Epoxy/TaTiO/sub 3/ composite films and pastes for high dielectric constant and low tolerance embedded capacitors fabrication in organic substrates

Epoxy/BaTi0₃ composite embedded capacitor films (ECFs) were newly designed for high dielectric constant and low tolerance (less than ±5%) embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of specially formulated epoxy resin and latent curing agent, and in terms of coating process, a comma roll coating method is used for uniform film thickness in large area. Dielectric constant of ECF in high frequency range (0.5∼3GHz) is measured using cavity, resonance method. In order to estimate dielectric constant, the reflection coefficient is measured with a network analyzer. Dielectric constant is calculated by observing the frequencies of the resonant cavity modes. Calculated dielectric constants in this frequency range are about 3/4 of the dielectric constants at 1 MHz. This difference is due to the decrease of the dielectric constant of epoxy matrix. Dielectric relaxation of BT powder is not observed within measured frequency. Alternative material for embedded capacitor fabrication is epoxy/BaTiO₃ composite embedded capacitor paste (ECP). It uses similar materials formulation like ECF and a screen printing method for film coating. The screen printing method has the advantage of forming capacitor partially in desired part. But the screen printing makes surface irregularity during mask peel-off. Surface flatness is significantly improved by adding some additives and by applying pressure during curing. As a result, dielectric layer with improved thickness uniformity is successfully demonstrated. Using epoxy/BaTiO₃ composite ECP, dielectric constant of 63 and specific capacitance of 5.InF/c² were achieved.