JPH06325903A - Film fixed resistor - Google Patents

Abstract

PURPOSE:To lessen the amount of heat conduction to a mounting substrate by a method wherein conductive caps, which are respectively mounted on both end parts of a resistive element, are made of stainless steel. CONSTITUTION:Conductive caps 2 are respectively mounted on both end parts of a resistive element 1 formed by providing a resistance film on the surface of a porcelain base body. The caps 2 are made of stainless steel and after a trimming is performed on the caps 2, the caps 2 on both end parts of the element 1 are respectively provided with a lead wire 3 consisting of copper, iron, stainless steel or the like. Moreover, an insulative film 4 consisting of a silicon oxide, a resin or the like is provided in such a way as to cover the exposed part of the element 1. Thereby, the amount of heat, which is transmitted to a mounting substrate, can be decreased to be 30% or thereabouts less than one in the case where conventional conductive caps made of iron are used. Moreover, as there is no need to provided a plated layer on the conductive caps, a plating process can be omitted and the problem of a change in a resistance value due to a plating scum can be dissolved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film fixed resistor (hereinafter simply referred to as "resistor").

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a resistor is a resistance element 1 having a resistance film such as metal oxide or carbon provided on the surface of a ceramic base such as ceramic.
The conductive caps 12 made of iron are attached to both ends of the, and the lead wires 3 made of copper are provided on each of the conductive caps 12. An insulating coating film 4 made of silicon oxide (SiO ₂ ) or the like is provided on the surface of the resistance element 1.

After the conductive caps 12 are attached to both ends of the resistance element 1, the resistance of the resistor is adjusted (hereinafter referred to as "trimming") by cutting the resistance film with a laser, a disk cutter or the like. A lead wire is welded to each of the conductive caps 12, and subsequently, an insulating coating film 4 is provided so as to cover the exposed portion of the resistance element 1 for manufacturing.

Since the conductive cap 12 is made of iron, it is inferior in moisture resistance, rust resistance and the like as it is, and the welding strength when the lead wire is welded becomes insufficient. Therefore, the plating layer 5 of copper, tin, solder or the like has to be previously provided on the surface of the conventional conductive cap before being mounted on both ends of the resistance element 1.

[0005]

Since the conventional resistor uses the conductive cap having the plated layer as described above, the manufacturing process, that is, the process of mounting the conductive cap on the resistance element is omitted. The following problems occur during the process of providing the insulating coating film.

Since the surface of the conductive cap is plated, foreign matter such as plating residue will inevitably adhere to the surface of the conductive cap during the plating process. In particular, if there is a burr on the edge of the conductive cap, the plating layer easily grows from the burr in the plating process, resulting in a plating residue. In addition, a large number of plated conductive caps are accommodated in the same container and transferred to the step of mounting the conductive caps, so that the conductive caps rub against each other to cause plating residue.

As described above, when the conductive cap is attached to the resistance element with the plating residue attached, the trimming groove 6 formed by trimming as shown in FIG. 3 in the steps up to the step of forming the insulating coating film. On the other hand, the plating residue 7 is often adhered to the surface, which may change the adjusted resistance value.

Although the plating layer is used to prevent oxidation of the conductive cap, it is still easily oxidized when moisture, heat, etc. are applied in the manufacturing process, and the lead wire is welded to the conductive cap. In the process, if the plating layer is oxidized, the conductivity is deteriorated, and there is a high risk of defective welding, resistance change, and the like.

On the other hand, since the conventional conductive cap is made of iron, its thermal conductivity is much higher than that of an insulating coating film made of silicon oxide, resin, etc., and when heat is generated in the resistance element, Much of the heat generated is inevitably transferred to the conductive cap made of iron. Therefore, when the conventional resistor is mounted on the mounting board, heat is transferred from the conductive cap to the mounting board through the lead wire made of copper having a higher thermal conductivity.

Since the above-mentioned resistor is usually mounted on a mounting board together with a plurality of various electronic components, when the conventional resistor is mounted on the mounting board, most of the heat generated by the resistive element is generated. It is transmitted to the mounting board, and other electronic parts on the board, especially the electronic parts near the film-fixing resistor are easily affected by heat. For example, the influence of heat is greatly reflected in semiconductor parts such as ICs, in which various characteristics such as the amplification factor greatly change due to heat. Such a problem is prominent in a resistor which uses a metal oxide as a resistance film, which is generally used for high power.

Therefore, when the conventional resistor is mounted on the mounting board, the design of the circuit pattern on the mounting board is restricted because it is necessary to consider the influence of the heat.

According to the present invention, it is not necessary to provide a plating layer on the conductive cap, and moreover, the heat at the time of heat generation is dispersed and radiated into the air to reduce the amount of heat conduction to the mounting board.
It is an object of the present invention to provide a film fixed resistor that eliminates thermal influence on other electronic components on the same substrate.

[0013]

The present inventor has conducted intensive studies as a result of paying attention to the problem of plating residue in the process of manufacturing a resistor and the heat dissipation property of the heat generated by the resistor into the air. When making the sex cap made of stainless steel,
It has been found that there is no need for plating and that heat generated during heat generation can be suppressed from being transferred to the conductive cap, and as a result, the amount of heat conduction to the mounting board can be made relatively small.

That is, according to the present invention, in a film fixed resistor in which conductive caps are attached to both ends of a resistance element having a resistive film on the surface of a porcelain substrate, the conductive cap is made of stainless steel. The present invention relates to a film fixed resistor.

[0015]

In the present invention, the conductive cap of the resistor is made of stainless steel, which is extremely excellent in moisture resistance and rust resistance, so that it can be manufactured without providing a plating layer.

The thermal conductivity of stainless steel (0.0
Since 4) is as low as about 1/4 or less of the thermal conductivity of iron (0.17) that has been conventionally used, when the resistance element generates heat, the heat is efficiently transferred to the insulating coating film and the conductive cap. It is possible to increase the amount of heat that is dissipated and transmitted and is released from the insulating coating film into the air.

When the present invention is applied to a resistor in which a metal oxide is used as a resistance film, as described above, stainless steel is excellent in moisture resistance, rust prevention and the like. Since the problem of rust on the conductive cap due to moisture intrusion is reduced, the particle size of silicon oxide or the like forming the insulating coating film can be made larger than before. Therefore, the amount of heat radiated from the insulating coating film into the air can be further increased.

[0018]

Embodiments of the present invention will now be described with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 is a sectional view of the resistor of the present invention.
In FIG. 1, reference numeral 1 represents a resistance element, reference numeral 2 represents a conductive cap, reference numeral 3 represents a lead wire, and reference numeral 4 represents an insulating coating film.

The resistance element 1 in the present invention is not particularly different from that used in the conventional resistor, and for example, a ceramic porcelain substrate having a resistance film such as metal oxide or carbon formed on the surface thereof is used. It

The conductive cap 2 in the present invention is made of stainless steel.

Stainless steel is excellent in moisture resistance and rust resistance and has a heat conductivity much lower than that of iron or the like.

The conductive caps 2 are provided on both ends of the resistance element 1 without providing a plating layer. After that, trimming is performed, and lead wires 3 made of, for example, copper, iron, stainless steel, or the like are provided on the conductive caps 2 at both ends of the resistance element 1, for example, silicon oxide,
The insulating coating film 4 made of resin or the like is provided so as to cover the exposed portion of the resistance element 1 to obtain the resistor of the present invention.

The lead wire 3 can be welded in the conventional manner, and if necessary, a plating layer of copper, tin, solder or the like may be provided on the surface of the lead wire 3. In particular, when stainless steel is applied to the lead wire 3, the thermal conductivity of stainless steel is much lower than that of copper, iron, etc., so that the heat insulating effect is high, which is preferable.

In the thus obtained resistor of the present invention, the amount of heat transferred to the mounting board can be reduced by about 30% as compared with that using the conventional iron conductive cap.

Although the resistor having the lead wire has been described above, the present invention can be applied to leadless, that is, surface mounting. In the case of surface mounting, the conductive caps 2 are attached to both ends of the resistance element 1, trimmed, and the insulating coating film 4 is provided, and then the solderability is improved on the exposed portion of the conductive cap 2. Therefore, plating of copper, tin, solder or the like may be applied if necessary. When performing the above plating,
Since it is performed after the insulating coating film 4 is provided, there is no problem of resistance value change due to the plating residue.

[0027]

According to the resistor of the present invention, particularly the resistor having a lead wire, it is not necessary to provide a plating layer on the conductive cap. Therefore, the problems of the omission of the plating step and the change of the resistance value due to the plating residue in the manufacturing process can be solved.

According to the resistor of the present invention, the amount of heat radiated into the air when the resistive element generates heat can be made extremely large as compared with the conventional resistor, so that the amount of heat transferred to the mounting substrate can be extremely suppressed, Almost no adverse thermal effect on other electronic components on the mounting board.

Since the resistor of the present invention has a small amount of heat transferred to the mounting board even if it generates heat, when the mounting board is mounted together with a plurality of various electronic components, the influence of the heat on the electronic components in the vicinity of the resistor is not affected. The size is small, and the range of choice when designing a circuit pattern on a mounting board is widened.

Further, since the resistor of the present invention uses stainless steel for the conductive cap, it is extremely excellent in moisture resistance and rust resistance and is practically usable regardless of the operating environment.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a resistor of the present invention.

FIG. 2 is a cross-sectional view showing a conventional resistor.

FIG. 3 is a side view showing a state in which plating residue is attached to a trimming groove in a conventional resistor.

[Explanation of symbols]

 1 Resistive element 2, 12 Conductive cap 3 Lead wire 4 Insulating coating film 5 Plating layer 6 Trimming groove 7 Plating residue

Claims (1)

[Claims] 1. A film fixed resistor in which conductive caps are attached to both ends of a resistance element having a resistance film formed on the surface of a porcelain substrate, wherein the conductive cap is made of stainless steel. Film fixed resistor.