Sona:

I am not going to try to advise whether to switch to Tin plating, but rather I  want to address what you/how you Tin plate, if you do make the switch.

Tin plating today is normally done in either a Sulfate, or methane sulfonate electrolyte.  Tin/Lead is done in a fluoborate electrolyte...

I am going to advise you to fly in the face of the industry norms, and if you do switch to pure Tin, keep the fluoborate electrolyte... and I suspect most readers of this would think me daft.

When you plate Tin, you are plating from the Stannous form of Tin, but you inevitably form some of the Stannic form also, as this is the form that the Stannous Tin goes to when it contacts atmospheric Oxygen, or there is too high a current density at the  anodes in the Tin bath.

The Stannic Tin is quite soluble in a fluoborate bath, but is quite insoluble in the Sulfate, or Methane sulfonate bath, and this is why the fluoborate bath looks clear, if dark, and the normal Tin baths all have a heavy white, creamy look to them.  This white is the Stannic Tin.

When you are plating Tin from a sulfate, or Methane Sulfonate bath, you will co-deposit the Stannic oxide with the metal.  Stannic Oxide is soluble in strong alkali, like photoresist strippers, and thus can dissolve during photoresist stripping.  Because of this the Tin plate can become porous, as the Stannic Oxide is dissolved during photoresist stripping, and thus not protect the Copper under it during etching as well as it would if it were pure metal.

Since the Stannic is completely in solution in the fluoborate electrolyte, and completely unavailable for plating, the deposits are pure metal, with no oxide, thus allowing you to plate less, and get full coverage, without risk of porosity.

What I am suggesting is perhaps not being done anywhere, but would be easy to impliment, using the same tank, and brightener you are currently using, merely convert the electrodes to pure Tin, and when making up the bath, replace the Lead fluoborate with Stannous fluoborate.

And good luck.

Rudy Sedlak



---------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
 Yahoo! Music Unlimited - Access over 1 million songs. Try it free.