Characterization of non-conductive adhesives

This study uses a global-local finite element study to determine the residual contact stress developed during fabrication of non-conductive adhesive (NCA) bonded flip-chip-on-flex (FCOF) systems. Electrical contact is made by pressure contact between gold bumps on the silicon die and gold coated copper bumps on the flex substrate. This study uses previous work on the determination of the bonding forces required due to variability of the bump height. The magnitude of the residual compressive contact forces is key to the performance and durability of the interconnects under life cycle loads. Key findings include: the accuracy of the simulation is very sensitive to the accuracy of the gold and flex constitutive models used; the inclusion of viscoelastic properties for the epoxy has a significant effect on simulations; and better stress development comes from a higher concentration of short bumps than tall bumps.