I believe intermetallic growth and oxidation are separate paths to poor solderability. It's my understanding that intermetallics are poorly soluble in solder, whether oxidized or not. Gregg Temkin Sr. Manufacturing Engineer Korry Electronics -----Original Message----- From: Leadfree [mailto:[log in to unmask]]On Behalf Of Kane, Joseph E (US SSA) Sent: Monday, March 20, 2006 8:01 AM To: [log in to unmask] Subject: Re: [LF] Component Long Term Storage J-STD-033 says that the shelf life of parts dry-packed in moisture barrier bags must be at least 12 months. Of course, we open bags older than that all the time, and the HIC still looks good, so I don't know what the real performance limit is. If you open the bag after X years and the HIC looks pink, then of course you can bake. As for lead finish, we had problems years back with matte tin. Theory was that the finish was porous and allowed oxidation of base metal. Hot solder dip almost always restored solderability. If the problem had been caused by intermetallic growth, the dipping should have been less effective. My understanding is that intermetallic only becomes a problem when it grows out to the surface and oxidizes. Intermetallic growth might not be a problem with underlying nickel (slow diffusion rate), or if your copper is covered with a decent layer of fused tin/lead or hot solder dip. Some parts still solder perfectly well after 10 years. Cooling would slow the growth rate of intermetallic, but the ratio is probably based on degrees K, so it wouldn't help that much unless you used liquid nitrogen for storage (not recommended). Leads made of Kovar or Alloy 42 don't seem to last as long, not sure why. Don't know about nickel/palladium/gold and some of the newer flavors, I guess we'll see. Joe Kane BAE Systems Johnson City, NY -----Original Message----- From: Colin Weber [mailto:[log in to unmask]] Sent: Sunday, March 19, 2006 11:34 PM To: [log in to unmask] Subject: [LF] Component Long Term Storage Hello Folks, Could anyone please advise on what realistic long term storage (many years) can be achieved, and how to achieve it, for components such as integrate circuits? Any articles or guidelines would be helpful. We are facing some obsolete component issues and do not have resources to redesign many boards for incompatible replacements or new devices. After searching the archives I have ascertained that it seems the hygroscopic nature of the packages is not a great problem. J-STD-033 should help with determining storage requirements for this issue. Would it be true to say baking the components can eliminate any absorbed moisture, even after many years of long term storage? A bigger problem appears to be intermetallic growth on the legs, between the coating (tinning) and the actual leg material. The intermetallic can grow over time, eventually causing the legs to lose solderability. I suspect the growth rate is temperature dependent and could be slowed by cooling. Regards, Colin Weber ------------------------------------------------------------------------ -------Leadfee Mail List provided as a 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 Leadfree To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL) Search previous postings 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 ------------------------------------------------------------------------ ------- ---------------------------------------------------------------------------- ---Leadfee Mail List provided as a 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 Leadfree To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL) Search previous postings 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 ---------------------------------------------------------------------------- --- -------------------------------------------------------------------------------Leadfee Mail List provided as a 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 Leadfree To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL) Search previous postings 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 -------------------------------------------------------------------------------