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EMI/RFI Shield Plastic Boxes

shield plastic boxes

MG Chemicals provides various conductive coatings. You can use these to shield plastic boxes for your electronics projects.

As you know, I 3D print lots of plastic boxes to hold my electronics projects. I have never been into metal working. Designing and creating a plastic box is much easier for me than nibbling away at an aluminum box, and much cheaper.

But plastic is basically invisible to electronic and radio interference. We get no shielding at all from a plastic container. Up until now, I have used thin aluminum tape to shield plastic boxes. You will find this works pretty well, as long as you carefully wrap the seams together to ensure mechanical continuity.

For some time now, I have wanted to try a conductive paint. So, I took the plunge and bought some MG Chemicals 841AR Nickel Conductive Coating in an aerosol can from Amazon. This cost me about CDN $42 but should last me for many projects.

A word of warning: this is strong stuff. You will find it contains a lot of volatile organic compounds (VOC) and must be used in a well ventilated area. I did my spray work in the garage with doors all open. Also, I wore a mask, protective gloves and eye coverings. Strong smell for a while and takes 24 hours to cure at normal room temperature. I found that two coats an hour apart did the job and it was easy to get good coverage.

The 841AR data sheet indicates it will bond well to shield plastic boxes. It seems to chemically etch and adhere to ABS. I used it with PETG without problems, at least so far. We will see how it holds up over time. I have tried spraying either the outside or inside of a plastic box, and I think my preference is inside, as shown above.

Shield Plastic Boxes – Does It Work?

My tests have been minimal so far. The data sheet indicates I should get > 70 dB of shielding up to 1 MHz and more than 40 dB through HF, which are my frequencies of interest. This is much less than the 70 to 100 dB shielding from aluminum panel, but obviously a ton more than plastic, which is zero.

You can test the surface for continuity and resistance with a VOM after you spray. Over a short distance, I get around 0.2 Ω with aluminum panel or tape, and around 0.8 Ω with the 841AR. I could probably bring this down if I added more coats to increase thickness.

Even without more serious tests, I can tell that this approach to shield plastic boxes reduces ingress of RFI in the shack. You can read more about these conductive paints here.

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