Jason: Standard immersion Sn has an extremely short shelflife and is difficult to solder even on it's best day. That's why it went away 25 years ago, although I'm sure some people are still using it. The most bullet proof coating for high frequency(giga)PTFE boards is bright acid electroplated Sn(BAT). Typically 0.2-0.4 mils. This will give you a 6-12 month shelflife due to it's fine grain structure, doesn't expose the board to high thermal exposures such as fusing during fab(MLB delamination) and will have enough Sn to provide decent solderability. We have used this approach for many years on high frequency signal generators/calibrators. With that said, I am not a fan of bright Sn. It additives are hard to control, it can have problems with organics and is prone to causing shorts from Sn slivers. You may also have a hard time finding a board fabricator that can supply you with a good solderable bright acid Sn electroplate. Most are using matte/semimatte Sn for etch resist and if they are using BAT it may not be in proper balance for optimal solderability and shelflife. If you can find a fabricator that can provide you with a properly controlled and solderable BAT I would go with that. If not you may want to consider one of the new generation immersion Sn's, however I have no idea how these coatings may influence signal propagation and effects for high frequency design. Good Luck. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett Wa. 425-356-6076 -----Original Message----- From: jason gregory [mailto:[log in to unmask]] Sent: Tuesday, September 21, 1999 5:39 AM To: [log in to unmask] Subject: [TN] solderability of PTFE Taconic material boards Hello all you technetters, Question for all the "high-freq" guys out there. We have been building PTFE boards quite some tme and a long-running problem has been the solderability of these boards. They are .018" thick and are used for high frequency applications. The spec is for tin immersion plating. No matter what reflow profiles I use, there are non-wetting signs all over the board. The solder just won't flow properly on the pads. It looks as though the solder flows, then stops. I've eliminated surface contamination by washing the boards prior to build and still the same problem. Are there any other platings available that will promote flow and won't affect high freq reliability. Please help. Thanks. Jason Gregory Process Tech Tadiran Microwave Networks (281)263-6671 [log in to unmask] ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################