CA1244374A

CA1244374A - Electroplating bath containing palladium amine complex and stress reducing agent

Info

Publication number: CA1244374A
Application number: CA000444727A
Authority: CA
Inventors: Irina Movshina
Original assignee: OMI International Corp
Current assignee: OMI International Corp
Priority date: 1983-01-07
Filing date: 1984-01-05
Publication date: 1988-11-08
Also published as: HK100086A; SG66786G; DE3400139A1; JPS59133394A; FR2539145B1; NL8400049A; GB2133041B; DE3400139C2; GB8400288D0; FR2539145A1; GB2133041A

Abstract

ABSTRACT OF THE DISCLOSURE
A high speed ductile palladium electroplating bath cap-able of giving a plating rate of 6 microns per minute and higher. The bath comprises a palladium amine complex salt as a source of the palladium metal, ammonium sulfate, an ammonium halide, an alkali metal pyrophosphate; and a stress reducing agent. The bath may also contain an anionic fluorochemical surfactant to minimize or eliminate any tendency toward pit-ting. The pH of the bath will range from about 7 to 9.
Electrolytic deposition will be carried out at a temperature of from about 50 to 80 degrees C at high current densities up to about 3000 ASF. The method of depositing ductile palladium foil on a variety of substrates is also described and claimed.

Description

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_ ELD OF THE INVENTIO_ The present invention relates to electropla-ting baths and methods for the high speed electrodepositioil oi ductile palladium metal on substrates from baths formu-late from a particular combination of components.
BACKGROUND OF THE INVENTION
A considerable body of paten-t literature exists over a period of many years relating to the elec-trodeposition of palladium metal. This prior art is represented by the following U.S. Patents:
330,149 - Pilet-et al~
1,921,941 - Powell et al.
1,993,623 - Raper

2,207,358 ~ Powell et al.
2,451,340 - Jernstedt

3,150,065 - Fatzer 3,206,382 - Wilson 3,458,409 - Hayashi 3,480,523 - Tyrrell 3,530,050 - Ickenham et al.
3,544,435 - Angu~ et:al.
3,580,820 - Yamamura et al.
3,933,602 - Henzi et al.

4,076,599 - Caricchio, Jr. et al.
4,092,225 - Davis 4,098,656 - Deuber 4,144,141 - Schuster et al.

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12~9L374 The problems usually encounte'red in the known palladium metal electroplating baths, including limited deposition rates and brittleness due to hydrogen embrittlement were recently set forth in several papers presented at The Second AES 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 Characteristics and Film Properties" and by H.S. Trop and A.V. Siaweleski "Application of BTL Pd Technology to Barrel Plating."
It is apparent therefore that there is a need for co~mercial 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 of substrates.
OBJECTS OF THE INVENTION
One object of -this invention is to provide means for overcoming the problems associated with using the prior pal-ladium metal electroplating baths.
Another object of this invention is to provide electro-plating baths with the right combination of components topermit the efficient deposition of palladium metal on various substrates.
A further object of this invention is to provide palladium amine complex-containing electroplating baths wherein high speed deposition of ductile palladium metal is readily achieved.

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A still further object of this invention is to provide an improved method for plating ductile palladium metal on a variety of substrates with high tolerance to metallic impuri-ties such as copper utilizing these special electroplating

5 baths.
These and other objects of the present invention will become more readily apparent from the following description of the specific features thereof.
SUM~ RY OF T~ TION
. . .
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 utilizing, 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 sulfate, ammonium halide salt, an alkali metal pyrophosphate, and a stress reducing agent. The electroplating baths of this invention will generally be oper-ated under slight basic conditions, preferably at a pH of from about 7 to 9. The temperature of the bath will range from about 50 to 80 degrees C, while current densities as high as 3000 ASF
may be effectively utilized in the practice of the present invention. In another feature of the invention the electro-plating bath may also contain a surfactant, preferably an alkali metal fluorochemical sulfonate, to minimize or avoid a pitting probl~em that may be encountered.

`` ~Z~374 t Dl~l'AILED DESCRIPTION OF THE INVENTION
, . . _ , _ _ As set forth above, one of the principal ingredients of the electroplating baths is the palladium amine complex which can be the halide, nitrite, nitrate, sulphate, or sulphamate.
Illustrative complexes include the following:
S Palladous diamine chloride - Pd(NH3)2C12 Palladous diamine dinitrite Pd(NH3)2(NO2)2 Palladous tetramine nitrate Pd(NH3)4(NO3)2 Palladous diamine sulfate Pd(NH3)2SO4 The above chloride and dinitrite complexes are preferred for the present purposes.

Other palladium salts which may be utilized are dichlorodiamine palladium and the like.
The palladium metal in the bath is used in amounts ranging from about 10 to 80 g/l, and preferably about 40 to 70 g/l.
The other four essential electroplating bath components are ammonium sulfate, 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 that these three components are known conducting salts or electrolytes.

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t Ammonium sulfate will be used in amounts ranging rom about 20 to 60 g/l, and preferably from about 30 to S0 g/l.
The ammonium halide may be ammonium chloride, 5 - 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 10 to 80 g/l, and preferably from about 20 to 30 g~l.

Tetrapotassi.um pyrophosphate is the prefer-red alkali metal pyrophosphates which can be employed in formulating the electroplating baths of this in-vention. Nevertheless other tetra alkali metal py-rophosphates such as tetrasodium pyrophosphate, ammo-lS nium pyrophosphate, and the like may be utilized.
The tetra alkali metal pyrophosphate is used in amounts ranging from about 20 to 150 g/l, and preferably from about 80 to 100 g/l, expressed as the trihydrated salt. The use of electroplating baths containing palladous diamine dinitrite and tetrapotassium pyro-phosphate is described in the U.S. Patent 4,092,225 to Davis, but it has a current density limitation of about 50 ASF.

The fifth essential ccmponent of the palladiu~ electro-plating baths of this invention is a stress reducing agent. Pre-ferably, 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 use~ul in many operations.

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-t Other stress reducing agents which may be employed in the present invention include, for example, saccharin, and 2-butene 1,4-dione. In general, the amount of stress reducing agent usually employed will range from about 1 to 10 g/l, and preferably from about 3 to 5 g/l.
The electroplating baths of this invention also contain other ingredients useful in this art, provided that they do not have any deleterious results on the formation of ductile palladium or the high rate of deposition that can be achieved herein. As previously mentioned, one of these other in-gredients is a surfactant which can minimize or eliminate any metal pitting problem that may occur in the practice of this invention. Minor amounts of an anionic fluorochemical wetting agent or surfactant such as a blend of potassium perfluoroalkyl sulfonates, sold under the trademarks FC-98 and ~C-95 by the Minnesota Mining and Manufacturing Company, may be employed to prevent pitting. The amount of wetting agent or surfactant will generally range from about 5 to 20 ml/l, preferably from about 7 to 15 ml/l for the present purposes.

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FC-95 and FC-98 are potassium perfluoroalkyl sulfonates, 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 perfluoro-cyclohexyl sulfonate, 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 oxidiz-ing systems. The method of preparing these perfluoro-alkyl sulfonates is disclosed in U.S. Patent 2,5i9,983 to Simons; while a prior art use of such surfactan-ts in electroplating is illustrated by U.S. Patent 2,750,334 to Brown.
The pH of the electroplating baths will be from about 7 to 9, preferably from about 7 to 8; and the baths will be operated at temperatures of from about 30 to 80 degrees C., preferably from about 60 to 70 degrees C. Although the tank current densities which can be effectively utilized with the baths of this in-vention may range from about 10 to 200 ASF, somewhat higher current densities are preferred, i.e. from about 130 up to about 200 ASF. However, in contrast, a cur-rent density range of from about 200~3,000 ~SF can be attained by the practice of the present invention in high speed plating systems. Under the preferred operat-ing 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 of from about 1 to 25 being readily attained.

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lne ~a~lls or ~nls 1nvenclon can ~e use~ ln con~unctlon wlth insoluble platinum, platinum clad, tantalum, or columbium anodes. In general, raek plating is employed and wcrkpiecesl e.g. box and pin eontaets, printed eircuit board eontacts, deeorative jewelry, ete. have surfaces of metals sueh as eopper, brass, bronze, nickel, silver, steel, etc. The palla-dium metal, or when desired, palladium metal alloy duetile deposits are of high quality.
Eleetroplating baths aeeording to the present invention have the following composition:
Component Concentration, q/l (a) Pd metal complex 40 to 80 (b) (NH4)2SO4 30 to 60 (e) NH4Cl 10 to 80 (d) OFB 1 to 10 (e) K4P27 20 to 150 (f) FC-98 5 to 20 ml (g) NH~OH up to pH 8 (h) Watar Remainder The inventi~n will be more fully understood by referenee to the following illustrative embodiments wherein eoncentrations are given in grams per liter (g/l) unless otherwise indicated.
EXAMPLE I
A series of runs were carried out with electroplating baths having the formulations set forth in Table A. All plating was carried out in a tank at current density of 200 ASF, temperature of 70 degrees C., pH 8, with rapid agitation and a constant anode/eathode ratio. The susbtrate used was copper, and the palladium metal complex was palladosamine chloride, Pd(NH3)2C12. The pH was adjusted with NH40H.

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~t The above data indicate that in addition to the palladium metal complex and ammonium the electroplating baths had to contain ammonium sulfate, a stress reducing agent, and tetra-potassium pyrophosphate in order to achieve the desired re-sults. Run A, which was formulated in accordance with thepresent invention, gave excellent results: a high speed, duc-tile palladium metal deposit. In contrast, the other Runs which did not utilize electroplating with all of the necessary components failed to give satisfactory results.
EXAMPLE II

A palladium electroplating bath was prepared by dis-solving the following ingredients in water:
Com~onents Concentration, q/l Pd, as Pd(NH3)2Cl2 7 (NH4)2so4 - 50 ~4P207 . '3H20 - 100 FC-98 (l g/l sol'n) 10 ml The bath was operated at a pH of 9, 70-75 degrees C., and at an achieved current density in the range of 195 ASF. 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.

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EXAMPLE III

Another electroplating bath was prepared by dissolving the following ingredients in water:
Com~onents Concentration, g/l Pd, as Pd(NH3)2C12 60 (NH4)2so4 50 K4p207 3H20 100 OFB
FC-98 (1 g/l sol'n) 10 ml This bath was also operated at a pH of 8 and a temperature of about 70-75 degrees C. Spot cell tests were done with this bath, and current densities up to 3000 ASF were achieved. Good ductile deposits with a deposition rate up to ~ microns~minute were obtained.

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EXAMPLE ~V

Components Concentration q/l Pd, as Pd(NH3)2C12 60 (NH4)2SO4 50 NH4Cl 30 K4p207 3H20 100 OFB
FC~98 ( 1 g/l sol'n) lO ml Cu, as CuSO~ . 5H20 2 The bath was operated at a pH of 7.5~ 70C., current density of 200 ASF. A ductile foil of 25 microns thick was obtained with no codeposition of copper.
The foregoing data reveal that the palladium electro-plating baths of this invention permit the high speed de-position of ductile palladium metal at high current densities,i.e. up to about 200 ASF in a tank and 3000 ASF or higher in a spot cell. In addition, the data show that the bath is highly tolerant to copper, nickel, iron and gold.
It will be further understood that the examples set forth above are illustrative only, and that the invention is subject to variations and modifications without departing from the broader concepts and Eeatures.

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A high speed bath for the electrodepo-sition of ductile palladium metal comprising from about 40 to 80 g/l of palladium metal in the form of a palladium amine complex; from about 20 to 90 g/l of ammonium sulfate; from about 10 to 70 g/l of ammonium halide; from about 20 to 150 g/l of an alkali metal pyrophosphate; and a stress reducing agent, said bath having a pH within the range of from about 7 to about 9.

2. The high speed bath of claim 1 which also contains a minor amount of an anionic fluorochemical surfactant.

3. The high speed bath of claim 2 wherein the surfactant is an alkali metal perfluoro-alkyl sul-fonate.

4. The high speed bath of claim 1 wherein said ammonium halide is ammonium chloride.

5. The high speed bath of claim 1 wherein the palladium amine complex is palladium diamine chloride.

6. The high speed bath of claim 1 wherein the stress reducing agent is a derivative of benzene sulphonic acid.

7. The high speed bath of claim 6 wherein the benzene sulphonic acid derivative is o-formyl benzene sulphonic acid.

8. A method for electrodepositing high speed ductile palladium on a metallic substrate which comprises immersing said substrate in an electroplating bath operated at a pH within the range of from about 7 to 9, a temperature of from about 50 to 80°C, and a current density of from about 10 to 3000 ASF; said electroplating bath comprising an aqueous solution having the following components:
(a) palladium metal, as the palladous amino complex 40 to 60 g/l (b) (NH4)2SO4 30 to 50 g/l (c) NH4Cl 20 to 30 g/l (d) alkali metal pyrophosphate 80 to 100 g/l (e) stress reducing agent 3 to 5 g/l

9. The method of claim 8 wherein the pH of the electroplating bath is about 7 to 9.

10. The method of claim 8 wherein the tem-perature of the bath is from about 60 to 70°C.

11. The method of claim 8 wherein the current density is from 180 to 3000 ASF.

12. The method of claim 8, wherein the subs-trate is selected from the group consisting of copper, nickel, brass, iron, gold, and alloys thereof.

13. The method of claim 8 wherein the pal-ladous amine complex is palladous amine chloride.

14. The method of claim 8 wherein the pal-ladous amine complex is palladous amine nitrite.

15. The method of claim 8 wherein the stress reducing agent is a derivative of benzene sulphonic acid.

16. The method of claim 15 wherein the ben-zene sulphonic acid derivative is o-formyl-benzene sulphonic acid.

17. The method of claim 8 wherein the bath also contains a minor, anti-pitting amount of an anionic fluorochemical surfactant.

18. The method of claim 17 wherein the sur-factant is an alkali metal perfluoroalkyl sulfonate.

19. The method of claim 8 wherein the alkali metal pyrophosphate is tetrapotassium pyrophosphate.