Note: Descriptions are shown in the official language in which they were submitted.
3~
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NIC~EL~UA'ED EIECTRICAL CONT~CT DEVICE
T_chn~cal_Fleld
The in~ention is conceLnecl with devices havlnq
an electrically conducting member havirlg electrical
contact surface of nickel-based materials.
B__k~___n__of__he_I_yent__n
T~pically, the manufacture of high-quality
electrical contacts has involved the usa~e of gold whose
properties of low contact resistance and high chemical
stability are key advantages in such usage. However, as
the price of gold rematns hiyh, efforts continue at
finding alternative materials for contact manufacture.
Prominent among such alternatives are precious metals
other than gold; e~g., silver-palladium alloys have been
found suita~le for certain applications.
While such alternate alloys are less expensive
than gold, still further cost reduction is desired, and
nonPreCiouS metal alloys such as, e.g., copper~nickel
alloys have been investigated for contact resistance and
stability over time. See S, M. Garte et al., "Contact
Properties of Nickel-Containing Alloys", Elec_rica
Contacts, 1972, Illinois Institute of Technology.
SummaEy_of_the_Inv_n_i__
It has been discovered that a material
consisting essentially of nickel and a controlled amount
of hydrogen has contact pro~erties comparable to those of
gold such as, in particular, low and stable contact
resistance. ~referred amounts of hydrogen in nickel are
regarded to be such as to associate atoms of hydrogen with
nickel atoms on dislocations, thus blocking oxidation at
critical sites. Typically, surface contact resistance of
the material is significantly less than 100 milliohms even
after prolonged exposure to an oxidizing ambient.
q~
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In accordance with an aspect oE the invention
there is provided a device compr;sing an electrically
conducting member having a contact surface, said contact
surface being the surface of a surface region oE said
member, said surface region consisting of a contact
material, an amount of at least 70 atom percent of said
contact material consists of nickel and hydrogen, and
hydrogen being present in said amount in a significant
small percentage so as to enhance an electrical contact
property of said contact surface.
In accordance with another aspect of the
invention there is provided a method for making an
electrically conducting member in a device, said method
comprising a step of providing said member with a surface
which is the surface of a contact material comprising an
amount of at least 70 atom percent of nickel and hydrogen,
and hydrogen being present in said amount in a significant
small percentage so as to enhance an electrical contact
property of said contact surface.
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Br-ef-Des~ o~-of the_DraWlng
FIG. 1 is a perspective view of an electricaL
connector deYlce ln accordance with the invention; and
FIG. 2 is a schema-tic cross-sectional vie~ oE a
portion of a device in accordance with the invention.
Detailed D_s__ipti__
The electrical connector device showr, in FIG. 1
comprises housing 11 and contact pins 12. Housing 11 is
made of an elec~rically insulatirg material, and contact
pins 12 have contact surfaces in accordance with the
illV ention.
Sho~n in EIG. 2 are, in cross section, an
electrically conducting member 21 on ~hich layer 22 is
situated. Member 2~ may consist of a copper conductor
material~ and s~lrface layer 22 is a nic~el material which
comprises hydrogen at least in a surface region 23. The
incorporation of controlled amounts of hydrogen into
nickel material results in enhanced contact properties
such as low contact resis-tance and long-term stability of
such resistance~
Hydrogen may be incorporated in a nickel
material in a variety of ways such as, e.g., in the course
of electroplating, by sputtering in an argon-hydrogen
atmosphere, and by indiffusion at a bulk surface which,
preferably, has been subiected to Plastic deformation by
cold working. Preferred concentrations of hydrogen depend
on conditions under which layers or bodies of nickel are
produced and processed, and it is postulated thal
preferred concentrations increase in direct relationship
with the number of nickel atoms on dislocations. In
particular, greater amounts of hydrogen are beneficial for
cold worked material, preferred amounts being directly
related to level of cold working. In the case of
electrodeposited laYers, preferred amounts are in the
range of from 0.0004 to 0.0009 atom concentration of
h~drogen in nickel; when severe cold work is applied u~ to
0.01 atom concen-tration is preferred.
Fortuitously, as dislocation slip bands produced
by cold workin~ also -facilitate indifEusion of hydrogen,
contact properties of cold-worked bulk nickel materlal are
most favorably affectecl by hYdrogen indiffusion.
Accordingly, applications are preferred in which nickeL
mateLial is ~lasticallY defornned by a significant amount,
such as, e.g., corresponding to at least 50 percent
reduction of cross-sectional area prior to hydrogen
diffusion, the latter being carried out at a temperature
which is less than the recrystallization temperature of
Ni. H~drogen indiffusion is tYPicallY e-ffected over a
time of a few minutes, and indiffusion is facilitated by
heating at a temperature belo~ the recrYstallization
temperature of Ni. Among applications of cold-worked
material are those involving the use of microscopic flakes
dispersed or embedded in a non-conductive matrix material
as, e.g., in electrically conducting in]cs, pastes, and
adhesives.
Conveniently, hydrogen can be incorporated in
nickel layers b~ electroplating out of a suitable nickel
bath, solutions of nickel salts being considered most
suitable where the anion is but weakly oxidizing.
~ hile a contact material of the invention may be
free or essentially free of elements ot~er than nickel and
hydrogen, impurities may be present and additional
elements maY be included such as, e~g., boron, silicon,
germanium~ phosphorus, arsenic~ ant:Lmony, or bismuth.
When present in solid solution or~ in other words, when
incorporated in the nickel structure, impurities and
additives ars considered not to interfere with the
beneficial effect of hydrogen in nickelO Amounts of at
least 70 atom percent nickel~hYdrogen are preferred in the
contact material.
Contacts of the invention may receive a final
coating of "flash" comprising a significant amount of a
coating material such as gold, one or several platinum-
group elements, or ~old and one or several Platinum-group
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elements, the amount being sufficierlt to impart to -the
coated surface the appearance of such coating material.
The structure of such coatinca may be essentiall~
homogeneous oE la~ered, and coating -thickness typically is
ln a range from 0.01 to 0.05 micrometer~ For example, a
cobalt-hardened gold coating maY be electro-dePosited ~rom
a sli(Jhtly acidic solution (pH 5) comprisin~ ~otassium
gold cyanide, cobalt citride, and a citric buffer. (The
presence of cobalt, nominally in a range of from 0.2 to
0.5 percent by weiyht, enhances surface hardness
especially in the case of thicker coatings.) Preferred
temperature of the p;ating bath is approximately 35
degrees C, and a platin~ current of approximately
5 milliarnperes per cm~ 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-ionized
~ater, and dipping in dilute hydrochloric acid at elevated
temperature.
Examv~ layer having a thickness of approximately
1.68 micrometer and havinç approximatel~r 0.005 atom
concentration of hydrogen in nickel l~as deposited on a
copper substrate by sput-tering from an essentially ~ure
nickel target in an atmosphere of approximately 10 percent
by volume hYdro~en, remainder essent:Lally argon. The
layer was exposed to atmospheric test conditions at
75 de~rees C and 95 percent relative humiditY for
65 hours. After such exposure contact resistance was
determined to be in the range of from 7 to 10 milliohms.
30 Example 27 A layer having a thickness of approximately
0.4~ micrometer ~as deposited as further described in
Example 1 above, Ultimate contact resistance ~as in the
range of from 10 to 13 milliohms.
Example_3. A layer having a thickness of approximately
4.5 micrometers was de~osited on a copper substrate by
electroplatin~ from a 2~molar nickel chloride solution at
a temperature of appcoximately 75 degrees C, ~H of the
- ~,
solution uas ap~roximately 3 as obtainecl hy the addition
of amlnoni.uln hydroxide, and current clensi-ty during
deposition was approxi.mately 150 milliarnperes/cln2. The
layer was exposecl to a~mos~heI:ic test cond.itions as
described in Examrle 1 above, and contact resistance was
determined to be in the range of from 1 to 10 milliohms.
Exam~1e_4~ A layer ~as deposited as described in
Exalnple 3 a~ove except that a 2-molar nickel citrate
solution was used at a pH of approximately 60 Contact
resistance of the laYer was found to be in the range of
from 0O8 to 10 milliohms.
Example 5. A layer was deposited as described in
Example 3 above except that a 1/2-molar nickel acet.ate
solution was used at a pH of approximately 8. Contact
resistance of the layer was in the range of from 2 to
15 milliohms.
