Essential PCB Layout Tips Every Designer Should Be Familiar With

Engineers often prioritize circuits, component selection, and programming as crucial aspects of electronics projects. However, it is crucial to recognize the importance of PCB layout as an integral component to the success of the design.

Poor PCB layout can cause functional and reliability problems. This article offers practical suggestions for PCB layout to guarantee accurate and dependable performance of your projects.

Selecting Trace Dimensions

Minimize Loop Sizes

For best results in high-frequency applications, keep loops as compact as possible to minimize inductance and resistance. Additionally, situating loops above a ground plane helps to reduce inductance even further.

Using smaller loops helps reduce high-frequency voltage. It also lessens the number of signals that get inductively coupled into the node from external sources or broadcast from it.

This approach is optimal, except for cases involving antenna design. Also, to prevent unwanted noise from being introduced into the circuit, it is essential to maintain small loops in op-amp circuits.

Placement of Decoupling Capacitors

To improve decoupling efficiency, place decoupling capacitors in close proximity to the power and ground pins of integrated circuits. Introducing extra distance may cause stray inductance to be introduced.

Kelvin Connections

Four-terminal sensing, also known as Kelvin sensing, is a technique invented by William Thomson, Lord Kelvin, in 1861 for measuring very low resistances with great accuracy. Each set of two-wire connections is called a Kelvin connection.

Using Kelvin connections improves measurement accuracy by establishing connections at precise points to minimize stray resistance and inductance.

When dealing with a current sense resistor, it is vital to position Kelvin connections directly on the resistor pads instead of an arbitrary point on the traces to ensure maximum accuracy.

When creating a schematic, it may seem like connecting to either the resistor pads or a random point is the same. However, actual traces exhibit inductance and resistance, making Kelvin connections crucial for accurate measurements. Avoiding these connections could potentially cause inaccuracies in your readings.

Separate Digital and Noisy Traces from Analog Traces

When conductors or traces run parallel to one another, they create a capacitive effect. These traces can become coupled and interfere with one another, especially at higher frequencies. It is important to separate high-frequency and noisy traces from those in which noise interference needs to be minimized.

Ground is Not Ground

Although ground serves as a conductor, it's important to note that it's not ideal. Be sure to separate noisy grounds from signals that require low noise levels. Ensure that ground tracks are adequately sized to handle the expected currents. Using a ground plane directly under signal traces reduces impedance, which is very beneficial.

Optimal via size and quantity

Vias have both inductance and resistance. If you are routing a trace across the board and want to achieve low inductance or low resistance, consider using multiple vias. Larger vias provide lower resistance, which is especially beneficial for grounding filter capacitors and high current nodes.

Use PCB as heat sink

Surround surface mount components with additional copper to increase surface area for more efficient heat dissipation. Certain component datasheets, particularly those for power diodes, power MOSFETs, or voltage regulators, may contain recommendations for using PCB surface area as a heat sink.

Thermal Vias

Vias serve as conduits for heat transfer through a PCB, which is especially beneficial when the PCB is mounted to a heatsink on a chassis to provide additional heat dissipation. Larger vias are more effective at transferring heat than smaller ones.

Using multiple vias for heat transfer is more efficient than relying on a single via. This leads to lower operating temperatures for components, ultimately enhancing overall reliability.

Thermal Relief

Thermal relief involves creating small connections between a trace or fill and a component pin to facilitate soldering. These reduced connections are intentionally kept short to minimize their impact on electrical resistance.

Leaving out thermal relief on component pins can lead to a slightly lower operating temperature because of an increased thermal connection with traces or fills that can dissipate heat effectively. However, it may also make soldering and desoldering more difficult.

Distance between Traces and Mounting Holes

Leave a gap between copper tracks or pads and mounting holes to reduce potential shock hazards. Remember that solder mask may not provide reliable insulation, so make sure there is adequate clearance between the copper and any mounting hardware.

Heat Sensitive Components

Maintain separation between heat-sensitive components, such as thermocouples and electrolytic capacitors, and other heat-generating components.

Positioning thermocouples too close to heat sources can result in temperature measurement inaccuracies. Placing electrolytic capacitors in close proximity to heat-generating components can lead to a shorter operational lifespan.

Components that produce heat include bridge rectifiers, diodes, MOSFETs, inductors, and resistors, with the level of heat generated depending on the current passing through the components.

Conclusion

This article has provided basic, yet critical, practical PCB layout tips that can significantly improve the functionality and reliability of your design.

Let's remember these points.