David Lead free BGAs can be soldered with SnPb solder in a SnPb soldering process. Even if you stay below the liquidus of SnAgCu the liquid solder will solve the ball forming a lower melting alloy at the interface. The process of the solution of the ball into the solder ends if - The alloy that formes due to the continuous solution of Cu and Ag into the SnPb has ist liquidus at the solder temperature - The temperature is lowered below the liquidus of the SnAgCuPb alloy This means that depending on temperature and time different fractions of the balls are are solver in the solder. we made some trials and used the temperature- time integral approach of James Vincent to characterise the influence of the production parameters on the solder structure. Originally I was worried that the interface where the original ball meets the solder will be the week point where degradation will take place. However, looking at the slides of Dave Hillman I see that the rupture takes place in the SnPb solder along the pad. This makes sense, since SnAgCu it mor creep resistant than SnPb and thus the strain occurring due to thermal cycling will be dominantly in the SnPb solder. I have no quantitative data in hand to say how much crack growth is accelerated due to this material combination. A problem which is evident is the fact that you have no collapsing balls (or not the entire balls) to compensate for coplanarity problems of the balls. Best regards Guenter EMPA Swiss Federal Laboratories for Materials Testing and Research Centre for Reliability Guenter Grossmann, Senior Engineer 8600 Duebendorf Switzerland Phone: xx41 1 823 4279 Fax : xx41 1 823 4054 mail: [log in to unmask] >>> [log in to unmask] 13.12.2005 15:30:24 >>> Is it possible to get an acceptable solder joint if a Pb free BGA is put onto a board using SnPb solder paste and normal SnPb profiles? The lead free solder balls are SnAgCu 96.5/3/0.5. Seems nigh impossible to get DDR2 packages with SnPb balls. I'm designing a high end DSP into an industrial instrument. The DSP is not available lead free, nor does the application call for lead free (thankfully). There is no option to use a different memory type with the DSP. Nor is there any possibility of using a different DSP or FPGA due to time/cost/sanity. Don't want to explore going lead free on this one (for obvious reasons), and certainly do not welcome the expense of reballing 0.8mm DDR2 chips. Best Regards David Greig ______________________________ GigaDyne Ltd Buchan House Carnegie Campus Dunfermline KY11 8PL United Kingdom t: +44 (0)1383 624 975 www.gigadyne.co.uk <http://www.gigadyne.co.uk/> ______________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 -----------------------------------------------------