JP4630403B2 - Protective element - Google Patents

Description

  The present invention relates to a protection element that operates by melting a low melting point alloy, and is useful as a thermal fuse or a thermal fuse with resistance.

  An alloy-type thermal fuse that melts a low-melting-point alloy due to overheating of the protected device and cuts off power supply to the protected device. The movable electrode is joined by a low-melting-point alloy across a pair of lead fixed electrodes. A spring-type alloy type thermal fuse that is provided with a compression spring that applies a force in a direction to be isolated from the lead fixed electrode, and that urges the movable electrode by the compression spring by melting the low melting point alloy and isolates it from the lead fixed electrode. It is known. (For example, Patent Documents 1 to 3 etc.)

Japanese Utility Model Publication No. 47-10830 Japanese Utility Model Publication No. 57-37382 Japanese Utility Model Publication No.59-23340

FIG. 7 shows an example of a conventional spring type alloy type thermal fuse.
In FIG. 7, 2a ′ and 2b ′ are a pair of lead fixed electrodes, 2c ′ is a movable electrode, and 5 ′ is joining each end of the movable electrode 2c ′ to the tip of each lead fixed electrode 2a ′ and 2b ′. A low melting point alloy, 4 'is a compression spring. Reference numeral 1 'denotes an insulating base, and 7' denotes a case.
In this spring-type alloy-type thermal fuse, it is attached to a protected device with a sufficiently low thermal contact resistance, and when the low melting point alloy 5 ′ is melted by overheating of the protected device, the compression release elasticity of the compression spring 4 ′. The movable electrode 2c ′ is isolated from the lead fixed electrodes 2a ′ and 2b ′ by the force, and the power supply to the protected device is cut off, so that abnormal heat generation of the protected device and thus a fire can be prevented.

In the spring type alloy type thermal fuse, the compression reaction force of the compression spring 4 'always acts on the low melting point alloy 5' joining the lead fixed electrode 2a '(2b') and the movable electrode 2c ', The low melting point alloy 5 ′ eventually creep ruptures, and there is a possibility that it is difficult to ensure the original normal operation. In addition, if the spring has only a spring stress that does not cause the low melting point alloy 5 'to break, creep rupture can be prevented, but it may deteriorate in a heating atmosphere until actual operation. There is no guarantee that a release elastic force sufficient to isolate the movable electrode is obtained.
In particular, in recent years, there has been a demand for lead-free low melting point alloys such as solder for environmental protection, and the lead free low melting point alloy includes at least one of Sn and In, and a low melting point alloy containing Bi or Sb as a component. (Hereinafter referred to as Bi-based low melting point alloys and Sb-based low melting point alloys) have been developed, but when DC electricity is passed through these low melting point alloys, Bi and Sb precipitate at the interface between the cathode side electrode and the low melting point alloy. The present inventors have recognized that this deposited portion becomes brittle.
When such a Bi-based low melting point alloy or Sb-based low melting point alloy is used as the low melting point alloy of the spring-type alloy type thermal fuse and used in a direct current system, Bi or Sb precipitates are generated in the low melting point alloy. It is broken by the compression reaction force of the compression spring, and there is concern about the early failure of the spring type alloy type thermal fuse.

The object of the present invention is to join the lead fixed electrode and the movable electrode with a low melting point alloy, attach a compression spring that pressurizes the movable electrode in a direction away from the lead fixed electrode, and compress the melt by melting the low melting point alloy. In a spring-type soluble alloy type protective element that releases the spring from compression and isolates the movable electrode from the lead fixed electrode, the creep of the low melting point alloy due to the compression reaction force of the compression spring is well prevented and the protective element is It is to ensure operation.
A further object of the present invention is to provide a Bi-based low melting point alloy or Sb-based low melting point alloy containing Bi or Sb as an alloy component and depositing Bi or Sb in the low melting point alloy in contact with the cathode side electrode under direct current energization. It is an object of the present invention to provide a spring-type soluble alloy type protective element that can satisfactorily eliminate breakage due to the compression reaction force of the compression spring at the brittle Bi precipitation site or Sb precipitation site even when used as a low melting point alloy.

The protection element according to claim 1 includes a pair of lead fixed electrodes, a guide shaft is juxtaposed with the lead fixed electrodes, and the movable electrode is inserted through the guide shaft and spans between the lead fixed electrodes. Arranged, the tip of each lead fixed electrode and the movable electrode and the guide shaft and the movable electrode are joined by a low melting point alloy, and a force in a direction to isolate the movable electrode from the lead fixed electrode acts. A compression spring is provided, and the movable electrode is urged by the compression spring by the melting of the low melting point alloy and is isolated from the lead fixed electrode.
The protection element according to claim 2 is the protection element according to claim 1, wherein one lead conductor of a resistor having lead conductors attached to both ends of the resistor body is used as a guide shaft, and a coil spring is used as a compression spring. The coil spring is inserted into the one lead conductor between the resistor main body and the movable electrode, and a resistor energization heating circuit is connected between one lead conductor of the resistor and either of the lead fixed electrodes. It is characterized by that.
The protection element according to claim 3 is the protection element according to claim 1, wherein one lead conductor of a resistor having lead conductors attached to both ends of the resistor body is used as a guide shaft, and a coil spring is provided as a compression spring. The coil spring is inserted into the one lead conductor while being pressed by the movable electrode, and a resistor energization heating circuit is connected between the other lead conductor of the resistor and either of the lead fixed electrodes. It is characterized by that.
The protection element according to claim 4 is the protection element according to claim 3, wherein an insulator is interposed between the movable electrode and one end of the compression coil spring or between the other end of the compression coil spring and the resistor main body end. An insulator different from the above is interposed between the inside of the compression coil spring and the guide shaft.
The protective element according to claim 5 is the protective element according to any one of claims 1 to 4, wherein the movable electrode is provided with a mortar-shaped hole for receiving each lead fixed electrode tip, and the tip of each lead fixed electrode and the movable electrode The low melting point alloy is joined to the mortar-shaped hole by melt filling and solidification of the low melting point alloy.
According to a sixth aspect of the present invention, in the protective element according to any one of the first to fourth aspects, the lead fixed electrode tip and the movable electrode are in surface contact.
A protective element according to claim 7 is the protective element according to any one of claims 1 to 6, wherein the low melting point alloy is a lead-free alloy containing at least one of Sn and In.
A protective element according to an eighth aspect is the protective element according to any one of the first to seventh aspects, wherein the low melting point alloy is a lead-free alloy containing Bi.
The protective element according to claim 9 is the protective element according to any one of claims 1 to 7, wherein the low melting point alloy is a lead-free alloy containing Sb.
The protection element according to claim 10 is the protection element according to any one of claims 2 to 9, wherein the movable electrode and the resistor main body are accommodated in the case, and one lead conductor of each lead fixed electrode and the resistor is from the case. It is drawn out.
The protective element according to an eleventh aspect is the protective element according to any one of the first to tenth aspects, wherein the protective element is for direct current.
A protection element according to claim 12 is the protection element according to any one of claims 1 to 11, wherein the lead fixing electrode is made of copper, and at least a portion of the lead fixing electrode surface bonded to the low melting point alloy is bonded to the copper. It is characterized by providing a copper transition prevention film that prevents transition to a low melting point alloy.
A protection element according to claim 13 is the protection element according to claim 12, wherein the material of the movable electrode is copper or a copper alloy, and at least a portion of the surface of the movable electrode joined to the low melting point alloy is bonded to the low melting point alloy of copper. It is characterized by providing a copper transition prevention film that prevents the transition to.
According to a fourteenth aspect of the present invention, in the protective element according to the twelfth or thirteenth aspect, the copper migration prevention film is a film of at least one or more of Ni, Ni-P, Ni-B, Fe, Pd, and Pd-P. It is characterized by being.

(1) The location where the compression reaction force of the compression spring acts on the low melting point alloy is the low melting point alloy locations a and a that join each end of the movable electrode and each lead fixed electrode tip and the intermediate portion of the movable electrode. Compared to a conventional protection element in which the compression reaction force of the compression spring is applied to only two places a and a, which is a low melting point alloy part b that joins the guide shaft, two low melting point alloy parts a and a. The protective element according to the present invention in which the compression reaction force is applied to a total of three places, one place and one place b, can reduce the stress at the compression reaction force acting place of the low melting point alloy. Accordingly, creep of the low melting point alloy can be reduced, and proper operation of the protective element can be ensured.

(2) In the protective element according to the present invention, when using a Bi-based low-melting-point alloy or Sb-based low-melting-point alloy containing Bi or Sb as an alloy component for the low-melting-point alloy, Bi or Sb is deposited on the interface in contact with the electrode, and the deposited portion becomes brittle. However, the fracture at the brittle portion can be satisfactorily prevented by the stress reducing effect. Therefore, even if a Bi-based or Sb-based lead-free alloy is used for the low melting point alloy of the protective element according to the present invention and the protective element is used in a direct current system, reliable operation can be ensured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A is a longitudinal sectional view showing an embodiment of the protective element according to the present invention, and FIG. 1B is a cross-sectional view of FIG.
In FIG. 1, 1 is a heat-resistant insulating base, for example, a ceramic plate. Reference numerals 2a and 2b denote a pair of parallel lead fixing electrodes, which are inserted into the insulating base 1 and fixed to the base 1 with, for example, a heat-resistant adhesive. The lead fixing electrode can be made of, for example, copper. The cross-sectional shape of the lead fixing electrode can be square or circular, and is not particularly limited. Reference numeral 3 denotes a guide shaft, which can use either a metal or an insulator, and is arranged in parallel with the lead fixing electrodes 2a and 2b, and one end is fixed to the base 1 with an adhesive such as glass. 2c is a movable electrode, 4 is a coil spring, the movable electrode 2c is inserted through the guide shaft 3 (20 is a hole of the movable electrode 2c), and both ends of the movable electrode 2c are in contact with the tip surfaces of the lead fixed electrodes 2a and 2c. And the coil spring 4 is compressed, and in this state, the low melting point alloy 5a is formed between the leading end surfaces of the lead fixed electrodes 2a and 2b and the end portions of the movable electrode 2c and between the movable electrode 2c and the guide shaft 3. , 5c. As the low melting point alloy 5c, the same alloy as the low melting point alloy 5a may be used, or an alloy having a lower melting point than the low melting point alloy 5a may be used.
As shown in FIG. 1 (c), a stepped surface is provided on the tip surface of each lead fixed electrode, the tip side surface of the movable electrode is brought into contact with the vertical surface of the cross section, and the back surface of each movable electrode end is brought into contact with the flat surface of the cross section. The contact area is made as wide as possible, and the electrical contact resistance is made sufficiently low. A stopper 30 is provided at the tip of the guide shaft 3 and has a hook shape. An insulating case may be attached.

If the mechanical state in the above is simplified, the compression reaction force of the compression spring 4 as shown in FIG. 2 (a) [sectional view] and FIG. 2 (b) [top view with respect to FIG. 2 (a)]. Therefore, the shear stress F acts on the cross-section SS of the low melting point alloy portion 5a (5a) that joins each lead fixed electrode and the movable electrode, and the movable electrode and the guide shaft are joined together. A state in which the shear stress f acts on the interface s-s of the melting point alloy portion 5c can be achieved.
In FIG. 2, the area of the cross section SS is S, the area of the interface s-s is s, the compression reaction force of the compression spring 4 is T, and the thickness of the portion where the shearing force acts on the low melting point alloy portion 5c is t high. Where b is the low melting point alloy and the shear Young's modulus of the low melting point alloy is G,
2SF + sf = T
F / G = ft / G
Is established.
Since the area s of the interface s−s is s≈2πrb, where r is the radius of the guide shaft, the stress F is given by [Expression 1] F≈0.5 T / [S + (πrb) / (t) ]
Given in.

  In Equation 1, the radius r of the guide shaft contributes to the reduction of the stress F because the movable electrode 2c and the guide shaft 3 are joined by the low melting point alloy 5c, and the lead fixed electrode 2a or 2b and the movable electrode Since the shear stress F acting on the low melting point alloy spot SS joining 2c can be reduced by increasing the radius r, the creep at the low melting point alloy spot SS can be well prevented. The electrical contact state between 2a, 2b and the movable electrode 2c can be stably maintained.

As shown in FIG. 3, the movable electrode and the fixed lead electrode are joined with a low melting point alloy by providing a mortar-shaped hole 200 in the movable electrode, and receiving the tip of the fixed lead electrode 2a (2b) in the hole 200, Subsequently, the low melting point alloy 5a can be melt filled and solidified into the mortar-shaped hole 200.
According to this configuration, it is possible to suppress the variation in the bonding area and to stabilize the bonding due to the wedge-fastening effect on the mortar-shaped hole of the low melting point alloy.

For the low melting point alloy, it is preferable to use a lead-free alloy for environmental protection.
In this lead-free alloy, when a Bi-based low melting point alloy or an Sb-based low melting point alloy is used as the low melting point alloy of the protective element, Bi or Sb is deposited at the interface in contact with the cathode side electrode when the protective element is used with a direct current. Phenomenon occurs. The reason why Bi and Sb are precipitated can be estimated as follows.
Low melting point alloys include eutectic type alloys, solid solution type alloys, and intermetallic compound type alloys. From a microscopic viewpoint, these two types of metal atoms are mixed to create a crystal lattice with a new atomic arrangement. It can be said that the ionized atoms at the lattice points are in an equilibrium state. However, Bi atoms and Sb atoms are likely to jump out of the equilibrium position, and are given energy by the applied voltage, jump out of the lattice points, dislodge in the crystal lattice as a dislocation atom, and in the case of direct current, the dislocation atom is a cathode. Moves to the side and deposits at the cathode interface. In the vacancies where the dislocation atoms jumped out, as if a certain seat was vacant in the full seat, the passengers next to the vacant seat moved one by one and moved to fill the new vacant seat. Then, it reaches the surface of the crystal, and vacancies coalesce on the surface.

An example of the deposition of Bi metal or Sb metal is as follows.
[Example 1]
A copper lead conductor with a diameter of 1 mmφ was welded to both ends of a 57 wt% Bi-remainder Sn, 1 mmφ diameter, 5 mm length low melting point alloy piece, and a 15 ampere direct current was applied for 5000 hours. A Bi metal layer having a thickness of 200 μm was deposited in contact therewith.
[Example 2]
A copper lead conductor with a diameter of 2 mmφ was welded to both ends of a 5 wt% Sb-remainder Sn, a diameter of 2 mmφ, and a length of 7 mm, and a 30 VDC current was applied for 5000 hours. A Sb metal layer having a thickness of 50 μm was deposited.

In the protective element according to the present invention, when a Bi-based low-melting-point alloy or an Sb-based low-melting-point alloy is used as the low-melting-point alloy, In the protective element according to the present invention, the stress acting on the interface can be well reduced based on the reaction force of the compression spring. The proper operation of the protection element can be ensured by eliminating the above.
In the protective element according to the present invention, even if the Bi-based low-melting-point alloy or the Sb-based low-melting-point alloy is used as the low-melting-point alloy and used under direct current, the electrical contact area between the movable electrode and the lead fixed electrode is If the step contact is made wider, the bypass current to the low melting point alloy side can be reduced accordingly, so that the precipitation of Bi metal or Sb metal can be well suppressed.

4A is a cross-sectional view showing an embodiment of a protection element with resistance according to the present invention, and FIG. 4A is a cross-sectional view of FIG. 4A. is there.
In FIG. 4-1, 1 is a heat-resistant insulating base, for example, a phenol resin plate. Reference numerals 2a and 2b denote a pair of parallel lead fixing electrodes which are inserted into the insulating base 1 and fixed to the base 1 by, for example, integral molding. The lead fixing electrode can be made of copper. The cross-sectional shape of the lead fixing electrode can be square or circular, and is not particularly limited. Reference numeral 300 denotes a wire-wound resistor. Caps 301 with lead conductors are attached to both ends of a heat-resistant insulating core 302, for example, a ceramic score, and a resistance wire 303 is wound around the core 302. It is joined by welding or the like, and is arranged in parallel between the lead fixed electrode portions 2a and 2b on the base 1, and one lead conductor 3 is used as a guide shaft. The other lead conductor 3 ′ is drawn from the base 1 and fixed to the base 1 with an adhesive, for example, glass. Reference numeral 6 denotes a spacer interposed as required. Reference numeral 2 c denotes a movable electrode, which is inserted through one lead conductor 3. Reference numeral 4 denotes a coil spring. For example, a stainless steel spring can be used, and is inserted into one lead conductor 3 between the movable electrode and the resistor body, and both end portions of the movable electrode 2c and the leading end surfaces of the lead fixed electrodes 2a and 2b ( And the lead conductor 3 and the movable electrode 2c are joined together by the low melting point alloy 5c so that the coil spring 4 is in a compressed state.
Reference numeral 7 denotes an insulator case, and one lead conductor 3 is terminated in contact with the inner surface of the case. Reference numeral 8 denotes a mold body such as an insulating sleeve such as ceramics or a heat-resistant insulating paint provided as necessary. The mold body occupies the periphery of the resistor body without filling the coil spring 4. The case 7 can be omitted when an insulating sleeve or a mold body is provided. In this case, it is necessary to provide a stopper at the tip of one lead conductor 3 of the resistor 300.

In this protective element with resistance, similarly to the protective element described above, the low melting point alloys 5a and 5c can be melted by overheating of the protected device to cut off the power supply to the protected device.
In another use mode, the lead fixing electrodes 2a and 2b are connected to the power supply path of the protected device, and the resistor is energized between the other lead conductor 3 ′ of the resistor and the one lead fixing electrode 2a or 2b. In this case, the resistor energization heat generation circuit is normally turned off. When an abnormality occurs in the protected device, the sensor detects the abnormality and the resistor energization heat generation circuit is turned on. The resistor body generates heat, the low melting point alloys 5a and 5c are melted, the compression spring 4 is released, the movable electrode 2c is isolated from between the lead fixed electrodes 2a and 2b, and the power supply to the protected device is cut off. . In this case, since the heat transfer distance from the resistor main body to each of the low melting point alloys 5c, 5a, 5a is short, and the temperature rise rate of the resistor main body can be increased rapidly due to the heat dissipation suppression effect by the insulating sleeve 8, the operating speed Can be faster.

In the protection element shown in FIG. 4A, the resistor energization heating circuit including the lead fixed electrode 2a or 2b → the movable electrode 2c → the lead conductor 3 → the resistor body 300 → the lead conductor 3 ′ The resistor main body 300 is energized to generate heat and the generated heat melts the low melting point soluble materials 5a and 5b to cut off the lead fixed electrodes 2a and 2b. Accordingly, the specific resistance value of the spring 4, for example, the stainless spring 4 is not so high as the specific resistance value of the lead conductor 3, and the lead is heated after the resistor energization heating circuit is turned on until the low melting point soluble material is melted. Current flows through the path of the fixed electrode 2a or 2b → movable electrode 2c → spring 4 → resistor cap electrode 301 → resistor body 300, the spring 4 generates heat, and the spring characteristics are deteriorated, thereby hindering the operation of the protection element. There is drowning.
Therefore, as shown in FIG. 4B, it is preferable to interpose insulating spacers 901 and 902 between the spring 4 and the movable electrode 2c or between the spring 4 and the resistor cap electrode 301. Both of these insulating spacers 901 and 902 can be interposed. Further, instead of the insulating spacer 902, the resistor cap electrode 301 can be coated with an insulating film.
Further, since the upper end inner periphery and the lower end inner periphery of the spring 4 may come into contact with the lead conductor 3 due to the inclination of the spring 4, current may be bypassed to the spring 4. It is preferable to interpose an insulating cylinder 903.

Also in the protective element with resistance shown in FIGS. 4-1 and 4-2, the compression reaction force of the compression spring 4 is applied to a portion other than the joint portion by the low melting point alloy 5a between the movable electrode 2c and the lead fixed electrode 2a (2b). In addition, since the low melting point alloy 5c between the movable electrode 2c and the one lead conductor 3 of the resistor is supported at the joints, the stress acting on each joint can be reduced, and the creep of the low melting point alloy can be reduced. It can prevent well.
In addition, when a low melting point alloy is a Bi-based low melting point alloy or an Sb-based low melting point alloy and is used under a direct current, the stress reduction can be achieved even if the low melting point alloy is embrittled due to Bi metal or Sb metal precipitation. Therefore, breakage of the low melting point alloy can be prevented well.
Furthermore, unlike an alloy-type thermal fuse that operates by melting the spheroid of the molten alloy by melting the fuse element and backing up the flux, it is not always necessary to attach the flux to the low melting point alloy. The problem of carbonization can be avoided, arc damage can be prevented, and sufficient voltage resistance after the interruption operation can be ensured, which is suitable for large current interruption. However, from the viewpoint of surface protection for moisture resistance and the like, flux or wax can be present to such an extent that the above-mentioned voltage resistance does not become a problem.

FIG. 5A is a cross-sectional view showing another embodiment of the protective element with resistance according to the present invention.
In FIG. 5A, reference numeral 1 denotes a heat-resistant insulating base such as a polyphenylene sulfide plate. Reference numerals 2a and 2b denote a pair of parallel lead fixing electrodes which are inserted through the insulating base 1 and fixed to the base 1 by, for example, a press-fitting method. Copper can be used for the lead fixing electrode. The cross-sectional shape of the lead fixing electrode can be square or circular, and is not particularly limited. Reference numeral 300 denotes a wire-wound resistor. Caps with lead conductors are attached to both ends of a heat-resistant insulating core such as a ceramic score, resistance wires are wound around the core, and each end of the winding is bonded to each cap by welding or the like. Thus, one lead conductor 3 is arranged on the base 1 and is fixed to the base with an adhesive such as glass 1 perpendicular to the base 1 and used as a guide shaft. Reference numeral 2c denotes a movable electrode, which is inserted into one lead conductor 3, and both ends of the movable electrode 2c and the lead fixed electrodes 2a and 2b are joined by low melting point alloys 5a and 5a, and the movable electrode 2c and one of the movable electrodes 2c are connected to each other. The lead conductor 2a or 2b is joined by a low melting point alloy 5c. In joining the movable electrode 2c and the lead fixed electrode 2a (2b) with the low melting point alloy 5a, a mortar-shaped hole 200 is provided in the movable electrode 2c, and the tip of the lead fixed electrode 2a (2b) is received in the hole 200. Then, the low melting point alloy 5a is melt-filled and solidified in the mortar-shaped hole. A coil spring 4 is inserted into one lead conductor 3 and is pressed and compressed by the movable electrode 2c. Reference numeral 7 denotes a case from which the other lead conductor 3 'of the resistor is drawn.

In this protective element with resistance, similarly to the protective element described above, the low melting point alloy can be melted by overheating of the protected device to cut off the power supply to the protected device. In another use mode, the lead fixing electrodes 2a and 2b are connected to the power supply path of the protected device, and a resistor is provided between the other lead conductor 3 'of the resistor 300 and the one lead fixing electrode 2a or 2b. In this case, the resistor energization heat generation circuit is normally turned off. When an abnormality occurs in the protected device, the sensor detects the abnormality and the resistor energization heat generation circuit is turned on. The resistor body generates heat, the low melting point alloys 5a, 5a, 5c are melted, the compression spring 4 is released, and the movable electrode 2c is isolated from between the lead fixed electrodes 2a, 2b as shown in FIG. As a result, the power supply to the protected device is cut off. Also in this case, the melting points of the low melting point alloys 5a and 5b can be set so that the low melting point alloys 5a, 5a and 5c are melted by overheating of the protected device and the power supply to the protected device is interrupted.
In the protection element with resistance shown in FIG. 5 as well, the compression reaction force of the compression spring is applied between the movable electrode and one lead conductor of the resistor other than the joint portion of the low melting point alloy between the movable electrode and the lead fixed electrode. Therefore, the stress acting on each of the joining points can be reduced, and the creep of the low melting point alloy can be satisfactorily prevented.
Further, a mortar-shaped hole 200 is provided in the movable electrode 2c, and the tip of the lead fixed electrode 2a (2b) is received in the hole 200, and then the low-melting point alloy 5a is melt-filled and solidified in the mortar-shaped hole. 2c and the lead fixing electrodes 2a and 2b are joined by the low melting point alloy 5a, so that the variation in the joining area can be suppressed and the stabilization of the joining by the wedge-fastening effect on the mortar-shaped hole 200 of the low melting point alloy 5a is achieved. I can expect.
Furthermore, unlike an alloy-type thermal fuse that operates by melting the spheroid of the molten alloy by melting the fuse element and backing up the flux, it is not always necessary to attach the flux to the low melting point alloy. The problem of carbonization can be avoided, arc damage can be prevented, and sufficient voltage resistance after the interruption operation can be ensured, which is suitable for large current interruption. However, from the viewpoint of surface protection for moisture resistance and the like, flux or wax can be present to such an extent that the above-mentioned voltage resistance does not become a problem.

The lead fixing electrodes 2a and 2b are made of copper, and can be coated with Sn or an alloy based on Sn for preventing oxidation of the surface.
In this copper lead fixed electrode, there is a possibility that copper diffuses and migrates to the low melting point alloy 5a at the bonding interface with the low melting point alloy 5a, the mechanical strength of the low melting point alloy 5a is lowered, and the melting temperature is fluctuated. Therefore, a portion of the lead fixing electrodes 2a, 2b to be bonded to at least the low melting point alloy 5a, preferably a copper migration blocking film such as Ni, Ni-P, Ni-B, Fe on the entire surface of the lead fixing electrodes 2a, 2b. , Pd, and Pd—P can be provided between at least one of the films and the Sn or Sn-based alloy coating layer.
The material of the movable electrode 2c can be copper or a copper alloy such as brass, and can be coated with an alloy based on Sn or Sn to prevent oxidation of the surface. In order to prevent copper from diffusing and transferring from the copper alloy movable electrode 2c to the low melting point alloy 5a for joining the movable electrode 2c and the lead fixed electrodes 2a and 2b, the movable electrode 2c is joined to at least the low melting point alloy 5a. At least one layer of Ni, Ni-P, Ni-B, Fe, Pd, and Pd-P is provided between the Sn and Sn-based alloy coating layer. Can do. Furthermore, a copper migration blocking film can also be provided at a portion of the movable electrode 2c that is joined to the low melting point alloy 5c. It is preferable to provide a copper migration blocking film on the entire surface of the movable electrode 2c.
The lead conductor 3 of the guide shaft or the resistor is a composite wire in which a copper layer is coated on a copper wire or a copper alloy wire, a nickel wire, an iron wire, or a steel wire in balance with the resistance value of the resistor (in either case, (It is possible to coat Sn or an alloy based on Sn to prevent oxidation of the surface), and at least the portion bonded to the low melting point alloy 5c, preferably the copper transfer to the entire surface of the lead conductor A blocking film, for example, at least one film of Ni, Ni-P, Ni-B, Fe, Pd, and Pd-P may be provided between the Sn or Sn-based alloy coating layer.
By providing these intermediate layers, the strength of the lead fixing electrode is increased, and there is an advantage that the fatigue resistance is improved. There is also an advantage that Sn whisker growth can be suppressed from Sn or an alloy based on Sn.

The protective element with resistance can be used for protection against overheating and overcharge / overdischarge of a secondary battery such as a lithium ion battery, and FIG. 6 shows an example of the protection circuit.
In FIG. 6, E is a secondary battery, S is a charging power source (or load), A is an overcharge prevention FET, B is an overdischarge prevention switch FET, and C is a protective element with a resistor according to the present invention. is there. D is an IC control unit that detects overcharge when a secondary battery is charged and generates an overcharge prevention signal to switch off the overcharge prevention switch FET (detects overdischarge of the secondary battery during load). Then, an overdischarge prevention signal is generated to switch off the overdischarge prevention switch FET). When these FETs cannot cope, an ON signal is sent from the IC control unit to the transistor Tr, and the resistor body of the protective element C with a resistor is energized and heated using the secondary battery as a power source due to the conduction of the transistor Tr. The molten alloys 5a and 5c are melted, and the secondary battery E and the charging power source S are disconnected during charging (the secondary battery E and the load S are disconnected during loading).
The protective element with a resistor is attached to the secondary battery with a low thermal contact resistance. Even if the secondary battery is abnormally heated, the fusible alloys 5a and 5c are melted between the secondary battery E and the charging power source S or two. The secondary battery E is disconnected from the load.

1 is a view showing an embodiment of a protection element according to the present invention. It is drawing which shows the stress state in the protection element shown in FIG. It is drawing which shows an example of the joining structure by the low melting-point alloy of the lead fixed electrode and movable electrode in the protection element which concerns on this invention. It is drawing which shows one Example of the protection element with a resistor which concerns on this invention. It is drawing which shows the principal part of another Example different from the above of the protection element with a resistor which concerns on this invention. It is drawing which shows another Example different from the above of the protection element with a resistor which concerns on this invention. 1 is a diagram illustrating a secondary battery protection circuit using a protection element with a resistor according to the present invention. It is drawing which shows a prior art example.

Explanation of symbols

1 base 2a lead fixed electrode 2b lead fixed electrode 2c movable electrode 3 guide shaft 4 compression spring 5a low melting point alloy 5c low melting point alloy 200 mortar-shaped hole 300 resistor 3 'other lead conductor of resistor 7 case 8 insulating heat resistant paint

Claims (14)

A pair of lead fixed electrodes, a guide shaft is juxtaposed with these lead fixed electrodes, and a movable electrode is inserted between the lead fixed electrodes in a state of being inserted through the guide shaft. A compression spring is provided between the tip and the movable electrode and between the guide shaft and the movable electrode by a low melting point alloy, and a compression spring is provided to apply a force in a direction to isolate the movable electrode from the lead fixed electrode. A protective element, wherein the movable electrode is urged by a compression spring when the melting point alloy melts and is isolated from the lead fixed electrode. 2. The protection element according to claim 1, wherein one lead conductor of a resistor having lead conductors attached to both ends of the resistor body is used as a guide shaft, a coil spring is used as a compression spring, and the coil spring is a resistor body. A protective element, wherein a resistor energizing heat generation circuit is connected between one lead conductor of the resistor and either one of the lead fixed electrodes. . 2. The protection element according to claim 1, wherein one lead conductor of a resistor having lead conductors attached to both ends of the resistor body is used as a guide shaft, a coil spring is used as a compression spring, and the coil spring is the one of the ones. A protective element which is inserted into a lead conductor while being pressed by the movable electrode, and a resistor energization heating circuit is connected between the other lead conductor of the resistor and either of the two lead fixing electrodes. An insulator is interposed between the movable electrode and one end of the compression coil spring, or at least one of the other end of the compression coil spring and the resistor main body end, and is separated from the inside of the compression coil spring and the guide shaft. The protection element according to claim 3, wherein an insulator is interposed. The movable electrode is provided with a mortar-shaped hole that accepts the tip of each lead fixed electrode, and the tip of each lead-fixed electrode and the movable electrode are joined by a low-melting alloy to the mortar-shaped hole. The protective element according to claim 1, wherein the protective element is formed by: The protective element according to any one of claims 1 to 4, wherein each lead fixed electrode tip and the movable electrode are in surface contact. The protective element according to any one of claims 1 to 6, wherein the low melting point alloy is a lead-free alloy containing at least one of Sn and In. The protective element according to claim 1, wherein the low melting point alloy is a lead-free alloy containing Bi. The protective element according to claim 1, wherein the low melting point alloy is a lead-free alloy containing Sb. The protective element according to claim 2, wherein the movable electrode and the resistor main body are accommodated in a case, and one lead conductor of each lead fixed electrode and the resistor is drawn out from the case. The protective element according to claim 1, wherein the protective element is for direct current. The lead fixed electrode is made of copper, and at least a portion of the surface of the lead fixed electrode joined to the low melting point alloy is provided with a copper transition blocking film that prevents the transition of the copper to the low melting point alloy. The protective element according to claim 1. The material of the movable electrode is copper or a copper alloy, and at least a portion of the surface of the movable electrode to be joined to the low melting point alloy is provided with a copper transition prevention film that prevents the transition of the copper to the low melting point alloy. The protective element according to claim 12. The protection element according to claim 12 or 13, wherein the copper migration blocking film is a film of at least one layer of Ni, Ni-P, Ni-B, Fe, Pd, and Pd-P.

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