My question would be why such a thick gold? No body want to put more gold than it is necessary. Either the part was mean to be contact only, e.g. Connector chage from contact to solder on; or someone try to save money to use the wrong vendor, normally, the good flash or igen, and hard gold electrolytic gold plater are not the same vendor. The 3rd possibility, you got a newbie designer with tennis shoes, copy and paste the old drawing notes without proper review and signing off process in place. If it is the last case, may god be with you. -------------------------- Sent using BlackBerry ----- Original Message ----- From: TechNet <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Sent: Wed Apr 15 12:01:43 2009 Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? Hi Guy! Ah, the whole "lost in conversion issues" discussion. As TechNet pointed out yesterday, one system would be soo nice. Ok, back to gold embrittlement. Your 3.8 microns is 152 microinches (thanks George Wenger) so yes, you had a very high probability that your solder joints were gold embrittled to some level. Now, let's split this discussion into "classic" and "new" gold embrittlement. The industry tribal knowledge has always been that you needed to satisfy two conditions to avoid gold embrittlement: a) do you have enough solder volume to allow for uniform distribution (e.g. keep the gold percentage below 3 weight percent) for the amount of gold present?; 2) Are you using a soldering process that has sufficient time/temperature parameters to allow (a) to occur? If we are talking about gold plating situations with no nickel finishes involved, then these rules hold true. If you get the gold evenly distributed across the solder joint and stay below 3 wt. %, you will not have a gold embrittlement issue. However, the use of the ENIG surface finish has changed the rules slightly. The presence of nickel plating causes a diffusion reaction that we didn't see with a copper surface. The energy of formation for the gold/tin intermetallic is influenced by the presence of nickel (you get some interesting Sn/Ni/Au phases) such that the gold does not always stay evenly distributed across the solder joint. The majority of the time, this redistribution and phase formation is so small/minimal that there is no gold embrittlement issue. ENIG is considered a non-gold embrittlement generator as a general industry rule. However, if you have an ENIG finish and a heavily plated gold finished component, you could have a gold embrittlement risk. As Richard pointed out, there are a number of good paper documenting this phenomena available for reading (Journal of Electronics has had some good papers on the topic). Dave Guy Ramsey <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/15/2009 10:11 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Guy Ramsey <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Gold/Tin Intermetallics, why are we afraid? I think microns and micrometers are the same thing. http://en.wikipedia.org/wiki/Micron Our board house considers 3 to 10 micro-inches to be gold flash, 50-150 is heavy plate. 3.8 micrometers is something like 150 micro-inches From: [log in to unmask] [mailto:[log in to unmask]] Sent: Wednesday, April 15, 2009 8:49 AM To: TechNet E-Mail Forum; Guy Ramsey Cc: [log in to unmask] Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? Hi Guy! I am metrically impaired - what is 3.8 micron in inches? Is your 3.8 micron referring to micrometers or nonSI units? (Given our recent SI units discussion, my question is way too ironic!). Dave Hillman Rockwell Collins [log in to unmask] Guy Ramsey <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/15/2009 07:37 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Guy Ramsey <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Gold/Tin Intermetallics, why are we afraid? We build a lot of boards with electroplated gold finish, primarily for the semiconductor test sector of our industry. On one occasion we were populating little printed circuit wave guides with SMT SMA shrouds. We noticed very poor solder appearance and very weak solder connections. Some connections broke while attaching the cables. We determined that the gold plate was 3.8 micron. And judged the thickness of the gold to be the cause of poor mechanical performance of the solder connection. We replaced the boards with versions having about 0.3 micron gold plate. The connections were much stronger. We were able to install all the cables, no connection failures. To satisfy my own curiosity, I attempted to break one of the connectors off the board. The solder connection did not fail. The copper peeled off the board. Thoughts? Guy -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Wednesday, April 15, 2009 2:42 AM To: [log in to unmask] Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? Thank you, George, sometimes one needs kind of technical pragmatism. Inge -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M. Sent: tisdag 14 april 2009 23:41 To: [log in to unmask] Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? I think both you and Vladimir are correct. If the bond Ingemar, I think both you and Vladimir are correct. If the bond sits are room temperature without any power cycling or mechanical stress it probably won't degrade. I assume Vladimir has seen the same kinds of failures I've seen and there has always been a thermal and/or mechanical stress associated with the failures. Regards, George George M. Wenger Andrew Wireless Solutions Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [Office] (732) 309-8964 [Cell] [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Sent: Tuesday, April 14, 2009 5:15 PM To: [log in to unmask] Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? You mean that such a bond degrades even if just being in constant room temperature and no power switching? Inge ----- Original Message ----- From: <[log in to unmask]> To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge" <[log in to unmask]> Sent: Tuesday, April 14, 2009 11:07 PM Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid? > Hi Inge, > > Yes, the intermetallics itself is strong, BUT it doesn't count, as all > failures I've seen goes at the tin/intermetallics interface. The larger > were the platelets, the worse it looked. > > Regards, > > Vladimir > ------Original Message------ > From: Inge > Sender: TechNet > To: [log in to unmask] > ReplyTo: TechNet E-Mail Forum > ReplyTo: Inge > Sent: Apr 14, 2009 16:55 > Subject: [TN] Gold/Tin Intermetallics, why are we afraid? > > These infamous IMCs are like parias or ghosts in most people's mind in our > business. I shocked our production guys recently by giving the advice to > let > the boards go on. Large crystals and bad looking. But I always try to > avoid > exaggerations. If no serious temp changes are predicted, nor any severe > power switching, why rework and risk introducing failures? The actual > components were very hard to rework, the cost had been unacceptable. I can > see many of you get the coffee wrong. I don't mean to spread quality > distractions, I talk about very few boards and a unique situation. My > statement was based on the fact that a gold tin intermetallic bond is > extremly strong and can last long, if not exposed to what I pointed at > earlier. I expect to be hammered down in the shop floor until only the > nose > is visible.... > > Inge > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 15.0 > 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 or (re-start) delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest > Search the archives of previous posts 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 > ----------------------------------------------------- > > > > SENTEC > 11 Canadian Road, Unit 7. > Scarborough, ON M1R 5G1 > Tel: (416) 899-1882 > Fax: (905) 882-8812 > www.sentec.ca > --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts 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 ----------------------------------------------------- ---------------------------------------------------------------------------- -------------------- This message is for the designated recipient only and may contain privileged, proprietary, or otherwise private information. 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