I would add to this that the rate of oxidation to stannic tin is dependent on the temperature of the solution, so we keep ours around 70F. Peter Blokhuis --- "<Rudy Sedlak>" <[log in to unmask]> wrote: > Sean: > > The murky solution is due to Stannic Tin, and since > Stannic is converted from > Stannous, by oxidation, there really is only two > ways it can happen. > > The first obvious one is by reaction with Oxygen in > the air. This is > certainly a factor always, but if you are entraining > a lot of air with the > eductors, you could raise the rate of this occurring > many times. > > The other way it can occur is by excessive (anode) > current density..so if you > are using bar anodes ask if they are being > replenished as often as they > should be. > > The next question to ask is, what is the effect of > STannic Tin in the plating > bath, and the answer, as in all of PCB's is "That > depends"... > The oxide dissolves a helluva lot faster in alkaline > solutions than the > metal, and this COULD cause/allow (apparent) etching > of the Tin at a much > faster rate, and thus could cause apparent > overetching, or perhaps pitting of > the Copper. > > And the other thing that can happen is that this > Stannic Oxide in the deposit > can dissolve into the photoresist stripper. Some > resist strippers lack the > key ingredient in them to prevent immersion plating > back on to the Copper, > and thus you can wind up with copper partly unetched > due to the presence of > immersion Tin. This is especially the case if you > are attempting to strip in > a tank, although, in this day of insane tight > dimension specs, I have seen it > cause problems in spray stripping as well. > > Filtration of Stannic is EXTREMELY difficult due to > the extreme fine particle > size (the brightener/leveler in the Tin plating is a > surfactant that causes > extreme small particles to form). > > Rudy Sedlak > RD Chemical > > --------------------------------------------------------------------------------- > Technet Mail List provided as a free service by IPC > using LISTSERV 1.8d > 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 delivery of Technet send the > following message: SET Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line > Resources & Databases > E-mail Archives > Please visit IPC web site > (http://www.ipc.org/html/forum.htm) for additional > information, or contact Keach Sasamori at > [log in to unmask] or 847-509-9700 ext.5315 > --------------------------------------------------------------------------------- __________________________________________________ Do You Yahoo!? Make international calls for as low as $.04/minute with Yahoo! Messenger http://phonecard.yahoo.com/ --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------