To add some spice to the soup, I would like to comment on the wetting characteristics of a WS vs NC flux on Pd/Ag thick film metallization. As a IMHO comment, the WS does NOT wet as well as the NC in THIS application. The WS flux does an excellent job of wetting WHERE IT HAD BEEN DEPOSITED, however, we saw very little spontaneous wetting across pads not covered by the initial solder paste deposit. Whereas, a NC flux will tend to flow beyond the point of initial deposit and allow extended wetting. Standard RMA's being the ultimate in extended pad wetting. We attributed these characteristics to the WS flux burning off early, leaving nearby (non-solder-covered solderable) areas unaffected, whereas the NC fluxes tended to 'passivate/activate' the surrounding non-solder-covered solderable pads during reflow. The RMA's were the ultimate in passivation/activation. Having said all that, unless the PWB is badly oxidized, I do not see how the WS flux can NOT wet better than the NC due to it activity level! ..... IMHO Steven Creswick Gentex Corporation -----Original Message----- From: Brian Ellis [mailto:[log in to unmask]] Sent: Thursday, May 17, 2001 4:22 AM To: [log in to unmask] Subject: Re: [TN] No-clean vs Water-soluble wetting? Rick The activity of typical water-soluble fluxes is approximately 1,000 to 10,000 times higher than that of typical "no-clean" fluxes. Of course, like all generalisations, you will find exceptions to this statement. After soldering, the ratio of the activity of the residues will have dropped by an order of magnitude, because the hydrohalide activators in the W/S will have largely decomposed at soldering temperature, while the comparatively poor sublimability (if there is such a word!) of the dibasic carboxylic acid activators in the N/C (usually) will mean that a large proportion will remain. The high activity of W/S means that it can be used for solder wetting almost any reasonable and solderable surface, even if fairly heavily oxidised. The low activity of the N/C means that it will allow solder-wetting of only clean, very solderable, surfaces which are not heavily oxidised. In other words, not only does W/S promote fast, wide and reliable wetting, it offers a much wider process window which pardons many errors, whereas N/C offers a very narrow process window with little margin for error. Anyone who has worked with both will know that the retouch rate (expensive) with N/C is often as much as an order of magnitude higher than with W/S, all other things being equal and optimised. Of course, the down side of W/S is that you MUST clean and you must clean demonstrably well (although it is not difficult). I also say that the down side of N/C is that you should not clean, under most circumstances, because the flux is not formulated to be cleaned and cleaning may actually reduce the reliability under some of these circumstances. I suggest you may care to buy wour QA manager any of the usual books on soldering, such as Klein Wassink, Manko, Strauss etc. or that he simply speaks to your paste vendor's technical guys. You think right. Brian Rick Thompson wrote: > > I've been having an ongoing discussion with our QA Manager regarding the > wetting capabilities of No-clean versus Water-soluble solder pastes. He > believes that no-clean wets better, I think the opposite. This is in an air > reflow environment. I'm curious as to what some of you might have to offer > on the subject? > > Thanks in advance, > > Rick Thompson > Ventura Electronics Assembly > 2655 Park Center Dr. > Simi Valley, CA 93065 > > +1 (805) 584-9858 x-304 voice > +1 (805) 584-1529 fax > [log in to unmask] > > ---------------------------------------------------------------------------- ----- > 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 > ---------------------------------------------------------------------------- ----- ---------------------------------------------------------------------------- ----- 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------