JP3483030B2 - Thermal fuse and wire for thermal fuse element - Google Patents

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 having a thermal fuse element formed of a lead-free fusible alloy that melts at a predetermined temperature and a wire for a thermal fuse element. .

[0002]

2. Description of the Related Art Fuses include an electric fuse that blows to protect a circuit when an overcurrent flows in an electric circuit, and a thermal fuse that blows to protect a circuit when the temperature around the electric circuit rises. Electric fuses for TVs, washing machines, etc.
In addition, the thermal fuse is used for mobile phones, laptop computers, etc.
Each is incorporated and has a role of protecting these electric appliances. Above all, it is necessary for the thermal fuse to surely and quickly fuse at the set fusing temperature to protect the electric circuit. For this reason, the thermal fuse is required to be blown accurately under various temperature conditions. Recently, many electronic parts such as semiconductors have low heat resistance.
Many are damaged at a temperature of 40 ° C to 150 ° C. Also, like a lithium-ion secondary battery, the temperature is 14
Some are dangerous when the temperature rises to around 0 ° C to 150 ° C. For this reason, a thermal fuse that is capable of accurately and promptly melting in a temperature range around 140 ° C to 150 ° C is required.

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

Heretofore, as a fusible alloy for a thermal fuse having a melting point of around 140 ° C. to 150 ° C., one containing lead as a kind of raw material metal (hereinafter referred to as a lead alloy) has been mainly used. However, in recent years, when electrical products are discarded, lead is leached out into the natural environment from the thermal fuses incorporated therein. When humans ingest lead dissolved in the environment, it becomes lead poisoning, depending on the amount of intake, fatigue,
Poisoning symptoms such as sleep deprivation, constipation, tremors, abdominal pain, anemia, neuritis, and brain degeneration appear. Therefore, in order to prevent environmental pollution due to lead, there is a worldwide demand that lead should not be used as an industrial material as much as possible, and the study of an industrial material to replace lead is one of the important issues in the industry. There is. For this reason, Japanese Patent Laid-Open No. 11-25829 discloses a thermal fuse which does not use a lead alloy and which is formed of an alloy containing 52 to 100% by weight of indium and the balance of tin.

[0005]

The melting point of indium is 1
Since the temperature is as low as 56 ° C., the melting point of the alloy containing indium as a main component, that is, the alloy having a high indium content is low.
However, since indium is soft, there is a problem that the thermal fuse and the wire made of an alloy having a high indium content are easily scratched and are inconvenient to handle. Also,
In order to improve the fusing property with respect to the temperature of the fuse, the fuse element is often installed with a certain tension applied in a tubular fuse or a tube fuse, but the fuse element made of a wire material having a high indium content is soft. Since the ductility is high, there is a problem that it is difficult to install under tension and the fusing property of the thermal fuse deteriorates.

Therefore, as a result of earnest studies on the Sn--In alloy forming the thermal fuse and the wire, the inventor of the present invention newly added silver to this alloy to obtain 14
It was found that it is possible to obtain a lead-free fusible alloy that melts at a temperature of 0 ° C. or higher and 150 ° C. or lower and that has suitable strength and ductility for forming a thermal fuse element.

A thermal fuse and a wire for a thermal fuse element of the present invention have been made based on the above findings, and an object of the present invention is to provide a thermal fuse capable of ensuring a fusing temperature of 140 ° C. or higher and 150 ° C. or lower. . Another object of the present invention is to provide a wire for a thermal fuse element suitable for manufacturing this thermal fuse.

[0008]

The thermal fuse of the present invention is a thermal fuse having a fuse element that blows at a predetermined temperature, and the fuse element is 1 wt% to 3 wt% tin and 0. 1 wt% to 5 wt% both inclusive of silver, is formed by fusible alloy consisting of the remainder of the indium, the cross-sectional area of the fuse element, 0.3 mm ² or more
It is characterized by being set below .

Further, the wire for a thermal fuse element of the present invention comprises 1% by weight or more and 3% by weight or less of tin and 0.1% by weight.
It is made of a fusible alloy consisting of 5% by weight or less of silver and the balance of indium, and has a cross-sectional area of 0.3 mm ²
It is characterized by being set as follows .

The inventor of the present invention was found to be lead-free and
A fusible alloy for fuses that melts at a temperature of 0 ° C. or more and 150 ° C. or less was studied, and an alloy in which silver was added to tin and indium, that is, a Sn—In—Ag alloy was studied.

Since indium has a low melting point as described above, it has the property of lowering the eutectic point of the alloy in the alloy. However, on the other hand, indium also has a property of being ductile and soft, so that if the indium content in the alloy is high, the alloy itself becomes soft.

Therefore, the inventor of the present invention focused on silver as a component element. Similar to indium, silver has the property of lowering the melting point of the alloy, and also has the property of forming a fine intermetallic compound with another metal in the alloy to refine the alloy structure and increase the strength of the alloy. Therefore, even if the lead-free fusible alloy has a high indium content, a lead-free fusible alloy having the same melting temperature and strength as the lead alloy can be obtained by adjusting the content of silver in the alloy.

However, in order to obtain such a lead-free fusible alloy, it is necessary to overcome the following new derivational problems. First, if the content of silver in the alloy is too high,
The intermetallic compound that silver forms in the alloy becomes coarse. If a coarse intermetallic compound crystallizes in the alloy, the alloy becomes brittle. Since silver is more expensive than tin and indium, it is necessary to set the silver content low so long as the object of the present invention can be achieved. 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 solid phase surface temperature of the fusible alloy, the fuse begins to melt, so that the difference between the liquid phase surface temperature and the solid phase surface temperature of the alloy (hereinafter referred to as ΔT) is large. ,
It takes time to reach the liquidus surface temperature after reaching the solidus surface temperature. A large ΔT means that it takes time to blow the fuse, and if the blowing takes time, electronic parts such as a semiconductor may be damaged. For this reason, the fuse is required to have a fast-breaking property that quickly fuses at a desired temperature, and ΔT of the fusible alloy is preferably as small as possible.

The thermal fuse of the present invention made of the above-mentioned fusible alloy is 140 in the same manner as the conventional lead alloy thermal fuse.
It is a practical thermal fuse that can secure a fusing temperature of not lower than 150 ° C. and not higher than 150 ° C. and can overcome the above-mentioned derivative problems. Further, as compared with a wire for a temperature fuse element, which is made of a normal alloy having a high indium content, the wire for a temperature fuse element of the present invention, which is made of the fusible alloy, has appropriate strength and is hard to be scratched and crushed. Since it is difficult to use, it can be used for electronic parts and small electronic devices having relatively low heat resistance.

[0015]

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

<Fusable Alloy> First, an embodiment of a fusible alloy which is a material for forming the thermal fuse and the wire for the thermal fuse element of the present invention will be described. The fusible alloy used in the thermal fuse and the wire of the present invention contains 1% by weight or more and 3% by weight or more.
The following tin and 0.1 wt% or more and 5 wt% or less silver,
The balance is indium. The reason why the fusible alloy has such a composition will be described.

First, the silver content in the alloy will be described. As described above, silver has a property of forming a fine intermetallic compound with other alloys in the alloy, refining the alloy structure, and increasing the strength of the alloy. This property can neutralize the softening of the alloy by indium. However, if the silver content becomes excessively high, the fine intermetallic compound becomes coarse, and the strength of the alloy gradually deteriorates.
Further, as described above, silver has a property of lowering the melting point of the alloy, but even if the content ratio of silver is small, this property appears in the alloy. For example, the melting point of indium that does not contain silver is 1.
Although the temperature is 56 ° C, the melting point drops to 141 ° C even if the silver content is only 3% by weight when silver is contained. Furthermore, since silver is expensive, the high content of silver in the alloy increases the cost of manufacturing fuses and wires. From these things, it is desirable that the silver content in the alloy is low. Therefore, the silver content of the fusible alloy forming the fuse and the wire of the present invention is set to 0.1% by weight or more and 5% by weight or less.

Next, the tin content in the alloy will be described. Tin has a low melting point of 231.9 ° C. and has the property of lowering the melting point of the alloy. Even if the tin content is small, this property appears in the alloy. On the other hand, an alloy having a high tin content has a large ΔT and is not preferable for a fuse wire. Therefore, the tin content is set to 1% by weight or more and 3% by weight or less.

For the above reasons, the fusible alloy forming the thermal fuse and the wire for fuse element of the present invention contains tin in an amount of 1% by weight or more and 3% by weight or less, silver is 0.1% by weight or more and 5% by weight or less, The balance has a composition of indium.

Within this composition range, the melting point of the alloy can be freely controlled by changing the compounding ratio of tin, silver and indium.
Thermal fuses and wires can be provided for any target temperature between.

It is possible that impurities that are unavoidable from raw material metals are mixed in the fusible alloy. The fusible alloy forming the fuse and wire of the present invention does not specifically exclude the inclusion of impurities, and the alloy having the above composition also corresponds to the alloy containing unavoidable impurities.

<Thermal Fuse> An embodiment of the thermal fuse of the present invention will be described with reference to the drawings. Figure 1
A sectional view of a cylindrical thermal fuse as an example of the thermal fuse of the present invention is shown in FIG. The thermal fuse 1 shown in FIG. 1 includes a fuse element 10 that melts at a constant temperature, and a fuse element 10
A lead wire 2 which is joined to both ends of the fuse 2 and passes a current, and a flux 1 which is filled in a cylindrical shape around the fuse element 10 and covers the melted section after the fuse element is melted to prevent re-conduction.
1 and a cylindrical ceramic case 12 accommodating a part of the fuse element 10, the flux 11 and the lead wire 2.

In electronic equipment, the thermal fuse 1 is installed between a power source such as a battery and an electric circuit. If the ambient temperature of the thermal fuse 1 rises for some reason and reaches the set temperature of the thermal fuse 1, the fuse element 10
Melts and the flux 11 is covered with the flux 11 to cut off the electrical connection between the power source and the circuit. In this way, the thermal fuse 1 can protect the power supply, the electric circuit and the like.

The thermal fuse 1 of this embodiment can be manufactured by various methods conventionally used for manufacturing fuses. For example, a fuse element 10 is formed by cutting a wire material described later, and the fuse element 10 and the lead wire 2 are joined to each other to form the fuse element 10.
It can be manufactured by a method in which the flux 11 is filled in the periphery of and the ceramic case 12 is installed on the outside to protect the fuse element 10 and the like from the outside.

The thermal fuse of the present invention may be a tubular fuse shown in FIG. 1 or a thermal fuse having various shapes conventionally used such as a claw fuse, a tube fuse, and a plug fuse. .

The thermal fuse of the present invention has a temperature of 140 ° C.
It can be rapidly fused to any temperature in the temperature range from 1 to 150 ° C. Therefore, it can be used for various purposes such as protection of electronic devices having relatively low heat resistance.

<Wire Material for Thermal Fuse Element> Next, an embodiment of the wire material for thermal fuse element of the present invention used in the above-mentioned thermal fuse will be described. The wire rod of the present invention can be manufactured by various methods conventionally used for manufacturing wire rods. The drawing method will be described as an example.

The drawing method includes a raw material blending step of blending a raw material of a fusible alloy forming a wire into a melting furnace, a billet producing step of melting the blended raw material to prepare an alloy and casting it into a mold to form a billet, and a billet from a rough wire An extrusion process to produce
It consists of a wire drawing process for forming a fine wire from a coarse wire.

First, in the raw material mixing step, the raw materials of the wire, tin, indium and silver ingot, are weighed and mixed so as to have a desired composition, and then charged into a melting furnace. Next, in the billet production step, the compounded raw materials are melted at a temperature of 300 to 350 ° C. to prepare a Sn—In—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, put on an extrusion molding machine, and extruded to form a coarse wire.
Finally, in the wire-drawing step, the coarse wire is applied to a drawing machine and a linear alloy is drawn out from a circular die hole provided in the molding machine to form a fine wire, that is, a wire rod. The diameters of the die holes are successively reduced, and a predetermined diameter can be obtained while passing through many die holes. In order to obtain the wire rod by drawing the alloy from the die hole, it is necessary to apply tension to the wire rod at the exit side of the die hole. Therefore, the wire rod is passed through the gap between the pair of rolls on the die hole exit side. The roll is tensioned and the alloy is pulled through the die holes. After that, the wire rod that has left the roll is wound around a bobbin or the like and stored.

In the method of forming a wire by tension like the above-mentioned drawing method, when the indium content in the wire is high, the wire becomes too soft. The wire may be damaged or crushed when wound on the bobbin. Therefore, it cannot be molded by such a method. On the other hand, the wire for a thermal fuse element of the present embodiment has a high indium content, but since the alloy contains silver and has an appropriate strength, the wire is not damaged even if it is passed through a roll gap or wound on a bobbin. It can be molded by such a method without sticking or crushing. The wire rod may be a wire rod having a cross section in the direction perpendicular to the axial direction that is a perfect circle, or a wire rod having various cross-sectional shapes that have been conventionally used such as an elliptical shape and a polygonal shape.

The wire of the present invention, which can be made thinner than wires manufactured by other methods, can meet the following requirements when used. In a thermal fuse that blows at a relatively low temperature, quick disconnection against a set temperature is required to protect electronic components such as semiconductors having low heat resistance. As mentioned above, the fuse element made of wire material
In order to ensure quick disconnection, the fuse is often installed with a certain tension applied. The smaller the cross-sectional area of the fuse element installed in this state is, the faster the fuse will blow. Therefore, the wire used for such a fuse element is also required to have a small cross-sectional area.

The wire rod of the present invention has a melting temperature of 140 ° C.
Although the temperature is 150 ° C. or lower, a fuse having a wire material that melts in this temperature range is in high demand for protection of small electronic devices such as laptop computers. In recent years, these electronic devices have continued to be miniaturized from the convenience of use, and in order to miniaturize the device, it is required that the temperature fuse, which is a component thereof, be also small. A small cross section is required.

Due to the above requirements, the cross-sectional area of the wire is 0.3 mm.
It must be ² or less. For such a wire having a small cross-sectional area, it is fatal that the wire is damaged or crushed. That is, if the wire is damaged or crushed, the cross-sectional area changes only at that portion, and even if the fuse has the same set temperature, the fusing time varies depending on the presence or absence of the damage and the crushing condition. Since the fuse wire having only a high indium content was soft, it was easily scratched and crushed. For this reason, there are many cases where the fusing time tends to vary and the reliability is low. On the other hand, the wire of the present invention has a high indium content but contains silver to have a high strength, so that it is hard to be scratched or crushed. Therefore, it is possible to obtain a highly reliable wire rod with a small variation, and it is possible to sufficiently meet the above requirements.

[0034]

Example Based on the above-described embodiment, a sample made of Sn-In-Ag alloy having a predetermined composition was prepared and an experiment was conducted. This will be described as an example.

Example The sample of the example is composed of a fusible alloy having a composition of 2% by weight tin, 3% by weight silver, and 95% by weight indium. This sample was manufactured by the following method. First, tin with a purity of 99.99%, silver with a purity of 99.99%, and indium with a purity of 99.99% were weighed and put into a melting furnace. Next, the raw material was melted and stirred in a melting furnace at a temperature of 300 ° C. to prepare an alloy, and the prepared alloy was poured into a mold and allowed to cool and then demolded. A sample was taken from the ingot thus produced and used as an example. Further, when the prepared alloy was poured into the mold, the alloy composition was confirmed by chemical analysis.

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

<Experimental Results> FIG. 2 shows the results of measurement by TA when the temperature of the sample of the example was raised with this heating pattern. From FIG. 2, it can be seen that the temperature curve becomes flat from about 143 ° C to about 144 ° C. Moreover, the measurement result by DSC is shown in FIG. From Figure 3, the temperature is about 143.
It can be seen that there is a peak start point in the differential thermal curve at ℃. From these facts, the soluble alloys constituting the samples of the Examples change from a single-phase state of a solid phase to a two-phase coexistence state of a solid phase and a liquid phase at about 143 ° C., and a two-phase coexistence state at about 144 ° C. From this, it can be seen that the liquid phase changes to a single phase. That is, it can be seen that the solid phase surface temperature is about 143 ° C., the liquid phase surface temperature is about 144 ° C., and ΔT is about 1 ° C.

From the above experiment, the liquidus surface temperature of the example is 14
It was found that the liquidus surface temperature is within the temperature range of 4 ° C and the solidus surface temperature is 143 ° C or less. It was also found that ΔT in the example was as small as 1 ° 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, 1% by weight or more than 3% by weight of tin, and 5 wt% or less of silver or 0.1 wt%, is formed by fusible alloy consisting of the remainder of indium,該Hi
The fuse element is characterized in that the cross-sectional area thereof is set to 0.3 mm ² or less .

The wire for a thermal fuse element of the present invention is
It is formed of a fusible alloy consisting of 1% by weight or more and 3% by weight or less tin, 0.1% by weight or more and 5% by weight or less silver, and the balance indium, and has a cross-sectional area of 0.3 mm ² or less.
It is set to .

In this way, Sn-In- is used as the fusible alloy.
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 drawings]

FIG. 1 is a sectional view of a thermal fuse.

FIG. 2 is a graph showing the result of measurement by TA in the example.

FIG. 3 is a graph showing the measurement results by DSC of the example.

[Explanation of symbols]

1: Thermal fuse 10: Fuse element 11: Flux 12: Ceramic case 2: Lead wire

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-25829 (JP, A) JP-B 6-80881 (JP, B2) JP-B 46-34292 (JP, B1) (58) Field (Int.Cl. ⁷ , DB name) H01H 37/76 C22C 28/00

Claims (2)

(57) [Claims] 1. A thermal fuse having a fuse element that melts at a predetermined temperature, wherein the fuse element is 1 wt% to 3 wt% tin and 0.1 wt% to 5 wt% silver. And a balance of indium and a fusible alloy , and the cross-sectional area of the fuse element is
A thermal fuse characterized by being set to 0.3 mm ² or less . 2. Tin of 1% by weight or more and 3% by weight or less,
It is made of a fusible alloy consisting of 0.1% by weight or more and 5% by weight or less of silver and the balance of indium, and has a cross-sectional area of
A wire for a thermal fuse element set to 0.3 mm ² or less .