Note: Descriptions are shown in the official language in which they were submitted.
PALLADIUM ANn PALLA~IUM ALLOYS
ELECTROPLATING PXOCEDURE
Technical Field
The invention is a process for electroplatin~
palladium and palladium alloys from an aqueous plating
bath.
Backc~round of the Invention
Precious metals are used as protective Eilms on
surfaces for a varie-ty of reasons. In the jewelry trade,
it is used to improve the appearance of an article as in
gold plated jewelry. In other applications, it is used to
protect against corrosion of metals and other surface
materials. In the electrical arts protective films made oE
1~ precious metals are used as conduction paths in electrical
circuits and as contact surfaces in devices with electrical
contacts. Gold is used extensively in these applications
with great success. ~lowever, the increased price of gold
makes it attractive to look at other precious metals as
protective films on various surEaces.
Palladium and palladium alloys are used
extensively in a variety of industrial applications.
Typical examples are the jewelry trade where such films are
used to protect surfaces against corrosion and to improve
appearance, in the electrical arts in various electrical
devices and electronic circuits and in the optical field
for various types of optical devices
Because of chemical inertness and reasonable
hardness, palladium is especially attractive as an
electrical contact material in electrical connectors, relay
contacts, switches, etc. Various palladium alloys such as
palladium-silver, palladium-nickel, and palladium-copper
are also useful for the same applications. Indeed, because
of the increasing cost of gold, palladium and palladium
alloys become more and more attractive economically as a
contact material, surface material, and in other
applications In many applications where gold is now used,
it is often economically attractive to use palladium, pro-
vided an inexpensive and efficient method of plating ductile
and adherent palladium is available.
Highly desirable is a process for plating palladium
from an aqueous solution which is rapid and yields palladium
and palladium~alloy films which are ductile, adherent and
free from hydrogen. Further, it is desirable to have a
palladium electroplating process which does not require sub-
lQ sequent heat treatment to remove hydrogen, improve ductility
or adherence. In many applications, it is desirable that
the palladium plating bath not chemically attack the surface
being plated so that the bath remains uncontaminated during
the plating proçess. Palladium plating processes have been
described in a number of references including U.S. Patent
1,970,950, issued to E. M. Wise on August 21, 1934; U.S.
Patent 1,993,623, issued to A. R. Raper on March 5, 1935;
and U.S. Patent 3,290,234, issued to E. ~. Parker et al
on December 6, 1966. Ethylenediamine has been used in
2Q a palladium alloy plating procedure (U.S.S.R. Patent No~
519,497 issued 30 June 1976); (C.A. 85: 113802m) and it was
known to the inventors that ethylenediamine is useful in
palladium electroplating in the following composition bath:
28 gm/l pdC12, 140 gm/l Na2SO4 ancl sufficient ethylene-
diamine to dissolve the PdC12. The bath is used at roomtemperature, the current density is 20 mA/cm and the pH
between 11 and 12.
Summary of the Invention
According to one aspect of the invention there is
provided a process for electroplating a metallic substance
on a surface, said metallic substance comprising at least
10 mole percent palladium, any remainder being at least one
metal selected from the group consisting of silver, copper
and nickel, comprisin~ the step of passing current through
a cathode, an electroplating bath and an anode with cathode
potential great enough to electroplate palladium, said
~ 2a -
electrochemical bath having a conductivity greater than
10 3 mho~cm and a pH between 7.5 and 13.5, character-
ized in that the electroplating bath comprises an aqueous
solution of palladium-aliphatic polyamine complex in which
the aliphatic polyamine is selected from the group con-
sisting of diaminopropane (including 1,3-diaminopropane),
diethylenetriamine, 1,4-diaminobutane, 1,6-diaminohexane,
N, N, N', N'-tetramethyl-ethylenediamine and 2-hydroxy-1,
3-diaminopropane.
I0 According to another aspect of the invention
there is provided a process for electroplating a metallic
substance on a surface, said metallic substance comprising
palladium, comprising the step of passing current through
a cathode, an electroplating bath and an anode with a
cathode potential great enough to electroplate palladium,
said electrochemical bath having conductivity greater than
10 3 mho-cm and pH between 7.5 and 13.5, characterized
in that the electrochemical bath comprises an aqueous
solution of palladium-aliphatic po:Lyamine complex, said
complex being the same as results irom reactin~ a source
o~ palladium with at least one aliphatic polyamine
selected from the group consisting of diaminopropane
(includin~ 1,3-dlaminopropane), diethylenetriamine, 1,4-
diaminobutane, 1,6-diaminohexane, N, N, N', N'-tetra-
methyl-ethylenediamine and 2-hydroxy-1, 3-diaminopropane.
The invention is a process for electroplating
palladium (both pure metal and alloys with various metals)
from an aqueous plating solution in which the plating
solution comprises palladium in the form of a comple~ ion
and the complexing agent is one or more organic aliphatic
polyamines as defined aboveO
-- 3
The aqueous electroplating bath should be alkaline
(pH greater than 7.0) to avoid corrosion of the surface
being plated and suffieiently conduc~ive to allow plating
(generally greater than 10 3 mho-cm). Additional sub-
stances may be added to the palladium plating bath toeontrol and adjust pH (such as buffer), to increase
conduetivity and to improve the properties of the plated
metal. Typical substances used to improve the plated
metal are laetones (i.e., phenolphthalein, phenolsulfone-
phthalein, etc.), laetams, cyclic sulfate esters, cyclicimides and eyelie oxazolinones~ Certain polyalkoxylated
alkylphenols may also be useful. The proeess is also
useful for plating eertain palladium alloys ineluding 10
mole percent palladium, remainder copper, nickel and/or
lS silver.
Brief Description of the Drawing
The Figure shows a typical apparatus use~ul in
eleetroplating palladium and palladium alloys in
aeeordanee with the invention.
netailed Description
The invention is a proeess for electroplating
palladium metal or palladium alloy in which a certain
class of organie aliphatie polyamines is used as
eomplexing agent in the palladium plating bath. Most
useful are aliphatie polyamines with from three to 20
earbon atoms. Complexing agents with less than three
carbon atoms yield useful results but tend to evaporate
and limit the lifetime of the bath. Complexing agents
with more than 20 earbon atoms usually have limited
solubility in aqueous solutions.
Aromatic poly~mines are also useful but oEten are difficult
to work with (often poisonous with undesirable odor). ~lost
preferred are the complexin~ agents l,3-diaminopropane and
diethylenetriamine because of the excellent quality oF the
palladium plating obtained, especially at high plating
current density (above sn ~SF). In addition, the
conditions (pH, temperature, etc.) under which optimum
platin~ occurs with these preferred complexing a~ents
~ermits rapid plating without incorporation or evolution of
1() l1ydro~en. Also, ~lndesirable chemical attack 011 the surEace
being plated is minimal or insignificant under optimum
conditions of plating with these complexing agentsO
Within the limitations set forth above, the
structure of the complexing agent may vary considerably.
In particular, these complexing agents may contain certain
substituents which do not significantly alter their
complexing properties but may increase solubility~
stability, electrochemical reduction (or oxidâtion)
potential, etc. Typical substituents are hyclroxyl groups,
chloric1e and bromide. The complexing agents should be
stable to the conditiol1s oE the electroplating process and
ir1 particular not undergo oxidation or reduction under the
conditions of the electroplating process. ~or example,
carboxylic acid groups should be avoided because such
substituted aliphatic polyamines are generally not
electrochemically stable. ~lso, the reduction potential is
more noble such that their electrochemical reduction occurs
along with hydrogen.
Often the choice of a particular polyamine
3n complexing agent depends on electrochemical stability. It
is often advantageous to have a reduction potential far
removed from the reduction potential of water so that even
at high plating ratesr hydrogen is not liberated as
palladium is electroplated~
Alloy plating may also be carried out using the
polyamine complexing agent. Typical elements alloyed with
palladium are silver, copper/ nickel, cobalt, iron, gold,
chromium, manganese, ruthenium, rhodium, platinum and
iridium. Particularly useful are copper, nickel and
silver. Preferred are alloys comprising at least 10
mole percent palladium, remain~er copper, silver and/
or nickel. Other use~ul alloys are 60 mole percent
palladium, remainder silver, copper and/or nickel, 40
mole percent palladium, remainder silver, copper and/or
nickel, etc. The palla~ium-sllver alloys are particu~
larly useful, especially for electrical contact surfaces.
A large variety of counter ions (anions) may be
used in the electroplating bath provided the anions are
stable (chemically and electrochemically) and in particular
are not subject to oxidation or reduction under conditions
of the electroplating process. In addition, the anion
should not interfere with the plating process by either
chemical attack on the surface being plated or on the
metal complex system. Typical anions are halides,
nitrates, sul~ates, and phosphates. Chloride ion is
preferred because of the low cost of palladium chloride
and the stability of the chloride ion under conditions
of the electroplating process. Also, certain ions~ in-
cluding those set forth above, may be use~ as supporting
electrolyte to increase conductivity of the electroplat-
ing bath. The cation used for the supporting electrolyte
may be any soluble ion which does not inte~fere with the
electroplating process. Alkali-metal ions (Na, K, Li) are
particularly preferred because of solubility and stability~
Various compounds may be used as a source of
palladium. Palladium chloride is preferred because of
availability and stability. Also, useful are compounds
yielding tetrachloropalladate ion in aqueous solution such
as alkall-metal tetrachloropalladate (i~e., K2PdCl~)o
These compounds may be used initially to make the bath and
to replenish the batnO
Particular advantages of the electroplating bath
using organic aliphatic polyamines as complexing agent are
the improved conditlons of plating which reduce chemical
- 6 -
~ttack on the surface being plated, avold production of
hydrogen even at high plating rates, such as above 215 or
even above 53~ mA/sq. cm (above 200 or even above 500 ASF~
respectively) and improve the quality of plating even at
very hign platlng rates. For example/ the p~ of the ~ath
may vary over large limits, but generally an alkaline
aqueous solutlon is preferred (typically pH from 7.5 to
13.5) with the range from 11.0 to 12.5 most preferred.
The preference particularly applies when the preferred
polyamines are used, namely 1,3-diaminopropane and diethyl-
enetriamlne. Within the pH range, very rapid plating can
be carried out with excellent plating results. Generally,
a bath composition which permits rapid plating with more
alkaline condition is preferred because of decreased
attack on the surface being plated and decreased chances
of hydrogen evolution.
The plating process may be carried out with or
without a buffer system. A buffer system is often pre~
ferred because it maintains consl:ant pH and adds to the
conductivity of the bath. Typical buffer systems are the
phosphate system, borax, bicarbonate, etc. Preferred is
tl)e HPO4 /P4 3 system often made by adding an alkali-
metal hydroxide (KOH, NaOH, etc.) to an aqueous solution
of the hydrogen phosphate ion. Generally, the ooncentra-
tion of buffer varies from about 0.1 Molar to 2 Molar
(about 1.0 + 0.2 Molar preferred) and the mole ratio of
hydrogen phosphate to phosphate varies from 5/1 to 1/5
(with equal mole amounts within ~ 50 percent preferred).
These mole ratios often depend on the particular pH
desired for the plating bath.
The bath temperature may vary over large limits,
typically from the freezing point to the boiling point of
the electroplating bath. Often, the preferred plating
temprature range depends on bath composition and CGncen-
tration, plating cell design7 p~ and plating rateO Pre-
ferred temperatures for typical conditions are from room
temperature to about 80 degrees C with 40 to 60 degrees C
3~l6
mos~ preferred.
Various surfaces may be plated using the
disclosed process. Usually, the plating would be carried
out on a metal surface or alloy surface, but any conducting
surface would appear sufficient. Also, elec~rolessly
plated surfaces may be usefu]. Typical me~al and alloy
surfaces are copper, nickel, gold, platinum, palladium (as,
for example, a surface electrolessly plated Witil palladium
and then electroplated with palladium in accordance with
the invention). Various alloy surfaces may also be used
sucl~ as copper-nickel-tin alloys.
The composition of the bath may vary over large
limits provided it contains a source of palladium and
significant amounts of one or more polyamines of the class
set forth above. In general, sufficient polyamine shoulcl
be present to complex with the palladium. Usually, it is
advantageous if excess polyamine is presel-lt in the bath
solution.
The palladium concentration in the bath typically
2() varies from 0.01 Molar to saturation. Preferred
concentrations often depend on plating rate, cell geometry,
agitation, etc. Typical preferred palladium concentration
ranges for high-s~eed plating (54 to 1076 mA/sq. cm.) [50
to 1000 ASF~ are higher than for low-speed plating (up to
5~ mA/sq. cm.) [up to 50 ASF]. Preferred palladium
concentration ran~es for high-speed plating vary from 0.1
to 1.0 Molar. For low-speed plating, the preferred range
is from 0.05 to 0.2 Molar. Where palladium alloy plating
is included, the alloy metal (usually copperl silver or
3Q nickel) replaces part of the palladium in the composition
of the plating bath. I~p to gO mole percent of palladium
may be replaced by alloy metal.
The amount of complexing agent ~polyamine) may
vary over large limits, typically from 0.5 times (on the
3S basis of molesj the concentration of the palladium species
to saturation of the complexing agent~ Generally, it is
preferred to have excess complexing agent, typically from
two times to 12 times the mole concentration of the
palladium species. Most preferred is abou~ six times the
mole concentration of palladium. The preferred ranges of
comple~ing agent in terms of palladium species are the same
for high-speed and low-speed baths.
The concentration of buffer may vary over large
limits. Such concentrations often depend on cell design,
plating rates, etc. Typically, the buffer concentration
varies from 0.1 ~olar to saturation with from 0.2 to
2.0 Molar preferred.
The bath may be prepared in a variety of ways
well known in the art. A typical preparation procedure
which yields excellent result is set forth below: Equal
volumes (142 mls) of 1,3-diaminopropane and water are mixed
in a beaker. Heat of solution is sufficient to heat the
resulting solution to about 60 degrees C. To this solution
with vigorous stirring are added 50 c~ms of PdC12 in
portions of 0.5 gms every two minut:es. Since the resulting
reaction is exothermic, the solution can be maintained at
60 de~rees C by adjustin~ the rate of acldition of PdC12.
The solution is Eiltered to remove solid matter (generally
undissolved PdC12 or PdO) and dilut.ed to one liter.
To this solution are added 127 gms of K3PO4 and
70 gms of K2HPO4. The pH is 12.3 at 25 degrees C and can
be adjusted upward by the addition o~ KO~I and downward by
the addition of H3PO~.
Electroplating experiments are carried out in an
electroplating cell provided with means for high agitation.
Temperature is maintained between 50 and 65 degrees C,
55 degrees preferred. Current is passed through anode,
electroplating bath and cathode. The electrical energy is
supplied by a conventional power supply. The current
density is 18~ mA/sq. cm. (175 ASF). Typical thicknesses
in these experiments are 10~ to 381~m(40 to
150 microinches). The deposit is crack free as determined
by a scanning electron micrograph at 10,000 magnificationO
Both adherence and duc-tility are excellent. Similar
C~6
results are obtained using 0.1 Molar palladium and
0.5 Molar palladium. Plating rate is often deter~ined by
the thickness desired after a predeter~ined period of
plating. For example, in a strip line plating apparatus
(see, for example, U. S. Patent No. ~,153,523 issued -to
D. E. Koontz and ~ R. Turner on May ~, 1979 and U. S.
Patent No. ~,230,53~ issued to D. R. Turner on October 28,
1980) the strip line being plated is exposed to the plating
solution for a set period of time (depending on the speed
the strip is moving down the line and the length of the
plating cell) and the plating rate is adjusted to give the
desired thickness in this period of time. Similar results
are obtained with diethylenetriamine. Experiments carried
out with 2 hydroxypropanediamine, 1,4-diaminobutane, 1,5-
diaminopentane and 1,6-diaminohexane yield similar results.
Similar results are obtained with low-speed
baths. Here the preparation procedure is exactly the same
except the quantity of reagents are different. ~ typical
bath contains 16.66 gms PdC12, ~2 gms polyamine complexing
2n agent, 42 gms K3PO~, 139 gms K2~PO~ and sufficient water to
malce one liter. The preparation procedure is exactly the
same as above. The pH is about 10.8 at 55 degrees C and
plating is carried out in the temperature range from 50 to
65 degrees C. Typical slow plating rates are about
11 mA/sq. cm. (10 ASF).
Similar experiments were carried out on the
Eollowing bath compositions. In these, in Examples 1 to 7
current densities varied over wide ranges including up to
861 mA/sq. cm. (800 ASF) thicknesses were up to 508~ m (200
microinches), and electroplating was carried out on a
copper substrate.
Æxample 1 13.3 gm/l PdC12, 15.5 gm/l diethylenetriamine
and phosphate buffer. Electroplating was carried out at
55 degrees C.
Example 2 6.67 gm/l PdC12, 12.0 gm/l 1,6-hexadian~ine and
phosphate buffer. Electroplating was carried out at
55 degrees C.
- 10 -
Example 3 6.67 gm/l Pd(NO3)2, 12.0 gm/l 1,5-hexadiamine
and phosphate buffer. Electroplating was carried out at
55 degrees C.
Example 4 12.0 gm/l PdC12, 18.0 gm/l 1,4-butadiamine and
phosphate buffer. Electroplating was carried out at 55
degrees C.
Example 5 0.05 Molar Pd(NO3)2, 0.1 Molar
diethylenetriamine, no buffer, 0.4 Molar i~NO3. The pH was
varied by the addition of KOH from 10 to 14, temperature
~rom 20 degrees C to 70 degrees C.
Example 6 0.1201 Molar Pd(NO )2' 3.2 Molar
diethylenetriamine, 0.5 Molar KNO3, no buffer. The pH was
varied from 12 to 14 ~y additlon of NaOH. Temperature was
about 65 degrees C.
Exa_ ~ 0.02097 Molar PdSO4 2H2O, 0.1 Molar
diethylenetriamine, 0.419 Molar Na2SO~. The p~l range was
varied from 10.2 to 13.5 by addition of NaOH, temperature
varied from 20 degrees C to 70 degrees C.
Example 8 0.052 Molar PdC12, 0.4 Molar l,~-diaminobutane,
-
~() Na2SO~ and NaCl as supporting elect:rolyte, no buffer.
~lectroplated at A6 mA/sq. cm. (~3 ASF) to 351 ~Im tl38
microinches) on copper. Deposit is bright ancl adherent.
Repeat as 70 mA/sq. cm. (65 ASF) to 351 ~m
(138 microinches).
Example 9 0.11 Molar PdSO~ o 2H2O, 0.97 Molar
diethylenetriamine, 1 Molar KNO3 as supporting electrolyte
and NaOH to pH of 12.5. Temperature 65 to 70 degrees C,
high agitation, plated on copper at rates 164, 211, 257,
2~3 and 323 mA/sq. cm. (152, 196, 239, 272 and 300 ASF,
respectively) to a thickness of 351~m (138 microinches).
Excellent brightness and adherence. On adding more
PdSO4 2H2O, went to plating rate of 594 mA/sq. cm.
(552 AS~).
Example 10 Similar to Example 9, but Eor 0.027 Molar
Pd(NO3)2 2H2O, 0.10 Molar 1,3-diaminopropane, no buffer~
pH varied from 11.2 to 13Ø
Example 11 Similar to Example 9, but for 0.054 Molar
Pd(NO3)2 2H2O, 0.2 Molar diethylenetriamine, phosphate
buf~er, p~ adjusted to 13 with NaOH, temperature of
55 degrees C. Electroplated on Pt, Pcl and Au.
Example 12 0.282 Molar PdC12, 0.7 Molar 1,3-
diaminopropane, 75 gm/l Na2SO4 supporting electrolyte,12.5 gm/l K2HPO4 buffer. Electroplated on both gold and
copper surfaces at 60 to 65 degrees C, pH of 12.5 at 161,
215, 269, 323, 431 and 538 mA/sq. cm. (150, 200, 250l 300,
400 ancl 500 ASF, respectively). All deposits were adherent
ln and bright to semibriyht.
Example 13 Similar to Example 12, but Eor 10 gm/l
Pd(NO3)2 2H2O, 5 gm/l 1,3-diaminopropane.
Example 14 60 gm/l PdC12, 75.2 gm/l 1,3-diaminopropane,
17S gm/l 1~2HPO~, pH adjusted with NaOH to pH of 11~0,
temperature oE 65 to 7(~ degrees C. Electroplated at rates
of 161, 215, 323, ~31, 538, 6~6, 753, 861, 969 and
1076 mA/sq. cm. (150, 200, 300, 400, 500, 600, 700, 800,
900 and 1000 ASF, respectively).
Exalnple 15 Same as in Example 14 except 100 gm/l K3PO~
2~ s~ead o~ K2HPO4) and the pH was 11.~.
~xample 1~ Same as in Example 14, but pH was 12.~, plating
rate 161 mA/sq. cm. (150 ASF).
Example 17 127.5 gm/l PdC12, 214 ~m/l 1,3-diamine propane,
104.5 gm/l K2HPO4, 84.9 gm/l K3PO~, initial pH was 11.7 at
25 deyrees C, adjust with NaOH to 12.0 at 25 degrees C.
~lectroplated at 60 to 65 degrees at 54, 161, 269 and 538
mA~sq. cm. (50, 150, 250 and 500 ASF, respectively).
Palladiurn alloys may also be electroplated in
accordance with the invention. A typical bath composition
for palladium alloy plating is as follows: 69.6 gms Ag2O,
53.2 gms PdC12, 222 gms 1,3-diaminopropane, 106.2 gms
K3PO4, 86.5 gms K2HPO4 and water to one liter. The pH of
the bath is adjusted to 11.3 by the addition of KOH or
H3PO4. The bath temperature is maintained between 40 and
65 degrees C and current density between 1.1 and 538 mA/sq.
cm. (1 and 500 ASF). The other polyamine complexing
- 12 -
acJents mentioned above are also useful, including
diethylenetriamine. A useEul bath for palladium-niclcel
plating is as follows: 3~.9 gms NiCl~, 53u2 gms PdCl2,
222 gms 1,3-diaminopropane, lOh gms 1~3P04, 8~.5 gms K2HPO~
and water to one liter. Preferred operating temperature is
from 40 to 65 degrees C, pH is about 12 and current density
from 1.1 to 538 mA/sq. cm (1 to 500 ASF). ~xperiments were
also dcne with cobalt salt added to the bath.
The stripline plating apparatus deseribed in the
above-cited patents are particularly advantageous for
carrying out the process. They permit good control of the
bath conditions, the rate of plating and permit rapid
palladium plating. The palladium plating proeess is highly
advanta~eous for plating eleetrieal eontact pins for
electrieal conneetors sueh as described in the above
re~erenees.
FIG. 1 shows apparatus 10 useful in the praetiee
_.
of the invention. The surfaee to be plated 11 is made the
eathode in the eleetrolytie proeess. The anode 12 is
2n eonveniently ~ade of platinized titanium or may be made of
various other materials sueh as oxides of platinum (~roup
metals, binder metal oxides, ete. Both anode and cathode
are at least partially immersed in the electroplating
bath 13 containing souree of pallaclium eomplex with an
or~anie aliphatie polyamine. A eontainer 14 is used to
hold the palladium plating solution and the anode 12 ancl
eathode ll are eleetrically eonneeted to an adjustable
source of electrical energy 15. .~n ammeter 16 and
voltmeter 17 are used to monitor current and voltage.
