To really answer your question, we need to know a lot more about your process, including the type of paste, the solder mask and various other factors. In my book, I identified five different basic causes of "white residues", each subdivided into a number of other causes, over 20 in all and this list is by no means exhaustive. However, there is one possible cause that I have seen in both Thailand and Malaysia and that is lack of appropriate humidity control in the workshops. Many solder pastes absorb atmospheric humidity like gangbusters on the printer and during all the wait periods up to reflow. If this happens, then some of the components will hydrolyse, producing the effect you see: it can also happen even after reflow. This is a real problem in the tropics and even in humid temperate climates. Close humidity control to <40% RH is a must. Hydrolysed compounds are generally very difficult to remove. Certainly, IPA, which is a poor solvent at the best of times, is not going to look at them. On top of this, "no-clean" fluxes are not even meant to be removed; they are designed for a minimum of low-activity residues, not for cleaning. If you really must clean, then you will probably have to use an aggressive saponifier, which ain't at all a pleasant job unless you have adequate equipment for it. However, there are other possible causes: for example, if the solder mask is under cured, the surface may be attacked by the paste chemistry, revealing fillers. Brian Somtawin Pornpottanamas wrote: > Has anyone ever seen white contaminate ( like a crystal) on assembly > boards , between IC lead? I found white residue on some board after > reflow . I try to clean by used IPA, flux removal solvent and also DI > water. But could not remove it. I also found that after we used the > solvent to clean, the white residue increase more. > > Our process used no clean . What is this residue? What type of solvent > that should be use to clean flux residue when we have to rework or > Dedug? > > > > Thanks & Regards, > > > > Somtawin Pornpottanamas > > Material Engineer > > Kimball Electronics (Thailand) > > Tel. 038-401566 ext. 211 > > Fax. 038-495029 > > > > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 1.8e > 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > ----------------------------------------------------- > > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------