Method of laminating a flexible circuit to a substrate

A method of attaching a flexible plastic film having electronic circuit traces to a rigid plastic substrate. The film and substrate are made from different incompatible plastic materials that do not bond to one another and have different CTE. The use of different or incompatible materials is useful where the properties of the backing structure and film are selected to achieve different results. For example, the flexible film may be selected from a material that provides a high melting point to withstand soldering while the backing material is selected from a low-cost and light weight plastic material that has a lower melting point. The film has conductive traces on at least one surface thereof and a backing surface. A heat activated adhesive is applied to the backing surface. The film is placed within an open injection mold and the mold is closed. A hot plastic resin is injected into the mold adjacent the adhesive. The resin heats the adhesive above its activation temperature and causes the adhesive to bond to both the backing surface and the plastic resin. The resin is allowed to cool and the finished circuit assembly is removed from the mold.