I would suggest 1.yes, not only to make assembly easier, but also to enable probing at BBT less hit and miss, and don't forget to add a small extension to the pads to show under Xray inspection that the solder reflowed completely 2.yes, High Tg FR4 should stand up to the thermal stress, all other things being equal (plating quality etc), but not all the High Tg materials perform the same. You could always add IST coupons and compare different materials to find the one that suits your purpose Dougal Stewart email: [log in to unmask] phone: +44 1896 822204 mob: +44 7984 629667 www.pwbsolutions.co.uk ----- Original Message ----- From: "Ofer Cohen" <[log in to unmask]> To: <[log in to unmask]> Sent: Monday, March 03, 2003 12:16 PM Subject: [TN] Finish and material > Hi, folks, > I have two questions of a layman, regarding PCB 0f 22 layers, 3.4 mm thick > (controlled impedances in all the signal layers, what else?): > 1. Until recently I succeeded to protect the fortress and avoid using > BGA with pitch of less than 1 mm. Lately I missed a battle, and a 0.8 mm BGA > was implemented. Does it necessarily mean that I have to leave my old and > favor HASL finish and migrate to the immersion field? > > 2. Will FR4 (of course - Tg=180 deg C) withstand the thermal stresses > of this stack up, or should I migrate to more stable material (lower Cte-z > axis)? > > Regards > Ofer Cohen > Quality Assurance Manager > Seabridge Ltd. > > --------------------------------------------------- > Technet Mail List provided as a free 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/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > ----------------------------------------------------- > --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------