PCB Trace: The Basic Introduction About Circuit Board Trace in 2024

PCB trace is one of the essential factors in PCB circuit design, and trace width is one of the crucial and challenging aspects of PCB design. Experienced circuit designers often face the challenge of determining the appropriate trace width. Thus, this article provides brief guidelines about the PCB trace. 

Table content

• 1. What is a PCB Trace?
• 2. Material and Dimensions of PCB Traces
• 3. How to calculate PCB trace width?
• 4. Benefits of Proper Trace Routing
• 5. Considerations for Trace Width and Spacing
• 6. Challenges in PCB Trace Design
• 7. Advancements in PCB Trace Technology

What is a PCB Trace?

A PCB trace is a thin conductor on a printed circuit board (PCB) that carries electrical signals between components. These traces can be made of materials, typically copper, and are designed to have specific widths and thicknesses to handle different current loads. The layout and routing of traces on a PCB are essential factors in the performance and reliability of a circuit. The design of traces must consider issues such as crosstalk, signal loss, and electromagnetic interference (EMI) to ensure the circuit functions correctly. 

Typically, the copper thickness of a PCB is fixed and determined by the manufacturer's specifications. For standard PCBs, the most common copper thickness is 35µm, equivalent to 1oz/sq ft. Therefore, in the design process, we can only control the trace width. For most manufacturers, the minimum trace width is 6mil or 0.152mm, mainly due to limitations in the etching process and target production yield. However, to allow for certain tolerances, trace widths of 0.254mm to 0.3mm are generally used.

Material and Dimensions of PCB Traces

The material used to manufacture PCB traces is typically copper, known for its good conductivity, low resistance, and ease of manufacturing. The copper used in PCB traces is a thin sheet of copper foil laminated onto the PCB substrate. While on it can also be a thicker layer of copper that is etched to form the desired trace pattern.

The width and thickness of the trace are essential factors in determining its current carrying capacity. Thicker and wider traces can carry more current than thinner and narrower ones. You must carefully calculate the trace width to ensure that it can safely handle the expected current load without overheating or causing other electrical issues. The trace spacing, which refers to the distance between two adjacent traces, is also essential. As it can affect the amount of crosstalk between the traces, which can impact the quality of the electrical signals being carried.

In general, PCB trace dimensions are specified in mils (thousands of an inch), depending on the specific requirements of the designed circuit. The trace width and spacing can range from a few mils for high-speed and high-density circuits to several hundred mils for simpler circuits with lower current loads.

How to calculate PCB trace width

1. Using a PCB Trace Width Calculator

You can use a trace width calculator to determine the trace width based on the required current capacity. In the calculator, you need to provide design specifications such as the maximum current flowing through the trace, the total trace length, and the temperature rise due to the resistance of the trace.
Once the specifications are provided, the calculator will automatically generate the calculated width, which is typically the minimum required width. This width ensures the current can safely pass without causing damage to the PCB.
You may find that the trace width for inner layers is wider than for outer layers, as inner layers tend to generate more heat. The outer layers receive less heat due to convection.
For safety reasons, it is recommended to use the internal trace width across the entire PCB.

2. Using Formulas

1) PCB Trace Width Table

A PCB trace width table can help you determine the width of the PCB traces while also giving insights into the current-carrying capacity and the effect of temperature rise. You can refer to the table below:

PCB trace width table

2) PCB Trace Width Formula

As defined by IPC-2221, you can use a formula to calculate the allowable current through the trace to find the required PCB trace width. The formula is as follows:

• I represents the current, which is treated as a constant.
• ΔT refers to the temperature change.
• A is the cross-sectional area of the trace.

You can rearrange the formula to derive the trace width by finding the cross-sectional area needed for the selected current to pass safely.

• A is the cross-sectional area of the trace, measured in square mils (mils²).
• I is the current, measured in amperes (Amps).
• k is a constant, with k=0.048 for outer layers and k=0.024 for inner layers.
• ΔT is the temperature rise, measured in degrees Celsius (°C).

Next, consider the trace thickness to find the required width:

• Width is the trace width, measured in mils.
• Area is the cross-sectional area of the trace, measured in square mils (mils²).
• Thickness refers to the copper thickness, measured in ounces per square foot (oz/sq ft), with typical values being 1oz, 2oz, etc.
• 1.378 [mils/oz] is the constant used to convert copper thickness (in ounces) to mils. For instance, 1oz of copper corresponds to approximately 1.378 mils in thickness.

This formula is valid for currents ranging from 0 to 35A and allows for temperature rises from 10°C to 100°C. It can accommodate trace widths up to 400 mils, and you can use copper thicknesses ranging from 0.5 to 3 oz.
By inserting a current of 2A into the calculation above, we get a minimum trace width of approximately 30 mils. However, voltage drop cannot be calculated directly from this; to do so, you'll need to compute the trace's resistance. In the next section, we will discuss how to calculate trace resistance.

Benefits of Proper Trace Routing

Proper trace routing is crucial to the performance and reliability of a circuit. Poor trace routing can result in electrical issues such as increased resistance, crosstalk, signal loss, and electromagnetic interference (EMI). Proper trace routing also helps to minimize the overall size of the circuit board and can improve the manufacturing yield, which can lower the cost of production.

Some of the benefits of proper trace routing include the following:

Minimizes Resistance: Proper route of traces reduces the circuit's resistance, which helps maintain the integrity of the electrical signals being carried.

Prevents Crosstalk: Crosstalk occurs when electrical signals from one trace interfere with signals on another trace. Proper trace routing helps to minimize crosstalk and maintain the quality of signals.

Avoids Signal Loss: Signal loss can occur when traces are too long or not properly designed to carry the electrical signals. Proper trace routing helps to prevent signal loss and maintain the strength of the signals.

Reduces Electromagnetic Interference (EMI): EMI is the unwanted electromagnetic radiation generated by electrical circuits. Proper trace routing helps to reduce EMI by decreasing the amount of crosstalk between the traces.

Improves Circuit Performance: Proper trace routing helps improve the circuit's overall performance by reducing resistance, preventing crosstalk, and avoiding signal loss.

Considerations for Trace Width and Spacing

The spacing and width of PCB traces play a crucial role in the performance and reliability of a circuit. The following are some of the key considerations when determining the width and spacing of the trace:

Current Load: The trace width must be calculated based on the expected current load. This is to ensure that it can safely carry the electrical signals without overheating or causing other electrical issues. Thicker and broader traces can carry more current than thinner and narrower ones.

Signal Frequency: The trace width must also be calculated based on the frequency of the electrical signals it will carry. Higher frequency signals require wider traces to prevent signal loss and maintain the signal's integrity.

Crosstalk: The spacing between two adjacent traces affects the crosstalk amount between them. Increasing the spacing between traces reduces the crosstalk amount while decreasing the spacing increases the crosswalk amount.

Electromagnetic Interference (EMI): Proper trace spacing helps to reduce EMI by reducing the crosstalk amount between the traces.

Signal Strength: The spacing between two adjacent traces affects the strength of the signals being

Challenges in PCB Trace Design

Designing PCB traces can be challenging. You must consider various factors to ensure that the circuit board functions as intended. Some of the common challenges in PCB trace design include the following:

High-Speed Signaling: High-speed signaling requires special design considerations for trace width, spacing, and routing to prevent signal loss and maintain signal integrity.

Power Distribution: Designing power distribution traces requires careful consideration of the current load, trace width, and thermal management to prevent overheating and other electrical issues.

Electromagnetic Interference (EMI): Minimizing EMI requires careful trace routing, shielding, and other design considerations to reduce the amount of crosstalk between the traces.

Circuit Density: High-density circuits require careful trace routing and design to ensure that the traces fit within the limited space available on the circuit board.

Thermal Management: Proper thermal management is crucial to prevent overheating and other thermal issues. This requires careful design of the trace width, spacing, and routing to ensure that heat is dissipated correctly.

Signal Integrity: Ensuring signal integrity requires careful trace routing, design, and impedance matching prevents signal loss. Besides, it also maintains the quality of the electrical signals being carried.

Cost and Manufacturing Considerations: Designing PCB traces that meet the requirements of the circuit and are cost-effective and easily manufacturable is a critical challenge in the design process.

Advancements in PCB Trace Technology

The technology used for designing and manufacturing PCB traces has advanced significantly over the years. Some of the latest advancements in PCB trace technology include:

High-Speed Signaling: Advances in trace routing and design have made it possible to support high-speed signaling with reduced signal loss and improved signal integrity.

High-Density Circuits: Advances in trace routing and design have made it possible to design high-density circuits with smaller trace widths and spacings. Thus, it is possible to fit more components on a single circuit board.

Improved Thermal Management: Advances in trace design and materials have made it possible to improve thermal management. It helps to dissipate heat more efficiently and prevent overheating in high-power circuits.

Improved Signal Integrity: Advances in trace routing and design, along with the use of advanced materials, have made it possible to improve signal integrity. Moreover, it also reduces the amount of signal loss in high-speed circuits.

Automated Trace Routing: Advances in CAD tools have made it possible to automate the trace routing process. It reduces the time and cost involved in the design process and improves the accuracy of trace routing.

Conclusions

The advancements in PCB trace technology have significantly improved circuit boards' performance, reliability, and cost-effectiveness. It has become easier to design and manufacture highly complex and advanced circuits. Thus, proper trace routing is an essential factor in ensuring the functionality and reliability of a circuit. And it is critical to the success of the overall circuit board design.