Coating processes – Immersion or partial immersion – Chemical compound reducing agent utilized
Patent
1998-01-25
2000-04-11
Talbot, Brian K.
Coating processes
Immersion or partial immersion
Chemical compound reducing agent utilized
427 98, 427305, 427438, 106 122, 106 129, B05D 118, B22R 700
Patent
active
06048585&
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
This invention relates to electroless nickel plating baths which employ a hypophosphite reducing agent. More particularly, this invention relates to improved electroless nickel plating baths which are made long running by(a) controlling and removing undesirable phosphite anions produced as a by-product during the electroless plating reaction (b) minimizing the formation of sludge in the bath and (c) minimizing the presence and effect of undesirable ions. The invention also relates to nickel deposits having low porosity and low compressive stress.
BACKGROUND OF THE INVENTION
Electroless nickel plating is a widely utilized plating process which provides a continuous deposit of a nickel metal coating on metallic or non metallic substrates without the need for an external electric plating current. Such a process is described generally as a controlled autocatalytic chemical reduction process for depositing the desired nickel metal and is simply achieved by immersion of the desired substrate into an aqueous plating solution under appropriate electroless plating conditions.
In conducting electroless nickel plating, particularly from a bath which utilizes a hypophosphite as the reducing agent, the bath basically contains a source of nickel cations such as nickel sulfate and a hypophosphite reducing agent such as sodium hypophosphite. The deposition reaction takes place in the bath and generally involves the reduction of a nickel cation to form a nickel metal alloy as a deposit on the desired substrate surface. The reduction reaction is generally represented by the following equation: +2HPO.sub.3.sup.-2 +P+Ni.sup.o
It is seen that the electroless reaction produces phosphite ions, hydrogen ions and hydrogen gas; it also produces a counterion of the nickel source compound used, typically a sulfate, SO.sub.4.sup.-2 The nickel and hypophosphite are consumed in the reaction and they, accordingly, must be frequently replenished. In addition, as the hydrogen ions produced in the reaction accumulate they result in a lowering of the pH from the optimum plating ranges. In order to maintain the desired pH range, and in usual practice, a pH adjustor such as a hydroxide or carbonate especially of an alkali metal such as sodium is added frequently during the plating reaction. This significantly increases the monovalent sodium cation concentration of the electroless plating bath.
Additionally, nickel usually in the form of nickel sulfate is added to maintain the optimum nickel concentration thereby increasing the concentration of undesirable sulfate anion. As the reaction continues, the by-products and bath conditions created thereby present problems which adversely affect the desired plating process.
These problems are the buildup of the phosphite anion produced from the oxidation of the hypophosphite reducing agent, the buildup of the anion of the nickel salt employed, typically sulfate, as well as the increased concentration of extraneous cations, especially sodium. This build-up or increase in the concentration of such anions and cations as they accumulate in the bath produces a deleterious effect on the plating reaction and also adversely affects the quality of the plating deposited on the substrate. In particular, the phosphite anion causes an increase in stress of the nickel deposit and shifts the stress from compressive to tensile; this increased stress reduces the corrosion resistance of the nickel deposit. Also, the accumulation of ionic species in the bath degrades the quality of the nickel deposit and makes it unacceptable for such high-level applications as hard discs for computers, as well as CD-ROM and other optical disc storage. Further, the phosphite anions adversely affect the bath by often reacting with and precipitating the nickel cation as nickel phosphite; this slows the rate of deposition of nickel, prevents long lasting baths and results in the bath becoming unsatisfactory and thus terminated at low levels of metal turnover, i.e., the number of times that the original nickel so
REFERENCES:
patent: 5221328 (1993-06-01), Bishop et al.
patent: 5258061 (1993-11-01), Martyak et al.
patent: 5277817 (1994-01-01), Martyak et al.
patent: 5338342 (1994-08-01), Mallory, Jr.
patent: 5944879 (1999-08-01), Martyak
Martyak Nicholas M.
McCaskie John E.
Atotech Deutschland GmbH
Marcus Stanley A.
Rudman Gilbert W.
Talbot Brian K.
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