Protective element and electrode for protective element

Abstract

The invention provides a protection element and an electrode for the protection element. The protection element is provided with: an insulating substrate; a plurality of protection element electrodes provided on the surface of the insulating substrate so as to be separated from each other; the present invention relates to an electrode for a protective element, which comprises a plurality of electrodes, and a fuse element that is bonded so as to straddle the surfaces of the plurality of electrodes and contains a lead-free solder, and in which the content of an oxide of a platinum group element is 3.0-11.0 mass% inclusive, the total content of oxides of Cu, Sn and Mn is 0.3-4.0 mass% inclusive, and the remainder contains Ag and SiO2-based glass. The SiO2-based glass does not contain oxides of Cu, Sn and Mn.

Description

Technical Field

[0001] The present invention relates to a protective element for electrical and electronic equipment and an electrode for the protective element. Background Art

[0002] Conventionally, there is a known surface-mount protection element that is installed in the internal circuit of a small electronic device such as a smartphone to protect a secondary battery such as a battery pack of the small electronic device from overcurrent and overvoltage (for example, Patent Document 1). The surface-mount protection element has a plurality of fuse electrodes mainly composed of Ag provided on the surface of an insulating substrate, and a fuse element made of a fusible conductor (specifically, a solder alloy) is joined in a manner spanning the surfaces of the plurality of fuse electrodes, and a resistor element serving as a heater is provided on the back of the insulating substrate.

[0003] When an overcurrent is applied to the secondary battery, such a protection element operates in an overcurrent mode by utilizing the self-heating generated by the energized resistance to melt the fuse element and cut off the circuit. When an overvoltage is applied to the secondary battery, such a protection element operates in an overvoltage mode by energizing the resistance element and utilizing the heat generated from the resistance element to melt the fuse element and cut off the circuit. Prior art literature Patent Literature

[0004] Patent document 1: Japanese Patent Publication No. 2021-168272 Summary of the invention Problems to be solved by the invention

[0005] However, in such protection elements, in order to comply with the RoHS directive, a solder alloy having a lead content of 1000 ppm or less (so-called lead-free solder) is often used as a constituent material of the fuse element.

[0006] In this case, since the lead-free solder has a high liquidus, the fuse element is heated to a high temperature when the protection element is actuated. However, if the Ag electrode is used alone as the fuse electrode at this time, the components of the fuse electrode will be eroded by the solder that melts into the fuse element. Therefore, in order to prevent such solder erosion, it is necessary to cover the surface of the Ag electrode with a Ni plating layer as a protective layer. If this is done, since the Ni plating layer with poor thermal conductivity is sandwiched between the resistor element on the back of the insulating substrate and the fuse element on the surface, there is a problem that it takes a long time for the fuse element to heat up and it takes a long time for the circuit to be cut off when operating in the overvoltage mode.

[0007] Furthermore, if the surface of the Ag electrode is covered with a Ni plating layer, solderability during installation of the fuse element deteriorates, and therefore an expensive Au plating layer having excellent solder wettability must be further provided on the surface of the Ni plating layer, which also causes a problem of high cost.

[0008] Therefore, a main object of the present invention is to reduce the cost and shorten the time required for circuit interruption during overvoltage operation in a protection element using lead-free solder as a constituent material of a fuse element. Means for solving problems

[0009] In order to solve the above-mentioned problems, the inventors of the present application conducted in-depth research and found that by making the chemical composition of the electrode for the protection element to be: Ag as the main component, the content of oxides of platinum group elements is not less than 3.0 mass% and not more than 11.0 mass%, and the total content of oxides of Cu, Sn and Mn is not less than 0.3 mass% and not more than 4.0 mass%, both the solder wettability and the resistance to solder corrosion can be improved, and the protection element can be constructed without applying Ni plating or Au plating, thereby completing the present invention.

[0010] That is, the protection element of the present invention comprises: an insulating substrate; a plurality of protection element electrodes, which are arranged separately from each other on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, and comprises lead-free solder, wherein the content of oxides of platinum group elements in the protection element electrodes is greater than 3.0 mass % and less than 11.0 mass %, the total content of oxides of Cu, Sn and Mn is greater than 0.3 mass % and less than 4.0 mass %, and the remainder comprises Ag and SiO2-type glass, and the SiO2-type glass does not contain oxides of Cu, Sn and Mn.

[0011] In addition, the electrode for the protection element of the present invention comprises: an insulating substrate; a plurality of electrodes for the protection element, which are arranged separately from each other on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, and comprises lead-free solder, the content of oxides of platinum group elements is greater than 3.0 mass% and less than 11.0 mass%, the total content of oxides of Cu, Sn and Mn is greater than 0.3 mass% and less than 4.0 mass%, and the remainder comprises Ag and SiO2-type glass, and the SiO2-type glass does not contain oxides of Cu, Sn and Mn. Effects of the Invention

[0012] According to the present invention thus constituted, by using electrodes for protection elements having excellent solder wettability and solder corrosion resistance, it is not necessary to apply Ni plating with poor thermal conductivity or expensive Au plating as in the past. Thus, in a protection element using lead-free solder as a constituent material of a fuse element, it is possible to suppress costs and shorten the time required for circuit disconnection during overvoltage operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a diagram schematically showing the configuration of a protection element according to one embodiment of the present invention. Figure 2 It is a diagram schematically showing the configuration of a protection circuit in which a protection element according to the same embodiment is mounted. Figure 3 This is a diagram schematically showing a circuit configuration used in a heater operation test of the example. DETAILED DESCRIPTION

[0014] Hereinafter, a protection element 100 according to an embodiment of the present invention will be described with reference to the drawings.

[0015] 1. Configuration of the protection element 100 The protection element 100 of this embodiment is mounted on a small electronic device such as a smartphone, for example, to protect a secondary battery 210 such as a battery pack of the small electronic device from overcurrent and overvoltage. The protection element 100 is a so-called surface-mounted element installed in a protection circuit 200 of a secondary battery 210 of the small electronic device.

[0016] Specifically, if Figure 1 As shown in FIG. 1 , the protection element 100 includes: an insulating substrate 1 made of ceramic, alumina, etc.; a pair of fuse electrodes 2 provided on one surface of the insulating substrate 1; an intermediate electrode 3 provided between the pair of fuse electrodes 2; a fuse element 4 including a fusible conductor, joined in a manner spanning the surface of the pair of fuse electrodes 2 and the intermediate electrode 3, and electrically connected to the pair of fuse electrodes 2 and the intermediate electrode 3; an operating flux 5 applied on the surface of the fuse element 4; and a resistor 6 (heater) provided on the other surface side of the insulating substrate 1, and electrically connected to the intermediate electrode 3 and the heating electrode (not shown). The pair of fuse electrodes 2, the intermediate electrode 3, the fuse element 4, and the operating flux 5 are covered by a cover 7 provided on one surface side of the insulating substrate 1.

[0017] As a material constituting the operating flux 5, a known material can be used. In addition, the fuse element of the present embodiment includes a lead-free solder, for example, a fuse element including a SnAg alloy, a SnAgCu alloy, a SnCu alloy, a SnBi alloy, etc., but is not limited to this. As a specific example of the fuse element 4, for example, a Sn-Ag-Cu / Sn-Cu clad element can be mentioned. The fuse electrode 2 and the intermediate electrode 3 (hereinafter also referred to as the protection element electrode) include, for example, a sintered electrode, which is composed of a SiO2-type glass component added for bonding with the insulating substrate 1 including ceramics and metal particles as an electrode material. The chemical composition of the protection element electrode will be described later.

[0018] like Figure 2 As shown, the protection element 100 configured in this way is connected in series with the secondary battery 210 in the protection circuit 200, and when an overcurrent or an overvoltage is applied, the circuit is cut off by melting the fuse element 4.

[0019] Specifically, when an overcurrent is applied to the secondary battery 210 of the protection circuit 200 , the protection element 100 operates in an overcurrent mode in which the fuse element 4 is melted by self-heating generated by the on-resistance to cut off the circuit.

[0020] On the other hand, when an overvoltage is applied to the secondary battery 210 of the protection circuit 200, the protection element 100 operates in an overvoltage mode in which the circuit is cut off by energizing the resistor element 6 and melting the fuse element 4 using the heat generated from the resistor element 6. Specifically, the protection circuit 200 includes a detection device 220 that detects the voltage applied to the secondary battery 210 and switches the conduction and disconnection of the current flowing in the resistor element 6 of the protection element 100. The detection device 220 is composed of a voltage detection IC and a FET. When the detection device 220 detects an overvoltage, it conducts the current flowing through the resistor element 6, thereby using the heat of the resistor element 6 to melt the fuse element 4.

[0021] 2. Chemical composition of electrodes used for protection elements Next, the composition of the material constituting the protection element electrode of the present embodiment will be described.

[0022] (1) Content of oxides of platinum group elements: 3.0 mass % or more and 11.0 mass % or less The platinum group element is contained in the protection element electrode of the present embodiment as an oxide. The platinum group element is an element that improves the solder corrosion resistance and solder wettability of the protection element electrode. The protection element electrode of this embodiment contains one or more selected from Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium) and Pt (platinum) as the platinum group element. When the content of the oxide of the platinum group element is less than 3.0 mass%, the solder corrosion resistance is reduced, and at high temperature, the electrode for the protection element melts into the fuse element 4. Therefore, the content of the oxide of the platinum group element is 3.0 mass% or more, preferably 4.5 mass% or more, more preferably 9.0 mass%, and further preferably 9.5 mass% or more. On the other hand, if the content of the oxide of the platinum group element exceeds 11.0 mass %, solder wettability decreases, and solderability deteriorates when mounting the fuse element 4. Therefore, the content of the oxide of the platinum group element is 11.0 mass % or less, preferably 10.0 mass % or less.

[0023] (2) Total content of Cu, Sn, and Mn oxides: 0.3 mass % or more and 4.0 mass % or less Cu (copper) oxide (CuO and / or Cu2O), Sn (tin) oxide (SnO2) and Mn (manganese) oxide (Mn2O3 and / or MnO2) are contained as glass components and are elements for improving the adhesion between the insulating substrate 1 and the electrode. When the total content of Cu, Sn and Mn oxides is less than 0.3 mass %, the adhesion between the insulating substrate 1 and the electrode may be reduced. Therefore, the total content of Cu, Sn and Mn oxides is preferably 0.3 mass % or more, more preferably 1.0 mass % or more, and further preferably 2.0 mass % or more. On the other hand, if the total content of Cu, Sn and Mn oxides exceeds 4.0 mass %, the glass component may float to the electrode surface and reduce the welding performance. Therefore, the total content of Cu, Sn and Mn oxides is preferably 4.0 mass % or less.

[0024] (3) Remaining part In a preferred embodiment, the remainder is Ag and SiO 2 -based glass, wherein the SiO 2 -based glass does not contain oxides of Cu, Sn, and Mn. SiO2-based glass has SiO2 as a main component and contains one or more selected from B, oxides of alkali metals, alkaline earth metals and Bi2O3. In this embodiment, preferably, the Ag content is 81.0 mass % or more and 96.4 mass % or less, and the content of SiO2-type glass is 0.3 mass % or more and 4.0 mass % or less. In addition, as inevitable impurities, it is envisaged that trace elements doped due to the conditions of raw materials, materials, manufacturing equipment, etc. are mixed. Various elements as these inevitable impurities can be contained in a range of 1.0 mass % or less (including 0 mass %).

[0025] The reason why both solder wettability and solder corrosion resistance can be improved by setting the content of each component to such a range is still unclear. Based on the insights obtained so far, the mechanism considered by the inventors is described below. In addition, it should be noted that the purpose of the following description of the mechanism is not to limit the technical scope of the present invention.

[0026] The sintered electrode material includes a glass component added for bonding with a ceramic substrate, a platinum group metal oxide, and silver metal particles as an electrode material. Among them, the platinum group metal oxide is selected as a material that can appropriately adjust the affinity with the electrode metal composed of silver, the glass component, and the solder material welded to the electrode material. The electrode material of one embodiment of the present invention includes a silver metal phase as a main component, a platinum group metal oxide that is discharged to the grain boundary of the silver metal phase during firing and retained at the grain boundary, and a glass component. The electrode material has a structure in which the platinum group oxide and the glass component are distributed at the grain boundary of the silver metal phase. The corrosion caused by molten solder is a phenomenon in which the electrode disappears because the electrode base metal in the depth direction of the silver electrode rapidly melts in the molten solder starting from the grain boundary of the sintered silver electrode. However, the electrode material of one embodiment of the present invention can suppress the melting of the silver electrode caused by molten solder because the platinum group oxides with excellent high-temperature stability are distributed at the grain boundary of the silver electrode, thereby improving the high-temperature durability of the electrode itself. In addition, based on the excellent chemical resistance and oxidation resistance of the platinum group oxides, the silver electrode can be protected from the influence of oxygen and oxidizing atmosphere, and the deterioration of the material can be suppressed, thereby increasing the chemical stability of the electrode material and ensuring the reliability of the electrode for a long time. On the other hand, the surface of the silver electrode does not have a compound coating film such as oxides, exposing a relatively clean metal surface, so that good solder wettability can be ensured. Therefore, the electrode material according to one embodiment of the present invention can suppress solder corrosion of the silver electrode caused by molten solder due to the platinum group oxide metal distributed in the grain boundaries of the silver electrode, and can achieve excellent solderability on the electrode surface. [Example]

[0027] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples and can be implemented with modifications within the scope of the above and following gist. Such modifications are all within the technical scope of the present invention.

[0028] (1) Preparation of test samples (Electrode Preparation) Ag powder, ruthenium oxide (RuO2) powder, copper oxide (CuO) powder, tin oxide (SnO2) powder, manganese oxide (MnO2) powder, glass powder, organic binder and solvent were mixed to prepare a conductive paste, and then the paste was sintered at 850°C to produce 10 electrode samples with a thickness of 6 to 8 μm and different chemical compositions. The chemical composition of each electrode sample (sintered electrode material) obtained is shown in Table 1. "Ru, Cu, Sn, Mn" in Table 1 represents the total content of each oxide of Ru, Cu, Sn and Mn. In addition, the chemical composition of each electrode sample can be determined, for example, using SEM-EDX, EPMA, etc.

[0029] (Production of protection element samples) The obtained electrode samples were used as fuse electrodes and intermediate electrodes to produce protection element samples (test samples) of the above-mentioned embodiment. Three test samples were produced for each electrode sample with different chemical composition. In addition, lead-free solder (specifically Sn-Ag-Cu / Sn-Cu) was used as the fuse element in each test sample.

[0030] (2) Solder wettability test A solder wettability test was conducted on the electrode samples used for the obtained test samples by immersing the samples in molten solder, and the solder wetted areas were measured. The test conditions are as follows. Solder: Lead-free (96.5Sn-3Ag-0.5Cu) Flux: 25wt% (Rosin ethanol solution) Immersion depth: 2 to 2.5 mm Solder temperature: 245±5℃ Immersion time: 3.0±0.5 seconds Dipping and pulling speed: 25±2.5mm / sec The measurement results of the solder wetted area of ​​each electrode sample thus obtained are shown in Table 1. Samples with a solder wetted area of ​​95% or more were evaluated as "good solder wettability (○)", and samples with a solder wetted area of ​​less than 95% were evaluated as "poor solder wettability (×)".

[0031] (3) Heater operation test Next, the obtained test sample was subjected to a heater operation test and the residual film thickness was measured. Figure 3 In the circuit shown, the lower limit voltage of the product's operating voltage range (here 6.4V) was applied to the resistor element, and a heater operation test was performed to melt the fuse elements on both sides of the intermediate element. Then, the film thickness of the thinnest part of each electrode after the heater operation test was taken as the residual film thickness, and samples with a residual film thickness of 0.5μm or more were evaluated as "good solder corrosion resistance (○)", and samples with a residual film thickness of less than 0.5μm were evaluated as "poor solder corrosion resistance (×)". The measurement results are shown in Table 1.

[0032] [Table 1]

[0033] (4) Summary As shown in Table 1, it can be confirmed that the protection element samples made using electrode samples of level numbers (2) to (4) and (7) to (10) in which the content of Ru oxide, a platinum group element, is 3.0 mass % or more and 11.0 mass % or less and the total content of Cu, Sn and Mn oxides is 0.3 mass % or more and 4.0 mass % or less obtained good results in both solder wettability and solder corrosion resistance. On the other hand, the protective element samples made using the electrode samples of level number (1) with excessive content of Ru oxide, which is a platinum group element, had a small solder wettability and poor solder wettability. In addition, the protective element samples made using the electrode samples of level numbers (5) and (6) with low content of Ru oxide, which is a platinum group element, had a small residual film thickness and poor solder corrosion resistance.

[0034] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the protection element of the present invention includes the following aspects 1 to 6.

[0035] (Method 1) A protection element comprises: an insulating substrate; a plurality of protection element electrodes, which are separated from each other and arranged on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, and includes lead-free solder, wherein the content of oxides of platinum group elements in the protection element electrodes is greater than 3.0 mass% and less than 11.0 mass%, the total content of oxides of Cu, Sn and Mn is greater than 0.3 mass% and less than 4.0 mass%, and the remainder includes Ag and SiO2-type glass, and the SiO2-type glass does not contain oxides of Cu, Sn and Mn.

[0036] (Method 2) The protection element according to aspect 1, wherein the content of the oxide of the platinum group element is 4.5 mass % or more and 11.0 mass % or less.

[0037] (Method 3) The protection element according to aspect 2, wherein the content of the oxide of the platinum group element is 9.0 mass % or more and 11.0 mass % or less.

[0038] (Method 4) The protection element according to any one of aspects 1 to 3, wherein the total content of oxides of Cu, Sn, and Mn is 1.0 mass % or more and 4.0 mass % or less.

[0039] (Method 5) The protection element according to aspect 4, wherein the total content of the oxides of Cu, Sn, and Mn is 2.0 mass % or more and 4.0 mass % or less.

[0040] (Method 6) The protection element according to any one of aspects 1 to 5, wherein the fuse element includes lead-free solder.

[0041] (Method 7) The protection element according to any one of aspects 1 to 6, wherein the protection element includes a resistance element provided on the back surface of the insulating substrate, and the fuse element is melted by heating of the resistance element during operation.

[0042] (Method 8) A protection element electrode, the protection element comprising: an insulating substrate; a plurality of protection element electrodes, which are separated from each other and arranged on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, comprising lead-free solder, wherein the content of oxides of platinum group elements is greater than 3.0 mass % and less than 11.0 mass %, the total content of oxides of Cu, Sn and Mn is greater than 0.3 mass % and less than 4.0 mass %, and the remainder comprises Ag and SiO2-type glass, wherein the SiO2-type glass does not contain oxides of Cu, Sn and Mn. Description of reference numerals:

[0043] 200: protection circuit; 210: secondary battery; 220: detection device; 100: protection element; 1: insulating substrate; 2: fuse electrode; 3: intermediate electrode; 4: fuse element; 5: operating flux; 6: resistance element; 7: cover.

Claims

1. A protection element, characterized in that: The protection element comprises: an insulating substrate; a plurality of protection element electrodes, which are separated from each other and arranged on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, and includes lead-free solder. In the protection element electrode, The content of the oxide of the platinum group element is 3.0 mass % or more and 11.0 mass % or less, The total content of the oxides of Cu, Sn and Mn is 0.3 mass % or more and 4.0 mass % or less, The remainder includes Ag and SiO 2 -based glass, which does not include oxides of Cu, Sn, and Mn.

2. The protection element according to claim 1, characterized in that: The content of the oxide of the platinum group element is 4.5 mass % or more and 11.0 mass % or less.

3. The protection element according to claim 2, characterized in that: The content of the oxide of the platinum group element is 9.0 mass % or more and 11.0 mass % or less.

4. The protection element according to claim 1, characterized in that: The total content of the oxides of Cu, Sn, and Mn is 1.0 mass % or more and 4.0 mass % or less.

5. The protection element according to claim 4, characterized in that: The total content of the oxides of Cu, Sn, and Mn is 2.0 mass % or more and 4.0 mass % or less.

6. The protection element according to claim 1, characterized in that: The fuse element includes lead-free solder.

7. The protection element according to claim 1, characterized in that: The protection element includes a resistor element, and the resistor element is provided on the back surface of the insulating substrate. During operation, the fuse element is melted by heating of the resistor element.

8. An electrode for a protective element, characterized in that: The protection element comprises: an insulating substrate; a plurality of protection element electrodes, which are separated from each other and arranged on the surface of the insulating substrate; and a fuse element, which is joined in a manner spanning the surfaces of each of the plurality of electrodes, and includes lead-free solder. The content of the oxide of the platinum group element is 3.0 mass % or more and 11.0 mass % or less, The total content of the oxides of Cu, Sn and Mn is 0.3 mass % or more and 4.0 mass % or less, The remainder includes Ag and SiO 2 -based glass, which does not include oxides of Cu, Sn, and Mn.

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