Author Topic: ESD without enclosure  (Read 636 times)

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Offline chagliTopic starter

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ESD without enclosure
« on: September 19, 2019, 10:09:20 am »
Hi all,

I was wondering how can I pass the ESD tests for product which is a PCB mounted on a DIN rail. There's no enclosure so the top layer of the PCB is accessible to touch.


Here's my first thoughts :

- Use only ESD protected devices (maybe not possible)

or

- Put all sensitive devices on the bottom (not accessible to touch). The vias are still accessible so tent/fill the sensitive vias with soldermask.  Put a protective earth (PE) plane on top and expose many PE vias to catch the arcs. (preferred solution)

or

- put a cover, so only the connectors are exposed (not preferred solution)

Did you already have the same issue or do you have any idea/solution/comment ?

Thank you
 

Offline Gyro

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Re: ESD without enclosure
« Reply #1 on: September 19, 2019, 06:34:19 pm »
It depends also on what ESD standard you are required to meet and also the permitted disturbance - 'Needs power cycle to recover', 'operational disturbance but recovers without intervention' , 'no disturbance in operation' etc.

Putting a ground flood on the top side may help but I doubt that tented vias would resist most esd tests. You can certainly use supply rail clamps, esd protectors on critical signals etc. but I think it's probably virtually impossible to design a (electronic) circuit with zero susceptible nodes.

Putting the active stuff and nodes on the underside of the PCB would help of course, but beware of clearances needed against a probe applied at the edge of the PCB.

A cover is clearly not your preferred solution but it might turn out to be the safest and even possibly the cheapest solution too.

Another key issue on anything Din rail mounted - presumably on a plastic base, is how good your protective ground connection is, relative to its I/Os.
« Last Edit: September 19, 2019, 06:37:49 pm by Gyro »
Best Regards, Chris
 

Offline MosherIV

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Re: ESD without enclosure
« Reply #2 on: September 19, 2019, 06:48:21 pm »
What Gyro said.

I just want to add that you can either
1 pot the circuit board (full cover the circuit board with an epoxy coating, look up potting compund)
2 cover the circuit and components with conformal coating.

Both should create a physical barrier between circuit, components and physical contact.
 

Offline max_torque

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Re: ESD without enclosure
« Reply #3 on: September 19, 2019, 07:03:56 pm »
With the assumption that "din rail" means an industrial application, i'd never buy anything that was a bare pcb on a din rail mount!  Way too vulnerable in that environment just to physical damage.

Plenty of people sell low cost COTS din rail enclosures to take pcbs ie:



 

Offline chagliTopic starter

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Re: ESD without enclosure
« Reply #4 on: September 20, 2019, 12:25:58 pm »
Dear all,
Thank you for your remarks and suggestions.
 


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