An electrically continuous, grounded conformal EMI protective shield and
methods for applying same directly to the surfaces of a printed circuit
board. The EMI shield adheres and conforms to the surface of the
components and printed wiring board. The shield takes the shape of the
covered surfaces while adding little to the dimensions of the surfaces.
The EMI shield includes low viscosity, high adherence conductive and
dielectric coatings each of which can be applied in one or more layers
using conventional spray techniques. The conductive coating prevents
substantially all electromagnetic emissions generated by the shielded
components from emanating beyond the conformal coating. The dielectric
coating is initially applied to selected locations of the printed circuit
board so as to be interposed between the conductive coating and the
printed circuit board, preventing the conductive coating from electrically
contacting selected components and printed wiring board regions. A high
viscosity, non-electrically-conductive filler material is applied to
printed circuit board regions that have surfaces that are cavitatious
and/or which have a highly variable slope. The filler material can be used
in conjunction with conformal EMI shield board level coating. The high
viscosity, electrically non-conductive filler material substantially
covers each cavity such that the covered cavity is inaccessible and that
the covered region of the printed circuit board has a contiguous,
contoured surface. A pre-manufactured non-electrically-conductive
component cover can be mounted over a corresponding component and secured
to the printed wiring board. The component cover and printed wiring board
surround the component, forming a sealed enclosure. The component cover
has a thin cross-section and an interior surface that follows closely the
surface of the component. This minimizes the volume enclosed by the
component cover. In addition, the exterior surface of the component cover
has a low profile, and prevents the conformal EMI shield from physically
contacting the covered component. Instead, the exterior surface of the
component cover is coated with the EMI shield. This enables the covered
component to be removed from the printed circuit board for repair,
replacement or salvage without having to risk damage to the printed wiring
board or component that may occur with the removal of a conformal EMI
shield applied directly to the component.
