# Heat transfer: Electronic design¶

## Overview¶

The aim of this test case is to validate the following:

• Heat transfer in electronics
• Transient analysis

The simulation results of SimScale are compared with the results presented in [Bruce]. The mesh used was created using first order tetrahedral elements with local mesh refinement algorithm on the SimScale platform.

Open the validation project into workspace

## Geometry¶

The current analysis is carried out on a high-power IC package that is attached between the heatsink base and the PCB substrate as shown in figure below. The components explicitly represented in the model are the die, TIM1, lid, TIM2 and the heat sink base (where TIM = Thermal Interface Material). To proceed with the simulation, only a portion of the geometry is considered with width and length of all components equal to that of the die.

High-power IC package geometry

The simulation ready CAD model with its specific dimensions are as shown below.

Dimensions of all the components
Component Length Width Thickness
Die 13 mm 13 mm 0.50 mm
TIM1 13 mm 13 mm 0.10 mm
Lid 13 mm 13 mm 0.50 mm
TIM2 13 mm 13 mm 0.05 mm
Heat sink base 13 mm 13 mm 6.00 mm

## Analysis type and Domain¶

Tool Type : Code_Aster

Analysis Type : Transient heat transfer

Mesh and Element types :

Mesh information
Mesh algorithm No. of nodes No. of 3D elements Solver
Tetrahedral with local refinements 327326 1045594 Code_Aster

A tet-dominated mesh elements with fine local mesh refinements at the interfaces between the components are as shown in the figure below.

Meshed geometry

## Simulation Setup¶

Material:

Material data information
Component Material Thermal conductivity $$(W/m K)$$ Density $$(kg/m^3)$$ Specific heat $$(J/kg K)$$
Die Silicon 111 2330 668
TIM1 Ag-Epoxy 2.0 4400 400
Lid Copper 390 8890 385
TIM2 Grease Aluminium filler particle 1.0 2500 900
Heat sink base Copper 390 8890 385

Initial Condition:

• Temperature = $$273.15K$$

A power of 1 W is applied to the top surface of the die which is in contact with the TIM. Therefore, the surface heat flux that is applied on the top surface of the die is calculated by dividing the power with respect to the die surface area.

• Surface heat flux = $$5917.1598W/m^2$$ (top of the die)

Convective heat flux:

The cooling effect of the heatsink fins are collectively represented through a heat transfer coefficient that is directly applied to the heatsink base, top surface. Therefore, a convective heat flux boundary condition is used to represent the thermal resistance offered by the heatsink to the surrounding air.

• Convective heat flux = $$20000W/m^2K$$ (heat sink to air top surface)

## Results¶

Most of the temperature rise occurs at the TIM surfaces. The temperature distribution of the IC package is as shown below.

Temperature distribution

Comparison of the SimScale results with that of [Bruce] is as shown below.

Temperature change w.r.t ambient temperature versus time plot comparison with [Bruce] and SimScale simulation results for 3 different location of the model, Die-top, Lid-top and heatsink-bottom

A slight deviation in temperature graphs from [Bruce] with SimScale is due to the approximation error caused during the extraction of temperature values from the digital plots.

## References¶

 [Bruce] (1, 2, 3, 4) Bruce Guenin, “Calculation Corner: Transient Thermal Modeling of a High-Power IC Package, Part 1” Calculation Corner, Computer, IT Products, Number 4, Software/Modeling, Volume 17, December 22, 2011