Great point George! That is exactly what I suggested a few e-mails earlier: data are much better than guessing :-) Vladimir SENTEC SENTEC 11 Canadian Road, Unit 7. Scarborough, ON M1R 5G1 Tel: (416) 899-1882 Fax: (905) 882-8812 www.sentec.ca -----Original Message----- From: "Wenger, George M." <[log in to unmask]> Date: Wed, 27 May 2009 11:02:18 To: <[log in to unmask]> Subject: Re: [TN] humidity test failure Without some analytical data it is difficult to determine Wayne, Without some analytical data it is difficult to determine exactly what the problem is. The photo you sent Steve appears to show flux residue coming from under the capacitor rather than a dendritic growth but an analysis should be able to tell what it is. I don't have lots of experience with Axarel 2200 but I do know that IPA isn't an effective cleaning solvent for RMA and soak tanks are certainly not an effective process for cleaning flux residue from under chip capacitors. My experience in the Bell System has convinced my that using Bellcore (Telcoria) compliant fluxes, which I call 'leave-behind' because if you don't clean them off they aren't a reliability issue, you wouldn't see dendritic growth if the flux residue wasn't cleaned off. However, the worst thing you can do when using a Belcore compliant RMA flux is to use try and clean if off with marginal cleaning solvent/process because all you wind up doing is removing most, but not all, of the rosion/resin which was trapping the ionic activators thus allowing the ionics to cause problems when heat and humidity are applied. Regards, George George M. Wenger Andrew Solutions Senior Principal FMA/Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 (Office) (732) 309-8964 (cell) [log in to unmask] -----Original Message----- From: Thayer, Wayne [mailto:[log in to unmask]] Sent: Wednesday, May 27, 2009 9:50 AM To: 'TechNet E-Mail Forum'; Wenger, George M. Subject: RE: [TN] humidity test failure 1. Air convection reflow. 2. RMA 3&4. Axarel 2200 then IPA in soak tanks with circulating pumps. Thanks! Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M. Sent: Wednesday, May 27, 2009 8:31 AM To: [log in to unmask] Subject: Re: [TN] humidity test failure In order to give you an meaningful answer I think we need Wayne, In order to give you an meaningful answer I think we need more information from your side. 1. Where the capacitors wave soldered or reflow soldered? 2. What type of flux was used? 3. What solvent was used? 4. What type of cleaning process was used? Regards, George George M. Wenger Andrew Solutions Senior Principal FMA/Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 (Office) (732) 309-8964 (cell) [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden Sent: Wednesday, May 27, 2009 8:24 AM To: [log in to unmask] Subject: Re: [TN] humidity test failure Looks like whatever it is it may have started from residues leaching from UNDER the component. The voltage bias and environment would have only accelerated this. The solder joints exposed to the cleaning process look fine. You should review your cleaning procedures and perform testing (IC/SIR) to determine if you are adequately cleaning, rinsing, and drying to remove contaminants from under low-standoff components. My suspicion is that if that is in fact the case, and you decided to try to conformal coat, the problem would have only manifested itself sooner with conformal coat adhesion problems. -----Original Message----- From: Steve Gregory [mailto:[log in to unmask]] Sent: Wednesday, May 27, 2009 8:00 AM To: [log in to unmask] Subject: Re: [TN] humidity test failure Good Morning! Half the week down already. That's another nice thing about 3-day weekends; you also get a 4-day work week either prior to, or after the weekend. I have Wayne's picture posted now. It's at: http://stevezeva.homestead.com/files/C23_Humidity_failure.JPG Definitely some kinda' junk there! Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne Sent: Tuesday, May 26, 2009 9:01 PM To: [log in to unmask] Subject: [TN] humidity test failure Hi Technet Gurus! I have attached a picture of a part responsible for excess current draw during an extended humidity/temperature cycling test. (I copied Steve so he can hopefully post!) The board was carefully solvent cleaned, but no SIR test validating the process strips all ionic contamination. The board is in an enclosure where plenty of ionic contaminants are available. Humidity was supposed to not exceed 90% and was to be non-condensing during cycling. There were a handful of components which displayed similar deposits on the same circuit board. These were the only parts biased during the humidity test. I believe the evidence suggests at least some condensation occurred. To me the deposits look like salts. But what do "the experts" think? Is there any rule of thumb as to humidity levels where we are nuts to try to survive without conformal coating? Part of the adjacent circuitry contains RF devices and those guys get panic-stricken when told we probably need to conformal coat! 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