Problem Description

This tutorial uses the results from the model created in the Circuit Board Steady-State Heat Transfer Analysis tutorial. If this tutorial was not completed use the Circuit Board Results.ach archive file in your tutorial models folder.
Retain the material properties (thermal conductivity values) that were defined for the prerequisite steady-state analysis. However, additional properties (mass density and specific heat) must be defined for a transient heat transfer analysis. As was done for the steady-state analysis, the material properties are the average of the metallic and non-metallic portions of the circuit board and edge connectors. The properties are based on an assumed 90%/10% proportion of insulating and conducting materials, respectively.
- Board (Part 1): Mass Density = 2.39 x 10^{- 4} lbf · s²/in / in³; Specific Heat = 86,900 J/(lbf · s²/in · °F)
- Chip (Part 2): Silicon, Si. This is a library material, and it already has the required additional properties defined.
- Edge Connectors (Parts 3 through 6): Mass Density = 2.22 x 10^{- 4} lbf · s²/in / in³; Specific Heat = 91,300 J/(lbf · s²/in · °F)
Note: You could perform a more precise simulation by including the metallic and non-metallic parts of the board and edge connectors as separate parts, assigning the appropriate properties to each. For a simpler CAD model construction and analysis example, we use the weighted average of the properties and treat each component as a single, monolithic material.
Start with the temperature profile from the steady-state heat transfer analysis.
The internal heat generation is zero (0) over the first 300 seconds. During this time the assembly is cooling off.
From 300 seconds to 301 seconds, the heat generation ramps back up to 5W (Load Curve Multiplier = 1). Then, heat generation continues at this level for the remainder of the 1200 second simulation event. In other words, the heat generation is off for 5 minutes and on for 15 minutes, for a total event duration of 20 minutes (1200 seconds).
The convection loads remain constant throughout the analysis. Keep the same convection load parameters that were defined for the steady-state analysis.