Abstract: A method of producing a fluidic module from two or more pieces (B.sub.1 B.sub.2) of plastic material having an intermolecular bonded interface, comprises forming an interface surface (2) on each piece, forming at least one fluidic passageway (4) in at least one of the interface surfaces, assembling the pieces with the interface surfaces in contact with each other and confining them against expansion. Heat is applied to the assembled pieces to induce their expansion against total or limited confinement to cause transmigration of molecules from one interface surface to the other to bond the pieces together.