“Those dreams that on the silent night intrude, and with false flitting shapes our minds delude ... are mere productions of the brain. And fools consult interpreters in vain.” Jonathan Swift

Electroless Plating

Electroless nickel (EN) plating is a chemical reduction process which depends upon the catalytic reduction process of nickel ions in an aqueous solution (containing a chemical reducing agent) and the subsequent deposition of nickel metal without the use of electrical energy. Due to its exceptional corrosion resistance and high hardness, the process finds wide application on items such as valves, pump parts etc., to enhance the life of components exposed to severe conditions of service ,particularly in the oil field and marine sector. With correct pretreatment sequence and accurate process control , good adhesion and excellent service performance can be obtained from EN deposited on a multitude of metallic and non-metallic substra6tes.

In the EN plating process, the driving force for the reduction of nickel metal ions and their deposition is supplied by a chemical reducing agent in solution. This driving potential is essentially constant at all points of the surface of the component, provided the agitation is sufficient to ensure a uniform concentration of metal ions and reducing agents. Electroless deposits are therefore very uniform in thickness all over the part's shape and size. This process offers distinct advantages when plating irregularly shaped objects, holes, recesses, internal surfaces, valves or threaded parts. Distinct advantages of EN plating are:

The versatility of electroless nickel plating is demonstrated by the wide range of coatings possible. The following are important types of coatings industrially available (reference):

A unique bath providing an as-plated deposit hardness of up to 60 Rockwell This bath provides a deposit nearly as hard as Hard Chrome, with the advantage of a uniform thickness inside complex configurations, as well as outside. The deposit is so uniform that grinding after plating is eliminated. Low Phosphorous Electroless Nickel offers excellent resistance to alkaline corrosive environments.

This is a workhorse electroless nickel. It has proven itself over the years. Steel parts plated with Medium Phosphorous electroless nickel will in many cases perform like stainless steel. Electroless nickel will not build up on edges or ends, and it plates inside and out giving uniform total coverage. With heat treatment, medium phosphorous electroless nickel can be hardened from 45 Rockwell C to as high as 68 Rockwell C.

This finish provides maximum corrosion resistance. High Phosphorous electroless nickel is standard in industries that require resistance to strongly acidic corrosive environments like oil drilling and coal mining. High Phosphorous electroless nickel has a low degree of solderability. It will remain solderable for only a brief period of time after plating. This makes it a desirable finish for electronics parts such as connector housings and semiconductor packaging.

Teflon adds to the already slick surface of the electroless nickel, yielding a very low friction surface. This product is a relatively new one. It consists of microscopic beads of Teflon co-deposited up to 20% with the electroless nickel. This finish can be the solution to sticking, galling or drag problems with moving parts, or heated seal surfaces. In some cases, liquid lubricants can be eliminated with the use of Nickel/Teflon plating.

Electroless nickel can be applied directly to zinc die cast without a copper layer. This has many applications where corrosion resistance and resistance to chipping and flaking is necessary

The selection of a specific grade of EN-plating is done in accordance with the nature of application, where a high hardness and low coefficient of friction is desired, low phosphorous EN is preferred (1-3%P). For general applications where a bright finish is required and the operating conditions are not very corrosive, medium phosphorous (6-8% P) EN is used e.g.. Computer printer rollers, machine components, plastic molding dies etc. When the conditions of use for an EN plated components are severely corrosive, a high phosphorous EN (12-13% P) is usually selected. The high phosphorous EN is amorphous in nature and is compressively stressed unlike the low and medium phosphorous EN which are Crystalline and tensile stressed. Proper process sequence and maintaining the correct operating parameters helps ensure a virtually non porous deposit of high phosphorous ENP which finds wide application in areas such as valve components, aerospace industry, oil & gas and chemical industries etc.

Physical Properties

Specifications and Testing

ASTM specifications are generally followed in evaluating EN plated components some of the relevant tests are as follows

Areas of Application

Due to its unique properties of excellent corrosion resistance, combined with a high wear resistance and uniformity of coating, EN finds extensive applications in a number of fields. Some of the prominent areas of application are:

See also: Cladding, Electroplating, Pack cementation, Electroless plating, Vapor deposition, Hot dip galvanizing, Thermal spraying, Zinc coatings

Solderability of E/N coatings

Most suppliers of E/N now recommend using low phos. for the best solderability, and longest shelf life. Standards ISO 4527, DIN 50966 and ONORM C 2550 (Austrian) reference this important property.

A paper submitted at the Electroless Nickel conference of 1989 held in Cincinnati Ohio, Titled "Solderability Parameters of Elecroless Nickel Bearing Electronic Finishes" By Louis Kosarek of STB Systems, Inc. report that "An electroless nickel deposit which contains a concentration of phosphorus ranging from 0.1% to 3.0% is readily solderable on an "As-plated Basis" per Mil-Std 883c method 2003. The frequency of solderability tests which fail per Mil-Std 883c will increase as the phosphorus content of electroless nickel alloy increases from 3.0 to 7.0% phosphorus. A solderability test conducted per Mil-Std 883c method 2003 incorporating an as-plated surface finish containing phosphorus in excess of 7%, the components will consistently fail. The mode of failure is non-wetting of the surface."

Mr. Kosarek's work is referenced in "Electroless Nickel Plating" by Wolfgang Riedel, Published by ASM International, ISBN 0-904477-12-6, under physical properties. This book is the best source for information on E/N plating, in my humble opinion.

On a personal note, most solderability problems I have heard over the years is when a purchaser switches vendors, and the new vendor does not have low phos. nickel, and uses mid. or high phos. instead or the vendor simply stops using the low phos. because of low demand and substitutes mid or high phos. thinking they are the same. I have heard of many solderability problems "disappear" when purchasers required certification to the low phos. requirement from their supplier.

The present consensus seems to be "the purer the nickel alloy the better the solderability."

Paul Szymanowski, Micro Plating, Inc.