If my understanding is correct, IMC's continue to grow throughout the life of a board. If we're discussing what is too thick and what is too thin, we need to look at the stage in the board's life at which the IMC thickness is being considered and the effect that it's thickness has at that point. Military boards are intended to last for 15+ years, operating (in theory) between -40C and +125C. This degree of thermal stressing is going to be a fertile breeding ground for IMC growth, especially when coupled with stresses due to vibration. Many "older technology" boards last the distance still in working condition, so the IMC layer growth can't be a major issue there. I know SMT is a lot more fussy and fragile, but are we being more concerned about IMC's that we need be, apart from ensuring products get through the warranty period before we make money on repairs or replacements? When is max IMC thickness achieved (how many 'degree.hours' does it take)? Is IMC thickness self-limiting in any way, or does the whole solder joint eventually become a homogenous IMC? How MUCH weaker than the newly-born solder joint is the senior citizen solder joint? What can we do, if anything to ensure that the old, fully-matured joints are still strong enough to do their job? i.e. what homgenous IMC alloy is strong enough as a solder joint? Just a (cynical) thought to stoke the fire with. Regards Peter Duncan Earl Moon <[log in to unmask] To: [log in to unmask] M.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Sent by: Subject: Re: [TN] IMC's TechNet <[log in to unmask] ORG> 10/09/01 02:58 AM Please respond to "TechNet E-Mail Forum." Phil, So the following is of concern: :The thickness of the intermetallic formed by thermal aging had little effect on the peel strength until the intermetallic thickness reached above 25 microns (0.001 inch). Then the lead rich layer appeared to be a major the contributor, it formed large lead crystals the fractured easily along grain boundaries." Is this then a thickness specification not to be exceeded, and how easily under what conditions did the fracture occur? Earl --------------------------------------------------------------------------------- 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 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------