Correlation of Dielectric Film Flex Fatigue Resistance and Package Resin Cracking Failure

Abstract

Resin cracking is a common failure mechanism in electronic packaging using organic chip carrier. Chip carrier made of organic material has been industry standard for the past decade as they provide significant advantages over the ceramic dielectric-based predecessors in manufacturing cost and electrical performance. However, the CTE mismatch between the silicon chip and the organic laminate leads to substantial stress in the laminate particularly at the outmost fiber. Such stress when combined with the temperature fluctuation in field operation, causes low cycle fatigue in dielectric layer and eventually impairs the circuits in the laminate, which is known as dielectric resin cracking failure. During the evolution of organic laminate technology, the demands for high speed transmission drives the need for material with low dielectric loss, which usually is associated with low ductility and in turn makes dielectric resin cracking an even greater concern. A cost effective evaluation method for testing the resin cracking robustness of an interested material before building expensive laminate is therefore critical. This paper focuses on correlation of raw dielectric film material properties and the reliability performance of the corresponding electronic package. A fabricated in-house strain controlled fatigue testing machine will be introduced. The fatigue life vs strain of a typical dielectric material will be discussed. A flip chip package using this dielectric material will be described. Its resin cracking failure rate subjected to thermal cycling stress with various delta T will be illustrated. The thermal-mechanical modeling methodology will be outlined and verification of simulations with experimental results will be presented. A predictive model for correlation of dry film flex fatigue life and the corresponding resin cracking risk in a flip chip package will be proposed.