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Electroless gold plating



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Tutorial & lingo:
(to provide context, hopefully helping readers more quickly understand the Q&A's)

When platers speak of "electroless plating", they are referring to "autocatalytic plating" ... a sort of 'spring-loaded' process where a reducing agent is already in the solution, and the presence of a catalyst causes deposition, but where the deposited metal itself is a catalyst for the process to continue (the "auto" part).

There is another type of plating process which proceeds without electricity, called "immersion plating" or "replacement plating". In this case a more noble metal plates out on a more active one through a simple replacement mechanism. You may have seen this back in high school science class, where copper spontaneously plates out onto an iron nail.

Immersion plating is very limited in plating thickness because as soon as the noble metal coats the active one a few atoms thick, there is no active metal exposed on the surface anymore so the process stops. But autocatalytic plating can continue essentially indefinitely, allowing much greater plating thickness.

When this thread started in the year 2000, although electroless nickel and electroless copper were well established processes, there was no such thing at autocatalytic gold plating yet. Between about 2005 and 2010 autocatalytic gold plating became a commercially available process. These days, in the plating for electronics field, you see requirements for ENIG (electroless nickel followed by immersion gold) as well as ENEG (electroless nickel followed by electroless [autocatalytic] gold plating).

Q. Hello,

I am polishing and subsequently internally plating a section of copper tube for use as a laser gain volume. I plan to have the part plated with electroless gold per MIL-G-45204. Following a rinse in DI water and blow dry, the inside of the tube will be pulled to high vacuum, below 1x10^-8 torr. With electroless gold on copper in this environment, is there a chance that additional byproducts of the electroless bath could remain on the gold surface or within the structure that may contaminate the laser? Additionally, do other compounds exist after any standard electroless gold plating process?

Thank you!

Ike H.
- Seattle, Washington
September 14, 2022




Closely related historical posts, oldest first ...

"Electroless Plating"
by Mallory & Hajdu
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Q. Anyone out there familiar with electroless Au plating? Most literature is dominated by EN. The only information I have at hand is <= 'Electroless Plating Fundamentals and Applications'. The application is for a Au contact pad. The underlying film to plate to will be Ti-Au. Plating Au-to-Au is a strike required or surface prep prior to plate? TIA Pat Franklin Indigo Systems

Patrick Franklin
- Santa Barbara, California, USA
2000


A. There are different kinds of electroless gold plating solutions. It will not be wise to try to make up such a solution on your own. Do contact one of the big supply houses, they will be more than happy to serve you.

sara michaeli
sara michaeli signature
Sara Michaeli
Tel-Aviv-Yafo, Israel



Q. Dear Sir,

We are trying to deposit electroless gold on Si. The silicon substrate is etched with few micron in size and about 15 micron in depth small holes. The gold layer is expected to coat through inside the holes to make electrical contact. We have tried electroless Ni, however, the bubbles stopped the plating in the holes. Is any electroless gold plating processes suitable for this application?

Susan Hua
- Buffalo, New York
2001


A. Metal vapor deposition guys, this one's for you I guess.

Guillermo Marrufo
Monterrey, NL, Mexico


A. I think that:

- applying tin chloride to Si as a catalyst

- replace Tin to Gold by immersion sodium gold sulfide solution.

Nelson NK Key
- Seoul, Korea



RFQ: I am seeking a supplier for electroless gold plating materials.

Ian Harrison
- Manila, Philippines
2001

----
Ed. note: Sorry, this RFQ is outdated, but technical replies are welcome. No public brand/source suggestions please ( huh? why?)


A. Are you looking for electroless or immersion gold? They are two very different animals. From what I've heard, no one has really developed a good, stable electroless gold yet. The baths tend to make flakes (spontaneously drop out) quite readily. There are a number of good immersion processes available.

bill vins
Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona


thumbs up sign Mr. Vins' response is several years old, Ian, and I think if you check again with vendors like Technic you will find that there have been substantial improvements in electroless (autocatalytic) gold plating in the intervening years. Good luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007



Q. Hi,

We are working on a research based on electroless gold plating. We want to create gold plating at room temperature (25-35 °F). So we would like to know if you could help us.

Tom Johnson
- Buffalo, New York, US
2001



Electroless gold plating on gold?

Q. We commonly use electroplated gold on our products (GaAs and InP chips for the optical industry). We now need a process for electroless gold plating for some experiments. The surface to be plated is gold. I have found some suggestions on plating baths including the following chemicals: KAu(CN)2 , KCN , KOH , KBH4. However I do not know if this will work on a gold surface or if there is any risk that the bath will etch on the semiconductor which in this case is GaAs. Anyone who uses a similar process or can suggest an alternative?

Pia Wickenberg
communication components - Stockholm, Sweden
2003


A. Pia,

If the surface is already plated with gold so I can't see any problem with a commercial gold strike to get a good adhesion before electroless gold plating. If you have a gold plated surface surface already no commercial etching solution will destroy the base material if the gold plated deposit is free from pores. My suggestion to you to talk with a plating supplier here in Sweden like Atotech or Enthone-OMI. Also you must know the electro gold solution chemical composition to get good adhesion.

Regards,

Anders Sundman
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden




To minimize searching & thrashing, multiple threads were merged; please forgive repetition, chronology errors, or disrespect of other responses (they probably weren't there) :-)



Q. Hi,
I recently was suggested to use the OTOTEMP RTU gold electroless plating solution to deposit 10 µm of gold layer on to a gold substrate,

May I ask the standard operating procedure for this, since I am not used to electroless plating (only electroplated copper once). I know that the reducing ions is in the solution, is this correct? Do we need to use external potential etc? What about the electrodes?
Does anyone has any info on this, thanks.

Amani Salim
Purdue University - West Lafayette, IN, USA
2006


A. No power source or electrodes are required for electroless plating because, indeed, the reducing agent is in the solution. The manufacturer of the electroless gold plating solution will give you a technical data sheet which contains the recommended operating conditions; it concerns me if someone has given you access to specialized chemicals without providing the MSDS and technical data sheet. Good luck.

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



"Ghosting" of electroless gold plated parts

Q. We have had a recent problem with some parts "ghosting" in our Electroless gold plating bath. What could be the cause of this?

Jason Combs
Plating - Chattanooga, TN, United States
2007


A. Jason,
Ghosting, as I know it is when ultra violet light is able to penetrate through the substrate. There are UV blocking laminates that contain UV blocking fillers. Are you currently using this type of laminate?

Mark Baker
Process Engineer - Syracuse, New York


thumbs up sign Since posting this question I have came to learn that our DP nickel Process is adhering to Molly in our black body ceramic and once that occurs our gold is then adhering to the nickel Deposits.

Jason Combs [returning]
ceramics - Chattanooga, Tennessee, USA
2007



To minimize searching & thrashing, multiple threads were merged; please forgive repetition, chronology errors, or disrespect of other responses (they probably weren't there) :-)



Q. Hi, I am trying to get electroless gold plating for bonding pads which will be wirebonded. What would be the best (including commercial solutions) way to go about this?

Kiran Chikkadi
Researcher - Zurich, Switzerland
September 24, 2008


A. Hi, Kiran. I believe Technic offers electroless gold and there may be other suppliers. Note that, to many of us in industry, electroless plating means "autocatalytic plating", not "immersion plating". If immersion plating is all you really seek, it may be possible to do home-brew, although you are probably still better served with commercial solutions.

Regards,

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


A. FOR WIRE BONDING GENERALLY YOU NEED AT LEAST 1.27 MICRONS OF PURE GOLD. THIS IS VERY HARD TO GET IN ELECTROLESS GOLD BUT EASY IN AN ELECTROLYTIC SOLUTION

Ricardo Burstein
Bnei Berak, Israel


A. General on the market, a minimum of 1 microns electrolytic plated gold is required for gold wire bonding. However, there is technology where industries are using 0.3 to 0.5 microns of electroless gold to do gold wire bonding. The trick is to tune the bonding machine slightly.

For the chemistry, Electroless gold plating is better for gold wire bonding than immersion gold because of the porosity and surface cleanliness.

Robin C.Y. Chua
Freelance - Singapore



Bare spots on electroless gold parts

Q. We run a electroless barrel plating process. We are having trouble running more than 1200 pieces at one time..We have tried a 1600 piece lot and 2000 both have failed. We use a 6x6 barrel for the procedure and the parts have DP Ni on them prior to the gold plating... The spots look as if tho they have no gold on them at all, in spots... Could this have something to do with our Dp Nickel or Electroless Au or could it just simply be the parts sticking together... thanks...

Jason Combs
Plating - Chattanooga, Tennessee, USA
January 7, 2008


A. Sounds like the barrel is too full and you are not getting solution flow to the inner parts or the solution is depleted by the time it gets to the center parts. Also, tank overloading prevents proper part movement.
Greed is probably the biggest problem in barrel plating.

James Watts
- Navarre, Florida


A. I'm assuming you are talking about a direct displacement immersion plating bath, ~2-5 microinches of Au. It sounds to me like you are either not getting enough agitation of the parts for the initiation of the plating reaction. The parts must be agitated well when first placed in the bath. Another common problem with plating Au over Ni is oxidation of the nickel deposit. One solution we found to this problem is prewetting the parts in the dragout for the gold bath for 2 minutes. Another issue with overloading the Au bath can be the temperature drop when the parts are placed in the bath. This can be addressed by increasing the heating capacity and/or the circulation of the bath or by increasing the bath volume. As previously mentioned the you may also be depleting the Au content or raising the Ni content of the bath beyond the effective limits too quickly. I hope this helps. Good luck.

Brian DeBadts
- Rochester, New York


Q. The barrel is probably about 1/2 shot and 1/8 parts or so... Does anyone think that this is too much shot?

Jason Combs [returning]
- Chattanooga, Tennessee, USA
January 17, 2008


A. I have limited barrel experience, but thought that you never loaded the barrel more than half full, total load to get proper mixing.

James Watts
- Navarre, Florida



Q. Hi,

I have exactly the same situation. I want to deposit 20 nm to 80 nm Gold layer on Gold surface using electroless gold plating. Have you solved the problem?

I want to know what solution or company you use for this application.

Thank you

Chao Liu
University of Minnesota - Minneapolis, Minnesota, United States
March 17, 2014


A. For Jewelry, immersion gold on top of gold is achieved quite simply by cleaning and activating (dipping in activating liquid) then immersing the piece into immersion gold plating. But that is for jewelry that doesn't have a specific nanometer/micron thickness need.

Regards.
Marvin

Marvin Sevilla
- Managua, Nicaragua
January 15, 2016

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