Failure mechanism and reliability test method for USB interface circuitry on CPUs for mobile devices

This study investigated the failure mechanism of the Universal Serial Bus (USB) interface circuitry on CPUs for mobile devices. Specifically, CPUs of an MP3 player that had suffered only USB communication failure were taken as representative examples, and the failure mode was analyzed by system- and device-level fault isolation. Microscopic analysis revealed junction burnout in the USB interface circuitry to be the reason for failure. Root cause analysis was then conducted to identify the cause of junction burnout. Three kinds of electrical stresses, as identified by fault tree analysis, were applied to an undamaged chip and the type of resulting damage was assessed. It was found that a transient surge with a duration of current 20 μs reproduced the damage seen in the representative devices. Furthermore, we prove that such a transient surge event can occur when a device is connected via USB to a host personal computer; we also detected such a real transient surge waveform. Finally, we suggest a reliability test method for evaluating robustness to transient surges in the USB interface circuit of mobile devices.