I acknowledge your observations and concerns, but to date we have had no problems. Best regards, Leo Leo M. Higgins III, Ph.D. Sr. Vice President, Engg and Technology ASAT, Inc. 13809 Research Blvd., Suite 635 Austin, Texas 78750 office phone 512-249-4758 mobile 512-423-2002 [log in to unmask] www.asat.com -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Mike Fenner Sent: Friday, July 20, 2007 8:10 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin Even if you do all the thing that everyone says, you could still have difficulties. Immersion tin seems to be a very supplier dependent process so that the possibility of batch to batch variation, differences in supplier performance for the same specification etc, is higher than other finishes. Shelf life/storage certainly does need to be controlled, and can be much shorter than thought. If you view the first side reflow as an artificial ageing process you can see that you easily can slip in to difficulty even with a batch of boards that was previously OK on both sides. Regards Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins Sent: Wednesday, July 18, 2007 10:46 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin Hi folks, In the different world of IC assy and pkgg, use of imm Sn on BGA pads is not uncommon. After eutectic Sn-Pb flip chip reflow in Nitrogen with low Oxygen (about 20ppm ), followed by several thermal processes at between 125 - 165C for substrate baking and underfill curing in air, PbFree SAC305 ball attach is performed with excellent results. Imm Sn is about 1 um thick. Thanks. Best regards, Leo Leo M. Higgins III, Ph.D. Sr. Vice President, Engg and Technology ASAT, Inc. 13809 Research Blvd., Suite 635 Austin, Texas 78750 office phone 512-249-4758 mobile 512-423-2002 [log in to unmask] www.asat.com -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard D. Sent: Tuesday, July 17, 2007 3:45 PM To: [log in to unmask] Subject: Re: [TN] Immersion Tin Larry, Reuven Any thickness of tin is going to oxidize somewhat after going through two reflow passes. Even lead-free components that are baked out overnight at 150 C show a marked darkening on the tin-plated terminations, even with 90 uinches of tin or more. Circuit boards with immersion tin finish are also susceptible to oxidation. The nitrogen exposure is only in the reflow portion of the tunnel. But it helps a little, as that is the hottest. However, any time you heat tin above 100 deg. C or so, it oxidizes somewhat quickly. That is one of the reasons (just one) that immersion tin is not always a preferred finish. Is there a particular reason why you wanted to use it? You may wish to try immersion silver instead, but without looking at your assembly configuration and its intended use it is hard to recommend a finish. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Reuven Rokah Sent: Tuesday, July 17, 2007 3:14 PM To: [log in to unmask] Subject: Re: [TN] Immersion Tin The thickness of the Tin finish is below the minimum. Short term solution: Lower peak profile as possible. Use Nitrogen Long term Replace supplier of PCBs Corrective actions of existing supplier Best Regards Reuven ROKAH -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Larry K Sent: Tuesday, July 17, 2007 10:35 PM To: [log in to unmask] Subject: [TN] Immersion Tin We are having problems with solderability of the PCB on oursecond side reflow. Everything looks good after reflowon the first side but when we run the second side we have non-wetting of the pads of this side. Just to ensure we were doing everything correctly,we switched sides (we did the second side first and then did the first side as a second reflow) and the problem was still after the second reflow. We are thinking this validated our process because the side causing us problems switched with our experiment. As I said in the suject line, this is Immersion Tin. Any suggestions for a cure? thanks, Larry --------------------------------- Get your own web address. Have a HUGE year through Yahoo! 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