What EMC problems can result from poor grounding of the metal spring contacts on the edge box?

Edge computing boxes commonly use metal spring contacts as the grounding connection between the PCB and the casing. If the spring contact grounding is poor (contact resistance >100mΩ) or has a loose connection, it will cause the following problems:

1. Increased ESD discharge path impedance: During discharge, a secondary arc is generated at the spring contact, coupling to the internal circuit and breaking down ESD devices.

2. Increased grounding impedance: This causes ground potential fluctuations, interfering with sensitive analog circuits.

3. The casing becomes a radiating antenna, enhancing common-mode radiation in the 30-100MHz frequency band.

Improvement measures include using low-resistance zinc-plated or stainless steel spring contacts with a contact positive pressure >50g, gold plating or applying conductive grease to the contact surface, opening windows on the PCB pads, and adding vias for main ground connections. Audiotech recommends conductive spring contacts paired with a common-mode magnetic ring CMZ7060A-701T with an impedance of 700Ω at 100MHz, which can suppress existing radiation. Actual measurements show that after rectification, the grounding impedance decreased from 300mΩ to 15mΩ. ESD testing showed no abnormalities, and radiated emissions decreased by 7dB.