ELECTROPLATING PALLADIUM

PALLADIUM POUR ELECTRO-DEPOSITION

English 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.

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.
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Description

8864
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
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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
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" 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
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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