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3D Corner Delamination Analysis for Fan-Out Chip Scale Package
Keywords: Fan-out CSP, interface delamination, virtual crack closure technique
Driven by the need for electrical performance improvement and system integration, the interconnection between silicon die and its package has become one key area for packaging technology development. One of the interconnection schemes received a lot of attention lately is die surface fan-out redistribution. In a fan-out package the silicon die is first encapsulated in molding compound except its top surface. A metal-polymer redistribution layer is then fabricated on top for interconnection between die-level bond pads and BGA pads. This type of interconnect involves structures in thin-layered configuration and materials having high coefficients of thermal expansion. As a result, the structure is susceptible to interfacial delamination during package assembly or under service condition. Therefore, it is important to understand the interaction of materials and geometry and its effect on delamination driving force to ensure reliability of the package. In this paper fracture mechanics approach is applied to study the corner delamination problem in a fan-out chip scale package. The corner delamination between die and fan-out redistribution layer is considered using quarter-point singular crack-tip finite element with 3D virtual crack closure technique (VCCT). In this study VCCT is applied to obtain the variation of fracture driving forces including strain energy release rate, stress intensity factors and phase angles along a realistic curvilinear delamination crack front. For the case of fan-out package under thermal cycling, the analysis shows that partial contact occurs between the delamination crack faces. However, the crack front remains open. In addition, near the location where the delamination crack front intersects die-to-molding compound interface, mode-I and mode-III stress intensity factors are very strong, while mode-II stress intensity factor is suppressed. Parametric study is also conducted to investigate the effects of material properties and geometrical dimensions on the delamination driving forces. The calculated fracture mechanics parameters may be combined with data on the resistance to interface fracture for predicting reliability of the package.
Tz-Cheng Chiu, Assistant Professor
National Cheng Kung University
Tainan, Taiwan 701,

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