TWS (True Wireless Stereo) earphone becomes a spot-light and fast-growing wearable device after Apple successfully launched in 2017 the Airpod, which is one of Apple’s best selling accessories in the market. Unlike conventional over-ear headphones, a high-end TWS earphone requires ear-canal bearing X-Y-Z dimension with good wireless connectivity, bigger speaker and acoustic chamber for better audio quality, larger battery capacity for longer use case and plenty of sensors to enable power saving and biosensing function. In addition, the integration of AI functions would include additional processing and memory. All of the above requirements and functionality challenge designers how to integrate and miniaturize all hardware, while staying with as small volume and as conforming to ear shape of housing as possible. ASE proposes and demonstrates a solution to these issues. It consists of a 7.5mmX7.5mmX2.5mm SOM with Flex to help customers to meet TWS earphone design challenges as well as cost reduction. SOM is a system-level over-molded System-in-Package module with sensors and board-to-board connectors exposed (unmolded) on top. All the core functions that are common to TWS are implemented in the SOM. The multiple MEMS sensors, or any other customized components, associated with mechanical housing and ID design can be assembled on Flex. Hence multiple TWS earphone designs can re-use the same SOM. By adapting advanced SiP technologies developed by the semiconductor assembly industry, the dimension of SOM is shown to be reduced to 1/3 of traditional PCBA’s. It makes room for enlarger acoustic chamber 2-3 times more and keeps assemble flexible for stack up with battery and speaker driver for better performance and longer operation time. In addition, this solution provides the benefit of lower material cost compared to rigid-flex PCBA, and higher assembly yield.