JP2020173920A - Protection element - Google Patents

Abstract

To provide a protection element with a high blocking speed due to heat generation blocking.SOLUTION: A protection element 1a includes an insulation board 10, a first electrode 11 and a second electrode 12 provided on the upper surface 10a of the insulation board 10, a heating element provided on the upper surface 10a of the insulation board 10, a first heating element electrode 13 and a second heating element electrode 14 connected to the heating element, a third electrode 16 connected to the second heating element electrode 14 via a leader wire 15, a low melting point metal 30 placed on the third electrode 16, a first short wire 31 connecting between the first electrode 11 and the low melting point metal 30, and a second short wire 32 connecting between the second electrode 12 and the low melting point metal 30. When the low melting point metal 30 is melted, a part of the first short wire 31 and the second short wire 32 in contact with the low melting point metal 30 is eroded and fused.SELECTED DRAWING: Figure 1

Description

The present invention relates to a protective element.

As a protective element that cuts off the current path when an overcurrent exceeding the rating occurs, an element that cuts off the current path by generating heat and blowing the fuse element itself is known. A metal wire (thin metal wire) is used as the fuse element for cutting off the current (Patent Documents 1 to 3).

Further, as a protective element that cuts off the current path in the event of an abnormality other than the occurrence of an overcurrent, an element using a heating element (heater) is known. This protective element is configured to blow a fuse element by using the heat generated by the heating element by passing a current through the heating element in the event of an abnormality other than the generation of an overcurrent. As a fuse element for blocking heat generation using this heating element, a coated structure (soluble conductor) in which the inner layer is a low melting point metal layer and the outer layer is a high melting point metal layer is known (Patent Documents 4 and 5). ). In this coated structure, the low melting point metal layer of the inner layer is melted by the heat generated by the heating element, and the high melting point metal layer is eroded (eroded) by the generated melt of the low melting point metal and fused. When an overcurrent flows, the low melting point metal layer itself generates heat and melts, so that the coated structure also functions as a fuse element for interrupting current. Therefore, a protective element having this coated structure is used. , There is an advantage that both current cutoff and heat generation cutoff can be achieved.

JP-A-2002-373565 Japanese Unexamined Patent Publication No. 63-254634 Japanese Unexamined Patent Publication No. 62-162347 Japanese Unexamined Patent Publication No. 2013-229293 Japanese Unexamined Patent Publication No. 2013-229295

The protective element is used, for example, as a protective element for a charge / discharge circuit of a battery pack using a lithium ion secondary battery. Packed batteries using lithium-ion secondary batteries are used in mobile devices such as notebook computers, mobile phones, and smartphones. In recent years, it has also been used as a power source for driving motors of electric tools, electric bicycles, electric motorcycles and electric vehicles. It is desired that the charging time of mobile devices be shortened, and that the power supply for driving a motor is desired to have a short charging time and a high output, and the amount of current flowing through the charge / discharge circuit of the battery pack tends to increase. Therefore, in the charge / discharge circuit of the battery pack, a protective element that can quickly cut off the current path when an overcurrent occurs or other abnormality is desired. In particular, in the charge / discharge circuit of the battery pack, it is assumed that an abnormality other than the occurrence of overcurrent such as voltage fluctuation due to the battery life occurs. Therefore, it is desirable that the protective element used in the charge / discharge circuit has a high interruption speed due to heat generation interruption.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a protective element having a high blocking speed by blocking heat generation.

The present invention provides the following means for solving the above problems.

(1) The protective element according to one aspect of the present invention includes an insulating substrate, a first electrode and a second electrode provided on at least one surface of the insulating substrate, and at least one surface of the insulating substrate. On one of the heating element provided above, the first heating element electrode and the second heating element electrode connected to the heating element, and the first heating element electrode and the second heating element electrode. A third electrode to be connected, a low melting point metal arranged on the surface of the third electrode, and at least one fuse element wire connecting the first electrode and the second electrode. The low melting point metal is in contact with at least a part of the fuse element wire, and the melting of the low melting point metal melts at least a part of the fuse element wire in contact with the low melting point metal. It is configured to be eaten and melted.

(2) In the embodiment described in (1) above, the fuse element wire may have a diameter in the range of 0.01 mm or more and 0.20 mm or less.
(3) In the embodiment described in (1) or (2) above, the fuse element wire includes a first short wire connecting between the first electrode and the low melting point metal, and the second electrode. The configuration may include a second short wire connecting the low melting point metal and the low melting point metal.
(4) In the embodiment described in (1) or (2) above, the fuse element wire may include a long wire connecting between the first electrode and the second electrode.

(5) In the embodiment according to any one of (1) to (4) above, the low melting point metal may be configured to contain tin.
(6) In the embodiment described in any one of (1) to (5) above, the fuse element wire may be configured to contain copper, silver or gold.

According to the present invention, it is possible to provide a protective element having a high blocking speed due to heat generation blocking.

It is a schematic plan view of the protection element which concerns on 1st Embodiment of this invention. It is a schematic plan view which shows the arrangement of the electrode of the protection element and the heating element which concerns on 1st Embodiment of this invention. FIG. 3 is a sectional view taken along line III-III of FIG. It is a schematic circuit diagram which shows the structure of the protection circuit using the protection element which concerns on 1st Embodiment of this invention. It is a schematic plan view of the protection element which concerns on 2nd Embodiment of this invention. FIG. 5 is a sectional view taken along line VI-VI of FIG. It is a schematic plan view of the protection element which concerns on 3rd Embodiment of this invention. FIG. 7 is a cross-sectional view taken along the line VIII-VIII of FIG. It is a schematic plan view of the protection element which concerns on 4th Embodiment of this invention. 9 is a cross-sectional view taken along line XX of FIG. It is a schematic plan view of the protection element which concerns on 5th Embodiment of this invention. FIG. 11 is a sectional view taken along line XII-XII of FIG.

Hereinafter, the present embodiment of the protective element according to the present invention will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, the featured portion may be enlarged for convenience in order to make the feature easy to understand, and the dimensional ratio of each component may be different from the actual one. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately modified and carried out within the range in which the effects of the present invention are exhibited.

[First Embodiment]
FIG. 1 is a schematic plan view of the protective element according to the first embodiment of the present invention, and FIG. 2 is a schematic plan view showing the arrangement of electrodes and heating elements of the protective element according to the first embodiment of the present invention. Yes, FIG. 3 is a sectional view taken along line III-III of FIG.

The protective element 1a of the first embodiment shown in FIGS. 1 to 3 includes the insulating substrate 10, the first electrode 11 and the second electrode 12 provided on the upper surface 10a of the insulating substrate 10, and the upper surface of the insulating substrate 10. The heating element 20 provided on the 10a, the first heating element electrode 13 and the second heating element electrode 14 connected to the heating element 20, and the second heating element electrode 14 are connected via a leader wire 15. The third electrode 16, the low melting point metal 30 arranged on the third electrode 16, the first short wire 31 connecting between the first electrode 11 and the low melting point metal 30, and the second electrode. It has a second short wire 32 that connects between the 12 and the low melting point metal 30. The first short wire 31 and the second short wire 32 form a fuse element wire that connects the first electrode 11 and the second electrode 12.

The insulating substrate 10 has a rectangular shape, and a first electrode 11 and a second electrode 12 are formed on both opposite ends of a set, and a first heating element electrode 13 and a first heating element electrode 13 and a pair of opposing ends are formed on the other end. A second heating element electrode 14 is formed. As shown in FIG. 2, a first heating element electrode 13 and a second heating element electrode 14 are connected to opposite ends of the heating element 20.

The insulating substrate 10 is not particularly limited as long as it is made of a material having insulating properties. For example, in addition to substrates used for printed wiring boards such as ceramic substrates and glass epoxy substrates, glass substrates, resin substrates, and insulating treatments. A metal substrate or the like can be used. Of these, a ceramic substrate, which is an insulating substrate having excellent heat resistance and good thermal conductivity, is preferable.

The first electrode 11, the second electrode 12, the first heating element electrode 13 and the second heating element electrode 14 are formed of a low resistance conductive material having a relatively low resistance. As the low resistance conductive material, a single metal such as Cu or a material whose surface is at least formed of Ag, Ag-Pt, Ag-Pd, Au or the like can be used. The first electrode 11, the second electrode 12, the first heating element electrode 13, and the second heating element electrode 14 are coated with a paste of these metals or alloys and fired as necessary, vapor deposition, and sputtering. It is formed by a known method used as a method for forming an electrode such as.

The first electrode 11, the second electrode 12, the first heating element electrode 13 and the second heating element electrode 14 are formed on the upper surface 10a and the lower surface 10b of the insulating substrate 10, respectively. As shown in FIG. 3, the first electrode 11a on the upper surface side and the first electrode 11b on the lower surface side are connected via the first conductive portion 11s, and the second electrode 12a on the upper surface side and the second electrode on the lower surface side The electrodes 12b of the above are connected via the second conductive portion 12s. Similarly, in the first heating element electrode 13 and the second heating element electrode 14, the upper surface side electrode and the lower surface side electrode are connected via a conductive portion. The first electrode 11, the second electrode 12, the first heating element electrode 13 and the second heating element electrode 14 are provided with solder portions 41 to 44, respectively, and are protected via the solder portions 41 to 44, respectively. Connected to the circuit.

The heating element 20 (heater) is made of a high-resistance conductive material that has a relatively high resistance and generates heat when energized. The heating element 20 is coated with a resistance paste composed of, for example, a conductive material such as ruthenium oxide or carbon black and an inorganic binder such as water glass or an organic binder such as a thermosetting resin, and fired as necessary. It is formed by doing. Further, as the heating element 20, a thin film such as ruthenium oxide or carbon black may be formed through the steps of printing, plating, vapor deposition, and sputtering, or may be formed by sticking or laminating these films.

The heating element 20 is covered with an insulating member 21. A third electrode 16 is arranged on the upper surface of the insulating member 21. The third electrode 16 is connected to the second heating element electrode 14 via the leader wire 15, and when the heating element 20 generates heat, the heat is transferred through the second heating element electrode 14 and the leader wire 15. Therefore, it is transmitted to the third electrode 16.

As the material of the insulating member 21, for example, an insulating material such as ceramics or glass can be used. The insulating member 21 can be formed by a method of applying a paste of an insulating material and firing it.

As the material of the leader wire 15 and the third electrode 16, the same materials as those of the first heating element electrode 13 and the second heating element electrode 14 can be used. Similar to the first heating element electrode 13 and the second heating element electrode 14, the leader wire 15 and the third electrode 16 are coated with a metal or alloy paste and fired as necessary, vapor deposition, and sputtering. It is formed by a known method used as a method for forming an electrode such as.

The melting point of the low melting point metal 30 is preferably in the range of 280 ° C. or lower, which is higher than the heating temperature (usually about 220 ° C.) at the time of reflow performed when the protective element 1a is mounted. Examples of low melting point metals include Sn-Sb alloy, Bi-Sn-Pb alloy, Bi-Pb alloy, Bi-Sn alloy, Sn-Pb alloy, Sn-Ag alloy, Pb-In alloy, Zn-Al alloy, and In-. Sn alloy, Pb-Ag-Sn alloy, Sn-Ag-Cu alloy, SN-Ag-Ni alloy, SN-Ag-Cu-Ni alloy, Sn-Ag-Cu-Bi-Ni alloy, Sn-Cu alloy, Sn -Bi-Cu alloy, Sn-Pb-Sb alloy and the like can be used. Among these alloys, a tin alloy containing tin is preferable.

It is preferable that the first short wire 31 and the second short wire 32 have a melting point higher than that of the low melting point metal 30 and can be eroded by the melt in which the low melting point metal 30 is melted. For example, when the low melting point metal 30 contains tin, it is preferable to use a copper wire, a silver wire, or a gold wire.

In the first short wire 31 and the second short wire 32, the capacity of the current flowing through the wire can be changed depending on the diameter of the wire, whereby the characteristics at the time of current interruption can be adjusted. Further, depending on the diameter of the wire, the time until the wire is eroded by the melt of the low melting point metal 30 and is melted can be changed, whereby the characteristics at the time of heat generation interruption can be adjusted. The first short wire 31 and the second short wire 32 preferably have a wire diameter in the range of 0.01 mm or more and 0.20 mm or less, and more preferably 0.01 mm or more and 0.10 mm or less. , 0.02 mm or more and 0.05 mm or less is particularly preferable. If the wire diameter becomes too large, the time required for the wire to be eroded by the melt of the low melting point metal 30 and to be melted may become too long. On the other hand, if the wire diameter becomes too small, the current capacity that can flow through the wire becomes too small. Further, the current capacity that can be passed between the electrodes can be secured by arranging the wires in parallel and increasing the number of wires connecting the electrodes. If a part of the current is eroded and fused, the amount of current that can flow between the electrodes may decrease.

A method of connecting the first short wire 31 to the first electrode 11 or the third electrode 16 and a method of connecting the second short wire 32 to the second electrode 12 or the third electrode 16 include a ball bonding method. A known method used as a method for connecting a metal plate and a wire, such as a wedge bonding method and a soldering method, can be used. When the first short wire 31 and the third electrode 16 and the second short wire 32 and the third electrode 16 are connected by a soldering method, a low melting point metal 30 can be used as the solder material.

Next, the configuration of the protection circuit using the protection element 1a and the current cutoff operation according to the first embodiment will be described. FIG. 4 is a schematic circuit diagram showing a configuration of a protection circuit using the protection element 1a according to the first embodiment.

The protection circuit 2 shown in FIG. 4 is incorporated in the packed battery of the lithium ion secondary battery 51. The first electrode 11 and the second electrode 12 of the protective element 1a are connected to the positive electrode side power supply line. The first heating element electrode 13 of the protection element 1a is connected to the negative electrode side power supply line via the switching element 52. The switching element 52 is composed of a field effect transistor (FET) and is connected to the control element 53. The control element 53 detects an abnormality other than the occurrence of an overcurrent, and when the abnormality is detected, operates the switching element 52. For example, the control element 53 measures the voltage of the lithium ion secondary battery 51, and when the voltage of the lithium ion secondary battery 51 becomes an abnormal value, the switching element 52 is operated.

When an overcurrent occurs in the protection circuit 2, the first short wire 31 or the second short wire 32 generates heat due to the overcurrent and blows, thereby interrupting the current path of the protection circuit 2 (current cutoff). ).

On the other hand, when an abnormality other than the occurrence of an overcurrent occurs in the protection circuit 2, the control element 53 operates the switching element 52 to pass a current through the heating element 20. When a current flows, the heating element 20 generates heat, and the heat is transferred to the third electrode 16 via the second heating element electrode 14 and the leader wire 15. Then, the heat transferred to the third electrode 16 heats and melts the low melting point metal 30 arranged on the third electrode 16, and the first short wire 31 and the melt of the low melting point metal 30 produced are melted. When the second short wire 32 is eroded and blown, the current path of the protection circuit 2 is cut off (heat generation cutoff).

Since the protective element 1a of the present embodiment configured as described above uses the first short wire 31 and the second short wire 32 having a small diameter as the fuse element wire, it can be used for both current cutoff and heat generation cutoff. The cutoff speed can be increased. In particular, the ends of the first short wire 31 and the second short wire 32 are directly connected to the low melting point metal 30 arranged on the third electrode 16, and heat is easily transferred, so that the heat is melted when the heat is cut off. Eating is easy and the blocking speed is fast. Further, the short wire is easy to be fixed to the electrode. Further, in the protective element 1a of the present embodiment, since the fuse element wire is only partially in contact with the low melting point metal 30 arranged on the third electrode 16, for example, the protective element 1a is mounted. Even when the low melting point metal 30 is partially melted by the heating at the time of reflow, the fuse element wire is not easily deformed.

[Second Embodiment]
FIG. 5 is a schematic plan view of the protective element according to the second embodiment of the present invention, and FIG. 6 is a sectional view taken along line VI-VI of FIG.
The protective element 1b according to the second embodiment shown in FIGS. 5 to 6 is the first embodiment in that the heating element 20 and the insulating member 21 covering the heating element 20 are arranged on the lower surface 10b of the insulating substrate 10. It is different from the protective element 1a. The parts common to the protective element 1b of the second embodiment and the protective element 1a of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The heating element 20 is connected to a first heating element electrode and a second heating element electrode (not shown) formed on the lower surface 10b of the insulating substrate 10. The third electrode 16 is connected to the second heating element electrode 14 formed on the upper surface 10a of the insulating substrate 10 via a leader wire 15. In the protection element 1b of the second embodiment, when the heating element 20 generates heat, the heat is transferred from the second heating element electrode formed on the lower surface 10b of the insulating substrate 10 via a conductive portion (not shown). It is transmitted to the second heating element electrode 14 formed on the upper surface 10a of the insulating substrate 10. Then, the heat is transferred to the third electrode 16 via the leader wire 15.

[Third Embodiment]
FIG. 7 is a schematic plan view of the protective element according to the third embodiment of the present invention, and FIG. 8 is a sectional view taken along line VIII-VIII of FIG.
The protective element 1c according to the third embodiment shown in FIGS. 7 to 8 is first in that the fuse element wire is a long wire 33 that directly connects the first electrode 11 and the second electrode 12. It is different from the protective element 1a according to the embodiment. The parts common to the protective element 1c of the third embodiment and the protective element 1a of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Like the first short wire 31 and the second short wire 32 of the protective element 1a of the first embodiment, the long wire 33 has a melting point higher than that of the low melting point metal 30, and the low melting point metal 30 is melted into a melt. It is preferable that it can be eroded. The wire diameter of the long wire 33 is preferably in the range of 0.01 mm or more and 0.20 mm or less, more preferably the wire diameter is in the range of 0.01 mm or more and 0.10 mm or less, and 0.02 mm. It is particularly preferable that the temperature is within the range of 0.05 mm or more. As the long wire 33, for example, when the low melting point metal 30 contains tin, it is preferable to use a copper wire, a silver wire, or a gold wire. Further, as a method of connecting the long wire 33 to the first electrode 11 or the second electrode 12, it is used as a method of connecting a metal plate and a wire such as a ball bonding method, a wedge bonding method, and a soldering method. Known methods can be used.

The long wire 33 is in contact with the low melting point metal 30 arranged on the third electrode 16. As a method of bringing the long wire 33 into contact with the low melting point metal 30, for example, first, the long wire 33 is connected to the first electrode 11 or the second electrode 12, and a part of the long wire 33 is connected. , A method can be used in which a melt of the low melting point metal 30 is applied onto the third electrode 16 and solidified while being pressed against the third electrode 16.

Since the protective element 1c of the present embodiment configured as described above uses a long wire 33 having a small diameter as the fuse element wire, it is possible to increase the breaking speed for both current cutoff and heat generation cutoff. it can. Further, by connecting the first electrode 11 and the second electrode 12 with one long wire 33, the connection location can be changed as compared with the case where the first short wire 31 and the second short wire 32 are used. Since the number is reduced, the variation in the conductive resistance value can be reduced and the processing time can be shortened. Further, in the protective element 1c of the present embodiment, since the long wire 33 is only partially in contact with the low melting point metal 30 arranged on the third electrode 16, for example, the protective element 1c is mounted. Even if the low melting point metal 30 is partially melted by the heating at the time of reflow, the long wire 33 is not easily deformed.

[Fourth Embodiment]
9 is a schematic plan view of the protective element according to the fourth embodiment of the present invention, and FIG. 10 is a sectional view taken along line XX of FIG.
In the protective element 1d according to the fourth embodiment shown in FIGS. 9 to 10, the fuse element wire directly connects the first electrode 11 and the second electrode 12 as compared with the protective element 1b according to the second embodiment. It differs in that it is a long wire 33. Further, as compared with the protective element 1c according to the third embodiment, the heating element 20 and the insulating member 21 covering the heating element 20 are arranged on the lower surface 10b of the insulating substrate 10. The parts common to the protection element 1d of the fourth embodiment, the protection element 1b according to the second embodiment, and the protection element 1c of the third embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In the protective element 1d according to the fourth embodiment, the heat generated by the heating element 20 is transferred in the same manner as in the case of the protective element 1b according to the second embodiment. The material of the long wire 33, the method of connecting the long wire 33 to the first electrode 11 or the second electrode 12, and the method of contacting the long wire 33 with the low melting point metal 30 are the third embodiments. It is the same as the case of the protection element 1c of.

[Fifth Embodiment]
FIG. 11 is a schematic plan view of the protective element according to the fifth embodiment of the present invention, and FIG. 12 is a sectional view taken along line XII-XII of FIG.
The protective element 1e according to the fifth embodiment shown in FIGS. 11 to 12 is different from the protective element 1c according to the third embodiment in that a plurality of long wires 33 are provided. The parts common to the protective element 1e of the fourth embodiment and the protective element 1c of the third embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Since the protective element 1e of the fifth embodiment has a plurality of long wires 33, even if the diameter of each long wire 33 is reduced, the first electrode 11 and the second electrode 12 are connected. The capacity of the current that can flow between them can be increased. Then, by reducing the diameter of each long wire 33, the time until the long wire 33 is eroded by the melt of the low melting point metal 30 and melted can be shortened.

As described above, according to the protection elements 1a to 1e of the present embodiment, when an overcurrent occurs, the current path can be cut off by cutting off the current, and when an abnormality other than the occurrence of the overcurrent occurs, the current is cut off by heat generation. The route can be blocked. Further, the cutoff time due to current cutoff and the cutoff time due to heat generation cutoff can be adjusted by adjusting the diameter and the number of parallel wires of the fuse element wires (first short wire 31, second short wire 32, long wire 33). Further, the cutoff time due to heat generation cutoff can be adjusted by the type of the fuse element wire and the low melting point metal 30.

Further, in the protective elements 1a to 1e of the present embodiment, since the fuse element wire is only partially in contact with the low melting point metal 30 arranged on the third electrode 16, for example, the protective element 1a Even if the low melting point metal 30 is partially melted by the heating at the time of reflow performed at the time of mounting, the fuse element wire is not easily deformed.

In the present embodiment, the first electrode 11, the second electrode 12, the first heating element electrode 13 and the second heating element electrode 14 are formed on the upper surface 10a and the lower surface 10b of the insulating substrate 10, respectively. However, the present invention is not limited to this. The first electrode 11, the second electrode 12, the first heating element electrode 13 and the second heating element electrode 14 may be formed on either the upper surface 10a or the lower surface 10b of the insulating substrate 10.

Further, in the present embodiment, the third electrode 16 has been described as being connected to the second heating element electrode 14 via the leader wire 15, but the present invention is not limited thereto. The third electrode 16 may be connected to the first heating element electrode 13.

Next, the present invention will be described with reference to Examples.

[Example 1]
In Example 1, the protective element 1c according to the third embodiment shown in FIGS. 7 to 8 was produced.
First, a rectangular insulating substrate 10 was prepared. A first electrode 11 and a second electrode 12 are formed on a pair of facing ends of an insulating substrate, and a first heating element electrode 13 and a second heating element electrode 12 are formed on the other pair of facing ends. 14 was formed. The heating element 20 was arranged so as to be in contact with the first heating element electrode 13 and the second heating element electrode 14.

Next, the surface of the heating element was covered with an insulating member. A third electrode 16 was formed on the surface of the insulating member, and a leader wire 15 was formed between the third electrode 16 and the second heating element electrode 14.

Next, the first electrode 11 and the second electrode 12 were connected using a silver wire (diameter D: 0.05 mm, length L: 0.5 mm) as a long wire 33. The connection between the first electrode 11 and the second electrode 12 and the silver wire was performed by a ball bonding method. Finally, in a state of being pressed against the third electrode 16 of the silver wire, a melt of the low melting point metal 30 (tin alloy) was applied onto the third electrode 16 and solidified to prepare a protective element. ..

[Example 2]
Except that the number of silver wires connecting the first electrode 11 and the second electrode 12 was two, and the silver wires had a diameter of D: 0.035 mm and a length of L: 0.5 mm. , A protective element was produced in the same manner as in Example 1.

[Example 3]
Except that the number of silver wires connecting the first electrode 11 and the second electrode 12 was four, and the silver wires had a diameter of D: 0.025 mm and a length of L: 0.5 mm. , A protective element was produced in the same manner as in Example 1.

[Evaluation]
(1) The following physical properties were calculated for the produced silver wire of the protective element. The results are shown in Table 1.

Cross-sectional area S: Calculated from the following formula.
Cross-sectional area S = (diameter D / 2) x (diameter D / 2) x π

Cut portion length: The length of the cut portion when the silver wire is cut by an electric current or heating element heating. The length of the cut portion was 0.1 mm.

Cut part volume: The cut part volume is the volume of the cut part when cut by an electric current or heating element. The cut portion volume was calculated from the following formula.
Cut volume = cross-sectional area S x cut length x number of silver wires

Cut portion volume ratio: The cut portion volume ratio is a relative value with the cut portion volume of Example 1 as 1.

Conductor resistance: Conductor resistance is the resistance value in the length direction of the silver wire. The conductor resistance was calculated from the following formula.
Conductor resistance = Silver specific resistance (1.62 x ^10-5 Ω · mm) x length L / cross-sectional area S

Surface area: The surface area is the surface area of the entire silver wire. The surface area was calculated from the following formula.
Surface area = diameter R x π x length L x number of silver wires

Surface area ratio: The specific surface area ratio is a relative value with the surface area of Example 1 as 100%.

(2) Breaking time due to current cutoff The time from when a current of 6 mA is passed between the first electrode 11 and the second electrode 12 until the current path is cut off due to heat generation and melting of the silver wire. Was measured. The results are shown in Table 1.

(3) Breaking time due to heating cutoff After a current of 1 mA was passed between the first heating element electrode 13 and the second heating element electrode 14, the heating element 20 generated heat and the tin alloy was melted and formed. The time until the current path was cut off by the silver wire being eroded and fractured in the molten tin alloy was measured. The results are shown in Table 1.

In the protective elements produced in Examples 1 to 3, the interruption time due to current interruption was the same at 10 seconds. It is considered that this is because the conductor resistances of the silver wires of Examples 1 to 3 have the same value.

In the protective elements produced in Examples 1 to 3, the interruption time due to heat generation interruption was the shortest in Example 3, the next shortest in Example 2, and the longest in Example 1. It is considered that this is because the larger the surface area ratio of the silver wire, the wider the contact area with the tin alloy, and the more easily it is eroded by the melt of the tin alloy.

From the above results, it was confirmed that in the protection element of this embodiment, the cutoff time due to heat generation cutoff can be adjusted by changing the number and diameter of the silver wires without changing the cutoff time due to current cutoff.

1a, 1b, 1c, 1d, 1e Protective element 10 Insulated substrate 10a Upper surface 10b Lower surface 11 First electrode 11a Upper surface side first electrode 11b Lower surface side first electrode 11s First conductive part 12 Second electrode 12a 2nd electrode on the upper surface side 12b 2nd electrode on the lower surface side 12s 2nd conductive part 13 1st heating element electrode 14 2nd heating element electrode 15 Leader wire 16 3rd electrode 20 Heating element 21 Insulating member 30 Low Melt melting metal 31 1st short wire 32 2nd short wire 33 Long wire 41, 42, 43, 44 Solder part

Claims (6)

Insulated substrate and
A first electrode and a second electrode provided on at least one surface of the insulating substrate,
A heating element provided on at least one surface of the insulating substrate and
A first heating element electrode and a second heating element electrode connected to the heating element,
A third electrode connected to either the first heating element electrode or the second heating element electrode, and
A low melting point metal disposed on the surface of the third electrode,
It has at least one fuse element wire connecting the first electrode and the second electrode.
The low melting point metal comes into contact with at least a part of the fuse element wire, and by melting the low melting point metal, at least a part of the fuse element wire in contact with the low melting point metal is eroded. A protective element that is configured to be blown. The protective element according to claim 1, wherein the diameter of the fuse element wire is within the range of 0.01 mm or more and 0.20 mm or less. The fuse element wire includes a first short wire that connects between the first electrode and the low melting point metal, and a second short wire that connects between the second electrode and the low melting point metal. The protective element according to claim 1 or 2, which includes. The protective element according to claim 1 or 2, wherein the fuse element wire includes a long wire connecting between the first electrode and the second electrode. The protective element according to any one of claims 1 to 4, wherein the low melting point metal contains tin. The protective element according to any one of claims 1 to 5, wherein the fuse element wire contains copper, silver or gold.

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