Dave, My bag is humor, you're SAC is hope. Good work. I hope you will be allowed to share the data. Dewey -----Original Message----- From: Leadfree [mailto:[log in to unmask]]On Behalf Of David D. Hillman Sent: Tuesday, December 07, 2004 12:16 PM To: [log in to unmask] Subject: Re: [LF] Transition questions, Pb to Pbfree wave soldering ?? Hi Genny! Well, since ya asked for an example! Rockwell Collins may present a paper on the issues of having a SAC solderball in a typical Sn63 soldering reflow profile at the Pbfree Conference in Toronto in May (yes, Bev, I know I owe ya the abstract!). We have conducted a couple of tests to see what can happen. The issue with the SAC solderball in a Sn63 profile is that you get a very nonuniform microstructure that, depending on your use environment, will impact solder joint integrity. The SAC solderball never melts so that the Sn63 solderpaste diffuses into the solderball from the bottom up. This diffusion pattern results in lead (Pb) being segregated at the SAC solder alloy interdendritic (aka grain boundry in a simplistic sense) regions causing wetting defect issues. This SAC solder ball in a Sn63 issue has already been reported in the industry literature as problem for some use environments. Some of the published literature shows that the SAC solderball goes molten then the nonuniform microstructure issue resolves itself. I recommend Carol take a good look at her microsections to determine if the solder joint integrity has been compromised. I'll send Steve a photo to post of a cross section illustrating what happens to the solder joint microstructure. Also, the JCAA/JGPP consortia has included several variations of SAC solderballs/Sn63 reflow profile situation on their test vehicles - that data will be very useful to the industry and should be available in early 2005. Hope this helps. Dave Hillman Rockwell Collins [log in to unmask] Genny Gibbard <Genny.Gibbard@VC OM.COM> To Sent by: Leadfree [log in to unmask] <[log in to unmask] cc > Subject Re: [LF] Transition questions, Pb 12/07/2004 12:40 to Pbfree wave soldering ?? PM Please respond to "(Leadfree Electronics Assembly Forum)" <[log in to unmask] >; Please respond to Genny Gibbard <Genny.Gibbard@VC OM.COM> I am curious, Carol, who provided the choices you could pick from? And why did you choose None of the Above? We have a customer who tells us the product we make for them is exempt so they don't want leadfree, (Server) but their lead free policy states that leadfree BGA's are not backwards compatible with a SnPb process. So if the BGA's we use are suddenly not available with SnPb, we will be forced to go lead free. No choices. Even if we could provide the documentation you are currently gathering on your BGA, I doubt they would change their mind I have heard from many directions that Pbfree BGA's should NOT be soldered with standard PbSn solder. Does anyone know of a good reference paper or such that can explain clearly why? -----Original Message----- From: Carol Spiers [mailto:[log in to unmask]] Sent: December 7, 2004 12:23 PM To: [log in to unmask] Subject: Re: [LF] Transition questions, Pb to Pbfree wave soldering ?? Thanks for the input Rick, I totally agree with you. Makes sense since the two swipe thing would be totally inefficient (costly) as I would have to mask of the footprints for the leaded parts, put the non leaded parts in after the first Pbfree swipe and then wave in th SnPb. Now for my next question. Here's a real life scenario that I am living with. I now have a board that is populated with SnPb parts, the component supplier has converted the BGA to lead free. I had the choice to a) change my process to high temp SnPb solder at smt (and adjust oven to higher temp and assume I am still within scope of thermal limits of all components on board) to help ensure joint reliability or b) convert the whole smt process to lead free paste and subsequently adjust ovens to even higher temp, (at this point not sure if thermal limits on all parts can withstand the potentially 20 Deg C adjustment) for this product. I opted to go with c) ran the BGA in my current process with no adjustments. We have completed all functional testing with no failures, but, I have sent samples to a lab for xray and cross sectioning and comparison evaluations to determine long term reliability. I haven't received the results back yet. What would you have done? Carol ---------------------------------------------------------------------------- ---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 -------------------------------------------------------------------------------