I've got water pump device that needs to pass ESD testing (IEC 61000-4-2, 8kV contact, 15kV air discharge).
On this device (as circled in red), there are these four metal inlets.
At 2kV with an ESD gun this device is hard resetting, on any contact with the metal inlets. So I'm assuming the ESD is triggering the reset pin (or some other condition) on the microcontroller.
This is a friend's device, and built by a hobbyist of sorts. He used a single layer board with no signal GND plane of sorts, and we are going to redesign the board to 4 layers with TVS, ferrites, and series resistors as needed to protect the microcontroller lines. There'll be as large a possible signal GND plane on this board for the TVS to shunt the ESD transients.
So in the ideal, that will fix our ESD issues.
BUT, what about ground straps from each metal inlet to provide a low impedance path for the ESD transient before it even approachs the board?
The enclosure is all plastic, and there is no chassis GND.
On the four metal inlets, where could you ground those if you just have the one PCB in the system?
I'm thinking we would have an isolated area on the PCB that runs straight to signal GND with these four straps from the metal inlets?
How are folks making these types of connections to chassis ground (if we had a chassis ground)?
I'm thinking of soldering a wire to the metal inlet -- is there something off-the-shelf that works better that's commonly used for these types of connections?
Should all four straps run to one central location in the far corner of the PCB that feeds to the signal GND?
I was brainstorming a wire with a ferrite in series that would dissipate the ESD as it comes in from the metal inlets and goes to our PCB signal GND?