What is a PCB Trace? A Complete Guide

PCB trace is the backbone of electronic circuits. It forms the pathways that link components together, transmitting power and signals. This guide explores its function, material options, features, and much more, including its repair methods.

What is a PCB Trace?

A PCB trace is a narrow, conductive path linking components on a printed circuit board (PCB). Without traces, circuit boards would not work. They function like wires, enabling electrical connections between components and circuits.

Modern electronics are pushing trace requirements to higher limits, given the need for high reliability and long life. For this reason, PCB designers and users must understand what makes traces high-quality.

PCB Trace Material

PCB traces are typically made of copper. The material offers excellent electrical conductivity, thermal performance, and durability in different applications.

Copper isn’t the only material in use today. Others include silver and aluminum. However, these are rarely used. That’s because trace material must balance between good properties and cost.

Scientists are also looking into new materials to meet various needs, such as weight and flexibility. One of them is graphene. It has impressive electrical properties, reduced weight, and greater flexibility.

Key PCB Trace Parameters

Various features specify circuit board traces. They include length, width, thickness (collectively ‘size’), current carrying capacity, and electrical resistance. Here’s more about them and how they impact a circuit board’s performance and quality.

Length, Width, and Thickness

PCB trace length, width, and thickness are collectively its size. Traces are either narrow or wide, depending on the needs they must meet. They can also be long or short.

Trace thickness or copper weight, indicated in ounces per square foot (oz. /ft²), measures its height. Options range from 0.5 to 6 oz. Most traces are 1-2 oz. or 35 to 70 microns thick.

The length depends on the board’s design and layout. However, shorter traces are recommended. They help minimize signal issues, especially in circuit boards for high-frequency signals.

Current Carrying Capacity

PCB trace current capacity indicates the maximum amount of electricity it can pass. In other words, the trace must do so without overheating or experiencing voltage drops across its ends.

The current capacity of PCB traces depends on the material used to make them. Some are more electrically conductive than others. It also depends on the trace size, or more specifically, its width and height.

Trace Resistance

Trace resistance refers to its opposition to current flow. Some materials are more electrically resistive than others. Copper, for instance, has excellent electrical conductivity (5.96×10⁷ S/m).

Resistance also varies by trace size. Smaller sizes resist current more than wider and thicker sizes. Designers use this relationship to find the trace size to avoid unwanted temperature rise and resistive power losses.

PCB Trace Design Considerations

PCB designers must carefully create and place traces. It ensures the circuit board’s proper operation by minimizing signal transmission problems, EMI (Electromagnetic Interference) effects, and thermal issues. The following are key design considerations.

Current and Thermal Management

Traces must safely handle the current running in them. They must also effectively dissipate the resulting heat. Wider, thicker traces can handle more current, making them suitable for high-power circuits.

On the other hand, thin traces suit signal transmission where current levels are predominantly low. The designer places the components on the board with these requirements in mind.

Signal Integrity

Signal quality is a fundamental aspect when designing printed circuit board traces. Engineers strive to keep the conductive paths as short as possible. It helps reduce signal transmission delays and interference.

Designers also adopt rounded corners when changing the direction of traces. Sharp corners increase trace width, potentially causing reflections.

Other measures include avoiding placing high-frequency traces close together. At high frequencies, signals are more prone to issues, including traces acting like antennas.

Spacing Between Traces

Proper PCB trace spacing is essential when placing traces. It helps minimize crosstalk and its effects. Correct spacing also controls impedance and prevents electrical incidents like arcing in power circuits.

The design requirements for trace widths and spaces go hand in hand. A general rule of thumb is to maintain a distance of three times the trace width between the traces.

How to Calculate Trace Width

Trace width is an important feature when creating PCB designs. It influences signal quality, power transmission, and thermal performance. Designers can use various PCB tools to calculate it. Some are available online.

The trace width formula is I = 0.024 × dT⁰.⁴⁴ × A⁰.⁷²⁵ for internal traces and I = 0.048 × dT⁰.⁴⁴ × A⁰.⁷²⁵ for external types. Here, ‘I’ stands for current, ‘dT’ for the temperature rise in °C, and ‘A’ for the cross-sectional area in square mils.

You can also use a PCB trace width calculator online. These tools allow you to estimate the ideal size by inputting various values. They are available on manufacturer websites and various dedicated sites.

What Can Cause PCB Trace Damage?

Circuit board traces are mainly damaged by heat and corrosive materials. On the other hand, physical damage can result from cutting and impact. Here’s how each type of damage affects the traces and the PCB in general.

Overheating

Too much heat can cause traces to expand, lift, or peel from the substrate. Temperature rise in PCB traces also often leads to cracks and disrupted power or signal transmission.

Trace temperature rise often results from excessive current flowing through them or incorrect trace sizes. Usage environments where ambient temperature levels are too high can also lead to thermal damage.

Corrosion

Certain materials, such as moisture and chemicals, can corrode traces. Galvanic action between metals can also cause corrosion. Traces that corrode cannot perform their function. Sometimes, damage breaks electrical connections.

Physical Stress

Physical stress causes mechanical damage. It can result from bending, vibrations, mechanical impact or shock, and abrasion. Some occur over time, while some are sudden and caused by careless handling.

Can You Repair PCB Traces?

The answer is yes, you can repair traces. The type of repair to use mainly depends on the extent of damage. Fixing broken or lifted traces restores the board’s function, saving replacement costs.

It’s usually recommended to restore surface traces. Those buried deep in the board’s internal layers are more challenging to fix, requiring more care and specialized tools. The following are the available repair options.

• Solder Bridging — joining the broken ends by melting solder across the ends. It mainly works when the traces are thick and the ends are close together.
  
• Jumper Wire — you solder a jumper wire across the break to restore the electrical connection. This method is by far the most effective. It’s also easier to use.
  
• Conductive Ink — you apply a conductive material (usually silver or carbon-based) to close the gap left by the damage. It mainly suits signal traces since the ink’s conductivity is low.
  
• Foil Patches — this method involves placing an adhesive-backed sheet on the affected part and soldering its ends.
  

How to Repair a PCB Trace

Knowing how to repair circuit board traces is essential, especially if you’re a DIY enthusiast or a user looking to save a damaged circuit board. The following are key repair steps.

1. Assess the area of damage and determine its severity. It will help you decide which repair method to use. Use a magnifier to inspect thinner traces or high-density circuit boards.

2. Take time to understand the board’s schematics. Check it to identify the damaged trace’s connections and routing.

3. Clean the PCB or affected part to remove dust and residuals. You may use an alcohol solvent or a specialized cleaning material. Gently scrub the trace surface to reveal the copper. Allow the cleaned area to dry.

4. Use the preferred method to restore the electrical connection. As we saw earlier, you may use solder, jumper wire, copper foil, or conductive ink.

5. Use a multimeter or other testing instrument to measure the connection’s resistance and continuity. The test results should show adequate conductivity.

6. Apply a protective coating to the area and let it dry. Immobilize jumper wires with PCB glue, such as epoxy.

Conclusion

Traces are essential parts of circuit boards. PCB designers must size and space them correctly, or the board may experience reduced performance and other functionality issues.

Venture is your one-stop shop for PCB manufacturing services. We ensure every part of the board is reliable, including the traces.

Our methods are built on years of experience, state-of-the-art equipment, and a skilled workforce. Contact us now for any questions about our PCB solutions and services.