Doug, I like your answer. One needs to know what animal they are dealing with before one can determine that the characteristics are. "No Clean" means different things to different people. There are no clean low solids fluxes (No-Clean LSF) based on dicarboxylic acids. There are even No-Clean LSF's which have a rosin content. In my years with Lucent we used typical RMA (89% metal 11% flux vehicle)solder pastes and RMA liquid fluxes (5-40% rosin solids) and we didn't clean them off so many people referred to them as No-Clean but I liked to call them "leave behind" systems. I don't like the No-Clean name because it doesn't give one much information. Regards, George George M. Wenger (908)-546-4531 [log in to unmask] Distinguished Member Technical Staff Celiant Corporation, FMA Lab, 40 Technology Drive, NJ 07059 -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Thursday, February 28, 2002 11:33 AM To: [log in to unmask] Subject: Re: [TN] No No-clean? Kathy Kuhlow asks: Not to use was explained to me as such: No clean leaves a residue that with heat can reliquify and then start to move which will cause an air bubble where the flux was originally at and now isn't. So the question comes to: does and at what temperature would it take for the no clean residue you are using to reliquify if it does at all? Then if it does liquify is there any activation that is occurring? Does the coating withstand the proper adhesion for the application if the air bubble does occur? Doug Pauls, now fully tanked up with Dew, responds. Kathy, you are treating the low solids flux as if it were a single animal with tightly identified characteristics. The residues that you have on the board can be generically called weak organic acids, or dicarboxylic acids. A paper by Al Schneider (who has forgotten more about flux than I will ever know) a few years back listed the menu from which a flux manufacturer has to choose. If I recall, that information found its way into J-HDBK-001, section 4. The list is over 36 materials, each of which would give you a different blend of properties in the final residue. A residue that is 50% adipic and 50% maleic acid would give you different characteristics than one that is 33% succinnic, 33% glutaric, and 34% fufu dust / gnats noses. So the question of "what point does the residue soften and creep" depends entirely on what flux you are using and a generic classification cannot be made.. Your flux manufacturer would have to answer the question. They would also have to address the issue of whether or not the residues had any kind of chemical activity in the softened condition. Think of it this way: At what temperature does solder reflow? Kind of depends on the alloy, right? Some residues will soften under high heat and may creep. It depends on whether the residue acts more like a thermoplastic or more like a thermoset. The latter will resist heat better. If your application has a high amount of heat, or point heat sources, then LSFs may not be good for that application, or topical cleaning may be needed for that area. In my experience, you either want to leave a LSF residue totally alone, or totally remove it. Doing a half-ass job of cleaning results in an amalgam of cleaner, flux, and interactive products. Not a pretty sight and often detrimental. If you have conformal coating over a residue that will soften and creep, I would suspect you would have adhesion problems and blister formation. The same problem arises when solder mask is put over a melting metal. The metal melts and moves, wrinkling or blistering the mask. Same with conformal coat. Doug Pauls ------------------------------------------------------------------------ --------- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ------------------------------------------------------------------------ --------- --------------------------------------------------------------------------------- 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------------