a method attaches a liquid - repellent filter to an air vent of a resin molded article accommodating a component / electronic part . a thermal processing tip and a thermally welding tip and a molded article are provided . the thermal processing tip forms a filter attachment surface at the inlet or outlet of an air vent in a thermoplastic resin molded article . a filter fixing rib is formed around the attachment surface . the porous filter is dropped onto the filter attachment surface , and a thermal welding tip is used to melt the filter fixing rib such that the melted resin flows onto and covers a circumferential edge portion of the filter , penetrating the body of the filter . the melted resin penetrating the filter 18 and covering the circumferential edge portion of the filter are cooled to solid , whereby the filter is fixed to the filter attachment surface .