Hi Amol, 
High Sn solders do have lower creep rates, higher strengths, and higher 
modulii of ductility relative to SnPb—this clearly contributes to the problems you 
observe. what you can do is slow down the cooling rates from reflow to no more 
than 1.5C/sec to avoid the thermal shock causing pad cratering and to some 
extent brittle interfacial failures.
The PCb material may also contribute—some of the LF-soldering capable PCB 
base materials are   more brittle. 

Werner Engelmaier
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 17, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 17, 
London
Solder Joint Reliability: Parts 1 through 4, July 17/18, Thal, Switzerland
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, 
Orlando
Reliability Issues with Lead-Free Soldering Processes, September 22, 
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 
ENIG), September 22, Schaumburg



**************
Gas prices getting you down? Search AOL Autos for 
fuel-efficient used cars.
      (http://autos.aol.com/used?ncid=aolaut00050000000007)

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