A systematic corrosion failure analysis of Li-ion powered hearing aids from various markets

Hearing aids (HA) are low-power electronic devices used worldwide. The ongoing trend in the HA industry has been to move towards Li-ion battery technology replacing conventional zinc-air batteries. The corrosion reliability of HA devices is a critical issue, due to their exposure to harsh user environments including body fluid contact, high humidity, and temperature. The combined effect of higher operating voltage (4.3 V) and design miniaturisation poses new risks for corrosion reliability. To fully understand the environmental reliability issues of the Li-ion powered HA, it is crucial to investigate field performance by conducting root cause failure analysis on the field-returned failed devices. This study investigated two different HA models (open vs. glued model). The analysis used a systematic FMEA-based approach to identify and understand failure modes, mechanisms, and potential causes using various analysis techniques (e.g., LOM, SEM&EDS, and ICP-OES). Furthermore, statistical analysis was conducted based on the repair data created by the global service centre to reveal the failure percentage, and time to failure of different components. Passive components, solder connections, and galvanic charging contact showed the highest failure percentages. The most common causes of corrosion failures were high levels of chloride ions, high humidity, flux residues, and insufficient coating protection.