SOLIDWORKS Flow Simulation Electronics Cooling Part 2: PCB & Two-resistor Components

Welcome back to this discussion about the SOLIDWORKS Flow Simulation Electronics Cooling Module. Find a link to Part 1 Here. In part one we discussed Joule heating. Using my neat CATI Printed Circuit board model we were able to simulate the heat generated from electrical power flowing through PCB busses. In that study, we left the heat generated by the IC chip out of the analysis. The purpose of this blog is to take the analysis a bit further. We will add an actual PCB definition to the board itself as well as add a two-resistor component model to the chip in the center of the board. Both features are exclusive to the electronics cooling module of SOLIDWORKS Flow Simulation.

First, we will add the PCB definition to our study. In order to do this, we need to activate the “Printed Circuit Boards” command on our study tree using “customize tree.” Next, we will add the PCB definition we desire to our board. I will be using a 2S2P (2 signal 2 power) board definition included with the Electronics Cooling Module. These definitions are very specific to the board in use, so the following parameters should be defined for any custom boards.

Notice that there are thermal parameters for both the conductor and insulator of the board, as well as board thickness and total layers. These can be customized through a table for their thickness, percent coverage of conductor and number of layers.

With all the parameters entered, SOLIDWORKS Flow Simulation will now more accurately calculate heat dissipation & conduction through the board. This is a superior method to simply assuming a board is homogeneous orthotropic/isotropic.

The next part of our analysis will focus on the IC chip itself. These chips are often the premier heat generating part on any board. Without the electronics cooling module, the only way to simulate the heat they generate is by applying a volume or surface heat source. The flaw in this method is that it essentially assumes the IC chip is a single homogeneous piece of material.

The two-resistor component allows the heat generation and dissipation to be more accurately simulated. It accomplishes this by dividing the part into a case and junction. Both of these virtual “components” have their own thermal properties and thermal resistances between them. The two graphics below are located in the SOLIDWORKS Knowledge base S-064106.

Example of Case and Junction:

The graphic below shows how the two-resistor component is simulated.

The two-resistor component breaks the chip into case and junction virtual parts and assumes no heat transfer through the sides of the chip. From here, you have heat transfer calculations done at 3 interfaces:

1. Between the top face of the chip and ambient. (Or any interfacing material such as heat syncs)
2. Between the case and junction.
3. Between the junction and the board itself.

For our study, I applied a two-resistor component definition from the Flow Simulation Engineering Database that matches the size of the chip. I applied a 10W power through the chip as well.

Now for the results. See the cut plot below for overall temperatures of the board.

Notice that the heat seems to be dissipating to the sides of the board. This is mostly due to the heat that the PCB conductor busses are carrying, covered in the Previous blog post.

The steady-state temperatures of this chip are much too high for most electronics applications. Mostly due to the lack of a heat sync. We can find out how much energy is being transmitted and to where by using a “Flux Plot.” The Flux plot allows us to see how energy is being transferred from a body to its fluid or solid surroundings.

In this case, you can see that most of the heat in our board is being transferred through the board itself and only a fraction of it is being transferred through fluid convection. To draw more heat from the IC we will add a heat sync in the next blog!

Note: There are no entries for heat transfer through the conductor buses because the side walls of the chip are adiabatic.

A special output from the two-resistor component is the ability to plot the board, junction, and case temperatures separately. Below are goal plots for this board heating up for 2 minutes.

The global trends are the same, as we would expect. But the actual values are different. Most notably, the board interface is about 100 degrees cooler than the IC itself. As with any of my SIM blogs, they are not complete without a neat animation!

I hope this blog has enlightened you to some more capabilities of the SOLIDWORKS Flow Simulation Electronics Cooling Module. There is still more to see! Keep an eye open for part 3 where we will add a heat sync and start talking about heat pipes and other capabilities.

Matt Sherak
Applications Engineer, Simulation
Computer Aided Technology, LLC