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    SimScale DocumentationValidation CasesValidation Case: Thermal Effects in High Power LED Packaging

    Validation Case: Thermal Effects in High Power LED Packaging

    This LED cooling validation case, for high power LED packaging with one heat sink, aims of to validate the following parameters:

    • Heat transfer solver
    • Multiple materials and contact heat transfer

    The simulation results of SimScale were compared to the theoretical results presented in [Adam]\(^1\).

    View Project

    Geometry

    The typical geometry used for the case is as follows:

    geometry model validation case thermal high power led packaging
    Figure 1. Main dimensions of the quarter model of the heat sink, with shown gap of 10 mm.

    It represents a heat sink of dimensions 100 x 100 \(mm\) with 25 LEDs attached through Thermal Interface Material (TIM) patches of dimensions 7 x 7 x 0.1 \(mm\). Only one-quarter of the geometry is modeled to leverage the symmetry. Gaps of 10, 5, and 1 \(mm\) between LEDs were tested, with each model shown below for comparison:

    geometry variations validation case thermal high power led packaging
    Figure 2. Models with gaps between LEDs of 10, 5, and 1 mm (left to right).

    Analysis Type and Mesh

    Tool Type: Code Aster

    Analysis Type: Heat transfer, linear, steady-state.

    Mesh and Element Types:

    CaseGap
    \([mm]\)    		Mesh TypeNumber of
    Nodes    		Element Type
    A101st order tetrahedral828917Standard
    B51st order tetrahedral824569Standard
    C11st order tetrahedral824369Standard
    Table 1. Mesh details.

    The meshes were computed using the Tet-dominant algorithm with manual mesh sizing and local refinements for the TIM regions. The goal was to keep 2 elements across the thickness of the thin-walled parts, like the heat sink fins and TIM patches.

    tetrahedral mesh validation case thermal high power led packaging
    Figure 3. Typical tetrahedral mesh for 5 \(mm\) gap model.
    tetrahedral mesh detail validation case thermal high power led packaging
    Figure 4. Typical mesh refinement showing local details of the tetrahedral elements on a TIM body.

    LED Performace Packaging

    Material:

    • Aluminum Heat Sink:
      • Density \( \rho = \) 2700 \( kg/m^3 \)
      • Thermal conductivity \( \kappa = \) 202.40 \( W/(mK) \)
      • Specific heat \(C_p = \) 897 \( J/(kgK) \)
    • TIM (Thermal Interface Material):
      • Density \( \rho = \) 7870 \( kg/m^3 \)
      • Thermal conductivity \( \kappa = \) 0.22 \( W/(mK) \)
      • Specific heat \(C_p = \) 480 \( J/(kgK) \)

    The thermal conductivity of the TIM was computed to achieve a total resistance of 9 \(K/W\), according to [INFINEON]\(^2\) with the relation:

    $$ \kappa = \frac{t}{RA} $$

    Where:

    • \(\kappa\) is the conductivity, \( W/(mK) \)
    • \(t\) is the thickness of the body, 0.1e-3 \(m\)
    • \(R\) is the thermal resistance, 9 \(K/W\)
    • \(A\) is the cross-sectional area, 4.9e-5 \(m^2\)

    Boundary Conditions:

    • Heat Flux Load:
      • Surface heat fluxes of 1, 3, and 5 \(W\) per LED applied to the top surfaces of TIM bodies.
    • Convective Heat Flux:
      • Convective heat fluxes with heat transfer coefficients of 10, 25, 50, 75, and 100 \(W/(m^2K)\) with reference temperature of 300.15 \(K\) on all heat sink faces except the contact patches with TIM bodies and symmetry planes.

    The following table relates the simulation runs for each case and the combinations of applied boundary conditions:

    RunLoad
    1 \([W]\)    		Load
    3 \([W]\)    		Load
    5 \([W]\)    		Convective flux
    10 \([\frac{W}{m^2K}]\)    		Convective flux
    25 \([\frac{W}{m^2K}]\)    		Convective flux
    50 \([\frac{W}{m^2K}]\)    		Convective flux
    75 \([\frac{W}{m^2K}]\)    		Convective flux
    100 \([\frac{W}{m^2K}]\)
    1XX
    2XX
    3XX
    4XX
    5XX
    6XX
    7XX
    8XX
    9XX
    10XX
    11XX
    12XX
    13XX
    14XX
    Table 2. Simulation runs and their respective boundary conditions matrix.

    Reference Solution

    The reference solution is of the analytical type, as presented in [ADAM]\(^1\). It is given in terms of the temperature at the center point as a function of the thermal load and convection coefficients.

    Result Comparison: High Power LED Packaging

    Comparison of temperature at the mid point is shown for each case:

    results comparison validation case thermal high power led packaging
    Figure 5. Results comparison for Case A.
    results comparison validation case thermal high power led packaging
    Figure 6. Results comparison for Case B
    results comparison validation case thermal high power led packaging
    Figure 7. Results comparison for Case C

    The deviation of the results with respect to [ADAM]\(^1\) in the cases of gap 5 mm and 1 mm can be attributed to a non-uniform temperature distribution at the base of the fins:

    temperature plot validation case thermal high power led packaging
    Figure 8. Temperature contour plot for Case C, Run 12: 1 mm gap, 5 W/LED load and Convection coefficient of 50.

    Tutorial: Thermal Analysis of a Differential Casing

    References

    • Christensen, Adam, and Samuel Graham. “Thermal effects in packaging high power light emitting diode arrays.” Applied Thermal Engineering 29.2 (2009): 364-371.
    • “Thermal Resistance Theory and Practice – Infineon” http://www.infineon.com/dgdl/smdpack.pdf?fileId=db3a304330f6860601311905ea1d4599

    Note

    If you still encounter problems validating you simulation, then please post the issue on our forum or contact us.

    Last updated: March 22nd, 2021

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