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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.

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The standards DIN EN ISO 10992 Part1:12-2003 and Part 5:11-1999 demand different tests for cytotoxicity including in vitro methods for evaluation materials in application of medical devices. Special features are materials for packaging processes in the field of medical micro devices. In this context the working group selected fundamental systems of materials and contact layers for testing in contact with the standard cell 3T3 clone A 31 and NCTC clone L929. One of the advanced methods includes a spectroscopic measurement of the metabolism. The results permit a gentle differentiation of materials cytotoxicity. Examples are shown in this paper. IntroductionExtracorporeal or implantable medical devices driven by electricity do not only set the choice of the energy source in accordance with the European medical device directive 93/42/EWG and the standard IEC 601-1 certified safety class systems I or II, the enterprise of these devices in the application types B, BF or CF and at least the classification of the product into one of the risk classes I to III and ahead, but require a careful choice of materials and characterization of the packaging for assembly and finished products. The packaging has the task to convert the functional and technological requirements of system integration starting from the level of the board upward up to the housing medical device -if necessary wholesale packing, medical packaging -for the micro system. A condition for the application of packaging materials, which are used in these medical devices, is the test of the biological compatibility using the standards DIN EN ISO

During the last years a lot ofactive implantable medical devices like neural prostheses [1] and sensors have been produced. For such systems a long term reliability under the influence of aggressive physiological conditions is very important. To protect them a stiff housing is normally utilised. In some cases, ifthe requirements for a low weight, flexibility and perhaps a need to transmit optical signals have to be fullfiled, they aren't the best choice. Another possibility is the use offlexible protection materials like polymers, which have the advantageous properties. Finally their structure isn't completely impermeable for different components contained in physiological fluids. Some promising polymers are Poly-Para-Xylylen (Parylene C) and silicone rubber . This paper shows the results of our tests to their ability to function as encapsulants for the PCB configurations FR4+Cu+Ni+Au, FR4+Cu+chem. Sn and FR4+Cu+HAL Sn.