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Biocompatible polymers utilized for flexible encapsulations of implantable microsystems provide many advantages compared to widely used rigid titanium or ceramic packages. However, polymers alter their properties due to interactions with their environment. As a result the protective function of these materials especially for long-term implants is not reliable. Therefore, we investigated barrier properties against water vapor of silicone and Parylene C membranes. And we combined these polymers to a multi-layer membrane to enhance the protective function of such an encapsulation system. Applying a bonding agent between two polymer layers increases the strength of the sample as well as the barrier properties significantly.

Biocompatible polymers used as encapsulation and packaging materials for implantable electronic devices have to comply with numerous requirements. Especially their barrier properties against water molecules and ions are of particular interest regarding the reliability of the encapsulation as well as functional integrity of the electronic components since water and ions on the circuit board may evoke corrosion, leakage current and finally the failure of the device. This paper describes a measurement setup to investigate the ionic permeability under in vitro conditions of polymeric membranes manufactured from various biocompatible polymers. Ionic permeability and water vapor transmission rate representing the barrier properties of these membranes were investigated. First results were obtained for polyimide, silicone, polyether ether ketone and polyamide, whereas polyimide evinced the best properties.

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