JPH0411966B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to contacts for reed switches.

Conventionally, gold-based diffusion contacts, gold alloy contacts, or platinum group metal contacts have been used as contacts for reed switches, but in all cases the contact layer thickness is approximately several microns, so the contact cannot be made by interrupting the current. It has the disadvantage that it suffers from wear and dislocation, and has a short lifespan compared to other electromagnetic relays that have bulk contacts with thick contact layers. In particular, under load conditions such as a resistive load of about 50 volts and 100 mA, and a cable is involved, short arcing will occur significantly, contact transfer will occur locally, and a hole will be formed in one contact, and a hole will be formed in the other contact. Due to the protrusions, poor contact and inability to separate easily occur with a small number of operations. In order to prevent this, after forming a plating layer of gold hard alloy on the lead piece, we apply a special diffusion treatment of rapid heating and cooling.
By making the above plating layer spongy,
It is known to extend life under load conditions with short arcs as described above. However, in the above-mentioned process, the heat treatment conditions after plating are difficult and the productivity is poor.

The purpose of the present invention is to solve the above-mentioned conventional drawbacks and
To provide a reed switch contact that has a long life even under load conditions where short arc occurs and is easy to manufacture.

In the contact of the present invention, a base layer made of tin, zinc, cadmium, lead, indium, etc. is formed at the tip of the lead piece of a reed switch, and has a volume ratio of 30% to 150% with respect to the uppermost layer described below. It is characterized by the formation of a top layer of gold or gold alloy.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention. That is, a gold strike 2 is formed at the tip of the lead piece 1, a tin base layer 3 is formed thereon, and a gold cobalt gold alloy layer 4 is formed on the top layer by plating. The gold strike was provided to facilitate the formation of the tin underlayer 3. The volume ratio of the base layer 3 to the gold alloy layer 4 is 30 to 150%. This is because if the volume ratio of the top layer and the base layer is too different, as will be explained later, an appropriate spongy layer will not be formed. The thickness of the underlayer was selected to be within the above range relative to the uppermost gold or gold alloy layer. The contact of this embodiment has the effect of having a significantly long life under load conditions where short arc occurs (DC 50 volts, 100 mA resistive load), as described below.

In order to confirm the above-mentioned effect, a reed switch in which a pair of reed pieces 1 having various configurations of contacts were enclosed in a glass tube 5 as shown in FIG.
A life test was conducted under a 100mA resistive load.
The contact configurations are A contact with plating thickness of the top gold cobalt gold alloy layer 4 and tin underlayer 3 of 0.3 and 2.7 microns, respectively, B contact with 1 and 2 micron plating, and C contact with 1.5 and 1.5 micron plating thickness. Contact 2, D contact with 1 micron and E contact with 2.7, 0.3 micron.
There are five types of contacts.

The results of the life test are shown in Figure 3. In FIG. 3, the horizontal axis represents the number of operations, and the vertical axis represents the cumulative failure rate of the reed switch with respect to the number of operations. Curves A to E show the characteristics corresponding to the various contacts described above, and curve F shows the life characteristics of a conventionally known reed switch with contacts made of gold and rhodium. As can be understood from the figure, contact B,
Both C and D have a lifespan 5 to 10 times longer than conventional reed switches. This can be considered as follows.

Under load conditions where short arc occurs significantly, in conventional contacts, the transfer of the contact material is concentrated locally, and protrusions and holes grow quickly. When exposed directly to the contact surface, the contact resistance increases, and the protrusion and hole become entangled and cannot be separated, resulting in a shortened lifespan. In contrast, the contact according to the present invention has a low melting point metal layer formed as a base layer, and a layer of gold or a hard gold alloy such as gold cobalt that is extremely easily diffused into the base layer is formed on top of the low melting point metal layer. Therefore, the two layers mentioned above diffuse into each other due to heating during sealing in the glass tube, forming a sponge-like diffusion layer on the surface, preventing protrusions from growing even if shot arc occurs, and preventing contact transfer. It is also believed that the wear and tear is not concentrated locally but spreads over the contact surface, extending the service life. Note that the contact A with a thin tin layer and the contact E with a thick tin layer both had approximately the same lifespan as conventional contacts. This is thought to be because the volume ratio of the top gold alloy layer and the tin underlayer is too different, making it difficult to form a suitable spongy layer. Therefore, the volume ratio of the base layer to the gold alloy layer is preferably about 30 to 150%.

In this embodiment, a gold-cobalt alloy is used for the top layer and tin is used for the underlayer, but the same effect can be obtained by using a gold-nickel alloy, a gold-silver alloy, or gold for the top layer. Moreover, zinc, lead, indium, etc. may be used for the base layer.

In addition, in order to prevent the material of the lead piece, such as iron or nickel, from being directly exposed to the surface, the base layer 3 of the above-mentioned tin or the like, or a layer further below the gold strike 2, is added.
Plating a metal whose diffusion coefficient with the metal of the underlayer is lower than the diffusion coefficient between the underlayer and the metal of the uppermost layer, such as rhodium, ruthenium, palladium, palladium-nickel alloy, rhenium, platinum, and tungsten. Good too. Thereby, the effect of the present invention can be further enhanced.

As described above, in the present invention, a gold or gold alloy layer is formed on the top layer of the tip of the lead piece, and a base layer of tin, zinc, etc.
Since the structure is formed with a volume ratio of 150%, a sponge-like contact is formed by diffusion of the metal in the base layer and the top layer, which extends the life of the contact under resistive load conditions where shot arc occurs. It has the effect of significantly improving

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
The figure shows a reed switch prepared for the experiment, and FIG. 3 shows the results of a life test of the reed switch using various contacts. In the figure, 1... lead piece, 2... gold strike, 3... tin base layer, 4... gold alloy layer, 5... glass tube.

Claims (1)

[Claims] 1. A base layer is formed of a metal containing tin, zinc, cadmium, lead, or indium as a main component on the tip of the lead piece on which a gold strike or a thin precious metal plating layer is applied. A top layer of gold or gold alloy is formed on the base layer, and the volume ratio of the base layer to the top layer is 30%.
A contact point for a reed switch characterized by 150% or more.