JPS63142802A - Variable resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to surface mounting on printed circuit boards, etc., in which the resistance value is made variable by rotating a slider on a resistor formed on an insulating substrate. Regarding usable variable resistors.

2. Description of the Related Art Conventionally, as shown in FIG. 8, a variable resistor of this type has an arc-shaped cermet resistor 5 formed on the upper surface of an insulating substrate 1, and a slider (see FIG. (not shown) is rotatably mounted so as to slide on the resistor 5. Note that the slider is rotatably attached to the center hole 2 of the insulating substrate 1 via an electrode (not shown).

Furthermore, external electrodes 6, 6 made of a silver-palladium alloy are provided at both ends of the resistor 5. As shown in FIG.
Palladium alloys 6a and 6b are printed and baked, and a silver-palladium alloy 60 is similarly deposited and baked on the end face, and then the resistor 5 is printed and baked.

While λ weeks are trying to resolve 5. .

However, in the above-mentioned variable resistor, a silver-palladium alloy is used as the external electrode 6 in order to prevent the silver from diffusing into the solder and improve the solder heat resistance. It has problems in that it is expensive and it is impossible to reliably prevent silver corrosion. In addition, the film thickness of the silver-palladium alloy 60 provided on the end face inevitably becomes thick, and the glass frit is exposed on the surface, which impairs the properties of soldering, and requires complicated preliminary soldering. are doing.

Means to Solve the Problem of Skin Feet Therefore, the variable resistor according to the present invention has a lower layer suitable for plating the external electrode, a middle layer plated with a material that improves solder heat resistance characteristics, and a lower layer suitable for plating the external electrode. It is characterized by being composed of an upper layer made of a superior material and plated.

In other words, in the present invention, an underlayer suitable for plating (e.g. silver,
The silver-palladium alloy (silver-palladium alloy) is protected by an intermediate layer plated with a material (for example, nickel, nickel alloy) that improves solder heat resistance, and silver corrosion is reliably prevented. Furthermore, by coating it with an upper layer made by plating a material with excellent properties (for example, tin, tin-lead alloy), the glass frit is prevented from being exposed to the surface, and soldering is prevented. has improved characteristics, eliminates the need for preliminary soldering, and can be used with eutectic solder.

Epilepticism 1 to 4 show a first embodiment of the present invention.

This variable resistor is composed of an insulating substrate 10 and a slider 20 installed on the surface of the insulating substrate 10.

The insulating substrate 10 is made of molded and sintered alumina, has a center hole 11, and has an arc-shaped cermet resistor 15 and an annular collector pole 17 formed on its surface. Both ends of the resistor 15 and the collector electrode 17 extend to one end of the substrate 10, and are connected to external electrodes 16.16, which will be described in detail below.
．． It is electrically connected to 18.

As shown in FIG. 2, the slider 20 has a dish-shaped portion 21, a cylindrical portion 22 provided at the center, and an arm portion 23 provided at the outer periphery. This slider 20 is constructed by inserting the cylindrical part 22 into the center hole 11 of the insulating substrate 10 and caulking it on the back side, so that the dish-shaped part 21 comes into contact with the collector electrode 17 and the lower part of the arm part 23 A contact portion 24 protruding from the resistor 15 is rotatably attached to the resistor 15 in contact with the contact portion 24 .

Next, the structure of the external electrode 16 will be explained.

As shown in FIG. 4, the external electrode 16 has a lower layer 16a and a first
plating layer (middle layer) 16b and second plating layer (upper layer) 1
It is composed of three layers with 6c. The lower layer 16a has silver or silver-palladium alloy printed and baked on the front side, and silver printed and baked on the back side and end faces, and has a thickness of, for example, 15 μm. The first plating layer 16b is made of nickel or a nickel alloy, and has a thickness of, for example, 2 μm. The second plating layer 16c is made of tin or a tin-lead alloy, and has a thickness of, for example, 4 μm.

The first plating Jffl 16b functions as a barrier against the lower F) 16a to prevent silver corrosion, and has the effect of improving solder heat resistance. The second plating layer 16c has the effect of increasing solder wettability and improving soldering characteristics, and also has the effect of omitting preliminary soldering.

In the manufacturing process of the external electrode 16, first, the insulating substrate 10 is
A lower layer 168 is formed on the front, back, and end surfaces of the resistor 15. Next, a metal resist 25 (indicated by a dashed line in FIG. 4) is applied on the resistor 15, and the first plating layer 16 is coated.
b. A second plating Ji16c is formed, and then the plating resist 25 is removed.

On the other hand, Collector 7! The outer N of the pole 17 and the pole 18 also have a three-layer structure similar to the external electrode 16. Furthermore, the first
In the figure, reference numeral 19 indicates an idle electrode, and this idle electrode 19 also has a three-layer structure similar to the external electrode 16.

Note that the materials for the plating layers 16b and 16c are not limited to those mentioned above; the plating layer 16b may be made of a material that improves solder heat resistance, and the plating layer 16c may be made of a variety of materials as long as they have excellent soldering properties. can do.

5 to 7 show a second embodiment of the invention.

In this variable resistor, an electrode 30 is provided in place of the collector electrode in the variable resistor shown in FIG.
The slider 20 is rotatably attached by caulking the upper part of the outer electrode 16 of the cermet resistor 15.
, 16 have a three-layer structure similar to the first embodiment.

Effects of the Invention As is clear from the above explanation, according to the present invention, the outer electrode has a lower layer suitable for plating, a middle layer plated with a material that improves solder heat resistance characteristics, and a layer with excellent soldering characteristics. Since it is composed of an upper layer made of plated material, the middle layer acts as a protective barrier for the lower layer, and even if silver is used for the lower layer, it can reliably protect against silver cracks and improve solder heat resistance. , it is not necessary to use an expensive silver-palladium alloy as the electrode. Furthermore, the soldering of the upper layer acts to improve the characteristics, eliminates the need for complicated preliminary soldering, and allows sufficient use of eutectic solder, making it possible to manufacture the device at low cost as a whole.

[Brief explanation of the drawing]

1 to 4 show a first embodiment of the present invention.
2 is a perspective view of the resistor, FIG. 3 is a plan view of the insulating substrate, and FIG. 4 is a sectional view taken along line A-A showing details of the external electrodes. 5 to 7 show a second embodiment of the present invention;
The figure is a plan view, FIG. 6 is a central sectional view, and FIG. 7 is a bottom view. FIG. 8 is a perspective view of an insulating substrate of a conventional variable resistor, and FIG. 9 is a sectional view showing its external electrode. 10...Insulating substrate, IS...Nahmet resistor, 1
6... External electrode, 16a... Lower layer, 16b... First plating layer (middle layer), 16c... Second plating layer (
upper layer), 17... collector electrode, 18... external electrode, 20... slider.

Claims (4)

[Claims] (1) In a variable resistor in which a slider that slides on the resistor is rotatably mounted on an insulating substrate with an arc-shaped resistor formed on the surface, the external electrode is a lower layer suitable for plating. A variable resistor comprising: a middle layer plated with a material that improves soldering heat resistance; and an upper layer plated with a material excellent in soldering properties. (2) The variable resistor according to claim 1, wherein the lower layer is made of silver. (3) The variable resistor according to claim 1, wherein the intermediate layer is made of nickel or a nickel alloy. (4) The variable resistor according to claim 1, wherein the upper layer is made of tin or a tin-lead alloy.