Tape for rF shielding

[cncjerry]

Hi,   

I was wondering if there are any tapes that would provide some level of RF shielding?  I keep staring at the aluminum tape (and also the copper tape I have) wondering if they would provide some level of RF shielding.  In this case, I have a small mixer board I am testing and though I could throw it in a metal box, I wanted to 3d print one and the cover it in a layer of tape on both sides (inner and outer).  I have the aluminum tape used in HVAC work and I also have copper tape.  I think they are both about the same thickness, though I would probably use the copper tape either way unless the aluminum was significantly thicker.  I can solder the copper tape with low temp paste pretty easily.  The signal levels coming in are +4dBm and I have noticed interference from other 10Mhz sources in my lab.  I was thinking maybe this 3d print and tape solution might help.  this is not to prevent strong magnetic fields.

Thanks

Jerry

[Andy Chee]

Copper tape is my recommendation, due to ease of soldering should the need arise (for example, soldering seams and joins).

[Bud]

Things above 200MHz start noticably sneak through seams and gaps. Coppert tape can be soldered to seal the seams, but as it oxidizes and attracts fingerprints it will look awful with time unless sprayed with paint or lacquer.

[ConKbot]

3m tape specifically for EMI work comes in quite a few flavors. Copper (bare and nickel plated) aluminum. With each having conductive or nonconductive adhesive. The non-conductive adhesive tape comes with a cross hatch embossed (well, inwards, so "debossed" ) pattern to enable metal on metal contact even with the nonconductive adhesive.

Aluminum HVAC tape could work, if there is enough capacitive coupling at overlaps. There still is a slot, but it's 1 adhesive layer thick and much much wider that the adhesive line, so it's a waveguide below cutoff, and still effective in providing some attenuation. Is it perfect? No. But you have it, and it's "free" so feel free to line a 3d printed box and give it a shot. The big if, is making sure your board is connected to the tape with a good connection. This is probably easier with copper tape you can solder at strategic points and run to the housing.

[selcuk]

Skin depth is 20um for copper at 10MHz. You may calculate the thickness of the material for an expected attenuation. There are online tools like this:

https://learnemc.com/EXT/calculators/SE4_Calculator/index.html

[Berni]

Metal tape is often used for EMI shielding in products.

Most of the time it is used to cover the gaps in shielding, like bonding the metal back cover of an LCD module onto the metal frame, gaps to shielded connector housings..etc

Aluminum self adhesive tape is perfectly fine for this. The copper one has the advantage of being solderable, but will look kinda ugly as it oxidizes. There is also aluminium or stainless steel fabric tape that is a bit more flexible (this is the one you tend to find if you google "EMI tape")

At 10 MHz it should be reasonably easy to shield, So feel free to give it a shot. If you want really good shielding you can always step it up to buying a copper sheet, cut it out and bend it into a box, then use RF filtering passtrough bulkheads to get signals in and out of it. Most of the interference tends to come in via the cables.

[cncjerry]

Good, thanks for the link.  3M conductive adhesive?  Have to go looking for that.  I don't care what it looks like. 

Issue I'm having is that I'm getting some kind of modulation in a mixer at a period of 165 seconds or so.  This seems like the offset between my Rubidium standard and oscillators I am phase noise testing.  the amplitude is only about +/- 4e-16. But is is probably coming in on the cables.  They are the blue, 100% shielded 50ohm type.  I've swapped out everything (e.g. oscillators, counters, TICs, mixers, phase detectors, amps (using QB-188 now), attenuators, cables, DDS units, etc.)  All the easy things to plug in as it's all connectorized.  I've put filters on things, and taken filters off.  I've tried directional couplers, resistive vs reactive power splitters, loads.  I've ordered some non-reflective filters too.  I've measured impedance circuit by circuit with an HP4815 vector impedance meter (my personal fav).  I've put the VNA on everything, changed scopes, tried several spectrum analyzers, batteries, lt3045 regulators, different opamps, loose shielding and I would CNC a nice box if I knew it would correct the problem!!!!! 

If I can see a reduction with the tape then I will machine the box.

Thanks

Jerry

[jbb]

I think you can get spray-on copper EMI paint too. No idea how available / expensive / fiddly / toxic though.

[xrunner]

I was thinking maybe this 3d print and tape solution might help.  this is not to prevent strong magnetic fields.

I've used 3D printed case parts and copper tape for many RF projects. It works very well. The copper tape's adhesive is conductive and therefore, you don't have to solder the separate pieces together. Just overlap the pieces a bit. You can get the tape on Amazon in various widths -

https://www.amazon.com/gp/product/B09Z6F9RFG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[Emo]

Hi Jerry,

Please take into account that coaxial shielding is limited to 90 -120 dB.

Eric

[jonpaul]

So, at Sequerra in 1970s I Learned from Dick Sequerra (1960s Marantz RF genius) worjing at 10.7 MHz and FB band 100 MHz,  to use copper tape,
Only copper is easily solderable .

3M tape in various  thicknesses and smooth or embossed.
Conductive paint/glue is not suitable.

We use copper foil up to 6" width rolls for transformer shielding.

Jon

[cncjerry]

Those 3d printed boxes are great, I'm going to have to change my userid to 3djerry. I've been Cncjerry since the internet.   I have tape, have to check if the glue is conductive. I ordered some last night but went cheap.  I'll regret it.   The 3m was 45 a roll and the cheap stuff, $9 or less.  I think the stuff I have in the lab is conductive.  Someone told me the carbon fiber filament was conductive and decent shielding so I bought some.  It was expensive at the time, about 4x normal, I've never been able to get it to print and I can't get a decent reading even with my electrometer on the scraps.

Thanks for all the input,  great help!  I'll return with results.

3djerry (sure it is taken)

p.s. those boxes remind me of the old drake radios. They copper flashed or coated the chassis.  I used to drool over them (not good for the electronics) but went with a Swan 700 for the power.  Still have a Swan 750 someplace but they replaced the modulator in the 750 with a 1496 and ruined the radio.  The old dual pentode? modulator was so much smoother.

[Qmavam]

I have read about using chalkboard paint for EMI shielding. I'm not finding the link I saw, but have found people that know people that say it works , the devil is in the details. Something like this, https://www.lowes.com/pd/Magnetize-It-Black-chalkboard-Water-based-Chalkboard-Paint-1-quart/5014445855
 If anyone finds more info about using chalkboard paint as EMI shielding, please post links. They do sell paint for EMI shielding, but is is very expensive.
                      Thanks, Mike

[Randy222]

I bought some Eterrart copper foil tape X003TRO69D to do some shielding on some projects.
You can solder to it. I typically will solder a small wire over seams and overlaps to make continuous electrical bond.

[Qmavam]

yes, copper has some attenuation, I have ask some Youtoube experimenters to paint copper tape with magnetic paint and measure the effect.

[wilhe_jo]

I'd give copper tape a try. Just be sure you bond it to your ground plane.

Btw: the cheapest copper tape I found so far is the stuff you get in the garden department of home improvement stores. It's used to prevent snails to eat your precious salads and stuff..
That's relatively thin but does the job well....and you can get it everywhere.

73

[CosteC]

In my experience some copper foils have poorly conductive glue, some have quite well conductive glue. Some foils are also well insulated on both sides (for example for screens inside transformers)
Often each piece of foil need to be soldered to each other to provide enough HF screening. Maybe due to oxidation which always is there. Relying on contact is not recommended in perspective of months even.

[SeanB]

I have read about using chalkboard paint for EMI shielding. I'm not finding the link I saw, but have found people that know people that say it works , the devil is in the details. Something like this, https://www.lowes.com/pd/Magnetize-It-Black-chalkboard-Water-based-Chalkboard-Paint-1-quart/5014445855
 If anyone finds more info about using chalkboard paint as EMI shielding, please post links. They do sell paint for EMI shielding, but is is very expensive.
                      Thanks, Mike

No, you need a graphite based spray, like Graphit33 from Kontact Chemie.

http://www.kontaktchemie.com/koc/KOCproductdetail.csp?division=&product=GRAPHIT%2033&ilang=en&plang=en

Makes a conductive layer on plastic, and adheres well. Not as good as pure copper, but has the advantage it will cover irregular surfaces, and the easiest way to provide a bond to it is to use a copper strip stuck down firmly before painting, that the paint bonds to.

[Randy222]

In my experience some copper foils have poorly conductive glue, some have quite well conductive glue. Some foils are also well insulated on both sides (for example for screens inside transformers)
Often each piece of foil need to be soldered to each other to provide enough HF screening. Maybe due to oxidation which always is there. Relying on contact is not recommended in perspective of months even.

The tape I have does say the adhesive is conductive, but it really needs to be tested. I just solder overlaps together, but not the whole length of seam. Sometimes I will fold over an edge onto the adhesive before placing tape overlapped onto another piece, firmly press the overlap down, that's copper-on-copper, and then a few solder spots. Not the easiest way, but works ok.

[xrunner]

The tape I have does say the adhesive is conductive, but it really needs to be tested ...

Well - test it. 

I did after acquiring a roll for my last project. All I did was stick about 5 pieces end-to-end to make a strip. The only solder used was to attach wires. I then passed a current of 20 200 mA through it all day. It works just fine no solder needed.

[Randy222]

The tape I have does say the adhesive is conductive, but it really needs to be tested ...

Well - test it. 

I did after acquiring a roll for my last project. All I did was stick about 5 pieces end-to-end to make a strip. The only solder used was to attach wires. I then passed a current of 20 mA through it all day. It works just fine no solder needed.

20mA? Did you have to crank up the volteg to 63v? Did you happen to take ohm measurements?

The adhesive changes over time, and changes differently depending on environmentals, heat cycles of the device/box, etc.
The initial mA & ohms testing is good, but still do need some long term testing too.

And I guess long term degradation effects will be related to how much overlap there is.

All good info. Thanks.

[xrunner]

20mA? Did you have to crank up the volteg to 63v? Did you happen to take ohm measurements?

Uh ... why don't you examine the pic I attached, it just might answer some of your questions. 

[Randy222]

20mA? Did you have to crank up the volteg to 63v? Did you happen to take ohm measurements?

Uh ... why don't you examine the pic I attached, it just might answer some of your questions. 

It shows 20v ?

1000 ohms ! Is the ceramic a 10w 1000ohm ?

Maybe just ohm meter the foil, to get ohms? Why the need to pass mA ?

I'll ohm my tape later today.

[xrunner]

20mA? Did you have to crank up the volteg to 63v? Did you happen to take ohm measurements?

Uh ... why don't you examine the pic I attached, it just might answer some of your questions. 

It shows 20v ?

1000 ohms ! Is the ceramic a 10w 1000ohm ?

Maybe just ohm meter the foil, to get ohms? Why the need to pass mA ?

I'll ohm my tape later today.

I apologize, I mis-typed I should have typed 200 mA. I used a 100 ohm resistor, so the resistance of the copper tape connection is very small.


Note: I've never made a mistake before. I thought I did once but I was wrong about that time.

[CosteC]

Connection looks really good - I am pretty impressed. Still I would not trust glue in months or years time. On other hand, maybe the tape can be arranged in such way seam resistance is not very important.

[Randy222]

Connection looks really good - I am pretty impressed. Still I would not trust glue in months or years time. On other hand, maybe the tape can be arranged in such way seam resistance is not very important.

I guess as long as each piece is tied to ground, then continuity of overlap seams is less worry.
I just hit a seam with a spot of solder, and one small wire to gnd.

The spray was listed. If the shielding is of high importance, I would go MuMetal foil.
https://www.pmlindia.com/pages/mumetal-foil

[cncjerry]

 A couple tapes arrived today.  One that is interesting is something called Aluminum Faraday cage tape.  It is more like cloth.  Comes in different sizes.  I stuck pieces on top of a longer strip and can't read the difference with my Agilent hand held DMM.  I have more accurate meters, just not handy and will do more testing.  I also have 2" wide copper tape that also reads low ohms when stuck on the same tape. Its so thin you can wrap the side edge over and pound it flat.

It seems to me that if you take a very sharp probe and stick down thru the top layer a bunch of times, sort of pinning the top to the underlayers, it makes a difference.  I haven't tested my problem device yet. 

This opens up a whole new world of boxes for me without worrying about RF shielding.  I have a bunch of low noise RF amps and reflectionless filters to build and I had thought of CNC machining them into little connectorized bricks like what MiniCircuits does with their small devices.

Really neat.

Jerry