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Immersion gold plating vs electroless gold plating

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Is there a substantive difference between electroless gold and immersion gold, and if so can you define this for me. I am not a finishing professional but I deal with components that mount to printed circuit boards.

Roger Williams
- Missouri

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Hello, Roger.

By "electroless plating", industry professionals really mean "autocatalytic plating". So your question becomes what is the difference between immersion plating solutions and autocatalytic plating solutions.

An immersion plating solution operates on the principal of displacement of the surface skin of the substrate by a more noble metal that is in solution. In science class, high school kids put iron nails in beakers of copper sulphate and watch as the outermost layer of iron goes into solution and is replaced by copper ions coming out of solution. There are several weaknesses to immersion plating. First, the thickness is limited to a few atoms: once the surface is covered by the new plating, the solution doesn't "see" the substrate anymore, so no more substrate atoms can dissolve, and consequently no more noble metal ions deposit. The second problem is that you can't immersion deposit a baser metal onto a more noble metal; for example, you can't immersion deposit copper onto gold, because the built in battery that drives immersion reactions is wired the wrong way. Thirdly, immersion deposits tend to exhibit poor adhesion; now I'm just guessing, but this might be related to the fact that the substrate is dissolving as the reaction proceeds.

Autocatalytic solutions are sort of "spring loaded" reactions which are driven by reducing agents in the solution, but which will only take place in the presence of a catalyst; but the metal being deposited is one of the catalysts. So you start the reaction either with electricity or by depositing onto a substrate which is also catalytic to the solution; and the reaction continues as long as the surface being plated remains in the solution, continuing to catalyze the reaction. Consequently the thickness can be much, much greater. Autocatalytic gold plating is a relatively recent development whereas immersion plating was probably known to the ancients.

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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I am investigating moving to immersion silver from HASL surface finish for PWBs. I noticed Mr. Ted Mooney stated I.S. has poor adhesion. Would this be only in the as-plated state? After assembly with solder, the silver has alloyed into the joint and is no longer a layer, isn't it?

Thank you,

Lisa P Koland
- Minneapolis, Minnesota

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Immersion plating processes do tend to have poorer adhesion than electroplating processes. This is perhaps because the plating process is not metered or controlled by an external electrical source; rather, atoms of the plating deposit on the substrate at the rate of their choosing, often not slowly building a solid crystal structure, but instantly converting from ions to metal of a powdery form. But sometimes the adhesion is adequate to the task. For example, virtually all plating onto aluminum begins with an immersion deposit of zinc.

As for whether immersion silver will actually be an improvement over HASL, Lisa, sorry but the question is not within my experience; hopefully a more knowledgeable reader will reply.

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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February 11, 2008

I have been operating an immersion silver line as a finish for printed circuits for the past year or so and am unaware of any adhesion problems.

David Moyer
printed circuits manufacturing - St.Paul, Minnesota

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March 5, 2009

I do copper electroforming of vegetal material (leaves, flowers) and then gold electroplate it directly over copper, with very poor results. I can't use nickel before gold plating as I produce anti-allergic jewels.

I guess my answer is going into the Electroless gold plating, directly over the copper electroformed organic object, if appropriate.

Would I need to do both steps? First do an immersion gold plating and then the autocatalytic process? Or is the autocatalytic one enough?

If so, many of my finishing quality problems would be solved.

Thanks for your comments and advise.

Hernando Durana
- Bogota, Colombia

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March 9, 2009

Hi, Hernando. Gold directly on copper is theoretically not a good idea because they diffuse together. A better approach would be cobalt plating in lieu of nickel, or ideally white bronze plating in lieu of nickel. However, in non-critical and room temperature applications like jewelry plating, there is also a lot of evidence that this theoretical problem is often not a serious real-world problem.

Regards,

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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April 12, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

sir,

I want to know how to gold plate on a big article without current?

Harish Upadhyay
plating shop employee - Udaipur, India

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April 12, 2011

Hi, Harish.

We appended your inquiry to a thread that explains the general situation. If you can describe the component that you wish to plate, including the environment it will see, why you want to plate it, and what it is made of, we can offer more guidance. For decorative gold plating it is typical to nickel plate or white bronze plate under the gold as otherwise it may not be shiny.

Regards,

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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December 15, 2011

Dear Ted: Thanks for your advise of March 9, 2009, but after years my thinking is back to my original statement and I would like your consideration again. That is, go directly from copper base to gold, via gold by immersion and then, over it, electroless gold plating. Will it work? Is it technically feasible? Thanks again but I still would like to change my technique.
Regards,

Hernando Durana
- Bogota, Colombia

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December 15, 2011

Hi, Hernando.

There are proprietary immersion gold plating solutions designed for plating directly on copper, and there are autocatalytic gold baths, so it should be possible to do what you wish. But I don't know how well this two-layer gold process will adhere to your copper. Since the application is not critical, it's certainly worth a trial. But if I were you I would not sell millions until I verified the real-world durability of the product.

Regards,

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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January 3, 2012

Hi Mr Ted,
You said in your first response that

"the thickness is limited to a few atoms: once the surface is covered by the new plating, the solution doesn't "see" the substrate anymore, so no more substrate atoms can dissolve, and consequently no more noble metal ions deposit"

I believe this statement to be correct. However, I have been experiencing thickness variations with immersion gold. (The process I'm using is ENEPIG). What do you think would account for the difference? What factor could possibly cause this when as you said, the solution wouldn't see the substrate anymore once everything is covered with plating?

Would appreciate your expert opinion. Thanks!

Joel Olave
- Clark, Pampanga, Philippines

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February 28, 2012

I'm new and (hopefully) learning about gold plating as I want to start a local mobile business. Am I to understand from the opening question/answer in this thread there are three means to gold plate: autocatalytic plating, immersion plating and electroplating? If so what are the advantages/disadvantages particularly between autocatalytic and electroplating? I will be offering a decorative service, not industrial. Many thanks to all who answer.

David Caple
- Heathfield, East Sussex, UK

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February , 2012

Hi David.

A mobile business will in all likelihood be doing electroplating. It should be easiest and least expensive. It will work on the most substrates, the thickness will be easily controlled, and it will be easier to do alloy plating for different color, hardness, and karat. The only real disadvantage, and it may not apply to your mobile business, is that the thickness in any area is proportional to the current flowing to that spot (see Faraday's Law). This means that you can't practically plate the inside of small diameter tubes and, if doing tank plating, inside corners will have significantly less thickness than outside corners.

Autocatalytic gold plating is proprietary, relatively new, complex to keep operating properly, and limited. It is not a general purpose "jobber" solution, but something designed for specific purposes like plating of electronic circuits which it may be hard to bring electricity to.

Regards,

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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February 28, 2012

Hi Ted and thanks ... yes I will be electroplating and will stick to that (and understand the basics of that process from school physics!). I also understand what I think you are describing as the immersion method where the component and solution effectively makes a battery which is 'lost' once a thin skin of plating forms on the item but how does autocatalytic plating work?

Also because of the difficulties of getting into blind spots and corners with the electro process is there a case for using the immersion or autocatalytic process first to make sure the whole of the object is given a covering (albeit thin) and then using electroplating to build the thickness on the more accessible (more exposed) parts if desired?

David

David Caple
- Heathfield, East Sussex, UK

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February 28, 2012

Hi, again.

Before addressing auto-catalytic gold plating, let me speak about auto catalytic nickel plating first because it has been around for a long time, is widely used, very well understood, and offered by enough vendors that the general principle is not a trade secret.

The electroless nickel solution (auto-catalytic nickel solution) will contain nickel hypophoshite or nickel borohydride. Hyposphosphite and borohydride are powerful reducing agents, but they only work in the presence of a catalyst. The catalyst can be a steel surface, a zinc surface, or (importantly!) a nickel surface. The fact that a nickel surface is catalytic is why it is called autocatalytic rather than just catalytic. The plating doesn't stop when a very thin layer of nickel has been deposited, but it keeps going. Electroless nickel has some inherent problems: it can spontaneously plate out -- picture a spec of random nickel sticking on a tank wall and growing and growing and growing; it it gets exhausted or contaminated -- as the hypophosphite or borohydride reduces the nickel to metal, it gets oxidized to undesirable and not easily removed contaminants.

Back to auto-catalytic gold plating. This is a rather new technology, perhaps one or two suppliers, and far less understood. And who can afford to have gold autocatalytically plate out on a tank wall? In short, I don't know too much about it, you'd have to get a technical data sheet from a supplier (try Technic), but I seriously doubt that it will play a role in your jobber service. A more likely scenario would be to use electroless nickel for corrosion resistance and top it off with gold for color.

Regards,

Ted Mooney, P.E. RET finishing.com Brick, New Jersey