Week 9 - PCB Thermal Simulation

Printed Circuit Board (PCB) Flow and Thermal simulation:

1. Introduction:

Stands for "Printed Circuit Board." A PCB is a thin board made of fiberglass, composite epoxy, or other laminate material. Conductive pathways are etched or "printed" onto the board, connecting different components on the PCB, such as transistors, resistors, and integrated circuits.

PCBs are used in both desktop and laptop computers. They serve as the foundation for many internal computer components, such as video cards, controller cards, network interface cards, and expansion cards. These components all connect to the motherboards, which is also a printed circuit board.

While PCBs are often associated with computers, they are used in many other electronic devices besides PCs. Most TVs, radios, digital cameras, cellphones, and tablets include one or more printed circuit boards. While the PCBs found in mobile devices look similar to those found in desktop computers and large electronics, they are typically thinner and contain finer circuitry.

2. Problem Description:

A PCB board, library files, and traces are imported to create the model. The model is first solved for conduction only, without the components and then solved using the actual components with forced convection.

2.1. Modeling:

1. Create a new project
2. Import board layout *.bdf & *.ldf (The board and the associated library files have to be chosen at this step and the trace file can be imported later.)
3. Form the nonconformal assembly
4. Import ECAD file (*.anf) A1.anf can be found in the folder containing the input files downloaded for his tutorial.
5. Once the import process is completed, you can edit the layer information in the Board layer and via information panel (metal layers are pure Cu and the dielectric layers are FR-4.)
6. Enter the layer thickness as shown in the table below.

Layer No.	Layer Thickness (mm)
1	0.04
2	0.45364
3	0.062
4	0.467
5	0.055
6	0.442
7	0.045

• As per the guidelines provided in the challenge, we have imported the IDF file and also inserted a .anf file into the PCB.
• The above picture represents the layer thickness provided in the challenge is used and created the layers and at the same time also created the traces on the layers.

7. Specify Grid density by size (0.508 mm X 0.508 mm)

• We can see the density of the grid allocated by rows and columns as 0.508 * 0.508.

Conduction only model: Here in this part we only study the conductivity of the PCB, by giving some amount of heat flux to the plates allocated beside the PCB.

3. Meshing & BC setting:

1. consider a board without any components. Make all objects (including the openings) inactive except the BOARD_OUTLINE.1 object.
2. Select the cabinet and select Autoscale from the Edit window to make the size of the board and the cabinet the same.

• By autoscaling the cabinet we can have a compact geometry, which makes the job easy for us to conduct the simulation. The above coordinates represent the geometrical representation of a PCB.
• Place two heat walls beside the PCB in the direction of Z in the cabinet. Walls are Min Z, and Max Z.

3. Min z: Temperature from the External conditions drop-down list, and keep the ambient temperature (20°C).

• Ambient temperature is maintained on the wall surface to keep the PCB at the ambient temperature from one side.

4. Max z: specify a Heat flux of 20000 W/m2 in the Thermal specification

• A 20000 W/m2 heat flux is applied on the other sidewall of the PCB. The amount of heat flux given is generally coming from the electric components.

5. The rest of the sides are insulated. The board will be simulated using a conduction-only model.

6. Generate mesh. Specify a Max element size for X, Y, and Z as 2.032, 2.032, and 0.05 mm respectively, and a Minimum gap for X, Y, and Z as 1, 1, and 0.01 mm respectively.

• Mesh assemblies separately is toggled to achieve the non-conformal mesh.

4. Numerical setting:

1. Basic parameters: Flow & Radiation is off

• The flow specification is toggled off because in this case we only calculating how the conduction is behaving on the PCB while the heat flux is applied.
• The radiation toggle is also set to off because here we are only calculating the conduction part. So, we are neglecting the convection and radiation terms.
• The flow regime is set to the laminar because the flow (velocity) is neglected.

• The mesh is well arranged for the problem to be solved. Here we no cross-sections of mesh lines grid points etc.
• As the .anf file is included, we have given 7 layers of the PCB inside. So we need to see whether the inside layers meshed properly or not.

• We can see in the above figure that all the layers properly mesh inside the PCB.

2. set no of iterations 500 and convergence criteria for energy to 1e-12

• The number of iterations are set to 500 to see the stability of the solution. But actually the 500 iterations are not needed. The solution is converged in 3 iterations only.
• The Energy convergence criteria is set to 1e-12, by using this number the accuracy of the solution increases.

3. Temperature Linear solver: F cycle is selected for Type Enter 1e-6 for both the Termination criterion and Residual reduction tolerance

4. Select Double for the solver Precision.

5. Save the model.

6. Solve the model.

• An F type linear solver is used for the temperature and the termination criterion and residual reduction tolerance is set to 1e-6.
• Actually the F cycle linear solver is the process of applying the multigrid method to the problem domain.
• A double is used for the solver precision.

5. Examine and post-process the results:

1. view the traces in three different ways, i.e. single color, color by layer, or color by trace

• In electronics, a signal trace on a printed circuit board (PCB) is the equivalent of wire for conducting signals. Each trace consists of a flat, narrow part of the copper foil that remains after etching or printing.
• Printed circuit boards are typically made with copper. Depending on the requirements, the copper is plated to a substrate and carved away to expose the design of the board. Since there are multiple layers, they must be lined up and bonded together for a secure fit.

• The above figure represents the traces of the PCB on different layers we are imported into it.
• By using one color we cannot see the difference in different layers. So it is always better to visualize the layers and traces in different colors.

• Visualization of the layers and traces still a little difficult using the color - by - layers.

• The above figure seems like seeing the traces and dividing layers is easy when we put the traces in color-by-layers.
• In the above figure, we can see where the power cables are passing, from where the traces lines are connected to, signaling to process from one component to another, etc.

2. View the fraction of metal traces based on the grid density:

• The metal fraction of the PCB gives us an estimation of what's the copper content in the PCB and what's the FR4 content in the PCB.
• This case setup gives us the visualization of the metal fraction which is effective in understanding the PCB characteristics more.

• So, in the given PCB we have implemented the total seven number of layers in it.
• We have top and bottom layers on both sides of the PCB, inside of PCB we can see the other five layers.
• The below figure is the top side of the PCB. The metal fraction is ranges from 0 to 1.

• The below figure shows the metal other than the copper, the other metal has seen in the figure is FR4.

• The red color is seen on the layer is the metal content provided on the top layer of the PCB. Here the material we considered is copper.
• The blue color refers to other materials.

• The figure is shown above is the second layer of the PCB, this layer is called as metal-internal-1.
• Here we can see the content of the copper and at the same time the copper content in the traces also.

• The above figure represents the third layer of the PCB. Here we can see there is nearly zero percent of the metal components are there except the keyholes provided for the screw fitting.
• The blue material showing in the figure is FR4.

• Here we can see again a lot of metal component is provided in this layer. Means, we are providing the metal layer by layer alternatively.
• The other figure also the same as these, which are shown below.

• The figure shown above is the bottom layer in the PCB. Here we can see how the amount of metal percentage is varied across the layer.

3. The plane cut Point and normal. Make sure that PX, PY, PZ are 0, 0, and 0.78232, respectively, and NX, NY, and NZ are 0, 0, and 1, respectively.

• The coordinates provided above takes us to the middle of the Z-plane in the contour plot.
• But some of the contours will not come to see while using these coordinates. So, we can adjust these coordinates according to the convenience.

4. Temperature contour

• Here we changed the coordinate system of the z-plane to view the minimum and maximum temperatures on the geometry obtained.

• The minimum temperature is shown as 20 degrees centigrade which is an ambient temperature we have given as an initial condition.
• The maximum temperature is recorded at the bottom of the PCB, where we provide the power to the PCB through power adopters. The max. temperature recorded is 109.4 degrees centigrade.

Temperature animation: https://youtu.be/QsUohaGp2mI

5. K_Z contour:

• The thermal conductivity of the geometry represents how the heat is conducted from one layer to another layer.

• We can see from the above figure that the minimum thermal conductivity recorded in terms of 0.35 W/m-k. Which is acceptable.
• FR-4 has a poor thermal conductivity of 0.25 W / m-K; the thermal insulance factor of a 0.7-mm FR-4 layer is 2040°C-mm2 / W. In the IMS PCB, the thermal insulance factor of a 0.152-mm dielectric layer of thermal conductivity 3 W / m-K is 50°C-mm2 / W. (web source).
• So, the least thermal conductivity recorded is for the material FR-4.
• The maximum thermal conductivity recorded as 387.6 W/m-k, which is the same for the taken material in the simulation.

Thermal Conductivity animation: https://youtu.be/rlabU4u-F2E

Force convection model: To visualize the flow over the geometry and to see how the heat is dissipated when the flow is attached to the geometry, we need to perform the Forced convection problem over the geometry.

• As we have inactivated all the components except the boundary line component to study the conduction only problem by attaching two heat plates beside the PCB.
• Now inactive those heat plates and active all the components in the geometry to study the forced convection problem.

• We have removed some components from the geometry which doesn't have shown any effect on the flow or thermal simulations.
• We have kept only those components that abstract the flows, changed the direction of the flow, change in temperature.

1. Meshing & BC setting:

1. put the actual components back into the model

2. Highlight the two wall objects created for the “conduction only" model and drag them into the Inactive folder. Click on the Cabinet and Autoscale it from the Edit window.

• After auto-scaling the cabinet, provide the properties for the cabinet. Place the openings for the cabinet in the x-direction for the flow entry and exit.
• Place the two heat walls in the Z-direction for the heat generation from bottom side and maintaining the ambient temperature on the top of the PCB.

3. assign an X Velocity of -1.5 m/s for Max-x side of the cabinet, and 0 m/s for the Min-x side.

4. Generate mesh. Specify a Max element size for X, Y, Z as 9.5, 7, and 0.7 mm respectively.

• The max elements size for the meshing is maintained
• The mesh is perfectly distributed for all the components in the geometry. Even we have applied to mesh separately option, still there is some mesh bleeding in the mesh. But that doesn\t affect the solution.
• The shown mesh dense in the below figure has meshed for the heat sink.

• A mesher-HD type mesh is selected with the given max and min element size provided in the problem.
• The mesh separately option is toggled because we have considered PCB and it's alls as one assembly for the better solution.

2. Numerical setting:

1. Basic parameters toggle on the Flow button. Keep and choose Turbulent and Zero equation for the flow regime

• The flow option is toggled on for the problem because we have to calculate the velocity and behavior of the temperature inside the problem domain.
• The turbulent equation is set to the Zero equation.

2. set no of iterations 500 and convergence criteria for energy to 1e-12

• The number of iterations had to set for the 500 iterations, but the solution is getting converged after 280 iterations.
• So, the case set up is calculated for 300 iterations.
• For getting accurate results in case of the temperature, we have provided the convergence criteria of energy as 1e-12.

3. Temperature Linear solver: F cycle is selected for Type Enter 1e-6 for both the Termination criterion and Residual reduction tolerance

• An F type linear solver is used for the temperature and the termination criterion and residual reduction tolerance is set to 1e-6.
• Actually the F cycle linear solver is the process of applying the multigrid method to the problem domain.
• A double is used for the solver precision.

4. Select Double for the solver Precision.

5. Save the model.

6. Enable Sequential solution of flow and energy equations

7. Solve the model.

3. Examine and post-process the results:

1. view the traces in three different ways, i.e. single color, color by layer, or color by trace

• In electronics, a signal trace on a printed circuit board (PCB) is the equivalent of wire for conducting signals. Each trace consists of a flat, narrow part of the copper foil that remains after etching or printing.
• Printed circuit boards are typically made with copper. Depending on the requirements, the copper is plated to a substrate and carved away to expose the design of the board. Since there are multiple layers, they must be lined up and bonded together for a secure fit.

• The above figure represents the traces of the PCB on different layers we are imported into it.
• By using one color we cannot see the difference in different layers. So it is always better to visualize the layers and traces in different colors.

• Visualization of the layers and traces still a little difficult using the color - by - layers.

• The above figure seems like seeing the traces and dividing layers is easy when we put the traces in color-by-layers.
• In the above figure, we can see where the power cables are passing, from where the traces lines are connected to, signaling to process from one component to another, etc.

2. View the fraction of metal traces based on the grid density:

• The metal fraction of the PCB gives us an estimation of what's the copper content in the PCB and what's the FR4 content in the PCB.
• This case setup gives us the visualization of the metal fraction which is effective in understanding the PCB characteristics more.

• So, in the given PCB we have implemented the total seven number of layers in it.
• We have top and bottom layers on both sides of the PCB, inside of PCB we can see the other five layers.
• The below figure is the top side of the PCB. The metal fraction is ranges from 0 to 1.

• The below figure shows the metal other than the copper, the other metal has seen in the figure is FR4.

• The red color is seen on the layer is the metal content provided on the top layer of the PCB. Here the material we considered is copper.
• The blue color refers to other materials.

• The figure is shown above is the second layer of the PCB, this layer is called as metal-internal-1.
• Here we can see the content of the copper and at the same time the copper content in the traces also.

• The above figure represents the third layer of the PCB. Here we can see there is nearly zero percent of the metal components are there except the keyholes provided for the screw fitting.
• The blue material showing in the figure is FR4.

• Here we can see again a lot of metal component is provided in this layer. Means, we are providing the metal layer by layer alternatively.
• The other figure also the same as these, which are shown below.

• The figure shown above is the bottom layer in the PCB. Here we can see how the amount of metal percentage is varied across the layer.

3. The plane cut Point and normal. Make sure that PX, PY, PZ are 0, 0, and 0.78232, respectively, and NX, NY, and NZ are 0, 0, and 1, respectively.

• The coordinates provided above takes us to the middle of the Z-plane in the contour plot.
• But some of the contours will not come to see while using these coordinates. So, we can adjust these coordinates according to the convenience.

4. Residual and Monitor points:

• Monitor points have been set to some of the components. So that we can see the temperature is stabilizing or not for the chosen components.

• We can conclude that the solution is converged by seeing the residual plot. Here we did not see any up's and clusters in the energy, continuity, or velocity residuals.

• By seeing the temperature monitor points, we can conclude that after the iteration number 270, the solution gets converged.

5. Temperature contour:

• Here we changed the coordinate system of the z-plane to view the minimum and maximum temperatures on the geometry obtained.

• Here in this contour, we are not able to see the max and min temperatures because of the usage of the given coordinates.
• So, to see the max and min temperature and locations of those, here provided the animation for that.
• But we can say the max.temperature recorded is 122.7 degrees centigrade by observing the temperature legend.

Temperature Contour: https://youtu.be/ZCQfrE0SoA8

6. Velocity Contour:

• We have given a -1.5 m/s velocity to the Min-x side for the generation of flow inside the problem domain.

• From the above figure, we can say that the max.velocity is 7.8 m/s and the given velocity is seen in the range of the velocity legend.
• We can see where the max and min velocities are located inside the problem domain.

• Here in this picture, we can have more clarity about the way velocity is behaving inside the problem domain.

Velocity Animation: https://youtu.be/Nw-pjqcIYks

Speed animation: https://youtu.be/oKA1Cv-rTZU

7. K_Z contour:

• The thermal conductivity of the geometry represents how the heat is conducted from one layer to another layer.

• We can see from the above figure that the minimum thermal conductivity recorded in terms of 0.35 W/m-k. Which is acceptable.
• FR-4 has a poor thermal conductivity of 0.25 W / m-K; the thermal insulance factor of a 0.7-mm FR-4 layer is 2040°C-mm2 / W. In the IMS PCB, the thermal insulance factor of a 0.152-mm dielectric layer of thermal conductivity 3 W / m-K is 50°C-mm2 / W. (web source).
• So, the least thermal conductivity recorded is for the material FR-4.
• The maximum thermal conductivity recorded as 387.6 W/m-k, which is the same for the taken material in the simulation used.

Thermal conductivity animation: https://youtu.be/JYt9pnd20SI

Joule/Trace Heating:

Since PCB traces have electrical resistance, they heat up as current flows through them. Modeling this phenomenon will provide us with an accurate prediction of the temperature distribution in the PCB, which can be important, for example, in evaluating the performance of the cooling system. The model in the tutorial contains imported traces and will be used in this tutorial. You will determine the Joule/trace heating capacity of the traces.

a. Build the Model – Edit the Board outline of the previous model to open the model trace heating
panel select INT1_3 layer -> filter the trace to view by setting Min Area in the Display traces
filter group box uses a Min Area of 4124 mm2.

b. Before you create a solid trace of trace A3V3_2784 set the Max angle filter to 135 and the Min
length filter to 1.0 m to ignore the fine details in the trace geometry and reduce the mesh count.

c. Create a solid polygonal solid block for trace A3V3_2784 by clicking on create solid trace.

• The trace is imported from the list of the various traces.

d. Select the polygonal trace just created from the Model manager window  Under Thermal
specification next to Joule heating, click Edit to open the Joule heating power panel.  Set
Resistivity, temperature coefficient (C), and reference temperature (Tref)

• The terms present in the joule heating power are kept as it is without changing them. These terms considered as the initial conditions.

e. One source is for the current source (source.1) and the other for the voltage source (source.2).
Both sources are created on the same layer as the layer of the wire. The area of each
source in the area to apply the voltage or the current. • The recommendation of the source
objects pair for joule heating is the current-voltage pair or voltage- voltage pair.

• The two sources are placed on the trace path as per the given coordinates.
• Source.1 provides the 25 amps of current to the trace at one side and source.2 provides just a voltage path for the trace with 0 volts.

Meshing & BC setting:

a. Create a non-conformal assembly for the trace. Since we are performing a joule heating calculation, it is necessary to have a high or medium-mesh quality in case the joule heating calculation diverges. To create a high-quality mesh, we will create an assembly with the 3D trace geometry and set a small element size.

• The components that are attache to the PCB are assembled.
• Using this we can mesh separately for the assembly so that there will be fewer chances of getting the solution divergence.

b. Ensure the Mesh type is Mesher-HD.
c. Generate mesh. Specify a Max element size for X, Y, Z as 9.5, 7, and 0.75 mm
respectively.

• While we assemble some of the parts from the geometry, the number of elements and nodes have been increased.
• The number of elements generated are 1446717 and the number of nodes generated are 1576223.
• The solution may take more computational time because of large number of elements and nodes.

Numerical setting:

f. Basic parameters toggle on the Flow button. Keep and choose the Turbulent and Zero
the equation for the flow regime

• The flow option is toggled on for the problem because we have to calculate the velocity and behavior of the temperature inside the problem domain.
• The turbulent equation is set to the Zero equation.

g. set no of iterations 500 and convergence criteria for energy to 1e-8 and Flow is 1e-4

• The number iterations for convergence is set to 500. The convergence criteria for the flow are set to 1e-4, convergence criteria for energy is set to 1e-8 and joule heating is 1e-7.

h. Temperature Linear solver: F cycle is selected for Type Enter 1e-6 for both the termination criterion and Residual reduction tolerance

i. Ensure that BCGSTAB is chosen as the Stabilization criterion for both Temperature and
Joule Heating Potential.
j. Select Double for the solver Precision.
k. Save the model.
l. Enable Sequential solution of flow and energy equations
m. Solve the model.

• Whenever our mesh elements crossed the 1 million, it is always advisable for any kind of simulation to use the linear solver specialization to BCGSTAB (Bi Conjugate Stabilization).
• ANSYS FLUENT usually builds diagonally dominant matrices for the linear solver. However, this is not always possible. A linear system with highly dominant off-diagonal coefficients may occur during the discretization of complex physical models such as multiphase cavitation. Using the BCGSTAB or RPM (recursive projection method) option in such cases can be helpful. In addition, the AMG convergence in parallel can be improved using the BCGSTAB option with AMG.

Examine and post-process the results:

n. view the traces in three different ways, i.e. single color, color by layer, or color by trace

• In electronics, a signal trace on a printed circuit board (PCB) is the equivalent of wire for conducting signals. Each trace consists of a flat, narrow part of the copper foil that remains after etching or printing.
• Printed circuit boards are typically made with copper. Depending on the requirements, the copper is plated to a substrate and carved away to expose the design of the board. Since there are multiple layers, they must be lined up and bonded together for a secure fit.

• The above figure represents the traces of the PCB on different layers we are imported into it.
• By using one color we cannot see the difference in different layers. So it is always better to visualize the layers and traces in different colors.

• Visualization of the layers and traces still a little difficult using the color - by - layers.

o. View the fraction of metal traces based on the grid density

• The above figure seems like seeing the traces and dividing layers is easy when we put the traces in color-by-layers.
• In the above figure, we can see where the power cables are passing, from where the traces lines are connected to, signaling to process from one component to another, etc.

• The metal fraction of the PCB gives us an estimation of what's the copper content in the PCB and what's the FR4 content in the PCB.
• This case setup gives us the visualization of the metal fraction which is effective in understanding the PCB characteristics more.

• So, in the given PCB we have implemented the total seven number of layers in it.
• We have top and bottom layers on both sides of the PCB, inside of PCB we can see the other five layers.
• The below figure is the top side of the PCB. The metal fraction is ranges from 0 to 1.

• The below figure shows the metal other than the copper, the other metal has seen in the figure is FR4.

• The red color is seen on the layer is the metal content provided on the top layer of the PCB. Here the material we considered is copper.
• The blue color refers to other materials.

• The figure is shown above is the second layer of the PCB, this layer is called as metal-internal-1.
• Here we can see the content of the copper and at the same time the copper content in the traces also.

• The above figure represents the third layer of the PCB. Here we can see there is nearly zero percent of the metal components are there except the keyholes provided for the screw fitting.
• The blue material showing in the figure is FR4.

• Here we can see again a lot of metal component is provided in this layer. Means, we are providing the metal layer by layer alternatively.
• The other figure also the same as these, which are shown below.

• The figure shown above is the bottom layer in the PCB. Here we can see how the amount of metal percentage is varied across the layer.

p. The plane cut Point and normal. Make sure that PX, PY, PZ are 0, 0, and 0.78232,
respectively, and the NX, NY, and NZ are 0, 0, and 1, respectively.

• The coordinates provided above takes us to the middle of the Z-plane in the contour plot.
• But some of the contours will not come to see while using these coordinates. So, we can adjust these coordinates according to the convenience.

Residual Plot:

• The disturbances in the last of the residual plot indicate the solution converged and repeating.

q. Temperature contour on trace layer

• Here we changed the coordinate system of the z-plane to view the minimum and maximum temperatures on the geometry obtained.

• The temperature distribution on the trace is shown in the above figure.
• As per the joule heating, we have given 25 amps of the current at source.1, the temperature increased at the source.1 due to resistance has been visualized.
• Due to the voltage mentioned as 0 at the source.2, we can see there is a little temperature gained by trace with the resistance.

r. K_Z - thermal conductivity:

• The thermal conductivity of the geometry represents how the heat is conducted from one layer to another layer.

• We can see from the above figure that the minimum thermal conductivity recorded in terms of 0.35 W/m-k. Which is acceptable.
• FR-4 has a poor thermal conductivity of 0.25 W / m-K; the thermal insulance factor of a 0.7-mm FR-4 layer is 2040°C-mm2 / W. In the IMS PCB, the thermal insulance factor of a 0.152-mm dielectric layer of thermal conductivity 3 W / m-K is 50°C-mm2 / W. (web source).
• So, the least thermal conductivity recorded is for the material FR-4.
• The maximum thermal conductivity recorded as 387.6 W/m-k, which is the same for the taken material in the simulation used.

s. Electrical potential:

• An electric potential is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration and its SI unit is joule per coulomb I.e Volts.
• It gives us the idea about how the source.1 current is passed to source.2 in the prepared solid layer.