A low-profile Universal-Serial-Bus (USB) assembly includes a modular USB core component that is retractably mounted into an external housing. The modular USB core component includes a PCBA in which all passive components and unpackaged IC chips are attached to a single side of a PCB opposite to the metal contacts. The IC chips (e.g., USB controller, flash memory) are attached to the PCB by wire bonding or other chip-on-board (COB) technique. The passive components are attached by conventional surface mount technology (SMT) techniques. The housing includes a retractable mechanism that facilitates selective exposure of metal contacts, either by sliding a front portion of the modular USB core component into and out of a front opening of the housing, or by providing a cover plate that slidably covers the front portion of the modular USB core component.