JP2017147162A - Fuse element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuse element that can hold a maximum amount of flux at a predetermined position even when made compact and short, and also enables stable operation by preventing a soluble conductor from varying in fusion characteristics.SOLUTION: A fuse element comprises an insulation substrate 10, a fusible conductor 13 arranged on the insulation substrate 10 and connected to a current path, and fusing to block the current path, a cover member 20 having a side wall 21 and a top face 22 covering a surface 10a, mounted with the fusible conductor 13, of the insulation substrate 10, and flux 17 applied over the fusible conductor 13, and is provided with a flux holding wall 24 for holding the flux 17 at a predetermined position on the fusible conductor 13 inside the top face 22 of the cover member 20, a minimum distance D between an outer surface 24a of the flux holding wall 24 and an inner wall surface 21a of the side wall 21 of the cover member 20 being 0.08 mm or larger.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuse element that is connected to a power supply line, a signal line, and the like and cuts off a power supply line, a signal line, and the like by fusing a built-in soluble conductor.

  Conventionally, for example, as a fuse element of a protection circuit for a lithium ion secondary battery, a fusible conductor is connected between a first electrode, a heating element extraction electrode, and a second electrode formed on an insulating substrate, thereby providing a current path. The circuit side intends to make the fusible conductor on this current path blown by self-heating due to overcurrent, or by energizing a heating element provided inside the fuse element by an external signal. There are some which melt the soluble conductor. In this fuse element, the melted liquid soluble conductor is collected on the conductor layer connected to the heating element, whereby the first and second electrodes are separated to interrupt the current path.

  As shown in FIG. 6A, such a fuse element 60 generally has a fusible conductor 65 on an insulating substrate 64 on which first and second electrodes 61 and 62 and a heating element extraction electrode 63 are formed. In addition to being mounted and covered by a cover member 66 adhered to the surface of the insulating substrate 64, the inside is protected and the handleability is improved.

  The fuse element 60 is coated with a flux 67 on the surface of the soluble conductor 65 for the purpose of preventing oxidation, promoting melting, and maintaining and improving the fusing characteristics. Since the flux 67 is uniformly held at the melted portion of the soluble conductor 65, the soluble conductor 65 is oxidized and the fusing temperature rise due to the oxidation can be prevented, and fluctuations in the fusing characteristics can be suppressed.

  Further, in order to hold the flux 67 uniformly at a predetermined position on the fusible conductor 65 and increase the holding amount, the fuse element 60 has a cylindrical protrusion on the inner side of the top surface of the cover member 66. There exists what formed the flux holding | maintenance part 68 which becomes (refer patent document 1). The flux holding portion 68 is provided at a position facing the substantially central portion of the soluble conductor 65 formed in a rectangular plate shape. Even when the flux 67 is heated when the fuse element 60 is reflow-mounted on a circuit board or the like due to the flux 67 coming into contact with the fusible conductor 65 and the flux holding portion 68, the flux holding portion 68 and its periphery The flux 67 can be held.

JP 2010-3665 A

  By the way, with miniaturization of electronic equipment, miniaturization and low profile of the fuse element are also required. For example, a fuse element having an outer dimension of about 3 mm × 2 mm has been proposed. However, when the fuse element is further reduced in size and height, the space inside the cover member is also narrowed, causing a problem that the flux cannot be held at a predetermined position on the soluble conductor.

  As shown in FIG. 6B, this is because the distance between the flux holding portion 68 and the side wall of the cover member 66 has become shorter due to the downsizing and lowering of the height of the fuse element 60. Since the holding power of the flux 67 has been reduced due to a reduction in height, the flux 67 held by the flux holding portion 68 comes into contact with the side wall of the cover member 66 and is sucked to the side wall side, and the flux holding portion 68. It is thought that it will flow out from.

  In this way, when the flux 67 flows from a predetermined position of the fusible conductor 65 and is unevenly distributed on the side wall side of the cover member 66, or the holding amount of the flux 67 on the central portion of the fusible conductor 65 is reduced, During actual use, it is difficult to suppress oxidation at the melted portion of the soluble conductor 65, and the fusing characteristics may fluctuate, for example, the fusing time may be extended.

  On the other hand, if the flux holding portion 68 is downsized in order to sufficiently maintain the distance from the side wall of the cover member 66, the holding amount of the flux 67 is reduced, and the antioxidant effect may be reduced.

  Therefore, the present invention improves the holding performance by the flux holding section, can hold the maximum amount of flux in a predetermined position even when the fuse element is reduced in size and height, and prevents fluctuations in the fusing characteristics of the soluble conductor. It is an object of the present invention to provide a fuse element that can be stably operated.

  In order to solve the above-described problems, a fuse element according to the present invention includes an insulating substrate, a fusible conductor disposed on the insulating substrate, connected to a current path, and cut off the current path by fusing. A cover member having a side wall and a top surface covering the surface of the insulating substrate on which the soluble conductor is mounted, and a flux coated on the soluble conductor, the top surface of the cover member Inside, a flux holding wall for holding the flux at a predetermined position on the soluble conductor is provided, and a minimum distance D between the outer surface of the flux holding wall and the inner wall surface of the side wall of the cover member is 0. It is 08 mm or more.

  According to the present invention, the minimum distance D between the outer surface of the flux holding wall and the inner wall surface of the side wall is 0.08 mm or more, so that the flux is covered even when the flux is softened by heating by reflow mounting or the like. It can be prevented from adhering to, being sucked from, and flowing out to the side wall side of the member, and the flux can be held at a predetermined position. Therefore, according to the present invention, a fuse element that can stably maintain a predetermined fusing characteristic can be obtained.

FIG. 1A is a plan view showing a fuse element to which the present invention is applied without a case, and FIG. 1B is a cross-sectional view of a circuit module in which the fuse element is surface-mounted on a circuit board. It is. FIG. 2 is an external perspective view showing the back surface of the fuse element to which the present invention is applied. FIG. 3 is a bottom view of the cover member. FIG. 4 is a diagram illustrating a circuit configuration of a battery pack to which the fuse element and the circuit module are applied. FIG. 5 is a diagram illustrating a circuit configuration of the fuse element. FIG. 6A is a cross-sectional view showing a conventional relatively large fuse element and a bottom view showing a case member thereof. FIG. 6B shows that the flux is reduced by downsizing and low profile. It is sectional drawing which shows the fuse element which flowed out to the side wall side from the flux holding | maintenance part, and a bottom view which shows the case member.

  Hereinafter, a fuse 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.

  The fuse element 1 to which the present invention is applied is, for example, surface-mounted by reflow on a circuit board such as a protection circuit for a lithium ion secondary battery, so that the soluble conductor 13 is placed on the charge / discharge path of the lithium ion secondary battery. Incorporated. When a large current exceeding the rating of the fuse element 1 flows, this protection circuit cuts off the current path by melting the fusible conductor 13 by self-heating (Joule heat). In addition, the protection circuit energizes the heating element 14 at a predetermined timing by a current control element provided on a circuit board or the like on which the fuse element 1 is mounted, and the fusible conductor 13 is blown by the heat generation of the heating element 14. Can cut off the current path. 1A is a plan view showing the fuse element 1 to which the present invention is applied with the case omitted, and FIG. 1B is a cross-sectional view of the fuse element 1 mounted on a circuit board. It is.

[Fuse element]
As shown in FIG. 1A, the fuse element 1 includes an insulating substrate 10, a heating element 14 stacked on the insulating substrate 10 and covered with an insulating member 15, and first elements formed at both ends of the insulating substrate 10. The electrode 11 and the second electrode 12, the heating element extraction electrode 16 laminated on the insulating member 15 so as to overlap the heating element 14, and both ends thereof are connected to the first and second electrodes 11 and 12, respectively. The fusible conductor 13 has a central portion connected to the heating element lead electrode 16 and a cover member 20 covering the surface 10a on which the fusible conductor 13 of the insulating substrate 10 is mounted. In the fuse element 1, a flux 17 is retained on the soluble conductor 13 to remove an oxide film generated on the soluble conductor 13 and improve the wettability of the soluble conductor 13.

  The insulating substrate 10 is formed in a substantially rectangular shape by an insulating member such as alumina, glass ceramics, mullite, zirconia, and the like. In addition, the insulating substrate 10 may be made of a material used for a printed wiring board such as a glass epoxy board or a phenol board.

[First and second electrodes]
The first and second electrodes 11 and 12 are opened by being spaced apart from each other in the vicinity of opposite side edges on the surface 10a of the insulating substrate 10, and a soluble conductor 13 to be described later is mounted. Thus, they are electrically connected via the soluble conductor 13. Further, the first and second electrodes 11 and 12 have a large current exceeding the rating flowing through the fuse element 1 and the fusible conductor 13 is melted by self-heating, or the heating element 14 is heated by energization and the fusible conductor is heated. 13 is cut off by fusing.

  As shown in FIG. 2, the first and second electrodes 11 and 12 are provided on the back surface 10f through castellations provided on the first and second side surfaces 10b and 10c of the insulating substrate 10, respectively. The external connection electrodes 11a and 12a are connected. The fuse element 1 is connected to the circuit board 2 on which an external circuit is formed via these external connection electrodes 11a and 12a, and constitutes a part of the energization path of the external circuit.

  The first and second electrodes 11 and 12 can be formed using a general electrode material such as Cu or Ag. In addition, a coating such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating is coated on the surfaces of the first and second electrodes 11 and 12 by a known method such as plating. Preferably it is. As a result, the fuse element 1 can prevent the first and second electrodes 11 and 12 from being oxidized, and can prevent a change in rating due to an increase in conduction resistance. Further, when the fuse element 1 is reflow-mounted, when a low melting point metal layer is formed on the outer layer of the connecting solder or the soluble conductor 13 to which the soluble conductor 13 is connected, the low melting point metal melts. It is possible to prevent the first and second electrodes 11 and 12 from being eroded (soldered).

[Heating element]
The heating element 14 is a conductive member that generates heat when energized, and is made of, for example, nichrome, W, Mo, Ru, Cu, Ag, or an alloy containing these as main components. The heating element 14 is obtained by mixing a powdered material of these alloys, compositions, or compounds with a resin binder or the like, forming a paste on the insulating substrate 10 using a screen printing technique, and firing it. Etc. can be formed. The heating element 14 has one end connected to the first heating element electrode 18 and the other end connected to the second heating element electrode 19.

  In the fuse element 1, an insulating member 15 is disposed so as to cover the heating element 14, and a heating element extraction electrode 16 is formed 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 10. As the insulating member 15, for example, glass can be used.

  One end of the heating element extraction electrode 16 is connected to the first heating element electrode 18 and is continuous with one end of the heating element 14 via the first heating element electrode 18. The first heating element electrode 18 is formed on the third side surface 10 d side of the insulating substrate 10, and the second heating element electrode 19 is formed on the fourth side surface 10 e side of the insulating substrate 10. The second heating element electrode 19 is connected to an external connection electrode 19a formed on the back surface 10f of the insulating substrate 10 through a castellation formed on the fourth side surface 10e.

  The heating element 14 is connected to an external circuit formed on the circuit board 2 via the external connection electrode 19a by mounting the fuse element 1 on the circuit board 2. The heating element 14 can be connected to the first and second electrodes 11 and 12 by being energized through the external connection electrode 19a at a predetermined timing to cut off the energization path of the external circuit and generating heat. The molten conductor 13 can be blown. Moreover, since the heat generating body 14 also cut | disconnects its energization path | route when the soluble conductor 13 blows, heat_generation | fever stops.

[Soluble conductor]
The fusible conductor 13 is made of a material that is quickly melted by the heat generated by the heating element 14, and for example, a low melting point metal such as solder or Pb-free solder whose main component is Sn can be suitably used.

  Further, the fusible conductor 13 may use a high melting point metal such as In, Pb, Ag, Cu, or an alloy mainly composed of any of these, or the inner layer may be a low melting point metal layer and the outer layer may be a high layer. It may be a laminate of a low melting point metal and a high melting point metal such as a melting point metal layer. By including the high melting point metal and the low melting point metal, even when the reflow temperature exceeds the melting point of the low melting point metal when the fuse element 1 is reflow mounted, Outflow to the outside can be suppressed and the shape of the soluble conductor 13 can be maintained. Further, even when fusing, the low melting point metal melts, and the high melting point metal is eroded, so that the fusing can be quickly performed at a temperature lower than the melting point of the high melting point metal.

  The soluble conductor 13 is connected to the heating element extraction electrode 16 and the first and second electrodes 11 and 12 by soldering or the like. The fusible conductor 13 can be easily connected by reflow soldering. The fusible conductor 13 is superimposed on the heating element 14 by being mounted on the heating element extraction electrode 16. The soluble conductor 13 connected between the first and second electrodes 11 and 12 via the heating element extraction electrode 16 is connected between the heating element extraction electrode 16 and the first electrode 11 and generates heat. The body extraction electrode 16 and the second electrode 12 are melted, and the first and second electrodes 11 and 12 are blocked. That is, the fusible conductor 13 is supported at the central portion by the heating element extraction electrode 16 and at both sides of the central portion supported by the heating element extraction electrode 16 as fusing parts 13a.

  The soluble conductor 13 is coated with a flux 17 to prevent oxidation, improve wettability, and the like. The fusible conductor 13 can be melted quickly by preventing the fusing temperature from rising due to the oxidation of the fusible conductor 13 and the oxidation by holding the flux 17, suppressing fluctuations in the fusing characteristics.

[Cover member]
Further, in order to protect the inside of the fuse element 1, a cover member 20 is provided on the surface 10a on which the soluble conductor 13 of the insulating substrate 10 is mounted. The cover member 20 is formed in a substantially rectangular shape according to the shape of the insulating substrate 10. Further, as shown in FIG. 1B, the cover member 20 has a side wall 21 and a top surface 22 that covers the surface 10a of the insulating substrate 10, and fills and holds the flux 17 on the soluble conductor 13. Has a possible internal space. The cover member 20 forms an outer casing of the fuse element 1 by, for example, connecting the side wall 21 onto the surface 10a of the insulating substrate 10 with an adhesive.

  As shown in FIG. 3, a flux holding wall 24 that holds the flux 17 at a predetermined position on the soluble conductor 13 is provided inside the top surface 22 of the cover member 20. The flux holding wall 24 is provided so as to protrude from the top surface 22 of the cover member 20 to the inside of the fuse element 1 and includes, for example, a ring-shaped protrusion. In the cover member 20, a flux holding portion 23 protruding in a cylindrical shape is formed on the surface 10 a side of the insulating substrate 10 by the flux holding wall 24. In the fuse element 1, the flux 17 is filled between the flux holding portion 23 and the soluble conductor 13, so that the flux 17 is formed in a cylindrical shape with the surface of the soluble conductor 13 by the tension with the flux holding wall 24. It is hold | maintained between the inside of the flux holding | maintenance part 23 which protrudes, and its periphery.

  The flux holding portion 23 is formed at a position facing the fusible conductor 13, and preferably formed at a position facing substantially the center of the fusible conductor 13 overlapping the heating element 14, and the flux 17 generates heat from the fusible conductor 13. The body extraction electrode 16 and the heating element 14 are held at the overlapping position. For this reason, it is preferable that the flux holding part 23 is formed in the approximate center of the top surface 22 of the cover member 20.

  By providing the flux holding portion 23 so as to face the substantially center of the fusible conductor 13, the flux 17 can cover the surface of the fusible conductor 13 over a wide range. The molten conductor 13 is uniformly diffused over the entire surface. Accordingly, the fuse element 1 can quickly melt the current path between the first and second electrodes 11 and 12 by preventing the soluble conductor 13 from being oxidized and improving wettability.

  At this time, since the flux holding portion 23 is formed so as to overlap with the heating element 14, the flux 17 is diffused from the overlapping position of the soluble conductor 13 with the heating element 14 to the outer edge portion by the heat of the heating element 14, and is allowed. By evenly diffusing over the entire surface of the molten conductor 13, the soluble conductor 13 can be quickly blown out.

  In addition, the flux holding part 23 may form a slit in the height direction in a part of the flux holding wall 24. Further, the flux holding part 23 may form an opening in a part of the flux holding wall 24. Further, the fuse element 1 includes a plurality of flux holding portions 23 such that the flux holding portions 23 protruding in a cylindrical shape are arranged in parallel along the longitudinal direction of the fusible conductor 13 or in parallel along the longitudinal direction of the heating element 14. It may be formed.

  Further, the flux holding portion 23 may be a plurality of concentric cylinders. Further, the flux holding portion 23 is not limited to a cylindrical shape, and can adopt any shape that can hold the flux 17 such as an elliptical shape.

  Such a fuse element 1 has been reduced in size and height in accordance with recent miniaturization of electronic devices. For example, the outer dimension of the cover member 20 is 3 mm × 2.2 mm according to the insulating substrate 10. The thickness of the side wall 21 is 0.2 mm, and the internal dimensions are 2.6 mm × 1.8 mm. Of course, the cover member 20 can be formed with other dimensions.

[Minimum distance D between the outer surface of the flux retaining wall and the inner wall surface of the side wall]
The cover member 20 has a minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 of 0.08 mm or more. The outer surface 24a of the flux holding wall 24 refers to a surface facing the side wall 21 of the flux holding wall 24. In the cover member 20 shown in FIG. 3, the flux holding wall 24 that forms a flux holding portion 23 protruding in a cylindrical shape. The outer peripheral surface. Further, the inner wall surface 21 a of the side wall 21 refers to a wall surface inside the cover member 20 of the side wall 21. The inner wall surface 21a is a surface that is wide enough to allow the tension to act when the flux 17 comes into contact with the wall surface of the side wall 21, and does not include a portion that protrudes locally. .

  When the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 is 0.08 mm or more, the fuse element 1 is heated by reflow mounting or the like and the flux 17 is softened. The flux 17 can be prevented from adhering to and sucked from the side wall 21 of the cover member 20 and flowing out of the flux holding portion 23, and the flux 17 can be held at the flux holding portion 23 and its periphery.

  That is, the fuse element 1 has a flux holding portion in order to prevent the fusible conductor 13 from being oxidized and maintain the fusing characteristics even when the internal space of the cover member 20 is narrowed due to downsizing and low profile. It is preferable to take 23 large and supply as much flux 17 as possible. On the other hand, when the outer peripheral surface of the flux holding wall 24 constituting the flux holding portion 23 and the inner wall surface 21a of the side wall 21 of the cover member 20 are close to each other, the flux 17 comes into contact with the side wall 21 and is attracted to the side wall 21 side. . For this reason, the fuse element 1 secures the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 to 0.08 mm or more, and provides the flux 17 by providing the flux holding portion 23 as large as possible. While holding as much as possible, the supplied flux 17 can be stably held, and the flux 17 can be held around the flux holding portion 23 and its periphery even after reflow heating.

  Here, as the flux 17, a flux having a viscosity of approximately 3 to 20 Pa · s when softened can be used. The fuse element 1 has a viscosity when softened by setting the minimum distance D between the outer surface 24a of the flux holding wall 24 constituting the flux holding portion 23 and the inner wall surface 21a of the side wall 21 of the cover member 20 to 0.08 mm or more. However, even when the flux 17 having a low viscosity of about 3 Pa · s is used, it can be held in the flux holding portion 23.

  In addition, when the viscosity when the flux 17 is softened exceeds 20 Pa · s, the workability at the time of supplying the fusible conductor 13 is deteriorated, but this is not an essential problem in the present invention and is applied to the fuse element 1. Is possible. Further, the height of the flux holding wall 24 is reduced according to the internal space of the cover member 20 that is narrowed by downsizing and lowering the height of the fuse element 1, and is, for example, 0.1 mm. .

  Even when a plurality of flux holding portions 23 are arranged in parallel, the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 constituting each flux holding portion 23 is 0.08 mm or more. The minimum distance between adjacent flux holding walls 24 is not limited and may be less than 0.08 mm, and the flux 17 may adhere to the adjacent flux holding walls 24. When the flux holding portion 23 is formed of a plurality of concentric cylinders, the minimum distance D between the outer periphery 24a of the outermost flux holding wall 24 and the inner wall surface 21a of the side wall 21 is 0.08 mm or more.

  The side wall 21 of the cover member 20 is connected to the surface 10 a of the insulating substrate 10 by an adhesive 26. The fuse element 1 also sets the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 to 0 even when the excess amount of the adhesive 26 crawls up along the inner wall surface 21a of the side wall 21. By securing 0.08 mm or more, the adhesive that has been scooped up along the inner wall surface 21a and the flux 17 do not come into contact with each other and are not attracted to the inner wall surface 21a side.

  Such a fuse element 1 is incorporated on a current path of the external circuit by being surface-mounted by reflow or the like on a circuit board on which an external circuit such as a protection circuit of a lithium ion secondary battery is formed. At this time, the fuse element 1 has a minimum distance D between the outer periphery 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 of 0.08 mm or more even when the flux 13 is softened by reflow heating. The softened flux 17 is prevented from coming into contact with the inner wall surface 21 a of the side wall 21 and flowing out from the flux holding portion 23.

  Therefore, the fuse element 1 can hold the flux 17 at a predetermined position on the fusible conductor 13, prevent the fusible conductor 13 from being oxidized and increase in fusing temperature due to oxidation, and stabilize the fusing characteristics. be able to.

  In the fuse element 1, when the heating element 14 is energized and generates heat via the external connection electrode 19 a, the fusible conductor 13 is melted and the first and second electrodes 11 and 12 and the heat generation are caused by the wettability. It is attracted onto the body extraction electrode 16. As a result, the fuse element 1 can cut off the current path between the first and second electrodes 11 and 12 by melting the fusible conductor 13. Further, since the fusible conductor 13 is cut off, the power supply path to the heating element 14 is also cut off, so that the heating of the heating element 14 is also stopped.

  Further, when an unexpected large current exceeding the rating flows on the energizing path extending between the first and second electrodes 11 and 12, the fuse element 1 causes the fusible conductor 13 to melt by self-heating, thereby The route can be blocked.

  In the fuse element 1 described above, a configuration in which the heating element 14 is provided and the soluble conductor 13 is blown by the heat generation of the heating element 14 in addition to the self-heating cutoff of the soluble conductor 13 due to a large current exceeding the rating has been described. However, the fuse element 1 to which the present invention is applied may be one in which the current path is interrupted by the self-heating cutoff of the fusible conductor 13 due to a large current exceeding the rating without including the heating element 14.

[Circuit board]
As the circuit board 2 on which the fuse element 1 is mounted, a known insulating substrate such as a rigid substrate such as a glass epoxy substrate, a glass substrate, or a ceramic substrate, or a flexible substrate is used. Further, as shown in FIG. 1B, the circuit board 2 has a mounting portion on which the fuse element 1 is surface-mounted by reflow or the like, and is provided on the back surface 10f of the insulating substrate 10 of the fuse element 1 in the mounting portion. Connection electrodes connected to the external connection terminals 11a, 12a, and 19a are provided. The circuit board 2 is mounted with an element such as an FET for energizing the heating element 14 of the fuse element 1.

[Usage of circuit module]
Next, a method of using the fuse element 1 and the circuit module 3 in which the fuse element 1 is surface-mounted on the circuit board 2 will be described. As shown in FIG. 4, the circuit module 3 is used as a circuit in a battery pack of a lithium ion secondary battery, for example.

  For example, the fuse element 1 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 fuse 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 fuse 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 fuse element 1 is connected, for example, on 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 the detection signal output from the detection circuit 46, the fuse 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 fuse element 1 will be specifically described.

  First, the fuse element 1 to which the present invention is applied has a circuit configuration as shown in FIG. That is, the fuse element 1 generates heat that melts the soluble conductor 13 by energizing 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 fuse 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. The first electrode 11 of the fuse element 1 is connected to the open end of the battery stack 45 via the external connection electrode 11a, and the second electrode 12 is connected to the positive terminal 40a side of the battery pack 40 via the external connection electrode 12a. Connected to the open end. The heating element 14 is connected to the charge / discharge current path of the battery pack 40 by being connected to the fusible conductor 13 via the heating element extraction electrode 16, and is also connected to the heating element extraction electrode 16 and the external connection electrode 19a. Are connected to the current control element 47.

  In such a battery pack 40, when the heating element 14 of the fuse element 1 is energized and generates heat, the fusible conductor 13 is melted and is drawn onto the heating element extraction electrode 16 due to its wettability. As a result, the fuse element 1 can reliably cut off the current path when the fusible conductor 13 is melted. Further, since the fusible conductor 13 is cut off, the power supply path to the heating element 14 is also cut off, so that the heating of the heating element 14 is also stopped.

  In addition, when an unexpected large current exceeding the rating of the fuse element 1 flows on the charge / discharge path, the battery pack 40 can block the current path by fusing the fusible conductor 13 by self-heating. .

  Note that the fuse element 1 to which the present invention is applied 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. The fuse element 1 includes a short-circuit element that connects a current path and a signal path via a melted conductor of a fusible conductor, a fusible conductor in addition to a protective element (SCP) that cuts off a current path and a signal path. And a switching element that switches a current path and a signal path through a melted conductor of a soluble conductor.

  Next, examples of the present invention will be described. In the present embodiment, the size of the flux holding portion 23 provided at a position facing the substantially center of the fusible conductor 13 and the outer surface 24a of the flux holding wall 24 using a cover member that is reduced in size and reduced in height. The presence or absence of flux flow after heating at a temperature (260 ° C.) corresponding to the reflow temperature was confirmed by changing the minimum distance D between the inner wall 21a and the inner wall 21a of the side wall 21.

  As shown in FIG. 3, the cover member 20 according to the example and the comparative example has an outer dimension of 3 mm × 2.2 mm, a thickness of the side wall 21 of 0.2 mm, and an inner dimension of 2.6 mm × 1.8 mm. ing. The flux holding part 23 is formed by a flux holding wall 24 protruding in a cylindrical shape. The flux holding wall 24 has a thickness of 0.1 mm, and the protruding height from the top surface of the cover member is 0.1 mm.

  In each of the examples and comparative examples, 20 fuse element samples were prepared and heated at a temperature corresponding to the reflow temperature (260 ° C.), and then the cover member 20 was removed to check whether or not flux flowed out.

[Example 1]
In Example 1, the inner diameter φ of the flux holding portion 23 was 1.44 mm, and the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.08 mm on both the left and right sides. In the fuse element according to Example 1, the number of fluxes flowing out from the flux holding portion 23 was 4 out of 20.

[Example 2]
In Example 2, the inner diameter φ of the flux holding portion 23 was 1.4 mm, and the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.1 mm on both the left and right sides. In the fuse element according to Example 2, the number of fluxes flowing out of the flux holding portion 23 was 0 out of 20.

[Example 3]
In Example 1, the inner diameter φ of the flux holding portion 23 was 1.3 mm, and the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.15 mm on both the left and right sides. In the fuse element according to Example 3, the number of fluxes flowing out of the flux holding part 23 was 0 out of 20.

[Example 4]
In Example 4, the inner diameter φ of the flux holding portion 23 was 1.2 mm, and the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.2 mm on both the left and right sides. In the fuse element according to Example 4, the number of fluxes flowing out of the flux holding portion 23 was 0 out of 20.

[Comparative Example 1]
In Comparative Example 1, the inner diameter φ of the flux holding portion 23 was 1.5 mm, and the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.05 mm on both the left and right. In the fuse element according to Comparative Example 1, the number of fluxes flowing out of the flux holding portion 23 was 16 out of 20.

  As shown in Table 1, in Example 1 in which the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 is 0.08 mm compared to Comparative Example 1 in which 0.05 mm, The number of fuse elements causing flux outflow was drastically reduced from 16 to 4. Further, in Examples 2 to 4 in which the minimum distance D between the outer surface 24a of the flux holding wall 24 and the inner wall surface 21a of the side wall 21 was 0.1 mm or more, the number of fuse elements in which flux flowed out was zero. It was.

  That is, in the fuse element, by setting the minimum distance D between the outer surface of the flux holding wall of the cover member and the inner wall surface of the side wall to 0.08 mm or more, the flux can be held in the flux holding portion even after reflow heating. I understand. Moreover, it turns out that the outflow of a flux can be prevented more reliably by making the minimum distance D of the outer surface of a flux holding wall and the inner wall surface of a side wall into 0.1 mm or more.

DESCRIPTION OF SYMBOLS 1 fuse element, 2 circuit board, 3 circuit module, 10 insulating substrate, 10a surface, 10b 1st side surface, 10c 2nd side surface, 10d 3rd side surface, 10e 4th side surface, 10f back surface, 11 1st Electrode, 11a External connection electrode, 12 Second electrode, 12a External connection electrode, 13 Soluble conductor, 13a Fusing part, 14 Heating element, 15 Insulating member, 16 Heating element extraction electrode, 18 First heating element electrode, 19 Second heating element electrode, 19a External connection electrode, 20 case, 21 side wall, 21a inner wall surface, 22 top surface, 22a side edge, 23 flux holding portion, 24 flux holding wall, 24a outer surface, 40 battery pack, 41 to 41 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 (2)

An insulating substrate;
A fusible conductor disposed on the insulating substrate, connected to the current path, and cut off the current path by fusing; and
A cover member having a side wall and a top surface covering the surface on which the soluble conductor of the insulating substrate is mounted;
A flux applied on the soluble conductor,
Inside the top surface of the cover member, a flux holding wall that holds the flux in a predetermined position on the soluble conductor is provided,
A fuse element in which a minimum distance D between the outer surface of the flux holding wall and the inner wall surface of the side wall of the cover member is 0.08 mm or more.   The fuse element according to claim 1, wherein the flux has a viscosity of 3 to 20 Pa · s.

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