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
  • C25D3/52—Electroplating: Baths therefor from solutions of platinum group metals characterised by the organic bath constituents used
• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/567—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of platinum group metals

Definitions

• the invention relates to the electrodeposition of pure palladium or palladium alloys and to alkaline electrolytic plating solutions containing palladium metal, a complexing agent, and, when desired, one or more alloying metals.
• Electrodes and connectors are generally fabricated from copper alloys onto which is electrodeposited a thin layer of a precious metal such as gold or palladium.
• the electrodeposit must possess certain metallurgical properties such as corrosion resistance, freedom from porosity, wear resistance, low and stable contact resistance, ductility, etc. In most cases, gold which has been hardened with a small amount of nickel or cobalt is used as the electrodeposit.
• Such prior art plating baths have several disadvantages, including evolution of ammonia fumes, frequent replenishment of the ammonium stabilizing compound and the required use of strike baths for certain basis metals.
• the present invention proposes electrolytes and methods for the electrodeposition of pure palladium or palladium alloys that present an improvement over the prior art electrolytes and their deposits.
• An objective of this invention is to provide an alkaline electrolyte for the electrodeposition of palladium or palladium alloys.
• This electrolyte has a minimum attack on the basis metals being plated, and is stable so that it will not deteriorate with extended use.
• the electrolyte formulation is commercially feasible and able to operate satisfactorily in modern electroplating equipment.
• Another objective of this invention is to electroplate a palladium or palladium alloy by utilizing these novel electrolytes.
• Such palladium or palladium-alloy electrodeposits are lustrous, semi-bright to bright deposits having suitable ductility, freedom of porosity, wearability, corrosion resistance and low contact resistance. These are the physical and metallurgical characteristics which are necessary for applications involving electrical contacts and connectors.
• the invention relates to an alkaline electrolyte for the electrodeposition of palladium or palladium alloys which comprises at least one soluble palladium compound, at least one complexing agent and, when desired, one or more soluble alloying metal compounds.
• the amount and type of the complexing agent should be sufficient to provide electrodeposition potentials of palladium and the alloying metals sufficiently close to obtain the desired palladium alloy deposits.
• these deposits should have a palladium content of at least about 20%.
• the complexing agent should be present in an amount sufficient to maintain the palladium and the alloying metal compounds in solution in the electrolyte. Also, the electrolyte must have a sufficiently alkaline pH to solubilize the complexing agent and metal complexes.
• the pH of these electrolytes normally ranges from about 8 to 14, with 12 to 14 being preferred.
• the complexing agents of the invention include any organic compound which is soluble in the electrolyte and which contains at least one heterocyclic ring having at least one nitrogen atom in the ring, with at least one of the ring carbons containing a hydroxyl or carbonyl oxygen group, and the ring being substituted with at least one carboxyl group.
• a single four, five, six or seven member heterocyclic ring or groups of such rings may be utilized in the invention.
• Specifically preferred complexing agents include chelidamic acid, orotic acid, or 2-pyrrolidone-5-carboxylic acid.
• the invention also relates to methods for formulating electrolytes which can be used for electroplating palladium or palladium alloys.
• the electrolytes are formulated by adding the palladium compound, the complexing agent, and, optionally, an alloying metal compound, to water and adjusting the amount of complexing agent as well as the pH of the solution to solubilize these compounds.
• the electroplating methods include immersing a suitable anode and a substrate to be plated into these electrolytes and electroplating palladium or a palladium alloy thereupon by passing an electric current through the electrolyte.
• the invention achieves substantial improvements over prior art palladium and palladium alloy baths and plating methods by supplying an electrolyte that contains palladium and, when used, the alloying metal, in an alkaline bath.
• These metals are complexed by chelating or complexing agents so that their electrodeposition potentials are close enough to permit the electroplating of palladium alloys having the desired palladium content.
• All metal compounds in the electrolyte are complexed by the complexing agent provided.
• “Complexing agents. or "chelating agents” are equivalent for purposes of this invention.
• the complexing agents which are suitable for this invention include any organic compound which is soluble in the electrolyte and which contains at least one heterocyclic ring having one or more nitrogen atoms in the ring, at least one carboxyl group substituted on a ring carbon and/or at least one hydroxyl or carbonyl oxygen attached to a ring carbon.
• a single heterocyclic ring is utilized as a complexing agent, it preferably should contain between four and seven members. Multiple-rings are also contemplated by the invention.
• the nitrogen heterocycle may be a mono, di, or tricyclic ring system which is saturated or unsaturated and fused or joined by single bonds.
• These compounds can be represented by the general formula: wherein:
• the carboxyl group of R 1 is preferably attached directly to a ring carbon. However, it may also be indirectly attached to a ring carbon through another substituent as long as the solubility, stability, and complexing ability of the compound is not adversely affected. Similarly, the carbonyl oxygen and its hydroxyl tautomer may also be directly or indirectly attached to a ring carbon.
• Preferred compounds include those described above which have at least 1 carboxyl group substituted on a ring carbon and at least 1 hydroxyl or carbonyl oxygen attached to a ring carbon, singly or in combination.
• Other preferred compounds are those having at least two carboxyl groups attached to ring carbons.
• these compounds may also have a hydroxyl or carbonyl oxygen attached to a ring carbon.
• the compound must be soluble in the electrolyte.
• solubilizing groups may be added to these compounds to increase their ability to remain soluble in the electrolyte.
• the pH of the solution can be adjusted to increase the solubility of the compound in the electrolyte.
• the heterocyclic ring compound must be capable of complexing the palladium compound as well as the alloying metal compounds, over an alkaline pH range of 8-14 in order the plating potentials of the metals can be brought sufficiently close so that the desired alloy can be plated.
• a pH range of about 12 to 14 is usually optimum.
• heterocyclic ring compounds examples include those that are substituted with at least one carbonyl group and at least one carboxyl group. These compounds, which must be stable and form soluble metal complexes at the operating pH of the bath, include:
• the compound of choice should be readily soluble in the bath at the operating pH and should be capable of complexing the selected metals. Also, the metal complexes should likewise be bath soluble.
• TMcomplexing ability as used herein includes both the complexing and/or chelating functions of the compound.
• the pH of the bath can be varied by adding a base such as lithium, sodium, ammonium, or potassium hydroxide (for raising the pH) or by adding a suitable acid to reduce the pH.
• a base such as lithium, sodium, ammonium, or potassium hydroxide (for raising the pH) or by adding a suitable acid to reduce the pH.
• the pH range to be used is that which maintains all metals in solution so that the proper alloy can be deposited containing the desired metallurgical characteristics.
• Plating tests are run at the pH values which produce homogeneous solutions.
• the metallurgical characteristics of the deposits are then examined for suitability for the intended application, i.e., such as for use on electrical contacts or connectors.
• the most desirable compounds for complexing palladium from those disclosed in this invention are, as mentioned above, those heterocyclic ring compounds that contain one or more carboxyl groups attached to one or more carbons in the ring, along with one or more carbonyl or hydroxyl groups each attached to one or more carbons in the ring.
• Specific examples of preferred compounds are chelidamic acid, orotic acid and 2-pyrrolidone-5-carboxylic acid. These compounds are illustrated below.
• the second complexing agent can be a lesser substituted compound (i.e., an organic compound having a nitrogen heterocycle wherein the ring is substituted with one carboxyl, carbonyl or hydroxyl group. This is because alloying metals in general, will not form the same strength of complexation as palladium.
• secondary complexing agents may be added. These agents include ammonia, amines, amino acids, phosphonates and the like.
• bases such as ammonium hydroxide or other hydroxide compounds (i.e., alkali hydroxides and the like) are also suitable as secondary complexing agents.
• hydroxyl ion present which can also form complexes certain with metal in the electrolyte.
• the metals may be present in the solution as an equilibrium mixture of the organic metal complex, the metal complex of the secondary complexing agent and/or the hydroxyl complex, depending upon the strength and amounts of the various metal complexes formed in the electrolyte.
• the concentrations of complexing compounds or mixtures of complexing compounds used in these electrolytes can vary from 10-200 g/1 or more depending on the metal concentrations and solubility. In general, the higher the metal concentration, the higher the concentration of the complexing compounds required.
• the minimum amount of complexing compound is that which is required to complex the metals sufficiently in solution to produce the desired electrodeposited alloy. The maximum amount of such agent is controlled by its solubility in the bath. If the concentration is too high, there will be a lack of solubility and crystallization or precipitation will take place.
• the preferred concentrations of palladium and alloying elements can vary widely.
• palladium concentrations vary from about 8-30 g/1 and other metal concentrations according to the values shown in Table 2.
• Operating temperatures can vary from ambient (i.e., 70°F) to about 170°F, with 120-150°F preferred.
• Current densities can vary from 1-200 ASF or higher depending upon degree of agitation, temperature and metal concentration.
• the pH can vary from 8-14 depending upon compounds chosen, solubility and ability to complex the metals, with a range of 12 to 14 being especially advantageous.
• the strength of the complexing agent used must be such that it can complex silver in the presence of chloride ion. If this is not the case, then silver must be supplied as another metal salt such as silver nitrate or silver hydroxide, and the solution should be free of substantial amounts of chloride ions.
• Palladium can be supplied in a salt form such as palladium sulphate, palladium nitrate, palladium hydroxide, or palladium chloride, if chloride does not cause precipitation. It may also be possible to separately form the palladium and or other metal complexes of the desired compound and then add the metal to the electrolyte in the form of the metal complex which is soluble in the electrolyte at the operating pH.
• a plating bath was prepared by adding the disclosed components into water.
• a stock solution was prepared as follows:
• predetermined amounts of cobalt, zinc, or cadmium metal can also be added to the stock solution to provide the desired alloy.
• the only limitation on the alloying metal is that it should be soluble in the electrolyte.
• a ternary, rather than binary, alloy can be electrodeposited.
• the following example illustrates a ternary alloy according to the invention.
• Example 7 1 g/l silver metal (as silver nitrate) and 1 g/l gold metal (as gold chloride) were added to the stock solution. The deposit was sound and bright and analyzed 43.8% palladium, 55.4% silver, and 0.6% gold.
• Hull cell testing produced lustrous deposits from 0-20 ASF.
• Hull cell testing produced lustrous deposits from 0 - 10 ASF.
• Hull cell testing produced lustrous deposits from 0-3 ASF.
• Examples 10 through 17 produce palladium-silver alloy deposits ranging from about 70:30 to 50:50 composition.

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• Electroplating And Plating Baths Therefor (AREA)

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Citations (5)

• 1986
  • 1986-06-06 JP JP13044186A patent/JPS62139893A/ja active Pending
  • 1986-06-06 EP EP86107737A patent/EP0225422A1/fr not_active Ceased

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