Keep the module's factory thermal interface unless its manufacturer documents an alternative. Build a controlled, clamped conduction path from that interface through the enclosure to the external cold plate. Treat every joint as a thermal resistance, and verify the complete assembly in its installed orientation. A thick metal base alone does not establish that the module will stay within its temperature limits.
Define the complete heat route
Start with a section drawing showing every layer between the module and the external heat sink. A typical route contains:
- The module's internal thermal assembly and exposed mating surface.
- A thermal interface material between the module and an enclosure pedestal or spreader.
- The enclosure base, including any lateral spreading distance.
- A second thermal interface between the enclosure and the external deck.
- The deck and its connection to the system that ultimately removes heat.
A separate spreader adds another joint unless it forms an integral part of the enclosure. Include coatings, electrical isolation pads, and adapter plates wherever they interrupt the route.
Do not assume the entire module power passes through its exposed thermal surface. Some heat may enter the carrier board or adjacent components. Establish those paths from manufacturer documentation, then include carrier-board losses in the enclosure heat balance.
For the underlying resistance calculation, use heat sink thermal resistance in sealed enclosures. The additional task here is connecting those resistances into one module-to-deck assembly with controlled mechanical interfaces.
Set the cold plate boundary before choosing metal
The cold plate temperature must be a specified operating condition, not an assumption that the deck stays near ambient. Its temperature can rise because of other equipment, limited cooling capacity, or resistance between the deck and its ultimate sink.
Specify the highest deck temperature directly beneath the enclosure at the required continuous load. Also identify startup conditions and how long that temperature can remain elevated.
For a hypothetical module dissipating 75 W through its mating surface, suppose that surface must remain below 185 °F [85 °C]. If the local deck can reach 131 °F [55 °C], the available rise is 54 °F [30 °C]. The maximum resistance between those two surfaces is:
R_path = (85 - 55) / 75 = 0.40 K/W
This is a design example, not a module temperature specification. Obtain the permitted mating-surface temperature and its measurement location from the module manufacturer.
The 0.40 K/W allowance includes both external interfaces, enclosure conduction, and spreading between their footprints. It does not include the module's internal junction-to-surface resistance because the starting limit is already at the mating surface.
If your limit is instead a semiconductor junction temperature, include the appropriate documented internal thermal model. Do not substitute a case temperature for a junction limit or apply one component's resistance to every device.
Allocate less than the full calculated allowance to the nominal design. Leave an explicit margin for power uncertainty, assembly variation, measurement error, and interface aging.
Size the interfaces, not just the enclosure wall
For a uniform interface layer, the bulk conduction estimate is R_TIM = t / (k × A). Here, thickness is in metres, conductivity is in W/(m·K), and area is in square metres.
Consider a hypothetical interface measuring 2.95 × 2.87 in [75 × 73 mm]. A compressed thickness of 0.020 in [0.5 mm] and conductivity of 3 W/(m·K) give approximately 0.030 K/W. At 75 W, that layer's calculated bulk temperature rise is about 4.1 °F [2.3 °C].
That estimate excludes surface contact resistance and assumes uniform heat flow across the stated area. A small internal heat source, uneven pressure, or incomplete contact can produce a larger temperature rise.
Use the interface manufacturer's thermal impedance data at the intended compressed thickness and pressure when available. A conductivity value alone does not establish installed performance.
Apply the same scrutiny to the enclosure-to-deck interface. A large enclosure footprint does not guarantee a large effective contact area. Bowed surfaces, raised mounting feet, recessed bases, or perimeter-only contact can leave most of the base thermally disconnected.
For the metal route, distinguish direct through-thickness conduction from lateral spreading. At room temperature, 6061 aluminum has thermal conductivity around 167 W/(m·K). Common stainless enclosure grades are roughly 14–16 W/(m·K). These are representative material values, not finished-enclosure performance guarantees.
A stainless shell may suit the environment while requiring a separately engineered conduction route. Do not assume an aluminum spreader automatically compensates for a long stainless bottleneck. The geometry matters, as explained in sealed enclosure conductive cooling through the wall.
Control pressure without loading the circuit board
Thermal contact requires repeatable compression, but more tightening is not automatically better. Excessive load can distort the module, carrier board, enclosure base, or factory thermal assembly.
Obtain the module manufacturer's permitted attachment locations, loading limits, and mounting sequence. Obtain the interface supplier's recommended compression range and pressure-dependent performance data.
Design the stack around those limits:
- Define the minimum and maximum assembled gap, including machining tolerances and surface flatness.
- Select an interface that accommodates that gap within its approved compression range.
- Provide a structural load path that does not use the circuit board as an uncontrolled spring.
- Use documented stops, spacers, or compliant fasteners where needed to control compression.
- Check differential thermal expansion across the full operating temperature range.
Fastener torque is an assembly control, not a direct measurement of interface pressure. Thread friction, lubrication, and fastener geometry affect the resulting clamp load.
Retain the factory thermal assembly unless the module manufacturer documents a supported replacement approach. Removing it changes more than one resistance. It can also change component contact heights, load distribution, electrical clearances, and cooling of secondary devices.
When checking the tolerance stack, include the enclosure mounting arrangement. A deck attachment that bends the base can change the module interface after an otherwise acceptable bench assembly.
Separate orientation effects from airflow effects
Solid conduction does not require gravity or airflow. An inverted metal conduction path can work if contact, clamping, and boundary temperatures remain controlled.
A heat pipe is different. Its performance depends on its internal construction, operating temperature, heat load, and orientation. Some designs tolerate adverse gravity well; others lose transport capacity. An external drawing alone does not establish those limits.
Do not infer that an enclosed heat pipe needs surrounding air to operate. Its condenser needs a sufficiently cold heat-rejection path, which can be a solid connection. However, removing airflow may expose other module components that previously depended on air cooling.
Ask the module manufacturer to confirm whether its published thermal data cover the exact assembly and orientation. Request the specified measurement locations and any limits on the external cooling interface.
An inverted test under terrestrial gravity does not qualify hardware for zero gravity. Likewise, a conduction-cooled installation is not automatically suitable for vacuum. Vacuum introduces separate concerns about materials, outgassing, interface behavior, and heat rejection.
For an inverted terrestrial installation, test that orientation with the actual interface materials and mounting hardware. Do not take credit for internal air circulation if the application requires operation without convection.
Validate what component ratings do not cover
A module power rating does not prove that your enclosure can remove that power. Interface data also do not qualify the assembled path through the enclosure and deck.
Test the completed mechanical stack with representative electrical operation. Use the intended carrier board, cable arrangement, base finish, interface thickness, and fastener procedure.
A useful validation sequence is:
- Record the assembly dimensions, interface materials, compression controls, and fastener settings.
- Instrument the accessible module surface, both sides of significant joints, enclosure base, and local deck.
- Use manufacturer telemetry for internal temperatures where available, while respecting its measurement limitations.
- Apply representative sustained workloads and the highest credible simultaneous carrier-board load.
- Hold the deck at its worst specified operating temperature and allow temperatures to stabilize.
- Repeat in the installed orientation and across representative tolerance extremes.
- Recheck after the assembly and environmental cycling expected in service.
Keep sensors out of compressed interfaces unless their installation is specifically designed for that measurement. A trapped sensor can create the gap you are trying to measure.
Compare measured temperature drops with the resistance budget. A large drop across one joint points toward contact, compression, or interface thickness rather than insufficient metal elsewhere.
Watch for throttling during testing. A module that reduces its power can appear thermally acceptable while failing the required processing load. Record both temperatures and delivered performance.
The broader module integration issues are covered in conduction cooling for a hot single-board computer. This validation must also include the final deck connection, not just the module and enclosure on a bench.
Keep sealing, condensation, and bonding in the design
Thermal hardware must not create an uncontrolled leak path. Through-bolts, removable base plates, and thermal inserts need engineered sealing details compatible with the exposure.
Use mounting screws through an outdoor enclosure without leaks when deck attachment penetrates the enclosure boundary. Do not count on thermal grease to serve as a water seal.
A cold deck can also pull interior surfaces below the trapped air's dew point. Check startup, shutdown, and unpowered conditions, especially when the deck operates below ambient temperature. The mechanism is explained in cold-surface condensation inside an enclosure.
Electrical isolation and protective bonding require separate decisions. If a dielectric thermal pad is required, include its thermal resistance and qualified electrical properties. Do not assume thermal contact provides a reliable protective bond. Use the enclosure grounding and bonding guide for that design.
For our custom enclosures, ratings are manufacturer ratings for the specified design; the enclosures are not UL listed. Environmental ratings do not establish thermal performance or vacuum suitability.
What to specify for the enclosure drawing
A quote request should define the thermal interface as a controlled mechanical feature, not simply request a thicker bottom. We build custom enclosures with customer-defined material, dimensions, and cutouts, starting from one piece.
Include the following information with the enclosure requirements:
| Drawing or requirement | Information to provide |
|---|---|
| Module interface | Approved mating surface, contact footprint, mounting points, and allowable loads |
| Heat load | Continuous module dissipation, transient duty, and carrier-board losses |
| Cold boundary | Maximum local deck temperature and how that condition is maintained |
| Resistance budget | Permitted module-surface-to-deck resistance, with design margin |
| Metal route | Base material, pedestal geometry, spreading distance, and any separate joints |
| Contact surfaces | Flatness, finish, coating exclusions, and inspection requirements |
| Interface materials | Material identification, compressed thickness range, and compression requirements |
| Attachment | Fastener pattern, structural load path, access, and assembly controls |
| Installation | Operating orientation, deck geometry, environment, and electrical isolation requirements |
| Acceptance | Temperature limits, workloads, sensor locations, and stabilization criteria |
Keep thermal contact lands distinct from gasket lands and mounting datums on the drawing. That makes inspection and assembly repeatable without treating a sealing surface as an assumed heat-transfer surface.
Approve the thermal stack, structural loads, and sealing arrangement together. Changing any one after drawing approval can invalidate the assumptions behind the other two.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Should the factory thermal plate remain on the module?
Keep the factory thermal plate unless the module manufacturer documents a supported alternative. Removing it changes component contact, loading, and the internal thermal model. Design your enclosure interface around the approved mating surface and request clarification when the published thermal data do not cover your installation.
Will an inverted module work without airflow?
Solid conduction does not depend on gravity, but contact pressure and mechanical loading still matter. Internal heat pipes can have orientation-dependent limits. Validate the complete assembly in its installed position and obtain manufacturer confirmation that the module's thermal data apply to that orientation.
How do you calculate the allowed module-to-deck thermal resistance?
Divide the permitted temperature difference between the module mating surface and local deck by the heat passing through that path. Include both external interfaces, metal conduction, and spreading. If the temperature limit is at a semiconductor junction instead, include the applicable documented internal thermal resistance.
Does a large enclosure base guarantee good contact with the cold plate?
A large footprint only helps where the surfaces make effective thermal contact. Flatness, base distortion, interface thickness, and clamp loading determine that contact. Measure the assembled temperature drop and specify the contact geometry rather than assuming the enclosure's outside dimensions define its heat-transfer area.
