Thermal and Dynamic Simulation of Electronic Assembly

Simulated. Designed. Delivered.

Thermal and Dynamic Simulation of an Electronic Assembly

By

Kamalesh Kuduva – Delivery Head, ProSIM

Presented At:Vibration Analysis & Correlation Symposium

IISc, Bengaluru.


IntroductionPurpose of conducting the simulation:

• The electronic component consists of chassis, covers, connectors mosfets, diodes, capacitors, PCB, etc.

• The electronic assembly experiences different types of loads during its operation such as thermal, dynamic and static loading.

• In the recent years the testing and prototyping of the newer designs are simulation driven to reduce the cost and time for the product development.

• Current component under study is the electronic equipment used for defense application. Task at hand is to study the component for thermal and random vibration loading.


Scope To perform FE analysis of electronic component to verify and validate the design for thermal and random loading.

To study the behavior of electronic assembly under following load cases:

Case-1: Thermal Simulation (without fins and with fins)

• Thermal analysis is performed to find thermal hotspots due to heat dissipating from the electronic chips and PCB inside the electronic assembly.

• If temperature exceeds the permissible limit appropriate geometric modification are to be made to reduce the temperature effect.

• Counter measures suggestion : Inclusion of fins reduces the temperature of the entire assembly

Case-2: Random Vibration Simulation (Modal + Random vibration)

• Random vibration is performed to study the electronic assembly behavior for the provided PSD (power spectral density).

• The area under G-acceleration versus frequency response is equal to the square of the standard deviation of the response.

• The stress, displacement and acceleration were to capture on the provided probing location in the electronic assembly.


Coordinate reference:

X = Transverse direction

Y = Vertical direction

Z = Longitudinal direction

Isometric view

Fins and placement of the electronic assembly on the fins

Geometry / FE Model


Load case 1: Modelling Strategy•Geometric cleanup and FE modelling (Solid elements)

•Steady state thermal simulation with natural convection

•Radiation scenario is not considered.

•Ambient temperature at 70 deg C.

•Thermal Conductivity

•Contact conductance at the interface of individual electronic component connected to chassis and cover.

•On external surface of chassis and cover exposed to ambient, natural convection is defined.

•Wattage loading is applied for internal electronic component present inside the cover, chassis and PCB.

•Maximum wattage is dissipated from PCB due to numerous child components present in it.

Load Case Description Analysis Type Acceptance

CriterionReference Value

LC 1 Thermal analysis Steady state thermal analysis Temperature < 105 deg C


Load Case 1: Loading and Convection

Convection Wattage


Temperature plot (without fins)

Temperature contours and hotspot were observed. Excessive temperature was observed on the PCB and the pot cores connected to it.


Temperature plot (with fins)

To reduce the excessive temperature generated in the assembly fins are introduced for thermal management. These fins help in dissipating maximum thermal load as possible. Inclusion of fins reduces the temperature of the entire assembly which comes down to permissible temperature range.


Load case 2: Modelling Strategy

Load Case Description Analysis Type Acceptance Criterion Reference Value

LC II Random vibration analysis Modal + Spectrum analysis von-Mises stress,

displacement and acceleration Stress to be within permissible range

•Geometric cleanup and FE modeling (Solid elements).

•Electronic component masses were matched by adjusting the density.

•Lumped masses were applied on to PCB for accounting masses of child parts present in it

•Material property such as young's modulus, poisson's ratio and density

•Constraining the model at the mounting location in all three translation degree of freedom (X, Y and Z).

•Perform modal analysis for Eigen modes and Eigen values.

•Random analysis is carried out by exposing the electronic component to base acceleration in X, Y, Z and XYZ combined direction.

•Two percent of structural damping is considered for simulation.


Load Case 2: Loading /Boundary condition

PSD curve

Random load excitation location – Mounting location


Load case 2 : Mode shapes

Mode 1- 640 Hz Mode 2-707 Hz Mode 3 - 782 Hz

Mode 4- 1000 Hz Mode 5- 1099 Hz Mode 6- 1250Hz

Mode shapes extracted from modal simulation


Load case 2: Acceleration plot

Logarithmic plot of Acceleration response (g2/ Hz) versus frequency (Hz) at the probe location provided by the customer

X-Direction, RMS = 51.5g Y- Direction, RMS = 259.8g

XYZ Combined, RMS = 319.4g Z-Direction, RMS = 19.3g

Load case Acceleration (g)X-Direction 51.48Y-Direction 259.84Z-Direction 19.269X, Y and Z –Direction 319.4


Load case 2: von-Mises stress plot

Logarithmic plot of von-Mises stress response (MPa)2/ Hz) versus frequency (Hz) at the probe location provided by the customer

Load case Von-Mises (MPa)X-Direction 2.2Y-Direction 11.2Z-Direction 0.28X, Y and Z –Direction 13.8

X-Direction, RMS = 2.2 MPa Y-Direction, RMS = 11.2 MPa

XYZ Combined, RMS = 13.8 MPa Z-Direction, RMS = 0.28 MPa


Load case 2 :Displacement plot

Logarithmic plot of displacement response ((mm)2/ Hz) versus frequency (Hz) at the probe location provided by the customer

Load case Displacement (mm)2/HzX-Direction 4.85e-11Y-Direction 4.85e-11Z-Direction 4.85e-11X, Y and Z –Direction

4.85e-11

X-Direction, 4.85E-11 (mm)2/Hz Y-Direction, 4.85E-11 (mm)2/Hz

XYZ Combined, 4.85E-11 (mm)2/HzZ-Direction, 4.85E-11 (mm)2/Hz


Conclusion•Thermal analysis:

To reduce the excessive temperature generated in the assembly fins are introduced for thermal management.

These fins help in dissipating maximum thermal load as possible.

Inclusion of fins reduces the temperature of the entire assembly which comes down to permissible temperature range.

•Random vibration analysis:

The maximum random response (acceleration) and PSD von-Mises stress, aretabulated at 3 probe locations

It is observed that the peak von-mises stress at one of the probe location (R2) is well with in permissible limits (yield stress 120 Mpa)

•ProSIM has developed expertise in fabrication drawing creation considering manufacturing feasibility

•ProSIM collaborates in iterative procedure with customer in qualification of electronic equipment by actual testing

Thermal and Dynamic Simulation of Electronic Assembly

Engineering

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