JPS6312332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contact configuration of a reed switch that closes or connects circuits of measuring instruments, testing machines, electronic computers, peripheral devices, etc.

Normally, one of the important phenomena of this type of electrical contact is contact wear. Contact wear is mainly a phenomenon in which the contact metal transfers, that is, as the contact repeats its operation, the contact metal gradually transfers from the contact surface.The causes are (1) short arc that occurs just before the contact is connected or disconnected; 2) While the contacts are energized,
There are two causes: (1) melting of the contact metal due to Joule heat generated by the contact resistance of the contact portion; and (3) transfer of the contact metal due to bridge formation when the contact is broken. When contact wear occurs, the transfer will concentrate on one of the electrodes. For example, a hole is formed on the anode side contact and a protrusion is formed on the cathode side contact, and as these grow, the protrusion and the hole remain connected, and they no longer function as a contact. The degree of such contact wear differs depending on circuit conditions such as voltage, current density, and load. Furthermore, under the same circuit conditions, there are differences in contact wear depending on the type of contact metal used. Therefore, the selection of the metal used for the contact is an extremely important issue that affects the life of the contact.
For this reason, electrical contacts made from various metals have been proposed. For example, gold-based metal materials,
That is, there are contacts using high-melting point noble metals such as ruthenium, rhodium, and rhenium.

However, even at these contacts, high level load conditions (voltage around 50V, current over 100mA)
The reality is that as the number of operations increases, the contacts wear out and cannot reach a fully satisfactory lifespan.
Therefore, after applying high melting point metals such as rhodium, rhenium, ruthenium, iridium, tungsten and molybdenum on low melting point metals such as tin, zinc, cadmium, lead and indium, the low melting point metal and high melting point metal are diffused by heat treatment. Although it is thought that by doing so, a long life under high-level load conditions can be achieved, there are problems such as variations in the degree of diffusion due to variations in heat treatment conditions and plating thickness, and an increase in the number of man-hours.

An object of the present invention is to provide a reed switch having a contact portion that can significantly prevent contact wear even under high-level load conditions and can withstand long-term use.

The present invention is a reed switch in which a reed piece made of an alloy whose main components are iron and nickel is sealed in an airtight container such as a soft glass tube, in which a gold-cobalt alloy plating is applied to the contact portion of the reed piece to a thickness of 2μ or less. , the upper layer contains tin, zinc, cadmium,
Either low melting point metal such as lead or indium
It is characterized by being applied to a thickness of 0.5μ or less.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross-sectional configuration of a commonly used reed switch, which consists of leads 1 and 1' and a soft glass tube 2.

FIG. 2 is a sectional view of the contact portion of the reed switch according to the present invention, in which a gold-cobalt alloy plating layer 3 is applied on the lead 1 made of iron-nickel alloy,
Furthermore, a low melting point metal plating layer 4 is applied thereon. In the case of this example, the study was conducted by plating tin as the low melting point metal plating layer 4. In other words,
High-level load conditions shown in Figure 3 (DC50V-100m
A life test was conducted under A), the contacts were turned on and off until they became inoperable, and the correlation between the number of operations and defective rate was investigated. FIG. 4 is a diagram comparing the life characteristics of a reed switch with the contact treatment of the present invention, a conventional reed switch, and a reed switch with the contact treatment outside the plating thickness range of the present invention.
In Fig. 4, a shows the characteristics of a reed switch that has been subjected to the contact treatment (gold-cobalt alloy plating) of the present invention, and a tin plating layer with a thickness of 0.2 to 0.5 μm is formed on a gold-cobalt alloy plating layer with a thickness of 1 μm. The life characteristics of a reed switch with contacts treated with , b is the thickness
0.2~ thick on 3μ gold-cobalt alloy plating layer
Life characteristics of a reed switch with contacts coated with a 0.5μ tin plating layer; c is the life characteristics of a conventional reed switch that has the same dimensions as the reed switches a and b, but differs only in contact treatment; d is the life characteristics of a and b An example of the life characteristics of a conventional reed switch that is slightly smaller than , c is shown. As is clear from this result, reed switches with conventional contact treatment or reed switches with a thicker gold-cobalt alloy plating layer than the reed switch of the present invention can be operated approximately 50 to 1 million times under high-level load conditions. In contrast, the inability to open occurs after approximately 4 to 5 million operations, whereas the reed switch to which the contact treatment of the present invention has been applied does not occur until approximately 4 to 5 million operations.

The reason why a reed switch with a conventional contact treatment has a shorter life than a reed switch with a contact treatment of the present invention is because the growth of protrusions and holes due to dislocation causes the contact to become inseparable. However, since the reed switch with the contact treatment of the present invention has a low melting point metal plating layer on the contact surface, it differs from the reed switch with the conventional contact treatment.
The growth of protrusions and holes due to transfer is prevented, and a smooth transition occurs instead of a sharp transition, which has the effect of preventing the inability to separate due to protrusions and holes, and is thought to extend the life of the contact. In addition, by applying a gold-cobalt alloy plating layer below the low-melting point metal plating layer, it has the effect of promoting smoothing of the transition caused by impurities contained in the gold-cobalt alloy plating layer, making it resistant to cracking. Improved inseparability and stability of contact resistance can be obtained. However, gold-
If the cobalt alloy plating layer is too thick (more than 3μ),
After the transition of the low melting point metal plating layer, the transition of the gold-cobalt alloy plating layer tends to proceed in the vertical direction b rather than the horizontal direction a shown in Fig. 2, so that the transition is faster than when the gold-cobalt alloy plating layer is thinner. It is thought that sharp protrusions are likely to occur. Therefore, the thickness of the cobalt alloy plating layer is preferably 2 μm or less.

In the above embodiments, the low melting point metal plating layer is made of tin, but it can also be made of zinc, cadmium, lead, indium, etc., which also have low melting points.

As explained above, according to the present invention, by applying a low melting point metal plating outer layer to the gold-cobalt alloy plating inner layer, it is possible to extend the life and stabilize the contact resistance under high-level load conditions.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a commonly used reed switch, Fig. 2 is a cross-sectional view showing the contact configuration of an embodiment of the reed switch according to the present invention, and Fig. 3 is a test of the life of the reed switch according to the present invention. The circuit diagram and FIG. 4 are diagrams showing the results of a life test of a reed switch with conventional contact treatment and a reed switch with contact treatment of the present invention. 1, 1'...Reed piece, 2...Soft glass tube,
3... Gold-cobalt alloy plating layer, 4... Low melting point metal plating layer.

Claims (1)

[Claims] 1. In a reed switch in which a reed piece made of an alloy mainly composed of iron and nickel is sealed in a sealed container, the contact part of the reed piece is coated with an inner layer of gold/cobalt alloy plating with a thickness of 2μ or less, tin, zinc, A reed switch characterized by comprising an outer layer of low melting point metal plating with a thickness of 0.5μ or less and made of any one of cadmium, lead, and indium.