JPH1050191A - Manufacture of chip fuse element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chip fuse element which can be electrically connected excellently and operates stably by producing terminal electrodes by successively forming a fuse conductor thin film and a glass film on a substrate, forming plating layers on exposed terminal parts, and then applying a conductive resin to the parts and curing the resin. SOLUTION: A glaze glass layer 11 is formed on the surface of a rectangular insulator substrate 1 made of, for example, an alumina ceramic. A fuse conductor thin film 3 of a metal thin film of such as Al is formed on the layer 11 into a prescribed pattern by photolithographic technique. After both ends of the film 3 are exposed, a low melting point glass film 5 is formed and further an overcoat resin coating 6 of epoxy type resin is formed on the film 5. The exposed both end parts 3a, 3b are treated with nitric acid, etc., and then plated with zinc by displacement plating. After that, overlaying terminal electrodes 2a, 2b and end face electrodes 4a, 4b are formed by applying a conductive resin produced by mixing Ag powder with an epoxy resin, curing the resin, and if necessary, plated with tin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a chip fuse element for protecting a circuit against abnormal current of a predetermined circuit.

[0002]

2. Description of the Related Art A chip fuse element has a glaze layer formed on a main surface of an insulating substrate 1 as shown in a sectional view of FIG.
Further, a fuse conductor thin film 3 was formed. The insulating substrate 1 is connected to the end of the fuse conductor thin film 3.
The terminal electrodes 2a and 2b are formed on both ends facing each other, a glass film 5 is further formed, and the overcoat resin 6 is covered.

In such a chip fuse element, a blown portion of the fuse conductor thin film 3 generates heat due to an abnormal current applied between the terminal electrodes 2a and 2b. At this time, the thermal conductivity of the glaze layer is appropriately set so that the generated heat does not excessively escape to the insulating substrate side. Then, due to this heat generation, the fuse conductor thin film 3 is melted and acts as a fuse. Furthermore, the softened glass film 5 was filled in the blown portion, and high insulation after the blow was maintained.

[0004] Such fusing characteristics vary greatly depending on the melting point, conductivity, shape, and the like of the metal forming the fuse conductor thin film 3.

In consideration of the above, the fuse conductor thin film 3 is generally formed of an Al thin film and formed into a predetermined pattern according to characteristics by using a photolithography technique.

[0006]

However, when an Al thin film is used as the fuse conductor thin film 3 of the chip fuse element,
There is a problem that the Al surface is easily oxidized. Moreover, when the glass film 5 is formed on the fuse conductor thin film 3, the glass film 5 is printed with a low-melting glass paste,
Due to the firing (500 ° C. or higher), an oxide film is formed on the exposed portion surface of the fuse conductor thin film 3. The thickness of this oxide film is about several tens to 100 degrees.

When the terminal electrodes 2a and 2b are formed in a state where an oxide film is formed on the exposed end of the fuse conductor thin film 3 to which the terminal electrodes 2a and 2b are connected, the terminal electrodes 2a and 2b and the fuse conductor thin film 3 The electrical continuity between them becomes defective.

For example, if the terminal electrode 2a is formed directly on the exposed end of the fuse conductor thin film 3, a resistance of about 50 KΩ will be present. In this case, the terminal electrode 2
The fusing characteristics of the fuse conductor thin film 3 with respect to the abnormal currents applied to a and 2b greatly change.

After forming the terminal electrodes 2a and 2b,
The surface of the terminal electrodes 2a, 2b is pressed by a sharp pressing member, for example, a needle or the like, so that the fuse conductor thin film 3 and the terminal electrodes 2
Although it is possible to improve the resistance to about 250 mΩ by mechanically destroying the oxide film between a and 2b and to establish conduction with each other, the variation is about 180 to 315 mΩ.
The characteristics vary among the elements.

The present invention has been devised in order to solve the above-mentioned problem, and an object of the present invention is to form a fuse conductor thin film, form a glass film, and then form a terminal electrode. An object of the present invention is to provide a method of manufacturing a stable chip fuse element which has good electrical connection between a terminal electrode and a fuse conductor thin film.

[0011]

According to the present invention, a step of forming a fuse conductor thin film made of aluminum on a rectangular insulating substrate, and exposing both ends of the fuse conductor thin film to the glass paste Forming a glass film by baking, and performing a surface etching treatment on the exposed both ends of the fuse conductor thin film with an acid, and applying a plating layer with a metal having a smaller metal ionization tendency than the fuse conductor thin film. And a step of forming a terminal electrode by applying and curing a conductive resin paste on the surface of the plating layer and both ends of the insulating substrate.

The plating layer is formed by "substitution plating" in which the metal of the base material (aluminum of the fuse conductor thin film) and the metal in the plating solution are substituted and deposited, depending on the magnitude of the ionization tendency of the metal. For example, zinc or Ni plating.

[0013]

In the chip fuse element of the present invention, the glass film is baked so as to expose both ends to the fuse conductor thin film, and the exposed portion is subjected to a surface etching treatment with an acid. As a result, the oxide film on the exposed end of the fuse conductor thin film is removed.

Then, a metal plating layer is formed. Since a high temperature is not applied in forming the metal plating layer, the formation of the oxide film again on the exposed portion of the fuse conductor thin film from which the oxide film has been removed can be suppressed, and the metal plating layer can be stably covered. Can be formed.

Thereafter, a terminal electrode is formed on the metal plating layer. Since the terminal electrode is formed by using a conductive resin and thermosetting at a relatively low temperature (about 200 ° C.), the metal plating layer and the fuse are formed. The fuse conductor thin film is stably connected to the conductor thin film, and at the same time, the number of times that the heat history is given to the fuse conductor thin film is minimized, so that the fuse conductor thin film can be prevented from peeling off due to the heat history and the characteristics are stabilized.

Accordingly, the connection state between the terminal electrode and the fuse conductor thin film is very stable, the resistance value between them can be reduced, and the resistance variation can be suppressed.
Variations in characteristics between elements can be made very small.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a chip fuse element according to the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a chip fuse element according to the present invention, FIG. 2 is a cross-sectional structural view in a longitudinal direction,
FIG. 3 is a schematic view of a connection portion between the fuse conductor thin film and the terminal electrode.

In the figure, 1 is an insulating substrate, 2a and 2b are terminal electrodes, 3 is a fuse conductor thin film, 4a and 4b are end electrodes, 5 is a low melting point glass film, and 6 is an overcoat resin.

The insulating substrate 1 is made of, for example, alumina ceramic and has a shape of, for example, 1.6 mm × 3.2 m.
m. A glaze glass layer 11 is formed on the surface of the insulating substrate 1. The glaze glass layer 11 usually has a thickness of 10 to 20 μm.
It may be a thickness such as μm.

The fuse conductor thin film 3 is made of a metal thin film of Al or the like, extends in the longitudinal direction of the insulating substrate 1, and has an extremely fine fusing portion at the center. Terminal electrodes 2a and 2b are connected to both ends of the fuse conductor thin film 3 via metal plating layers (hereinafter, referred to as zinc plating layers) 3a and 3b, respectively. The terminal electrodes 2a and 2b are made of a conductive resin containing an Ag-based powder or the like, and a part of the surface thereof is plated with Ni, solder, or tin as needed.

A low melting point glass film 5 is formed on the blown portion of the fuse conductor thin film 3, and an overcoat resin 6 is coated on the fuse conductor thin film 3 including the low melting point glass film 5. .

The low-melting glass film 5 is made of lead borosilicate glass and is softened and filled in a fusing groove formed by fusing the fuse conductor thin film 3, thereby providing a high insulation after fusing. To maintain their sexuality.

The overcoat resin 6 is made of, for example, an epoxy resin, and is formed mainly for improving the moisture resistance reliability.

If necessary, the fuse conductor thin film 3 is ruptured between the low melting point glass film 5 and the overcoat resin 6 due to excessive abnormal current, and the low melting point glass film 5
An elastic layer 7 having elasticity, such as silicon, is disposed to prevent the air from being blown off.

Further, end face electrodes 4a, 4b connected to the terminal electrodes 2a, 2b are formed on a pair of opposing end faces in the longitudinal direction of the insulating substrate 1. This end face electrode 4a,
4b is formed by curing a conductive resin containing a conductive metal powder such as Ag, for example. Then, the end face electrode 4a,
A Ni plating layer, tin or solder plating layer is formed on the surface of 4b as needed.

Next, a method of manufacturing the above-described chip fuse element will be described with reference to the process chart of FIG.

First, a large-sized substrate having a divided groove for dividing a region to be a plurality of chip fuse elements is prepared.
In addition, in order to improve the dividing property, on both main surfaces of the large substrate,
It is desirable to form a first dividing groove and a second dividing groove. A region formed by the two first division grooves and the two second division grooves is called an element region.

Next, a glass glaze layer 11 is formed on the surface of each element region of the large substrate. Specifically, it is formed by printing and firing a lead borosilicate glass paste.

Next, on the surface of each element region of the large substrate, A
1 is formed. Specifically, Al
Thin film deposition, photoresist film application, selective exposure,
The photoresist film is formed into a predetermined pattern by a selective development of the photoresist film, a selective etching of the Al thin film, and a photolithography technique by peeling the photoresist film.

Next, a low-melting glass film 5 is formed so as to cover the blown portion of the fuse conductor thin film 3 in each element region of the large substrate. Specifically, so as to cover the fuse conductor thin film 3,
It is formed by printing and firing a low melting glass paste.
The material is a lead borosilicate glass component, and its film thickness is 10 to 20 μm.

By this step, the fuse conductor thin film 3 is fired in an air atmosphere with both end portions, that is, portions where the terminal electrodes 2a and 2b are overlapped and connected exposed.
An oxide film will be formed.

Next, an overcoat resin 6 is formed while leaving both ends of the fuse conductor thin film 3 in each element region of the large substrate. Examples of the overcoat resin 6 include a thermosetting resin such as an epoxy resin and an ultraviolet curable resin.
For example, it is formed by heat treatment or ultraviolet irradiation.
This thickness is, for example, 20 to 50 μm.

When the elastic layer 7 is disposed between the overcoat resin layer 6 and the fuse conductor thin film 3 or the glass film 5, the formation is performed before the overcoat resin 6 is formed. The elastic layer 7 is formed by applying, for example, a silicon paste of # 8130 manufactured by Shin-Etsu Co., Ltd., and curing by heat treatment at 120 ° C. for 1 hour.

Next, zinc plating layers 3a and 3b are formed on both ends of the fuse conductor thin film 3 in each element region of the large substrate in order to form terminal electrodes 2a and 2b.

As a pretreatment before forming the zinc plating layers 3a and 3b, the oxide films on both ends of the fuse conductor thin film 3 are removed to clean the surface to be plated.

Specifically, the substrate is immersed in an acidic liquid of nitric acid having a concentration of 50% for one minute. Thus, the oxide film of aluminum oxide on the exposed portion of the fuse conductor thin film 3 is removed. Note that, in addition to nitric acid, phosphoric acid can also be used.

Subsequently, a zinc plating process is performed. Specifically, displacement plating is performed by immersion in a zinc plating solution for about 10 minutes. This displacement plating treatment is performed according to the magnitude of the ionization tendency of the metal.
l) and the metal in the liquid are replaced and precipitated. In the embodiment, zinc is plated. However, in order to perform substitution precipitation according to the difference in the magnitude of ionization of the metal, a metal having a small ionization tendency can be used even if aluminum of the fuse conductor thin film 3 which is a base metal is used. Other metals may be used instead of zinc. For example, Ni is mentioned.

Since the zinc plating layers 3a and 3b are formed by displacement plating, the reaction stops when the zinc plating layers 3a and 3b are applied to the exposed surfaces of the ends of the fuse conductor thin film 3. Therefore, the exposed surface can be completely plated, the Al of the fuse conductor thin film 3 is not significantly damaged, and the plating process can be managed relatively easily.

Between the removal of the oxide film, which is the pretreatment, and the deposition of the zinc plating layers 3a and 3b, the fuse conductor thin film 3
Is slightly exposed to the atmosphere, and no heat is applied. Therefore, after the oxide film is removed, the oxide film is hardly formed again.

Next, terminal electrodes 2a and 2b are formed so as to overlap the zinc plating layers 3a and 3b at both ends of the fuse conductor thin film 3 in each element region of the large substrate. More specifically, the fuse conductor thin film 3 overlaps the zinc plating layers 3a and 3b at the ends thereof,
In addition, the shape reaches the first division groove. The terminal electrodes 2a and 2b are coated with a conductive resin such as an epoxy resin mixed with a metal powder such as Ag, and thermally cured at 200.degree.

Incidentally, a conductor film may be similarly formed on both ends in the longitudinal direction on the back surface side of each element region.

Next, a primary division process is performed along a first division groove for dividing each element region of the large substrate. As a result, the large substrate becomes a strip-shaped substrate, and the end surface electrodes 4a, 4
The plane forming b will appear due to the division.

Next, end surface electrodes 4a and 4b are formed on the divided surfaces of the respective element regions of the strip-shaped substrate. Thereby, the terminal electrode 2a, the end face electrode 4a, and the terminal electrode 2b in each element region are formed.
And the end face electrode 4b are connected to each other. This end face electrode 4
a and 4b are made of an epoxy resin conductive resin mixed with a metal powder such as Ag, like the terminal electrodes 2a and 2b.
This conductive resin is applied by dipping or printing, and
Thermoset at 0 ° C.

Next, a secondary division process is performed along a second division groove extending in the other direction that divides each element region of the strip-shaped substrate. As a result, each element region is completely divided individually.

Finally, if necessary, the terminal electrodes 2a, 2a
b and the surfaces of the end face electrodes 4a and 4b
Apply plating, tin or solder plating.

According to the above-described manufacturing method, after forming the fuse conductor thin film 3 by the thin film technique, only a relatively high baking process (about 500 ° C.) is performed in the step of forming the glass film 5. Moreover, the oxide film formed on the exposed surface of the fuse conductor thin film 3 by this baking treatment is removed by the surface etching by the acid performed before the galvanized layers 3a, 3b are applied. 3 and the galvanized layers 3a, 3b have very good electrical continuity. The terminal electrodes 2a, 2b are further formed on the zinc plating layers 3a, 3b so as to overlap with each other. As a result, the electrical connection between the terminal electrodes 2a, 2b and the fuse conductor thin film 3 is performed stably and reliably. be able to.

The terminal electrodes 2a and 2b, the end face electrodes 4
a and 4b indicate the application of a conductive resin and its heat curing (about 20
0 ° C.), the formation of the oxide film of the fuse conductor thin film 3 and the formation of a new oxide film do not occur at all.
a, 2b can be reliably connected electrically.

Further, since the glass film 5 is the only film fired at a relatively high temperature after the formation of the fuse conductor thin film 3, the number of heat histories given to the fuse conductor thin film 3 is very small. There is no peeling of the thin film 3 at all, so that stable characteristics can be derived.

[0050]

EXPERIMENTAL EXAMPLE In order to clarify the operation and effect of the product of the present invention, the present inventor made the product of the present invention and the conventional manufacturing process, that is, the acidic portion between the connection portion between the fuse conductor thin film 3 and the terminal electrodes 2a and 2b. Twenty chip fuse elements (conventional products) each having no oxide film removed by a liquid and no galvanized layer adhered were prepared. In each element, the fuse conductor thin film 3
The average resistance value between the terminal electrodes 2a and 2b was measured.

As a result, in the product of the present invention, the average resistance value was 5
The average resistance was 50 kΩ, while the resistance was 0 mΩ.

After the terminal electrodes 2a and 2b are formed on the conventional product, the surfaces of the terminal electrodes 2a and 2b at the portions where the terminal electrodes 2a and 2b overlap with the fuse conductor thin film 3 are pressed by a needle-like sharp pressing member having a sharp tip. , An oxide film between the terminal electrodes 2a, 2b and the fuse conductor thin film 33 is mechanically broken to achieve conduction (comparative product), and the respective fuse conductor thin film 3 and the terminal electrodes 2a, 2b , And the maximum and minimum values of the resistance value, and the degree of variation (3σ) were measured.

As a result, in the product of the present invention, the average resistance value was 5
0 mΩ, the maximum value was 52 mΩ, and the minimum value was 48 mΩ, and the degree of variation was 4. On the other hand, in the comparative product, the average resistance value was 250 mΩ, the maximum value was 318 mΩ, and the minimum value was 180.
mΩ, and the degree of variation was 132.

That is, it has been confirmed that the chip fuse element manufactured by the manufacturing method of the present invention can have a very small resistance value and can be excellent, and can also make the variation between elements extremely small.

In the manufacturing method of the present invention, after the overcoat resin 6 is formed, the immersion treatment with an acidic liquid and the formation of the zinc plating layers 3a and 3b are performed for the plating treatment. As the resin 6, it is necessary to use a resin having excellent plating resistance. For the above-mentioned plating, immersion treatment with an acidic liquid and zinc plating layer 3 are performed.
The formation of a and 3b may be performed immediately after the glass coating layer 5 is formed, and then the overcoat resin 6 may be formed.

After removing the oxide film, forming the galvanized layers 3a and 3b on the exposed surfaces, performing primary division and secondary division to form individual elements, the end of the element is placed in a conductive resin tank. And the terminal electrodes 2a and 2b, the end surface electrodes 4a and 4b, and the conductor on the back surface side of the substrate may be simultaneously formed by thermosetting.

[0057]

As described above, according to the method for manufacturing a chip fuse element of the present invention, a plating layer is formed on the interface between the fuse conductor thin film and the terminal electrode, and the fuse conductor thin film is formed before the plating layer is formed. Since the exposed surface is subjected to a surface treatment using an acid, the oxide film is removed from the exposed surface of the fuse conductor thin film, and as a result, the connection state between the fuse conductor thin film and the terminal electrode becomes extremely good. Also, since the firing process after forming the fuse conductor thin film is extremely small, the characteristics are also stabilized by this, and the characteristics of the fuse conductor thin film having a predetermined pattern can be faithfully reflected on the characteristics of the chip fuse element, This is a manufacturing method capable of preventing variation in characteristics between elements.

[Brief description of the drawings]

FIG. 1 is a plan view of a chip fuse element according to the present invention.

FIG. 2 is a sectional view of a chip fuse element according to the present invention.

FIG. 3 is an enlarged sectional view of a connection portion between a fuse conductor thin film and a terminal electrode according to the present invention.

FIG. 4 is a process chart showing the steps of the production method of the present invention.

FIG. 5 is a plan view of a conventional chip fuse element.

[Explanation of symbols]

 1 ... insulating substrate 11 ... glaze layer 2a, 2b ... terminal electrode 3 ... fuse conductor thin film 4a, 4b ... end face electrode 5 ... .... Low melting point glass film 6 ..... Overcoat resin film

Claims (1)

[Claims] A step of forming a fuse conductor thin film made of aluminum on a quadrangular insulating substrate; exposing both ends of the fuse conductor thin film on the fuse conductor thin film;
A step of forming a glass film by baking a glass paste, and performing a surface etching treatment with an acid on the exposed end surfaces of the fuse conductor thin film, and forming a plating layer with a metal having a smaller metal ionization tendency than the fuse conductor thin film. A method for manufacturing a chip fuse element, comprising: a step of applying; and a step of forming a terminal electrode on a plating layer surface and both ends of an insulating substrate by applying and curing a conductive resin paste.