Applying Residual Control Charts to Identify the False Alarms in a TFT-LCD Manufacturing Process

Statistical Process Control (SPC) is widely applied to monitor and improve highly integrated and automated manufacturing processes. Adopting proper SPC charts and corresponding detection mechanisms is crucial for a TFT-LCD manufacturing process. This study conducts an empirical study of highly complex TFT-LCD manufacturing processes to identify the most suitable SPC method. The TFT-LCD manufacturing process is generally divided into three main procedures, namely Array Engineering to create the TFT array, Cell Engineering to join the TFT array, liquid crystal and color filter together, and Module Engineering to integrate PCB and semiconductor chips into final products. The crucial step in Cell Engineering is injecting the liquid crystal into the layer between the TFT array and color filter substrates and the thickness of the layer is the main control target. Applying traditional Shewhart and EWMA control charts to real TFT-LCD manufacturing data reveals a significant false alarm rate, and these false alarms can adversely impact manufacturing efficiency. Based on time series analysis, this study proposes a residual control chart using an AR(1) model to avoid false alarms that could obstruct TFT-LCD manufacturing flow. The results of the proposed approach provide a useful guideline for improving the TFT-LCD manufacturing.