Protection element

Abstract

To suppress the solder erosion of a dummy terminal electrode due to a connecting solder of other terminal electrodes in a surface-mount type protection element.SOLUTION: A protection element includes a dummy terminal electrode 71 that electrically connects an intermediate electrode and a heating element 5 via a castellation formed on the outer peripheral end surface of an insulating substrate 1, and a first terminal electrode 72 that is provided on the underside of the insulating substrate and electrically connects the heating element and the circuit board, and the edge region around the castellation of the dummy terminal electrode is covered with a barrier layer that suppresses solder erosion.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a protection element for an electric / electronic device. [Background technology]

[0002] Conventionally, there has been known a surface-mounted protective element that is mounted on a circuit board of a small electronic device such as a smartphone to protect a secondary battery such as a battery pack included in the small electronic device from overcurrent or overvoltage (for example, Patent Document 1).

[0003] This surface-mounted protection element is configured by providing a pair of fuse electrodes, primarily composed of Ag, on the upper surface of an insulating substrate, and joining a fuse element made of a fusible conductor (specifically, a solder alloy) across the surfaces of the pair of fuse electrodes. The lower surface of the insulating substrate is provided with terminal electrodes that are soldered to the circuit board and electrically connect the conductor wiring of the circuit board to the fuse electrodes. When an overcurrent is applied to a secondary battery, for example, this protection element operates in an overcurrent mode, where the fuse element melts due to self-heating caused by current-carrying resistance, thereby interrupting the circuit.

[0004] The protective element includes an intermediate electrode between a pair of fuse electrodes on the upper surface of the insulating substrate, and a heating element on the lower surface of the insulating substrate. The lower surface of the insulating substrate is provided with a dummy terminal electrode for electrically connecting the intermediate electrode on the upper surface with the heating element on the lower surface, and a terminal electrode soldered to the conductor wiring of the circuit board for electrically connecting the circuit board and the heating element. When an overvoltage is applied to the secondary battery, the protective element operates in an overvoltage mode, passing current through the heating element and using the heat generated by the heating element to melt the fuse element and break the circuit.

[0005] Such surface-mounted protective elements include those that have both one or more terminal electrodes solder-connected to the circuit board and dummy terminal electrodes that are not solder-connected to the conductor wiring of the circuit board, provided on the underside of an insulating substrate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-168272 Summary of the Invention [Problem to be solved by the invention]

[0007] When soldering a protective element such as the one described above to a circuit board, solder balls can form around the connection points due to the solder used to connect the terminal electrodes to the circuit board. For example, solder paste (also known as cream solder) is used for surface mounting. During reflow soldering, some of the solder paste can be blown away by solvent vapor or soften and drip around due to the pressure and temperature rise caused by component mounting, resulting in solder balls on the circuit board. These solder balls can then float on the board and unintentionally wet the dummy terminal electrodes. Compared to other terminal electrodes soldered to the circuit board, dummy terminal electrodes that are not soldered have poor heat dissipation properties. Therefore, when applying power to the fuse in overvoltage mode after circuit mounting, the dummy electrodes can be melted by the heat generated by the heating element and disappear, potentially stopping power to the heating element before the fuse element blows, preventing proper circuit interruption. Such problems are particularly likely to occur in a structure in which the intermediate electrode on the upper surface side and the dummy terminal electrode on the lower surface side are connected via a castellation (half-through hole) provided on the end surface of the insulating substrate, and the dummy terminal electrode becomes thin at the boundary with the castellation.

[0008] The present invention has been made in consideration of these problems, and its main objective is to prevent the dummy terminal electrode from being eroded by the connecting solder of other terminal electrodes in a surface-mounted protective element that has a heat-generating element and a dummy terminal electrode electrically connected to the heat-generating element on the underside of an insulating substrate, thereby enabling the heat-generating element to properly interrupt the circuit. [Means for solving the problem]

[0009] That is, the protective element of the present invention is solder-mounted to a circuit board for use, and comprises an insulating substrate, a pair of fuse electrodes provided on the upper surface of the insulating substrate and electrically connected to the circuit board, an intermediate electrode provided between the pair of fuse electrodes, a fuse element joined across the pair of fuse electrodes and the intermediate electrode, a heat-generating element provided on the lower surface of the insulating substrate, a dummy terminal electrode provided on the lower surface of the insulating substrate and electrically connecting the intermediate electrode and the heat-generating element via a castellation, one end of which is formed on the outer peripheral end surface of the insulating substrate, and a first terminal electrode provided on the lower surface of the insulating substrate and electrically connecting the heat-generating element and the circuit board, wherein the edge region around the castellation of the dummy terminal electrode is covered with a barrier layer that suppresses solder erosion. [Effects of the Invention]

[0010] According to the present invention configured in this manner, the edge region around the castellation, where solder erosion is most likely to occur in the dummy terminal electrode, is covered with a barrier layer that suppresses solder erosion. Therefore, even if the connecting solder breaks off from the other terminal electrodes and wets onto the dummy terminal electrode when mounted on the circuit board, the progress of solder erosion of the dummy terminal electrode when current is applied to the heating element can be delayed, and the circuit can be properly interrupted by the heating element. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view schematically illustrating a configuration of a protection element according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view schematically showing the configuration of the protection element of the embodiment. [Figure 3] 2 is a cross-sectional view taken along line AA' in FIG. 1, schematically illustrating the configuration of the protection element of the embodiment. FIG. [Figure 4] 2 is a cross-sectional view taken along line BB' in FIG. 1, schematically illustrating the configuration of the protection element of the embodiment. FIG. [Figure 5] FIG. 2 is a plan view schematically showing the configuration of the upper surface side of the insulating substrate of the protection element of the embodiment. [Figure 6] FIG. 2 is a plan view schematically showing the configuration of the lower surface side of the insulating substrate of the protection element of the embodiment. [Figure 7] FIG. 2 is a diagram schematically illustrating the configuration of a protection circuit in which the protection element of the embodiment is mounted. DETAILED DESCRIPTION OF THE INVENTION

[0012] A protection element according to one embodiment of the present invention will be described below with reference to the drawings.

[0013] The protective element of this embodiment is mounted on 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. This protective element is a so-called surface-mount type that is solder-mounted on a protection circuit of the secondary battery of the small electronic device.

[0014] 1 to 5, the protective element includes a rectangular insulating substrate made of ceramic, alumina, or the like, a pair of fuse electrodes provided on one surface (top surface) of the insulating substrate, an intermediate electrode provided between the pair of fuse electrodes, a fuse element made of a fusible conductor joined across the surfaces of the pair of fuse electrodes and the intermediate electrode and electrically connected to the pair of fuse electrodes and the intermediate electrode, and operating flux applied to the surface of the fuse element. The pair of fuse electrodes, the intermediate electrode, the fuse element, and the operating flux are covered by a lid provided on one surface of the insulating substrate.

[0015] Known materials may be used to form the fuse electrode and intermediate electrode, and for example, they may be formed from sintered electrodes containing an SiO2-based glass component added to bond them to an insulating ceramic substrate and metal particles that serve as the electrode material.

[0016] The fuse element of this embodiment is made of lead-free solder, such as, but not limited to, an Sn-Ag alloy, an Sn-Ag-Cu alloy, an Sn-Cu alloy, or an Sn-Bi alloy. A specific example of the fuse element is an Sn-Ag-Cu / Sn-Cu clad element. Known materials may be used for the operating flux.

[0017] As shown in Figures 3, 4 and 6, the protective element also includes a heating element made of a thick film resistor provided in the center of the lower surface of the insulating substrate, and a plurality of terminal electrodes arranged around the heating element.

[0018] The heating element has a rectangular shape in plan view, and its entire surface is covered with an insulating layer made of, for example, silicon dioxide glass, silicon salt glass, polymer glass, epoxy resin, polyimide resin, glass epoxy, or the like.

[0019] The protection element includes terminal electrodes, including a dummy terminal electrode electrically connecting the intermediate electrode and the heat generating element, a first terminal electrode electrically connecting the heat generating element and the circuit board, and a pair of second terminal electrodes electrically connecting the pair of fuse electrodes and the circuit board, respectively. The dummy terminal electrode and the first terminal electrode are provided as a pair with the heat generating element sandwiched between them. The pair of second terminal electrodes are also provided as a pair with the heat generating element sandwiched between them.

[0020] The dummy terminal electrode is an electrode that is not soldered when mounted on a circuit board, and after mounting on the circuit board, a gap is formed between it and the surface of the circuit board. It is connected to the intermediate electrode via a castellation (metallized half-through hole) formed on the outer peripheral edge surface of the insulating substrate.

[0021] On the other hand, the first and second terminal electrodes are electrodes that are soldered when mounted on a circuit board. The pair of second terminal electrodes are connected to the pair of fuse electrodes via castellations formed on the outer peripheral end surface of the insulating substrate.

[0022] Known materials may be used to form each terminal electrode, and for example, the terminal electrodes may be formed of sintered electrodes containing an SiO2-based glass component added to bond the electrodes to an insulating ceramic substrate, and metal particles that serve as the electrode material.

[0023] In the protective element of this embodiment, at least the edge region around the castellation on the surface of the dummy terminal electrode (the boundary with the castellation and its periphery) is covered with a barrier layer that suppresses solder leaching. In the protective element of this embodiment, the entire region on the surface of the dummy terminal electrode between the castellation and the heat-generating element is covered with the barrier layer. More specifically, the entire surface of the dummy terminal electrode is covered with the barrier layer, except for the vicinity of the linear outer edge of the insulating substrate.

[0024] In this embodiment, a part of the inner wall surface of the castellation is covered with a barrier layer. Specifically, at least the lower surface region of the inner wall surface of the castellation is covered with the barrier layer, and preferably the entire inner wall surface is covered with the barrier layer.

[0025] The barrier layer may be made of any material that can prevent solder erosion of the dummy terminal electrodes. For example, it may be a glass-based insulating material such as silicon dioxide glass, silicon salt glass, polymer glass, epoxy resin, polyimide resin, or glass epoxy, or a metal material such as nickel plating. Furthermore, it is preferable that the barrier layer has heat resistance sufficient to prevent melting during reflow (260°C) and overvoltage mode operation (400°C or higher). It is more preferable that the barrier layer be applied by printing.

[0026] The barrier layer may be made of the same material as the insulating layer that covers the heating elements, or may be made of a different material. In this embodiment, the barrier layer and the insulating layer are made of the same material. That is, the heating elements and the dummy terminal electrodes are covered by a single common layer.

[0027] The protection element configured in this manner is connected in series to the secondary battery in a protection circuit, as shown in FIG. 7, and cuts off the circuit by blowing the fuse element when an overcurrent or an overvoltage is applied.

[0028] Specifically, when an overcurrent is applied to the secondary battery of the protection circuit, the protection element operates in an overcurrent mode, whereby the fuse element melts due to self-heating caused by the current-carrying resistor, thereby cutting off the circuit.

[0029] On the other hand, when an overvoltage is applied to the secondary battery of the protection circuit, the protection element operates in overvoltage mode, passing current through the heating element through the intermediate electrode and using the heat generated by the heating element to blow the fuse element, thereby interrupting the circuit. Specifically, this protection circuit detects the voltage applied to the secondary battery and is equipped with a detection means that switches on and off the current flowing through the heating element of the protection element. This detection means is composed of a voltage detection IC and an FET. When the detection means detects an overvoltage, it turns on the current flowing through the heating element, causing the fuse element to blow due to the heat from the heating element.

[0030] According to the protective element of this embodiment configured in this manner, the edge region around the castellation, where solder erosion is most likely to occur in the dummy terminal electrode, is covered with a barrier layer that suppresses solder erosion. Therefore, even if the connecting solder breaks off from the other terminal electrodes and wets onto the dummy terminal electrode when mounted on the circuit board, the progress of solder erosion of the dummy terminal electrode when current is applied to the heating element can be delayed, and the circuit can be properly shut off by the heating element.

[0031] The present invention is not limited to the above-described embodiment. For example, in the above embodiment, substantially the entire surface of the dummy terminal electrode and the inner wall surfaces of the castellations are covered with the barrier layer, but this is not limiting. In other embodiments, the inner wall surfaces of the castellations and the regions of the dummy terminal electrode other than the edge regions around the castellations may not be covered with the barrier layer.

[0032] Furthermore, while the protection element in the above embodiment is configured to operate in both the overcurrent mode and the overvoltage mode, this is not limiting. In other embodiments, the protection element does not have to operate in the overcurrent mode as long as it has a heating element, a terminal electrode to be soldered, and a dummy electrode that only conducts current on the underside of the insulating substrate.

[0033] In the above embodiment, the second terminal electrode is connected to the fuse electrode on the upper surface via a castellation, but this is not limited thereto. In other embodiments, the second terminal electrode may be connected to the fuse electrode on the upper surface via a through-hole that penetrates the insulating substrate.

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

[0035] (Aspect 1) a heat generating element provided on a lower surface of the insulating substrate; a dummy terminal electrode provided on the lower surface of the insulating substrate, the dummy terminal electrode having one end electrically connecting the intermediate electrode and the heat generating element via a castellation formed on an outer peripheral end surface of the insulating substrate; and a first terminal electrode provided on the lower surface of the insulating substrate, the heat generating element being electrically connected to the circuit board;

[0036] In this configuration, the edge region around the castellation, where solder erosion is most likely to occur in the dummy terminal electrode, is covered with a barrier layer that suppresses solder erosion. Therefore, even if the connecting solder breaks off from the other terminal electrodes and wets onto the dummy terminal electrode when mounted on the circuit board, the progress of solder erosion of the dummy terminal electrode when current is applied to the heating element can be delayed or completely prevented, and the circuit can be properly shut off by the heating element.

[0037] (Aspect 2) 2. The protection element according to embodiment 1, wherein the inner wall surfaces of the castellations are partially or entirely covered with the barrier layer. The plating on the inner wall surface of the castellation is thin and therefore prone to solder erosion, but with this configuration, even if the connecting solder that has spilled from other terminal electrodes wets onto the castellation, the progression of solder erosion of the castellation when the heating element is energized can be delayed, allowing the heating element to properly shut off the circuit.

[0038] (Aspect 3) 3. The protection element according to aspect 1 or 2, wherein the entire region of the dummy terminal electrode sandwiched between the castellation and the heat generating element is covered with the barrier layer. In this embodiment, by covering most of the dummy terminal electrodes with the barrier layer, it is possible to more efficiently prevent the dummy electrodes from being eroded by solder when the heating element is energized.

[0039] (Aspect 4) 4. The protection element according to any one of aspects 1 to 3, further comprising an insulating layer covering a surface of the heat generating element, the barrier layer and the insulating layer being made of the same material. In this case, by using the same material for the insulating layer and the barrier layer, the insulating layer on the surface of the heating element and the barrier layer on the surface of the dummy electrode can be formed in the same process, thereby improving production efficiency. In this case, it is desirable that the barrier layer and the insulating layer are made of a glass-based insulating material.

[0040] (Aspect 5) The protection element according to any one of aspects 1 to 4, further comprising a pair of second terminal electrodes provided on the lower surface of the insulating substrate and electrically connecting the pair of fuse electrodes to the circuit board. In this embodiment, the effect of the present invention is more pronounced because a plurality of terminal electrodes to be soldered are provided on the lower surface of the insulating substrate.

[0041] (Aspect 6) The protection element according to any one of aspects 1 to 5, wherein the first terminal electrode is solder-connected to the circuit board during solder mounting, and the dummy terminal electrode is not solder-connected to the circuit board during solder mounting. [Explanation of symbols]

[0042] 100...Protection element 1. Insulating substrate 21 Fuse electrode 22 Intermediate electrode 3. Fuse element 4. Operating Flux 5 Heating element 6. Cover 7...terminal electrode 71 Dummy terminal electrode 72...1st terminal electrode 73...Second terminal electrode 8. Castellation 91 Barrier layer 92 Insulating layer 200...protection circuit 210...Secondary battery 220....Detection means CB... Circuit Board S ···Connection solder

Claims

1. A protection element that is solder-mounted to a circuit board and used, an insulating substrate; a pair of fuse electrodes provided on an upper surface of the insulating substrate and electrically connected to the circuit board; an intermediate electrode provided between the pair of fuse electrodes; a fuse element joined across the pair of fuse electrodes and the intermediate electrode; a heating element provided on the lower surface of the insulating substrate; a dummy terminal electrode provided on the lower surface of the insulating substrate, one end of which electrically connects the intermediate electrode and the heating element via a castellation formed on the outer peripheral end surface of the insulating substrate; a first terminal electrode provided on a lower surface of the insulating substrate and electrically connecting the heat generating element and the circuit board; A protective element in which an edge region around the castellation in the dummy terminal electrode is covered with a barrier layer that suppresses solder erosion.

2. The protection element according to claim 1 , wherein a part or all of the inner wall surface of the castellation is covered with the barrier layer.

3. 3. The protection element according to claim 1, wherein the entire area of ​​the dummy terminal electrode sandwiched between the castellation and the heat generating element is covered with the barrier layer.

4. Further, an insulating layer is provided to cover the surface of the heating element.

3. The protection element according to claim 1, wherein the barrier layer and the insulating layer are made of the same material.

5. 3. The protection element according to claim 1, further comprising a pair of second terminal electrodes provided on a lower surface of the insulating substrate and electrically connecting the pair of fuse electrodes to the circuit board.

6. the first terminal electrode is solder-connected to the circuit board during solder mounting, 3. The protection element according to claim 1, wherein the dummy terminal electrode is not soldered to the circuit board when the element is mounted by soldering.

Images