Stannate (Tin) Plating Process

A. Hi, Brandon
The chemical symbol for tin is Sn. Practically, 'stannate' just means alkaline tin electroplating as opposed to acid tin plating (sometimes called stannous sulphate). There might be cyanide somewhere in the overall plating cycle, or in older versions of the stannate process but there need not be. Good luck.

Regards,

A. Let's read about the stannate process:

The Immersion Deposition Process, D.S. Lashmore, Aluminum Finishing Seminar,Vol II, St. Louis, MO, 30 Mar - 1 April, 1982, Aluminum Association, Washington, DC. and Pretreatment for Plating on Aluminum Using The Stannate Process, Jongkind and Seyb, ibid.

Related stuff for tin plating:
Control of Anodes in Alkaline Tin Plating, M&T Chemicals, Rahway, NJ, Technical Data.

Anode maintenance in the Alkaline Stannate Tin Plating Bath,
Lowenheim, Metal & Thermit Corp. New York, NY., reprinted from March 1951 issue of Metal Finishing.

Technical Bulletin, M&T Chemicals, Rahway, NJ, Alkaline Tin Plating with M&T Stannates

A. The stannate process is not going to make your aluminum adhesion problems go away.

A. Hi, Mark. I presumed the original inquiry was about a stannate plating process (alkaline tin electroplating) but the responses (from Tom regarding Lashmore's paper, and from Todd regarding adhesion) lead me to believe it might instead be about an alternative to zincate for preparing aluminum for electroplating (such as Atotech's Alstan process) -- but it's still not clear to me.

So now I have to ask which topic your stannate inquiry is about? :-)

Regards,

A. We sent you the missing pages, Larry. The acetate is mentioned, as is the necessity for filming the anodes -- but not why or how. That is covered in full detail though in the Garden State Branch AESF Electroplating Course Manual" in the "Tin Plating" chapter by F.A. Lowenheim. In brief, the anodes will dissolve as Sn+2 instead of Sn+4 if the anodes are not 'filmed' at high current density. Quoting Lowenheim:

Good luck.

A. You probably need to reduce the number of anodes to increase the anode current density and voltage. That should be all that is needed.

If that is not sufficient to get a good gold colored film, you may need to reduce the sodium hydroxide concentration a little with acetic acid [on eBay or Amazon].

A. Hi Larry. In his rather exhaustive coverage of Alkaline Tin Plating in the aforementioned "Garden State Branch AESF Electroplating Course Manual", Lowenheim never even mentions filtration. It is not necessary, but whether it should be employed is probably a matter of your Philosophy of Quality ... some shops feel filtration should be employed on all process tanks, and D.I. water used everywhere, and that failing to use these measures is old fashioned and loose. So, in answer to your questions --
1). Yes, it can improve the "quality of the plate" by insuring no particles are occluded.
2). No
3). No.

Regards,

A. If you add an alkaline nickel strike, at near room temperature and then go into the regular EN, I predict that your rejects will drop to a very low number (near zero) The ammonia [on eBay or Amazon] smell is about the only drawback and the results are fantastic. With one short rinse, the slightly alkaline film of water helps to kick off the EN.
Note, if you do not have a heavy use of the strike, consider adding cooling or you will plate out on the tank during idle periods. It is quite active at temperatures around 75 °F.

Q. Thank you, James. Many commentators of this site are proponents of an alkaline EN strike. Does your statement hold true even if the regular EN is maintained at 1~3 MTO for zincated 2024 ?

A. It certainly does. A big reason is that the alkaline EN strike does not eat off any (very little) of the surface of the zincate as the acid EN will do quite rapidly. 1-3 MTO's on EN is very expensive. The strike should allow you to go to 3-6 MTOs If you can load the EN tank to at least the minimum recommended surface area to be plated. Also, try to always have stuff in the tank as soon as it gets to temperature. Try to get the temperature down as soon as possible after the last part comes out. Cooling is great if you have it. I always saved my last water make-up for when the last part came out of the tank. Bad memory remembers it lowering the temp by 5 - 10F. Lowering the temp by 10F as soon as the last part comes out will probably get you an additional MTO as well as the nitric acid tank stripping is a lot easier.

James, thank you very much. That's a whole load of valuable information.

A. Stannate plating baths are great for thin deposits, like 0.2-0.4 mils, but tend to become rougher and treed on thick deposits. To plate 1-2 mils and get a smooth deposit, you may have much better luck with an acid tin plating bath.

A. Hi Bob,

Plating grade Sodium Stannate usually refers to Sn assay ≥42% with all impurities (Pb, Sb, As, Fe, NO3, free alkali, etc.) sum up together ≤3% by wt.

Regards,
David