John has given some good advice. My limited experience with stripping and refinishing ImSn lead to hourhenius results: the limited initial shelf life became one of hours. Going against the grain, I must say I will not consciously allow the use of Immersion Tin as a final surface for any high-rel Aerospace product. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke Sent: Friday, June 26, 2009 8:54 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin solderability eval Genny, I do not believe there is a "limit" to this but obviously you would not want to keep doing it..... The numbers for storage normally quoted are for "room temperature" The formation of the intermetallic between your plated tin and the copper will follow the general rule of an Arrhenius equation. So if you intend to store for a long time and do not want to keep sending them back I suggest that they be vacuum packed and put in a freezer, which if you do the math will give you many years of "shelf life". Kind regards, John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: Friday, June 26, 2009 8:20 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin solderability eval One last question, then. Is there a point of no return - or can they always be refreshed by this process no matter how long the boards have sat? Genny -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dorothy Lush Sent: June 24, 2009 11:10 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin solderability eval Genny, I have customers that when their immersion tin PCB has sat so many months on the shelf no matter how well it is stored it is sent back to the PCB maker to be re-tinned/plated. It takes only one pad to ruin your day. The smaller the pad the more likely a problem. Dorothy Lush Fine Pitch a Flextronics Company -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE) Sent: Wednesday, June 24, 2009 9:43 AM To: [log in to unmask] Subject: Re: [TN] Immersion Tin solderability eval Genny, You have to go with the flow. Sometimes localized hand soldering will give you a false positive. If you want to know whether to use them or not, sacrifice a few and run them though all the subsequent processes (especially thermal excursions) they would be exposed to in order to establish an expected level of success. If you have to have an official reason; test them per IPC J-STD-003 for solderability. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: Wednesday, June 24, 2009 9:16 AM To: [log in to unmask] Subject: [TN] Immersion Tin solderability eval We have some Immersion Tin boards that are several years old. From everything I have read here or elsewhere, ImmSn is supposed to have a short shelf life. 6 mos to a year. No one wants to scrap the boards without testing them, though. How would you verify whether they are still good? We hand-soldered some pads and actually had no problems which surprised me, considering the age of the boards, but I don't know if that is a valid test. 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