What is PCB Minimum Trace Width? Significance of PCB Trace Widths in PCB Design

The copper width is a crucial aspect of any PCB design, and it requires careful consideration by those knowledgeable in circuit design. Inexperienced designers often rely on the default trace width provided by the Printed circuit board layout software, but this may not be the most appropriate choice. Using the default trace width provided in PCB layout software may work for inexperienced designers to some extent. However, experienced designers understand that the default size is often too narrow for certain tracks, especially for electricity or ground connections. While some designers may adjust the width based on intuition. They may not know how to determine the appropriate trace widths for their design scientifically.

What Is a PCB Trace Width?

To begin with the fundamentals, a Printed circuit board trace refers to a slender, copper conducting line situated on an isolated or non-conductive substrate that transmits power and signals throughout the circuit. The copper trace possesses a distinct width, known as trace width & which has a specific thickness or height.

The thickness of the copper layer in PCBs is usually predetermined and dictated by the manufacturing company’s requirements. In the US, the thickness of PCBs is measured in ounces per square foot. The most prevalent copper thickness for typical PCBs is 35µm, known as 1oz copper.

Our design only allows us to regulate the size of traces, which must be at least six mil/ 0.152milimetre for most producers due to limitations in their etching processes and yield goals. To account for deviations, it’s customary to employ traces of 10-12 mil/ 0.254-0.3 mili meter.

Factors Are Essential for PCB Minimum Trace Width

To comprehend the significance of varying trace widths, it’s necessary to comprehend how they differ within a circuit. Within a standard Printed circuit board, there are 2 primary Varieties of traces: power traces and signal traces.

· Signal Traces

They are responsible for transmitting data. While varying trace widths may not make a significant difference in easy Printed circuit board designs involving digital or analog signals, it is crucial in High-data-rate digital and RF/analog designs. In such designs, trace impedance becomes a critical consideration, as impedance and trace width have an Inverse relationship. We will discuss this relationship further in the Impedance segment following.

· Power Traces

Conversely, power traces necessitate greater attention as they are liable for distributing power to each component within the circuit board. There are 2 primary reasons for implementing varying trace measurements within the PCB design.

· Current Carrying Capacity

The primary and evident reason for implementing varying trace widths is to ensure the current carrying ability. It is because the relationship between the width of the conductor and current carrying ability is straightforward.

When the electric current flowing through a given trace increases, the temperature rises, and the trace must cope with this temperature rise. One straightforward approach to verify this is by expanding the breadth of the trace.

To establish trace widths, the standard IPC-2152 provides a useful starting point. These standards utilize observational data to create tables that calculate current restrictions for the given temperature growth. Utilizing a table that compares Printed circuit board trace width against the current is an excellent way to evaluate your circuit board trace width or cross-sectional place. This table effectively determines the maximum permissible current in the traces. Due to the numerous variables in Printed circuit board stack-up. it is necessary to conduct simulations to determine current density or temperature rise accurately. However, for typical boards, the IPC diagrams are sufficient.

· Trace Impedance

To reduce coupling, crosstalk, and reflections in specific spacing, a high-speed circuit or impedance could be essential. Sensitive data paths, like RF/analog or quick transmission pathways, require precise calculations. At high frequencies, like GHz bands, Printed circuit board traces do not behave like easy connections.

While it may be easy to overlook in simple low-speed designs, copper traces possess specific series inductance or internal resistance. However, in fast circuitry, copper surface roughness, trace inductance, and the skin depth effect will enhance, significantly impacting the board’s proficiency. Furthermore, each signal trace contains a capacitance value among its return way or other nearby tracks

Trace Width and Signal Reflection

In the layout of high-operation electronic circuit boards, a reflection of the signal is a critical concern. Signal reflection refers to the phenomenon in which a part of a reflected signal is sent back toward a source. This reflection is unfavorable as it results in signal aberration and fluctuations.

The occurrence of signal reflection in printed circuit boards largely depends on the shape or routing of traces. Circuit disruptions are introduced whenever the trace changes the direction, interface, or shape of the component. For instance, when the path bends at a 90-degree angle, the path width changes significantly. At the bend point, the path width becomes 1.414 times greater than the original trace width. So this alteration in the trace width results in an impedance variation, causing signal reflection. Expert Printed circuit board designers are mindful of such problems or refrain from sharp bends & irregular path widths.

How is PCB Minimum Trace Width Calculated?

Let’s see how to calculate the minimum width of a trace that can carry enough power for a device. In this case, we will calculate the minimum width for the power path delivering power to the DC motor. A power pathway will start from a fuse, go through the H-bridge (a device used to control the power delivered to the DC motor), and end at the machine’s connector. The DC motor will use an average current of around two Amps continuously.

The trace on a PCB acts like a resistor and is narrower, and the longer the trace is, the higher resistance it adds. If a trace has no correct design, the higher current passing through it could harm the trace or cause a substantial voltage dip to the motor, causing a less pace. In this example, a power path starts at a fuse, goes through an H-bridge, and ends at a motor connector. The motor requires a continuous maximum current of 2 Amps. Besides, e need to calculate the smallest path width and predicted voltage decrease for a specific trace on the PCB. Assuming a one-ounce pour of copper or average room temperature during operation, we can calculate these values.

PCB Minimum Trace Width Spacing & Length

To minimize issues like cross-talk, reflections, and coupling in digital designs that require specific spacing, fast communication are necessary. In most cases, differential signaling routing is required for USB 2.0 at speeds of 480 Mbit/s= or higher. USB 2.0 operates at a lower voltage or differential, which can cause the signal level to be near the noise level.

When designing fast USB cables, there are three crucial factors: trace width, length, and spacing.

When routing fast-speed USB lines, there are three things to consider: trace width, spacing, and length. The most critical factor is ensuring that the two traces are similar as closely in length. For high-speed USB, if the traces differ in length by more than 50 miles. It can significantly increase the Threat of reflections, which can cause communication problems. A standard specification for pair routing is ninety Ohm matched impedance, which can be achieved by optimizing the traces’ width and spacing.

When designing a printed circuit board that uses a memory component with a parallel interface, like DDR3-SDRAM. It’s essential to pay close attention to the length of the traces used. Printed circuit board design software can help with this by optimizing the length of the traces for all the signals in the parallel bus. Figure 6 provides an instance of the DDR3 design that has been designed with precision length traces.

Calculating PCB Minimum Trace Width

If you are new to using trace thickness calculators, you may find the process confusing. If you have questions about our calculator, formulas, or results, you may find answers in the frequently asked questions (FAQs) section below.

  • What does the unit of the measurement “mils” mean? “Mils” comes from the Latin word “mille,” which means “thousand.” In the context of measurements, a mil equals 1000 of one inch.
  • In this context, temperature rise refers to the increase in temperature of a PCB above its average operating temperature up to the maximum safe operating temperature.
  • Can the trace width calculator calculate for any amount of the current?
  • No, there are limits to what the calculator can handle. It can measure a trace width of four hundred miles, thirty-five amps, and copper thickness between 0.5 and three ounces per square foot, with a temperature increase between ten or hundred degrees Celsius. If any of these parameters fall outside of the range, a calculator will estimate the data.

· What is the reason behind the calculator’s recommendation for Inner trace widths to be greater than external(outer) traces? Inner trace layers have lower heat dissipation due to poor heat conduction. It results in a higher tendency to store heat. This is why the calculator recommends higher trace widths for internal traces than external ones.

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