International Business Machines Corporation

Miquel A Jimarez

Eric A Johnson

Li Li

Jan Obrzut

Flip-chip electronic packages are provided with a compliant surface layer, normally positioned between an underfill layer and a substrate such as a chip carrier or a printed circuit board or card, which reduces stress and strain resulting from differences in coefficients of thermal expansion between the chip and substrate. The compliant layer, which should have a storage modulus of less than &frac12; the modulus of the substrate, preferably between about 50,000 psi and about 20,000 psi, may comprise rubbery materials such as silicone, virco-plastic polymers such as polytetrafluoroethylene or interpenetrating polymer networks (IPNs). Photosensitive IPNs used for solder marks are preferred.

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Newark Valley, NY, United States of America

Miquel A Jimarez