Enclosure Design Resources

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This thread aims to collate useful enclosure design resources. Before starting to list off materials, processes and tools, it might be worth reminding ourselves why we bother with enclosures:

  • Ingress protection - dust, liquids, small conductive bits that could short our circuits. We want to keep them away. Sometimes, if this is all you need and to a low level, conformal / silicone coatings can be all that is needed.
  • Mechanical strength - if our board is going to have mechanical loads transferred to and from it, an enclosure can help here - especially if there are connectors/cables. There also may be vibration damping to protect connections or sensitive components.
  • User interface - yes, the ergonomics of bare PCBs (especially if they get hot!) means an enclosure is often a lot easier to handle and mount to a bench or a robot, even before we get to adding inputs and outputs such as displays, LEDs and buttons. And some people would rather not to look at bare PCBAs all day, preferring to cover them in aesthetically improving surfaces. Can’t understand it myself. :grin:

There are also some other needs which, while not necessitating that an enclosure meets the need, it often makes sense to give these jobs to an enclosure:

  • Thermal dissipation/capacity and shielding. Ordinarily, you’d say “heatsink” or “radiator” for the first two. But there often needs to be an enclosure anyway and it has to take the heat somewhere. On the flipside, perhaps the environment you will be taking this circuit is unforgiving and an enclosure keeps it at much more “operationally conducive” temperatures than if you just chucked those lithium ion cells out in the snow…
  • Electromagnetic shielding. There is debate about the enclosure’s possible role in electromagnetic compatibility strategy but let’s remember that it can definitely play its part.

Based on this partial list of aims for enclosures, we can infer some of the following requirements and considerations:

  • We often need a good fit or seal between surfaces. Electrical connections outside the enclosure can become challenging.
  • The introduction of the enclosure means we need to think carefully about what residual access or access-for-assembly is needed. No good making a user-replaceable battery inaccessible. Likewise, you may achieve a spatial fit of your PCB assembly in the “installed position” but you haven’t left enough room for the assembly steps. For example, perhaps the connectors won’t mate/un-mate because you haven’t left enough room between the edge of the PCB and the enclosure wall. And don’t forget to accommodate your fingers or any assembly tools.
  • A good fit or seal around often changes the optical, thermal or RF environment of a board and this can introduce secondary requirements of windows/light pipes, heat dissipation and antenna placement.
  • In fact, even introducing new material in close proximity to integrated antennas (such as those formed from PCB traces and matching components) can detune them and impede the radio’s performance. While you may expect a metal enclosure to significantly block RF signals to and from your radio, even plastic enclosure too close to antennas can noticeably degrade their performance. For products that are going to be mounted in an enclosure with an internal antenna, repeatedly in the same position, antennas can be designed to account for the proximity of the enclosure materials and other parts of the assembly.
  • Off-the-shelf enclosures often have internal fixing positions for mounting screws and standoffs, so it’s often prudent to select an initial enclosure and check how the mounting holes might impact your circuit layout.
  • We also need to make sure the enclosure itself doesn’t become a short between circuits. Indeed, it also needs to make sure any higher voltages (such as mains AC ) don’t get conducted to people or surroundings. For that reason, conductive enclosures might need grounding.
  • The enclosure might need some external fixing points which don’t compromise any ingress protection or cable/UI egress/access.

What enclosures can look like:

  • Heatshrink tubing slid over a circuit, with cables routed out of the ends if required. Glue-lined heatshrink can be pressed together at the ends to make a basic seal. One-time-access only! Think radio control electronic speed controller circuits.
  • Potting compound poured over and around the circuit, often with a plastic tub or open-faced “pot” to contain the compound until it sets. Usually more expensive and mechanically robust than heat shrink tubing. About the most permanent option there is but you get very good ingress protection.
  • Low temperature overmoulding is usually a “product-grade” process where a (relatively) low melting point thermoplastic (typically in the region of 200*C) is injected into a mould around the circuitry. With hobby-grade/price machinery and materials this could be a realistic option for some. Can produce especially nice results for strain relieving cable-connector and cable-case junctions, relative to other methods.
  • Pipe / tube stock with end-caps. This could be PVC plumbing/drainage stock (often press-fit with good seals and easy to cut/form with domestic tools). Can also be found in optically transparent materials such as acrylic or polycarbonate and doesn’t have to be round cross-section. Think hobby rockets, underwater remotely operated vehicles.
  • Stacks of PCB (or other sheet stock cut to an outline), separated by some kind of spacer or standoff. Perhaps with a 3D printed or extruded perimeter. Some PCB can be reserved specifically as top/bottom plates. Think DIY synthesiser projects, small research robots.
  • Plastic or metal boxes, either injection moulded, die-cast, extruded, CNC subtractive machined or 3D printed / additively manufactured. Often with a custom face-plate. Think guitar pedal stomp boxes and many benchtop electronics measurement tools.

Some common components:

  • Seals - If you need an ingress protected enclosure, you need seals. This often pushes you towards customisation of an off-the-shelf enclosure but careful design can mean you can seal your own designs well.
  • Cable glands - these are usually a great way to route cables out of an enclosure while maintaining ingress protection. They do take up space on the inside and outside, so the enclosure envelope/footprint needs to be adjusted to take advantage of them. If you have cable that is not large enough to achieve a seal with the gland you have, you can thicken a section of it with a short length of heat-shrink tubing (preferably glue-lined to maintain seal).
  • Light pipes - These translucent plastic parts allow you to solder an LED on your PCB but then route the light to a face plate that is some distance away and perhaps in a different orientation.
  • Bulkhead connectors - Nearly every connector, from RF coaxial ones to ethernet and USB have “bulkhead” versions which allow you to fix them through an opening (e.g. a hole you have made) in an enclosure wall. Often a good way to achieve ingress protection if they come with seals.
  • Standoffs - small metal or plastic parts, often threaded, to space a PCB away from enclosure surfaces. This can be simply to accommodate the height of components between layers of a PCB assembly but it can also be key to lining up a connection with an egress point in the wall of the enclosure or preventing conductive material enclosures from short circuiting your PCB.
  • Feet / bumpers - small, grippy, often with adhesive tape already affixed. They are stuck or screwed to the outside of the enclosure and can really help your small enclosure stay put. Larger systems may benefit from anti-vibration dampers/feet if they are sensitive or are a source of vibration.
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Design Tools for Enclosures:

  • FreeCAD (free cost, not cloud, open source) - powerful but lacks UI polish of many paid-for/closed CAD packages. Very much worth persevering with IMHO. Includes tools for CAM and CFD, with python scripting interface for customisation if you want.
  • OpenSCAD (free cost, not cloud, open source) - sometimes preferred for parametrics and those more comfortable with programming than CAD.
  • Alibre CAD (paid-for, not cloud, closed source). One of the more popular options when Fusion 360 and Onshape’s licence tweaks get too much to bear for people.
  • Fusion 360 (free for many, cloud-based, closed source)
  • Onshape (free for many, cloud-based, closed source)

Other useful links:

  • To start with, I’ll just leave this link to the enclosure tag on Hackaday.com where there is a wide range of examples featured.
  • Here’s a NASA resource on electrical isolation and chassis grounding.

Computer Aided Machining (CAM) Tools

  • As mentioned, FreeCAD has the Path workbench for CAM.
  • laser.cut is a cool looking openSCAD plugin that can handle other subtractive processes such as CNC routing.
  • I don’t plan to list every slicer out there for 3D printers but kiri:moto stands out for running solely in your browser (but on your local machine - it’s definitely not cloud) and supporting fdm, laser and cnc routers.

Design Tips

  • For air flow, whether forced (by e.g. a fan) or natural ventilation is always improved by larger slots/holes. Realistically, when you don’t want screws/fingers etc getting into an enclosure you need too keep sizes down. @kvk recommends going no smaller than 1mm slot width. But go bigger if you can and you have heat to deal with!
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Please feel free to suggest amendments and additions to either the preamble or the list of tools and resources above!

Great idea for a thread.

For considerations I think it is worth noting RF requirements. Often this precludes the use of metal enclosures when using internal antennas, where because of their environment, they would be best suited. It may be also worth mentioning potting as a form of enclosure.

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EMI is an important issue to deal with and good reason for a metal/faraday enclosure. Either external EMI like in a machine environment or in the case of radio gear where secondary frequencies/harmonics/etc need to be blocked from getting out.

Also, let us not forget aesthetics. Even for a CNC machine in my shop, I want my electronics case to look good and professional.

A build technique you left off is sheet metal bending. F360 has a really nice sheet metal module that makes it super easy to make cases and, for homebrewers, a brake is pretty easy to build.

[opinion alert] On the subject of PCB as case material. While I know people do it, it makes for a terrible enclosure. Sharp edges and poor fit are pretty common. It think it has a terribly unprofessional look to it. Several Open Builds products are like that. I have seen it used for a faceplate where the edges are recessed and it looks good.

I have never had the need for a Faraday cage. Solving the EMI at the source is cheaper. Granted, you might have a special circumstance, I don’t know. My designs has included VF drives with high dV/dt and we have never had the need for shielding

If you use Metal enclosure, and have mains in, then you need to comply to bond wire testing and touch current etc

About enclosures, if you have openings for cooling, rule of thumb is that slots needs to be wider than 1mm for reasonable air flow

For “why bother with enclosures”, I’d add:

  • EMC / EMI / “grounding”
  • Heat rejection, thermal compliance / performance

Some interesting reading on isolation and enclosure grounding is at https://standards.nasa.gov/electrical-and-electronics-systems, specifically HDBK-4001. The “lessons learned” section is also interesting reading. There’s a fair amount of overlap with non-aerospace RF and automotive.

A common enclosure design scheme in aerospace and other harsh industrial environments is the “bathtub” with a flat sheet lid. The bathtub has openings on the “bottom” (bathtub orientation) where bulkhead connectors are mated. A flat lid is attached over the bathtub and that becomes the “bottom plate” that is thermally / electrically coupled to the chassis. PCBAs tend to look like this example from soeffects.com:

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FreeCAD is great for enclosure, bracket, and heat frame designs IMO. The learning curve is steep and the first few times I tried it, I wasn’t convinced it was any good at all (but it’s really good). It also has a decent sheet metal plugin which I’ve used to design various U-shaped enclosures. Nearly every action you take in FreeCAD shows up in the python console as something you can then take and script. It’s a good way to start collecting scripts to programmatically/parametrically duplicate an enclosure design with different dimensions.

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We are currently working on a project that has 28 CCTV cameras. The customer was unhappy with the $15 grey plastic junction boxes for the ethernet termination at the camera and insisted we come up with a better looking solution. So we quoted stainless steel junction boxes, that due to the environment they were in, had to be the fancy stainless steel (316), not the ordinary (304) stainless. Each junction box now cost $300 (excluding glands and fittings). The customer agreed that they were a better looking solution and signed off on it. It must be nice to have money :slight_smile:

If the client is spending a good chunk of money on NRE and the first run, finding a way to make the end result look good even if you/we/me have to absorb some of those costs means the client has something that looks the part, reflects their investment in the techy bit and acts as a calling card for our next project.

We live in the Apple design world now. People have “stuff” made that they don’t really understand and many of the people that they show it to may not understand, but hopefully they understand what it does and as Apicius said “the first taste is always with the eyes”.

It would be useful if we could share our low-cost looking-good techniques.

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You missed my total nightmare “component”, one that has been plaguing at least one project with very small batch sizes for months:

“The Window”

I have projects with small LCD status displays. Having them mounted nicely but behind at least one piece of transparent material to stop people poking the display with a finger, biro, screwdriver etc etc has been an ongoing nightmare.

Cutting the case and getting a window to fit nicely - meh. Please tell me someone knows how to do this.

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@nmcc, do you have an example of what you’re trying to build?

For me, even something seemingly simple as lining up a LCD comes out better when everything is dimensioned and parts are made/cut by machine. Getting comfortable with 3D and 2D CAD has been critical for me to do enclosure work.

If you want to do the enclosure yourself, a 3D printed cover plate (with holes for displays, lights, and connectors) with a clamshell housing is probably the easiest way to go.

Then, add a professionally produced coverlay – Maverick Labels (https://www.mavericklabel.com/products/industrial-labels-and-equipment-labels.html) offers samples. There are many other vendors that do this work – search for “nameplate” and “overlay” to find them.

BTW, https://www.takachi-enclosure.com/ makes nice enclosure products and offers customization services (CNC, coverlay, engraving).

No display, but here’s an example of a project I did with an inexpensive snap-together box from
https://www.budind.com (PC-11476) and a paper + laminate coverlay that I did with a Silhouette machine. In this particular case, I CNC’d the openings in the front cover piece, as it wasn’t a straight plate:

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I make liberal use of Hammond enclosures, as they have a small minimum qty (normally 25) and cost for custom versions (custom = CNC’d) is pretty similar to off-the-shelf. If you have a mill it’s even better because you can do the customizations yourself at prototype phase:

Or use a 3D printer for the end panels. I’ve even 3D printed a full “belly plate”, but here is for example the end plate detail (the ‘belly plate’ on that is also 3D printed):

Using this has given me basically 100% success on the test CNC item Hammond sends back.

If you combine the CNCd cases with laminated vinyl labels (I use a local print shop, but previous threads have good links like ‘Maverick Labels’ that might be more suitable in USA) you basically end up with something that looks as good as “real” test equipment in most cases IMO.

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I’ve used a laminated paper label with a cutout (in the paper) for the window. This was just a one-off, but I assume you could get a self-adhesive label printed with a clear section for the window. I guess it depends how “poke resistant” it needs to be!

Sorry guys, I think that’s only visible on the consultants’ side of the forum. You could ask the the OP to change its category but bearing in mind people may have answered in context of the limited audience it may not be the kindest thing to do. We can extract links into a post on this thread (I’ll try later once I’m on my PC).

Good catch! I updated my post to point out Maverick Labels and the search terms to use to look for other similar vendors.

Just now circled back to this topic. I’ve been playing around with laser etching powder coated metal plates. Pretty amazing stuff. Took me some time to really dial in the process and I am still working on multicolor but I am very happy with the results. The photo is of a 4 mm aluminum panel cut on a CNC machine, powder coated with the semi-gloss black and then etched with a 40W CO2 laser. Note - 4mm because I happened to have it. Much thinner would work. A bit more detail is in my blog on the topic.

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that looks good. i’m looking forward to doing some laser cut metal panels and anodising at home for panels as well. but powder coating seems a lot less of a hassle and still nice finish, great work.

I have thought about anodizing over the years but the acid and mess of it always dissuaded me. Powder coating is so easy and almost no clean up (compressed air to blow the excess dust out the door). Plus, it is a lot tougher than an anodized finish. I can barely make a mark in it with a screw driver.

I have to say I’m more impressed by your powder coating than I am the laser - that seemed really out of reach until I read your blog.