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topic 42416

Zincate formulas for plating on aluminum

A discussion started in 2000 but continuing through 2019


Q. Hi,

I'm trying to apply a layer of Zinc onto aluminum (3 microns thick; evaporated on Si wafers) using the Standard zincation solution (ZnO, NaOH, ferric chloride and rochelle salt). Before I do the zincation, I treat the aluminum surface in an acidic solution of Chromic and phosphoric acid to remove the native oxide. Thus I have to move the Al surface from a highly acidic to a basic solution; this calls for a Deionized water rinse in between. What are the chances that this DI water rinse will reoxidise the aluminum? Is there any other rinsing agent that I can use which won't oxidise the aluminum (like iso-propyl alcohol?). Please give me your suggestions/comments.

Also, do you have any suggestions for reagents for native oxide removal in aluminum (commercial solutions, formulations, whatever) and process conditions for the optimization of the zincation (uniform and fine grained structure is my aim).

Thanks a lot,

Ramanan Natarajan
Rensselaer Polytechnic Institute - Troy, New York


Q. I am interested in wet (immersion) process that will allow deposition of thin (about one micron each) nickel and gold films on aluminum die individually. Zincating is the process that I have heard of, but how mature is this process? Is controlled cleaning/etching of aluminum a problem even if the aluminum is of high purity (sputtered)?

Is this process mature enough that it can be used at flip chip attachment?


Adarsh Kumar
- Columbia, Maryland, USA


affil. link
"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
info on Amazon

A. Hi Ramanan, hi Adarsh.

I am not experienced in zincating of evaporated thin films, but zincating of aluminum as a preparatory step to electroplating on aluminum is a very popular and mature industrial process, at least for large parts. Thousands of miles of aluminum bus bar has been zincated then copper plated; hundreds of thousands (maybe millions) of aluminum automobile and truck bumpers have been zincated then copper-nickel-chrome plated; tens of millions of aluminum die castings and electronic parts have been zincated then plated.

So a lot of research has been done. Here are some good papers by David Lashmore that focus on what is happening at the molecular level, and which may be helpful to your studies:

General conclusions seem to include the observations that:
- Proprietary mixed metal zincates (such as Macdermid/Canning/Gumm's Bondal) really do work better, and
-The common procedure of zincating followed by stripping with nitric acid and re-zincating (commonly called double zincating) is essential to a fine grained deposit.

As for pretreatment, the same steps used for anodizing and chromate conversion coating (clean, etch, de-smut) are fine. Your evaporated films may, of course, not sustain the robust pretreatment used in industrial electroplating onto aluminum.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


A. The use of zincate is well established as an adhesion layer for Al. Developed a process for plating Ni and Au on very thin films of Al on power devices using zincate as an activation layer. It was a technology used to fabricate flip chips

RP Daniel
- Placentia, California

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)

Uneven, Discolored Zincate Film


affil. link
Electroless Plating
by Mallory & Hajdu
from Abe Books

Q. I tried to put together a zincate solution prior to plating aluminum pads on an IC. I started from the suggested recipe from Electroless Plating by Mallory and Hadju, pg. 198: =>

ZnO 50-100 g/L
KOH 250-500 g/L (We currently don't have NaOH in stock)
Temperature 27 °C (80 °F)
Time: 1 minute
Resultant thickness ~ 3K

The die was first cleaned in a 1:1 HNO3:H2O solution and then immersion plated in a basket, the solution in a beaker on a hotplate/stirrer (the stir set to 200 RPM to keep the ZnO suspended).

The resultant zinc film was uneven and brownish in color. I then stripped it off in a 2:1 (H20:HNO3) etchant and repeated the process several times with similar results.

It has been recommended to purchase a proprietary zincate solution to avoid such roadblocks. Still any information on what may have gone astray would be appreciated.

Patrick Franklin
Santa Barbara, California


A. Yes, that formulation doesn't have much to recommend it, except that it won't violate any patents, and you did not have to ply a formulator with strong drink to get it:-0

Die castings will take an uneven zincate, due to the exposed grain structure, but you might want to try degreasing the part with an alkaline cleaner and aluminium etch for your next experiments. A blotchy zincate could mean that the part was dirty with grease or oil too.

Proprietary formulas will do a much better job.

tom & pooky toms signature
Tom Pullizzi
Falls Township, Pennsylvania


A. As Tom mentioned, your preplating process is not good enough. You need to degrease, etch and desmut before the zincate. Using only Hydroxide with zinc oxide will give you an unstable zincate layer. (By the way, you have to use a double zincate). A proprietary zincate will be far better.

sara michaeli
Sara Michaeli sara michaeli signature
chemical process supplier
Tel-Aviv, Israel


A. Zincate is best double dipped but not necessary. We have a great zincate that uses a combo of zinc, copper, nickel and iron. The advantage of so many complexes is that they can attach to different sites on the alloy. 5 to 1 ratio is best for your zinc to hydroxide formulation, but try to add 10% sodium cyanide, 5% nickel carbonate, 3% ferric chloride, 6% copper cyanide. That's the best the industry can offer and is very forgiving in its nature.

regards and good luck


sandra de juliis
electroplating shop - toronto,canada

January 11, 2011

Q. Would it be possible to put Sandra's Zincate makeup in form of a recipe, please? I did not quite get it.

I understand the initial recipe given in the first post, this is not a really good recipe, I would really like to try Sandra's, but do not understand it. Any help is greatly appreciated.

Renar L [last name deleted for privacy by Editor]
- Tallinn, Estonia

January 12, 2011

A. Hi, Renar.

We can't say when or if Sandra will return to clarify her response, but the Metal Finishing Guidebook offers this (strong) formulation: NaOH 67 oz./gal
ZnO 13 oz./gal
FeCl.6H20 0.3 oz./gal.
Sodium Potassium Tartrate 1.3 oz. gal

So, combining this information with Sandra's, one way of following her suggestions would seem to be approximately:

NaOH 67 oz./gal
ZnO 13 oz./gal
FeCl.6H20 0.3 oz./gal.
NaCN 1.3 oz./gal
NiCO3 .6 oz./gal
CuCN 0.6 oz./gal

Please note that this is a very strong formulation, and it should be possible to very significantly reduce the NaOH and the ZnO as long as they are reduced proportionately, maintaining roughly a 5 to 1 ratio. Also note that this formulation includes cyanide and should not be used unless you are already familiar with cyanide-based processes and their dangers.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

2001 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,

Somebody tell me, what is the zincate formula for plating onto aluminum. I have now a formula like this:

caustic soda 300 grs x liter zinc oxide 50 grs x liter.

Thats all, but somebody in this forum wrote the formula is:

525 grs / liter caustic soda
100 grs / liter zinc oxide
1 gr / liter Ferric chloride
10 gr / liter rochelle salt. Is this formula correct?


Rafael Arencibia
- Caracas, Venezuela


A. There are many different formulations that can be used to make-up a zincate solution. The two you have are good and there are many others depending on what alloy you are using and what you would like your adhesion to be like. You can get the various recipes from literature, books and the internet.

Angie Molnar
- Fort Saskatchewan, Alberta, Canada


A. 1 - 245,100 L AGUA [water]
2 - 005,400 KG GLUCONATO DE SODIO [sodium gluconate] (DISSOLVINE NG C)
3 - 004,200 KG CLORETO FERRICO [ferric chloride]
4 - 138,000 KG SODA CAUSTICA [caustic soda] 99 / 98 % RAYON GRADE S/ CARB
5 - 020,400 KG OXIDO DE ZINCO [zinc oxide]
6 - 006,900 KG ACIDO SALICILICO [salicilic acid]

Jorge Vieira

Cyanide Zincate


-- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Does anyone plate electroless nickel on aluminum who uses a cyanide zincate? Does cyanide zincate help with adhesion of the Nickel to the substrate?

Brandon Hellenbrand
- Fairburn, Georgia, USA


A. To call it a cyanide zincate is probably a bit of an overstatement. A zincate or alloy zincate that contains a trace amount of cyanide would be a much fairer answer. When I was actively in plating, I never came across a plater that did not say that it had better adhesion. Harder to control and it does require special haz waste procedures for that tank and rinses. Not all that difficult. Very few platers use it because a normal double zincate will suffice for nearly all work.

James Watts
- Navarre, Florida


A. Yes cyanide zincate is used. I think there are non-cyanide zincates that have been developed. I don't know what process you use other than zincate and nitric acid to strip before copper strike/electroless nickel strike.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan

2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir
I am working in plating area and I do plating on door handles and I need to make a zincate for plating aluminum articles. The formula I have is to make a liter of zincate bath:

caustic soda 525 g
zinc oxide 100 g
ferric chloride 3 1 g
rochelle salt 10

But this is not giving me a good result. Each time I do it, some of the door handles look very good and on some the plating comes off. Would you please tell me what I am doing wrong?
thank you for your help,

Pari Asgarian
- Iran


A. Hi Pari. We appended your inquiry to an earlier thread. Please see above, which will refer you to some excellent investigations about zincating. Good luck. Regards,

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


A. Ted, it's a bit difficult obtaining ca. 1980 issues of Plating & Surface Finishing.

Pari, common problems are 1) inadequate surface pretreatment and 2) too thick zincate (porous, traps liquid). ASTM B253 [affil. link to spec at Techstreet] , 'Standard Guide for Preparation of Aluminum Alloys for Electroplating' gives more information. It includes your zincate bath recipe, but with ferric chloride hexahydrate at 1 g/L. It mentions problems associated with rinsing this high-NaOH bath; you may get better results with one of the more dilute formulae or a proprietary zincate.

Ken Vlach
- Goleta, California

contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.


thumbs up signYes, old issues of P&SF can be hard to find, Ken. But per the exec director's report at Sur/Fin, AESF is planning to put their old issues on line. As a side note, when I reference an article it's almost always because I have a copy of it; if a reader is interested enough to take the time to email the publisher for permission, I will copy the articles for them.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

February 22, 2011

A. Formulation of zincate:

Sodium Hydroxide 400-500 gm/l
Sodium Cyanide 5-7 gm/l
Zinc Oxide 20 gm/l
Rochelle Salt 50 gm/l
Sodium Nitrate 1 gm/l
Ferric Chloride 2 gm/l
Copper Sulphate 10-15 gm/l

Ghulam Fareed
- Lahore, Pakistan

2007 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I have customer that needs aluminium articles tin plated as a bright decorative finish, we do tin plating on ferrous materials but have not done any aluminium materials.
Can anyone help me with a working procedure to do this and a zincate solution formula.
I would really appreciate some technical info.

Ben Kok
Business owner - Pretoria, South Africa


A. Proprietary zincate solution are usually considered better, and the technical support may be useful. For do-it-yourself solutions, see ASTM B253 [affil. link to spec at Techstreet] , 'Standard Guide for Preparation of Aluminum Alloys for Electroplating.'

Ken Vlach
- Goleta, California

contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.

January 8, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,

While talking about zincating Cast aluminum, which type of zincating is recommended.

As there are two major types available, one is dual metal containing two metals mostly copper and zinc. While second one is quadra metal that is containing four metallic components with nickel as one of the ingredients.

Can you please provide guidelines for above. Does this have any bearing on final output.


Dilip Thakur
- Mumbai, India

Aluminum Activation For Electroless Nickel Plating

September 16, 2019

Q. We currently activate our aluminum for e-nickel(6061, 7075, & 2024) after cleaning by doing a standard double zincate (tri acid nitric zincate nitric zincate) with rinses in between and zincate dragout before entering zincate.

We struggle with consistently getting good e-nickel adhesion on aluminum panels. We get work out the door and I am convinced our operators just plate for 30 min max on panels to get them to pass, but any time I test at anything close to or over a mil they fail or are very inconsistent. You can do the ams 2404 bend test and they look good with minimal cracking but the minute you try to peel with a blade it comes right off.

I mainly suspect it is our zincate, its dump/maintenance schedule or our tri acid formulation.

Our zincate is a proprietary alloy zincate that we run to the TDS parameters but our supplier does not cover it any more. Are there any industry wide alloy zincates that may work better (Bondall I have heard of)? Or is there a heuristic I may be missing for the dump/maintenance schedule? How often, what to track (some sort of standard indication of the performance), only seed it 50% instead of fresh dump so as to mimic a "breaking it in" scenario?

Has anyone known a certain tri acid formulation to work better than others or specific ones for each alloy? Ours is about 90% nitric and the balance DI water with about 120 g/L ammonium bifluoride (no sulfuric which I find odd). We get a nice white look to the panels after it, so I assume it's good but sometimes when we remake it we start having issues.

Any and all advice is very much appreciated. And, I understand alkaline e-nickel strikes are recommended before going into a regular 4.9 pH high phos bath but I do not currently have that option.

Kevin Nowicki
- United States

September 16, 2019

1. You do not need "tri-acid" for the wrought alloys you listed, just use plain nitric acid without the ABF.
2. Select a "dilute" zincate from any reputable supplier.
3. My experience has found n reason for double zincate.
4. Strike first in an alkaline electroless nickel, then rinse, dip in ammonia rinse and go on into the acid electroless nickel. The expensive acid EN will last longer by not "seeing" the zinc, and the alkaline EN has far more tolerance for the zinc.

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Ed. note: We have other threads about this general topic, including
0878, "Zincating of aluminum for plating & electroless nickel";
4074, "Zincating of aluminum- single or double & why?";
8041, "Q&As on Nickel Plating of Aluminum"; and
39909, "Plating Electroless Nickel on Aluminum Substrate".
Or search the site for many more.

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