Buckling and Postbuckling Failure Analyses on a Rectangular Membrane for Touch Panel Applications

Thin conductive polymer membranes are the major sensing structure in resistive touch panels. However, device malfunctions such as early touching and false triggering have been reported during product development and reliability assessment. A surface profile examination has indicated that these membranes have considerable initial warpage, which could be a sign of membrane buckling, since the clamped design of the assembly may cause additional in-plane compression, in turn causing structural buckling. As a result, it is important to analyze the buckling and post-buckling behaviors of conductive polymer membranes due to initial imperfections, residual stress, or assembly issues in order to develop engineering solutions to ensure quality assurance. In this paper, both finite-element analyses and experimental characterizations are performed as the first step toward solving the observed problems. For the buckling analysis, we focus on the correlations between the calculated mode shapes and the observed surface warpage. Post-buckling analysis is also performed for exploring the performance of touch panels with initial warpage. In addition, several experimental investigations are conducted to validate the above mentioned mechanical analyses. The simulation results essentially agree with the observations. Both simulation and experimental investigations indicate that in-plane compression and shear can contribute to the observed failures. Engineering methods to increase buckling rigidity can be helpful for enhancing device reliability.