Ed, We actually did thermal shock testing of untinned LCCs (ceramic parts, right) on controlled CTE PWAs (best case) to try to determine how "bad" not tinning was. Answer: It was bad. Most parts failed at <100 cycles (normal parts were ~1000 cycles). We often go around on this (typically 1-2 parts per year we "just can't tin" and we re-visit this issue). We've always gone to tinning, even as far as recalling hardware to do it. Note that the Au "limit" is ~4% by weight (~1.8% by volume in Sn63); beyond that is BAD.). Also note that just a gross volume calculation (Au vs. Solder volume) can be misleading as the Au doesn't always evenly distribute in solder, it's the locallized concentrations that kill ya. I have some detailed info (too large to Technet) but if you can accept ~1 meg inputs I can mail to you. Let me know. Jim --------------------------------------------------------- Jim Maguire Boeing Phantom Works E/E M&P Phone (253)657-9063 fax (253)657-8903 Pager (206)982-3737 email: [log in to unmask] --------------------------------------------------------- > ---------- > From: Knowles, Ed[SMTP:[log in to unmask]] > Reply To: TechNet E-Mail Forum.;Knowles, Ed > Sent: Monday, April 05, 1999 2:28 PM > To: [log in to unmask] > Subject: [TN] Gold Embrittlement > > Please don't blast me on bringing this subject up again. I have searched > the TechNet archives and found lots of good information, and also noted that > it is a somewhat sensitive subject, having been around for 30+ years. We > have a condition that I believe is clearly unreliable based on what I have > read. The condition is: > > - 4 lead LCCC's (leadless with castellations) > - Approximately 50 microinches of glod plating on untinned castellations. > - Untinned parts mass reflow soldered onto PWB's (parts were supplied on > tape and reel, so subcontractors did not see that they were untinned). > - Microsectioning shows a 50 to 100 microinch layer of Au/Sn intermetallic > after soldering, on top of copper/nickel surface. Au concentration averages > about 25% in this intermetallic region. > - These assemblies will be subjected to high vibration and long term (years) > thermal cycling in actual use. > > Replacement of these parts would be expensive since they are on many boards > installed in closed and tested boxes. For this reason, mangement is hoping > that testing will qualify this condition. I hate to see the affected > program waste time and money, and am afraid they might even get a warm fuzzy > and fly these parts. > > Can any of the numerous industry experts in this group give me something > concrete to present to the program such as actual experiences or obtainable > reports? Is the above condition a no-brainer or is it not as bad as it > looks to me? I tried getting copies of the 2 reports listed in the > J-STD-001 Handbook, but struck out. > > Thank you for your time. > > Ed Knowles > Lockheed Martin > [log in to unmask] > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 > ################################################################ > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################