CZ72999A3 - Alloy for coating miniature switching contacts - Google Patents

Abstract

A gold-palladium-ruthenium alloy, used for miniature switch contact coatings and having a specified composition, is new. An alloy for miniature switch contact coatings has the composition 25-35 wt.% Pd, 1-5 wt.% Ru, optionally up to 0.5 wt.% Cu and balance Au. Independent claims are also included for the following: (1) a miniature switch contact coating of the above alloy; and (2) a miniature switch with a contact face having the above coating.

Description

Technical field

BACKGROUND OF THE INVENTION The present invention relates to an alloy for coating miniature switch contacts, coating miniature switch contacts with an appropriate alloy, a miniature switch having contact surfaces so coated, and the use of an alloy for coating contact surfaces of miniature switches.

BACKGROUND OF THE INVENTION

Over the last few years, the need for small and reliable electrical switching contacts has increased, especially in the telecommunications sector. At the same time, high demands are placed on the switching contacts used, in particular in the form of relays. In addition to high contact resistance, the switching contacts should have opal-resistant contact surfaces exhibiting a long service life.

The commonly used coating materials for the respective contact surfaces of the electric miniature switch contacts consist mainly of AuAg8 and AuNi2 alloys. However, after a certain number of switching operations, these have a relatively high material transfer and thus a low service life (often <500 000 switching operations). This occurs with AuAg8 cold welds occurring on the basis of frictional micro-shifts, especially during dry switching, leading to relay failure.

SUMMARY OF THE INVENTION

From the above facts, there is a problem of at least partial elimination of the above-mentioned drawbacks with the help of a new composition alloy.

According to the invention, this problem is solved by the alloy of item 1, by coating the miniature switching contacts of item 3, with the miniature switch of item 4, and by using the alloy of item 5.

The alloy contains 25-35% by weight of palladium, 1-5% by weight of ruthenium and the remainder in the form of gold.

This alloy is a contact material with a very high opal resistance due to surface erosion at each switching, which largely eliminates the possibility of non-switching during load switching and the occurrence of cold welds during dry switching due to reduced contact adhesion. This also results in a substantial increase in the service life of the respective miniature contact coatings and their switches.

According to the invention, miniature switch contacts are understood to be those whose operating range is at a power of up to 50 W, a voltage of up to 150 V and a current of up to 1 A. This also includes no-load switching (current and voltage). called dry switching. In dry switching, the operating voltage is below the so-called softening stress of the corresponding contact metal, so that no material feed is present.

The alloys according to the invention are produced by a metallurgical process and then applied to the respective contact surfaces as surface layers by rolling.

A further advantage of the alloy according to the invention lies in the stable contact resistance and in the saving of gold. Due to the relatively low electron output work of the alloy components (ruthenium: 4.52 V), surface erosion occurs, which is converted into a relatively large area movement of the resulting arc during switching.

In a preferred embodiment, the alloy of the invention further comprises copper up to 0.5% by weight. The copper additive serves to reduce the compliance of the core, to cure the alloy and all of this to increase the opal resistance.

All this leads to a stable contact resistance and thus to an increase in service life under load and no-load switching.

BRIEF DESCRIPTION OF THE DRAWINGS

The following examples illustrate the invention:

Example 1: Load switching Fig. 1a is a functional representation of the percentage dropouts after a certain number of switching cycles (AgPdSO, 80 microns, coated (PVD) with AuAg8, 2 microns);

Fig. 1b is a functional representation of the contact resistance after a number of switching cycles (AgPdSO, 80 microns, coated (PVD) with AuAg8, 2 microns);

Figure 2a is a functional representation of the failure rate as a function of the number of switching cycles (AgPd60, 80 microns, coated (PVD) with AuPd30 Ru2, 1.5-1.7 microns);

Fig. 2 is a functional representation of contact resistance versus number of switching cycles (AgPd60, 80 microns, coated (PVD) with AuPd30 Ru2, 1.5-1.7 microns);

Example 2: Load-free switching Fig. 3a is a functional representation of the frequency of outages depending on the number of switching cycles (AgPdSO, 80 microns, coated (PVD) with AuAg8, 2 microns);

Fig. 3b is a functional representation of the contact resistance (AgPd60, 80 microns, coated (PVD) with AuAg8, 2 microns);

Fig. 4a is a functional representation of the failure rate as a function of the number of switching cycles (AgPd60, 80 microns, coated (PVD) with AuPd30, Ru2, 1.5-1.7 microns);

Figure 4b is a functional representation of the contact resistance (AgPd60, 80 microns, coated (PVD) with AuPd30, Ru2, 1.5-1.7 microns).

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 relate to a relay whose switching contact surfaces consist of 80 micrometers AgPdSO coated with a 2 mm thick AuAg8 film by means of the PVD method. It is a load switching relay at 125 V and 0.25 A at • ·

3 Hz clock frequency. The required number of switches is 1 million. Six relays were subjected to the corresponding switching cycle, with a Weibull beta value of 814,000.

In Figure 1, it is clearly seen that the percentage failure rate rises rapidly from about 500,000 switching cycles. Also, a slight increase in contact resistance within the switching cycles can be seen in Figure 1b.

The relay is then deemed to have tripped if at least ten closing or opening errors occur, or when the contact resistance exceeds a freely determined limit, in this case 200 m Ohm.

Figures 2 are relay contacts coated according to the invention, the switching contact surfaces of which consist of AgPd 60 (80 microns) coated with a 1.5-1.7 micron thick AuPd30 Ru2 layer produced by the PVD method.

The operating conditions correspond to the above.

In this case, according to the invention, a Weibull beta value of 964,000 is achieved, which is clearly above the first value.

It can also be seen from Figure 2a that the percentage failure rate reaches a significant value only from about 900,000 switching cycles.

From Fig. 2b, slight contact resistance scrap within the switching cycles can then be observed.

0 00

0 0 0 0 0

In the second case, the clock frequency is 10 Hz

000 000.

it is a dry switch with the required number of switches

In the case of Figure 3, the contact areas are AgPdSO (80 microns) which are coated with a 2 micron thick AuAgS layer by the PVD method, with a Weibull beta value of 4.61 χ 10 ⁶ .

It can be seen in Figure 3a that the significant outage frequency is evident up to 1,000,000 switching cycles. It can also be seen in Figure 3b that the contact resistance reaches very high values from 1,000,000 switching cycles.

For the switch contact surfaces coated according to the invention (80 micrometers AgPdSO coated (PVD) with 1.5-1.7 micrometers AuPd30 Ru2), the Weibull beta value is 9.91 x 10 ^e , as can be seen from the nearly needle-shaped function in the figure 4a.

This is also reflected in the fact that the contact resistance reaches higher values only from 10 000 000 switching cycles (see

Claims (5)

PATENT CLAIMS 1. An alloy for coating miniature make contacts having the following composition: * - Pd: 25-35% by weight - Ru: 1-5% by weight - Au: the remainder% by weight 2. The alloy of claim 1, further comprising the following: - Cu: up to 0,5% by weight. 3. Coating the miniature make contacts with an alloy according to one of items 1 to 2. 4. Miniature switch with contact surfaces coated according to point 3. 5. Use of an alloy according to one of items 1 to 2 for coating the contact surfaces of a miniature switch.