Characterization of epoxy/BaTiO3 composite embedded capacitors for high frequency behaviors

Embedded capacitor technology is an essential method for miniaturization and high performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor materials because they have good processability, compatibility with printed wiring boards (PWB), and high dielectric constant. In previous works, epoxy/BaTiO₃ composite embedded capacitor films (ECFs) were successfully fabricated and the properties of the capacitors using newly developed ECFs were characterized. The ECFs were mainly composed of epoxy based polymer resin and barium titanate powder. The ECFs were B-stage films and tacky before curing, and coated on a releasing film. ECFs can be easily detached from the releasing film, and transferred to the surface of interlayer within multi-layered organic substrates. In this study, using ECFs and test vehicles specially designed for correcting stray effect around the capacitors, the dielectric constant and dielectric loss can be measured by the reflection coefficient measured with a network analyzer. For fabricating of test vehicles, ECFs patterning process, investigated in previous work, was applied. ECFs were coated on a releasing film with 10~15 mum thickness. Then, ECFs were laminated and cured on Cu coated a 4 inch Si wafer, and Cu was sputtered on ECFs. The sputtered Cu foil was patterned, which was used as a mask for ECFs patterning and also used as top electrodes. For forming vias, plasma etching which is one of the useful methods for removing the cured epoxy based polymer resin was used. Using O₂ and CF₄ mixed gases, the epoxy based polymer resin of epoxy/BaTiO₃ composite ECFs was removed by RIE (reactive ion etching) treatment. After RIE treatment, the agglomeration of BaTiO₃ powders with residue of epoxy based polymer resin was removed by a ultrasonic cleaning treatment. The eliminated space by RIE & ultrasonic cleaning was e- lectro-plated with Cu. Finally, top Cu was patterned for top electrodes. Then, using these test vehicles, the high-frequency characteristics are consistent with low frequency characteristics measured with an LCR bridge. The relative error between the high-frequency and the low frequency is estimated to be within 10%. The method is a practical way to obtain the characteristics of ECFs accurately and quickly in a final form.