JP6324684B2 - Protective element - Google Patents

Description

  The present invention relates to a protective element that cuts off a current path when an abnormality such as overcharge or overdischarge occurs, and a protective circuit board on which the protective element is mounted.

  Many secondary batteries that can be charged and used repeatedly are processed into battery packs and provided to users. Particularly in lithium ion secondary batteries with high weight energy density, in order to ensure the safety of users and electronic devices, in general, a battery pack incorporates a number of protection circuits such as overcharge protection and overdischarge protection, It has a function of shutting off the output of the battery pack in a predetermined case.

  This type of protection element includes an overcharge protection or overdischarge protection operation of the battery pack by turning on / off the output using an FET switch built in the battery pack. However, when the FET switch is short-circuited for some reason, when a lightning surge or the like is applied and an instantaneous large current flows, the output voltage drops abnormally due to the life of the battery cell, or conversely an excessively abnormal voltage Even when a battery pack is output, battery packs 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 possible abnormal state, a protection element made of a fuse element having a function of cutting off the current path by an external signal is used. .

  As shown in FIGS. 7A to 7C, the protective element 80 of the protective circuit for such a lithium ion secondary battery or the like includes the first and second electrodes connected on the current path. A fusible conductor 83 is connected between 81 and 82 to form part of the current path, and the fusible conductor 83 on the current path is self-heated due to overcurrent or a heating element provided inside the protection element 80. What is blown by H.84 is proposed. 7B is a cross-sectional view taken along the line AA ′ in FIG. 7A, and FIG. 7C is a cross-sectional view taken along the line BB ′ in FIG. 7A.

  Specifically, the protection element 80 includes an insulating substrate 85, a heating element 84 laminated on the insulating substrate 85 and covered with an insulating member 86, and first and second electrodes 81 formed on both ends of the insulating substrate 85. , 82, a heating element extraction electrode 88 laminated on the insulating member 86 so as to overlap the heating element 84, both ends are connected to the first and second electrodes 81, 82, respectively, and the central portion is the heating element extraction A soluble conductor 83 connected to the electrode 88.

  When an abnormality such as overcharge or overdischarge is detected, the protection element 80 generates heat when the heating element 84 is energized. Then, the soluble conductor 83 is melted by this heat, and the molten conductor is collected on the heating element extraction electrode 88, thereby interrupting the current path between the first and second electrodes 81 and 82.

JP 2010-003665 A JP 2004-185960 A JP 2012-003878 A

  By the way, as the soluble conductor 83 used for this kind of protection element 80, for example, a foil made of a low melting point metal 83a such as Pb-free solder is used, and a high melting point metal 83b such as Ag, Cu or an alloy containing these as a main component. The one coated with is proposed. The protective element 80 uses a soluble conductor 83 in which a foil of a low melting point metal 83a is covered with a high melting point metal 83b, thereby preventing fusing at a mounting temperature such as reflow and facilitating mounting. By using the erosion action (erosion phenomenon) of the high melting point metal 83b by the low melting point metal 83a, it is melted at a temperature equal to or lower than the melting point of the high melting point metal 83b, so that quick fusing can be realized.

  In such a soluble conductor 83, as a method of coating the foil of the low melting point metal 83a with the high melting point metal 83b, electrolytic plating that can continuously apply the high melting point metal plating to the long low melting point metal foil. The method is advantageous in terms of work efficiency and manufacturing cost.

  However, when refractory metal plating is performed by electrolytic plating, the electric field strength is relatively increased at the edge portion of the long low melting point metal foil, that is, the side edge portion, and the refractory metal 83b is thickly plated (see FIG. 2). In the fusible conductor 83, the thickness of the refractory metal 83b at the side edge reaches about 110 to 200% of the thickness of the refractory metal 83b at the main surface. Thus, the soluble conductor 83 in which the refractory metal 83b is formed thick along the side edge is cut into a predetermined length, and the first electrode 81 is cut as shown in FIGS. When the side edge portion is connected between the heating element extraction electrode 88 and the second electrode 82 and connected, the fusing time becomes long due to the thick side edge portion.

  That is, since the thick side edge portion formed of the refractory metal 83b is extended between the first electrode 81 to the heating element extraction electrode 88 to the second electrode 82 to be fused, In order to melt the edge, more heat energy is required. In addition, since the outer edge portion is formed relatively thick by the high melting point metal 83b, it takes a considerable time to blow out even by the erosion phenomenon caused by the low melting point metal 83a. Further, the protection element 80 is hotter at the center of the substrate farthest from the outer edge of the insulating substrate 85 and is radiated as it goes toward the outer edge of the substrate, making it difficult for the temperature to rise. And since the thick side edge part formed of the high melting point metal of the fusible conductor 83 is formed from the center of the insulating substrate 85 to the outer edge, the protective element 80 is more in order to blow out. Time is required.

  Moreover, in order to cut | disconnect the thick part formed along a side edge part, and to make the thickness of the whole soluble conductor 83 uniform, a cutting process will increase and productivity will fall. By not being covered with the refractory metal, the shape of the soluble conductor 83 becomes unstable depending on the temperature during reflow mounting or energization, and there is a possibility that the fusing characteristics may vary.

  Then, an object of this invention is to provide the protection element which can aim at shortening of fusing time, without increasing the manufacturing man-hour of a soluble conductor.

In order to solve the above-described problems, a protection element according to the present invention includes an insulating substrate, a heating element, an insulating member covering at least the heating element, and a heating element extraction electrode electrically connected to the heating element. The first and second electrodes are connected to the first and second electrodes from the heating element extraction electrode, and the current path between the first electrode and the second electrode is blown by heating. The soluble conductor is formed to be thicker than the main surface portion, and has a pair of first side edge portions opposed to each other and a thickness thinner than the first side edge portion. A pair of second side edges formed opposite to each other, and the second side edges are disposed along a current path extending from the heating element extraction electrode to the first and second electrodes. The fusible conductor has the first side edge covered with a refractory metal and the second side edge. The refractory metal covering the low melting point metal and the surface of the low melting point metal is one that is layered.

  According to the present invention, the fusible conductor has the second side edge portion formed to the same thickness as the main surface and disposed along the current path extending from the heating element extraction electrode to the first and second electrodes. Therefore, as compared with the case where the first side edge portion is disposed along the current path, the fusing can be performed quickly with less heat energy.

(A) is a top view of the protection element to which this invention was applied, (B) is A-A 'sectional drawing, (C) is B-B' sectional drawing. It is a perspective view which shows a soluble conductor. It is a circuit diagram of a battery pack to which a protection element is applied. It is a circuit diagram of a protection element. It is a figure which shows the state by which the soluble conductor was blown, (A) is a top view of a protection element, (B) is a circuit diagram of a protection element. It is a graph which shows the relationship between the plating thickness of the refractory metal layer which concerns on a 2nd Example, fusing time, and a fusion | melting incidence. (A) is a top view of the protection element which concerns on a reference example, (B) is A-A 'sectional drawing, (C) is B-B' sectional drawing.

  Hereinafter, a protection element to which the present invention is applied will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention. Further, the drawings are schematic, and the ratio of each dimension may be different from the actual one. Specific dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

[Protective element]
As shown in FIG. 1A, the protection element 1 to which the present invention is applied includes an insulating substrate 11, a heating element 14 stacked on the insulating substrate 11 and covered with an insulating member 15, and both ends of the insulating substrate 11. The first electrode 12 (A1) and the second electrode 12 (A2) formed on the heating member 14 are stacked on the insulating member 15 so as to overlap the heating member 14, and are electrically connected to the heating member. The lead electrode 16 and the soluble conductor 13 having both ends connected to the first and second electrodes 12 (A 1) and 12 (A 2) and the center connected to the heating element lead electrode 16 are provided.

  The insulating substrate 11 is formed of an insulating member such as alumina, glass ceramics, mullite, zirconia, and the like. In addition, although the material used for printed wiring boards, such as a glass epoxy board | substrate and a phenol board | substrate, may be used, it is necessary to pay attention to the temperature at the time of fuse blowing.

  The heating element 14 is a conductive member that has a relatively high resistance value and generates heat when energized, and is made of, for example, W, Mo, Ru, or the like. These alloys, compositions, or compound powders are mixed with a resin binder or the like to form a paste on the insulating substrate 11 by patterning using a screen printing technique and firing.

  An insulating member 15 is disposed so as to cover the heating element 14, and a heating element extraction electrode 16 is disposed so as to face the heating element 14 through the insulating member 15. In order to efficiently transfer the heat of the heating element 14 to the soluble conductor 13, an insulating member 15 may be laminated between the heating element 14 and the insulating substrate 11. As the insulating member 15, for example, glass can be used.

  One end of the heating element extraction electrode 16 is connected to the heating element electrode 18 (P1) and is continuous with one end of the heating element 14. The other end of the heating element 14 is connected to the other heating element electrode 18 (P2). The heating element electrode 18 (P1) is formed on the third side 11d side of the insulating substrate 11, and the heating element electrode 18 (P2) is formed on the fourth side 11e side of the insulating substrate 11. The heating element electrode 18 (P2) is connected to the external connection electrode 21 (P2) formed on the back surface 11a of the insulating substrate 11.

  The first electrode 12 (A1) and the second electrode 12 (A2) formed on both side edges 11b and 11c of the insulating substrate 11 and connected by the soluble conductor 13 are through holes (not shown). Are connected to the first and second external connection terminals 21 (A1) and 21 (A2) provided on the back surface 11a of the insulating substrate. The protection element 1 has a current path formed on the circuit board by connecting the external connection terminals 21 (A1) and 21 (A2) to connection electrodes provided on the circuit board on which the protection element 1 is mounted. Part of

  The first and second electrodes 12 (A1) and 12 (A2), the heating element extraction electrode 16 and the external connection terminals 21 (A1), 21 (A2), and 21 (P2) have Ni / An Au plating layer 22 is formed. Thereby, erosion of the first and second electrodes 12 (A1) and 12 (A2) and the heating element extraction electrode 16 by the low melting point metal 13a of the soluble conductor 13 and the solder 29 for connection of the soluble conductor 13 is suppressed. be able to.

  Further, the first and second electrodes 12 (A1) and 12 (A2) are made of an insulating material such as glass that prevents the melted conductor of the soluble conductor 13 and the solder for connecting the soluble conductor 13 from flowing out, which will be described later. The outflow prevention part 23 which becomes is formed.

[Soluble conductor]
The soluble conductor 13 is a laminated structure composed of an inner layer and an outer layer, and a low melting point metal layer 13a serving as an inner layer is covered with a high melting point metal layer 13b serving as an outer layer. The low melting point metal layer 13a is not particularly limited. For example, a metal mainly composed of Sn, and a material generally called “Pb-free solder” (for example, M705, manufactured by Senju Metal Industry Co., Ltd.) is preferably used. Can do. The melting point of the low melting point metal layer 13a is not necessarily higher than the temperature of the reflow furnace, and may be melted at about 200 ° C. The refractory metal layer 13b is also not particularly limited. For example, a metal having a high melting point that does not melt even when board mounting is performed by a reflow furnace, such as Ag or Cu, or a metal mainly composed of either of them. It can be used suitably.

  Even when the low melting point metal layer 13a is covered with the high melting point metal layer 13b and the reflow temperature exceeds the melting temperature of the low melting point metal layer 13a and the low melting point metal is melted, The protective element 1 can be easily mounted on the circuit board without being fused as the fusible conductor 13.

  Further, when the soluble conductor 13 is heated by the heating element 14, the low melting point metal layer 13a melts and erodes the high melting point metal layer 13b. Therefore, the protection element 1 can melt the fusible conductor 13 at a temperature equal to or lower than the melting temperature of the refractory metal layer 13 to quickly cut off the current path. The fusible conductor 13 can be melted by self-heating (Joule heat) even when an overcurrent exceeding the rating flows, and the current path can be cut off.

[First and second side edges]
Here, as shown in FIG. 2, the fusible conductor 13 includes a pair of first side edge portions 26 formed thicker than the main surface portion 25 and a pair formed to the same thickness as the main surface portion 25. Second side edge portion 27. A pair of first side edge portions 26 are provided opposite to each other, and a pair of second side edge portions 27 are provided substantially opposite to the first side edge portion 26 to face each other.

  The side surface of the first side edge portion 26 is covered with the refractory metal layer 13 b and is thereby formed thicker than the main surface portion 25 of the soluble conductor 13. The second side edge portion 27 has a low-melting-point metal 13a whose outer periphery is surrounded by the high-melting-point metal layer 13b on the side surface. The second side edge portion 27 is formed to have the same thickness as the main surface portion 25 except for both end portions adjacent to the first side edge portion 26.

  As shown in FIG. 1, the fusible conductor 13 has a second side edge portion 27 in a current path extending from the heating element extraction electrode 16 to the first and second electrodes 12 (A1) and 12 (A2). It is arranged along. Thereby, the protection element 1 can interrupt | block rapidly the electric current path | route from the heat generating body extraction electrode 16 to 1st and 2nd electrode 12 (A1), 12 (A2).

  That is, the second side edge portion 27 is formed to be relatively thinner than the first side edge portion 26. The second side edge portion 27 is formed by covering the low melting point metal layer 13a with a high melting point metal. As a result, the second side edge portion 27 acts on the erosion action of the refractory metal layer 13b by the low melting point metal layer 13a, and the thickness of the eroded refractory metal layer 13b also changes to the first side edge portion 26. Compared with the 1st side edge part 26 currently formed thickly by the high melting-point metal layer 13b, it can melt | disconnect rapidly with less heat energy by forming thinly compared with.

  In the protection element 1, the center of the insulating substrate 11 furthest from the outer edge is the hottest, and the temperature hardly rises due to heat radiation toward the outer edge, but the second side edge 27 is the first and second electrodes 12 (A1). , 12 (A2), the outer edge side of the insulating substrate 11 can be melted even with a small amount of heat energy, and the current path can be quickly cut off.

  Further, the second side edge portion 27 of the soluble conductor 13 is exposed to the relatively narrow heating element extraction electrode 16 although the low melting point metal layer 13a is exposed outward from the end surface according to the manufacturing method described later. Therefore, elution of the low melting point metal layer 13a is suppressed even in a high temperature environment such as when the protective element 1 is reflow-mounted, and the shape of the soluble conductor 13 can be maintained.

  That is, when the second side edge portion 27 is disposed on the first and second electrodes 12 (A1) and 12 (A2), the low melting point metal layer 13a exposed outward from the end surface is compared. When the low melting point metal layer 13a is melted to oppose the first and second electrodes 12 (A1) and 12 (A2) formed in a wide area, the first and second electrodes 12 ( It elutes into A1) and 12 (A2), and the shape may not be maintained. Therefore, the fusing time of the soluble conductor 13 varies for each product, and the fusing characteristics may become unstable.

  On the other hand, the protective element 1 has the low melting point metal layer 13a because the second side edge 27 where the low melting point metal layer 13a is exposed outward from the end face faces the narrow heating element extraction electrode 16. Elution is suppressed, and it has stable fusing characteristics.

[Production method of soluble conductor]
Next, the manufacturing process of the soluble conductor 13 will be described. The fusible conductor 13 is manufactured by coating the low melting point metal foil constituting the low melting point metal layer 13a with the metal constituting the high melting point metal layer 13b. As a method for coating a low melting point metal layer foil with a high melting point metal, an electrolytic plating method capable of continuously applying a high melting point metal plating to a long low melting point metal foil is advantageous in terms of work efficiency and manufacturing cost. It becomes.

  When refractory metal plating is performed by electrolytic plating, the electric field strength is relatively increased at the edge portion of the long low melting point metal foil, that is, the side edge portion, and the refractory metal layer 13b is thickly plated (FIG. 2). reference). Thereby, the elongate conductor ribbon 30 by which the side edge part was formed thickly by the high melting-point metal layer is formed. Next, the conductor ribbon 30 is cut into a predetermined length in the width direction (C-C ′ direction in FIG. 2) perpendicular to the longitudinal direction, whereby the soluble conductor 13 is manufactured. Thus, in the fusible conductor 13, the side edge portion of the conductor ribbon 30 becomes the first side edge portion 26, and the cut surface of the conductor ribbon 30 becomes the second side edge portion 27. The first side edge portion 26 is covered with a refractory metal 13b, and the second side edge portion 27 has a pair of upper and lower refractory metal layers 13b and a refractory metal on an end surface (cut surface of the conductor ribbon 30). The low melting point metal layer 13a sandwiched between the layers 13b is exposed to the outside.

  That is, the conductor ribbon 30 has a first side edge portion 26 connected to the first and second electrodes 12 (A1) and 12 (A2) in the longitudinal direction cut to a predetermined length. The width direction orthogonal to the direction becomes the second side edge 27 disposed between the first and second electrodes 12 (A1) and 12 (A2). Therefore, the conductor ribbon 30 has a width corresponding to the width between the first and second electrodes 12 (A1) and 12 (A2), and the first and second electrodes 12 (A1) and 12 (A2). Cut to length according to size.

  The soluble conductor 13 manufactured in this way is formed on the first and second electrodes 12 (A1) and 12 (A2) and on the heating element extraction electrode 16 by a low melting point metal such as the solder 29 for connection. Connected. At this time, the fusible conductor 13 is connected to the first and second electrodes 12 (A1) and 12 (A2) at the first side edge 26 formed thick by the refractory metal layer 13b, A second side edge 27 serving as a cut surface of the conductor ribbon 30 is disposed between the first and second electrodes 12 (A1) and 12 (A2).

  The fusible conductor 13 is coated with a flux 17 on almost the entire surface of the fusible conductor 13 in order to prevent oxidation of the outer refractory metal layer 13b. Further, the protection element 1 may be provided with the cover member 20 on the insulating substrate 11 in order to protect the inside of the protection element 1 configured as described above.

[How to use protection elements]
Next, a method for using the protection element 1 will be described. As shown in FIG. 3, the protection element 1 mentioned above is mounted and used for the circuit in the battery pack of a lithium ion secondary battery, for example.

  For example, the circuit on which the protection element 1 is mounted is used by being incorporated in a battery pack 40 having a battery stack 45 including battery cells 41 to 44 of a total of four lithium ion secondary batteries.

  The battery pack 40 includes a battery stack 45, a charge / discharge control circuit 50 that controls charging / discharging of the battery stack 45, a protection element 1 to which the present invention that cuts off charging when the battery stack 45 is abnormal, and each battery cell A detection circuit 46 that detects the voltages 41 to 44 and a current control element 47 that controls the operation of the protection element 1 according to the detection result of the detection circuit 46 are provided.

  The battery stack 45 includes battery cells 41 to 44 that need to be controlled for protection from overcharge and overdischarge states, and can be attached and detached via the positive terminal 40a and the negative terminal 40b of the battery pack 40. Are connected to the charging device 55, and the charging voltage from the charging device 55 is applied. The electronic device can be operated by connecting the positive terminal 40a and the negative terminal 40b of the battery pack 40 charged by the charging device 55 to the electronic device operated by the battery.

  The charge / discharge control circuit 50 includes two current control elements 51 and 52 connected in series to a current path flowing from the battery stack 45 to the charging device 55, and a control unit 53 that controls operations of these current control elements 51 and 52. Is provided. The current control elements 51 and 52 are configured by, for example, field effect transistors (hereinafter referred to as FETs), and control the gate voltage by the control unit 53 to control conduction and interruption of the current path of the battery stack 45. . The control unit 53 operates by receiving power supply from the charging device 55, and controls the current so that the current path is interrupted when the battery stack 45 is overdischarged or overcharged according to the detection result by the detection circuit 46. The operation of the elements 51 and 52 is controlled.

  The protection element 1 is connected to, for example, a charge / discharge current path between the battery stack 45 and the charge / discharge control circuit 50, and its operation is controlled by the current control element 47.

  The detection circuit 46 is connected to each battery cell 41 to 44, detects the voltage value of each battery cell 41 to 44, and supplies each voltage value to the control unit 53 of the charge / discharge control circuit 50. Further, the detection circuit 46 outputs a control signal for controlling the current control element 47 when any one of the battery cells 41 to 44 becomes an overcharge voltage or an overdischarge voltage.

  The current control element 47 is composed of, for example, an FET, and when the voltage value of the battery cells 41 to 44 exceeds a predetermined overdischarge or overcharge state by a detection signal output from the detection circuit 46, the protection element 1 is operated to control the charge / discharge current path of the battery stack 45 to be cut off regardless of the switch operation of the current control elements 51 and 52.

  In the battery pack 40 having the above configuration, the configuration of the protection element 1 will be specifically described.

  First, the protection element 1 to which the present invention is applied has a circuit configuration as shown in FIG. That is, the protection element 1 generates heat by melting the soluble conductor 13 by causing the soluble conductor 13 connected in series via the heating element extraction electrode 16 and the connection point of the soluble conductor 13 to generate heat. This is a circuit configuration comprising the body 14. In the protection element 1, for example, the fusible conductor 13 is connected in series on the charge / discharge current path, and the heating element 14 is connected to the current control element 47. One of the two electrodes 12 of the protection element 1 is connected to A1 via the external connection terminal 21, and the other is connected to A2. Further, the heating element extraction electrode 16 and the heating element electrode 18 connected thereto are connected to P1, and the other heating element electrode 18 is connected to P2 via the external connection terminal 21.

  The protection element 1 having such a circuit configuration can melt the soluble conductor 13 on the current path by the heat generation of the heating element 14 and block the charge / discharge path of the battery pack 40. At this time, the protection element 1 has a second side edge portion 27 of the fusible conductor 13 along a current path extending from the heating element extraction electrode 16 to the first and second electrodes 12 (A1) and 12 (A2). Arranged. Since the second side edge portion 27 is formed relatively thin, a current path extending from the heating element extraction electrode 16 to the first and second electrodes 12 (A1) and 12 (A2) is reduced in heat. Can be cut off with energy.

  Further, since the high melting point metal layer 13b is laminated on the upper and lower surfaces of the low melting point metal layer 13a, the second side edge portion 27 has the melting point of the high melting point metal due to the erosion action of the high melting point metal by the low melting point metal. It can be melted at a low temperature before reaching, and can be melted more quickly.

  As shown in FIG. 5A, the melted conductor of the fusible conductor 13 is attracted to the heating element lead electrode 16 having high wettability and the first and second electrodes 12 (A1) and 12 (A2) and blown. Is done. Therefore, the fusible conductor 13 can surely melt the space between the first electrode 12 (A1) to the heating element extraction electrode 16 to the second electrode 12 (A2) (FIG. 5B). In addition, when the fusible conductor 13 is melted, power supply to the heating element 14 is also stopped.

  The protection element of the present invention is not limited to use in a battery pack of a lithium ion secondary battery, and can of course be applied to various uses that require interruption of a current path by an electric signal.

  Next, a first embodiment of the present invention will be described. In the first example, a conductive ribbon obtained by coating a low melting point metal foil with a high melting point metal by electrolytic plating was prepared, and a soluble conductor was obtained by cutting in the width direction. As the low melting point metal foil, a Pb-free solder foil having a thickness of 60 μm was used, and Ag plating was applied to the entire surface of the low melting point metal foil by an electrolytic plating method to form a high melting point metal layer having a thickness of 4 μm on one side.

  In Example 1, the first side edge portion of the fusible conductor, which is formed thick by coating with a refractory metal, is disposed on the first and second electrodes, and the cut surface of the conductor ribbon The second side edge portion is arranged along a current path extending from the first electrode to the heating element extraction electrode to the second electrode (see FIG. 1). In Comparative Example 1, the first side edge was disposed along the current path, and the second side edge was disposed on the first and second electrodes (see FIG. 7).

  In both Example 1 and Comparative Example 1, a power of 35 W was applied and the fusing time was compared. The results are shown in Table 1.

  As shown in Table 1, in Comparative Example 1, it took 0.30 seconds to melt the fusible conductor, whereas in Example 1, it was possible to blow in 0.24 seconds. This was shortened to 80% as compared with the fusing time of Comparative Example 1, and quick fusing became possible by arranging the second side edge portion along the current path.

  In Example 1, this was formed relatively thin compared to the first side edge portion formed thick with the high melting point metal, and the low melting point metal and the high melting point metal were laminated. Since the second side edge portion is disposed along the current path extending to the first and second electrodes, it can be quickly utilized with less thermal energy and by utilizing the erosion action of the high melting point metal by the low melting point metal. It depends on being able to blow.

[Thickness of refractory metal layer]
Next, the optimum thickness of the refractory metal layer 13b of the soluble conductor 13 will be described. As described above, in the soluble conductor 13 according to the present invention, the low melting point metal layer 13a serving as the inner layer is covered with the high melting point metal layer 13b serving as the outer layer.

  Here, as the film thickness of the high melting point metal layer 13b is thinner, the soluble conductor 13 is rapidly eroded by the low melting point metal when the heating element 14 generates heat, and the fusing time can be shortened. Therefore, in the soluble conductor 13, it is preferable to form the refractory metal layer 13b as thin as possible from the viewpoint of fast fusing.

  On the other hand, when the protective element 1 is mounted on the circuit board by solder reflow, if the refractory metal layer 13b is thin, the soluble conductor 13 is deformed by being eroded by the low melting point metal during reflow heating. There is a risk that stable fusing characteristics cannot be maintained, such as variations in fusing time. Therefore, it is preferable that the fusible conductor 13 is formed as thick as possible from the viewpoint of maintaining the fusing characteristics while enabling the mounting by reflow mounting.

  Therefore, the fusible conductor 13 is formed with the refractory metal layer 13b with an optimum film thickness that can achieve both fast fusing, reflow mounting, and maintenance of fusing characteristics when the heat generating element 14 generates heat. Specifically, the soluble conductor 13 is formed such that the thickness of the refractory metal layer 13b in the main surface portion 25 is 2 μm or more on each of the front and back sides. By forming the film thickness of the refractory metal layer 13b to 2 μm or more, the fusible conductor 13 is eroded by the low melting metal even when the protective element 1 is mounted on the circuit board by reflow mounting. Therefore, deformation of the soluble conductor 13 can be prevented. Therefore, the soluble conductor 13 has stable fusing characteristics without variation in fusing time for each product by setting the film thickness of the refractory metal layer 13b to 2 μm or more regardless of the rating or size.

  Moreover, it is preferable that the soluble conductor 13 forms the film thickness of the high melting-point metal layer 13b in the main surface part 25 below 6 micrometers on both sides. By forming the film thickness of the refractory metal layer 13b to 6 μm or less, the fusible conductor 13 quickly corrodes the refractory metal when the heating element 14 generates heat regardless of the rating or size. Can be blown out in a short time. When the film thickness of the high melting point metal layer 13b is greater than 6 μm, the fusible conductor 13 increases the amount of erosion caused by the low melting point metal, so that the fusing time is increased accordingly.

  As described above, the fusible conductor 13 can continuously form the high melting point metal layer 13b on the long low melting point metal foil by the electrolytic plating method. At this time, the soluble conductor 13 can form the refractory metal layer 13b with a desired film thickness by current control.

  Next, a second embodiment of the present invention will be described. In the second embodiment, samples of soluble conductors with different thicknesses of the high melting point metal layer covering the low melting point metal foil are prepared, and the protective elements formed using these samples are soldered on the circuit board. It was mounted by reflow, and each soluble conductor sample was examined for deformation and fusing. Moreover, electric power was applied to each protection element, and the fusing time of the soluble conductor sample was measured.

  The fusible conductor sample used in the second example uses a Pb-free solder foil having a thickness of 60 μm as a low melting point metal foil, and Ag plating is performed on the entire surface of the Pb-free solder foil by an electrolytic plating method. A refractory metal layer of ˜7 μm was formed. In addition, each soluble conductor sample can form an Ag plating layer with a desired film thickness by controlling the amount of current. Each soluble conductor sample is cut across the width direction after electrolytic plating and formed into a predetermined length.

  As each soluble conductor sample, in Comparative Example 2, a refractory metal layer having a thickness of 1 μm on one side was formed. In Example 2, a refractory metal layer having a thickness of 2 μm on one side was formed. In Example 3, a refractory metal layer having a thickness of 3 μm on one side was formed. In Example 4, a refractory metal layer having a thickness of 4 μm on one side was formed. In Example 5, a refractory metal layer having a thickness of 5 μm on one side was formed. In Example 6, a refractory metal layer having a thickness of 6 μm on one side was formed. In Example 7, a refractory metal layer having a thickness of 7 μm on one side was formed.

  Each soluble conductor sample according to Comparative Example 2 and Examples 2 to 7 is disposed on the first and second electrodes with the first side edges formed thick by coating a refractory metal. Then, the second side edge portion that becomes the cut surface of the conductor ribbon is disposed along the current path extending from the first electrode to the heating element extraction electrode to the second electrode, whereby the protection element according to the second embodiment (See FIG. 1). 24 protection elements were prepared for each of the soluble conductors according to Comparative Example 2 and Examples 2 to 7.

  Next, each protection element was mounted on the circuit board by solder reflow. The reflow temperature is about 260 ° C. After reflow mounting, the cover member of the protective element was opened, the soluble conductor sample was visually observed, the deformation of the soluble conductor was evaluated, and the melting rate (%) of the soluble conductor was determined. In addition, after reflow mounting, a power of 35 W was applied to each protection element, and the fusing time (sec) was compared.

  The evaluation of the deformation of the fusible conductor is × when the fusible conductor is blown by reflow heating, but the fusible conductor is not blown by reflow heating, but there is no deformation in practical use. The case where it was observed was marked with ◯, and the case where the soluble conductor was not melted by reflow heating and almost no deformation was observed.

  The melting occurrence rate of the fusible conductor was determined from the number of samples that resulted in fusing out of 24 samples of each fusible conductor. The results are shown in Table 2 and FIG.

  As shown in Table 2 and FIG. 6, in the protective elements according to Examples 2 to 7 in which the film thickness of the refractory metal layer is 2 μm or more, any sample can be used for a soluble conductor by reflow mounting. There was no significant deformation. Further, in Examples 2 to 6 in which the Ag plating thickness was 2 to 6 μm, the melting time of the soluble conductor was as short as 0.44 sec or less, and it was possible to sufficiently meet the demand for fast melting.

  On the other hand, in Comparative Example 1 in which the Ag plating thickness was 1 μm, although the fusing time was shortened, 30% of the samples in which the soluble conductor was melted by reflow mounting occurred. This is because the Ag plating layer is too thin, the solder foil is melted by reflow heating, and the Ag plating layer is eroded by the molten solder.

  From the above, it can be seen that the Ag plating layer constituting the outer layer of the soluble conductor is preferably formed with a thickness of 2 μm or more, and more preferably 6 μm or less.

DESCRIPTION OF SYMBOLS 1 Protection element, 11 Insulation board | substrate, 11a Back surface, 11b 1st edge | side, 11c 2nd edge | side, 11d 3rd edge | side, 12 electrode, 13 soluble conductor, 14 heat generating body, 15 insulating member, 16 heating element extraction electrode , 17 flux, 18 heating element electrode, 20 cover member, 21 external connection terminal, 25 main surface portion, 26 first side edge portion, 27 second side edge portion, 30 conductor ribbon, 40 battery pack, 41 to 44 battery Cell, 45 battery stack, 46 detection circuit, 47 current control element, 50 charge / discharge control circuit, 51, 52 current control element, 53 control unit, 55 charging device

Claims (9)

An insulating substrate;
A heating element;
An insulating member covering at least the heating element;
A heating element extraction electrode electrically connected to the heating element;
First and second electrodes;
A soluble conductor connected from the heating element extraction electrode to the first and second electrodes, and by heating to melt a current path between the first electrode and the second electrode;
The fusible conductor is formed to be thicker than the main surface portion, and is formed to have a pair of first side edge portions facing each other and a thickness thinner than the first side edge portion. A second side edge, and the second side edge is disposed along a current path extending from the heating element extraction electrode to the first and second electrodes ,
The soluble conductor has the first side edge covered with a refractory metal, and the second side edge is laminated with a low melting point metal and the refractory metal covering the surface of the low melting point metal. Protective element. The accepted溶導body, the surface of the foil of the low melting point metal formed into an elongated shape, the conductor ribbon in which the refractory metal is coated, according to claim 1 wherein formed by cutting in the width direction Protective element. The accepted溶導body, above the low melting point metal surfaces of the protective element according to claim 1 or 2 the refractory metal is coated by electroplating. Said second side edge, the protection device according to claim 1 or claim 2 said low melting point metal is exposed to the outside from the end face. The protection element according to claim 4 , wherein the soluble conductor has the second side edge portion opposed to the heating element extraction electrode. The accepted溶導body, the first side edge of the protection element according to any one of claims 1 to 5 connected to the first and second electrodes. The low melting point metal is a Pb-free solder, the refractory metal is protective device according to any one of claims 1 to 6 is a metal mainly composed of Ag or Cu or Ag or Cu. The accepted溶導body, the thickness of the refractory metal laminated on both surfaces of the low melting point metal in the main surface portion, the protection device according to any one of claims 1 to 7 is respectively 2μm or more. The protective element according to claim 8 , wherein the refractory metal has a film thickness of 6 μm or less.

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