Protection element and circuit protection device thereof

Abstract

A protection element comprises a substrate, a fuse and a heating element. A first electrode and a second electrode are provided on the surface of the substrate. The fuse is arranged on the substrate, and two ends of the fuse are electrically connected to the first electrode and the second electrode. The fuse comprises a first metal layer and a second metal layer, the second metal layer is arranged on the surface of the first metal layer, and the melting point of the second metal layer is 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. The thickness of the second metal layer is 40% to 95% of the thickness of the fuse.

Description

Technical Field

[0001] The present invention relates to a protection element used in an electronic device and a circuit protection device including the protection element, and in particular to a protection element having the function of preventing overvoltage, overcurrent or overtemperature and a circuit protection device thereof. Background Art

[0002] As a well-known protection element for cutting off overcurrent, it is widely known that there is a current fuse composed of a low melting point metal such as lead, tin, silver, bismuth, copper, etc. Later, in terms of preventing overcurrent and overvoltage, a protection element was continuously developed, which includes a heating layer and a fusible element stacked in sequence on a flat substrate. When there is an overvoltage, the heating layer will heat up, and the heat will be transferred from the bottom to the top, heating and melting the fusible element, thereby cutting off the current flowing through, so as to protect the related circuits or electronic devices.

[0003] In recent years, mobile devices have become highly popular. Information products such as mobile phones, computers, and personal mobile assistants can be seen everywhere, making people increasingly dependent on information products. However, from time to time, there are news reports about the explosion of batteries in portable electronic products such as mobile phones during the charging and discharging process. Therefore, manufacturers have gradually improved the design of the above-mentioned overcurrent and overvoltage protection components, and enhanced the protection measures for the battery during the charging and discharging process to prevent the battery from exploding due to overvoltage or overcurrent during the charging and discharging process.

[0004] The protection method of the protection element proposed by the prior art is to connect the fuse in the protection element in series with the circuit of the battery, and to electrically connect the fuse and the heating layer in the protection element to the switch and the integrated circuit (IC) element. In this way, when the IC element measures an overvoltage, it will start the switch to conduct, so that the current passes through the heating layer in the protection element, so that the heating layer generates heat to melt the fuse, and then the circuit of the battery is in an open circuit state to achieve overvoltage protection. Those skilled in the art can also fully understand that when an overcurrent occurs, a large amount of current flowing through the fuse will cause the fuse to heat up and melt, thereby achieving overcurrent protection.

[0005] However, in order to prevent the fuse in the above-mentioned existing protection components from melting due to high temperature in the subsequent reflow process, high melting point solder containing lead (Pb) with a melting point of more than 300°C is usually used. However, according to the specifications of the RoHS (Restriction of Hazardous Substances Directive) environmental protection directive, the use of Pb-containing solder will be restricted. Therefore, how to still perform reflow when using a fuse with a lower melting point is a problem that the protection component needs to overcome urgently. Summary of the invention

[0006] The present invention provides a protection element and a circuit protection device including the protection element, which has the functions of overvoltage, overcurrent and / or overtemperature protection. The fuse of the protection element includes two metal layers with different melting points, and uses high and low melting point composite materials to achieve the effect of effectively melting the fuse.

[0007] According to a first aspect of the present invention, a protection element is provided, which comprises a substrate, a fuse and a heating element. A first electrode and a second electrode are provided on the surface of the substrate. The fuse is arranged on the substrate, and two ends are electrically connected to the first electrode and the second electrode. The fuse comprises a first metal layer and a second metal layer, the second metal layer is arranged on the surface of the first metal layer, and the melting point of the second metal layer is 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. The thickness of the second metal layer is 40% to 95% of the thickness of the fuse.

[0008] In one embodiment, the thickness of the second metal layer is greater than the thickness of the first metal layer.

[0009] In one embodiment, the first metal layer includes silver (Ag), copper (Cu), gold (Au), nickel (Ni), zinc (Zn) or alloys thereof.

[0010] In one embodiment, the second metal layer includes tin (Sn) or an alloy thereof.

[0011] In one embodiment, the first metal layer forms an inner layer of the fuse element, and the second metal layer forms an outer layer of the fuse element.

[0012] In one embodiment, the second metal layer has two layers, which are respectively formed on the upper and lower surfaces of the first metal layer.

[0013] In one embodiment, the first metal layer forms a lower surface of the fuse, and the second metal layer forms an upper surface of the fuse.

[0014] In one embodiment, when the thickness of the first metal layer is greater than or equal to 16 μm, the thickness of the second metal layer is greater than 50% of the thickness of the fuse.

[0015] In one embodiment, when the thickness of the first metal layer is greater than or equal to 18 μm, the thickness of the second metal layer is greater than 60% of the thickness of the fuse.

[0016] According to a second aspect of the present invention, a circuit protection device is provided, which includes a protection element, a detector and a switch. The protection element includes 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 is arranged on the substrate, and both ends are electrically connected to the first electrode and the second electrode. The fuse includes a first metal layer and a second metal layer. The second metal layer is arranged on the surface of the first metal layer. The melting point of the second metal layer is lower than the melting point of the first metal layer. The thickness of the second metal layer is 40% to 95% of the thickness of the fuse. The heating element is arranged on the substrate. The detector is used to detect a voltage drop or temperature of a circuit to be protected. The switch is connected to the detector to receive its detection signal. When the detector detects that the voltage drop or temperature exceeds a preset value, the switch is turned on, and current flows through the heating element, so that the heating element heats up to melt the fuse.

[0017] The fuse in the protection element of the present invention is a multi-layer metal layer composite structure, wherein the melting point of the first metal layer is higher than that of the second metal layer, and the thickness of the second metal layer accounts for a certain proportion of the thickness of the fuse. In this way, during the subsequent reflow, even if the reflow temperature is higher than the melting point of the second metal layer, the second metal layer will not flow arbitrarily or deform seriously because it has a certain thickness, and the melting of the second metal layer will erode the first metal layer, thereby accelerating the melting of the fuse and providing protection. The fuse of the protection element of the present invention includes metal layers with different melting points. Compared with the traditional lead-tin sheet, the resistance value of the fuse can be reduced to achieve the characteristics of low surface temperature and high current. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram showing the structure of a protection element according to an embodiment of the present invention is shown.

[0019] Figure 2 show Figure 1 Equivalent circuit diagram of the protection element.

[0020] Figures 3 to 6 Several embodiments of the fuse of the protection element of the present invention are shown.

[0021] Figure 7 A circuit diagram showing a circuit protection device according to an embodiment of the present invention.

[0022] The reference numerals are described as follows:

[0023] 10. Protection components

[0024] 11 base plate

[0025] 12 Heating element

[0026] 13 Heating electrode

[0027] 14 Insulation layer

[0028] 15. Intermediate electrode

[0029] 16 Fuse

[0030] 16a First metal layer

[0031] 16b Second metal layer

[0032] 17 Solder

[0033] 18 Electrode layer

[0034] 18a First electrode

[0035] 18b Second electrode

[0036] 19a Lower electrode

[0037] 19b Lower electrode

[0038] 20 Cover

[0039] 21. Flux

[0040] 22 Conductive parts

[0041] 60 Circuit protection device

[0042] 61 detector

[0043] 62 Switch DETAILED DESCRIPTION

[0044] In order to make the above and other technical contents, features and advantages of the present invention more clearly understood, relevant embodiments are given below and described in detail with reference to the accompanying drawings.

[0045] Figure 1The structural diagram of the protection element 10 according to an embodiment of the present invention is shown. The protection element 10 comprises a substrate 11, a heating element 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 an outer cover 20. The outer edge of the outer cover 20 is arranged on the surface of the substrate 11, and an internal space is provided to accommodate the heating element 12 and the fuse 16. The substrate 11 is usually a planar insulating substrate. The heating element 12 is arranged on the substrate 11, and its two ends are electrically connected to the left and right heating electrodes 13. The two ends of the fuse 16 are electrically connected to the first electrode 18a and the second electrode 18b located on both sides of the electrode layer 18, and the middle part of the fuse 16 is connected to the intermediate electrode 15 arranged on the surface of the insulating layer 14, wherein the two ends of the fuse 16 can be connected to the first electrode 18a and the second electrode 18b through the solder 17. The first electrode 18a and the second electrode 18b can be connected to the left and right lower electrodes 19a and 19b through the conductive member 22 located on the side of the substrate 11. The lower electrodes 19a and 19b can be used as an interface for surface adhesion to a circuit board (not shown). The insulating layer 14 covers the heating element 12 and the heating electrode 13. The fuse 16 is arranged above the insulating layer 14 as a fuse on the circuit. The fuse 16 includes a first metal layer 16a and a second metal layer 16b arranged on the surface of the first metal layer 16a, and is a composite structure. In order to prevent the second metal layer 16b or the first metal layer 16a from oxidizing, the fuse 16 can be fully or partially coated with a flux 21. The flux 21 can mainly form an anti-oxidation layer on the surface of the outermost second metal layer 16b, which can effectively prevent the second metal layer 16b from oxidizing, thereby maintaining a fast fuse efficiency. When overvoltage or overtemperature occurs, the heater 12 generates heat and transfers the heat to the fuse 16, so that the fuse 16 melts and flows to the first electrode 18a, the second electrode 18b and the middle electrode 15 on both sides, causing the fuse to melt, thereby cutting off the current to achieve the purpose of protection. Figure 2 show Figure 1 The equivalent circuit diagram of the protection element 10 is shown in FIG. 1 . In this embodiment, the fuse 16 includes two fuses through the arrangement of the intermediate electrode 15. When an overvoltage occurs, the heating element 12 generates heat to melt the fuse 16. The fuse includes a low melting point metal and can be melted to provide protection when an abnormal event occurs.

[0046] The substrate 11 may be a square structure, wherein the material may be an insulating material such as alumina, aluminum nitride, zirconium oxide, glass ceramic, etc., or a material used for a printed wiring substrate such as a glass epoxy substrate, a phenolic substrate, etc. The thickness of the substrate 11 is about 0.1 to 2 mm. The electrode layer 18, the heating electrode 13 and the intermediate electrode 15 may include silver, gold, copper, tin, nickel or other conductive metals, with a thickness of about 0.005 to 1 mm, or in particular 0.01 mm, 0.05 mm, 0.1 mm, 0.3 mm, 0.5 mm. In addition to using printing to make electrodes, metal sheets can also be used to make them suitable for high voltage applications.

[0047] In this embodiment, the fuse 16 is a composite structure composed of an inner layer and an outer layer, which can be a rectangular 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 as the outer layer on the upper and lower surfaces of the first metal layer 16a is a low melting point metal layer. That is, the second metal layer 16b has a lower melting point than the first metal layer 16a. The second metal layer 16b can be formed on the surface of the first metal layer 16a by electroplating, evaporation, lamination, rolling, etc. In one embodiment, the first metal layer 16a includes, for example, Ag, Cu, Au, Ni, Zn, or a metal or an alloy thereof with any one of them as the main component. The second metal layer 16b preferably comprises a metal with Sn as the main component 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 in particular, a Pb-free material may be selected to comply with the RoHS directive. In one embodiment, the melting point of the second metal layer 16b is 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, so that the surface of the second metal layer 16b as the outer layer may flow slightly, the first metal layer 16a still does not reach its melting point, so the fuse 16 will not be melted, and the existing shape of the fuse 16 can be maintained. The material of the heating element 12 may include additives such as ruthenium oxide (RuO2), silver (Ag), palladium (Pd), and platinum (Pt). The material of the insulating layer 14 separating the heating element 12 from the fuse 16 may be glass, epoxy, alumina, silicone, or glaze.

[0048] In one embodiment, the thickness T of the fuse 16 is about 15 μm to 150 μm, wherein the thickness T1 of the first metal layer 16a is about 5 to 30 μm, and the thickness of the upper and lower second metal layers 16b is about 5 to 50 μm, that is, the total thickness T2 of the second metal layer 16b is about 10 to 100 μm. Specifically, the thickness T2 of the second metal layer 16b may be greater than or less than the thickness T1 of the first metal layer 16a, and the ratio of the thickness of the second metal layer to the total thickness of the fuse (T=T1+T2) is preferably 40 to 95%, such as 50%, 60%, 70%, 80% or 90%. Preferably, the second metal layer 16b is relatively thick, and the first metal layer 16a is relatively thin, or the volume of the second metal layer 16b in the fuse 16 is larger than the volume of the first metal layer 16a. When an abnormal condition such as overvoltage or overcurrent occurs, the second metal layer 16b has a thicker thickness or a larger volume, which can effectively erode the first metal layer 16a, accelerating the fuse 16 to melt in a short time. In summary, the ratio of the thickness and volume of the first metal layer 16a and the second metal layer 16b has an appropriate value. The second metal layer 16b that is too thin or too small cannot melt the fuse 16 quickly and effectively.

[0049] Figure 3 , Figure 4 , Figure 5 and Figure 6 Different embodiments of the fuse 16 are shown. Figure 3 As shown, the second metal layer 16b has two layers, which are respectively arranged on the upper surface and the lower surface of the first metal layer 16a. Figure 4 As shown, except for the two opposite end surfaces of the fuse 16, the second metal layer 16b covers the periphery of the first metal layer 16a. Figure 5 As shown, the entire first metal layer 16a including both end surfaces is covered by the second metal layer 16b. Figure 3 , Figure 4 and Figure 5 The first metal layer 16a forms the inner layer of the fuse 16, and the second metal layer 16b forms the outer layer of the fuse 16. Figures 3 to 5 The thickness of the second metal layer 16b referred to in the present invention is the sum of the thicknesses of the upper and lower second metal layers 16b. Figure 6 The fuse 16 shown includes a first metal layer 16a and a second metal layer 16b formed on the surface of the first metal layer 16a, the first metal layer 16a forms the lower surface of the fuse 16, and the second metal layer 16a forms the upper surface of the fuse 16. Preferably, the thickness of the second metal layer 16b is greater than the thickness of the first metal layer 16a.

[0050] The test examples shown in Table 1 below use Figure 3The fuse is designed with a length and width of 1.85 mm, and an upper and lower second metal layer 16b are respectively arranged on the upper and lower surfaces of the first metal layer 16a. The first metal layer 16a is a silver layer with thicknesses of 5 μm, 7 μm, 9 μm, 12 μm, 14 μm, 16 μm, 18 μm and 20 μm. The second metal layer 16b is a tin layer with thicknesses of 5 μm, 10 μm, 20 μm and 30 μm, respectively. Table 1 shows the percentage of the thickness T2 of the second metal layer (tin layer) in the total thickness T of the fuse. Because the second metal layer has two layers, the thickness T2 is twice the thickness of a single layer. In all the tests in Table 1, the value range of T2 / T is approximately 32% to 95%. The upper right corner block in Table 1 is a test case in which the second metal layer has a larger proportion of T2 / T (the tin layer is thicker), and the lower left corner block is a test case in which the second metal layer has a smaller proportion of T2 / T. The fuses of all the test cases in Table 1 were tested in a reflow furnace at a reflow temperature of 260° C. After the reflow test, the fuses of all the test cases could still maintain their original shapes without deformation, and there was no obvious tin melting phenomenon.

[0051] Table 1

[0052]

[0053] The fuse shown in Table 1 is then further manufactured as follows Figure 1 The protection element shown in the figure is then subjected to an overvoltage test of overvoltage simulation. The overvoltage test is based on the heater of the protection element passing different currents to generate different powers such as 7W, 10W and 35W, so as to test whether the fuse can effectively blow to form an open circuit or cannot blow and remains a closed circuit. The test results are shown in Table 2. The test is passed (PASS) if an open circuit is formed, and failed (NG) if it is still a closed circuit. From the results of Tables 1 and 2, the T2 / T ratio that passes the overvoltage test is between 40 and 95%. In addition, when the first metal layer is thicker, the T2 / T ratio needs to be higher. When the thickness of the first metal layer (silver layer) of the fuse is greater than or equal to 16μm, the T2 / T ratio must be above 50% to effectively blow (PASS). Table 2 shows that when the thickness of the first metal layer is 16μm and T2 / T is 38.46%, the result is NG. When the thickness of the first metal layer (silver layer) is greater than or equal to 18μm, the T2 / T ratio must be above 60% to effectively blow (PASS). When the thickness of the first metal layer (silver layer) is 20μm, the T2 / T ratio must be greater than 70% to effectively blow PASS. In other words, the thicker the first metal layer, the larger the T2 / T ratio needs to be to effectively blow the fuse to form an open circuit.

[0054] Table 2

[0055]

[0056] The examples shown in Table 3 use Figure 3 The fuse design has a length and width of 1.85 mm. The thickness of the first metal layer (silver layer), the thickness of the second metal layer (tin layer), the resistance of the fuse and the melting time of the heater under different powers in the related overvoltage test are recorded. The powers applied to the heater are 7W, 10W and 35W respectively. Table 3 shows that under the same tin layer thickness, the melting time will increase as the thickness of the silver layer increases. In other words, the one with a higher proportion of tin layer thickness has a shorter melting time and has a better melting efficiency. The fuses of the embodiments listed in Table 3 can all be melted within 5 seconds.

[0057] Table 3

[0058]

[0059]

[0060] The equivalent circuit diagram of the protection element 10 of the present invention can also be as follows Figure 7The circuit in the dashed box is shown in the figure. The first electrode 18a is connected to a terminal A1 of a device to be protected (such as a secondary battery or a motor), and the second electrode 18b is connected to a terminal B1 of a charger or other similar device. The middle electrode 15 is connected to a heating electrode 13, and the other heating electrode 13 is connected to the switch 62. According to the circuit design of the protection element 10, the circuit formed by the fuse 16 includes two fuses connected in series, and the heating element 12 forms a heater (shown as a resistor symbol). In one embodiment, the switch 62 can be, for example, a field effect transistor (FET). The gate of the switch 62, such as a FET, is connected to the detector 61, and is connected to the other terminal A2 of the circuit to be protected, and the other terminal B2 of the charger. The detector 61 can be an IC component with the function of detecting voltage drop or temperature. When there is no overvoltage or overtemperature, the switch 62 is open, and the current passes through the fuse 16, but no current flows through the heating element 12. If an overcurrent occurs at this time, the fuse 16 will melt and provide overcurrent protection. When the detector 61 detects that the voltage exceeds a preset value (overvoltage) or the temperature exceeds a preset value (overtemperature), the switch 62 switches to a closed-circuit conduction state, and the current flows from the source (source) to the drain (drain) of the switch 62 and flows through the heating element 12. The heating element 12 generates heat and melts the fuse 16, thereby providing protection against overvoltage or overtemperature. In summary, B1 to A1 and B2 to A2 form two 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 a circuit protection device 60. When the detector 61 detects that the voltage drop or temperature of the circuit to be protected exceeds the preset value, the heating element 12 is activated to melt the fuse 16.

[0061] The equivalent circuit of the protection element of the aforementioned embodiment includes 2 fuses and 1 heater. However, other different structural circuit designs can also be used to make a circuit form including, for example, 2 fuses and 2 heaters, or 1 fuse and 1 heater, which is still covered by the innovative technology of the present invention. In another embodiment, the fuse is electrically connected to 2 pads to form a conductive path, and the heating element is connected to another 2 pads to form another conductive path, so that the current flowing through the heating element can be independently controlled to blow the fuse.

[0062] The protection element of the present invention uses a low melting point metal layer (second metal layer) and a high melting point metal layer (first metal layer) to form a composite structure fuse, and the thickness of the low melting point metal layer must account for a certain proportion of the thickness of the fuse, so that when the fuse melts, the low melting point metal layer can corrode the high melting point metal layer and quickly achieve melting. The present invention uses a high melting point metal layer and a low melting point metal layer as the main components of the fuse, which can be made of but not limited to Pb-free materials.

[0063] The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and modifications based on the teachings and disclosures of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to those disclosed in the embodiments, but should include various substitutions and modifications without departing from the present invention, and be covered by the following claims.

Claims

1. A protection element, comprising: A substrate, with a first electrode and a second electrode provided on the surface; a fuse, disposed on the substrate, with two ends electrically connected to the first electrode and the second electrode, the fuse comprising a first metal layer and a second metal layer, the second metal layer being disposed on the surface of the first metal layer, and the melting point of the second metal layer being lower than the melting point of the first metal layer; a heating element, disposed on the substrate, which generates heat to melt the fuse when overvoltage or overtemperature occurs; and An outer cover is disposed on the surface of the substrate and is provided to accommodate the heating element and the fuse; in, The thickness of the first metal layer is 9-14 μm, and the thickness of the second metal layer is at least 40% and less than 60% of the thickness of the fuse, wherein the second metal layer has two layers, which are respectively formed on the upper and lower surfaces of the first metal layer; wherein the protection element passes an overvoltage test, wherein a current is passed through the heating element of the protection element to generate a power of 7W, 10W or 35W to blow the fuse on a circuit, thereby causing the circuit to form an open circuit; and When the power applied to the protection element is 7W, 10W or 35W, the fuse blows within 5 seconds. 2 . The protection element according to claim 1 , wherein a thickness of the second metal layer is greater than a thickness of the first metal layer.

3. The protection element according to claim 1, wherein the first metal layer comprises silver, copper, gold, nickel, zinc or an alloy thereof. The protection element according to claim 1 , wherein the second metal layer comprises tin or an alloy thereof.

5. A circuit protection device, comprising: A protection element, comprising: A substrate, with a first electrode and a second electrode provided on the surface; A fuse, disposed on the substrate, with two ends electrically connected to the first electrode and the second electrode, the fuse comprising a first metal layer and a second metal layer, the second metal layer being disposed on the surface of the first metal layer, the melting point of the second metal layer being lower than the melting point of the first metal layer, the thickness of the first metal layer being 9 to 14 μm, and the thickness of the second metal layer being at least 40% and less than 60% of the thickness of the fuse, wherein the second metal layer has two layers, respectively formed on the upper and lower surfaces of the first metal layer; a heating element, disposed on the substrate; An outer cover is disposed on the surface of the substrate and is provided to accommodate the heating element and the fuse; The protection element passes an overvoltage test, wherein a current is passed through the heating element of the protection element to generate a power of 7W, 10W or 35W to melt the fuse on a circuit, thereby forming an open circuit in the circuit; and When the power applied to the protection element is 7W, 10W or 35W, the fuse blows within 5 seconds; a detector for detecting a voltage drop or a temperature of a circuit to be protected; as well as a switch connected to the detector to receive a detection signal thereof; When the detector detects that the voltage drop or the temperature exceeds a preset value, the switch is turned on, and current flows through the heating element, so that the heating element generates heat to melt the fuse.

6. The circuit protection device of claim 5, wherein a thickness of the second metal layer is greater than a thickness of the first metal layer.

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