Design and Optimization of a Permeation Testing System for Polymer Films

Introduction of the next generation of active implantable medical devices (AIMDs) is dependent on the demonstrated safety and reliability of proposed packaging materials. Because conformal polymeric coatings will form the primary interface between electronic components and the biological environment inside the body, permeation testing will play a vital role in demonstrating the polymers’ long-term barrier effectiveness.

An analytical system has been developed and optimized to accurately and precisely measure water transport through polymeric conformal coatings proposed for use with AIMDs. The system features an on-line detector capable of measuring water vapor in the sweep gas at parts-per-billion levels up through saturated humidities, as well as a distinct gravimetric technique to facilitate comparison to existing standards and to provide additional assurance of accuracy. The system has been developed to ensure that the first traces of water to appear at the surface of the test film are detected with high statistical confidence and subsequently continuously measured to allow for the construction of time-dependent permeation profiles.

Computational modeling of sweep gas flow within the test cell has enabled optimization prior to fixture fabrication and experimental evaluation.  Reducing the thickness of the boundary layer adjacent to the surface of the test material decreases diffusional resistance and brings the permeate-side boundary condition closer to zero concentration, thereby enhancing the accuracy and utility of the partial differential equations commonly used to model permeation. This approach to improving test-cell collection efficiency is broadly applicable to permeation research and facilitates advances in both theoretical modeling and transport measurement.