Jack: In answer to your responses below. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Evans Sent: Wednesday, March 21, 2007 12:04 PM To: [log in to unmask] Subject: Re: [TN] Whisker contamination is solder pot Michael, thanks for your reply and here are the answers, best I know: 1. What is the capacity of the solderpot? This solder pot holds about 12 lbs. Based on your earlier input you are dumping this every month after tinning @ 500 parts. This does not seem like a high loading factor. So I wouldn't suspect high contamination levels from the parts your are pretinning but it would be worthwhile to have Kester analyze the pot for impunities when the problem is occurring. Among other things you could be getting high gold or copper impurities. 2. What is the flux being used? Almost exclusive to Kester 186-25, but a few drops of a kester OA might be used in extreme circumstances. The exceptional use of OA is so infrequent that I would rule it out all together, being used maybe once or twice every six months. This is a RMA medium solids flux so I don't believe this is causing any reaction problems. Is this flux really old? As a test you might try a flux from a different supplier, possibly an RA. 3. What is the material the pot is made of? I am almost completely sure that this is milled out of stainless, but the photo copied manual that I have for this doesn't specify. It does not appear to be magnetic. Next time you change out the pot thoroughly inspect it for breakdown, deterioration, pitting, etc. 4. Does the problem show up on a new pot charge or does it require time to develop if so how long? I have this problem today and it has been two weeks since I changed the solder. We had a HUGE batch (for us) of parts go through this this week, about six hundred soic's. These particular components were lead free and we were having a difficult time getting them to reflow in the smt process without pre tinning them. It's possible your are getting contamination from the leads. It could be oxides, organics, plating salts, mold release, etc. Are you doing any wire tinning, where sleeving or wire fines could be getting in the pot? 5. What is your definition of "polarized metal stuff"? Are you saying magnetic or are we getting into dipole moments and ligand field theory? Well, often when we see this fine hairlike strand, we have to heat the lead and scrape it off with an iron. It doesn't become molten in normal soldering temperatures and it doesn't want to let go of the lead that it is attached to. If we use braid, we often find ourselves chasing it up and down the lead. Sometimes it seems to attracted to the soldering iron tip, as if magnetic and sometimes not. We use metcal tips. See item 4 above Also are you cleaning/de-drossing the pot regularly i.e. before every use? I changed this solder pot today and used a new lot/date code of solder. So, I expect that this problem will appear to go away and I will assume that I have solved the problem. Then, sometime in the future, I will rear it's ugly head again. I don't think it's the actual feeder stock solder causing the problem. We had this problem in our Corfin tinning system and we blamed the solder for several months. Finally, they removed the solder pot and replaced it with a brand new lot of solder and the problem went away. The lot date codes of solder that I am using have nothing to do with that story, but I wonder if in the past, this pot could have been contaminated and there are gremlins floating around in there that only show up on occasion??? If you are doing a good job of cleaning out the pot during change out this shouldn't be an issue. However this would probably show up during the analytical analysis of the solder in item 1 above. Jack Evans, Aeroflex Colorado --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 847-615-7100 ext.2815 ----------------------------------------------------- This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. 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