Fifth Generation Reduced Ion Electroless Nickel Systems
Through R&D efforts over the last decade, EN technology suppliers have demonstrated many advances toward replacing lead and cadmium as stabilizing and brightening systems in 50-year-old nickel phosphorus alloy technology.
Since year 2002, various legislative drivers have fueled the evolution of Electroless Nickel (EN) technology. Through Research and Development (R&D) efforts over the next decade, EN technology suppliers demonstrated many advances toward replacing lead and cadmium as stabilizing and brightening systems in 50 year old Nickel Phosphorus alloy technology that over these prior decades were successfully utilized for automotive, aerospace, electronics and industrial applications. A historic evolution time-line by generation is shown in figure 1. From our perspective, the evolution phase of Electroless Nickel development today exists as a 5th generation which is offering some exciting results for applicators.
The commercial results of EN systems from the 4th generation developed platforms have demonstrated good success. There are numerous examples where EN Environmentally Friendly (EF) technologies today out-perform their predecessor lead stabilized systems. This generation of systems developed has been a “win” for our industry but challenges still exist that offer opportunity for continued development.
From an R&D & formulation perspective, new knowledge gained during the development work replacing lead stabilizing systems of the 4th generation (4G) EF EN systems opened the door to new opportunity to think about EN formulations differently. New “additives”, those critical species for EN chemistries including metallic, non-metallic or organic chemical species have been discovered and are being utilized today. Their uses are shown to provide overall improved solution stability, enhanced deposition rates but more importantly the discovery that with their use allows the 4G EN system platform to experience a new range of operating conditions and allow basic chemistry variations that result in greater extended performance which is what applicators expect from systems they utilize today.
However, as an industry, the need for continued evolution with EN technology is in demand because there remains much volatility in the market. Still today, continued regulatory demands pending for nickel and burdens felt as a result of the REACh initiative continue to push EN chemistry providers into reactive mode. These demands are also stretching applicators ability to maintain profitability in an environment where operating costs continue to increase. Applicators “feel the pain” as regulations make it more difficult for maintaining business sustainability and profitability, an important recognized driver for business. It does not appear that regulations will go away anytime soon. Squeezing profitability impacts everyone across the EN supply chain in our industry but is a driver for directing the next evolution development. Continued regulatory turmoil causes well-known companies including suppliers and applicators to consolidate, long time industry publications to cease operation, and companies who once recycled EN solutions to get out of that business, all actions that further disrupt industry and impact cost and profit structures. As a result, it makes sense that applicators are searching for increased value at lower cost. So what is available today for EN applicators looking to improvement the management of their processing costs without redesigning their existing operations, modifying or adding a piece of equipment for their EN department?
Coventya's Brad Durkin on 5G EN Systems
Evolution of Fifth Generation (5G) Reduced Ion Development:
EN formulation basics are well defined in our industry through patents and prior art or knowledge in various teachings and publications. One commonly accepted mechanism for the reduction and deposition of nickel in a hypophosphite reduced bath is as follows:
1. NiSO4 + H2O → Ni++ + SO4 = + H2O
2. NaH2PO2 + H2O → Na+ + H2PO2- + H2O
3. Ni++ + H2PO2- + H2O → Nio + H2PO3- + 2H+
4. H2PO2- + H2O → H2PO3- + H2↑
Equations (1) and (2) simply show the dissociation of the nickel salt and sodium hypophosphite in water. Sulfate and sodium are the by-products of these two reactions that build up with usage. Equation (3) shows the reduction of the nickel ion by hypophosphite to form nickel metal on the parts and an orthophosphite anion which is another major by-product. Equation (4) shows a parallel reaction of hypophosphite with water to form orthophosphite and hydrogen gas.
In these reactions, from the by-products produced perspective provides a clear understanding of what limits EN solution MTO potential. For every 1 g of nickel metal plated, 3.9 g of orthophosphite ion (5.0 g as sodium orthophosphite), 1.64 g of sulfate, and 1.1 g of sodium are produced, and remain in the plating bath as the solution ages. The build-up of these major by-products and salts over the course of the bath life is the primary reason EN is a self-limiting process. This increase, specifically of sodium orthophosphite and sodium sulfate including some other anions, increases the density of the solution at a rapid rate that eventually causes a further degradation in the solubility of other components, which often tend to be the “additives” and stabilizing species which are most critical for sustainability of the EN reactions.
As noted, the primary difference impacting plating performance between nickel phosphorus EN systems results from the “additives” being utilized. The selection of ”additives” representing many types of chemical species are the secrets utilized by EN suppliers for enhancing EN performance and operation, often used in mg/L concentration ranges. The primary functionality for these additives in any EN chemistry is to control solution diffusion efficiencies that take place at the part (substrate) EN solution interface when the applicator places parts into the EN tank. Figure 2 represents a graphical illustration of these solution interactions. As Nickel plating continues in this diffusion zone, the Ni-P alloy builds layers upon itself for providing the final deposit thickness. Additives are known to be very critical and selective for establishing the proper equilibrium for the EN chemical reactions to take place in this diffusion zone as illustrated in figure 3.