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Which is better Ni over tin plating or copper over tin plating on brass parts

Presently we are doing 3 microns Ni and then 8 Microns tin plating on brass parts. We would like to know is there any disadvantage if we do 3 microns Copper and then 8 microns tin plating on these brass parts?

Basically what is the purpose of doing Nickel or copper before tin plating on brass parts?

Zankar Desai
Sr Engineer - Vadodara, Gujarat, India
2007

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Dear Mr. Deasi,
Copper have the tendency to diffuse through the top layer and I am afraid the product may fail in your tests if copper plated.Black spots may appear on the plated surface sooner or later.Nickel plating acts as a barrier layer as brass you know is 80:20 Cu/ZN.As of now I think you cannot avoid or replace Nickel.Nickel plating also gives you a leveled deposit.Having said this there are two processes which can replace Nickel i.e; Palladium and White bronze with proper ratio of Copper/tin/Zinc.Generally 10 Microns of Nickel= 3 Microns of White bronze= 0.2 Microns of Palladium.The selection of the process usually depends on the requirements and cost.
Regards

T.K. Mohan
plating process supplier - Mumbai, India
2007