Parylene C and silicone as biocompatible protection encapsulants for PCBs

During the last years a lot of active implantable medical devices like neural prostheses 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, if the 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 of flexible 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 (MED6-6606). 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.