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|Miniaturized Hermetic Modules for Medical Implants|
|Keywords: Implanted Modules, Hermetic, Miniaturization|
|1. Introduction Liquid Crystal Polymer (LCP), a thermoplastic dielectric film material with very low water absorption (< 0.04%), high chemical stability and low thermal expansion is best suited both as a substrate material and as the encapsulate for small miniaturized electronic modules. LCP stands out among other polymer materials used for microelectronics. The permeability for water and gases is the lowest among all polymeric materials. With proper design considerations LCP packages can achieve a sufficient hermeticity for exposures in harsh environments. 2. Methods Processing techniques for LCP substrates are the same as for other flexible substrate materials. Resolution of lines, spacing and vias are comparable. In combination with other metals (e.g. Au, Cr, Ti, Pd, Constantan, etc.) thin film resistors, thermocouples, thermistors, heaters can be integrated. If needed the integration of thinned semiconductor components into the flex substrate is also an option. LCP substrates can be connected and sealed without the need for any adhesives by benefiting from its thermoplastic properties. For this purpose localized heat is used to melt a part of the structure locally and produce strong bonding between the involved surfaces. Using this method separated LCP substrates can be sealed and connected in a single process step without the need of any connectors. In another variation this process can be used to seal a completed assembly with an LCP Lid in a single process step. LCP is a homogenous material and can be easily machined with UV lasers with a precision down to the micrometer scale. Cavities, openings for recessed components can be integrated. It is conceivable to even embed a glass window into the lid covering the assembled substrate. Finally the structures can be thermoformed by applying heat and mechanical support into any desired shape. 3. Results Long term soak tests in phosphate buffered saline solution (PBS) at elevated temperatures prove the usability of LCP to encapsulate electronic assemblies in harsh environments. In LCP encapsulated structures passed PBS soak testing at 77°C exposed for > 12 months without failure. Silicon test dies embedded in LCP passed tests exposed in concentrated sulfuric acid and saline solution at 50°C for > 9 months without failures. 4. Discussion & Conclusion Encapsulation in LCP can provide hermetic sealed and chemically inert miniaturized electronic modules for sensors applications in medical, industrial and automotive markets. 5. References  J.-H. Lee, E. M. Tentzeris, Three-Dimensional Integration and Modeling, A Revolution in RF and Wireless Packaging, Morgan & Claypool, 2008  A.-V. Pham, M.J. Chen, K. Aihara, LCP for Microwave Packages and Modules, Cambridge University Press, 2012|
|Eckardt Bihler, Program Manager