ESD Protection- chase grounding & connector protection

Hi Guys,

I have a prototype that has an nRF24L01 RF module. I have serious problems with ESD. To increase ESD immunity of the PCB, I have some ideas.

Pcb is inserted into shelf of an aluminum chase. I thought to ground chase is a good solution for RF immunity for nRF24L01( like faraday cage / RF shield). Therefore, I have left the right and left edges of the PCB as pads as you can see in the figure below. I am convinced that RF immunity and RF performance of the module is boosted. And, I have decided to place a small aluminum RF shield which only closes the nRF24L01 module on the PCB. Therefore, if ESD immunity is increased, I remove these grounding pads.

Shortly, Does grounding aluminum chase boost ESD immunity?

  1. There is a 1x8 PCB header connector in the middle of the front edge of PCB. However, some pins in the connector go directly to MCU. Therefore, after removing this connector and hole for the connector, the PCB is isolated from the environment.

Does leaving no naked pins to help ESD immunity?

At this moment, Is ESD test conducted by spark gun on directly on the PCB or the product which used by end user?

Thank you for your contributions in advance

The figure is attached below

What sort of ESD issues? Is it interfering with other devices or is it being affected by other devices? Please explain how you got to this conclusion and your results.

Thank you for the picture. Is the plastic enclosure specified as being ESD conductive? Probably not, so being worried about ESD is pointless.

Paul

A spark gun near any electronics is a very efficient way to destroy it.

Standard ESD protection ratings for components assumes an indirect pathway via the human body, modelled as a 2k resistor or some such. The measures taken to reduce the risk of handling pcbs and connectors from causing damage are not designed for anything as drastic as high voltage arcing.

With any high voltage arcing or discharge the electronics needs to be fully enclosed in a shielded metal enclosure, maybe with feed-through capacitors on all the cables, this is not easily compatible with an RF module with antenna.

In such an environment the comms would normally be wired(*) or optical.

(*) With heavy protection circuitry.

wolframore: What sort of ESD issues? Is it interfering with other devices or is it being affected by other devices? Please explain how you got to this conclusion and your results.

I have sent the prototype to the test laboratory to check its ESD immunity. Unfortunately, it seems that the result will come negative.

Paul_KD7HB: Thank you for the picture. Is the plastic enclosure specified as being ESD conductive? Probably not, so being worried about ESD is pointless.

Paul

Yes, Mr. Paul, you are right. It is enclosure is not ESD certificated. It is made of aluminum. :(

MarkT: A spark gun near any electronics is a very efficient way to destroy it.

Standard ESD protection ratings for components assumes an indirect pathway via the human body, modelled as a 2k resistor or some such. The measures taken to reduce the risk of handling pcbs and connectors from causing damage are not designed for anything as drastic as high voltage arcing.

With any high voltage arcing or discharge the electronics needs to be fully enclosed in a shielded metal enclosure, maybe with feed-through capacitors on all the cables, this is not easily compatible with an RF module with antenna.

In such an environment the comms would normally be wired(*) or optical.

(*) With heavy protection circuitry.

I think that the fatal mistake in the design is picking aluminum boxes instead of plastic. Even if I remove the grounding pads on both sides of the PCB, a spark can jump from aluminum chase to anywhere in the PCB. one concern in the design is Since it is a wireless device, it is not possible to earth or ground the device.

How do they do for laptops and mobile phones? Do they fully isolate PCB from chase? I know there is couple of ways to protect connectors such as TVS/ESD diodes or ferrite beads. How about for chase?

Thank you for all your contributions

You are asking about a product you’re going to market with since it’s in ESD testing? Not sure what this is doing in a hobby forum with volunteers, hire an engineer.

wolframore:
You are asking about a product you’re going to market with since it’s in ESD testing? Not sure what this is doing in a hobby forum with volunteers, hire an engineer.

I don’t understand it either.

ESD damage is cumulative over time. You will never feel or see a spark. Control of ESD damage begins with the production facility. That means grounding foot straps with daily testing, grounding wrist straps, grounded ESD mats for the assembly area, and most of all an ESD rated floor material. IF you skip just one of these, your product may suffer damage without you ever knowing it.

I recall an engineer with a disk drive manufacturer relating that just 100 volts would damage and possible destroy some of their devices.

ESD protection is not something you can add and test after the device is manufactured.

Paul

wolframore: You are asking about a product you’re going to market with since it’s in ESD testing? Not sure what this is doing in a hobby forum with volunteers, hire an engineer.

Ohh no. I am just a student. It was a project university. My professor has sent the device to ESD test to check it. I am asking to know my mistake and not to repeat it for the next projects. Thank you for your help

wolframore: You are asking about a product you’re going to market with since it’s in ESD testing? Not sure what this is doing in a hobby forum with volunteers, hire an engineer.

Paul_KD7HB: I don't understand it either.

ESD damage is cumulative over time. You will never feel or see a spark. Control of ESD damage begins with the production facility. That means grounding foot straps with daily testing, grounding wrist straps, grounded ESD mats for the assembly area, and most of all an ESD rated floor material. IF you skip just one of these, your product may suffer damage without you ever knowing it.

I recall an engineer with a disk drive manufacturer relating that just 100 volts would damage and possible destroy some of their devices.

ESD protection is not something you can add and test after the device is manufactured.

Paul

I see no marginal improvement in this design without changing PCB for now. I will pay attention to design accordingly for the next versions. I do not want to be misunderstood. I do not have any benefit or profit except than self-learning for this project

Thank you all for your contributions.

by FS

Sparkgap is destructive testing in most cases. It’s very expensive to add the proper circuitry to build for such abuse and in many cases not necessary

No one noticed that the NRF24L01 transceiver module is inside the aluminum case? The range must be measured in inches.

Don't confuse a Faraday shield with ESD protection, though a Faraday Shield will in most cases protect from ESD.

Laptops do it with lots and lots of bypass capacitors and conductive plastic cases. Shielding is used to prevent RF radiation or incoming interference. ESD protection means the ability to represent a path to ground for electrostatic charges.