TWI907063B - Protective component and electrodes for protective component - Google Patents

Abstract

A protective component has an insulating substrate, multiple electrodes for the protective component set on a surface of the insulating substrate and separated from each other, and a fuse element bridging across surfaces of the multiple electrodes and containing lead-free solder. The electrodes for the protective component are characterized in that a content of oxides of platinum group element of is 3.0 wt% or more and 11.0 wt% or less, a sum of content of oxides of copper, tin, and manganese is 0.3 wt% or more and 4.0 wt% or less, and a remaining part contains silver and silicon dioxide glass (not including oxides of copper, tin, and manganese).

Description

Protection components and electrodes for protection components

This invention relates to protective elements for electrical and electronic equipment and electrodes for protective elements.

Known surface-mount protection elements (e.g., Patent 1) are installed in the internal circuitry of small electronic devices (such as smartphones) to protect the secondary batteries, such as battery packs, of the small electronic device from overcurrent or overvoltage. The structure of this surface-mount protection element is as follows: multiple silver-based fuse electrodes are disposed on the surface of an insulating substrate, and fuse elements containing a fusible conductor (specifically, a solder alloy) are connected across the surfaces of the multiple fuse electrodes. Simultaneously, a resistive element serving as a heater is disposed on the back side of the insulating substrate.

This protective element operates in overcurrent mode when the secondary battery experiences an overcurrent, using the heat generated by the energized resistor to melt the fuse and break the circuit. When the secondary battery experiences an overvoltage, it operates in overvoltage mode, supplying current to the resistor and using the heat generated by the resistor to melt the fuse and break the circuit. [Prior Art Documents] [Patent Documents]

[Patent Document 1] Japanese Patent Application Publication No. 2021-168272

[The problem the invention aims to solve]

In addition, in order to comply with the RoHS directive, solder alloys with a lead content of less than 1000ppm (i.e., lead-free solder) are usually used as the constituent materials of the fuse element in such protective components.

In this situation, due to the high liquidus temperature of lead-free solder, the fuse element will be heated to a high temperature during operation. If only silver electrodes are used as fuse electrodes at this time, the components of the fuse electrode will dissolve into the solder in the fuse element, causing solder corrosion. Therefore, to prevent this solder corrosion, a nickel plating layer needs to be plated on the surface of the silver electrode as a protective layer. However, this results in a nickel plating layer with poor thermal conductivity between the resistive element on the back of the insulating substrate and the fuse element on the surface. This causes the fuse element to take a longer time to heat up during overvoltage operation, thus prolonging the time required for the circuit to break, which becomes a problem.

Furthermore, when the surface of the silver electrode is coated with nickel, the solderability of the fuse component deteriorates. Therefore, an expensive gold plating layer with excellent solder wetting properties needs to be applied to the surface of the nickel plating layer, which also leads to increased costs.

Therefore, the main challenge of this invention is to reduce the time required for the circuit to disconnect during overvoltage operation in protective components using lead-free solder as a component material for fuses, while simultaneously controlling costs. [Means for Solving the Problem]

To solve the above problems, the inventors, through in-depth research, discovered that by setting the chemical composition of the electrodes of the protection element to be mainly silver (Ag), with the content of platinum group element oxides being 3.0% by mass or more and 11.0% by mass or less, and the total content of copper (Cu), tin (Sn), and manganese (Mn) oxides being 0.3% by mass or more and 4.0% by mass or less, the solder wettability and solder corrosion resistance can be improved simultaneously, and the protection element can be constructed without the need for nickel plating or gold plating, thus completing the present invention.

In other words, the protective element of the present invention includes an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder connected across each surface of the plurality of electrodes. The protective element electrodes are characterized in that: the content of platinum group element oxides in the protective element electrodes is 3.0% by mass or more and 11.0% by mass or less, the total content of copper, tin and manganese oxides is 0.3% by mass or more and 4.0% by mass or less, and the remainder is composed of silver and silicon dioxide glass (excluding copper, tin and manganese oxides).

Furthermore, the protective element electrode of this invention includes an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder connected across the surfaces of the plurality of electrodes. Its characteristics are: the content of platinum group element oxides is 3.0% by mass or more and 11.0% by mass or less; the combined content of copper, tin, and manganese oxides is 0.3% by mass or more and 4.0% by mass or less; and the remainder is composed of silver and silicon dioxide glass (excluding copper, tin, and manganese oxides). [Effects of the Invention]

This invention, with its specially constructed structure, eliminates the need for conventional nickel plating or expensive gold plating due to the use of electrodes for protective components that offer excellent solder wetting and resistance to solder erosion. Consequently, in protective components using lead-free solder as a component of the fuse element, the time required for the circuit to disconnect during overvoltage operation can be shortened while simultaneously reducing costs.

The protective element 100 of one embodiment of the present invention is described below with reference to the figures.

1. Structure of Protection Element 100 The protection element 100 of this embodiment is installed, for example, in a small electronic device such as a smartphone, to protect the secondary battery 210, such as the battery pack of the small electronic device, from overcurrent or overvoltage. This protection element 100 is a surface-mount type element, installed in the protection circuit 200 of the secondary battery 210 of the small electronic device.

Specifically, as shown in Figure 1, the protective element 100 includes: an insulating substrate 1 made of ceramic or alumina; a pair of fuse electrodes 2 disposed on one side surface of the insulating substrate 1; an intermediate electrode 3 disposed between the pair of fuse electrodes 2; and a surface bridging the pair of fuse electrodes 2 and the intermediate electrode 3. A fuse element 4, made of a fusible conductor, is electrically connected to the pair of fuse electrodes 2 and intermediate electrode 3; a working flux 5 is coated on the surface of the fuse element 4; and a resistor element 6 (heater) is disposed on the other side of the insulating substrate 1 and electrically connected to the aforementioned intermediate electrode 3 and heating electrode (not shown in the figure). The pair of fuse electrodes 2, intermediate electrode 3, fuse element 4, and working flux 5 are covered by a cover 7 disposed on one side of the surface of the insulating substrate 1.

The flux 5 can be composed of known materials. Furthermore, the fuse element of this embodiment contains lead-free solder, and can be made of, for example, tin-silver alloys, tin-silver-copper alloys, tin-copper alloys, tin-bismuth alloys, etc., but is not limited to these. The fuse element 4 can be, for example, a tin-silver-copper/tin-copper composite element. The fuse electrode 2 and the intermediate electrode 3 (hereinafter also referred to as the electrode for protection elements) are composed of sintered electrodes containing silicon dioxide (SiO2) glass components added for bonding with the ceramic insulating substrate 1, and metal particles as electrode materials. The chemical composition of the electrodes used in the protective components will be described in detail later.

The protection element 100 thus constructed, as shown in Figure 2, is connected in series with the secondary battery 210 in the protection circuit 200. When overcurrent and overvoltage are applied, the circuit is disconnected by blowing the fuse element 4.

Specifically, when an overcurrent is applied to the secondary battery 210 of the protection circuit 200, the protection element 100 will operate in overcurrent mode, melting the fuse element 4 by the heat generated by the energized resistor, thereby disconnecting the circuit.

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 overvoltage mode, energizing the resistor element 6. The heat generated by the resistor element 6 melts the fuse element 4, thereby disconnecting the circuit. Specifically, this protection circuit 200 has a detection means 220, which detects the voltage applied to the secondary battery 210 and switches the current flow through the resistor element 6 of the protection element 100. This detection means 220 is composed of a voltage detection IC and a field-effect transistor (FET). When an overvoltage is detected, the detection means 220 switches on the current flowing through the resistor element 6, thereby using the heat of the resistor element 6 to melt the fuse element 4.

2. Chemical Composition of the Electrode for the Protective Element Next, the material composition of the electrode for the protective element of this embodiment will be explained.

(1) Content of platinum group element oxides: 3.0% by mass or more and 11.0% by mass or less The electrode for the protective component of this embodiment contains platinum group elements as oxides. Platinum group elements are elements that can improve the solder erosion resistance and solder wettability of the electrode for the protective component. The electrode for the protective component of this embodiment contains one or more platinum group elements, selected from ruthenium (Ru), rhodium (Rh), palladium (Pd), ilium (Os), iridium (Ir), and platinum (Pt). If the content of platinum group element oxides is less than 3.0% by mass, the solder erosion resistance will decrease, and the electrode for the protective component will dissolve into the fuse element 4 at high temperatures. Therefore, the content of platinum group element oxides is 3.0% by mass or more, preferably 4.5% by mass or more, more preferably 9.0% by mass, and even more preferably 9.5% by mass or more. On the other hand, if the content of platinum group element oxides exceeds 11.0% by mass, solder wettability will decrease, and solderability when installing fuse component 4 will deteriorate. Therefore, the content of platinum group element oxides is 11.0% by mass or less, preferably 10.0% by mass or less.

(2) The total content of copper, tin and manganese oxides: Copper (Cu) oxide (CuO and/or _Cu₂O ), tin (Sn) oxide ( _SnO₂ ) and manganese ( _Mn ) oxide ( _Mn₂O₃ and/or _MnO₂ ) are included as glass components and are elements that can improve the adhesion between the insulating substrate 1 and the electrode if the total content of copper, tin and manganese oxides is less than 0.3% by mass. Therefore, the total content of copper, tin and manganese oxides is preferably 0.3% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more. On the other hand, if the total content of oxides of copper, tin, and manganese exceeds 4.0% by mass, glass components may float on the surface of the electrode, posing a risk of reduced solderability. Therefore, the total content of oxides of copper, tin, and manganese is preferably 4.0% by mass or less.

(3) In a preferred embodiment, the remaining portion is a silver (Ag) and silicon dioxide ( _SiO2 ) based glass (excluding oxides of copper, tin, and manganese). The silicon dioxide based glass is primarily composed of silicon dioxide and contains one or more oxides selected from boron (B), alkali metals, alkaline earth metals, and bismuth trioxide ( _Bi2O3 ). In this embodiment, it is preferred that the silver content is 81.0% by mass or more and 96.4% by mass or less, and the silicon dioxide based glass content is 0.3% by mass or more and 4.0% by mass or less. _Furthermore , as unavoidable impurities, trace elements introduced due to raw materials, manufacturing equipment, etc., are expected to be present. These elements, as unavoidable impurities, may each be present in amounts of 1.0% by mass or less (including 0% by mass).

The reason why setting the content of each component within this range can simultaneously improve solder wettability and solder erosion resistance remains somewhat unclear. Based on currently available knowledge, the following explains the mechanism as believed by the inventors. Please note that the following explanation of the mechanism is not intended to limit the scope of the invention.

The sintered electrode material is composed of a glass component for bonding with a ceramic substrate, platinum group metal oxides, and silver metal particles as the electrode material. The platinum group metal oxides are selected to appropriately adjust the affinity between the silver electrode metal, the glass component, and the solder material for welding the electrode material. In one embodiment of the invention, the electrode material consists of a silver metal phase as the main component, and platinum group metal oxides and glass components that are discharged to the grain boundaries of the silver metal phase and accumulate at the grain boundaries during sintering. The electrode material forms a structure in which the platinum group oxides and glass components are distributed at the grain boundaries of the silver metal phase. Erosion caused by molten solder is a phenomenon where the base metal of the silver electrode rapidly dissolves into the molten solder along its longitudinal direction, starting from the grain boundaries of the sintered silver electrode, leading to the disappearance of the electrode. In one embodiment of the invention, the electrode material has platinum group oxides with excellent high-temperature stability distributed at the grain boundaries of the silver electrode. This suppresses the dissolution of the silver electrode by the molten solder, improving the electrode's high-temperature resistance. Furthermore, the excellent chemical and oxidation resistance of the platinum group oxides protects the silver electrode from oxygen or oxidizing environments, inhibiting material degradation and increasing the chemical stability of the electrode material, thus ensuring long-term electrode reliability. On the other hand, the surface of the silver electrode exposes a relatively clean metal surface, free of oxide or other compound films, thus ensuring good solder wettability. Therefore, an embodiment of the electrode material of this invention, through the platinum group oxide metal distributed at the grain boundaries of the silver electrode, can suppress solder erosion of the silver electrode by molten solder, while simultaneously achieving excellent solderability of the electrode surface. [Embodiment]

The following embodiments are provided to illustrate the invention more specifically, but the invention is not limited to the following embodiments. Modifications are also possible within the scope of the foregoing and the following description, and these are all included within the technical scope of the invention.

(1) Preparation of Test Samples (Electrode Preparation) Silver powder, ruthenium dioxide ( _RuO₂ ) powder, copper oxide (CuO) powder, tin dioxide (SnO₂) powder, manganese dioxide ( _MnO₂ ) powder, glass melt, organic binder, and solvent were mixed to form a conductive paste, which was then sintered at 850°C to produce 10 electrode samples, each with a thickness of 6–8 μm but different chemical compositions. The chemical compositions of the obtained electrode samples (sintered electrode materials) are shown in Table 1. In Table 1, "Ru, Cu, Sn, Mn" indicates the total content of the oxides of Ru, Cu, Sn, and Mn. Furthermore, the chemical composition of each electrode sample can be measured using methods such as SEM-EDX and EPMA.

(Fabrication of Protective Component Samples) Using the obtained electrode samples as fuse electrodes and intermediate electrodes, protective component samples (test samples) with the aforementioned configuration were fabricated. Three test samples were fabricated for each electrode sample with a different chemical composition. Furthermore, lead-free solder (specifically Sn-Ag-Cu/Sn-Cu) was used as the fuse element in each test sample.

(2) Solder Wetting Test For each of the obtained test samples, a solder wetting test was conducted by immersing the sample in molten solder, and the solder wetting area was measured. The test conditions are as follows: ・Solder: Lead-free (96.5Sn-3Ag-0.5Cu) ・Fluoride: 25wt% (rosin ethanol solution) ・Immersion depth: 2~2.5mm ・Solder temperature: 245±5°C ・Immersion time: 3.0±0.5 seconds ・Immersion and pull-out speed: 25±2.5mm/second Table 1 shows the measurement results of the solder wetting area of each electrode sample obtained in this manner. A solder wetted area of 95% or more is rated as "Good solder wettability (〇)", while a wetted area of less than 95% is rated as "Poor solder wettability (×)".

(3) Heater Operation Test Next, a heater operation test was performed on the obtained test samples, and the residual film thickness was measured. Specifically, the test sample was installed in the circuit shown in Figure 3, and the lower limit voltage of the product operating voltage range (6.4V in this case) was applied to the resistive element to perform a heater operation test that caused the fuses clamping the middle electrode to blow. The film thickness at the thinnest point of each electrode after the heater operation test was then taken as the residual film thickness. A residual film thickness of 0.5μm or more was evaluated as "Good solder erosion resistance (〇)", and a residual film thickness of less than 0.5μm was evaluated as "Poor solder erosion resistance (×)". Table 1 shows the measurement results.

Table 1

(4) Conclusion As shown in Table 1, it can be confirmed that the protective component samples made using electrode samples of level numbers (2)~(4) and (7)~(10) with a ruthenium (Ru) oxide content of 3.0% by mass or more and 11.0% by mass or less, and a combined ruthenium, copper, and manganese oxide content of 0.3% by mass or more and 4.0% by mass or less, achieved good results in terms of solder wettability and solder corrosion resistance. On the other hand, the protective component samples made using the level number (1) electrode sample with an excess of ruthenium (Ru) oxide as a platinum group element had a smaller solder wettability area and poor solder wettability. The protective component samples made using oxides containing less ruthenium (Ru) as platinum group elements (level numbers 5 and 6) exhibited reduced residual film thickness and poor resistance to solder erosion.

Furthermore, the present invention is not limited to the foregoing embodiments, and various modifications can be made without departing from its spirit. For example, the protective element of the present invention includes the following forms 1 to 6.

(Sample 1) A protective element includes an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder connected across the surfaces of the plurality of electrodes, characterized in that: The protective element electrodes contain amounts of platinum group element oxides of 3.0% by mass and less than 11.0% by mass, amounts of oxides of copper, tin, and manganese of 0.3% by mass and less than 4.0% by mass, the remainder is composed of silver and silica-based glass (excluding oxides of copper, tin, and manganese).

(Form 2) The protective element as described in Form 1, wherein the content of platinum group element oxides is 4.5% by mass or more and 11.0% by mass or less.

(State 3) The protective element as described in State 2, wherein the content of platinum group element oxides is 9.0% by mass or more and 11.0% by mass or less.

(Patent 4) The protective element as described in any of Patents 1-3, wherein the total content of oxides of copper, tin, and manganese is 1.0% by mass or more and 4.0% by mass or less.

(Patent 5) The protective element as described in Patent 4, wherein the total content of oxides of copper, tin, and manganese is 2.0% by mass or more and 4.0% by mass or less.

(Sample 6) A protective element as described in any of Samples 1-5, wherein the fuse element contains lead-free solder.

(Sample 7) The protective element as described in any of Samples 1 to 6 includes a resistive element disposed on the back side of the insulating substrate, which, during operation, causes the fuse element to melt by heating the resistive element.

(Sample 8) An electrode for a protective element, comprising an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder bridging the surfaces 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 copper, tin, and manganese oxides is 0.3% by mass or more and 4.0% by mass or less; The remainder is composed of silver and silicon dioxide glass (excluding copper, tin, and manganese oxides).

1: Insulating substrate 2: Fuse electrode 3: Intermediate electrode 4: Fuse component 5: Operating flux 6: Resistor component 7: Cover 100: Protection component 200: Protection circuit 210: Battery 220: Detection method

Figure 1 is a schematic diagram showing the structure of a protection element according to an embodiment of the present invention. Figure 2 is a schematic diagram showing the structure of the protection element of the same embodiment installed in a protection circuit. Figure 3 is a schematic diagram showing the circuit structure used in the heater operation test of the embodiment.

1: Insulating substrate

2: Fuse electrodes

3: Middle electrode

4: Fuse Components

5: Applying flux

6: Resistive components

7: Cover Body

100: Protective Components

Claims (8)

A protective element includes an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder connected across the surfaces of the plurality of electrodes, characterized in that: the protective element electrodes contain amounts of platinum group element oxides of 3.0% by mass and less than 11.0% by mass, amounts of copper, tin, and manganese oxides in aggregate of 0.3% by mass and less than 4.0% by mass, the remainder is composed of silver and silicon dioxide glass (excluding oxides of copper, tin, and manganese). The protective element as described in claim 1, wherein the content of the oxide of the platinum group elements is 4.5% by mass or more and 11.0% by mass or less. The protective element as described in claim 2, wherein the content of the oxide of the platinum group elements is 9.0% by mass or more and 11.0% by mass or less. The protective element as claimed in claim 1, wherein the total content of oxides of copper, tin and manganese is 1.0% by mass or more and 4.0% by mass or less. The protective element as described in claim 4, wherein the total content of oxides of copper, tin and manganese is 2.0% by mass or more and 4.0% by mass or less. The protective element as claimed in claim 1, wherein the fuse element contains lead-free solder. The protective element as described in claim 1 includes a resistive element disposed on the back side of the insulating substrate, that, during operation, heating of the resistive element causes the fuse element to melt. An electrode for a protective element includes an insulating substrate, a plurality of protective element electrodes disposed on the surface of the insulating substrate and spaced apart from each other, and a fuse element containing lead-free solder bridging the surfaces 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 copper, tin, and manganese oxides is 0.3% by mass or more and 4.0% by mass or less; the remainder is composed of silver and silicon dioxide glass (excluding copper, tin, and manganese oxides).