US3274022A

US3274022A - Palladium deposition

Info

Publication number: US3274022A
Application number: US267947A
Authority: US
Inventors: Richard N Rhoda
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1963-03-26
Filing date: 1963-03-26
Publication date: 1966-09-20
Anticipated expiration: 1983-09-20
Also published as: BE645775A; DE1247804B; GB994560A; NL6403078A

Description

United States Patent 3,274,022 PALLADIUM DEPOSITION Richard N. Rhoda, Westlield, N..I., assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware N0 Drawing. Filed Mar. 26, 1963, Ser. No. 267,947 6 Claims. (Cl. 117130) The present invention relates to electroless deposition of metal and, more particularly, to electroless deposition of palladium on metallic substrates.

It is well known that copper and copper-rich alloys have considerable utility in the communications field. In producing connectors, circuit components and other devices useful in the electronic communications art from copper and copper-rich alloys, it is often desirable to plate or coat such alloys with palladium in order to minimize corrosion and to provide low noise-level and low resistance contacts. While electrolytic and non-electrolytic methods of depositing palladium are known, such methods are not particularly well adapted for use in the production of many electronic components. Thus, for the production of components having deep cavities, for example, connectors, or the production of components having electrically isolated islands of metal, for example, printed cir cuits, electrolytic methods of palladium deposition are not practical. Electroless methods of palladium deposition known heretofore have not been successful in producing relatively thick, continuous coatings of palladium directly on copper and copper-rich alloys. In at least one prior known electroless bath for depositing palladium, copper acts as a poison to halt the catalytic and autocatalytic deposition of the palladium. I Although attempts were made to overcome the foregoing difiiculties and other disadvantages, none, as far as I am aware, Was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by means of a novel autocatalytic process, relatively thick, continuous deposits of palladium can be produced on copper and copper-rich alloy substrates.

It is an object of the present invention to provide a novel autocatalytic process for the electroless deposition of palladium.

Another object of the invention is to provide a novel autocatalytic process for the electroless deposition of palladium on copper-rich metallic substrates.

The invention also contemplates providing a novel process for producing metallic electronic components having a copper-rich base and a surface of palladium metal.

It is a further object of the invention to provide a novel bath for the electroless deposition of palladium.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates a process for the electroless deposition of palladium which comprises establishing an aqueous bath containing about 100 to about 350 grams per liter (g.p.l.) of ammonia substantially as ammonium hydroxide, up to about 80 g.p.l. of ethylenediaminetetraacetic acid (E.D.T.A.), about 0.04 to about 0.50 g.p.l. of unsymmetrical dimethylhydrazine (U.D.M.H.) and about 1 to about 20 g.p.l. of divalent palladium added advantageously as tetramminepalladium (II) chloride, immersing or dipping a body having a catalytic surface in said aqueous bath while maintaining the temperature of said bath at about 68 C. to about 100 C. to effect catalytic and autocatalytic deposition of metallic palladium from said bath on said surface while maintaining the concentration of U.D.M.H. within the aforesaid range. The present invention also contemplates the palladium bath which contains water, ammonia, divalent palladium and U.D.M.H. as essential ingredients.

3,274,022 Patented Sept. 20, 1966 In carrying the invention into practice, it is advantageous to maintain the composition of the aqueous bath within the compositional limits set forth in the table and to maintain the temperature of said bath at about C.

TABLE Advanta- Illustrative Ingredient geous Rlange, Value, g.p.l.

NI-Ia -170 13 5-10 10 5-24 7. 9 0. 05-0. 45 0. 086 Balance Balance Dissolved in the divalent state.

Objects to be plated in the bath of the present invention and according to the process of the present. invention must have a surface of a catalytic metal such as aluminum, chromium, cobalt, copper, gold, iron, molybdenum, nickel, palladium, platinum, ruthenium, silver, tin, tungsten, and alloys rich in cobalt, nickel and/or copper. Of course, such objects can be composed of such a catalytic metal. The bath and process of the present invention are particularly adapted to be employed in the plating of copper and alloys rich in copper, that is, alloys containing more than about 60% copper. Alloys rich in copper include brass, cupro-nickel, German silver and bronze.

Objects made of materials such as glass, plastics and ceramics which do not catalyze the reduction of palladium can be coated with a preliminary deposit of a catalytic substance such as nickel, silver, palladium, etc., and thus, by this means, it is possible in accordance with the present invention to chemically deposit smooth and adherent plates of palladium on substantially any object.

A bath for the chemical deposition of palladium in accordance with the present invention is advantageously made by dissolving tetramminepalladium II) chloride in an aqueous solution of ammonium hydroxide to which is added E.D.T.A. as the disodium salt. Palladous palladium can also be added to the ammoniacal bath of the present invention (that is, an alkaline bath containing ammonium hydroxide or free ammonia) as palladous chloride and palladous nitrate. The bath can be employed statically or in a dynamic system such as in a rotating barrel. When objects are ready to be plated, that is, when they have been carefully cleaned in the manner normal to electroplating techniques, the deposition bath is brought to or maintained at operating temperature and the requisite amount of U.D.M.H. is added to the bath. The object or objects to be plated are then brought in contact with said bath. As plating progresses, periodic additions of U.D.M.H. should be made to the bath so that the concentration thereof is maintained within the required limits. In general, plating resulting from chemical deposition in the bath proceeds at a deposition rate of about 40 to about 60 microinches per hour. At these plating rates it has been found to be advantageous to add about 0.48 gram of U.D.M.H. per hour to the bath for each 1000 square centimeters (cm?) of area being plated. Addition rates as high as about 2 grams of U.D.M.H. per hour per 1000 cm. have been employed. Conveniently, these additions can be made in aliquot portions at intervals of about hour or, of course, the addition can be continuous.

The proportions of ingredients in the aqueous baths of the present invention are important in that if divalent palladium and U.D.M.H. are present in too large a concentration, the baths will tend to decompose spontaneously. On the other hand, if too little of these ingredients are present, the plating rate will be very slOW. Too little amine, e.g., ammonia, also causes low plating rates. Amounts of ammonia in excess of about 280 g.p.l. are usually not advantageous in that at the operating temperabetter understanding of the'invention, the following illustrative examples are given:

Example I An aqueous solution containing g.p.l. of palladous palladium, 280 g.p.l. of ammonium hydroxide and 8 g.p.l. of the disodium salt of E.D.T.A. was placed in a rotatable plating barrel and maintained at a temperature of 75 C. Enough U.D.M.H. was added to provide a concentration of about 0.086 g.p.l. thereof in the solution. A brass object having a surface area of 500 cm. was thoroughly cleaned and placed in the solution in the barrel. The barrel was then rotated and at fifteen minute intervals, about 0.06 gram of U.D.M.H. was added to the solution. After one hour, the brass sample exhibited an adherent metallic deposit of palladium about 43 microinches thick.

Example II A bronze object having a surface area of about 500 cm. was suspended in :a. U.D.M.H. containing solution as em ployed in Example I. The solution was maintained at 85 C. and the concentration of U.D.M.H. was maintained. Over a period of time, an adherent deposit of palladium metal was obtained on the bronze sample.

Example 111 After being suspended for one hour at 90 C. in an aqueous solution containing the same amounts of U.D.M.H., ammonium hydroxide and the disodium salt of E.D.T.A. as employed in Example I but containing 10 g.p.l. of palladous palladium, a brass object having a surface area of 500 cm. was found to have an adherent deposit of metallic palladium about 59 microinches thick.

Example IV To an aqueous solution containing 5 g.p.l. of palladous palladium, about 280 g.p.l. of ammonium hydroxide and about 0.08 g.p.l. of U.D.M.H. in a rotatable barrel, was introduced a brass object having a surface area of about 500 cm. The barrel was rotated for about one hour while the temperature of the solution was maintained at about 83 C. and while the concentration of U.D.M.H. was maintained by additions every fifteen minutes of about 0.06 gram of U.D.M.H. After one hour, the object was found to have an adherent plate of metallic palladium about 45 microinches thick.

Example V Boiling aqueous solutions containing 10 g.p.l. of palladous palladium, 280 g.p.l. of ammonium hydroxide and 0.08 g.p.l. of U.D.M.H. were employed to plate copper and bronze objects. The objects each had about 500 cm. surface area. After one hour, during which the U.D.M.H. concentration was maintained by periodic additions, the copper object suspended in the bath exhibited a metallic palladium deposit about 60 microinches thick, whereas the bronze object, plated in a rotating barrel, exhibited a metallic palladium deposit about 52 microinches thick.

The foregoing examples contrast remarkably with the behavior of specimens made of copper or copper-rich alloys inserted in hydrazine-containing baths such as disclosed in US. Patent No. 2,915,406. In the hydrazinecontaining baths no palladium is deposited directly on copper and/ or copper-rich alloys. In addition, under the process conditions of the present invention, hydrazine causes catastrophic deposition of palladium throughout the bath. Thus, hydrazine cannot be used as a substitute for U.D.M.H. in the process of the present invention.

The present invention is particularly applicable to the production of electrical and/or electronic components made of copper and coated with an adherent bright deposit of palladium. In employing the process and the plating bath of the present invention, it is to be noted that other ingredients can be employed in the bath. For example, mole for mole amounts of stabilizing substances such as ammonium chloride and ammonium sulfate can be employed in place of or in addition to E.D.T.A. Other amines such as aminoethyl ethanolamine and/ or amylamine can be employed mole for mole in addition to or in place of part of the ammonium hydroxide. In addition, substances for brightening, leveling, etc., can be employed in the bath. Care must be taken, however, to exclude substances such as iodide ion, stannous ion and other divalent palladium, precipitants (for example, dimethylglyoxime, cyanides, thionalide, pyridine, hydroxyquinolines, metallic zinc and metallic magnesium) from the bath.

It is to be noted that the present invention is not to be confused with processes for electroless deposition of palladium involving the use of hydrazine. Objects made of copper or alloys rich in copper cannot be directly coated with palladium from ammoniacal baths containing high concentrations of ammonia and containing hydrazine as the sole agent for reducing palladium ion to palladium metal. Thus, the process of the present invention is particularly adapted to be employed in the plating of electrical and electronic components made of copper and/or copper-rich alloys.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A bath for the electroless deposition of palladium comprising an aqueous solution containing about 1 to about 20 grams per liter of divalent palladium, about 0.04 to about 0.50 gram per liter of unsymmetrical dimethylhydrazine, an amine selected from the group consisting of ammonia, aminoethyl ethanolamine and amylamine in an amount equivalent in molar concentration to about 100 to about 350 grams per liter of ammonia and a stabilizing agent selected from the group consisting of ammonium chloride, ammonium sulfate and ethylenediaminetetraacetic acid in an amount equivalent in molar concentration to up to about grams per liter of ethylenediaminetetraacetic acid.

2. A bath for the electroless deposition of palladium comprising an aqueous solution containing about 1 to 20 grams per liter of divalent palladium, about 0.04 to about 0.50 gram per liter of unsymmetrical dimethylhydrazine, about to about 350 grams per liter of ammonia and up to about 80 grams per liter of ethylenediaminetetraacetic acid.

3. A bath for the electroless deposition of palladium comprising anaqueous solution containing about 5 to about 10 grams per liter of divalent palladium, about 0.05 to about 0.45 gram per liter of unsymmetrical dimethylhydrazine, about to about grams per liter of ammonia and about 5 to about 24 grams per liter of ethylenediaminetetraacetic acid.

4. A process for the electroless deposition of palladium which comprises establishing an aqueous bath containing about 1 to about 20 grams per liter of divalent palladium, about 0.04 to about 0.50 gram per liter of unsymmetrical dimethylhydrazine, an amine selected from the group consisting of ammonia, aminoethyl ethanolamine and amylamine in an amount equivalent in molar concentration to about 100 to about 350 grams per liter of ammonia and a stabilizing agent selected from the group consisting of ammonium chloride, ammonium sulfate and ethylenediaminetetraacetic acid in an amount equivalent in molar concentration to up to about 80 grams per liter of ethylenediaminetetraacetic acid and placing a body having a catalytic surface in contact with said aqueous bath while maintaining the temperature of said bath at about 68 C. to about 100 C. to effect a deposition of metallic palladium from said bath on said surface and while replenishing said bath with unsymmetrical dimethylhydnazine to maintain the concentration thereof within said range of about 0.04 to about 0.50 gram per liter.

5. A process for the electroless deposition of palladium which comprises establishing an aqueous bath containing about 100 to about 350 grams per liter of ammonia, up to amout 80 grams per liter of ethylenediaminete-traacetic acid, about 0.04 to about 0.50 gram per liter of unsymmetrical dimethylhydrazine and about 1 to about 20 grams per liter of divalent palladium, placing a body having a catalytic surface in contact with said aqueous bath while maintaining the temperature of said bath at about 68 C. to about 100 C. to effect a deposition of metallic palladium from said bath on said surface and while replenishing said bath with unsymmetrical dimethylhydrazine to maintain the concentration thereof within said range of about 0.04 to about 0.50 gram per liter.

6. A process for the electroless deposition of palladium which comprises establishing an aqueous bath containing about 120 to about 170 grams per liter of ammonia, about 5 to about 24 grams per liter of ethylenediaminetetraacetic acid, about 0.05 to about 0.45 gram per liter of unsymmetrical dimethylhydrazine and about 5 to about 10 grams per liter of divalent palladium, placing a body having a catalytic surface in contact with said aqueous bath While maintaining the temperature of said bath at about 68 C. to about 100 C. to effect a deposition of metallic palladium from said bath on said surface and while replenishing said bath with unsymmetrical dimethylhydrazine to maintain the concentration thereof within said range of about 0.05 to about 0.45 gram per liter.

References Cited by the Examiner UNITED STATES PATENTS 2,915,406 12/1959 Rhoda et al 117-430 X 3,156,634 11/1964 Duva et al 106-1 ALFRED L. LEAVITT, Primary Examiner. R. S. KENDALL, Assistant Examiner.

Claims

4. A PROCESS FOR THE ELECTROLESS DEPOSITION OF PALLADIUM WHICH COMPRISES ESTABLISHING AN AQUEOUS BATH CONTAINING ABOUT 1 TO ABOUT 20 GRAMS PER LITER OF DIVALENT PALLADIUM, ABOUT 0.04 TO ABOUT 0.50 GRAM PER LITER OF UNSYMMETRICAL DIMETHYLHYDRAZINE, AN AMINE SELECTED FROM THE GROUP CONSISTING OF AMMONIA, AMINOETHYL ETHANOLAMINE AND AMYLAMINE IN AN AMOUNT EQUIVALENT IN MOLAR CONCENTRATION TO ABOUT 100 TO ABOUT 350 GRAMS PER LITER OF AMMONIA AND A STABILIZING AGENT SELECTED FROM THE GROUP CONSISTNG OF AMMONIUM CHLORIDE, AMMONIUM SULFATE AND ETHYLENEDIAMINETETRAACETIC ACID IN AN AMOUNT EQUIVALENT IN MOLAR CONCENTRATION TO UP TO ABOUT 80 GRAMS PER LITER OF ETHYLENEDIAMINETETRAACETIC ACID AND PLACING A BODY HAVING A CATALYTIC SURFACE IN CONTACT WITH SAID AQUEOUS BATH WHILE MAINTAINING THE TEMPERATURE OF SAID BATH AT ABOUT 68* C. TO ABOUT 100* C. TO EFFECT A DEPOSITION OF METALLIC PALLADIUM FROM SAID BATH ON SAID SURFACE AND WHILE REPLENISHING SAID BATH WITH UNSYMMETRICAL DIMETHYLHYDRZINE TO MAINTAIN THE CONCENTRATION THEREOF WITHIN SAID RANGE OF ABOUT 0.04 TO ABOUT 0.50 GRAM PER LITER.