Novel Low Temperature Curable Photo-Patternable Polyamide with High Planarity for Wafer Level Fan-Out Packaging (WLFO)

Abstract

As Wafer Level Fan-Out Packaging (WLFO) designs continue to evolve, higher pattern densities for Cu lines and interconnects continue to increase while thickness continues to decrease. As Cu densities increase, the patterning resolution of the RDL dielectric needs to shrink to allow increased bump density. The higher Cu density in turn requires enhanced dielectric performance to minimize Cu migration, whilst utilizing lower temperature and shorter cure times which result in lower levels of wafer warpage. Minimizing mechanical stress, continues to be a critical function of the RDL dielectric. Warpage leads to poor yields, distorting the planarity of the package and ultimately leading to stress induced failure from cracking and delamination. Reduction of the thermal budget is the primary means of reducing mechanical stress in WLFO designs. The amount of Cu in the package continues to increase. Differences in thermal expansions of such and the dielectric increase with temperature. Further, conventional solder reflow processes and set points will continue to be used, therefore the RDL dielectric must continue to be thermally and mechanically stable but capable of being cured at lower temperatures, 180–200 °C to minimize overall mechanical stresses from thermal expansion. We present a novel polyamide based RDL dielectric, KMRD, designed to achieve current and future WLFO design requirements. KMRD is a low temperature curable, aqueous (2.38%TMAH) developable dielectric capable of meeting industry standards for mechanical and electrical requirements, with a high level of reliability while utilizing a single stage cure at 185 °C. KMRD provides clear advantages over incumbent materials, with low temperature cure, improved pattern resolution, wide process latitudes, superior adhesion, chemical compatibility, and cost benefits using standard processing equipment and chemistry.