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topic 39274

Why it is necessary to add boric acid to acid tin bath plating


A discussion started in 2006 but continuing through 2019

2006

Q. Hi
I am not getting why it is necessary to add the boric acid in acid bath plating, and what should be amount of the boric acid in the bath. And on which parameter I should decide this. Anyone who finds this problem or experienced this in past can help me.
Thanking in advance

More Hemant
- Pune Maharashatra, India


simultaneous 2006

A. Electroplating is a very aggressive process, electrochemically speaking, and to keep a relatively constant pH, you need to buffer it, so it doesn't vary too much. Boric acid is a good buffer.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


2006

A. Hello More,
If you have a Tin Fluoborate bath the free boric acid is usually maintained at 23-35 g/l. If you have a tech data sheet it will give you analysis methods for determination, I don't have one handy. I'm pretty sure the function of free boric acid is to help minimize stannic tin formation. Hope this will be some help to you.

Mark Baker
process engineer - Malone, New York


2006

A. I looked at two references and it appears that it is only used in a fluoborate bath.
The common reason for adding boric acid is to maintain the pH at the interface of the part-liquid. A bath that evolves hydrogen gas will leave two OH radicals for each hydrogen gas molecule evolved. This will momentarily lower the pH at the part and normally cause a darkening of the plate.

James Watts
- Navarre, Florida


2006

A. I was in error with the purpose of boric acid. I had it confused with another constituent in the bath. James and Trevor were right in the well house. Thanks!

Mark Baker
Process Engineer - Syracuse, New York


2006

A. Boric acid is a good buffer agent in order to control the ph decrease due to OH formation in the part-electrolyte interface as my colleagues stated. But be very careful about solubility of boric acid in your specific bath constituents and at the temperature utilized! Excess amount would precipitate and you would have to change entire bath solution.

Cemil Bayakla
- Turkey


2006

A. Not totally true Cemil. You can always lower the temperature to ambient and scoop out the precipitated material. We used a pan that looked like a dustpan on a long PVC handle. Keep it clean and it is reusable.
The evil of precipitated boric is that it can cause shelf roughness on the part if the tank is saturated and you put a cold part in the solution.

James Watts
- Navarre, Florida


2006

A. As we know , we use stannous sulphate as the main resource of Tin. And the stannous salts are easily to be oxided to Tin(4+) when the pH value is not acidic. So we must keep the solution in acid circumstance. But when the content of the sulfuric acid is high, the color the surface will turn gray. So we must choose some weak acid to keep the pH value.

Paula Lee
trading co.- Wuhan, Hubei, China


2006

A. James, you are right about the solubility of boric acid, but only to a certain limit. Most nickel platers use boric acid in the range of 25-40 g/l, but I knew of one very well known record company who used concentrations of 95 g/l and a bath temperature of 80 °C. Furthermore, the bath was sulphamate based and they claim they had no problems with stress! They also said that they needed to keep the bath hot to prevent the boric acid precipitating out (surprise surprise!). They also reckoned that when it precipitated, it would block the pipes and that would cause them a lot of problems. The company was really good at stating the obvious, but they made excellent vinyl records! I know from personal experience that if boric acid does precipitate out, it becomes more difficult to re-dissolve; I suspect it is due to a change in crystal form or some other structural effect, but I have no real evidence for that.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


2006

A. The roll of boric acid in an acid fluoborate solution is to help prevent the formation of HF. Fluoboric acid is made from HF and Boric acid. Adding excess boric acid makes sure that HF does not form and if there is an excess of boric acid makes fluoboric acid.

George Shahin
George Shahin
Atotech - Rock Hill, South Carolina



June 26, 2019

Q. Well, How the darkness in component associated with pH of Fluoboric bath.

Sandeep S Jain
- India, Agra


June 30, 2019

A. I suspect contamination with other metals, more than pH. If it is pH, then just adding some fluoboric acid would help.

Lyle Kirman
Consultant - Cleveland Heights, Ohio USA

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