Local shielding is required for strong radiation circuits or highly sensitive circuits on the circuit board. The partial shielding method on the circuit board is: use the copper foil on the surface of the circuit as one surface of the shielding box, install a pentahedral metal box on this surface, and the pentahedral metal box is very dense (below 1 cm) The spacer is connected with the copper foil as the other side to form a complete hexahedral metal box. A key factor for the success of partial shielding of circuit boards is whether the selection of the shielding interface is reasonable. Because all wires passing through the shield require filtering, there are two main principles for selecting the shield interface:
- The minimum number of wires passing through the shield interface.
- All wires passing through the shielding interface can be effectively filtered.
The wire filter on the circuit board can adopt a chip capacitor, which is installed on the interface where the wire passes through the shield. If the filter capacitor is installed on the inside to prevent interference from the shielding box, if the filter capacitor is installed to prevent external interference from entering the box, filter The capacitors are mounted on the outside of the box. Three-terminal chip capacitors are the most suitable devices for this application. The principle of three-terminal chip capacitors is similar to that of feedthrough capacitors. However, since it is not a 360-degree connection to the ground, the high frequency effect is not as good as the feedthrough capacitor.