How to do Electroless Nickel Plating

Equipment

• The plating tank should be constructed of polypropylene, stainless steel (Type 316) or mild steel with a suitable tank liner depending on bath in use and other considerations.  Stainless steel tanks may be anodically protected if desired.

• Filtration through a 10-micron or finer rated polypropylene filter bag system is suggested.  Polypropylene wound cartridge filters are also permissible, but are not as easy to use as filter bags.  The filtering pump system should turn the bath over at a rate of at least 10 times per hour.  Filter bags should be well rinsed in hot water before use. For the specific filtration recommended for each bath, consult the appropriate Parameters Page.

• Agitation is useful in maintaining bath homogeneity and consistent finish.  Air spargers with air from a high volume, low-pressure air blower is recommended.  Compressed air is not recommended due to potential oil contamination.  Other types of agitation, may also be used. For the specific agitation recommended for each bath, consult the Data Sheet.

• Heating of the bath may be accomplished by various methods including heat exchangers and immersion heaters.  The bath temperature should be monitored and maintained closely.

• Cooling of the bath with an appropriate cooling apparatus should be done rapidly at the end of a shift or any time the bath will not be used for an extended period of time.

• Rack, barrel, and fixturing devices should only be constructed of compatible materials such as polypropylene, CPVC, stainless steel, PTFE, Viton, silicone rubber, and others that can withstand the chemicals and temperature of the plating bath and pretreatment process.

• Masking should only be accomplished with compatible materials such as certain vinyl tapes, stop-off paints, plugs and gaskets made of Viton, silicone rubber, and others that can withstand the chemicals and temperature of the plating bath and pretreatment process.

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Operation

• Review the data sheet, MSDS, and product labels for all components for safety and handling information.  Only operate according to the Data Sheet.

• Contact us for any assistance on the pretreatment of the base materials to be plated.

• The tank should be clean and passivated.  The most common method is with a solution of 40-50% nitric acid for 2-3 hours at room temperature, followed by rigorous rinsing and neutralizing of the tank and verification that no nitrate contamination remains.

• Maintain the bath between 80% and 100% concentration of nickel, hypophosphite, stabilizers, or other chemicals.  Tighter control will further help performance.

• Titrate the bath before and after every batch of parts that is plated.  Replenish during plating cycles if the workload will lower the nickel concentration to 90% or less.

• Continual and accurate measurement of bath temperature, pH, and bath solution level is important.  Evaporation will reduce bath volume and give false indication of actual concentration.  Add DI water as needed during the plating cycle to keep solution at proper level.

• Only use reagent grade ammonium hydroxide (50% concentration or less) and reagent grade sulfuric acid (25% concentration or less) to adjust the pH of bath.

• Air quality in plating shop should be clean and ventilated.  Do not draw dirty air over plating or other tanks.

• Deposition rate depends upon operating temperature, bath loading, pH, agitation, and age of the bath.  

• Plating thickness can be determined by various methods including witness panel measurements, electronic devices, and cross section analysis.

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Bath Maintenance

• The plating bath is maintained by simple analytical procedures and subsequent replenishment. 

• Nickel Metal Concentration

  • The following reagents are required:  Concentrated ammonium hydroxide, Murexide indicator mix (2 grams murexide powder in 100 grams sodium chloride), and 0.0575M E.D.T.A. solution.

  • Analysis procedure:

    • Pipette 10 ml of plating solution into a 250 ml Erlenmeyer flask.

    • Add 100 ml of deionized water, 10 ml of concentrated ammonium hydroxide, and about 0.2 grams murexide indicator mixture and mix well.

    • Titrate immediately with standard 0.0575M E.D.T.A. solution to purple endpoint, and record the number of ml of the E.D.T.A. solution used.

    • The grams/liter of nickel metal in the bath = ml of 0.0575M EDTA used x 0.336.

• Replenishment

  • Replenish according to the Dat Sheet for the EN system in use, based upon the ml of E.D.T.A. consumed in the titration procedure above. 

  • If the nickel metal concentration in the bath falls below 80%, it is best to replenish in two steps to avoid over-stabilization. 

  • Each replenishment component should be added separately to the bath.

  • All replenishments should be made slowly with good mixing, and not directly over the workload.

• Sodium Hypophosphite Concentration

  • With proper make-up and replenishment of the bath, the concentration of sodium hypophosphite should be self regulating.  From time to time, however, it is recommended that this analysis for sodium hypophosphite be done independently to assure the bath is at its optimum concentration. 

  • The following reagents are required:  6N HCl solution, 0.1N iodine solution, 0.1N sodium thiosulfate solution, and standard starch indicator.

  • Analysis procedure:

    • Pipette 5 mL of the plating bath into a 250 mL Erlenmeyer or iodine flask.

    • Add 25 mL of the 6N HCl to the sample.

    • Pipette 50 mL of 0.1N iodine solution to the sample.

    • Stopper the flask and let it stand in the dark for 30 minutes.

    • Titrate the sample with 0.1N sodium thiosulfate solution, adding starch indicator when    a pale yellow color is reached.

    • Continue to carefully titrate until the purple starch color disappears.

    • Calculate the hypophosphite content of the plating solution from the volume of thiosulfate solution used: 5 – (0.1 x mL thio used) = meq hypophosphite in solution

    • (meq hypo) x (10.5) = g/L of hypophosphite

 

Post-Treatment

• • Contact us for any assistance on the treatment of your parts following plating, such as rinsing, passivation, heat treatment, mechanical finishing, stripping, etc.

 

Waste Treatment

• • Contact us for any assistance on the proper treatment/disposal methods of the used plating bath.

  • All usage and waste treatment of the chemicals associated with this process must comply with all federal, state, and local regulations for health, environmental and safety requirements.

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Information About EN provided by Progress for Industry, Inc.​