JP2002025403A - Temperature fuse and wire material for temperature fuse element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature fuse, which can secure meltdown temperature from 135 deg.C or higher to 130 deg.C or less lower, and a wire material for a temperature fuse element suitable for manufacturing of this temperature fuse. SOLUTION: The temperature fuse is a temperature fuse, having a fuse element melting at a given temperature, and the fuse element is formed from a fusible alloy, consisting of silver of 0.1 weight% or more and 1.5 weight% or less, tin of 35 weight% or more and 50 weight% or less and the rest of bismuth. Furthermore, a wire material for the temperature fuse element is also formed from a fusible alloy of similar composition. That is to say, by adjusting the silver content in the fusible alloy, a temperature fuse and wire material are provided with superior fusion temperature characteristics and with moderate strength and ductility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal fuse and a wire for a thermal fuse element, and more particularly, to a thermal fuse and a thermal fuse element wire having a thermal fuse element formed of a lead-free fusible alloy that melts at a predetermined temperature. .

[0002]

2. Description of the Related Art There are two types of fuses: an electric fuse that is blown when an overcurrent flows through an electric circuit to protect the circuit, and a thermal fuse that is blown and protected when the temperature around the electric circuit rises. Electric fuses are used in TVs, washing machines, etc.
Thermal fuses are used in mobile phones, notebook computers, etc.
Each is incorporated and has a role of protecting these electrical products. Above all, the thermal fuse must be blown reliably and quickly at the set fusing temperature to protect the electric circuit. For this reason, the thermal fuse is required to be blown with high accuracy under various temperature conditions. Recent electronic components such as semiconductors often have low heat resistance.
Many of them break at temperatures around 35 ° C to 145 ° C. For this reason, a thermal fuse that is accurately and quickly blown in a temperature range of about 135 ° C. to 145 ° C. is required.

Here, the melting temperature of the fuse depends on the melting point (liquidus temperature) of the fusible alloy constituting the fuse element in the thermal fuse, and the melting point depends on the component metals of the alloy and the compounding ratio thereof, that is, the composition. Decided. Therefore, the choice of alloy composition is extremely important.

Conventionally, as a fusible alloy for a thermal fuse having a melting point of 135 ° C. to 145 ° C., an alloy containing lead as a kind of raw material metal (hereinafter referred to as a lead alloy) has been used exclusively.

[0005]

However, when electric appliances are discarded in recent years, there is a problem that lead elutes from the thermal fuse incorporated therein into the natural environment. When humans take in the lead eluted into the environment, they become poisoned, and depending on the amount of intake, toxic symptoms such as fatigue, lack of sleep, constipation, trembling, abdominal pain, anemia, neuritis, and cerebral degeneration appear. Therefore, in order to prevent environmental pollution due to lead, it is required worldwide not to use lead as an industrial material as much as possible, and studying industrial materials to replace lead is one of the important issues in the industry. I have.

Accordingly, as a result of intensive studies on a fusible alloy for forming a lead-free thermal fuse and a wire for a fuse element, the inventors of the present invention have found that even if lead is not contained, the present invention provides a temperature of 135 ° C. to 145 ° C. It has been found that a fusible alloy that melts at a temperature of can be obtained.

The thermal fuse and the wire for thermal fuse element of the present invention have been made based on the above findings, and have a temperature of 135 ° C. or more without containing lead in the fusible alloy.
An object of the present invention is to provide a thermal fuse capable of securing a fusing temperature of 5 ° C. or less. It is another object of the present invention to provide a wire for a thermal fuse element suitable for manufacturing the thermal fuse.

[0008]

A thermal fuse according to the present invention is a thermal fuse having a fuse element that blows at a predetermined temperature, wherein the fuse element has a silver content of 0.1% by weight or more and 1.5% by weight or less. And a fusible alloy comprising 35% by weight or more and 50% by weight or less of tin and the balance of bismuth.

Further, the wire for a thermal fuse element of the present invention may be composed of 0.1% to 1.5% by weight of silver, 35% to 50% by weight of tin, and the balance of bismuth. It is characterized by being formed of a molten alloy.

The inventor of the present invention has found that lead-free and 13
A fusible alloy for fuses that melts at a temperature of 5 ° C. or more and 145 ° C. or less was studied, and tin, which has a relatively low melting point,
Focusing on bismuth, an alloy consisting of these two metals (S
n-Bi alloy). Of these, bismuth was included in the conventional lead alloys in an amount of about 10% by weight to 60% by weight in order to lower the melting point. Therefore, the melting temperature is 135 ° C. or higher14
When determining the composition of the Sn—Bi alloy such that the temperature is 5 ° C. or lower, the bismuth content in the alloy needs to be set high as in the case of the conventional lead alloy. However, bismuth has high hardness but poor ductility and is brittle, so this property appears in Sn-Bi alloys with a high bismuth content.

Therefore, the inventor of the present invention has newly focused on silver and has developed Sn-Bi-A by further adding silver to the Sn-Bi alloy.
g alloy was studied. Silver has the property of lowering the melting point of the alloy, similar to bismuth, but, contrary to bismuth, metal is more ductile than gold. Also, silver forms fine intermetallic compounds with other metals in the alloy, refines the alloy structure,
It also has the property of increasing the strength of the alloy. Therefore, even for a lead-free fusible alloy having a high bismuth content, a lead-free fusible alloy having a melting temperature and ductility equivalent to those of a lead alloy can be obtained by adjusting the silver content in the alloy.

However, in order to obtain such a lead-free fusible alloy, it is necessary to overcome the following problems that arise newly. First, if the content of silver in the alloy is too high,
The intermetallic compound that silver makes in the alloy becomes coarse. When a coarse intermetallic compound is crystallized as a primary crystal in the alloy, there is a problem that the alloy becomes brittle. Further, since silver is more expensive than tin and bismuth, it is necessary to set the silver content low within a range that can achieve the object of the present invention. Further, as described above, the fusing temperature of the fuse is determined by the melting point of the fusible alloy. However, when the temperature around the electric circuit reaches the solidus temperature of the fusible alloy, the fuse begins to melt, so that the difference between the liquidus temperature and the solidus temperature of the alloy (hereinafter referred to as ΔT) is large. It takes a long time to reach the liquidus surface temperature after reaching the solidus surface temperature. A large ΔT means that it takes a long time to blow the fuse, and if the blow takes a long time, there is a possibility that electronic components such as semiconductors may be damaged. For this reason, the fuse is required to have a quick-disconnect property to quickly melt at a desired temperature, and it is desirable that the △ T of the fusible alloy be as small as possible, and ultimately 0 ° C. In order to make ΔT 0 ° C., the liquidus surface temperature and the solidus surface temperature must be equal, that is, it is necessary to obtain a fusible alloy having a eutectic composition.

The thermal fuse of the present invention made of the above-mentioned lead-free fusible alloy has the same characteristics as the conventional thermal fuse made of lead alloy.
This is a practical thermal fuse that can ensure a fusing temperature of 35 ° C. or more and 145 ° C. or less and can also overcome the above-mentioned problems. In addition, compared to a wire for a thermal fuse element made of an alloy having a high bismuth content, the wire for a thermal fuse element of the present invention made of the above-mentioned fusible alloy has an appropriate ductility and can be thinned. Therefore, it can be used for electronic components with low heat resistance, small electronic devices, and the like.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a thermal fuse and a thermal fuse element wire according to the present invention will be described below for each of the items of fusible alloy, thermal fuse, and thermal fuse element wire.

<Soluble Alloy> FIG. 1 shows a liquid phase diagram of the Sn—Bi—Ag alloy. In the figure, point A indicates the eutectic point of the Ag-Sn binary alloy, and point B indicates the eutectic point of the Sn-Bi-Ag ternary alloy.

First, an embodiment of a fusible alloy which is a material for forming a thermal fuse and a thermal fuse element wire according to the present invention will be described. The fusible alloy used for the thermal fuse and the wire of the present invention is composed of 0.1% to 1.5% by weight of silver, 35% to 50% by weight of tin, and the balance of bismuth. . The reason why the fusible alloy has such a composition will be described with reference to FIG.

First, the silver content in the alloy will be described. As described above, silver has the property of forming a fine intermetallic compound with another alloy in the alloy, making the alloy structure finer, and increasing the strength of the alloy. For example, in the case of an Ag—Sn binary alloy, as shown in FIG. 1, a very fine Ag ₃ Sn intermetallic compound having a particle size of 1 μm or less is produced. As the content of silver in the alloy increases, the amount of the fine intermetallic compound increases, so that the strength and ductility of the alloy increase.
Eutectic composition (3.5% by weight of Ag-96.5% by weight of S)
The peak is reached at the time of n). However, when the alloy has a hypereutectic composition (ie, a composition where Ag> 3.5% by weight), the strength and ductility of the alloy gradually deteriorate.
This is due to the coarse Ag ₃ having a grain size of several tens μm or more as the primary crystal.
This is because the Sn platelet crystallizes. Therefore, the silver content needs to be set near the eutectic composition.
When bismuth is gradually added to the Ag-Sn binary alloy while maintaining the eutectic composition, a curve AB (Ag-S
n along the projection line of the binary eutectic line), the silver content in the eutectic composition decreases, and finally the composition at point B (43.5 wt% Sn)
−55.8 wt% Bi-0.7 wt% Ag), that is, the eutectic composition of the Sn—Bi—Ag ternary alloy (eutectic temperature 13
5 ° C). The silver content needs to be near the eutectic composition, and as described above, the content of expensive silver is preferably low in order to suppress the manufacturing costs of fuses and wires.
Therefore, the fusible alloy forming the fuse and wire of the present invention has a silver content of 0.1% by weight or more and 1.5% by weight or less.

Next, the bismuth content in the alloy will be described. As described above, bismuth has a property of high hardness but poor ductility and brittleness. If the bismuth content in the alloy is high, this property of bismuth also appears in the alloy. However, in the alloy for forming the fuse and wire of the present invention, silver is added in order to prevent the property of bismuth from appearing in the alloy. Therefore,
The alloy does not become brittle even if it contains bismuth to the same extent as the conventionally used bismuth-containing alloy. Therefore,
The upper limit of the bismuth content of the fusible alloy forming the fuse and wire of the present invention was less than 60% by weight.

Finally, the tin content in the alloy will be described. As described above, since the silver content in the alloy needs to be near the eutectic composition, the tin content is set to 40% by weight or more and 50% by weight or less to include the vicinity of the eutectic composition.

For the above reasons, as shown by hatching in FIG. 1, the fusible alloy forming the thermal fuse and the wire for the fuse element of the present invention contains silver in an amount of 0.1% by weight or more and 1.5% by weight or less. And tin in the range of 35% by weight to 50% by weight, with the balance being bismuth.

By changing the mixing ratio of silver, tin, and bismuth within this composition range, the melting point of the alloy can be freely controlled, and the temperature corresponding to an arbitrary target temperature between 135 ° C. and 145 ° C. Fuses and wires can be provided. Further, since this composition range includes the eutectic point and its vicinity, a good fusible alloy with extremely small ΔT can be obtained regardless of the composition set within this range.

It is conceivable that unavoidable impurities from the raw material metal and the like may be mixed into the fusible alloy. The fusible alloy constituting the fuse and the wire of the present invention does not specifically exclude the inclusion of impurities, and the alloy having the above composition also includes alloys in which unavoidable impurities are incorporated.

<Thermal Fuse> An embodiment of the thermal fuse of the present invention will be described with reference to the drawings. FIG.
FIG. 1 shows a sectional view of a cylindrical thermal fuse as an example of the thermal fuse of the present invention. The thermal fuse 1 shown in FIG. 2 includes a fuse element 10 that blows at a constant temperature and a fuse element 10.
And a flux 1 filled around the fuse element 10 in a columnar shape and covering the fused surface after the fuse element is blown to prevent conduction again.
1 and a cylindrical ceramic case 12 for housing a part of the fuse element 10, the flux 11 and the lead wire 2.

In an electronic device, the thermal fuse 1 is installed between a power supply such as a battery and an electric circuit. When the temperature around the thermal fuse 1 rises for some reason and reaches the set temperature of the thermal fuse 1, the fuse element 10
Is melted, the flux 11 covers the melted section, and the conduction between the power supply and the circuit is cut off. In this way, the thermal fuse 1 can protect a power supply, an electric circuit, and the like.

The method of manufacturing the thermal fuse 1 of the present embodiment can be performed by various methods conventionally used for manufacturing a fuse. For example, a wire to be described later is cut to form a fuse element 10, and the fuse element 10 and the lead wire 2 are joined to form a fuse element 10.
And a method in which a ceramic case 12 for protecting the fuse element 10 and the like from the outside is provided by filling a flux 11 around the surroundings.

The thermal fuse of the present invention can be various types of thermal fuses conventionally used, such as a fuse with a nail, a tubular fuse, and a plug-type fuse, in addition to the cylindrical fuse shown in FIG. .

The thermal fuse of the present invention has a temperature of 135 ° C.
145 ° C. to any temperature in a temperature range of 145 ° C. Therefore, it can be used in a wide variety of applications such as protection of electronic devices having relatively low heat resistance.

<Temperature Fuse Element Wire> Next, an embodiment of the temperature fuse element wire of the present invention used in the above-described temperature fuse will be described. The wire of the present invention can be manufactured by various methods conventionally used for manufacturing wires. The drawing method will be described as an example.

The drawing method includes a raw material blending step of blending the raw material of the fusible alloy constituting the wire into a melting furnace, a step of melting the blended raw materials, preparing an alloy and pouring the alloy into a mold to form a billet; An extrusion process to make the
It consists of a drawing step of forming a fine wire from a coarse wire.

First, in a raw material blending step, tin, bismuth, and silver base metals, which are raw materials of a wire, are weighed and blended so as to have a desired composition, and then put into a melting furnace. Next, in the billet production step, the blended raw materials are melted at a temperature of 300 to 350 ° C. to prepare an Sn—Bi—Ag alloy, and the prepared alloy in a molten state is poured into a mold to produce a columnar billet. Next, in the extrusion step, the billet is taken out of the mold, set in an extruder, and extruded to form a coarse wire. Finally, in the wire drawing step, the coarse wire is applied to a drawing forming machine, and a thin alloy, that is, a wire is formed by drawing a linear alloy from a die hole provided in the forming machine. The drawing is performed by passing a linear alloy through a large number of die gaps. The diameter of the dice is gradually reduced so that a predetermined diameter can be obtained while passing through a large number of dice.
A tension is applied to the alloy by the die, and the wire is formed in the present embodiment.

In the method of forming a wire by tension as in the above-described drawing method, if the bismuth content in the wire is high, the wire is cut during the drawing. On the other hand, since the wire for a thermal fuse element of the present embodiment contains an appropriate amount of silver and has appropriate ductility, it can be manufactured using a method of forming a wire by tension such as the above-described drawing method. is there. A wire formed by tension can be made thinner than a wire manufactured by another forming method such as extrusion. Such a thin wire can be wound around a bobbin or the like, for example, and can be stored compactly, so that it has excellent storage properties. The wire may have various cross-sectional shapes conventionally used, such as an elliptical shape and a polygonal shape, in addition to a true circular shape in a cross section in a direction perpendicular to the axial direction.

The wire of the present invention, which can be made finer than wires manufactured by other methods, can meet the following requirements when used. In a thermal fuse, a fuse element made of a wire is often installed in a state where a constant tension is applied in the fuse in order to ensure quick disconnection. Since the fuse element installed in this state blows more rapidly as the cross-sectional area is smaller, the wire used for the thermal fuse is required to have a smaller cross-sectional area. Since the wire of the present invention is thinner than a wire manufactured by another method, that is, has a smaller cross-sectional area, it can sufficiently meet this demand.

The wire of the present invention has a fusing temperature of 135 ° C.
A fuse having a wire that is not less than 145 ° C. but melts in this temperature range is often used for small electronic devices. Since small electronic devices are required to have small components, the cross-sectional area of a wire used for a thermal fuse is required to be 0.3 mm ² or less. There is no conventional alloy wire having a high bismuth content that can meet this demand. However, since the wire of the present invention is thinner than a wire manufactured by another method, it can sufficiently meet this demand.

[0034]

EXAMPLES Based on the above embodiment, an ingot having a predetermined composition was produced, and a sample was taken from this ingot for an experiment. This will be described as an example.

<Example> The sample in the example was 1.0% by weight.
Of silver, 42% by weight of tin and 57% by weight of bismuth. This sample was manufactured by the following method. First, purity 99.99%
Of silver, 99.99% pure tin, and 99.99% pure bismuth were weighed and placed in a melting furnace. Next, the raw material was melted and stirred at a temperature of 300 ° C. in a melting furnace to prepare an alloy, and the prepared alloy was poured into a mold, allowed to cool, and demolded. A sample was collected from the ingot thus manufactured, and this was used as an example. When the prepared alloy was poured into a mold, the composition of the alloy was confirmed by chemical analysis.

<Experiment Method> In the experiment, the sample of the example was gradually heated in a heating furnace, and the sample was analyzed using a thermal analyzer (hereinafter referred to as TA) and a differential scanning calorimeter (hereinafter referred to as DSC). This was performed by examining the melting temperature characteristics. The heating pattern of the heating furnace was 50 ° C. before the experiment, the heating rate was 10 ° C./min, and the final holding temperature was 200 ° C.

<Experimental Results> FIG. 3 shows the measurement results by TA when the temperature of the sample of the embodiment was raised according to this temperature rising pattern. FIG. 3 shows that the temperature curve becomes flat from about 133 ° C. to about 134 ° C. Therefore, from the standpoint of FIG. 3 only, in the example, about 133 ° C. is the solidus temperature, about 134 ° C. is the liquidus temperature, and ΔT is about 1 °.
° C. However, since the eutectic temperature of the alloy forming the sample of the example is 135 ° C. as described above, a liquidus temperature lower than this temperature cannot exist. In general, in the measurement using only TA, such a measurement result may sometimes be obtained depending on measurement conditions and the like. In order to compensate for this, measurement using DSC is performed at the same time. Further, not all the measurement results obtained by TA cannot be adopted, and absolute values (specifically, the values themselves of 133 ° C. and 134 ° C.) cannot be adopted, but relative values (specifically, ΔT is about 1 ° C.) Is generally widely known that can be adopted.

Next, FIG. 4 shows the measurement results by DSC. FIG. 4 shows that there is a peak start point when the temperature is about 137 ° C. That is, it can be seen that the solid phase temperature of the example is 137 ° C. The solid phase temperature of the example was 137 ° C. from the measurement result by DSC, and ΔT was 1 ° C. from the measurement result by TA. From this, it was found that the liquidus surface temperature of the example was 138 ° C.

[0039]

The thermal fuse of the present invention is a thermal fuse having a fuse element that blows at a predetermined temperature,
The fuse element is formed of a fusible alloy composed of 0.1% to 1.5% by weight of silver, 35% to 50% by weight of tin, and the balance of bismuth. And

Further, the wire for a thermal fuse element of the present invention comprises:
0.1% to 1.5% by weight of silver and 35% by weight
It is characterized by being formed of a fusible alloy comprising at least 50% by weight of tin and the balance of bismuth.

As described above, Sn-Bi-
By selecting an Ag alloy and adjusting the silver content in the alloy, a thermal fuse and wire having excellent fusing temperature characteristics and appropriate strength and ductility can be obtained.

[Brief description of the drawings]

FIG. 1 is a liquidus surface diagram of a Sn—Bi—Ag alloy.

FIG. 2 is a sectional view of a thermal fuse.

FIG. 3 is a graph showing a measurement result by TA in Examples.

FIG. 4 is a graph showing a measurement result by DSC of an example.

[Explanation of symbols]

 A: Eutectic melting point of Ag-Sn binary alloy B: Eutectic melting point of Sn-Bi-Ag ternary alloy 1: Thermal fuse 10: Fuse element 11: Flux 12: Ceramic case 2: Lead wire

Claims (2)

[Claims] 1. A thermal fuse having a fuse element that blows at a predetermined temperature, wherein the fuse element includes a fuse element.
A thermal fuse characterized by being formed of a fusible alloy comprising 1% by weight to 1.5% by weight of silver, 35% by weight to 50% by weight of tin, and the balance of bismuth. 2. A thermal fuse element formed of a fusible alloy comprising 0.1% to 1.5% by weight of silver, 35% to 50% by weight of tin, and the remaining bismuth. Wire.