JPH10135009A - Chip type variable resistor - Google Patents

Abstract

(57) [Summary] Even with a terminal electrode made of an Ag-based conductor film, stable connection characteristics are ensured without breaking the connection between the horseshoe-shaped thick film resistor film and the terminal electrode. Provide a chip-shaped variable resistor that can be derived. A horseshoe-shaped thick-film resistor film and a slider that slides on the surface of the thick-film resistor film are arranged on a surface of an insulating substrate, and a surface of an end portion of the substrate is provided. This is a chip-shaped variable resistor made of an Ag-based thick film conductor film on the end face and the back face, and having terminal electrodes 4a and 4b connected to a part of the thick film resistor film 2 or a slider. Insulating films 6 and 6 are formed on the corners C on the surface side of the terminal electrodes 4a and 4b formed at the end of the substrate 1.
Is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip-shaped variable resistor, and more particularly to a chip-shaped resistor excellent in thermal shock resistance.

[0002]

2. Description of the Related Art Generally, a chip-shaped electronic component is a small electronic component that can be surface-mounted on a predetermined wiring pattern of a printed wiring board together with other electronic components by a solder reflow method, a solder flow method, or the like. Capacitors, resistors,
There are coils and the like.

[0003] Further, a chip-shaped resistor component includes a fixed resistor having a structure in which a fixed resistor value such as a chip resistor, a multiple resistor, a resistor network element or the like is derived or a combination thereof is combined with an optional resistor. It can be classified into a variable resistor that can obtain a resistance value.

[0004] In chip-type electronic components, it is necessary not only to have electrical characteristics, but also to perform solder bonding firmly and stably in surface mounting, and for example, solder erosion of Ag metal components constituting terminal electrodes is required. It is very important to prevent soldering and to have good solder paste (excellent solder wettability).

[0005] The above-mentioned solder erosion and solder wettability may be caused by the fact that, for example, in the case of a terminal electrode of a chip capacitor, an Ag-based material The problem has been solved by forming a thick-film conductor electrode and applying Ni plating, Sn plating (solder plating) or the like to the surface thereof.

In the fixed resistor, a terminal electrode formed at an end of the insulating substrate also has a structure in which an Ag-based thick-film conductor electrode is formed, and Ni plating and Sn plating (solder plating) are formed on the surface thereof.
And so on.

That is, prevention of solder erosion of the terminal electrode material,
Regarding the wettability of solder, it has been particularly solved by forming a plating layer on the surface.

This plating layer is formed at the final stage in the manufacturing process. The above-mentioned chip capacitor and fixed resistor are structurally configured such that an element portion for deriving a capacitance component, a resistance component, and the like is formed in an insulating substrate. And the surface is completely covered with the glass protective film, so that the plating process was possible without changing the electrical characteristics.

In the case of a variable resistor, as shown in FIG. 3, a horseshoe-shaped thick-film resistor film 2 is printed and baked on an insulating substrate 1 by printing and baking a thick-film resistor paste mainly containing ruthenium oxide or the like. The slider 3 was disposed on the thick resistor film 2.

Further, the terminal electrodes 4a and 4b are
Was formed by applying and baking an Ag-based (metal component is Ag alone, Ag alloy) conductive paste at the end of the conductive paste. For example, the terminal electrodes 4 a and 4 b are formed on the front surface, the end surface, and the back surface of one end of the pair of ends of the insulating substrate 1, and are electrically connected to the ends of the thick film resistor film 2. In addition, the terminal electrode 4c
Is a terminal electrode connected to the slider 3, and is composed of, for example, a member formed by metal working.

[0011]

The variable resistor has a structure in which the thick-film resistor film 2 and the slider 3 slide on the structure.
A glass coating film cannot be formed on the thick-film resistance film 2 like a fixed resistor, and the thick-film resistor film 2 is exposed to the outside.

As a result, in the chip-shaped variable resistor,
It has been difficult to form a plating layer on the surface of the terminal electrodes 4a and 4b for preventing solder erosion of Ag as a metal material and improving solder wettability. For example, when plating is performed on the terminal electrodes 4a and 4b, a plating layer is also deposited on the thick film resistor film 2 at the same time, and the substantial conductivity of the thick film resistor film 2 becomes extremely low. This is because it does not operate as a resistor.

That is, in the chip-shaped variable resistor, since the slider 3 is in direct contact with the thick-film resistor film 2 exposed to the outside, a terminal like a fixed resistor or a chip capacitor is used. A plated layer could not be formed on the electrode, and solder erosion and solder wettability were inferior to these other chip components.

Further, the terminal electrode 4 having such a restriction
a and 4b are the front surface, the end surface, and the back surface of the insulating substrate 1;
However, when the conductive paste is printed on three surfaces to form the terminal electrodes 4a and 4b, the thickness of the corners between the front surface and the end surface and between the back surface and the end surface becomes extremely thin. In addition, solder erosion is remarkably generated at the corners on the front side and the back side where the film thickness is reduced. In particular, the solder erosion occurs at the corners on the front side of the insulating substrate 1. When cracks occur, a disconnection occurs between the thick resistor film 2 and the terminal electrodes 4a and 4b, and as a result, there is a fatal problem that a predetermined resistance value cannot be obtained.

The present invention has been devised in view of the above-described problems, and has as its object to provide a horseshoe-shaped thick-film resistor film even if it is a terminal electrode formed of an Ag-based conductive film. An object of the present invention is to provide a chip-shaped variable resistor in which connection with a terminal electrode is not broken.

[0016]

SUMMARY OF THE INVENTION The present invention provides a horseshoe-shaped thick-film resistor film on a surface of an insulating substrate, and a slider for sliding on the surface of the thick-film resistor film. Surface,
In a chip-shaped variable resistor formed of an Ag-based thick-film conductor film on an end face and a back face and having a terminal electrode connected to the thick-film resistor film, an insulator is provided at a corner between the surface of the terminal electrode and the end face. A chip-shaped variable resistor having a coating applied thereto.

[0017]

According to the present invention, in the terminal electrode of the chip-shaped variable resistor, the portion where the thickness of the Ag-based thick conductor film becomes the thinnest, that is, the angle between the surface of the end portion of the substrate and the end surface. Since the portion is covered with the insulator film, the solder is not applied to the terminal electrode having a thinner film at the corner portion on the front surface even when reflow soldering or flow soldering is performed. Therefore,
At this corner, since the Ag component of the terminal electrode does not cause solder erosion, there is substantially no electrical disconnection in the terminal electrode.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a chip-shaped variable resistor according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a chip-shaped variable resistor of the present invention, FIG. 2 is a plan view of an insulating substrate used for the chip-shaped variable resistor, and FIG. 3 is an insulating substrate of the chip-shaped variable resistor of the present invention. It is the schematic of one process of the manufacturing process of (1).

In the figure, 1 is an insulating substrate, 2 is a horseshoe-shaped thick-film resistor film, 3 is a slider, 4
Reference numerals a and 4b denote terminal electrodes formed of thick film resistors, 4c denotes a terminal electrode formed by processing a metal piece, and 5 denotes a terminal electrode 4c.
This is a holding member for the slider 3 integrated with the above.

The insulating substrate 1 is made of alumina ceramic or the like, and has a through hole 11 formed in the center thereof.
A recess 12 is formed at one end of the pair of ends of the insulating substrate 1, and as a result, the two protrusions 13 and 14 are formed.
Are formed.

The terminal electrodes 4a, 4b are formed on the protruding portions 13, 14 at one end of the insulating substrate 1.

A horseshoe-shaped thick resistor film 2 is formed around the through hole 11 of the insulating substrate 1.

The terminal electrodes 4a and 4b are
Is formed over three surfaces of the front surface, the end surface, and the back surface. Such terminal electrodes 4a and 4b are formed by printing and baking an Ag-based conductive paste containing Ag (Ag alone or an Ag alloy) as a metal component as a main component. Specifically, 2 of the front and back surfaces of the protrusions 13 and 14
One surface is printed and baked with an Ag-based conductive paste, and then formed on the end surfaces of the projections 13 and 14 so as to be connected to both the above-mentioned thick film conductor film on the front surface and the thick film conductor film on the rear surface. Then, printing and baking of the Ag conductive paste are performed.

The thick resistor film 2 has a horseshoe shape centered on the through hole 11, and both ends thereof extend to the protruding portions 13 and 14.
Connected to terminal electrodes 4a, 4b. Such a thick-film resistor film 2 is formed by printing and baking a resistance paste containing ruthenium oxide as a main component.

A slider 3 is arranged on the surface of the insulating substrate 1. The slider 3 has a dish shape formed by mechanically processing a metal material having elasticity such as phosphor bronze. A driver groove 31 for rotating the slider 3 is formed in the dish-shaped upper flat plate portion 32, and at the same time, extends downward from the outer peripheral portion of the flat plate portion 32, and is formed on the thick film resistor film 2. A sliding contact 33 is formed. Further, a through hole 34 that matches the through hole 11 of the insulating substrate 1 is formed at the center of the slider 3.

Such a slider 3 is disposed on the insulating substrate 1, and the contact member 33 of the slider 3 is slid by the holding member 5 in contact with the thick-film resistor film 2. Become.

The holding member 5 includes a cylindrical caulking pin 51
And a flat terminal portion 52, and the tip of the terminal portion 52 is a terminal electrode 4c. For example, the cylindrical caulking pin portion 51 is inserted into the through hole 11 of the insulating substrate 1 from the back side of the insulating substrate 1, is inserted into the through hole 34 of the slider 3, and is inserted in the slider 3. The tip is crimped. The flat plate portion 52 is arranged along the back surface of the insulating substrate 11 and extends to the other end of the insulating substrate 1. The portion exposed on the other end surface of the insulating substrate 1 is a terminal electrode 4
c.

The slider 3 is held by the holding member 5 on the insulating substrate 1 so that the contact 33 slides on the thick-film resistor film 2. The electrical conduction is made to the electrode 4c.

With the above configuration, when the contact 33 of the slider 3 comes into contact with a predetermined position of the horseshoe-shaped thick film resistor film 2,
A predetermined resistance value can be derived between the terminal electrode 4a (4b) electrically connected to one end of the horseshoe-shaped resistor film 2 and the terminal electrode 4c connected to the contact point 33.

In such a structure, the present invention is characterized in that the insulator films 6, 6 are formed particularly on the corners C formed by the surfaces of the protrusions 13, 14 of the insulating substrate 1 and the end faces.

The insulating film 6 is made of glass or resin.
The protrusions 13 and 14 are formed over the entire width.

As shown in FIG. 3, the insulating film 6 has the projecting portions 13 and 14 with the other end of the insulating substrate 1 facing upward and the surface of the insulating substrate 1 inclined downward.
Is immersed in a bath 30 of, for example, a molten glass paste or a resin paste, and then can be easily formed by baking or thermosetting.

The thus formed insulator films 6, 6
It is formed over the entire width of the corner C at one end of the insulating substrate 1, and the terminal electrode 4a, 4b generally formed of a thick conductor film has the thinnest corner C. Can be stably coated with the insulator films 6 and 6.

When the chip-shaped variable resistor constructed as described above is surface-mounted on a predetermined wiring of a printed wiring board by reflow soldering or flow soldering, on the terminal electrode 4c side, the insulating substrate is centered on the terminal electrode 4c. 1 is firmly adhered to the flat plate portion 52 disposed on the back surface of the substrate 1.

In the terminal electrodes 4a and 4b, not only the thick conductor films on the back surfaces of the protruding portions 13 and 14 but also
The solder will adhere to the end face.

However, even if the solder adheres to the end surfaces of the terminal electrodes 4a and 4b, since the insulating films 6 and 6 are formed on the corners C on the front surface, the insulating films 6 and 6 are formed. No solder adheres to the six portions. Therefore, this corner C
Thus, the terminal electrodes 4a and 4b are not eroded by the Ag component solder at all, and the connection between the terminal electrodes 4a and 4b and the thick-film resistor film 2 is never broken at the corner C. .

The corners on the back surface formed by the back surfaces and the end surfaces of the protrusions 13 and 14 may be formed in the same manner as the corners C on the surface on which the insulating films 6 and 6 are formed. Incidentally, the corners on the rear surface side are liable to be eroded by solder, and even if they are disconnected, the fatal problem of disconnection between the horseshoe-shaped thick film resistor film 2 and the terminal electrodes 4a and 4b does not occur. .

Although the molten solder adheres to the terminal electrodes 4a and 4b to cause solder erosion, this portion is basically a flat portion and can be made relatively thick. Also, the problem of disconnection due to solder erosion can be avoided. The thickness of the end surfaces of the terminal electrodes 4a and 4b may be about 10 to 20 μm.

As described above, structurally the terminal electrodes 4a, 4a
In the case of a chip-shaped variable resistor in which a plating layer for preventing solder erosion and improving solder wettability cannot be formed on the surface of the terminal b, an insulator film is formed on the corners C of the terminal electrodes 4a and 4b. By forming 6 and 6, disconnection due to solder erosion can be prevented beforehand.

[0040]

As described above, according to the present invention, even if the terminal electrode is made of an Ag-based conductor film, the connection between the horseshoe-shaped thick film resistor film and the terminal electrode may be broken. Absent,
It becomes a chip-shaped variable resistor that can derive stable characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view of a chip-shaped variable resistor according to the present invention.

FIG. 2 is a plan view of an insulating substrate used for the chip-shaped variable resistor of the present invention.

FIG. 3 is a schematic view of one step of a process for manufacturing an insulating substrate of a chip-shaped variable resistor according to the present invention.

FIG. 4 is a sectional view of a conventional chip-shaped variable resistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2 ... Thick film resistor film 3 ... Slider 4a, 4b ... Terminal electrode from thick film conductor film 4c ... Terminal electrode 6 ... Insulator film C ... Corner

Claims (1)

[Claims] 1. A horseshoe-shaped thick-film resistor film on a surface of an insulating substrate, a slider sliding on the surface of the thick-film resistor film, and a surface, an end surface, and a back surface of an end portion of the substrate. In a chip-shaped variable resistor made of an Ag-based thick-film conductor film and having a terminal electrode connected to the thick-film resistor film, an insulator film is applied to a corner portion between a surface of the terminal electrode and an end face. A chip-shaped variable resistor.