Patent Application
20240029976
The present disclosure relates to a protective element used in electric devices and electronic devices.
With rapid spread of small electronic devices such as mobile devices in recent years, a protective element also smaller in size and thickness is mounted on a protective circuit for a mounted power supply. For example, for a protective circuit for a secondary battery pack, a chip protective element for a surface mount device (SMD) is suitably used. The chip protective element includes a one-shot protective element that senses excessive heat generation caused by an overcurrent in a protected device and blows a fuse to cut off an electric circuit under a prescribed condition, or blows a fuse to cut off an electric circuit under a prescribed condition in response to abnormal overheating of ambient temperature.
When the protective circuit senses an abnormal condition that occurs in a device, the protective element has a resistive element generate heat with a signal current in order to ensure safety of the device. The protective element cuts off the circuit by fusing a fuse element composed of an alloy material fusible by generated heat of the resistive element or cuts off the circuit by fusing the fuse element with an overcurrent.
Japanese Patent Laying-Open No. 2013-239405 (PTL 1) discloses a protective element in which a resistive element that generates heat at the time of occurrence of an abnormal condition is provided on an insulating substrate such as a ceramic substrate.
Currently, a fusible alloy that makes up the fuse element of the protective element described above tends to be lead-free in order to follow stronger regulations on chemical substances under an amended RoHS directive or the like. A fuse element composed of a lead-free metal composite material described in Japanese Patent Laying-Open No. 2015-079608 (PTL 2) is available. The fuse element is composed of a fusible low-melting-point metal material that can melt at a working temperature of soldering in surface mount of the protective element on an external circuit substrate and a high-melting-point metal material in a solid phase that can be dissolved into the low-melting-point metal material in a liquid phase at the working temperature of soldering. In the fuse element, the low-melting-point metal material and the high-melting-point metal material are integrally formed, thereby holding the low-melting-point metal material that has been converted to the liquid phase with the use of the high-melting-point metal material in the solid phase until the soldering work is completed.
The low-melting-point metal material and the high-melting-point metal material of the fuse element are formed in a state of being secured to each other. While the low-melting-point metal material that has been converted to the liquid phase at the working temperature of soldering is held without being fused by the high-melting-point metal material in the solid phase at the working temperature of soldering, the fuse element is joined to an electrode pattern of the protective element with the low-melting-point metal material in the liquid phase. Fusing of the fuse element at the working temperature of soldering in surface mount of the protective element on the circuit substrate is prevented. The protective element performs a fusing operation by having a contained resistive element generate heat to diffuse or dissolve with heat, the high-melting-point metal material of the fuse element into the low-melting-point metal material serving as a medium.
In the protective element, it is necessary to apply an operating flux to a surface of the fuse element and hold the operating flux on the surface until the fuse element is fused, in order to guarantee normal fusing of the fuse element. Since a conventional flux for a protective element is rich in thermal fluidity, the flux applied to the surface of the fuse element flows from a surface of a fuse alloy when the protective element is exposed to thermal environment such as a reflow furnace at the time of mounting of the protective element on the circuit substrate. As a result, the operating flux may in some cases be lost from the surface of the fuse alloy.
When the flux is lost from the surface of the fuse alloy, spherical fusing of the fuse alloy is prevented, which leads to non-fusing, or poor fusing such as stringing caused by an oxide or the like remaining on the alloy surface. Therefore, as described in Japanese Patent Laying-Open No. 2010-003665 (PTL 3), for example, an insulating cover member that covers a fuse element of a protective element is provided with a stepped portion that holds a flux at a prescribed position. The stepped portion is formed by a protrusive stripe. The flux is applied while being brought into contact with the circularly formed stepped portion and a center part of a fuse alloy, and the flux is held using interfacial tension of the flux and the insulating cover member.
As described in Japanese Patent Laying-Open No. 2014-091162 (PTL 4), a protective element having adhesiveness improved by containing an inorganic filler in an operating flux is available.
A conventional flux contains an organic thixotropic agent, and when a temperature of the flux is increased to a reflow temperature (maximum temperature of 250 to 260° C.), the flux loses thixotrophy and cannot hold the shape for flowing. Therefore, as described in PTL 3, restriction of a flow range of the operating flux that flows under thermal environment is necessary. In order to restrict the flow range, it has been necessary to use a particular package structure such as a structure in which the stepped portion is provided on a portion of the insulating cover member that faces the center part of the fuse element. In addition, as described in PTL 4, it has been necessary to carry, with filler particles, the operating flux that has been liquefied under thermal environment and improve the holding force by adding the filler particles to the operating flux.
However, when the insulating cover member is provided with the stepped portion as described in PTL 3, the stepped portion of the insulating cover member makes an internal space narrower particularly in a small and thin package. As a result, when the fuse alloy is fused, the molten fuse alloy is pushed out from an electrode portion to form a bridge between electrodes, or wet flowing of the molten fuse alloy to the electrode portion is inhibited, which leads to poor fusing.
More specifically, the molten fuse alloy gathers in a dome shape on the heated electrode due to surface tension and is fused, while wetting the heated electrode portion. A height of the molten alloy formed in a dome shape is restricted by the stepped portion (protrusive stripe) provided on the cover member. Therefore, the excess molten alloy overflows around the electrode and forms a bridge between the electrodes, which leads to non-fusing.
In addition, since the insulating cover member is provided with the stepped portion, the insulating cover member increases in thickness. This structure is disadvantageous for reduction in profile of a product. Furthermore, forming a part of the package into a particular shape makes the package structure complicated, which leads to an increase in component cost.
In the operating flux having the filler particles added thereto as described in PTL 4, the inorganic filler is contained in the operating flux to thereby form a paste having low fluidity. By holding the operating flux between the filler particles, the operating flux applied to the surface of the fuse alloy is less likely to flow from the surface of the fuse alloy even when the protective element is exposed to thermal environment. However, surface tension of the operating flux decreases with an increase in temperature. Therefore, under a severe heating condition, the holding capacity of the filler reaches a limit when a prescribed temperature is exceeded, and thus, flowing cannot be completely suppressed.
An object of the present disclosure is to provide a protective element for electric devices and electronic devices that prevents an operating flux applied to a surface of a fuse element from flowing from the surface of the fuse element even when the protective element is exposed to severe thermal environment.
A protective element according to an aspect of the present disclosure includes: at least two electrode portions supported by an insulating support; a fuse element that connects the electrode portions; and an operating flux provided on the fuse element. The operating flux has, on a surface thereof, a coating layer that covers the operating flux to prevent the operating flux from flowing.
In the protective element, the coating layer may be a film formed by curing of a surface of the operating flux itself.
In the protective element, the coating layer may be made of a coating material that covers a surface of the operating flux, the coating material being different from the operating flux.
In the protective element, the coating material may be sheet-shaped.
In the protective element, the coating layer may be made of a thermosetting resin.
In the protective element, the coating layer may be made of an ultraviolet curable resin.
In the protective element, the coating layer may be made of an electron beam curable resin.
In the protective element, the coating layer may be made of an epoxy resin.
In the protective element, the coating layer may be made of an acrylic resin or an acrylic ester resin.
In the protective element, the operating flux may be partially provided on a surface of the fuse element.
A protective element according to another aspect of the present disclosure includes: an insulating substrate; a heat generation element provided on the insulating substrate; at least two main electrodes provided on the insulating substrate; a current-conducting electrode provided on the insulating substrate, for current conduction through the heat generation element; a fuse element provided on the at least two main electrodes and the current-conducting electrode; and an operating flux provided on the fuse element. The operating flux has, on a surface thereof, a coating layer that covers the operating flux to prevent the operating flux from flowing.
In the protective element, the coating layer may be made of a thermosetting resin.
In the protective element, the coating layer may be made of an ultraviolet curable resin.
In the protective element, the coating layer may be made of an electron beam curable resin.
In the protective element, the coating layer may be made of an epoxy resin.
In the protective element, the coating layer may be made of an acrylic resin or an acrylic ester resin.
In the protective element, the current-conducting electrode may be arranged between the at least two main electrodes with gap portions interposed, and the operating flux may be provided on a portion of the fuse element that overlaps with the current-conducting electrode, and a portion of the fuse element that overlaps with the gap portions extending from the current-conducting electrode to ends of the at least two main electrodes.
In the protective element, the fuse element may be made of a composite material of a first fusible metal and a second fusible metal.
In the protective element, the first fusible metal or the second fusible metal may be made of a tin-based alloy containing one or both of silver and copper.
In the protective element, at least one of the first fusible metal and the second fusible metal may be made of a lead-free tin-based solder material.
In the protective element, at least one of the first fusible metal and the second fusible metal may be an alloy material selected from an Sn—Ag alloy containing 3 to 4 mass % of Ag and a remainder of Sn, an Sn—Cu—Ag alloy containing 0.5 to 0.7 mass % of Cu, 0 to 1 mass % of Ag and a remainder of Sn, an Sn—Ag—Cu alloy containing 3 to 4 mass % of Ag, 0.5 to 1 mass % of Cu and a remainder of Sn, and an Sn—Bi alloy containing 10 to 60 mass % of Bi and a remainder of Sn.
In the protective element, at least one of the first fusible metal and the second fusible metal may be an alloy material selected from a 96.5Sn-3.5Ag alloy, a 99.25Sn-0.75Cu alloy, a 96.5Sn-3Ag-0.5Cu alloy, a 95.5Sn-4A5-0.5Cu alloy, and a 42Sn-58Bi alloy.
A protective element according to still another aspect of the present disclosure includes: an insulating substrate; a heat generation element provided on the insulating substrate; at least two main electrodes provided on the insulating substrate; a current-conducting electrode provided on the insulating substrate, for current conduction through the heat generation element; a fuse element provided on the at least two main electrodes and the current-conducting electrode; and an operating flux provided on the fuse element. The operating flux contains a curable resin component, and the operating flux has a coating layer that covers a surface of the operating flux, the coating layer being made of the curable resin component.
In the protective element, the coating layer may be composed of a film formed by curing of the surface of the operating flux.
In the protective element, the curable resin component may be made of an epoxy resin.
In the protective element, the current-conducting electrode may be arranged between the at least two main electrodes with gap portions interposed, and the operating flux may be provided on a portion of the fuse element that overlaps with the current-conducting electrode, and a portion of the fuse element that overlaps with the gap portions extending from the current-conducting electrode to ends of the at least two main electrodes.
In the protective element, the fuse element may be made of a composite material of a first fusible metal and a second fusible metal.
In the protective element, the first fusible metal or the second fusible metal may be made of a tin-based alloy containing one or both of silver and copper.
In the protective element, at least one of the first fusible metal and the second fusible metal may be made of a lead-free tin-based solder material.
In the protective element, at least one of the first fusible metal and the second fusible metal may be an alloy material selected from an Sn—Ag alloy containing 3 to 4 mass % of Ag and a remainder of Sn, an Sn—Cu—Ag alloy containing 0.5 to 0.7 mass % of Cu, 0 to 1 mass % of Ag and a remainder of Sn, an Sn—Ag—Cu alloy containing 3 to 4 mass % of Ag, 0.5 to 1 mass % of Cu and a remainder of Sn, and an Sn—Bi alloy containing 10 to 60 mass % of Bi and a remainder of Sn.
In the protective element, at least one of the first fusible metal and the second fusible metal may be an alloy material selected from a 96.5Sn-3.5Ag alloy, a 99.25Sn-0.75Cu alloy, a 96.5Sn-3Ag-0.5Cu alloy, a 95.5Sn-4Ag-0.5Cu alloy, and a 42Sn-58Bi alloy.
According to an embodiment of the present disclosure, there can be provided a protective element that prevents an operating flux applied to a surface of a fuse element from flowing from the surface of the fuse element even when the protective element is exposed to severe thermal environment.
A protective element according to the present disclosure includes: at least two electrode portions supported by an insulating support; a fuse element that connects the electrode portions; and an operating flux provided on the fuse element. The operating flux has a coating layer that covers the operating flux to prevent the operating flux from flowing.
Any coating layer may be used as the coating layer as long as it can cover an entire surface of the operating flux. The coating layer may be a film formed by curing of the surface of the operating flux itself. The coating layer may be a coating material different from the operating flux that covers the surface of the operating flux after the operating flux is applied.
The coating layer may be formed by applying a liquid coating material onto the operating flux and then forming a film. The coating layer may be formed by putting a flexible and easily-deformable solid-sheet-shaped coating material or a flexible and easily-deformable semi-solid (such as semi-polymerized resin)-sheet-shaped coating material on the operating flux. The sheet-shaped coating material is adsorbed or compression-bonded to the surface of the operating flux. At the time of adsorption or compression bonding, the sheet-shaped coating material may be heated. The coating material may be a thermosetting resin unless it exhibits fluidity at a desired temperature.
As one example of the protective element, a protective element 10 shown in
Insulating substrate 11 forms an insulating support that supports main electrodes 13 (electrode portions). The insulating support is not limited to the insulating substrate.
Operating flux 16 does not necessarily need to be applied to an entire exposed surface of fuse element 15. Operating flux 16 may be partially applied to a portion of the surface of fuse element 15 required for operation.
Coating layer 17 extends on a surface of operating flux 16 and on a part of fuse element 15 beyond an end surface where operating flux 16 is applied. Any alloy may be used as first fusible metal 15a and second fusible metal 15b as long as it is a fusible metal that can melt as a result of heating by heat generation element 12. Although the alloy is not particularly limited, an Sn—Ag alloy containing 3 to 4 mass % of Ag and a remainder of Sn, an Sn—Cu—Ag alloy containing 0.5 to 0.7 mass % of Cu, 0 to 1 mass % of Ag and a remainder of Sn (here, silver is not essential and is added as needed), an Sn—Ag—Cu alloy containing 3 to 4 mass % of Ag, 0.5 to 1 mass % of Cu and a remainder of Sn, and an Sn—Bi alloy containing 10 to 60 mass % of Bi and a remainder of Sn can be used as a first example. A tin-based solder material such as a 96.5Sn-3.5Ag alloy, a 99.25Sn-0.75Cu alloy, a 96.5Sn-3Ag-0.5Cu alloy, a 95.5Sn-4Ag-0.5Cu alloy, or a 42Sn-58Bi alloy can be used as a second example of the alloy (the coefficients of each alloy material represent mass % of the elements).
Instead of the above-described fusible metal, a metal material that is dissolved into first fusible metal 15a as a result of heating by heat generation element 12 may be used as second fusible metal 15b. Although the metal material is not particularly limited, silver, copper, or an alloy containing these can be suitably used as one example. For example, a lead-free tin-based solder material such as an Sn—Ag alloy containing 25 to 40 mass % of Ag and a remainder of Sn can be used as a silver alloy.
In protective element 10, film-like coating layer 17 encloses an outer layer portion of operating flux 16 and covers an end of fuse element 15. Thus, operating flux 16 liquefied by heat during fusing can be held within coating layer 17 to prevent operating flux 16 from flowing from the applied surface of fuse element 15 until fuse element 15 melts.
As another example of the protective element, a protective element 20 shown in
Operating flux 26 does not necessarily need to be applied to an entire exposed surface of fuse element 25. Operating flux 26 may be partially applied to at least a portion of the surface of fuse element 25 required for operation.
Coating layer 27 is a film formed by curing of the surface of operating flux 26. Any alloy may be used as first fusible metal 25a and second fusible metal 25b as long as it is a fusible metal that can melt as a result of heating by heat generation element 22. Although the alloy is not particularly limited, an Sn—Ag alloy containing 3 to 4 mass % of Ag and a remainder of Sn, an Sn—Cu—Ag alloy containing 0.5 to 0.7 mass % of Cu, 0 to 1 mass % of Ag and a remainder of Sn (here, silver is not essential and is added as needed), an Sn—Ag—Cu alloy containing 3 to 4 mass % of Ag, 0.5 to 1 mass % of Cu and a remainder of Sn, and an Sn—Bi alloy containing 10 to 60 mass % of Bi and a remainder of Sn can be used as a first example. A tin-based solder material such as a 96.5Sn-3.5Ag alloy, a 99.25Sn-0.75Cu alloy, a 96.5Sn-3Ag-0.5Cu alloy, a 95.5Sn-4Ag-0.5Cu alloy, or a 42Sn-58Bi alloy can be used as a second example of the alloy (the coefficients of each alloy material represent mass % of the elements).
Instead of the above-described fusible metal, a metal material that is dissolved into first fusible metal 25a as a result of heating by heat generation element 22 may be used as second fusible metal 25b. Although the metal material is not particularly limited, silver, copper, or an alloy containing these can be suitably used as one example. For example, a lead-free tin-based solder material such as an Sn—Ag alloy containing 25 to 40 mass % of Ag and a remainder of Sn can be used as a silver alloy.
In protective element 20, the curable resin component, which is an additive contained in operating flux 26, is cured on the surface to generate film-like coating layer 27. Coating layer 27 encloses an outer layer portion of operating flux 26 and is fixed to a perimeter end of fuse element 25. Thus, operating flux 26 liquefied by heat during fusing can be held within coating layer 27 to prevent operating flux 26 from flowing from the applied surface of fuse element 25 until fuse element 25 melts.
As shown in
Protective element 10 includes fuse element 15 provided on main electrodes 13 and current-conducting electrode 14 and made of a composite material of first fusible metal 15a and second fusible metal 15b, first fusible metal 15a being made of a 96.5Sn-3Ag-0.5Cu alloy, second fusible metal 15b being made of silver. Protective element includes operating flux 16 applied to fuse element 15. Operating flux 16 has, on a surface thereof, coating layer 17 made of an epoxy resin and provided to cover operating flux 16 to prevent operating flux 16 from flowing.
Protective element 10 includes a cap-shaped lid 18 made of liquid crystal polymer and fixed to insulating substrate 11 to cover fuse element 15 and operating flux 16. A protective insulating film made of glass glaze is provided on a surface of heat generation element 12. Protective element 10 includes wiring means 110 formed of a half through hole made of sintered silver. Wiring means 110 is for electrically connecting main electrodes 13 and current-conducting electrode 14 that are provided on the upper surface of insulating substrate 11 to pattern electrodes 19 and current-conducting electrode 14 that are provided on the lower surface of insulating substrate 11. Instead of the thermosetting epoxy resin, coating layer 17 can be made of an ultraviolet (UV) curable resin such as an acrylic acid-based resin or an acrylic ester-based resin, or an electron beam (EB) curable resin.
As shown in
Protective element 20 includes fuse element 25 provided on main electrodes 23 and current-conducting electrode 24 and made of a composite material of first fusible metal 25a and second fusible metal 25b, first fusible metal 25a being made of a 96.5Sn-3Ag-0.5Cu alloy, second fusible metal 25b being made of a 70Sn-30Ag alloy. Operating flux 26 contains an epoxy resin component as a blended component, and has coating layer 27 made of an epoxy resin component and provided to cover the surface of operating flux 26.
Protective element 20 includes a cap-shaped lid 28 made of liquid crystal polymer and fixed to insulating substrate 21 to cover fuse element 25 and operating flux 26 including coating layer 27. Glass glaze (protective insulating film) is provided on a surface of heat generation element 22. Main electrodes 23 and current-conducting electrode 24 provided on the upper surface of insulating substrate 21 include wiring means 210 formed of a half through hole made of sintered silver for electrical connection to a pattern electrode 29 provided on the lower surface of insulating substrate 21. Heat generation element 22 of the protective element in Example 2 is provided on the same surface (upper surface) as the surface (upper surface) of insulating substrate 21 where fuse element 25 is provided.
The portion of protective element 10 in Example 1 to which operating flux 16 is applied may be changed and an operating flux 36 may be applied as shown in
The portion of protective element 20 in Example 2 to which operating flux 26 is applied may be changed and an operating flux 46 may be applied as shown in
In the protective element in each of Example 1 and Example 2, the wiring means that electrically connects the main electrodes and the current-conducting electrode to the pattern electrode, which are separated by the insulating substrate, may be a conductor through hole passing through the insulating substrate, or may be a surface wiring formed by a planar electrode pattern, instead of the half through hole. Instead of silver or copper, a tin-based alloy containing at least one or both of silver and copper can be used as the second low-melting-point metal material.
Although the embodiments of the present disclosure have been described, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
The protective element according to the present disclosure can be mounted on another circuit board by, for example, reflow soldering and can be used in a protection device for a secondary battery, such as a battery pack.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-071449 | Apr 2020 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17770424 | Apr 2022 | US |
| Child | 18372941 | US |
