Metal finishing Q&As since 1989

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Advantages of multilayer gold plating

I performing Gold Electroplating on a semi conductor test products. I seem to have better results with the products I have plated with Two layers. Are Two layers of gold Harder than One?

Michael Drush
Semi Condutor Test Division- Rio Rancho, New Mexico
2005

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Two thin layers can be harder than one thick layer because what tends to make electroplating hard is dislocations in place of large grains. When a new layer starts there is stretching and straining as the crystal structure of the deposit tries to match the structure of the substrate.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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2005

Ted,

Is this principle the same for all types of plated metal? I mean for example two layers of zinc plating, or two layers of tin.

Thanks

Guillermo Castorena G.
Jobshop - San Luis Potosí, México

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I have read explanations about how plating initiates, initially trying to mimic the structure and atomic spacing of the substrate, but gradually evolving to its own inherent crystal structure, thus allowing larger grains as the thickness increases, that I am confident that the initial thickness is always harder because of these dislocations. Unfortunately, whether this fact has real engineering utility in individual cases is something I don't know. The many reports of harder deposits available via pulse plating seem to support it however.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

There are several US Patents that claims better performances on multilayered or double layered electroplating especially on gold.

Hamilton Solidum
- Mays Landing, NJ
2006

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2006

Ted/Michael
Sorry to join you late.
For plating on semi conductors, usually 2 layer plating is done. 1.strike/flash plating with preferably 24kt pure gold to get even/leveled plating which will make the surface pore free deposit with pure gold.
2. Usually semi conductors will have a hard gold deposit followed by pure gold deposit, hardened by addition of either nickel or cobalt as hardeners( Nickel will give pale yellow colour where as Cobalt will give you reddish yellow for the final finish.The deposit is usually 23.5KT (0.5Kt will be of Ni/Co).
Michael please explain the composition of the bath you plate, i.e., for 2 layers. I will be able to help you on the basis of your explanation.
regards.

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

Gold solutions are formulated to plate at a certain hardness. Current density, metal concentrations, PH, temperature, bath purity are also things that can effect hardness. Two layers of pure gold will not be any harder than one layer. Knoop hardness tests have proved that. Two layers of hard acid gold maybe slightly harder than one, but not enough to to make a difference. The reason a gold strike or flash is important under an alloyed or hard gold is because if the gold is to be soldered, the outer layer of gold is absorbed into the solder layer, and you are soldering directly to the pure gold layer, or underlying barrier layer which in most cases is Nickel Sulfamate or EN. A gold strike also promotes good adhesion, just like any other metal strike. I think what is important here is double layer deposited thickness, not double layer deposited hardness. You have the added corrosion resistance directly related to added thickness plated. Is the gold deposit harder when you have to give the part additional time in the bath, lets say to add another 20 microinches to achieve proper thickness? Not happening! Other metal plating solutions are not as stringent on hardness. Gold has to be! That is why there are types, grades, purity levels, and knoop hardness values in Mil Specs. I would be willing to answer further questions on gold plating if you have them. Best regards,

Mark Baker
process engineer - Malone, New York
2006

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In my opinion the major benefits of 2 layer plating of the same metal are decreased porosity and plating speed. By doing 2 step plating the cathode diffusion layer is completely eliminated when going out of one solution and into another. So the second layer really starts out with a high metal content at the surface and this reduces porosity and increases speed.

This is especially important on reel to reel lines where multiple short cells have always plated faster than 1 long cell.

Pat Mentone
St Paul, Minnesota
2006