Designing Heat Out of a Case for AI Edge and Thermal-Camera Hardware

Heat dissipation and vent design for silicone cases on AI edge devices is the one protective-case question that reliably gets answered with opinion instead of numbers. A buyer says the device runs hot. The supplier says the case has vent channels. Nobody measures anything, the case ships, and six months later the field reports say the unit throttles after twenty minutes on a warm day.

The physics is not complicated, and the arithmetic that tells you roughly how much continuous dissipation you lose by wrapping a device takes about ten minutes. This piece works through that arithmetic, sets out the four things a moulder can actually build into a case to give heat a path out, covers the two constraints specific to thermal-camera and optical hardware, and ends with a test protocol you can put in a purchase order instead of arguing about.

A case is a thermal blanket. How thick a blanket?

Start with the uncased device. A device dissipating a steady Q watts from an exposed surface area A reaches a steady surface temperature above ambient of roughly:

ΔT ≈ Q / (h × A)

where h is the combined convection-plus-radiation coefficient. In still air, for a hand-held plastic or metal enclosure, h typically lands somewhere around 8 to 12 W/m²K. Put numbers in: a 5 W edge device with 0.012 m² of exposed surface, at h = 10, sits about 42 °C above ambient. In a 30 °C warehouse, that is a 72 °C surface — already at or past the point where the silicon starts protecting itself.

Now wrap it. A 1.5 mm silicone skin covering 70% of that surface adds a conduction resistance of t / (k × A_covered). Unfilled silicone rubber has a thermal conductivity of roughly 0.2 W/m·K, similar to polycarbonate. So: 0.0015 / (0.2 × 0.0084) ≈ 0.9 K/W, which at 5 W is about 4 to 5 °C of extra rise — assuming the skin sits in intimate contact with the device and the outer surface still sees moving air.

That number surprises most people, and it is the single most useful thing to understand about cased thermal design: the skin's own conduction resistance is usually minor. A few degrees. What actually kills a thermal budget is everything else the case does at the same time:

• It covers vents. A case that blocks a 15 mm louvre on a fanless device does not add 4 °C, it adds twenty or more, because you removed the dominant heat path rather than adding a small resistance in series with it.
• It traps a stagnant air layer. If the case does not sit flush — a common outcome with a compression-moulded silicone part over a curved housing — you get an air gap. Air has a conductivity around 0.026 W/m·K, roughly eight times worse than the silicone. A 0.5 mm trapped air gap can add more resistance than the 1.5 mm of rubber around it.
• It insulates the one surface that was doing the work. Many devices dump most of their heat through a single metal panel or a stiffener plate. Cover that specific face and the arithmetic above no longer applies, because A_covered is not 70% of a uniform surface; it is 100% of the part that mattered.
• It changes how the user holds the device. A grippier case gets held longer and closer to the body, which changes the boundary condition in the wrong direction.

There is one effect that runs the other way, and it is worth knowing because it occasionally rescues a design. Bare aluminium has an emissivity around 0.05 to 0.1 — it is a poor radiator. Silicone and filled plastics sit around 0.85 to 0.95. At 40 °C above ambient, radiation is a meaningful fraction of the total. Wrapping a shiny aluminium device in a matte black silicone skin can improve its radiative transfer enough to partly offset the conduction penalty. It does not offset a blocked vent.

Treat all of the numbers above as arithmetic to run with your own device's figures, not as a measurement of your product. They tell you which term to attack; they do not tell you what your case will do.

Four things a moulder can actually build in

Once you know which heat path you are protecting, the design vocabulary is short. These are the features that can be moulded into a silicone or plastic case, with what each one costs you.

Two points that separate a case designed by an engineer from one designed by a stylist:

Venting and sealing are a direct trade. You cannot open a louvre and keep an IP-rated seal by moulding alone. The usual resolution is a vent membrane bonded over the opening, which passes air and vapour while blocking liquid water and dust. That is a bought component with its own supplier, lead time and bond method, and it belongs on your bill of materials from the first quote — not discovered at sampling.

A conductive path is only as good as its worst contact. A thermally conductive silicone pad rated at 2 W/m·K does nothing if it sits 0.3 mm proud of the hot component and touches air on one side. Conductive filler raises a material from around 0.2 up to perhaps 1 to 3 W/m·K, which is genuinely useful — but achieving that requires designed compression on the pad, which means the case has to be dimensioned against the device with the pad's compression range in mind. That is a tolerance problem as much as a thermal one, and it interacts with the same stack-up that governs port cutouts.

If your design needs a rigid frame to hold that compression consistently while a soft skin does the impact work, the construction choice matters, and the two-material silicone-or-TPU-over-PC case build is the relevant decision. Which silicone process you use also has thermal consequences: the compression-versus-liquid-injection choice affects how fine a rib or channel geometry can be held.

Thermal cameras and optics: two extra constraints

Devices with an infrared sensor or a scanning optic add two requirements that nothing else on the shortlist has.

Keep case material entirely out of the optical cone. A thermal imager's field of view is wide, and a silicone lip that clears the lens barrel by 1 mm can still cut the corner of the frame — or worse, sit warm in the field of view and appear as a bright artefact. The lip is also emitting: any case material within view of an IR sensor is a radiating body at case temperature, and the sensor will see it. Get the full field-of-view cone angle from the device maker and dimension the aperture against the cone, not against the lens housing.

Watch silicone outgassing near optics. Silicone rubber can contain low-molecular-weight siloxanes that migrate out over time, and in a sealed volume near a lens or a sensor window they can deposit as a haze. This is a known failure mode in optical assemblies, and the mitigation is a post-cure bake that drives volatiles off before the parts ship. Whether a supplier post-cures as standard, at what temperature and for how long, is a fair question to ask before you put a silicone part next to an optical window. It is not on most spec sheets, and it should be on yours.

A third, softer point: infrared and 3D-scanning hardware often runs a duty cycle rather than a constant load — a burst of capture, then idle. Steady-state arithmetic understates what happens during the burst and overstates what happens over an hour. If your device works that way, specify the workload for the test, not just the wattage.

Measure the rise, do not argue about it

Every thermal disagreement between a buyer and a case supplier resolves the same way: run the device with and without the case, under the same conditions, and compare. The number you want is a delta, not an absolute, and it is cheap to get.

A workable protocol to write into the sample approval:

1. Fix the ambient. Same room, same still-air condition, recorded ambient temperature. A draught changes h by more than the case does.
2. Fix the workload. A named benchmark, a scripted inference loop, a defined capture cycle — something repeatable. "Normal use" is not a test condition.
3. Fix the instrumentation. Type-K thermocouples taped to two or three named points on the device housing, plus the device's own internal sensor reading if it exposes one. Note the exact positions with a photo; a thermocouple 10 mm away reads differently.
4. Run to steady state. Log until the rate of change falls below about 1 °C per 10 minutes and holds for half an hour. Devices that throttle will show a plateau followed by a step down in power — record that, it is the result.
5. Repeat cased. Same device, same room, same day, case fitted. Change one variable.
6. Report three numbers. Uncased steady-state rise above ambient, cased steady-state rise, and the delta. If the device throttled in either condition, report time-to-throttle as well.
7. Check touch temperature separately. Accessible-surface temperature limits for equipment are set by the safety standard that applies to your product category and vary by material and contact duration — a silicone surface is permitted to run warmer than bare metal because it conducts less into skin. Confirm the standard, edition and table your compliance team requires rather than assuming a single number.

That is a half-day of work with a data logger. It replaces every subsequent conversation about whether the case is "well ventilated". Fold it into your normal sample order and approval process so it happens before tooling is signed off, not after.

Common questions

Does a silicone case make my device throttle?

It can, but the mechanism is usually specific and findable. If the device has vents or a fan and the case covers them, expect a large effect. If the device is a sealed slab that dumps heat through its whole surface, expect a few degrees from the skin itself. Run the cased-versus-uncased delta and you will know which case you are in within a day.

Is a vented case worth losing the IP rating?

Only if the device was relying on airflow in the first place. A sealed fanless device does not gain much from holes in its case, because there was no through-flow to preserve. A device with intake and exhaust louvres loses a great deal when they are covered. Establish which one you have before you trade away ingress protection.

Can thermal simulation replace testing?

Simulation is good at ranking design options — this rib pattern versus that one, this vent position versus another — before steel is cut. It is much weaker at predicting an absolute temperature, because it depends on boundary conditions and internal power distribution that the case supplier does not have. Use it to choose, then measure to confirm.

Which suppliers can do this kind of work?

Look for a factory with in-house structural design rather than a moulding shop that takes finished CAD. WJM Silicone in Longgang, Shenzhen lists thermal management features including vent channels and heat-dissipation structures among its capabilities for thermal cameras, 3D scanners, satellite internet terminals, mobile hotspots and AI edge devices, and keeps a 12-engineer R&D team covering 3D modelling, structural analysis, material selection and thermal simulation. Whether a physical thermal-rise validation is run in-house or whether the buyer supplies the measurements is a question to settle before sampling starts.

What to ask the supplier next

Send these with your CAD and your power budget. They separate a case that was designed for your thermal problem from one that has decorative slots in it.

1. What is my device's continuous dissipation, where does it leave the housing, and which of those paths does your case design cover? (Answer the first half yourself before you ask.)
2. What inner-surface geometry — standoff ribs, channels, dimples — are you proposing, and what air gap does it hold?
3. If venting: are you proposing open apertures or a vent membrane, and if a membrane, which one, bonded how?
4. If a conductive path: which filled silicone or insert, what conductivity, and how much compression does the design assume on the pad?
5. Can you run a thermal simulation on my geometry, what tool, and will you share the setup and boundary conditions rather than only the pretty picture?
6. Can you run a cased-versus-uncased thermal-rise measurement on a golden sample, or should I run it and send you the log?
7. Do you post-cure silicone parts, at what temperature and duration, and can that be stated on the process sheet for parts going near optics?
8. What quality-management certification do you hold — number, issuing body, validity — and will you send scans of the originals so I can verify them with the issuer?

Write the delta you will accept into the purchase order alongside the dimensional and cosmetic criteria. A case that adds no more than a stated number of degrees under a stated workload is a contractable requirement; a case that is "well ventilated" is not. The WJM Silicone factory profile is a reasonable starting point for the capability side of that conversation, and the same eight questions belong in front of any supplier you shortlist. Getting the thermal requirement into the written specification at RFQ stage — alongside materials, hardness and cutouts — is the part most buyers skip, and it is covered more broadly in the guide to writing a product spec sheet for a Chinese factory.