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

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