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