CN215869263U - Protection element and circuit protection device thereof - Google Patents

Abstract

The utility model discloses a protective element and a circuit protection device thereof, which comprise a substrate, a fuse element and a heating element; the surface of the substrate is provided with a first electrode and a second electrode; the fuse is arranged on the substrate, and two ends of the fuse are electrically connected with the first electrode and the second electrode; the fuse element sequentially comprises a second metal layer, a first metal layer and a third metal layer which are laminated, and the melting points of the second metal layer and the third metal layer are lower than the melting point of the first metal layer; the heating element is arranged on the substrate; when overvoltage or overtemperature occurs, the heating element generates heat to melt the fuse element; the sum of the thickness of the second metal layer and the third metal layer is 40-95% of the thickness of the fuse. The utility model has the functions of overvoltage, overcurrent and/or overtemperature protection; the lead-free solder is developed by combining the structural design with the ceramic substrate, the thick film lamination design and the high-temperature lead-free fuse material, so that the lead-free requirement of the product is met, and the lead-free fuse is more environment-friendly.

Description

Protection element and circuit protection device thereof

[ technical field ] A method for producing a semiconductor device

The present invention relates to a protection device for an electronic device and a circuit protection device including the same, and more particularly, to a protection device and a circuit protection device having a function of preventing an overvoltage, an overcurrent, or an overtemperature.

[ background of the utility model ]

Aiming at the development trend of lithium secondary power sources, the development plan develops a three-terminal fuse form factor (form factor)1612 series lead-free product, and the lead-free product is matched with the sensing capability of an IC and an MOSFET, and simultaneously provides the functions of overcharge protection, overdischarge protection, overcurrent protection and the like of a lithium battery module. In recent years, energy storage devices are highly popular, and for information products such as low-power mobile phones and notebook computers, and high-power electric tools and manned electric vehicles, secondary power supplies are required, the most common mode is to use dry batteries or rechargeable batteries, and besides the design of primary protection, secondary protection measures are required when the primary protection function fails, and the required secondary protection measures, namely, the key components and the whole scheme which have monitoring and acute response of over-current, over-temperature and over-voltage are provided simultaneously, so that the safety of the whole battery is ensured to be improved, and the purpose of battery protection is achieved.

Generally, the fuse and the solder of the three-terminal fuse mainly comprise tin and lead, so as to avoid the fuse melting phenomenon caused by the over-high reflow temperature when the client performs the Surface Mount Technology (SMT) process to assemble the device, thereby forming the whole circuit open, and therefore, the fuse and the solder need to be made of a material with a higher melting point, so as to ensure that the phenomenon does not occur. The melting point of the material is improved by a material alloy, the main materials of the alloy are tin and lead, the melting point is higher as the proportion of lead is higher, however, with the gradual rise of environmental awareness, although the high-lead product is an excluded item of international green management, the undeniable lead is a harmful substance, and causes damage to the environment and phenomena harmful to the human body, such as dizziness, anemia, insomnia, memory decline, arthralgia and the like.

Therefore, it is necessary to provide a new protection device and a circuit protection apparatus thereof to solve the above technical problems.

[ Utility model ] content

It is an object of the present invention to provide a protection device having overvoltage, overcurrent and/or overtemperature protection functions; the lead-free solder is developed by combining the structural design with the ceramic substrate, the thick film lamination design and the high-temperature lead-free fuse material, so that the lead-free requirement of the product is met, and the lead-free fuse is more environment-friendly.

The utility model realizes the purpose through the following technical scheme: a protection element comprises a substrate, a fuse and a heating element; the surface of the substrate is provided with a first electrode and a second electrode; the fuse part is arranged on the substrate, and two ends of the fuse part are electrically connected to the first electrode and the second electrode; the fuse comprises a first metal layer, a second metal layer and a third metal layer, wherein the second metal layer and the third metal layer are respectively arranged on the upper surface and the lower surface of the first metal layer, the melting point of any one of the second metal layer and the third metal layer is lower than that of the first metal layer, and the second metal layer and the third metal layer have different melting points; the heating element is arranged on the substrate; when overvoltage or overtemperature occurs, the heating element generates heat to melt the fuse element; the sum of the thickness of the second metal layer and the third metal layer is 40-95% of the thickness of the fuse.

In one embodiment, the combined thickness of the second metal layer and the third metal layer is greater than the thickness of the first metal layer.

In one embodiment, the melting point of the second metal layer is higher than the melting point of the third metal layer, or the melting point of the second metal layer is lower than the melting point of the third metal layer.

In one embodiment, the first metal layer comprises silver, copper, gold, nickel, zinc or alloys thereof.

In one embodiment, any one of the second metal layer and the third metal comprises tin or an alloy thereof.

In one embodiment, the first metal layer forms an inner layer of the fuse, and the second metal layer and the third metal layer form an outer layer of the fuse.

In one embodiment, when the thickness of the first metal layer is greater than or equal to 16 μm and less than 18 μm, the sum of the thickness of the second metal layer and the thickness of the third metal layer is greater than or equal to 50% of the thickness of the fuse; and wherein when the thickness of the first metal layer is 18 μm or more, the sum of the thicknesses of the second metal layer and the third metal layer is 60% or more of the thickness of the fuse.

Another objective of the present invention is to provide a circuit protection device, which includes a protection device, a detector and a switch; the protective element comprises a substrate, a fuse and a heating element; the surface of the substrate is provided with a first electrode and a second electrode; the fuse part is arranged on the substrate, and two ends of the fuse part are electrically connected to the first electrode and the second electrode; the fuse comprises a first metal layer, a second metal layer and a third metal layer, wherein the second metal layer and the third metal layer are respectively arranged on the upper surface and the lower surface of the first metal layer, the melting point of any one of the second metal layer and the third metal layer is lower than that of the first metal layer, the second metal layer and the third metal layer have different melting points, and the sum thickness of the second metal layer and the third metal layer is 40-95% of the thickness of the fuse; the heating element is arranged on the substrate; the detector is used for detecting the voltage drop or the temperature of a circuit to be protected; the switch is connected with the detector to receive a detection signal of the detector; when the detector detects that the voltage drop or the temperature exceeds a preset value, the switch is conducted, and current flows through the heating element, so that the heating element generates heat to melt the fuse element.

Compared with the prior art, the protection element and the circuit protection device thereof have the advantages that: the fuse in the protective element is a multi-layer metal layer composite structure, wherein the first metal layer has a higher melting point than the second metal layer and the third metal layer, and the second metal layer and the third metal layer have different melting points. In addition, the thickness of the second metal layer and the third metal layer is more than a certain proportion of the thickness of the fuse. Therefore, even if the reflow temperature is higher than the melting points of the second metal layer and the third metal layer during subsequent reflow, the second metal layer and the third metal layer have a certain thickness, and will not flow or deform seriously, and the melting of the second metal layer and the third metal layer will corrode (anode) the first metal layer. Then, for the second metal layer and the third metal layer, the one with the lower melting point will further erode the one with the higher melting point, thereby accelerating the fusing of the fuse element and providing protection. The fuse of the protective element comprises metal layers with different melting points, and compared with the traditional lead-containing tin sheet, the resistance value of the fuse can be reduced, so that the characteristics of low surface temperature and high current are achieved.

[ description of the drawings ]

FIG. 1 is a schematic structural diagram of a protection device according to an embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram of the protection device of FIG. 1;

FIG. 3 is a schematic structural view of a fuse in an embodiment of the present invention;

FIG. 4 is a circuit diagram of a circuit protection device according to an embodiment of the present invention;

description of reference numerals:

10 protective element

11 substrate

12 heating element

13 heating electrode

14 insulating layer

15 intermediate electrode

16 fuse

16a first metal layer

16b second metal layer

16c third metal layer

17 solder

18 electrode layer

18a first electrode

18b second electrode

19a lower electrode

19b lower electrode

20 outer cover

21 scaling powder

22 conducting part

60 circuit protection device

61 Detector

62 switch

[ detailed description ] embodiments

The utility model will now be further described with reference to the accompanying drawings.

According to the utility model, the thick film lamination printing process uses ceramic as a substrate material and is processed by laser, the circuit is integrated on the ceramic by a screen printing technology, a lamination circuit substrate with a heating function is formed by a high-temperature eutectic firing mode, high-conductivity silver paste is selected to manufacture an inner layer circuit layout, resistance paste is selected to manufacture a heating layer, high-insulation paste is selected to manufacture an electric insulation layer, each layer of circuit is combined to form a lamination circuit, and the loadable power of the battery and the required withstand voltage are limited by the design and material technology. When the battery is overcharged, the IC provides signal, FET provides driving power to start the heating layer, and the fuse is fast fused to reach the protection effect. The selection of the materials is as follows:

(1) high-conductivity silver paste: the high-conductivity silver paste is selected as the conductor for connecting the circuit layout of each layer by utilizing the characteristics of excellent conductivity and large current density allowed to flow.

(2) Resistance paste: the method selects the resistance slurry with higher power, makes a heating layer on the ceramic substrate, limits the loadable power of the battery through the resistance, and can match the resistance required by the working voltage of the lithium ion battery in series and parallel, thereby utilizing the characteristics of the lithium ion battery to improve the product characteristics.

(3) High-insulation slurry: the insulating slurry with high insulating degree is selected as the insulating layer between the lamination loops, the insulating slurry has better insulation performance under the condition that the element is kept electrified for a long time, when the upper layer and the lower layer are electrified, the material can be effectively protected from contacting with air, the phenomenon of oxidation is isolated, the reliability of the product can be improved, the above advantages of the material are utilized, the moisture isolation characteristic is improved, and the testing can be carried out in a high-temperature, high-humidity and severe environment.

As for the fuse wire (i.e. the fuse link), the first layer of high-temperature metal layer material is rolled into a sheet shape, then the second layer of low-temperature metal layer material is added after processing, and the sheet metal is manufactured into a metal sheet, and the product structure is used as the fuse wire of the overcurrent protection, and the lead-free solder is matched during welding and is lapped on the electrode of the laminated circuit substrate, under the regulation and control of precise reflow furnace parameters, the fuse wire can not be damaged or partially fused, otherwise, the stability of the fuse wire fusing when the overcurrent is generated is influenced.

Different from the prior art, in the brand-new design of the embodiment, three electrodes are arranged below the fuse, when heat is transferred to the three electrodes of the fuse, the molten metal of the fuse is attracted towards the three electrodes below the fuse, so that the fuse is blown, and the problem of inaccurate blowing time in the traditional technology can be solved. The insulating and heat insulating layer of the protection element can prevent heat dissipation, effectively concentrates heat generated by the heating layer on the fuse to accelerate the fusing efficiency of the fuse, ensures that a protection mechanism can be started in time, and is particularly suitable for application occasions with strict requirements on protection speed.

The following description will specifically refer to the related embodiments and will be made in detail with reference to the accompanying drawings.

Fig. 1 shows a block diagram of a protective element 10 according to the utility model. The protective member 10 has a substrate 11, a heating member 12, a heating electrode 13, an insulating layer 14, an intermediate electrode 15, a fuse 16, a solder 17, an electrode layer 18, lower electrodes 19a and 19b, and a cover 20. The outer edge of the housing 20 is disposed on the surface of the substrate 11 to provide an inner space for accommodating the heating member 12, the fuse 16, and the like. The substrate 11 is typically a planar insulating substrate. The heater 12 is disposed on the substrate 11, and both ends thereof are electrically connected to the left and right heater electrodes 13. The fuse 16 has both ends electrically connected to the first electrode 18a and the second electrode 18b on both sides of the electrode layer 18, and the middle portion of the fuse 16 is connected to the middle electrode 15 disposed on the surface of the insulating layer 14, wherein both ends of the fuse 16 may be connected to the first electrode 18a and the second electrode 18b by solder 17. The first electrode 18a and the second electrode 18b may be connected to the left and right lower electrodes 19a and 19b through the via 22 located at the side of the substrate 11. The lower electrodes 19a and 19b may serve as an interface for surface mounting to a circuit board (not shown). The insulating layer 14 covers the heating member 12 and the heating electrode 13. The fuse 16 is disposed above the insulating layer 14 as a fuse (fuse) on the circuit. The fuse 16 includes a first metal layer 16a and a second metal layer 16b disposed on a surface of the first metal layer 16a, and is a composite structure. The fuse 16 may be coated with a flux 21 over all or part of the fuse 16 in order to prevent oxidation of the second metal layer 16b or the first metal layer 16 a. The flux 21 mainly forms an anti-oxidation layer on the surface of the outermost second metal layer 16b, and can effectively prevent the second metal layer 16b from being oxidized, thereby maintaining the fast fusing efficiency. When overvoltage or overtemperature occurs, the heating member 12 generates heat and transfers the heat to the fuse 16, so that the fuse 16 is melted and flows to the first electrode 18a, the second electrode 18b and the middle electrode 15 at two sides to be fused, and current is cut off to achieve the purpose of protection. Fig. 2 shows an equivalent circuit diagram of the protection device 10 of fig. 1, and in this embodiment, the fuse 16 includes two fuses (fuses) through the arrangement of the middle electrode 15. When an overvoltage occurs, the heating member 12 generates heat to melt the fuse 16. The fuse element comprises low-melting-point metal and can be fused to provide protection when an abnormal event occurs.

The substrate 11 may have a square structure, and the material may be an insulating material such as alumina, aluminum nitride, zirconia, glass ceramics, or a material used for a printed wiring board such as a glass epoxy substrate or a phenol substrate. The thickness of the substrate 11 is about 0.1 to 2 mm. The electrode layer 18, heater electrode 13, and intermediate electrode 15 may comprise silver, gold, copper, tin, nickel, or other conductive metal, and may have a thickness of about 0.005 to 1mm, or more particularly 0.01mm, 0.05mm, 0.1mm, 0.3mm, 0.5 mm. Instead of using printing to make the electrodes, metal sheets can be used to make them suitable for high voltage applications.

In this embodiment, the fuse 16 is a composite structure composed of an inner layer and an outer layer, and may be a rectangular long strip or a round strip, the first metal layer 16a as the inner layer is a high melting point metal layer, and the second metal layer 16b and the third metal layer 16c as the outer layers on the upper and lower surfaces of the first metal layer 16a are low melting point metal layers. That is, the second metal layer 16b and the third metal layer 16c have lower melting points than the first metal layer 16 a. The melting points of the second metal layer 16b and the third metal layer 16c are different, and the melting point of the second metal layer 16b may be higher than the melting point of the third metal layer 16c, or the melting point of the second metal layer 16b may be lower than the melting point of the third metal layer 16 c. The second metal layer 16b and the third metal layer 16c may be formed on the surface of the first metal layer 16a by plating, vapor deposition, lamination, rolling, or the like. In one embodiment, the first metal layer 16a includes, for example, Ag, Cu, Au, Ni, Zn, or a metal or an alloy thereof having any one of them as a main component. The second metal layer 16b and the third metal layer 16c preferably comprise a metal having a Sn-based constituent or an alloy thereof, such as Sn, Sn-Ag, Sn-Sb, Sn-Zn, Sn-Ag-Cu, Pb-Sn-Ag, Sn-Zn-Cu, Sn-Bi-Ag, and Sn-Bi-Ag-Cu, and particularly or optionally a Pb-free material to comply with the RoHS directive. In one embodiment, the melting point of the second metal layer 16b and the melting point of the third metal layer 16c are lower than the melting point of the first metal layer 16a, and the melting point of the first metal layer 16a is higher than the reflow temperature. In this way, even if the reflow temperature exceeds the melting temperature of the second metal layer 16b and the third metal layer 16c, and the surfaces of the second metal layer 16b and the third metal layer 16c as the outer layers may slightly flow, the first metal layer 16a does not reach its melting point, so that the fuse 16 is not fused, and the existing shape of the fuse 16 can be maintained. The material of the heating element 12 may include ruthenium oxide (RuO2) and additives such as silver (Ag), palladium (Pd), and platinum (Pt). The insulating layer 14 for isolating the heating element 12 from the fuse element 16 may be made of glass (glass), epoxy (epoxy), alumina or silicone, or glaze (glaze).

In one embodiment, the fuse 16 has a thickness T of about 15-150 μm, wherein the thickness T1 of the first metal layer 16a is about 5-30 μm, and the thicknesses of the upper, lower second metal layers 16b and the third metal layer 16c are about 5-50 μm, respectively, i.e., the total thickness T2 of the second metal layer 16b and the third metal layer 16c is about 10-100 μm. Specifically, the thickness T2 of any one of the second metal layer 16b and the third metal layer 16c may be greater than or less than the thickness T1 of the first metal layer 16a, and the ratio of the sum of the thicknesses of the second metal layer and the third metal layer to the total thickness of the fuse (T1 + T2) is preferably 40 to 95%, for example, 50%, 60%, 70%, 80%, or 90%. Preferably, either the second metal layer 16b or the third metal layer 16c is relatively thick, while the first metal layer 16a is relatively thin, or the fuse 16 has a larger volume of either the second metal layer 16b or the third metal layer 16c than the first metal layer 16 a. When an abnormal condition such as overvoltage or overcurrent occurs, the first metal layer 16a can be effectively eroded if one of the second metal layer 16b and the third metal layer 16c has a large thickness or a large volume. Furthermore, after the second metal layer 16b and the third metal layer 16c are eroded by the first metal layer 16a, since the second metal layer 16b and the third metal layer 16c have different melting points, the one with the lower melting point will further erode the one with the higher melting point. Such a structural design can accelerate the fusing of the fuse 16 in a short time. To sum up, the ratio of the thickness and the volume of the first metal layer 16a to the sum of the second metal layer 16b and the third metal layer 16c has a proper value, and the second metal layer 16b and the third metal layer 16c, which are too thin or too small in volume, cannot fuse the fuse 16 quickly and efficiently.

In a preferred embodiment, when the thickness of the first metal layer is greater than or equal to 16 μm and less than 18 μm, the sum of the thicknesses of the second metal layer and the third metal layer is greater than or equal to 50% of the thickness of the fuse. In another preferred embodiment, when the thickness of the first metal layer is 18 μm or more, the sum of the thicknesses of the second metal layer and the third metal layer is 60% or more of the thickness of the fuse.

Fig. 3 shows a schematic structural view of an embodiment of the fuse 16. As shown in fig. 3, the second metal layer 16b and the third metal layer 16c are disposed on the upper surface and the lower surface of the first metal layer 16a, respectively.

Generally, the SMT process condition is 245-260 ℃, and the fuse material used by competitors is tin-lead alloy, in order to meet the condition that the fuse reaches a non-melting state after the SMT process, the proportion of lead is generally increased to more than 85%, but the higher the lead content is, the deeper the damage to human body is, and the fuse without lead material is adopted in the embodiment, so as to achieve the purpose of lead-free product development. In addition, under the restriction of product size and structural design space, the fuse size is also restricted, and the fuse material of the embodiment has lower resistance characteristic, and under the same fuse size as a competitor, the rated current of the application can be increased from 12A to 22A, so that the market of the original application, such as information products of mobile phones, notebook computers and the like, can be expanded to the market application of larger current, such as electric tools, dust collectors and the like.

The equivalent circuit diagram of the protection element 10 of the present embodiment may also be shown as a circuit of a dashed box in fig. 4. The first electrode 18a serves as a terminal a1 to which a device to be protected (e.g., a secondary battery or a motor) is connected, and the second electrode 18B is connected to a terminal B1, such as a charger or other similar device. The intermediate electrode 15 is connected to one heating electrode 13, and the other heating electrode 13 is connected to the switch 62. The fuse element 16 forms a circuit comprising 2 fuses (fuses) connected in series, and the heating element 12 forms a heater (shown as a resistance symbol), depending on the circuit design of the protection element 10. In one embodiment, the switch 62 may be a Field Effect Transistor (FET), for example. A switch 62, for example a gate (gate) of a FET, is connected to the detector 61 and to the other terminal a2 of the circuit to be protected and to the other terminal B2 of the charger. The detector 61 may be an IC device, and has a function of detecting a voltage drop or a temperature. When there is no over-voltage or over-temperature, the switch 62 is open and current passes through the fuse element 16, but no current flows through the heating element 12. If an overcurrent occurs, the fuse 16 will be blown to provide overcurrent protection. When the detector 61 detects a voltage exceeding a predetermined value (overvoltage) or a temperature exceeding a predetermined value (overtemperature), the switch 62 is switched to a closed conducting state, and current flows from the source (source) to the drain (drain) of the switch 62 through the heating element 12. The heating element 12 heats to fuse the fuse element 16, thereby providing overvoltage or overtemperature protection. To summarize, B1 to a1, B2 to a2 form 2 power lines provided to the circuit to be protected, and the combination of the protection element 10, the detector 61 and the switch 62 connects the two power lines to form the circuit protection device 60. When the detector 61 detects that the voltage drop or temperature of the circuit to be protected exceeds a preset value, the heating element 12 is activated to melt the fuse element 16.

The equivalent circuit of the protection device of the previous embodiment includes 2 fuses and 1 heater. Other different circuit designs can be used to make a circuit form including, for example, 2 fuses and 2 heaters, or 1 fuse and 1 heater, and still be covered by the innovative technology of this embodiment. In yet another embodiment, the fuse element is electrically connected to 2 pads to form one conductive path, and the heating element is connected to another 2 pads to form another conductive path, whereby current flowing through the heating element can be independently controlled to fuse the fuse element.

In the protection element of this embodiment, the low-melting-point metal layer (the second metal layer and the third metal layer) and the high-melting-point metal layer (the first metal layer) form the fuse element with a composite structure, and the thickness of the low-melting-point metal layer needs to account for the thickness of the fuse element by a certain ratio, so that the low-melting-point metal layer can erode the high-melting-point metal layer when the fuse element is melted, thereby achieving the fusing rapidly. In this embodiment, the high melting point metal layer and the low melting point metal layer are used as main components of the fuse, and a Pb-free material may be used, but not limited thereto.

While the technical content and the technical features of the utility model have been disclosed, those skilled in the art can make various substitutions and modifications based on the teaching and the disclosure of the utility model without departing from the spirit of the utility model. Therefore, the protection scope of the present invention should not be limited to the embodiments shown, but should include various alternatives and modifications without departing from the utility model and covered by the claims.

Claims (12)

1. A protective element, characterized by: which comprises the following steps:

the surface of the substrate is provided with a first electrode and a second electrode;

the fuse part is arranged on the substrate, two ends of the fuse part are electrically connected with the first electrode and the second electrode, the fuse part comprises a first metal layer, a second metal layer and a third metal layer, the second metal layer and the third metal layer are respectively arranged on the upper surface and the lower surface of the first metal layer, the melting points of the second metal layer and the third metal layer are lower than that of the first metal layer, and the second metal layer and the third metal layer have different melting points; and

a heating member disposed on the substrate, the heating member generating heat to melt the fuse when an overvoltage or an overtemperature occurs;

wherein the combined thickness of the second metal layer and the third metal is 40-95% of the thickness of the fuse.

2. The protective element according to claim 1, characterized in that: the combined thickness of the second metal layer and the third metal is greater than the thickness of the first metal layer.

3. The protective element according to claim 1, characterized in that: the melting point of the second metal layer is higher than that of the third metal layer, or the melting point of the second metal layer is lower than that of the third metal layer.

4. The protective element according to claim 1, characterized in that: the first metal layer includes silver, copper, gold, nickel, zinc, or an alloy thereof.

5. The protective element according to claim 1, characterized in that: either one of the second metal layer and the third metal comprises tin or an alloy thereof.

6. The protective element according to claim 1, characterized in that: the first metal layer forms an inner layer of the fuse, and the second metal layer and the third metal layer form an outer layer of the fuse.

7. The protective element according to claim 1, characterized in that: when the thickness of the first metal layer is more than or equal to 16 mu m and less than 18 mu m, the sum of the thickness of the second metal layer and the thickness of the third metal layer is more than 50 percent of the thickness of the fuse link; and wherein when the thickness of the first metal layer is 18 μm or more, the sum of the thicknesses of the second metal layer and the third metal layer is 60% or more of the thickness of the fuse.

8. A circuit protection device, characterized by: which comprises

A protection device, comprising:

the surface of the substrate is provided with a first electrode and a second electrode;

a fuse disposed on the substrate, both ends of the fuse being electrically connected to the first electrode and the second electrode, the fuse including a first metal layer, a second metal layer and a third metal layer, the second metal layer and the third metal layer being disposed on the upper surface and the lower surface of the first metal layer, respectively, a melting point of either of the second metal layer and the third metal layer being lower than a melting point of the first metal layer, the second metal layer and the third metal layer having different melting points, a sum thickness of the second metal layer and the third metal layer being 40% -95% of a thickness of the fuse; and

a heating element disposed on the substrate;

a detector for detecting the voltage drop or temperature of a circuit to be protected; and

a switch connected to the detector for receiving the detection signal;

when the detector detects that the voltage drop or the temperature exceeds a preset value, the switch is conducted, and current flows through the heating element, so that the heating element generates heat to melt the fuse element.

9. The circuit protection device of claim 8, wherein: the combined thickness of the second metal layer and the third metal layer is greater than the thickness of the first metal layer.

10. The circuit protection device of claim 8, wherein: the melting point of the second metal layer is higher than that of the third metal layer, or the melting point of the second metal layer is lower than that of the third metal layer.

11. The circuit protection device of claim 8, wherein: the first metal layer forms an inner layer of the fuse, and the second metal layer forms an outer layer of the fuse.

12. The circuit protection device of claim 8, wherein: when the thickness of the first metal layer is more than or equal to 16 mu m and less than 18 mu m, the sum of the thickness of the second metal layer and the thickness of the third metal layer is more than 50 percent of the thickness of the fuse link; and wherein when the thickness of the first metal layer is 18 μm or more, the sum of the thicknesses of the second metal layer and the third metal layer is 60% or more of the thickness of the fuse.

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