PCB Trace Length Thickness and Impedance Calculations
Traces in your printed circuits are one of the most important features in your board and need to be carefully designed. The right cross-sectional area in a trace can be used to ensure your trace impedance is consistent throughout your board. It can also help suppress temperature rise if your board will operate at high current. Choosing the right trace dimensions in your printed circuits represents a tradeoff between these performance aspects. A top-notch PCB design program can help you choose the right trace dimensions so that your trace impedance is consistent throughout your board and your traces are routable. Altium Designer contains the interconnect design and routing tools you need for any PCB in a single platform.
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The only unified PCB design package with trace impedance calculation and automated routing features.
Any circuit board includes components that provide important functionality, and those components must be connected together with copper traces. Different applications require different trace geometry to properly route signals and ensure signal integrity throughout your board. So what is the best way to design PCB traces and interconnects, and how can PCB software help you do this properly?
Without a doubt, printed circuit trace design really depends on the application for a given board. In general, boards that will experience higher temperature rise also carry higher mechanical requirements, which will also require the use of thicker copper traces. In contrast, if your board will operate in at RF frequencies or at high speed, you will generally opt for thinner traces or will use differential pairs with controlled impedance.
No matter the application for your next circuit board, your design software plays a critical role in ensuring your board has the right trace geometry throughout the board. The routing tools in your PCB design software are also critical for ensuring your traces have the right clearances, length matching, and bends. With the right design software, you can quickly route consistent copper traces throughout your board that comply with important design rules.
Different boards have different requirements on trace width and on the lengths of copper conductors in general. If a certain design uses a wider track width for a given thickness, the resistance of a trace will be lower, and the trace will dissipate less heat if used as a power rail.
The width and thickness of a trace will also affect its impedance, which becomes important in high frequency and high speed design. With modern boards and routing standards running at higher speeds and frequencies, it is generally a good idea to use impedance controlled routing in your board in order to ensure that your traces have consistent impedance. This makes impedance matching in high speed and high frequency circuits much easier and eliminates the need to impedance match every trace in a board.
Picking The Right Trace Width For Your Next PCB Design
The right trace you need for your board depends on a number of factors. Trace width is usually quantified in terms of weight per unit of board space, i.e., in ounces per square foot of board space. Using a heavier copper weight will help ensure that temperature rise in your board is kept in check as traces will have larger width and copper thickness. When high density interconnect (HDI) PCB design is used, copper weight will be lower in order to accomodate a lower trace width in your PCB design.
If you are designing a board for a purely DC system that operates at high current, then your goal should be to design your board with the widest and thickest copper traces possible in order to maximize the cross-sectional area and minimize IR drop and combat temperature rise. If you are working with a high speed or high frequency system, you will need to pick just the right trace width and thickness to control the trace impedance in your circuit board.
- Combatting temperature rise in your board is an important design aspect in many PCBs. This helps ensure your board remains reliable during operation.Learn about designing your board to withstand high temperature.
- Impedance needs to be controlled within certain tolerances in high speed and high frequency boards.Learn more about controlled impedance routing and design.
- Impedance management and temperature rise throughout your board requires choosing the right stackup. Power and ground plane placement can have a major effect on temperature rise and will affect your trace impedance.Learn more about impedance management with the right PCB stackup.
Copper teardrop design for traces in Altium Designer
Obviously, the relationship between ground plane placement, layer stackup, and trace geometry in your circuit board are interrelated. Changing the stackup and copper ground plane location will change the trace geometry required to maintain the right impedance value during routing. This will also affect the power dissipated along a trace, which then affects temperature rise. Trace impedance is also related to the dielectric constant of the substrate material and is also affected by temperature.
When it comes to calculating copper microstrip trace width and thickness for a given impedance value, you will need to solve a transcendental equation for the ratio of trace width to thickness, where the height of the trace above its ground plane is used as a parameter. This requires manually calculating an intersection between the microstrip trace impedance curve and a linear function defining the width to thickness ratio. The right design software can implement this calculation for you, saving you time to spend designing your board instead of calculating this important parameter.
Trace Routing and Signal Integrity
Once you’ve determined the right trace geometry you need for your board, you’ll need to route your traces throughout your board. The goal is to ensure signal integrity while making the required connections. It is generally a good idea to minimize the use of vias on interconnects in your printed circuits as they can act as impedance discontinuities and can couple noise from nearby ground or power planes into your signals.
The right routing tools in your PCB design software can save you a significant amount of time and help you easily implement the right routing strategy. Your routing features should interface with your design rules and constraints as this allows you define the appropriate trace width tolerances and clearance requirements between neighboring traces. The goal is to keep crosstalk and other signal integrity problems to a minimum while still creating the required connections in your PCB layout.
Many signal integrity problems can be alleviated with differential pair routing as these traces can reject common mode noise in a printed circuit. They also don’t require the use of a ground plane as a return signal is routed alongside the primary signal. This also helps maintain characteristic impedance as long as you maintain proper clearance and consistent trace length. These constraints can also be defined within your design rules with the right design software.
- Working with trace impedance calculators can be confusing, but the right design software can help you ensure your trace impedance is accurate and complies with important design standards.
- Most PCB design packages include a number of autorouter options. Choosing the right can expedite your PCB layout process and ensure you comply with your design rules.
- With differential or single-ended routing, you’ll need to define net clearance rules and ensure length matching throughout your traces.Learn more about working with net clearance rules in your PCB design software.
Auto-interactive routing in Altium Designer
Altium Designer contains a full suite of design tools and includes autorouting and interactive routing tools that help expedite layout of your printed circuit board. You’ll have the tools you need to define consistent trace geometry and tolerances throughout your board, and you’ll have access to a layer stack manager with an impedance calculator. This makes controlled impedance design much easier and by making the entire process semi-automated.
Rules-Driven Design: The Core of Altium Designer
These important design features are integrated into a single program on top of a rules-driven design engine. This engine ensures that your traces will comply with important design rules that govern routing standards and manufacturability. You’ll also be able to prepare deliverables for PCB manufacturing without sending your data to an external program.
- The rules-driven design engine is built to ensure your design choices comply with important design rules and industry standards for any application.Learn more about rules-driven design in Altium Designer.
- Fusion between autorouting and interactive routing is one of the latest advances in PCB design and layout. Integrating these features into a single tool saves you time and improves your routing accuracy.Learn more about auto-interactive routing in Altium Designer.
- Real-time supply chain information and bill of materials generation features in Altium Designer will help you prepare you board for PCB fabrication.Learn more about real-time BOM management in Altium Designer.
Most PCB design programs still enforce an outdated design model and interface, and you may not be able to access all the features you need for PCB layout. Altium Designer contains all these important design features for trace routing and much more in a single program. The production planning, documentation, and data management features will also help you take your designs to the next level.
The integrated design environment in Altium Designer has set a new standard in the PCB design industry, and Altium will be there with the resources you need to succeed. You’ll have access to an extensive knowledge base, the AltiumLive forum, webinars and podcasts with PCB design experts, and detailed feature tutorials. No other PCB design software company offers you this level of support.
While other design software companies are busy separating important design features into different programs and are still using user interfaces from the mid-90’s, Altium Designer offers the most modern PCB design interface with full integration among design tools. This is by far the best environment for PCB design for any application. Whether you’re a professional PCB designer or you’re getting started in PCB design, Altium Designer has something for you. Only Altium Designer offers all these design tools and much more in an integrated design environment.