Note: Descriptions are shown in the official language in which they were submitted.
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The' present invention~relates to compositions for the' electrodeposi~ - .
tion of palladium for a cyanide-free'bath-and to methods of electroplating palladium ' ,- .
using such baths'. .:~
' Various compositions have.been proposed for the' deposition of
. . ~ .
palladium and various electrolytes' have been utilize'd to provide sufficient conduc~
tivity in such compositions. As is true with many of the noble metals, cyanide ' ;~;
electrolytes have enjoyed' considerable commercial application, and it is the ; .'
desire to control pollution problerns which have created' an increasing trend toward
the' substitution of other electrolytes'. . .
` ! ' , .
10 . As is true with many of the' noble metals, small amounts of brighten- '. '
ers are highly de~irable to effect optimum specWar brightness in the electrodepo- ::
sit.: .~lthough some brighteners will produce specular brightness j the:re is ~ome-
times a ten'dency for the' brightener'itself to reduce' the' ductilit~r of the' deposit o:r
to reduce the adhesion to the substrate.
It is an object of the' present invention to provide a novel 'composition ..
for the' electrodeposition of palladium in bright, highly adherent coatings upon
. various types'.of conductive substrates.
It is also an obje¢t to provide such' composition which' is operable over ;
a wide range of :current density and at ambient to low elevated temperatures . ' .
20: Another object is to provide a method'for'the electroplating of palla- .
.... .
dium which: is relatively trouble-free and relatively insensitive to minor variations ~' .
in operating conditions and which'.will produce bright, highly adherent electro-
deposits of palladium. '
It has now been found that the' orégoing and related objec-ts may he ' .,
obtained in an aqueous bath .for the' electroplating of palladium which consists
essentially of 0 . 02-0 . 25' gram mole per liter' oE palladium ion; 0 . 9-3 . 6 'gram moles' .
per'liter of a soluble electrolyte :selectéd' from the' group consisting of alkali metàl
and ammonium sulfates', sulfamates, phosphates, nitrates', nitrites and mixtures'
. ''.
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thereof; and a soluble metallic brightener selected from the group consist-
ing of 0. 002. -0. 04 gram mole per liter of cobalt ion, 0. 004-0. 02 gram
mole per liter of nickel ion and mixtures thereof providing 0. 003-0. 068
gram mole per liter of the metal ions combined. The weight ratio of pal-
ladium to cobalt, when cobalt is present, should be within the range of 10-
50 and preferably 10-33. The weight ratio of palladium to nickel when
nickel is present should be within the range 7. 6-19. 2 and preferably 7. 5-
12. 8. The bath :may contain up to 6xlO gram mole per liter of cetyltri-
methylammonium bromide, and the p~I thereof is adjusted to be within the
range o:E 7. 5-11. 0.
The preferred soluble electrolyte is a ~ulfate saltl and potassium
sulate has becn ~ownd hlghly advantageous. Th~ pr~e:rred compos:lt:lon~
employ cetyltrimethylammonium bromide in an amount of at least 3x10-5
gram mole per liter. The palladium ion is desirably present in the amount
of 0. 05-0.1 gram mole per liter; the ammonium hydroxide is preferably
present in an amount of 1. 4-2.1 gram moles per liter; and the electrolyte
is desirably present in an amount of 0. 2-0. 4 gram mole per liter; this pre-
ferred bath composition is desirably utilized at a pH of 8. 5-9. 5. `
In the method of electroplating, a workpiece having a conductive .;
surface is immersed in the aqueous bath described hereinbe:Eore while the
temperature is maintained at 2680 Centigrade. A potential is applied -;
across the workpiece and anode inert to the bath so as to provide a current
density oE 0. 05-2, 0 amperes per square decimeter, and the anode to cath-
ode surface ratio is maintained at about 1. 0-5. 0:1. 0. A;Eter application of :
the potential Ior a period of time st~ficient to develop the desired thickness
of palladium depo~it, the workpiece is removed :Erom the bath, In barrel
plating, the current density is maintained at about 0. 05-0. 5 amperes per
s~are decimeter and in rack plating the current density is maintained at
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about 0. 2-2. 0 amperes per square decimeter. The preferred baths are -
operated at a temperature of 46-52 Centigrade under conditions of vigorous
agitation. . .
As has been indicated hereinbe~ore, the compositions OI the present
invention essentially comprise an aqueous solution of palladium ion, an . . `
electro-
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3a
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lyte, a brightener selected' from the group consisting of cobalt ion, nickel ion or
the combination thereof, and 'ammonium hydroxide sufficient to provide a pH of
about 7 . 5-11. 0 . A desirable optional additive is cetyltrimethylammonium bro-
mide .
Turning first in detail to the' palladium ion, it may be' introduced' as
any soluble compound having a non-interering anion. Thus, the' palladium may
be introduced as palladiùm sulfate, palladium chloride, palladiùm nitrate, or as a
palladium complex such as di`aminepalladium hydroxide, ' dichlorodiaminepalladi- ;
um or tetraminepalladium chloride.' The'`amount of palladium in the bath may :
broadly range from 0.02' 0.25:gram mole per'liter'and is preferably within
the' range oE 0 . 05-0 .10 gram mole per liter'.
As indicated` hereinbefore, the electrolyte may 'be' providecl `by any
one or mixture o alkali metal: and ammonium suleates, sulfamates, phosp'hate~', ;;
nitrates'and nitrites'. Of the various electrolytes, the' alkali metal and ammonium ~'
sulfates have proven to bé' most advantageously employed'; postassium sulfate
is preferred`. The` concentration of the' electrolyte salt may vary from as little as
O .1 'gram mole per:liter:to as much' as O . 7 'grani mole per liter'. Preferably, the`
concentration of the` electrolyte salt is within the' range of 0 . 2-0. '4 gram mole per
liter .
20' Ammorlium hydroxide is advantageously used' to re~gulate the' pH of
the'bath and is present in an amount of 0.9-3.6 gr'am moles per`liter'calculated' ~
as ammonium hydroxide exclusive of water'. For the` preferred compositions, ; ';
the''ammonium hydroxide is present in an 'amount o-f 1.'4-2.1 gram mole per'liter. `
Dllost desirably, the``ammonium hydroxide i`s added' as a high'ly concentrated ''
aqueous solution 129%' by weight) in order to minimize' dilution, although less
concentrated compositions may also be' `èmployed` if the` water introduced the:rèby
is entered' into the' calculations as to concentration of the` remaining ions .
In the` event that it is desired` to adjust the' pH downwardly (i.e .,
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to make it more acid), an acid having non-interfering anion should be' employed~ ~ -
Most conveniently, thiS is :sulfuric acid, although nitric acid, hydrochloric acid ~ ~ '
and sulfamic acid may be' employed'.
As has been:indicated heretofore, the brightener'is a metal ion se-
lected' from the group consisting of' cobalt, nickel 'and the' combination thereof .
As such, the metal ions may be' introduced in the' form of any soluble compound . .'
which' will not introduce an interfering anion. For the preferred' sulfate baths, ';
these metal ions are introduced' as sulfate salts . However', they' may also be' in-
troduced as chloride or nitrate salts and as complexes.such: as di'aminecobalt '
10' chloride, hex'aminecobalt chloride,:hex'aminecobalt nitrate, aquapentaminecobalt
chloride,'diaquatetraminenickel'nitrate, he'x'aminenickel'nitrate and hexaminenic-
kel 'chloride . ' ' .
When' co'balt is u~ed alone as t'he''brightener', it i~ prosent in an
amount of 0 . 002' 0, 04'. gram mole per liter and preferably 0 . 003-0 . 02 gram mole '.
per'liter . When' nickel is used' alone as the' brightener, it is present in an amount .;
~;~ , o . ~ol/ . o~
F~ ( of o . 00'40 . 0~ \gram mole per' liter' and preferably 0 . 010-0 . 015 gram mole per :
liter'. When' bhe' two metal ions are .used' in combination with .each' other, the' '
total 'amount thereof should provide about 0 . 5-4 . 0 'grams per' liter of metàl ion or -'
~.-.. ..
about 0 . '003 '0 . 068 gram mole per:liter' of lons c'ombined . Preferably ~ the' metal : . -
. . .
ions combined:equal 0.8-2.~'grams per'liter or'about 0.005 0.03'4'gram molè per . .
liter', . .
The' ratio of palladium ion'to :cobalt or nickel ion must be' fairly
closely controlled' in order'to obtain stress-free' deposits . The' weight'ratio of :
palladium to cobalt should adjusted' to .within the' range of 10-50 and preferably
10=33 . The' palladlum to nickel 'metal: welght 'ratio. sho'uld be'. adjusted to within
the' range 7, 5-19'. 2 and preferably 7 . 5-12 . 8 .
Cetylbrimethylammonium bromide is an optional but desirable additive
to e:Efectively eliminate gas pitting in .the' palladium deposit . The 'amount of " ':
this additive should be' closely controlled' since' excessive 'amounts will produce ;
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excessive foaming and interfere with the plating operation, As a result, the'
maximum amount which~ should be' employed' is abo'ut 6x10~4 gram mole per' liter
or 0 . 2 gram per liter. Preferably, the maximum concentration is less than 0 . 06 -''
gram per liter. An amount of as little as 2.7x10-5 gram mole per liter and :;
preferably 8x10~5 gram mole per'liter (0 . Ol' and 0 . '03 gram per liter' respectively) .;
will produce highly advantageous results.
The'pH of the'bath is maintained'within the range of 7.5-ll.0 and
preferably within the' range of 8.5-9.5. As indicated hereinbefore, the' pH may
be adjusted' by the addition of 'ammonium hydroxide or by the' use o~ a suitable ':':
acid providing a non-interfering anion such' as sulfuric acid.
The' temperature of the' bath .should be' within the' range o.E 26-60
Centigrade, and pre:eera'bly 46-52 Cent:igrade.' Although the'bnt:ti may be '
utilize'd without agitation, it is de~irable to employ agitation and vigorous agita- .
tion ha's been Iound extremely beneficial. Filtration i9 highly desirable if
pore-free'.adherent deposits. are t'o be' obtained' because the' presence'of any :
solid contaminants will have a profound effect upon'the' quality of the deposit.
Standard filter cartridges:of polypropylene or other'filter media may clesirably ; .
be:employed'for continuous filtration'of the'bath.' '~
The' anode to cathode :surface:area ratio sho'uld be within the' range
20' . of 1.0-5.0:1.0 and preferably 2.0:1Ø'~ For rack'plating, the' current density .
sho'uld be within the' range of 0.. 2-2 . 0 amperes'per' square decimeter and pref~
erably abo'ut 0.5-l.0'amperes per'square decimeter'. For barrel plating, the cur- .'
rent density should be' within the' range of 0 . 05-0 . 5 'ampere9 per ~quare decimeter
and preferably about 0 . 'l-0 . 3 'amperes: per' square decimeter .
It has been' ound that the' palladium deposits produced b~ the' present .
invention:are relatively stress-free'and can be''employed without further treatment :
for :the' great bulk of 1ntended applications . In some instances:, where the work- "
piece is to be' subjected' to severe mechanical defo~rmation or to heavy wearing ' .
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and abrasion, it is desirable to heat treat the' workpieces at a temperature of:about 30'0-450. Centigrade for '1/2 to :3 hours in order'to relieve all residual '
internal stresses. The heat treatment may be' conducted' either under vacuùm .
or in an inert gas atmosphere.' ' ;`
Various anodes' which: are inert to the plating bath may be employed'
and generally such' anode6' will have: a :surface ' of noble metal, although carbon
anodes do have limited' utility . The' preferred' anodes' are platinum-clad tantalum ' `'''
although gold-clad tantalum, platinum and palladium electrodes'have all been' em-
ployed' effectively. '
10' Exemplary of the'present invention'are the'following specific examples: .
' 'Example' One ' ~ ' '
A bath is prepared by adding to deionized'water'pallaflium ~ul:t`ate su.E- .
ficient to provide 5 . O gr'ams per liter ' as pallaclium metal, 80 c . c . per ' liter '
of ammanium hydroxide (29~6' by weight 'NEI3) ., 1. 05'. grams per liter:co'balt sul:Eate, : .
50 ~rams per'liter'potassium sulfate and 0.04' grams per'liter'cetylbrimethylammo-
nium br'om'ide . ' The' resulting bath has a pH of 8 . 5 'and is introduced' into a plating
cell where .the' temperature is maintained' at 44 . 5. Centigrade. ' '
. A potential: of 1. 7 'volts is applied' across a platinum surfaced anode
and a Hull.cell panel '3 centimeters by 5 centimeters in dimension, the' anode ' .'
20' to cathode surface:area'ratio being 3;1.' The:current density is determined `~
to be' 0 . '5 "amperes'per s(luare decimeter' and the' current is continued for 20' minutes
~during which' there .is fast agitation of the' plating bath .'
The' panel is then: r'emoved' and the' palladium deposit thus formed' is
found to have a thickness of 2 . 5 microns and to be' specular bright.: :E;lexing
of the' panel 'repeatedly indieates'that the' deposit is highly :adherent . .
' Ex'ample` Two
To deionize'd'water:are added'the'various componçnts in 'amounts
sufficient to provide 9. 0 grams per'liter'of palladium determined' as the metal,
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~.Q36534 : i
lOO.c.c. per liter'of ammonium hydroxide ~29%'by weight'NH3)., 2.63 grams per :':
liter'nickel sulfate, lO'0' grams per'liter potassium sulfate and 0..03' gram per
liter cetyltrimethylammonium bromide . ' The' pE of the formulation 'is 7 . 9 and
the' temperature is maintained' at 37'. 8 Centigrade . ' ....
A Hull celI panel is used' as the' cathode and a platinum-surfaced ` '
anode is employed'. A potential of 2 .'2 volts is applied' thereacross during fast
agitation of the' solution'in the' cell . The' anode to cathode surface' area :ratio is . ; ;'
3:'1 andthe'current density.is 0.5'amperes'per'square decimeter'. ' ,'
After plating for 20' minutes, the panel 'is removed' and is found to ., '.
10 . have a specular bright 'palladium deposit of 1. 0 microns thickn'e5s . Ei'lexing
the' panel indicates' the' deposit to he' highly :adherent i .
' Ex'am'ple' Thr'ee ,:
To evaluate the' effe,ct of other'e'lectrolyte~, a mixed electrolyte
is prepared'using 25'grams per'liter:potassium sulfate,'? grams per'liter'ammo~
nium nitrate and 1 gr'am per:liter ammonium chloride.' The'bath contains palla~
dlum sulfate :suffi,cient to provide 5 grams per'liter:of palladium as metal and ,' '"'
60 c . c . .per' liter: ammonium hydroxide (29% by weight NH3), and 0 . 06~ gram per ~''
liter:cetyltrimethyl'ammonium bromide .:: 'Used as the' brightener is 0 . 46 gram per' - ~ '
liter:cobalt :sulfate .: The pH of this fo'r,mulation 'is 9 . 9 'and the bath is introduced '-. -
20. ' into a test barrel plating installation wherein it is maintained' at 49' Centigrade.'
The' workpieces:to be plated' are nickel pins about one centimeter in . ~
len'gth :and about 0:. 5 'millimeters in dïameter'. . The' anode to cathode surface area ' ~ '
ratio i~ calculated' at 1: '1 and a potential, of 5, volts is applied' to provide a cu'rrent .: ;" . ','
. density of 0,.2 amperes:per square decimeter'. The'plating operation is continued ; .
for :a period'of 9.0' minutes'.after which: ~he' parts are remoued' and found to have a ': '
specular bright'.depo~it o:E 2.'5 microns thickness. The' deposit is highly adherent , , '
as evidenced by the' lack: of exfoliation'aEter'ben'ding of the' pins through 90' . ::'.. ', . .
Thus it can be seen: from' the foregoing detailed specification and ex- '` ,' '
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amples that the baths of the present invention :provide bright, highly adherent
electrodeposits on various types of conductive substrates. They are operable -`.
over a wide range of current density :and at ambient to low elevated temperatures,
The plating operation is relatively trouble-free and relatively insensitive to
minor variations in operating conditions and will yield deposits which are sub- .
~tantially ~ree from internal stresses. ~ .
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