PCB static electric arcing problem

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I have a project that I am working on and would like some in... - Nov 08, 2012 by Jed

So, what is the battery going to do when you push your 'high... - Nov 08, 2012 by davef

Some people put spark gaps on the PCB it a trace that comes ... - Nov 10, 2012 by KaHrpr

My first attempt was similiar to that. It was a straight gro... - Nov 12, 2012 by Jed

Jed

#67611

PCB static electric arcing problem | 8 November, 2012

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

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davef

#67614

PCB static electric arcing problem | 8 November, 2012

So, what is the battery going to do when you push your 'high voltage' through the 1-2 ohm internal resistance of the 9V battery?

How about you doing a Google search on ... esd protection circuit?

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KaHrpr

#67622

PCB static electric arcing problem | 10 November, 2012

Some people put spark gaps on the PCB it a trace that comes to a point that's exposed from the circuit you are trying to protect to a trace that comes to a point from the ground trace. The 2 points are about .005 inches apart. When the charge hits the trace it jumps the gap to ground. I have never seen it on a battery powered circuit.

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Jed

#67630

PCB static electric arcing problem | 12 November, 2012

My first attempt was similiar to that. It was a straight ground trace running past the circular pads that were recieving the shocks. It was hit and miss when the arcs would occur. When I cut notches in the trace so the ground line had a point next to the pads, the arc occured every time. I was using .013" distance. The problem I am going to have is that the Pads that the static shock enters the unit at are solderable pads. If I make the ground trace that close without soldermask there is the chance to bridge solder in a production assembly enviornment.

Question: Do you think it would be better if I changed the round pads to square pads and rotated them 45 degreers so the point of the pad is close to the point on the ground trace? I am sending a picture so you can see what I am talking about. I have two different ideas (model 1 and model 2). Which one do you think would work best.

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