Effective PCB design | How to ensure your PCB Trace Widths are Effective

Sarah Santangelli takes us through the importance of Trace Widths and what they mean for your PCB design.

What is Trace Width?

Trace widths

Trace width is an important design factor in PCB design. PCB trace could be analog, digital or power, from one junction to another.

The junction can be the pin of a component, a branch off of a larger trace or plane, or an empty pad or test-point intended for probing. Trace widths are often measured in mils, or thousands of an inch. A standard trace width for an ordinary signal (no special requirements) may be in the 7-12 mil range and be as long as a few inches, but there are many things that should be considered when defining the width and length of a trace.

Efficient Trace Width

To ensure effective operation in transmitting signal and power the importance of PCB Trace Width and resistance is crucial. So, what steps do you need to take?

Determine the standard track width to be used

  • It is important to balance the standard track size to be used within the design. Too narrow and too close means there is a higher chance of it shorting. If they are too wide and far apart, it can restrict the number of tracks in a given area and this may force the use of additional planes in the boards to ensure the PCB design can be routed. It is a balancing act that needs to be right.

 

Consider track size for lines carrying current

  • The thin tracks used in today’s printed circuit boards can only carry a limited current. Consideration needs to be given to the size of the trace for any that carry power rails rather than low level signals. The table below gives some track widths or a 10degree C temperature rise for different thickness copper boards.

 

RECOMMENDED MAXIMUM CURRENT FOR PCB TRACE
CURRENT
(AMPS)
WIDTH FOR 1 OZ BOARD
(THOUS)
WIDTH FOR 2 OZ BOARD
(THOUS)
1105
22015
35025

Fix the printed circuit board pad to hole ratio and size

  • At the beginning of the PCB design it will be necessary to determine the pad and hole dimensions. Typically a ratio of about 1.8: 1 (pad : hole) is used, although sometimes a pad 0..5 mm larger than the hole is used as the measure. This allows for hole drilling tolerances, etc. The manufacturer of the bare PCB will be able to advise on the standards that are required for their process. The ratio becomes more important as the size of the pads and holes reduces, and it is particularly important for via holes.

Determine PCB pad shapes

  • Component libraries associated with PCB CAD systems will have libraries for the schematic and PCB footprints for the different components. However these may vary according to the manufacturing process. Typically they need to be large for wave soldering than for infra-red reflow soldering. Thus the manufacturing process needs to be determined before the design starts so that the optimum pad sizes can be chosen and used on the PCB CAD system and hence on the printed circuit board itself.

 

Need Support with your PCB Design?

Qyadra Solutions have been designing, assembling, and fabricating PCBs for over 20 years and our ability to design and manufacture the highest quality PCB designs and prototypes means the world to every single member of the Quadra team. You can rely on our highly experienced and IPC CID+ accredited team of PCB Design Engineers to provide a full range of PCB Design Services that leave you free to focus on the design concept and product strategy.

Our PCB Design Services

UKAS-ISO-9001-1-150x150Our ISO 9001 accredited team deliver complex, high-speed multi-layered circuit board design layout, testing, library management and manufacturing services for hundreds of happy customers each year, using a wide range of PCB design software packages including;

 

  • Altium
  • Mentor
  • eCADSTAR and CADSTAR
  • PADS
  • Cadence

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Quadra PCB design and Manufacturing Services

  • Data Preparation
  • Library Creation
  • Circuit Board Design
  • Layout Service
  • PCB Assembly and Manufacture
  • PCB Reverse Engineering
  • Reverse engineering
  • High-Speed PCB Design
  • Post PCB Layout
  • ECAD / MCAD Integration

 

8 PCB Design and Layout Tips You Should Know

8 PCB Design and Layout Tips You Should Know

PCB’s are all around us and we are probably never more than a metre away from a PCB at all times. Your smartwatch/fitness tracker, your laptop or your mobile. We can’t go a day without relying on a PCB somewhere! And as a result, PCB design is more important than ever. In this post, we explore some of the most important elements of successful PCB design and our top 8 layout tips that you should know.

1. Node Location Is Critical

Perhaps the most important tip on our list is this – Node accessibility. This could help solve your design issues and solve issues when testing. If nodes aren’t accessible, testing will be even harder whatever type of nodes you have used. If they are easy to probe then they are easy to test.

2. Space Matters

Today’s circuit boards support far more components per square centimetre than ever before. That’s great from an end-user standpoint. The more components on a board, the more functionality it supports, and the more users can do with the device. However, what is an advantage for end users can be a challenge for designers.

Simply put, the more components you add to a board, the more cramped they become within the design. And, make no mistake, component spacing matters a lot. Why is that? You’ll find several reasons. One of those is that without the appropriate amount of spacing, you lack room for wire routing. Another challenge is that those components create heat, and the closer they’re packed, the more heat builds up in the board. In some cases, that might be enough to compromise the board material itself, particularly if you’re using something like FR-4 rather than a material designed to handle high levels of heat.

3. Feeling the heat

Heat will always be a problem, but it is not insurmountable. One quick tip to help you get around high-heat-related issues is to add extra copper around surface mount components. This creates additional surface area and helps dissipate more heat, faster, effectively turning a portion of the PCB design into a heatsink.

4. Pay Attention to Arrangement

Sometimes, rotating your components is simply not enough. When that happens, it’s important to come at the situation with a bit of strategy in terms of component arrangement. How, though?

Cascaded Components: Cascaded components play a vital role in many PCB design options. However, they can be challenging to arrange correctly. Keep them near one another, and make sure that they are in sequence on the board. That will immediately remove the challenge of trying to route traces all across the board to connect cascaded components located in different areas.
Consolidate: Why use multiple smaller resistors when a single higher resistance one will work better? Consolidating your design ensures that there’s more room for components and traces, as resistors will take up less of your available space.
Cascade from the Edge: When laying out your PCB design, identify any component that must be attached via a connector placed on or near the edge. Locate those components as close to the connector as you can. The rest of the chain should cascade away from that point, grouped into functional blocks near one another and in sequence.

5. Making space

Does the following situation sound familiar? You’re staring at your PCB design, struggling to fit each component in and route traces between them. No matter where you put them, you’re left with problems, particularly if the board is smaller.

The answer? Rotate your components and find the best arrangement that allows you to route traces directly between them while maximizing the use of space across the entire board. This can take some time and effort, but it’s well worth the minimal investment you’ll make.

6. That Shrinking Feeling

Struggling with an unrouteable board? Use smaller components. By going with a smaller footprint, you leave more room for copper traces to pass each component. Proper spacing is easier to maintain with smaller components, too, helping you avoid overcrowding the board and the other problems that go hand in hand with stacking components too close to one another.

What should you do? While quad flat package components might be your first option, you might want to consider going with ball grid array components, instead. Of course, there is a trade-off here – smaller components make repair work more challenging.

7. Dense Boards

If you are struggling with PCB design, chances are good that the space required for traces, vias, and clearance is a problem. You can get around that by going denser. With HDI, you can create very dense boards with very dense traces, clearances, and vias that still deliver performance. However, you do need to consider controlled impedance routing, differential pairs, and check creepage, clearance, and width when it comes to high-current and high-voltage design.

8. Keep the Noise Down

Signal noise can be problematic when it comes to some traces. However, placing high-frequency signal carrying traces too close together can couple those signals, ratcheting up the noise and possibly creating problems with traces where no noise is desired. Make sure that you keep noisy digital traces away from analog traces to avoid this problem.

 

More about Quadra Solutions PCB Design Service

We have been designing, assembling and fabricating PCB’s for over 20 years and our ability to design and manufacture the highest quality PCB designs and prototypes means the world to every single member of the Quadra team.You can rely on our highly experienced and IPC CID+ accredited team of PCB Design Engineers to provide a full range of PCB Design Services that leave you free to focus on the design concept and product strategy.

UKAS-ISO-9001-1-150x150Our ISO 9001 accredited team deliver complex, high-speed multi-layered circuit board design layout, testing, library management and manufacturing services for hundreds of happy customers each year, using a wide range of PCB design software packages including;

 

  • Altium
  • Mentor
  • eCADSTAR and CADSTAR
  • PADS
  • Cadence
pcb design ebook
Have you read our PCB ebook yet? Read now

Quadra PCB design and Manufacturing Services

  • Data Preparation
  • Library Creation
  • Circuit Board Design
  • Layout Service
  • PCB Assembly and Manufacture
  • PCB Reverse Engineering
  • Reverse engineering
  • High-Speed PCB Design
  • Post PCB Layout
  • ECAD / MCAD Integration

Routing Differential Pairs in eCADSTAR

In this eCADSTAR demonstration, we are going to look at basic configurations and routing of differential pairs in the PCB Editor.

First of all we open our constraint browser, then I click on the create multiple differential pairs icon. This scans both Enets and net lists for matching names with a differentiating suffix which you can also customize here.

You can use nets or Enets as your target object for example if you have passive components in between your differential pairs you will use the nets as the target object instead.

The constraint browser automatically assigns a name using your net or Enet names.

I now need to assign a rule stack to them. This is one I have configured earlier so I am going to assign this rule stack and we will have a look and see how I have set this up.

In my differential pair rule-stack, you can see I have defined track widths and spacings. I now select calculate differential impedance, then using my track widths, spacings and PCB material stack up the embedded field solver returns the expect impedance and delay values. The calculation feature to the left of this incorporates the use of a target impedance for more complex designs.

Now with our rules defined let’s see how this affects our routing environment. When selecting one of the nets it automatically picks up the second one and routes them both at the same time, whilst adhering to the rule stacks we defined earlier.

On the approach to the final connection, you can see a directional arrow. This is indicating that my nets are crossed and it would be better to approach from the opposing side.

Let’s repeat that again with another differential pair.

And that’s how you set up and route basic differential pairs with the useful features in eCADSTAR.

 

More about eCADSTAR

eCADSTAR brings together the latest advances in collaboration and connected engineering in a borderless electronic design environment, connecting the engineering desktop with comprehensive design and manufacturing services.

In the 2020 Release |   Read More

SIGNAL INTEGRITY   |    Add sophisticated Signal Integrity Analysis capabilities to eCADSTAR. Simulation in the Schematic (pre-layout SI) as well as in the PCB Layout (post-layout SI).

POWER INTEGRITY AND EMI   |    Embedded into eCADSTAR, these functions share the same design data and simulation library used for Signal Integrity.

IBIS-AMI   |    Analyse SERDES channels (e.g. PCI-Express Gen3+, HDMI, SATA, USB, etc.) based on IBIS-AMI models, S-Parameter characterisation of the channel, Eye diagram results, BER estimation and bath-tub curves and import IBIS-AMI devices into the simulation library.

Contact us for a Virtual Demonstration

eCADSTAR – PCB Routing – Positive Thermal Connectivity Options

PCB Routing

In this video we’re going to take a quick look at the versatility eCADSTAR offers designers with respect to PCB Routing and Thermal Connectivity.

This is a great example. Here we have a net with 4 different pad sizes. The smallest being the QFN package Rectifier. You can see that the output is being decoupled by two caps and then it transitions from layer 1 to layer 2. At the transition point we have a device that appears to be shorted out. But it’s going to be used as a current sense device. We’ll look at this closer in a moment.

The same thermal spoke width is not going to suit all these different pad sizes so outside of flooding them all what options do we have?

Well, in the first instance the thermal connectivity preference is assigned to the copper flood. To the shape. In the settings for the copper flood we can define thermal or flooded and we can also isolate Vias from pads. But this setting is then applied to all pads that make contact with that particular copper flood.

If I change the settings you can see the impact on the pads. Here the smallest dimension on any of the pads on the QFN @ 0.3mm. So I will set my minimum spoke with for that copper flood to 0.3mm

Now let’s review the impact if I decided to flood all those pads and have no thermal relief.
I’m not happy with that result so I’m going to CTRL Z and undo it.

But eCADSTAR offers another level of flexibility that is really easy to configure. We can override the shape, the flood connectivity preferences by defining them at the next level down which is at the device pads directly.

I’ve just changed the two large decoupling capacitors to have flooded connections.

Now focusing on our current sense device I’m going to change one pad to flooded and the other pad to isolated.

I also need to replicate the isolated connection at the QFN device.

Now we can see both of those pads are connected to the same net, the output net but they are now isolated from the copper flood.

The reason we’ve isolated these two pads is because the rectifier has an inbuilt current monitoring facility. If the pad that measures the current is connected directly to the copper flood then the measurement will be inaccurate. We need to measure as closely as possible to the final output stage before the conductor travels around delivering its power to the receiving circuits.

eCADSTARS flexibility regarding the thermal, flooded and isolated connections makes this really easy for us.

We are not just limited to overriding the copper flood connectivity with flooded or isolated connections. We can also define different thermal connectivity.

So in this example I can pick a pad, change to a really thin spoke width and specify any number of spokes. Up to a max of 12. Where possible it will add as many spokes as it can. In this instance it achieved 5.

Just for fun lets see if one of the larger pads can handle 12 connections for us.

So there you have it. A huge amount of flexibility regarding thermal connectivity in eCADSTAR.

 

For more information about PCB Routing with eCADSTAR contact us

eCADSTAR – Routing Automatic Via Flood

In this video, Damian our eCADSTAR Applications Engineer takes a look at eCADSTAR’S routing ability to be able to automatically flood copper areas with vias, an extremely useful, timesaving feature within eCADSTAR.

eCADSTAR – Routing Automatic Via Flood

First of all, I go to the padstack tab and select reinforcing via. So we have a few options here.

I can flood the inner, the perimeter or all of the board. We can choose which specific via we would like to use. We can also change the layer span here and we can also configure our via matrix.

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Routing with eCADSTAR

The software prompts us to select two pieces of copper. This is an 8 layer board and we are only looking at 1 and 8 right now. But if the copper existed on more layers it will also connect to the additional layers.

Or provide clearance if a connection is not needed. As soon as the second copper shape is selected eCADSTAR builds a preview image for us so we can review the matrix.

 

Whilst still in preview mode I can change the matrix dimensions so I can review each result and finally commit to adding them to my design. Now I’ve committed the vias to my design then still work within the rules of our DRC and can be pushed out of the way or even deleted.

For more information about eCADSTAR go to www.quadrasol.co.uk/ecadstar

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