PALLADIUM AND PALLADIUM ALLOYS ELECTROPLATING PROCEDURE

Description

[0001] The invention is a process for electroplating palladium and palladium alloys of the type described in the preamble clause of claim 1.

[0002] Precious metals are used as protective films on surfaces for a variety 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 of 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. However, the increased price of gold makes it attractive to look at other precious metals as protective films on various surfaces.

[0003] 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.

[0004] Because of chemical inertness and resonable hardness, palladium is especially attractive as an electrical contact material in electrical connectors, relay contacts, switches, etc. Palladium alloys with at least 10 mole percent palladium, remainder at least one of the metals silver, nickel and 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 used, it is often economically attractive to use palladium, provided an inexpensive and efficient method of plating ductile and adherent palladium is available.

[0005] 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 subsequent 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 process. 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. A. Parker et al on December 6, 1966. Ethylenediamine has been used in a palladium alloy plating procedure (U.S.S.R. Patent No. 519,497 issued 30 June 1976); (C. A. 85: 113802 m) and it was known to the inventors that ethylenediamine is useful in palladium electroplating in the following composition bath: 28 gm/I PdC1₂, 140 gm/I Na₂S0₄ and sufficient ethylenediamine to dissolve the PdCI₂. The bath is used at room temperature, the current density is 20 mA/cm² and the pH between 11 and 12.

[0006] DE-A-22 44 437 discloses electroplating of gold and gold alloys including gold alloyed with palladium. It describes a large number of complexing agents for the metallic ions in the bath, including various aliphatic polyamines with diethylenetriamine being mentioned as an example, and it is essentially directed to the production of ductile and bright decorative platings.

[0007] In contradistinction thereof it is one of the purposes of the present invention to allow the production of advantageous electrical contact material and, in particular, to find a way on which palladium and palladium alloys with at least 10 mole percent palladium, remainder at least one of the metals silver, nickel and copper, may be electroplated without incorporation or evolution of hydrogen, even if the plating is performed with high plating current density.

[0008] According to the invention this problem is solved for the palladium and palladium alloys electroplating procedure under discussion with the characterizing features of claim 1.

[0009] In other words, the invention is based on a critical selection of a few complexing agents from myriades of compounds; and it has been found that palladium and its mentioned alloys may be electroplated without simultaneous hydrogen evolution, if the used complexing agent is one or more organic aliphatic polyamines selected from diaminopropane (particularly 1,3-diaminopropane), diethylenetriamine, 1,4-diaminobutane, 1,6-diaminohexane, N,N,N'N'-tetramethylethylenediamine 2-hydroxy-1,3-diaminopropane. The aqueous electroplating bath is alkaline, i.e. pH between 7.5 and 13.5 to avoid corrosion of the surface being plated and sufficiently conductive to allow plating i.e. greater than 10-³ ohm^-1cm^-1. Additional substances may be added to the palladium plating bath to control and adjust pH (such as a buffer), to increase conductivity and to improve the properties of the plated metal. Typical substances used to improve the plated metal are lactones (i.e., phenolphthalein, phenol- sulfone-phthalein, etc.), lactams, cyclic sulfate esters, cyclic imides and cyclic oxazolinones. Certain polyalkoxylated alkylphenols may also be useful. The process is also useful for plating certain palladium alloys including at least 10 mole percent palladium, remainder copper, nickel and/ or silver.

[0010] The Figure shows a typical apparatus useful in electroplating palladium and palladium alloys in accordance with the invention.

[0011] The invention is a process for electroplating palladium metal or palladium alloy in which the indicated group of organic aliphatic polyamines is used as complexing agent in the palladium plating bath. Most preferred are the complexing agents 1,3-diaminopropane and diethylenetriamine because of the excellent quality of the palladium plating obtained, especially at high plating current density (above 50 ASF=0.054 A/cm²). In addition, the conditions (pH, temperature, etc.) under which optimum plating occurs with these preferred complexing agents permits rapid plating without incorporation or evolution of hydrogen. Also, undesirable chemical attack on the surface being plated is minimal or insignificant under optimum conditions of plating with these complexing agents.

[0012] It is highly advantageous to have a reduction potential far removed from the reduction potential of water so that even at high plating rates, hydrogen is not liberated as palladium is electroplated.

[0013] Alloy plating may also be carried out using the indicated complexing agents. Concerned palladium alloys consists of at least 10 mole percent palladium, remainder copper, silver and/ or nickel. Other useful alloys are 60 mole percent palladium, remainder silver, copper and/or nickel, or 40 mole percent palladium, remainder silver, copper and/or nickel, etc. The palladium-silver alloys are particularly useful, especially for electrical contact surfaces.

[0014] 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, nitrate, sulfate 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, including those set forth above, may be used as supporting electrolyte to increase conductivity of the electroplating bath. The cation used for the supporting electrolyte may be any soluble ion which does not interfere with the electroplating process. Alkali-metal ions (Na, K, Li) are particularly preferred because of solubility and stability.

[0015] 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 alkali-metal tetrachloropalladate (i.e., K₂PdCI₄). These compounds may be used initially to make the bath and to replenish the bath.

[0016] Particular advantages of the electroplating bath using the indicated complexing agents are the improved conditions of plating which reduce chemical attack on the surface being plated, avoid production of hydrogen even at high plating rates, such as above 215 or even above 538 mAlcm² (above 200 or even above 500 ASF, respectively) and improve the quality of plating even at very high plating rates. The pH of the bath may vary from 7.5 to 13.5, with the range of from 11.0 to 12.5 preferred. The preference particularly applies when the preferred polyamines are used, namely 1,3-diaminopropane and diethylenetriamine. 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 solution is preferred because of decreased attack on the surface being plated and decreased changes of hydrogen evolution.

[0017] The plating process may be carried out with or without a buffer system. A buffer system is often preferred because it maintains constant pH and adds to the conductivity of the bath. Typical buffer systems are the phosphate system, borax, bicarbonate, etc. Preferred is the HP04-'/POI-' system often made by adding an alkali-metal hydroxide (KOH, NaOH, etc.) to an aqueous solution of the hydrogen phosphate ion. Generally, the concentration 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.

[0018] The bath temperature often depends on bath composition and concentration, plating cell design, pH and plating rate. Contemplated temperatures for typical conditions are from room temperature to about 80 degrees C with 40 to 60 degrees C most preferred.

[0019] 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, electrolessly plated surfaces may be useful. Typical metal and alloy surfaces are copper, nickel, gold, platinum, palladium (as, for example, a surface electrolessly plated with palladium and then electroplated with palladium in accordance with the invention). Various alloy surfaces may also be used such as copper-nickel-tin-alloys.

[0020] The composition of the bath may vary within the claimed limits. In general, sufficient polyamine should be present to complex with the palladium. Usually, it is advantageous if excess polyamine is present in the bath solution.

[0021] The palladium concentration in the bath 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-speed plating (54 to 1076 mA/cm²) [50 to 1000 ASF] are higher than for low-speed plating (up to 54 mAlcm²) [up to 50 ASF]. Preferred palladium concentration ranges for high-speed plating vary also 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 (i.e. copper, silver or nickel) replaces part of the palladium in the composition of the plating bath. Up to 90 mole percent of palladium may be replaced by alloy metal.

[0022] The amoumt of complexing agent may vary from 0.5 times (on the basis of moles) 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 about six times the mole concentration of palladium. The preferred ranges of complexing agent in terms of palladium species are the same for high-speed and low-speed baths.

[0023] 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 Molar to saturation with from 0.2 to 2.0 Molar preferred.

[0024] 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 ml) 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 gms of PdC1₂ in portions of 0.5 g every two minutes. Since the resulting reaction is exothermic, the solution can be maintained at 60 degrees C by adjusting the rate of addition of PdC1₂. The solution is filtered to remove solid matter (generally undissolved PdCl₂ or PdO) and diluted to one liter.

[0025] To this solution are added 127 g of K₃PO₄ and 70 g of K₂HP0₄. The pH is 12.3 at 25 degrees C and can be adjusted upward by the addition of KOH and downward by the addition of H₃PO₄.

[0026] 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 188 mA/cm² (175 ASF). Typical thicknesses in these experiments are 102 to 381 µm (40 to 150 microinches). The deposit is crack free as determined by a scanning electron micrograph at 10,000 magnification. Both adherence and ductility are excellent. Similar results are obtained using 0.1 Molar palladium and 0.5 Molar palladium. Plating rate is often determined by the thickness desired after a predetermined period of plating. For example, in a strip line plating apparatus (see, for example, US-A-4,153,523 US-A-4,230,538) 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 hydroxy-1,3-diaminopropane, 1,4-diaminobutane and 1,6-diaminohexane yield similar results.

[0027] Similar results are obtained with low-speed baths. Here the preparation procedure is exactly the same except the quantity of reagents are different. A typical bath contains 16.66 g PdCI₂, 42 g polyamine complexing agent, 42 g K₃PO₄, 139 g K₂HP0₄ and sufficient water to make 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/cm² (10 ASF).

[0028] Similar experiments were carried out on the following 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 pm (200 microinches), and electroplating was carried out on a copper substrate.

Example 1

[0029] 13.3 g/l PdCl₂, 15.5 g/I diethylenetriamine and phosphate buffer. Electroplating was carried out at 55 degrees C.

Example 2

[0030] 6.67 g/I PdCI₂, 12.0 g/l 1,6-hexanediamine and phosphate buffer. Electroplating was carried out at 55 degrees C.

Example 3

[0031] 6.67 g/I Pd(N0₃)₂, 12.0 g/I 1,6-hexanediamine and phosphate buffer. Electroplating was carried out at 55 degrees C.

Example 4

[0032] 12.0 g/I PdCl₂, 18.0 g/I 1,4-butanediamine and phosphate buffer. Electroplating was carried out at 55 degrees C.

Example 5

[0033] 0.05 Molar Pd(NO₃)₂, 0.1 Molar diethylenetriamine, no buffer, 0.4 Molar KN0₃. The pH was varied by the addition of KOH from 10 to 14, temperature from 20 degrees C to 70 degrees C.

Example 6

[0034] 0.1201 Molar Pd(N0₃)₂, 3.2 Molar diethylenetriamine, 0.5 Molar KN0₃, no buffer. The pH was varied from 12 to 14 by addition of NaOH. Temperature was about 65 degrees C.

Example 7

[0035] 0.02097 Molar PdS0₄.2H₂0, 0.1 Molar diethylenetriamine, 0.419 Molar Na₂S0₄. The pH 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

[0036] 0.052 Molar PdCl₂, 0.4 Molar 1,4-diaminobutane, Na₂S0₄ and NaCl as supporting electrolyte, no buffer. Electroplated at 46 mA/cm² (43 ASF) to 351 µm (138 microinches) on copper. Deposit is bright and adherent. Repeat as 70 mA/cm² (65 ASF) to 351 µm (138 microinches).

Example 9

[0037] 0.11 Molar PdSO₄· 2H₂O, 0.97 Molar diethylenetriamine, 1 Molar KN0₃ 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, 293 and 323 mA/cm² (152, 196, 239, 272 and 300 ASF, respectively) to a thickness of 351 pm (138 microinches). Excellent brightness and adherence. On adding more PdS0₄ - 2H₂0, went to plating rate of 594 mA/cm² (552 ASF).

Example 10

[0038] Simiar to Example 9, but for 0.027 Molar Pd(NO₃)₂ · 2H₂0, 0.10 Molar 1,3-diaminopropane, no buffer, pH varied from 11.2 to 13.0.

Example 11

[0039] Similar to Example 9, but for 0.054 Molar Pd(NO₃)₂· 2H₂0, 0.2 Molar diethylenetriamine, phosphate buffer, pH adjusted to 13 with NaOH, temperature of 55 degrees C. Electroplated on Pt, Pd and Au.

Example 12

[0040] 0.282 Molar PdCl₂, 0.7 Molar 1,3-diaminopropane, 75 g/I Na₂S0₄ supporting electrolyte, 12.5 g/I 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 mAlcm² (150, 200, 250, 300, 400 and 500 ASF, respectively). All deposits were adherent and bright to semibright.

Example 13

[0041] Simialr to Example 12, but for 10 g/I Pd(NO₃)₂· 2H₂O, 6 g/I 1,3-diaminopropane.

Example 14

[0042] 60 g/I PdCI₂, 75.2 g/I 1,3-diaminopropane, 175 g/l K₂HP0₄, pH adjusted with NaOH to pH of 11.0, temperature of 65 to 70 degrees C. Electroplated at rates of 161, 215, 323, 431, 538, 646, 753, 861, 969 and 1076 mA/cm² (150, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 ASF, respectively).

Example 15

[0043] Same as in Example 14 except 100 g/I K₃P0₄ (instead of K₂HP0₄) and the pH was 11.4.

Example 16

[0044] Same as in Example 14, but pH was 12.4, plating rate 161 mA/cm² (150 ASF).

Example 17

[0045] 127.5 g/I PdC1₂, 214 g/I 1,3-diaminopropane, 104.5 g/l K₂HP0₄, 84.9 g/I K₃PO₄, initial pH was 11.7 at 25 degrees C, adjust with NaOH to 12.0 at 25 degrees C. Electroplated at 60 to 65 degrees at 54,161,269 and 538 mA/cm² (50,150,250 and 500 ASF, respectively).

[0046] Palladium alloys may also be electroplated in accordance with the invention. A typical bath composition for palladium alloy plating is as follows: 69.6 g Ag₂0, 53.2 g PdCl₂, 222 g 1,3-diaminopropane, 106.2 g K₃PO₄, 86.5 g K₂HP0₄ 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/cm² (1 and 500 ASF). The other polyamine complexing agents mentioned above are also useful, including diethylenetriamine. A useful bath for palladium-nickel plating is as follows: 38.9 g NiC1₂, 53.2 g PdCl₂, 222 g 1,3-diaminopropane, 106 g K₃P0₄, 86.5 g K₂HP0₄ 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/cm² (1 to 500 ASF). Experiments were also done with cobalt salt added to the bath.

[0047] The stripline plating apparatus described 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 process is highly advantageous for plating electrical contact pins for electrical connectors such as described in the above references.

[0048] Fig. 1 shows apparatus 10 useful in the practice of the invention. The surface to be plated 11 is made the cathode in the electrolytic process. The anode 12 is conveniently made of platinized titanium or may be made of various other materials such as oxides of platinum group metals, binder metal oxides, etc. Both anode and cathode are at least partially immersed in the electroplating bath 13 containing source of palladium complex with an organic aliphatic polyamine. A container 14 is used to hold the palladium plating solution and the anode 12 and cathode 11 are electrically connected to an adjustable source of electrical energy 15. An ammeter 16 and voltmeter 17 are used to monitor current and voltage.

Claims

1. A process for electroplating palladium and palladium alloys containing at least 10 mole percent palladium, remainder being at least one of silver, copper and nickel, which comprises passing current through a cathode, an electroplating bath and an anode with cathode potential being great enough to electroplate palladium, said, bath including an aqueous solution of palladium-aliphatic polyamine complex and having conductivity greater than 10-³ Ohm^-1cm^-1, and carrying out the electroplating process at a temperature ranging from room temperature to 80°C, characterized in that the pH is from 7.5 to 13.5, and the aliphatic polyamine is selected from diaminopropane, diethylenetriamine, 1,4-diaminobutane, 1,6-diaminohexane, N,N,N¹,N¹ - tetramethyl - ethylenediamine and 2-hydroxy-1,3-diaminopropane, the aqueous solution of palladium-aliphatic polyamine complex results from reacting a source of palladium with at least one of the said aliphatic polyamines, the palladium mole concentration is from 0.01 Molar to saturation, and the mole concentration of aliphatic polyamine is from 0.5 times the mole concentration of palladium to saturation of the aliphatic polyamine.

2. The process according to claim 1, characterized in that said diaminopropane includes 1,3-diaminopropane.

3. The process according to claim 1 or 2, characterized in that the mole concentration of aliphatic polyamine is from 2 to 12 times the mole concentration of palladium.

4. The process according to claim 1 or 2 or 3, characterized in that the electroplating process is carried out at a temperature between 40 to 60 degrees C.

5. The process according to claim 1 or 2 or 3 or 4, characterized in that the palladium mole concentration ranges from 0.1 to 1.0 Molar and the plating current density is between 0.054 and 1.076 AIcm² (50 and 1000 ASF).

6. The process according to claim 1 or 2 or 3 or 4, characterized in that the palladium mole concentration ranges from 0.05 to 0.2 Molar and the plating current density is up to 0.054 A/cm² (50 ASF).

7. The process according to any one of the preceding claims 1-6, characterized in that the electroplating bath includes a buffer comprising hydrogen phosphate ion and phosphate ion.

8. The process according to claim 7, characterized in that 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.

9. The process according to any one of the claims 1 to 8, characterized in that the pH is from 11.0 to 12.5.

Revendications

1. Procédé d'électrodeposition du palladium et d'alliages de palladium contenant au moins 10% en mole de palladium, le reste étant l'un au moins des métaux que sont l'argent, le cuivre et le nickel, qui consiste à faire passer du courant électrique dans une cathode, dans un bain d'élec- trodeposition et dans une anode, sous un potentiel cathodique suffisamment grand pour l'electrodeposition du palladium, ce bain comprenant une solution aqueuse d'un complexe de palladium et d'une polyamine aliphatique et ayant une conductivité supérieure à 10-³ ohm^-1 cm-¹, et à effectuer le processsus d'électrodéposition à une température allant de la température ambiante à 80°C, caractérisé en ce que le pH est de 7,5 à 13,5 et la polyamine aliphatique est choisie parmi un diaminopropane, la diéthylènetriamine, le 1,4-diaminobutane, le 1,6-diaminohexane, la N,N,N¹,N^1-tétraméthyl- éthylènediamine et le 2-hydroxy-1,3-diaminopropane, la solution aqueuse du complexe de palladium et de polyamine aliphatique provenant de la réaction d'une source de palladium sur au moins l'une desdites polyamines aliphatiques, la concentration molaire de palladium allant de 0,01 mole à la saturation, et la concentration molaire de polyamine aliphatique allant de 0,5 fois la concentration molaire de palladium à la saturation en la polyamine aliphatique.

2. Procédé suivant la revendication 1, caractérisé en ce que le diaminopropane comprend du 1,3-diaminopropane.

3. Procédé suivant la revendication 1 ou 2, caractérisé en ce que la concentration molaire de polyamine aliphatique représente de 2 à 12 fois la concentration molaire de palladium.

4. Procédé suivant la revendication 1, 2 ou 3, caractérisé en ce que le procédé de dépôt électrolytique est effectué à une température comprise entre 40 et 60°C.

5. Procédé suivant la revendication 1 ou 2 ou 3 ou 4, caractérisé en ce que la concentration molaire de palladium est de 0,1 à 1,0 mole et la densité de courant de dépôt est comprise entre 0,054 et 1,076 A/cm² (50 et 1000 ASF).

6. Procédé suivant la revendication 1 ou 2 ou 3 ou 4, caractérisé en ce que la concentration molaire de palladium est de 0,05 à 0,2 mole et la densité de courant de dépôt va jusqu'à 0,054 AIcm² (50 ASF).

7. Procédé suivant l'une quelconque des revendications précédentes 1 à 6, caractérisé en ce que le bain d'électrodéposition inclut un tampon comprenant un ion phosphate acide et un ion phosphate.

8. Procédé suivant la revendication 7, caractérisé en ce que la concentration du tampon va de 0,1 à 2 moles et le rapport de l'ion phosphate acide à l'ion phosphate va de 5/1 à 1/5.

9. Procédé suivant l'une quelconque des revendications 1 à 8, caractérisé en ce que le pH va de 11,0 à 12,5.

Ansprüche

1. Verfahren zum Elektroplattieren von Palladium und Palladiumlegierungen mit wenigstens 10 Mol-% Palladium, Rest wenigstens eines der Elemente Silber, Kupfer und Nickel, wobei das Verfahren umfaßt Hindurchschicken von Strom durch eine Kathode, ein Elektroplattierungsbad und eine Anode, wobei das Kathodenpotential groß genug ist, um Palladium zu elektroplattieren, und das Bad eine wäßrige Lösung eines aliphatischen Palladiumpolyamin-Komplexes aufweist sowie eine spezifische Leitfähigkeit von mehr als 10-³ Ohm-¹ cm-' besitzt, und Ausführen des Elektroplattierungsprozesses in einem Temperaturbereich, der von Raumtemperatur bis 80°C reicht, dadurch gekennzeichnet, daß der pH-Wert zwischen 7,5 und 13,5 liegt, und das aliphatische Polyamin ausgewählt wird aus Diaminopropan, Diethylentriamin 1,4-Diaminobutan, 1,6-Diaminohexan, N,N,N',N'-Tetramethylethylendiamin und 2-Hydroxy-1,3-diaminopropan, wobei die wäßrige Lösung des aliphatischen Palladiumpolyaminokomplexes von einer Reaktion einer Palladiumquelle mit wenigstens einem der aliphatischen Polyamine herrührt, die Palladium-Molkonzentration zwischen 0,1 Molar und Sättigung liegt und die Molkonzentration des aliphatischen Polyamins zwischen dem 0,5 fachen der Palladium-Molkonzentration und Sättigung des aliphatischen Polyamins liegt.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Diaminopropan 1,3-Diaminopropan einschließt.

3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Molkonzentration des aliphatischen Polyamins das 2 fache bis 12 fache der Palladiummolkonzentration beträgt.

4. Verfahren nach Anspruch 1 oder 2 oder 3, dadurch gekennzeichnet, daß der Elektroplattierungsprozess bei einer Temperatur zwischen 40 und 60°C durchgeführt wird.

5. Verfahren nach Anspruch 1 oder 2 oder 3 oder 4, dadurch gekennzeichnet, daß die Palladium-Molkonzentration von 0,1 bis 1,0 Molar reicht und die Plattierungsstromdichte zwischen 0,054 und 1,076 AIcm² (zwischen 50 und 1000 ASF) liegt.

6. Verfahren nach Anspruch 1 oder 2 oder 3 oder 4, dadurch gekennzeichnet, daß die Palladium-Molkonzentration von 0,05 bis 0,2 Molar reicht und die Plattierungsstromdichte bis zu 0,054 AIcm² (50 ASF) beträgt.

7. Verfahren nach einem der vorstehenden Ansprüche 1-6, dadurch gekennzeichnet, daß das Elektroplattierungsbad einen Puffer mit Hydrogenphosphationen und Phosphationen enthält.

8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß die Pufferkonzentration zwischen 0,1 und 2 Molar variiert und das Verhältnis von Hydrogenphosphat/Phosphat-Ionen von 5/1 bis 1/5 reicht.

9. Verfahren nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß der pH-Wert zwischen 11,0 und 12,5 liegt.

Drawing