Pins for electronic assemblies

The pin for electronic assemblies according to the present invention consists of a core alloy with 0.2 to 1.5 wt. % Ag, the remainder copper, whereby at least the contact surface of the pin is provided with one or several highly conductive and/or easily solderable coatings. With this not only a higher electric conductivity of the contact is obtained but also a comparatively high strength with simple production and good workability, which makes it possible to miniaturize the pins.

The invention relates to pins according to the Oberbegriff of claim 1. The 
demands on pins for electronic assemblies are very high since they must 
have, on the one hand, a good electric conductivity and thus a good heat 
conductivity and, on the other hand, a high strength so that they, on the 
one hand, are not bent during insertion and, on the other hand, experience 
little wear. Furthermore, these pins, which serve as contacts, must also 
be very flexible and must be suited for coating. A high strength is 
furthermore necessary if one wants to reduce the dimensions, in particular 
the cross sections, of the contacts. 
Standard alloys, as for example brass or bronze, are presently used for 
such contacts, which, however, have a comparatively low electric 
conductivity. Materials with a higher electric conductivity with a 
simultaneously higher strength are, for example, CuFe2P-alloys. Theses 
alloys, however, have the disadvantage that they, because of their high 
iron content, have the tendency to precipitate iron with the corresponding 
corrosion problems. In particular when these pins are used for 
safety-relevant parts, it cannot be guaranteed that a sufficiently and 
secure contact transfer exists at all times. 
Alloys for contacts are known from U.S. Pat. No. 5,139,890, which are 
assembled out of a core material, which has a coating. Either copper or, 
however, copper alloys like beryllium copper or nickel copper alloys are 
used as core material. A silver coating is then applied onto this alloy 
forming a contact, whereby here, if necessary, blocking layers of gold are 
also inserted. The reason for this construction of the contacts is that 
these have a good wear resistance, are condensation-resistant, and are 
insensitive to sulfating. 
A welding electrode is known from FR-1 298 462, which is supposed to have a 
high thermal and electric conductivity, and which is heat-resistant at 
high temperatures. As such a welding electrode an alloy of 96.35% copper, 
3.50% silver and 0.15% zircon is suggested. 
The basic purpose of the invention is to provide contacts of the 
above-mentioned type in such a manner that they, aside of a high electric 
conductivity and a comparatively high strength, can be easily 
manufactured, can be easily worked, and are very flexible, and experience 
no disadvantageous precipitations. 
This purpose is attained with the characteristics of claim 1.

A pin of the invention is distinguished by a high conductivity, which, 
compared with pure copper, is only slightly less. A conductivity of over 
40 Siemens can be achieved with this contact of CuAg-alloys. The tensile 
strength as such can be compared with the CuFe2P-alloy, whereby here 
strength values of over 600 N/mm.sup.2 are obtained. Furthermore, the 
contacts of the invention are distinguished by a slight temperature 
increase during an electric load. The corrosion resistance is, in 
comparison to copper, further increased by the addition of silver. 
The contacts can be provided in accordance with the invention comparatively 
easily with a coating, for example, with a rhodium, palladium, silver, 
indium, iridium, platinum, gold, tin, nickel, copper or lead coating. A 
coating with the aforementioned metals or their alloys results, on the one 
hand, in a good soldering ability and, on the other hand, in a low 
transfer resistance, namely a good contact ability. Thus, the one end of 
the contact can advantageously be provided with an easily solderable 
coating and the other end with a highly conductive coating. Due to the 
higher strength and conductivity it is possible to design the contacts 
with smaller cross sections so that the density of the number of plugs can 
be increased. A blocking layer of nickel or copper is advantageously 
provided between the core alloy and the outer coating, which blocking 
layer prevents phase-limit reactions between the core material and the 
outer coating. 
The content of the core alloy of iron and manganese should each not exceed 
0.8 wt. % and the content of silicon and aluminum should not exceed 0.3 
wt. %. Phosphorus should in turn not exceed 0.1 wt. %. Zinc can 
advantageously be added up to 2 wt. %. Furthermore, titanium and chromium 
can be added to the core alloy, whereby these are added in amounts of each 
no more than 0.2 wt. %. The alloy elements iron and manganese are 
strength-increasing, whereas the other alloy elements act both as a 
deoxidation means and act also, due to precipitations, 
strength-increasingly. Chromium has proven to be particularly 
advantageous.