Static Electic Arcing On Pcb, PCB static electric arcing problems

[jmartens1978]

I have a project that I am working on and would like some input from anyone that has some knowledge on High Voltage Arcing on PCBs.

Problem: I have a PCB that is enclosed in a plastic enclosure that has metal pins and switch that extend to the outside of the enclosure. Static electrical shock is hitting those pins and switches and the high voltage from that shock appears to be traveling through the circuit and taking out ICs. When I transferred the shock into the pins I noticed that there was arcing from trace to trace and trace to pads trough out the PCB coming from the trace connected to the external switch and pins. The system is a 9v system and the static generator that I used to test the PCB was a Van de Graff generator 10-060. The PCB is extremely compact.

My solution: My solution whether it will work or not is to place ground rings around the external pins on the PCB and the external mechanical switch on the PCB. I am hoping to force the high voltage from the static shock to arc to ground (taking the high voltage straight back to the battery) as soon as it enters the PCB and not travel down the trace to other parts of the circuit. As a back up just in case the static shock does not have a high enough voltage to arc I have MOVs in line with the traces connected to the external parts to hopefully lessen the effects of the higher voltage spike.

I primarily want to force an arc to ground at the point where the high voltage spike enters the PCB. I have little knowledge of high voltage in PCBs.

Questions: Do you think this will work? If not I am open to suggestions. What is the best way to construct the ground ring to guarantee the static shock will arc to the GND ring every time?

Thank you,
Jed

[kellys_eye]

You can't 'make' static jump to a particular place reliably - what you CAN do is restrict the damage it causes. A spark gap (as found in telephone equipment - basically a miniature neon bulb) with back-to-back zeners rated at 15V across he input pin to ground will fix most problems.

[MacFromOK]

Or perhaps a MOV?

[Ice-Tea]

- You are talking about ESD damage here.
- Your Van Der Graaf geny does 200kV? Well above what you will ever encounter from ESD.
- Whatever you want to do, there's little point unless you have a place where the energy goes to... GND needs to be actual ground, not just the common return for your voltage rails...

[jmartens1978]

I am actually taking a 15-20kV shock from the Van de Graaf genertator. The only place to send the energy is into the battery GROUND. I don't have any other choice.

[jmartens1978]

I do have MOVs in line with ICs to help protect. But what I found was there was arcing that bypassed the MOVs.

[MacFromOK]

I'd do as Dave (kellys_eye) suggested then, try a neon. You can parallel more than one MOV or neon if necessary (MOVs are probably a bit slower though). If the problem persists, your PCB traces and components may need to be farther apart.

However... if you're just trying to protect against normal ESD, the Van de Graff generator is probably severe overkill. Electricity arcs across air at a rate of approx 1mm per kV, but ESD is of very short duration and can be shunted much easier than sustained high voltage.

[Geek]

MOV, zener, even a 1M static bleed resistor are common.

But if you have to have this hooked to something really HV, your best bet is isolation.

Cheers!