JPH11126556A - Chip type fuse and manufacture of fuse thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the fusion precision as much as possible in a chip type fuse comprising a fusible body made of a metal thin film. SOLUTION: In a chip type fuse 1 comprising an insulating base 2 having electrodes in both ends, a protective layer 4 forming a space shut out of the outside in combination with the insulating base 2, and a fusible body 3 made of a metal thin film and fixed between the insulating base 2 and the protective layer 4 while the intermediate part being lifted in the space, the face on the electrode 6 side of the insulating base 2 is flat and the fusible body 3 is curved in the direction of parting from the flat face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chip type fuse and a method for manufacturing the same.

[0002]

2. Description of the Related Art An electronic device has a built-in fuse for protecting a circuit element such as an expensive IC mounted on a printed circuit board from an abnormal current and preventing ignition of the printed circuit board. For the purpose, a fuse is required to have excellent quick disconnection and reliable shutoff characteristics. On the other hand, with the demand for miniaturization of electronic devices, small fuses such as chip type fuses are generally used in the electronic devices. The smaller the fuse, the smaller the heat capacity of the fusible body, so it is difficult to maintain a constant balance between the amount of heat generation and the amount of heat radiation, and characteristics tend to vary.

In order to keep the fusing characteristics constant while minimizing the size of the fuse, the main body is composed of a laminated substrate made of a heat-resistant insulating material and having a space, and a fusible body composed of a metal thin film is interposed between the substrates. A chip-type fuse has been proposed in which a fusible body is stretched in a space inside a main body by sandwiching the fuse (JP-A-7-105824). This seems to apply the basic concept of a conventional fuse such as a glass tube type fuse to a chip type fuse.

[0004]

However, in the case of the chip type fuse described in the '824 publication, since the fusible body is a thin metal film, the heat capacity is small, and the characteristics are still likely to vary. Therefore, an object of the present invention is to improve the fusing accuracy of a chip type fuse having a fusible body made of a metal thin film as much as possible.

[0005]

In order to achieve the object, a chip-type fuse according to the present invention forms an insulating substrate provided with electrodes at both ends and a space cut off from the outside in combination with the insulating substrate. In a chip-type fuse including a protective layer and a fusible body made of a metal thin film having both ends fixed between an insulating substrate and a protective layer so that an intermediate portion floats in the space, an electrode surface of the insulating substrate is provided. Is flat, and the fusible body is curved in a direction away from the flat surface.

[0006] The fusible body floating in the air once thermally expands and curves before being blown by an abnormal current. In the case of the fuse described in the '824 publication, since the fusible body is stretched linearly in the space, the bending direction at the time of abnormality is indefinite.
Therefore, it is considered that the heat release rate differs depending on whether the substrate is bent in the vertical direction or in the surface direction, which is considered to be a cause of variation. On the other hand, in the case of the fuse of the present invention, since the fusible body is always curved in a certain direction, it also bends in the same direction even when an abnormal current flows. Therefore, the fusing characteristics are kept constant, and the accuracy is improved.

[0007] The fusible body is not limited to a uniform single component. The fusible body is composed of a plurality of layers of a first layer having a large coefficient of thermal expansion and a second layer having a small coefficient of thermal expansion in order to more reliably maintain the bending direction at the time of abnormality, and the first layer is more than the second layer. It is preferable that the insulating substrate is provided on the side closer to the flat surface. By doing so, the curved portion always expands in the direction in which the first layer pushes up the second layer at the time of an abnormality. The first layer is mainly composed of copper Cu, and the second layer is nickel N
A combination having i as a main component is exemplified.

[0008] The intermediate portion of the fusible body is not necessarily uniform in width, but may have a wide portion and a narrow portion. By doing so, the wide portion can dissipate the heat generated by the rush current when the power is turned on, and can delay the fusing operation.

[0009] A suitable method of manufacturing the chip type fuse of the present invention is to prepare an insulating substrate having a flat surface provided with electrodes on both ends, forming a base having a predetermined height between the electrodes, After forming a fusible body composed of a metal thin film connecting the two electrodes across the base, the base is removed. Here, the foundation is a photoresist,
Any material, such as a tape, may be used as long as it maintains a predetermined height during the formation of the fusible body and can be removed after the formation of the fusible body. According to the method of the present invention, it is not necessary to process the insulating substrate, and the intermediate portion of the fusible body can be easily floated in the air.

[0010]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a cross-sectional view illustrating a chip-type fuse of the embodiment, and FIGS. 2 to 11 are plan views illustrating a method of manufacturing the chip-type fuse of the embodiment in the order of steps.

The chip type fuse 1 includes an insulating substrate 2 having a flat main surface, a fusible body 3 formed on the main surface of the insulating substrate 2, and a portion of the insulating substrate 2 except for both ends of the fusible body 3. The protective layer 4 includes a covering protective layer 4 and terminals 5 connected to the exposed both ends of the fusible member 3 and extending to the rear surface via the side surface of the insulating substrate 2.

The insulating substrate 2 contains alumina as a main component, and the flatness of the main surface is determined by the content of alumina. For example, when the alumina content is 96% by weight, the surface roughness is 10 to 10.
It is 5 μm, and when it is 99.5% by weight, it is 1-2 μm. Copper Cu electrodes 6 are provided at both ends of the insulating substrate 2. The insulating substrate 2 has a thickness of 0.38 mm and an area of 1.25 mm × 2 mm.

As shown in FIG. 1B, the fusible body 3 includes a first layer 31 made of copper Cu and nickel phosphorus NiP.
The both ends are respectively connected to the electrodes 6, and the intermediate portion is curved in a direction away from the main surface of the insulating substrate 2. The height of this middle part is 15
２０20 μm. In order to secure a distance between the intermediate portion and the main surface of the insulating substrate 2, the surface roughness of the insulating substrate 2 is
It must be sufficiently smaller than the height of this middle part.

The protective layer 4 has a first inner layer 41 made of a photoresist and an outer second layer 42 made of a heat-resistant insulating organic material such as an epoxy resin. The first layer 41 secures a space where the fusible body 3 exists in combination with the insulating substrate 2. The second layer 42 prevents the non-heat-resistant first layer 41 from being deformed at a high temperature such as when the fuse 1 is soldered to a printed circuit board or the like.

In the fuse 1 having the above-described configuration, the heat generated from the fusible body 3 does not escape to the insulating substrate 2 because the intermediate portion of the fusible body 3 is floating in a space isolated from the surrounding environment. In addition, since the fusible body 3 has a larger thermal expansion coefficient in the inner first layer 31 than in the outer second layer 32, the first layer 31 expands up to just before fusing when the heat is generated, and the first layer 31 pushes up the second layer 32. Therefore, the fusible member 3 is always deformed in a direction away from the insulating substrate 2, the fusing characteristics are kept constant, and the fusing is performed with excellent accuracy. The chip type fuse 1 is manufactured by the following procedure.

[Formation of Base] It is assumed that a large number of chip-type fuses are simultaneously obtained from one large-sized substrate made of alumina. First, a NiCr alloy, a CuNi alloy, and Cu are sequentially sputtered on the main surface of the substrate (FIG. 2). FIG. 2 shows only a planar shape for one fuse. 3 to 8
The same applies to. A photoresist is applied so that the electrode pattern is exposed, and Cu is plated on the exposed portion (FIG. 3). The sputtering thin film other than the electrode portion is removed by etching. Then, the base 7 of the fusible body 3 is formed of a liquid photoresist (FIG. 4). A film resist may be stuck instead of the liquid photoresist, or another peelable resin may be screen-printed.

[Formation of Soluble Body] A Cu thin film serving as a base of the first layer of the fusible body 3 is sputtered on the entire surface to form a fusible body pattern by a photolithographic technique (FIG. 5). First layer 3 on top
Cu as 1 is plated. The pattern width, length, and plating thickness at this time are determined so as to obtain a desired fuse rating. Subsequently, NiP as the second layer 32 is plated.

[Removal of Base] Thereafter, the base 7 is melted and peeled off (FIG. 6), and annealing is performed at 280 ° C. for 60 minutes. This annealing removes the distortion of the plating film and the C of the electrode.
This is performed for bonding the u component and the Cu component of the first layer. Due to the peeling of the base 7, the intermediate portion of the fusible body floats from the substrate surface.

[Formation of Protective Layer] Side walls 43 are formed of a photosensitive film resist so as to surround the floating portions of the fusible member 3 (FIG. 7). The height of the side wall 43 is set to be 50 μm or more higher than the height of the fusible member 3. Further, a ceiling is formed above the fusible body with the same film resist, and an intermediate portion of the fusible body is shielded from the outside air. The side wall and the ceiling are combined to form the first layer 41 of the protective layer. Further, the second layer 42 of the protective layer is provided by covering the side wall and the ceiling with a heat-resistant resin such as an epoxy resin. The rated current value of the fuse (2 amps in this example) is displayed (FIG. 8).

[Division into Individual Chips] Grooves are formed with a laser so that individual chips can be divided (broken lines in FIG. 9), and a predetermined number of chips are divided into rods in a line (FIG. 10 (A) )). NiCr and Cu are sequentially sputtered on the end face to form the base of the terminal (FIG. 10).
(B)). Cut into single chips. C on the base of the terminal
u, Ni, and solder are sequentially plated, and the resistance is inspected to complete a chip-type fuse (FIG. 11).

As is apparent from the above steps, according to the manufacturing method of the present invention, the intermediate portion of the fusible body can be floated in the air only by the thin film technique without machining the insulating substrate. Therefore, the manufacturing cost is low.

[0022]

The chip type fuse of the present invention has excellent fusing accuracy and is therefore useful for protecting circuit elements of small electronic equipment.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a chip type fuse according to an embodiment, where (A) is an entire view and (B) is an enlarged view of a B portion of (A).

FIG. 2 is a plan view showing an initial stage of a base forming step in the method of manufacturing the chip fuse of the embodiment.

FIG. 3 is a plan view showing a middle stage of a base forming step in the method of manufacturing the chip fuse of the embodiment.

FIG. 4 is a plan view showing a later stage of a base forming step in the method of manufacturing the chip fuse of the embodiment.

FIG. 5 is a plan view showing a fusible member forming step in the method for manufacturing the chip fuse of the embodiment.

FIG. 6 is a plan view showing a base removing step in the method of manufacturing the chip fuse of the embodiment.

FIG. 7 is a plan view showing an initial stage of a protective layer forming step in the method of manufacturing the chip fuse of the embodiment.

FIG. 8 is a plan view showing a later stage of a protective layer forming step in the method of manufacturing the chip fuse of the embodiment.

FIG. 9 is a plan view showing an initial stage of a dividing step into individual chips in the method of manufacturing the chip fuse of the embodiment.

FIG. 10 shows a later stage of the step of dividing into individual chips in the method of manufacturing the chip fuse of the embodiment;
(A) is a plan view, and (B) is a right side view.

FIG. 11 is a plan view showing a completed state in the method for manufacturing the chip fuse of the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 chip type fuse 2 insulating substrate 3 fusible material 31 first layer 32 second layer 4 protective layer 5 terminal 6 electrode 7 base

Claims (5)

[Claims] 1. An insulating substrate having electrodes provided at both ends, a protective layer forming a space which is shielded from the outside together with the insulating substrate, and an insulating substrate and a protective layer having both ends such that an intermediate portion floats in the space. And a fusible body made of a metal thin film fixed between the fusible body and the insulating substrate, wherein the surface of the insulating substrate on the electrode side is flat, and the fusible body curves in a direction away from the flat surface. Fuse. 2. The method according to claim 1, wherein the fusible body includes a plurality of layers including a first layer having a large thermal expansion coefficient and a second layer having a small thermal expansion coefficient, wherein the first layer is closer to the flat surface of the insulating substrate than the second layer. 2. The fuse according to claim 1, wherein the fuse is provided. 3. The fuse according to claim 2, wherein said first layer has copper Cu as a main component, and said second layer has nickel Ni as a main component. 4. The fuse according to claim 1, wherein the intermediate portion of the fusible has a wide portion and a narrow portion. 5. A metal thin film for preparing an insulating substrate having flat surfaces on both ends of which electrodes are provided, forming a base having a predetermined height between the electrodes, and connecting the two electrodes across the base. A method for manufacturing a chip-type fuse, comprising: forming a fusible body comprising: