Hi folks, We specify a thickness range for ImmAg on our PCBs of 6-16 microinches (0.15-0.4 um). A supplier is requesting to use a range of 6-20 u". These boards will be assembled with silver-bearing solder paste (SAC305). Should I be worried about silver embrittlement (i.e., the weakening of the solder joint due to excessive presence of Ag-Sn IMC platelets in the bulk) at this increased thickness range? I know there was much discussion about this issue during the latest rev of IPC-4553A, in which the upper limit of ImmAg was set at 16u". I found the thread below between Werner and Dave Hillman in the archives, in which Dave suggests no embrittlement concern with ImmAg, although the thickness is not specified in that discussion (which took place before the IPC-4553 revision). Does anyone have any thoughts on this? Thanks in advance, Todd P.S. I couldn't find any Tech Reports on the IPC 4-14 Committee page, so perhaps the study Dave mentions below was not completed? -----Original Message----- From: "David D. Hillman" Date: Tue, 27 Jan 2009 10:45:30 To: Subject: Re: [TN] SnPbAg solder and Immersion Silver PCBs Hi Werner! I don't believe that there is an silver embrittlement issue with the use of ImAg PCBs. Rockwell Collins has been using ImAg PCBs for over 10 years with no issues of silver embrittlement. We have also conducted several lead-free assembly studies using the SAC305 solder alloy and have found no issue with silver embrittlement. And, the IPC 4-14 Plating committee did not find any silver embrittlement issues with a test assembly that was excessively silver loaded - ImAg PCB finish and silver in the solder paste - and we did not find any evidence of silver embrittlement. The 4-14 committee will be publishing that study as an IPC Technical Report in the near future after completing the necessary committee reviews. As a general rule of thumb, I think silver embrittlement is on a much lower risk register than gold embrittlement. However, I have seen the PLCC study data and it indeed was a case of silver embrittlement so I think that each situation needs to be understood to avoid having an embrittlement issue. Dave Hillman Rockwell Collins [log in to unmask]<http://listserv.ipc.org/scripts/wa.exe?LOGON=A2%3DTECHNET%3B2b12bd15.0901> ----------------------------------------------- Werner engelmaier Sent by: TechNet 01/27/2009 10:30 AM Please respond to TechNet E-Mail Forum Subject Re: [TN] SnPbAg solder and Immersion Silver PCBs Hi Kevin, That "thin (?) silver finishes...prevent the dissolution of the component lead into the solder joint" is a Red Herring. All you may be getting is AG-embrittlement which is just as bad as Au-embrittlement. It was just such 'silver finishes' on TI PLCCs that caused those PLCCs to fall off PCBs during bed-of-nail testing in 1982 at IBM-Austin and resulted in the formationof the IEEE Compliant Lead Task Force. Also, how would an Ag-finish prevent the formation of IMCs with the lead metal? Werner ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 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 For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------