DE3420231C1 - Silver-rich materials for low-voltage contacts - Google Patents

Description

The invention relates to materials rich in silver for weak current contacts, in particular for plug connections and sliding contacts, which are in a thin layer over a nickel intermediate layer on a carrier of a Base metal material are applied, consisting of 45 to 72 atomic% silver, 9 to 32 atomic% gold, 9 to 32 atom% palladium, 0.01 to 1 atom% iridium and / or osmium, 0 to 10 atom% copper and / or 0 to 5 Atom% lead and / or 0 to 5 atom% tin.

So-called connectors are present to a considerable extent in electronic devices. With reliable contact, they guarantee that defective assemblies can be replaced quickly. As the performance of electronic devices has advanced, the demands on the quality of the materials used in such connectors have changed. Above all, it is important to be resistant to the formation of a foreign layer on the contact surface due to environmental pollutants. In addition, the materials must have a high level of wear resistance, which, in spite of only a few μm layer thickness, must ensure a sufficiently long service life without abrasion. The price of the material also plays an important role.
While only a few years ago considerable electrical loads were flowing through the contacts, today only the smallest currents and voltages in the micro and nano range are often transmitted. In addition, the increasing miniaturization of the components and thus also the connector on the one hand and the increasing air pollution on the other hand, have aggravated the problem of tarnish resistance of the contacts used to a considerable extent. While previously any foreign layer films that might have been present on the contact pieces could easily be destroyed by the applied voltages by so-called fritting or easily broken through mechanically by the high contact forces, the voltages applied today or the contact forces, which have been significantly reduced due to progressive miniaturization, are not sufficient for such self-cleaning of the contacts more out. The resistance to the formation of a foreign layer, which is often invisible to the eye, has therefore become the most important criterion for modern contact materials for connectors.

These requirements can of course be met by alloys with a high gold content. Included In particular, alloys made of gold and silver with more than 70% by weight of gold have proven successful. There are too high-carat alloys known, which in addition to gold and silver also contain copper and / or nickel, however, despite their high gold content, even these alloys are often not sufficiently corrosion-resistant.

so The wear resistance, which is also important, is not only determined by the material properties of the contact materials, such as B. shaped their hardness, but it depends just as much on the contact pairing and the The construction of the connector system depends, in particular, on the contact force. By adding In general, base metals can be used to increase the wear resistance of the materials, but this increases but also the tendency to form foreign layers. On the other hand, materials resistant to foreign layers show usually poor wear resistance.

Given the high precious metal prices, especially the high gold price, comes the cost of materials increasing importance too. The aim is therefore to keep the gold content in these materials as low as possible keep.

There are therefore from DE-OS 26 37 807 and from DE-OS 29 40 772 contact materials based on gold-silver-palladium became known, which is characterized by a good tarnish resistance at the same time reduced Award gold content. However, in addition to at least 35% by weight gold, they also contain a few percent Base metals such as indium, tin or nickel. However, these base metal components affect the optimal tarnish resistance of the pure noble metal alloy and increase the recrystallization temperature of the Contact material, which can lead to difficulties in further processing. In addition, the wear resistance these materials are not sufficient.

From EP-OS 82 647 contact materials have become known, which in addition to palladium as a remainder 10 to 58 % By weight silver, 32 to 58.5% by weight gold, small proportions of rhodium and / or iridium and up to 3% by weight Contain copper, nickel or indium. These contact materials also show with regard to the formation of foreign layers

and wear resistance are not optimal properties.

It was therefore the object of the present invention to develop silver-rich materials for low-current contacts, in particular for plug-in connections and sliding contacts, which are applied in a thin layer over a nickel intermediate layer on a carrier made of a base metal material, consisting of 45 to 72 atomic% silver, 9 to 32 Atom% gold, 9 to 32 atom% palladium, 0.01 to 1 atom% iridium and / or osmium, 0 to 10 atom% copper and / or 0 to 5 atom% lead and / or 0 to 5 Atomic percent tin. These materials should be as resistant as possible to the formation of foreign layers, have the highest possible wear resistance, be easy to apply to the carrier materials and show no significant increase in the electrical contact resistance ^{even after prolonged exposure at 125 ° C.}

This object was achieved according to the invention in that the contents of silver and gold are in relation to one another atomic ratio of 2: 1.3: 1.4: 1.5: 1 or 6: 1 and / or the contents of gold and palladium to one another in an atomic ratio of 1: 3.1: 2.2: 3.1: 1.3: 2.2: 1 or 3: 1 and / or the contents of silver and palladium are in an atomic ratio of 2: 1.3: 1.4: 1.5: 1 or 6: 1. ■

Preferably there are two pairs of precious metals in the specified atomic ratios to one another, d. That is, the contents of gold and palladium together with the contents of gold and silver or the contents of gold and palladium together with the contents of silver and palladium.

It has surprisingly been found that silver-gold-palladium alloys in the claimed range despite their high silver content a significant improvement in their properties with regard to foreign layer resistance and show wear resistance when the atomic proportions of gold, silver and palladium are in the given proportions to each other.

The base metal additives are particularly advantageous when both contact pieces of a contact pair can be made from the same material.

Because of their high silver content, these materials are cheaper than the previously known gold-silver-palladium materials. They are easy to process and do not experience any increase in the electrical contact resistance after prolonged storage at 125 ^° C.

The following table shows some exemplary alloys within the range according to the invention.

For this purpose, the alloys were melted from the metals and processed into test specimens. The increase in the contact resistance was determined after 21 days after the test specimens had been exposed to a gas mixture of purified air with 0.5 ppm hydrogen sulfide and 5 ppm sulfur dioxide at 75% relative humidity at 30 ^{° C. during this time.}

No. Composition in atomic% Au Pd Ir / Os Cu Pb Sn Increase in Ag Transition resistance 26.78 13.38 0.03 ' [mQ] 1 59.81 30.94 15.47 0.03 4.3 2 53.56 12.69 25.38 0.03 2.7 3 61.90 29.42 19.6 0.03 3.5 4th 50.95 16.77- 25.16 0.03 3.0 5 58.04 22.49 22.49 0.03 1.5 6th 54.99 18.32 18.32 0.03 2.1 7th 63.33 24.99 24.99 0.03 6.5 8th 49.99 18.17 27.26 0.03 2.8 9 54.59 14.28 28.56 0.03 2.5 10 57.13 9.99 29.99 0.03 1.5 11th 59.99 19.99 19.99 0.03 2.2 12th 59.99 11.10 22.21 0.03 2.0 13th 66.66 11.75 17.64 0.03 7.6 14th 70.58 27.26 18.17 0.03 3.3 15th 54.54 28.56 14.28 0.03 4.5 16 57.13 22.21 11.10 0.03 2.0 17th 66.66 29.99 9.99 0.03 4.0 18th 59.99 14.28 21.42 0.03 1.9 19th 64.27 24.99 12.49 0.03 1.9 20th 62.49 15.37 23.07 0.03 3.0 21 61.53 13.32 19.99 0.03 2.3 22nd 66.66 23.07 23.01 0.04 7.69 3.0 23 46.13 26.86 17.90 0.03 1.0 1.5 5.3 24 53.71 26.08 13.04 0.04 8.69 3.8 25th 52.15 29.54 9.85 0.05 0.3 1.0 6.2 26th 59.08 18.74 18.74 0.06 6.23 3.2 27 56.23 17.81 26.72 0.03 2.0 6.8 28 53.44 22.49 12.49 0.03 4.5 29 64.99 17.49 22.49 0.03 72.0 30th 59.99 21.00 25.00 0.03 68.0 31 53.97 32.49 12.51 0.03 57.3 32 54.97 89.5

In the case of alloys 1 to 7, gold and palladium are in the preferred atomic ratio, in the case of the Alloys 8 to 22 simultaneously gold, palladium and silver. The alloys 29 to 32 are outside of the stressed atomic proportions and therefore show a significantly higher increase in contact resistance. All alloys showed high wear resistance.

Claims (4)

Patent claims: 1. Silver-rich materials for weak current contacts, especially for plug connections and sliding contacts, in a thin layer over a nickel intermediate layer on a carrier made of a base metal material are applied, consisting of 45 to 72 atom% silver, 9 to 32 atom% gold, 9 to 32 atom% Palladium, 0.01 to 1 atom% iridium and / or osmium, 0 to 10 atom% copper and / or 0 to 5 atom% Lead and / or 0 to 5 atomic% tin, characterized in that the contents of silver and gold to each other in an atomic ratio of 2: 1.3: 1.4: 1.5: 1 or 6: 1 and / or the contents of silver and Palladium to one another in an atomic ratio of 2: 1.3: 1.4: 1.5: 1 or 6: 1 and / or the contents Gold and palladium have an atomic ratio of 1: 3.1: 2.2: 3.1: 1.3: 2.2: 1 or 3: 1 to one another. 2. Silver-rich materials according to claim 1, characterized in that the contents of gold and Palladium to each other in an atomic ratio of 1: 3.1: 2.2: 3.1: 1.3: 2.2: 1 or 3: 1 and at the same time the silver and gold contents are in an atomic ratio of 2: 1.3: 1.4: 1.5: 1 or 6: 1. 3. Silver-rich materials according to claim 1, characterized in that the contents of gold and Palladium to each other in an atomic ratio of 1: 3.1: 2.2: 3.1: 1.3: 2.2: 1 or 3: 1 and at the same time the contents of silver and palladium to one another in an atomic ratio of 2: 1, 3: 1.4: 1.5: 1 or 6: 1 stand. 4. Silver-rich materials according to claim 1, characterized in that when copper is added, too Gold and copper are in an integral atomic ratio to one another, preferably in a ratio of 3: 1.