Digital Shadow Moiré Measurement of Out-of-Plane Hygrothermal Displacement of TFT-LCD Backlight Modules

Abstract

As the light source device of the thin film transistor-liquid crystal display (TFT-LCD), backlight modules (BLM) suffers not only the heat produced by itself own but also the possible high temperature and/or high humidity of the operating environment. In this paper, based on the specially designated hygrothermal reliability test conditions, the digital shadow moire method was applied to inspect out-of-plane displacement fields of BLMs installed in 4.3” TFT-LCDs which are commonly employed in smart phones and navigators. Three hygrothermal reliability test conditions were selected in this paper, i.e. (1) high temperature storage; (2) high temperature operation; (3) high temperature and high humidity. In addition, test specimens of three different tolerances in the normal direction inside the BLMs were prepared to investigate the tolerance effects on the out-of-plane displacement. The current inspection procedures adopted in the TFT-LCD industry is to remove BLM periodically from the oven to measure the variation of the illumination of the BLM after experiencing the hygrothermal effects. With the whole-field and real-time inspection features, the digital shadow moire inspection system developed in this paper can be employed to replace the current inspection procedures adopted by the TFT-LCD manufacturers. The experimental results showed that the out-of-plane displacement of the BLM under the high temperature and high humidity condition is the largest one among three conditions.