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REQ: Spark Gap Distance for ESD Protection

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Full Member level 5
May 18, 2001
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spark gap distance

Hi All,

Spark gap discharge is always the common method of prevent ESD (electrostatic Discharge)! I want to know is there any data or measurement that how the ESD discharge voltage related to Spark gap distance?


spark gap pcb

Spark gaps are more frequently used to guard against lightning strikes. They break down at too high a voltage for ESD protection by themselves. The breakdown voltage is also a strong function of the shape of the points and the gas near them. They are usually made in glass containers with a special gas in it.

The breakdown is in the area of many kV/mm.

pcb spark gap

Here annexed you can see a picture of this system applied to two differnt PCB. The scan has been made at 200 DPI, so you can have the distance.
Hope it helps.


P.S. In any case consider that both the PCB didn't survive to a lightning, so make your considerations about the utility of this system.
It helps with the brute force, but is not enough, this is my point of view.
esd spark gap

I myself have found little reference from a book. And share with the forum friend. But it has no equation or experiement for verification.
esd distance

I have used these on the antenna pads of cell phones. They really help in passing the ESD testing. Just make points in the ground that point to the corners of the square pad. Make the spacing as close as your process will allow.

spark gap esd

I have used spark gap features on telecomm boards, the recomended spacing was 6 thou. Also, the points should be shiny copper, no solder resist.

esd gap

btbass is right. our process allowed 5 thou so it looks like we are pretty close.

spark gaps pcb

Hi all,

Any figures related to kV/ separation?

Best Rgs


esd spark pcb

I just got into this spark gap things, I've got introduced to it becasue of a consultant we have. He says that 5 mils spacing it gives you protection up to 1500 V.

esd protection spark gap

Harris company which now makes the MOV has an application note that says spark gaps are 150 V/0.001 inch. Your gap will depend greatly on the sharpness of the points. The sharper the smaller the voltage the break down occurs at.

pcb spark gaps

Just be aware that the spark gaps are a bit slow to limit the voltage enough without some other secondary protection. When that is said, I have good experience with spark gaps on the PCB with 6 mils gap between points. They help, by taking away a great deal of energy from the ESD discharge.

PCB layout is VERY critical, not only the sharpness of points and low impedance grounding (to correct grond, which can take the discharge current!). Also how the gap is connected to the signal is important. The signal wire must essentially go via the gap, no stubs. Otherwise they do not work too well. The high speed pulse likes traveling in a straight line, so I have sometimes formed the track so that the gap is in the sharp end of a "v" corner. That maximises the energy going to the gap itself. Of course, on HF signals the added inductance of such V corner might be unwanted, but for low speed/frequency it is OK.

Hello guys, not sure if the thread is active, but I have a question regarding spark gaps.
If a discharge can be grounded using a spark gap, is it not possible that stray discharges jump from the ground tip of the spark gap on to the signal end?!
Any such experiences?

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