Very neat Bill thanks. May I suggest a refinement, or at least a flag, to test 3 the heat gun? If the residues are partially removed rosin or resin, which can also have a white or off white appearance, the heat gun will melt it to a translucent or clear appearance. Visually this would be similar to the powder disappearing. So the refinement would be to either know the generic flux type in use, or carry out an additional inspection, or pick at the area to see if the resides flake off. Regards Mike Fenner Indium Corporation T: + 44 1908 580 400 M: + 44 7810 526 317 F: + 44 1908 580 411 E: [log in to unmask] W: www.indium.com Pb-free: www.Pb-Free.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: 19 March 2004 05:33 To: [log in to unmask] Subject: Re: [TN] White residue I will summarize some points re your problem which hopefully will make it easier for others to add their thoughts- 1. The residue- while there are many causes to white, tan, yellow, gray residues; the most likely cause in your case would be the insoluble activator residues from your no clean flux. As Brian points out, these residues are meant to be left behind, and their presence is not supposed to be harmful. Most likely they are a dibasic acid, generally adipic acid, although succinnic, tartaric and malic acids have also been used. Check in a Chemical Handbook and you will find that adipic acid is not really very soluble in anything, which gives some insight on why it remains on the completed assembly. 2. Quick identification of the (flux) residue-- if it is a dibasic acid, dip a Q-tip in 0.1 N NaOH, touch it to the residue, rinse with water, rinse with IPA, and blow dry with dry, oil-free compressed air. Best to do this on a scrap board that is run through the soldering process so it can be discarded afterwards. If the spot is now clean, contaminant is most likely dibasic acid. 3. Quick identification of the (solder mask) residue- if it is the white powder fumed silica used to thicken liquid solder masks, you will often see it appear as Brian has noted. If the solder mask is undercured, any cleaning step may strip off part of the green solder mask, exposing the white thickener powder (typical trade name is 'Cab-O-Sil"). Heat the white area with a heat gun. If the residue is the Cab-O-Sil, the heat softened solder mask will allow the Cab-O-Sil to sink back into the green solder mask. Residue disappears, problem is insufficient UV cure during solder mask processing. [Quick, cheap tests are great !] 4. A-610 residue allowance- Most folks using 610 follow the rules that visible residues are not acceptable. Arguing with customers that the residue is x or y or z normally tends to be an uphill battle, especially when the customer asks you to accept the liability that the residue will be x every time... You will sleep much easier if you can find a way to eliminate the residue, even if a cleaning step is required. 5. Many US companies offer cleaning agents that will quickly remove no clean flux residues. Certain of these companies even offer contract cleaning services, where they maintain a cleaning centre staffed by experts with all different types and sizes of cleaning equipment and appropriate cleaning agents, plus testing equipment. They will accept the problem PWAs, clean them, test them and return them to you via express shipping. In the long run, this is much more economical than maintaining cleaning experts and processes in house. Let me know if clarification or elaboration of any of these points is needed. Bill Kenyon Global Centre Consulting 3336 Birmingham Drive Fort Collins, CO 80526 USA Tel: 970.207.9586 Cell: 302.377.4272 --------------------------------------------------- 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 ----------------------------------------------------- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: This email, its content and any files transmitted with it are intended solely for the addressee(s) and may be legally privileged and/or confidential. 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