Application of interfacial fracture mechanics approach for obtaining design rules for flip chip interconnections

Abstract

The reliability of an electronic package can be described by a physics-of-failure approach. Crack initiation and propagation in the bulk material and interface leads to catastrophic mechanical and finally to electrical failure. Therefore, bulk and interfacial fracture mechanics is a suitable method to describe the reliability of an electronic package. As package, a stud bump bonding flip chip interconnection on a thermoplastic substrate material [liquid crystal polymer (LCP)] is studied. The paper focuses on the description of the interfacial cracking between the underfill and the LCP. This is used to obtain design rules for flip chip interconnection on LCP by means of finite element analysis. Geometry design parameters-fillet shape, chip and substrate sizes-are studied. Moreover, the influence of material properties of the substrate and underfill are investigated. The impacts of the parameters are evaluated by analyzing the energy release rate (ERR) and mode-mixity in the interface. For determination of the critical ERR as function of the mode-mixity, a modified button shear test is utilized. The button, made out of underfill, is cured on the LCP substrate. A pre-delamination is established using a Teflon strip. The critical ERR for different mode-mixities is obtained by varying the shearing height of the button test. Additional, the influence of oxygen plasma treatment of the LCP substrate on the interfacial cracking is taken into account. In the investigation, design rules for increasing the reliability of flip chip interconnections are obtained. Moreover, a modified button-test is applied to obtain critical energy releases rates for different mode-mixities for the interface underfill/LCP. These results are used to optimize the geometry and materials of flip chip interconnections for automotive sensor applications in respect to delamination risk between substrate and underfill

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“…buttons molded on a wafer in an array sheared off by a programmed shear tester which also records the force-displacement curves). Via the point of attack of the shear tool, different mode-mix conditions can be obtained from mode-I dominated to mode II dominated [9,35,36]. Recently it was shown [10] that a also negative mode-II conditions and corresponding phase an gles can be obtained by shear tests on molding compound but tons of triangular cross section, allowing to pinpoint a minimum Gc( 1jJ') and exploiting a found symmetry.…”

Determination of adhesion and delamination prediction for semiconductor packages by using Grey Scale Correlation and Cohesive Zone Modelling

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“…Unfortunately, adhesion is at the same time a difficult subject and not yet fully understood. Still, unlike for soft solders, fracture mechanics has been successfully applied to crack propagation problems in microelectronics for polymers, metals and interfaces, evaluating the energy balance at the crack tip (Auersperg et al 2001;Dressler et al 2008;Yao and Qu 2002). Although the theory is readily available and implementation into FE has been made ( Fig.…”