A hearing aid circuit includes a plurality of sub-circuits implemented as a plurality of flexible circuit boards. In various embodiments, the plurality of flexible circuit boards includes a motherboard that can be used with multiple hearing aid models and different peripheral boards that can provide different hearing aid models with their unique styles and/or functional features. In various embodiments, the hearing aid circuit is assembled in an automated process that connects the motherboard to one or more peripheral circuit boards using surface mount technology (SMT).