Epoxy/BaTiO3 (SrTiO3) Composite Films and Pastes For High Dielectric Constant and Low Tolerance Embedded Capacitors in Organic Substrates

Epoxy/BaTiO₃ composite embedded capacitor films (ECFs) were newly designed for high dielectric constant and low tolerance (less than plusmn5%) 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 properties of BaTiO₃ (BT) & SrTiO₃ (ST) composite ECF is measured MIM capacitors with oxygen plasma etched ECFs on 10times10 cm PCBs. For 1times1 mm capacitors with 12 um thickness and 50 vol.%BTO ECFs, dielectric constant of 39, dielectric loss of 0.017, capacitance density of 2.4 nF/cm2, and less than 10% tolerance were obtained. Dielectric constant of BTOECF is bigger than that of STECF, and it is due to difference of permittivity of BT and SrTiO₃ particles. Dielectric constant of BT & ST ECF in high frequency range (0.5~10 GHz) is measured using a cavity resonance method. In order to estimate dielectric constants at high frequency, the reflection coefficient is measured with a network analyzer. Dielectric constant is calculated by observing the frequencies of the resonant cavity modes. Although there was no dielectric relaxation observed at pure epoxy, for BT ECF, there is the dielectric relaxation at 5~9GHz. It is mainly due to changing of polarization mode of BT powder itself. In contrast, there is no relaxation for ST ECF up to 10 GHz. Alternative material for embedded capacitor fabrication is epoxy/BT composite embedded capacitor pastes (ECPs). It uses similar materials formulation like ECFs and a screen printing method for film coating. The screen printing method has the advantage of forming capacitor partially in desired area. But the screen printing makes surface irregularity during mask peel-off. Surface flatness is significantly improved by adding some additives and by applyi- ng pressure during curing. As a result, dielectric layer with improved thickness uniformity is successfully demonstrated. For 4times4 mm capacitors with 11 um thickness and 50 vol.% BT ECFs, dielectric constant of 39, dielectric loss of 0.023, capacitance density of2.6nF/cm2, and 22% tolerance were obtained