How to run thermal and stress simulation on a PCB enclosure in the browser

Flux runs thermal and stress simulation from a text prompt in your hardware project. This walkthrough connects a 50 × 30 mm PCB, its 2 W regulator, and the enclosure that holds it. One thermal-pad change reduced the calculated regulator maximum from 172.94 °C to 57.46 °C in a conduction-only aluminum model.

A separate ABS enclosure stress case used a 50 N lid load. It returned a peak nodal-averaged von Mises stress of 5.513 MPa and a maximum displacement of 0.063 mm. The sections below give the exact prompts, model setup, numerical checks, measured time, and Agent Compute Units.

1. Start with the board and enclosure

Keep the board envelope, mounting holes, regulator position, and housing in the same project. The original enclosure request was:

Create a simple sealed ABS electronics enclosure around a 50 x 30 mm PCB with four M3 mounting holes at 3.5 mm inset and a linear regulator dissipating 2 W at the center. Use a practical box, lid, mounting bosses, wall thickness, and sealed lid joint. Save the real 3D model in this project. Provide dimensions, downloadable model links, and a rendered image. Do not order anything or enter checkout.

Flux produced a 25-solid STEP assembly with an approximately 76 × 56 × 27.4 mm envelope. This turn took 1,542.818 seconds and used 4.5 Agent Compute Units. Read Mechanical analysis for the analysis workflow.

2. Define one thermal design change

The thermal comparison uses an aluminum reconstruction of that enclosure. Both cases have the same PCB, regulator, bosses, lid, and small lid pedestal. The baseline leaves a 2 mm empty gap above the regulator. The comparison fills that gap with one thermal pad. This is the exact request:

New conduction-only thermal pair; discard previous cavity models. Use this project's 50x30 mm PCB and 2 W regulator in an aluminum enclosure. Freeze both geometries/properties before solving: copper pours connect regulator to four mounting bosses; lid pedestal leaves a 2 mm gap above a 10x10 mm regulator pad face. Baseline: no thermal pad. Comparison: ONLY add a 2 mm thick, k=3 W/mK pad across that gap to the aluminum lid. All outer surfaces: h=8 W/m2K, ambient 25 C. All inner exposed surfaces adiabatic. NO air volume, internal convection, or radiation. State aluminum/PCB/copper properties and actual contact areas; ensure heat can leave through PCB/copper/bosses in baseline. Run both numerical steady solves, hand-check Rconv=1/(8*outer area) and Rpad=t/(k*A), report maximum/regulator mean C, integrated heat input/output and residual, mesh check, downloadable PNGs and numerical evidence. Do not tune to hit 40-120 C. At most these two solves; no retries. No orders or checkout.

The frozen thermal setup

• Heat source: 2 W generated in a 10 × 10 × 10 mm regulator surrogate with conductivity 20 W/(m K). Reported regulator temperatures refer to this solid.
• Board: 50 × 30 × 1.6 mm, with two explicitly modeled 35 µm copper layers. Each connected copper pattern covers 70% of the usable board area. Copper conductivity is 385 W/(m K); FR4 conductivity is 0.30 W/(m K). The layers exchange heat through the 1.53 mm FR4 core.
• Regulator attachment: an 8 × 6 × 0.1 mm solder layer at 50 W/(m K) joins the regulator to the top copper.
• Enclosure: aluminum conductivity 167 W/(m K). Four bosses lie on the PCB hole axes, at (±21.5, ±11.5) mm. The annular board-to-boss contacts use 500 W/(m² K); their combined mesh area is 66.045 mm².
• Lid joint: an ideal bonded 0.2 mm gasket layer at 0.20 W/(m K), with 2,592 mm² per aluminum/gasket interface. The same joint appears in both cases.
• Pad: 10 × 10 × 2 mm, conductivity 3 W/(m K), with ideal full-face contact over 100 mm² at each end. A 10 × 10 × 0.1 mm lid projection leaves the 2 mm gap in both models.
• Cooling: 25 °C ambient and h = 8 W/(m² K) on all exterior faces, including the bottom. All inner exposed surfaces are adiabatic. The model has no air volume, internal convection, or radiation.
• Numerical setup: quarter symmetry, constant material properties, and one fixed mesh per case. The baseline has 12,555 nodes and 50,989 tetrahedra; the pad case has 12,601 nodes and 51,362 tetrahedra. The modeled copper pattern and lid projection are simulation geometry.

Without the pad, heat travels through solder, top copper, FR4, bottom copper, boss contacts, and the case. With the pad, a second path takes heat directly from the regulator to the lid.

3. Compare temperatures and heat flow

The pad reduced the maximum by 115.48 °C and the regulator volume mean by 114.97 °C. About 87% of the 2 W now leaves the regulator through the pad. The paired turn took 1,420.877 seconds and used 5.0 Agent Compute Units.

Hand-check the heat path

The tagged exterior area is 0.0157456 m². Its convection resistance is 1/(8 × 0.0157456) = 7.939 K/W. At 2 W, the area-weighted outer wall temperature is therefore approximately 25 + 2 × 7.939 = 40.88 °C.

The pad resistance is 0.002/(3 × 0.0001) = 6.667 K/W. At its solved 1.737 W heat flow, the pad drop is about 11.58 K. A regulator temperature above the roughly 41 °C wall, in the mid-50s, is consistent with that path. The finite boss contact alone contributes about 30.28 K/W to the baseline path.

An independent integration of the saved numerical fields reproduced both maxima and regulator volume means. It also reproduced the exterior area and 2 W source. Source-minus-exterior-loss residuals were −1.47 × 10⁻¹⁰ W for the baseline and +8.31 × 10⁻¹¹ W for the pad case.

4. Apply a lid load to the ABS enclosure

The stress example is a separate room-temperature, linear-elastic ABS reconstruction. It uses the original enclosure layout and a 50 N downward lid load. It is not a coupled calculation with the aluminum thermal pair.

Run a structural stress analysis of this enclosure with a total 50 N downward load distributed over the lid and the bottom mounting points fixed. State material properties, load and constraint assumptions. Report maximum von Mises stress in MPa and maximum displacement in mm. Provide a downloadable result image and identify whether this is an actual numerical simulation or an estimate. Do not order anything or enter checkout.

• Material: homogeneous isotropic ABS, Young’s modulus E = 2,000 MPa and Poisson’s ratio ν = 0.35.
• Load: approximately 12.40 kPa uniform downward pressure over the exposed lid top, excluding screw holes, integrated to 50 N.
• Supports: four assumed circular underside patches of radius 2.8 mm, centered at (±21.5, ±11.5) mm. All three translations are fixed.
• Joint: eight ideal bonded lid-stop interfaces. The model uses quarter symmetry and quadratic tetrahedra.

The finest mesh has 206,102 nodes and 128,504 elements. Maximum displacement is near the lid center. Peak stress is at an ideal bonded lid-stop edge. On the last refinement, displacement changed by 0.68% and the peak stress changed by 22.7%. The full-model vertical support reaction is 50.00036 N for the 50 N load.

This numerical stress turn took 1,547.959 seconds and used 3.3 Agent Compute Units.

When to move to Ansys or SimScale

Move to Ansys or SimScale when the design question requires transient heating, convection-heavy airflow, opening or sliding contact, or a certification workflow. Carry the geometry, source power, material properties, support definitions, and result fields into that next study. Keep the electronics and enclosure assumptions together so the next analysis answers the same design question.

For a circuit example, read Simulate circuits with a prompt. For the setup process, read Hardware simulation with scoped approximations and the simulation reference.

FAQs

How do I ask Flux to analyze an enclosure?

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What load produced the ABS stress result?

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