JP2010140709A - Low-melting alloy element with lead conductor for thermal fuse, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a property of a parting operation of a thermal fuse by decreasing an oxide content as coming closer to a side welded to a lead conductor end of a thermal fuse element as compared to the center, and by varying a distribution of content density even when the oxide content of the whole thermal fuse remains unchanged. <P>SOLUTION: The low-melting alloy element 2 is welded between the ends of a pair of lead conductors 1, and the oxide content of the low-melting alloy element is decreased as reaching the end side of the lead conductor and is increased as reaching the center of the low-melting alloy element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a low-melting-point alloy element with a lead conductor for a thermal fuse and a manufacturing method thereof.

In order to manufacture an alloy type thermal fuse used for overheating protection of a secondary battery, for example, a lithium ion battery, a low melting point alloy element processed by drawing or roll rolling is welded between both lead conductors, and this low melting point alloy A flux is applied to the element, and the flux-coated low melting point alloy element is sealed with a heat-resistant insulator.
Recently, in view of environmental sanitation, lead-free low melting point alloy elements are required, and many low melting point alloy elements having a lead-free composition have been developed.
Some of these lead-free compositions are difficult to process such as drawing and rolling, and it is known to produce a low melting point alloy element by casting (for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-225754

In low-melting-point alloys, the formation of oxides is unavoidable, and it cannot be denied that the oxides hinder the operation of dividing the thermal fuse element.
The operating mechanism of the alloy-type thermal fuse is that the low-melting-point alloy element is melted by overheating of the protected device to which the thermal fuse is attached, and the molten alloy is divided by the wetness of the molten alloy to the lead conductor. Oxides in the alloy inhibit the wetting of the lead conductor. In particular, the fusible alloy part at the end of the low melting point alloy element welded to the lead conductor is involved in the wetting with a large weight. This greatly reduces the temperature dividing operation of the thermal fuse.

  Therefore, the oxide content is substantially the same in the lead conductor side portion and the central side portion, both in the thermal fuse element manufactured by the casting and the thermal fuse element processed by wire drawing or roll rolling. There is room for improving the operational performance of thermal fuses from the viewpoint of the distribution of oxide content.

  The object of the present invention is to reduce the oxide content to the side welded to the end of the lead conductor of the thermal fuse element from the center side, and even if the oxide content of the entire thermal fuse does not change, the content density distribution Is to improve the breaking operation characteristics of the thermal fuse.

According to a first aspect of the present invention, there is provided a method for producing a low-melting-point alloy element with a lead conductor for a thermal fuse, wherein a pair of lead conductors are arranged on a workbench with a predetermined gap interval, and the gap and the ends of both lead conductors are extended. The molten metal of the low melting point alloy is supplied, and the molten metal is cooled at a faster speed toward the end of the lead conductor and solidified by cooling at a slower speed toward the center of the gap while surface tension is applied with the surface of the molten metal open. It is characterized by welding between the end portion of the lead conductor and the solidified alloy.
The low melting point alloy element with a lead conductor for a thermal fuse according to claim 2 has the low melting point alloy element welded between the end portions of the pair of lead conductors, and the oxide content of the low melting point alloy element is on the lead conductor end side. It is characterized by being made so low that it reaches the center of the low melting point alloy element.
A low melting point alloy element with a lead conductor for a thermal fuse according to claim 3 is the low melting point alloy element with a lead conductor for a thermal fuse according to claim 2, wherein one of the low melting point alloy elements is provided between the leading ends of the opposing lead conductors. It is characterized in that the part has entered.

(1) In claim 1, the molten metal of the low-melting point alloy for the thermal fuse element is solidified at a faster cooling rate as it reaches the end portion of the lead conductor while acting the surface tension with the surface open, and reaches the central portion of the molten metal. Since the tangent angle on the surface of the molten metal becomes smaller, the surface tension acting on the molten metal increases as it reaches the center of the molten metal, and oxides that tend to float on the molten metal surface gather in the middle of the molten metal. Since the speed is slow, the density of the grain boundary increases toward the center, and the floating oxide, which becomes denser toward the center, is trapped in the high density grain boundary. The oxide density decreases from the center of the element to the welded portion with the end of the lead conductor.
(2) In claim 2, since the oxide-containing density of the low-melting-point alloy element decreases from the center to the end of the low-melting-point alloy element, the low-melting-point alloy at the initial stage of spheroidization of the low-melting-point alloy element It is possible to effectively generate the wetting of the end of the element to the lead conductor, and to ensure the quick cutting operation of the thermal fuse.
(3) The thermal expansion force of the low-melting-point alloy element generated during the heat cycle of the alloy-type thermal fuse is also the contact surface between the low-melting-point alloy element part and the leading end of the lead conductor that have entered between the leading ends of the opposing lead conductors. Since it is supported, the reaction force acting on the welded portion between the low melting point alloy element and the lead conductor tip is reduced with respect to the thermal expansion force. Accordingly, it is possible to improve the heat cycle stability of the welded portion between the low melting point alloy element and the lead conductor tip, and from this point, it is possible to guarantee a good cutting operation of the thermal fuse.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a view showing a low melting point alloy element with a lead conductor for a thermal fuse according to the present invention.
In FIG. 1, reference numerals 1 and 1 denote strip-shaped lead conductors, which can be nickel conductors, copper conductors, or the like. The surface of the nickel conductor can be plated or clad with Sn, Au, Cu, Ag or the like, and the copper conductor can be coated with Ni as a copper migration blocking film in addition to the entire surface or a portion where the low melting point alloy element is welded. It can be plated or clad, and Sn, Au, Cu, Ag, etc. can be plated on Ni.
Reference numeral 2 denotes a low melting point alloy element, and the upper surface is a curved surface with a tangent angle increasing toward both ends, and a part 20 of the intermediate portion faces the leading end surfaces 11 and 11 of the opposing lead conductors as shown in FIG. The both end portions 21 and 21 are welded to the upper surfaces of the respective strip-like lead conductor end portions 10 and 10.
The volume of the low-melting-point alloy element entering between the leading ends of the opposing lead conductors is 10 to 20% of the total volume of the low-melting-point alloy element. As shown in FIG. 2B, the lower surface of the entering portion 20 and the lower surfaces of the strip-shaped lead conductors 1 and 1 can be substantially flush with each other. In FIGS. 2A and 2B, m indicates the above-described plating film or cladding layer.

In order to manufacture the element with a lead conductor for a thermal fuse according to the present invention, as shown in FIG. 3, a lead conductor base material is formed on a worktable A having heat resistance and releasability from a molten alloy, for example, a stainless steel base. 100 and 100 (with the above-mentioned plating or cladding) are arranged at a predetermined gap interval and melted with a soldering iron while supplying a low-melting-point alloy wire between the base materials 100 and 100, or low melting By supplying the alloy with the traveling nozzle, the molten metal 200 of the low melting point alloy is supplied across the gap and the end portion of the lead conductor base material.
The molten metal 200 is cooled by heat radiation through the high heat conduction path of the lead conductor base materials 100 and 100 simultaneously with the supply, and the portion closer to the end portion of the lead conductor base material is cooled at a faster cooling rate and solidification proceeds.

In this process of cooling and solidification, the surface tangent angle decreases toward the center of the melt surface, so the surface tension of the melt surface increases toward the center, and the oxide floating on the surface of the melt moves toward the center. . In addition, since the cooling rate is slower toward the center, the grain boundary density increases toward the center and the density of oxide traps increases, so that the oxide concentrated in the center is high in the center. The oxide-containing density increases as it is trapped by the crystal grain boundary and reaches the center of the solidified low melting point alloy, and the oxide-containing density decreases toward the end of the lead conductor.
Thus, the solidification of the supplied low melting point alloy melt was completed and cut into a strip shape. “The low melting point alloy element was welded between the ends of the pair of lead conductors, and the oxide content of the low melting point alloy element was reduced. A low-melting-point alloy element with a lead conductor for a thermal fuse that is lowered toward the end portion of the lead conductor and raised toward the center of the low-melting-point alloy element can be obtained.

  As the material of the low melting point alloy molten metal, elements such as Cu, Ag, Sb, Zn are used for improving mechanical strength and adjusting temperature characteristics in the In-Bi system, Sn-In-Bi system, and these alloy systems. What added 0.1-4.0 mass% can be used.

  In order to adjust the cooling rate by heat dissipation by obtaining the heat conduction path of the lead conductor base material, the back side of the gap is kept warm, the lead conductor base material is air blown, or the lead conductor base material is a heat conductive member. Or can be supported.

In the element with the lead conductor for thermal fuse obtained by the manufacturing method, as shown in FIG. 1, a part 20 of the low melting point alloy element is inserted between the leading end faces 11 and 11 of the opposing lead conductor.
In order to manufacture an alloy-type thermal fuse using this element with a lead conductor for thermal fuse, a flux is applied to the upper surface side of the low melting point alloy element 2 as shown by reference numeral 31 as shown in FIG. The melting point alloy element is applied to the lower surface of the entry portion 20 of the melting point alloy element and the lower surface portion of the strip-shaped lead conductor that is present on the lower surface as indicated by reference numeral 32.
The upper flux 31 is applied so as to cover 70% or more of the low melting point alloy element portion welded to the upper surface of the end portion of the strip-shaped lead conductor, and can also reach the upper surface of the strip-shaped lead conductor. The coating thickness of the upper surface side flux 31 is preferably 70 to 100% of the average thickness of the low melting point alloy element portion welded to the upper surface of the end portion of the strip-shaped lead conductor.
The coating thickness of the lower flux 32 is the thickness of the lower surface insulator (lower film and lower adhesive) in order to ensure heat transfer (temperature sensitivity) from the lower surface side of the thermal fuse body to the low melting point alloy element. The total thickness is preferably 50% or less.
As the flux, a rosin-based component and an activator such as a dicarboxylic acid (for example, fumaric acid, maleic acid, or oxalic acid) can be used.

4A is a perspective view of a thermal fuse using a low melting point alloy element with a lead conductor for the thermal fuse according to the present invention, and FIG. 4-2 is a sectional view taken along the line II in FIG. .
In FIGS. 4A and 4B, 1 and 1 are strip-shaped lead conductors, and 2 is a low-melting point alloy element. As described above, an intermediate portion of the low-melting point alloy element is located in the space between the leading ends of the opposing lead conductors. The flux is applied not only to the upper surface of the low melting point alloy element but also to the entering surface of the low melting point alloy element and the lead conductor portion facing the surface.
4 and 4 are heat-resistant films for upper and lower films, and 5 is an adhesive that fills the space between the upper and lower films 4 and 4. The upper flux 31, the exposed surface of the low melting point alloy element 2 with respect to the upper flux 31, and the lower flux 32 are bonded. It is in contact with the agent.

The thermal fuse according to the present invention is manufactured by (1) placing a flux-coated low-melting-point alloy element with a lead conductor on the lower heat-resistant film on the workbench, and applying the adhesive force of the lower-coated flux to the placement position. Secure the fixed state, then place the uncured adhesive-coated heat-resistant film on the lower heat-resistant film with the adhesive side down, and hold the upper heat-resistant film on the upper side with a jig. (2) An uncured adhesive-coated heat-resistant film is placed on the workbench with the adhesive side facing up, and a flux-coated low-melting-point alloy element connection lead conductor is placed on the lower heat-resistant film. The adhesive strength of the uncured adhesive ensures the fixed state at the position, and then the uncured adhesive-coated heat-resistant film is disposed on the lower heat-resistant film with the adhesive surface facing downward. Disposed heat-resistant film of the upper can be conducted by a method of curing the adhesive in a state of pressing by a jig.
As the upper and lower heat-resistant films, engineering plastic films such as PET, PC, and PEN, glass cloth base epoxy resin films, and the like can be used. It is also possible to use a single sheet that is used.
As the adhesive, epoxy resin, ultraviolet curable resin, silicon resin, or the like can be used.

In the alloy-type thermal fuse using the element with the lead conductor for the thermal fuse according to the present invention, the low-melting-point alloy in which the thermal expansion force of the low-melting-point alloy element generated during the heat cycle enters between the tips of the opposing lead conductors Since the contact surface between the element portion and the leading end of the lead conductor is also supported, the reaction force acting on the welded portion between the low melting point alloy element and the leading end of the lead conductor is reduced against the thermal expansion force. Therefore, the heat cycle stability of the welded portion between the low melting point alloy element and the lead conductor tip can be improved.
In addition, since the thickness of the low heat transfer material (flux) can be reduced by the penetration depth of the low melting point alloy element with respect to the heat transfer from the lower surface side of the thermal fuse body, the heat sensitivity from the lower surface side can be increased accordingly.

  FIG. 5 shows the cutting operation state of the low melting point alloy element of the alloy type thermal fuse according to the present invention, in which the low melting point alloy element and the flux are accommodated in the cavity 50 secured by the hardened adhesive without any empty space. The low melting point alloy element is divided in a state where there is no gap, and the molten flux 30 bites between the divided souls 200, 200, and the distance between the divisions is increased. Accordingly, the flux is applied to the lower surface of the portion where the low melting point alloy element enters between the leading ends of the opposing lead conductors and the lower surface of the leading end portion of the lead conductor existing on the lower surface, thereby increasing the volume of the cavity 50. Therefore, the distance between the splits can be increased, the insulation distance between the splits can be sufficiently secured, and reliable current interruption can be guaranteed.

It is a perspective view which shows the low melting-point alloy element with a lead conductor which concerns on this invention. It is drawing which shows the penetration part of the low melting-point alloy element with a lead conductor based on this invention. It is drawing which shows another example of the said penetration part. It is drawing which shows the manufacturing method of the low melting-point alloy element with a lead conductor based on this invention. It is a perspective view which shows the alloy type | mold thermal fuse which uses the low melting-point alloy element with a lead conductor based on this invention. FIG. 4 is a cross-sectional view taken along the line II in FIG. 4-1. It is drawing which shows the cutting | disconnection operation state of the alloy type thermal fuse using the low melting-point alloy element with a lead conductor based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lead conductor 100 Lead conductor base material 2 Low melting-point alloy element 20 Entering part 200 Molten metal

Claims (3)

A pair of lead conductors are arranged on the workbench with a predetermined gap interval, and a molten metal of a low melting point alloy is supplied across the gap and the ends of both lead conductors, and surface tension is applied with the molten metal surface open. The molten metal is cooled at a higher speed toward the end of the lead conductor and solidified at a lower speed toward the center of the gap, and is welded between the end of each lead conductor and the solidified alloy. Manufacturing method of low melting point alloy element with lead conductor for thermal fuse. A low melting point alloy element is welded between the ends of a pair of lead conductors, and the oxide content of the low melting point alloy element decreases as it reaches the end of the lead conductor and increases as it reaches the center of the low melting point alloy element. A low-melting-point alloy element with a lead conductor for a thermal fuse. 3. A low-melting-point alloy element with a lead conductor for a thermal fuse according to claim 2, wherein a part of the low-melting-point alloy element is inserted between the leading ends of the opposing lead conductors.

Images