What is PCB trace and how is it calculated?

Just as efficient train routes are achieved through well-planned tracks, a clear track layout on a printed circuit board is equally important. However, there’s a distinction: while train tracks only need to determine how to get from A to B, in circuits, it’s not just about that. Because current needs to pass through these tracks, factors like thickness, width, and length, in addition to the directional planning, directly impact performance. To address this, this TechSparks article provides a PCB trace size calculations guide!

What is a PCB Trace

circuit board trace

What is a trace in a PCB, and what is its purpose? This is a significant question. Routing holds immense importance in the PCB design process. Let’s draw a parallel with a city’s train system for clarification:

  • City = Printed Circuit Board
  • Residential Buildings = Electronic Components
  • Train Track = PCB Trace
  • Train = Current

From this analogy, we understand that the trace acts as the conduit for the circuit’s current. When a device powers up, the current courses through the track to reach components, triggering them to perform their designated functions.

Is it enough to simply arrange the circuit board trace logically?

This assumption is unequivocally inaccurate. Apart from arranging the circuit sensibly to control current flow, a designer’s role entails addressing numerous factors: wiring’s current capacity, impedance, and capacitance, to name a few.

Recalling our physics lessons, we learned that current magnitude relates to voltage, resistor dimensions, and length. Similarly, the PCB copper trace serves as a conductor. This implies that designers must calculate both the maximum current the circuit can handle and the minimum it requires. Such calculations are crucial to avert circuit overheating, overload, and other complications. Clearly, calculating PCB copper traces’ attributes holds undeniable significance.

PCB Track Width Design Considerations

Since trace significantly influences circuit current – either positively or negatively – it’s imperative that it’s not arbitrarily configured. Hence, let’s delve into the factors demanding consideration during this setup. Here, we will discuss this matter:

Project Requirements:

The operational principle of a circuit board relies on its electronic components. These components exhibit varying capacities for carrying current, differing from the minimum required for activation. For instance, relays and switches demand substantial current for reliable operation, while small integrated circuits and signal diodes function with minimal current.

Signal Rate:

In high-frequency applications, signal rate and integrity gain prominence, greatly impacting trace width and thickness. Wider PCB traces, for instance, possess lower resistance and inductance, thereby mitigating signal loss and distortion. This is crucial to facilitate higher signal rates.

Pad Size:

PCB pads serve as metal areas where electronic components attach to the printed circuit board, enabling connection and fixation. Consequently, trace width should align with pad size. Apt alignment aids in heat dissipation and streamlines the design process.

PCB Trace Calculation Formula

Minimum Trace Width

IPC Recommended PCB Trace Width Ammeter

PCB Trace Current Trend Table

PCB Trace Maximum Current Calculation Formula

Imax=k⋅T⋅ΔTAImax=Ak⋅T⋅ΔT

Where:

  • Imax: Maximum current (in Amperes) the trace can carry without exceeding the specified temperature rise.
  • k: Constant depending on the material properties and the allowed temperature rise (typically around 0.024 for standard FR-4 PCBs).
  • T: Trace width (in meters).
  • ΔT: Allowed temperature rise (in degrees Celsius).
  • A: Cross-sectional area of the trace (in square meters).

PCB Trace Resistance Calculation Formula

R=ρ⋅LAR=Aρ⋅L

Where:

  • R: Resistance of the trace (in Ohms).
  • ρ: Resistivity of the trace material (in Ohm-meters).
  • L: Length of the trace (in meters).
  • A: Cross-sectional area of the trace (in square meters).

It should be noted that in this formula we assume that the cross-section of the trace is uniform and the resistivity of the material used is constant. In practical applications, the width may vary along its length, and the resistivity may vary with temperature.

PCB Trace Voltage Drop Calculation Formula

The voltage drop along a PCB trace can be calculated using Ohm’s Law, which relates voltage, current, and resistance.

ΔV = I * R

Where:

  • ΔV: Voltage drop along the trace in volts (V).
  • I: Current flowing through the trace in amperes (A).
  • R: Resistance of the trace in ohms (Ω).

In high-frequency applications or when dealing with very small traces, you might also need to consider the skin effect and other factors that affect the effective resistance of the trace.

PCB Trace Power Consumption Calculation Formula

The power consumption of a PCB trace can be calculated using the formula for electrical power:

P = I^2 * R

Where:

  • P: Power consumption in watts (W).
  • I: Current flowing through the trace in amperes (A).
  • R: Resistance of the trace in ohms (Ω).

It’s important to note that power consumption in PCB traces is generally undesirable, as it results in heat generation. This heat can impact the overall performance and reliability of the circuit.

PCB Trace Width Calculator









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