An interconnect board (ICB) assembly suitable for a battery module of horizontal stack structure including unidirectional battery cells stacked with cell leads facing each other includes an ICB frame in which cell leads of unidirectional battery cells are configured to be received such that the unidirectional battery cells having the cell leads at one end are configured to be placed facing each other with the cell leads facing each other, and busbars formed in the ICB frame and configured to be electrically connected to the cell leads, wherein the ICB frame is configured to be connected to another ICB frame with a hinge structure in a lengthwise direction of the ICB frame. A battery module including the ICB assembly and a method for fabricating the battery module are also provided.