Protective element and electrode for protective element

Abstract

To shorten the time required for circuit break during an overvoltage operation even while suppressing cost in a protection element using a lead-free solder as a constituent material of a fuse element.SOLUTION: A protection element comprises an insulation substrate, a plurality of electrodes for protection elements provided while being separated from each other on a surface of the insulation substrate, and a fuse element consisting of a lead-free solder joined to the plurality of electrodes so as to be spread over the surfaces thereof. In the protection element, regarding the electrode for protection elements, a content of an oxide of a platinum group element is from 3.0 mass% or more to 11.0 mass% or less, a total content of an oxide of Cu, Sn and Mn is from 0.3 mass% or more to 4.0 mass% or less, and the remainder consists of Ag and SiO2-based glass (excluding the oxide of Cu, Sn and Mn).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a protection element for electric and electronic devices and an electrode for the protection element.

Background Art

[0002] Conventionally, for example, a surface-mounted protection element is known for protecting a secondary battery such as a battery pack provided in a small electronic device from overcurrent and overvoltage, which is mounted on an internal circuit of a small electronic device such as a smartphone (for example, Patent Document 1). This surface-mounted protection element is configured by providing a plurality of fuse electrodes mainly composed of Ag on the surface of an insulating substrate, joining a plurality of fuse elements made of a soluble conductor (specifically, a solder alloy) so as to straddle the surfaces of the plurality of fuse electrodes, and providing a resistor element, which is a heater, on the back surface of the insulating substrate.

[0003] When an overcurrent is applied to the secondary battery, such a protection element operates in an overcurrent mode in which the fuse element is melted by self-heating generated by the energization resistance, thereby interrupting the circuit. When an overvoltage is applied to the secondary battery, the resistor element is energized, and the fuse element is melted using the heat generated from the resistor element, thereby interrupting the circuit, and operates in an overvoltage mode.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in such a protection element, 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, because lead-free solder has a high liquidus level, the fuse element is heated to a high temperature when the protective element operates. If an Ag electrode is used alone as the fuse electrode, solder corrosion occurs, where components of the fuse electrode dissolve into the fuse element. Therefore, to prevent such solder corrosion, it is necessary to coat the surface of the Ag electrode with a Ni plating layer as a protective layer. However, this results in a Ni plating layer with poor thermal conductivity being interposed between the resistive element on the back of the insulating substrate and the fuse element on the front. This causes a problem in overvoltage mode operation, where it takes time for the fuse element to heat up and thus takes time to interrupt the circuit.

[0007] Furthermore, if the surface of the Ag electrode is coated with a Ni plating layer, the solderability when installing the fuse element deteriorates. Therefore, it becomes necessary to further apply an expensive Au plating layer with excellent solder wettability to the surface of the Ni plating layer, which increases costs.

[0008] Therefore, the primary objective of the present invention is to provide a protective element using lead-free solder as a constituent material for the fuse element, which can reduce costs while also shortening the time required for circuit interruption during overvoltage operation. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors of this invention conducted diligent research and found that by setting the chemical composition of the electrode for the protective element to be mainly composed of Ag, with a content of platinum group element oxides of 3.0% to 11.0% by mass, and a total content of Cu, Sn, and Mn oxides of 0.3% to 4.0% by mass, both solder wettability and solder corrosion resistance can be improved, and a protective element can be constructed without applying a Ni plating layer or an Au plating layer, leading to the present invention.

[0010] In other words, the protective element of the present invention comprises an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate at a distance from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, wherein the protective element electrodes have a platinum group element oxide content of 3.0% by mass or more and 11.0% by mass or less, a total content of Cu, Sn, and Mn oxides of 0.3% by mass or more and 4.0% by mass or less, and the remainder consists of Ag and SiO2-based glass (excluding Cu, Sn, and Mn oxides).

[0011] Furthermore, the electrode for the protective element of the present invention is for a protective element comprising an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate spaced apart from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, characterized in that the content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less, the total content of Cu, Sn and Mn oxides is 0.3% by mass or more and 4.0% by mass or less, and the remainder consists of Ag and SiO2-based glass (excluding Cu, Sn and Mn oxides). [Effects of the Invention]

[0012] According to the present invention configured in this way, by using electrodes for protective elements that have excellent solder wettability and solder corrosion resistance, it becomes unnecessary to apply Ni plating layers with poor thermal conductivity or expensive Au plating layers, as was done in the past. As a result, in protective elements using lead-free solder as a component material of the fuse element, it is possible to reduce the time required to interrupt the circuit during overvoltage operation while keeping costs down. [Brief explanation of the drawing]

[0013] [Figure 1] A schematic diagram showing the configuration of a protective element according to one embodiment of the present invention. [Figure 2] A schematic diagram showing the configuration of a protection circuit with the protection element of the same embodiment implemented. [Figure 3] A schematic diagram showing the circuit configuration used in the heater operation test of the embodiment. [Modes for carrying out the invention]

[0014] A protective element 100 according to one embodiment of the present invention will be described below with reference to the drawings.

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

[0016] Specifically, as shown in Figure 1, the protective element 100 comprises an insulating substrate 1 made of ceramics or alumina, 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 made of a fusible conductor that is joined so as to straddle the surfaces of the pair of fuse electrodes 2 and the intermediate electrode 3 and is electrically connected to the pair of fuse electrodes 2 and the intermediate electrode 3, an operating flux 5 applied to the surface of the fuse element 4, and a resistive element 6 (heater) provided on the other surface of the insulating substrate 1 and electrically connected to the intermediate electrode 3 and a 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 of the insulating substrate 1.

[0017] Known materials may be used as the material constituting the operation flux 5. Further, the fuse element of the present embodiment is made of lead-free solder, and examples thereof include, but are not limited to, those made of SnAg-based alloys, SnAgCu-based alloys, SnCu-based alloys, SnBi-based alloys, etc. Specific examples of the fuse element 4 include, for example, Sn-Ag-Cu / Sn-Cu clad elements. The fuse electrode 2 and the intermediate electrode 3 (hereinafter, also simply referred to as the electrode for the protection element) are composed of a sintered electrode made of a SiO2-based glass component added for bonding to an insulating substrate 1 made of, for example, ceramics and metal particles serving as an electrode material. The chemical composition of the electrode for the protection element will be described later.

[0018] The protection element 100 configured as described above is connected in series to the secondary battery 210 in the protection circuit 200 as shown in FIG. 2, and cuts off the circuit by melting the fuse element 4 when an overcurrent or an overvoltage is applied.

[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 conduction resistance, thereby cutting 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 energizes the resistance element 6 and melts the fuse element 4 using the heat generated from the resistance element 6, thereby operating in an overvoltage mode in which the circuit is cut off. Specifically, this protection circuit 200 includes detection means 220 that detects the voltage applied to the secondary battery 210 and switches the on / off of the current flowing through the resistance element 6 of the protection element 100. This detection means 220 is configured using a voltage detection IC and a FET. When the detection means 220 detects an overvoltage, it turns on the current flowing through the resistance element 6, and thereby the fuse element 4 is melted by the heat of the resistance element 6.

[0021] 2. Chemical Composition of the Electrode for the Protection Element Next, the composition of the material constituting the electrode for the protection element of the present embodiment will be described.

[0022] (1) Content of oxide of platinum group element: 3.0 mass% or more and 11.0 mass% or less In the electrode for the protection element of the present embodiment, a platinum group element is contained as an oxide. The platinum group element is an element that improves the solder resistance and solder wetting property of the electrode for the protection element. The electrode for the protection element of the present 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 resistance deteriorates, and the electrode for the protection element melts into the fuse element 4 at high temperatures. 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 still more preferably 9.5 mass% or more. On the other hand, when the content of the oxide of the platinum group element exceeds 11.0 mass%, the solder wetting property deteriorates, and the soldering property when attaching the fuse element 4 deteriorates. Therefore, the content of the oxide of the platinum group element is 11.0 mass% or less, and preferably 10.0 mass% or less.

[0023] (2) Total content of oxides of Cu, Sn, and Mn: 0.3 mass% or more and 4.0 mass% or less Cu (copper) oxides (CuO and / or Cu2O), Sn (tin) oxide (SnO2), and Mn (manganese) oxides (Mn2O3 and / or MnO2) are included as glass components and are elements that improve the adhesion between the insulating substrate 1 and the electrode. When the total content of the oxides of Cu, Sn, and Mn is less than 0.3 mass%, there is a risk of deteriorating the adhesion between the insulating substrate 1 and the electrode. Therefore, the total content of the oxides of Cu, Sn, and Mn is preferably 0.3 mass% or more, more preferably 1.0 mass% or more, and still more preferably 2.0 mass% or more. On the other hand, if the total content of Cu, Sn, and Mn oxides exceeds 4.0% by mass, glass components may rise to the electrode surface, potentially reducing soldering performance. Therefore, the total content of Cu, Sn, and Mn oxides is preferably 4.0% by mass or less.

[0024] (3) Remainder In one preferred embodiment, the remainder is Ag and SiO2-based glass (excluding oxides of Cu, Sn, and Mn). SiO2-based glass is a material whose main component is SiO2, and which contains one or more elements selected from B, alkali metals, alkaline earth metal oxides, and Bi2O3. In this embodiment, preferably, the Ag content is 81.0% by mass or more and 96.4% by mass or less, and the SiO2-based glass content is 0.3% by mass or more and 4.0% by mass or less. In addition, trace elements may be introduced as unavoidable impurities depending on the raw materials, materials, manufacturing equipment, etc. Each of these unavoidable impurities may be contained in a range of 1.0% by mass or less (including 0% by mass).

[0025] The reason why setting the content of each component within this range improves both solder wettability and solder corrosion resistance remains unclear. Based on the knowledge obtained to date, the mechanism proposed by the inventor is described below. Please note that the following explanation of the mechanism is not intended to limit the technical scope of the present invention.

[0026] The sintered electrode material is composed of a glass component added to bond to the ceramic substrate, a platinum group metal oxide, and silver metal particles that serve as the electrode material. Of these, the platinum group metal oxide is selected as a material that can appropriately adjust the affinity between the silver electrode metal, the glass component, and the solder material soldered to the electrode material. The electrode material of one embodiment of the present invention consists of a silver metal phase as the main component, and platinum group metal oxide and glass component that are discharged to the grain boundaries of the silver metal phase during firing and accumulate at the grain boundaries. The electrode material has a configuration in which the platinum group oxide and glass component are distributed at the grain boundaries of the silver metal phase. Solder corrosion is a phenomenon in which the electrode base metal in the longitudinal direction of the silver electrode rapidly dissolves into the molten solder, starting from the grain boundaries of the sintered silver electrode, causing the electrode to disappear. However, in the electrode material of one embodiment of the present invention, platinum group oxides, which have excellent high-temperature stability, are distributed at the grain boundaries of the silver electrode. Therefore, the dissolution of the silver electrode by molten solder can be suppressed, and the high-temperature durability of the electrode itself can be improved. Furthermore, due to the excellent chemical resistance and oxidation resistance of the platinum group oxides, the silver electrode can be protected from oxygen and oxidizing atmospheres, suppressing material deterioration, thereby increasing the chemical stability of the electrode material and ensuring the reliability of the electrode over a long period of time. On the other hand, since the surface of the silver electrode exposes a relatively clean metal surface without compound films such as oxides, good solder wettability can be ensured. Therefore, the electrode material of one embodiment of the present invention can suppress solder erosion of the silver electrode by molten solder due to platinum group oxide metals distributed at the grain boundaries of the silver electrode, while achieving excellent solderability of the electrode surface. [Examples]

[0027] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and can be implemented with modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0028] (1) Preparation of test samples (Electrode fabrication) A conductive paste was prepared by mixing Ag powder, ruthenium oxide (RuO2) powder, copper oxide (CuO) powder, tin oxide (SnO2) powder, manganese oxide (MnO2) powder, glass frit, an organic binder, and a solvent. This paste was then fired at 850°C to produce 10 electrode samples, each with a thickness of 6-8 μm and a different chemical composition. The chemical composition of each electrode sample (sintered electrode material) is shown in Table 1. In Table 1, "Ru, Cu, Sn, Mn" indicates the total content of each oxide of Ru, Cu, Sn, and Mn. The chemical composition of each electrode sample can be measured using, for example, SEM-EDX or EPMA.

[0029] (Preparation of protective element samples) Each of the obtained electrode samples was used as a fuse electrode and an intermediate electrode to prepare protective element samples (test samples) with the configuration of the embodiment described above. Three test samples were prepared for each electrode sample with a different chemical composition. In each test sample, lead-free solder (specifically, Sn-Ag-Cu / Sn-Cu) was used as the fuse element.

[0030] (2) Solder wettability test For each test sample obtained, a solder wettability test was performed by immersing the electrode sample in molten solder, and the solder wetted area was measured. The test conditions are as follows. Solder: Pb-free (96.5Sn-3Ag-0.5Cu) Flux: 25 wt% (Rosin ethanol solution) • Immersion depth: 2-2.5 mm • Soldering temperature: 245±5℃ Immersion time: 3.0 ± 0.5 seconds • Immersion and withdrawal speed: 25 ± 2.5 mm / second Table 1 shows the measurement results of the solder wetted area for each electrode sample obtained in this manner. Samples with a solder wetted area of ​​95% or more were evaluated as having "good solder wettability (○)", and those with a solder wetted area of ​​less than 95% were evaluated as having "poor solder wettability (×)".

[0031] (3) Heater operation test Next, a heater operation test was performed on the obtained test samples, and the remaining film thickness was measured. Specifically, the test samples were mounted on the circuit shown in Figure 3, and a heater operation test was performed by applying the lower limit voltage of the product's operating voltage range (6.4V in this case) to the resistive element to melt the fuse elements on both sides of the intermediate element. The film thickness at the thinnest point on each electrode after the heater operation test was defined as the remaining film thickness. Samples with a remaining film thickness of 0.5 μm or more were evaluated as having "good solder corrosion resistance (○)", and those with a remaining film thickness of 0.5 μm or less were evaluated as having "poor solder corrosion resistance (×)". The measurement results are shown in Table 1.

[0032] [Table 1]

[0033] (4) Summary As shown in Table 1, protective element samples prepared using electrode samples with levels (2) to (4) and (7) to (10), in which the content of platinum group element Ru oxide was 3.0% to 11.0% by mass and the total content of Cu, Sn, and Mn oxides was 0.3% to 4.0% by mass, were all confirmed to yield good results in terms of solder wettability and solder corrosion resistance. On the other hand, protective element samples prepared using electrode samples of level (1), which have an excessive content of Ru oxide (a platinum group element), had a small solder wettable area and poor solder wettability. Furthermore, protective element samples prepared using electrode samples of level (5) and (6), which have a low content of Ru oxide (a platinum group element), had a small remaining film thickness and poor solder corrosion resistance.

[0034] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. For example, the protective element of the present invention includes the following embodiments 1 to 6.

[0035] (Aspect 1) A protective element comprising an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate at a distance from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, The electrode for the protective element is The content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less. The total content of Cu, Sn, and Mn oxides is 0.3% by mass or more and 4.0% by mass or less. A protective element characterized in that the remainder consists of Ag and SiO2-based glass (excluding oxides of Cu, Sn, and Mn).

[0036] (Aspect 2) The protective element according to Embodiment 1, wherein the content of platinum group element oxides is 4.5% by mass or more and 11.0% by mass or less.

[0037] (Aspect 3) The protective element according to embodiment 2, wherein the content of platinum group element oxides is 9.0% by mass or more and 11.0% by mass or less.

[0038] (Aspect 4) A protective element according to any one of embodiments 1 to 3, wherein the total content of Cu, Sn, and Mn oxides is 1.0% by mass or more and 4.0% by mass or less.

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

[0040] (Aspect 6) The protective element according to any one of embodiments 1 to 5, wherein the fuse element is made of lead-free solder.

[0041] (Aspect 7) The insulating substrate is provided with a resistive element on its back surface, A protective element according to any one of embodiments 1 to 6, configured to melt the fuse element by heating the resistive element during operation.

[0042] (Pattern 8) An electrode for a protective element comprising an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate at a distance from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, The content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less. The total content of Cu, Sn, and Mn oxides is 0.3% by mass or more and 4.0% by mass or less. An electrode for a protective element, characterized in that the remainder consists of Ag and SiO2-based glass (excluding oxides of Cu, Sn, and Mn). [Explanation of Symbols]

[0043] 200...protection circuit 210...Secondary battery 220...Detection means 100... Protective element 1 ···Insulating substrate 2 ···Fuse electrode 3...Intermediate electrode 4 ···Fuse element 5. Operating flux 6 ··· Resistor element 7 ···Lid

Claims

1. A protective element comprising an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate at a distance from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, The electrode for the protective element is The content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less. The total content of Cu, Sn, and Mn oxides is 0.3% by mass or more and 4.0% by mass or less. The remainder is Ag and SiO ２ A protective element characterized by being made of a glass system (excluding oxides of Cu, Sn, and Mn).

2. The protective element according to claim 1, wherein the content of platinum group element oxides is 4.5% by mass or more and 11.0% by mass or less.

3. The protective element according to claim 2, wherein the content of platinum group element oxides is 9.0% by mass or more and 11.0% by mass or less.

4. The protective element according to claim 1, wherein the total content of Cu, Sn, and Mn oxides is 1.0% by mass or more and 4.0% by mass or less.

5. The protective element according to claim 4, wherein the total content of Cu, Sn, and Mn oxides is 2.0% by mass or more and 4.0% by mass or less.

6. The protective element according to claim 1, wherein the fuse element is made of lead-free solder.

7. The insulating substrate is provided with a resistive element on its back surface, The protective element according to claim 1, configured to melt the fuse element by heating the resistive element during operation.

8. An electrode for a protective element comprising an insulating substrate, a plurality of protective element electrodes provided on the surface of the insulating substrate at a distance from each other, and a fuse element made of lead-free solder joined so as to span each surface of the plurality of electrodes, The content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less. The total content of Cu, Sn, and Mn oxides is 0.3% by mass or more and 4.0% by mass or less. The remainder is Ag and SiO ２ An electrode for a protective element, characterized by being made of a glass system (excluding oxides of Cu, Sn, and Mn).

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