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Thermo-mechanical reliability of flip chip structures used in DCA and CSP

: Schubert, A.; Dudek, R.; Vogel, D.; Michel, B.; Reichl, H.


Wong, C.P. ; International Microelectronics and Packaging Society -IMAPS-; IEEE Components, Packaging, and Manufacturing Technology Society:
4th International Symposium on Advanced Packaging Materials - Processes, Properties and Interfaces 1998. Proceedings
Reston, Va.: IMAPS, 1998
ISBN: 0-7803-4795-1
ISBN: 0-7803-4796-X
International Symposium on Advanced Packaging Materials <4, 1998, Braselton/Ga.>
Conference Paper
Fraunhofer IZM ()
creep; encapsulation; finite element analysis; flip-chip devices; integrated circuit packaging; integrated circuit reliability; Soldering; thermal expansion; thermal stress

The continuing demand towards high-density and low profile integrated circuit packaging has accelerated the development of flip chip structures as used in direct chip attach (DCA) technology and chip size packages (CSP). The advantages in density, cost and electrical performance are obvious. Solder joints, the most widely used flip chip interconnects, have a relatively low structural compliance due to the large thermal expansion mismatch between silicon die and the organic substrate. This causes high thermally induced creep strain on the interconnects during temperature cycling and leads to early failure of the solder connections. The reliability of flip chip structures can be enhanced by applying an epoxy-based underfill between the chip and the substrate, encapsulating the solder joints. However, over ranges of design, process, and material parameters, different failure modes are observed with significant dependence on material properties and geometry. Nonlinear finite element analysis for flip chip structures is carried out to investigate the reliability impact due to a number of selected design and material parameters. Especially two fundamental issues are addressed, namely, the optimization of thermomechanical properties of underfill materials and manufacturing process-induced defects.