JP2000149760A - Overcurrent breaking method and current fuse element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize miniaturization, by installing a metal film having a locally narrowed part on an easily splitting board, and by making centralized heat generation occur on the locally narrowed part of the metal film by overcurrent carrying, and by braking the easily splitting board by thermal stress generated by the centralized heat generation. SOLUTION: A metal film 1 having a locally narrowed part 11 of this current fuse element is installed on an easily splitting board 2. A breaking mechanism of an overcurrent by using the current fuse element is composed of such serial steps that, first of all, Joule heat is generated on the locally narrowed part 11 of the metal film 1 by an overcurrent, and then the locally narrowed part 11 of the metal film 1 and a nearby easily splitting board part 20 are heated by the Joule heat, and furthermore the easily splitting board 2 is broken by thermal stress by the heating. In this case, by the centralized heating of the locally narrowed part 11 of the metal film 1, the locally narrowed part 11 itself is changed into an insulator by oxidation, and the overcurrent breaking is preferably executed both by breaking by the thermal stress of the locally narrowed part 11 of the metal film 1 and by the change thereof into the insulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for interrupting an overcurrent and a current fuse element used in the method.

[0002]

2. Description of the Related Art In recent years, in order to reduce the size of electronic equipment using semiconductor devices, resistors and capacitors have also been made to have a chip size, and a chip size has also been demanded for current consumption. Conventionally, heat is deposited on an insulating substrate by evaporation or the like.
A thin film type current fuse provided with a noise element belongs to a known art. For example, in a fuse resistor, that is, a resistor that functions as a general circuit resistor during normal operation of a device and disconnects a circuit due to disconnection of an abnormal overcurrent, a resistor film is provided on an insulating substrate. Are known.

[0003]

However, in the conventional thin film current fuse, a residue is left on the insulating substrate after the interruption, and the insulation after the interruption is reduced accordingly. The distance between the electrodes must be set,
It is disadvantageous for miniaturization.

An object of the present invention is to reduce the size of a current fuse element by modifying the breaking mechanism of the current fuse element.

[0005]

An overcurrent interrupting method according to the present invention uses a current fuse element in which a metal film having a locally narrow portion is provided on an easily breakable substrate, and the overcurrent is applied to the metal film. The configuration is characterized in that concentrated heat is generated in a locally narrow portion, and the easily breakable substrate is broken by thermal stress generated by the concentrated heat.

[0006] The current fuse element according to the present invention comprises:
A configuration in which a metal film having a locally narrow portion is provided on a glass substrate, and a breaking groove can be provided in the glass substrate in the vicinity of the locally narrow portion of the metal film,
As the metal film, a magnesium or magnesium alloy film can be used.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 (a) and 1 (b) [a cross-sectional view taken along the roll of FIG. 1 (a)] show an example of a current fuse element used in the present invention. A metal film 1 having an easily splittable substrate 2
It is provided above.

The overcurrent blocking mechanism using the current fuse element has the following features: (1) Joule heat is generated in the local narrow portion 11 of the metal film 1 due to the overcurrent, and (2) the joule heat is generated. Heat causes the local narrow portion 11 of the metal film and the easily breakable substrate portion 20 in the vicinity thereof to be heated, and (3) the heating causes the breakable substrate to break due to thermal stress. Become.

In this case, due to the concentrated heating of the local narrow portion of the metal film in the above (2), the local narrow portion itself is made into an insulator by oxidation, so that the above-mentioned overcurrent interruption is performed. It is preferable to perform both of the breaking due to the thermal stress in the narrow portion and the formation of the insulating material. Such a metal film may be a magnesium or magnesium alloy film. In magnesium or magnesium alloy,
At room temperature to about 300 ° C, no significant activity is exhibited.
If the temperature exceeds 00 ° C., it is activated and violently oxidized, and is vaporized by the heat of the reaction to instantaneously become magnesium oxide, and this magnesium oxide exhibits high insulating properties.

The thickness of the magnesium or magnesium alloy film is several hundreds to several thousand degrees, preferably about 0.1 μm. The magnesium alloy includes, for example, a type 1 magnesium alloy plate (Al:
2.5 to 3.5% by weight, Zn: 0.5 to 1.5% by weight, M
n: 0.15% by weight or more, Fe: 0.01% by weight or less,
Cu: 0.10% by weight or less, Ni: 0.005% by weight or less, Ca: 0.04% by weight or less, balance Mg) can be used. The magnesium or magnesium alloy film can be formed by a vacuum deposition method, an ion plating method in which a vaporized metal is ionized in a discharge atmosphere and is vapor-deposited on a substrate surface by an applied voltage, sputtering, or the like.

In order to locally heat the easily breakable substrate in the above (2), the easily breakable substrate is heated at a low temperature so that the Joule heat of the locally narrow portion of the metal film can be well transmitted to the substrate side. It is necessary to have a resistance, and in order to break the easily breakable substrate by thermal stress due to local heating, it is required that the easily expandable substrate has a large thermal expansion coefficient and a large Young's modulus and low mechanical strength. .

When the metal film is a magnesium or magnesium alloy film having a thickness of about 0.1 μm, it is preferable to use a glass plate having a thickness of about 0.2 to 0.8 mm for the easily breakable substrate. Selecting this glass plate has the advantage that the glass plate is manufactured by cast molding, the surface is smooth, and the above-mentioned magnesium or magnesium alloy film of about 0.1 μm is easily formed (ceramic substrate). In this case, the surface is rough because of the firing method, and it is difficult to form an ultrathin metal film having a thickness of about 0.1 μm).

The breakage of the breakable substrate due to the thermal stress is caused by the fact that the breakable substrate is partially heated and the breakable substrate is broken by the thermal stress caused by the partial heating. The simplification will be described as follows. That is, in FIG. 1, the portion of width a is locally heated and its temperature rise is ΔT, the Young's modulus of the substrate is E, the coefficient of thermal expansion of the substrate is α, and the thickness of the metal film is remarkably compared to the thickness of the substrate. Assuming that the mechanical effects (thermal expansion and thermal stress) of the metal film can be neglected because of the thinness, the thermal stress δ acting on each portion of the width b / 2 is

Δ = aEαΔT / (a + b)

When the thermal stress δ exceeds the tensile rupture stress of the glass plate, the glass substrate is broken and the current is cut off.

In the above description, the local narrow portion of the metal film is provided by trimming from both sides of the width, but may be provided on the other side by trimming from one side of the width.
As shown in FIG. 2A, a groove 21 can be formed in each portion of the width b / 2 to make the substrate 2 easily cracked. In this case, a magnesium or magnesium alloy film is coated on the surface of the glass plate. It is possible to use a processing method of forming the metal film of each part of the width b / 2 with a laser by forming by vapor deposition or the like. After the glass part is melt-cut and the glass is exposed, the laser is transmitted and no more glass is cut). In addition, as shown in FIG.
The groove 22 for breaking can also be machined by diamond cutting on the back surface of. Further, a bending stress is left on the easily breakable substrate in advance, and a thermal stress generated by Joule heat generated in a locally narrow portion of the metal film is superimposed on the residual stress to break the easily breakable substrate. It is also possible.

FIG. 3 shows an example of a current fuse using the fuse element according to the present invention. In FIG. 3, reference numeral 3 denotes an insulating substrate such as a ceramic insulating substrate, an epoxy resin impregnated glass substrate, or the like.
31 are formed. A is a current fuse element according to the present invention, which is disposed on the insulating substrate 3 with the metal film 1 side down, and a solder bump or a conductive material is provided between each end of the metal film 1 and each electrode 31. They are joined by an adhesive 4 or the like. The dimension of the current fuse (dimension of the insulating substrate) is, for example, length (2.0 to 1.5) mm × width (2.0 to 1.0) mm, and the dimension of the current fuse element is For example, length (1.0 to 0.5) mm × width (0.5 to 0.3) mm.

[0018]

Example 1 One side of a glass plate having a thickness of 0.5 mm was coated with a metal magnesium film having a thickness of 0.1 μm by vacuum deposition, and the metal magnesium film was locally narrowed with a laser trimmer. Was processed to form a current fuse element. When a current cutoff test was performed on this current fuse element, a break occurred in the glass plate and the current was cut off. DC 80
When a withstand voltage test of 0 V was performed, the leakage current was less than 1 mA, and no insulation failure was observed.

[Embodiment 2] An alumina smooth substrate for a thin film is used in place of the glass plate in the embodiment 1, and when forming a locally narrow portion with a laser trimmer on the metal magnesium film, the substrate is not deeply formed. A groove of about 0.2 mm was cut. As in the case of Example 1, the current fuse element was also subjected to a current cutoff test. As a result, the glass plate was cracked and the current was cut off, and the withstand voltage of 800 V DC was measured for the sample subjected to the current cutoff test. As a result of the test, the leakage current was less than 1 mA, and no insulation failure was observed.

[Embodiment 3] JI was used as a deposition source for vacuum deposition.
One side of a glass plate having a thickness of 0.5 mm was coated with a magnesium alloy film having a thickness of 0.1 μm by vacuum deposition using a SH 4201 type 1 magnesium alloy plate, and the magnesium alloy film was locally formed with a laser trimmer. A current fuse element was prepared by processing the narrow portion. As in Example 1,
The current fuse element was also subjected to a current interruption test. As a result, the glass plate was cracked and the current was interrupted.
When a withstand voltage test of 0 V was performed, the leakage current was less than 1 mA, and no insulation failure was observed.

[Comparative Example] With respect to Example 1, when a copper film was used in place of the metal magnesium film, and the sample subjected to the power cutoff test was subjected to a withstand voltage test of 800 V DC, the withstand voltage test was rejected. Poor insulation was observed.

[0022]

According to the present invention, the easily breakable substrate integrated with the metal film having a locally narrow portion is subjected to thermal stress destruction when an overcurrent is applied, and the current is cut off. Even if the size is high and the size is small, a sufficiently high insulating property can be guaranteed after the current is cut off, and it is extremely useful for the chip size of the current fuse element.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a current fuse element according to the present invention.

FIG. 2 is a view showing a main part of another different example of the current fuse element according to the present invention.

FIG. 3 is a drawing showing a current fuse using a current fuse element according to the present invention.

[Explanation of Signs] 1 Metal film 11 Local narrow portion 2 Easily splittable substrate

Claims (4)

[Claims] A current fuse element comprising a metal film having a locally narrow portion provided on an easily breakable substrate, and causing a local narrow portion of the metal film to generate heat by applying an overcurrent; An overcurrent interruption method, wherein the easily breakable substrate is broken by thermal stress generated by the concentrated heat generation. 2. A current fuse element wherein a metal film having a locally narrow portion is provided on a glass substrate. 3. The current fuse element according to claim 2, wherein a breaking groove is provided in the glass substrate in the vicinity of a locally narrow portion of the metal film. 4. The current fuse element according to claim 2, wherein the metal film is a magnesium or magnesium alloy film.