble conductor using a low-melting point metal layer whose thickness has been controlled in advance.

[0018] Therefore, this technology makes it possible to achieve both fuse characteristics, which are in a trade-off relationship between stable fusible conductor connection, efficient melting of the fusible conductor by heating the heating element, and improved rated current.

[0019] FIG. 1 is a diagram showing an example of a configuration of a protection element to which the present technology is applied, where (A) is a plan view showing the cover member omitted, (B) is a cross-sectional view in the current-carrying direction of the fusible conductor, and (C) is a bottom view. FIG. 2 is a plan view showing a state in which the fusible conductor has melted. FIG. 3 is a circuit diagram showing an example of a configuration of a battery pack. FIG. 4 is a circuit diagram of a protection element. FIG. 5 is a diagram showing an example of a configuration of a protection element having a surface heater structure, where (A) is a plan view showing the cover member omitted, (B) is a cross-sectional view in the current-carrying direction of the fusible conductor, and (C) is a bottom view. FIG. 6 is a cross-sectional view showing an example of a configuration of a protection element in which an insulating substrate has a layer structure of an upper layer and a lower layer, and a heating element is formed between the upper and lower layers. FIG. 7 is a diagram showing an example of a manufacturing process for a protective element, where (A) and (B) are cross-sectional views showing the mounting process of a fusible conductor, (C) is a cross-sectional view showing the heating, melting, and connection process of the fusible conductor, (D) is a cross-sectional view showing the state in which a coated flux is applied to the fusible conductor and a cover member is provided, and (E) is a cross-sectional view showing the process of mounting the protective element on a circuit board. FIG. 8 is a diagram schematically showing the interdiffusion of different metal atoms at the laminate interface of different metals. FIG. 9 is a binary alloy phase diagram of silver (Ag) and tin (Sn). FIG. 10 is a binary alloy phase diagram of lead (Pb) and tin (Sn). FIG. 11 is a cross-sectional view schematically showing the state change of the laminate during the heating, melting, and connection process. FIG. 12 is a cross-sectional view schematically showing a case in which the second low-melting point metal layer is a laminate structure of an alloy of a high-melting point metal and a first low-melting point metal and the first low-melting point metal layer. 13 is a cross-sectional view showing the state change of the laminate in the heating, melting, and connection process. Figure 14 is a cross-sectional view showing the case where the second low-melting point metal layer is a laminated structure of an alloy of a high-melting point metal and a first low-melting point metal and a first low-melting point metal layer. Figure 15 is a diagram showing the process of heating and pressing the laminate with a heating head, (A) is a cross-sectional view showing the state in which the laminate is mounted, (B) is a cross-sectional view showing the process of heating and pressing the laminate with a heating head, and (C) is a cross-sectional view showing the state in which the fusible conductor is mounted.16 is a diagram showing the process of mounting a fusible conductor while pressing the laminate with a weight, (A) is a cross-sectional view showing the state in which the laminate is mounted, (B) is a cross-sectional view showing the process of heating the laminate while pressing with a weight, and (C) is a cross-sectional view showing the state in which the fusible conductor is mounted. Figure 17 is a cross-sectional view showing a protective element in which a restricting wall is provided on the inner surface of the cover member to hold down the portion where the second low-melting point metal layer of the fusible conductor contacts the insulating substrate. Figure 18 is a diagram showing the manufacturing process of a protective element in which the second low-melting point metal layer contacts the insulating layer, (A) is a cross-sectional view showing the mounting process of the laminate, (B) is a cross-sectional view showing the state in which the first low-melting point metal layer melts and the liquid phase contacts the insulating layer, and (C) is a cross-sectional view showing a protective element in which the second low-melting point metal layer is in close contact with the insulating layer. 19A and 19B are diagrams showing a manufacturing process of a protective element in which the insulating layer is thicker than the sum of the thicknesses of the heating element lead electrodes and the first low-melting-point metal layer, where (A) is a cross-sectional view showing the step of mounting a laminate, (B) is a cross-sectional view showing a state in which the first low-melting-point metal layer has melted and the liquid phase has contacted the insulating layer, and (C) is a cross-sectional view showing a protective element in which the second low-melting-point metal layer has adhered to the insulating layer. 20A and 20B are diagrams showing a manufacturing process of a protective element in which the second low-melting-point metal layer has contacted a convex portion, where (A) is a cross-sectional view showing the step of mounting a laminate, (B) is a cross-sectional view showing a state in which the first low-melting-point metal layer has melted and the liquid phase has contacted the convex portion, and (C) is a cross-sectional view showing a protective element in which the second low-melting-point metal layer has contacted the convex portion. 21 is a diagram showing the manufacturing process of a protective element in which the height of the convex portion is higher than the sum of the film thickness of the heating element lead electrode and the film thickness of the first low-melting point metal layer, (A) is a cross-sectional view showing the mounting process of the laminate, (B) is a cross-sectional view showing the state in which the first low-melting point metal layer is melted and the liquid phase is in contact with the convex portion, (C) is a cross-sectional view showing a protective element in which the second low-melting point metal layer is in close contact with the convex portion. Figure 22 is a diagram showing a protective element according to a modified example, (A) is a plan view showing the cover member omitted, (B) is a cross-sectional view in the current-carrying direction of the soluble conductor, and (C) is a bottom view. Figure 23 is a cross-sectional view of a soluble conductor according to a modified example.24 is a diagram showing an example of a manufacturing process of a protective element according to a modified example, (A) is a cross-sectional view showing the conductive connecting material formation process, (B) is a cross-sectional view showing the soluble conductor mounting process, (C) is a cross-sectional view showing the conductive connecting material heating and melting process and the soluble conductor connecting process, (D) is a cross-sectional view showing the state in which a coating flux is applied to the soluble conductor and a cover member is provided, and (E) is a cross-sectional view showing the process of mounting the protective element on a circuit board. Figure 25 is a cross-sectional view showing a protective element in which a restricting wall is provided on the inner surface of the cover member to hold down the portion where the soluble conductor contacts the insulating substrate via the conductive connecting material. Figure 26 is a diagram showing a manufacturing process of a protective element in which the soluble conductor indirectly contacts the insulating substrate via an insulating layer, (A) is a cross-sectional view showing the soluble conductor mounting process, (B) is a cross-sectional view showing the state in which the conductive connecting material melts and the soluble conductor contacts the insulating layer, and (C) is a cross-sectional view showing a protective element in which the soluble conductor contacts the insulating layer. 27 is a diagram showing the manufacturing process of a protective element in which the film thickness of the insulating layer is made thicker than twice the film thickness of the heating element lead electrode, (A) is a cross-sectional view showing the mounting process of the soluble conductor, (B) is a cross-sectional view showing the state in which the conductive connecting material melts and the soluble conductor contacts the insulating layer, and (C) is a cross-sectional view showing a protective element in which the soluble conductor contacts the insulating layer. Figure 28 is a diagram showing the manufacturing process of a protective element in which the soluble conductor contacts the convex portion via the conductive connecting material, (A) is a cross-sectional view showing the mounting process of the soluble conductor, (B) is a cross-sectional view showing the state in which the soluble conductor contacts the convex portion via the conductive connecting material, and (C) is a cross-sectional view showing a protective element in which the soluble conductor contacts the convex portion via the conductive connecting material. Figure 29 shows the manufacturing process of a protective element in which the height of the convex portion is made higher than twice the film thickness of the heating element extraction electrode, where (A) is a cross-sectional view showing the mounting process of the soluble conductor, (B) is a cross-sectional view showing the state in which the soluble conductor is in contact with the convex portion via the conductive connecting material, and (C) is a cross-sectional view showing a protective element in which the soluble conductor is in contact with the convex portion via the conductive connecting material.

[0020] Hereinafter, a protection element to which the present technology is applied will be described in detail with reference to the drawings. It should be noted that the present technology is not limited to the following embodiments, and various modifications are possible within the scope of the present technology. Furthermore, the drawings are schematic, and the ratios of the dimensions may differ from the actual dimensions. Specific dimensions should be determined with reference to the following explanation. It should be noted that the drawings may also include portions with different dimensional relationships and ratios. Furthermore, although this specification describes multiple protection elements and their manufacturing processes, the same components and processes as those in the previously described protection elements and their manufacturing processes may be designated by the same reference numerals, and their details may be omitted.

[0021] [Protection element 1] Figure 1 shows a protection element 1 to which the present technology is applied, (A) is a plan view, (B) is a cross-sectional view in the current direction of the soluble conductor, and (C) is a bottom view. As shown in Figure 1, the protection element 1 includes an insulating substrate 2, a heating element 5 provided on the insulating substrate 2, a first electrode 3 and a second electrode 4 provided on the insulating substrate 2, and a heating element lead electrode 6 electrically connected to the heating element 5 on the current path between the first electrode 3 and the second electrode 4, and a soluble conductor 7 connected across the first electrode 3, the heating element lead electrode 6, and the second electrode 4, which fuses between the first electrode 3 and the second electrode 4 due to self-heating and / or heat generation of the heating element 5 caused by the passage of an overcurrent exceeding the rated current, and cuts off the current path.

[0022] The soluble conductor 7 is a laminate of a high-melting point metal layer 10 and a second low-melting point metal layer 12 composed of an alloy of a high-melting point metal 10a constituting the high-melting point metal layer 10 and a first low-melting point metal 12b having a melting point lower than that of the high-melting point metal 10a, or a laminate of an alloy of the high-melting point metal 10a and the first low-melting point metal 12b and the first low-melting point metal layer 11 of the laminate 35 described later, and is connected to the first electrode 3, the second electrode 4 and the heating element extraction electrode 6 via the second low-melting point metal layer 12 in a direction facing the insulating substrate 2.

[0023] Furthermore, between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6, at least a portion of the second low-melting point metal layer 12 of the soluble conductor 7 is in direct contact with the insulating substrate 2.

[0024] When the second low-melting point metal layer 12 melts due to heat generated by the heating element 5 or self-heating caused by overcurrent, the fusible conductor 7 causes a dissolution phenomenon (corrosion) in which the high-melting point metal layer 10 dissolves into the molten second low-melting point metal layer 12, and is attracted to the first electrode 3, the second electrode 4, and the heating element lead electrode 6, which have high wettability to the molten metal. At this time, according to the protective element 1, at least a portion of the second low-melting point metal layer 12, which has a relatively low melting point, is in contact with the insulating substrate 2 between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6, so that the current paths between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6 can be reliably interrupted.

[0025] That is, in a conventional configuration in which a high-melting-point metal film is in contact with an insulating substrate, there is a problem in that the current path is not completely blocked due to the etched residue of the high-melting-point metal film. However, in the protective element 1, the second low-melting-point metal layer 12, which has a relatively low melting point, is in contact with the insulating substrate 2, so that the molten second low-melting-point metal layer 12 is prevented from remaining on the insulating substrate 2, and is attracted to the heating element lead electrode 6 and the first and second electrodes 3 and 4 while the high-melting-point metal layer 10 is dissolving.

[0026] Furthermore, when the fusible conductor 7 is melted by the heat of the heating element 5, the heat generated by the heating element 5 heats the second low melting point metal layer 12 via the heating element lead electrode 6, and also directly heats the second low melting point metal layer 12, at least a portion of which is in contact with the insulating substrate 2, via the insulating substrate 2. As a result, a wide range of the second low melting point metal layer 12 melts in a short time, which efficiently melts the high melting point metal layer 10 and improves the fast melting characteristics of the fusible conductor 7.

[0027] Furthermore, in the case where the soluble conductor 7 melts due to self-heating caused by an overcurrent, the second low-melting point metal layer 12 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6 comes into contact with the insulating substrate 2, so that the heat generated by the self-heating of the soluble conductor 7 is dissipated directly to the insulating substrate 2, thereby improving the current rating of the protective element 1.

[0028] In addition, since the soluble conductor 7 is connected to the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 via the second low-melting point metal layer 12 whose thickness has been controlled in advance, precise control of the solder paste is not required.

[0029] Therefore, the protective element 1 can achieve the fuse characteristics that are in a trade-off relationship: "stable connection of the fusible conductor", "efficient melting of the fusible conductor by heating the heating element", and "improvement of the rated current".

[0030] Each component of the protection element 1 will be described in detail below.

[0031] [Insulating Substrate] The insulating substrate 2 is formed of an insulating material such as alumina, glass ceramics, mullite, zirconia, etc. Alternatively, the insulating substrate 2 may be made of a material used for printed wiring boards, such as a glass epoxy board or a phenol board.

[0032] [First and Second Electrodes] First and second electrodes 3 and 4 are formed on opposite ends of the insulating substrate 2. The first and second electrodes 3 and 4 are each formed of a conductive pattern such as Ag or Cu. The surfaces of the first and second electrodes 3 and 4 may 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 3 and 4, and prevents fluctuations in the rating due to an increase in the conduction resistance. Furthermore, when the protective element 1 is reflow mounted, the second low-melting point metal layer 12 connecting the fusible conductor 7 melts, preventing the first and second electrodes 3 and 4 from being corroded (soldered).

[0033] The first electrode 3 is connected to the first external connection electrode 13 formed on the back surface 2b of the insulating substrate 2 via a castellation (not shown). The second electrode 4 is connected to the second external connection electrode 14 formed on the back surface 2b of the insulating substrate 2 via a castellation (not shown). When the protection element 1 is mounted on an external circuit board, the first and second external connection electrodes 13, 14 are connected to connection electrodes provided on the external circuit board, and the soluble conductor 7 is incorporated into part of the current path formed on the external circuit board.

[0034] The first and second electrodes 3, 4 are electrically connected via the fusible conductor 7. As shown in Figure 2, the first and second electrodes 3, 4 are disconnected when a large current exceeding the rated current flows through the protective element 1, causing the fusible conductor 7 to melt due to self-heating (Joule heat), or when the heating element 5 heats up due to current flow and the fusible conductor 7 melts.

[0035] [Heater Element] The heater 5 is a conductive material with a relatively high resistance that generates heat when current is applied, and is made of, for example, nichrome, W, Mo, Ru, or a material containing these. The heater 5 can be formed by mixing a powder of these alloys, compositions, or compounds with a resin binder or the like to form a paste, forming a pattern on the insulating substrate 2 using a screen printing technique, and firing the paste. As an example, the heater 5 can be formed by adjusting a mixed paste of a ruthenium oxide paste, silver, and glass paste according to a predetermined voltage, forming a film of a predetermined area at a predetermined position on the back surface 2b of the insulating substrate 2, and then firing it under appropriate conditions. The shape of the heater 5 can be designed as desired, but a roughly rectangular shape corresponding to the shape of the insulating substrate 2, as shown in FIG. 1(C), is preferred to maximize the heat generation area.

[0036] Furthermore, one end 5a of the heating element 5 is connected to the first extraction electrode 15, and the other end 5b is connected to the second extraction electrode 16. The first extraction electrode 15 is formed by being extracted from the heating element electrode 17 along one end 5a of the heating element 5, and in the protection element 1 shown in Figure 1, it extends along one side edge of the heating element 5, which is formed in a substantially rectangular shape, and overlaps one side edge of the heating element 5. Similarly, the second extraction electrode 16 is formed by being extracted from the back surface-side intermediate electrode 18b along the other end 5b of the heating element 5, and in the protection element 1 shown in Figure 1, it extends along the other side edge of the heating element 5, which is formed in a substantially rectangular shape, and overlaps the other side edge of the heating element 5.

[0037] The heating element electrode 17 and the back-side intermediate electrode 18b are formed on opposing side edges of the insulating substrate 2 that are different from the side edges on which the first and second external connection electrodes 13, 14 are provided. The heating element electrode 17 is a power supply electrode to the heating element 5, and is connected to one end 5a of the heating element 5 via the first extraction electrode 15.

[0038] The first and second extraction electrodes 15, 16, the heating element electrode 17, and the back-side intermediate electrode 18b can be formed by printing and firing a conductive paste of Ag, Cu, or the like, similar to the first and second electrodes 3, 4. Furthermore, by using the same material for each of these electrodes formed on the back surface 2b of the insulating substrate 2, they can be formed in a single printing and firing process.

[0039] The heating element electrode 17 may be connected to a resistance measurement electrode (not shown) formed on the surface 2 a of the insulating substrate 2 via a castellation. The first and second electrodes 3 and 4 may be provided with a restricting wall to prevent connection solder provided on the electrodes of the circuit board 34 connected to the first and second external connection electrodes 13 and 14 from melting during reflow mounting or the like, creeping up onto the first and second electrodes 3 and 4 via the castellation, and spreading onto the first and second electrodes 3 and 4. The resistance measurement electrodes may also be provided with a restricting wall. The restricting wall can be formed using an insulating material that is not wettable by solder, such as glass, solder resist, or an insulating adhesive, and can be formed on the first and second electrodes 3 and 4 by printing or the like. Providing the restricting wall prevents the molten connection solder from spreading to the first and second electrodes 3 and 4 or the resistance measurement electrodes, thereby maintaining the connectivity between the protection element 1 and the circuit board 34.

[0040] The intermediate electrode 18 is an electrode provided between the heating element 5 and the heating element lead electrode 6 formed on the front surface 2a of the insulating substrate 2, and includes a front surface-side intermediate electrode 18a formed on the front surface 2a of the insulating substrate 2 and a back surface-side intermediate electrode 18b formed on the back surface 2b of the insulating substrate 2, which are connected via castellations. The front surface-side intermediate electrode 18a is connected to the heating element lead electrode 6. The back surface-side intermediate electrode 18b is connected to the other end 5b of the heating element 5 via the second lead electrode 16.

[0041] 1(B) and 1(C), the heating element 5, the first extraction electrode 15, and the second extraction electrode 16 are covered with an insulating protection layer 8. The insulating protection layer 8 is provided to protect and insulate the heating element 5, and is made of an insulating material such as glass that has heat resistance to the heat generation temperature of the heating element 5. Examples of glass raw materials that make up the insulating material include silica-based glass overcoat glass paste and insulating glass paste.

[0042] The insulating protective layer 8 can be formed by applying, for example, a glass-based paste by screen printing or the like, followed by baking. The thickness of the insulating protective layer 8 is set in consideration of the applicability of the glass paste or the like, and is, for example, greater than 10 μm and equal to or less than 40 μm, and preferably equal to or greater than 20 μm and equal to or less than 40 μm.

[0043] [Heater element lead electrode] The heater element lead electrode 6 formed on the surface 2a of the insulating substrate 2 has one end connected to the surface-side intermediate electrode 18a and is connected to the soluble conductor 7 between the first and second electrodes 3 and 4 via the second low-melting point metal layer 12. In addition, the heater element lead electrode 6 overlaps with the heater element 5 via the insulating substrate 2.

[0044] The heating element lead electrode 6 can be formed by printing and firing a conductive paste of Ag, Cu, or the like, similarly to the first and second electrodes 3 and 4. The surface of the heating element lead electrode 6 may be coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by a known method such as plating.

[0045] [Fusible conductor] Next, we will explain the fusible conductor 7. The fusible conductor 7 is mounted between the first and second electrodes 3 and 4, and melts down due to heat generated by the passage of current through the heating element 5 or due to self-heating (Joule heat) caused by the passage of current exceeding the rated current, thereby interrupting the current path between the first electrode 3 and the second electrode 4.

[0046] The soluble conductor 7 is a laminated structure consisting of an upper layer and a lower layer, with a high-melting-point metal layer 10 as the upper layer and a second low-melting-point metal layer 12 as the lower layer, and in the protective element 1, it forms a rectangular plate shape in a plan view. High-melting-point metals and low-melting-point metals are metals that have a difference in melting point and can melt, with a metal with a relatively low melting point being referred to as a "low-melting-point metal" and a metal with a relatively high melting point that dissolves into the molten low-melting-point metal being referred to as a "high-melting-point metal." In this specification, the high-melting-point metal constituting the high-melting-point metal layer 10 is referred to as a "high-melting-point metal 10a," and the low-melting-point metal contained in the high-melting-point metal layer 10 is referred to as a "low-melting-point metal 10b." Furthermore, the high-melting-point metal contained in the second low-melting-point metal layer 12 is referred to as a "high-melting-point metal 12a," and the low-melting-point metal constituting the second low-melting-point metal layer 12 is referred to as a "low-melting-point metal 12b." Furthermore, the high-melting-point metal contained in the first low-melting-point metal layer 11 of the laminate 35 described below is referred to as the "high-melting-point metal 11a," and the low-melting-point metal constituting the first low-melting-point metal layer 11 is referred to as the "low-melting-point metal 11b." This definition is an example based on a binary alloy, but in the case of a multi-component alloy such as a ternary alloy or more, definitions are similarly given for each component.

[0047] The high-melting point metal 10a constituting the high-melting point metal layer 10 is, for example, Ag or Cu, or a metal containing either of these as its main component, and has a high melting point that prevents it from melting even when the first and second electrodes 3, 4 and the heating element extraction electrode 6 are connected to the soluble conductor 7 or when the protective element 1 is mounted on the circuit board 34 by reflow.

[0048] The second low-melting-point metal layer 12 is composed of an alloy of a high-melting-point metal 12a, which is the high-melting-point metal 10a constituting the high-melting-point metal layer 10, and a first low-melting-point metal 12b having a melting point lower than that of the high-melting-point metal 12a. The second low-melting-point metal layer 12 is formed by mutual diffusion and / or dissolution of part of the high-melting-point metal layer 10 and the metals of the first low-melting-point metal layer 11 when a laminate 35 having the high-melting-point metal layer 10 as an upper layer and the first low-melting-point metal layer 11 composed of the first low-melting-point metal 11b as a lower layer is connected across the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by heating such as reflow mounting (see FIGS. 7 and 11 ). In addition, the second low melting point metal layer 12 may have a laminated structure of an alloy of the high melting point metal 12a and the first low melting point metal 12b and the first low melting point metal layer 11 due to the first low melting point metal layer 11 of the laminate 35 not being completely melted and remaining. The soluble conductor 7 is connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by this second low melting point metal layer 12.

[0049] The first low-melting-point metal 12b is preferably a solder or a metal containing Sn as a main component, which is a material commonly called “Pb-free solder.” The melting point of the first low-melting-point metal 12b does not necessarily need to be higher than the reflow temperature, and may melt at, for example, about 200°C.

[0050] The melting point of the first low-melting point metal 12b may be higher than the reflow temperature for mounting the fusible conductor 7. As will be described later, in the laminate 35, at the lamination interface between the high-melting point metal layer 10 and the first low-melting point metal layer 11, atoms 10aA of the high-melting point metal 10a and atoms 11bA of the first low-melting point metal 11b interdiffuse to form the second low-melting point metal layer 12. The melting point of the second low-melting point metal layer 12 decreases as the diffusion progresses, approaching the eutectic temperature. Therefore, even if the melting point of the first low-melting point metal 11b is higher than the reflow temperature, if the eutectic line of the second low-melting point metal layer 12 is lower than the reflow temperature, the second low-melting point metal layer 12 will be in a liquid phase, or at least in a state where a solid phase and a liquid phase are mixed. Thereafter, as the second low-melting point metal layer 12 cools, a soluble conductor 7 consisting of a laminate of a high-melting point metal layer 10 and a second low-melting point metal layer 12 is formed, and the soluble conductor 7 is connected to the first and second electrodes 3, 4 and the heating element extraction electrode 6 via the second low-melting point metal layer 12.

[0051] The second low-melting point metal layer 12 is formed by interdiffusion and / or dissolution of a portion of the high-melting point metal layer 10 and the first low-melting point metal layer 11. However, if the thickness of the first low-melting point metal layer 11 is less than 1 / 10 of the thickness of the high-melting point metal layer 10 (the ratio varies depending on the material) or if the reflow mounting temperature is higher than the liquidus temperature of the first low-melting point metal layer 11, at any time during the process from mounting on each electrode of the soluble conductor 7 to mounting on the circuit board 34 of the protective element 1, the temperature rise due to reflow mounting causes a portion of the high-melting point metal layer 10 and the entire first low-melting point metal layer 11 to interdiffuse and / or melt, forming an alloy of the high-melting point metal layer 10 and the first low-melting point metal layer 11.

[0052] The soluble conductor 7 is connected to the first electrode 3, the second electrode 4, and the heating element lead electrode 6 via the second low-melting point metal layer 12, with the second low-melting point metal layer 12 facing the insulating substrate 2. Therefore, the protective element 1 does not require precise control of the film thickness of the solder paste, the reflow temperature, etc., which are necessary to connect the soluble conductor 7 and each electrode via the solder paste.

[0053] In addition, in the soluble conductor 7, at least a portion of the second low-melting point metal layer 12 is in direct contact with the insulating substrate 2 between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6. Therefore, when the soluble conductor 7 is to be blown by the heat of the heating element 5, the heat generated by the heating element 5 heats the second low-melting point metal layer 12 through the heating element lead electrode 6 and also directly heats the second low-melting point metal layer 12, at least a portion of which is in contact with the insulating substrate 2, through the insulating substrate 2. As a result, between the first electrode 3 and the heating element lead electrode 6 that need to be blown and the second electrode 4 and the heating element lead electrode 6, the second low-melting point metal layer 12 melts over a wide range in a short time, thereby efficiently melting the high-melting point metal layer 10 and improving the fast-fusing characteristics of the soluble conductor 7. Furthermore, by directly heating the heating element lead electrode 6 by the heating element 5, the molten conductor 7a of the fusible conductor 7 can be more easily coagulated.

[0054] In addition, in the case where the soluble conductor 7 melts due to self-heating caused by an overcurrent, the second low-melting point metal layer 12 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6 comes into contact with the insulating substrate 2, so that the heat generated by self-heating due to the flow of current through the soluble conductor 7 is dissipated directly to the insulating substrate 2, thereby improving the current rating of the protective element 1.

[0055] Therefore, according to the protective element 1, it is possible to achieve the fuse characteristics, which are in a trade-off relationship between "stable fusible conductor connection," "efficient melting of the fusible conductor by heating of the heating element," and "improvement of the rated current." The process of contacting the second low-melting point metal layer 12 with the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element lead electrode 6 will be described in detail later.

[0056] Here, the manner in which the second low-melting point metal layer 12 contacts the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element lead electrode 6 may include a manner in which the second low-melting point metal layer 12 is in complete contact with the surface of the insulating substrate 2, as well as a manner in which there is a gap of several μm to several tens of μm. When the second low-melting point metal layer 12 is cooled from a state in which it is in close contact with the surface 2a of the insulating substrate 2, it undergoes hardening shrinkage and may also develop a gap of several μm to several tens of μm from the surface 2a of the insulating substrate 2 due to cracks, etc. In this case, a heat transfer path is formed between the heating element 5 and the second low-melting point metal layer 12 via radiant heat, thereby achieving the same effect as when they are in contact.

[0057] [Liquidus Point of Second Low-Melting Point Metal Layer] The protective element 1 is mounted on the circuit board 34 and cuts off current to at least a portion of the circuit board 34 when an abnormality occurs in the circuit board 34. The protective element 1 can be mounted efficiently on the circuit board 34 by reflow soldering. Here, the liquidus point of the second low-melting point metal layer 12 is preferably higher than the mounting temperature of the protective element 1 on the circuit board 34.

[0058] Since the liquidus point of the second low-melting point metal layer 12 is higher than the mounting temperature on the circuit board 34, the second low-melting point metal layer 12 melts when mounted on the circuit board, and gaps are prevented from occurring between the second low-melting point metal layer 12 and the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element extraction electrode 6.

[0059] [Contact area between the second low melting point metal layer and the insulating substrate] The contact area between the second low melting point metal layer 12 and the insulating substrate 2 is preferably 50% or more of the area between the first electrode 3 overlapping with the soluble conductor 7 and the heating element lead electrode 6, and 50% or more of the area between the second electrode 4 overlapping with the soluble conductor 7 and the heating element lead electrode 6. This makes it possible to further demonstrate the effect of the contact between the second low melting point metal layer 12 and the insulating substrate 2 described above.

[0060] [Layer thickness] In addition, the thickness of the high melting point metal layer 10 in the stacking direction is preferably thicker than the thickness of the second low melting point metal layer 12 in the stacking direction. By using a metal with a low resistance value such as Ag as the high melting point metal layer 10, the increase in the internal resistance of the soluble conductor 7 can be suppressed, and the rating can be improved while suppressing the increase in size of the protective element 1.

[0061] The fusible conductor 7 can improve the resistance (pulse resistance) to surges in which an abnormally high voltage is instantaneously applied to an electrical system incorporating the protective element 1. In other words, the fusible conductor 7 must not melt even when, for example, a 100 A current flows for several milliseconds. In this regard, since large currents flowing in an extremely short time flow through the surface layer of the conductor (skin effect), the fusible conductor 7 has a high-melting-point metal layer 10, such as Ag, as an upper layer, which has a low resistance value, making it easy to pass the current applied by the surge and preventing melting due to self-heating. Therefore, the fusible conductor 7 can significantly improve its resistance to surges compared to fuses made of conventional solder alloys.

[0062] The fusible conductor 7 is coated with a coating flux 9 to prevent oxidation and improve wettability during fusing. The interior of the protective element 1 is protected by covering the insulating substrate 2 with a cover member 19. The cover member 19 can be formed using insulating materials such as various engineering plastics, thermoplastic plastics, ceramics, and glass epoxy substrates. The cover member 19 has an internal space on the surface 2a of the insulating substrate 2 that is sufficient to allow the fusible conductor 7a to expand spherically when the fusible conductor 7 melts, and to aggregate on the heating element lead electrode 6 and the first and second electrodes 3 and 4.

[0063] [Circuit Configuration Example] Such a protection device 1 is used by being incorporated into a circuit in a battery pack 20 of, for example, a lithium ion secondary battery. As shown in Fig. 3, the battery pack 20 has a battery stack 25 consisting of, for example, a total of four battery cells 21a to 21d of lithium ion secondary batteries.

[0064] The battery pack 20 includes a battery stack 25, a charge / discharge control circuit 26 that controls the charging and discharging of the battery stack 25, a protection element 1 to which the present invention is applied that cuts off the charge / discharge path when an abnormality occurs in the battery stack 25, a detection circuit 27 that detects the voltage of each battery cell 21a to 21d, and a current control element 28 that serves as a switch element that controls the operation of the protection element 1 in accordance with the detection result of the detection circuit 27.

[0065] The battery stack 25 is a series connection of battery cells 21a to 21d that require control to protect against overcharge and overdischarge, and is detachably connected to a charging device 22 via the positive terminal 20a and negative terminal 20b of the battery pack 20, and is applied with a charging voltage from the charging device 22. The battery pack 20 charged by the charging device 22 can be used to operate an electronic device that runs on a battery by connecting the positive terminal 20a and negative terminal 20b to the electronic device.

[0066] The charge / discharge control circuit 26 includes two current control elements 23a, 23b connected in series in a 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, 23b. The current control elements 23a, 23b are configured, for example, by field-effect transistors (hereinafter referred to as FETs), and the control unit 24 controls the gate voltage to control conduction and interruption of the current path of the battery stack 25 in the charging and / or discharging directions. The control unit 24 controls the operation of the current control elements 23a, 23b to interrupt the current path when the battery stack 25 is overcharged or overdischarged, depending on the detection result by the detection circuit 27.

[0067] The protection element 1 is connected, for example, on a charge / discharge current path between a battery stack 25 and a charge / discharge control circuit 26 , and its operation is controlled by a current control element 28 .

[0068] The detection circuit 27 is connected to each of the battery cells 21a to 21d, detects the voltage value of each of the battery cells 21a to 21d, and supplies each voltage value to the control unit 24 of the charge / discharge control circuit 26. The detection circuit 27 also outputs a control signal for controlling the current control element 28 when any one of the battery cells 21a to 21d reaches an overcharge voltage or an overdischarge voltage.

[0069] The current control element 28 is composed of, for example, a FET, and when the detection signal output from the detection circuit 27 indicates that the voltage value of the battery cells 21a to 21d exceeds a predetermined over-discharge or over-charge state, it activates the protection element 1 and controls the charge / discharge current path of the battery stack 25 to be cut off regardless of the switch operation of the current control elements 23a and 23b.

[0070] The protective element 1 to which the present invention is applied and used in the battery pack 20 configured as described above has a circuit configuration as shown in Figure 4. That is, the protective element 1 has the first external connection electrode 13 connected to the battery stack 25 side and the second external connection electrode 14 connected to the positive terminal 20a side, thereby connecting the soluble conductor 7 in series to the charge / discharge path of the battery stack 25. Furthermore, in the protective element 1, the heating element 5 is connected to the current control element 28 via the heating element electrode 17, and the heating element 5 is connected to one end of the battery stack 25. In this way, one end of the heating element 5 is connected to the soluble conductor 7 and one end of the battery stack 25 via the heating element lead electrode 6, and the other end is connected to the current control element 28 and the other end of the battery stack 25 via the heating element electrode 17. This forms a power supply path to the heating element 5 whose current flow can be controlled by the current control element 28.

[0071] [Operation 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. The current control element 28 then controls the current to energize the heating element 5. The protection element 1 allows current to flow from the battery stack 25 to the heating element 5, causing the heating element 5 to start generating heat. In the protection element 1, heat from the heating element 5 is transferred to the fusible conductor 7 via the intermediate electrode 18 and heating element lead electrode 6, which have excellent thermal conductivity, and via the insulating substrate 2, causing the fusible conductor 7 to melt and cut off the charge / discharge path of the battery stack 25. In addition, since the protective element 1 is formed by stacking the soluble conductor 7 on a high-melting point metal layer 10 and a second low-melting point metal layer 12, the second low-melting point metal layer 12 melts before the high-melting point metal layer 10 melts, and the soluble conductor 7 can be melted in a short time by utilizing the dissolving action of the high-melting point metal layer 10 by the molten second low-melting point metal layer 12.

[0072] When the fusible conductor 7 of the protection element 1 melts, the power supply path to the heating element 5 is also cut off, and the heating element 5 stops generating heat.

[0073] In addition, even if an overcurrent exceeding the rated current flows through the battery pack 20, the protective element 1 can cut off the charge / discharge path of the battery pack 20 by causing the fusible conductor 7 to melt due to self-heating.

[0074] In this way, the protective element 1 melts the soluble conductor 7 due to heat generated by the passage of current through the heating element 5 or self-heating of the soluble conductor 7 due to overcurrent. As described above, the protective element 1 has a structure in which the second low-melting point metal layer 12 is laminated on the high-melting point metal layer 10, so that deformation of the soluble conductor 7 is suppressed even when the protective element 1 is reflow-mounted on the circuit board 34 or when the circuit board 34 on which the protective element 1 is mounted is further exposed to a high-temperature environment such as reflow heating. Therefore, fluctuations in the fusing characteristics due to fluctuations in resistance value due to deformation of the soluble conductor 7 are prevented, and the soluble conductor 7 can be quickly melted by a predetermined overcurrent or heat generated by the heating element 5.

[0075] The protective element 1 according to the present invention is not limited to use in a battery pack for lithium ion secondary batteries, and can of course be applied to various uses that require the interruption of a current path by an electrical signal.

[0076] [Surface heater structure] The above-mentioned heating element 5 may be formed on the surface 2a of the insulating substrate 2. FIG. 5 is a diagram showing a protection element 30 to which the present technology is applied, where (A) is a plan view, (B) is a cross-sectional view in the direction of current flow of the fusible conductor, and (C) is a bottom view. In the protection element 30 shown in FIG. 5, the heating element 5 is formed on the surface 2a of the insulating substrate 2. Accordingly, the insulating protective layer 8, the first extraction electrode 15, the second extraction electrode 16, the heating element electrode 17, and the intermediate electrode 18 are also formed on the surface 2a of the insulating substrate 2. Note that, unlike the protection element 1, the intermediate electrode 18 is only formed on the surface 2a of the insulating substrate 2, and the second extraction electrode 16 and the heating element extraction electrode 6 are connected.

[0077] The heating element electrode 17 and the intermediate electrode 18 are provided on one and the other of a pair of side edges perpendicular to the pair of side edges on which the first electrode 3 and the second electrode 4 are provided. The heating element electrode 17 is connected from the front surface 2a of the insulating substrate 2 via a castellation to a third external connection electrode 31 formed on the back surface 2b. The heating element 5 of the protection element 30 is connected to the current control element 28 via the heating element electrode 17 and the third external connection electrode 31, and the heating element 5 is connected to one end of the battery stack 25. The intermediate electrode 18 may be connected from the front surface 2a of the insulating substrate 2 via a castellation to a fourth external connection electrode (not shown) formed on the back surface 2b for mounting on a circuit board 34.

[0078] The heating element lead electrode 6 is formed on the insulating protective layer 8, so that one end is connected to the intermediate electrode 18 and is overlapped with the heating element 5 via the insulating protective layer 8. The protective element 30 is thermally connected to the heating element 5 by overlapping the fusible conductor 7 via the insulating protective layer 8 and the heating element lead electrode 6, and the heat of the heating element 5 is transferred to the fusible conductor 7 also via the insulating protective layer 8 and the heating element lead electrode 6, allowing for faster melting.

[0079] [Internal Heater Structure] The heating element 5 may also be provided inside the insulating substrate 2. In the protective element 40 shown in Fig. 6, the insulating substrate 2 has a two-layer structure consisting of an upper layer and a lower layer, and the heating element 5, a first extraction electrode 15, and a second extraction electrode 16 are formed between the upper and lower layers. The first extraction electrode 15 is connected to a heating element electrode 17 provided on the front surface 2a or the back surface 2b of the insulating substrate 2 via a castellation or a conductive through-hole (not shown). The second extraction electrode 16 is connected to an intermediate electrode 18 provided on the front surface 2a or the back surface 2b of the insulating substrate 2 via a castellation or a conductive through-hole (not shown).

[0080] [Manufacturing process of protective element 1] Next, we will explain the manufacturing process of the protective element 1. As shown in Figure 7, the manufacturing process of the protective element 1 includes a mounting process of the laminate 35, a heating process of heating the laminate 35, a melting process of melting the first low melting point metal layer 11, and a connecting process of forming the soluble conductor 7 and connecting it to the electrode.

[0081] 7A and 7B are cross-sectional views showing the mounting process of the soluble conductor 7. Prior to the mounting process, the first electrode 3, the second electrode 4, the heating element lead electrode 6, and the surface-side intermediate electrode 18a are formed on the surface 2a of the insulating substrate 2, and the heating element 5, the first external connection electrode 13, the second external connection electrode 14, the first lead electrode 15, the second lead electrode 16, the heating element electrode 17, the back-side intermediate electrode 18b, and the insulating protective layer 8 are formed on the back surface 2b of the insulating substrate 2. It is preferable that a connection flux 29 is applied in advance to the first electrode 3, the second electrode 4, the heating element lead electrode 6, and between these electrodes. Next, a laminate 35 is formed on the insulating substrate 2 over the first electrode 3, the heating element lead electrode 6, and the second electrode 4, and the laminate 35 is formed by stacking a high-melting point metal layer 10 and a first low-melting point metal layer 11 made of a first low-melting point metal 11b having a melting point lower than that of the high-melting point metal 10a constituting the high-melting point metal layer 10, in an orientation where the first low-melting point metal layer 11 contacts the first electrode 3, the heating element lead electrode 6, and the second electrode 4.

[0082] The laminate 35 is formed by laminating a high melting point metal layer 10 and a first low melting point metal layer 11. As a lamination method, known lamination methods such as rolling, pressure bonding, plating coating, etc. can be used.

[0083] [Heating Process] Figure 7 (C) is a cross-sectional view showing the heating, melting, and connection process of the soluble conductor 7. The soluble conductor 7 can be efficiently connected to each electrode by reflow mounting. In the heating process, the insulating substrate 2 on which the laminate 35 is mounted is heated at a mounting temperature equal to or higher than the eutectic temperature of the alloy of the high-melting-point metal 10a and the first low-melting-point metal 11b. Note that heating may also be performed at a temperature lower than the solidus temperature of the first low-melting-point metal 11b.

[0084] [Melting Step] In the melting step, the second low melting point metal layer 12 is formed by mutual diffusion and / or dissolution of a part of the high melting point metal layer 10 and the first low melting point metal layer 11 .

[0085] [Connection process] In the connection process, the molten second low-melting point metal layer 12 cools, and the soluble conductor 7 is connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 through the second low-melting point metal layer 12 of the soluble conductor 7, which is laminated with the high-melting point metal layer 10 and the solidified second low-melting point metal layer 12.

[0086] Here, the heating temperature for mounting the fusible conductor 7 (reflow temperature in the case of reflow mounting) is equal to or higher than the solidus temperature of the alloy between the high melting point metal layer 10 and the first low melting point metal layer 11. In the laminate 35, at the lamination interface between the high melting point metal layer 10 and the first low melting point metal layer 11, atoms 10aA of the high melting point metal 10a and atoms 11bA of the first low melting point metal 11b interdiffuse to form the second low melting point metal layer 12. The liquidus temperature of the second low melting point metal layer 12 decreases as the diffusion progresses, approaching the eutectic point and becoming liquid.

[0087] 8 is a diagram showing the interdiffusion of dissimilar metal atoms at the interface between different metal layers. As shown in FIG. 8, when a laminate of dissimilar metals is heated, dissimilar metal atoms (e.g., high-melting-point metal atoms 10aA and first low-melting-point metal atoms 11bA) interdiffuse at the interface between the dissimilar metal layers, forming an alloy layer (e.g., second low-melting-point metal layer 12) between the dissimilar metals. When the ratio of the dissimilar metals exceeds a predetermined ratio (atomic %) and the liquidus of the alloy with that ratio falls below the heating temperature, the alloy becomes liquid, and the high-melting-point metal 10a dissolves in the liquid alloy, further lowering the liquidus.

[0088] 9 is a binary alloy phase diagram of silver (Ag) and tin (Sn). Assuming that tin (Sn) is used as the first low-melting-point metal 11b, the solidus and liquidus of the first low-melting-point metal 11b (Sn) are 232°C (231.9681°C). The eutectic line of the alloy of the high-melting-point metal 10a (Ag) and the first low-melting-point metal 11b (Sn) is 221°C. When a reflow temperature lower than 232°C and equal to or higher than 221°C is applied, interdiffusion of the high-melting-point metal 10a (Ag) and the first low-melting-point metal 11b (Sn) progresses at the lamination interface between the high-melting-point metal layer 10 and the first low-melting-point metal layer 11, causing the second low-melting-point metal layer 12 to become liquid. Then, the high melting point metal 10a dissolves in the liquid Ag—Sn alloy, and the liquidus line further drops, approaching the eutectic line (221° C.). －４ Since the dissolution rate of the molten Ag—Sn alloy into the high melting point metal 10 a is about twice as fast as the diffusion rate of the first low melting point metal 11 b into the high melting point metal layer 10 .

[0089] 10 is a binary alloy phase diagram of lead (Pb) and tin (Sn). When tin (Sn) is assumed as the first low-melting-point metal 11b, the solidus and liquidus of the first low-melting-point metal 11b (Sn) are 232°C (231.9681°C). In addition, the eutectic line of the alloy of the high-melting-point metal 10a (Pb) and the first low-melting-point metal 11b (Sn) is 183°C.

[0090] When a reflow temperature of less than 232°C and equal to or greater than 183°C is applied, the interdiffusion of the high melting point metal 10a (Pb) and the first low melting point metal 11b (Sn) proceeds at the lamination interface between the high melting point metal layer 10 and the first low melting point metal layer 11, causing the solidus of the second low melting point metal layer 12 to drop and become liquid. Then, dissolution of the high melting point metal 10a by the liquid Pb-Sn alloy occurs, further lowering the liquidus, and approaching the eutectic line (183°C). Note that the diffusion coefficient in the solid is approximately 10 times that of the liquid. －４ Since the dissolution rate of the molten Pb--Sn alloy into the high melting point metal 10a is about twice as fast as the diffusion rate of the first low melting point metal 11b into the high melting point metal layer 10, the dissolution rate of the molten Pb--Sn alloy into the high melting point metal 10a is faster than the diffusion rate of the first low melting point metal 11b into the high melting point metal layer 10.

[0091] 11A and 11B are cross-sectional views schematically illustrating the state changes of a laminate 35 during the heating, melting, and bonding processes. The laminate 35 is a laminate of a high-melting-point metal layer 10, which is a single-layer alloy (Sn—Ag alloy) of a high-melting-point metal 10a (e.g., Ag) and a first low-melting-point metal 10b (e.g., Sn), and a first low-melting-point metal layer 11, which is made of a first low-melting-point metal 11b (e.g., 100% Sn) (FIG. 11A). The high-melting-point metal layer 10 is phase-separated into a phase (solid phase) of the high-melting-point metal 10a and a phase (solid phase) of the first low-melting-point metal 10b, which are mixed together.

[0092] The laminate 35 has a first low-melting-point metal layer 11 mounted on each electrode. In the initial stage of reflow heating, the two types of metals form an alloy at the interface between the layers (see FIG. 8 ), and the liquidus of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 becomes lower than the liquidus of each of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 alone, forming a liquid phase 35L at the interface between the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 ( FIG. 11(B) ).

[0093] In the later stage of reflow heating, a liquid phase 35L formed at the interface between the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 dissolves part of the high-melting-point metal layer 10 and almost all of the first low-melting-point metal layer 11, wetting and spreading over the surface of each electrode. However, because dissolution of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 by the liquid phase 35L continues to occur on and between the electrodes during reflow heating, the liquid phase 35L is not drawn toward each electrode to the extent that it disappears completely, but remains below the high-melting-point metal layer 10 between the electrodes (FIG. 11C).

[0094] After cooling, when the liquid phase 35L drops below the eutectic line, it separates into a solid phase α (high-melting point metal 10a: Ag-rich) and a solid phase β (first low-melting point metal 12b: Sn-rich) through a eutectic reaction, forming a second low-melting point metal layer 12 with a eutectic structure that forms a marbled pattern (Figure 11 (D)).

[0095] Thus, even if the liquidus temperature of the first low-melting-point metal 11b is higher than the mounting temperature (reflow temperature), as long as the eutectic line of the second low-melting-point metal layer 12 is lower than the mounting temperature (reflow temperature), the high-melting-point metal 10a (Ag) and the first low-melting-point metal 11b (Sn) are mixed in a liquid phase, and the liquid phase region expands as the melting proceeds. By cooling from this state and solidifying, the high-melting-point metal 10a (Ag) and the first low-melting-point metal 12b (Sn) are precipitated to form the second low-melting-point metal layer 12 with a stable eutectic composition.

[0096] The second low-melting-point metal layer 12, which has a eutectic composition of the high-melting-point metal 10a and the first low-melting-point metal 12b, can also be formed by setting the mounting temperature (reflow temperature) below the solidus temperature of the first low-melting-point metal 11b, as long as the mounting temperature (reflow temperature) is equal to or higher than the eutectic temperature of the alloy of the high-melting-point metal and the first low-melting-point metal. Therefore, in the heating step, the insulating substrate 2 on which the laminate 35 is mounted may be heated at a mounting temperature that is lower than the solidus temperature of the first low-melting-point metal 11b and equal to or higher than the eutectic temperature of the alloy of the high-melting-point metal 10a and the first low-melting-point metal 11b. Of course, the mounting temperature may also be equal to or higher than the solidus temperature of the first low-melting-point metal 11b.

[0097] 12 is a cross-sectional view schematically showing a case where the second low-melting-point metal layer 12 has a laminated structure of an alloy of a high-melting-point metal 12a and a first low-melting-point metal 12b, and the first low-melting-point metal layer 11. As shown in FIG. 12(C), in the later stage of reflow heating, the first low-melting-point metal layer 11 of the laminate 35 may not be completely melted and may remain. As a result, after cooling, the second low-melting-point metal layer 12 has a laminated structure of the alloy of a high-melting-point metal 12a and a first low-melting-point metal 12b, and the first low-melting-point metal layer 11 (FIG. 12(D)).

[0098] 13 is also a cross-sectional view schematically illustrating the state changes of the laminate 35 during the heating, melting, and bonding steps, but the configuration of the laminate 35 is different from that shown in FIGS. 11A and 12A. In the laminate 35 shown in FIG. 13, the high-melting-point metal layer 10 is composed almost entirely of the high-melting-point metal 10a with a small amount of the first low-melting-point metal 10b mixed in, and the first low-melting-point metal layer 11 is composed almost entirely of the first low-melting-point metal 11b. In FIG. 13, the first low-melting-point metal layer 11 is completely melted, and the second low-melting-point metal layer 12 is formed.

[0099] Figure 14 is a cross-sectional view that schematically shows a case in which, in the configuration shown in Figure 13, the first low-melting point metal layer 11 of the laminate 35 is not completely dissolved and remains, and the second low-melting point metal layer 12 has a laminated structure of an alloy of a high-melting point metal 12a and the first low-melting point metal 12b and the first low-melting point metal layer 11.

[0100] In the configurations shown in FIGS. 11 to 14, the first low melting point metal layer 11 may contain a small amount of high melting point metal 11a, although this is not shown.

[0101] [Mounting on a circuit board] As shown in Fig. 7 (D), the protective element 1 connected to the fusible conductor 7 is protected inside by applying a coating flux 9 to the fusible conductor 7 and then providing a cover member 19 on the surface 2a of the insulating substrate 2. Next, as shown in Fig. 7 (E), the protective element 1 is mounted on a circuit board 34, and cuts off at least part of the current flow within the circuit board 34 when an abnormality occurs in the circuit board 34.

[0102] There are no particular limitations on the method for mounting the protection element 1 on the circuit board 34, but it can be efficiently performed by reflow. A connection material such as solder paste is applied to the multiple terminals 34a provided on the circuit board 34, and the first and second external connection electrodes 13, 14 and the heating element electrode 17 provided on the back surface 2b of the insulating substrate 2 are mounted, and then reflow heating is performed. As a result, the fusible conductor 7 is connected in series to the current path formed on the circuit board 34, and the heating element 5 is connected to the current control element 28 via the heating element electrode 17, and the heating element 5 is connected to one end of the battery stack 25 via the current control element 28.

[0103] At this time, as described above, by making the liquidus point of the second low-melting point metal layer 12 higher than the mounting temperature (reflow temperature) of the protection element 1 on the circuit board 34, the second low-melting point metal layer 12 melts when mounted on the circuit board 34, and gaps can be prevented from occurring between the second low-melting point metal layer 12 and the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element extraction electrode 6.

[0104] In addition, due to the heating during mounting on the circuit board 34, the second low melting point metal layer 12 of the soluble conductor 7 begins to melt again, and by melting the high melting point metal layer 10, the area of ​​the second low melting point metal layer 12 spreads to the upper layer side. Even at this time, on the electrodes and between the electrodes during heating, the high melting point metal layer 10 continues to melt due to the liquefied second low melting point metal layer 12. Therefore, the second low melting point metal layer 12 is not attracted to each electrode side so that it disappears completely, but remains below the high melting point metal layer 10 between the electrodes, and the laminated structure is maintained (see FIG. 11 (C)).

[0105] Furthermore, if the liquidized second low-melting point metal layer 12 completely dissolves the high-melting point metal layer 10, that is, if the entire soluble conductor 7 becomes liquid, the soluble conductor 7a will aggregate on the first and second electrodes 3, 4 and the heating element lead electrode 6 as shown in Figure 2, causing the soluble conductor 7 to melt and become unable to function as a protective element 1. Therefore, by selecting appropriate materials for the high-melting point metal layer 10 and the low-melting point metal layer 11 and controlling their respective thicknesses, the high-melting point metal layer 10 will not be completely dissolved, and the laminated structure of the high-melting point metal layer 10 and the second low-melting point metal layer 12 will be maintained.

[0106] In addition, the laminate 35 mounted on the insulating substrate 2 is designed to take into account the heating during reflow mounting to the circuit board 34, and the thickness of the metal and first low melting point metal layer 11 of the high melting point metal layer 10 and the first low melting point metal layer 11. That is, since the protective element 1 is used in a state mounted on the circuit board 34, the applied voltage (for example, 4 V), the resistance value of the heating element 5 (for example, 2.5 Ω), the heat generation temperature (for example, 300 ° C. to 400 ° C.), and the melting time after heat generation (for example, melting within 5 seconds) When the melting conditions such as are set, if it is Sn-Pb solder, by referring to the Sn-Pb binary phase diagram, it is possible to design the configuration of the soluble conductor 7 that is compatible with it (the respective volume ratios of the high melting point metal layer 10 / second low melting point metal layer 12). From this viewpoint, it is preferable that the protective element 1 be designed so that, when the soluble conductor 7 is mounted, the thickness of the high melting point metal layer 10 in the stacking direction is thicker than the thickness of the second low melting point metal layer 12 in the stacking direction.

[0107] 7C , in the manufacturing process of the protection device 1, it is preferable to apply pressure to the upper part of the high-melting-point metal layer 10 toward the insulating substrate 2 between the heating step and the connecting step. This allows at least a part of the second low-melting-point metal layer 12 to be in direct contact with the insulating substrate 2 between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6.

[0108] 15 shows an example of a method for applying pressure to the high-melting-point metal layer 10. The heating head 36 preferably has a pressing surface that is larger than or equal to the surface area of ​​the laminate 35, and heats and presses the entire surface of the laminate 35. The heating head 36 heats and presses the laminate 35 at a predetermined temperature, for example, a mounting temperature that is lower than the solidus temperature of the first low-melting-point metal 11a and higher than the eutectic temperature of the alloy of the high-melting-point metal 10a and the first low-melting-point metal 11a.

[0109] After the mounting process of the laminate 35, the heating head 36 heats and presses the laminate 35 from above the high-melting-point metal layer 10 at a predetermined temperature, pressure, and time. As a result, through the melting process of the first low-melting-point metal layer 11 and the melting process of a portion of the high-melting-point metal layer 10 in the above-described reflow mounting (see FIG. 11), a fusible conductor 7, which is a laminate of the high-melting-point metal layer 10 and the second low-melting-point metal layer 12, is formed, and the fusible conductor 7 is connected to the first and second electrodes 3 and 4 and the heating element lead electrode 6 via the second low-melting-point metal layer 12. In addition, the second low-melting-point metal layer 12 can be brought into contact with the insulating substrate 2 between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6.

[0110] It is preferable that the heating head 36 continues to press the second low-melting point metal layer 12 until it is cooled and solidified, thereby allowing the solidified second low-melting point metal layer 12 to come into contact with the insulating substrate 2 over a wider area between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6.

[0111] In addition, in the heating and pressing process using the heating head 36, the laminate 35 may also be heated and pressed at a mounting temperature that is equal to or higher than the solidus temperature of the first low-melting point metal 11a and equal to or higher than the eutectic temperature of the alloy of the high-melting point metal 10a and the first low-melting point metal 11a.

[0112] 16, the high-melting-point metal layer 10 may be pressed by a weight 37. The weight 37 preferably has a pressing surface that is at least as large as the surface area of ​​the laminate 35 and presses the entire surface of the laminate 35. After the mounting step of the laminate 35, the weight 37 is placed on the high-melting-point metal layer 10, and in this state is subjected to the reflow step.

[0113] As a result, through the melting process of the first low-melting point metal layer 11 and the melting process of part of the high-melting point metal layer 10 in the reflow mounting described above (see FIG. 11), a soluble conductor 7 is formed, which is a laminate of the high-melting point metal layer 10 and the second low-melting point metal layer 12, and the soluble conductor 7 is connected to the first and second electrodes 3, 4 and the heating element lead electrode 6 via the second low-melting point metal layer 12. In addition, the second low-melting point metal layer 12 can be in contact with the insulating substrate 2 between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6.

[0114] The weight 37 is preferably left on the insulating substrate 2 until the second low-melting point metal layer 12 is cooled and solidified, thereby allowing the solidified second low-melting point metal layer 12 to come into contact with the insulating substrate 2 over a wider area between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6.

[0115] [Limiting Wall] As shown in FIG. 17, the protective element 1 may have a limiting wall 39 on the inner surface of the cover member 19 that holds down the portion where the second low-melting point metal layer 12 of the soluble conductor 7 contacts the insulating substrate 2. The limiting wall 39 is provided in a position facing the first electrode 3 of the insulating substrate 2 and the heating element lead electrode 6, and the second electrode 4 and the heating element lead electrode 6. The limiting wall 39 may be integrally molded with the cover member 19, or may be formed separately and connected by adhesion, welding, or the like. The limiting wall 39 only needs to have heat resistance to the reflow temperature equivalent to that of the cover member 19, and may be made of the same material as or a different material from the cover member 19.

[0116] Even when the second low-melting point metal layer 12 of the soluble conductor 7 melts due to heating when the protective element 1 is mounted on the circuit board 34, the regulating wall 39 prevents the soluble conductor 7 from floating, and prevents gaps from occurring between the second low-melting point metal layer 12 and the insulating substrate 2 between the first electrode 3 of the insulating substrate 2 and the heating element extraction electrode 6, and between the second electrode 4 and the heating element extraction electrode 6.

[0117] [Insulating Layer] An insulating layer 51 having a thickness greater than the thickness of either the first or second electrode 3, 4 or the heater lead electrode 6 may be formed between the first electrode 3 and the heater lead electrode 6 on the insulating substrate 2 and between the second electrode 4 and the heater lead electrode 6. The protective element 50 shown in Figure 18 is in indirect contact with the insulating substrate 2 as the second low-melting point metal layer 12 is in contact with the insulating layer 51.

[0118] The insulating layer 51 can be formed of an insulating material such as glass or ceramic. The insulating layer 51 can be formed by known methods such as printing and firing a glass paste, or bonding ceramic. The insulating substrate 2 provided with the insulating layer 51 has a connection flux 29 applied to each of the first electrode 3, the second electrode 4, and the heating element lead electrode 6. Then, the insulating substrate 2 is subjected to a mounting process of the laminate 35, a heating process of heating the laminate 35, a melting process of melting the first low-melting point metal layer 11, and a connecting process of forming a fusible conductor 7 and connecting it to the electrode, thereby forming the protective element 50 (FIG. 18(C)).

[0119] Since the thickness of the insulating layer 51 is greater than the thickness of any of the first and second electrodes 3 and 4 and the heating element lead electrode 6, as shown in Fig. 18(A), the insulating layer 51 and the first low-melting point metal layer 11 of the laminate 35 come into contact with each other in the mounting process. When the laminate 35 is heated in this state by reflow or the like and the first low-melting point metal layer 11 melts, the liquid phase 35L comes into contact with the insulating layer 51 regardless of the tension. When the laminate 35 is then cooled, the second low-melting point metal layer 12 contracts in volume as it cools, causing it to adhere to the insulating layer 51, as shown in Fig. 18(B).

[0120] This allows the second low-melting point metal layer 12 to be in indirect contact with the insulating substrate 2 via the insulating layer 51 between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6. By forming the insulating layer 51 using an insulating material with excellent thermal conductivity, the protective element 50 achieves the same effect as the protective element 1 in which the second low-melting point metal layer 12 is in direct contact with the insulating substrate 2.

[0121] 19 , the thickness of the insulating layer may be greater than the sum of the thickness of the heater lead electrode 6 and the thickness of the first low-melting point metal layer 11. In the protective element 60 shown in FIG. 19 , a thick insulating layer 61 is provided between the first electrode 3 of the insulating substrate 2 and the heater lead electrode 6, and between the second electrode 4 and the heater lead electrode 6.

[0122] The thick insulating layer 61 can be formed, for example, by printing and firing an insulating material such as glass paste. The insulating material may be printed multiple times to increase its thickness. During the formation process, the insulating layer 61 is formed into an arc-shaped cross section due to the tension of the insulating material. As a result, during the mounting process of the fusible conductor 7 and the mounting process of the protective element 60 on the circuit board 34, the molten second low-melting point metal layer 12 adheres to the periphery of the insulating layer 61 due to volumetric contraction caused by cooling (FIG. 19B).

[0123] In addition, the thickness of the insulating layer 61 is formed to be thicker than the sum of the thickness of the heating element lead electrode 6 and the thickness of the first low melting point metal layer 11. Therefore, the area of ​​the liquid phase 35L expands while dissolving the high melting point metal layer 10, covering the insulating layer 61, and due to volume contraction caused by cooling of the second low melting point metal layer 12, it adheres to the insulating layer 61. By widening the contact area in this way, the force of the soluble conductor 7 toward the insulating substrate 2 further increases, allowing for close contact without gaps.

[0124] In addition, the insulating layer 61 is formed in an arc shape and does not have corners. For this reason, no voids due to the tension of the liquid phase 35L are formed near the corners, and the soluble conductor 7 can be in close contact with the insulating layer 61 without any gaps.

[0125] [Convex Portion of Insulating Substrate] Furthermore, convex portions 71 having a height greater than the thickness of any of the first and second electrodes 3, 4 and the heater lead electrode 6 may be formed on the insulating substrate 2 between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6. The protective element 70 shown in Fig. 20 is in direct contact with the insulating substrate 2 as the second low-melting point metal layer 12 contacts the convex portions 71.

[0126] The convex portion 71 is a portion formed on the insulating substrate 2. After the connecting flux 29 is applied to each of the first electrode 3, the second electrode 4, and the heating element lead electrode 6, the insulating substrate 2 provided with the convex portion 71 undergoes a mounting process of the laminate 35, a heating process of heating the laminate 35, a melting process of melting the first low melting point metal layer 11, and a connecting process of forming the soluble conductor 7 and connecting it to the electrode, thereby forming the protective element 70 (FIG. 20C).

[0127] The height of the protrusion 71 is greater than the thickness of any of the first and second electrodes 3 and 4 and the heating element lead electrode 6, so the protrusion 71 protrudes from the other electrodes, and as shown in Fig. 20(A) , the protrusion 71 comes into contact with the first low-melting-point metal layer 11 of the laminate 35 during the mounting process. When the first low-melting-point metal layer 11 is melted by heating in this state by reflow or the like, the liquid phase 35L comes into contact with the protrusion 71 regardless of the tension. When the first low-melting-point metal layer 11 is then cooled, the second low-melting-point metal layer 12 contracts in volume as it cools, causing it to adhere closely to the protrusion 71, as shown in Fig. 20(B) .

[0128] This allows the second low-melting point metal layer 12 to be in direct contact with the insulating substrate 2 via the protrusions 71 between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6. The protective element 70 has the same effect as the protective element 1 in which the second low-melting point metal layer 12 is in direct contact with the insulating substrate 2 between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6.

[0129] 21 , the height of the protrusions may be greater than the sum of the thickness of the heating element lead electrode 6 and the thickness of the first low-melting point metal layer 11. In the protective element 80 shown in FIG. 21 , tall protrusions 81 are formed between the first electrode 3 of the insulating substrate 2 and the heating element lead electrode 6, and between the second electrode 4 and the heating element lead electrode 6.

[0130] The convex portion 81 is a portion formed on the insulating substrate 2. The convex portion 81 is preferably formed to have an arc-shaped cross section. As a result, in the mounting process of the fusible conductor 7 and the mounting process of the protective element 80 on the circuit board 34, the molten second low-melting point metal layer 12 adheres to the periphery of the convex portion 81 due to volumetric shrinkage caused by cooling (FIG. 21 (B)). By widening the contact area in this way, the force of the fusible conductor 7 toward the insulating substrate 2 further increases, allowing for close contact without gaps.

[0131] In addition, the film thickness of the convex portion 81 is formed thicker than the sum of the thickness of the heating element lead electrode 6 and the thickness of the first low melting point metal layer 11. Therefore, the area of ​​the liquid phase 35L expands while dissolving the high melting point metal layer 10, covering the convex portion 81, and due to volumetric contraction caused by cooling of the second low melting point metal layer 12, it adheres to the convex portion 81. By widening the contact area in this way, the force of the soluble conductor 7 toward the insulating substrate 2 further increases, allowing for close contact without gaps.

[0132] In addition, the convex portion 81 is formed in an arc shape and does not have corners. For this reason, no voids due to the tension of the liquid phase 35L are formed near the corners, and the soluble conductor 7 can be tightly attached to the convex portion 81 without any gaps.

[0133] In addition, the above-mentioned protective elements 50, 60, 70, and 80 form the heating element 5 on the back surface 2b of the insulating substrate 2, but as with the protective element 1 shown in FIG. 5, the heating element 5, the insulating protective layer 8, the first extraction electrode 15, the second extraction electrode 16, the heating element electrode 17, and the intermediate electrode 18 may be formed on the surface 2a of the insulating substrate 2. Also, as with the protective element 1 shown in FIG. 6, the protective elements 50, 60, 70, and 80 have a two-layer structure of an upper layer and a lower layer, and the heating element 5, the first extraction electrode 15, and the second extraction electrode 16 may be formed between the upper and lower layers. Furthermore, in the protective elements 50, 60, 70, and 80, as with the protective element 1 shown in FIG. 17, a restricting wall 39 may be provided on the inner surface of the cover member 19 to hold down the portion where the second low-melting point metal layer 12 of the fusible conductor 7 contacts the insulating substrate 2.

[0134] [Protection element 100] Next, a modified example of a protection element to which the present technology is applied will be described. Figure 22 shows a protection element 100 according to a modified example, where (A) is a plan view, (B) is a cross-sectional view in the current-carrying direction of the soluble conductor, and (C) is a bottom view. As shown in Figure 22, the protection element 100 differs from the protection element 1 described above in the configuration of the soluble conductor and the connection form of the soluble conductor. In addition, the protection element 100, like the protection element 1, is used as a protection element for a battery pack 20 and other electronic devices.

[0135] The protective element 100 comprises an insulating substrate 2, a heating element 5 provided on the insulating substrate 2, a first electrode 3 and a second electrode 4 provided on the insulating substrate 2, a heating element lead-out electrode 6 electrically connected to the heating element 5 on the current path between the first electrode 3 and the second electrode 4, and a fusible conductor 101 connected across the first electrode 3, the heating element lead-out electrode 6, and the second electrode 4, which melts between the first electrode 3 and the second electrode 4 due to self-heating caused by the passage of an overcurrent exceeding the rated current and / or heat generation by the heating element 5, thereby interrupting the current path.

[0136] The soluble conductor 101 has a coating structure in which both sides of the low-melting-point metal layer 102 are coated with a high-melting-point metal layer 103 having a melting point higher than that of the low-melting-point metal layer 102, and is connected to each of the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 via a conductive connecting material 105 such as solder.

[0137] Furthermore, at least a portion of the soluble conductor 101 is in indirect contact with the insulating substrate 2 via the conductive connecting material 105 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6.

[0138] In the protective element 100, the insulating substrate 2, the heating element 5, the insulating protective layer 8, the first electrode 3, the second electrode 4, the heating element extraction electrode 6, the first external connection electrode 13, the second external connection electrode 14, the first extraction electrode 15, the second extraction electrode 16, the heating element electrode 17, the intermediate electrode 18, and the cover member 19 have the same configuration as the protective element 1 described above, and therefore details thereof will be omitted.

[0139] [Fusible conductor] The soluble conductor 101, like the soluble conductor 7, is implemented between the first and second electrodes 3 and 4, and melts due to heat generated by the passage of current through the heating element 5 or due to self-heating (Joule heat) caused by the passage of current exceeding the rated current, thereby interrupting the current path between the first electrode 3 and the second electrode 4.

[0140] 23, the soluble conductor 101 has a coating structure in which both sides of the low-melting-point metal layer 102 are coated with a high-melting-point metal layer 103 having a melting point higher than that of the low-melting-point metal layer 102, and in the protective element 100, it has a rectangular plate shape in plan view. The high-melting-point metal constituting the high-melting-point metal layer 103 and the low-melting-point metal constituting the low-melting-point metal layer 102 are metals that have a melting point difference and can melt, and a metal with a relatively low melting point is a "low-melting-point metal", and a metal with a relatively high melting point that dissolves in the molten low-melting-point metal is a "high-melting-point metal".

[0141] The high-melting point metal that constitutes the soluble conductor 101 can be a metal similar to the high-melting point metal 10a in the protective element 1 described above, and the low-melting point metal can be a metal similar to the first low-melting point metal 11b in the protective element 1 described above.

[0142] Such a soluble conductor 101 can be formed, for example, by forming a high-melting point metal layer on a low-melting point metal foil using plating technology, or can be formed using other well-known lamination techniques and film formation techniques. The soluble conductor 101 may also have a structure in which the entire surface of the low-melting point metal layer 102 is covered with the high-melting point metal layer 103, or a structure in which only a pair of opposing side surfaces of the low-melting point metal layer 102 are covered. The soluble conductor 101 can be formed in various configurations, such as a multilayer structure of three or more layers in which the low-melting point metal layer 102 and the high-melting point metal layer 103 are alternately stacked, or an opening is provided in part of the outer layer to expose part of the inner layer.

[0143] The soluble conductor 101 is coated with a low-melting-point metal layer 102 as an inner layer and a high-melting-point metal layer 103 as an outer layer, so that even if the mounting temperature, such as the reflow temperature, exceeds the melting temperature of the low-melting-point metal layer 102, the soluble conductor 101 can maintain its shape and will not melt. Therefore, the connection between the first and second electrodes 3, 4 and the heating element lead electrode 6 and the soluble conductor 101, and the mounting of the protective element 100 on the circuit board 34 can be efficiently performed by reflow. In addition, even if the soluble conductor 101 is deformed by reflow, the resistance value becomes locally high or low, etc., and fluctuations in fusing characteristics such as not melting at a predetermined temperature or melting at a temperature lower than the predetermined temperature can be prevented.

[0144] In addition, the soluble conductor 101 will not melt even due to self-heating while a predetermined rated current is flowing. When a current higher than the rated current flows, it melts due to self-heating and cuts off the current path between the first and second electrodes 3 and 4. In addition, when the heating element 5 is energized and generates heat, it melts and cuts off the current path between the first and second electrodes 3 and 4.

[0145] At this time, the molten low-melting point metal layer 102 of the soluble conductor 101 corrodes (solder-eats) the high-melting point metal layer 103, causing the high-melting point metal layer 103 to melt at a temperature lower than the melting temperature. Therefore, the soluble conductor 101 can be blown out in a short time by utilizing the melting action of the high-melting point metal layer 103 by the low-melting point metal layer 102. In addition, the molten conductor 101a of the soluble conductor 101 is divided by the physical pulling action of the heating element extraction electrode 6 and the first and second electrodes 3, 4, so that the current path between the first and second electrodes 3, 4 can be quickly and reliably interrupted.

[0146] In addition, it is preferable that the soluble conductor 101 has a volume of the low-melting point metal layer 102 greater than the volume of the high-melting point metal layer 103. The soluble conductor 101 is heated by self-heating due to overcurrent or by heat generation from the heating element 5, and the low-melting point metal melts, corroding the high-melting point metal, thereby quickly melting and fusing. Therefore, by forming the volume of the low-melting point metal layer 102 in the soluble conductor 101 to be greater than the volume of the high-melting point metal layer 103, this dissolution action can be promoted and the first and second electrodes 3, 4 can be quickly disconnected.

[0147] In addition, since the fusible conductor 101 is configured such that the inner layer, a low-melting-point metal layer 102, is coated with a high-melting-point metal layer 103, the fusing temperature can be significantly reduced compared to conventional chip fuses made of high-melting-point metals. Therefore, the fusible conductor 101 can have a larger cross-sectional area and a significantly improved current rating compared to chip fuses of the same size. In addition, it can be made smaller and thinner than conventional chip fuses with the same current rating, and has excellent fast-fusing properties.

[0148] In addition, the soluble conductor 101 can improve the resistance (pulse resistance) to surges in which an abnormally high voltage is instantaneously applied to an electrical system incorporating the protective element 100. In other words, the soluble conductor 101 must not melt even when, for example, a 100 A current flows for several milliseconds. In this regard, since a large current that flows in an extremely short time flows through the surface layer of the conductor (skin effect), the soluble conductor 101 has a high-melting point metal layer 103 such as Ag plating with a low resistance value as an outer layer, making it easy to pass the current applied by the surge and preventing melting due to self-heating. Therefore, the soluble conductor 101 can significantly improve its resistance to surges compared to fuses made of conventional solder alloys.

[0149] In addition, the soluble conductor 101 is coated with a coating flux 9 to prevent oxidation and improve wettability during fusing. In addition, the inside of the protective element 100 is protected by covering the insulating substrate 2 with a cover member 19.

[0150] Here, at least a portion of the soluble conductor 101 is in indirect contact with the insulating substrate 2 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6. In the protection element 100 shown in FIG. 22, the soluble conductor 101 is in contact with the insulating substrate 2 via the conductive connecting material 105.

[0151] When the soluble conductor 101 melts due to heat generated by the heating element 5 or self-heating due to overcurrent, the high melting point metal layer 103 melts into the molten low melting point metal layer 102, causing a dissolution phenomenon (corrosion) and being attracted to the first electrode 3, the second electrode 4, and the heating element lead electrode 6, which have high wettability to the molten metal. At this time, according to the protective element 100, between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6, at least a portion of the soluble conductor 101 is in indirect contact with the insulating substrate 2, so that the current paths between the first electrode 3 and the heating element lead electrode 6 and between the second electrode 4 and the heating element lead electrode 6 can be reliably blocked.

[0152] That is, in the conventional configuration in which the high-melting-point metal film is in contact with the insulating substrate, the problem occurs that the current path is not completely blocked due to the erosion residue of the high-melting-point metal film. However, in the protective element 100, the soluble conductor 101 is in direct or indirect contact with the insulating substrate 2 via a conductive connecting material 105 such as solder, or via an insulating layer or a protrusion as described below. Therefore, the molten high-melting-point metal layer 10 is prevented from remaining undissolved on the insulating substrate 2, and is attracted to the heating element lead electrode 6 and the first and second electrodes 3 and 4 while the high-melting-point metal layer 10 is dissolved.

[0153] In addition, when the soluble conductor 101 is melted by the heat of the heating element 5, the heat generated by the heating element 5 heats the soluble conductor 101 through the heating element lead electrode 6 and also directly heats the soluble conductor 101 that is at least partially in contact with the insulating substrate 2 through the insulating substrate 2. As a result, a wide range of the soluble conductor 101 melts in a short time, efficiently melting the high-melting point metal layer 103 and improving the fast-melting characteristics of the soluble conductor 101.

[0154] Furthermore, in the case where the soluble conductor 101 melts due to self-heating caused by an overcurrent, the soluble conductor 101 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6 comes into direct or indirect contact with the insulating substrate 2, so that the heat generated by the self-heating of the soluble conductor 101 is dissipated directly to the insulating substrate 2, thereby improving the current rating of the protective element 100.

[0155] In addition, since the soluble conductor 101 is connected to the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 via the conductive connecting material 105, precise control of the solder paste is not required.

[0156] Therefore, the protective element 100 can achieve a balance between the fuse characteristics that are in a trade-off relationship: "stable connection of the fusible conductor," "efficient melting of the fusible conductor by heating the heating element," and "improvement of the rated current."

[0157] [Liquidus Point of Conductive Connecting Material] The protective element 100 is mounted on the circuit board 34 and cuts off electrical current in at least a portion of the circuit board 34 in the event of an abnormality in the circuit board 34. The protective element 100 can be mounted efficiently on the circuit board 34 by reflow. Here, the liquidus point of the conductive connecting material 105 is preferably higher than the mounting temperature of the protective element 100 on the circuit board 34.

[0158] As shown in Figure 22, in the protective element 100, the conductive connecting material 105 is in contact with the insulating substrate 2 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6, and the soluble conductor 101 is in contact with the insulating substrate 2 via the conductive connecting material 105.

[0159] Since the liquidus point of the conductive connecting material 105 is higher than the mounting temperature on the circuit board 34, the conductive connecting material 105 melts when mounted on the circuit board, preventing gaps from forming between the conductive connecting material 105 and the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element extraction electrode 6.

[0160] [Contact area between the soluble conductor and the insulating substrate] Between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6, the contact area between the soluble conductor 101 and the insulating substrate 2 is 50% or more of the area between the first electrode 3 overlapping with the soluble conductor 101 and the heating element extraction electrode 6, and is preferably 50% or more of the area between the second electrode 4 overlapping with the soluble conductor 101 and the heating element extraction electrode 6. This allows the effect of the contact between the soluble conductor 101 and the insulating substrate 2 to be more effectively exerted.

[0161] The protective element 100 is used by being incorporated into a circuit or the like in a battery pack 20 of a lithium ion secondary battery, similar to the protective element 1 and the like (see FIG. 3).

[0162] [Manufacturing process of the protection element 100] Next, a description will be given of the manufacturing process of the protection element 100. As shown in Figure 24, the manufacturing process of the protection element 100 includes a conductive connecting material forming process for providing a conductive connecting material 105, a mounting process of the soluble conductor 101, a heating and melting process for heating and melting the conductive connecting material 105, and a connecting process for connecting the soluble conductor 7 to each electrode.

[0163] 24A is a cross-sectional view showing the conductive connecting material forming step. Prior to the conductive connecting material forming step, the first electrode 3, the second electrode 4, the heater lead electrode 6, and the front-side intermediate electrode 18a are formed on the front surface 2a of the insulating substrate 2, and the heater 5, the first external connection electrode 13, the second external connection electrode 14, the first lead electrode 15, the second lead electrode 16, the heater electrode 17, the back-side intermediate electrode 18b, and the insulating protective layer 8 are formed on the rear surface 2b of the insulating substrate 2 to form an element body 100A. An uncured conductive connecting material 105 is provided on the first electrode 3, the heater lead electrode 6, and the second electrode 4 formed on the insulating substrate 2, as well as between the first electrode 3 and the heater lead electrode 6 and between the second electrode 4 and the heater lead electrode 6. The conductive connecting material 105 can be provided by a known method, such as screen printing or application using a dispenser.

[0164] 24 (B) is a cross-sectional view showing the mounting process of the soluble conductor 101. In the mounting process, the soluble conductor 101 is mounted on the first electrode 3 formed on the insulating substrate 2, the heating element lead electrode 6, and the second electrode 4 via the conductive connecting material 105.

[0165] 24(C) is a cross-sectional view showing the heating and melting process of the conductive connecting material 105 and the connection process of the soluble conductor 101. The soluble conductor 101 can be efficiently connected to each electrode by reflow mounting. In the heating and melting process, the insulating substrate 2 on which the soluble conductor 101 is mounted is heated and melted at a mounting temperature higher than the solidus temperature of the conductive connecting material 105, preferably at a mounting temperature higher than the liquidus temperature.

[0166] [Connection process] In the connection process, the molten conductive connecting material 105 cools, and the soluble conductor 101 is connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 via the conductive connecting material 105.

[0167] [Mounting on a circuit board] As shown in Figure 24 (D), the protective element 100 to which the soluble conductor 101 is connected is protected inside by applying a coating flux 9 to the soluble conductor 101 and then providing a cover member 19 on the surface 2a of the insulating substrate 2. Next, as shown in Figure 24 (E), the protective element 100 is mounted on the circuit board 34, and cuts off at least part of the current flow within the circuit board 34 when an abnormality occurs in the circuit board 34.

[0168] The protective element 100 can be efficiently mounted on the circuit board 34 by reflow. A connection material such as solder paste is applied to a plurality of terminals 34a provided on the circuit board 34, and the first and second external connection electrodes 13, 14 and the heating element electrode 17 provided on the rear surface 2b of the insulating substrate 2 are mounted thereon, followed by reflow heating. As a result, the soluble conductor 101 is connected in series to the current path formed on the circuit board 34, and the heating element 5 is connected to the current control element 28 via the heating element electrode 17, and the heating element 5 is connected to one end of the battery stack 25 via the current control element 28.

[0169] At this time, as described above, by setting the liquidus point of the conductive connecting material 105 higher than the reflow temperature of the protective element 100 onto the circuit board 34, the conductive connecting material 105 melts during reflow mounting onto the circuit board 34, and gaps can be prevented from occurring between the conductive connecting material 105 and the insulating substrate 2 between the first and second electrodes 3, 4 and the heating element extraction electrode 6.

[0170] Furthermore, even if the low melting point metal layer 102 of the soluble conductor 101 melts due to heating during reflow mounting on the circuit board 34, the high melting point metal layer 103 covering the low melting point metal layer 102 will not be completely melted and the entire soluble conductor 101 will not become liquid, and the soluble conductor 101 will not melt and the coating structure will be maintained.

[0171] [Pressure mounting] In addition, in the manufacturing process of the protective element 100, as in the manufacturing process of the protective element 1, it is preferable to pressurize the upper part of the soluble conductor 101 toward the insulating substrate 2 between the heating / melting process and the connection process. As a result, between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6, at least a part of the soluble conductor 101 can be brought into contact with the insulating substrate 2 via the conductive connecting material 105.

[0172] As a means for pressurizing the fusible conductor 101, the above-mentioned method of heating and pressing with the heating head 36 (see FIG. 15) or the method of pressing with the weight 37 and heating by reflow or the like (see FIG. 16) can be used. The pressure mounting method using the heating head 36 and the weight 37 has been described above, so it will not be described here.

[0173] [Limiting wall] As shown in FIG. 25 , the protective element 100 may be provided with a restricting wall 39 on the inner surface of the cover member 19 to hold down the portion where the soluble conductor 101 contacts the insulating substrate 2 via the conductive connecting material 105.

[0174] Even when the conductive connecting material 105 connecting the soluble conductor 101 melts due to heating when the protective element 100 is mounted on the circuit board 34, the regulating wall 39 prevents the soluble conductor 101 from floating, and prevents gaps from occurring between the conductive connecting material 105 and the insulating substrate 2 between the first electrode 3 and the heating element extraction electrode 6 of the insulating substrate 2, and between the second electrode 4 and the heating element extraction electrode 6, thereby maintaining contact of the soluble conductor 101 with the insulating substrate 2 via the conductive connecting material 105.

[0175] [Insulating layer] An insulating layer 51 having a thickness thicker than the thickness of any of the first and second electrodes 3, 4 and the heating element extraction electrode 6 may be formed between the first electrode 3 and the heating element extraction electrode 6 of the insulating substrate 2 and between the second electrode 4 and the heating element extraction electrode 6. In the protective element 110 shown in FIG. 26, the conductive connecting material 105 contacts the soluble conductor 101 and the insulating layer 51, and the soluble conductor 101 indirectly contacts the insulating substrate 2 via the insulating layer 51.

[0176] After the forming process of the conductive connecting material 105, the insulating substrate 2 provided with the insulating layer 51 undergoes the mounting process of the soluble conductor 101, the heating process of the conductive connecting material 105, and the connecting process of the soluble conductor 101, and the protective element 110 is formed (FIG. 26 (C)).

[0177] Since the thickness of the insulating layer 51 is thicker than the thickness of either the first and second electrodes 3, 4 or the heating element lead electrode 6, as shown in FIG. 26 (A), in the conductive connecting material forming process, the insulating layer 51 and the conductive connecting material 105 come into contact. After the soluble conductor 101 is mounted, it is heated by reflow or the like, and when the conductive connecting material 105 melts, the soluble conductor 101 comes into contact with the insulating layer 51 regardless of its tension. After that, when cooled, as shown in FIG. 26 (B), the conductive connecting material 105 solidifies with the soluble conductor 101 in contact with the insulating layer 51.

[0178] This allows the soluble conductor 101 to be indirectly in contact with the insulating substrate 2 via the insulating layer 51 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6. The protective element 110 has an insulating layer 51 formed using an insulating material with excellent thermal conductivity, and thus has the same effect as the protective element 1 in which the second low-melting point metal layer 12 is in direct contact with the insulating substrate 2.

[0179] [Thickness of insulating layer] Also, as shown in Figure 27, the thickness of the insulating layer may be more than twice the thickness of the heating element extraction electrode 6. In the protective element 120 shown in Figure 27, a thick insulating layer 61 is provided between the first electrode 3 and the heating element extraction electrode 6 of the insulating substrate 2 and between the second electrode 4 and the heating element extraction electrode 6. As a result, in the mounting process of the soluble conductor 101 and the mounting process of the protective element 120 on the circuit board 34, the molten conductive connecting material 105 is adhered to the periphery of the arc-shaped insulating layer 61 due to volumetric shrinkage caused by cooling.

[0180] In addition, the thickness of the insulating layer 61 is formed to be thicker than twice the thickness of the heating element extraction electrode 6. Therefore, the molten conductive connecting material 105 covers the insulating layer 61 and adheres to the insulating layer 61 due to volumetric shrinkage caused by cooling. By widening the contact area in this way, the force of the soluble conductor 101 toward the insulating substrate 2 further increases, so the soluble conductor 101 and the insulating substrate 2 can be closely contacted with each other without any gaps via the insulating layer 61 (FIG. 27 (B)).

[0181] Since the insulating layer 61 is formed in an arc-shaped cross section without corners, no voids are formed near the corners due to the tension of the molten conductive connecting material 105, and the soluble conductor 101 can adhere to the insulating layer 61 without any gaps.

[0182] [Convex portion of insulating substrate] Further, a convex portion 71 having a height greater than the thickness of any of the first and second electrodes 3, 4 and the heating element extraction electrode 6 may be formed between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6 of the insulating substrate 2. In the protective element 130 shown in FIG. 28, the conductive connecting material 105 contacts the convex portion 71, so that the soluble conductor 101 indirectly contacts the insulating substrate 2 via the conductive connecting material 105.

[0183] The convex portion 71 is a portion formed on the insulating substrate 2. The height of the convex portion 71 is higher than the thickness of any of the first and second electrodes 3, 4 and the heating element extraction electrode 6. After the forming process of the conductive connecting material 105, the insulating substrate 2 provided with the convex portion 71 undergoes the mounting process of the soluble conductor 101, the heating process of the conductive connecting material 105, and the connecting process of the soluble conductor 101, thereby forming the protective element 130 (FIG. 28 (C)).

[0184] As shown in FIG. 28 (A), in the mounting process, the soluble conductor 101 is mounted over the first and second electrodes 3 and 4, the heating element lead electrode 6, and the convex portion 71 via the conductive connecting material 105. After the soluble conductor 101 is mounted, it is heated by reflow or the like, so that the soluble conductor 101 is connected to the first and second electrodes 3 and 4 and the heating element lead electrode 6 via the molten conductive connecting material 105, and the conductive connecting material 105 contacts the convex portion 71. The soluble conductor 101 is indirectly contacted with the convex portion 71 of the insulating substrate 2 via the conductive connecting material 105 that has been solidified by cooling. Then, as shown in FIG. 28 (C), a coating flux 9 is applied to the soluble conductor 101, and a cover member 19 is provided.

[0185] This allows the soluble conductor 101 to be in contact with the insulating substrate 2 via the conductive connecting material 105 between the first electrode 3 and the heating element extraction electrode 6 and between the second electrode 4 and the heating element extraction electrode 6. The protective element 130 uses an insulating substrate 2 on which a convex portion 71 is provided using an insulating material with excellent thermal conductivity, and thereby achieves the same effect as the protective element 1 in which the second low melting point metal layer 12 is in direct contact with the insulating substrate 2.

[0186] 29 , the height of the protrusions may be greater than twice the film thickness of the heater lead electrode 6. In the protective element 140 shown in FIG. 29 , tall protrusions 81 are formed between the first electrode 3 of the insulating substrate 2 and the heater lead electrode 6, and between the second electrode 4 and the heater lead electrode 6.

[0187] The convex portion 81 is a portion formed on the insulating substrate 2. The convex portion 81 is preferably formed to have an arc-shaped cross section. As a result, in the mounting process of the soluble conductor 101 and the mounting process of the protective element 140 on the circuit board 34, the molten conductive connecting material 105 covers the convex portion 81 and adheres to the periphery of the arc-shaped convex portion 81 due to volumetric shrinkage caused by cooling (FIG. 29 (B)).

[0188] Furthermore, since the convex portion 81 is formed in an arc shape without corners, no voids are formed near the corners due to the tension of the molten conductive connecting material 105, and the soluble conductor 101 can be tightly attached to the convex portion 81 without any gaps.

[0189] In addition, the above-mentioned protective elements 100, 110, 120, 130, and 140 form the heating element 5 on the back surface 2b of the insulating substrate 2, but as with the protective element 1 shown in FIG. 5, the heating element 5, the insulating protective layer 8, the first extraction electrode 15, the second extraction electrode 16, the heating element electrode 17, and the intermediate electrode 18 may be formed on the surface 2a of the insulating substrate 2. Also, as with the protective element 1 shown in FIG. 6, the protective elements 100, 110, 120, 130, and 140 have a two-layer structure of an upper layer and a lower layer, and the heating element 5, the first extraction electrode 15, and the second extraction electrode 16 may be formed between the upper and lower layers. Furthermore, in the protective elements 100, 110, 120, 130, and 140, as with the protective element 1 shown in FIG. 17, a restricting wall 39 that holds the portion where the soluble conductor 101 contacts the insulating substrate 2 may be provided on the inner surface of the cover member 19.

[0190] 1 Protective element, 1A Element body, 2 Insulating substrate, 2a Surface, 2b Back surface, 3 First electrode, 4 Second electrode, 5 Heating element, 5a One end, 5b Other end, 6 Heating element lead electrode, 7 Fusible conductor, 7a Melting conductor, 8 Insulating protective layer, 9 Coating flux, 10 High melting point metal layer, 10a High melting point metal, 10b Low melting point metal, 11 First low melting point metal layer, 11a First high melting point metal, 11b First low melting point metal, 12 Second low melting point metal layer, 12a High melting point metal, 12b Low melting point metal, 13 First external connection electrode, 14 Second external connection electrode, 15 First lead electrode, 16 Second lead electrode, 17 Heating element electrode, 18a Surface side intermediate electrode, 18b Back side intermediate electrode, 19 Cover member, 20 REFERENCE SIGNS LIST: Battery pack, 20a: Positive electrode terminal, 20b: Negative electrode terminal, 21: Battery cell, 22: Charging device, 23: Current control element, 24: Control unit, 25: Battery stack, 26: Charge / discharge control circuit, 27: Detection circuit, 28: Current control element, 29: Connection flux, 30: Protection element, 31: Third external connection electrode, 34: Circuit board, 34a: Terminal, 35: Laminate, 36: Heating head, 37: Weight, 39: Restricting wall, 40: Protection element, 50: Protection element, 51: Insulating layer, 60: Protection element, 61: Insulating layer, 70: Protection element, 71: Convex portion, 80: Protection element, 81: Convex portion, 100: Protection element, 100A: Element body, 101: Fusible conductor, 101a: Fusible conductor, 102: Low melting point metal layer, 103: High melting point metal layer, 105: Conductive connecting material, 110 Protection element, 120 protection element, 130 protection element, 140 protection element

Claims

1. An insulating substrate; a heating element provided on the insulating substrate; a first electrode and a second electrode provided on the insulating substrate; a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode; and a fusible conductor connected across the first electrode, the heating element lead electrode, and the second electrode, which melts between the first electrode and the second electrode and cuts off the current path due to self-heating caused by the passage of an overcurrent exceeding a rated current and / or heat generation from the heating element, wherein the fusible conductor has a laminated structure of a high-melting point metal layer and a second low-melting point metal layer composed of an alloy of a high-melting point metal constituting the high-melting point metal layer and a first low-melting point metal having a melting point lower than that of the high-melting point metal, and the fusible conductor is connected to the first electrode, the second electrode, and the heating element lead electrode via the second low-melting point metal layer with the second low-melting point metal layer facing the insulating substrate, A protective element, wherein at least a portion of the second low-melting point metal layer of the soluble conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode.

2. A protective element as claimed in claim 1, which is mounted on a circuit board and cuts off electrical current in at least a portion of the circuit board when an abnormality occurs in the circuit board, and wherein the liquidus point of the second low-melting point metal layer is higher than the temperature at which the protective element is mounted on the circuit board.

3. A protective element as described in claim 1, comprising a cover member provided on the surface of the insulating substrate on which the fusible conductor is provided, covering the fusible conductor, and the inner surface of the cover member having a restricting wall that holds down the portion where the second low-melting point metal layer of the fusible conductor comes into contact with the insulating substrate.

4. A protection element as described in claim 1, wherein the insulating substrate has an insulating layer formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the insulating layer having a thickness greater than the thickness of either the first or second electrode or the heating element lead electrode, and the second low-melting point metal layer is in contact with the insulating layer.

5. A protective element as described in claim 4, wherein the thickness of the insulating layer is greater than the sum of the thickness of the heating element lead electrode and the thickness of the first low-melting point metal layer of a laminate having an upper layer of the high-melting point metal layer and a lower layer of the first low-melting point metal layer composed of the first low-melting point metal.

6. A protective element according to claim 1, wherein the insulating substrate has protrusions formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the protrusions having a height greater than the thickness of either the first or second electrode or the heating element lead electrode, and the second low-melting point metal layer is in contact with the protrusions.

7. A protective element as described in claim 6, wherein the height of the convex portion is greater than the sum of the thickness of the heating element extraction electrode and the thickness of the first low-melting point metal layer of a laminate having an upper layer made of the high-melting point metal layer and a lower layer made of the first low-melting point metal.

8. A protective element according to any one of claims 1 to 7, wherein the heating element is provided on the surface of the insulating substrate on which the fusible conductor is provided or on the back surface opposite to the surface, and the insulating substrate has an insulating member provided thereon so as to cover at least the heating element.

9. A protection element according to any one of claims 1 to 7, wherein the heating element is provided inside the insulating substrate.

10. A protective element described in any one of claims 1 to 7, wherein the contact area between the second low-melting point metal layer and the insulating substrate is 50% or more of the area between the first electrode overlapping the soluble conductor and the heating element extraction electrode, and 50% or more of the area between the second electrode overlapping the soluble conductor and the heating element extraction electrode.

11. A protective element according to any one of claims 1 to 7, wherein the second low-melting-point metal layer is formed by interdiffusion and / or dissolution of a part of the high-melting-point metal and the entirety of the first low-melting-point metal constituting the first low-melting-point metal layer of a laminate having the high-melting-point metal layer as an upper layer and a first low-melting-point metal layer composed of the first low-melting-point metal as a lower layer.

12. A protection element according to any one of claims 1 to 7, wherein the thickness of the high melting point metal layer in the stacking direction is greater than the thickness of the second low melting point metal layer in the stacking direction.

13. A protective element according to any one of claims 1 to 7, wherein the second low-melting-point metal layer comprises the first low-melting-point metal layer of a laminate in which the high-melting-point metal layer and a first low-melting-point metal layer made of the first low-melting-point metal are laminated.

14. An insulating substrate; a heating element provided on the insulating substrate; a first electrode and a second electrode provided on the insulating substrate; a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode; and a fusible conductor connected across the first electrode, the heating element lead electrode, and the second electrode, which melts between the first electrode and the second electrode and cuts off the current path due to self-heating caused by the passage of an overcurrent exceeding a rated current and / or heat generated by the heating element, wherein the fusible conductor has a coating structure in which both sides of a low-melting-point metal layer are coated with a high-melting-point metal layer having a melting point higher than that of the low-melting-point metal layer, and the fusible conductor is connected to each of the first electrode, the second electrode, and the heating element lead electrode via a conductive connecting material, and at least a portion of the fusible conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, Protection element.

15. A protective element mounted on a circuit board, which cuts off at least a portion of the current flow within the circuit board when an abnormality occurs in the circuit board, wherein the conductive connecting material is in contact with the insulating substrate between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode, at least a portion of the soluble conductor is in contact with the insulating substrate via the conductive connecting material, and the liquidus point of the conductive connecting material is higher than the mounting temperature of the protective element on the circuit board.

16. A protective element as described in claim 14, comprising a cover member provided on the surface of the insulating substrate on which the soluble conductor is provided and covering the soluble conductor, wherein the conductive connecting material contacts the insulating substrate between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, at least a portion of the soluble conductor contacts the insulating substrate via the conductive connecting material, and the inner surface of the cover member has a restricting wall that holds down the portion where the soluble conductor contacts the insulating substrate via the conductive connecting material.

17. A protective element as described in claim 14, having an insulating layer formed on the insulating substrate between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode, the insulating layer having a thickness greater than the thickness of either the first or second electrode or the heating element extraction electrode, and the fusible conductor being in contact with the insulating layer.

18. The protection element according to claim 17, wherein the thickness of the insulating layer is more than twice the thickness of the heating element lead electrode.

19. A protection element as described in claim 14, wherein the insulating substrate has protrusions formed between the first electrode and the heating element extraction electrode and between the second electrode and the heating element extraction electrode, the protrusions having a height greater than the thickness of either the first or second electrode or the heating element extraction electrode, and the conductive connecting material is in contact with the protrusions.

20. The protection element according to claim 19, wherein the height of the protrusion is more than twice the thickness of the heating element lead electrode.

21. A protective element according to any one of claims 14 to 20, wherein the heating element is provided on the surface of the insulating substrate on which the fusible conductor is provided or on the back surface opposite to the surface, and the insulating substrate has an insulating member provided thereon so as to cover at least the heating element.

22. A protection element according to any one of claims 14 to 20, wherein the heating element is provided inside the insulating substrate.

23. A protective element according to any one of claims 1 to 7 and 14 to 20, wherein the high-melting-point metal layer is made of Ag or Cu or a metal containing Ag or Cu as its main component, and the first low-melting-point metal layer is made of Sn or a metal containing Sn as its main component.

24. A method for manufacturing a semiconductor device comprising: a heating element; an insulating substrate provided with a first electrode, a second electrode, and a heating element lead electrode electrically connected to the heating element on a current path between the first and second electrodes; a mounting step of mounting a laminate formed by stacking a high-melting point metal layer and a first low-melting point metal layer composed of a first low-melting point metal having a melting point lower than that of the high-melting point metal constituting the high-melting point metal layer over the first electrode, the heating element lead electrode, and the second electrode formed on the insulating substrate, in an orientation where the first low-melting point metal layer, the first electrode, the heating element lead electrode, and the second electrode are in contact with each other; and a heating step of heating the insulating substrate on which the laminate is mounted at a mounting temperature equal to or higher than the eutectic temperature of an alloy of the high-melting point metal and the first low-melting point metal. A method for manufacturing a protective element, comprising: a melting step of forming a second low-melting point metal layer composed of an alloy of the high-melting point metal and the first low-melting point metal by mutual diffusion and / or melting of a part of the high-melting point metal and the first low-melting point metal, the second low-melting point metal layer having a solidus temperature lower than the mounting temperature; and a connecting step of connecting the soluble conductor with the first electrode, the heating element lead electrode, and the second electrode via the second low-melting point metal layer of a soluble conductor in which the second low-melting point metal layer solidified with the high-melting point metal layer is stacked by cooling the molten second low-melting point metal layer.

25. A method for manufacturing a protective element as described in claim 24, wherein the protective element is mounted on a circuit board and cuts off at least a portion of the current flow within the circuit board when an abnormality occurs in the circuit board, and the liquidus point of the second low-melting point metal layer is higher than the mounting temperature of the protective element on the circuit board.

26. A method for manufacturing a protective element as described in claim 24, wherein, between the heating step and the connecting step, the upper part of the high melting point metal layer is pressed against the insulating substrate, thereby bringing the second low melting point metal layer of the fusible conductor into contact with the insulating substrate.

27. A method for manufacturing a protective element as described in claim 24, wherein the insulating substrate has an insulating layer formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the insulating layer having a thickness greater than the thickness of either the first or second electrode or the heating element lead electrode, and the second low-melting point metal layer is in contact with the insulating layer.

28. The method for manufacturing a protective element according to claim 27, wherein the thickness of the insulating layer is greater than the sum of the thickness of the heating element lead electrode and the thickness of the first low-melting point metal layer.

29. A method for manufacturing a protective element as described in claim 24, wherein the insulating substrate has protrusions formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the protrusions having a height greater than the thickness of either the first or second electrode or the heating element lead electrode, and the second low-melting point metal layer is in contact with the protrusions.

30. The method for manufacturing a protective element according to claim 29, wherein the height of the convex portion is greater than the sum of the thickness of the heating element lead electrode and the thickness of the first low-melting point metal layer.

31. A method for manufacturing a protective element described in any one of claims 24 to 30, wherein the contact area between the second low-melting point metal layer and the insulating substrate is 50% or more of the area between the first electrode overlapping the soluble conductor and the heating element extraction electrode, and 50% or more of the area between the second electrode overlapping the soluble conductor and the heating element extraction electrode.

32. A method for manufacturing a protective element according to any one of claims 24 to 30, wherein in the melting step, a portion of the high-melting-point metal and all of the first low-melting-point metal melt together due to interdiffusion at the interface between the high-melting-point metal layer and the first low-melting-point metal layer, thereby forming the second low-melting-point metal layer.

33. A method for manufacturing a protective element according to any one of claims 24 to 30, wherein the thickness of the high melting point metal layer in the stacking direction is greater than the thickness of the second low melting point metal layer in the stacking direction.

34. A method for manufacturing a protective element according to any one of claims 24 to 30, wherein in the heating step, the insulating substrate on which the laminate is mounted is heated at a mounting temperature lower than the solidus temperature of the first low-melting point metal.

35. A method for manufacturing a protective element according to any one of claims 24 to 30, wherein the second low-melting-point metal layer comprises the first low-melting-point metal layer of the laminate.

36. A device comprising a heating element, a first electrode, a second electrode, and an insulating substrate provided with a heating element lead electrode electrically connected to the heating element on a current path between the first electrode and the second electrode, comprising: a conductive connecting material forming step of providing a conductive connecting material on the first electrode, the heating element lead electrode, and the second electrode formed on the insulating substrate, and between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode; a mounting step of mounting a fusible conductor having a coating structure in which both sides of a low-melting point metal layer are coated with a high-melting point metal layer having a melting point higher than that of the low-melting point metal layer, via the conductive connecting material, on the first electrode, the heating element lead electrode, and the second electrode; and a heating and melting step of heating the conductive connecting material at a temperature higher than the solidus temperature of the conductive connecting material to melt it. and a connecting step of connecting the soluble conductor with the first electrode, the heating element lead electrode, and the second electrode by cooling the molten conductive connecting material, wherein at least a portion of the soluble conductor is in direct or indirect contact with the insulating substrate between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode.

37. A method for manufacturing a protective element as described in claim 36, wherein the protective element is mounted on a circuit board and cuts off electrical current in at least a portion of the circuit board when an abnormality occurs in the circuit board, and the liquidus point of the conductive connecting material is higher than the mounting temperature of the protective element on the circuit board.

38. The method for manufacturing a protective element according to claim 36, wherein the fusible conductor is pressed against the insulating substrate during the heating step and the connecting step, thereby bringing the conductive connecting material into contact with the insulating substrate.

39. A method for manufacturing a protection element as described in claim 36, wherein the insulating substrate has an insulating layer formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the insulating layer having a thickness greater than the thickness of either the first or second electrode or the heating element lead electrode, and the conductive connecting material is in contact with the insulating layer.

40. The method for manufacturing a protective element according to claim 39, wherein the thickness of the insulating layer is more than twice the thickness of the heating element lead electrode.

41. A method for manufacturing a protective element as described in claim 36, wherein the insulating substrate has protrusions formed between the first electrode and the heating element lead electrode and between the second electrode and the heating element lead electrode, the protrusions having a height greater than the thickness of either the first or second electrode or the heating element lead electrode, and the conductive connecting material is in contact with the protrusions.

42. The method for manufacturing a protective element according to claim 41, wherein the height of the protrusion is more than twice the thickness of the heating element lead electrode.

43. A protective element according to any one of claims 24 to 30 and 36 to 42, wherein the high-melting-point metal layer is made of Ag or Cu, or a metal containing Ag or Cu as its main component, and the first low-melting-point metal layer is made of Sn or a metal containing Sn as its main component.

44. A battery pack comprising: one or more battery cells; a protection element connected to a charge / discharge path of the battery cell and blocking the charge / discharge path; and a current control element that detects the voltage value of the battery cell and controls the flow of current to the protection element, wherein the protection element is a protection element as defined in any one of claims 1 to 7 and 14 to 20.

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