Electronic apparatus includes a laminated multi-layer circuit substrate, including first and second rigid cards and a flexible section between the first and second rigid cards. First and second sets of electrical terminals are disposed respectively on the first and second rigid cards and arranged to mate with respective bus connectors configured in accordance with a predefined bus standard. At least one bus interface circuit is configured to communicate over a bus in accordance with the predefined bus standard and disposed on the first rigid card. Printed conductors run continuously from the first rigid card, over the flexible section of the substrate, to the second rigid card and connect the at least one bus interface circuit on the first rigid card to the second set of electrical terminals on the second rigid card.