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.