GENERAL OVERVIEW OF ELECTROLESS NICKEL PLATING
An electroless nickel coating is a dense alloy of nickel and phosphorus. The amount of phosphorus co-deposited can range from less than 2% to more than 12%, depending upon bath formulation, operating pH and bath age. The deposition process is autocatalytic; i.e., once a primary layer of nickel has formed on the substrate, that layer and each subsequent layer becomes the catalyst that causes the above reaction to continue. Thus, very thick coatings can be applied, provided that the ingredients in the plating bath are replenished in an orderly manner. In general commercial practice, thickness range from 0.1 mil to 5 mils, but in some salvage operations 30 mil deposits are not uncommon
Electroless nickel deposits are functional coatings and are rarely used for decorative purposes only. The primary criteria for using electroless nickel generally falls within the following categories
Corrosion resistance
Wear resistance
Hardness
Lubricity
Solderability and bondability
Uniformity of deposit regardless of geometries
Nonmagnetic properties of high-phosphorus nickel alloy
In the early years, platers encountered many problems with electroless nickel because of poor formulations, inferior equipment, misapplications and a general misunderstanding of the process and the deposit. In the first decade and a half of its existence, electroless nickel plating had an aura of “black magic” attached to it. Modern bath formulations, however, use only the purest grades of chemicals, delicately balanced and blended to give the processor plating baths with long life, exceptional stability, consistent plating rates, self-maintaining pH and most importantly, reproducible quality. In addition, advancements in tank design; filtration systems, heating and agitation have virtually eliminated the problems that plagued the user years ago
Furthermore, in the past decade, advancements have been made in autocatalytic nickel-plating solutions. Reducing agents other than sodium hypophosphite are used for special applications; composites of nickel with diamonds, silicon carbide and PTFE are available; and ternary alloys may be applied. Also, baths have been formulated to yield specific results, i.e., high corrosion resistance, brightness, high plating rate, improved ductility and low levels of magnetic response. Today, chemistries that utilize extended life strategies are becoming more common
