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Working with small volume product and tight schedule it might become an option to pass EMI limits by use of copper/aluminium foil on inside of enclosure. What is your experience with the labs on this point? Would they accept a device where foil has been applied during the measurements?

Would you say that it is acceptable industry ptactice to later on in production replace the foil with metallic part or spray without re-test?

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    \$\begingroup\$ No experience with labs but: why should it not be valid, if the foil is actually part of the product? But I assume that you have to test after changing the foil to spraypaint, because the spraypaint and the foil are different. \$\endgroup\$ Commented Mar 1, 2023 at 11:25
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    \$\begingroup\$ The test house will take pictures as part of their documentation. If you test with copper foil, the results are only valid for a unit assembled the same. \$\endgroup\$
    – Kartman
    Commented Mar 1, 2023 at 11:36
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    \$\begingroup\$ My experience is that test houses will test whatever you want, however you want, and happily take your money for it. If you want their opinion on whether things are a good idea regarding compliance with a particular standard, they will happily produce a report for you in exchange for your remaining arm and leg. \$\endgroup\$
    – Jon
    Commented Mar 1, 2023 at 12:54
  • \$\begingroup\$ What does the person in your company who has to sign the declaration of conformity say about that. \$\endgroup\$
    – lalala
    Commented Mar 2, 2023 at 9:59

2 Answers 2

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Working with small volume product and tight schedule it might become an option to pass EMI limits by use of copper/aluminium foil on inside of enclosure. What is your experience with the labs on this point? Would they accept a device where foil has been applied during the measurements?

This is an OK thing to do. Labs normally have several reels of copper tape in a cupboard along with a bunch of clamp on ferrites for this very reason but, it won't hurt to take your own.

It's down to you to ensure that what gets added at the lab gets fully documented and implemented when you build production units.

Would you say that it is acceptable industry practice to later on in production replace the foil with metallic part or spray without re-test?

Unless it is clear-cut and 2nd opinions are sought from experts, it's not advisable.

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You are the one who has to define what your product is and how it will be designed and produced, the test house won't do that. So they only care if the product lives up to the EMC criteria or not - they don't care how you get there. As for what's acceptable for a certain kind of product, that's a very big topic.

Should you fail an EMC test but do something "ad hoc" while in the lab (hello, ferrite beads) in order to pass the test, this patch will be documented in the report and the test engineer will need to take photos of it.

From there it is your responsibility to produce the products the same way as they were tested. If you release a product on the market and it causes EMC problems, you are in serious trouble in case the production units are notably different from what was tested and you can't present a sensible argument regarding why. For example by presenting a product log explaining changes made after EMC testing and why you believe that each change done does not affect EMC.

Would you say that it is acceptable industry ptactice to later on in production replace the foil with metallic part or spray without re-test?

Obviously not since this is a change of an important EMC component - you cannot sensibly argue and say that it does not affect EMC. And from my personal experience of such sprays, they are of questionable quality at best and do not work well over time either.

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