1. Field of the Invention
The present invention relates to a method of manufacturing an electronic circuit assembly from two or more flexible films. More specifically, the present invention relates to a method of simultaneously connecting two or more flexible films and integrally molding a rigid backing on the flexible films by injection molding and the article produced by this method.
2. Description of the Related Arts
It is known to manufacturing circuit assemblies from flexible films having flexible electronic circuits printed or traced thereon. An example of commercially available films produced by this construction is illustrated in U.S. Pat. No. 5,461,202. Flexible films enable the production of electronic circuit boards into highly contoured, three-dimensional shapes. They also allow the electrical circuits to be manufactured separately from the backing structure. This enables the use of different materials for the backing structure and film. One way that flexible films are used is through a process called film capture or in-molding. In-molding refers to the process where a flexible film of either metal, polymer or a combination of both is inserted into a mold and subsequently molded into a circuit assembly. The film becomes adhered to the backing structure by either mechanical interlocking, adhesives or an interdiffusion of the resin and polymer film. These films typically contain electrical wiring features or circuits to create a functional electronic module when fully assembled with electronic components.
One example of an electronic circuit made from an in-molding process is illustrated in U.S. Pat. No. 5,118,458 ('458). This reference teaches a method of producing a multi-layer circuit assembly by sequentially building up layers of flexible films. A first flexible film has a circuit traced thereon and a hot-melt adhesive is placed on the reverse side. The film is then placed within a molding tool and a resin is injected against the facing side of the film. The mold is heated to cure the circuit traces. Additional film layers are sequentially added. Through-holes are formed through the layers of film and the through-holes filled with a conductive paste. Electronic circuits are then attached to the layers of flexible film. The '458 reference requires a number of steps and complicated tooling to form the multi-layer circuit assembly. Each layer is separately built-up. Additionally, the layers are only interconnected at one point when the through-holes are made in the built-up film. This reduces the flexibility of interconnecting the separate film layers at multiple locations and the possibility of connecting only two film layers of a multi-layer stack.
It is also known to manufacture electronic circuit assemblies by forming a backing only along a portion of a flexible film as shown in U.S. Pat. No. 5,220,488 ('488). The '488 patent teaches placing an elongated film into a mold tool where only a portion of film receives an injection molding backing. The '488 device does not teach the use of multi-layer films to create a complex circuit design. While the films and backing produced by the '488 device can be folded into compact shapes, three-dimensional backings are not taught.