CA1089796A

CA1089796A - Electroplating palladium

Info

Publication number: CA1089796A
Application number: CA289,192A
Authority: CA
Inventors: Thomas F. Davis
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1976-11-17
Filing date: 1977-10-20
Publication date: 1980-11-18
Also published as: JPS6035439B2; DE2751055C2; ES464140A1; FR2371530A1; NL183534B; DE2751055A1; IT1088629B; JPS5363226A; NL7711735A; NL183534C; FR2371530B1; GB1534452A

Abstract

Abstract 1. A method of electroplating palladium on a substrate comprises passing an electric current between an anode and the substrate in a bath comprising an aqueous solution of palladium diammonium dinitrite (Pd (NH3)2 (NO2)2) and tetrapotassium pyrophosphate. In a preferred method the electric current passes at a current density of 2 to 50 ASF (0.2 to 5.4 ASD) in a bath containing 4 to 18 gpl of palladium and 5 to 300 gpl of tetrapotassium pyrophosphate, the solution being at a pH of 8.5 to 11 and being maintained by the addition of pyrophosphoric acid or potassium hydroxide.
The baths for the electrodeposition of palladium also form part of the invention.

Description

Methods of electroplating palladium on a substrate are known and comprise passing an electric current between an anode and the substrate in a bath comprisinq an aqueous solution of a palladium salt.
In accordance with this invention the solution contains palladium diammonium dinitrite (Pd (NH3)2 (N02)2) and tetrapotassium pyrophosphate. It is preferred that the solution containX 4 to 18 gpl of palladium and 5 to 300 gpl of tetr~potassium pyrophosphate, ~ at a pH of 8.5 to 11, - 10 the pH being maintained by the addition of pyrophosphoric acid or potassium hydroxide to the solution, and the current pass~ at a density of 2 to 50 amperes per square foot (ASF) (0.2 to 5.4 amperes per square decimeter (ASD)).
The plating baths in question form a further feature of this invention.
Current densities higher than 50 AS~ (5.4 ASD) tend to result in burning of ths surface of the substrate. At current densities lower than 2 ASF the plating rate is low.
Below pH 8.5 the current efficiency tends to fall off and above pH 11 there is little increase in the plating rate.
We have found that a most satisfactory method involves plating at a current density of 20 ASF (2.1 ASD), the pH
being 8.7 to 9.5, the temperature of the bath being 125F
t57 C) and the solution containing 8 gpl of palladium.
The tetrapotassium pyrophosphate content of the solution can advantageously be 150 gpl; while this salt is conveniently added to the solution in the trih~drate form ' - : :

- :
., . ~ .

concentrations of the salt refer to the anhydrous form.
The current e~ficiency of plating methods in accordance with the invention is higher than has heretofore been obtainable for the electroplating of palladium. The efficiency is expressed as cathode efficiency and can be as high as 95% in accordance with the invention. The theoretical value for palladium deposition is calculated to be 33.1 milligrams per ampere-minute. If the current efficiency is 95%,palladium is being deposited at a rate of 31.4 milligrams per ampere-minute.
The anode used in the plating method may be in-soluble platinum, platinum-clad or tantalum bodies. An anode to cathode ratio of 1:1 as a minimum should be em-, ployed and the bath should be vigorously agitated, for example by mechanical means.
The substrate may be a base metal, such as copper and alloys thereof, such as brass and bronze, or nickel, silver, steel or alloys of nickel, silver, or iron e.g. stainless steel.
; The invention will now be described with reference to the following Examples.
; EXAMPLE 1 A solution was made up with the following composition and concentrations:
10 gpl Palladium (derived from Pd (~H3)2 (N02)2) ; 150 gpl Potassium Pyrophosphate.
~:- The solution was adjusted to pH 9 by the addition of pyrophosphoric acid or potassium hydroxide and heated to ':~

,.
,~

. . .

. , " 8864 130 F (54 . 5 C) .
The solution was then used as a bath to rack-plate palladium on copper samples, the current density being 20 ASF (2.1 ASD). During plating the bath was mechanically agitated. The cathode efficiency of the plating method was found to be approximately 94%.
; EXAMPLE 2 Example 1 was repeated at other current densities of 10, 30, 40 and 50 ASF (1.1, 3.2, 4.3 and 5.4 ASD) and the ; 10 cathode efficiency remained at approximately 94~ at densities of 10, 30 and 40 ASF (1.1, 3 . 2 and 4. 3 ASD). At 50 ASF
(5.4 ASD) the efficiency was 76%.

Example 3 was repeated at a temperature of 125 E
tS7C) with the solution at varying pH values, the pH having been adjusted by the addition of pyrophosphoric acid or potassium hydroxide. The cathode efficiencies were as follows:
pH Cathode Efficiency 8.0 89.3 ' 8.5 92.4 9.0 94.0 , 9.5 93.7 ` 10.0 94.3 ."

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Claims

The embodiments of the invention for which an exclusive property or privilege is claimed are as follows:

1. A method of electroplating palladium on a substrate which comprises passing an electric current between an anode and the substrate in a bath comprising an aqueous solution of palladium diammonium dinitrite (Pd (NH3)2 (NO2)2) and tetrapotassium pyrophosphate.

2. A method of electroplating palladium on a substrate which comprises passing an electric current between an anode and the substrate at a current density of 2 to 50 ASF (O. 2 to 5. 4 ASD) in a bath comprising an aqueous solution of Pd (NH3)2 (NO2)2 in an amount to provide 4 to 18 gpl of palladium and 5 to 300 gpl of tetrapotassium pyrophosphate at a pH of 8. 5 to 11, the pH being maintained by the addition of pyrophosphoric acid or potassium hydroxide to the solution.

3. A method according to claim 1 or claim 2 in which the current density is 20 ASF (2.1 ASD), the pH 8.7 to 9.5 and the temperature of the bath 125°F (57°C).

4. A method according to claim 1 or claim 2 in which the solution contains 8 gpl of palladium.

5. A bath for the electrodeposition of palladium which comprises an aqueous solution of Pd (NH3)2 (NO2)2 in amount to provide 4 to 18 gpl of palladium and 5 to 300 gpl of tetrapotassium pyrophosphate at a pH of 8.5 to 11.