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Package is a critical part in biomedical implantable systems. Many factors affecting the host body and the life time of implantable systems need to be considered. Package becomes more critical for microfabricated systems with wireless charging and communication. This paper presents the first phase study on micro package techniques for short term (30 to 90 days) implantable systems. A MEMS implantable telemetry model system was designed for packaging evaluation. The transmitter was custom designed and fabricated using MOSIS processes and an external receiver was designed and built for data collection. For short term implantable systems, medical grade silicone outer coating is used for "tissue compatibility"; while multilayer polymeric and nanometer-thin metal or ceramic films were used for inner coatings to provide mechanical strength and to block vapor and moisture penetration. The total coating thickness is less than 0.6 mm. The electrical performances (leakage resistance) of test board and model devices coated with various package materials and processes are evaluated in 40 degrees C saline. This paper presents: the model system; the evaluation methods and analysis of failure modes of polymeric coating on test boards; the solution to the failures and suggested coating techniques of polymeric materials; and the evaluation of model systems packaged with multi-layer coatings in 40 degrees C saline. The expected performance of developed packaging method was verified by experiments. Implantable wireless MEMS system can be packaged with thin multilayer materials to have an expected life time greater than 30 days.
Bu et al. (Tue,) studied this question.