JP2014053233A - Welding method of thermal fuse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method capable of stably welding a thermal fuse having a low fuse-down temperature to an external terminal.SOLUTION: After placing a terminal electrode 13 on an external terminal 14, a current is applied between a first welding electrode 15 in contact with the terminal electrode 13 and a second welding electrode 16 in contact with the external terminal 14 to thereby weld the terminal electrode 13 and the external terminal 14 therebetween. An area where the terminal electrode 13 comes into contact with the first welding electrode 15 is set to be larger than an area where the external terminal 14 comes into contact with the second welding electrode 16.

Description

  The present invention relates to a method for welding a thermal fuse used in a secondary battery such as a lithium ion battery or a lithium polymer battery.

  In recent years, secondary batteries such as lithium ion batteries and lithium polymer batteries are often used in portable electronic devices such as mobile phones and notebook computers. In a secondary battery such as a lithium ion battery, it is required to cut off the current when the temperature becomes high from the viewpoint of safety. Therefore, a thermal fuse is used in these secondary batteries so that the current is cut off at a predetermined temperature and does not return. As a method of using this thermal fuse, it is carried out by resistance welding at a portion close to an electrode which is a heat source.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2003-45492 A

  However, for further safety, there is a need for a thermal fuse that cuts off the current at a lower temperature than before. On the other hand, there is a need for a smaller fuse (shorter terminal electrode) and withstands a larger current than the current product. It has been. There is a movement to change the terminal material from conventional nickel to copper in order to increase the current of the thermal fuse. When copper is used as the terminal material, heat conductivity is high, and when the terminal electrode dimensions are shortened, the heat during resistance welding is easily transferred to the fusible body, and in addition, if the melting temperature of the fusible body is lowered, its effect Is even easier to receive. An object of the present invention is to provide a method for stably welding a thermal fuse having a short terminal electrode to an external terminal while suppressing the influence of heat on a fusible body.

  In order to solve the above-mentioned problems, the present invention is a method of welding a thermal fuse having a main body portion enclosing a fusible body and flat terminal electrodes led out from both sides of the main body portion, and an external terminal. Then, the terminal electrode and the external terminal are overlapped, and a current is passed between the first welding electrode that contacts the terminal electrode and the second welding electrode that contacts the external terminal, thereby connecting the terminal electrode and the external terminal. The area of contact between the terminal electrode and the first welding electrode is larger than the area of contact between the external terminal and the second welding electrode.

  With the above configuration, more of the heat generated by welding can be transferred to the first welding electrode side in contact with the terminal electrode, heat transmitted to the fusible body can be reduced, and the heat generated by welding can be reduced. Damage to the solution can be reduced.

The figure which shows the welding method of the thermal fuse in one embodiment of this invention The figure which shows another welding method of the thermal fuse in one embodiment of this invention

  Hereinafter, a thermal fuse welding method according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the thermal fuse used in the present invention puts flux 19 around the fusible body 11 joined so as to bridge between the pair of terminal electrodes 13, and is sealed with an insulating film 20. This is a main body 12. Here, the terminal electrode 13 is made of a copper plate having a thickness of about 0.1 mm and a width of about 2.3 mm, the fusible body 11 is made of a Sn—Bi—In alloy, and has a melting temperature of 80 to 90 ° C. . The surface of the terminal electrode 13 is preferably provided with a plating layer such as tin in order to prevent copper oxidation.

  The external terminal 14 is overlapped on the terminal electrode 13 and sandwiched between the first welding electrode 15 that contacts the terminal electrode 13 and the second welding electrode 16 that contacts the external terminal 14, and current flows between them. Thus, the terminal electrode 13 and the external terminal 14 are welded. The external terminal 14 is made of a nickel plate having a thickness of about 0.1 mm, and its width is equal to the width of the terminal electrode 13. In the present embodiment, the projection 21 is provided on the terminal electrode 13 and projection welding is performed. Two protrusions 21 are provided in the width direction. However, the protrusions may be provided on the external terminals or spot welding may be performed without providing the protrusions. However, when the protrusion is provided, it is easy to form a softer material. Therefore, when the copper electrode is used for the terminal electrode 13 and the nickel plate is used for the external terminal 14 as in this embodiment, the protrusion is provided on the terminal electrode 13 side. It is more desirable.

  Both the first welding electrode 15 and the second welding electrode 16 are made of chrome copper, and the surface of the first welding electrode 15 that makes contact with the terminal electrode 13 is φ5 mm, and the second welding electrode 16 and the external terminal 14 are in contact with each other. The contacting surface is 2 mm. By doing so, heat is generated in the welded portion, but since the contact area between the terminal electrode 13 and the first welding electrode 15 is large, most of the heat transferred to the terminal electrode 13 side is the first welding. It is transmitted to the electrode 15. Therefore, the heat transmitted to the fusible body 11 can be suppressed, and damage to the fusible body 11 due to heat during welding can be reduced.

  Here, if the surface contacting the external terminal of the second welding electrode is φ5 mm as in the case of the first welding electrode, even if projection welding is performed as in the present embodiment, the protrusion Since the current flows not only in the portion in contact with the portion but also in the portion in contact with each welding electrode, a large current is required and the amount of heat generation is increased, so that damage to the fusible body is likely to increase.

  On the other hand, as in this embodiment, the area where the external terminal 14 and the second welding electrode 16 are in contact is 1/3 or less of the area where the terminal electrode 13 and the first welding electrode 15 are in contact. By reducing the area where the current flows, the amount of heat generated can be suppressed, and the amount of heat escaping toward the first welding electrode 15 can be increased. Damage can be reduced.

  Further, in order to reduce damage to the fusible body 11 due to heat during welding, it is desirable to perform as shown in FIG. In FIG. 2, the temperature fuse and the welding electrode are configured in the same manner as in FIG. 1, and a stopper 17 is disposed between the second welding electrode 16 and the main body 12.

  The stopper 17 is formed by bonding a graphite sheet 18 to the surface of an aluminum base material. First, the external terminal 14 is positioned by bringing the external terminal 14 into contact with the stopper 17. Thereby, the position which welds the terminal electrode 13 and the external terminal 14 can be determined correctly. It is desirable that the surface of the stopper 17 with which the external terminal 14 abuts is insulated. Thereby, it is possible to prevent current from leaking to the stopper side.

  Further, when the terminal electrode 13 and the external terminal 14 are welded, the bottom surface of the stopper 17 is brought into contact with the terminal electrode 13. As shown in FIG. 2, the graphite sheet 18 bonded to the surface of the stopper 17 is preferably bonded to at least a part of the bottom surface and side surface of the stopper 17. The thermal conductivity of copper used for the terminal electrode 13 is about 400 W / m · K, while the thermal conductivity of a pyrolytic graphite sheet having a thickness of about 25 μm is about 1600 W / m · K, for example. Since it is four times as much, the heat flowing toward the terminal electrode 13 during welding is transferred to the graphite sheet 18 in contact with the terminal electrode 13 and is carried to the side surface of the stopper 17. Therefore, heat transmitted to the fusible body 11 due to heat generated during welding can be suppressed, and damage to the fusible body 11 due to heat during welding can be reduced. Moreover, since this graphite sheet 18 is excellent also in heat dissipation, since it can radiate | emit quickly in the air from the side surface of the stopper 17, heat is not accumulated even if it welds continuously, and it can be operated continuously. Further, as shown in FIG. 2, a cradle 22 in which a graphite sheet 18 is bonded to the surface of the base material is disposed on the first welding electrode 15 side as well as the stopper 17. It is desirable to perform welding with the electrode 13 interposed therebetween. By doing so, the contact state between the terminal electrode 13 and the stopper 17 and the pedestal 22 can be improved, so that heat can be released more and mechanical stress that may occur during welding is generated. Since it can prevent transmitting to the soluble body 11, it is more desirable.

  The method for welding a thermal fuse according to the present invention is industrially useful because even a thermal fuse having a low cutting temperature can be stably welded to an external terminal.

DESCRIPTION OF SYMBOLS 11 Soluble body 12 Main body part 13 Terminal electrode 14 External terminal 15 1st welding electrode 16 2nd welding electrode 17 Stopper 18 Graphite sheet 19 Flux 20 Insulating film 21 Protrusion part 22 Base

Claims (2)

A method of welding a thermal fuse having a body part encapsulating a fusible body, a flat terminal electrode led out from both sides of the body part, and an external terminal, the terminal electrode and the external terminal The terminal electrode and the external terminal are welded by passing an electric current between the first welding electrode that is in contact with the terminal electrode and the second welding electrode that is in contact with the external terminal. A method for welding a thermal fuse, wherein an area in which the terminal electrode and the first welding electrode are in contact with each other is larger than an area in which the external terminal and the second welding electrode are in contact with each other. A positioning stopper is disposed between the second welding electrode and the main body, the external terminal is brought into contact with the stopper to position the external terminal, and the stopper is used as the terminal electrode during welding. 2. The method for welding a thermal fuse according to claim 1, wherein the stopper has a surface having a thermal conductivity higher than that of the terminal electrode.

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