Phil, We have built a number of PCAs with lead-free and leaded balls with mixed success.. The first thing to consider is the type of metal in the solder paste...This is what forms the joint...You must first reflow the solder paste... Next, what thermal profile will the PCB take... This determines the amount of stress the joints will see after the solder solidifies and before the PCB material reaches its final rest state....At this point you may also want to look at the type of PCB surface finish...HASL seems more forgiving than ENIG.. Lastly the solder paste thickness and metals content...These give you joint volume and flux amount which reduces ball surface tension...This plays a very big role in ball collapse... Assuming you are using convection driven reflow ovens.. and we have a HASL PCBs with standard PCB material, running 90%-91% 63-37 metal water-soluble solder paste, with 6+mil thick stencils, we are successful at 10C over our current peak with standard profiles. Paul Edwards Process Engineering [log in to unmask] Tel: 408-433-4700 FAX: 408-433-9988 Surface Art Engineering 81Bonaventura Dr. San Jose, CA 95134 DUNS: 944740570 CAGE/NCAGE: 1XZ48 -----Original Message----- From: DUTTON Phil [mailto:[log in to unmask]] Sent: Thursday, February 10, 2005 8:18 PM To: [log in to unmask] Subject: [TN] Mixing Lead free BGAs with normal BGAs Hello, We've run into a problem where a PB Assembly will have a mixture of BGAs, some with regular tin/lead solder balls, some with lead free solder balls. This raises the question as to what temperature profile to run. Do we need to ask our loader to do a Pb free profile first, followed by a Pb profile? Or will it be ok to solder both together using the regular, lower temperature Pb profile? Personally I'd like to avoid the extra run through reflow. thanks, Phil Dutton C.I.D. --------------------------------------------------- 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 -----------------------------------------------------