# SOLIDWORKS Flow Simulation – Two-Resistor Component

Article by Irfan Zardadkhan, PhD, CSWE updated March 9, 2015

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The Two-Resistor Component Model captures the thermal behavior of small electronic packages like Integrated Circuits (ICs). A small package is considered as consisting of two flat solid plates: Junction and Case, which are mounted on the Board. The junction represents a die or a chip. The case represents the die’s case. It is used to simplify the simulation of heat transfer problems involving ICs in an electronic enclosure. It features an increased accuracy compared to using a classic single-resistor model.

In Flow Simulation a Two-Resistor Component Model is modeled simplistically two identical parallelipipedic solid bodies, one on top of the other, and mounted on another solid body representing the board or PCB.

The Junction and Case plates are modeled as a high conductivity bodies with heat-insulating side walls (No material applied to them). So each of them will have an almost uniform temperature.
Sidewalls are insulated (adiabatic). The generated heat only spreads through the package top and bottom

NOTE: You have to make sure the dimensions in the Engineering Database totally match (or are very close to) the dimensions of the solid bodies.

The Two-Resistor Component Model is represented by

• 2 solid blocks of specific dimensions
• Input of power dissipation [W] (Source)
• Thermal resistance [°C/W] between Junction and Case (Rjc) as well as between Junction and Board (Rjb)

The temperature in the Junction body is the highest temperature of the IC. The maximum Junction temperature is typically specified in an IC’s datasheet and is used when calculating the necessary case-to-ambient thermal resistance for a given power dissipation. This in turn is used to select an appropriate heat sink and/or fan if necessary. Using a Two-Resistor Component will therefore allow to ensure the thermal safety of the Junction.

The required mesh density is highly dependent on the size of the component and the amount of heat the specific component is dissipating. The Flow developers recommend the “Grid convergence”
method. Start with a coarse mesh and run the analysis. This is the baseline result. Increase the refinement and rerun the analysis. If the component temperature results change significantly from the baseline result than the more refined mesh becomes the new baseline result. Increase the refinement again and rerun again and compare results to the new baseline results. This is the best method available for meshing the components.

NOTE: The Two-Resistor Component Model is available in the Electronics Cooling Module of the SOLIDWORKS Flow Simulation