Low Temperature Curable Low Dk & Df Polyimide for Antenna in Package

Abstract

In this paper, we developed novel low temperature curable (around 200~250 °C) low Dk (2.7) & Df (0.002) polyimide with high glass transition temperature (170 °C) and elongation (100%). We also developed negative tone photosensitive polyimide with low Dk (3.0) & Df (0.007) by photo initiator and cross linker. Material types of them are liquid or B-stage sheet materials. Patterning methods of the non-photosensitive polyimides were imprint and UV laser ablation. Resolution of those process were 10um via and 30um via respectively. Photosensitive polyimide was patterned by photolithographic tool. We fabricated fine patterned polyimide of photosensitive polyimide by photolithography. We investigated the frequency dependence of the novel low Dk & Df polyimide up to 95 GHz, and confirmed that Df gradually increased from 0.002 to 0.005 as the frequency increased. To confirm effect of the novel polyimide, insertion loss of micro-strip line whose length was 10 mm were measured using the new developed polyimide. Insertion loss (S21 parameter) of the novel polyimide was 0.8 and that was less than half of conventional polyimide. RDL structure was fabricated by novel low Dk and Df polyimide and we tested bump shear strength after thermal cycle test. All shear mode were ductile solder failure without polyimide delamination. Because our novel polyimides show excellent dielectric, thermal and mechanical properties, they are suitable to insulator of RDL for FO-AiP.