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

Definitions

• ABSTRACT A composition for producing adherent deposits of palladium from a cyanide-free bath uses small amounts of cobalt or nickel or the combination thereof as the brightener.
• the bath employs as an electrolyte alkali metal and ammonium sulfates, sulfamates, phosphates, nitrates, nitrites and mixtures thereof.
• the brightener concentration is 0.004-002 gram mole per liter nickel or 0002-004 gram mole per liter cobalt, or the combination thereof.
• Cetyltrimethylammonium bromide is an optional component for the bath which is maintained at a pH of 7.5-] 1.0 and at a temperature of 26-60 Centigrade.
• the current density is 005-05 amperes per square decimeter and for rack plating the current density is 0.2-2.0 amperes per square decimeter.
• Another object is to provide a method for the electroplating of palladium which is relatively trouble-free and relatively insensitive to minor variations in operating conditions and which will produce bright, highly adherent electrodeposits of palladium.
• aqueous bath for the electroplating of palladium which consists essentially of 0.02-0.25 gram mole per liter of palladium ion; 0.9-3.6 gram moles per liter of a soluble electrolyte selected from the group consisting of alkali metal and ammonium sulfates, sulfamates, phosphates, nitrates, nitrites and mixtures thereof; and a soluble metallic brightener selected from the group consisting of 0.0020.04 gram mole per liter of cobalt ion, 0.004-002 gram mole per liter of nickel ion and mixtures thereof providing 0003-0068 gram mole per liter of the metal ions combined.
• the bath may contain up to 6X10 gram mole per liter of cetyltrimethylammonium bromide, and the pH thereof is adjusted to be within the range of 7.5-1
• the preferred soluble electrolyte is a sulfate salt and potassium sulfate has been found highly advantageous.
• the preferred compositions employ cetylitrimethylammonium bromide in an amount of at least 3X10 gram mole per liter.
• the palladium ion is desirably present in the amount of 005-01 gram mole per liter; the ammonium hydroxide is preferably present in an amount of 1.4-2.1 gram moles per liter; and the electrolyte is desirably present in an amount of 0.2-0.4 gram mole per liter; this preferred bath composition is desirably utilized at a pH of 8.5-9.5.
• a workpiece having a conductive surface is immersed in the aqueous bath described hereinbefore while the temperature is maintained at 2660 Centigrade.
• a potential is applied across the workpiece and an anode inert to the bath so as to provide a current density of 005- amperes per square decimeter, and the anode to cathode surface ratio is maintained at about 1.0-5.0: l .0.
• the workpiece is removed from the bath.
• the current density is maintained at about 0.05-0.5 amperes per square decimeter and in rack plating the current density is maintained at about 0.2-2.0 amperes per square decimeter.
• the preferred baths are operated at a temperature of 465 2 Centigrade under conditions of vigorous agitation.
• compositions of the present invention essentially comprise an aqueous solution of palladium ion, an electrolyte, a brightener selected from the group consisting of cobalt ion, nickel ion or the combination thereof, and ammonium hydroxide sufficient to provide a pH of about -110
• a desirable optional additive is cetyltrimethylammonium bromide.
• the palladium ion it may be introduced as any soluble compound having a noninterfering anion.
• the palladium may be introduced as palladium sulfate, palladium chloride, palladium nitrate, or as a palladium complex such as diaminepalladium hydroxide, dichlorodiaminepalladium or tetraminepalladium chloride.
• the amount of palladium in the bath may broadly range from 0.02-0.25 gram mole per liter and is preferably within the range of 0.05-0.10 gram mole per liter.
• the electrolyte may be provided by any one or mixture of alkali metal and ammonium sulfates, sulfamates, phosphates, nitrates and nitrites.
• the alkali metal and ammonium sulfates have proven to be most advantageously employed; potassium sulfate is preferred.
• the concentration of the electrolyte salt may vary from as little as 0.1 gram mole per liter to as much as 0.7 gram mole per liter.
• the concentration of the electrolyte salt is within the range of 0.2-0.4 gram mole per liter.
• Ammonium hydroxide is advantageously used to regulate the pH of the bath and is present in an amount of 0.9-3.6 gram moles per liter calculated as ammonium hydroxide exclusive of water.
• the ammonium hydroxide is present in an amount of 1.4-2.1 gram mole per liter.
• the ammonium hydroxide is added as a highly concentrated aqueous solution (29 percent by weight) in order to minimize dilution, although less concentrated compositions may also be employed if the water introduced thereby is entered into the calculations as to concentration of the remaining ions.
• acid having non-interfering anion should be employed.
• this is sulfuric acid, although nitric acid, hydrochloric acid and sulfamic acid may be employed.
• the brightener is a metal ion selected from the group consisting of cobalt, nickel and the combination thereof.
• the metal ions may be introduced in the form of any soluble compound which will not introduce an interfering anion.
• these metal ions are introduced as sulfate salts.
• they may also be introduced as chloride or nitrate salts and as complexes such as diaminecobalt chloride, hexaminecobalt chloride, hexaminecobalt nitrate, aquapentaminecobalt chloride, diaquatetraminenickel nitrate, hexaminenickel nitrate and hexaminenickel chloride.
• cobalt When used alone as the brightener, it is present in an amount of 0.002-0.04 gram mole per liter and preferably 0003-002 gram mole per liter.
• nickel When used alone as the brightener, it is present in an amount of 0.004-002 gram mole per liter and preferably 0.0l-0.0l5 gram mole per liter.
• the two metal ions When the two metal ions are used in combination with each other, the total amount thereof should provide about 0.5-4.0 grams per liter of metal ion or about 0.003-0068 gram mole per liter of ions combined.
• the metal ions combined equal 0.8-2.0 grams per liter or about 0005-0034 gram mole per liter.
• the ratio of palladium ion to cobalt or nickel ion must be fairly closely controlled in order to obtain stress-free deposits.
• the weight ratio of palladium to cobalt should adjusted to within the range of l0-50 and preferably -33.
• the palladium to nickel metal weight ratio should be adjusted to within the range 7.5-19.2 and preferably 7.5l2.8.
• Cetyltrimethylammonium bromide is an optional but desirable additive to effectively eliminate gas pitting in the palladium deposit.
• the amount of this additive should be closely controlled since excessive amounts will produce excessive foaming and interfere with the plating operation.
• the maximum amount which should be employed is about 6X10 gram mole per liter or 0.2 gram per liter.
• the maximum concentration is less than 0.06 gram per liter.
• An amount of as little as 2.7 10- gram mole per liter and preferably 8X10 gram mole per liter (0.01 and 0.03 gram per liter respectively) will produce highly advantageous results.
• the pH of the bath is maintained within the range of 7.5-1 1.0 and preferably within the range of 8.5-9.5.
• the pH may be adjusted by the addition of ammonium hydroxide or by use of a suit able acid providing a non-interfering anion such as sulfuric acid.
• the temperature of the bath should be within the range of 2660 Centigrade, and preferably 4652 Centigrade.
• the bath may be utilized without agitation, it is desirable to employ agitation and vigorous agitation has been found extremely beneficial. Filtration is highly desirable if pore-free adherent deposits are to be obtained because the presence of any solid contaminants will have a profound effect upon the quality of the deposit. Standard filter cartridges of polypropylene or other filter media may desirably be employed for continuous filtration of the bath.
• the anode to cathode surface area ratio should be within the range of l.0-5.0: l .0 and preferably 2.0:].0.
• the current density should be within the range of 0.2-2.0 amperes per square decimenter and preferably about 0.5-1.0 amperes per square decimeter.
• the current density should be within the range of 005-05 amperes per square decimeter and preferably about 0.1-0.3 amperes per square decimeter.
• the palladium deposits produced by the present invention are relatively stress-free and can be employed without further treatment for the great bulk of intended applications.
• the heat treatment may be conducted either under vacuum or in an inert gas atmosphere.
• anodes which are inert to the plating bath may be employed and generally such anodes will have a surface of noble metal, although carbon anodes do have limited utility.
• the preferred anodes are platinumclad tantalum although gold-clad tantalum, platinum and palladium electrodes have all been employed effectively.
• a bath is prepared by adding to deionized water palladium sulfate sufficient to provide 5.0 grams per liter as palladium metal, c.c. per liter of ammonium hydroxide (29 percent by weight Nl-l 1.05 grams per liter cobalt sulfate, 50 grams per liter potassium sulfate and 0.04 grams per liter cetyltrimethylammonium bromide.
• the resulting bath has a pH of 8.5 and is introduced into a plating cell where the temperature is maintained at 445 Centigrade.
• a potential of 1.7 volts is applied across a platinum surfaced anode and a Hull cell panel 3 centimeters by 5 centimeters in dimension, the anode to cathode surface area ratio being 3;l.
• the current density is determined to be 0.5 amperes per square decimeter and the current is continued for 20 minutes during which there is fast agitation of the plating bath.
• the panel is then removed and the palladium deposit thus formed is found to have a thickness of 2.5 microns and to be specular bright. Flexing of the panel repeatedly indicates that the deposit is highly adherent.
• EXAMPLE TWO To deionized water are added the various components in amounts suffcient to provide 9.0 grams per liter of palladium determined as the metal, c.c. per liter of ammonium hydroxide (29 percent by weight NR 2.63 grams per liter nickel sulfate, 100 grams per liter potassium sulfate and 0.03 gram per liter cetyltrimethylammonium bromide.
• the pH of the formulation is 7.9 and the temperature is maintained at 37.8 Centigrade.
• a Hull cell panel is used as the cathode and a platinum surfaced anode is employed. A potential of 2.2 volts is applied thereacross during fast agitation of the solution in the cell.
• the anode to cathode surface area ratio is 3:1 and the current density is 0.5 amperes per square decimeter.
• the panel After plating for 20 minutes, the panel is removed and is found to have a specular bright palladium deposit of 1.9 microns thickness. Flexing the panel indicates the deposit to be highly adherent.
• a mixed electrolyte is prepared using 25 grams per liter potassium sulfate, 2 grams per liter ammonium nitrate and 1 gram per liter ammonium chloride.
• the bath contains palladium sulfate sufiicient to provide 5 grams per liter of palladium as metal and 60 c.c. per liter ammonium hydroxide (29 percent by weight NH and 0.06 gram per liter cetyltrimethylammonium bromide. Used as the brightener is 0.46 gram per liter cobalt sulfate.
• the pH of this formulation is 9.9 and the bath is introduced into a test barrel plating installation wherein it is maintained at 49 Centigrade.
• the workpieces to be plated are nickel pins about one centimeter in length and about 0.5 millimeters in diameter.
• the anode to cathode surface area ratio is calculated at l :1 and a potential of 5 volts is applied to provide a current density of 0.2 amperes per square decimeter.
• the plating ope ration is continued for a period of 90 minutes after which the parts are removed and found to have a specular bright deposit of 2.5 microns thickness. The deposit is highly adherent as evidenced by the lack of exfoliation after bending of the pins through 90.
• the baths of the present in vention provide bright, highly adherent electrodeposits on various types of conductive substrates. They are operable over a wide range of current density and at ambient to low elevated temperatures. The plating operation is relatively trouble-free and relatively insensitive to minor variations in operating conditions and will yield deposits which are substantially free from internal stresses.
• a soluble electrolyte selected from the group consisting of alkali metal and ammonium sulfates, sulfamates, phosphates, nitrates, nitrites and mixtures thereof;
• said bath having a pH of 7.5-1 1.0.
• a soluble electrolyte selected from the group consisting of alkali metal and ammonium sulfates, sulfamates, phosphates, nitrates, nitrites and mixtures thereof;
• a soluble metallic brightener selected from the group consisting of 0.002-004 gram mole per liter of cobalt ion, 0.004-002 gram mole per liter of nickel ion and mixtures thereof providing 0003-0068 gram mole per liter of metal ions;
• said bath having a pH of 7.5-1 1.0;

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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)

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Cited By (20)

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Citations (2)

• 1974
  • 1974-01-23 US US435844A patent/US3925170A/en not_active Expired - Lifetime
• 1975
  • 1975-01-07 CA CA217,526A patent/CA1036534A/en not_active Expired
  • 1975-01-22 JP JP966175A patent/JPS548537B2/ja not_active Expired

Patent Citations (4)

Non-Patent Citations (1)

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