Ceramics are repeatedly investigated as packaging materials because of their gas tightness, e.g., as hermetic implantable housing. Recent advances also make it possible to print the established aluminum oxide in a Fused Filament Fabrication process, creating new possibilities for manufacturing personalized devices with complex shapes. This study was able to achieve integration of channels with a diameter of 500 µm (pre-sintered) with a nozzle size of 250 µm (layer thickness 100 µm) and even closed hemispheres were printed without support structures. During sintering, the weight-bearing feedstock shrinks by 16.7%, resulting in a relative material density of 96.6%. The well-known challenges of the technology such as surface roughness (Ra = 15–20 µm) and integrated cavities remain. However, it could be shown that the hollow structures in bulk do not represent a mechanical weak point and that the material can be gas-tight (<10⁻¹² mbar s⁻¹). For verification, a volume-free helium leak test device was developed and validated. Finally, platinum coatings with high adhesion examined the functionalization of the ceramic. All the prerequisites for hermetic housings with integrated metal structures are given, with a new level of complexity of ceramic shapes available.

Substrates and packages of active implantable medical devices are often fabricated from ceramics like alumina. Screen printed PtAu paste is the state of the art metallization for functional structures. Due to solid state and liquid diffusion of Au during thermal exposure, solder times are limited. Otherwise, metal structures tend to delaminate. Moreover, it was shown that PtAu with solder fails after 37.4 years. We established a thin film metallization on alumina process to overcome these disadvantages. We used sputtered platinum with an underlying adhesion layer made of tungsten-titanium to increase the adhesion strength to the alumina substrate. We avoided using gold in this work due to its high diffusion tendency. All used materials provided relatively low diffusion properties, which increases independency from joining techniques and mechanical longevity during use. Utilizing the Design of Experiment (DoE) methodology, we derived an optimal Pt thickness of 500 nm with 43 nm of WTi as an adhesion promoting layer. After accelerated aging at 150 °C, corresponding to 125 years at body temperature (37 °C), the contact pad adhesion strength was 32.75 MPa ± 7.08 MPa. This exceeded the safety limit of 17 MPa by far, set as recommendation for robust screen-printing metallization processes. Soldering times of up to 120 s did not influence the adhesive strength. The new process reduced the minimum track distance to 50% of screen printing values and is capable to be transferred into rapid prototyping techniques. It helps to make the assembly process independent of the manufacturing person, in order to increase the yield of device fabrication and -most important in implantable device manufacturing-to make it more robust and thereby safer for the patient.

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/cm ² while delivering suitable water leak rates for realistic implantation durations of miniaturized packages (feedthrough-count > 50, package-volume <; 2 cm ³ ) of more than 50 years. All manufacturing steps require temperatures below 420 °C and are suitable for maskless rapid prototyping.

Implantable medical electronics are almost exclusively packaged in titanium shells to ensure reliability and longevity. Additional silicone rubber encapsulation improves structural biocompatibility and limits the diffusion of ion from the body to package materials. These capsules must be hermetically sealed and provide electrical feedthroughs that are insulated against each other by connecting ceramic parts. In this study, a novel RoHS-compliant low-temperature soldering process is presented, allowing the required assembly. Tungsten/titanium as adhesion material and platinum as wetting layer were deposited by physical vapor deposition as thin films and were structured by a rapid prototyping laser process. Different devices were soldered with a tin-silver alloy below 300 °C resulting in low thermal stress. The platinum acts as an excellent solder pad. A 50-nm tungsten/titanium adhesion promoter efficiently strengthens the bond to the titanium substrate. The results show that the platinum layer must be thicker than 300 nm to guarantee high bonding strength. Analyses of cross sections of the joint show occurrence of diffusion of platinum and silver during the soldering process. At soldering times above 30 s, a large intermetallic layer forms at the soldering contact, which is prone to crack formation. Likewise, intermixing of tungsten and platinum were observed but without detrimental effects. Limitations in solder times are therefore advisable, for example, by introduction of automatic processes. Soaking tests were performed with sealed capsules in water at 60 °C for one year without measurable increase of humidity inside the package. In the used accelerated aging model, this would correspond to a hermetic sealing of about five years at 37 °C.

Lifetime estimation of implanted electronics in hermetic packages requires the prediction of the humidity induced lifetime. Classical approaches are limited in applications where miniaturized packages and a buffered humidity at low values are being utilized. An approach to overcome these limitations is described and investigations on suitable materials and measurement setups are presented. The findings support the usability of a Zeolite-silicone based desiccant system as a dielectric for a new type of online sensor. The future exploitation of this new sensing principle can allow the monitoring and prediction of humidity conditions inside of highly reliable miniaturized hermetic implantable packages.