A sensor module for a wearable vital sign monitoring device is disclosed. The sensor module includes a substrate having a first side and a second side opposite the first side. The sensor module also includes a sensor die mounted to the first side of the substrate. The sensor die is configured to monitor a vital sign of a user. The sensor module further includes a waterproof coating that conformally covers the sensor die, at least a portion of the first side of the substrate, and at least a portion of the second side of the substrate.