Low tolerance epoxy/BaTiO3 composite embedded capacitor films (ECFs)

Embedded capacitor technology is one of effective packaging technologies for further miniaturization and higher performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor material, because they have good process compatibility with multilayer organic substrates applications such as printed circuit boards (PCBs). In this work, less than 7% tolerance embedded epoxy/BaTiO₃ composite capacitors made of newly developed embedded capacitor films (ECFs) composed of low temperature rapid curing epoxy resin, latent curing agent, and barium titanate powder were successfully fabricated on PCBs and Si wafers. Then capacitor properties were characterized. Compared to epoxy/BaTiO₃ composite capacitor solutions (or pastes) deposited by a spin coating method, ECFs have excellent advantages such as lower capacitance tolerance over large area, no waste of materials, good film formation capability and processability, long shelf life, and good thermo-mechanical stability after final epoxy cure. Over 100 dielectric constant numbers were obtained using two different size BaTiO₃ powders mixtures. Another important capacitor property of the capacitor films, leakage current, was also less than 10^-7 A/cm² which is excellent enough for decoupling capacitor applications. Epoxy resin formulation, curing agent, dispersant, and several additives were optimized to produce good film formation capability, fast curing characteristics at 180°C of less than 20 seconds, good BaTiO₃ powder dispersion control, and excellent shelf life for handling. Typically, capacitors of ±7 μm film thickness with 10 nF/cm² with less than 7% tolerances and low leakage current (less than 10^-7 A/cm² at 10 V) were successfully demonstrated on PCBs and Si wafers using newly developed epoxy/BaTiO₃ composite capacitor films. These capacitor films can be embedded on selective areas of PCBs during build-up processes or other substrates such as Si and ceramic substrates.