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20 The PCB Magazine • November 2014 traces and may contaminate the electrode pads. To guarantee biocompatible PCBs a final clean- ing is mandatory. The substrates have been suc- cessfully tested according to ISO 10993-5 for in vitro cytoxicity, a standard for evaluating bio- compatibility. The combination of conventional PCB pro- cesses and the use of noble metals allows for the manufacturing of directly implantable struc- tures (Figure 6). For short term implants (< 30 days) a hybrid of the already established cop- per technology for parts without direct body contact and noble metals for body contact parts may be used. For permanent implants (> 30 days) the substrates need to be completely biocompatible by implementing noble metals only. A detailed description of necessary tests for surface devices, external devices or implant- able devices can be found in the regulation ISO 10993-1:2009 + Cor 1:2010. Such devices have been successfully fabri- cated for short term implants like blood glu- cose sensors, balloon catheters and diagnostic catheters as well as for permanent implants like cochlear and neurostimulating applications (Figure 7). Achieving more complex artwork architec- tures and connectivity in the Z axes using pure noble metallization is under further investiga- tion, as are ongoing activities focusing on long term reliability, especially with daisy-chained patterned, interconnect stress test designs that accomplish the biocompatible noble metal components. PCB figure 7: examples of implantable PCb layouts and their corresponding application. daniel schulze is engineering manager at dYConeX aG. rené tölke is product engineer at dYConeX aG. ilse widmann is director of marketing at micro systems technologies. NOBLE METAL PCB MANuFACTuRING FOR DIRECT IMPLANTS continues