ESD Concerns w/Plastic Enclosure

[Vidaman]

Hello All,

Pardon the intrusion from an ME here, but my company is currently working on a specialized solenoid valve controller that will packaged in a plastic case with aluminum front and rear panels. The front panel will be covered by a polyester membrane keypad. The product is powered by an external 24VDC power supply. The question that has been asked is how this product will handle ESD. Appart from standard CE, type testing, what are the concerns with such a product with regard to ESD? We would like to sell this into the semicon automation industry and I would like to understand that industry's concerns. Clearly, without a direct tie to ground, the enclosure and its inards will be floating, but your typical Keyence panel mount pressure display or Watlow heater controllers are packaged in plastic enclosures. They do not appear to have any special modifications that I can see.

Thoughts?

Thanks,

Mike

 

[jraef]

You have a little too much ambiguity in this task at this point.

First you need to define the term "handle". ESD can work both ways in this case, which means the question could be interpreted differently.

Will this plastic enclosure protect my internal equipment against ESD if coming from the outside?

or

Will using plastic for the enclosure present a risk of creating ESD that could end up being discharged onto other equipment in the area?

Secondly, the answer(s) to either question will also depend greatly on your definition of "plastic" as well. Not all plastics are created equal.

JRaef.com
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[Vidaman]

jraef,

Thanks for the quick reply. You've actually hit the nail on the head. I can't seem to get the voice of the customer with regard to which ESD direction they are most concerned. I could metalize the enclosure (the plastic is a PC/ABS blend that accepts plating) and make mods to provide a ground lug, but I might not need to do anything. I would hate to spend the money for non-value added features. An existing customer of ours took a similar product and encased it in a stainless steel box among other modifications to meet their ESD requirements. I'm working to find out what those requirements are without much luck so far.

-Mike

 

[itsmoked]

Well you have told us so little it is hard to make any good suggestions.

For example a solenoid in a box has no EMI problems per se but if you are rapidly cycling it and your control system is generating RFI or EMI then you may need to do something. My semi customers are starting to want CE on most things even if it doesn't make sense. You could take a unit to a LAB and see what it can take or dishes out. Then you would know if you need further expensive housing mods or not.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Keith, he didn't say EMI or RFI, it was ESD.

 

[itsmoked]

Oh so now you expect me to read the questions!!?

Doh!

Question makes less sense to me now.

If you are truly concerned about ESD it is relatively easy to test for with an ESD gun. Why would you even expect much of an ESD problem in a Semi Fab environment? There must be about 800 million consumer products handled daily that live in purely plastic boxes in some very high static environments with no troubles.

Well as far as Semi concerns about ESD they don't really exist except as required by CE which has a specific test for susceptibility or actually lack thereof.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com