Low Temperature Curable Low Dk & Df Polyimide for Millimeter-Wave Device

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 (Tg) and elongation. Tg and elongation of the polyimide is 175°C and 100% respectively. The non-photosensitive polyimide can be patterned by laser ablation and imprint process. We also developed negative tone photosensitive polyimide with low Dk & Df by photo initiator and cross linker. To confirm effect of the novel polyimide, we measured insertion loss of micro-strip line using the new developed polyimide. We found that insertion loss (S21 parameter) was less than half of conventional polyimide. We also measured insertion loss the micro-strip line circuit after being immersed in water at room temperature for 48 hours, and found that the loss didn't change even after the treatment. 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. The developed PI shows high adhesion strength (6N/mm) to smooth surface copper foil whose roughness is 1um. These properties of the novel polyimide indicated it is suitable to insulator of RDL for FO-AiP