Thermal Results Visualization – Ansys SIWave Icepak and Ansys Electronics Desktop Icepak

As a typically mechanical / systems engineer, I am not exactly qualified to go through and list exactly what SIWave does and why you need it for any given situation (shoutout to Aleksandr, our actual expert, whose assistance has been invaluable for my simple example case). However, what I think I have grasped is that SIWave is just one of those Ansys tools where if you need it, you probably really need it. Where this becomes relevant to me is of course in a PCB thermal analysis. DCIR is typically the electrical half of this problem that is within SIWave’s expansive toolkit, though SIWave also contains some very easy-to-use thermal-oriented options for co-simulation with Icepak. I’ll admit that I have tended to somewhat dismiss this on my end, as I am already familiar with a couple more advanced thermal analysis tools, so why wouldn’t I just use these if I wanted to look at the thermal response of A PCB? Despite this, I have recently (begrudgingly) taken a more in-depth look at the thermal side of SIWave, and what I have found is that even if the settings available are a little more simplistic than I might always like, it really is incredibly accessible and provides some nice visualization capability. What’s more, it provides not only an easy path to view your existing thermal results in a full Icepak interface, but also serves as a great starting point if you need to analyze some more complex setups than Icepak.

So, having just been through much of this on my own, it seems like a great opportunity to share some tips and tricks for thermal visualization in both Ansys SIWave and Ansys Electronics Desktop (EDT) Icepak, see where each is strong relative to the other, and then perhaps even share some suggestions for using the SIWave solution as a starting point to take an Icepak PCB simulation to the next level!

To start with, we need a SIWave DCIR project. A DCIR solution is required for providing thermal loads for a thermal solution. I am glossing over this, but basically, you need a PCB definition, a voltage source, and a current source. In the model I borrowed from Aleks, I am using these sources to push some current through one section of my PCB’s power layer and then referencing them to the ground layer. To complete the loop. This means that there are EM losses on both the ground layer and power layer.

For the first simulation, we’ll want to set a baseline temperature for our electrical material properties and make sure the toggle for “Export power dissipation for use in ANSYS Icepak and Mechanical” is enabled.

Now, we can set up an Icepak simulation! As I alluded to, the settings available within SIWave are somewhat primitive, although they do an overall good job of adhering to typical best practices. Our choices are basically using a board model without components and strictly modeling thermal conduction within that board, using a board model with components that includes explicit thermal convection to the environment, manipulating a mesh detail slider bar, and choosing the cooling regime used (natural vs forced convection). For this model, I’ll be using forced convection with surface components and “Detailed” meshing so that I have the most to look at, but obviously the exact settings will vary somewhat depending on your use-case. In 2021R2, the default SIWave-Icepak behavior will be to use EDT Icepak as the solver, however, we can choose to specify “Use Classic Icepak” in the simulation setup window. This determines which version of Icepak we have to use for additional postprocessing in as well, so I will leave “Use Classic Icepak” turned off.

The first method of visualization in SIWave is to simply right-click an Icepak simulation definition in the “Results” window and Display temperature.

This gives us a nice temperature contour on the outer surface of all the solid bodies considered during the simulation. If we stick with the top-down view, we can make use of a nice temperature probe that automatically displays at the mouse location. Once we rotate around into a 3D view with the middle mouse button or other view options, we lose this probe but of course, gain a nice graphical representation of the full geometry.

The second method is to use the View > Temperature Plots toolbar option, which gives us some more flexibility for viewing temperature through each layer.

Most commonly, we will probably be working with the XY cutting plane and then selecting the layer of interest from the drop-down menu so that we can see a plane through the entire PCB. For more precise control, we can also use the slider bar or input the exact plane-normal location to use for plotting.

One of the benefits of this approach is that we can use the other cutting plane definitions to get a cross-section view, along with whatever ECAD board elements we would like to plot. For instance, if we’d like to see more clearly how the temperature varies with depth underneath active components, or around via definitions, we can easily explore this, as in the image below.

Depending on your needs, this may be sufficient flexibility for observing the temperatures of interest, and the smoothly moving cut plane with the slider-bar position is certainly an easy way to get a sense of the board’s behavior. However, SIWave only gives us access to temperature within the solid bodies of our PCB/components, and we can free ourselves from this limitation by moving into EDT Icepak. There are a couple of primary ways to do this – one is to right-click on the Icepak simulation definition in Results and “Open project in Icepak” and the other is to use the same option from the “Results” section of the top toolbar. The more manual method is to directly open the .aedt file that gets generated alongside the SIWave project file.

Much like SIWave, temperatures in EDT Icepak are primarily displayed on cut-planes or object surfaces. Three-dimensional contour plots are also available but tend to be less clear, especially on very thin bodies (like layers of a PCB). For a cut-plane, the most straightforward option is to directly draw a plane or create a new coordinate system (a coordinate system will automatically create the 3 component planes), which can both be done through the top toolbar. 

Personally, I find it easiest to quickly create the objects in the graphical window and then select them in the model tree to fine-tune their locations through the properties display, as above. I do think this is one of the places that SIWave has an edge in ease-of-use – having that slider bar definition for a plane is much nicer. Although, using this method in Icepak also lets us angle the plane however we like, so there are still trade-offs to be considered.

Once we have a plane defined, it is then very easy to select this plane in the model tree and right-click > Temperature > Temperature to create a temperature plot.

One of the immediately observable differences is that we can now view temperature contours throughout the volume of air surrounding our PCB in addition to the PCB itself. So, if we were trying to compare against something like an experimental setup with a thermocouple placed in-air near the board, this would be the way to do it!

If we’re not interested in quite so large of a plot, we can also limit it to a certain model volume by choosing one of the objects in the “In Volume” list of the plot properties. In this case, Box1 and Box2 are smaller volumes enclosing the PCB that were automatically generated for mesh controls, which we can easily reuse for trimming down our temperature plot.

To instead plot on the surface of an object, we can select that object in the model tree (for the whole PCB, it is convenient to right-click it in the tree and use the “Select All” option), follow the same Plot Fields > Temperature > Temperature as before, and then make sure to enable “Plot on surface only”.

This should produce a plot that is very similar to what we obtained in SIwave. Another advantage of doing this in Icepak should now become clear — we have the capability to stack multiple field plots! As below, we can see the solid body surface temperatures alongside our cut plane temperature down the center.

We can get as creative with this as we’d like, plotting on many different cut planes simultaneously, or even combining types of plots. Since we have access to the air volume solution, we can even do things like plot velocity vectors around the PCB for more insight into the overall system.

Having access to the full solution field (fluid and solids) means we can also visualize some other helpful values. The surface heat transfer coefficients can help us understand how to improve our setup in some cases, for instance. In the below plot, we can see some clear shadowing behind surface components which is indicative of the primary flow separating from the surface of the PCB. This certainly explains why the back end of the board is so hot – the components in the back are somewhat hidden from the flow field by those in the front. Since component (and component power) density is higher in the back, we might choose to reverse the direction of flow so that the particularly dense section of components receives the brunt of the airflow, or maybe we might explore angling the board relative to the inlet such that the entire top receives more direct flow.

While we might reach the same or similar conclusions by looking at data through SIWave’s interface, we certainly wouldn’t have access to the tools necessary to actually implement all these changes to the simulation.

As an example, I can pretty easily create a new coordinate system, rotate it by 11° from the original, and then assign my air box to the rotated reference. In effect, this angles all of PCB related volumes with respect to the flow field in just a couple of steps.

After solving, I can then compare the new temperature fields to the old and pretty quickly find that the hotspot on the top surface has been greatly reduced and that the maximum temperature of the system has dropped by about 9 °C. Not too bad! Of course, since I have modified at least one of the simulation bodies, we do have to remesh and solve from scratch, however, we already have an existing DCIR simulation to make use of, and it was much easier getting to this point having started in SIWave.

For my last set of tips, the visualization of the PCB itself in Icepak has been rudimentary so far, but we can also adjust this. Much like in SIWave, we can turn on and off the visualization of features for individual layers independently of anything else. These visualization settings are accessible by selecting our board in the 3D components list and then looking at the properties section.

Since these settings are independent of the 3D geometry visualization, we can selectively hide our model objects in order to isolate the detailed ECAD features. In my test case, the dielectric “Unnamed” layers include via definitions – so I can turn on visualization of these layers, hide the geometry for every layer except the bottom, and plot a temperature cut plane to get a nice visualization of how temperature varies around particular vias.

We could do the same for a temperature cut plane through the width/length of the board as well or even look at heat transfer coefficients on the PCB surface in regions of high via density. As is often the case with Ansys tools, the sky is the limit here.  

In summary, the SIWave interface can be both a great starting and ending point for thermal simulation depending on your needs. It makes setting up a complicated simulation very easy, albeit by removing some user flexibility, but it does allow for several methods of viewing thermal results. These include a smooth slider bar visualization for cut-plane temperatures and a dynamic mouse-probe for checking temperature values in the top-down 2D view. Since SIWave makes use of the full Icepak solver in the background, we can also access a whole lot of additional information by simply opening the existing Icepak solution in the full EDT Icepak interface after a solution has been generated. This gives us access to new thermal solution variables, variables from the fluid portion of our solutions, and new ways to plot and visualize all this information. The combination of SIWave and EDT Icepak also provides us with the opportunity to run an initial set of thermal simulations for relatively simple setups and then build on top of those with more complex boundary conditions or geometry configurations, if we either need greater detail or want to try out some more advanced cooling scenarios.

Welcome to a New Era in Electronics Reliability Simulation

Simulation itself is no longer a new concept in engineering, but individual fields, applications, and physics are continually improved upon and integrated into the toolbox that is an engineer’s arsenal. Many times, these are incremental additions to a particular solver’s capabilities or a more specialized method of post processing, however this can also occasionally be present through new cross-connections between separate tools or even an entirely new piece of software. As a result of all this, Ansys has now reached critical mass for its solution space surrounding Electronics Reliability. That is, we can essentially approach an electronics reliability problem from any major physics perspective that we like.

So, what is Electronics Reliability and what physics am I referring to? Great question, and I’m glad you asked – I’d like to run through some examples of each physics and their typical use-case / importance, as well as where Ansys fits in. Of course, real life is a convoluted Multiphysics problem in most cases, so having the capability to accommodate and link many different physics together is also an important piece of this puzzle.

Running down the list, we should perhaps start with the most obvious category given the name – Electrical Reliability. In a broad sense, this encompasses all things related to electromagnetic fields as they pertain to transmission of both power and signals. While the electrical side of this topic is not typically in my wheelhouse, it is relatively straightforward to understand the basics around a couple key concepts, Power Integrity and Signal Integrity.

Power integrity, as its name suggests, is the idea that we need to maintain certain standards of quality for the electrical power in a device/board/system. While some kinds of electronics are robust enough that they will continue to function even under large variations in supplied voltage or current, there are also many that rely on extremely regular power supplies that only vary above certain limits or within narrow bounds. Even if we’re looking at a single PCB (as in the image below), in today’s technological environment it will no doubt have electrical traces mapped all throughout it as well as multiple devices present that operate under their own specified electrical conditions.

Figure 1: An example PCB with complex trace and via layouts, courtesy of Ansys

If we were determined to do so, we could certainly measure trace lengths, widths, thicknesses, etc., and make some educated guesses for the resulting voltage drops to individual components. However, considerably more effort would need to be made to account for bends, corners, or variable widths, and that would still completely neglect any environmental effects or potential interactions between traces. It is much better to be able to represent and solve for the entire geometry at once using a dedicated field solver – this is where Ansys SIwave or Ansys HFSS typically come in, giving us the flexibility to accurately determine the electrical reliability, whether we’re talking about AC or DC power sources.

Signal integrity is very much related, except that “signals” in this context often involve different pathways, less energy, and a different set of regulations and tolerances. Common applications involve Chip-signal modeling and DDRx virtual compliance – these have to do with not only the previous general concerns regarding stability and reliability, but also adherence to specific standards (JEDEC) through virtual compliance tests. After all, inductive electromagnetic effects can still occur over nonconductive gaps, and this can be a significant source of noise and instability in cases where conductive paths (like board traces or external connections) cross or run very near each other.

Figure 2: Example use-cases in virtual compliance testing, courtesy of Ansys

Whether we are looking at timings between components, transition times, jitter, or even just noise, HFSS and SIWave can both play roles here. In either case, being able to use a simulation environment to confirm that a certain design will or will not meet certain standards can provide invaluable feedback to the design process.

Other relevant topics to Electrical Reliability may include Electromagnetic Interference (EMI) analysis, antenna performance, and Electrostatic Discharge (ESD) analysis. While I will not expand on these in great detail here, I think it is enough to realize that an excellent electrical design (such as for an antenna) requires some awareness of the operational environment. For instance, we might want to ensure that our chosen or designed component will adequately function while in the presence of some radiation environment, or maybe we would like to test the effectiveness of the environmental shielding on a region of our board. Maybe, there is some concern about the propagation of an ESD through a PCB, and we would like to see how vulnerable certain components are. Ansys tools provide us the capabilities needed to do all of this.

The second area of primary interest is Thermal Reliability, as just about anyone who has worked with or even used electronics knows, they generate some amount of heat while in use. Of course, the quantity, density, and distribution of that heat can vary tremendously depending on the exact device or system under question, but this heat will ultimately result in a rise in temperature somewhere. The point of thermal reliability basically boils down to realizing that the performance and function of many electrical components depends on their temperature. Whether it is simply a matter of accounting for a change in electrical conductivity as temperature rises or a hard limit of functionality for a particular transistor at 150 °C, acknowledging and accounting for these thermal effects is critical when considering electronics reliability. This is a problem with several potential solutions depending on the scale of interest, but generally we cover the package/chip, board, and full system levels. For the component/chip level, a designer will often want to provide some package level specs for OEMs so that a component can be properly scoped in a larger design. Ansys Icepak has toolkits available to help with this process; whether it is simplifying a 3D package down to a detailed network thermal model or identifying the most critical hot spot within a package based on a particular heat distribution. Typically, network models are generated through temperature measurements taken from a sample in a standardized JEDEC test chamber, but Icepak can assist through automatically generating these test environments, as below, and then using simulation results to extract well defined JB and JC values for the package under test.

Figure 3: Automatically generated JEDEC test chambers created by Ansys Icepak, courtesy of Ansys

On the PCB level of detail, we are likely interested in how heat moves across the entire board from component to component or out to the environment. Ansys Icepak lets us read in a detailed ECAD description for said PCB and process its trace and via definitions into an accurate thermal conductivity map that will improve our simulation accuracy. After all, two boards with identical sizing and different copper trace layouts may conduct heat very differently from each other.

Figure 4: Converting ECAD information into thermal conductivity maps using Ansys Icepak, courtesy of Ansys

On the system level of thermal reliability, we are likely looking at the effectiveness of a particular cooling solution on our electronic design. Icepak makes it easy to include the effects of a heat exchanger (like a coldplate) without having to explicitly model its computationally expensive geometry by using a flow network model. Also, many of today’s electronics are expected to constantly run right up against their limit and are kept within thermal spec by using software to throttle their input power in conjunction with an existing cooling strategy. We can use Icepak to implement and test these dynamic thermal management algorithms so that we can track and evaluate their performance across a range of environmental conditions.

The next topic that we should consider is that of Mechanical Reliability. Mechanical concepts tend to be a little more intuitive and relatable due to their more hands-on nature than the other two, though the exact details behind the cause and significance of stresses in materials is of course more involved. In the most general sense, stress is a result of applying force to an object. If this stress is high compared to what is allowed by a material, then bad things tend to happen – like permanent deformation or fracture. For electronic devices consisting of many materials, small structures, and particularly delicate components, we have once again surpassed what can be reasonably accomplished with hand calculations. Whether we are looking at an individual package, the integrity of an entire PCB, or the stability that a rigid housing will provide to a set of PCBs, Ansys has a solution. We might use Ansys Mechanical to look at manufacturing allowances for the permissible force used while mounting a complicated leaded component onto a board, as seen below. Or maybe, we will use mechanical simulation to find the optimal positioning of leads on a new package such that its natural vibrational frequencies are outside normal ambient conditions.

Figure 5: A surface component with discretely modeled leads, courtesy of Ansys

At the PCB level, we face many of the same detail-oriented challenges around representing traces and vias that have been mentioned for the electrical applications. They may not be quite as critical and more easily approximated in some ways, but that does not change the fact that copper traces are mechanically quite different from the resin composites often used as the substrate (like FR-4). Ansys tools like Sherlock provide best in class PCB modeling on this front, allowing us to directly bring in ECAD models with full trace and component detail, and then model them mechanically at several different levels depending on the exact need. Automating a materials property averaging scheme based on the local density of traces may be sufficient if we are looking at the general bending behavior of a board, but we can take it to the next level by explicitly modeling traces as “reinforcement” elements. This brings us to the level of detail where we can much more reliably look at the stresses present in individual traces, such that we can make good design decisions to reduce the risk of traces peeling or delaminating from the surface.

Figure 6: Example trace mapping workflow and methods, courtesy of Ansys

Beyond just looking at possible improvements in the design process, we can also make use of Ansys tools like LS-DYNA or Mechanical to replicate testing or accident conditions that an existing design could be subjected to. As a real-world example, many of us are all too familiar with the occasional consequences of accidentally dropping our smart phones – Ansys is used to test designs against these kind of shock events, where impact against a hard surface can result in high stresses in key locations. This helps us understand where to reinforce a design to protect against the worst damage or even what angle of impact is most likely to cause an operational failure.

As the finale for all of this, I come back to the first comment of reality being a complex Multiphysics problem. Many of the previous topics are not truly isolated to their respective physics (as much as we often simplify them as such), and this is one of the big ways in which the Ansys ecosystem shines: Comprehensive Multiphysics. For the topic of thermal reliability, I simply stated that electronics give off heat. This may be obvious, but that heat is not just a magical result of the device being turned on but is instead a physical and calculable result of the actual electrical behavior. Indeed, this the exact kind of result that we can extract from one of the relevant electronics tools. An HFSS solution will provide us with not only the electrical performance of an antenna but also the three-dimensional distribution of heat that is consequently produced. Ansys lets us very easily feed this information into an Icepak simulation, which then has the ability to give us far more accurate results than a typical uniform heat load assumption provides.

Figure 7: Coupled electrical-thermal simulation between HFSS and Icepak, courtesy of Ansys

If we find that our temperatures are particularly high, we might then decide to bring these results back into HFSS to locally change material properties as a function of temperature to get an even more accurate set of electrical results. It could be that this results in an appreciable shift in our antenna’s frequency, or perhaps the efficiency has decreased, and aspects of the design need to be revisited. These are some of the things that we would likely miss without a comprehensive Multiphysics environment.

On a more mechanical side, the effects on stress and strain from thermal conditions are very well known and understood at this point, but there is no reason we could not use Ansys to bring the electrical alongside this established thermal-mechanical behavior. After all, what is a better representation of the real physics involved than using SIwave or HFSS to model the electrical behavior of a PCB, bringing those result into an Icepak simulation as a heat load to test the performance of a cooling loop or heat sink, and then using at least some of those thermal results to look at stresses through not only a PCB as a whole but also individual traces? Not a whole lot at this moment in time, I would say.

The extension that we can make on these examples, is that they have by and large been representative cases of how an electronics device responds to a particular event or condition and judging its reliability metrics based on that set of results, however many physics might be involved. There is one more piece of the puzzle we have access to that also interweaves itself throughout the Multiphysics domain and that is Reliability Physics. This is mostly relevant to us in electronics reliability for considering how different events, or even just a repetition of the same event, can stack together and accumulate to contribute towards some failure in the future. An easy example of this is a plastic hinge or clip that you might find on any number of inexpensive products – flexing a thin piece of plastic like in these hinges can provide a very convenient method of motion for quite some time, but that hinge will gradually accumulate damage until it inevitably cracks and fails. Every connection within a PCB is susceptible to this same kind of behavior, whether it is the laminations of the PCB itself, the components soldered to the surface, or even the individual leads on a component. If our PCB is mounted on the control board of a bus, satellite, or boat, there will be some vibrations and thermal cycles associated with its life. A single one of these events may be of much smaller magnitude and seemingly negligible compared to something dramatic like a drop test, and yet they can still add up to the point of being significant over a period of months or years.

This is exactly the kind of thing that Ansys Sherlock proves invaluable for: letting us define and track the effect of events that may occur over a PCB’s entire lifecycle. Many of these will revolve around mechanical concepts of fatigue accumulating as a result of material stresses, but it is still important to consider the potential Multiphysics origins of stress. Different simulations will be required for each of mechanical bending during assembly, vibration during transport, and thermal cycling during operation, yet each of these contributes towards the final objective of electronics reliability. Sherlock will bring each of these and more together in a clear description of which components on a board are most likely to fail, how likely they are to fail as a function of time, and which life events are the most impactful.

Figure 8: Example failure predictions over the life cycle of a PCB using Ansys Sherlock, courtesy of Ansys

Really, what all of this comes down to is that when we design and create products, we generally want to make sure that they function in the way that we intend them to. This might be due to a personal pride in our profession or even just the desire to maximize profit through minimizing the costs associated with a component failure, however at the end it just makes sense to anticipate and try to prevent the failures that might occur under normal operating conditions.

For complex problems like electronics devices, there are many physics all intimately tied together in the consideration of overall reliability, but the Ansys ecosystem of tools allows us to approach these problems in a realistic way. Whether we’re looking at the electrical reliability of a circuit or antenna, the thermal performance of a cooling solution or algorithm, or the mechanical resilience of a PCB mounted on a bracket, Ansys provides a path forward.

If you have any questions or would like to learn more, please contact us at info@padtinc.com or visit www.padtinc.com.

Signal & Power Integrity Updates in Ansys 2021 R1 – Webinar

The use of Ansys Electronics solutions minimizes the testing costs, ensures regulatory compliance, improves reliability and drastically reduces your product development time. All this while helping you build the best-in-class and cutting-edge products.

With signal and power integrity (SI & PI) analysis products, users can mitigate many electrical and thermal issues affecting printed circuit boards such as electromagnetic interference, crosstalk, overheating, etc. Ansys integrated electromagnetics and circuit simulation tools are essential for designing high-speed serial channels, parallel buses, and complete power delivery systems found in modern high-speed electronic devices.

Leverage the simulation capability from Ansys to solve the most critical aspects of your designs. Join PADT’s Electronics expert and application engineer Aleksandr Gafarov for a detailed look at what is new for SI & PI in Ansys 2021 R1, including updates available within the following tools:

• SIwave – Granta support & differential time domain crosstalk

• Q3D – Uniform current terminals

• Circuits – Network data explorer & SPISim

• HFSS 3D – Parallel meshing, encrypted 3D components & IC workflow improvements

• Electronics Desktop – Ansys cloud, Minerva & optiSLang integration

• And much more

Register Here

If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

Windows Update KB4571756 Triggers Error 3221227010 for Ansys Electronics Products

On September 7, 2020 Microsoft released a Windows update KB4571756, which may cause the Ansys electronic products to fail with the Error:

3221227010 at ‘reg_ansysedt.exe’ and ‘reg_siwave.exe’ registration.

This is the error message, users would see if they right-mouse-click and run the following file as administrator:

C:\Program Files\AnsysEM\AnsysEM20.2\Win64\config\ConfigureThisMachine.exe

To resolve this issue, here are the steps we recommend users take:

  1. Revert the updates.
    1. If the issue is not resolved or something your IT won’t let you do, continue to the next steps.
  2. Set an environment variable that turns off the driver that is causing the error. 
    1. Use windows search and type “system environment” and click on “Edit the system environment variables”
    2. This opens the “System Properties” tool
    3. Go to the “Advanced” tab
    4. Click on “Environment Variables…” at the bottom
    5. In the System Variables window click on “New…”
    6. Create the following variable:

      Variable Name: ANSYS_EM_DONOT_PRELOAD_3DDRIVER_DLL
      Variable Value: 1
    7. Click OK 3 times to exit out of the tool and save your changes. 
  3. If the issue is still not resolved, there is one more step:
    1. Go to C:\Program Files\AnsysEM\AnsysEM20.2\Win64\config\
    2. Right-Mouse-Click on “ConfigureThisMachine.exe” and run as Admin. 

If these steps helped to resolve the issue, you will see the following info message when ‘ConfigureThisMachine.exe’ is run:

If this does not work, please contact your Ansys support provider. 

Reduce EMI with Good Signal Integrity Habits

Recently the ‘Signal Integrity Journal’ posted their ‘Top 10 Articles’ of 2019. All of the articles included were incredible, however, one stood out to me from the rest – ‘Seven Habits of Successful 2-Layer Board Designers’ by Dr. Eric Bogatin (https://www.signalintegrityjournal.com/blogs/12-fundamentals/post/1207-seven-habits-of-successful-2-layer-board-designers). In this work, Dr. Bogatin and his students were developing a 2-Layer printed circuit board (PCB), while trying to minimize signal and power Integrity issues as much as possible. As a result, they developed a board and described seven ‘golden habits’ for this board development. These are fantastic habits that I’m confident we can all agree with. In particular, there was one habit at which I wanted to take a deeper look:

“…Habit 4: When you need to route a cross-under on the bottom layer, make it short. When you can’t make it short, add a return strap over it..”

Generally speaking, this habit suggests to be very careful with the routing of signal traces over the gap on the ground plane. From the signal integrity point of view, Dr. Bogatin explained it perfectly – “..The signal traces routed above this gap will see a gap in the return path and generate cross talk to other signals also crossing the gap..”. On one hand, crosstalk won’t be a problem if there are no other nets around, so the layout might work just fine in that case. However, crosstalk is not the only risk. Fundamentally, crosstalk is an EMI problem. So, I wanted to explore what happens when this habit is ignored and there are no nearby nets to worry about.

To investigate, I created a simple 2-Layer board with the signal trace, connected to 5V voltage source, going over an air gap. Then I observed the near field and far field results using ANSYS SIwave solution. Here is what I found.

Near and Far Field Analysis

Typically, near and far fields are characterized by solved E and H fields around the model. This feature in ANSYS SIwave gives the engineer the ability to simulate both E and H fields for near field analysis, and E field for Far Field analysis.

First and foremost, we can see, as expected, that both near and far Field have resonances at the same frequencies. Additionally, we can observe from Figure 1 that both E and H fields for near field have the largest radiation spikes at 786.3 MHz and 2.349GHz resonant frequencies.

Figure 1. Plotted E and H fields for both Near and Far Field solutions

If we plot E and H fields for Near Field, we can see at which physical locations we have the maximum radiation.

Figure 2. Plotted E and H fields for Near field simulations

As expected, we see the maximum radiation occurring over the air gap, where there is no return path for the current. Since we know that current is directly related to electromagnetic fields, we can also compute AC current to better understand the flow of the current over the air gap.

Compute AC Currents (PSI)

This feature has a very simple setup interface. The user only needs to make sure that the excitation sources are read correctly and that the frequency range is properly indicated. A few minutes after setting up the simulation, we get frequency dependent results for current. We can review the current flow at any simulated frequency point or view the current flow dynamically by animating the plot.

Figure 3. Computed AC currents

As seen in Figure 3, we observe the current being transferred from the energy source, along the transmission line to the open end of the trace. On the ground layer, we see the return current directed back to the source. However at the location of the air gap there is no metal for the return current to flow, therefore, we can see the unwanted concentration of energy along the plane edges. This energy may cause electromagnetic radiation and potential problems with emission.

If we have a very complicated multi-layer board design, it won’t be easy to simulate current flow on near and far fields for the whole board. It is possible, but the engineer will have to have either extra computing time or extra computing power. To address this issue, SIwave has a feature called EMI Scanner, which helps identify problematic areas on the board without running full simulations.

EMI Scanner

ANSYS EMI Scanner, which is based on geometric rule checks, identifies design issues that might result in electromagnetic interference problems during operation. So, I ran the EMI Scanner to quickly identify areas on the board which may create unwanted EMI effects. It is recommended for engineers, after finding all potentially problematic areas on the board using EMI Scanner, to run more detailed analyses on those areas using other SIwave features or HFSS.

Currently the EMI Scanner contains 17 rules, which are categorized as ‘Signal Reference’, ‘Wiring/Crosstalk’, ‘Decoupling’ and ‘Placement’. For this project, I focused on the ‘Signal Reference’ rules group, to find violations for ‘Net Crossing Split’ and ‘Net Near Edge of Reference’. I will discuss other EMI Scanner rules in more detail in a future blog (so be sure to check back for updates).

Figure 4. Selected rules in EMI Scanner (left) and predicted violations in the project (right)

As expected, the EMI Scanner properly identified 3 violations as highlighted in Figure 4. You can either review or export the report, or we can analyze violations with iQ-Harmony. With this feature, besides generating a user-friendly report with graphical explanations, we are also able to run ‘What-if’ scenarios to see possible results of the geometrical optimization.

Figure 5. Generated report in iQ-Harmony with ‘What-If’ scenario

Based on these results of quick EMI Scanner, the engineer would need to either redesign the board right away or to run more analysis using a more accurate approach.

Conclusion

In this blog, we were able to successfully run simulations using ANSYS SIwave solution to understand the effect of not following Dr.Bogatin’s advice on routing the signal trace over the gap on a 2-Layer board. We also were able to use 4 different features in SIwave, each of which delivered the correct, expected results.

Overall, it is not easy to think about all possible SI/PI/EMI issues while developing a complex board. In these modern times, engineers don’t need to manufacture a physical board to evaluate EMI problems. A lot of developmental steps can now be performed during simulations, and ANSYS SIwave tool in conjunction with HFSS Solver can help to deliver the right design on the first try.

If you would like more information or have any questions please reach out to us at info@padtinc.com.

ANSYS 17.2 Executable Paths on Linux


ansys-linux-penguin-1When running on a machine with a Linux operating system, it is not uncommon for users to want to run from the command line or with a shell script. To do this you need to know where the actual executable files are located. Based on a request from a customer, we have tried to coalesce the major ANSYS product executables that can be run via command line on Linux into a single list:

ANSYS Workbench (Includes ANSYS Mechanical, Fluent, CFX, Polyflow, Icepak, Autodyn, Composite PrepPost, DesignXplorer, DesignModeler, etc.):

/ansys_inc/v172/Framework/bin/Linux64/runwb2

ANSYS Mechanical APDL, a.k.a. ANSYS ‘classic’:

/ansys_inc/v172/ansys/bin/launcher172 (brings up the MAPDL launcher menu)
/ansys_inc/v172/ansys/bin/mapdl (launches ANSYS MAPDL)

CFX Standalone:

/ansys_inc/v172/CFX/bin/cfx5

Autodyn Standalone:

/ansys_inc/v172/autodyn/bin/autodyn172

Note: A required argument for Autodyn is –I {ident-name}

Fluent Standalone (Fluent Launcher):

/ansys_inc/v172/fluent/bin/fluent

Icepak Standalone:

/ansys_inc/v172/Icepak/bin/icepak

Polyflow Standalone:

/ansys_inc/v172/polyflow/bin/polyflow/polyflow < my.dat

Chemkin:

/ansys_inc/v172/reaction/chemkinpro.linuxx8664/bin/chemkinpro_setup.ksh

Forte:

/ansys_inc/v172/reaction/forte.linuxx8664/bin/forte.sh

TGRID:

/ansys_inc/v172/tgrid/bin/tgrid

ANSYS Electronics Desktop (for Ansoft tools, e.g. Maxwell, HFSS)

/ansys_inc/v172/AnsysEM/AnsysEM17.2/Linux64/ansysedt

SIWave:

/ansys_inc/v172/AnsysEM/AnsysEM17.2/Linux64/siwave