Hi Syed, >Is the reason that Tessera parts do not "need" underfill that their finish >is not underfill friendly? Otherwise is the underfill not expected to >increase the life of the flipchip systems? No. Tessera-concept-based CSPs have compliancy built into the package effectively decoupling the low-CTE die from the package solder pads and thus also from the high-CTE PCB. You certainly could underfill them, but you do not need to to assure SJ reliability in that fashion--so whhy would you want the extra expense and non-repairability of an underfill? Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 386-437-8747, Fax: 386-437-8737 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------