Implantable electronic packages for neural implants utilize reliable electrical feedthroughs that connect the inside of a sealed capsule to the components that are exposed to the surrounding body tissue. With the ongoing miniaturization of implants requiring ever higher integration densities of such feedthroughs new technologies have to be investigated. The presented work investigates the sealing of vertical feedthroughs in aluminum-oxide-substrates with gold stud-bumps. The technology enables integration densities of up to 1600/cm² while delivering suitable water leak rates for realistic implantation durations of miniaturized packages (feedthrough-count > 50, package-volume <; 2 cm³) of more than 50 years. All manufacturing steps require temperatures below 420 °C and are suitable for maskless rapid prototyping.