CA1189016A - Palladium and palladium alloys electroplating procedure - Google Patents

Abstract

Abstract:
A procedure for electroplating palladium and palladium alloys is disclosed which permits rapid and efficient plating and yields ductile, adherent palladium films. The electroplating bath comprises a unique complex of palladium and aliphatic polyamine is selected from the group consisting of diaminopropane (including 1,1-di-aminopropane), diethylenetriamine, 1,4-diaminobutane, 1,6-diaminohexane, N,N,N',N'-tetramethyl-ethylenediamine and 2-hydroxy-1,3-diaminopropane.

Description

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

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 ~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.

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 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.

Claims (21)

Claims:

1. 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, comprising the step of passing current through a cathode, an electroplating bath and an anode with cathode potential great enough to electroplate palladium, said electrochemical bath having a conductivity greater than 10-3 mho-cm and a pH between 7.5 and 13.5, characterized in that the electroplating bath comprises an aqueous solution of palladium-aliphatic polyamine complex in which the aliphatic polyamine is selected from the group consisting 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.

2. The process of claim 1 in which the metallic substance consists essentially of palladium.

3. The process of claim 1 in which the aliphatic polyamine is selected from the group consisting of 1,3-diaminopropane and diethylenetriamine.

4. The process of claim 1 in which the pH varies from 11.0 to 12.5.

5. The process of claim 1 in which the electroplating bath comprises a buffer.

6. The process of claim 5 in which the buffer comprises hydrogen phosphate ion and phosphate ion.

7. The process of claim 6 in which the buffer concentration varies from 0.1 to 2 Molar and the ratio of hydrogen phosphate to phosphate ion is from 5/1 to 1/5.

8. The process of claim 1 in which the electroplating process is carried out at a temperature between room temperature and 80 degrees C.

9. The process of claim 8 in which the temperature is between 40 and 60 degrees C.

10. The process of claim 1 in which the palladium concentration is from 0.01 Molar to saturation.

11. The process of claim 10 in which the palladium is from 0.05 to 1.0 Molar.

12. The process of claim 1 in which the molar concentration of aliphatic polyamine is from 0.5 times the concentration of palladium to saturation of the aliphatic polyamine.

13. The process of claim 12 in which the molar concentration of aliphatic polyamine is from two to 12 times the mole concentration of palladium.

14. The process of claim 1 in which the plating current density is between 50 and 1000 ASF.

15. The process of claim 1 in which the palladium in the electroplating bath is replenished by the addition of a source of palladium.

16. The process of claim 15 in which the source of palladium is palladium chloride.

17. The process of claim 15 in which the source of palladium is a source of tetrachloropalladate ion.

18. The process of claim 1 in which the the plating current density is up to 50 ASF.

19. 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 polyamine complex, said complex being the same as results from reacting a source of palladium with at least one aliphatic polyamine selected from the group consisting 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.

20. The process of claim 19 in which the source of palladium is palladium chloride.

21. The process of claim 19 in which the aliphatic polyamine is selected from the group consisting of 1,3-diaminopropane and diethylenetriamine.