Root Cause Analysis of Intermittent Digital System Reset and Its Reliability Evaluation

With the advancement of technology, modern electronic devices have mostly transitioned to using touchscreens instead of physical buttons for their operation, aiming for a more aesthetic and intuitive user experience. However, certain special buttons have been retained despite technological evolution, such as the power button and the reset button. The main reason for preserving the reset button is its crucial importance in certain situations, particularly when a device encounters a malfunction or system anomaly. In some cases, a device may become stuck in a state where it cannot enter the system, rendering the operation through a touchscreen unavailable. In such scenario, only the use of a physical "reset button" can restore the device back to normal. This work shares a case study from an operator of China railway transportation industry. The customer utilized Moxa's products at their stations to transmit train operation data from the station to the Communication Based Train Control (CBTC). After two years of operation, the customer reported a failed case that the device reset to its factory default settings by itself, resulting in the loss of previously saved system configurations. This work aims to identify the root cause of the reported failure, through the identification of the failure mechanism which is found to be related to silver electrochemical migration. After knowing the failure mechanism, the design of the experiment (DOE) method was also applied to determine the most feasible solution to this failure. Additionally, to assess the risk of the devices installed at the customer's field site, the warranty data analysis was conducted to develop a failure model so as to evaluate its reliability in the field.