Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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NICKEL-BASED ELECTRIC~L CONTACT
Technical Field
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The invention is concerned with electrical contact
surfaces and, more specifically, with nickel-based contact
surface materials.
_ ckground of the Invention_ _ _______ _ _ ____ _ __
Typically, the manufacture of high-quality
electrical contacts has involved the use of gold whose
~roperties o~ low contact resistance and high chemical
stability are key advantages in such usage. However, as
the price oE gold remains high, efforts continue at
finding alternative materials for contact manuEacture.
Prominent among such alternatives are precious
metals other than gold; e.g., silver-palladium alloys have
been found suitable for certain applications. While such
alternate alloys are less expensive than gold, still
Eurther cost reduction is desired, and nonprecious metal
alloys such as, eAg., copper-nickel alloys have also been
investigated for contact resistance and stability over
time. See S. ~. Garte et al., "Contact Properties of
Nickel-Containing Alloys", Electrlcal_Con_acts, 1972,
Illinois Institute of Technology.
Summary of the Invention
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It has been discovered that certain nickel alloys
have contact properties of high stability and low contact
resistance comparable to those of gold.
In accordance with an aspect of the invention
there is provided apparatus comprising an electrical
contact, said contact comprising a surface of a body of
contact material, said contact material comprising nickel
and at least one glass forming additive selected from the
group consisting of boron, germanium, phosphorus, arsenic,
antimony, and bismuth, said at least one glass ~orming
additive bein~ present in said contact material in an
amount in the range ~rom 2 to 10 atom percent of the
combined amount of nickel and said at least one glass
Eorming additive, said combined amount being greater than
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or equal to 70 atom percent of said contact material,
whereby at least a surface portion of said contact material
is crystallographically disordered at least upon exposure
to an oxidizing ambient.
The addi-tion of one or several glass-forming
elements results in a crystallographically disordered
structure at least upon exposure of the layer to an
oxidizing ambient, this as contrasted with the formation
of crystalline nickel oxide in the absence of preferred
addition of a glass-forming element. Alternatively,
crystallographically disordered structure can be produced
by ion bombardment, alpha particles being conveniently
used for this purpose.
Surface contact resistance less than 100 milliohms
is typically maintained even after prolonged exposure to an
oxidizing ambient.
Brief Descri~tion of the Drawin~
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FIG. 1 is a perspective view of an electrical
connector device in accordance with the invention; and
FIG. 2 is a schematic cross-sectional view of a
portion of a device in accordance with the invention.
Detailed Descr~tion
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The electrical connector device shown in ~IG. 1
comprises housing 11 and contact pins 1~. Housing 11 is
made of an electrically insulating material, and contact
pins 12 have contact surfaces in accordance with the
invention.
Shown in FIG. 2 are, in cross section, an
electrically conducting member 21 on which a surface layer
~2 is situated. In accordance with the invention surface
layer 22 is made of an alloy of nickel and at least one
glass-forming additional element. Upon e~posure to an
oxidizing atmosphere, portion 23 of layer 22 further
comprises oxygen.
Preferred glass-forming additive elements are
boron, silicon, germanium, phosphorus, arsenic, antimonyr
and bismuth, and their presence in the contact layer is in
a preferred amount in the range of from 1 to 40 and
preferably 2 to 10 atom percent relative to the combined
.
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amount of nickel and the additive element; preEerred al.so
in the range of from 25 to 35 a~om percent where
thermodynamically stable, stoichiometric compounds are
formed.
In combination, nickel and the ~lass-forming
additive element or elements constitute a preferred amount
of at least 70 atom percent of the contact layer material.
In the interest of enhanced electrically and mechanical
contact properties, the addition of cobalt is desirable,
elements other than cobalt preferably being limited to
amounts less than S atom percent in combination and
preferably less than 1 atom percent. Particularly
undesirable is the presence of Group VI elements such as
sulfur, selenium, and tellurium, and their combined amount
is preferably limited to less than 0.5 atom percent.
. In the case of non-stoichiometric aggregates,
glass-forming additives to nickel are considered to inhibit
the formation of semiconducting nickel oxide in an
oxidizing ambient. Instead of such semiconducting nickel
oxide, in the presence of the glass-forming additive, a
surface layer of an aggregation including nickel, oxygen~
and the glass-forming additive is believed to be formed in
sufficiently large regions of the layer, such aggregation
having essentially metallic conduction properties. Based
on experimental evidence the thickness of the oxygen-
containing surface layer is estimated to be on the order of
2.5 nm.
Crystallographically disordered structure in
nickel-containing layers is produced also upon ion
bombardment which results in a crystallographically
disordered structure even before exposure to an oxidizing
ambient. Still, it is the disordered, quasi-amorphous,
glass-like nature of an oxidized surface portion which is
considered to be conducive to desired low contact
resistance of a contact laver for use in an oxidizing
ambient. A crystallographically disordered nickel
aggregate preferably comprises nickel in an amount of at
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least 50 atom percent.
The following examples specifically illustrate the
suitability of contacts in accordance with the invention.
Example 1. A layer consisting essentially of 95 atomic
percent nickel and 5 atomic percent antimony was deposited
by getter-sputtering approximately 3 micrometers thick on a
copper substrate. Standard four-point probes were used to
determine surface contact resistance; such resistance was
found to be in the range of from 5 to 7 milliohms. The
deposited film was then subjected to a test for stability
at elevated temperature and humidity ~65 hours at a
temperature of 75 degrees C, relative humidity of 95
percent), and contact resistance was then found to be in
the range of from 15 to 20 milliohms.
Example 2. An experiment was carried out, analogous to
Example 1, on a layer consisting essentially of 95 atomic
percent nickel and 5 atomic percent phosphorus. Contact
resistance was 1.8 milliohm before the test and 4~4 to 5
milliohms after the test.
Example 3. An experiment was carried out, analogous to
Example 1, on a layer consisting essentially of 95 atomic
percent nickel and 5 atomic percent boron. Contact
resistance was in the range of from 2.9 to 3.5 milliohms
before the test and in the range of from 10 to 14 milliohms
after the test.
Example 4. An experimen~ was carried out, analogous to
Example 1, on a layer consisting essentially of 95 atomic
percent nickel and 5 atomic percent silicon. Contact
resistance was in the range of from 1.6 to 2.1 milliohms
before the test and in the range of from 4.5 to 6 milliohms
after the test.
Example 5. An experiment was carried out f analogous to
~xample 1, on a layer consisting essentially of 95 atomic
percent nickel and 5 atomic percent germanium. Con~act
resistance was in the range oE from 1.5 to 1.85 milliohms
before She test and 10 to 14 milliohms af~er the ~es~.
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Example 6. An aqueous solution was prepared containing
208 gm/1 NiC12.6H20, 49 gm/1 H3PO4 85 percent, and
5 gm/1 H3PO3. The solution was used to electroplate
onto a copper electrode; plating bath temperature was 75
degrees C, current density was 150 mA/cm2, and plating
rate was approximately 3 micrometers per minute. The
deposited layer had a thickness of approximately 4,5
micrometers. Contact resistance of the deposited layer was
less than 10 milliohms after exposure to the testing
ambient.
Example 7. An aqueous solution of 0.087 molar of As2Os
and 0.5 molar of NiCl2.6H2O was prepared~ A copper
electrode was plated with nickel arsenide by pulse-plating
from the solution at a temperature of 75 degrees C; current
pulses of 200 mA/cm2 were on for 1.5 seconds and off for
0.5 seconds. Deposited layer thickness was approximately
4.5 micrometers. Contact resistance of the deposited layer
was less than 10 milliohms after exposure to the testiny
ambient.
Example 8. To a solution of 5 gm GeO2 in 50 c~ water
plus 4 cc ammonium hydroxide and 0.5 molar of
NiCl~.6H20, ~50 gm/l ammonium citrate were ~dded~ The
solution was filtered, and ammonium hydroxide ~as added
until pH was 8.5u A layer of nickel-germanium was plated
25 from the solution at a temperature of 75 degrees C onto a
copper electrode; current density was 150 mA/cm2 and
plating rate was approximately 2.5 micrometers per minute.
Deposited layer thickness was approximately 4.5
micrometers. Contact resistance of the deposited layer was
less than 10 milliohms after exposure to the testing
ambient.
Example 9~ A layer o nickel having a thickness of
approximately 350 nm was deposited on a polished copper
foil. A portion oE the nickel layer was covered wi~h an
aluminum foil, and alpha-particles were implanted in the
uncovered portion of the nick~l layer. Alpha-particles had
an energy of approximately 1.8 MeV, and a dose of
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approximately 1.6x1016 particles per cm2 was found to
be optimal or near-optimal for minimized contact
resistance (less than 10 milliohms) after exposure to humid
air at elevated temperature as described in Example 1
above. (This test is considered to be an approximate
equivalent of exposure to ordinary atmospheric conditions
for a duration of 5 years.) Also, visual inspection of the
implanted portion after the test as compared with the
portion which had been covered with aluminum foil, showed
the latter to be dull and brownish while the former
appeared bright and shiny.
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SUPPLEMENTARY DISCLOSURE
Contacts of the invention may receive a final
coating or "Elash" comprising a significant amount of a
coating material such as gold, one or several platinum-
group elements, or gold and one or several platinum-group
elements, the amount being sufficient to impart to the
coated surface the appearance of such coating material.
The structure of such coating may be essentially
homogeneous or layered, and coating thickness typically is
in a range o~ from 0.01 to O.Oi micrometer. For example,
a cobalt-hardened gold coating may be electro-deposited
from a slightly acidic solution (pH 5) comprising
potassium gold cyanide, cobalt citride, and a cltric
buffer. (The presence of cobalt, nominally in a range of
from 0.2 to 0.5 percent by weight, enhances surface
hardness especially in the case of thicker coatings.)
Preferred temperature of the plating bath is approximately
35 degrees C, and a plating current of approximately 5
milliamperes per cm2 is convenient. Typical plating
times are of the order of half a minute Prior to plating,
a surface may be cleaned, e.g., by electrolytic scrubbing
in an alkaline solution, rinsing in de-ioni2ed water, and
dipping in dilute hydrochloric acid at elevated
temperature.
