JP7220344B2 - circuit protection element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit protection element that fuses and protects various electronic devices when overcurrent flows.

As shown in FIG. 3, this type of conventional circuit protection element comprises: an insulating substrate 1; an underlying layer 4 formed between the element portion 3 and the insulating substrate 1; end face electrodes formed at both ends of the insulating substrate 1 and connected to the upper surface of the element portion 3; 5 and an insulating layer 6 for protecting the element portion 3 .

For example, Patent Document 1 is known as a prior art document related to the invention of this application.

Japanese Unexamined Patent Application Publication No. 2001-273847

In the conventional structure described above, when a metal such as silver that easily generates sulfide is used in the element portion 3, when the circuit protection element is used in a sulfurizing atmosphere, silver causes a chemical reaction with the sulfide factor to generate sulfide. However, there is a problem that the resistance value fluctuates and the anti-sulfurization property deteriorates.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a circuit protection element capable of improving anti-sulfurization characteristics.

A circuit protection element according to a first aspect includes an insulating substrate, a pair of upper surface electrodes provided on both ends of the upper surface of the insulating substrate, an element portion electrically connected to the pair of upper surface electrodes, and the and an insulating layer covering an element portion, wherein the element portion is formed by laminating a plurality of metal layers in order of decreasing specific resistance from the upper surface side of the insulating substrate, and the entire surface of the lower metal layer is covered with the upper metal layer. I covered it with a metal layer.

In the circuit protection element according to the second aspect, in the first aspect, the metal layer is composed of a silver layer, a copper layer, and a nickel layer in this order from the upper surface side of the insulating substrate.

In the circuit protection element according to the third aspect, in the second aspect, the insulating layer is arranged so as to cover the oxide layer formed on the surface of the nickel layer.

As described above, in the circuit protection element of the present invention, a metal or nickel layer that is resistant to sulfurization and has a high specific resistance is formed as the uppermost layer of the element, so that the sulfurization resistance can be improved. It works.

1 is a cross-sectional view of a circuit protection element according to one embodiment of the present invention; Partially cutaway top view of the same circuit protection device Cross-sectional view of a conventional circuit protection device

FIG. 1 is a cross-sectional view of a circuit protection element according to an embodiment of the present invention, and FIG. 2 is a partially cutaway top view of the main part of the same circuit protection element. A circuit protection element according to an embodiment of the present invention comprises an insulating substrate 11, a pair of upper surface electrodes 12 provided at both ends of the upper surface of the insulating substrate 11, and a pair of upper surface electrodes 12 bridging the pair of upper surface electrodes 12. and electrically connected to the pair of upper surface electrodes 12, an underlying layer 14 provided between the element portion 13 and the insulating substrate 11, and the upper surface of the underlying layer 14 and a fusing portion 15 formed in the element portion 13 located at .

Edge electrode layers 16 made of a silver-based material are formed on both ends of the insulating substrate 11 so as to partially overlap the element portions 13, and the surfaces of the edge electrode layers 16 are coated with a plating film (Fig. not shown) are formed. Furthermore, an insulating layer 17 made of silicone resin is provided on the element portion 13 exposed from the end face electrode layer 16 . In FIG. 2, the end face electrode layer 16 and the insulating layer 17 are omitted for simplification of explanation.

In the above configuration, the insulating substrate 11 has a square shape and is made of alumina containing 55% to 96% Al ₂ O ₃ .

The pair of upper surface electrodes 12 are provided on both ends of the upper surface of the insulating substrate 11 and are formed by printing Ag or the like.

Further, the element portion 13 is formed so as to cover at least a portion of the insulating substrate 11 and is positioned on the upper surfaces of the underlying layer 14 and the pair of upper surface electrodes 12 . The element portion 13 includes a lower layer (hereinafter, not shown) formed by using a physical vapor deposition method such as sputtering and vapor deposition of Cr, Cu, and Ni in this order; 13b, and a metal layer 13d on which a nickel layer 13c is sequentially formed.

The silver layer 13a is formed by electroplating using the lower layer as a nucleus. In addition, the silver layer 13 a covers the entire surface of the pair of upper electrodes 12 . The copper layer 13b is formed by electroplating so as to cover the entire surface of the silver layer 13a, and the nickel layer 13c is formed so as to cover the entire surface of the copper layer 13b. Since the nickel layer 13c covers the entire surface of the silver layer 13a and the copper layer 13b, which have poor anti-sulfurization characteristics, the anti-sulfurization characteristics of the circuit protection element are improved. Furthermore, the entire surface of the nickel layer 13c is covered with an insulating layer 17. As shown in FIG.

Two trimming grooves 18 are formed in the central portion of the element portion 13 by a laser from the side surfaces of the element portion 13 facing each other toward the center of the element portion 13 . A region surrounded by is a fusing portion 15 that melts and disconnects when an overcurrent is applied.

Note that the trimming groove 18 may have another shape such as an L shape instead of the straight shape shown in FIG. Furthermore, a trimming groove for adjusting the resistance value may be formed separately.

Further, the underlying layer 14 is provided in the central portion of the upper surface of the insulating substrate 11, and the underlying layer 14 is located between the element portion 13 located between the pair of upper surface electrodes 12 and the insulating substrate 11. is provided. Further, the base layer 14 is mainly composed of glass made of SiO ₂ or the like.

If the nickel layer 13c is left for a certain period of time after formation, a nickel oxide film is formed on its surface. By forming the insulating layer 17 so as to cover the oxide film, the adhesion between the element portion 13 and the insulating layer 17 is improved as compared with the case where the surface of the element portion 13 is made of metal (nickel layer 13c).

In the above-described embodiment of the present invention, since the element portion 13 is formed of a metal that is difficult to sulfurize, that is, has a high specific resistance, particularly nickel, as the uppermost layer, the sulfuration resistance can be improved. is obtained.

At this time, the silver layer 13 a having the worst anti-sulfurization property is the lowest layer of the element portion 13 . As the element portion 13, since the silver layer 13a, the copper layer 13b, and the nickel layer 13c are laminated in order of poor anti-sulfurization property (that is, in descending order of specific resistance), the anti-sulfurization property is reliably improved. be able to.

Further, when the trimming grooves 18 are formed by a laser, the nickel layer 13c, which has a high laser absorptivity, is the uppermost layer of the element portion 13, so that the power of the laser can be set low. Since the temperature rise of 13 can be suppressed, the resistance value is stabilized and the fusing characteristics are improved.

Furthermore, since the silver layer 13a and the copper layer 13b are in contact with each other, a eutectic alloy of molten silver and copper is formed when an overcurrent flows. This alloyed and melted copper diffuses into the nickel layer 13c, thereby lowering the melting point of the entire element portion 13, thereby allowing the fusion portion 15 to be fused in a short period of time.

The circuit protection element according to the present invention has the effect of being able to improve anti-sulphurization characteristics, and is particularly useful as a circuit protection element that fuses when an overcurrent flows and protects various electronic devices. is.

REFERENCE SIGNS LIST 11 insulating substrate 12 upper surface electrode 13 element portion 13a silver layer 13b copper layer 13c nickel layer 13d metal layer 17 insulating layer

Claims (2)

an insulating substrate, a pair of upper surface electrodes provided on both ends of the upper surface of the insulating substrate, an element portion having a fusing portion electrically connected to the pair of upper surface electrodes, and an insulating layer covering the element portion. wherein the element part has a plurality of metal layers stacked in order of a silver layer, a copper layer, and a nickel layer having a low specific resistance from the upper surface side of the insulating substrate, and the nickel layer is the uppermost layer of the metal layers, A circuit protection element in which the upper metal layer covers both ends of the lower metal layer, both outer side surfaces in the vertical direction, and the entire upper surface . 2. The circuit protection element according to claim 1, wherein said insulating layer is arranged so as to cover the nickel oxide layer formed on the surface of said nickel layer.

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