Ingemar, 1) I'm afraid we are going to see more and more of this, not less. In the blind race to lead-free, some of the suppliers are becoming "enviro friendly" (Hmm, if a plane crashes because of tin dendrites does that count as enviro friendly because there are fewer humans or enviro nasty because it burned some trees?) by replacing perfectly good 63/37, 60/40, 90/10, 98/2 coatings with pure tin - unrelieved of course since they can't take the heat to reflow the pure tin. 2) What in the world is McFenner's glue?! 3) Can you post the picture on Steve's website? I would love to see this! 4) I don't believe you need heat as a stressor. I think the heat/humidity just accelerates the process that would happen any way. The stressor is internal, in the tin coating. And since there is no place for the tin to move in the x-y plane (no soft lead to push around) they (tin crystals) grow in the z axis to relieve the stress. 5) What do you mean by sealed package? 6) Most academic studies to produce tin whiskers on demand have failed. However, I do seem to recall reading a paper that said/showed having nickel under the tin retarded whisker formation. What are the underlayers of your tin coating on this part? 7) Certainly one un-named large Canadian-based telecommunications equipment company would not use leaded devices with 100% tin coatings. regards, Bev Christian Research in Motion -----Original Message----- From: Ingemar Hernefjord (EMW) [mailto:[log in to unmask]] Sent: May 9, 2001 6:41 AM To: [log in to unmask] Subject: [TN] Sn whiskers, TT (Technical Topic) Hi all, thought Tin whiskers belonged to stories from those day when..etc. To my surprise we do experience that phenomenon in one of our many hundreds of products, so not a problem that hits the whole organisation, but that keeps a small local group awake. Now, description: small Kovar package with alumina substrate and Au thickfilm and among components there are a number of ceramic caps which are all glued with ol' McFenner's glue, nothing wrong with that. The but: the end terminals of those caps are pure tinned instead of traditional Ag/Pd or Au which are much used materials for glueing components. Mc Fenner has my story in details and he has already given his view on my problem. What even he did not predict was that single Tin + stress + x+y+ ? can generate tin whiskers. After a number of tempcycles the caps (terminals) look like a mature burdock, never seen something like that. Thousands of needles with different cross sections: T, X, circular, ellipses etc. All like piped fro! m a cream press for making tartes, but less in size of course. The strange thing is (yes, I have read everything about tin whiskers in Wassink and Manko) that the dominating driving force, heat, has created no such whiskers at all. Sealed packages passed 500hs +90Centigrade and tempcycling 300 cycles -40/+90C. No whiskers in the heat aged, whiskers in all packages that passed cycling. Also seen, is that the cap's terminal tin finish is totally fatigued and structure is broken up into coars grains or rather 'flakes'. Litterature says that using some percentage Lead in the tin will stop whisker growth. Or, if you have 100% tin, you should pass all caps through a temperature that remelts the tin, also a method for minimizing the creation of whiskers. Is there anyone else that has seen Sn whiskers on inside of a sealed package, and if so, what components and what environment did start the whiskers growing? Would you dare use burdock fastener caps in a HiRel product? Obstinate as I am I conclude with something that is forbidden, a line from the world of fun: "I bought my wife a new car. She called late in the evening and said, "Sorry, know I'm late, but there is some water in the carburetor." I asked her , "Where's the car?" She replied, "In the lake." > Henny Youngman See you all Ingemar Hernefjord Ericsson Microwave Systems ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------