CA1163952A - Palladium electrodeposition compositions and methods - Google Patents
Palladium electrodeposition compositions and methodsInfo
- Publication number
- CA1163952A CA1163952A CA000340923A CA340923A CA1163952A CA 1163952 A CA1163952 A CA 1163952A CA 000340923 A CA000340923 A CA 000340923A CA 340923 A CA340923 A CA 340923A CA 1163952 A CA1163952 A CA 1163952A
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- Prior art keywords
- palladium
- bath
- nitrite
- ions
- compound
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electroplating And Plating Baths Therefor (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Compositions and processes for electrodepositing metallic palladium on surfaces at substantially constant bath efficiencies for prolonged periods are described. The composi-tions comprise a source of palladium ions such as a water soluble palladium compound and a source of free nitrite ions in stoichiometric excess relative to the palladium. These can be used to prepare articles coated with adherent layers of metallic palladium.
Compositions and processes for electrodepositing metallic palladium on surfaces at substantially constant bath efficiencies for prolonged periods are described. The composi-tions comprise a source of palladium ions such as a water soluble palladium compound and a source of free nitrite ions in stoichiometric excess relative to the palladium. These can be used to prepare articles coated with adherent layers of metallic palladium.
Description
~39~2 17 ,l ~ FIELD O~ THE I~VE~TION
19 11 l 20 1I This invention relates to the electrodeposition of 21 'I palladium on substrates, and more particularly, to the achieve-22 1I ment of palladium electrodeposition baths having stabilized 23 ll bath efficiencies, 2l, "
25 I BACKG~G~ 3 OF THE I~tVE~TIG~
26!', 27 ¦I Processes for electrodepositing metal in varlous 28 '' ~nicknesses on subs~rates, also sometimes referred to as 29l eleccrolytic deposition and electroplating, are well kno~l in 30~" the metallizing art. T~?ically, a deposition bath comprising ions of the metal to be deposited and a suitable electrolyte is provided, the article or object to be plated is immersed in or otherwise contacted with the bath while connected as the cathode to an external current source, and a metal electrode is connected as the anode to the same current source. During operation, ions of the metal to be deposited are reduced in the bath to zero valent metal which plates out on the workpiece surface.
Special mention is made of methods for electro-depositing metallic palladium on substrates, particularlymetallic surfaces. In such cases, the palladium deposition bath tends to be unstable and cannot be used continuously for extended periods without undergoing significant losses in bath efficiency. The term "bath efficiency" herein refers to the comparison at a given current density between the actual bath plating rate and the theoretical bath plating rate as deter-mined mathematically from Faraday'S Law.
Without wishing to be bound by any theory, it is believed that the palladium ions in the bath are oxidized to higher valence states during operation, thus making it more difficult to reduce the palladium ions to metallic palladium and plate out without supplying more current to the bath.
Although conventional palladium electrodeposition baths may display good efficiency initially and shortly after plating has begun, this efficiency often decreases sharply within a few hours, and in some cases dropping off to less than 50% of the original value after only about twenty-four hours li .
~ ~ 63952 IC-L ¦¦
of continuous use. To maintain the palladium plating rate at
19 11 l 20 1I This invention relates to the electrodeposition of 21 'I palladium on substrates, and more particularly, to the achieve-22 1I ment of palladium electrodeposition baths having stabilized 23 ll bath efficiencies, 2l, "
25 I BACKG~G~ 3 OF THE I~tVE~TIG~
26!', 27 ¦I Processes for electrodepositing metal in varlous 28 '' ~nicknesses on subs~rates, also sometimes referred to as 29l eleccrolytic deposition and electroplating, are well kno~l in 30~" the metallizing art. T~?ically, a deposition bath comprising ions of the metal to be deposited and a suitable electrolyte is provided, the article or object to be plated is immersed in or otherwise contacted with the bath while connected as the cathode to an external current source, and a metal electrode is connected as the anode to the same current source. During operation, ions of the metal to be deposited are reduced in the bath to zero valent metal which plates out on the workpiece surface.
Special mention is made of methods for electro-depositing metallic palladium on substrates, particularlymetallic surfaces. In such cases, the palladium deposition bath tends to be unstable and cannot be used continuously for extended periods without undergoing significant losses in bath efficiency. The term "bath efficiency" herein refers to the comparison at a given current density between the actual bath plating rate and the theoretical bath plating rate as deter-mined mathematically from Faraday'S Law.
Without wishing to be bound by any theory, it is believed that the palladium ions in the bath are oxidized to higher valence states during operation, thus making it more difficult to reduce the palladium ions to metallic palladium and plate out without supplying more current to the bath.
Although conventional palladium electrodeposition baths may display good efficiency initially and shortly after plating has begun, this efficiency often decreases sharply within a few hours, and in some cases dropping off to less than 50% of the original value after only about twenty-four hours li .
~ ~ 63952 IC-L ¦¦
of continuous use. To maintain the palladium plating rate at
2 Ilor reasonably near original levels, it is usually necessary to
3 iI su??Ly ~o~e curren~ to the plating bath, a costly procedure.
4 '.
' OBJECTS OF TH~ I~VE~ITION
, ~ i 7 !~ It is an object of this invention to provide composi-8 'iI tions which, when subjected to electrodeposition techniques, g 11 are capable of depositing metallic palladium at substantially 10 I~ constant bath efficiencies for extended periods of use. ,`
12 !i It is another obJect of this invention to provide `I
3 !j compositions ~or replenishing palladium electrodeposition baths ~`14 Ij which also serve to maintain the bath at substantially constant 15 ~¦ bath efficiencies.
17 ii It is a further object of this invention to provide 18 ~l improved methods for electrodepositing metallic palladium from 9 1! an aqueous deposition bath.
20 i' 1 li These and other objects which will be apparent from 22 ¦~ the following description are achieved by pracSice of the in~
: ~ 23 ,,l ven.ion now desc,ibe1.
; 25 i~ S~f~RY OF THE I~VE~TION ;~
26 1, i 27 lll The compositions of the invention, briefly describéd, 28 ~, com?rise a water soluble palladium compound capable of dissociat-29 ', ing in wa~er to provide palladium ions, an electrolyte compound , 30 li and a source of free nitrite ions in an amount ca?able of pro~
,~ :1,i , I
1, I
- 1, : I
3 - : ~
!, 1 l, viding a stoichiometric excess of the nitrite ions relative to 2 1, the ?alladium ions.
3 ,`
The ingredi-nts may be mixed together to form a sale- ¦
~ a~ile arti~le of commerce which is then.added ,~o water with the 6 ,I pH adjusted to be above 7~ or the ingredients may be added 7 ~ separa~ely tO water ~o form tne bath. .
8 ,' 9 Ij The foregoing compositions are capable, when subjected 10 'i to electrolytic deposition techniques, of depositing metallic 1, 11 1! palladium on a substrate for prolonged periods without the ii ~ j 12 Ij need to adjust the current upwards to maintain the pla-ting rate.
13 1' 14 !', This invention also provides compositions useful in 15 l~ replenishing the palladium bath and helping to maintain bath 16 ,' efficiency over extended periods. Such compositions comprise j 17 1 an admi:~ture, without an electrolyte, of a water soluble palladium 18 "~ compound and a water soluble nit.ite compound, the latter being 19 i, present in an amo~mt sufficient to provide an excess of nitrite ~20 ' ions relative -to the palladium ions in the mi~ture when dissolved 21 ~ in water.
2~ '~, 4 23 ' Another aspect of this invention provides an improved 24 .I method of electrodepositin~ palladium rom a bath comprising an 25 . aqueous soLution of a palladium compound, preerably a palladium 26 ~ (II) compound, comprising maintaining in the bath an'e~cess of 27 free nitrite ions relative to the palladium ions and thus 28 stabilizing the bath eficiency.
29 `
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..
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.. ...
~ ~ 63~52 DETAILED DESCRIPTION OF THE INVENTIO~
Because bath efficiency will begin to fall off almost as soon as the bath begins to be operated, it is important that an excess of free nitrite ions be present in the bath at the outset and maintained in the bath throughout the plating cycle.
A water soluble palladium compound such as palladium diamine dinitrite, suitable as a source of palladium ions in the bath, while containing nitrite does not serve as a source of "free"
nitrite because the nitrite remains complexed even after the compound is dissolved in the bath. Thus, it is necessary to include initially in the bath some other nitrite compound which is capable of dissociating in water to provide free, i.e., uncomplexed, nitrite ions.
Preferably, the source of free nitrite ions is a water soluble inorganic nitrite compound, and especially preferably an alkali metal nitrite, such as sodium nitrite, potassium nitrite, or the like and ammonium nitrite.
A small excess of nitrite ions is sufficient to maintain bath stability, usually at least about 0.05% by weight relative to the palladium ions in the bath. In most cases, the bath is formulated to provide an excess of free nitrite ions, initially, of from about 0.1 to about 50% by weight, relative to the palladium ions in the bath.
It is to be noted that, as the bath is operated and palladium is consumed by plating out, some of the free nitrite ions in the bath simultaneously undergo oxidation to the nitrate !j ~ 39~2 l, 1 jl for~. Thus, even if a large excess is provided in the bath 2 l~ iniLially, the free nitrite will eventually exhaust itself as f e ~n~ s ~ /i o~ c f/~
3 1I the bath i~ opcrat_~. To ensure that an excess of free nitrite 4 ¦1 is maintained throughout plating, fresh amounts of the free ¦I nit.i.e source should be added to the bath from time to time.
6 ~l' A con~-enient wa~J o~ doing thls is to add the nitrite compound 7 1l to the bath with each periodic addition of the palladium compou~d 8 j, used to replenish the palladium consumed. As a general rule, 9 ¦! in each case the nitrite compound is added in an amount sufficien~
10 ¦I to provide at least about a 10% by weight e~cess of nitrite ions ~ relati~re to the palladium ions provided by the palladium compound.
12 ~ ` .
13 I The palladium is ~supplied to the bath, lnitially and 14 upon replenishment, preferably in the form o a water soluble ~ organic or inorganic palladium ~II) compound selected from among ~16 I materlals conventionally employed for such purposes in palladium ii 17 ¦ electrodeposition baths. E~amples include palladium diamine ~;~
18 I dinitrite [Pd(~H3~2(NO2)2~, palladium chlorlde (PdC12), palladium 19 I sulfate, palladosamine chloride, diamine palladium hydroxide, 20 Ij tet~amine palladium chloride and dichlorodiamine pa~ladium 21 1l chloride. Among these, palladium diamine dinitrite and palladium~
22 lll chloride are especially preferred for use in this inventlon.
23 1'~
~! The electrolyte for the bath may be any water soluble 25 ,I compound capable of dissolving in water to form an electrically 26 1', conductive ionic medium. These may be selected from among 27 'l, the con~entional materials. In the usual case, this is a water 28 !I soluble nitrate compound, and preferably ammoni~ nitrate or .
29 ¦. an alkali metal nitrate, e.g., potassium nitrate or sodillm 30 i! nitrate.
i'i !
~ I - 6 -~ ~ 639~
The ingredients of the compositions according to this invention may be present in a wide range of amounts. Preferably, however, prior to addition to water the compositions comprise an admixture as follows:
Ingredients Amount, parts by weight Water soluble palladium (II) compound, preferably palladium diamine dinitrite or palladium chloride 30-40 Water soluble electrolyte compound, preferably alkali metal nitrate or ammonium nitrate 65-75 Water soluble source of free nitrite, preferably alkali metal nitrite 5-15 These may be formulated into a palladium deposition bath having the following preferred ranges and which are operated under the following conditions:
Inqredients Amount, grams per liter Water soluble palladium (II) compound, preferably palladium diamine dinitrite or palladium chloride 40-60 grams per liter Water soluble electrolyte compound, preferably alkali metal nitrate or ammonium nitrate 85-95 grams per liter Water soluble source of free nitrite, preferably alkali metal nitrite 5-15 grams per liter Water to make 1 liter Temperature 50-70 C~
pH 8-9 Current density 1-500 amperes per square foot !l I
6 3 9 ~ 2 l ¦I The bath pH may be adjusted before and/or during 2 i~ operation in t;le usual manner such as by addition OL- suitable 3 i, amounts o' an acid, e.g., nitric acid, or a base, e.g., 4 Ij am~onium hydroxide.
!
~ , I
6 Other ingredients may also be included in the composi- , 7 ~ ior ~neir conven~ionaîly employed purposes. ~y way o~j 8 1! illustration, such materials include brightening agents, g 1I wetting a~7ents or surfactants, comple~ing agents for palladium 10 j ions, ant:ioxidants, etc., all of which are well kno~.~n to those 11 ¦ skilled in the art. 1 12 I i 13 I In carrying out the electrodeposition process of the 4 ¦~ invention, the bath may be operated over a wide range of tempera-15 1I tures, such as from room temperature, e.g., 25C., almost up to 16 ¦i but below the ~oiling poin~ of the bath, e.g., 100C.
17 ~
18 1~ Plating times will vary, depending on factors such 9 1! as the supplied current densi~y, bat'n temperature and palladium ~¦
20 li deposit thickness desired. For the particular current density I
21 ¦1 and tem~erature-ran~es indicated above, i.e., 1-500 amps per ~¦
22 1i square foot and 50-70C., a plating period of about lO minutes ~ j or less i:, usually sufficient to yield a palladium deposit ~ ¦
24 ~' thickness of about one thousandth of an inch.~ ~ ¦
25 ~
26 l~ By this invention, metallic palladium is deposited ~ I o h C~ S
27 1 ~ a metallic substrate~ substantially smootl~, bright and -28 l adherent 12yers. Examples of metal surfaces on which palladium 29 ! ma~J be deposited include copper, nickel, silver and steel, 30 1 as well a~ alloys of these such as brass, bronze, ~tainless ,i ~ - 8 - I
- . . : .. .. . ~ ... . . ..
~ ~ 63952 steel or the like.
By practice in accordance with this invention, bath efficiencies of greater than 90% are provided and efficiencies of from 80 to 95% are typical even when the baths are operated over extended periods. Additionally, it is found that these high bath efficiencies are obtainecl when operating the baths at high current densities of 300 - 350 amps per square foot.
Moreover, even at current densities as high as 450 - 500 amps per square foot, bath efficiencies of 60 - 70% are still obtained.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
-The invention is illustrated further in the following examples:
A small piece o~ flat copper is pretreated to remove any surface dirt and grease, pre-weighed and immersed in a palladium electrodeposition bath having the following com-posltlon:
Palladium diamino dinitrite, Pd(NH3)2(No2)2 50 grams/liter Ammonium nitrate, NH4NO3 90 grams/liter Sodium nitrite, NaNO2 10 grams/liter Water (to make 1 liter) A piece of platinized tantalum/titanium is immersedin the bath and connected as the anode to the positive side of a D.C. power supply unit. The copper piece is connected as the cathode to the negative supply of the D.C. power supply, and plating begins.
_ g _ J~ 1 6 3 9 5 2 1 l¦ The bath has an initial weight ratio of nitrite ions 2 1. to palladium ions of 1.5:1. The initial bath pH is between 3 il 8 and 9. The temperature of the ba.h is adjusted to and main- i ; 4 1~ tained at 70C.
6 il The current supply is regulated to deposit palladium 7 j, ac a current aensity of 1~ amperes per square foot. At this 8 ¦! current density, metallic palladium plates out on the surface 9 1l of the copper workpiece at a rate of 30 milligrams per ampere-j minute.
11 .
12 From time to time, the bath is replenished by adding 13 more palladium diamine dinitrite in amounts so as to maintain 14 I the initial palladium concentration in the bath. Upon each ¦ addition of the palladium compound, the sodium ni~rite is 16 1 also added in an amount providing a 10% e~cess of the nitrite I ion relative to the palladium ion of the diamine dinitrite I ~ 18 I compound.
19 I : I
20 l¦ A palladium deposit having a thickness of about 0.001 21 !jl, inch is ol~tained after about six minutes of operation. As 22 ¦ computed from the known current density, plati~ng time and 23 ¦ palladium deposit thickness, the bath efficiency is found to be 24 I g5%.
25 i 26 il Thereafter, plating is resumed and the consumable 27 ¦I bath ingredients are periodically replaced in the bath in the 28 " manner previously described. In this way, the bath is operated 29 ¦~ continuously for several days with bath efficiency being main-30 ¦¦ tained at or near 95%.
, .
~1 10- I
' . .. . . . .
i 1 63952 1 ! E~A~PLE 2 2 i For purposes of comparision, the plating procedure of 3 , E~ample 1 is repeated e~cept that fresh amounts of the nitrite 4 , compound are not added to the bath after operation has begun. It S j is observed that the bath efficiency begins to fall off after 6 !I several hours and the amount of palladium being deposited 7 !~ decreases significan-ly.
9 jj E~A~IPLE 3 ~I
¦¦ A plating bath was made up ~ith the following composi- ¦
tion and concentrations in accordance ~ith E~ample I of U.S.
12 I Patent 4,092,225:
13 10 g/l Pd 14 150 g/l Potassium Pyrophosphate 15 I 130F Temperature 16 pH=9 adjusted by pyrophosphate or potassium hydroxide 17 This bath ~as used to rack plate copper coupons ~ith 18 good mechanical agitation at several different current densities 19 ~1 and the follo~ring results were obtained:
2 0 i¦ TABLE A
21 1I Current Density Bath Efficiency 22 (am~ ~er square foot) ~%) ' l ~
2~ 10 94 94 ' 26 ~0 94 28 ~ By comparision, the procedure of E~ample 1 was repeated 29 11 at several different current densities and the follo~.~ing resul~s ¦ ~ere obtained I
~ 1 1 639~2 1 ., TABLE B
.. , i 2 .... ... Current Density Bath Efficiency 3 1 (Amps rer Square Foot) (%) 25. 97 6 ! 50 97 7 ., ` 100 94 .
8 , 200 86 g j~ 300 80 11 i, 400 73 12 ! 450 67 . I
13 ,j 500 60 14 iI From the above, it is apparent that not only does the l, composition and method of the present invention provide high 16 1 bath efficiencles over prolonged periods of operation, but 17 l additionally, the current density at which such efficiences are 18 l obtained is e~tended at least seven fold as compared with prior 19 1 art baths and processes. .
I
~1 Other modifications and variations of the invention 21 1~ will suggest themselves to those skilled in the art in view of Z2 ¦¦ the desc~iption. It is to be understood, therefore, that 1:
23 1l changes may be made in the specific emobidments described wi~hout~
~24 1I departing from the scope and principles of the invention as defined in ~he appended claims, and without sacrificing its chief 26 ~ advan ~ges.
~1 1~ 1 ~ ~' .
' OBJECTS OF TH~ I~VE~ITION
, ~ i 7 !~ It is an object of this invention to provide composi-8 'iI tions which, when subjected to electrodeposition techniques, g 11 are capable of depositing metallic palladium at substantially 10 I~ constant bath efficiencies for extended periods of use. ,`
12 !i It is another obJect of this invention to provide `I
3 !j compositions ~or replenishing palladium electrodeposition baths ~`14 Ij which also serve to maintain the bath at substantially constant 15 ~¦ bath efficiencies.
17 ii It is a further object of this invention to provide 18 ~l improved methods for electrodepositing metallic palladium from 9 1! an aqueous deposition bath.
20 i' 1 li These and other objects which will be apparent from 22 ¦~ the following description are achieved by pracSice of the in~
: ~ 23 ,,l ven.ion now desc,ibe1.
; 25 i~ S~f~RY OF THE I~VE~TION ;~
26 1, i 27 lll The compositions of the invention, briefly describéd, 28 ~, com?rise a water soluble palladium compound capable of dissociat-29 ', ing in wa~er to provide palladium ions, an electrolyte compound , 30 li and a source of free nitrite ions in an amount ca?able of pro~
,~ :1,i , I
1, I
- 1, : I
3 - : ~
!, 1 l, viding a stoichiometric excess of the nitrite ions relative to 2 1, the ?alladium ions.
3 ,`
The ingredi-nts may be mixed together to form a sale- ¦
~ a~ile arti~le of commerce which is then.added ,~o water with the 6 ,I pH adjusted to be above 7~ or the ingredients may be added 7 ~ separa~ely tO water ~o form tne bath. .
8 ,' 9 Ij The foregoing compositions are capable, when subjected 10 'i to electrolytic deposition techniques, of depositing metallic 1, 11 1! palladium on a substrate for prolonged periods without the ii ~ j 12 Ij need to adjust the current upwards to maintain the pla-ting rate.
13 1' 14 !', This invention also provides compositions useful in 15 l~ replenishing the palladium bath and helping to maintain bath 16 ,' efficiency over extended periods. Such compositions comprise j 17 1 an admi:~ture, without an electrolyte, of a water soluble palladium 18 "~ compound and a water soluble nit.ite compound, the latter being 19 i, present in an amo~mt sufficient to provide an excess of nitrite ~20 ' ions relative -to the palladium ions in the mi~ture when dissolved 21 ~ in water.
2~ '~, 4 23 ' Another aspect of this invention provides an improved 24 .I method of electrodepositin~ palladium rom a bath comprising an 25 . aqueous soLution of a palladium compound, preerably a palladium 26 ~ (II) compound, comprising maintaining in the bath an'e~cess of 27 free nitrite ions relative to the palladium ions and thus 28 stabilizing the bath eficiency.
29 `
;, .
~! r 3 0 , I
..
, " : - 4 -. , ` ~ !
.. ...
~ ~ 63~52 DETAILED DESCRIPTION OF THE INVENTIO~
Because bath efficiency will begin to fall off almost as soon as the bath begins to be operated, it is important that an excess of free nitrite ions be present in the bath at the outset and maintained in the bath throughout the plating cycle.
A water soluble palladium compound such as palladium diamine dinitrite, suitable as a source of palladium ions in the bath, while containing nitrite does not serve as a source of "free"
nitrite because the nitrite remains complexed even after the compound is dissolved in the bath. Thus, it is necessary to include initially in the bath some other nitrite compound which is capable of dissociating in water to provide free, i.e., uncomplexed, nitrite ions.
Preferably, the source of free nitrite ions is a water soluble inorganic nitrite compound, and especially preferably an alkali metal nitrite, such as sodium nitrite, potassium nitrite, or the like and ammonium nitrite.
A small excess of nitrite ions is sufficient to maintain bath stability, usually at least about 0.05% by weight relative to the palladium ions in the bath. In most cases, the bath is formulated to provide an excess of free nitrite ions, initially, of from about 0.1 to about 50% by weight, relative to the palladium ions in the bath.
It is to be noted that, as the bath is operated and palladium is consumed by plating out, some of the free nitrite ions in the bath simultaneously undergo oxidation to the nitrate !j ~ 39~2 l, 1 jl for~. Thus, even if a large excess is provided in the bath 2 l~ iniLially, the free nitrite will eventually exhaust itself as f e ~n~ s ~ /i o~ c f/~
3 1I the bath i~ opcrat_~. To ensure that an excess of free nitrite 4 ¦1 is maintained throughout plating, fresh amounts of the free ¦I nit.i.e source should be added to the bath from time to time.
6 ~l' A con~-enient wa~J o~ doing thls is to add the nitrite compound 7 1l to the bath with each periodic addition of the palladium compou~d 8 j, used to replenish the palladium consumed. As a general rule, 9 ¦! in each case the nitrite compound is added in an amount sufficien~
10 ¦I to provide at least about a 10% by weight e~cess of nitrite ions ~ relati~re to the palladium ions provided by the palladium compound.
12 ~ ` .
13 I The palladium is ~supplied to the bath, lnitially and 14 upon replenishment, preferably in the form o a water soluble ~ organic or inorganic palladium ~II) compound selected from among ~16 I materlals conventionally employed for such purposes in palladium ii 17 ¦ electrodeposition baths. E~amples include palladium diamine ~;~
18 I dinitrite [Pd(~H3~2(NO2)2~, palladium chlorlde (PdC12), palladium 19 I sulfate, palladosamine chloride, diamine palladium hydroxide, 20 Ij tet~amine palladium chloride and dichlorodiamine pa~ladium 21 1l chloride. Among these, palladium diamine dinitrite and palladium~
22 lll chloride are especially preferred for use in this inventlon.
23 1'~
~! The electrolyte for the bath may be any water soluble 25 ,I compound capable of dissolving in water to form an electrically 26 1', conductive ionic medium. These may be selected from among 27 'l, the con~entional materials. In the usual case, this is a water 28 !I soluble nitrate compound, and preferably ammoni~ nitrate or .
29 ¦. an alkali metal nitrate, e.g., potassium nitrate or sodillm 30 i! nitrate.
i'i !
~ I - 6 -~ ~ 639~
The ingredients of the compositions according to this invention may be present in a wide range of amounts. Preferably, however, prior to addition to water the compositions comprise an admixture as follows:
Ingredients Amount, parts by weight Water soluble palladium (II) compound, preferably palladium diamine dinitrite or palladium chloride 30-40 Water soluble electrolyte compound, preferably alkali metal nitrate or ammonium nitrate 65-75 Water soluble source of free nitrite, preferably alkali metal nitrite 5-15 These may be formulated into a palladium deposition bath having the following preferred ranges and which are operated under the following conditions:
Inqredients Amount, grams per liter Water soluble palladium (II) compound, preferably palladium diamine dinitrite or palladium chloride 40-60 grams per liter Water soluble electrolyte compound, preferably alkali metal nitrate or ammonium nitrate 85-95 grams per liter Water soluble source of free nitrite, preferably alkali metal nitrite 5-15 grams per liter Water to make 1 liter Temperature 50-70 C~
pH 8-9 Current density 1-500 amperes per square foot !l I
6 3 9 ~ 2 l ¦I The bath pH may be adjusted before and/or during 2 i~ operation in t;le usual manner such as by addition OL- suitable 3 i, amounts o' an acid, e.g., nitric acid, or a base, e.g., 4 Ij am~onium hydroxide.
!
~ , I
6 Other ingredients may also be included in the composi- , 7 ~ ior ~neir conven~ionaîly employed purposes. ~y way o~j 8 1! illustration, such materials include brightening agents, g 1I wetting a~7ents or surfactants, comple~ing agents for palladium 10 j ions, ant:ioxidants, etc., all of which are well kno~.~n to those 11 ¦ skilled in the art. 1 12 I i 13 I In carrying out the electrodeposition process of the 4 ¦~ invention, the bath may be operated over a wide range of tempera-15 1I tures, such as from room temperature, e.g., 25C., almost up to 16 ¦i but below the ~oiling poin~ of the bath, e.g., 100C.
17 ~
18 1~ Plating times will vary, depending on factors such 9 1! as the supplied current densi~y, bat'n temperature and palladium ~¦
20 li deposit thickness desired. For the particular current density I
21 ¦1 and tem~erature-ran~es indicated above, i.e., 1-500 amps per ~¦
22 1i square foot and 50-70C., a plating period of about lO minutes ~ j or less i:, usually sufficient to yield a palladium deposit ~ ¦
24 ~' thickness of about one thousandth of an inch.~ ~ ¦
25 ~
26 l~ By this invention, metallic palladium is deposited ~ I o h C~ S
27 1 ~ a metallic substrate~ substantially smootl~, bright and -28 l adherent 12yers. Examples of metal surfaces on which palladium 29 ! ma~J be deposited include copper, nickel, silver and steel, 30 1 as well a~ alloys of these such as brass, bronze, ~tainless ,i ~ - 8 - I
- . . : .. .. . ~ ... . . ..
~ ~ 63952 steel or the like.
By practice in accordance with this invention, bath efficiencies of greater than 90% are provided and efficiencies of from 80 to 95% are typical even when the baths are operated over extended periods. Additionally, it is found that these high bath efficiencies are obtainecl when operating the baths at high current densities of 300 - 350 amps per square foot.
Moreover, even at current densities as high as 450 - 500 amps per square foot, bath efficiencies of 60 - 70% are still obtained.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
-The invention is illustrated further in the following examples:
A small piece o~ flat copper is pretreated to remove any surface dirt and grease, pre-weighed and immersed in a palladium electrodeposition bath having the following com-posltlon:
Palladium diamino dinitrite, Pd(NH3)2(No2)2 50 grams/liter Ammonium nitrate, NH4NO3 90 grams/liter Sodium nitrite, NaNO2 10 grams/liter Water (to make 1 liter) A piece of platinized tantalum/titanium is immersedin the bath and connected as the anode to the positive side of a D.C. power supply unit. The copper piece is connected as the cathode to the negative supply of the D.C. power supply, and plating begins.
_ g _ J~ 1 6 3 9 5 2 1 l¦ The bath has an initial weight ratio of nitrite ions 2 1. to palladium ions of 1.5:1. The initial bath pH is between 3 il 8 and 9. The temperature of the ba.h is adjusted to and main- i ; 4 1~ tained at 70C.
6 il The current supply is regulated to deposit palladium 7 j, ac a current aensity of 1~ amperes per square foot. At this 8 ¦! current density, metallic palladium plates out on the surface 9 1l of the copper workpiece at a rate of 30 milligrams per ampere-j minute.
11 .
12 From time to time, the bath is replenished by adding 13 more palladium diamine dinitrite in amounts so as to maintain 14 I the initial palladium concentration in the bath. Upon each ¦ addition of the palladium compound, the sodium ni~rite is 16 1 also added in an amount providing a 10% e~cess of the nitrite I ion relative to the palladium ion of the diamine dinitrite I ~ 18 I compound.
19 I : I
20 l¦ A palladium deposit having a thickness of about 0.001 21 !jl, inch is ol~tained after about six minutes of operation. As 22 ¦ computed from the known current density, plati~ng time and 23 ¦ palladium deposit thickness, the bath efficiency is found to be 24 I g5%.
25 i 26 il Thereafter, plating is resumed and the consumable 27 ¦I bath ingredients are periodically replaced in the bath in the 28 " manner previously described. In this way, the bath is operated 29 ¦~ continuously for several days with bath efficiency being main-30 ¦¦ tained at or near 95%.
, .
~1 10- I
' . .. . . . .
i 1 63952 1 ! E~A~PLE 2 2 i For purposes of comparision, the plating procedure of 3 , E~ample 1 is repeated e~cept that fresh amounts of the nitrite 4 , compound are not added to the bath after operation has begun. It S j is observed that the bath efficiency begins to fall off after 6 !I several hours and the amount of palladium being deposited 7 !~ decreases significan-ly.
9 jj E~A~IPLE 3 ~I
¦¦ A plating bath was made up ~ith the following composi- ¦
tion and concentrations in accordance ~ith E~ample I of U.S.
12 I Patent 4,092,225:
13 10 g/l Pd 14 150 g/l Potassium Pyrophosphate 15 I 130F Temperature 16 pH=9 adjusted by pyrophosphate or potassium hydroxide 17 This bath ~as used to rack plate copper coupons ~ith 18 good mechanical agitation at several different current densities 19 ~1 and the follo~ring results were obtained:
2 0 i¦ TABLE A
21 1I Current Density Bath Efficiency 22 (am~ ~er square foot) ~%) ' l ~
2~ 10 94 94 ' 26 ~0 94 28 ~ By comparision, the procedure of E~ample 1 was repeated 29 11 at several different current densities and the follo~.~ing resul~s ¦ ~ere obtained I
~ 1 1 639~2 1 ., TABLE B
.. , i 2 .... ... Current Density Bath Efficiency 3 1 (Amps rer Square Foot) (%) 25. 97 6 ! 50 97 7 ., ` 100 94 .
8 , 200 86 g j~ 300 80 11 i, 400 73 12 ! 450 67 . I
13 ,j 500 60 14 iI From the above, it is apparent that not only does the l, composition and method of the present invention provide high 16 1 bath efficiencles over prolonged periods of operation, but 17 l additionally, the current density at which such efficiences are 18 l obtained is e~tended at least seven fold as compared with prior 19 1 art baths and processes. .
I
~1 Other modifications and variations of the invention 21 1~ will suggest themselves to those skilled in the art in view of Z2 ¦¦ the desc~iption. It is to be understood, therefore, that 1:
23 1l changes may be made in the specific emobidments described wi~hout~
~24 1I departing from the scope and principles of the invention as defined in ~he appended claims, and without sacrificing its chief 26 ~ advan ~ges.
~1 1~ 1 ~ ~' .
Claims (4)
1. In a method for electrodepositing metallic palladium from a bath comprising an aqueous solution of a palladium compound to provide palladium ions, the improvement which serves to substantially stabilize the bath efficiency thereof comprising maintaining in the bath an excess of free nitrite ions relative to the palladium ions.
2. The method of Claim 1 in which the excess is maintained by the periodic addition of a water soluble nitrite compound capable of dissolving in water to provide free nitrite ions.
3. The method of Claim 2 in which the water soluble nitrite compound is an alkali metal nitrite.
4. me method of Claim 2 in which the water soluble nitrite compound is added in an amount sufficient to maintain an excess of free nitrite ions in the bath in the range of 0.1 and 50% by weight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US6813479A | 1979-08-20 | 1979-08-20 | |
| US68,134 | 1979-08-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1163952A true CA1163952A (en) | 1984-03-20 |
Family
ID=22080625
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000340923A Expired CA1163952A (en) | 1979-08-20 | 1979-11-29 | Palladium electrodeposition compositions and methods |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5629689A (en) |
| BE (1) | BE879682A (en) |
| BR (1) | BR8000087A (en) |
| CA (1) | CA1163952A (en) |
| CH (1) | CH649581A5 (en) |
| DE (1) | DE2943399C2 (en) |
| ES (1) | ES8101658A1 (en) |
| FR (1) | FR2463823B1 (en) |
| GB (1) | GB2057503B (en) |
| HK (1) | HK67886A (en) |
| NL (1) | NL185577C (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE8106693L (en) * | 1980-12-17 | 1982-06-18 | Hooker Chemicals Plastics Corp | ELECTROPLETING BATHROOM INCLUDING PALLADIUM |
| US4392921A (en) * | 1980-12-17 | 1983-07-12 | Occidental Chemical Corporation | Composition and process for electroplating white palladium |
| US4545868A (en) * | 1981-10-06 | 1985-10-08 | Learonal, Inc. | Palladium plating |
| US4622110A (en) * | 1981-10-06 | 1986-11-11 | Learonal, Inc. | Palladium plating |
| JPS5920992U (en) * | 1982-07-29 | 1984-02-08 | 東京瓦斯株式会社 | Automatic internal circumference welding device for fixed pipes |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1970950A (en) * | 1932-06-20 | 1934-08-21 | Int Nickel Co | Electrodeposition of platinum metals |
| GB958685A (en) * | 1960-10-11 | 1964-05-21 | Automatic Telephone & Elect | Improvements in or relating to palladium plating |
| US3925170A (en) * | 1974-01-23 | 1975-12-09 | American Chem & Refining Co | Method and composition for producing bright palladium electrodepositions |
-
1979
- 1979-10-18 CH CH937179A patent/CH649581A5/en not_active IP Right Cessation
- 1979-10-23 FR FR7926305A patent/FR2463823B1/en not_active Expired
- 1979-10-26 BE BE0/197858A patent/BE879682A/en not_active IP Right Cessation
- 1979-10-26 DE DE19792943399 patent/DE2943399C2/en not_active Expired
- 1979-10-30 NL NL7907968A patent/NL185577C/en not_active IP Right Cessation
- 1979-10-31 JP JP14114579A patent/JPS5629689A/en active Granted
- 1979-11-29 CA CA000340923A patent/CA1163952A/en not_active Expired
-
1980
- 1980-01-08 BR BR8000087A patent/BR8000087A/en unknown
- 1980-01-15 ES ES487727A patent/ES8101658A1/en not_active Expired
- 1980-08-15 GB GB8026622A patent/GB2057503B/en not_active Expired
-
1986
- 1986-09-11 HK HK67886A patent/HK67886A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| NL7907968A (en) | 1981-02-24 |
| FR2463823B1 (en) | 1985-10-31 |
| DE2943399C2 (en) | 1983-12-08 |
| GB2057503A (en) | 1981-04-01 |
| ES487727A0 (en) | 1980-12-16 |
| FR2463823A1 (en) | 1981-02-27 |
| GB2057503B (en) | 1983-05-18 |
| HK67886A (en) | 1986-09-18 |
| BR8000087A (en) | 1981-03-24 |
| ES8101658A1 (en) | 1980-12-16 |
| JPS5629689A (en) | 1981-03-25 |
| CH649581A5 (en) | 1985-05-31 |
| DE2943399A1 (en) | 1981-03-26 |
| JPS6229516B2 (en) | 1987-06-26 |
| BE879682A (en) | 1980-04-28 |
| NL185577C (en) | 1990-05-16 |
| NL185577B (en) | 1989-12-18 |
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