A major problem associated with many electronic circuits is shielding them from unwanted radiation, such as radio frequency interference (RFI) or electromagnetic interference (EMI). This need to shield high-frequency circuits, especially in electronic equipment such as two-way radios, is critical. Conventional shielding systems are generally characterized by a conductive metallic enclosure constructed to completely surround the device or circuit to be shielded. This enclosure acts either to protect the electrical equipment from external RFI or EMI signals or to prevent the escape of RFI or EMI signals generated by the device. Typically, these shielded enclosures are made from a conductive material that is electrically coupled to ground. In prior art, the shielded enclosures have been made by attaching a drawn metallic casing over the affected device(s) and soldering it to a substrate.
Unfortunately, this method of shielding makes it difficult or impossible to tune or adjust the circuit that is shielded on the interior of the metal enclosure. Circuits containing components that need to be adjusted after assembly, for example, a voltage controlled oscillator (VCO) in a two way radio, cannot be adjusted unless the shield is removed. Removing the shield then affects the circuit and changes the output, thereby rendering any adjustment questionable. Other components, such as laser trimmed resistors, cannot be adjusted without making some type of permanent opening in the shield, again degrading the shielding effectiveness. Most conventional systems try to cover the opening with a separate piece of adhesive-backed metal tape or to solder another piece of metal to the enclosure. Neither of these methods is preferred because they require additional pieces. In the case of the metal tape, the long term integrity of the closure is questionable, and in the case of the soldered patch, another soldering operation is required, exposing the circuitry to additional heat. As a result, a need exists for a method to provide RFI shielding that is economical, reliable, and does not generate excessive temperatures.