a method of producing a fluidic module from two or more pieces of plastic material having an intermolecular bonded interface , comprises forming an interface surface on each piece , forming at least one fluidic passageway 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 their confinement to cause transmigration of molecules from one interface surface to the other to bond the pieces together .