Hi Nigel - One of my mentors always cautioned me to "consider the source 
of the data and why potential conflicts of interest may be present" when 
digesting industry published test results or data analysis. My 
recommendation is to read the specific references that are discussed in 
the CEL ppt file and determine/interpret those results yourself. Rockwell 
Collins/Iowa State University did extensive thermal cycle testing of SnBi 
surface finishes for both tin/lead and leadfree solder joints (published 
at the SMTAI Conference in 2007). Our test results were in agreement with 
the NIST (Dr. Carol Handwerker), Celestica (Dr. Polina Snugkovsky) and NPL 
(Dr. Chris Hunt) published data. Also look at the JCAA/JGPP test report 
which demonstrated that tin/lead components used with a leadfree solder 
alloy that contains bismuth can result in significant solder joint 
integrity degradation. The current industry data set supports the use of a 
SnBi surface finish in a tin/lead soldering process as long as the overall 
solder joint Bismuth content remains below approximately 6%. The ability 
of SnBi surface finish to eliminate tin whisker  - well, that is a whole 
different discussion that requires lots of beverages.

Dave Hillman
Rockwell Collins
[log in to unmask]




Nigel Burtt <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
08/13/2010 02:34 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Nigel Burtt <[log in to unmask]>


To
[log in to unmask]
cc

Subject
[TN] SnBi finish






The received wisdom on having Bismuth involved in any lead to lead-free 
assembly transition is that it should be avoided because of the 
possibility of 
forming a low-melt Sn-Pb-Bi phase within the solder joint, possibily at 
grain 
boundaries and risks realiability problems. But how likely is it that for 
example, 
SMT AE caps RoHS-compliant from Panasonic using a SnBi termination finish 
will provide the right Sn/Pb/Bi contributions to create the troublesome 
alloy?

I found a presentation from NEC which explains their choice of SnBi finish 
and 
explains research they commissioned that found the low-melt phase will not 

occur.

<http://www.alpha.cooksonelectronics.com/sacxdatalibrary/pdfs/NECSMT.PDF
>

---------------------------------------------------
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 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 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
-----------------------------------------------------