Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Phosphorus or compound containing same
Reexamination Certificate
2000-07-24
2001-08-28
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Phosphorus or compound containing same
C502S208000, C502S022000, C502S025000, C502S026000, C502S027000, C502S028000, C502S029000, C502S033000, C427S430100, C427S435000, C427S436000, C427S437000, C427S438000
Reexamination Certificate
active
06281157
ABSTRACT:
FIELD OF THE INVENTION
1. Field of the Invention
The present invention relates to the formulation of a bath enabling the preparation of a deposit of nickel-phosphorus (Ni—P) alloy on substrates used in the manufacture of printed circuit wafers and more particularly, to deposition of such alloys by chemical self-catalysis.
2. Discussion of the Related Art
Existing nickel baths are all relatively short-lived. Typical nickel baths include combinations of complexing agents, buffers and stabilizers as well as nickel salt and phosphites. Typical complexing agents have included lactic acid, maleic acid, aspartic acid, propionic acid, succinic acid, citric acid, etc. Several different complexing agents are generally associated with one another. It is known that the complexing agents, and especially citric acid or its derivatives, are incapable of tolerating large quantities of phosphites. The phosphite content determines the quantity of phosphorus that can be deposited, and hence the lifetime of the bath. Therefore, depletion of the bath's phosphite content decreases the bath lifetime.
Due to the short lifetimes of baths that presently exist in the market, it is very difficult to create conditions for making the deposits. It is known that a small quantity of citric acid or of one of its derivatives causes a rapid decomposition of these baths by the precipitation of nickel phosphites, therefore, citric acid and its derivatives are not typically used as complexing agents. In addition, stabilizers are reputed to be poisons in the self-catalytic reaction, and therefore require handling with care. At present, the use of gluconates has been limited to cleansing solutions.
Therefore, due to the difficulties associated with creating the conditions necessary for making such deposits, the quality of the coatings is reduced and their cost price remains very high.
SUMMARY OF THE INVENTION
The present invention provides a self-catalytic bath having a longer lifetime than presently existing baths. The bath according to the present invention includes nickel sulfate, sodium hypophosphite as a reducing agent, acetic acid as a buffer, and traces of lead as a stabilizer. More particularly, the bath includes a citrate complexing agent, associated with a gluconate used both as a catalyst and a stabilizer. In preferred embodiments, the citrate is sodium tricitrate and the gluconate is sodium gluconate.
Advantages provided by the bath includes high quality deposits, very high deposition rates, easy handling, and simple conditions of implementation. In addition, such deposits can also be made on non-conductive substrates.
The bath according to the invention can tolerate large quantities of hypophosphite, thereby considerably increasing its lifetime. When used in continuous operation, the bath can provide about 38 grams of Ni—P alloy per liter of solution. Furthermore, the bath according to the invention can be used to obtain amorphous deposits containing 13% by weight of phosphorus. Such deposits have a decorative appearance, greatly improved adhesion and hardness, and high corrosion resistance.
In another aspect, the present invention provides a method for the deposition of Ni—P alloy on a substrate by self-catalytic chemical means. The method involves plunging a substrate directly into the bath described above. Preferably, the substrate is made of iron, mild steel, copper or again of a non-conductive material.
REFERENCES:
patent: 4019901 (1977-04-01), Mallory, Jr.
patent: 4038085 (1977-07-01), Scannell
patent: 4152164 (1979-05-01), Gulla et al.
patent: 5221328 (1993-06-01), Bishop et al.
patent: 5614003 (1997-03-01), Mallory, Jr.
patent: 5718745 (1998-02-01), Itoh et al.
Bachir Ali Ben
Cherkaoui Mohamed
Ebntouhami Mohamed
Elhark Mohamed
Saaoudi El Mustapha
Galanthay Theodore E.
Morris James H.
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
Wood Elizabeth D.
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