COMSOL 6.3 - Importing PCBs — Using the Add-In

This tutorial series demonstrates how to import printed circuit board (PCB) data from the IPC-2581 file format and generate simulation-ready geometry. Key topics include selecting the import type, handling drill layers, creating simplified 3D components and pads, and previewing file content before importing. The tutorials also show how to remove small details, such as short edges, either through Automatic Geometry Cleanup or by simplifying and repairing geometry during import. Geometry finalization is done using Form Union or Form Assembly, followed by mesh generation with adjusted element sizes to resolve small copper trace features using the Free Tetrahedral and Swept mesh generators.

This tutorial, the fourth in the series, uses the PCB to Material data add-in to prepare a PCB for simulation by replacing its detailed internal structure with a space-dependent interpolation function for the material properties. The model also considers the influence of thermal expansion caused by the heat dissipation from several resistors placed on the board.

The first tutorial in the series, Importing PCBs — Generating Shell Traces, shows how to model copper traces as shell geometry, automatically remove small details with Automatic Geometry Cleanup, and use import-generated selections to assign materials.

The second tutorial, Importing PCBs — Creating Component Domains, demonstrates how to import PCBs with extruded copper traces, simplify and repair geometry during import, and create pads for simplified components. The geometry is finalized with Form Assembly and meshed using the Swept operation.

The third tutorial, Importing PCBs — Working with Nets, shows how to use the 2D Preview to selectively import nets and prepare a simplified geometry. It also demonstrates how to partition the board geometry with a bounding box for selected nets.

Model Definition

The IPC-2581 file imported in this tutorial contains a PCB with four copper layers connected by vias.

This model uses the PCB to Material Data add-in available from the Add-in Libraries with the ECAD Import module. Instead of explicitly modeling every trace and via in the geometry, the add-in creates an interpolation function that captures the different material properties across the board. A resulting simplified geometry is then generated by extruding the PCB outline according to the layer stackup defined in the input file. With the user interfaces provided by the add-in, you can choose the material properties for the traces, dielectric regions, and via cores, and select the components to include in the model. In this tutorial, the simplified domains of a few resistors are generated to study the heat dissipation across the board. For the physics setup, assume that a resistor dissipates 62.5 mW of power as heat. Conduction to the PCB and convection to the surrounding air provide cooling. All boundaries are cooled with a heat transfer coefficient of 5 W/(m2·K) that corresponds to natural convection. The thermal conductivities are chosen to be similar to:

•

Alumina, for the resistors

•

FR4, for the dielectric layer of the PCB

•

Copper, for the metal layer of the PCB

The displacements in the Solid Mechanics interface are constrained in such way that the PCB can freely deform while its rigid body motions are suppressed.

The PCB to Material Data Add-In

The settings window for the add-in is used to select the PCB file and to configure the import. First, you can review the layers to consider for the analysis, and if necessary change the layer names and thicknesses. The material properties for skipped copper layers will be replaced with dielectric material properties in the interpolation file. At least one copper or dielectric layer with nonzero thickness needs to be selected for the import.

Next, you can choose the materials for the metal and dielectric layers and the via cores. The default choices are copper for the metal domains and FR4 for the dielectric domains. You can also select custom materials defined under the global Materials node in the model. Make sure that the materials contain at least the following six material properties: heat capacity, density, thermal conductivity, Young’s modulus, Poisson’s ratio, and coefficient of thermal expansion. These properties are necessary for simulations involving heat transfer, solid mechanics, and thermal stress. Note that only constant values are supported.

Once run, the add-in starts with determining an appropriate interpolation grid size that is selected to correspond to the radius of the smallest via in the PCB. If no valid drill layers can be found in the file, a grid size will instead be estimated based on the bounding box of the PCB.

The add-in then processes metal and dielectric layers, evaluating for each layer the material properties on the generated grid, and storing the property values in the file that will be used as input for the interpolation function added later. The interpolation data is written using a grid file format, where the first section of the file defines a regular grid - points inside the PCB volume where the material data is evaluated. The second section contains the material property values. You can easily reuse the interpolation data in other models by creating a copy of the generated file, which you can find in the folder for user files specified under > > .

Interpolation Function

When the processing of the PCB file is complete, an Interpolation feature, inserted under the Definitions branch of the target Component, is used to load the generated file. Another possibility for creating a copy of the interpolation data is by clicking Export from the settings for the interpolation feature.

The interpolation and extrapolation settings determine how values are evaluated between grid points and outside the defined coordinate domain. By default, both use Nearest neighbor, which preserves the discrete layer transitions. You can select one of the other available alternatives to interpolate between points where material property values are defined.

Figure 1: Material properties of the board (top), geometry (bottom) of the inner layer 1.

The heat capacity evaluated at the elevation of the inner layer 1 using the interpolation function set up by the add-in can be compared to the geometry generated for the layer in Figure 1.

Simplified Geometry and Meshing

To generate a simplified PCB geometry, the outline of the board is extruded to match the layer elevations. The geometric domains for the selected components are also created at this stage. Finally, a mesh is generated using the quad and swept mesh generators. The mesh element size is determined based on the interpolation grid size.

Results and Discussions

Figure 2 illustrates the temperature distribution inside the PCB.

Figure 2: Multislice plot of the temperature distribution in the PCB close to heat dissipating components.

Figure 3 shows the displacement magnitude due to thermal expansion.

Figure 3: Magnitude of displacement in the PCB (exaggerated by a factor of 160).

ECAD_Import_Module/Tutorials/pcb_import_addin

Modeling Instructions

From the menu, choose .

New

In the window, click

Model Wizard

In the window, click

In the tree, select > > .

Click .

Click

In the tree, select > .

Click

Add Material

Start by adding materials to the that will be used to define material properties of the PCB.

In the toolbar, click

to open the window.

Go to the window.

In the tree, select > and > .

Click the button in the window toolbar.

In the toolbar, click

to close the window.

Global Definitions

FR4 (Circuit Board) (mat2)

In the toolbar, click

and choose .

Add-in Libraries

In the window, in the tree, select the checkbox for the node > .

Click

In the toolbar, click

and choose > .

PCB to Material Data

In the window, under click .

In the window for , locate the section.

Click .

Browse to the model’s Application Libraries folder and double-click the file audioStreamingPCB.xml.

Locate the section.

The table contains the layer stackup for the PCB, including only the metal, dielectric and drill layers. By default, all layers are selected to be processed by the add-in.

Locate the section.

Here you can choose where the interpolation function and the simplified geometry will be created. By default, the add-in inserts them in a new 3D component. Alternatively, you can select an already existing 3D component.

From the list, choose .

Locate the section.

You can assign different materials for metal and dielectric layers of the PCB. By default, copper is assigned for metal and FR4 for dielectric material. You can use other materials, like composite epoxy materials, metal-core substrates or specialized copper composites defined under . Note that each material must provide six constant values, see The PCB to Material Data Add-In.

From the list, choose .

Locate the section.

In this section you can choose the material properties for the via cores and optionally their plating. By default, via cores are defined by copper material properties, but you can also choose between FR4 or a user-defined material.

From the list, choose . From the list, choose .

Locate the section.

Here you can select the components to import from the PCB file. While these components do not affect the interpolation function, their outline will be extruded to generate domains that can become useful for setting up a simulation, for example when defining heat sources. After the add-in finishes, you could also create component domains manually using the geometry functionality or import from other sources.

From the list, choose . In the table, select the checkboxes for .

Click button in the window toolbar to create material data.

While the add-in is running, the progress window is displayed. The top progress bar shows the total progress of the add-in, while bottom bar shows the progress for the current step that the add-in is working on, for example Processing layer: F.Cu.

Component 1 (comp1)

In the window, click .

Click the

button in the toolbar.

The simplified PCB geometry does not contain any copper traces and vias, as these are instead captured by the interpolation data with the material properties.

Click the

button in the toolbar.

Geometry 1

Import 1 (imp1)

The geometry sequence generated by the add-in includes the operations for creating the simplified representation of the components and the PCB where the board’s outline, thickness and layer distribution are preserved.

In the window, expand the > node, then click .

In the window for , click

The first import node is set up to generate the components. The outlines are read from the file and extruded to create the component domains.

Extract 1 (extract1)

In the window, click .

In the window for , click

Since the import generates domains for all components, the feature is used to retain only those selected earlier.

Click the

button in the toolbar.

Import 2 (imp2)

In the window, click .

In the window for , click

This second import node is configured to import one dielectric layer with the thickness set to zero. The resulting face is used at the next step to extrude the board geometry.

Click the

button in the toolbar.

Extrude 1 (ext1)

In the window, click .

In the window for , click

The distances specified in the Distances table for correspond to the layer elevations in the PCB file. Thus, in the resulting object the separate domains represent the layers from the PCB file.