The authoritative public forum
  for Metal Finishing since 1989
-----

Agitating an acid tin fluoborate bath

Hi. I want to know what can I use to agitate my acid tin fluoborate bath. I read somewhere that mechanical agitation is recommended by I am not sure what to use. I have been looking my there is no help.

thanks for your help!

DUMISANI MKHWANAZI
DURBAN INSTITUTE OF TECHNOLOGY - SOUTH AFRICA
2005

---

You are right that mechanical agitation should be used for tin plating because air agitation is a poor idea because of the likelihood of oxidizing the tin ions. Please see my article "Solution Agitation and Mixing" in the Metal Finishing Guidebook for ideas on mechanical agitation. That article predates the widespread use of eductors, so that is another technology you should consider.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

---

Mechanical agitation usually means the workpieces are gently oscillated by having a moving carrier bar. Alternatively the plating solution can be pumped around the tank by using a submersible pump; this can also be done with eductors and these can increase the operating current density quite significantly, thereby reducing plating times. The trick to it is to make sure the surface of the plating solution is not stirred up too much, so it won't react wiht the air. Tin fluorobrate solutions should NOT be used with air agitation as the oxygen in the air will oxidise the Sn(II) to Sn(IV), thereby making the bath much less efficient and running the risk of a not so good deposit. If you want to use an air-type agitation, you can use a nitrogen gas agitation and a nitrogen blanket, but that will be expensive in consumables.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005