Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-10-03
2004-06-01
Wong, Edna (Department: 1753)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C205S257000, C205S259000, C205S265000
Reexamination Certificate
active
06743950
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel complex salt based on ethylene-diamine and palladium sulfate and to its use for adjusting the palladium concentration of an electrolysis bath for the deposition of palladium or one of its alloys.
The electrical contacts and the connectors used in the field of electronics receive, as a finish, thin layers of electroplated precious metals which have to be suitably bright, have good ductility, be non-porous and have corrosion resistance, frictional resistance and low contact resistance. Industry started by using deposits of gold hardened with small amounts of codeposited nickel or cobalt, often referred to as hard gold. Palladium is a precious metal whose deposits have a lower density (12 g/cm
3
) than those of hard gold (17.3 g/cm
3
); it also has a greater hardness and a lower porosity. Being less expensive, palladium and its alloys were considered suitable gold substitutes for the majority of applications. As a finish in a wide variety of applications, industry uses thin deposits (also called flash deposits) of gold on palladium or a palladium alloy. The main palladium alloys used are palladium-nickel or palladium-silver alloys. Techniques commonly used for the electroplating of palladium and its alloys are the barrel, the vibrating basket, the rack, batch metallization, high-speed continuous metallization (or jet plating) or pad metallization. Industry is constantly in search of more efficient electrolysis baths and processes. Palladium and its alloys are also used for decorative applications as an undercoat or finish.
The majority of palladium and palladium alloy baths currently on the market are ammoniacal baths most frequently containing chloride ions. These baths nevertheless have a high nuisance factor, both in terms of the operators' health and in terms of corrosion of the equipment, and they require a large number of maintenance operations.
Attempts have also been made to use non-ammoniacal baths:
The first baths of this type to have been described were pure palladium baths in very acidic media free of organic amines. They were difficult to use. In fact, at pH values of between 0 and 3, the substrates are attacked too strongly; furthermore, many of these formulations contain chlorides.
A second type consists of pure palladium or palladium alloy baths containing organic amines, which operate at 40 to 65° C., typically in a pH range of 9 to 12, i.e. under strongly alkaline conditions. At these high pH values and these temperatures, polyamines tend to evaporate appreciably and to rapidly become carbonated and produce crystals. Furthermore, under these conditions, the passivation of nickel-plated substrates is even greater than in ammoniacal baths. To overcome the lack of adherence, it is necessary to palladium-plate the substrates beforehand in a preliminary step, thereby increasing the cost price of these deposits accordingly.
A third type of bath, described in particular in patent U.S. Pat. No. 4,278,514, is a pure palladium bath containing organic amines. These baths, whose pH values are intermediate at between 3.0 and 7.0, generally contain phosphates and use a compound of the imide type, such as succinimide, as a brightening agent.
Among the organic amines used in this type of bath, ethylenediamine is particularly preferred because, as described especially in patent U.S. Pat. No. 4,278,514, it serves inter alia to complex the palladium so as to render it soluble in the electrolysis bath. Said document also envisages introducing the palladium into the electrolysis bath via an aqueous solution of a palladium/ethylenediamine complex in which each palladium atom is already complexed with two molecules of ethylenediamine.
Electrolyte formulators are well aware that the life of the baths increases with the extent to which the processes developed make it possible to avoid the rapid concentration of salts in the electrolysis baths used.
Now, electrolysis baths containing palladium complexed with ethylene-diamine have hitherto had relatively short lives because the methods of reloading these baths with metal involved introducing this metal in one of the following two ways:
either in the form of a simple, non-complexed inorganic salt which, whether in solid or liquid form, is necessarily in a very acidic medium in order to avoid the formation of palladium hydroxide, the latter usually being very difficult if not impossible to resolubilize once it has formed;
or in the form of water-soluble palladium, because in the form of palladium-bisethylenediamine sulfate, which is a water-soluble complex having a molar ratio [ethylenediamine]:[palladium] of about 2. In practice, this type of addition entails adding a liquor which results from the addition of an inorganic palladium salt in a very acidic medium to a solution of ethylenediamine containing at least two moles of diamine per mole of palladium.
In both cases a substantial accumulation of ions takes place during the life of the bath.
In fact:
In both cases the bath accumulates salts originating from the introduction of all the anions associated with the initial acidity of the simple inorganic salt used.
In the second case the bath also accumulates a large amount of diamine which it is unable to eliminate under the operating conditions. The electrolyte then rapidly becomes saturated with an ethylenediamine salt.
SUMMARY OF THE INVENTION
The inventors of the present invention have now developed a novel compound which makes it possible to introduce the palladium with a particularly reduced amount of counterions, and consequently to make a remarkable reduction in the ion loading of the electrolysis baths. This compound contains a reduced amount of complexing agent that is adapted so as to be very close to the amount just necessary to maintain its concentration at a stable level over time. The result of this process is considerably to improve the life of these baths.
Thus, according to a first feature, the invention relates to a novel palladium compound.
According to a second feature, the invention further relates to a process for the preparation of this compound.
According to a third feature, the invention further relates to the use of this novel compound for introducing palladium into an electrolysis bath for the electro-chemical deposition of palladium or its alloys, or for adjusting its concentration throughout the electrochemical deposition.
The invention further relates to an electrolysis bath for the deposition of palladium or its alloys, in which the palladium is introduced in the form of the novel compound forming the subject of the first feature of the invention, and in which, still with the same concern to avoid loading the electrolysis bath with salts, the other compounds are introduced in appropriately adapted forms.
More precisely, according to one of its essential characteristics, the invention relates to a complex salt of palladium sulfate and ethylenediamine which contains 31 to 41% by weight of palladium and in which the molar ratio [SO
4
]:[Pd] is between 0.9 and 1.15 and the ratio [ethylenediamine]:[Pd] is between 0.8 and 1.2.
As explained above, by virtue of this novel compound, palladium can be introduced in a form already partially complexed with ethylenediamine into electrolysis baths for the electroplating of palladium or its alloys. The dissolution of this compound in an aqueous bath containing excess ethylenediamine corresponds only to completing the total complexation of the palladium.
The compound of the invention therefore has the advantage that the amount of sulfate introduced into the electrolysis bath is much smaller than that which would be necessary to introduce the palladium in one of the two forms of the prior art described above.
In fact, the complex used according to the prior art to introduce the palladium into the baths consisted of a water-soluble complex, namely palladium-bisethylenediamine sulfate, in which the molar ratio [ethylenediamine]:[pa
Chalumeau Lionel
Gonzalez Jose
Limayrac Michel
Dennison Schultz Dougherty & MacDonald
Metalor Technologies France SAS
Wong Edna
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