Immersion gold plating vs. electroless gold plating

A. Hi Amir. My guess is that it was simply a standard gold plating solution, which will immersion deposit onto copper without need for electricity. Any time you put a metal object into a plating solution, a battery is automatically formed between the metal of the substrate and the metal in the plating solution. If the metal in the plating solution is more noble than the metal of the substrate (and gold is more noble than copper), the "battery" is wired in the direction to cause deposition, and the plating solution will spontaneously plate out onto the substrate (this is a slight simplification because if the concentration is extremely low this may not happen).

If you can, please give us a URL for that video because we can only guess at what you saw and then try to answer with "ifs-ands-&-buts" :-)

Luck & Regards,

A. Hi again, Amir. You can send it to mooney@finishing.com please, but we already know that it's possible to do immersion/replacement gold plating. The question isn't whether it can be done, it's whether the approach is applicable for your particular situation, but after your 2nd letter I still know nothing of your situation, and a 3rd letter with a video you saw won't help much :-) What substrate material are you trying to plate, and with what metal, and why (why does the part need this plating) ?

Luck & Regards,

A. Hello, Roger.

By "electroless plating", industry professionals really mean "autocatalytic plating". So your question becomes what is the difference between chemical displacement plating operations/solutions and autocatalytic plating operations/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 ⇦this on eBay or Amazon [affil links] 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 opposite direction. Thirdly, immersion deposits can tend to exhibit poor adhesion; now I'm just guessing on the cause, but this might be related to the fact that the substrate is dissolving as the reaction proceeds, the newly deposited ions stand on feet of clay washing away below them.

Autocatalytic solutions are sort of "spring loaded" reactions which are driven by reducing agents in the solution, but which reduction reactions will only take place in the presence of a catalyst; but the metal being deposited is one of those catalysts. So you start the reaction either with electricity or by depositing onto a substrate which is also catalytic to the solution; then 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 or "true electroless" gold plating is a relatively recent development whereas immersion plating was probably known to the ancients.

A. 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. As previously mentioned, another possible reason may be that the substrate is dissolving; picture a gold atom which has just replaced a copper atom, and bonded well to it, when the underlying copper atom it has formed upon then dissolves away.

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.

A. 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.

"Gold Plating Technology"
by Reid & Goldie
(hard to find & expensive; if you
see a copy cheap, act fast)


on AbeBooks

or eBay or

Amazon

(affil links)

Hi David. Thanks for the feedback. Your response motivated me to look a little deeper ...

In Chapter 10, "Immersion Solutions" in Reid & Goldie's "Gold Plating Technology" .
there are several interesting pages devoted to predicting whether a particular immersion plating operation will produce adherent, bright, and continuous coatings on the base metal. One of the several factors is how close the two metals are to each other in half-cell voltages.

Regards,

A. 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,

A. 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,

A. 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 hopefully offer additional 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. Gold leafing may be an alternative to gold plating without electricity. Good luck.

Regards,

Hi Joel. If you look at the entry below from Shyam Sunder, he is suffering a 18:1 ratio from one side to the other :-(

I currate the site and make suggestions when my limited specific experience or my book knowledge permits ... but there are lots of processes I know little about and ENEPIG [electroless nickel - electroless palladium - immersion gold] is one of them. Any theory I raised, beyond the simple observation that these processes are not known for their stability, would only be a wild guess :-)

Regards,

A. 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,

A. 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; and 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 plating for color.

Regards,

A. Electroless Nickel Electroless Palladium Immersion Gold finish for non-PCB (Printed Circuit Boards) applications as an inexpensive gold plating alternative? There is nothing inexpensive when you include Palladium and Gold on the same sentence. There is really nothing less expensive than electroless nickel followed by immersion gold out there.

lets explore the alternatives.

ECIG (Electroless Copper Immersion gold) is about as expensive as ENIG but with the caveat of copper diffusing into gold. A barrier like silver is recommended adding the extra cost of immersion silver. But ECISIG (Electroless Copper Immersion Silver Immersion Gold) would still be more affordable than ENIPIG.
What surfaces are you trying to gold plate? ABS plastics? Organic articles? Jewelry? Would be nice if you specified your needs.

Regards.
Marvin

A. Hi. Plastics are non-conductive so you cannot plate gold directly onto them. You must metallize them first. Please see our FAQ about plating on organic materials. Good luck.

Regards,