JPH0831286A - Substrate type resistor and thermal fuse operation method - Google Patents

Abstract

PURPOSE:To surely conduct current-carrying breaking by fusing a low melting point metal piece by Joule's heat caused by excess current. CONSTITUTION:A film conductor 2 and a low melting point metal piece 3 are arranged on one surface of an insulating substrate 1 such as a ceramic board, and they are connected with film conductors 4 in series, the low melting point metal piece is coated with flux 30, lead wires 5 are connected to each lead wire connecting land of the film conductors 4 respectively, and an insulating covering layer 6 is formed on one surface of the insulating substrate. When excess current is supplied, the low melting point metal piece 3 is fused by Joule' s heat of the low melting point metal piece 3 caused by excess current to break current flow. Generation of cracks of the film resistor 2 caused by Joule's heat by excess current can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a substrate type resistance / temperature fuse used for maintenance of electronic or electric equipment.

[0002]

2. Description of the Related Art A substrate type resistance / temperature fuse is one in which a film conductor having a predetermined pattern is formed on an insulating substrate such as a ceramics substrate, and a film resistor and a low melting point metal piece are connected in series in the middle of the film conductor. Insert and connect to, apply flux to the low melting point metal piece,
This is a configuration in which an insulating coating layer of epoxy resin or the like is provided on the insulating substrate.

This substrate type resistance / temperature fuse is used by inserting it into a circuit of an electronic or electric device to be protected, and normally, the heat generated by the film resistor is transferred to the low melting point metal piece to reduce the heat. The melting point metal piece is melted, coexisting with a molten flux, spheroidized by surface tension, the molten metal is divided by the progress of spheroidization, and at the initial stage of division, an arc occurs due to a short division interval, The spheroidization progresses to increase the division distance, and when the arc extinction distance is reached, the arc disappears and the current flow is cut off. Thus, since a sufficient disconnection distance is guaranteed, energization can be surely cut off and re-conduction can be eliminated.

[0004]

However, in the case of a large power overcurrent, in the conventional substrate type resistance / temperature fuse, the film resistor is affected by thermal strain due to a rapid temperature rise due to its jule heat. The current is cut off by cracking, and the melting of the low melting point metal piece by receiving the Jule heat of the film resistor does not occur.

FIG. 3 shows the current interruption characteristics of the conventional substrate type resistance / temperature fuse. In the current range of I ₀ or less, the low melting point metal piece is melted and cut by the heat of the film resistor. The current is cut off (curve a), but under a large electric power exceeding I ₀ , the low melting point metal piece is melted by the heat of the Jules heat of the film resistor (dotted line a ′ in FIG. 3). Is the cut-off characteristic calculated assuming that the low melting point metal piece was blown by the heat of the film resistor's jule heat, and b is the cut-off characteristic due to the crack of the film resistor due to the jule heat of the film resistor itself. Before), the film resistor has cracked due to thermal strain due to the rapid temperature rise due to its jule heat.

However, the crack due to the thermal strain of the film resistor is a gap having a fine width, has a low withstand voltage, is likely to be re-conducted under the application of voltage, and has an uncertainties of the energization interruption state. Unavoidable.

An object of the present invention is to provide a substrate type resistance / temperature fuse.
Under a large electric power overcurrent that cannot melt the low melting point metal piece due to the transfer of the jule heat of the film resistor, the film resistor itself is energized by cracks due to thermal strain due to the jule heat. It is an object of the present invention to provide a method of operating a substrate type resistance / temperature fuse which can eliminate the indefinite interruption of electric current and guarantee a reliable electric current interruption.

[0008]

A method of operating a substrate type resistance / temperature fuse according to the present invention is a method in which a film resistor and a low melting point metal piece are provided on an insulating substrate and these are connected in series. Is a resistance-temperature fuse that melts the low melting point metal piece by means of the Jule heat of the film resistor to cut off the energization. The low melting point metal piece is melted and cut off by means of the jule heat, and the film resistance is prevented from cracking due to the jule heat due to the overcurrent.

The present invention will be described below with reference to the drawings. 1A and 1B are explanatory views showing different substrate type resistance / temperature fuses used in the present invention, in which a film resistor is provided on one surface of an insulating substrate 1 such as a ceramic plate. 2 and the low melting point metal piece 3 are provided, these are connected in series by the membrane conductor 4, the flux 30 is applied on the low melting point metal piece 3, and the lead wire 5 is the lead wire connection of the membrane conductor. An insulating coating layer 6 is provided on one surface of the insulating substrate, connected to the land for use.

The substrate type resistance / temperature fuse is formed by forming a film conductor on one surface of an insulating substrate, forming a film resistor and adjusting a resistance value, connecting a lead wire, connecting a low melting point metal piece, and a flux. Is applied and the insulating coating layer is formed. The ceramic plate 1 has a thickness of 0.1 mm to 2.0 mm.
Preferably 0.4 mm to 1.2 mm of 96% alumina,
Beryllia, silicon carbide, aluminum nitride, steatite, etc. can be used. The above-mentioned film conductor 4 is preferably formed by a thick film method such as screen printing of a conductor paste or a dispenser, and baking. The conductor paste is made of an Ag-based material, an Ag-Pt-based material, or a Cu-based material. , Pt-based or Au-based paste can be used, and the film thickness is usually 10 to 30 μm.

The film resistor 2 can be formed by printing and baking a resistance paste, and then overcoating glass thereon. The film resistor is formed by printing and baking a resistance paste to form a film resistor, baking the first glass coat on the film resistor, and then adjusting it to a predetermined resistance value by laser trimming. Then, it is preferable to use the method of baking a second glass coat.
RuO ₂ system, Ta-Tan system, Sn
O ₂ -Ta ₂ O ₅ system, LaB ₆ based, SnO ₂ -Ta system, Sr
RuO ₃ series, Ag—Pd series, TaSi ₂ series, MoSi ₂ series paste, etc. can be used, and the thickness of the film resistor is usually 10 to 10.
It is set to 40 μm.

For the low melting point metal piece 3, a round wire or a foil alloy having a melting point according to the operating temperature is used.
A 2- to 4-component eutectic alloy selected from Pb, In, Sb, Cd, etc. is used.

The flux 30 has a softening point sufficiently lower than the melting point of the low melting point metal piece 3 and is usually a natural rosin or a synthetic rosin to which an activator is added. The insulating coating 6 has a flux 3
What can be coated at a temperature sufficiently lower than the softening point of 0 is used, and for example, a drop coating of an epoxy resin at room temperature can be used.

In FIG. 2, B shows the current interruption characteristic of only the low melting point metal piece of the substrate type resistance / temperature fuse used in the present invention, and C shows the electricity interruption characteristic of only the film resistor (substrate). Type resistance / temperature fuse can be obtained by connecting both ends of the film resistor or both ends of the low melting point metal piece to the variable current source for testing), and the energization interruption time only by the low melting point metal piece It is shorter than the power interruption time due to only.

The crack of the film resistor due to the jule heat of the film resistor itself occurs when the film resistor is heated and is distorted by thermal stress, and the strain reaches a breaking strain. Since it is cut off, the time from the start of energization of the overcurrent to the interruption of the energization (breaking time) is greatly related to the heating temperature and the breaking strain or ductility of the film resistor, and lowering the resistance of the film resistor, Alternatively, by using a film resistor having a large breaking strain, the energization interruption time by only the low melting point metal piece can be made shorter than the energization interruption time by only the film resistor.

In FIG. 2, a curve A indicates that the heat generated by the film resistor is transferred to the low-melting metal piece, the low-melting metal piece is melted, and is spheroidized by the surface tension in the coexistence with the molten flux. Shows the current interruption characteristics when the molten metal is divided by the progress of.

The present invention resides in operating the substrate resistance / temperature fuse according to the curve a ₁ -c ₁ -c ₂ . That is, in the range up to the current I _1, Ju of the low-melting metal piece film resistor - is blown by the heat of Le heat to cut off the energization, for a current I ₁ or more large power overcurrent, low The melting point metal piece is melted by the Jules heat of the low melting point metal piece itself to cut off the electric current. In this case, in the film resistor, even if the film resistor is heated by the jule heat of the film resistor, the low-melting metal piece is heated by the jule heat of the low-melting metal piece itself before cracking due to thermal strain. Since it is melted and cut off, the current flow is not interrupted by the crack of the film resistor, and the current flow is always interrupted by the melting of the low melting point metal piece.

In order to impart the above-mentioned current interruption characteristics to the substrate type resistance / temperature fuse, the resistance value of the film resistor is lowered (for example, the resistance value of the low melting metal piece is 1 mΩ to 10 mΩ, whereas the film resistance is 1 mΩ to 10 mΩ). It is effective to use a flexible one as the binder of the resistance particles of the film resistor, for example, to use a heat resistant resin such as polyimide.

[0019]

In order to protect a device according to the present invention, the allowable load time for the overload power of the device is determined, and the energization / interruption characteristics (however, the relationship of allowable load time> interruption time) that substantially matches the overload curve are satisfied Insert the board type resistance / temperature fuse of the one) into the circuit of the device.

The cut-off characteristic of the substrate type resistance / temperature fuse is as shown by the curve a ₁ -c ₁ -c ₂ in FIG. 2, and the low melting point metal piece is the film resistance up to the overcurrent I ₁ of the overload power. Body ju
When it melts by receiving the heat of heat, it is spheroidized by the surface tension in the coexistence with the molten flux, the molten metal is divided by the progress of spheroidization, and when the division distance reaches the arc extinction distance, the current is surely supplied. It is cut off. When the overcurrent I ₁ or more,
The juule heat of the low melting point metal piece itself becomes large,
The low melting point metal piece is melted by the heat of heat. The film resistor is also heated by its own heat, but the resistance of the film resistor should be lowered to suppress the heat of the film resistor, or cracks due to thermal strain should not occur. Since the film resistor is provided with ductility, it is possible to eliminate the occurrence of cracks in the film resistor.

Thus, the jute of the low melting point metal piece itself.
In the fusing by heat, the spheroidization is accompanied by the surface tension in the coexistence with the molten flux.Therefore, the gap interval of the division can be sufficiently widened and the resistance between the divisions can be increased as compared with the crack due to the thermal strain of the film resistor. The voltage property can be sufficiently ensured, and re-conduction can be effectively prevented. This can be confirmed also from the results of interruption tests of the following Examples and Comparative Examples.

[0022]

【Example】

[Embodiment] The substrate type resistance / temperature fuse having the structure shown in FIG. A 96% alumina ceramic plate having a length of 10 mm, a width of 6 mm and a thickness of 0.5 mm is used as an insulating substrate, a film conductor is formed by printing and baking an Ag-based paste, and a film resistor is made of RuO ₂ system. Formed by printing and baking a resistance paste, baking a first glass coat on it, adjusting the resistance to 1Ω by laser trimming, and then baking a second glass coat. did. The low melting point metal piece has a diameter of 0.
A low melting point fusible alloy wire having a diameter of 4 mm, a melting point of 95 ° C. and a resistance value of 10 mΩ was used, and a flux containing natural rosin as a main component was used. The insulating coating was applied by dropping coating of an epoxy resin liquid at room temperature. [Comparative Example] The same as Example except that the resistance value was adjusted to 10Ω. The rated power of the substrate type resistance / temperature fuse of this example and the comparative example is 0.25w.

A current-carrying interruption test was carried out on the substrate type resistance / temperature fuses of these examples and comparative examples.
In the comparative example, energization was interrupted by cracks in the film resistor at a power of approximately 100 times or more the rated power. On the other hand, in the substrate-type resistance / temperature fuse of the example, cracking of the film resistor did not occur even under high power, and the low-melting metal piece was melted by its own heat. Power was cut off.
When the insulation resistance was measured after turning off the current, it was 5 in the comparative example.
In the example, it reached 1 × 10 ¹² Ω at 500 volt, whereas it was only 0 Ω at 00 volt.

[0024]

According to the present invention, when the electric equipment is maintained by the substrate type resistance / temperature fuse, even if an overcurrent of a large electric power is supplied, the energization is interrupted by the melting of the low melting point metal piece due to the jule heat. Since it is possible to eliminate the interruption of the current flow due to cracking of the membrane resistor due to its Jur heat, it is possible to increase the breaking distance of the breaking point at the breaking of the current flow and withstand voltage strength of the breaking point. Can be made sufficiently high, and reliable energization interruption without re-conduction can be guaranteed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing different examples of substrate type resistance / temperature fuses used in the present invention.

FIG. 2 is an explanatory diagram showing a cutoff characteristic of a substrate type resistance / temperature fuse used in the present invention.

FIG. 3 is an explanatory view showing a breaking characteristic of a conventional substrate type resistance / temperature fuse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Membrane resistor 3 Low melting point metal piece 4 Membrane conductor 5 Insulation coating lead wire 6 Insulation coating

Claims (1)

[Claims] 1. A film resistor and a low melting point metal piece are provided on an insulating substrate, and these are connected in series.
In resistance and temperature fuses that melt the low melting point metal piece by heat of the low melting point to cut off the energization, when the overcurrent of high power is generated, the low temperature is caused by the jule heat of the low melting point metal piece due to the overcurrent. A method for operating a substrate-type resistance / temperature fuse, characterized in that the melting point metal piece is melted to cut off energization to prevent cracking of the film resistor due to jule heat at the overcurrent.