JP2003151425A - Chip type current fuse and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chip type current fuse which has satisfactory prearcing time-current characteristics and can be readily manufactured. SOLUTION: This chip type current fuse 10 includes a fuse element 14 formed on the surface of a rectangular insulative substrate 11 and covered with a protective film 15, and an electrode 12 disposed on both ends of the substrate 11 wherein the glass-ceramic substrate is used for the insulative substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip-type current fuse, and more particularly to a chip-type current fuse element in which a fuse element is arranged on the surface of a rectangular plate-shaped insulating substrate having an outer dimension of about 1 to 2 mm.

[0002]

2. Description of the Related Art As a chip type current fuse, for example, one having a structure shown in FIG. In this structure, electrode portions 22 are provided on both sides of a ceramic substrate 21 made of alumina or the like, a heat insulating layer 23 serving as a heat storage layer is provided between both electrodes, and a metal coating serving as a fuse element is disposed on the insulating layer. . The metal film 24 is covered with a protective film 25, and the planar shape thereof has a narrow width portion at its substantially central portion, as shown in FIG. 3B.

In such a fuse element, when an overcurrent flows, the current is concentrated in the narrow portion of the fuse element 24 and heat is generated, whereby the fuse element is melted and various electronic elements connected to the chip type current fuse are fused. It is designed to protect equipment. However, the ceramic substrate 21 generally has high thermal conductivity and has a property that heat easily escapes. Therefore, the heat insulating material 23 made of glass or glass epoxy resin is used for the fuse element 2
4 and the ceramic substrate 21 to insert a heat storage section,
This prevents heat generated in the fusing portion of the fuse element from escaping and cooling.

[0004]

However, the formation of the heat storage layer complicates the process and is not preferable. Further, when a glass layer or the like to be a heat storage layer is formed on an alumina substrate, the metal material to be deposited flows, causing a wavy phenomenon to appear in the fuse element pattern, resulting in a variation in fusing characteristics.

[0005]

In the chip-type current fuse of the present invention, a fuse element is formed on the surface of a rectangular plate-like insulating substrate, the fuse element is covered with a protective film, and both ends of the substrate are covered. In a chip type current fuse having electrodes, a glass ceramic substrate is used as the insulating substrate.

According to the present invention described above, since the glass ceramic substrate is used as the square plate-shaped insulating substrate, the thermal conductivity is reduced by about one digit as compared with the conventional ceramic substrate such as alumina. As a result, good fusing characteristics of the fuse element can be obtained without the need to insert a glass layer or the like, which is a conventional heat storage layer. Therefore, since the heat storage layer is not required to be inserted, the structure can be further simplified, the manufacturing process can be shortened, and the manufacturing cost can be reduced. Further, since the glass ceramic substrate has a good bending strength characteristic, a good bending strength resistance after being mounted on the circuit board can be obtained.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 (a) and 1 (b).
The chip-type current fuse 10 employs a glass ceramic substrate 11 as a rectangular plate-shaped insulating substrate, and a fuse element 14 is directly arranged on the glass ceramic substrate 11. The size of the substrate 11 is, for example, 2 mm × 1.25 mm, 1.6 m
An ordinary standard chip part size of about m × 0.8 mm or 1.0 mm × 0.5 mm is adopted. The fuse element 14 is made of a thick film conductor paste (for example, Cu,
(Ag, Au, Al, etc.) or a thick film resistance paste screen-printed and fired. However, as the fuse element, for example, a metal thin film may be formed by sputtering or vapor deposition, and a pattern may be formed by photolithography, or may be formed by plating.

The fuse element 14 is covered with a protective film 15 such as glass and / or an epoxy resin (for example, a first underlying layer is glass and a second layer thereover is a protective film 15 such as epoxy resin). Protected. The electrode 12 is formed by performing Ni plating and solder plating on a base metal provided on the end surface and the back surface side of the substrate 11.

Further, the chip-type current fuse is subjected to a bending test after being mounted on a test board, but the load that the chip receives from the test board is considerably large, and the bending strength of the element body is required. The bending strength of the element body has a correlation with the bending strength of the substrate forming the fuse element. As shown in Table 1, the bending strength of the mica-based ceramic substrate and the quartz glass substrate is weak, and the bending amount of the bending test is less than 2 mm. The element body will crack. In the glass ceramic substrate, the bending strength of the substrate is also high, and the strength in the bending test of the element body is satisfied.

[Table 1]

In the chip type current fuse, a large number of sheet-shaped substrates are used in the manufacturing stage, and a large number of patterns are collectively formed and then separated into individual chips. A cutting process such as a dicing process is required for the mica-based ceramic substrate and the quartz glass substrate when separating the sheet-shaped substrate into individual chips. A glass-ceramic substrate (for example, LTCC or HTCC) can have a die slit in the substrate similarly to the alumina substrate, and can be cut in the vertical and horizontal directions at the corresponding positions on the front and back sides, or on the front or back main plane. Grooves can be provided and cracked to separate individual chips. Therefore, the chip-type current fuse can be manufactured easily and inexpensively.

In order to obtain stable fusing characteristics with the fuse function, it is necessary to process the fuse element pattern with high precision. Therefore, it is necessary to reduce the surface roughness of the base substrate. As shown in Table 1, the glass-ceramic substrate (for example, LTCC or HTCC) has high smoothness (surface roughness Ra <0.3 μm), and the formation of the fuse element pattern is stable and accurate with the thick film conductor paste. I can do it well. On the other hand, the mica-based ceramic substrate (machinable ceramics) requires treatments such as lapping, polishing and grinding in order to reduce the surface roughness.

As mentioned above, there is a glass-ceramic substrate called LTCC or HTCC. LTC
C (Low Temperature Co-fire)
dCeramic: low temperature co-fired ceramic) is a substrate formed by firing an alumina component and a glass component at a rate of about 50% each at 800 ° C to 1000 ° C. HTCC (High Tempera)
"Ture Co-fired Ceramic: high temperature co-fired ceramics" is a substrate formed by firing an alumina component and a glass component at a rate of about 50% each at 1000 ° C or higher. With these glass ceramic substrates, low thermal conductivity, high bending strength, and good surface roughness required for fuse characteristics can be obtained. The ratio of the alumina component to the glass component is not limited to the above ratio, and if the glass component is increased, the lower thermal conductivity can be achieved and the fuse characteristic can be improved.

Since these substrates are fired at 800 ° C. to 1000 ° C., a thick film conductor paste can be used as a fuse element. After forming a pattern on a ceramic green sheet, the heating element of the fuse is formed into an inner layer by simultaneous firing. It is also possible to do so.

On the other hand, the use of other insulating substrates has the following disadvantages. First, in the case of an alumina substrate (Al ₂ O ₃ 90% to 96%), the thermal conductivity is high as shown in Table 1. Therefore, an inorganic material (for example, glass, JCR) or an organic material (for example, polyimide, epoxy resin) is provided directly under the fuse blowout portion on the substrate.
As described above, the heat storage layer created in 1 is required. When such a heat storage layer is not provided, there is a problem that a stable fuse element cannot be produced and the fuse characteristic becomes unstable because the surface has no smoothness.

In the case of a mica-based ceramic substrate, since the bending strength is relatively low, the strength of the element body in the chip state is weak, and when the mounted circuit board is divided after mounting, a strong load is applied to the mounted circuit board. There is a risk of cracking the tip.
There is also a problem in that the chip may be damaged if the chip is overloaded by the mounter when the chip is mounted on the mounting circuit board. There is also a problem that the surface roughness is relatively large, the surface smoothness is poor, and it is difficult to form a stable fuse element.

Further, in the case of a quartz glass substrate, since the bending strength is similarly low, the element strength in the chip state is weak,
When the mounted circuit board is divided after mounting, the chip may be cracked if a strong load is applied to the mounted circuit board. Further, when the chip is overloaded by the mounter when mounted on the mounting circuit board, there is a risk of damaging the chip.

As shown in Table 1, each of the glass epoxy type and polyimide type substrates has a considerably low thermal conductivity and is a good substrate for directly forming a fuse element as a chip type current fuse. On the other hand, in order to obtain a stable fusing characteristic of the fuse, the material of the fuse element and the accuracy of the pattern are required, and the surface roughness of the substrate in the above table is a factor that impairs the dimensional accuracy of the fuse element pattern. There is. The surface roughness of the substrate is improved by lapping, polishing, grinding, etc., but it is expensive. In constructing the current fuse, the heat treatment temperature in the step of forming the fuse element pattern and the temperature in the subsequent heat step are important. Since the heat treatment method has a structure that can satisfy the fuse function on the substrate and the substrate, it is often restricted by the heat resistant temperature of the substance.Therefore, the process and method are often limited, and it is necessary to suppress it to less than half of the heat resistant temperature. is there. From this point of view, glass epoxy type,
The heat resistance temperature of the polyimide-based substrate is considerably low, and the method of forming the fuse element is limited.

Next, a method of manufacturing this chip type current fuse will be described with reference to FIGS. 2 (a) to 2 (d).
The left side of each drawing is a plan view, and the right side is a vertical sectional view. First, as shown in FIG. 2A, a glass ceramic substrate 11 is prepared. Each of the drawings shown in FIG. 2 is a part of a sheet-like (multi-cavity) substrate that becomes one chip-type current fuse after the substrate is divided along the dividing grooves of the substrate in the vertical and horizontal directions (not shown). Shows only. Next, FIG.
As shown in (b), a thick film conductor paste or a thick film resistor paste is applied by screen printing. And 6
Baking is performed at 00 to 900 ° C. to form a metal glaze type fuse element pattern 14. When the glass ceramic substrate is used as the base, the thermal contraction of the thick film paste is slight, so that the pattern is not deformed by heating and a stable fuse element pattern can be formed.

Further, a green sheet (green substrate) of a glass ceramic substrate is prepared, a thick film conductor paste is printed,
Both can be fired at the same time. Thereby, the firing of the glass ceramic substrate and the firing of the thick film conductor paste can be performed at the same time, so that the manufacturing cost can be reduced. Further, by sandwiching the fuse element in a glass ceramic substrate in a sandwich shape and incorporating it inside, it is possible to further reduce the manufacturing cost. L
Since TCC shrinks at a low temperature when it is fired at a low temperature, a green substrate (green sheet) and a conductor can be fired at the same time, and an internally laminated body can be collectively formed.

By using the thick film process in this way,
It is possible to easily and inexpensively manufacture the fuse element on the glass ceramic substrate.

Next, as shown in FIG. 2C, a glass coat layer and / or a resin coat layer are formed so as to cover a part of the fuse element portion and the electrode 12 (which also serves as the front electrode). Is provided. This glass coat / resin coat layer is formed by forming a glass paste / resin paste on a predetermined portion by screen printing or the like, and then heating and firing and / or curing with heating.

Next, as shown in FIG. 2D, the electrodes 12 on the back and end faces are formed. This electrode may be formed, for example, by screen printing using Ag paste and then heating and baking, or by depositing a metal on the entire surface by sputtering and removing unnecessary portions by photolithography. You may form. Further, the electrodes may be formed by sputtering with a partially deposited film using a metal mask or the like.

Further, the electrode portion is plated with Ni / solder. In this case, for example, Ni plating is first performed by electrolytic barrel plating, and then solder plating is performed to form the electrode 12 subjected to the above-described electrode plating. As a result, a chip type current fuse suitable for surface mounting is completed.

As described above, the glass ceramic substrate is
It is possible to provide break slits on the front surface of the substrate and the back surface corresponding thereto. Therefore, when the individual chips are separated from the multi-piece substrate, it is possible to separate the chips by break (cracking) like the alumina ceramic substrate. That is, it is not necessary to cut the chip into individual chips by using a dicing saw, which allows the chip-type current fuse to be manufactured at low cost.

In the above-described embodiment, the example of forming the fuse element by the thick film technique using the thick film conductor paste has been described, but other methods of forming the fuse element can also be adopted. For example, a metal thin film may be deposited on the substrate by sputtering or vapor deposition, and the fuse element pattern may be formed by using photolithography. Further, after forming the fuse element pattern of the metal thin film, the fuse element pattern of the thick metal film may be formed by electrolytic or electroless plating.

Although the above embodiment has been described with respect to the chip type current fuse, it is needless to say that the present invention can be applied to various current fuses in which fuse elements are arranged on a rectangular plate-shaped insulating substrate, other than the chip type. Is. in this way,
Various modifications can be made without departing from the spirit of the present invention.

[0027]

As described above, according to the present invention, there is provided a chip type current fuse having a simple structure and improved fusing characteristics.

[Brief description of drawings]

FIG. 1A is a vertical sectional view and FIG. 1B is a plan view of a chip-type current fuse according to an embodiment of the present invention.

FIG. 2 is a plan view on the left side showing the first half of the manufacturing process of the chip-type current fuse according to the embodiment of the present invention, and a vertical sectional view on the right side.

FIG. 3A is a vertical sectional view and FIG. 3B is a plan view of a conventional chip-type current fuse.

[Explanation of symbols] 10 Chip type current fuse 11 Glass-ceramic substrate 12 electrodes 14 Fuse element 15 Protective film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kanamaru Exhibition             14016 Nakaminowa, Minowa-cho, Kamiina-gun, Nagano Prefecture             Inside Coer Co., Ltd. F-term (reference) 5G502 AA01 BA08 BD02

Claims (4)

[Claims] 1. A chip-type current fuse in which a fuse element is formed on the surface of a rectangular plate-shaped insulating substrate, the fuse element is covered with a protective film, and electrodes are provided at both ends of the substrate. A chip-type current fuse characterized in that a glass ceramic substrate is used as the flexible substrate. 2. The chip-type current fuse according to claim 1, wherein the fuse element is formed by printing thick film conductor paste and firing it. 3. A method for manufacturing a chip-type current fuse in which a fuse element is formed on a surface of a rectangular plate-shaped insulating substrate, the fuse element is covered with a protective film, and electrodes are arranged at both ends of the substrate. A method for manufacturing a chip-type current fuse, characterized in that a thick film conductor paste is printed on a glass ceramic substrate and fired to form a fuse element. 4. The method for manufacturing a chip-type current fuse according to claim 3, wherein the thick-film conductor paste is printed on the green sheet of glass ceramic and is simultaneously fired.