Hygroscopic and thermal micro deformations of plastic substrates for flexible electronics using digital image correlation

Thin polymer substrates are promising materials for flexible electronics with many advantages. However, the dimensional stability of polymer substrates is low. Nowadays, this is overcome by laminating polymer substrates onto a rigid carrier. Nevertheless, carrier-less processing will be a foreseen next step for future manufacturing of plastic electronic devices, which will intensify the interest in dimensional stability of the plastic substrates. This paper describes a measurement method to characterise the in-plane hygroscopic and thermal properties of thin polymeric substrates using a Digital Image Correlation (DIC) based method. The precision and accuracy of the method is addressed, and the method was validated using copper, aluminium and silicon test samples. The hygroscopic and thermal properties of semi-crystalline Polyethylene Naphthalate (PEN) and amorphous Polyether Sulphone (PES) substrates, both attractive for flexible electronics, were characterized. The coefficients of thermal and moisture expansion were measured. Furthermore, the anisotropy in thermal and hygroscopic expansion was quantified using the full in-plane deformation measurement data.