Mitigating Cracking from RDL Stress in Glass Substrates with Low-CTE Electrodeposited Copper-Graphene Composites

As the demand for high-performance electronics persists, there is a rapid rise in interconnect density and in the number of redistribution layers (RDL) integrated into advanced package substrates. Glass has recently gained attention as a promising core substrate material owing to its favorable material properties, dimensional stability, and scalability of lithographic design rules. Nevertheless, the brittleness of glass poses a reliability challenge when combined with the potentially significant thermal expansion mismatch between copper (Cu) and glass, along with the increasing amount of Cu utilized for high-density wiring in the package. Electrodeposited copper-graphene (CuGr) composites have emerged as a promising solution to reduce the coefficient of thermal expansion of Cu while maintaining or even enhancing its electrical and thermal conductivity. This paper explores enhancements in the reliability of glass substrates enabled by this innovative class of nanoscale interconnect materials. Finite element analysis (FEA) simulations were conducted to examine the RDL-induced stress on glass and mechanisms of core cracking due to free-edge effect. The results indicate a 30% reduction in stress on glass when CuGr is employed instead of Cu. Likewise, the graphene reinforcement of the Cu-RDL leads to an approximately 17% reduction in the energy release rate at the tip of a pre-existing crack at the edge of the glass core. These findings underscore the benefits of employing such innovative metal nanocomposites in package interconnects to continue scaling density and layer count without compromising the reliability of advanced glass substrates.