JPH07192566A - Push button switch - Google Patents

Abstract

(57) [Abstract] [Purpose] The reliability of the contact part should be improved by preventing the deterioration of reliability due to whiskers and oxide film even if a part of the wire is directly used as a fixed contact without gold plating. (EN) Provided is a push button switch which can significantly reduce the cost without damaging it. [Structure] A wire base 1 having a portion exposed on the inner bottom of the housing as a fixed contact 9 and a portion exposed on the outside of the housing serving as a terminal is used, and a brass base material is covered with a Cu underlayer and a Sn layer. The movable contact 7 integrated with the rubber member 8 held by the housing and contacting with and separating from the fixed contact 9 was formed of conductive ink containing carbon particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and inexpensive push button switch having a fixed contact made by processing a wire and a movable contact integrated with a rubber member.

[0002]

2. Description of the Related Art This type of push button switch has an advantage that a material cost and a processing cost are low because a wire material is processed instead of a strip-shaped metal plate to form a fixed contact and a terminal. Since a so-called rubber contact is used in which the movable contact is integrated with the rubber member that causes a click feeling, it has the advantage that the number of parts and the number of assembly steps can be reduced, making it a versatile compact and inexpensive push button switch. It's being used.

A push button switch that has been widely adopted as such a push button switch has a wire material, which is formed by applying a solder plating to a brass base material, into a predetermined shape, and then supplies the wire material to a mold for molding a housing. By forming a housing in which the wire is partially embedded, a portion of the wire that has been gold-plated and crimped is exposed at the inner bottom of the housing to form a fixed contact, and the wire of the housing is located outside the housing. The part protruding to is used as a terminal. Then, by incorporating a rubber contact in which a movable contact is provided on the ceiling portion of a substantially bowl-shaped rubber member into the housing, and arranging the movable contact at a position where the movable contact can be brought into contact with and separated from the fixed contact, the cost can be reduced. We have obtained a highly reliable small push button switch.

That is, in such a push button switch, when the rubber contact is pushed in from the top surface side to elastically deform the substantially bowl-shaped rubber member, the movable contact is fixed immediately after the rubber member buckles and a click feeling is generated. When the contact is touched and the switch is turned on and the pushing operation force on the rubber contact is removed in this state, the elastically deformed rubber member returns to its original shape and the movable contact separates from the fixed contact, so switch off. It is supposed to return to the state.

[0005]

However, the above-mentioned conventional push-button switch has a limit in cost reduction because the contact portion (fixed contact) of the wire is plated with gold in order to ensure reliability. A technique for forming the contact portion at a lower cost has been desired.

Therefore, it is conceivable to use a tin-plated material, which is excellent in solderability, conductivity, and corrosion resistance, and which is used for various electronic parts and lead parts of electronic devices, as a wire material for pushbutton switches of this type. However, as is well known, whisker-like whisker-like crystals are easily generated on tin-plated materials, and an oxide film is easily generated on the surface. Therefore, high reliability cannot be maintained if the tin-plated wire is used as it is as a fixed contact. There was a difficulty.

The present invention has been made in view of the above technical background, and an object thereof is to provide a push button switch capable of achieving a large cost reduction without impairing the reliability of the contact portion.

[0008]

DISCLOSURE OF THE INVENTION The above-described object of the present invention is to expose a portion of a wire partly embedded in a housing to the inner bottom of the housing as a fixed contact and to the outside of the housing. In a push button switch in which a movable contact for connecting and disconnecting the fixed contact is formed integrally with a rubber member held in the housing, a brass base material is a copper base layer as the wire material. This is achieved by using a material that is coated with a tin layer and heat treated and heat-treated, and forming the movable contact with a conductive ink containing conductive particles.

[0009]

According to various experiments, the inventors of the present invention can prevent the generation of whiskers by heat-treating a tin-plated brass base material in a reflow furnace or the like, and the oxide film on the surface of the tin-plated material has a convex shape. It was found that they can be easily broken by the indenter, and it was confirmed that conductive particles such as carbon particles can be used as the indenter. Therefore, by adopting the above-mentioned solving means, there is no fear that reliability will be impaired even if a part of the wire is directly used as a fixed contact without being plated with gold.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the push button switch according to the present invention will be described below with reference to FIGS. Here, FIG. 1 is an explanatory view of a main part showing a contact portion of this embodiment, FIG. 2 is a cross-sectional view of the same embodiment, and FIG. 3 is the same embodiment in which an oxide film of a fixed contact is destroyed by carbon particles of a movable contact. FIG.

In the push button switches shown in these figures, a brass base material 2 is covered with a copper underlayer 3 and a tin layer 4 and then heat treated in a reflow furnace, and the wire material 1 processed into a predetermined shape. A housing 5 inserted into the mold and molded;
Moving contact 7 made of carbon nonwoven fabric and conductive ink
Is formed of a rubber contact 6 integrally provided on the ceiling of a substantially bowl-shaped rubber member 8. A part of the wire rod 1 partially embedded in the housing 5 is exposed at the inner bottom of the housing 5. The fixed contact point 9 is formed, and the portion of the wire rod 1 protruding outside the housing 5 is formed as a terminal (not shown). Then, the rubber contact 6 incorporated in the housing 5 is held by the housing 5 by fitting the outer peripheral portion of the rubber member 8, and the movable contact 7 at the center is positioned directly above the fixed contact 9 to fix the same. The contact 9 can be contacted and separated. Reference numeral 10 in FIG. 3 denotes a copper and tin diffusion layer formed between the copper underlayer 3 and the tin layer 4 of the wire rod 1, and 11 denotes oxidation generated on the surface of the tin layer 4 of the wire rod 1. The film 12 indicates fine carbon particles contained in the conductive ink of the movable contact 7.

In the push button switch constructed as described above, when the rubber contact 6 is pushed downward from the top surface side to elastically deform the rubber member 8 having a substantially bowl shape, the rubber member 8 buckles and a click feeling is generated. Immediately after the occurrence, the movable contact 7 comes into contact with the pair of fixed contacts 9 and 9, both fixed contacts 9 and 9 are conducted through the movable contact 7, and the switch is turned on. Further, when the pushing operation force on the rubber contact 6 is removed in the switch-on state, the elastically deformed rubber member 8 returns to its original shape and the movable contact 7 separates from the pair of fixed contacts 9, 9. The electrical connection between the fixed contacts 9 and 9 is released, and the switch is returned to the off state.

In the push button switch described above, the contact portion (fixed contact 9) of the wire material 1 which is a tin-plated material is not plated with gold, but as described above, the wire material in which the base material brass is plated with tin is reflowed. It has been confirmed that the treatment can prevent the generation of whiskers, and as shown in FIG. 3, it was also confirmed that the oxide film 11 on the surface of the tin layer 4 can be easily destroyed by the carbon particles 12 of the movable contact 7 during the pushing operation. Therefore, the fixed contact 9 in the present embodiment does not generate whiskers even if it is a tin-plated material, and there is no fear that the oxide film 11 interferes with the contact between the tin layer 4 and the movable contact 7. That is, in this embodiment, a part of the wire 1 is directly used as the fixed contact 9 without using an expensive material such as gold.
However, since the reliability of the contact portion is ensured, the small push button switch having the same high reliability as the conventional product can be manufactured at a very low cost.

In the above embodiment, the case where carbon particles are used as an example of the conductive particles has been described.
The same effect can be obtained by using other conductive particles such as silver or alumina instead.

[0015]

As described above, since the push button switch according to the present invention uses the wire rod that is tin-plated and then heat-treated in a reflow furnace or the like, whiskers are prevented from occurring and the surface of the wire rod is prevented. The generated oxide film is destroyed by the conductive particles of the movable contact during the pushing operation so that the movable contact and the tin layer can be surely brought into contact with each other. Even if it becomes a fixed contact, the reliability is not impaired, and therefore, it is not necessary to use expensive materials such as gold, and it is possible to achieve a significant cost reduction, and it has the same high reliability and small size as conventional products. The push button switch can be manufactured extremely inexpensively.

[Brief description of drawings]

FIG. 1 is a principal part explanatory view showing a contact portion of the present embodiment.

FIG. 2 is a sectional view of the same embodiment.

FIG. 3 is an explanatory view showing a state in which an oxide film of a fixed contact is destroyed by carbon particles of a movable contact in the same example.

[Explanation of symbols]

 1 wire rod 2 base material 3 copper underlayer 4 tin layer 5 housing 6 rubber contact 7 movable contact 8 rubber member 9 fixed contact 11 oxide film 12 carbon particles (conductive particles)

Claims (1)

[Claims] 1. A wire rod, a part of which is embedded in a housing, wherein a portion exposed to an inner bottom portion of the housing serves as a fixed contact and a portion exposed to the outside of the housing serves as a terminal, and the fixed contact serves as the fixed contact. A movable contact for contact and separation,
In the push button switch provided integrally with the rubber member held in the housing, a brass base material is used as the wire material.
A push button switch characterized in that it is formed of a u underlayer and an Sn layer and heat treated, and the movable contact is formed of a conductive ink containing conductive particles.