Author Topic: Prototyping RF shielding  (Read 663 times)

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Offline BurnedResistor

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Prototyping RF shielding
« on: April 21, 2018, 07:15:50 am »
Hey All,

I was looking at different options for shielding some prototype circuits I am working on.
One interesting option is the Harwin Shield Can Kit:

A sheet of metal with grooves cut which allows it to be cut and bent, and a bunch of clips with which it can be held to a pcb.
https://www.harwin.com/product-highlights/shield-can-kit/

however, they are REALLY expensive. For two of these sheets (60*80mm), and 24, you have the honor of shelling out 20Euro:
https://eu.mouser.com/ProductDetail/Harwin/S01-806005KIT?qs=sGAEpiMZZMtWZAo%2fKf1JUHiZzR%2fnLX4EUp7FJ%252b6aUyU%3d

I thought the idea was kind of neat however.

Has anybody got any experience with easily manufacturing such shields? This is 1-2 quantity: purely for prototyping/1off manufacture/

Also, I feel like it must be possible to buy flat sheet metal with such grooves for other purposes, which would most likely be cheaper + maybe even provide bigger sheets, or also sheets with different grid sizes. Any ideas?

Also, anyone know of any kind of flat metal stock that would work for this application? That could simply be bent and cut into shape? What metal and thickness should I be looking for?
 

Offline CopperCone

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Re: Prototyping RF shielding
« Reply #1 on: April 21, 2018, 08:34:54 am »
Why not just use regular copper sheet? Better then copper is nickle silver (not zinc sorry) sheeting material, does some H field attenuation.

0.025 copper sheet you can cut with scissors and form. You can roll this stuff with a rolling pin to flatten it if you want.

I have made some shield before, the #1 thing is to make sure your bends are good. What will fuck you up is getting frustrated with laying out your bending tools, then doing half assed bends. If you take your time cutting it out, and make nice square edge forms to bend it on (plexiglass will work with a clamp), you can make some nice stuff.

I think the clips will be compatible with something you make yourself.  Idon't know how you would make reliable clips though, I typically solder the shield on. The problem with the clips is that you want it springy, You can make copper springy by banging it with a hammer/peening it, but it might be a pain in the ass.
« Last Edit: April 21, 2018, 08:39:32 am by CopperCone »
 
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Offline Cerebus

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Re: Prototyping RF shielding
« Reply #2 on: April 21, 2018, 09:05:14 am »
You're probably better off investing your money in a small sheet metal folder (also known as a brake), ideally a box and pan folder, and then you can fold small metal sheet to your hearts content without relying on having any special pre-scoring or similar. Thin sheet metal, in most alloys, is as cheap as chips of you can pick it up from a local stockist.
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Offline cellularmitosis

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Re: Prototyping RF shielding
« Reply #3 on: April 21, 2018, 10:08:50 am »
Hammond cases (cast aluminum, e.g. the 1590B) seem to be pretty commonly used in the RF world, and are pretty cheap. http://www.eevblog.com/forum/metrology/kx-reference/msg1390978/#msg1390978

TEKO makes some steel cases, which will also shield against magnetic fields, and are pretty cheap.  You have to call a human using a telephone in order to buy them though (how archaic!): http://www.eevblog.com/forum/metrology/px-reference/msg1446980/#msg1446980

If you need something a bit larger, you can also use an ammo can (smaller ones are $15-$20 on ebay) if you replace the gasket with an RF gasket:

I use an aluminum dutch oven (fitted with a BNC adapter) for noise-sensitive measurements: https://github.com/cellularmitosis/logs/blob/master/20180324-ltz1000-1f-noise/README.md
LTZs: KX FX MX CX PX Frank A9 QX
 
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Online hagster

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Re: Prototyping RF shielding
« Reply #4 on: April 21, 2018, 01:29:08 pm »
Those do look like a handy kit for profesional work, but generally I would look for off the shell cans and design my board around that. There is almost certainly one availiable that is close to the size you need. I know Laird and Wurth Electronic have a range.
 
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Offline BurnedResistor

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Re: Prototyping RF shielding
« Reply #5 on: April 21, 2018, 06:35:19 pm »
Those do look like a handy kit for profesional work, but generally I would look for off the shell cans and design my board around that. There is almost certainly one availiable that is close to the size you need. I know Laird and Wurth Electronic have a range.

Yeah i looked, and might go down that route for this project. I just come accross this quite a few times and was hoping for an easy way to manufacture them myself in any size on the spot: Saves me having to order them, design around specific sizes, wait, etc.

Hammond cases (cast aluminum, e.g. the 1590B) seem to be pretty commonly used in the RF world, and are pretty cheap. http://www.eevblog.com/forum/metrology/kx-reference/msg1390978/#msg1390978

TEKO makes some steel cases, which will also shield against magnetic fields, and are pretty cheap.  You have to call a human using a telephone in order to buy them though (how archaic!): http://www.eevblog.com/forum/metrology/px-reference/msg1446980/#msg1446980

If you need something a bit larger, you can also use an ammo can (smaller ones are $15-$20 on ebay) if you replace the gasket with an RF gasket: - VIDEO -

I use an aluminum dutch oven (fitted with a BNC adapter) for noise-sensitive measurements: https://github.com/cellularmitosis/logs/blob/master/20180324-ltz1000-1f-noise/README.md

Those would be the easiest option, but sadly my project is size constraint in having to fit into an existing piece of gear - There is barely enough room for the parts, let alone shielding :) Thanks for the input thought.

Why not just use regular copper sheet? Better then copper is nickle silver (not zinc sorry) sheeting material, does some H field attenuation.

0.025 copper sheet you can cut with scissors and form. You can roll this stuff with a rolling pin to flatten it if you want.

I have made some shield before, the #1 thing is to make sure your bends are good. What will fuck you up is getting frustrated with laying out your bending tools, then doing half assed bends. If you take your time cutting it out, and make nice square edge forms to bend it on (plexiglass will work with a clamp), you can make some nice stuff.

I think the clips will be compatible with something you make yourself.  Idon't know how you would make reliable clips though, I typically solder the shield on. The problem with the clips is that you want it springy, You can make copper springy by banging it with a hammer/peening it, but it might be a pain in the ass.

You're probably better off investing your money in a small sheet metal folder (also known as a brake), ideally a box and pan folder, and then you can fold small metal sheet to your hearts content without relying on having any special pre-scoring or similar. Thin sheet metal, in most alloys, is as cheap as chips of you can pick it up from a local stockist.

This looks like a promising route.
Regarding the material: I am guessing copper is easily soldered to the board, and nickle silver shields better but probably requires clips?
I was planning on using clips anyway for maintenance/tuning reasons. I can pick up nickle silver sheets fairly cheaply.

Regarding breaks:
I can get normal breaks relatively cheaply (Both the kind that sits in a vice () and a standalone press ()), but am relatively inexperienced with this kind of tool. Because of the small size of the shields, they will need relatively small bend radi. Will any medium to small break be able to do this, or will I need specific small die?

Regarding a box and pan break:
I was not able to find any pan&box break with "clamping teeth" (Dont know what the technical term is :)) thin enough to actually fit into the sides of the 1-2cm big cans I am making. Am I missing something, or ar those tools more for large fabrications?
Same question as above - will a standard box and pan break be able to form a tight enough bend?

Thank you for all the help!

« Last Edit: April 21, 2018, 06:46:12 pm by BurnedResistor »
 

Offline Cerebus

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Re: Prototyping RF shielding
« Reply #6 on: April 21, 2018, 08:35:50 pm »
A standard sheet metal folder will make sharp, square folds in the thin sheet required for shielding boxes, no problem. Yes, you'll be hard put to find a box and pan folder that has narrow enough clamping fingers to deal with shielding can size boxes but there's a way around that. Just cut a solid former for the interior dimensions of your box out of hardwood, plastic, aluminium, whatever is to hand and is rigid enough. Clamp the sheet down with that former under the fingers of the brake and you're away. What you need is the height of clamping bar that a box and pan brake beings.

An alternative is the Magnabend, a cunning electromagnetically clamped folder that has open ends, meaning that you don't need separable fingers. Magnabend was originally a proprietary trade name but has become a generic and they are manufactured by a number of makers.

See someone folding an enclosed tetrahedron with a magnabend, at about 2:19. Warning: awful stock heavy metal background music:
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Offline tggzzz

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Re: Prototyping RF shielding
« Reply #7 on: April 21, 2018, 09:01:13 pm »
For quick and dirty prototype or one-off, consider using FR4 as the shield material. Cut it to whatever size/shape you want, then solder the joints.

Radio Hams have this kind of thing down to a fine art.

Search for "manhattan construction rf", and similar.
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Offline noname4me

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Re: Prototyping RF shielding
« Reply #8 on: April 21, 2018, 11:01:23 pm »
Kitchen foil and aluminium roofing tape (make sure it is conductive both sides).

I've had good results using that to shield an enclosure at up to 30V/m field strength at spot frequencies in the ISM band and 10V/m throughout 80 MHz to 1GHz (it works beyond this too, just didn't need to test it beyond this for compliance)

This is good to prototype if you are looking to do it on the cheap and just need something to work at the time.

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Offline David Hess

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Re: Prototyping RF shielding
« Reply #9 on: April 22, 2018, 04:10:19 am »
For quick and dirty prototype or one-off, consider using FR4 as the shield material. Cut it to whatever size/shape you want, then solder the joints.

That is what I do.  I am thinking of making a small precision radial arm type of saw which uses Dremel cut off wheels for cutting FR4.

Kitchen foil and aluminium roofing tape (make sure it is conductive both sides).

Adhesive copper foil can be soldered at the seams.
 

Offline tggzzz

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Re: Prototyping RF shielding
« Reply #10 on: April 22, 2018, 05:21:57 am »
For quick and dirty prototype or one-off, consider using FR4 as the shield material. Cut it to whatever size/shape you want, then solder the joints.

That is what I do.  I am thinking of making a small precision radial arm type of saw which uses Dremel cut off wheels for cutting FR4.

Kitchen foil and aluminium roofing tape (make sure it is conductive both sides).

Adhesive copper foil can be soldered at the seams.

A lot of the adhesive copper foil on the market has conductive adhesive and/or other tricks, so it might not be necessary to solder it.
There are lies, damned lies, statistics - and ADC/DAC specs.
Gliding aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline noname4me

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Re: Prototyping RF shielding
« Reply #11 on: April 22, 2018, 05:24:44 am »
For quick and dirty prototype or one-off, consider using FR4 as the shield material. Cut it to whatever size/shape you want, then solder the joints.

That is what I do.  I am thinking of making a small precision radial arm type of saw which uses Dremel cut off wheels for cutting FR4.

Kitchen foil and aluminium roofing tape (make sure it is conductive both sides).

Adhesive copper foil can be soldered at the seams.
Aluminium tape doesnt need soldering...it's sticky and conductive...and cheaper than copper tape.

Also...copper tape cuts my hands more easily... I'm very clumsy

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