The Evolution of a Process: Fifty Years of Electroless Nickel

lectroless nickel plating is a relaE. hvely new technological process. The first laboratory experiments were done in 1944 by A. Brenner and G. Riddelll during World War 11. Public announcements were made a few years later. This work bad been done without knowledge of the earlier observations by Roux in 1916* and by Wurtz3 in 1845. The early work was not successful due to poor quality reagents and other factors. Thus, Brenner and Riddel are credited as the discoverers of this technology, as they developed the first workahle baths and began scientific investigations of the process. This is not a very long history for a technology. Most of the details of its evolution are still readily available for study. These data show that the field has undergone a very rapid initial expansion in scientific understanding coupled with a wide range of practical uses. Further technological development has continued at a slower pace, hut usage has been rapidly increasing both in terms of number of applications and total usage. The field has not yet become static or mined out. Looking at the background of the process, it is obvious that electroless plating is not a unique field by itself, but is only one of a series of closely related surface-coating techniques. They can be conveniently divided into gas-phase and liquid-phase processes. The gas-phase types can be easily subdivided into many other categories, such as thermaland electron-beam evaporation, plasma spray or reactive sputtering. There are some hasic technical differences in the way these are divided. Liquid-phase processes are based on reactant reduction by an internal electron flow. Gas-phase processes usually use some form of thermal energy input rather than electron flow. (Some forms of ion plating using a charged substrate are exceptions.) In this view, electroplating and electroless plating are conceptually closely related. Despite the difference in techniques among the hasic categories, the same types of coatings can he obtained from each process, whether it be nickel, nickel-phosphorus or other alloys; for example, a nickel-phosphorus coating can be made by thermal decomposition of nickel carbonyl and a phosphine: electrolysis of a nickel solution containing hypophosphite? or by electroless deposition?-* These coatings may be the same by hulk chemical analysis, but important differences can be found. The most important practical differences may include: