Electroless Plating

Electroless plating, as the name implies, does not utilize an electric current for plating. Electroless plating can be carried out as autocatalytic and immersion plating. Autocatalytic plating is the process in which the metal ion in the solution is forced to convert into the metallic state and deposit onto the object to be plated by the use of reducing agents. The process is started by the catalytic action of the surface being plated. For this purpose the surface is pretreated, usually by the application of metal plating. Electroless plating can be applied to metal and nonmetal substrates. The process requires the use of specific chemicals in addition to reducing agents, such as complexing agents and stabilizers. Specific conditions such as pH and temperature also need to be satisfied. Hydrazine, dimethylamine borane (DMAB), hypophosphite, and formaldehyde are common reducing agents. Many types of complexing agents such as EDTA, Rochelle salt, tartrates, and citrates are used. Thiodiglycolic acid, mercaptobenzotiazone (MBT), thiourea, fluoride salts, heavy metals, thioorganic compounds, and cyanides are among the stabilizers used. HCl, H2SO4, NaOH, and ammonium hydroxide are used for pH adjustment. Copper and nickel electroless plating is commonly used for PCBs. Electroless plating of precious metals is also common.

Immersion plating is also carried out without the application of electric current. However, in this case the metal ion in solution is plated onto the base metal, not by forcing with reducing

Figure 1 Sequence of the metal finishing operations. (From Ref. 2.)

Figure 1 Sequence of the metal finishing operations. (From Ref. 2.)

Table 2 Common Electroplating Bath Compositions [4]

Electroplating baths

Composition

Table 2 Common Electroplating Bath Compositions [4]

Electroplating baths

Composition

Brass and bronze

Copper cyanide

Zinc cyanide

Sodium cyanide

Sodium carbonate

Ammonia

Rochelle salt

Cadmium cyanide

Cadmium cyanide

Cadmium oxide

Sodium cyanide

Sodium hydroxide

Cadmium fluoroborate

Cadmium fluoroborate

Fluoroboric acid

Boric acid

Ammonium fluoroborate

Licorice

Copper cyanide

Copper cyanide

Sodium cyanide

Sodium carbonate

Sodium hydroxide

Rochelle salt

Copper fluoroborate

Copper fluoroborate

Fluoroboric acid

Acid copper sulfate Copper sulfate

Sulfuric acid

Copper pyrophosphate Copper pyrophosphate

Potassium hydroxide Ammonia

Fluoride-modified copper cyanide Copper cyanide

Potassium cyanide Potassium fluoride

Chromium Chromic acid

Sulfuric acid

Chromium with fluoride catalyst Chromic acid

Sulfate Fluoride agents, but spontaneously and as a thin film only, by the difference of electrode potential of the metal in solution and base metal. The metal in solution has a higher electrode potential, that is, it has a higher tendency to be reduced. Immersion plating baths contain alkalis and complexing agents. Sometimes nonalkaline heated baths are used, as in the case of copper plating on steel, or aluminum. Complex agents commonly used are lactic, glycolic, and malic acid salts, ammonia, and cyanide. Sulfuric and hydrofluoric acids are used for nonalkaline applications. Aluminum, copper alloys, zinc, and steel are plated by immersion plating. Commonly used metals for plating are cadmium, copper, nickel, tin, zinc, and precious metals.

Was this article helpful?

0 0
Waste Management And Control

Waste Management And Control

Get All The Support And Guidance You Need To Be A Success At Understanding Waste Management. This Book Is One Of The Most Valuable Resources In The World When It Comes To The Truth about Environment, Waste and Landfills.

Get My Free Ebook


Post a comment