Principles of ESD protection design for equipment
For equipment-level ESD protection design, the focus should be on setting up a smooth discharge channel for electrostatic discharge. The following points should be done mainly.
(1) Good overlap should be achieved between chassis metals. Surface contact should be used at the overlap to avoid point contact. The DC resistance of the overlap should not exceed 5mΩ, and the DC resistance between any two conductive points in the overall overlap structure should not exceed 25mΩ. The chemical potential difference between the overlapping metals should not exceed 0.5V. If it exceeds, a transition metal (or plating) can be selected to reduce the contact corrosion of the original two metals.
(2) Metal parts such as keyboards, control panels, manual controllers, key locks, etc. that are in contact should be directly grounded through the rack. If grounding is not possible, the insulation distance between them and the circuit wiring should at least meet the following requirements: air gap 5mm, creepage distance 6mm.
(3) Connect at the rack grounding point or connect on the external grounding network to form a good electrostatic discharge path.
(4) Small and low-speed (frequency less than 10MHz) equipment can use floating ground at the working place (or single-point connection of the working place to the metal shell) and single-point grounding of the metal shell, so that static electricity can be discharged to the ground through the shell without affecting the internal circuit.
(5) The working place of small and high-speed (frequency greater than 10MHz) equipment should be grounded at multiple points with its metal shell, and the metal shell should be grounded at a single point.
(6) Reliable electrical connection must be ensured between the grounding point of the rack equipment and the external grounding pile, and the outer circumference of the connecting copper wire section should not be less than 20mm.
(7) The electrical discontinuity of the structure must be minimized to control the radiation entering and exiting through the bottom plate and the shell. Structural measures to improve the shielding effectiveness of gaps include increasing the gap depth, reducing the gap length, adding conductive pads to the joint surface, applying conductive paint on the joint, shortening the screw spacing, etc.