JPH0719075Y2 - Substrate type thermal fuse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of a substrate type thermal fuse.

<Prior Art> The structure of a substrate type thermal fuse is as shown in FIG. 2, and a pair of layered electrodes 2 ', 2'are provided on one surface of a heat resistant insulating substrate, for example, a ceramic plate 1', and both electrodes are provided. A low melting point metal body 3'is bridged in between, lead conductors 6 ', 6'are connected to each electrode, and an insulating layer 5', for example, an epoxy resin mold layer is coated on one surface of the insulating substrate. 4'is a flux layer which surrounds the low melting point metal body. When the electrical equipment to be protected rises in temperature due to overcurrent and the low melting point metal of the temperature fuse is melted, the insulating substrate 1'is poorly wettable by this molten metal, and the layered electrode 2'with respect to the molten metal. Since the wettability is good, this molten metal is repelled by the insulating substrate 1'and aggregates on the electrode 2 ', and is quickly divided to interrupt the electric power supply to the electric equipment, thereby preventing abnormal heat generation of the electric equipment. .

<Problems to be Solved by the Invention> However, according to the experimental results of the present inventors, in this substrate-type thermal fuse, the molten low-melting-point metal body travels through the interface between the electrode and the insulating layer during operation. It easily leaks to the outside along the lead wire. In such a case, the molten metal adheres to the electric device, which may cause damage to the electric device.

An object of the present invention is to provide a substrate type thermal fuse that can well prevent the molten low melting point metal from flowing out.

<Technical Means for Solving Problems> In the substrate type thermal fuse according to the present invention, a pair of layered electrodes are provided on one surface of an insulating substrate and a low melting point metal body is bridged between both electrodes, and each electrode is provided with Are connected to lead conductors respectively, and in a thermal fuse in which an insulating coating layer is provided on one surface of the substrate,
The layered electrode portion facing each end of the low melting point alloy body is cut out in a window shape to expose the surface of the insulating substrate to the layered electrode.

<Embodiment> Hereinafter, the present invention will be described with reference to the drawings.

In FIG. 1, 1 is an insulating substrate having excellent heat resistance,
For example, a ceramic plate can be used. Reference numerals 2 and 2 denote a pair of layered electrodes provided on one surface of the insulating substrate, which can be formed by printing or baking a conductive paste (copper-based paste, silver-based paste). 3 is a low melting point metal body such as Sn-
Pb-based alloy wire, bridged between electrodes, metal body end
31,31 are welded to the electrodes. The layered electrode portions 21, 21 immediately after each end of the metal body are cut out in a window shape to expose the surface of the insulating substrate to the layered electrode 2. 4 is a flux layer which surrounds the low melting point metal body. Reference numeral 5 is an insulating layer coated on one surface of the insulating substrate, for example, an epoxy resin mold layer. 6,
6 is a lead conductor.

In the above, a resistor, for example, a film resistor may be provided on the insulating substrate. When the resistor is provided on the other surface of the insulating substrate, the other surface may be covered with the insulating layer.

The board type thermal fuse is used by being attached to an electric device to be protected. In this case, in the electric device, the current is turned on and off according to the load, and thus the heat cycle is performed within a temperature range where the temperature fuse does not operate, and the flux 4 of the temperature fuse is repeatedly melted and solidified. However, the molten flux exhibits high wettability with respect to the electrode 2 and permeates into the interface between the electrode 2 and the insulating layer 5, and the interface is easily peeled off due to repeated melting of the flux. On the other hand, the window-shaped cutout portion 21 of the electrode 2 is the insulating substrate surface (ceramic surface), the wettability of the molten flux to the ceramic surface is poor, and the window-shaped cutout portion of the electrode 2 is formed.
The interface between 21 and the insulating layer 5 is not easily peeled off. Therefore, when the electric device generates heat due to an overcurrent and the low melting point metal body of the substrate type thermal fuse is melted, the molten metal is avoided at the window-shaped cutout portion 21 of the electrode in which the interface is fixed, and in FIG. Flowed in the direction of the arrow. Thus, this flow direction is a detour rather than the straight line in the conventional example, the resistance to this flow is large, and the molten metal is less likely to flow out.

Actually, in FIG. 1, the insulating substrate 1 has a vertical length of 10 mm and a horizontal width.
Using a ceramic plate with a thickness of 6 mm and a thickness of 1 mm, the electrode 2 is formed by coating and baking a silver-based paste to a size of 4 mm in height and 3 mm in width, and the window-like cutout portion 21 of each electrode 2 is 1 mm in width and 2 mm in width.
The distance between the front end of the electrode and the front end of the inner portion of the cutout portion 21 is 1 mm, and the melting point of the low melting point metal body 3 is 100 mm.
At 0 ° C, a round wire with a length of 3 mm and a diameter of 0.5 mmφ, a flux 4 containing a composition of rosin as a main component and a melting point of 60 ° C, a lead conductor 6 with a copper wire having a diameter of 0.6 mmφ, and an insulating layer 5 Is an example product using a drop coating layer of epoxy resin, and a comparative example product which is the same as the example product except that the window-like cutout portion is not provided for this example product. The number of each is 50). The above heat cycle was simulated by repeatedly immersing and pulling up 50 times in an oil bath at 80 ° C under voltage of 250 V and current of 2 amps, and then,
When the operation was simulated by immersing in a 120 ° C oil bath and melting the low melting point metal body, the outflow of molten metal was observed in 10 out of 50 of the comparative example products. No molten metal flowed out.

<Effects of the Invention> As described above, in the substrate type thermal fuse according to the present invention, the resistance to the melting outflow of the low melting point metal body can be increased, so that the outflow can be satisfactorily prevented and the damage to the electric equipment can be reliably avoided. it can.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a substrate type thermal fuse according to the present invention, and FIG. 2 is an explanatory view showing a conventional substrate type thermal fuse. In the figure, 1 is an insulating substrate, 2 and 2 are layered electrodes, 21 and 21 are electrode missing portions, 3 is a low melting point metal body, and 5 is an insulating coating layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Open 62-47170 (JP, U) Open 60-124069 (JP, U) Open 61-82339 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. A pair of layered electrodes is provided on one surface of an insulating substrate, a low melting point alloy body is bridged between both electrodes, and a lead conductor is connected to each electrode, and one surface of the substrate is insulated. A substrate-type thermal fuse, characterized in that, in the thermal fuse provided with a coating layer, the layered electrode portions facing each end of the low melting point alloy body are cut out in a window shape to expose the insulating substrate surface to the layered electrode.