GB2133041A - Palladium electroplating bath - Google Patents

Abstract

A high speed ductile palladium electroplating bath comprises a palladium amino complex salt as a source of the palladium metal, ammonium sulphate, an ammonium halide, an alkali metal pyrophosphate and a stress reducing agent. The bath may also contain an anionic fluorochemical surfactant to minimize pitting. The pH of the bath will range from about 7 to 9. Electrolytic deposition will be carried out at a temperature of from 50 to 80 degrees C at high current densities up to about 3000 ASF (330 ASD). Suitable stress reducing agents are o-formyl-benzene sulphonic acid, saccharin and 2-butene-1,4-dione.

Description

SPECIFICATION Bath and process for high speed electroplating of palladium The present invention relates to electroplating baths and methodsforthe high speed electrodeposition of ductile palladium metal on substrates from baths formulated from a particularcombinationofcompo nents.

A considerable body of patent literature exists over a period of many years relating to the electrodeposition of palladium metal. This prior art is represented bythefollowing U.S. Patents: 330,149 - Piletetal.

1,921,941 - Powelletal.

1,993,623 - Raper 2,207,358 - Powell et al.

2,451,340 - Jernstedt 3,50,065 - Fatzer 3,206,382 - Wilson 3,458,409 - Hayashi 3,480,523 - Tyrrell 3,530,050 - Ickenham etal.

3,544,435 - Angusetal.

3,580,820 - Yamamura etal.

3,933,602 - Henzietal.

4,076,599 - Cancchio,Jr.etal.

4,092,225 - Davis 4,098,656 - Deuber 4,144,141 - Schusteretal.

The problems usually encountered in the known palladium metal electroplating baths, including limited deposition rates and brittleness due to hydrogen embtittlementwere recently setforth in several papers presented atTheSecondAES Symposium On Economic Use of And Substitution For Precious Metals in The Electronics Industry held on October 5th and 6th, 1982 at Danvers, Mass. The papers were by J.

A. Abys"A Unique Palladium Electrochemistry Characteristicsand Film Properties" and by H. S. Trop and A. V. Siaweleski "Application of BTL Pd Technology to Barrel Plating." Itis apparenttherefore that there is a need for commercial palladium metal baths which will efficiently operate at high speeds over a wide range of current densities to produce a ductile palladium deposit on a variety ofsubtrates.

This invention enables the provision of means for overcoming or at least mitigating problems associated with using the prior palladium metal electroplating baths.

The invention also enables the provision of electroplating baths with the right combination of compo nentsto permitthe efficient deposition of palladium metal on various substrates.

This invention further enables the provision of palladium amine complex-containing electroplating baths wherein high speed deposition of ductile palladium metal is readily achievable.

This invention still further enables the provision of an improved method for plating ductile palladium metal on a variety of substrates with high tolerence to metallic impurities such as copper using these special electroplating baths.

These and otherfacets of the present invention will become more readily apparent from the fol lowing description ofthe features thereof.

In accordance with the present invention it has now been found that the efficient high speed deposition of ductile palladium metal can be achieved by using, as a source of the palladium in the bath, a palladium amine complex in combination with at least four other bath components. These other bath components include ammonium sulphate, ammonium halide salt, an alkali metal pyrophosphate, and a stress reducing agent.

The electroplating baths of this invention will generally be operated under slight basic conditions, preferably at a pH of from about 7 to 9. The temperature of the bath may range from about 50to 80 degrees C, while current densities as high as 3000 ASF (330 ASD) may be effectively used in the practice of the present invention. In anotherfeature of the invention, the electroplating bath may also contain a surfactant, preferably an alkali metal fluorochemical sulphonate, to minimize or avoid a pitting problem that may be encountered.

As setforth above, one ofthe principal ingredients of the electroplating baths is the palladium amine complexwhich can be a halide, nitrite, nitrate, sulphate, orsulphamate.

Illustrative complexes include the following: Palladous diamine chloride - Pd(NH3)2C12 Palladous diamine dinitrite Pd(NH3)2(NO2)2 Palladoustetramine nitrate Pd(NH3)4(NO3)2 Palladous diamine sulphate Pd(NH3)2SO4 The above chloride and dinitrite complexes are preferred for the present purposes.

Other palladium salts which may be used are dichlorodiamine palladium and the like.

The palladium metal in the bath may be used in amounts ranging from about 10 to 80 g/l, and preferably about 40 to 70 g/l.

The otherfouressential electroplating bath components are ammonium sulphate, ammonium halide, an alkali metal pyrophosphate, and a stress reducing agent. Although the amounts of these components used in the baths may vary over a wide range, the presence of each of these components is essential in order to attain the desired results. It will be understood thatthree ofthese components are know conducting salts or electrolytes.

Ammonium sulphate may be used in amounts ranging from about 20 to 60 g/l, and preferably from about 30 to 50 g/l.

The ammonium halide may be ammonium chloride, ammonium bromide, or ammonium fluoride. However, the use of ammonium chloride is especially preferred. Amounts of the ammonium halide in the bath may vary from about 10to 80 g/l, and preferably from about 20 to 30 g/l.

Tetrapotassium pyrophosphate is the preferred alkali metal pyrophosphate which can be employed in formulating the electroplating baths ofthis invention.

Nevertheless othertetra alkali metal pyrophosphates such as tetrasodium pyrophosphate, ammonium pyrophosphate, and the like may be used. The tetra alkali metal pyrophosphate may be used in amounts ranging from about 20 to 150 g/l, and preferablyfrom about 80 to 100 g/l, expressed as the trihydrated salt.

The use of electroplating baths containing palladous diamine dinitrite and tetrapotassium pyrophosphate is described in the U.S. Patent 4,092,225 to Davis, but it has a current density limitation of about 50 ASF (5.5 ASD).

The fifth essential component ofthe palladium electroplating baths ofthis invention is a stress reducing agent. Preferably, the stress reducing agent is a derivative of benzene sulphonic acid; and the use of o-formyl benzene sulphonic (OFB) was found to be particularly useful in many operations. Other stress reducing agents which may be employed in the present invention include, for example, saccharin and 2-butene-1, 4dine. In general, the amount of stress reducing agent usually employed will rangefrom about 1 to 10 g/l, and preferablyfrom about 3to 5 g/l.

The electroplating baths ofthis invention may also contain other ingredients useful in this art, provided thattheydo not have any deterious results on the formation of ductile palladium orthe high rate of deposition that can be achieved herein. As previously mentioned, one of these other ingredients is a surfactantwhich can minimize or eliminate any metal pitting problem that may occure in the practice ofthis invention. Minor amounts of an anionic fluorochemicalwetting agent of surfactant such as a blend of potassium perfluoroalkyl sulphonates, sod under the trade marks FC98 and FC-95 by the Minnesota Mining and Manufacturing Company, may be employedto prevent pitting.The amount of wetting agent or surfactantwill generally range from about5to 20 ml/l, preferably from about 7 to 15 ml/l for the present purposes.

FC-95 and FC-98 are potassium perfluoroalkyl sulphonates, and their use is generally preferred. Both FC-95 and FC-98 decompose at 390 degrees C. In a 0.1 % aqueous solution FC-95 has a pH of 7-8, while FC-98 has a pH of 6-8. FC-98, which is potassium perfluorocyclohexyl sulphonate, is slightly less surface active and is capable of producing foam that is less dense and less stable. Both types have outstanding chemical and thermal stability, especially in acidic and oxidizing systems. The method of preparing these perfluoroalkyl sulphonates is disclosed in U.S. Patent 2,519,938to Simons; while a prior art use of such surfactants in electroplating is illustrated by U.S.

Patent 2,750,334 to Brown. The teachings of these patents are incorporated herein by reference.

ThepH oftheelectroplating baths will be from about 7 to 9, preferably from about7 to 8; and the baths will be operated attemperatu res offrom about 30 to 80 degrees C., preferably from about 60 to 70 degrees C.

Although the tank current densities which can be effectively used with the baths of this invention may range from about 1 Oto 200 ASF (1.1 to 22 ASD), somewhat higher current densities are preferred, i.e.

from about 180 upto about 200 ASF (19.8to 22ASD).

However, in contrast, a current density range of from about 200-3,000 ASF (22 to 330 ASD) can be attained by the practice of the present invention in high speed plating systems. Under the preferred operating conditions of the present invention the rate of ductile palladium metal deposition on the substrate may be as high as 6 microns per minute, with ranges offrom about 1 to 25 being readily attained.

The baths of this invention can be used in conjunction with insoluble platinum, platinum clad, tantalum, orcolumbium anodes. In general, rack plating is employed andworkpieces, e.g. box and pin contracts, printed circuit board contacts, decorative jewellry, etc, have surfaces of metals such as copper, brass, bronze, nickel, silver, steel, etc. The palladium metal, orwhen desired, palladium metal alloy ductile deposits are of high quality.

Electroplating baths preferred in the present invention have the following composition: Component Concentration g/l (a) Pd metal complex 40to80 (b) (NH4)2SO4 30to 60 (c) NH4CI 10to80 (d) OFB 1 to 10 (e) K4P207 20to 150 (f) FC-98 sty 20 my (NH40H uptopH8 (h) Water Remainder The inventionwill be more fully understood by reference to the following illustrative embodiments wherein concentrations are given in grams per litre (g/l) unless otherwise indicated.

EXAMPLE I A series of runs were carried outwith electroplating baths having the formulations setforth in Table A. All plating was carried out in a tank at current density of 200 ASF (22 ASD), temperature of 70 degrees C., pH 8, with rapid agitation and a constant anodelcathode ratio. The substrate used was copper, and the palladium metal complex was palladosaminechloride, Pd(NH3)2CI2.The pH was adjusted with NH40H. TABLE A FORMULATION RUN A RUN B RUN C RUN D RUN E Pd metal complex, as Pd metal 60 60 60 60 60 (NH4)2SO4 50 50 50 - 50 NH4Cl 30 30 30 30 30 OFB(1) 5 5 - 5 0 K4P2O7 100 - 100 100 0 FC-98(1 g/l sol'n) 10 ml 10 ml 10 ml 10 ml 10 ml Results 200 ASF (22 ASD) Deposit burned 200 ASF (22 ASD) Deposit was Deposit burned at CD was achieved; at 200 ASF CD was achieved burned at 200 ASF 200 ASF (22 ASD); the deposit was (22 ASD) cracks were (22 ASD); maximummaximum CD was 40 (current density smooth and ductile;maximum CD observed when CD was 120 ASF ASF (4.4 ASD) deposit =CD 6% elongation was 40 ASF bend testing (13.2 ASD); cracked during the bend (4.4 ASD); the deposit; deposit test; thickness could not deposit was thickness was ductile be built up ductile could not be built up (1) Ortho-formyl benzene sulphonic acid The above data indicate that in addition to the palladium metal complex and ammonium the electroplating baths had to contain ammonium sulphate, a stress reducing agent, and tetra-potassium pyrophosphate in orderto achieve the desired results. Run A, which was formulated in accordance with the present invention, gave excellent results: a high speed, ductile palladium metal deposit. In contrast, the other Runs which did not use electroplating with all of the necessary components failed to give satisfactory results.

EXAMPLE II A palladium electroplating bath was prepared by dissolving the following ingredients in water: Components Concentration g/l Pd, as Pd(NH3)2Cl2 70 (NH4)2SO4 50 NH4CI 30 K4P2O7.3H2O 100 OFB 10 FC-98 (1 g/l sol'n) 10 mil The bath was operated at a pH of 9, 70-75 degrees C., and at an achieved current density in the order of 195ASF (21.45ASD). High speed ductile palladium foils of up to 75 microns were plated on a copper substrate at a rate of 6 microns per minute. The foils could be rolled into a cylinder and deformed into a square.

EXAMPLE 111 Another electroplating bath was prepared by dissolving the following ingredients in water: Components Concentration g/l Pd, as Pd(NH3)2C12 60 (NH4)2SO4 50 NH4CI 30 K4P2O7#3H2O 100 OFB 5 FC-98 (1 g/l sol'n) 10 mil This bath was also operated at a pH or8 and a temperature of about 70-75 degrees C. Spot cell tests were done with this bath, and current densities up to 3000 ASF (330 ASD) were achieved. Good ductile deposits with a deposition rate upto 25 microns minute were obtained.

EXAMPLE IV Components Concentration g/l Pd,as Pd(NH3)2Cl2 60 (NH4)2SO4 50 NH4Cl 30 K4P2O7#3H2O 100 OFB 5 FC-98 (1 g/l sol'n) 10 ml Cu, as CuSO4.5H2O 2 The bath was operated at a pH of 7.5, 70 C., current density of 200 ASF (22 ASD). A ductile foil of 25 microns thick was obtained with no codeposition of copper The foregoing data reveal that the palladium electroplating baths of this invention permitthe high speed deposition of ductile palladium metal at high current densities, i.e. upto about 200 ASF (22ASD) in a tank and 3000ASF (330 ASD) or higher in a spot cell.

In addition, the data showthatthe bath is highly tolerantto copper, nickel, iron and gold.

Claims (1)

1. CLAIMS:

   1. A high speed bath for the electrodesposition of ductile palladium metal comprising palladium metal in the form of a palladium amine complex, ammonium sulphate, ammonium halide, an alkali metal pyrophosphate and a stress reducing agent.

   2. A bath as claimed in Claim 1 comprising from 40to 80 g/l palladium metal.

   3. A bath as claimed in Claim 1 or 2 comprising from 20to 90 9/l ammonium sulphate.

   4. A bath as claimed in Claim 1,2 or3 comprising from lOto 70 g/l ammonium halide.

   5. A bath as claimed in any one of Claims 1 to 4 comprising from 20to 1 50 g/l alkali metal pyrophosphate.

   6. A bath as claimed in any one of Claims 1 to 5 which also contains a minor amount of an anionic fluorochemical surfactant.

   7. A bath as claimed in any one of Claims 1 to 6 wherein the surfactant is an alkali metal perfluoroalkyl sulphonate.

   8. Abath as claimed in any one of Claims 1 to 7 wherein the ammonium halide is ammonium chloride.

   9. A bath as claimed in anyone of Claim 1 to 8 wherein the palladium amine complex is palladium diamine chloride.

   10. A bath as claimed in any one of Claims 1 to 9, wherein the stress reducing agent is a derivative of benzene sulphonic acid.

   11. A bath as claimed in any one of Claims 1 to 10 wherein the benzene sulphonic acid derivative is o-formyl benzene sulphonic acid.

   12. A method of electrodepositing high speed ductile palladium on a metallic substrate which comprises immersing the substrate in an electroplating bath as claimed in any one of claims 1 to 11 and passing current between the substrate and a bath electrode.

   13. A method as claimed in Claim 12, wherein the bath is art a pH offrom 7 to 9.

   14. A method as claimed in Claim 12 or 13, wherein the bath is at a temperature offrom 50to 80"C.

   15. Amethod as claimed in Claim 12,13 or 14, wherein the bath is operated at a current density of from 10to3000ASF(1.1 to 330 ASD).

   16. A methodforelectrodepositing high speed ductile palladium on a metallic substrate which comprises immersing the substrate in an electroplating bath operated at a pH within the range offrom 7to 9, a temperature of from 50to 80 degrees C., and a current density offrom 10 to 3000 ASF (1.1 to 330 ASD); the electroplating bath comprising an aqueous solution having the following components: Components Concentration g/l (a) Palladium metal, asthe palladous amino complex 40 to 60 (b) (NH4)2SO4 30 to 50 (c) NH4CI 20 to 30 (d) alkalimetalpyrophosphåte 80 to 100 (e) stress reducing agent 3 to 5

   17. A method as claimed in any one of Claims 12 to 16whereinthe pHoftheelectroplating bath isfrom 7to9.

   18. A method as claimed in any one of Claims 12 to 17, wherein the temperature of the bath is from about60to 70 C.

   19. A method as claimed in any one of Claims 12 to 18, wherein the current density is from 180 3000 ASF(19.8to330ASD).

   20. A method as claimed in any one of Claims 12 to 19, wherein the substrate is selected from copper, nickel, brass, iron, gold, and alloys thereof.

   21. A method as claimed in Claim 16, wherein the palladous amine complex is palladous amine chloride.

   22. A method as claimed in Claim 16 or21 ,wherein the palladous amine complex is palladous amine nitrite.

   23. A method as claimed in Claim 16,21 or 22, wherein the stress reducing agent is a derivative of benzene sulphonic acid.

   24. A method as claimed in Claim 16,21,22 or 23 wherein the benzene sulphonic acid derivative is o-formyl-benzene sulphonic acid.

   25. A method as claimed in Claim 16 or any one of Claims 21 to 24 wherein the bath also contains a minor, anti-pitting amountofan anionicfluoroche- mica surfactant.

   26. A method as claimed in Claim 16 or any one of Claims 21 to 26, wherein the alkali metal pyrophosphate is tetrapotassium pyrophosphate.

   28. An electroplating bath substantially as herein described with reference to any one of Examples IA, II, lil and IV.

   29. A method of electroplating substantially as herein described with reference to any one of Example IA, 11,111 and IV.

   30. An article whenever electroplated by a bath as claimed in any one of Claims 1 to 15 and 28and/or by a method as claimed in any one of Claims 1 6to 27 and 29.