Ultralow and Tunable Thermal Conductivity of Parylene C for Thermal Insulation in Advanced Packaging

TL;DR

This study demonstrates that Parylene C thin films have ultralow and tunable thermal conductivity, which can be adjusted through post-annealing, offering valuable insights for thermal management in microelectronics packaging.

Contribution

It provides a comprehensive understanding of how the structure and annealing process influence the thermal conductivity of Parylene C, including experimental validation and theoretical modeling.

Findings

As-deposited Parylene C has a thermal conductivity of 0.10 W/m-K.

Post-annealing increases thermal conductivity to 0.18 W/m-K due to recrystallization.

The thermal conductivities are lower than Cahill model predictions, explained by diffuson-mediated models.

Abstract

Parylene C thin films have significant applications in advanced packaging of microelectronics. Their thermal properties are critical for thermal management of electronic devices. However, a unified understanding of the tunable structure and the corresponding thermal conductivity is still missing. This study investigated parylene C thin films of varying thickness and post-annealing temperatures grown via thermal chemical vapor deposition. The ultralow thermal conductivity of as-deposited parylene C measured by time domain thermoreflectance (TDTR) is 0.10 W/m-K. The thermal conductivity can be tuned by post-annealing. Significant increase in thermal conductivity is observed in the annealed samples (0.18 W/m-K) which induces melting and recrystallization. The results of XRD and polarized Raman spectroscopy show that the enhanced thermal conductivity is due to improved crystalline quality and the change in chain orientations. The measured thermal conductivities of the as-deposited and annealed films are much lower than the values predicted by the Cahill minimum thermal conductivity model, which can be explained by the diffuson-mediated minimum thermal conductivity model. Parylene C is found to possess the lowest thermal conductivity among dense low-k materials. Our work provides guidance for the structural design of ultra-low thermal conductivity polymers and corresponding thermal design of electronics.